Method and apparatus for lithographic imaging - Patents.com

Abstract

A system, method and computer program for providing a force to counter inertial forces present on a patterning device during an imaging operation of a photolithography system includes a means for providing coarse positioning of a pusher in combination with a short-stroke actuator and a pusher tip configured to engage an edge of the patterning device. In one embodiment, the coarse positioning is provided by providing a guide along which the short-stroke actuator can be translated, and a locking mechanism is configured to selectively hold the actuator in an appropriate position relative to the patterning device. In one embodiment, the coarse positioning is provided by a long-stroke actuator, for example an off-center linear drive actuator.

Description

[Technical field]

[0001]

[0001] The present disclosure relates generally to improving and optimizing lithography processes. More specifically, the present disclosure includes an apparatus, method and computer program that aids in stabilizing a patterning device during acceleration of a movement of a patterning device holder. [Background technology]

[0002] Lithographic projection apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device (e.g. a mask) may contain or be provided with a pattern (a "design layout") corresponding to an individual layer of the IC, and this pattern may be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g. a silicon wafer) that is coated with a layer of radiation-sensitive material ("resist"), such as by irradiating the target portion through the pattern on the patterning device. Generally, a single substrate will contain several adjacent target portions (one target portion at a time) onto which the pattern is successively transferred by the lithographic projection apparatus. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred onto one target portion at a time; such an apparatus may also be referred to as a stepper. In an alternative apparatus, a step-and-scan apparatus may move the substrate parallel or anti-parallel to a given reference direction (the "scan" direction) in synchronization with the projection beam scanning the patterning device in this reference direction. Different parts of a pattern on the patterning device are transferred progressively onto one target portion. Typically, a lithographic projection apparatus has a demagnification ratio M (e.g. 4), so that the speed F at which the substrate is moved is 1 / M times the speed at which the projection beam scans the patterning device. More information on lithographic devices can be found, for example, in U.S. Pat. No. 6,046,792, which is incorporated herein by reference.

[0003]

[0003] Before transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures such as priming, resist coating, and a soft bake. After exposure, the substrate may undergo other procedures such as a post-exposure bake (PEB), development, a hard bake, and measurement / inspection of the transferred pattern ("post-exposure procedures"). This sequence of procedures is used as a basis for making an individual layer of a device, e.g. an IC. The substrate may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, chemical-mechanical polishing, etc., all intended to finish off an individual layer of the device. If several layers are required for a device, the entire procedure, or a variant thereof, is repeated for each layer. Eventually, a device is present on each target portion on the substrate. These devices are then separated from one another by techniques such as dicing or sawing, so that the individual devices can be mounted on a carrier, connected to pins, etc.

[0004]

[0004] Thus, manufacturing a device such as a semiconductor device typically involves processing a substrate (e.g., a semiconductor wafer) using several manufacturing processes to form various features and layers of the device. Such layers and features are typically manufactured and processed using, for example, deposition, lithography, etching, chemical mechanical polishing, and ion implantation. Multiple devices can be fabricated on multiple dies on a substrate and then separated into individual devices. This device manufacturing process can be considered a patterning process. The patterning process includes a patterning step to transfer a pattern on a patterning device to a substrate, such as optical lithography and / or nanoimprint lithography using a patterning device in a lithography apparatus, and typically, but optionally, includes one or more associated pattern processing steps, such as developing a resist with a developer, baking the substrate using a bake tool, and etching using the pattern using an etcher.

[0005]

[0005] As mentioned above, lithography is a central step in the manufacture of devices such as ICs, where patterns formed on a substrate define the functional elements of devices such as microprocessors, memory chips, etc. Similar lithographic techniques are also used in the formation of flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0006]

[0006] As semiconductor manufacturing processes continue to improve, the dimensions of functional elements are continually decreasing, while the amount of functional elements, such as transistors, per device has been steadily increasing for decades, following a trend known as "Moore's Law". In the current state of the art, device layers are fabricated using lithographic projection apparatus that projects a design layout onto a substrate using illumination from a deep ultraviolet illumination source, producing individual functional elements with dimensions well below 100 nm (i.e., less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source)).

[0007]

[0007] This process, in which features with dimensions below the classical resolution limit of the lithographic projection apparatus are printed, can be called low k1 lithography with the resolution formula CD=k1×λ / NA, where λ is the wavelength of the radiation used (e.g., 248 nm or 193 nm), NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension" (typically the smallest feature size to be printed), and k1 is an empirical resolution factor. In general, the smaller k1 is, the more difficult it is to reproduce a pattern on a substrate that closely resembles the shape and dimensions planned by the designer to achieve a particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase-shifting patterning devices, optical proximity correction (OPC, sometimes also called "optical and process correction") in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). As used herein, the term "projection optics" should be broadly interpreted to encompass various types of optical systems, including, for example, refractive optics, reflective optics, apertures, and catadioptric optics. The term "projection optics" may also include components that collectively or independently operate according to any of these design types to direct, shape, or control a projection beam of radiation. The term "projection optics" may include any optical component in a lithographic projection apparatus, regardless of where the optical component is located on the optical path of the lithographic projection apparatus. The projection optics may include optical components for shaping, conditioning, and / or projecting radiation from the source before it passes through the patterning device, and / or optical components for shaping, conditioning, and / or projecting radiation after it has passed through the patterning device. The projection optics generally excludes the source and the patterning device. Summary of the Invention

[0008] A system, method and computer program for reducing movement of a patterning device on a patterning device holder during acceleration of the patterning device holder.

