Substrate holder, lithographic apparatus, computer program, and method

Abstract

A substrate holding system for supporting a substrate, comprising a substrate holder and a discharge conduit, the substrate holder including a body having a surface, a plurality of bars protruding from the surface and having distal ends forming a support surface for the substrate, and a discharge passage fluidly connected to the discharge conduit and a space between the surface and the substrate supported by the bars to form a discharge flow path, wherein a proportional valve is provided in the discharge flow path.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of European Application No. 22184122.4 filed on July 11, 2022, and European Application No. 23151317.7 filed on January 12, 2023, and both applications are incorporated herein by reference in their entirety.

Background Art

[0002]

[0002] The present invention relates to a substrate holder for supporting a substrate, a lithography apparatus including the substrate holder, a method of supporting a substrate on the substrate holder, and a method of clamping a substrate on the substrate holder.

[0003]

[0003] A lithography apparatus is a machine constructed to apply a desired pattern onto a substrate. The lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithography apparatus can project, for example, a pattern of a patterning device (e.g., a mask) (often also referred to as a “design layout” or “design”) onto a layer of radiation - sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004]

[0004] As semiconductor manufacturing processes have continued to advance, the dimensions of circuit elements have been continuously reduced, while on the other hand, the amount of functional elements such as transistors per device has steadily increased over several decades according to a trend generally called “Moore's Law”. To meet Moore's Law, the semiconductor industry is pursuing technologies that enable the creation of ever - smaller features. To project a pattern onto a substrate, a lithography apparatus can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features formed on the substrate. Typical wavelengths currently in use are 365 nm (i - line), 248 nm, 193 nm, and 13.5 nm.

[0005]

[0005] A lithographic apparatus may include an illumination system for providing a projection beam of radiation, and a support structure for supporting a patterning device. The patterning device may serve to impart a pattern in a cross-section of the projection beam. The apparatus may also include a projection system for projecting the patterned beam onto a target portion of a substrate.

[0006]

[0006] In a lithographic apparatus, a substrate (which may sometimes be called a product substrate) to be exposed may be held on a substrate holder (which may sometimes be called a wafer table). The substrate holder may be movable relative to the projection system. The substrate holder typically comprises a solid body made of a rigid material and having planar dimensions similar to those of the product substrate to be supported. A plurality of protrusions (which may be called bars) may be provided on a surface of the solid body facing the substrate. The distal surface of the bar may coincide with a flat surface and be able to support the substrate. The bars have several advantages, such as that contaminant particles on the substrate holder or on the substrate are likely to be located between the bars and thus do not cause deformation of the substrate, it is easier to machine the bars so that their ends coincide with a plane than to make the surface of the solid body flat, and the properties of the bars can be adjusted, for example, to control the clamping of the substrate to the substrate holder.

[0007]

[0007] The product substrate may warp during the processing of manufacturing the device, especially when a structure with a significant height (e.g., so-called 3D-NAND) is formed. Often, the substrate can be "bowl-shaped" (i.e., concave when viewed from above) or "umbrella-shaped" (i.e., convex when viewed from above). In the present disclosure, the surface on which the device structure is formed is called the top surface. In this context, "height" is measured in a direction perpendicular to the nominal surface of the substrate, and this direction may be called the Z direction. Bowl-shaped and umbrella-shaped substrates are flattened to some extent when clamped on the substrate holder, for example, by partially evacuating the space between the substrate and the substrate holder. However, typically, if the amount of warping, which is measured by the height difference between the lowest point and the highest point on the surface of the substrate, is too large, various problems may occur. In particular, it may be difficult to accurately clamp the substrate, there may be excessive wear of the burrs during loading and unloading of the substrate, and the residual height variation within the surface of the substrate may be too large, so that pattern formation cannot be corrected for all parts of the substrate, especially near the edges.

Summary of the Invention

[0008]

[0008] An object of the present invention is to provide a substrate holding system that enables effective pattern formation on a substrate. The substrate holding system according to one embodiment can enable a more consistent substrate loading and clamping process, which leads to a reduction in overlay.

[0009]

[0009] In a first embodiment, a substrate holding system for supporting a substrate is provided. The substrate holding system includes a substrate holder and a discharge conduit. The substrate holder includes a body having a surface, and a plurality of burrs protruding from the surface, the plurality of burrs having distal ends that form a support surface for the substrate, and a discharge passage that is in fluid connection with the discharge conduit and the space between the surface and the substrate supported by the burrs to form a discharge flow path. A proportional valve is provided in the discharge flow path.

[0010]

[0010] According to a first embodiment, there is also provided a method of clamping a substrate to a substrate holder, the substrate holder including a body having a surface, and a plurality of bars protruding from the surface and having distal ends forming a support surface for the substrate, and a discharge passage fluidly connected to a discharge conduit and a space between the surface and the substrate supported by the bars to form a discharge flow path, the method including positioning the substrate on the support surface, extracting fluid from the space between the surface and the substrate through the discharge flow path, and controlling a clamping variable to achieve full contact of the substrate with the support surface for a substantially predetermined period.

