SUBSTRATE HOLDER FOR USE IN A LITHOGRAPHIC APPARATUS AND A METHOD OF
MANUFACTURING A SUBSTRATE HOLDER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. Provisional Patent Application Number
63/036,028, which was filed on June 8, 2020, and which is incorporated herein in its entirety by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to substrate holders for use in a lithographic apparatus and methods of manufacturing substrate holders.
BACKGROUND
[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).
[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as “Moore’s law”. To keep up with Moore’s law the semiconductor industry is chasing technologies that enable the creation of increasingly smaller features. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i- line), 248 nm (KrF), 193 nm (ArF) and 13.5 nm (EUV).
[0005] In a lithographic apparatus the substrate to be exposed (which may be referred to as a production substrate) is held on a substrate holder (sometimes referred to as a wafer table). The substrate holder may be moveable with respect to the projection system. The substrate holder usually comprises a solid body made of a rigid material and having similar dimensions in plan to the production substrate to be supported. The substrate-facing surface of the solid body is provided with a plurality of projections (referred to as burls). The distal surfaces of the burls conform to a flat plane and support the substrate. The burls provide several advantages: a contaminant particle on the substrate holder or on the substrate is likely to fall between burls and therefore does not cause a deformation of the substrate; it is easier to machine the burls so their ends conform to a plane than to make the surface of the solid body flat; and the properties of the burls can be adjusted, e.g. to control the clamping of the substrate.
[0006] However, the burls of the substrate holder wear during use, e.g. due to the repeated loading and unloading of substrates. Uneven wear of the burls leads to unflatness of the substrate during exposure which can lead to a reduction of the process window and, in extreme cases, to imaging and or overlay errors. Due to the very precise manufacturing specifications, substrate holders are expensive to manufacture so that it is desirable to increase the working life of a substrate holder.
BRIEF SUMMARY
[0007] In an embodiment, there is provided a method of manufacturing a substrate holder for use in a lithographic apparatus. The substrate holder comprising a plurality of burls projecting from the substrate holder and each burl having a distal end surface configured to engage with a substrate. The method includes applying, via a plasma enhanced chemical vapor deposition, a coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls. The applying of the coating includes adjusting radio frequency (RF) power of RF electrodes in a range 100 to 1000 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 20 to 300 seem, the pre-cursor gas being Hexane.
[0008] Furthermore, in an embodiment, there is provided a method of manufacturing a substrate holder for use in a lithographic apparatus. The substrate holder comprising a plurality of burls projecting from the substrate holder and each burl having a distal end surface configured to engage with a substrate. The method includes applying, via a plasma enhanced chemical vapor deposition, a coating of a wear- resistant material at the distal end surface of one or more burls of the plurality of burls. The applying of the coating includes adjusting radio frequency (RF) power of RF electrodes in a range 50 to 750 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 10 to 100 seem, the pre-cursor gas being Acetylene.
[0009] Furthermore, in an embodiment, there is provided a substrate holder for use in a lithographic apparatus and configured to support a substrate. The substrate holder includes a main body having a main body surface; and a plurality of burls projecting from the main body surface. Each burl has a distal end surface, which is configured to engage with the substrate. The distal end surfaces of the burls substantially conform to a support plane and are configured for supporting the substrate; and the distal end surfaces of one or more burls of the plurality of burls are coated with of wear-resistant material having a hardness in a range 20-27 GPa or 25-35 GPa, and a corrosion rate in a range 0.1 to 2 nm/hr. The corrosion rate being measured by chronoamperometry in three-electrode electrochemical cell with approximately +2.5V potential difference between working and counter electrodes and applied with respect to a reference electrode in dilute NaCl solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:
[0011] Figure 1 is a block diagram of various subsystems of a lithography system, according to an embodiment.
[0012] Figure 2A illustrates substrate or wafer loading on substrate holder (also referred as wafer table (WT)) via an electro static clamp (ESC), the substrate being supported on e-pins in unloaded position, according to an embodiment;
[0013] Figure 2B illustrates the substrate in a loaded position on the substrate holder, according to an embodiment;
[0014] Figures 2C-2F illustrates a sequence of loading the substrate on the substrate holder, according to an embodiment;
[0015] Figure 3A is illustrates a substrate loaded on a substrate holder, a surface of the substrate holder includes burls with some roughness on which the substrate rests, according to an embodiment; [0016] Figure 3B is an example burl of the substrate holder of the Figure 3A, according to an embodiment;
[0017] Figure 4 is a flow chart of a method for manufacturing a substrate holder, according to an embodiment;
[0018] Figure 5 illustrates an example plasma-enhanced chemical vapor deposition setup, according to an embodiment;
[0019] Embodiments will now be described in detail with reference to the drawings, which are provided as illustrative examples so as to enable those skilled in the art to practice the embodiments. Notably, the figures and examples below are not meant to limit the scope to a single embodiment, but other embodiments are possible by way of interchange of some or ah of the described or illustrated elements. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to same or like parts. Where certain elements of these embodiments can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the embodiments will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the description of the embodiments. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the scope is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the scope encompasses present and future known equivalents to the components referred to herein by way of illustration.
DETAILED DESCRIPTION
[0020] While the present disclosure describes features herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
[0021] In the present disclosure, the term “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term “light valve” can also be used in this context. Besides the classic mask (transmissive or reflective; binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include:
-a programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident radiation as diffracted radiation, whereas unaddressed areas reflect incident radiation as undiffracted radiation. Using an appropriate filter, the said undiffracted radiation can be filtered out of the reflected beam, leaving only the diffracted radiation behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic means. More information on such mirror arrays can be gleaned, for example, from U. S. Patent Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference.
