Patent Application
20250180890
The disclosure relates to a micro-optical element, such as a micro-mirror. The disclosure relates further to a micro-mirror array (MMA). Further, the disclosure relates to an actuator device for a micro-optical element and an actuator system comprising a plurality of such actuator devices. Further, the disclosure relates to a micro-electromechanical system (MEMS). Further, the disclosure relates to a facet-mirror for a micro-lithography system, such as a facet-mirror module. Further, the disclosure relates to an illumination optics for a microlithography system, an illumination system for a microlithography system, a projection optics for a microlithography system and a microlithography system. Further, the disclosure relates to the use of a micro-mirror array. Further, the disclosure relates to a method for producing an optical component. Further, the disclosure relates to a method for producing micro- or nanostructured elements and such elements.
Micro-mirror arrays, such as for use in microlithography systems, are known. By way of example, a mirror array including a multiplicity of displaceable individual mirrors is known from WO 2010/049076 A2. The properties of the actuators which set the position the individual mirrors, can play a decisive role for the optical function and quality of such a mirror array. Actuator devices for displacing individual mirrors of a mirror array for a projection exposure apparatus are known from DE 10 2013 206 529 A1.
The disclosure seeks to provide an improved a micro-optical element, such as a micromirror, for example with respect to its actuation and/or its thermal conductivity.
According to an aspect, the disclosure provides a micro-optical element which comprises a body with an optical surface, and a substrate for suspending the body and an actuator device for tilting the body, wherein the actuator device is arranged on the opposite side of the substrate with respect to the body.
The actuator device can be arranged in a cavity, such as in a cavity being comprised in a supporting structure for providing mechanical support to the micro-optical element. The supporting structure can be arranged on the rear side of the substrate for suspending the body of the micro-optical element.
The substrate can be provided for mechanically holding the body of the micro-optical element.
Herein, a micro-optical element denotes an element with a size, such as a diameter, in the range of micrometers to at most several centimeters but for example at most several millimeters, for example less than 1 mm.
For simplicity's sake, the micro-optical element is also referred to as optical element, only, in the following.
An optical surface denotes a surface for guiding and/or shaping an optical beam. It can be a reflective surface, such as a mirror surface, or a refractive surface, for example a lens surface, or a surface with a diffractive structure, such as a grating. The optical surface can be formed by a multilayer structure which is designed to reflect EUV-radiation.
The optical surface of the body is also referred to as the front side (FS) of the body or, indeed, the optical element. The opposite side is correspondingly referred to as the rear side of the body or the rear side of the body of the optical element.
The micro-optical element can be a mirror, such as a micro-mirror, for example an EUV-mirror.
The mirror can have a reflection surface with a maximal size, for example a maximal diameter, of at most 1 cm, such as at most 5 mm, such as at most 3 mm, such as at most 2 mm, such as most 1 mm. Other dimensions are possible.
The surface of the mirror element can bear a reflective coating, such as an EUV reflective coating.
The body of the optical element can be embodied plate shaped. It can be embodied as mirror plate. In the following the body of the optical element is also referred to as mirror plate.
The mirror plate can be suspended on the substrate by a suspension mechanism. The suspension mechanism can be embodied as flexures. They can comprise a plurality of springs, such as leaf springs.
The suspension mechanism can be embodied as a Cardan joint. For details, reference is made to DE 10 2015 204 704 A1 and WO 2016/146541 A1, which are hereby incorporated into the present application in their entirety. The optical element can be suspended by a Cardan joint.
The optical element can be suspended in a way, such that its effective pivot point lies in front of the substrate. The effective pivot point of the optical element can be on the opposite side of the substrate with respect to the actuator device.
The actuator device can be part of a micro-electromechanical system (MEMS). It can itself be a MEMS, such as MEMS based on microstructured silicon.
The actuator device can be part of an actuator system.
The actuator device can be arranged within a supporting structure. The actuator device can be arranged in one or more cavities comprised in the supporting structure. Further details are described below. The supporting structure can be a physically separate entity with respect to the substrate for holding, such as suspending, the mirror plate.
The actuator device can be arranged in its entirety on the opposite side of the substrate with respect to the body of the micro-optical element.
The actor actuator device can comprise electrodes, which are arranged on the opposite side of the substrate relative to the body of the optical element. For example, all electrodes of the actuator device can be arranged on the opposite side of the substrate with respect to the body of the micro-optical element.
Further, the actuator device can be a physically separate entity. For example, all of the electrodes of the actuator device can be separate, for example arranged at a distance, to the structural parts of the body of the optical-element or any structural parts directly linked thereto. For example, the actuator device can be embodied such that none of the actuating electrodes is in physical contact with any of the structural parts of the body of the optical-element or any structural parts directly linked thereto.
For example, according to an aspect the actuation force generated by the actuator device can be applied or transferred to the body of the micro-optical element mechanically, for example by a mechanical mechanism for transferring such actuation force to the body of the micro-optical element. For the transfer of the actuation force to the body of the micro-optical element the mechanism for transferring such force can be brought in direct physical contact with the body of the micro-optical element.
The front side of the substrate for holding the body of the optical element can define a reference plane with a surface normal. The surface normal of the reference plane corresponds to the surface normal of the optical element, for example the surface normal of the reflection surface of the mirror, in the neutral, i.e. un-tilted state or position of the optical element.
The actuator device can be part of an actuator system comprising a plurality of such actuator devices.
The actuator device can comprise one or more comb drives. Further details of the embodiment of the actuator device are described below.
The micro-optical element can serve as an element of a microlithography system, for example an illumination optics of a microlithography system. Other uses of the micro-optical elements are possible.
The microlithography system is also referred to as projection exposure apparatus.
According to an aspect, the provides an actuator device which comprises a mechanism for transferring an actuation force to the body of the micro-optical element. Such a mechanism can extend along a length lz in the direction of the surface normal. Such direction is also referred to as longitudinal direction z.
The direction of actuation, for example the direction of an actuation force exertable by the actuator device on the body of the optical element can be parallel or at least have a component parallel to the direction of the surface normal. For example, the direction of the actuation force can have a main component parallel to the surface normal. This shall be understood to mean that the projection of the actuation force onto the surface normal (their scalar product) is larger than its projection onto the reference plane perpendicular to the surface normal.
The mechanism for transferring the actuation force can be embodied as a physical mechanism, such as a mechanical mechanism.
The mechanism for transferring the actuation force can comprise one or more pins.
The mechanism for transferring the actuation force can be made of a wafer.
The mechanism for transferring the actuation force can be made of silicon or a silicon compound.
The mechanism for transferring the actuation force can be produced by MEMS-technology.
The mechanism for transferring the actuation force can be mechanically guided, for example electro-mechanically guided.
The mechanism for transferring the actuation force to the optical element can be arranged within a cavity in the substrate for holding the body of the optical element. They can be arranged through a cavity, for example in form of a through silicon passage hole, which in the following is also referred to as through silicon via (TSV), in the substrate.
The length of the mechanism for transferring the actuation force to the optical element, for example in longitudinal direction, can be at least 1 mm, for example at least 2 mm, for example at least 4 mm. Without restricting the scope of the present disclosure, the extension can be up to 10 mm. The length of the mechanism for transferring the actuation force to the body of the optical element can be at least as large as a side length of the optical surface of the optical element, for example at least twice as large, for example at least three times as large, for example at least five times as large, for example at least ten times as large as a side length of the optical surface of the optical element.
The mechanism for transferring force from the actuator device to the optical element can be coupled to the body of the optical element such that they can transfer a force in one direction, only or such that they can transfer the force in two opposite directions. They can embodied as pins with a push-only coupling to the body of the optical element or as pins with a push and pull-coupling to the body of the optical element.
According to an aspect, the disclosure provides an optical element which comprises a sensor. It can comprise one or more integrated sensors. It can comprise tilt sensors, i.e. sensors for sensing the tilting of the body of the optical element.
The sensor can be arranged on the substrate, for example on the front side of the substrate. The sensor can be arranged between the mirror plate and the substrate.
The sensor can comprise a plurality of comb electrodes. The comb electrodes can be arranged to extend radially. For further details of the sensor electrodes reference is made to the aforementioned WO 2016/146541 A1.
According to an aspect, the disclosure provides a substrate which comprises a plurality of connections, for example electrical and/or thermal connections. The connections can comprise via-connections, for example through silicon via (TSV's).
According to an aspect, the disclosure provides a substrate which comprises an interface, for example an interface for electrical and/or thermal coupling. The interface can be arranged on the rear side of the substrate.
The cavities in the substrate for the arrangement of the mechanism for transferring force from the actuator device to the body of the optical element are also referred to as pockets.
The substrate can be provided with passages holes for the mechanism for transferring, force from the actuators to the mirrors. The passage holes can be in a wall delimiting the cavity.
According to an aspect the actuator device has a size Az also referred to as vertical length along the direction of the surface normal and a cross-sectional area perpendicular to the surface normal, wherein the cross sectional area of the actuator device is smaller than the optically active area of the optical element, for example smaller than the reflection surface of the mirror, and wherein the product of the largest diameter of the cross sectional area of the actuator device and its size Az along the direction of the surface normal is larger than the reflection surface.
By that, the space used for the actuator device in a plane parallel to the reference plane footprint, i. e. can be smaller than the optically active area, for example the reflection surface, of the optical element whilst the area of the actuator device, which can be used to generate the actuation force can be larger than the optically active area, for example the reflection surface.
For example, the actuation force, which can be generated by the actuator device within a given cross sectional area can be increased. This can be desirable, for example, if a large number of optical elements are arranged in a densely packed fashion, such that the space behind the optical elements available for arranging the actuator devices is very restricted.
According to an aspect the actuator device, for example all of the actuator devices of the optical element, is/are arranged completely within a volume having the same cross-sectional area as the reflection surface. The actuator device, for example all actuator devices of a given optical element can be arranged completely within a volume extending from the optically active area, for example extending from the reflection surface in the direction of the surface normal.
According to an aspect, it is possible to arrange one or more, for example all of the actuator devices of a given optical element to stand over the cross sectional area of a projection of the optically active area, for example the reflection surface of the optical element.
The cross sectional area of the volume, in which the actuator devices of a given optical element are arranged can be completely within a projection of the optically active area, for example of the reflection surface. Alternatively, the cross sectional area of the volume, in which the actuator device, for example all actuator devices of a given optical element arranged can also be larger than the cross sectional area of such a projection.
