Patent Application
20120026480
1. Field of the Invention
The present invention generally relates to lithography, and more particularly to an electrostatic chuck system configured to clamp an object (e.g., a patterning device such as a mask, or a substrate) to a support.
2. Background Art
Lithography is widely recognized as a key process in manufacturing integrated circuits (ICs) as well as other devices and/or structures. A lithographic apparatus is a machine, used during lithography, which applies a desired pattern onto a substrate, such as onto a target portion of the substrate. During manufacture of ICs with a lithographic apparatus, a patterning device (which is alternatively referred to as a mask or a reticle) generates a circuit pattern to be formed on an individual layer in an IC. This pattern may be transferred onto the target portion (e.g., comprising part of, one, or several dies) on the substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. In general, a single substrate contains a network of adjacent target portions that are successively patterned. Manufacturing different layers of the IC often requires imaging different patterns on different layers with different reticles. Therefore, reticles must be changed during a lithographic process.
In order to ensure good imaging quality the patterning device and substrate must be firmly held in place by a chuck. The chuck can be manufactured with errors or irregularities that cause the chuck to be non-planar or have some other geometric deformation. Likewise, both the patterning device and/or the substrate can suffer from similar manufacturing errors that that cause them to be non-planar. With regard to the patterning device and substrate, such deformations can occur during operation of the lithographic system due to variables, such as heat absorption. The patterning device imparts to a beam of radiation a pattern, which is then imaged onto a substrate. Image quality of this projected radiation beam can be affected by image errors, such as image curvature, focus, distortion, and astigmatism.
The chuck can be formed with a series of vacuum points that hold onto the patterning device and/or substrate. However, extreme ultraviolet (EUV) lithography requires a vacuum environment. Therefore, a common practice in EUV systems is to use an electrostatic chuck to hold the patterning device and/or substrate.
The market demands that the lithographic apparatus perform the lithography process as efficiently as possible to maximize manufacturing capacity and keep costs per device low. This means keeping manufacturing defects to a minimum, which is why the effect of the non-planar deformations in the chuck, patterning device, and substrate, as well as imaging errors due to field curvature, focus, distortion, astigmatism, and scanning errors need to be minimized as much as practical.
Given the foregoing, what is needed is an electrostatic chuck system and method that minimizes effects of manufacturing and operational deformations in a chuck, patterning device, and/or substrate. To meet this need, embodiments of the present invention are directed to an image-compensating addressable electrostatic chuck system and method.
According to an embodiment of the present invention, there is provided an electrostatic chuck, comprising: a substrate, a support layer to support an object, an electrode layer comprising an electrode and being disposed between the substrate and the support layer configured to apply an electrostatic attraction force on the object upon energization of the electrode, and a plurality of actuators configured to deform the support layer.
According to another embodiment of the invention, there is provided a lithographic system, comprising: a reticle support configured to clamp a reticle in a path of a radiation beam so that the reticle produces a patterned beam, a projection system configured to project the patterned beam onto a target portion of a substrate, a substrate support configured to support the substrate during a lithographic process, and an electrostatic chuck coupled to the reticle support, the electrostatic chuck comprising: a substrate, a support layer to support an object, an electrode layer comprising an electrode and being disposed between the substrate and the support layer configured to apply an electrostatic attraction force on the object upon energization of the electrode, and a plurality of actuators configured to deform the support layer.
According to another embodiment of the invention, there is provided a method, comprising: determining surface irregularities of an object (to obtain a surface irregularities map of the object), determining a plurality of compensation values (i.e., a compensation data set) based on the irregularities, correlating the plurality of compensation values with a plurality of matrix points each of which is formed by one of a plurality of actuators disposed between a substrate and a support layer of an electrostatic chuck, determining an actuation level for each actuator corresponding to the associated compensation value being applied to the object at each of the plurality of matrix points, and applying the actuation level to each of the actuators to deform the support layer in accordance with the compensation values at each matrix point whilst the object is clamped on the support layer.
According to another embodiment of the invention, there is provided a method, comprising: utilizing an image quality evaluation system to determine a plurality of image errors affecting an image quality of the imaged object, determining a plurality of electrostatic compensation force values based on the plurality of image errors, correlating the plurality of electrostatic compensation force values with a plurality of matrix points formed by first and second evenly spaced sets of electrodes disposed in a substrate beneath the support layer of an electrostatic chuck, the first and second set of electrodes being generally orthogonally oriented to the other set, determining an energizing level for each electrode in the first and second set of electrodes corresponding to the associated compensation force value being applied to the object at each of the plurality of matrix points, and applying the energizing level to each electrode in the first and second set of electrodes to generate an electrostatic compensation force on the object at each of the plurality of matrix points.