-a programmable LCD array. An example of such a construction is given in U. S. Patent No. 5,229,872, which is incorporated herein by reference.
[0022] As a brief introduction, Figure 1 illustrates an exemplary lithographic projection apparatus 10A. Major components are a radiation source 12A, which may be a deep-ultraviolet excimer laser source or other type of source including an extreme ultra violet (EUV) source (as discussed above, the lithographic projection apparatus itself need not have the radiation source), illumination optics which define the partial coherence (denoted as sigma) and which may include optics 14 A, 16Aa and 16Ab that shape radiation from the source 12A; a patterning device 18A; and transmission optics 16Ac that project an image of the patterning device pattern onto a substrate plane 22A. An adjustable filter or aperture 20A at the pupil plane of the projection optics may restrict the range of beam angles that impinge on the substrate plane 22A, where the largest possible angle defines the numerical aperture of the projection optics NA=sin(0max).
[0023] In a lithographic projection apparatus, a source provides illumination (i.e., light); projection optics direct and shapes the illumination via a patterning device and onto a substrate. The term “projection optics” is broadly defined here to include any optical component that may alter the wavefront of the radiation beam. For example, projection optics may include at least some of the components 14A, 16Aa, 16Ab and 16Ac. An aerial image (AI) is the radiation intensity distribution at substrate level. A resist layer on the substrate is exposed and the aerial image is transferred to the resist layer as a latent “resist image” (RI) therein. The resist image (RI) can be defined as a spatial distribution of solubility of the resist in the resist layer. A resist model can be used to calculate the resist image from the aerial image, an example of which can be found in commonly assigned U.S. Patent Application Serial No. 12/315,849, disclosure of which is hereby incorporated by reference in its entirety. The resist model is related only to properties of the resist layer (e.g., effects of chemical processes which occur during exposure, PEB and development). Optical properties of the lithographic projection apparatus (e.g., properties of the source, the patterning device and the projection optics) dictate the aerial image. Since the patterning device used in the lithographic projection apparatus can be changed, it is desirable to separate the optical properties of the patterning device from the optical properties of the rest of the lithographic projection apparatus including at least the source and the projection optics.
[0024] In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g., having a wavelength in the range 5-20 nm).
[0025] Further, the lithographic projection apparatus may be of a type having one or more substrate holders, for example two substrate holders (and/or one or more patterning device tables, for example two patterning device tables). In such "multiple stage" devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic projection apparatuses are described, for example, in US 5,969,441 , incorporated herein by reference.
[0026] In a lithographic apparatus (e.g., Figure 1) the substrate to be exposed (which may be referred to as a production substrate) is held on a substrate holder (sometimes referred to as a wafer table or substrate holder). The substrate holder WT is designed for accurate positioning of a substrate during exposure. The substrate table (e.g., WT in Figures 2A and 3 A) may be moveable with respect to the projection apparatus. The substrate holder usually comprises a solid body made of a rigid material and having similar in-plane XY dimensions to the production substrate to be supported. The substrate-facing surface of the solid body is provided with a plurality of projections or protrusions (referred to as burls). The distal surfaces of the burls (see Figure 3B) conform to a flat plane and support the substrate. The burls provide several advantages: a contaminant particle on the substrate holder or on the substrate is likely to fall between burls and therefore does not cause a deformation of the substrate; it is easier to machine the burls so their ends conform to a plane than to make the surface of the solid body flat; and the properties of the burls can be adjusted, e.g., to control the clamping of the substrate. In an embodiment, the burls reduce the contact area that reduces friction and adhesion between the substrate holder WT and the substrate W.
[0027] However, the burls of the substrate holder wear during use, e.g., due to the repeated loading and unloading of substrates. Uneven wear of the burls leads to un-flatness (e.g., surface profile out of specification in a z-direction) of the substrate during exposure which can lead to a reduction of the process window and, in extreme cases, to imaging and/or overlay errors. Due to the very precise manufacturing specifications, substrate holders are expensive to manufacture so that it is desirable to increase the working life of a substrate holder.
[0028] Some substrate holders may be provided with a diamond-like carbon coating (DLC) on the main body, which is typically SiC or SiSiC. However, the wear, oxidation and unstable friction of the DLC-coated burls are believed to cause significant issues for substrate holder degradation.
[0029] Therefore, it is desirable to coat the substrate holders or at least burls of the substrate holders with a coating such as diamond or other ultra-hard material. However, the available manufacturing CVD techniques, for instance, for diamond growth require higher deposition temperatures (400-1200 °C) which might result in higher thermal stresses and, as a result, lead to a warpage of the substrate holder. This, in turn, will require additional time-consuming manufacturing steps to bring the substrate holder to the flatness specifications.