Herein, the cross sectional area of the volume, in which the actuator devices are arranged, refers, in particular, to the smallest convex envelope of the actuator devices.
According to an aspect a micro-mirror array comprising a plurality of mirror elements, for example according to the previous description, comprises a supporting structure for providing mechanical support to at least some of the mirror elements. The supporting structure can be arranged on the rear side of the substrate for holding the mirror plates.
According to an aspect, the supporting structure comprises cavities for receiving actuator devices for displacing the mirror elements.
Herein, the actuator devices can be parts of the optical elements described above.
The substrate for holding the separate mirror elements can be monolithic or multi-part. For example, it is possible, that each of the mirror elements has a separate substrate. Alternatively, groups of mirrors can be arranged on a common substrate.
The one or more substrates are for example arranged between the mirror plates and the supporting structure, for example between the mirrors and the actuators.
As mentioned before, at least some, for example each of the mirror elements can comprise integrated tilt sensors. The sensors can be arranged on the substrate, for example between the mirror plate and the substrate. According to an aspect, the supporting structure can comprise different types of electrical and/or thermal connections.
According to an aspect, the plurality of mirror elements are arranged on a common supporting structure, which is also referred to as holder.
For example, in case of a hexagonal embodiment of the mirror elements, 19 mirror elements can be arranged on a common supporting structure. Without restricting the scope of the present disclosure, such supporting structure can comprise 57 or 76 pockets for actuator devices.
The supporting structure can comprise one, two, three, four or more pockets for actuator devices for each mirror.
According to an aspect the supporting structure can be made of ceramics.
For example, the supporting structure can be made of ceramic shells. For example, the supporting structure can be made of a plurality of identical ceramic shells, wherein, for example, neighboring shells are shifted relative to each other, for example in a direction perpendicular to the surface normal.
According to an aspect, in case of a rectangular, for example square, embodiment of the mirror elements, two pockets for actuator devices can be comprised in the supporting structure for each tilting degree of freedom of the mirror elements. For example, four pockets per mirror element can be comprised in the supporting structure, for example two for a first tilting direction and two for a second tilting direction perpendicular to the first tilting direction. These pockets can be in one level or in different levels, as the corresponding actuators can have pins of different lengths.
In case of triangular mirrors there can be three pockets per mirror element in the supporting structure.
The number of pockets of the supporting structure for each mirror element can be an integer multiple of some order of symmetry of the reflection surface of the mirror elements.
According to an aspect, the supporting structure is embodied by a low temperature cofired ceramics (LTCC) structure.
The supporting structure can comprise a plurality of vertical electrical connections.
The supporting structure can comprise thermal connections. It can serve as a mechanism for thermal conduction, such as to aid the heat transport away from the mirror elements towards a heat sink or another cooling structure, which can be arranged on the back side of the supporting structure.
At its front side, i.e. at its surface, which faces the substrate or substrates, on which the mirror elements are arranged, for example suspended, the supporting structure can have passage holes for the mechanism for transferring the actuator force to the optical elements.
Further aspects can be related to the actuator device.
The actuator device for the tiltable micro-optical element can comprise a plurality of stacked drives, for example stacked comb drives. Herein, stacked comb drives shall mean separate comb drives arranged in a stacked fashion and/or a single comb drive with a plurality of combs arranged in a stacked fashion. A combination of these variants is also possible. The number of drives and/or combs can be at least 2, for example at least 3, for example at least 4, for example at least 6, for example at least 10.
Herein, the micro-optical element can be a micro-mirror according to the preceding description.
The comb drives can be stacked in direction of the surface normal.
According to an aspect several combs are stacked above each other in a direction, which is parallel to the direction in which the actuation force acts.
The comb drives can be embodied to act in parallel, for example such that the forces generated by each of the comb drives act together.
The comb drives can be made of a single wafer.
The actuator device can comprise multiple on-chip driving levels, for example multiple on-MEMS-chip driving levels.
The actuator device can be an element, which is physically separate from the mirror element, to which it is to be connected.
The actuator device can be embodied as a vacuum-suitable device.
According to an aspect the comb drives comprise perforated comb fingers.
According to an aspect, the comp drives also comprise un-perforated comb fingers.
The perforated comb fingers can comprise micro-holes, having a diameter in the range of 1 μm to 5 μm.
The perforation of the comb fingers can be due to an underetching and release process.
Without loss of generality in the following the surface normal is denoted as z-direction. Such direction is also referred to as longitudinal direction or vertical direction.
The actuator device, for example the orientation of a chip, from which it is made, can be arranged to lie parallel to the vertical direction. For example, with the z-direction being parallel to the surface normal an in-drive chip plane of the actuator device can be denoted as yz-plane in a local coordinate system. In such a local coordinate system the z-direction corresponds to the height of the combs, for example the height of the comb fingers. The y-direction corresponds to the width or thickness of the comb fingers and/or their distance, whereas the x-direction corresponds to the depth of the combs, for example the comb fingers.
For example, the mechanism for transferring the force from the actuation device to the body of the optical element can be arranged to lie parallel to the vertical direction. This is not absolutely necessary. It can also be arranged obliquely to the vertical direction. It can enclose an angle with the vertical direction of up to 10°, for example up to 30°, for example up to 45°, for example up to 60° or more.
The angle between the orientation of the mechanism for transferring the force from the actuation device to the body of the optical element and/or the actuation direction and the vertical direction can be at most 60°, such as at most 45°, for example at most 30°, for example at most 20°, for example at most 10°.
The comb electrodes can have a thickness of a few micrometres. They can have an aspect ratio of height:thickness of up to 5:1, such as up to 10:1, for example up to 20:1.
The height of the comb fingers can be in the range of 20 μm to 200 μm. For further details reference is made to exemplary description of the embodiment with reference to the figures. Of course, the details provided in the description of the exemplary embodiment are not meant to be limiting.
It could be shown, that with the actuator device according to the present disclosure a force per unit area of more than 0.1 mN per mm2, for example more than 0.15 mN per mm2, for example more than 0.3 mN per mm2, for example more than 0.5 mN per mm2, for example more than 0.7 mN per mm2, for example more than 1 mN per mm2, for example more than 2 mN per mm2, for example more than 3 mN per mm2, for example more than 5 mN per mm2, for example more than 10 mN per mm2 can be generated.
According to an aspect an actuator device for a tiltable micro-optical element comprises comb fingers having a maximal size fz also referred to as fingers' height in a longitudinal direction z and a mechanism for transferring an actuation force from the actuator device to an optical element, wherein such a mechanism extends along a length lz in the longitudinal direction z, wherein at least one of the mechanisms for transferring the actuation force from the actuator device to an optical element has a length lz which is larger than the maximum height fz of the comb fingers. The ratio lz:fz is for example at least 3:1, such as at least 5:1, such as at least 10:1.
The longitudinal direction z herein correspondents for example to the direction of actuation.
By such embodiment of the actuator device, it is possible to arrange the actuator device at a distance to the optical element to be actuated, wherein such systems can be comparatively large, for example larger than the height of the comb fingers. Such embodiment can be desirable, if the physical space directly underneath the optical element is restricted.
According to an aspect the range of movement of the actuator device, for example of the mechanism for transferring the actuation force to the body of the optical element, for example in longitudinal direction z, can be at least 100 μm, such as at least 200 μm, such as at least 300 μm, such as at least 500 μm. It is generally at most as large as the comb fingers' height in longitudinal direction.
According to an aspect an actuator device for a tiltable micro-optical element, for example a micro-mirror, has a total size in longitudinal direction z, which is larger than its maximal size in any direction perpendicular thereto. The ratio of the total size of the actuator device in longitudinal direction z to its maximal size in any direction perpendicular thereto can be at least 2, for example at least 3, for example at least 5, for example at least 10.
Further, the ratio of the total size of the actuator device in longitudinal direction z to its minimal size in any direction perpendicular thereto can be at least 5, for example at least 10, for example at least 20, for example at least 50. Further, the ratio of the total size of the actuator device in longitudinal direction z to the range of movement can be at least 10, for example at least 20, for example at least 50, for example at least 100, for example at least 200, for example at least 500, for example at least 1000.
The total size in longitudinal direction z of the comb drive according to the preceding description can be more than 10 mm, for example more than 20 mm, for example more than 30 mm, for example more than 50 mm. It can be as large, as the diameter of a wafer, for example a silicon wafer.
According to an aspect, the actuator device can comprise actuation mechanisms of different types.
It can comprise at least one of the following actuation mechanisms: an electrostatic actuation mechanism, a Chevron-type actuation mechanism, a Piezo-type actuation mechanism.
According to an aspect the actuator device can be made of a single wafer.
The process for making the actuator device can comprise only MEMS processing steps.
According to an aspect, a plurality of actuator devices can be made of a single wafer. For example, the number of actuator devices, which can be made of a single wafer with a diameter of 200 mm can be at least 50, for example at least 100, for example at least 200, for example at least 300, for example at least 500. By making large number of actuator devices out of a single wafer the costs for each actuator device can be reduced.
According to an aspect, an actuator system comprises a plurality of actuator devices according to the preceding description, wherein the actuator devices are arranged in a supporting structure. The actuator devices can be arranged in cavities comprised by the supporting structure.
Herein, the supporting structure can be physically separate from the substrate for suspending the optical elements. The supporting structure can be coupled to the optical elements, for example connected to the optical elements in a separate processing step.
According to an aspect, the supporting structure can comprise a plurality of electrical connections, for example of different types, and/or thermal connections.
The supporting structure can comprise high voltage electrical comics and/or low voltage electrical connections and/or ground wires and/or thermal connections.
The front types of connections in the supporting structure can be made by different processing technologies and/or can be made of different materials.
The supporting structure can comprise connections to and/or from one or more sensor elements and/or connections to and/or from one or more actuator devices.
According to an aspect, the supporting structure is made of a plurality of ceramic shells. For further details reference is made to the preceding description as well as to the description of an exemplary embodiment shown in the figures, the latter being understood not to be limiting.
For example, the supporting structure can be made of LTCC.