In another embodiment of the invention, there is provided a method, comprising: utilizing an interferometer to determine surface irregularities of an object, determining a plurality of compensation values based on the irregularities, correlating the plurality of compensation values with a plurality of matrix points each of which is formed by one of a plurality of actuators disposed between a substrate and a support layer of an electrostatic chuck, determining an actuation level for each actuator corresponding to the associated compensation value being applied to the object at each of the plurality of matrix points, applying the actuation level to each of the actuators to deform the support layer in accordance with the compensation values at each matrix point whilst the object is clamped on the support layer, and determining, with the interferometer, the surface irregularities of the object remaining after application of the actuation level to each actuator.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.
The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.
The present invention is directed to an image-compensating addressable electrostatic chuck system (herein for sake of simplicity also referred to as an electrostatic chuck, or simply chuck or chuck/clamp). This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.
The embodiment(s) described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, or acoustical devices and the like. Further, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.
Detailed below are embodiments of an image-compensating electrostatic chuck system and methods of use thereof. In one embodiment an image-compensating electrostatic chuck itself comprises a substrate, a support layer to support an object such as a patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) and an actuator layer comprising a plurality of actuators configured to deform the support layer. Thereby the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) may be controllably deformed when it is attracted by electrostatic force to the support layer by an electrode layer of the electrostatic chuck that comprises an electrode configured to apply an electrode attraction force on the object upon energization of the electrode. The plurality of actuators maybe ranged in a 2 dimensional array in a plane substantially parallel to a surface of the support layer on which the patterning device (e.g., a mask) MA (or other object such as a substrate W to be imaged) is supported. Alternatively, the plurality of actuators is arranged in a 1 dimensional array extending in a first direction. A calculated actuation level is applied to each of the actuators to deform the support layer so that the patterning device (e.g., a mask) MA (or other object such as a substrate W to be imaged) is deformed by a required amount at each matrix point at least during the time at which the matrix point is being scanned i.e., whilst the patterning device (e.g., a mask) MA (or other object such as a substrate W to be imaged) is in a predetermined position during a scanning motion relative to an illumination slit.
Additionally, there are provided embodiments for using the image-compensating electrostatic chuck to improve image quality. Each method can comprise placing a patterning device (e.g., a mask) MA (or other object such as a substrate W to be imaged) to be chucked to a support layer on the support layer, converting known or measured/imaged errors into a plurality of compensation values and associating those values with one of a plurality of matrix points formed by one of a plurality of actuators. Then calculating and applying actuation levels necessary to result in the associated compensation values being applied at each matrix point. At least one embodiment involves receiving surface irregularities of associated components (e.g., patterning device chuck, patterning device, substrate chuck, substrate, etc.) and converting the surface irregularities to compensation values. This embodiment does not involve any active measurements of the associated components or use of the imaging system to provide feedback as to the image quality.
Another embodiment utilizes an interferometer system to determine the surface irregularities of an object. This embodiment performs the same converting, associating, calculating, and applying methodology as described above. However, this embodiment is capable of using the interferometer to determine, after the application of the compensation values, if any remaining surface irregularities exist. And if any remaining surface irregularities do exist, the applied compensation value is modified to compensate the remaining irregularities.
Additionally, another embodiment utilizes an image quality evaluation system to determine a plurality of image errors affecting the image quality of the imaged patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged). This procedure can be performed apriori to any imaging done in a system. Likewise, the image quality evaluation occurs in-situ in a lithographic tool, utilizing the imaging and image evaluation capabilities of the lithographic tool itself. In addition to possible surface irregularities in the chucks, reticles, and substrate wafers, the image quality evaluation system can correct a plurality of image errors (e.g., image curvature, image focus, image distortion, image astigmatism, etc.). This embodiment is also capable of using the image quality evaluation system to determine, after the application of the compensation value, if any remaining image quality errors exist. And if any remaining image quality errors do exist, modify the applied compensation value so as to compensate the remaining errors.
In yet another embodiment, the above methods can be utilized to correct for scanning inaccuracies that generate positional errors perpendicular to a patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) that effect image quality. The electrodes are typically addressed in a line perpendicular to the scan direction of a chucked patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged). In another embodiment, the electrodes can be addressed in an arc shape, perpendicular to the scan direction of a chucked patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged).
Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention can be implemented.
A. Example Reflective and Transmissive Lithographic Systems
The illumination system IL 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 the radiation B.
The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithographic apparatuses 100 and 100′, and other conditions, such as for example whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable, as required. The support structure MT may ensure that the patterning device is at a desired position, for example with respect to the projection system PS.
The term “patterning device” MA should be broadly interpreted as referring to any device that may be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C, such as an integrated circuit.
The patterning device MA may be transmissive (as in lithographic apparatus 100′ of
The term “projection system” PS may encompass 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. A vacuum environment may be used for EUV or electron beam radiation since other gases may absorb too much radiation or electrons. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.
Lithographic apparatus 100 and/or lithographic apparatus 100′ may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables) WT. In such “multiple stage” machines the additional substrate tables WT may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other substrate tables WT are being used for exposure.
Referring to
The illuminator IL may comprise an adjuster AD (
Referring to
Referring to
In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.
The lithographic apparatuses 100 and 100′ may be used in at least one of the following modes:
1. In step mode, the support structure (e.g., mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C may be exposed.
2. In scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.
3. In another mode, the support structure (e.g., mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation may be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to herein.
Combinations and/or variations on the described modes of use or entirely different modes of use may also be employed.
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.
In a further embodiment, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source (SO), which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system (see below), and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.
B. Example EUV Lithographic Apparatus
Collector chamber 48 includes a radiation collector 50 (which may also be called collector mirror or collector) that may be formed from a grazing incidence collector. Radiation collector 50 has an upstream radiation collector side 50a and a downstream radiation collector side 50b, and radiation passed by collector 50 can be reflected off a grating spectral filter 51 to be focused at a virtual source point 52 at an aperture in the collector chamber 48. Radiation collectors 50 are known to skilled artisans.
From collector chamber 48, a beam of radiation 56 is reflected in illumination optics unit 44 via normal incidence reflectors 53 and 54 onto a reticle or mask (not shown) positioned on reticle or mask table MT. A patterned beam 57 is formed, which is imaged in projection system PS via reflective elements 58 and 59 onto a substrate (not shown) supported on wafer stage or substrate table WT. In various embodiments, illumination optics unit 44 and projection system PS may include more (or fewer) elements than depicted in
In an embodiment, collector mirror 50 may also include a normal incidence collector in place of or in addition to a grazing incidence mirror. Further, collector mirror 50, although described in reference to a nested collector with reflectors 142, 143, and 146, is herein further used as example of a collector.
Further, instead of a grating 51, as schematically depicted in
The terms “upstream” and “downstream,” with respect to optical elements, indicate positions of one or more optical elements “optically upstream” and “optically downstream,” respectively, of one or more additional optical elements. Following the light path that a beam of radiation traverses through lithographic apparatus 200, a first optical elements closer to source SO than a second optical element is configured upstream of the second optical element; the second optical element is configured downstream of the first optical element. For example, collector mirror 50 is configured upstream of spectral filter 51, whereas optical element 53 is configured downstream of spectral filter 51.
All optical elements depicted in
Radiation collector 50 can be a grazing incidence collector, and in such an embodiment, collector 50 is aligned along an optical axis O. The source SO, or an image thereof, may also be located along optical axis O. The radiation collector 50 may comprise reflectors 142, 143, and 146 (also known as a “shell” or a Wolter-type reflector including several Wolter-type reflectors). Reflectors 142, 143, and 146 may be nested and rotationally symmetric about optical axis O. In
Reflectors 142, 143, and 146 respectively may include surfaces of which at least portion represents a reflective layer or a number of reflective layers. Hence, reflectors 142, 143, and 146 (or additional reflectors in the embodiments of radiation collectors having more than three reflectors or shells) are at least partly designed for reflecting and collecting EUV radiation from source SO, and at least part of reflectors 142, 143, and 146 may not be designed to reflect and collect EUV radiation. For example, at least part of the back side of the reflectors may not be designed to reflect and collect EUV radiation. On the surface of these reflective layers, there may in addition be a cap layer for protection or as optical filter provided on at least part of the surface of the reflective layers.