[0030] Figures 2A and 2B illustrates loading and unloading of the substrate W onto a substrate holder WT by means of a wafer handler WH. The substrate holder WT conventionally has a plurality of burls to support the substrate W. For example, more than 10,000 burls are provided on top of the substrate holder WT, these burls are in contact with the substrate W. When the substrate W is first loaded onto the substrate holder WT in preparation for exposure, the substrate W is supported by three or more ejection pins (e-pins) (e.g., two pins are marked as PI1 and PI2), which hold the substrate W. The wafer handler WH retracks when the substrate is positioned on the e-pins. To hold and support the substrate W on the substrate holder WT during step and scan, the substrate W is clamped on burls (e.g., see Figures 2A and 3 A). The clamping mechanism can comprise, for example, a vacuum force in DUV, or an electrostatic force in EUV. [0031] While the substrate W is being held by the e-pins, the substrate’s own weight and stresses of processed layers and back side coatings will cause the substrate W to distort, e.g., becoming convex or concave. To load the substrate W onto the substrate holder WT, the e-pins are retracted so that the substrate W is supported by burls of the substrate holder WT. As the substrate W is lowered onto the burls of the substrate holder WT, the substrate W will contact in some places, e.g. near the edge, before other places, e.g. near the center. Any friction between the burls (see Figures 2C-2F) and the lower surface of the substrate W may prevent the substrate W from fully relaxing into a flat unstressed state.
This can lead to focus and overlay errors during exposure of the substrate W.
[0032] Growing thick layers on the wafer causes bowed wafers, e.g., a wafer bends up to 400 pm. These deviations lead to overlay defects on the wafer due to misalignment and distorted patterns. When a bowed wafer is loaded and clamped on the substrate holder WT, in-plane stresses are introduced. Figures 2C-2F illustrate example loading sequence of the substrate W and friction between the burls and the substrate W. The sequence of wafer loading from e-pins to the substrate holder WT or electro static clamp (ESC). For example, the wafer W on e-pins travels downward to the substrate table WT (see Figure 2C), a bowed wafer W’ touches the substrate holder WT on edges (see Figure 2D), the wafer W clamped on the substrate holder WT (see Figure 2E), and stresses are locked into the wafer (Figure 2F). In this case, a combination of wafer shape, friction coefficient and normal forces causes the WLG issues, e.g., positioning error with respect to a reference grid.
[0033] The substrate holder WT is commonly made of a ceramic material such as silicon carbide
(SiC) or SiSiC, a material having SiC grains in a silicon matrix. Such a ceramic material can readily be machined to a desired shape using conventional manufacturing methods. When substrates W are loaded and unloaded from the substrate holder WT, the ceramic material can wear quickly. The comparably high frictional coefficient of the ceramic material may also prevent the substrate W from relaxing into a flat unstressed state when loaded onto the substrate holder WT.
[0034] Referring to Figures 3 A and 3B, in an embodiment, one or more burls 310 of the substrate holder WT includes a burl body 312 coated with a coating 311 of wear resistant material (e.g., diamond-like carbon (DLC)). The coating 311 is resistant to wear and reduces the friction between the substrate holder and the substrate W. In an example, DLC may be deposited directly onto the burls of the substrate holder WT. In an example, DLC can be deposited directly onto the entire substrate holder WT. Deposition of DLC is possible at temperatures below 300°C. Temperatures exceeding 300°C risk damage to the substrate holder.
[0035] In an embodiment, the coating 311 may include a first coating and a second coating of wear resistant material (e.g., DLC). The first coating and the second coating may include features similar to those of coating 311. The first coating may be deposited directly onto the substrate holder such that the substrate holder will be coated by the first coating. The second coating may be deposited onto the first coating. The second coating may include a different composition and/or different properties from the first coating as described herein.
[0036] The inventors have recognized that using existing coating technology, the performance of such DLC-coated substrate holders do not meet substrate performance specification (e.g., flatness, focus and overlay) (wear and corrosion off the substrate holder is root cause of focus and overlay issues at the substrate). The DLC deposited on the substrate holder WT (those areas arranged to be in contact with substrates) wears about 10 times faster than desirable, requiring re -polishing and re-conditioning of the substrate holder much sooner than the desired operational period. In an embodiment, a performance of the substrate holder WT is measured with parameters such as wafer load grid (WLG) and flatness.
[0037] Degradation of substrate holder WT leads to limited lifetime, hence early substrate holder
WT swaps or surface reconditioning may be required. The substrate holders may wear in flatness and smoothing of the burl tops, e.g., flower patterns. The origin of this degradation can be chemical wear, mechanical wear, or a combination thereof. Current substrate holder WT designs with DLC coating show significant WLG drift and flatness degradation. For example, WLG drift rate is 20 nm per 1 million substrate passes, and flatness degradation of 10 nm per 1 million due to wear. In an embodiment, wear refers to is a combination of ah wear.
[0038] In an embodiment, the coating 311 is configured to improve the substrate holder performance by reducing mechanical and chemical wear achieved though high coating hardness and corrosion inertness. Improved DLC coating process or improved DLC coatings, as described in the present disclosure, reduce the WLG drift from current value of, e.g., 20 nm per 1 million substrate passes to below 15 nm per million substrate passes. The DLC coating described herein can also improve flatness degradation, e.g., originating from mechanical wear. For example, flatness degradation can also be reduced from 10 nm per 1 million substrate passes to below 7 nm per 1 million substrate passes.
[0039] According to an embodiment, flatness degradation occurs due non uniform wear of the
DLC coating by large number substrate chucking and de-chucking. Mechanics of the process exerts higher lateral displacements on the periphery of substrate holder WT thus causing higher edge wear. Such non-uniform wear of the coating is responsible for the degradation and the flatness of the substrate holder, reducing process yield and causing the need for early substrate holder replacement and machine down time. As such, the coating process should be tailored to generate coating compositions with high hardness and wear resistant properties to minimize edge wear and maximize substrate holder WT lifetime.