[0009] In one embodiment, the patterning device holder includes a chuck configured to releasably hold and support the patterning device. The patterning device holder further includes an actuator configured to apply a holding force to an edge of the patterning device, the holding force opposing inertial forces on the patterning device in response to acceleration of the patterning device holder, the actuator including a fine stroke portion and a tip portion, the actuator slidably mounted on the guide. The locking mechanism is configured to selectively hold the actuator in an appropriate position relative to the patterning device, the actuator configured to controllably position the tip portion in a depressed position in which the tip portion engages the edge of the patterning device and in a released position in which the tip portion does not engage the edge of the patterning device, the actuator being movable along the guide from the released position to the depressed position. In one embodiment, the movement of the actuator is responsive to inertial forces due to acceleration of the patterning device holder.

[0010] In one embodiment, a patterning device transport system for use in holding and moving a patterning device in a lithographic imaging apparatus includes a patterning device holder, the patterning device holder including a chuck configured to releasably hold and support the patterning device. The patterning device transport system further includes an actuator configured to apply a holding force to an edge of the patterning device, the holding force opposing an inertial force on the patterning device in response to an acceleration of the patterning device holder. The actuator includes a long-stroke actuator portion including a linear eccentric drive, a brake configured to prevent parasitic forces from moving the long-stroke actuator portion, a short-stroke actuator portion connected to the long-stroke actuator portion, and a tip portion, the tip portion configured to apply a holding force to an edge of the patterning device, the long-stroke actuator portion having a longer movement stroke than the movement stroke of the short-stroke actuator portion, and the short-stroke actuator portion having a higher precision than the precision of the long-stroke actuator portion. The long stroke actuator portion is configured to controllably move the tip portion towards and away from the edge of the patterning device, such that the tip is controllably positioned in a pushing position where the tip portion engages the edge of the patterning device and in a released position where the tip portion does not engage the edge of the patterning device.

[0011] In an embodiment, a patterning device transport system for use in holding and moving a patterning device in a lithographic imaging apparatus includes a patterning device holder including a chuck configured to releasably hold and support the patterning device, The actuator is configured to apply a holding force to an edge of the patterning device held and supported by the patterning device holder, the holding force opposing an inertial force on the patterning device when the patterning device holder is accelerated. The actuator includes a long-stroke actuator portion including a linear eccentric drive, a short-stroke actuator portion connected to the long-stroke actuator portion, and a tip portion, the tip portion configured to apply a holding force to an edge of the patterning device, the long-stroke actuator portion having a longer travel stroke than that of the short-stroke actuator portion, the short-stroke actuator portion having a higher accuracy than that of the long-stroke actuator portion, and the actuator is mounted such that a tip portion of the actuator can be controllably moved by the long-stroke actuator towards and away from the edge of the patterning device, whereby the tip is positionable in a pushing position in which the tip portion engages the edge of the patterning device and in a released position in which the tip portion does not engage the edge of the patterning device.

[0012] In one embodiment, a photolithography system is configured to perform the method of operating any of the systems described above.

[0013]

[0013] Additionally, in one embodiment, a computer program product is provided that includes a non-transitory computer readable medium having instructions recorded thereon that, when executed by a computer, control the operation of the above-described system. [Brief description of the drawings]

[0014]

[0014] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the subject matter disclosed herein and, together with the description, help to explain some of the principles associated with the disclosed implementations.

[0015] [Figure 1] 1 shows a block diagram of various subsystems of a lithographic projection apparatus according to one embodiment. [Diagram 2]

[0016] 1 depicts a schematic diagram of a lithographic projection apparatus according to an embodiment; [Diagram 3]

[0017] 13A-13C illustrate timing of changes in acceleration for a patterning device holder according to one embodiment. [Figure 4A]

[0018] 1A and 1B illustrate schematic diagrams of a patterning device holder and some of the forces due to acceleration on a patterning device according to one embodiment; [Figure 4B]

[0019] FIG. 13 is a close-up view of a pusher according to one embodiment. [Diagram 5]

[0020] FIG. 13 is a schematic diagram of a translation and locking mechanism for a pusher, according to one embodiment. [Figure 6]

[0021] FIG. 13 is a schematic diagram of a translation and locking mechanism for a pusher, according to one embodiment. [Figure 7]

[0022] FIG. 7 is a schematic side view of the pusher of FIG. 6. [Figure 8]

[0023] FIG. 13 is a schematic side view of a translation and locking mechanism for a pusher, according to one embodiment. [Figure 9]

[0024] FIG. 9 is a schematic top view of the translation and locking mechanism of FIG. 8. [Figure 10]

[0025] FIG. 1 is a block diagram of an exemplary computer system, according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016]

[0026] While specific reference may be made in this document to the manufacture of ICs, it should be expressly understood that the description herein has many other possible applications. For example, the description herein may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will appreciate that in the context of such alternative applications, any use of the terms "reticle," "wafer," or "die" herein should be considered interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

[0017]

[0027] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having wavelengths of 365, 248, 193, 157, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having wavelengths in the range of about 5 to 100 nm).

