Patent Application
20070281149
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
a and 2b depict a top view and a side view of an encoder grid scale glued to a reticle chuck body according to prior art;
a and 3b depict a top view and a side view of an encoder grid scale glued to a reticle chuck body according to an embodiment of the present invention; and
a-4d depict four steps of a method to glue a first object part to a second object part according to the invention.
The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
The mask support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The mask support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The mask support structure may be a frame or a table, for example, which may be fixed or movable as required. The mask support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”
The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.
As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or “substrate supports” (and/or two or more mask tables or “mask supports”). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.
The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques can be used to increase the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that a liquid is located between the projection system and the substrate during exposure.
Referring to
The illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the mask support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioning device PM and another position sensor (which is not explicitly depicted in
The depicted apparatus could be used in at least one of the following modes:
1. In step mode, the mask table MT or “mask support” and the substrate table WT or “substrate support” are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT or “substrate support” is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
2. In scan mode, the mask table MT or “mask support” and the substrate table WT or “substrate support” are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT or “substrate support” relative to the mask table MT or “mask support” may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.
3. In another mode, the mask table MT or “mask support” is kept essentially stationary holding a programmable patterning device, and the substrate table WT or “substrate support” is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or “substrate support” or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
a and 2b depict a reticle chuck body 11 and an encoder grid scale 12 being attached to each other via a glue connection. The reticle chuck body 11 and the encoder grid scale 12 may be part of a reticle stage, as depicted in
The encoder grid scale 12 comprises a scale which can be read by an encoder sensor being mounted on a relative stationary frame, such as for instance the metro frame. With such encoder system the position of the reticle can be determined with a high accuracy (nanometer accuracy). Typically the encoder system is capable of determining the position of the reticle stage in x, y and Rz. To ensure that the encoder system does not incorrectly determine the position of the reticle, the position of the encoder grid scale should not be influenced by any environmental conditions such as temperature and humidity of the ambient atmosphere. Also, the position of the encoder grid scale 12 with respect to the reticle chuck body 11 should preferably not be influenced by the acceleration of the reticle chuck body, i.e. the assembly of the reticle chuck body 11 and the encoder grid scale 12 should behave as if it were a monolithic body which does not deform due to accelerations.
The encoder grid scale 12 is glued with a number of glue dots 13 to the reticle chuck body 11. To make such a glue connection, dots of glue are arranged on a glue surface 14 of the reticle chuck body 11 or a glue surface 15 of the encoder grid scale 12 in a predetermined pattern, subsequently the glue surfaces 14, 15 of the reticle chuck body 11 and the encoder grid scale 12, respectively, are positioned with respect to each other defining a glue gap between them, therewith defining a glue layer thickness. The thickness of such layer is typically 10 μm. A glue typically used in the known method is for instance a universal two component epoxy manufactured by Huntsman (Salt Lake City, Utah, USA) under the name Araldite 2011®.
In order to minimize creep of the glue after curing, which may result in deformation of the encoder grid scale 12, the stress in the dots of glue 13 should be kept as low as possible. To minimize stress in the dots of glue 13, the dots of glue 13 have to be arranged during the gluing process on the reticle chuck body 11 or encoder grid scale 12 with high accuracy with respect to both the amount of glue per dot and the position where such glue dot 13 is arranged. To ensure that this is performed with the desired accuracy, use is made of automated process devices such as robots for applying the glue dots 13 in the desired pattern and dose measuring devices to determine that the correct amount of glue is used for a single dot of glue 13.
The prior art glue connection using a pattern of dots of glue 13 is relatively sensitive to moisture. As a result, the object that is formed of at least two object parts being glued together may be influenced by moving the object between different environmental circumstances. For instance the encoder grid scale 12 may be glued to the reticle chuck body 11 in a clean room environment and, thereafter, be used in a micro-environment having clean dry air. The (relative) lack of moisture in the latter environment may lead to moisture vapouring out of the glue, and, as a consequence, shrinkage of the glue which may result in deformation of the encoder grid scale 12 with respect to the reticle chuck body 11. Such deformation of the encoder grid scale 12 may lead to incorrect position measurement of the reticle stage and thus for instance overlay errors during use of the lithographic apparatus.
In
To further decrease the influence of moisture on deformation of the encoder grid scale 2, the thickness of the glue layer is smaller than the prior art layer. The glue layer is preferably 1-8 μm, more preferably 2-6 μm, and even more preferably 2-4 μm. The thickness of the glue layer in the embodiment shown in
A very suitable epoxy resin to be used as a glue is an epoxy resin selected from the group consisting of Bisphenol A and Bisphenol F families, as these epoxy resins are relative less sensitive for moisture. In particular, an epoxy manufactured by Epoxy Technology, (Billerica, Mass., USA), named Epo-tek 302-3M® has shown to be very suitable due to the low moisture sensitivity and good capillary action. The advantage of the latter characteristic will be discussed later. Thus, the use of such epoxy resin may reduce the chance of deformations in the encoder grid scale 2 caused by the influence of moisture in the glue and/or direct environment.
In the embodiment of
As an alternative, it is possible to make use of capillary action and/or gravity to let enter the glue in a gap between the object parts. In this alternative, the chance on inclusions of air bubbles becomes considerably lower. However, the smaller width of the glue gap, as proposed in embodiments of the present invention, makes such use of capillary action and/or gravity with the desired epoxy resins practically impossible as the width of the glue gap is too small. A method according to embodiments of the invention to obtain the embodiment of
In
In
In order to position and maintain the glue surfaces 4 and 5 at the desired distance, spacers 6 may be placed between the two glue surfaces 4 and 5. Any other suitable means or method for positioning the glue surfaces 4 and 5 and maintaining the desired distance between the two glue surfaces 4 and 5 may also be used.
In
In
After that the spacers (when present) have been removed, the reticle chuck body 1 and the encoder grid scale are moved towards each other so that the glue surfaces 4 and 5 become arranged at a distance Gg (see
In
In general it can be concluded that the method according to the invention is less sensitive than conventional methods, as use is made of capillary action and/or gravity to apply the glue to one or both object parts. Furthermore, as one continuous layer of glue is used, the amount of glue applied is less sensitive and no difficult patterns have to be made. Therefore the method may be performed manually, so that no use has to be made of expensive automated equipment.
In the above description an example was given of two object parts which can be glued together to form one object. The present invention may be used to connect two object parts of any object in which moisture sensitivity is of importance, and/or in which nanometer stability of the resulting assembly is desired in view of environmental conditions such as humidity. All such embodiments are deemed to fall within the scope of the invention. An example of such object may be a mirror being connected to a projection optics box in a lithographic apparatus. In particular, the invention may be suitable to connect a component of a measurement system to a movable object, such as a reticle stage or wafer stage. The measurement system may be configured to measure any position quantity. In this context a position quantity may be any signal representative for a position of said movable object or a derivative thereof. Thus, such position quantity may comprise a position, speed or acceleration of said movable object, as well as combinations or equivalents thereof.
It is remarked that it is possible that a resulting object comprises more than two parts and that only some of these parts are attached to each other via a glue layer according to the present invention.
Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.
The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