[0040] According to an embodiment, a low coefficient of friction is desired to minimize the
WLG. Most commercially available coatings (e.g., DLC coatings) may meet specifications during the early phases of their use on WT burls. Fiowever, increasing number of substrate passes removes the burl’s top surface roughness thus causing the substrate to adhere to the substrate WT via, e.g., Van der Waals forces and capillary forces This chemical adhesion of the substrate to the burl’s top surface causes an increase in the coefficient of friction and WLG. The increase in WLG directly translates to overlay issues reducing process yield and forcing early substrate holder WT change in the field.
[0041] The present disclosure describes an improved coating composition and way to coat a substrate holder. For example, the coating can be performed using a parallel plate plasma-enhanced chemical vapor deposition (PE-CVD) reactor. The exiting settings of the PE-CVD are RF power of RF electrode of approximately 1500 W and hexane gas flow of 300 seem or more. However, using such process, existing a-c:H DLC coating has a hardness of approximately 21 GPa or less, and corrosion rate of 2.7 nm/h or higher. According to the present embodiment, an improved coating hardness of 23 GPa or more, and a corrosion rate of 1.1 nm/h or less is obtained.
[0042] In an embodiment, referring to Figure 4, the manufacturing process for coating a substrate is further described in detail below. Through a series of experiments, it has been discovered that reducing RF power increases the corrosion resistance of the films for given gas flow rate when using hexane as the source gas. Moreover, when this decrease in RF power is coupled with decrease in gas flow rate, resulting films will have superior corrosion resistance together with high hardness values. As discussed herein, the substrate holder WT includes a plurality of burls (e.g., see Figure 3B) projecting from the substrate holder and each burl having a distal end surface configured to engage with a substrate. [0043] In an embodiment, operation P401 includes applying, via a plasma enhanced chemical vapor deposition, a coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls. In an embodiment, the operation P401 includes several sub-operation, e.g., P403 and P405.
[0044] In an embodiment, operation P403 includes adjusting radio frequency (RF) power of RF electrodes in a range 100 to 1000 W for creating plasma. In an embodiment, operation P403 includes exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 20 to 300 seem (e.g., 20 to 200 seem), the pre-cursor gas being Hexane. In an embodiment, the chamber has a geometry described with respect to distance between different component inside the chamber. For example, a distance or diameter of an inside of the chamber (e.g., see D1 in Figure 5), a distance between a top of the chamber and the turntable TT (e.g., see D2 in Figure 5), a distance between a substrate holder and gas distribution line (see D3 in Figure 5), or other appropriate geometric measurements. In an example, in Figure 5, the distance D1 can be approximately 23 inches, the distance D2 can be approximately 6 inches, and the distance D3 can be approximately 5.25 inches. It can be understood the geometry of the chamber is present by example and other geometry of chamber may be used. [0045] In an embodiment, the operation P401 of applying the coating further includes adjusting one or more process parameters comprises at least one of: a vacuum level of the chamber in which the substrate holder is placed in a range 1x103 to 5x102 mbar; or a turn-table speed of a table on which the substrate holder is placed in a range 5 to 100 rpm.
[0046] In an embodiment, the coating with the wear-resistant material causes the distal end surface of the one or more plurality of burls to further have at least one property of: a friction coefficient of the resulting coating in a range 0.05 to 0.5; a surface of the resulting coating having high spots of less than 10 nm and a thickness uniformity across the plurality of burls of the substrate holder within 10% range for the coating thickness over a diameter of 300 mm or less; or a wafer load grid in a range of 0.1 to 1.5 nm, the wafer load grid being a relative positioning error of the substrate with respect to a reference. [0047] In an embodiment, the wear-resistant material is one of diamond-like carbon (DLC). In an embodiment, the DLC comprises: (i) B-, N-, Si-, 0-, F-, S-doped DLCs, and/or (ii) metal-doped DLCs doped with Ti, Ta, Cr, W, Fe, Cu, Nb, Zr, Mo, Co, Ni, Ru, Al, Au, or Ag. In an embodiment, a combination of DLC materials can be used to form the wear-resistant material.
[0048] In an embodiment, the coating of the wear-resistant material causes the distal surfaces of the one or more burls to have a hardness property in a range of 20 GPa to 27 GPa, and a corrosion rate property in a range of 0.1 nm/hr to 1.5 nm/hr, the corrosion rate was characterized by chronoamperometry measured in three-electrode electrochemical cell with approximately +2.5V potential difference between the working and counter electrodes and applied with respect to the reference electrode in dilute NaCl solution. The coating using hexane may include 50-65% sp3 and 25-35% hydrogen.
[0049] In an embodiment, the hardness is measured by a nano indentation method, wherein the measurements are done using a diamond Berkovich tip using a nano-DMA transducer and an indentation depth is kept under 10% of the coating thickness. In an embodiment, the thickness of the coating is between 200 nm to 3 micron.
[0050] In an embodiment, the method 400 further includes operation P410 that include cleaning, prior to applying the coating, the plurality of burls with argon (Ar) gas. In an embodiment, the cleaning step includes generating plasma at approximately 1000 W RF power using the Ar gas; adjusting the Ar gas flow rate between 75 seem for 100 seconds. In an embodiment, the method 400 further includes gradually decreasing the Ar flow rate, and simultaneously increasing the hexane flow rate; and gradually tuning the RF power between 100 to 1000 W for applying the coating.