[0018]

[0028] A patterning device may include or form one or more design layouts. A design layout may be generated utilizing a CAD (Computer Aided Design) program, a process often referred to as EDA (Electronic Design Automation). Most CAD programs follow a set of predefined design rules to create a functional design layout / patterning device. These rules are set by process and design constraints. For example, design rules define the space tolerance between devices (gates, capacitors, etc.) or interconnect lines to ensure that the devices or lines do not interact with each other in an undesirable way. One or more of the design rule constraints may be referred to as a "critical dimension" (CD). A critical dimension of a device may be defined as the minimum width of a line or hole, or the minimum space between two lines or two holes. Thus, the CD determines the overall size and density of the designed device. Of course, one of the goals of device fabrication is to faithfully reproduce the original design intent on the substrate (via the patterning device).

[0019]

[0029] The terms "mask" or "patterning device" as used herein can be broadly interpreted to refer to any general patterning device that can be used to impart an incoming radiation beam with a patterned cross-section that corresponds to the pattern to be produced in a target portion of a substrate, and the term "light valve" is also sometimes used in this context. In addition to typical masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0020]

[0030] An example of a programmable mirror array may be a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is that (for example) addressed areas of the reflective surface will reflect incident radiation as diffracted radiation, while unaddressed areas will reflect the incident radiation as undiffracted radiation. Using appropriate filters, said undiffracted radiation can be filtered out of the reflected beam, leaving only the diffracted radiation behind, and in this way the beam is patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic methods.

[0021]

[0031] An example of a programmable LCD array is given by US Pat. No. 5,229,872, which is incorporated herein by reference.

[0022]

[0032] 1 shows a block diagram of various subsystems of a lithographic projection apparatus 10A according to one embodiment. The main components are a source 12A, which may be a deep ultraviolet excimer laser source or other type of source including an extreme ultraviolet (EUV) source (as discussed above, the lithographic projection apparatus itself does not have to have a radiation source), illumination optics, which may include optics 14A, 16Aa and 16Ab for shaping the radiation from source 12A, e.g. defining a partial coherence (denoted as sigma), a patterning device (or mask) 18A, and transmission optics 16Ac for projecting an image of the patterning device pattern onto a substrate surface 22A.

[0023]

[0033] Pupil 20A may be included in transmission optics 16Ac. In some embodiments, there may be one or more pupils before and / or after mask 18A. As described in more detail herein, pupil 20A can provide patterning of the light that ultimately reaches substrate surface 22A. An adjustable filter or aperture in the pupil plane of the projection optics can limit the range of beam angles impinging on substrate surface 22A, where the maximum possible angle is determined by the numerical aperture of the projection optics, NA=nsin(Θmax ), n is the refractive index of the medium between the substrate and the last element of the projection optics, and Θ max is the maximum angle of the beam exiting the projection optics that can still impinge on the substrate surface 22A.

[0024]

[0034] In a lithographic projection apparatus, a source provides illumination (i.e., radiation) to the patterning device and the projection optics directs and shapes the illumination through the patterning device and onto the substrate. The projection optics may include at least some of the components 14A, 16Aa, 16Ab, and 16Ac.

[0025]

[0035] Lithographic apparatus may include components collectively referred to as "wavefront manipulators" that can be used to adjust the shape and / or phase shift of the wavefront and intensity distribution of the radiation beam. In an embodiment, the lithographic apparatus can adjust the wavefront and intensity distribution at any location along the optical path of the lithographic projection apparatus, for example in front of the patterning device, near the pupil plane, near the image plane, and / or near the focal plane. The wavefront manipulator may be used to correct or compensate for some distortion of the wavefront and intensity distribution and / or phase shift caused by, for example, temperature variations in the source, the patterning device, the lithographic projection apparatus, thermal expansion of components of the lithographic projection apparatus, etc. Adjusting the wavefront and intensity distribution and / or phase shift may change the value of the features represented by the cost function. Such changes may be simulated from a model or measured in practice. The design variables may include parameters of the wavefront manipulator.

[0026]

[0036] FIG. 2 depicts a schematic diagram of a lithographic projection apparatus according to an embodiment.

[0027]

[0037] The lithographic projection apparatus may include an illumination system IL, a first object table MT, a second object table WT, and a projection system PS.

[0028]

[0038] The illumination system IL is capable of conditioning the radiation beam B. In this embodiment, the illumination system also comprises a radiation source SO.

[0029]

[0039] A first object table (e.g. patterning device table) MT may be provided with a patterning device holder for holding a patterning device MA (e.g. a reticle) and connected to a first positioner for accurately positioning the patterning device with respect to the element PS. The first object table includes a part (called a chuck) for firmly holding the patterning device in position during acceleration of the first object table. The chuck for example uses a vacuum clamp to firmly fix the patterning device MA to the first object table MT.

[0030]

[0040] A second object table (substrate table) WT may be provided with a substrate holder for holding a substrate W (eg a resist-coated silicon wafer) and connected to a second positioner for accurately positioning the substrate with respect to element PS.

[0031]

[0041] A projection system ("lens") PS (eg a refractive, reflective or catadioptric optical system) can image an irradiated portion of the patterning device MA onto a target portion C of the substrate W (eg comprising one or more dies).

[0032]

[0042] As depicted, the apparatus may be of a transmissive type (i.e. have a transmissive patterning device); however, in general, it may be of a reflective type, for example (having a reflective patterning device). The apparatus may also employ other types of patterning device than a typical mask, including, for example, a programmable mirror array or an LCD matrix.