According to an aspect a MEMS for displacing an optical element comprises a substrate for suspending a mirror plate on its front side, a supporting structure for mechanically supporting the substrate and a plurality of actuator devices, for example according to the preceding description, wherein the supporting structure is arranged on the rear side of the substrate and wherein the actuator devices are arranged within the supporting structure, for example within cavities or pockets provided in the supporting structure.
As mentioned before, a plurality of mirror plates can be suspended on a common substrate.
The distance between the force generating part of the actuator devices and the mirror plate can be at least 1 mm, for example at least 2 mm, for example at least 4 mm.
The actuator devices can be arranged distantly to the mirror plates.
For the transfer of the actuation force to the mirror plates, s force transmitting mechanism can be used. Such a mechanism can comprise pins, which are also referred to as rods.
Reference is made to the preceding description.
According to an aspect, a facet mirror for a microlithography system, for example a field facet mirror, a pupil facet mirror or a specular reflector, comprises a plurality of micro-mirrors in form of micro-optical elements according to the preceding description and/or one or more micro-mirror arrays according to the preceding description.
The facet mirror can have a modular design, such that a plurality of responding modules can be combined to form a single element, for example a single facet mirror for a micro-lithography system. For example, a plurality of facet mirror modules can be arranged such that their reflection surfaces form a tiling of the total reflection surface.
The micro-optical elements, for example the micro-mirrors and/or the micro-mirror arrays described above can be used as components of an illumination optics, an illumination system or a projection optics for a microlithography system and thereby as components of such a microlithography system. Such illumination optics, illumination system, projection optics and microlithography system specifically belong to the subject matter of the present disclosure.
The micro-optical elements, for example the micro-mirror and/or the micro-mirror arrays described above can more generally be used for a projection system or any application using a flexible, shaping of a beam of illumination radiation.
Further aspects of the disclosure can relate to a method for producing an optical component.
Such methods can comprise the following steps:
The connection of the supporting structure to the mirror plate can comprise the dimension of at least one of the following types of connections: physical connections, for example mechanical connections, electrical connections and thermal connections.
Arranging the actuator devices in the cavities can comprise their mechanical fixation within the cavities and/or formation of electrical connections and/or formation of thermal connections.
By providing a micro-lithography system with micro-optical elements, for example micro-mirrors and/or micro-mirror arrays according to the preceding description a method for producing micro- or nanostructured elements can be improved. Also the micro- or nano-structured elements produced by such methods can be improved.
Further general details and features of different aspects are mentioned as follows.
The substrate on which the mirror elements are suspended is in general a mirror-holder body. It can provide mechanical support and/or electrical connections and/or thermal connections to the mirror elements.
The mirror elements are for example tiltable or pivotable in two axes, for example to axes perpendicular to each other.
The mirror elements can be suspended by spring elements.
The suspension of the mirror elements can be such that the mirror elements have 2 degrees of freedom.
The mirror elements can be suspended by a cardan joint.
Tilt angle sensors can be arranged between the mirror plates and the holder substrate.
The actuator devices can be embodied as linear actuators.
The actuator devices can be embodied as electrostatic actuators.
The spring element can be a cardanic flexure element.
The tilt angle sensor can be embodied as an electrostatic capacitive tilt angle sensor.
Different actuator devices for tilting a given mirror element in different tilt directions can be arranged stacked above each other. For example, the mechanism for transferring the actuation force from the actuator devices to the mirror element can have different lengths for different tilt directions. For example, an actuator device for an X-tilt can be arranged below or above an actuator device for a Y-tilt.
For example, all different actuator devices can be arranged at different levels. Alternatively, two or more, for example all of the actuator devices or all of the actuator elements of a given group of a single mirror element can be arranged at the same level in the longitudinal direction.
The actuator device can comprise a linear electrostatic comb drive. A multiple actuators “on-chip-arrangement” is possible.
According to an aspect, the mechanism for transferring the force from the actuator device to the mirror element can comprise a pin or a rod which
The mechanism for transferring a force from the actuator device to the mirror element can be coupled to the mirror plate in such way, that it can only push the mirror or in such a way that it can push and pull the mirror.
The comb structures of the actuator device can comprise movable double comb placed between two fixed combs each. They can also comprise single combs only, which can generate a force in one direction, only.
To generate higher driving forces multiple comb levels can be arranged in a stacked fashion in the longitudinal direction.
The pin or rod being the mechanism for transferring a force from the actuator device to the mirror element is for example fixedly connected to a multilevel comb structure. Such multilevel comb structure can comprise
At least one of the actuator devices, for example a plurality of the actuator devices, for example all of the actuator devices, comprise at least one mechanism for providing a linear guidance, such a mechanism being for example soft in the move direction and sufficiently stiff, for example at least three times as stiff, such as at least 10 times as stiff, such as at least 100 times as stiff, such as at least 1000 times as stiff, such as at least 10000 times as stiff, such as at least 100000 times as stiff, such as at least 1000000 times as stiff in the parasitic directions. By such a linear guidance mechanism parasitic shifts and rotations can be constrained.
The actuator device can comprise one or more end stops to prevent an accidental snap-in of the movable structure of the electrostatic comb actuator to its fixed parts under an electrical potential. By this consequent shortcut, breakage, total damage, etc. can be avoided.
The actuator device can be designed such that none of the electrical supply wires cross each other.
The drive line for supplying an electrical voltage to the comb structures can be arranged in a tunnel structure in the solid arms of the fixed combs. Such tunnel structure can be hollow or filled by an isolator. They can also overcross with an isolation in-between.
The mirror element can be held by an interposer plate. Such interposer plate can comprise connections for the conduction of electrical signals to functionalize the mirror element. It can also comprise thermal connections to conduct heat away from the mirror elements. Further, it can comprise sockets with electrical connections to connect the actuator devices, which are arranged in cavities of pockets of such interposer plate. For example, the interposer plate is made of our based on LTCC.
The inter-poser plate can be made by fixing together a plurality of shells, for example ceramic shells, with pockets for the actuator devices.
The shells can have a structured site open to a half space.
The interposer plate can be formed by fixing a plurality of such shells together.
It is possible to just arranged the actuator devices in the pockets and then fix the shells together to form the interposer plate.
The interposer plate can form the supporting structure.
It is also possible to first fit the half open shells together and then place the actuator devices in the pockets, where they are fixed and electrically connected.
The optical elements, for example the micro-mirrors can have shape of an equilateral triangle, a rectangle, for example with an aspect ratio unequal 1:1, for example an aspect ratio of at least 2:1, or square, a pentagon, a hexagon, for example an equilateral hexagon.
The in plane width of the actuator device can extend the mirror footprint. Alternatively, at least some of the actuator devices, for example all of the actuator, devices can be arranged completely within the mirror footprint.
The individual actuators can be arranged in a pattern that fills the actuator plane below the mirror plane.
The mirror elements can be arranged in mirror modules, which allow a tiling of a plane.
The in mirror plane width of the actuator devices can be smaller than the size of the mirror elements, for example smaller than half of the size of the mirror elements. For example, the actuator devices can be completely covered by the footprint of the mirror element.
The substrate for suspending the mirror elements and/or the mirror plate and/or the suspension, for example the cardan suspension, and/or the tilt sensors, which can be arranged between the mirror plate and the substrate for suspending the mirrors can be made of silicon or a silicon compound and/or can be produced by MEMS technology, for example by MEMS processing steps, only.
The actuator devices can be made of silicon or a silicon compound.
The actuator devices can be made by use of MEMS technology, for example by MEMS processing steps, only.
The actuator devices can be made from silicon on insulator (SOI) or from wafers covered by silicon oxide and with deposited doped poly-silicon as the movable and fixed combs.
Parts like the shuttle, the pin, the suspensions, the end stop etc. can be formed by vertical etching through the device silicon layer. The thickness of such parts can thus be defined by the thickness of the silicon layer. Movable parts can be released by underetching of the oxide as a sacrifice material.
The mirror elements can have a tilt range of at least 30 mrad, for example at least 50 mrad, and particular at least 100 mrad.
The mirror elements are suitable to work in a vacuum environment.
The mirror elements are suitable to work in an ionized environment.
The mirror elements can tolerate a high thermal load. They can tolerate temperatures of at least 200° C.
In the following, some features of the actuator devices and/or the suspension system are described briefly.
The actuators can fit within the non-occupied footprint of a single mirror.
The actuators can provide sufficient force/torque for the desired range of tilting even in case of stiff suspensions of the mirrors.
The actuators can generate a linear actuation. Thereby side-effects like hysteresis, creep and temperature dependence can be avoided.
The actuators can be embodied and/or comprise electrostatic combs and thin-layered PZTs with additional temperature sensing and compensation.
For the position sensing capacitive combs have been shown to be suitable. For example, in case of piezo-resistive (PZR) sensors, an additional temperature sensing with mK accuracy and calibration can be provided.
For example, side effects like temperature dependence of the sensors can be avoided, for example in the case of electrostatic/capacitive sensors.
The suspension, the actuators, and the sensors can all be placed directly below the mirrors. They can all share the same footprint.
It has been found, that sufficient force/torque to move/tilt the single mirrors of an array can be achieved by an architecture with distant placed thin MEMS-based actuators.
The actuators can have push-only pins or push and pull pins flexibly connected to the mirrors at points.
The pins can be symmetrically situated regarding the centrum of rotation of the mirrors.
The pins can be used to tilt the mirrors.
The actuator force can be generated by multiple on-MEMS-chip driving levels. The driving levels can be ordered vertically (z) along the pin. In this direction the design-size can be free to be chosen. It can for example be in the range of 2 mm to 22 mm or even up to 200 mm.
The larger the number of levels with actuator rows, the higher will be the created force.
The mirrors, for example the mirror array, can be made of silicon or a silicon compound. It can be micromachined from silicon or a silicon compound. It can be made by use of MEMS-processing, for example by a process comprising MEMS-processing steps, only.
The disclosure relates for example to composite mirrors with integrated actuators. The actuators can be monolithically integrated into the mirrors. All parts of the active mirrors can be formed from the same substrate. Alternatively, some of the parts can be fabricated separately and attached/assembled during an assembly process.
The chips for the mirrors can come from different supply chains.
For the tilting of the mirror two independent driving voltages can be applied.