[0051] In an embodiment, the method 400 can be performed for a different precursor gas (e.g.,
Acetylene gas) and process setting, as discussed below. For example, the method 400 can be modified as follows. Operation P401 includes applying, via a plasma enhanced chemical vapor deposition, a coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls. The applying of the coating includes (e.g., a modification at operation P403) adjusting radio frequency (RF) power of RF electrodes in a range 50 to 750 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 10 to 100 seem, the pre-cursor gas being Acetylene (e.g., a modification at operation P405). In an embodiment, the coating using Acetylene results in a coating having a relatively higher hardness (than Hexane), for example, hardness of greater than 25-35 GPa and corrosion resistance between 0.1 to 2 nm/hr may be achieved. The coating using acetylene may include 60-80% sp3 and 20-30% hydrogen.
[0052] In an embodiment, the applying of the coating may further include adjusting one or more process parameters comprises at least one of: a vacuum level of the chamber in which the substrate holder is placed in a range 1x103 to 5x102 mbar; or a turn-table speed of a table on which the substrate holder is placed in a range 5 to 100 rpm. In an embodiment, the coating with the wear-resistant material causes the distal end surface of the one or more plurality of burls to further have at least one property of: a friction coefficient of the resulting coating in a range 0.05 to 0.5; a surface of the resulting coating having high spots of less than 10 nm and a thickness uniformity across the plurality of burls of the substrate holder within 10% range for the coating thickness over a diameter of 300 mm or less; or a wafer load grid in a range of 0.1 to 1.5 nm, the wafer load grid being a relative positioning error of the substrate with respect to a reference.
[0053] In an embodiment, the method 400 can be modified such that a first coating using hexane as the precursor gas as previously described and a second coating using acetylene as the precursor gas a previously described are applied at the distal end surface of one or more burls of the plurality of burls. For example, referring to FIG. 3B, the first coating may include the coating using hexane and the second coating may include the coating using acetylene. The coating using hexane as the precursor gas may be applied at the distal end surface of one or more burls of the plurality of burls and the second coating using hexane as the precursor gas may be applied onto the first coating. In one example, the method 400 may include applying, via a plasma enhanced chemical vapor deposition, a first coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls. Applying the first coating may include adjusting radio frequency (RF) power of RF electrodes in a range 100 to 1000 W for creating plasma and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 20 to 300 seem, the pre-cursor gas being Hexane. The first layer may include features similar to those of the coating using hexane previously described. The method 400 may further include applying, via the plasma enhanced chemical vapor deposition, a second coating of a wear-resistant material at the distal end surface of the one or more burls of the plurality of burls (e.g., to the first coating). Applying the second coating may include adjusting radio frequency (RF) power of RF electrodes in a range 50 to 750 W for creating plasma and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 10 to 100 seem, the pre-cursor gas being Acetylene. The second coating may include features similar to those of the coating using acetylene previously described.
[0054] In an embodiment, the method 400 can be modified to provide a pre-cursor gas selected from cyclohexane, n-hexane, or a mixture of a carbon-rich and hydrogen-rich gases. For example, the mixture of carbon-rich and hydrogen-rich gases comprises at least one of: acetylene and methane, acetylene and hexane, acetylene and cyclohexane, or acetylene and hydrogen. Depending on the precursor gas, the process parameters of the PE-CVD can be adjusted so that the burls with coating having a hardness of greater than 21 GPa and corrosion resistance between 0.1 to 2 nm/hr may be achieved.
[0055] In an embodiment, the coating of the wear-resistant material includes, but not limited to, diamond, WC, CrN and TiN. The aforementioned coatings can be deposited on various types ceramic or glass substrates including, but not limited to, Si, CVD-Si SiC, SiSiC, CVD-SiC , zerodur, ULE, fused silica, BK-7 and Corning XG glass substrates by depositing thin adhesions layers such as Cr, CrN and other coatings with known good adhesion to DLC coatings.
[0056] Figure 5 illustrates an example reactor 500 used to perform the plasma-enhanced chemical vapor deposition process to apply coating on a substrate holder. PE-CVD process requires strict control of numerous parameters to achieve desired coating properties. For example, the control parameters include, but not limited to, pressure, p, gas flow, discharge excitation frequency/, power P. During deposition, bulk plasma parameters generally control the rate at which chemically active molecular fragments - free radicals, and energetic species such as electrons and ions are created and accelerated under electrical potentials toward the substrate surfaces exposed to plasma. Even for relatively simple gas mixtures, several plasma reactions are taking place and several new species of coating are created. However, reaction rates for most are not readily available making theoretical simulation of the process inefficient and inaccurate. For this reason, the experimental approach for process optimization is employed to determine process recipes that result in desired material properties.
[0057] In Figure 5, the PE-CVD reactor 500 comprises a chamber CBR within which PE-CVD is performed on a substrate holder WT. The substrate holder WT is placed on a turntable TT. The speed of the turntable TT is controlled during the coating process of the substrate holder WT. The chamber CBR also contain plasma created therein. In an embodiment, plasma is created by controlling radio frequency (RF) power to RF electrodes. For example, the RF power can be between 100 to 1000 W, or 50 to 750 W. [0058] The chamber CBR includes a gas distribution line GD though which a precursor gas is supplied in the chamber CBR. In an embodiment, the gas is hexane, acetylene, or other gases discussed herein. In an example, the gas flow rate of the hexane is controlled between 20 to 300 seem, while the RF power is controlled between 100 to 1000 W. In another example, the gas flow rate of the acetylene is controlled between 10 to 100 seem, and the RF power can be between 50 to 750 W. [0059] In an embodiment, the reactor 500 can be connected to a vacuum system VS to control a vacuum level of the chamber CBR. In an embodiment, the reactor 500 is connected to gas inlets though which gases such as argon (Ar) and Oxygen (O) can be supplied to the chamber CBR. In an embodiment, the gas can be supplied for cleaning the substrate holder WT before applying the coating on the substrate holder WT.