[0011]

[0011] According to a second embodiment, there is provided a device manufacturing method, the device manufacturing method including first clamping a substrate having a first radiation-sensitive layer to a first substrate holder of a first lithographic apparatus, first exposing the radiation-sensitive layer to a first pattern, first processing the substrate to form a first layer based on the first pattern, second clamping a substrate having a second radiation-sensitive layer to a second substrate holder of a second lithographic apparatus, second exposing the radiation-sensitive layer to a second pattern, and second processing the substrate to form a second layer based on the second pattern, wherein the clamping variables applied during the first clamping and the second clamping are determined to minimize an overlay between the first layer and the second layer.

[0012]

[0012] According to the present invention, there is also provided a lithographic apparatus including a substrate holder.

[0013]

[0013] Further embodiments, features, and advantages of the present invention will be described in detail below with reference to the accompanying drawings in conjunction with the structures and operations of various embodiments, features, and advantages of the present invention.

Brief Description of the Drawings

[0014]

[0014] Hereinafter, embodiments of the present invention will be described by way of example only, with reference to the accompanying schematic drawings in which corresponding reference numerals indicate corresponding parts.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figures 10A-10B

Figure 11

[0015]

[0015] The features shown in the figures are not necessarily to scale, and the sizes and / or arrangements shown are not limiting. It will be understood that the figures may include optional features that may not be essential to the invention. Further, not all features of the substrate holder are shown in each of the figures, and the figures may show only some of the relevant elements for explaining a particular feature.

DETAILED DESCRIPTION OF THE INVENTION

[0016] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including (for example) ultraviolet radiation with wavelengths of 436, 405, 365, 248, 193, 157, 126, or 13.5 nm.

[0017] As used herein, the terms "reticle", "mask", or "patterning device" may be broadly construed to refer to a general-purpose patterning device that can be used to impart to an incident radiation beam a cross-section in which a pattern corresponding to a pattern to be formed on a target portion of a substrate is formed. The term "light valve" may also be used in this context. Examples of such patterning devices other than classical masks (transmission or reflection masks, binary masks, phase-shift masks, hybrid masks, etc.) include programmable mirror arrays and programmable LCD arrays.

[0018] FIG. 1 schematically shows a lithographic apparatus LA. The lithographic apparatus comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation or DUV radiation), a mask support (e.g., a mask table) MT connected to a first positioner PM constructed to support a patterning device (e.g., a mask) MA and configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., a substrate table or a substrate holder) WT connected to a second positioner PW constructed to hold a substrate (e.g., a resist-coated wafer) W and configured to accurately position the substrate support WT according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0019]

[0019] During operation, the illumination system IL receives the radiation beam B from the radiation source SO, for example via the beam delivery system BD. The illumination system IL can include various types of optical components such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for guiding, shaping, and / or controlling the radiation. The illuminator IL can be used to adjust the radiation beam B in the plane of the patterning device MA such that its cross-section has a desired spatial and angular intensity distribution.

[0020]

[0020] As used herein, the term "projection system" PS should be construed broadly to encompass various types of projection systems, including refractive optical systems, reflective optical systems, refractive reflective optical systems, anamorphic optical systems, magneto-optical systems, electro-magneto-optical systems, and / or electro-static optical systems, or any combination thereof, depending on the exposure radiation used and other factors such as the use of an immersion liquid or the use of a vacuum. When the term "projection lens" is used herein, it can be considered synonymous with the more general term "projection system" PS.

[0021]

[0021] The lithographic apparatus can be of a type that is capable of covering at least a portion of a substrate with an immersion liquid (e.g., water) having a relatively high refractive index so as to fill the immersion space between the projection system PS and the substrate W, which is also referred to as immersion lithography. Further information regarding immersion techniques is given in U.S. Patent No. 6,952,253, which is incorporated herein by reference.

[0022]

[0022] The lithographic apparatus may be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel and / or, while another substrate on another substrate support WT is in use for exposing a pattern on another substrate W, steps for preparing a subsequent exposure of the substrate W located on one of the substrate supports WT may be carried out.

[0023]

[0023] In addition to the substrate support WT, the lithographic apparatus may comprise a measurement stage (not shown in FIG. 1). The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure the characteristics of the projection system PS or of the radiation beam B. The measurement stage may hold a plurality of sensors. The cleaning device may be arranged to clean a part of the lithographic apparatus (for example, a part of the projection system PS or a part of the system providing the immersion liquid). The measurement stage may be movable under the projection system PS when the substrate support WT is away from the projection system PS.

[0024]

[0024] During operation, the radiation beam B is incident on a patterning device (e.g., a mask) MA held on the mask support MT and is patterned by the pattern (design layout) present on the patterning device MA. The radiation beam B that has passed through the mask MA passes through the projection system PS, and the projection system PS focuses the beam onto the target portion C of the substrate W. With the aid of the second positioner PW and the position measurement system PMS, the substrate support WT can be accurately moved, for example, to position various target portions C at the focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner PM and, optionally, another position sensor (not explicitly shown in FIG. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B. The patterning device MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The illustrated substrate alignment marks P1, P2 occupy dedicated target portions, but they may also be arranged in the space between the target portions. The substrate alignment marks P1, P2 are known as scribe line alignment marks when they are arranged between the target portions C.