[0033]

[0043] A source SO (e.g. a mercury lamp or excimer laser, LPP (Laser Produced Plasma) EUV source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed a conditioning device, such as a beam expander Ex. The illuminator IL may be equipped with adjusting devices AD to set the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. Furthermore, the illuminator IL will generally comprise various other components, such as an integrator IN and a condenser CO. In this way, the beam B impinging on the patterning device MA has a desired uniformity and intensity distribution in its cross-section.

[0034]

[0044] In some embodiments, the source SO may be within the housing of the lithographic projection apparatus (as is often the case, for example, when the source SO is a mercury lamp), but may also be remote from the lithographic projection apparatus. The generated radiation beam is directed into the apparatus (for example, using suitable directing mirrors). In the latter scenario, the source SO may be an excimer laser (for example based on KrF, ArF or F2 lasing).

[0035]

[0045] The beam PB may then intercept the patterning device MA, which is held on a patterning device table MT. After passing through the patterning device MA, the beam B passes through a lens PL, which focuses the beam B onto a target portion C of the substrate W. Using the second positioning device (and the interferometric measurement system IF), the substrate table WT may be precisely moved, e.g. to position different target portions C in the path of the beam PB. Similarly, the first positioning device may be precisely used to position the patterning device MA with respect to the path of the beam B, e.g. after mechanical retrieval of the patterning device MA from a patterning device library or during a scan. Typically, movement of the object tables MT, WT may be achieved using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning). However, in the case of a stepper (as opposed to a step-and-scan tool) the patterning table MT may be connected to a short-stroke actuator only, or may be fixed.

[0036]

[0046] The depicted tool can be used in two different modes: step mode and scan mode. In step mode, the patterning device table MT is kept essentially stationary while the entire patterning device image is projected onto the target portion C at once (i.e. a single flash). The substrate table WT is moved in the x and / or y direction so that a different target portion C can be irradiated by the beam PB.

[0037]

[0047] In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single "flash". Instead, the patterning device table MT is movable in a given direction (the so-called "scan direction", e.g. the y direction) with a speed v, such that the projection beam B scans over the patterning device image. In parallel, the substrate table WT is simultaneously moved in the same or opposite direction with a speed V = Mv, in which M is the magnification of the lens PL (typically M = 1 / 4 or 1 / 5). In this way, a relatively large target portion C can be exposed, without compromising on resolution.

[0038]

[0048] In use, the patterning device table MT is scanned at a constant speed, e.g. 4.8 m / s, across the field of the projection lens along the scan direction. To achieve these speeds, the patterning device table is rapidly accelerated from rest to a high speed and, at the end of the scan, rapidly accelerated again to zero before reversing direction to scan in the opposite direction, as illustrated in Figure 3. The acceleration to achieve these speeds may be as much as 30g or more. In particular, it is believed that to achieve a processing speed of 400 wafers per hour (WPH), the machine may require a capability of acceleration of 31g.

[0039]

[0049] During constant velocity, there are no inertial forces on the patterning device. However, during acceleration and deceleration phases, there may be inertial forces of 100N to 150N on a patterning device having a mass of about 0.5 kg. This may lead to the patterning device potentially slipping relative to the patterning device holder during periods of high acceleration.

[0040]

[0050] Attempts to solve patterning device slippage include using a chuck containing a clamp, such as a vacuum system, to hold the patterning device in place, and / or using a friction coating to increase the friction between the patterning device and the clamp. However, ever-increasing production speeds require faster and faster changes of direction, and therefore higher accelerations have diminished the benefits of these solutions. In clamps, the normal forces between the patterning device and the clamp generate friction forces during the acceleration and deceleration parts of the scan. The friction forces hold the patterning device in place during these parts. However, in vacuum clamps, the friction forces are limited by the maximum pressure difference between the atmosphere and the vacuum, which is currently only about 1 bar. Furthermore, the small surface area of ​​the patterning device in contact with the clamp limits the normal forces that can be generated by the clamp. Currently, the highest friction coefficient of a suitable friction coating is only about 0.25.

[0041]

[0051] Accordingly, it has been proposed to provide an actuator that engages the edge of the patterning device to provide a force to counter the inertial forces during the acceleration phase. Such a system is described, for example, in U.S. Pat. No. 8,885,149, which is incorporated herein by reference. Although there will be some deformation of the patterning device due to the lateral forces generated by the edge clamps, this is generally so minor that it does not significantly affect the error budget for imaging (a few tenths of a nanometer at the patterning device level, translating to less than a tenth of a nanometer at the substrate level).

[0042]

[0052] 3, an example of acceleration timing 200 for a patterning device is illustrated. In a first period there is an increased acceleration phase 202, followed by a steady acceleration period 204, a decreased acceleration phase 206 and a steady motion period 208 (during which imaging takes place). This is followed by a second acceleration 210 (in the opposite direction), a second steady acceleration period 212 and a second decreased acceleration phase 214, followed by a second steady motion period 216.

[0043]

[0053] Figure 4 A 3 shows diagrammatically the forces acting on the patterning device holder 300 according to one embodiment, and in particular on the patterning device MA itself. I acts in a direction opposite to the acceleration or scanning direction of the patterning device MA. This force F I is the force F exerted by the vacuum clamping system of the chuck A To the extent that there is a difference between the inertial force and the chuck holding force, an additional holding or pushing force F H is necessary to prevent slippage of the patterning device MA. In the illustrated embodiment, this additional pushing force is provided by a set of pushers 302a-d located at the corners of the chuck. Since the chuck undergoes rapid scanning motion primarily in a single direction, the four inward pushers 302a-d can provide sufficient stabilizing force to prevent slippage along the direction of chuck motion. As shown, when the direction of motion is to the right in the drawing, the pushers 302a-b provide F I When the direction of acceleration is reversed, the pushers 302c-d provide the required pushing force F H to provide.