[0060] In an embodiment, the PE-CVD reactor 500 includes optical modulation spectroscopy
(OMS) can be used to study the CVD growth on the substrate holder WT. In an embodiment, reactor 500 is water cooled to control a temperature of the turntable TT.
[0061] In an embodiment, the chamber has a geometry described with relative to different components of inside the chamber. For example, the geometry can be characterized by a distance D1 or a diameter D1 of an inside of the chamber, a distance D2 between a top of the chamber and the turntable TT, a distance D3 between a substrate or turntable and gas distribution line (see D3 in Figure 5), or other appropriate geometric measurements. In an example, in Figure 5, the distance D1 can be approximately 23 inches, the distance D2 can be approximately 6 inches, and the distance D3 can be approximately 5.25 inches. It can be understood the geometry of the chamber is present by example and other geometry of chamber may be used.
[0062] Supporting examples 1 , 2 and 3 of process parameters used in the PE-CVD process and resulting coatings are discussed below.
[0063] In Example 1, Si and SiSiC substrates (e.g., burls) are coated with approximately 650 nm
DEC films using hexane as the source gas. This coating run was performed using hexane flow rate of 150 seem and RF power of 750 W. Resulting coating was uniform and dense. Hardness of these coating were measured between 23 ± 1.5 GPa using hysitron nano-indenter equipped with diamond Berkovich tip at a maximum contact depth <50 nm. Furthermore, corrosion characteristics of these coating were characterized using chronoamperometry measured in three-electrode electrochemical cell with +2.5V potential difference between the working and counter electrodes and applied with respect to the reference electrode in dilute NaCl solution. The calculated corrosion rate was determined to be 1.1 nm/hr. These values indicate that approximately 15% and 250 % increase in hardness and corrosion resistance, respectively, when compared to standard DEC coatings deposited using factory set power and gas flow parameters of approximately 1500 W and 300 seem respectively.
[0064] In example 2, Si and SiSiC substrates (e.g., burls) are coated with approximately 650 nm
DEC films using acetylene as the source gas. This coating run was performed using acetylene flow rate of 50 seem and RF power of 300 W. Resulting coating was uniform and dense. Hardness of these coatings were measured between 28 + 1.5 GPa using hysitron nano-indenter equipped with diamond Berkovich tip at a maximum contact depth <50 nm. Furthermore, the corrosion characteristics of these coatings were characterized using chronoamperometry measured in three-electrode electrochemical cell with +2.5V potential difference between the working and counter electrodes and applied with respect to the reference electrode in dilute NaCl solution. The calculated corrosion rate was determined to be 1.6 nm/hr. These values indicate approximately 40% and 250 % increase in hardness and corrosion resistance, respectively, when compared to standard DLC films deposited using factory set power and gas flow parameters of approximately 1500 W and 300 seem respectively.
[0065] In example 3, Si and SiSiC substrates (e.g., burls) are coated with approximately 650 nm
DLC films using acetylene as the source gas. This coating run was performed using acetylene flow rate of 30 seem and RF power of 150 W. Resulting coating was uniform and dense. Hardness of these coatings were measured between 31 + 1.5 GPa using hysitron nano-indenter equipped with diamond Berkovich tip at a maximum contact depth <50 nm. Furthermore, the corrosion characteristics of these coatings were characterized using chronoamperometry measured in three-electrode electrochemical cell with +2.5V potential difference between the working and counter electrodes and applied with respect to the reference electrode in dilute NaCl solution.. The calculated corrosion rate was determined to be 1.6 nm/hr. These values indicate approximately 40% and 250 % increase in hardness and corrosion resistance, respectively, when compared to standard DLC films deposited using factory set power and gas flow parameters of approximately 1500W and 300 seem respectively.
[0066] In an embodiment, there is provided a substrate holder (e.g., see Figures 3A and 3B) manufactured according to method of Figure 4. A substrate holder for use in a lithographic apparatus and configured to support a substrate, the substrate holder includes a main body (e.g., SiSiC) having a main body surface, and a plurality of burls projecting from the main body surface. In an embodiment, each burl has a distal end surface which is configured to engage with the substrate; the distal end surfaces of the burls substantially conform to a support plane and are configured for supporting the substrate; and the distal end surfaces of one or more burls of the plurality of burls coated with of wear-resistant material having a hardness in a range 20-27 GPa or 25-35 GPa, and a corrosion rate in a range 0.1 to 2 nm/hr, the corrosion rate being measured by chronoamperometry measured in three-electrode electrochemical cell with +2.5V potential difference between the working and counter electrodes and applied with respect to the reference electrode in dilute NaCl solution.. In an embodiment, the distal end surfaces has a hardness in the range 20-27 GPa, and the corrosion rate in a range 0.1 to 2 nm/hr.