[0025]

[0025] In this specification, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely the x-axis, the y-axis and the z-axis. Each of the three axes is orthogonal to the other two axes. A rotation about the x-axis is called an Rx rotation. A rotation about the y-axis is called an Ry rotation. A rotation about the z-axis is called an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system does not limit the present invention and is used only for clarification. For the purpose of clarifying the present invention, another coordinate system such as a cylindrical coordinate system may be used instead. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0026]

[0026] In a lithographic apparatus, the upper surface of the substrate to be exposed in the plane of best focus of the aerial image of the pattern projected by the projection system needs to be positioned extremely accurately. To achieve this, the substrate can be held on a substrate holder. On the surface of the substrate holder that supports the substrate, a plurality of bars can be provided whose distal ends can be in the same plane at the nominal support surface. Despite the large number of bars, since the cross-sectional area in a plane parallel to the support surface is small, the total cross-sectional area of their distal ends is a few percent (e.g., less than 5%) of the surface area of the substrate. The gas pressure in the space between the substrate holder and the substrate can be reduced with respect to the pressure above the substrate in order to create a force that clamps the substrate to the substrate holder.

[0027]

[0027] A partial cross-section of the substrate holder 1 according to the first embodiment is shown in FIG. 2. A plan view of the substrate holder 1 is shown in FIG. 3. The substrate holder 1 comprises a body 10 having a surface 11. The body 10 can form a substantial part of the substrate holder 1. The surface 11 can be the top surface of the body 10 when positioned as shown in FIG. 2. As such, the top surface can be the upper surface in the Z direction as shown in the figure.

[0028]

[0028] The substrate holder 1 comprises a plurality of support pins 20 connected to the surface 11 of the body 10. The support pins 20 can otherwise be called bars as described above. The plurality of support pins 20 have a proximal end 21 located near the body 10 when in the appropriate position, and a distal end 22. The distal end 22 is on the opposite side of the proximal end 21 of the plurality of support pins 20 (i.e., located at the end of the support pins 20 away from the body 10).

[0029]

[0029] The plurality of support pins 20 have a central longitudinal axis 23, and along the central longitudinal axis 23, a proximal end 21 is associated with one end of the support pin 20 and a distal end 22 is associated with the other end of the support pin 20. As such, each of the plurality of support pins 20 can have the central longitudinal axis 23 from the proximal end 21 to the distal end 22.

[0030]

[0030] The distal ends 22 of the plurality of support pins 20 form a support surface for the substrate W. The distal ends 22 of the plurality of support pins 20 can be provided in a plane. Preferably, the support surface is formed in a substantially flat surface (i.e., the distal surface of the support pin 20 can coincide with a flat surface and can support the substrate W). This is beneficial because the substrate W can be positioned so as to be substantially flat on the support surface, and errors can be reduced when forming a pattern on the substrate W.

[0031]

[0031] As shown in FIGS. 2 and 3, the plurality of support pins 20 may be substantially frustoconical (i.e., a truncated cone), or may be conical. Alternatively, the plurality of support pins 20 may be substantially cylindrical. The frustoconical support pins 20 are stronger than cylindrical pins and thus may be less likely to break. Preferably, the plurality of support pins 20 have the same shape as each other.

[0032]

[0032] The plurality of support pins 20 can be connected to the surface 11 of the main body 10 in any suitable manner. The plurality of support pins 20 can be separate components attached to the surface 11 of the main body 10. Alternatively, the plurality of support pins 20 can be integrated with the main body 10. In other words, the plurality of support pins 20 can be formed as protrusions from the surface 11 of the main body 10 (i.e., the plurality of support pins 20 can be formed as a single part including the main body 10).

[0033]

[0033] The substrate holder 1 can be configured to allow fluid to be extracted from between the substrate W supported on the support surface and the surface 11. The fluid at the edge of the substrate W can be drawn out from under the substrate and moved in the direction of arrow A shown in FIG. 2. As the fluid is extracted, the pressure below the substrate W is reduced compared to the pressure above the substrate W, and the edge of the substrate W is lowered toward the substrate holder 1. The substrate W can be clamped by extracting the fluid in the space below the substrate W to provide a reduced relative pressure in the space between the substrate holder 1 and the substrate W.

[0034]

[0034] The main body 10 may include at least one extraction opening 12 from which fluid is extracted. There may be a plurality of extraction openings 12. For example, simply, as shown in FIG. 3, there may be three extraction openings 12 (more or less are also possible).