In the following some aspects of the disclosure are summarized again:
According to an aspect, an active mirror element, comprises s mirror-holder body for a mechanical support and electrical and thermal connection, and a mirror plate, tiltable in two axes and suspended to the mirror holder by at least one spring element allowing a two-dimensional tilt, tilt-angle sensors between the mirror plate and the holder substrate, as the mirror is driven by distant linear electrostatic actuators, placed in the depth with a driving rod (the pin) orthogonal to the holder substrate and approaching the mirror plate through passage holes in the mirror-holder body.
According to an aspect, the spring element is a cardanic flexure element, and/or the tilt-angle sensor is an electrostatic capacitive tilt-angle sensor.
According to an aspect, at least one of the actuators is a separate distinct unit, realized separately from the mirror element (with the mirror plate, the mirror body, the suspension and the sensor), and attached to the mirror unit, forming the mirror device during an assembly step.
According to an aspect, the different actuators for the different tilt directions are stacked above each other and possess different long pins. For example, the actuator for x-tilt is below actuator that for y-tilt, or vice versa, or all actuators are at different levels. For example, there can be 4 actuators, as the x- and y-actuators are ordered in different levels and are turned in 90 deg to each other, or there can be 3 actuators in 3 levels, turned in 120 deg to each other. For example, the actuators responsible for different tilt can be orientated with the width (the local y-direction for the drive) along the radial direction on the mirror to the point of the pin's contact.
According to an aspect, at least one of the actuators comprises a linear electrostatic comb drive (more actuators-on-chip possible).
According to an aspect, at least one of the actuators have a pin, which can be extended in two opposite directions (toward and backward), and the pin:
According to an aspect, at least one of the actuators have a pin, which can be extended in two opposite directions (toward and backward). Wherever this bi-directional move is achieved by a movable grounded (or fixed potential) structure, to which is connected the pin, facilitated with movable combs with fingers in both toward and backward sides. The movable double combs are placed between two fixed on the substrate, independently supplied combs: one in the toward and one in the backward direction, each of which can attract the movable structure to its side, when supplied with a driving voltage.
According to an aspect, the mirror element is driven by the pins of distant linear actuators, as higher driving force/torque is achieved by ordering of multiple comb levels along the pin or in a direction, normal to the plane of the mirror plate.
According to an aspect, at least one of the actuators have a pin, rigidly connected and driven by a multi-level comb structure, as the plurality of movable combs are connected to:
According to an aspect, at least one of the actuators comprises at least one linear guidance, soft in the move direction and sufficient stiff in the parasitic directions and be able to constrain the parasitic shifts and rotations.
According to an aspect, an accidental side snap-in of the movable structure of the liner electrostatic comb actuator to its fixed parts under an electrical potential is prevented by end-stops.
According to an aspect, an actuator comprises a multi-level comb structure for a bi-directional push/pull action of the actuator by application of two different voltages, where the over-crossing of the thin planar supply wires is avoided by:
According to an aspect, the active mirror unit comprises 1) a mirror element with mirror-holder body for a mechanical support and electrical and thermal connection, a tiltable mirror plate, cardan suspension, and tilt sensors between the mirror plate, and 2) an interposer plate, which holds the mirror element, conducts electrical signals trough to functionalize the mirror element, conducts the heat away, and has sockets with electrical connections, where are placed and connected the distant actuators. Particular, the interposed is made of or based on LTCC.
According to an aspect, an interposer plate for the active mirror unit has sockets for the distinct actuators, created by fixing together of shells with pockets, as each shell has a structured side, open to the half space. Particular-such interposer and its shells, made of LTCC.
According to an aspect, an interposer plate has sockets for the distinct actuators for the active mirror unit, where:
According to an aspect, within a high fill-factor array of mirror elements or mirror units, the shape or shapes of the single mirrors allows full coverage of the space. The shape of the single mirrors can be chosen form the following list: equilateral triangle, rectangular or squares, pentagon, hexagon.
According to an aspect, within an array of active mirror elements, each driven by distant actuators, in accordance with the above description, the in-plane width of the actuator extends the mirror footprint and the individual actuators are arranged in a pattern that fills the actuator plane below the mirror plane.
According to an aspect, a composite mirror module is covered at high fill factor by arrays in accordance with the above description. The shape or shapes of the mirror arrays can be triangular, rectangular, pentagonal, or hexagonal. These shapes refer for example to the basic shape of the array. They can have a jagged edge.
According to an aspect, for an active mirror element and unit, driven by distant actuators, in accordance with the above description, the in-mirror plane width of the actuator is comparable, or smaller than, or smaller than the half of the size of the mirror element. For example, the actuator element is sufficiently narrow, that its footprint is completely covered by the mirror plate. Thus, an easier shaping and separation of arrays of such mirrors is possible, and higher fill factor for ordering of the arrays can be achieved.
According to an aspect, an active mirror element with a mirror-holder body for a mechanical support and electrical and thermal connection, a tiltable mirror plate, cardan suspension, and tilt sensors between the mirror plate, in accordance with the above description, is made mainly of Silicon, and/or realized by the MEMS technology.
According to an aspect, distinct linear electrostatic actuators for active mirror element, in accordance with the above description, are made mainly of Silicon, and/or realized by the MEMS technology.
According to an aspect, distinct linear electrostatic actuators for active mirror element, in accordance with the above description, are prepared from SOI or wafers covered by SiO2 and with deposited thick doped poly-Si, as the movable and fixed combs, and parts like the shuttle, the pin, the suspensions, the end stops, etc. are formed by vertical etching through the device silicon layer and thus have its thickness. Further, the movable structures: shuttle, pin, moveable combs, suspensions, are foreseen with thickness, or perforated at pitch, comparable with that of the buried oxide and released by underetching of the oxide as a scarified material.
According to an aspect, arrays of active mirror element, and/or distant actuators for their actuation, in accordance with the above description, comprise chips, wherein their chip size is smaller than one exposure field of a standard lithographic stepper or scanner.
According to an aspect, an active mirror element is tiltable in at least one direction of an angle at least 30 mrad, for example at least 50 mrad, for example at least 100 mrad. It is for example suitable to work under low-pressure and/or ionized environment and/or high thermal load.
Further features, details and particulars of the disclosure are evident from the description of exemplary embodiments with reference to the drawings, in which:
Firstly, the general construction of a projection exposure apparatus 1 (also called lithography system) and the constituent parts thereof will be described. For details in this regard, reference should be made to WO 2010/049076 A2, which is hereby fully incorporated in the present application as part thereof. The description of the general structure of the projection exposure apparatus 1 should only be understood to be exemplary. It serves to explain a possible application of the subject matter of the present disclosure. The subject matter of the present disclosure can also be used in other optical systems, for example in alternative variants of projection exposure apparatuses.
The reticle, which is held by a reticle holder (not illustrated), and the wafer, which is held by a wafer holder (not illustrated), are scanned synchronously in the y-direction during the operation of the projection exposure apparatus 1. Depending on the imaging scale of the projection optical unit 7, it is also possible for the reticle to be scanned in the opposite direction relative to the wafer.
The radiation source 3 is an EUV radiation source having an emitted used radiation with a wavelength in the range of between 5 nm and 30 nm. The wavelength of the radiation emitted by the radiation source 3 can be 13.5 nm or 7 nm.
The power of the radiation source 3 can be in the range of 1 kW or more.
The radiation source 3 can be a plasma source, for example a GDPP (Gas Discharge Produced Plasma) source or an LPP (Laser Produced Plasma) source. Other EUV radiation sources, for example those based on a synchrotron or on a free electron laser (FEL), are also possible.
EUV radiation 10 emerging from the radiation source 3 is focused by a collector 11. A corresponding collector is known for example from EP 1 225 481 A2. Downstream of the collector 11, the EUV radiation 10 propagates through an intermediate focal plane 12 before being incident on a field facet mirror 13. The field facet mirror 13 is arranged in a plane of the illumination optical unit 4 which is optically conjugate with respect to the object plane 6. The field facet mirror 13 may be arranged at a distance from a plane that is conjugate to the object plane 6. In this case, it is referred to, in general, as first facet mirror.
The EUV radiation 10 is also referred to hereinafter as used radiation, illumination radiation or as imaging light.
Downstream of the field facet mirror 13, the EUV radiation 10 is reflected by a pupil facet mirror 14. The pupil facet mirror 14 lies either in the entrance pupil plane of the projection optical unit 7 or in an optically conjugate plane with respect thereto. It may also be arranged at a distance from such a plane. In such case it is also referred to as specular reflector.
The field facet mirror 13 and the pupil facet mirror 14 are constructed from a multiplicity of individual mirrors, which will be described in even greater detail below. In this case, the subdivision of the field facet mirror 13 into individual mirrors can be such that each of the field facets which illuminate the entire object field 5 by themselves is represented by exactly one of the individual mirrors. Alternatively, it is possible to construct at least some or all of the field facets using a plurality of such individual mirrors. The same correspondingly applies to the configuration of the pupil facets of the pupil facet mirror 14, which are respectively assigned to the field facets and which can be formed in each case by a single individual mirror or by a plurality of such individual mirrors.
The EUV radiation 10 impinges on both facet mirrors 13, 14 at a defined angle of incidence. For example, the two facet mirrors are impinged with EUV radiation 10 in the range associated with normal incidence operation, i.e. with an angle of incidence that is less than or equal to 25° in relation to the mirror normal. Impingement with grazing incidence is also possible. The pupil facet mirror 14 is arranged in a plane of the illumination optical unit 4 which constitutes a pupil plane of the projection optical unit 7 or is optically conjugate with respect to a pupil plane of the projection optical unit 7. With the aid of the pupil facet mirror 14 and an imaging optical assembly in the form of a transfer optical unit 15 having mirrors 16, 17 and 18 designated in the order of the beam path for the EUV radiation 10, the field facets of the field facet mirror 13 are imaged into the object field 5 in a manner being superimposed on one another. The last mirror 18 of the transfer optical unit 15 is a mirror for grazing incidence (“grazing incidence mirror”). The transfer optical unit 15 together with the pupil facet mirror 14 is also referred to as a sequential optical unit for transferring the EUV radiation 10 from the field facet mirror 13 toward the object field 5. The illumination light 10 is guided from the radiation source 3 toward the object field 5 via a plurality of illumination channels. Each of these illumination channels is assigned a field facet of the field facet mirror 13 and a pupil facet of the pupil facet mirror 14, said pupil facet being disposed downstream of the field facet. The individual mirrors of the field facet mirror 13 and of the pupil facet mirror 14 can be tiltable by an actuator system, such that a change in the assignment of the pupil facets to the field facets and correspondingly a changed configuration of the illumination channels can be achieved. This results in different illumination settings, which differ in the distribution of the illumination angles of the illumination light 10 over the object field 5.