[0067] As discussed earlier, the distal end surfaces has a hardness in the range 25-35 GPa, and the corrosion rate in a range 0.1 to 1.5 nm/hr. As discussed earlier, the hardness is measured by, for example, nano indentation. The measurements are done using a diamond berkovich tip using a nano- DMA transducer and an indentation depth kept under 10% of the coating thickness. In an embodiment, the thickness of the coating is between 200nm to 3 micron. In an embodiment, the wear-resistant material is one of diamond-like carbon (DLC). In an embodiment, the DLC comprises: (i) B-, N-, Si-, 0-, F-, S- doped DLCs, and/or (ii) metal-doped DLCs doped with Ti, Ta, Cr, W, Fe, Cu, Nb, Zr, Mo, Co, Ni, Ru,
Al, Au, or Ag.
[0068] In an embodiment, the distal end surfaces further have at least one property of: a friction coefficient of the resulting coating in a range 0.05 to 0.5; a surface of the resulting coating having nano bumps of less than 10 nm and a thickness uniformity across the plurality of burls of the substrate holder within 10% range for coating thickness over a diameter of 300 nm or less; or a wafer load grid in a range of 0.1 to 1.5 nm, the wafer load grid being a relative positioning error of the substrate with respect to a reference.
[0069] While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of lithographic imaging systems, e.g., those used for imaging on substrates other than silicon wafers.
[0070] The embodiments may further be described using the following clauses:
1. A method of producing a substrate holder for use in a lithographic apparatus, the substrate holder comprising a plurality of burls projecting from the substrate holder and each burl having a distal end surface configured to engage with a substrate, the method comprising: applying, via a plasma enhanced chemical vapor deposition, a coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls, the applying of the coating comprises: adjusting radio frequency (RF) power of RF electrodes in a range 100 to 1000 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 20 to 300 seem, the pre-cursor gas being Hexane.
2. The method of clause 1, wherein the applying of the coating further comprises: adjusting one or more process parameters comprises at least one of: a vacuum level of the chamber in which the substrate holder is placed in a range 1x10-3 to 5x10-2 mbar; or a turn-table speed of a table on which the substrate holder is placed in a range 5 to 100 rpm.
3. The method of any of clauses 1-2, wherein the coating with the wear-resistant material causes the distal end surface of the one or more plurality of burls to further have at least one property of: a friction coefficient of the resulting coating in a range 0.05 to 0.5; a surface of the resulting coating having high spots of less than 10 nm and a thickness uniformity across the plurality of burls of the substrate holder within 10% range for a coating thickness over a diameter of 300 nm or less; or a wafer load grid in a range of 0.1 to 1.5 nm, the wafer load grid being a relative positioning error of the substrate with respect to a reference.
4. The method of any of clauses 1-3 wherein the wear-resistant material is a diamond-like carbon (DLC).
5. The method of clause 4, wherein the DLC comprises: (i) B-, N-, Si-, 0-, F-, S-doped DLCs, and/or (ii) metal-doped DLCs doped with Ti, Ta, Cr, W, Fe, Cu, Nb, Zr, Mo, Co, Ni, Ru, Al, Au, or Ag.
6. The method of any of clauses 1-5, wherein the coating of the wear-resistant material causes the distal surfaces of the one or more burls to have a hardness property in a range of 20 GPa to 27 GPa, and a corrosion rate property in a range of 0.1 nm/hr to 2 nm/hr, the corrosion rate is measured by a potentiostat chronoamperometry at approximately +2.5V in dilute NaCl solution.
7. The method of any of clauses 1-6, wherein the hardness is measured by a nano indentation, wherein the measurements are done using a diamond berkovich tip using a nano-DMA transducer and an indentation depth kept under 10% of the coating thickness.
8. The method of any of clauses 1-7, wherein the thickness of the coating is between 200nm to 3 micron.
9. The method of any of clauses 1-8 further comprising: cleaning, prior to applying the coating, the plurality of burls with argon (Ar) gas.
10. The method of clause 9, wherein the cleaning further comprises: generating plasma at approximately 1000W RF power using the Ar gas; adjusting the Ar gas flow rate between 75 seem for 100 seconds.
11. The method of clause 10, further comprising: gradually decreasing the Ar flow rate, and simultaneously increasing the hexane flow rate; and gradually tuning the RF power between 100W to 1000W for applying the coating.
12. The method of any of clauses 1-11, wherein the chamber has a geometry characterized by: a diameter of an inside of the chamber; a distance between a top of the chamber and a turntable; and/or a distance between a substrate or turntable and gas distribution line.
13. A method of producing a substrate holder for use in a lithographic apparatus, the substrate holder comprising a plurality of burls projecting from the substrate holder and each burl having a distal end surface configured to engage with a substrate, the method comprising: applying, via a plasma enhanced chemical vapor deposition, a coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls, the applying of the coating comprises: adjusting radio frequency (RF) power of RF electrodes in a range 50 to 750 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 10 to 100 seem, the pre-cursor gas being Acetylene.
14. The method of clause 13, wherein the applying of the coating further comprises: adjusting one or more process parameters comprises at least one of: a vacuum level of the chamber in which the substrate holder is placed in a range 1x10-3 to 5x10-2 mbar; or a turn-table speed of a table on which the substrate holder is placed in a range 5 to 100 rpm.
15. The method of any of clauses 13-14, wherein the coating with the wear-resistant material causes the distal end surface of the one or more plurality of burls to further have at least one property of: a friction coefficient of the resulting coating in a range 0.05 to 0.5; a surface of the resulting coating having nano-bumps of less than 10 nm and a thickness uniformity across the plurality of burls of the substrate holder within 10% range of a coating thickness over a diameter of 300 nm or less; or a wafer load grid in a range of 0.1 to 1.5 nm, the wafer load grid being a relative positioning error of the substrate with respect to a reference.