[0044]

[0054] Figure 4 B 3A illustrates a schematic example of a pusher 302c according to one embodiment. Although a particular pusher 302c is shown, it is contemplated that the other pushers 302a,b, and d have the same or similar structure.

[0045]

[0055] The pusher 302c is comprised of a tip portion 306 that engages with an edge of the patterning device MA when held by the patterning device holder, along with a fine stroke portion 308 that provides high resolution movement along an axis. For example, the fine stroke portion may be a piezo actuator designed to provide a single degree of freedom along a range of a few microns (e.g., about 10 μm) with a resolution of about 1 nm. Additionally, the pusher 302c is configured to allow coarse movement (e.g., by a coarse actuator 310) over a range of a few millimeters (e.g., about 2 mm) with a resolution of about 1 μm. The coarse movement can be obtained in various ways, as discussed in more detail below.

[0046]

[0056] In one embodiment, pusher 302c further includes a locking mechanism that can hold the actuator in the appropriate position relative to the patterning device or release it to allow the actuator to move freely relative to the patterning device.

[0047]

[0057] Fig. 5 shows an embodiment of a pusher including a locking mechanism. In the illustrated embodiment, the coarse motion is provided by inertia during acceleration of the patterning device table MT. The fine stroke part 308 is slidably mounted on a rail 312, which acts, for example, as a linear motion guide to guide its motion along the axis of motion of the patterning device table MT. When the patterning device MA is moved, for example, to the left, the fine stroke part 308 and its attached tip 306 undergo a relative motion of sliding along the rail 312, whereby the tip 306 moves into engagement with the edge of the patterning device. The fine stroke part 308 may include a piezo actuator. In the figure this is illustrated as a rightward movement along the arrow, but in reality it tends to remain stationary while the patterning device MA is accelerated to the left to cause engagement between the tip and the edge.

[0048]

[0058] The fine stroke portion 308 may be configured to include a strain gauge that can provide feedback to the system's controller to indicate when it engages the edge of the patterning device MA. In this way, the coarse inertial motion of the tip portion can be controllably positioned so that the tip portion is engaged or released in a pushed-in position, where the tip does not contact the edge of the patterning device. If the position is not as expected or desired, the controller can initiate a short acceleration outside of the normal imaging movement to move the pusher to its appropriate engaged or released position.

[0049]

[0059] In an embodiment, the inertial force approach can be replaced with other devices to provide coarse positioning. In one example, coarse positioning may be achieved using a linear actuator (voice coil or linear motor), a linear screw drive, a piezo actuator, a pneumatic actuator, or a solenoid.

[0050]

[0060] When the coarse motion results in the tip being positioned as desired, one or more brake members 314 are actuated to clamp the pusher in place to prevent movement along the linear guide. As shown, the brakes may include a pair of opposing piezo brake members 314 that provide a force perpendicular to the direction of movement of the coarse and fine actuators. In principle, a single brake member acting on one side can provide the necessary normal force to create sufficient friction between the brake pads contained on the brake members and the actuators to prevent movement. Similarly, a static or spring biased member on one side may cooperate with an opposing single brake to provide the normal force.

[0051]

[0061] 6 and 7, a single brake member 314 provides a normal force to prevent movement when the pusher is properly positioned. In this embodiment, a piezo brake member 314 extends to apply the normal force. A caliper 316 self-centers itself as the brake member extends. The caliper can be made, for example, from titanium, titanium alloy, steel, etc.

[0052]

[0062] The linear bearing or flexure 320 allows a single degree of freedom for the position of the caliper 316 parallel to the direction of the normal force applied by the piezo brake member 314. When the brake is extended, the caliper 316 is self-centering, and the linear bearing 320 allows the caliper to do so without introducing any off-axis moments or rotations about the z-axis. In one embodiment, the linear bearing 320 provides the caliper with a range of motion of at least about 20 μm.

[0053]

[0063] The forces generated by the braking action are largely contained within a loop that passes through the caliper 316 and the piezo brake member 314. Therefore, these forces do not generate any significant stress on the chuck walls 318 or chuck floor 319.

[0054]

[0064] In one embodiment, the piezo brake member 314 retracts when a voltage is applied and extends when the voltage drops to zero. That is, the movement of the carriage is normally locked and the carriage is only allowed to move freely when a voltage is applied. In the retracted configuration, there is a gap of about 5-10 μm between the brake pad and the carriage, separating them on either side. When extended, this gap is closed.