The radiation collector 50 may be placed in the vicinity of the source SO or an image of the source SO. Each reflector 142, 143, and 146 may comprise at least two adjacent reflecting surfaces, the reflecting surfaces further from the source SO being placed at smaller angles to the optical axis O than the reflecting surface that is closer to the source SO. In this way, a grazing incidence collector 50 is configured to generate a beam of (E)UV radiation propagating along the optical axis O. At least two reflectors may be placed substantially coaxially and extend substantially rotationally symmetric about the optical axis O. It should be appreciated that radiation collector 50 may have further features on the external surface of outer reflector 146 or further features around outer reflector 146, for example a protective holder, a heater, etc.
In the embodiments described herein, the terms “lens” and “lens element,” where the context allows, may refer to any one or combination of various types of optical components, comprising refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
Further, the terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, comprising ultraviolet (UV) radiation (e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm), extreme ultra-violet (EUV or soft X-ray) radiation (e.g., having a wavelength in the range of 5-20 nm, e.g., 13.5 nm), or hard X-ray working at less than 5 nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, it is usually also applied to the wavelengths, which can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and/or I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by air), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in an embodiment, an excimer laser can generate DUV radiation used within lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.
In one example, chuck substrate 310 provides backing and support for the entire assembly and can exceed the footprint of the electrode layer(s) 315, 320 and support layer 330.
In one example, electrode layer 320 itself, which may be directly on top of the chuck substrate 310 or disposed therein, is comprised of at least one electrode. The electrode layer 320 is disposed between the substrate 310 and the support layer 330. When the electrode of the electrode layer 320 is energized an electrostatic attraction force is applied on the patterning device (e.g., a mask) MA. Thus the patterning device (e.g., a mask) MA is removeably attachable to the chuck 300, for example by an electrostatic force. The patterning device (e.g., a mask) MA is separate from the electrostatic chuck 300 and table 400. The patterning device does not comprise any actuators. The patterning device may be a passive object.
The electrode layer 320 may comprise more than one electrode. The number, size and shape of electrodes can depend on a number of factors, such as overall footprint (i.e., size) of the desired electrostatic clamping force, required density (i.e., spacing between parallel electrodes) to effectuate the needed electrostatic force, and design characteristics of the required electrostatic force field.
In an embodiment the chuck 300 may comprise a further electrode layer 315 comprising at least one electrode configured to attach the chuck 300 to a moveable table 400. The moveable table 400 may comprise a table electrode 410. An electrostatic field generated between the further electrode layer 315 and the table electrode 410 is effective to clamp the chuck 300 to the table 400. Alternative ways of attaching the chuck 300 to the table 400 may be provided, for example mechanical fixing.
In one example, support layer 330 completes an encapsulation of the electrode layer 320 and provides the physical support for any object that is being clamped to the chuck. For example, the support layer 330 is commonly comprised of a plurality of very small glass protrusions with flat ends. All or some of the chuck substrate 310, electrode layer(s) 315, 320, support layer 330 and actuator layer 350 are attached together, e.g., by being laminated, glued, bonded or fixed together.
In one example, a patterning device (e.g., a mask) MA can be placed onto the outer surface of the support layer 330 and be fully supported. In one example, support layer 330 is made from glass so that pin chuck 330 is not conductive and does not have any effect on the electrostatic force coupling from the electrode layer 320 to the patterning device (e.g., a mask) MA. The support layer 330 does not clamp (i.e., hold in place) the patterning device (e.g., a mask) MA, rather the clamping is provided by the electrostatic field generated by energizing the electrode(s) that comprise(s) the electrode layer 320, the support layer 330 merely provides the physical contact support. The area above the electrode layer 320 where the electrostatic field is generated can be referred to as the electrostatic clamp area of the image-compensating addressable electrostatic chuck.
In an example, the chuck 300 is provided with the actuator layer 350 which comprises a plurality of actuators 351. In an example the actuators 351 are configured to deform the support layer 330. By deforming the support layer 330, when a patterning device (e.g., a mask) MA is clamped to the support layer 330 by an electrostatic force generated by the electrode layer 320, the deformations of the support layer 330 are transmitted to the patterning device (e.g., a mask) MA. Therefore, the plurality of actuators 350 can be used to deform the patterning device (e.g., a mask) MA.
In one embodiment the actuator layer 350 is positioned on a side of the substrate 310 opposite to the electrode layer 320. However, the actuator layer 350 may be positioned anywhere so long as the actuator layer 350 can deform the support layer 330. For example, the actuator layer 350 maybe positioned in any of the following positions from a non-limiting list: between the electrode layer 320 and the support layer 330, between the electrode layer 320 and the substrate 310, between the further electrode 315 and the table 400, in the table 400 on either side of the table electrode 410.
