Patent Application
20060035159
The present invention relates to lithographic apparatus and device manufacturing methods using lithographic apparatus.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
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, 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) or a metrology or 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.
The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of 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 “patterning device” used herein should be broadly interpreted as referring to means that can be used to impart a projection beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the projection beam may not exactly correspond to the desired pattern in the target portion of the substrate. Generally, the pattern imparted to the projection beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
Patterning devices 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; in this manner, the reflected beam is patterned. In each example of patterning device, the support structure may be a frame or table, for example, which may be fixed or movable as required and which 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 “projection system” used herein should be broadly interpreted as encompassing various types of projection system, including refractive optical systems, reflective optical systems, and catadioptric optical systems, as appropriate for example for the exposure radiation being used, or for other factors such as the use of an immersion fluid or the use of a vacuum. Any use of the term “lens” herein may be considered as synonymous with the more general term “projection system”.
The illumination system may also encompass various types of optical components, including refractive, reflective, and catadioptric optical components for directing, shaping, or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”.
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.
The lithographic apparatus may also be of a type wherein the substrate is immersed in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the first element of the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems.
Before exposing the substrate, it may be desirable or necessary to correctly align it to ensure that the functional features are imaged on the correct position on the substrate. Conventionally this is shown using the apparatus shown in
The marks are commonly on the front side of the substrate, but can also be on the back side of the substrate. Marks on the back side of the substrate are used, for example, when exposure is to take place on both sides of the substrate. This occurs particularly in the manufacture of micro electro mechanical systems (MEMS) or micro opto-electro mechanical systems (MIOEMS). When the substrate marks P1 and P2 (also referred to as “alignment marks” herein) are on the back surface of the substrate, they are re-imaged by front-to-back side alignment optics 22 at the side of substrate W to form an image Pi as shown for P2 in
However, apparatus with such front-to-backside alignment capability may not include other features such as a tight overlay accuracy or be capable of fine geometry features. On the other hand, lithographic apparatus capable of fine geometry features and tight overlay accuracy may not include front-to-backside alignment apparatus. Using a conventional method, it is not therefore possible to combine other features such as both tight overlay accuracy with correctly aligned exposures on both sides of the substrate.
According to one embodiment, a method of providing alignment marks on a substrate comprises providing a first alignment mark on said first side of said substrate; providing a second alignment mark on said first side of said substrate at a known displacement from said first alignment mark; turning over said substrate; using front-to-backside alignment optics to align said substrate using said first alignment mark; and providing a third alignment mark on a second side of said substrate, wherein the location of said first alignment mark is such that it can be detected using front to backside alignment optics.
According to a further embodiment, there is provided a method of aligning a substrate comprising a method as described above.
According to a further embodiment, a device manufacturing method comprises providing a first alignment mark on said first side of a substrate; providing a second alignment mark on said first side of said substrate at a known displacement from said first alignment mark; turning over said substrate; using front-to-backside alignment optics to align said substrate using said first alignment mark; providing a third alignment mark on a second side of said substrate, wherein the location of said first alignment mark is such that it can be detected using front to backside alignment optics; moving said substrate to another apparatus; using said second alignment mark to align said substrate; projecting a patterned beam onto the substrate; turning over said substrate; using said third alignment mark to align said substrate; and projecting a patterned beam onto the substrate.
According to a further embodiment, there is provided a device manufactured according to a method described above.
A substrate according to a further embodiment is provided with a first alignment mark and a second alignment mark on a first side of the substrate and a third alignment mark on a second side of the substrate, wherein the first alignment mark is positioned on the substrate to be in the object order of front-to-backside alignment optics of a lithographic apparatus, the second and third alignment marks being positioned to be detectable by a different lithographic apparatus.
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:
Embodiments of the present invention may be applied to provide alignment marks to enable a substrate to be exposed by both apparatus with front-to-backside alignment capabilities and other lithographic apparatus.
an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation).
a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters;
a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and
a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.
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 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 support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The 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 such 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 (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables 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 are well known in the art for increasing 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 liquid is located between the projection system and the substrate during exposure.
Referring to
The illuminator IL may comprise an adjuster AD for adjusting 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 comprise 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 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 positioner 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 positioner 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:
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
Prior to any device exposure, the substrate is etched with two first alignment marks 21, 22 as shown in
A layer of photoresist 40 is then applied to the first surface (i.e. the surface into which the first and second set of alignment marks, 21, 22, 23, 24 are etched) as a protective coating. As shown in
As the substrate has alignment marks corresponding to the lithographic apparatus used to expose the alignment marks, subsequent (device) exposures may be carried out using the same, or identical apparatus.
As the position of the second and third alignment marks 23, 24, 25, 26 need not be determined by the front-to-backside alignment optics, such position can be selected as appropriate for use with other lithographic apparatus. For example, if there was another lithographic apparatus which had other characteristics not available in the apparatus with front-to-backside alignment optics, the location of the second and third alignment marks could be governed by the desired location of alignment marks on the other lithographic apparatus. Additionally, the actual shape and nature of the second and third alignment marks 23, 24, 25, 26 may be selected as appropriate for use with this apparatus. Thus the second and third alignment marks 23, 24, 25, 26 enable the substrate to be exposed using other lithographic apparatus. Furthermore, even if the other apparatus does not have any front-to-backside alignment capability it is possible to correctly align exposures on the first side of the substrate to exposures on the second side of the substrate as the second alignment marks, 23, 24 and third alignment marks 25, 26 are a known displacement from each other. Thus, the alignment of the front and backside for exposure by any lithographic apparatus is now possible.
Although the second and third alignment marks are described as being opposite each other they need not be directly opposite each other, provided they are a known displacement from each other.
Although etching is commonly used to mark a substrate any method of marking a substrate is possible, e.g. fixing a mark to it and/or imprinting a mark upon it.
The mask used to expose the alignment marks should preferably be arranged in the center of the exposure beam to minimize any distortion.
Although each set of alignment marks described here comprises two alignment marks there may be one, three, four or even more alignment marks in each set.
In an application of an embodiment as disclosed herein, a substrate can thus be exposed by either lithographic apparatus with front-to-backside alignment capability, or by other lithographic apparatus. The second and third alignment marks are a known displacement from each other such that if the substrate is exposed by lithographic apparatus without front-to-backside alignment capability, the location of devices on the front side may still be related to the location of devices on the backside. Conveniently, the second and third alignment marks may be directly opposite each other on opposite sides of the substrate.
Preferably, the displacement between the first and second alignment marks is measured.
Such a method may further comprise providing a fourth alignment mark on the second side of the substrate, said fourth alignment mark being located such that it can be detected using front-to-backside alignment optics. An alignment mark can thus be detected through the front-to-backside alignment optics whichever side is facing down. The first and fourth alignment marks are preferably opposite each other.
To improve the accuracy of the readings, there may be a plurality of first, second, third or/and fourth alignment marks. First, second, third or/and fourth alignment marks may be commonly used.
The second and/or third alignment marks may be located at a position to be detected when the substrate is being exposed by another lithographic apparatus.
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.