[0035]

[0035] When clamping the substrate W, it is beneficial to reduce the leakage of fluid into the space between the substrate W and the main body 10. Therefore, providing a physical boundary positioned near the edge of the substrate holder 1 may be beneficial. The physical boundary can be formed towards the edge of the main body 10 as shown in FIGS. 2 and 3. The physical boundary can be formed by the seal member 40. The seal member 40 can be a wall-shaped protrusion formed around the edge of the main body 10 (for example, around the outer periphery of the main body 10). The seal member 40 can be formed to provide a seal between the lower side of the substrate W and the substrate holder 1 around the edge of the substrate W. The seal provided by the seal member 40 does not need to be a perfect seal, but can be a partial seal that reduces but does not eliminate the fluid flow into the space between the substrate holder 1 and the substrate W.

[0036]

[0036] The fixed seal member 40 can surround the plurality of support pins 20. The fixed seal member 40 can protrude from the surface 11 of the main body 10. The fixed seal member 40 can be connected to the main body 10 in any way. The fixed seal member 40 may be integrally formed with the main body 10.

[0037]

[0037] A pressure sensor (not shown in the figure) can be used to measure the pressure between the substrate W and the surface 11 of the main body 10. Various sensors for measuring the pressure in the space below the substrate W are known. For example, a pressure sensor as disclosed in International Application No. 2017 / 137129A1 provides an example of a suitable pressure sensor that can be used, and the entire disclosure of this application is incorporated herein by reference.

[0038]

[0038] A flow sensor (not shown in the figure) can be used to measure the flow rate of the fluid extracted through the extraction opening 12. Various sensors are known for measuring the flow rate from the space below the substrate W.

[0039]

[0039] In a first embodiment, a lithographic apparatus provided with a substrate holding system as described above may be provided. The lithographic apparatus may have any of the features described above and / or the features shown with respect to FIG. 1.

[0040]

[0040] In a conventional lithographic apparatus, the flow rate of the gas extracted from the space below the substrate W is predetermined for a given recipe. The lithographic apparatus may have several (e.g., two or three) selectable predetermined flow rates. For example, one known lithographic apparatus can be selected between 7.0, 2.7, and 1.3 Nl / min, although other flow rates are possible. For a given recipe, the flow rate is selected to provide a compromise between throughput, average overlay, and inter-substrate overlay variation. A high flow rate provides improved throughput through faster clamp processing and lower inter-substrate overlay variation, while a low flow rate provides a smaller average overlay.

[0041]

[0041] The inventors have found that, for a given discharge flow rate, changes in the substrate holder lead to changes in the time taken to complete the clamping process, which in turn lead to changes in the overlay. The clamping process can be considered to be completed when full contact with the support surface is achieved by the bottom of the substrate contacting the outermost ring of the beads on the substrate holder. The time taken to complete the clamping process is referred to herein as the clamp time. During clamping, especially on bowl-shaped substrates, the pressure gradient across the substrate changes over time. This means that the local stress in the substrate W changes over time during the clamping process. This can lead to local variations (hysteresis) in the virtual slip that depends on friction, and possibly local inaccuracies in the substrate position. In other words, the speed at which clamping is performed affects the clamping behavior and the inaccuracies that can occur in the substrate position.

[0042]

[0042] The present invention proposes to provide greater flexibility in the selection of the discharge flow rate, preferably through the provision of a proportional valve in the discharge channel, and to calibrate a particular substrate holder so that the discharge flow rate can be set to achieve completion of the clamping process in a substantially predetermined time. This means that when the same recipe is executed on different lithographic apparatuses, different flow rates can be set in the different lithographic apparatuses, and in the case of a lithographic apparatus having two substrate stages, different flow rates can be set depending on the substrate holder 1 and the substrate stage on which the substrate W is clamped.

[0043]

[0043] Experiments and simulations have suggested that achieving a consistent clamp time leads to a more consistent overlay between substrates in a batch, making it possible to perform overlay compensation, for example, during a subsequent exposure step. A consistent clamping process is thought to lead to more consistent stress in the clamped substrate, and thus to more consistent distortion of the substrate. A consistent duration of the clamping process can also have advantages when scheduling activities within the lithographic apparatus.

[0044]

[0044] Figure 4 shows a substrate holding system according to an embodiment of the present invention. The discharge system 50 is connected to the extraction opening 12 via an extraction passage to extract fluid from the space between the substrate W and the substrate holder 1. The discharge system 50 includes a vacuum pump 52 connected to the extraction opening 12 by a discharge conduit 56. The discharge conduit 56 and the extraction opening 12 form a discharge flow path. Other conduits and devices may be included in the discharge flow path. A proportional valve 51 is provided in the discharge flow path (for example, in the discharge conduit 56) to control the flow resistance of the discharge flow path and thus the discharge flow rate when the discharge pump 52 is active.

[0045]

[0045] Various types of valves can be used as the proportional valve 51 (for example, butterfly valve, disk valve, and diaphragm valve). Desirably, the opening amount of the proportional valve 51 is controlled by the actuator 53. Any suitable type of actuator 53 (for example, piezo actuator, solenoid, or stepper motor) can be used.

[0046]

[0046] Although only a single discharge conduit 56 is shown in FIG. 4, a plurality of parallel branches of the discharge conduit 56 and / or a plurality of extraction openings 12 may be provided to form a discharge flow path between the discharge pump 52 and the space between the substrate W and the substrate holder 1. Respective proportional valves 51 can be provided for different branches of the discharge conduit 56, and different branches of the discharge conduit 56 can be sized differently to improve the range over which the discharge flow can be controlled.