In order to facilitate the explanation of positional relationships, use is made below of, inter alia, a global Cartesian xyz-coordinate system. The x-axis runs perpendicular to the plane of the drawing toward the observer in
Different illumination systems can be achieved by tilting the individual mirrors of the field facet mirror 13 and a corresponding change in the assignment of said individual mirrors of the field facet mirror 13 to the individual mirrors of the pupil facet mirror 14. Depending on the tilting of the individual mirrors of the field facet mirror 13, the individual mirrors of the pupil facet mirror 14 that are newly assigned to said individual mirrors are tracked by tilting such that an imaging of the field facets of the field facet mirror 13 into the object field 5 is once again ensured.
Further aspects of the illumination optical unit 4 are described below.
The one field facet mirror 13 and/or the pupil facet mirror 14 in the form of a multi- or micro-mirror array (MMA) forms an example of an optical assembly for guiding the used radiation 10, that is to say the EUV radiation beam. The field facet mirror 13 and/or the pupil facet mirror 14 is formed as a microelectromechanical system (MEMS). The field facet mirror 13 and/or the pupil facet mirror 14 is composite by few hundreds of MEMS MMA (micro mirror array), or MMA bricks. Each MMA has a multiplicity of individual mirrors 20 arranged in a matrix-like manner in rows and columns in a mirror array 19. A different arrangement is also possible, e.g. hexagonal. The mirror arrays 19 can be embodied in a modular manner. They can be arranged on a carrying structure that is embodied as a base plate. Here, it is possible to arrange substantially any number of the mirror arrays 19 next to one another. Consequently, the overall reflection surface which is formed by the totality of all mirror arrays 19, for example the individual mirrors 20 thereof, is extendable as desired. For example, the mirror arrays are embodied in such a way that they facilitate a substantially gap-free tessellation of a plane. The ratio of the sum of the reflection surfaces 26 of the individual mirrors 20 to the overall area that is covered by mirror arrays 19 is also referred to as integration density. For example, this integration density is at least 0.5, for example at least 0.6, for example at least 0.7, for example at least 0.8, for example at least 0.9.
The mirror arrays 19 are fixed onto the base plate via fixing elements 29. For details, reference is made to e.g. WO 2012/130768 A2.
The field facet (FF) mirror 13 or FF module can comprise several hundred densely stacked mirror elements (field facets). Each mirror element can be actuated in two tilt axes. In such a way more advanced illumination small pupil fill ratio and high flexibility of illumination settings at minimal light loss can be matched.
The individual mirrors 20 are designed to be tiltable by an actuator system, as will be explained below. Overall, the field facet mirror 13 has approximately 100 000 of the individual mirrors 20. The field facet mirror 13 may also have a different number of individual mirrors 20 depending on the size of the individual mirrors 20. The number of individual mirrors 20 of the field facet mirror 13 is for example at least 1000, for example at least 5000, for example at least 10,000. It can be up to 100,000, for example up to 300,000, for example up to 500,000, for example up to 1,000,000.
A spectral filter can be arranged upstream of the field facet mirror 13 and separates the used radiation 10 from other wavelength components of the emission of the radiation source 3 that are not usable for the projection exposure. The spectral filter is not represented.
The field facet mirror 13 is impinged on by used radiation 10 which can have a power of e.g. 840 W or more and a power density of 6.5 kW/m2 or more, for example more than 20 kW/m2.
The entire individual mirror array of the facet mirror 13 has e.g. a diameter of 500 mm and is designed in a closely packed manner with the individual mirrors 20. In so far as a field facet is realized by exactly one individual mirror in each case, the individual mirrors 20 represent the shape of the object field 5, apart from the scaling factor. The facet mirror 13 can be formed from 500 individual mirrors 20 each representing a field facet and having a dimension of approximately 5 mm in the y-direction and 100 mm in the x-direction. As an alternative to the realization of each field facet by exactly one individual mirror 20, each of the field facets can be approximated by groups of smaller individual mirrors 20. A field facet having dimensions of 5 mm in the y-direction and of 100 mm in the x-direction can be constructed, e.g., via a 1×20 array of individual mirrors 20 having dimensions of 5 mm×5 mm through to a 10×200 array of individual mirrors 20 having dimensions of 0.5 mm×0.5 mm.
The tilt angles of the individual mirrors 20 are adjusted for changing the illumination settings. For example, the tilt angles have a displacement range of at least ±50 mrad, for example at least ±100 mrad, for example at least ±120 mrad. An accuracy of better than 0.2 mrad, for example better than 0.1 mrad, is achieved when setting the tilt position of the individual mirrors 20. An accuracy of better than 0.1 mrad, for example better than 0.05 mrad, for example better than 0.02 mrad is used when setting the tilt position of the individual mirrors 20. The individual mirrors 20 of the field facet mirror 13 and of the pupil facet mirror 14 in the embodiment of the illumination optical unit 4 according to
The individual mirrors 20 of the illumination optical unit 4 are accommodated in an evacuable chamber 21, a boundary wall 22 of which is indicated in
Together with the evacuable chamber 21, the mirror having the plurality of individual mirrors 20 forms an optical assembly for guiding a bundle of the EUV radiation 10.
Each of the individual mirrors 20 can have a reflection surface 26 having dimensions of 0.1 mm×0.1 mm, 0.5 mm×0.5 mm, 0.6 mm×0.6 mm, or else of up to 5 mm×5 mm or larger. The reflection surface 26 can also have smaller dimensions. For example, it has side lengths in the μm range or low mm range. The individual mirrors 20 are therefore also referred to as micro-mirrors. The reflection surface 26 is part of a mirror plate 27 of the individual mirror 20. The mirror plate 27 carries the multilayer coating. The mirror plate 27 is also referred to as mirror body or body of the optical element,
With the aid of the projection exposure apparatus 1, at least one part of the reticle is imaged onto a region of a light-sensitive layer on the wafer for the lithographic production of a micro- or nanostructured component, for example of a semiconductor component, e.g. of a microchip. Depending on the embodiment of the projection exposure apparatus 1 as a scanner or as a stepper, the reticle and the wafer are moved in a temporally synchronized manner in the y-direction continuously in scanner operation or step by step in stepper operation.
Further details and aspects of the mirror array 19 for example the actuators for displacing, for example for tilting the mirrors 20, are described below.
An optical element, for example a micro-optical element, comprises the individual mirror 20 which, for example, is embodied as a micro-mirror. The individual mirror 20 comprises the mirror plate 27 described above, on the front side of which the reflection surface 26 is formed. For example, the reflection surface 26 is formed by a multilayer structure. For example, it has a radiation reflecting property for the illumination radiation 10, for example for EUV radiation.
In accordance with variants represented in some of the figures, the reflection surface 26 can have a square or a hexagonal embodiment; It can also have a triangular, quadrangular, for example rectangular or pentagonal embodiment. In general, it has a tile-like embodiment such that a gap-free tessellation of a reflection surface by way of the individual mirrors 20 is possible.
The individual mirror 20 is suspended on a substrate 39 via a suspension mechanism, for example in form of a joint 32 which is only depicted schematically in the figures. For example, it is mounted in such a way that it has two degrees of freedom of tilting. For example, the joint 32 facilitates the tilt of the individual mirror 20 about two tilt axes. The tilt axes can be perpendicular to one another. They intersect at a central point of intersection, which is referred to as effective pivot point 35.
The optical element can comprise an integrated sensor device 43 for sensing a tilt position of the mirror element 20. The sensor device 43 can be arranged between the mirror plate 27 and the substrate 39. The sensor device 43 is for example arranged on the front side of the substrate 39, i.e. on the side of the substrate 39 facing the mirror plate 27. It can be placed elsewhere, in the depth vertically, horizontally or even external.
The sensor device 43 can comprise sensor transducer mirror electrodes 45 and sensor transducer stator electrodes 44.
Respectively two sensor transducer stator electrodes 44 that lie opposite one another in respect of the effective pivot point 35 can be interconnected in a differential manner. However, such an interconnection is not mandatory. In general, it can be desirable for respectively two sensor electrodes 44 that lie opposite one another in respect of the effective pivot point 35 to be embodied and arranged in such a way that they can be read in a differential manner.
The sensor transducer stator electrodes 44 are embodied as comb electrodes. For example, the sensor electrodes can comprise sensor transducer stator transmitter electrode that are arranged in alternation with the comb fingers of sensor transducer stator receiver electrode.
Further details of the sensor device are described in WO 2016/146541 A1, which is hereby incorporated by reference in its entirety.
The sensor transducer stator electrodes 44 can be embodied and arranged radially relative to the effective pivot point 35. For example, they can have comb fingers that extend in the radial direction. This reduces the sensitivity in relation to a possible thermal expansion of the individual mirror 20.
Respectively two sensor units that lie opposite one another in respect of the effective pivot point 35, each with a transmitter electrode and a receiver electrode, can be interconnected in a differential manner or at least readable in a differential manner. This renders it possible to eliminate errors in the measurement of the position of the mirror 20, for example on account of eigenmodes of the individual mirror 20.
The active constituent parts of the sensor device are arranged on the substrate 39. This renders it possible to measure the tilt angle of the individual mirror 20 directly relative to the substrate 39.
The joint 32 can be embodied as a Cardan-type flexure.
In accordance with a first variant, the joint 32 is embodied as a torsion spring element structure. For example, it comprises two torsion springs. The two torsion springs have an integral embodiment. For example, they are aligned perpendicular to one another and form a cross-shaped structure.
The joint 32 can be stiff in view of rotations about the surface normal 36. The joint 32 can be stiff in view of the linear displacement in the direction of the surface normal 36. In this context, stiff means that the natural frequency of the rotational vibrations about the surface normal 36 and the natural frequency of the vibrations in the direction of the surface normal lie above the actuated modes by more than one frequency decade. The actuated tilt modes of the individual mirror lie, for example, at frequencies below 1 kHz, for example below 600 Hz. The natural frequency of the rotational vibrations about the surface normal 36 lies at more than 10 kHz, for example at more than 30 kHz.