The number, size and position of the actuators 351 of the actuator layer 350 are chosen according to need. In one example, the actuators 351 are piezoelectric actuators.
The spacing between adjacent actuators 351 maybe uniform or non uniform in one or both of orthogonal directions. In one example the actuators 351 maybe controllable in direction of actuation and/or magnitude of actuation. This enables, for example, portions of both concave and convex shapes of the patterning device (e.g., a mask) MA to be corrected to flat using the plurality of actuators 351 under the concave and/or convex portion.
Thus, the clamping and compensating functions are independent allowing maximum clamping force to be achieved. Correction in both +Z and −Z is possible. A high density of actuators 351 is possible and actuators 351 and control components are readily available (e.g., for use in printer heads).
Once a desired deformation of the support layer 330 has been calculated, the actuators 351 of the actuator layer 350 may be controlled to deform the support layer 330 by the required amounts in the required areas. This may be done after the patterning device (e.g., a mask) MA 340 has been attached to the support layer 330 by the electrode layer 320 or before the patterning device (e.g., a mask) MA has been attached or clamped to the support layer 330. The patterning device (e.g., a mask) MA takes up the shape similar to that of the support layer 330. This makes it possible to deform the patterning device (e.g., a mask) MA thereby, for example, to make the patterning device (e.g., a mask) MA closer to being perfectly flat than would be the case in the absence of the actuators 351 of the of actuator layer 350 deforming the support layer 330. During a scanning movement the actuation level of each of the actuators 351 can be maintained constant, thereby providing easy control.
In
Thus, in comparison to the embodiment of
Therefore, the actuation value is applied at least partly during the scanning motion and during the applying the actuation level applied to each of the actuators 351a-351x varies according to the compensation value for the time of the scanning motion and/or a position of the object relative to the illumination slit 1120.
In at least one embodiment, the patterning device (e.g., a mask) MA to be clamped has fairly consistent deformations. In particular, the patterning device (e.g., a mask) MA is often deformed (e.g., curved) along the edges of the patterning device (e.g., a mask) MA. The patterning device (e.g., a mask) MA can take a bowed shape where the center is either above or below the outer edges of the patterning device (e.g., a mask) MA. Accordingly the chuck 300 should desirably provide more precise control of the deformation at the edges of the chuck 300 area. The actuators 351 are more densely placed at the edges of the electrostatic clamping area to achieve this.
In at least one embodiment of the present invention, the electrostatic chuck 300 may support an object different to the patterning device. For example the chuck 300 may support a substrate W to be imaged.
The chuck 300 may be a chuck other than an electrostatic chuck. For example, the chuck 300 may hold the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) to the support layer 330 by a different method such as by use of an under pressure clamp (e.g., a vacuum clamp).
JP 2009-164284, which is incorporated by reference herein in its entirety, discloses a pattern formation board that is attachable to a chuck. The pattern formation board has reflective and absorbing layers to form a pattern to be transferred to a substrate. The reflective and absorbing layers are laminated with a base substance part and piezoelectric elements. The piezoelectric elements can be energized to deform the reflective and absorbing layers. This system has the disadvantage that a separate array of piezoelectric elements needs to be provided for each different pattern to be imaged. That is, the system of JP 2009-164284 requires special manufacture of the patterning device to incorporate the piezoelectric elements whereas the present invention can be used in conjunction with conventional patterning devices (e.g., a mask) and additionally with other objects such as a substrate (which is not practical with the system of JP 2009-164284 because an array of piezoelectric elements would need to be laminated to each substrate).
A patterning device (e.g., a mask) MA may contain surface irregularities (illustrated in
In one example, deformation can be applied to a clamped patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) to correct surface irregularities of the chuck/clamp, to correct for imaging errors of the projection system, to correct for deformation/irregularity of the target substrate, and to correct for scanning errors that are perpendicular to the direction of scanning. Therefore, it is important to note that the plurality of actuators 351 is not only used to correct for patterning device (e.g., a mask) MA (or substrate W) deformations, but can induce patterning device (e.g., mask) MA (or substrate W) deformations to compensate the image for various other lithographic system errors and thus improve total image quality, which in turn, minimizes manufacturing defects and improves efficiency.