[0055]

[0065] 8 and 9 illustrate an alternative device for controlling the coarse position of the pusher tip 306. In this approach, the coarse actuator 310 includes an eccentric drive linear actuator. The motion of the pusher may be constrained, for example, by a flexure mount 320 that acts as a linear motion guide to allow motion along a single dimension. It will be understood that the flexure mount 320 may be replaced with other mounting systems to allow linear motion. In one embodiment, the eccentric drive linear actuator has an off-axis shaft. The shaft is rotated in its bearings 324 by a motor 322. The motor may be, for example, a servo motor or a DC brushless motor. The motor may be controlled with open loop control and is selected to have an appropriate stall torque. An eccentric drive member 326 is attached to the shaft in an off-axis relationship, for example, as a cam follower, to convert the rotational motion of the shaft into linear motion (e.g., of the fine stroke portion 308). To prevent backdrivability of the mechanism, the moment due to the force acting on the drive member should be less than the maximum resistive moment due to friction. A gearbox or motor brake may be provided for this purpose. Preventing backdrive in this manner more generally prevents any parasitic (i.e. unintentional due to externally applied forces) backdrive or frontdrive. As with the inertial embodiment, the piezo fine stroke portion 308 may include strain gauges to provide a control signal, allowing the tip to be accurately positioned relative to the edge of the patterning device.

[0056]

[0066] A set of baffles 328 may be provided to help contain any potential particles generated by the action of the pusher. In one embodiment, the eccentric drive member 326 may include a cam. The cam may be magnetically coupled to the carriage along which the fine stroke portion 308 moves. In this approach, the magnet acts to both push or pull the carriage and to attract or collect potential ferromagnetic particles generated by friction of the carriage moving along the rails or guides.

[0057]

[0067] In one embodiment, the tip 306 is made from a material that is generally stiff but does not impose too much stress on the edge of the patterning device. By way of example, a material such as borosilicate glass may provide a balance of this property. In a particular example, N-BK7 available from SCHOTT Glass may be used. One useful configuration of the tip includes a convex surface for engaging the edge of the patterning device, so that a commercially available lens component made from a suitable glass material can be utilized.

[0058]

[0068] In embodiments using electric actuators, the electrical connections required tend to be less stiff than, for example, pneumatic or hydraulic hoses.

[0059]

[0069] FIG. 10 is a block diagram illustrating a computer system 100 that can assist in embodying and / or implementing the pattern selection method disclosed herein. The computer system 100 includes a bus 102 or other communication mechanism for communicating information and a processor 104 (or multiple processors 104 and 105) coupled with the bus 102 for processing information. The computer system 100 also includes a main memory 106, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 102 for storing information and instructions executed by the processor 104. The main memory 106 may also be used to store temporary variables or other intermediate information during execution of instructions executed by the processor 104. The computer system 100 further includes a read-only memory (ROM) 108, or other static storage device, coupled to the bus 102 for storing static information and instructions for the processor 104. A storage device 110, such as a magnetic or optical disk, for storing information and instructions is provided and coupled to the bus 102.

[0060]

[0070] The computer system 100 may be coupled via bus 102 to a display 112, such as a cathode ray tube (CRT), flat panel, or touch panel display, for displaying information to a computer user. An input device 114, including alphanumeric and other keys, is coupled to bus 102 for communicating information and command selections to the processor 104. Another type of user input device is a cursor control 116, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor 104 and for controlling cursor movement on the display 112. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), allowing the device to be positioned within a plane. A touch panel (screen) display may also be used as an input device.

[0061]

[0071] According to one embodiment of the invention, portions of the simulation process may be performed by computer system 100 in response to processor 104 executing one or more sequences of one or more instructions contained in main memory 106. Such instructions may be read into main memory 106 from another computer-readable medium, such as storage device 110. Execution of the sequences of instructions contained in main memory 106 causes processor 104 to perform the process steps described herein. One or more processors in a multi-processing arrangement may be used to execute the sequences of instructions contained in main memory 106. In an alternative embodiment, hardwired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments herein are not limited to any specific combination of hardware circuitry and software.

[0062]

[0072] The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor 104 for execution. Such media may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as the storage device 110. Volatile media include dynamic memory, such as the main memory 106. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 102. Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tape, other magnetic media, CD-ROMs, DVDs, other optical media, punch cards, paper tape, other physical media with patterns of holes, RAM, PROMs, and EPROMs, FLASH-EPROMs, other memory chips or cartridges, carrier waves as described below, or other media from which a computer can read.

[0063]

[0073] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the processor 104 for execution. For example, the instructions may initially reside on a magnetic disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system 100 may receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to the bus 102 may receive the data carried in the infrared signal and place the data on the bus 102. The bus 102 carries the data to the main memory 106, from which the processor 104 reads and executes the instructions. The instructions received by the main memory 106 may optionally be stored on a storage device 110 either before or after execution by the processor 104.

[0064]

[0074] Computer system 100 preferably also includes a communications interface 118 coupled to bus 102. Communications interface 118 provides a two-way data communication coupling to a network link 120 that is connected to a local network 122. For example, communications interface 118 may be an Integrated Services Digital Network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communications interface 118 may be a Local Area Network (LAN) card to provide a data communication connection to a compatible LAN. A wireless link may also be implemented. In any such implementation, communications interface 118 sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0065]

[0075] Network link 120 typically provides data communication through one or more networks to other data devices. For example, network link 120 may provide a connection through a local network 122 to a host computer 124 or to data equipment operated by an Internet Service Provider (ISP) 126. ISP 126 in turn provides data communication services through a world wide packet data communication network, now commonly referred to as the "Internet" 128. Local network 122 and Internet 128 both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link 120 and through communication interface 118, which carry the digital data to and from computer system 100, are exemplary forms of carrier waves transporting the information.