The torsion springs can be made of a material with a coefficient of thermal conduction of at least 50 W/(m·K), for example at least 100 W/(m·K), for example at least 140 W/(m·K). This helps to conduct the thermal power absorbed by the mirror away from the mirror. What could be achieved by such torsion springs is that the temperature difference between the mirror plate 27 and the substrate 39 is less than 50 K, for example less than 40 K, for example less than 30 K, for example less than 20 K.
The torsion springs may be made of silicon or a silicon compound. The joint 32 can be produced from highly doped monocrystalline silicon. This opens up a process compatibility of the production process with established MEMS manufacturing processes. Moreover, this can leads to a high thermal conductivity and a good electric conductivity.
The mirror can be kept at a temperature of less than 200° C., for example less than 150° C., for example less than 100° C. The heat absorbed by the mirrors has to propagate a long path up to the MMA parts with fixed low temperature. A heat-sink can be provided at the backside of the MMA brick or at the holder behind it.
In another variant of the joint 32, two pairs of bending leaf springs are provided in place of the torsion springs. The joint 32 also has a great stiffness in the horizontal degrees of freedom in this alternative. In this respect, reference is made to the description of the preceding alternative. The design aspects in view of the horizontal stiffness and in view of the mode separation of the parasitic eigenmodes likewise correspond to what was described above.
The variant of the joint 32 is a Cardan-type flexure with orthogonally arranged, horizontal bending springs that are embodied as leaf springs. Respectively two of the bending springs are connected to one another via a plate-shaped structure, which is also referred to as an intermediate plate.
Horizontal leaf springs can be desirable from a process point of view. For example, they can simplify the production of the joint 32.
In the following further details of the mirror element 20, for example of its actuability are described.
Visible are also via-connections like through silicon vias 50 (TSVs) provided in the substrate 39 and an electrical interface at the back side or rear side of the substrate 39.
The substrate 39 comprises passage holes 51 for pins 52 of actuator devices 53.
Below the substrate 39 there is arranged a supporting structure 54. The supporting structure 54 can be embodied as low temperature cofire ceramic (LTCC) support.
The supporting structure 54 provides mechanical support for the mirror array 19.
The supporting structure 54 can comprise vertical electrical connections and/or thermal connections. It can serve for heat conduction and/or as interface to a heat sink or another cooling mechanism, provide for example at its back side.
The supporting structure 54 can comprise pockets 55 for the actuator devices 53.
The supporting structure 54 can comprise passage holes 55 for the actuator devices' 53 pins 52.
The actuator devices 53 can be embodied as actuator chips. They can be embodied as comb drives, details of which are described below. In the following the actuator devices 53 are also referred to as comb drives or simply as drives.
As shown in
The actuator devices 53 can have a width w, shown in the local coordinate system in
The actuator devices 53 can have a thickness t, which is smaller than a side length Is of the reflection surface 26 of the mirrors 20. The ratio of the thickness t to a side length ls of the reflection surface 26, t:ls, can be 1:3. It can be at most 1:2, for example at most 1:3, for example at most 1:4.
Moreover, the height (z-side in
The height h of the actuator devices 53 can be larger than a side length, for example larger than a diameter, for example larger than the maximal diameter dmax of the reflection surface 26 of the mirrors 20. The ratio of the height h to the maximal diameter dmax of the reflection surface 26, h: dmax, can be larger than 2, for example larger than 3, for example larger than 5, for example larger than 10.
The actuator devices 53 can occupy the complete space below the array 19. They can occupy at least 70%, for example at least 80%, for example at least 90% of the space below the array 19.
The footprint of each of the actuator devices 53 is for example smaller than the area of the reflection surface 26. For example, the sum of the footprint of all of the actuator devices 53 of a given mirror 20 is smaller than the area of the reflection surface 26.
Hexagonal or triangular mirrors 20 can be provided with three actuator devices 53.
Rectangular, for example square mirrors 20, can be provided with four actuator devices 53.
The pins 52 can contact the mirrors 20 at 95% of the distance of the mirror's 20 corner from the mirror's center.
Some exemplary details are given in the following. They were derived for a hexagonal mirror with a side length Is of 3 mm. They can be scaled with the mirror's size.
It was shown that the actuation range can be larger than 100 μm, for example larger than 120 μm, for example larger than 140 μm.
The torque M, which could be generated by the actuator devices 53, can be larger than 1 μN·m, for example larger than 3 μN·m, for example larger than 5 μN·m.
The force F, which could be generated by the actuator devices 53, can be larger than 0.2 mN, for example larger than 1 mN, for example larger than 10 mN.
The linear stiffness kz-mirr of the mirror 20, when the pin pushes, can be larger than 1 N/m, for example larger than 8 N/m, for example larger than 25 N/m.
Some basic properties of the actuator devices 53 which have been shown to be feasible are summarized in table 1.
Without restricting the scope of the present disclosure, each of these exemplary values can be different by a factor in the range of 0.5 to 2, for example in the range of 0.3 to 3, for example in the range of 0.2 to 5.
In
In the implementation example shown in
A driving potential can be applied to the fixed fingers 60.
The whole movable structure, including the pin 52, the side branches and the movable fingers 59 are perforated through by small holes 61. The holes 61 can have a diameter of about 2.5 μm. The space between two neighbouring holes 61 can correspond to their diameter. The holes 61 can facilitate the release of the movable structures by underetching of a layer of sacrificial SiO2 below them. The etching penetrates the holes 61 down to the sacrificial silicon dioxide and solve (etch) it isotropically in depth and laterally at the same rate.
The etching can take part in HF (hydrofluoric) acid.
The design of the fingers' pairs and their parameters are shown
The height zf of the fingers 59, 60 can be at most 10 to 50 times, for example at most 10 to 20 times, the size of the smallest structure to be etched. With a size of the holes 61 of 2.5 μm and some end-stops at a distance in the range of 1.5 to 2 μm, the fingers' 59, 60 height zf can be chosen as 25 μm. More generally the holes 61 can have a diameter in the range of 1 μm to 5 μm and the fingers' 59, 60 height can be in the range of 20 μm to 200 μm. for example up to 500 μm or even more.
The fingers' 59, 60 height is chosen to enable the pin's 52 range of movement. In the example the range of movement is 150 μm. This range ca be assured by the distance between the fixed fingers 60 and movable fingers 59, taking into account their overlap. In the implementation the fingers' 59, 60 have a length 175 μm and an overlap of 25 μm.
More range involves longer fingers. Some nominal overlap in the range of 10 μm to 50 μm can be used. This ensures to have remaining overlap in the real case, considering the fabrication tolerances or unproper displacement because the combs do not pull when run from one another. It was found that the value of the overlap is especially important in the configuration of differential driving, when both opposite fixed combs 60 are biased to some potential and the voltage change is applied to both of them, but with opposite sign. Generally, the approach linearizes the force/voltage characteristics, but only as long as opposite combs have remaining overlap.
The fingers width yf can for example be in the range of 5 μm to 50 μm. It can be in the range of 10 μm to 20 μm. It can be between three times and five times as large as the diameter of the holes 61.
The spacing df between the fingers can be in the range of 2 μm to 20 μm. It can be at least 3 μm, for example at least 5 μm. It can be at most 20 μm. A larger spacing leads to a better security against side snap in, when neighbouring fingers touch each other. A smaller spacing allows the generation of higher forces.
The spacing df is for example large enough to provide a safety margin against bending of the moveable comb fingers and/or tolerances of their production and/or movement. It could be shown that for the design of the actuator drives according to
It has been found that the geometric design of the comb fingers 59, 60 depends on the range of actuation voltages used. The values given above have been found to work for actuation voltages in the range of up to 200 V. With lower voltages the fingers 59, 60 can be made longer and/or thinner.
Application of an actuation voltage will also lead to a side force on the movable comb fingers 59 and thereby on other movable parts of the drive, for example the pin 52. To account for this, the movable parts of the drive are provided with guidance mechanism 65, providing a lateral stiffness (y-stiffness) of at least 104 N/m, such as at least 105 N/m, for example at least 106 N/m. Surprisingly, it could be shown, that such values are feasible and indeed achievable.
With the bi-directional design (
It could be shown that the force per unit area which could be generated with the actuators according to
The actuator devices 53, for example each single comb drive, i.e. each drive chip 56, 56′, comprise a plurality of rows 62 of combs. In
The forces generated by the different rows 62 of combs add together. Thus, the total force and thereby the total force per unit area generatable by the actuator device 53 scales with the number n of rows 62.
The rows 62 are arranged stacked behind each other. They are for example stacked in the direction of actuation and/or in the direction of movement of the pin 52.
The basic architecture of an exemplary embodiment of a comb drive chip 56 within its wafer's frame 63 is shown in
The guidance has two important functions:
Alternative exemplary variants of the drives' architecture are shown in
The embodiment shown in
As shown in
Pin 52 and frame 69 can also be combined (
The frame 69 may be rectangular (
In the example shown in
It has been found, that for some aspects it can be desirable, if the fixed combs 60 are open, for example freely accessible, from the side. This allows them to be connected electrically by extension structures or signal wires without overcrossing of the lines in-between or with other movable structures. An example of such architecture is shown is the uni-directional comb drive shown in
Some benefits of this architecture are the simpler production technology, using fewer steps and the reduced risk of shortcuts.
The architecture of the comb drives 53 may combine different guidance mechanisms 65, 65′ for suppression of different constrained degrees of freedom (DoF).
It is also possible to combine different actuators or actuator elements and/or mechatronical elements like different quidances, sensors, etc., for example different types of actuators or actuator elements in one and the same drive. For example short stroke actuators or actuator elements and long stroke actuators or actuator elements can be combined in one drive.
Such example is schematically shown in
Moreover, additional to the comb actuator the drive 53 shown in
Here, the drive 53 comprises a combination of straight 74, Π—75 and W—76 leaf springs.
The chevron actuators 77 are based on the principle of thermal expansion: when current is set through the beams, they heat and expand. These actuators possess small range but create high force.
The combination of the comb actuators with one or more other types of actuators, for example piezo actuators, is also possible.
In the following some aspects and details of a possible method for the production of the actuator devices 53 are described.