[0047]

[0047] Actuator 53 is controlled by controller 54. The controller 54 obtains the set point of the proportional valve 51 from the calibration data store 55 in order to achieve a predetermined clamping time using a specific substrate holder 1. The process of obtaining calibration data will be described below. Desirably, the calibration data is obtained from calibration measurements performed on the actual substrate holder 1 used to clamp the substrate W for device manufacturing. In some cases, the substrate holders can be grouped into groups having similar characteristics (e.g., type of substrate holder, type of coating, age, usage), and calibration data obtained from one or more exemplary groups of the groups can be used. In order to determine the set point of the proportional valve 51 to achieve the desired predetermined clamping time, the controller 54 can also take into account additional parameters along with the calibration data of the specific substrate holder 1 used. The additional parameters may relate to the substrate holder 1, for example, the length of time since the calibration data was obtained, or the number of times the substrate holder 1 has been used since the calibration data was obtained, etc., which can account for the wear of the substrate holder 1. The additional parameters may also relate to the recipe of the device being manufactured and / or the specific substrate W being clamped, for example, the shape, etc., which can affect the clamping time.

[0048]

[0048] The shape of the substrate W can be estimated. The estimated shape of the substrate W can be predicted based on previously performed measurements. For example, when a specific process or layer is formed, measurement values can be extracted from a previously patterned substrate. For example, the prediction can be based on previous measurements by generating an average shape that depends on these measurement values. The shape of the substrate W can be measured using at least one sensor (not shown in the figure). Any suitable sensor and / or system for measuring the shape of the substrate W can be used, such as an apparatus for measuring the bow and / or warp of the substrate W of MTI Instruments, Inc. (as described, for example, at https: / / www.mtiinstruments.com / applications / wafer-bow-and-warp / ). Data regarding the measured shape of the substrate W from the sensor can be provided as feedback to the controller 54.

[0049]

[0049] The process for obtaining calibration data of the substrate holder 1 is shown in FIG. 5. This process can be executed in a lithography apparatus or a test apparatus having the substrate holding system of FIG. 4. The substrate W is loaded onto the substrate holder 1 by a conventional method (for example, using a gripper robot and e-pins) (S1). The proportional valve 51 is set to the set point (S2), and the substrate W is clamped by evacuating the space between the substrate holder 1 and the substrate W (S3). The time taken to complete the clamping process is determined (for example, by determining the time when the substrate W contacts the outermost bead 20) (S4). The calibration data (for example, including the set point and the time taken to complete the clamping process) is stored in association with data identifying a specific substrate holder 1 and / or its related features (for example, the type of substrate holder, the type of coating, the number of years, the usage amount), and optionally, data related to the substrate W used (for example, the degree of warp and the nature of the backside coating). Then, it is determined whether sufficient data is available (S6), and if not, the process is repeated with different set points and / or different substrates. The steps of this process do not necessarily have to be executed in the order shown above. For example, S2 may be executed before S1 or in parallel with S1, and S6 may be executed before S5 or in parallel with S5.

[0050]

[0050] The clamping process according to an embodiment is shown in FIG. 6. First, the substrate holder 1 used and / or its related features are identified (S10). Based on this information, appropriate calibration data is obtained from the calibration data store 55 (S11). The desired clamping time is determined (S12), and from the calibration data, the valve set point is determined (S13) and set to the proportional valve 51. The substrate W is loaded (S14) and clamped by evacuating the space between the substrate holder 1 and the substrate W (S15). The steps of this process do not necessarily have to be executed in the order shown above. For example, S10 to S13 may be executed after S14 or in parallel with S14.

[0051]

[0051] In the manufacture of some devices having relatively tall features (e.g., DRAM and so-called 3D-NAND), the shape of the substrate W can vary significantly between the initial layer and the final layer (e.g., become more distorted or change from a bowl shape to an umbrella shape). In conventional practice, to minimize distortion, the discharge flow rate is selected according to the shape of the clamped substrate W. Different discharge flows may result in different clamp distortion patterns (sometimes called "fingerprints"). Thus, if the substrate W changes between patterning two layers, different discharge flows can be selected to clamp those two layers.

[0052]

[0052] The inventors have noted that this approach may not be advantageous in all situations. For example, when the overlay between a first layer (which may be low in the stack but not necessarily the first layer to be patterned) and a second layer (which is higher in the stack) is important or critical, the above method may be sub-optimal. As a result of the change in the shape of the substrate W between patterning the first layer and patterning the second layer, if different discharge flows are selected for those patterning steps, the different clamp distortion patterns that occur can increase the overlay between the first layer and the second layer.

[0053]

[0053] Thus, in a second embodiment, it is proposed to select the discharge flow rate and / or discharge pressure for clamping the substrate before both patterning of the first layer and patterning of the second layer in a way that minimizes the overlay between the first layer and the second layer. The selection of the discharge flow rate can take into account other relevant parameters such as the substrate holder used in each step, along with the expected substrate shape before both patterning steps.