[0066]

[0076] Computer system 100 can send messages and receive data, including program code, through one or more networks, network link 120 and communication interface 118. In the Internet example, a server 130 might transmit a requested code for an application program through Internet 128, ISP 126, local network 122 and communication interface 118. In accordance with the invention, one such downloaded application provides, for example, the test pattern selection embodiment. The received code may be executed by processor 104 as it is received, and / or stored in storage device 110 or other non-volatile storage for later execution. In this manner, computer system 100 may obtain application code in the form of a carrier wave.

[0067]

[0077] The following clauses may be used to further describe the embodiments. 1. A patterning device transport system for use in holding and moving a patterning device in a lithographic imaging apparatus, comprising: a patterning device holder comprising a chuck configured to releasably hold and support a patterning device; and an actuator configured to apply a holding force to an edge of the patterning device, the holding force opposing inertial forces on the patterning device in response to an acceleration of the patterning device holder, the actuator including a fine stroke portion and a tip portion, the actuator being slidably mounted on the guide; a locking mechanism configured to selectively hold the actuator in a suitable position relative to the patterning device; the actuator is configured to controllably position the tip portion into a pushed position in which the tip portion engages an edge of the patterning device and into a released position in which the tip portion does not engage the edge of the patterning device; The actuator is movable along the guide from a release position to a push-in position. 2. A patterning device transport system as described in clause 1, wherein the locking mechanism includes at least one piezo brake configured to apply a force to a side of the actuator in a direction substantially perpendicular to the extension direction of the guide. 3. A patterning device transport system as described in clause 1, wherein the fine stroke portion includes a strain gauge, the strain gauge operable to provide a signal to the controller in response to the tip portion engaging an edge of the patterning device. 4. The locking mechanism includes only one piezo brake configured to apply a force to a side of the actuator in a direction substantially perpendicular to the extension direction of the guide; 2. A patterning device transport system as described in clause 1, wherein the brake further comprises a floating caliper, the floating caliper constructed and arranged to apply a force to a side of the actuator when a piezo element of the piezo brake is actuated. 5. A patterning device transport system according to clause 4, wherein the piezo elements of the piezo brake are in a locked configuration when no voltage is applied to the piezo elements. 6. A patterning device transport system as described in clause 4, wherein the floating caliper is mounted on a mount providing a single linear degree of freedom in a direction parallel to the direction of the force applied to the side of the actuator. 7. A patterning device transport system according to clause 6, wherein the mount is a bearing or a flexure mount. 8. A patterning device transport system for use in holding and moving a patterning device in a lithographic imaging apparatus, comprising: a patterning device holder comprising a chuck configured to releasably hold and support a patterning device; and an actuator configured to apply a holding force to an edge of the patterning device, the holding force being responsive to an acceleration of the patterning device holder to oppose inertial forces on the patterning device; The actuator is a long stroke actuator portion including a linear eccentric drive; a brake configured to prevent parasitic forces from moving the long stroke actuator portion; a short stroke actuator portion connected to a long stroke actuator portion; a tip portion configured to apply a retaining force to an edge of the patterning device, the long-stroke actuator portion having a longer movement stroke than a movement stroke of the short-stroke actuator portion, the short-stroke actuator portion having a precision greater than a precision of the long-stroke actuator portion; A patterning device transport system, wherein the long-stroke actuator portion is configured to controllably move the tip portion toward and away from the edge of the patterning device, thereby controllably positioning the tip in a pushing position where the tip portion engages the edge of the patterning device and in a released position where the tip portion does not engage the edge of the patterning device. 9. A patterning device transport system as described in clause 8, wherein the long stroke actuator portion includes a motor having an off-axis shaft to cooperate with a linear guide member to convert rotational motion to linear motion. 10. A patterning device transport system according to clause 8, wherein the actuator is mounted on the patterning device holder via a linear motion guide. 11. A patterning device transport system as described in clause 9, wherein the linear motion guide comprises a flexure mount. 12. A patterning device transport system according to clause 9, wherein the motor is a servo motor or a brushless DC motor. 13. A patterning device transport system according to clause 18, wherein the fine stroke portion comprises a piezo actuator. 14. A patterning device transport system according to clause 1 or 8, wherein the tip portion has rounded surfaces on sides that engage the edge of the patterning device. 15. A patterning device transport system according to clause 1 or 8, wherein the tip portion comprises a material different from a material of the fine stroke portion. 16. A patterning device transport system as described in clause 15, wherein the tip portion comprises a borosilicate glass material. 17. A method for controlling a patterning device transport system, the method comprising: accelerating the patterning device holder in a scanning direction to controllably move the actuator from a released position, in which a tip portion of the actuator is not in contact with an edge of the patterning device held by the patterning device holder, to an engaged position, in which a tip portion of the actuator is in contact with the edge of the patterning device; locking the actuator in position relative to the patterning device in response to inertial movement of the actuator; applying a holding force on the patterning device with an actuator in a direction opposite to a direction of acceleration of the patterning device holder; A method comprising: 18. A method for controlling a patterning device transport system, comprising: coarse positioning the patterning device holder using a linear eccentric drive to controllably move the actuator from a released position, in which a tip portion of the actuator does not contact an edge of the patterning device held by the patterning device holder, to an engaged position, in which a tip portion of the actuator contacts the edge of the patterning device; locking the linear eccentric drive with a brake; applying a holding force on the patterning device with an actuator in a direction opposite to a direction of acceleration of the patterning device holder; A method comprising: 19. A computer program product including a non-transitory computer-readable medium having machine-executable instructions recorded thereon, the instructions, when executed, controlling a device according to any one of clauses 1 to 16 or a device according to any one of clauses 17 to 19. 18 A computer program product for performing any of the methods described above.