The process for the production of the actuator devices 53 can be kept as simple as reasonably possible, enabling a shorter development duration, less risky and high-yield manufacturing, and lower costs by a volume fabrication. A possible fabrication sequence will be presented below.
The actuator devices 53 are built as MEMS. They can be build using only MEMS-processing steps.
For the comb drives 53 described above for example two technologies have shown to be feasible and desirable: the SOI (silicon-on-insulator) approach (
The SOI approach (
The start is with SOI wafers 78: a holder wafer 79 with a thick buried oxide 80 (BOX) and upper device layer 81. The BOX 80 can have a thickness in the range of 2-3 μm. The upper device layer 81 can be as thick as will be the movable and fixed structures, for example 25 μm.
During a first etching step 83 the upper device layer 81 can be etched vertically with an etch stop on the BOX 80, leaving dense perforated structures 82 with holes size similar to the BOX 80 thickness, and large-base structures. The size of these base structures can be several to ten or more times the BOX 80 thickness.
Then, during a second etching step 84, the BOX 80 is etched isotopically in HF acid, thereby underetching and releasing the movable, perforated structures (
The wires are only schematically shown. They can be long narrow fixed paths of doped poly-Si, as high as the combs 59, 60 and the pin 52.
The poly-Si approach (
Regions with different combination of these materials can be created by proper structuring.
The released free structures are done like in the SOI approach: by perforating the thick poly-Si over the sacrificial SiO2 and the underetching of the later (
For the fixed and electrically connected combs or anchors the oxide is etched away and the thick poly-Si to be deposited on the thin highly doped poly-Si layer 90 (
An anchor can be just fixed and not electrically connected. For this the thick poly-Si can lay on the nitride (
The electrically connected combs may rest on the thin poly-Si wire in some areas. They get the potential and can further stay as fixed anchors (
A clever feature—a signal/wire crossing rigid bridge, can be realized employing the potential of this technology. Here, part of the fixed thick arm for the fixed comb fingers can propagate over a wire for another signal, covered and electrically isolated by sacrificial SiO2 (
Alternatively, the crossing area also can be perforated, and by the SiO2 etch step the oxide can be removed and the bridge will stay above another signal wire (air isolation:
Such signal crossing is implemented by the bi-directional architecture solutions shown in
For the architecture solutions with frame 69 as shown in
The gap g between the frame 69 and the signal lines of the wiring 66 is given by the difference between the thickness of the BOX layer 80, for example about 2.5 μm, and the thickness of the poly-Si wire (upper device layer 81), for example about 0.5 μm. Thus, the gap can be in the order of about 2 μm.
The frame and the lines form plate capacitors at these areas and the frame is attracted toward the substrate at every cross by a x force when a driving voltage is applied. In addition the whole frame 69 is pulled toward the floor by an electrostatic force. However, with the design shown above, there is another force, which counteracts the pull-in force toward the driving wires. At the same time, if a supply voltage is applied and if the movable combs are attracted and shift toward the floor, the capacity between them and the fixed combs increases and an electrostatic force in x-direction appear, trying to align back the combs. It could be shown, that a snap-in of the combs to the bottom substrate can safely be prevented by the designs shown above.
In the following further details of the fabrication technology and process flow for the production of the comb-actuator chips are described.
First it is described how a comb-drive chip according to the SOI-based process technology can be realized. As mentioned above, two types of structures can be pre-defined by this tech: 1. densely perforated structures, which can be released by underetching of a sacrificial layer, which, for example can be made of buried oxide and 2. anchored or fixed structures, which stay on a large base over the floor oxide. The process flow is schematically shown in
The fabrication starts with a SOI wafer 78 with a device layer 81 as thick as high in x will be the structures and a BOX layer 80 with a thickness, similar to the size of the perforation holes 61, e.g. 2-3 μm (
The known and reliable vertical processes for DRIE (deep reactive ion etching), also known as a Bosch process, are reproducible and effective by an aspect ratio of 1:10 up to 1:20. This ratio is reflected by the ratio of the diameter of the holes 61 to the thickness of the device layer 81. More generally, the aspect ratio can be as high as 1:50 and even higher. Generally, the hole size and/or the distance between neighboring holes can be in the range of 1 μm to 10 μm. The comb structures can have a height (hx) in the range of 10 μm to 100 μm, or even up to 200 μm or even higher.
Next, in a back side protection step 92 the back side (BS) of the wafer is protected by a deposited or growth of a SiO2 layer 91 (
The following preparation steps 93 prepare the front side (FS) of the wafer. As a preliminary step some metallic paths 94 or area are structured. This involves metal deposition, lithography and etching to form them. Thus, the bonding pads 67 are to be structured.
Moreover, thin metallic paths can be placed over the long paths where the future electrical signals propagate. This can significantly reduce their resistance.
Next comes a lithography step for the definition of the functional and supporting structures: movable 59 and fixed combs 60, the suspension with its free part and the anchors, the pin 52, the wiring Si hills, the bonding pads 67, and the bridges 64 which hold the chip to the frame 69. With the structured PR 95 as a definition mask the device layer is etched vertically by a DRIE process 96 with an etch stop on the BOX 80 (
Then the bulk chip body is separated. A separation channel 97 is etched from the BS: by a dry plasma process 98 (e.g. DRIE), using the structured oxide as an etch mask, or with a double PR+oxide mask, or wet chemically in KOH with an oxide mask (
By a KOH process the FS of the wafer can be protected in a chuck.
Finally, in a further etching step 99, the wafer is dipped into a BHF (buffered HF acid), which etches anisotropically SiO2 (
The process time can be estimated dividing the BOX 80 thickness with the SiO2 etch ratio. This is the time for which the etch process will go deep up to the bulk (holding) silicon, but also laterally until the next hole. Thus, all vertically defined and perforated structures will be underetched and released.
All structures, which have a base much larger than twice the BOX 80 thickness will remain with a slightly underetched, but solid base. Thus, they remain fixed.
After stripping of the PR 95, the chip is kept to the wafer's frame 69 by the side bridges 64 and can be separated if they are cut, sawed, or just broken.
A cross-section of such chip 56 along the pin 52, with a protection cap 58, which can also be structured from Si, is shown in
In the following some details of an example for the production of a chip 56 with a poly-Si process (schematically shown in
A comb-drive chip shown in
For this variant, the fabrication starts with a simple, double-side polished Si wafer (
In a deposition step 100 a heavily doped poly-Si layer 90 is deposited on the SiNx layer 86 and structured in a structuring cycle 101 which is also referred to as structuring sequence, (photolithography, RIE of poly-Si, PR stripping) to form the planar interconnections 102 on the substrate (
The poly-Si layer 90 can have a thickness of 500 nm.
As a next step, deposition step 103, a sacrificial oxide layer 104 is deposited from a gas-phase (gas TEOS=Tetraethyl orthosilicate) under low-pressure or plasma (LPCVD or PECVD process) (
TEOS SiO2 deposition up to 5 μm, or even 10 μm is possible.
Optionally, the surface can be planarized by CMP (chemical-mechanical polishing).
After that, optionally, few 1 μm to 3 μm small and ˜1 μm shallow cone or pyramidal holes 105 can be formed into the oxide (lithography, anisotropic RIE of SiO2, PR strip). When filled later with poly-Si, they will be x-endstops and will prevent the shuttle of parasitic move and snap-in on the floor.
Further, the areas for the anchors over the isolated floor, and the fixed structures, which steps on the poly-Si wires, is etched free form the sacrificial oxide. It is done in a structuring step 106, for example by photolithography and RIE or wet-chemical etching of SiO2 with a stop on the poly-Si or on the nitride (
Over the thus produced structures a thick in-situ doped poly-Si layer 107 is deposited in a deposition step 108. It has a thickness corresponding to the height of the combs 59, 60 and the pin 52.
In the considered design, the thickness of the poly-Si layer 107 is 25 μm, but it can be also up to 100 μm, for example up to 200 μm, or even higher.
It can be planarized by CMP (
For the generation 109 of the bonding pads 67 the areas for the future bonding pads 67 are metalized. For this a deposition of a metal layer 94, e.g. Au or Al, lithographically defined and structured by RIE or wet-chemical etching, or lift-off of metal (
The chip definition mask is now formed now on the wafer's back side (BS) by deposition of oxide 110 and its structuring by SiO2 RIE process 111. The bulk chip body is separated by etching of the surrounding channel 97 from the BS: by a dry plasma process (e.g. DRIE) with the structured oxide, or with a double PR+oxide mask, or wet chemically in KOH with the oxide mask (FS wafer's protection in a chuck necessary) (
It is followed by a lithography step 112 for the definition of the functional and supporting structures: movable 59 and fixed combs 60, the pin 52, the suspension with its free part and the anchors, the plateaus for the bonding pads 67, and the bridges 64 which hold the chip to the frame 69 (
With the structured photoresist (PR) 95 as a definition mask 113 the device layer is etched vertically by a DRIE process 114 with an etch stop on the BOX 80 (
Next, in an isolation step 115, the nitride isolation 116 is etched by RIE from the BS (
Then, in a release step 117, the wafer is dipped into a BHF (buffered HF acid), which etches anisotropically the sacrificial SiO2 (
This isotropic HF wet chemical process goes deep and at the side, until it meets nitride or poly-Si. Thus, all vertically defined and perforated, or narrow linear structures (e.g. the leaves of the suspension), which stay over a sacrificial oxide, will be underetched and released.
All structures, staying on nitride or poly-Si remain fixed since HF practically does not affect these materials.
After stripping 118 of the PR 95, the chip is kept to the wafer's frame 69 by the side bridges 64 and can be separated if they are cut, sawed, or just broken (
In the following some details of the arrangement of the actuator devices 53 and assembly concepts are described.
The mirror array 19 according the suggested architecture, as described above, comprises an assembly of the array of flexible connected mirrors 20 with integrated tilt sensors 43 for each mirror 20. The tilt sensors 43 can be micro-structured in silicon. Further the mirror array 19 comprises a holder (supporting structure 54) with pockets 121, providing mechanical support and electrical and thermal connection.
Further, the mirror array 19 comprises the comb drives' chips 56 plugged into these sockets, with the pins 52 in approach or fixed to the mirrors 20.