[0054]

[0054] In a lithographic apparatus having a small number of selectable discrete exhaust flows, a second embodiment is a case where significant clamp distortion can occur in one or both of the first and second layers, but the same exhaust flow rate for clamping can be selected before both patterning steps.

[0055]

[0055] When a larger number of exhaust flow rates can be selected, or when continuous control is possible for the exhaust flow rate (for example, because a proportional valve 51 is provided), the exhaust flow rate for clamping before patterning the first layer can be different from the exhaust flow rate before patterning the second layer, but the two flow rates can be more similar compared to when they are selected independently.

[0056]

[0056] In the second embodiment, it is also desirable to take into account what corrections are possible by other means (for example, automatic process control within the lithographic apparatus). Therefore, the selection of the exhaust flow rate may aim to minimize overlay patterns that cannot be corrected by other means. Alternatively, the selection of the exhaust flow rate for clamping can be part of a holistic control strategy that utilizes all controllable parameters of the patterning process.

[0057]

[0057] Needless to say, there may be multiple pairs of layers in the stack where overlay is important. Therefore, the optimization method of the second embodiment can be executed multiple times for multiple pairs of layers, and the multiple pairs of layers may be in any order in the stack or may be arranged alternately. The first layer can be patterned using a first lithographic apparatus, and the second layer can be patterned using a second lithographic apparatus. The second lithographic apparatus may be the same lithographic apparatus as the first lithographic apparatus or a different lithographic apparatus. When the same lithographic apparatus is used for both layers, the first substrate holder and the second substrate holder used may be the same or different.

[0058]

[0058] FIG. 7 shows a system for determining clamp variables such as discharge flow rates for different layers in the second embodiment. The substrate model incorporates, as input, the substrate loading shape associated with the fingerprint (clamp distortion pattern) as well as other substrate characteristics such as robustness, thickness, diameter, and backside coating. The substrate holder (WT) model has inputs such as the diameter of the substrate W, the number of extraction openings 12 (clamp holes), the support pin (bar) layout, the position of the e-pin, the geometric shape of the clamp holes, and the roughness of the support pins (bars). The substrate model provides substrate parameters, and the substrate holder model provides substrate holder parameters to the flow model. The flow model may have additional inputs such as the number of clamp holes, the layout of the extraction openings 12 (nozzles) in the substrate holder 1, the throughput (TPT), and the substrate load time. The flow model determines the flow settings (e.g., flow rate and timing) applied to clamp the substrate W prior to pattern formation of different layers.

[0059]

[0059] An alternative model of the second embodiment is shown in FIG. 8. The substrate model incorporates inputs including shape, thickness, robustness, and diameter to model the behavior of the substrate W. The substrate holder (WT) model has inputs including WT support pin (bar) roughness, the number of extraction openings 12 (clamp holes), the layout of the extraction openings, the layout of the bars, the position of the e-pin, and the geometric shape of the extraction openings 12. The substrate holder model models the behavior of the substrate holder 1 and outputs relevant parameters. The flow model incorporates inputs including substrate holder parameters and other parameters such as the position of the extraction holes, the clamp flow, the time sequence of the flow, the number of extraction openings 12, the layout of the extraction openings, and the geometric shape of the extraction openings 12. The flow model models the fluid flow during the clamp procedure, and its output is provided, together with the output of the substrate model, to the substrate loading shape model, which predicts the shape that the substrate W has when loaded onto the substrate holder 1. Data regarding the substrate loading shape, the substrate table model, and the substrate backside roughness are then used to predict the fingerprint (clamp distortion pattern).

[0060]

[0060] Another simpler model of the second embodiment is shown in FIG. 9. This has a substrate model and a substrate holder model that provide inputs to the flow model, which outputs a desired flow setting with reference to throughput and timing information as well. The substrate model has inputs of relevant substrate parameters such as shape, robustness, and diameter. The substrate holder model has inputs including the diameter of the substrate, the layout of the extraction openings 12, and the layout of the support pins (bars).

[0061]

[0061] It will be appreciated that the first and second embodiments can be combined and the flow settings, including flow rate, can be optimized to provide both a consistent clamp time and a consistent fingerprint between the matched layers.

[0062]

[0062] In either the first or second embodiment, it is possible to set a profile that defines the change in flow rate over time rather than a single set point for the flow rate during the clamping process.

[0063]

[0063] An example of the proportional valve 51 that can be used in the embodiment of the present invention is shown in FIGS. 10A and 10B. FIG. 10A shows the proportional valve 51 in a closed configuration, and FIG. 10B shows the proportional valve 51 in an open configuration. In the proportional valve 51, the proportional piezo valve 511 is used to control the control pressure in the input channel 512 connected to the control chamber 513. The control chamber 513 is divided by a flexible membrane 514 that can be impermeable into two isolated sections 513a, 513b. The input channel 512 is connected to the first section 513a of the control chamber 513, whereby the control pressure controls the position of the flexible membrane 514. When the control pressure is high as shown in FIG. 10A, the flexible membrane 514 is forced to move to the closed position, as a result, the inlet 515 connected to the discharge system 50 and the outlet 517 connected to a vacuum source such as the vacuum pump 52 shown in FIG. 4 are covered. In this configuration, since the vacuum source is isolated from the discharge system 50, no clamp vacuum is applied in the substrate holder 1.