16. The method of any of clauses 13-15 wherein the wear-resistant material is diamond-like carbon (DLC).
17. The method of clause 16, wherein the DLC comprises: (i) B-, N-, Si-, 0-, F-, S-doped DLCs, and/or (ii) metal-doped DLCs doped with Ti, Ta, Cr, W, Fe, Cu, Nb, Zr, Mo, Co, Ni, Ru, Al, Au, or Ag.
18. The method of any of clauses 13-17, wherein the coating of the wear-resistant material causes the distal surfaces of the one or more burls to have a hardness property in a range of 25 GPa to 35 GPa, and a corrosion rate property in a range of 0.1 nm/hr to 2 nm/hr, the corrosion rate is measured by chronoamperometry in three-electrode electrochemical cell with approximately +2.5V potential difference between working and counter electrodes and applied with respect to a reference electrode in dilute NaCl solution.
19. The method of any of clauses 13-18, wherein the hardness is measured by a nano indentation, wherein the measurements are done using a diamond berkovich tip using a nano-DMA transducer and an indentation depth kept under 10% of the coating thickness.
20. The method of any of clauses 13-19, wherein the thickness of the coating is between 200nm to 3 micron.
21. The method of any of clauses 13-20 further comprising: cleaning, prior to applying the coating, the plurality of burls with argon (Ar) gas. 22. The method of clause 21, wherein the cleaning further comprises: generating plasma at approximately 1000W RF power using the Ar gas; adjusting the Ar gas flow rate between 75 seem for 100 seconds.
23. The method of clause 22, further comprising: gradually decreasing the Ar flow rate, and simultaneously increasing the hexane flow rate; and gradually tuning the RF power between 100W to 1000W for applying the coating.
24. The method of any of clauses 13-23, wherein the chamber has a geometry characterized by: a diameter of an inside of the chamber; a distance between a top of the chamber and a turntable; and/or a distance between a substrate or turntable and gas distribution line.
25. A substrate holder for use in a lithographic apparatus and configured to support a substrate, the substrate holder comprising: a main body having a main body surface; a plurality of burls projecting from the main body surface, wherein: each burl has a distal end surface which is configured to engage with the substrate; the distal end surfaces of the burls substantially conform to a support plane and are configured for supporting the substrate; and the distal end surfaces of one or more burls of the plurality of burls coated with of wear-resistant material having a hardness in a range 20-27 GPa or 25-35 GPa, and a corrosion rate in a range 0.1 to 2 nm/hr, the corrosion rate being measured by chronoamperometry in three-electrode electrochemical cell with approximately +2.5V potential difference between working and counter electrodes and applied with respect to a reference electrode in dilute NaCl solution.
26. The substrate holder of any of clause 25, wherein the distal end surfaces has a hardness in the range 20-27 GPa, and the corrosion rate in a range 0.1 to 2 nm/hr.
27. The substrate holder of any of clause 26, wherein the distal end surfaces has a hardness in the range 25-35 GPa, and the corrosion rate in a range 0.1 to 1.5 nm/hr.
28. The substrate holder of any of clauses 25-27, wherein the distal end surfaces further have at least one property of: a friction coefficient of the resulting coating in a range 0.05 to 0.5; a surface of the resulting coating having nano-bumps of less than 10 nm and a thickness uniformity across the plurality of burls of the substrate holder within 10% range for a coating thickness over a diameter of 300 nm or less; or a wafer load grid in a range of 0.1 to 1.5, the wafer load grid being a relative positioning error of the substrate with respect to a reference. 29. The substrate holder of any of clauses 25-28, wherein the hardness is measured by nano indentation , wherein the measurements are done using a diamond berkovich tip using a nano-DMA transducer and an indentation depth kept under 10% of the coating thickness.
30. The method of any of clauses 25-29, wherein the thickness of the coating is between 200nm to 3 micron.
31. The substrate holder of any of clauses 25-30, wherein the wear-resistant material is one of diamond-like carbon (DLC).
32. The substrate holder of clause 31, wherein the DLC comprises: (i) B-, N-, Si-, 0-, F-, S-doped DLCs, and/or (ii) metal-doped DLCs doped with Ti, Ta, Cr, W, Fe, Cu, Nb, Zr, Mo, Co, Ni, Ru, Al, Au, or Ag.
33. A method of producing a substrate holder for use in a lithographic apparatus, the substrate holder comprising a plurality of burls projecting from the substrate holder and each burl having a distal end surface configured to engage with a substrate, the method comprising: applying, via a plasma enhanced chemical vapor deposition, a first coating of a wear-resistant material at the distal end surface of one or more burls of the plurality of burls, the applying of the first coating comprises: adjusting radio frequency (RF) power of RF electrodes in a range 100 to 1000 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 20 to 300 seem, the pre-cursor gas being Hexane; applying, via the plasma enhanced chemical vapor deposition, a second coating of a wear- resistant material at the distal end surface of the one or more burls of the plurality of burls, the applying of the second coating comprises: adjusting radio frequency (RF) power of RF electrodes in a range 50 to 750 W for creating plasma; and exposing, in a chamber, the one or more plurality of burls to a precursor gas at a gas flow rate between 10 to 100 seem, the pre-cursor gas being Acetylene.
[0071] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.