The holding body (supporting structure 54) provides an electrical connection for the mirror array 19. Through the holding body the sensor signals have to be conducted. The supporting structure 54 further comprises a grounding of the mirrors 20 and an electrical supply to the drive chips 56. For example, it comprises a plurality of electrical connections and interfacing bond/bump pads. Moreover, it allows the signals rerouting.
The supporting structure 54 can be made of a material with a high thermal conductivity, for example higher than 100 W/(m·K), such as comparable or higher than that of crystalline Si (149 W/(m·K)), for example higher than 200 W/(m·K), possibly higher than 300 W/(m·K).
It can be solid.
For low-pressure application It can have low outgassing.
It can be highly structured for the pockets 121 and openings 55.
A holder body (supporting structure 54), which can also be referred to as structured plate, can be created as a stack of separate ceramic shells 122 with shifted pattern, aligned and fixed one over the other in an aligning step 123 and a fixing step 124, respectively (
Each shell 122 can have sockets for the drive chip and their pins. In principle there can also be shells 122 without pockets 121.
The space between the shells 122 can be used for planar trough-propagating wires (not shown).
The shells 122 are also referred to as plates. The pockets 121 are also referred to as cavities.
Plates with cavities and wires can be created by the LTCC (low temperature cofire ceramics) technology. LTCC provides for robust assembly and packaging of electronic components, multi-layer packaging in the electronics industry, for example MEMS. The starting material is composite green tapes, consisting of ceramic particles mixed with polymer binders. Metal structures can be added to the layers, commonly using via filling and screen printing. The tapes are flexible and can be machined, for example using cutting, milling, punching and embossing. Individual tapes are then bonded together in a lamination procedure, where the polymer part of the tape is combusted and the ceramic particles sinter together, forming a hard and dense ceramic component.
In general, there are two possibilities for the production of the assembly of the drive chips 56 and the sockets' holder 54.
As schematically shown in
In this variant of the assembly, the chips can be electrically connected after they are fixed, e.g. by a multi-level wire bonding, if their bonding pads 67 are sufficiently accessible, or in advance bonded to individual PCB 125 or ceramic holders as shown in
A feature of this approach is, that the pocked-holder 54 can be mounted first to the element with the mirror array 20, e.g. by bumps in-between. As a next step the mirror array 20 with its ceramic holder 54 can be turned with the mirrors 19 below and the drive chips 56 can be plugged into their sockets (
The pins 52 can be fixed at the mirrors 19, e.g. by gluing or welding, or let free to slide on the mirror's 19 reverse side.
Then the drive chips can be fixed and electrically connected.
By the assembly of the drive chips 56 in the LTCC holder 54 all chips 56 can be arranged in pockets 121. They can all be arranged to be in one level parallel to the mirror's 19 surface. This can be desirable unless the footprint of the actuators is sufficient small to support the mirrors pitch. For example, if the actuators footprint is larger, the different actuators for every mirror can be ordered in pockets in different levels. This is also possible in general.
For example, it is possible to arrange the actuators for y-tilt in a different plane, for example below the actuators for x-tilt or vice versa.
Difference in the distance between the actuators 53 and the mirrors 19 can be accounted for by suitably adjusting the lengths of the pins 52 of the different actuators 53. For example, different actuators 53, for example different groups of actuators 53, can have pins 52 with different lengths. Here, the lengths of the pins 52 of actuators 53 of the same group can have identical lengths.
If the mirror 19 is tiltable by four actuators 53, two for a x-tilt and two for a y-tilt, the x- and y-actuators can be placed inside different LTCC holders 54 with pockets 121. Within their respective holder 54, the actuators can be mechanically, electrically and thermally connected, e.g. by micro-bumps.
A feature of such a design is, that the actuators for different tilt directions (DoF) can be orientated at angles in-between. This can be achieved by turning the LTCC holder plates in-between and then connecting them. Therefore, the parasitic reaction forces by pushing the mirror can be adjusted to act in the same direction in the local coordinate system of the actuator and to be suspended in the same way by the drive's guidance.
It can be beneficial, if the width of the actuator (the longer side of its footprint) is along the radial direction to the pin's contact point. In that case the reaction force when tilting the mirror 19 will act in the comb's y-direction, which is anyway stiff due to the risk of side snap-in.
Generally, it is possible that the drives for different tilt directions differ in their design and/or have pins 52 of different lengths.
It is also possible that all actuators 53 of a given mirror 19, for example all three or four actuators 53, are placed at different levels. For example, for the case of 3 driving actuators 53 per mirror 19, it can be desirable, if they are arranged in 3 different levels.
For example, actuators 53 of a given mirror 19 can be orientated with their width along the radial direction to the point of the pin's 52 contact. With three actuators 53 for a given mirror 19 they can be arranged turned each at 120 deg with respect to the others.
Alternatively, as shown in
A feature of this variant is, that the actuator chips 56 are fixed and connected in advance to the LTCC holder 54. Next, the holder 54 can be mounted and connected, for example bumped, to the mirror array 20 element. This involves fine control of the position and parallelism of the pins of such fixed chips.
Otherwise, due to the tolerances, they can press differently strong the corresponding mirrors, or to stay initially at different distance from the mirrors. Therefore, the mirrors 19 may be pressed and pre-tilt already by the assembly. To correct for such a pre-tilt an individual bias voltage to the actuator of each drive can be applied. For example, each actuator may have a different set-point. Thus, it is possible to make sure, that in a base state the pins press equally strong and the mirrors 19 stay parallel to the substrate and all point in one direction.
In the following, some bundling concepts for the mirrors 19 are described.
For parallel manipulation of light, which can lead to desirable properties for multi-optical beam systems like projectors, multi-beam sawing or welding machine, and especially by the modern lithographic projectors, such as EUV projection apparatuses, it can be possible to use arrays 20 of single mirrors 19. The handling is simple and safer, the production is shorter and the assembly-faster and not so risky. Moreover, the arrays of MEMS elements benefit from the parallel processing of all structures within a chip and all chips within a wafer, and the joint processing of a lot of wafers. The size of the array is limited by the yield and the size of one lithographic exposure field.
One implementation for bundling is a hexagonal array of hexagonal mirrors 19, i.e. mirrors 19 with a hexagonal reflection surface. Similar considerations as described below apply for other geometric realizations. For example, the mirrors 19 can also have a rectangular, for example a square reflection surface. They can also have a triangular reflection surface. Their reflection surface can be equilateral. Other shapes or embodiments are possible.
The number ntot of mirrors 19 in one such hexagonal array can be calculated as ntot=1+sum(6*(k−1)), where k is the number of the shells 122. The number ntot can be e.g. 19, or 91, or 331.
Further, one holder 54 with sockets can support one mirror array 20, but the actuator chips are discrete, and the ceramic holder should embrace them. The parallelism by them is in the processing: the processes are applied for all chips from one wafer, and the wafers from a batch are processed in one series. In the following some aspects of possible shapes of the actuators' holder 54 are described. It is possible to fill completely the area of the composite mirror with equal such holders, i.e. with bundles or modules of arrays of hexagonal mirrors with discrete actuators. Generally the mirror arrays 20 have a modular design. They can be embodied as modules, which can be freely combined with each other. This enables an easy replacement, in case some modules turn out to be faulty.
Below, a possible arrangement of the mirrors 19 and their actuators 53 is described with reference to
For hexagonal mirror arrays, if the width (y) of the actuator 53 is comparable or even larger than the size of the mirror 19, the actuator footprint falls partially outside the mirror contour, even if the pin 52 presses the mirror 19 not in the corner, but at smaller arm. In
A 19-mirror array is shown in
Further, in the arrangement shown in
It can be seen from
Thus, a more complicated form for the holder for the actuators 53 can be used. An example of such form is shown in
Since the mirrors 19 are positioned in a hexagonal step-and-repeat tessellation, the same applies also for the 19-mirror module or bundle (
The same rule also holds for larger hexagonal arrays: if the array is created by hexagonal step-and-repeat of the footprint of a mirror with its belonging actuators, and if the actuators do not intersect with their neighbors, the holder shape embracing the actuators can be copied by a multiple step-and-repeat pitch and the bundles will fill complete the 2D space without intersection.
Other arrangements of the actuators 53 relative to the mirrors 19 are shown in
Here, hexagonal mirrors 19 with 3 mm size and actuators 53 (
Mirrors 19 with 3 actuators 53 (
Obviously, bundling of the hexagonal mirror elements in rectangular (
The actuators 53 for every mirror 19 can be arranged at the same level. They can also be arranged at different levels. This would allow larger footprint, but involves difference in the design and the length of the pin 52.
The area of the mirror module can be easily filled by multiple step-and-repeat copy of such mirror elements/mirror modules with hidden actuators. The arrays can be formed triangular, or rectangular, as pentagons or hexagons. They can have straight or zig-zag-sides. The second approach is more complex technically, bur allows denser packing of the arrays/bundles within the mirror module.
Again, it could be shown that the footprint is feasible. The desire torque and force can be generated by the actuators 53.
A shorter arm 128 length means that a higher tilt range for the mirror 19 can be achieved with the same range of movement. For example, with an actuation range of the drive of 150 μm a tilt range of 100 mrad could be achieved.
The drives 56 described above can be produced by MEMS processing, for example by MEMS processing, only. They are MEMS devices. The MEMS devices profit from the parallel processing of all chips in a wafer and from the automated processing of a lot of 25 wafers. The lithography can be done on a stepper: step-and-expose systems, projecting a 5″ mask in an exposure field 130 by a size reduction of 1:4 to 1:5. One such field 130 can have a size, depending on the scanner of at least 22 mm×22 mm, for example at least 25 mm×25 mm, for example up to 32 mm×32 mm by some more-specialized steppers. Therefore, a 200 mm wafer can have 40 to 60 exposure fields 130, depending on their size. A field 130 may contain a plurality of chips, exposed at once. For example one field 130 can contain 1×3 (shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 208 488.8 | Aug 2022 | DE | national |
The present application is a continuation of, and claims benefit under 35 USC 120 to, international application No. PCT/EP2023/071842, filed Aug. 7, 2023, which claims benefit under 35 USC 119 of German Application No. 10 2022 208 488.8, filed Aug. 16, 2022. The entire disclosure of each of these applications is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2023/071842 | Aug 2023 | WO |
| Child | 19050352 | US |