[0064]

[0064] When the control pressure is reduced, the flexible membrane 514 moves away from the inlet 515 and the outlet 517, and as a result, the fluid connection between the vacuum source and the discharge system 50 is re-established. The control pressure is reduced by partially or fully closing the piezo proportional valve 511. The gas in the first section 513a of the control chamber 513 can be discharged, for example, into the atmosphere through the outlet 516, and as a result, the pressure in the first section 513a of the control chamber 513 is reduced. The position of the flexible membrane 514 depends on the pressure difference between the first section 513a and the second section 513b of the control chamber 513, the elasticity of the flexible membrane 514, and / or additional biasing means (not shown) that may be provided. Desirably, the flexible membrane 514 is biased to a position where the vacuum source is in fluid connection with the discharge system 50 through its own elasticity and / or additional biasing means when the pressures in the first section 513a and the second section 513b of the control chamber 513 are balanced. If the inlet 515 and the outlet 517 are not completely blocked, the position of the flexible membrane 514 affects the flow resistance between the inlet 515 and the outlet 517, and as a result, by changing the control pressure, a variable flow resistance is provided during discharge from the discharge system 50, thereby allowing a variable clamping pressure to be applied into the discharge system 50.

[0065]

[0065] The proportional membrane valve described above has various advantages. In particular, the proportional membrane valve can operate reliably even when incorporated into a substrate table that is subject to high acceleration and can be exposed to a changing strong magnetic field. The flexible membrane 514 can be selected to be impermeable to liquids (e.g., water), and as a result, no damage occurs even if the immersion liquid is extracted. It can also easily handle high flow rates (e.g., greater than 50 lpm).

[0066]

[0066] To monitor the exact operation of the proportional valve 51, a pressure sensor (not shown) may be provided, for example, in the first and second sections 513a, 513b of the control chamber 515.

[0067]

[0067] A simplified schematic diagram of a pneumatic system for controlling the clamping of a substrate is shown in FIG. 11. The pneumatic system includes several different channels that supply fluid to different parts of the substrate holder 1 or extract fluid from different parts of the substrate holder 1.

[0068]

[0068] The first channel 61 provides clean dry air during substrate loading and provides a connection to the atmosphere 615 if necessary. The piezo valve 611 controls the supply of extremely clean dry air (XCDA) to an outlet 616 near the edge of the substrate W to control the edge of the substrate W (known as edge lift) during load and unload operations. The piezo valve 613 controls the connection to the atmosphere 615. These valves can be replaced with proportional membrane valves as described above to provide additional control of edge lift and air flow as described in European Application No. 22179329.2, which is incorporated herein by reference. Pressure sensors 612, 614 are provided to measure the pressure in the atmosphere and extraction channels to confirm proper operation.

[0069]

[0069] The second channel 62 provides extraction near the e-pin 32 under the control of the solenoid valve 623 and is accompanied by a pressure sensor 622 for monitoring. Extraction of fluid (e.g., a mixture of liquid and gas) from near the edge of the substrate W is provided by an outlet 628a permanently connected to an extraction vacuum 628b and is accompanied by a pressure sensor 627 for monitoring. There is also a connection 626 to a supply of clean dry air (e.g., XCDA) monitored by the pressure sensor 625 and a common wet vacuum connection 629 monitored by the pressure sensor 624.

[0070]

[0070] The third channel 63 provides a clamping vacuum to the extraction opening 12 under proportional control by the piezo valve 631 and the membrane valve 632. The pressure sensor 633 provides monitoring.

[0071]

[0071] Channel 4, 64, provides a proportionally controlled extraction (often also referred to as "pre-clamping") during loading and unloading. The proportional control is provided by piezo valves 641 and membrane valve 642, while two piezo valves 644 and 645 provide a preset extraction speed. Pressure sensors 643, 646, and 647 provide monitoring. Channel 4, 64, is shown as being connected to extraction aperture 12, but may also be (or alternatively) connected to other dedicated apertures (not shown) of substrate holder 1.

[0072]

[0072] It will also be understood that the principles of the present invention are applicable to lithography tools and clamping systems using an electrostatic clamp. In such cases, rather than controlling the flow rate of the exhaust flow, other relevant parameters such as the voltage applied to the electrostatic clamp may be controlled.

[0073]

[0073] Although this text specifically refers to the use of a lithography apparatus in the manufacture of ICs, it should be understood that the lithography apparatus described herein may also 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. In the context of such alternative applications, those skilled in the art will recognize that when the terms "wafer" or "die" are used herein, they may be considered synonymous with the more general terms "substrate" or "target portion", respectively. The substrates referred to herein can be processed, before or after exposure, by, for example, a track (a tool typically used to apply a layer of resist to a substrate and develop the exposed resist), a metrology tool, and / or an inspection tool. Appropriately, the disclosure herein can be applied to the above-described and other substrate processing tools. Further, since the substrate can be processed multiple times, for example, to produce a multilayer IC, the term "substrate" as used herein can also refer to a substrate that already includes one or more processed layers.