[0068]

[0078] As used herein, the term "about" can be taken to mean within plus or minus 10%, for example, when referring to a distance, force, or other quantity. For example, the terms "concurrently" or "concurrently" describing something "occurring in parallel" or "varying in parallel" means that two or more things occur at approximately the same time, but not necessarily exactly the same time. For example, changing a pupil design in parallel with a mask pattern can mean making a small modification to the pupil design, then making a small adjustment to the mask pattern, then making another modification to the pupil design, and so on. However, this disclosure contemplates that in some parallel processing applications, concurrency can refer to operations that occur simultaneously or that overlap somewhat in time.

[0069]

[0079] Although the concepts disclosed herein may be used for imaging on substrates such as silicon wafers, it will be understood that the disclosed concepts may be used with any type of lithographic imaging system, for example those used for imaging on substrates other than silicon wafers.

[0070]

[0080] The above description is intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

1. 1. A patterning device transport system for use in holding and moving a patterning device in a lithographic imaging apparatus, comprising: a patterning device holder including a chuck configured to releasably hold and support the patterning device; and an actuator configured to apply a holding force to an edge of the patterning device, the holding force opposing inertial forces on the patterning device in response to an acceleration of the patterning device holder, the actuator including a fine stroke portion and a tip portion, the actuator being slidably mounted on a guide; a locking mechanism configured to selectively hold the actuator in a suitable position relative to the patterning device; the actuator is configured to controllably position the tip portion into a depressed position in which the tip portion engages the edge of the patterning device and into a released position in which the tip portion does not engage the edge of the patterning device; A patterning device transport system, wherein the actuator is movable along the guide from the release position to the push-in position.

2. The patterning device transport system of claim 1 , wherein the locking mechanism comprises at least one piezo brake configured to apply a force to a side of the actuator in a direction substantially perpendicular to an extension direction of the guide.

3. The fine stroke portion includes a strain gauge; The patterning device transport system of claim 1 , wherein the strain gauge is operable to provide a signal to a controller in response to the tip portion engaging the edge of the patterning device.

4. the locking mechanism includes only one piezo brake configured to apply a force to a side of the actuator in a direction substantially perpendicular to an extension direction of the guide; The brake further includes a floating caliper; The patterning device transport system of claim 1 , wherein the floating caliper is constructed and arranged to apply the force to the side of the actuator when a piezo element of the piezo brake is actuated.

5. The patterning device transport system of claim 4 , wherein the piezo elements of the piezo brake are in a locked configuration when no voltage is applied to the piezo elements.

6. The patterning device transport system of claim 4 , wherein the floating caliper is mounted on a mount that provides a single linear degree of freedom in a direction parallel to the direction of the force applied to the side of the actuator.

7. The patterning device transport system of claim 6 , wherein the mount is a bearing or a flexure.

8. 1. A patterning device transport system for use in holding and moving a patterning device in a lithographic imaging apparatus, comprising: a patterning device holder including a chuck configured to releasably hold and support the patterning device; and an actuator configured to apply a holding force to an edge of the patterning device, the holding force being responsive to an acceleration of the patterning device holder and opposing an inertial force on the patterning device; The actuator comprises: a long stroke actuator portion including a linear eccentric drive; a brake configured to prevent parasitic forces from moving the long stroke actuator portion; a short stroke actuator portion connected to the long stroke actuator portion; a tip portion configured to apply the retention force to the edge of the patterning device, the long-stroke actuator portion having a longer movement stroke than a movement stroke of the short-stroke actuator portion, the short-stroke actuator portion having a precision greater than a precision of the long-stroke actuator portion; A patterning device transport system, wherein the long-stroke actuator portion is configured to controllably move the tip portion towards and away from the edge of the patterning device, thereby controllably positioning the tip in a pushing position where the tip portion engages the edge of the patterning device and in a released position where the tip portion does not engage the edge of the patterning device.

9. The patterning device transport system of claim 8 , wherein the long stroke actuator portion includes a motor having an off-axis shaft for cooperating with a linear guide member to convert rotational motion to linear motion.

10. the actuator is mounted on the patterning device holder via a linear motion guide; the linear motion guide includes a flexure mount; The patterning device transport system according to claim 8 , wherein the motor is a servo motor or a brushless DC motor.

11. The patterning device transport system of claim 8 , wherein the fine stroke portion comprises a piezo actuator.

12. The patterning device transport system of claim 8 , wherein the tip portion has rounded surfaces on sides that engage the edge of the patterning device.

13. The patterning device transport system of claim 8 , wherein the tip portion comprises a material different from a material of the fine stroke portion.

14. The patterning device transport system of claim 13 , wherein the tip portion comprises a borosilicate glass material.

15. 1. A method for controlling a patterning device transport system, comprising the steps of: accelerating the patterning device holder in a scanning direction to controllably move the actuator from a released position, in which a tip portion of the actuator is not in contact with an edge of a patterning device held by a patterning device holder, to an engaged position, in which the tip portion of the actuator contacts the edge of the patterning device; locking the actuator in position relative to the patterning device in response to inertial movement of the actuator; applying a holding force on the patterning device with the actuator in a direction opposite to a direction of acceleration of the patterning device holder; A method comprising:

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