The embodiment of
In an example the compensation value is a displacement value that may be indicative of a displacement of a matrix point from an imaginary plane (e.g., perpendicular to the z axis). In an embodiment the actuation level maybe a signal proportional to the direction and/or magnitude of the compensation value required by the corresponding actuator 351 to achieve the compensation value at the associated matrix point. Therefore, the actuation level is applied to each of the actuators 351 to deform the support layer 330 in accordance with the compensation values at each matrix point whilst the patterning device (e.g., a mask) MA is clamped on the support layer 330.
In the case of the embodiment of
In an embodiment of the present invention, the patterning device (e.g., a mask) MA to be held in place (i.e., “chucked”) is first clamped (at step 710), via a standard uniform non-customized electrostatic field, to an image-compensating addressable electrostatic chuck 300 (as shown, for example, in
The image-compensating addressable electrostatic chuck 300 is not limited to correcting surface irregularities of the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) being clamped. The image-compensating addressable electrostatic chuck can also correct deformations if the support layer 330 and/or underlying chuck substrate 310 has manufacturing defects that cause the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) being clamped to be deformed. The manufacturing irregularities causing the deformation of the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) to be clamped must be mapped (i.e., identified) in advance, prior to correction. Likewise, if mapped irregularities of both the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) and the substrate/pin chuck exist, the controller can combine the two data sets and produce a correction that will compensate the image for both types of errors.
In another embodiment, image errors (e.g., image curvature, image focus, image distortion, astigmatism, etc.) created by the projection system are present and applying a non-uniform deformation to the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) compensates for the image errors. In some embodiments, the details of the image errors have been previously quantified. This data can be used by the controller to compensate for the image error, either alone or in combination with correcting the manufacturing defects of the chuck substrate/pin chuck and/or the surface irregularities of the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) itself. In another embodiment, repeatable scan errors that are perpendicular to the direction of scan can be compensated for. Data regarding the scan errors can also be received by the controller and compensated for by modifying the electrostatic force applied to the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) at the proper point during the scan. Correcting for the scanning errors can be done alone or in combination with compensation for the chuck substrate/pin chuck manufacturing, errors, the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) surface irregularities, and the image errors introduced by the projection system.
In the embodiment shown in
In an embodiment of the present invention, the patterning device (e.g., a mask) MA (or other clamped object such as a substrate W to be imaged) to be held in place (i.e., “chucked”) is clamped (at step 810) via a standard uniform non-customized electrostatic field to an image-compensating addressable electrostatic chuck 300 (as shown, for example, in
In one example, steps 820 through 828 are repeated in steps 840 and 850 to compensate for any residual errors, not originally measured or created by the first compensation method. The residual compensation is cumulative to the initial compensation. In an embodiment, the compensation using measurement and feedback for residual irregularities/errors is not continuous and considered complete after a user defined number of passes.
In an embodiment illustrated in
In one example, the image-compensating addressable electrostatic chuck can also correct for scan errors e.g., unflatness errors in the z-direction that are perpendicular to the direction of scan (y).
Image-compensating can also be achieved with addressable electrostatic chuck clamping of the target substrate (i.e., wafer), according to an embodiment of the present invention. Residual irregularities/errors in the image quality can be compensated for by applying a non-uniform electrostatic force to the image substrate.
In another embodiment of the present invention, a method of compensating for image errors/patterning device (e.g., a mask) MA/substrate W irregularities by measuring and compensating for a particular type of error/irregularity before measuring and compensating for another type of error/irregularity is performed. The types of image errors/patterning device (e.g., a mask) MA/substrate W irregularities occur with different frequencies within a lithographic system and in order to improve the efficiency of the lithographic system the errors/irregularities should be addressed in similar order.
In one example, these differing types of compensation are performed piecemeal until the image quality is satisfactory. For example, in some cases only chuck/clamp errors 1210 will need to be compensated for, but in other cases each type of error will need to be compensated in order to achieve acceptable image quality. The compensations are cumulative such that each level will further improve the overall image quality, and once the image quality has achieved an acceptable level, no further compensation is needed.
The descriptions above are intended to be illustrative, not limiting. It will be apparent to one skilled in the art that the invention is also represented by the clauses set out below.
It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more, but not all, exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.
The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been defined for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.
The foregoing description of the specific embodiments will so fully reveal the general nature of the invention. Others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the terminology or phraseology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.
The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
This applications claims benefit under 35 U.S.C. 119(e) to U.S. Provisional patent Application No. 61/367,595, filed, Jul. 26, 2010, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61367595 | Jul 2010 | US |