[0074]

[0074] Although the above has specifically referred to the use of embodiments of the present invention in the context of optical lithography, it will be understood that the present invention can also be used for other applications.

[0075]

[0075] Although specific embodiments of the present invention have been described above, it will be understood that the present invention can be practiced in ways other than those described.

[0076]

[0076] The foregoing description is illustrative and not restrictive. Thus, it will be apparent to those skilled in the art that changes can be made to the present invention as described without departing from the scope of the following claims.

Claims

1. A substrate holding system comprising a substrate holder and a discharge conduit for supporting a substrate, wherein the substrate holder has a body with a surface, a plurality of bars protruding from the surface, the plurality of bars having distal ends forming a support surface for the substrate, and an extraction passage fluidly connected to the discharge conduit and the space between the surface and the substrate supported by the bars to form a discharge flow path, wherein a proportional valve is provided in the discharge flow path, the substrate holding system.

2. The discharge flow path has a first branch and a second branch parallel to the first branch, the proportional valve is provided in the first branch, and / or The substrate holding system according to claim 1, further comprising an actuator connected to the proportional valve and configured to control the opening amount of the proportional valve.

3. further comprising an additional proportional valve in the second branch, and / or The substrate holding system according to claim 2, further comprising a controller configured to control the actuator during the substrate clamping process such that the time taken for the substrate clamping process is substantially equal to a predetermined period.

4. One of the first and second branches is configured to allow a greater flow rate to pass through than the other of the first and second branches, the substrate holding system according to claim 2 or 3.

5. The controller includes a set point storage device for storing one or more set points for the actuator, preferably, the substrate holding system according to claim 3 or 4, wherein the set points are derived from the calibration of the specific substrate holder.

6. The proportional valve includes a membrane valve, the substrate holding system according to any one of claims 1 to 5.

7. A lithographic apparatus comprising the substrate holding system according to any one of claims 1 to 6.

8. A method of clamping a substrate to a substrate holder, wherein the substrate holder has a body with a surface and a plurality of bars protruding from the surface, the plurality of bars having distal ends forming a support surface for the substrate, and an extraction passage fluidly connecting the discharge conduit and the space between the surface and the substrate supported by the bars to form a discharge flow path, the method comprising positioning the substrate on the support surface, Extracting fluid from the space between the surface and the substrate through the discharge channel; Controlling a clamping variable so that the substrate achieves complete contact with the support surface during a substantially predetermined period; A method comprising the above.

9. The clamping variable is the flow resistance of the discharge channel, Optionally, controlling the clamping variable includes controlling the position of one or more proportional valves in the discharge channel. The method according to claim 8.

10. Controlling includes searching for a control set point in a set point storage device that stores one or more set points. Desirably, the set point represents the position of the one or more proportional valves. Desirably, the set point is derived from the calibration of the specific substrate holder. The method according to claim 8 or 9.

11. A computer program for controlling a substrate holding system, The substrate holding system includes a substrate holder and a discharge channel for extracting fluid from the space between the substrate holder and the substrate, The discharge channel has a proportional valve for performing a clamping method, The method includes: Obtaining a set point related to the specific substrate holder of the substrate holding system; Controlling the proportional valve based on the set point; A computer program comprising the above.

12. A method for manufacturing a device, First clamping a substrate having a first radiation-sensitive layer to a first substrate holder of a first lithographic apparatus; First exposing the radiation-sensitive layer to a first pattern; First processing the substrate to form a first layer based on the first pattern; Second clamping the substrate having a second radiation-sensitive layer to a second substrate holder of a second lithographic apparatus; Second exposing the radiation-sensitive layer to a second pattern; Second processing the substrate to form a second layer based on the second pattern. The method includes: The clamping variables applied during the first clamping and the second clamping are determined to minimize the overlay between the first layer and the second layer. A method.

13. The clamping variable is the discharge flow rate, discharge pressure, timing of the clamping process, or clamping voltage, and / or The method according to claim 12, wherein the clamping variable is the same during the first clamping and during the second clamping. **Claim 14** The clamping variable is determined based on the value of the parameter of the substrate before the first clamping and the value of the parameter of the substrate before the second clamping, optionally, the parameter is selected from the group consisting of the shape of the substrate, the distortion of the substrate, the material of the substrate, the robustness of the substrate, the diameter of the substrate, the characteristics of the back side of the substrate, and / or The method according to claim 12 or 13, wherein the clamping variable is determined such that the distortion of the substrate occurring during the first clamping is similar to the distortion of the substrate occurring during the second clamping. **Claim 15** The first lithographic apparatus and the second lithographic apparatus are the same lithographic apparatus, and / or The method according to any one of claims 12 to 14, wherein the first substrate holder and the second substrate holder are the same substrate holder.

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