The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing have been needed.
For example, in the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while feature size (i.e., the smallest component or line that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs, but needs to be matched by improvements in the fabrication process. For instance, many fabrication processes utilize a photomask to form a pattern during photolithography. The pattern may contain a pattern of designed circuits that will be transferred onto a semiconductor wafer. However, because of the increasingly small patterns that are to be used during photolithography, photomasks have generally needed increasingly high resolutions.
In one embodiment, the present disclosure provides a photomask for forming a pattern during photolithography when illuminated with a predetermined wavelength of light. The photomask comprises a transparent substrate; an absorption layer proximate to the substrate, wherein the absorption layer has at least one opening formed therein; and a layer of wavelength-reducing material disposed in at least one opening, wherein a thickness of the wavelength-reducing material and the absorption layer form a generally planar surface.
a-3c illustrate various fabrication stages of the photomask of
a-6c illustrate various fabrication stages of the photomask of
a-9c illustrate various fabrication stages of the photomask of
a and 10b illustrate a top view and a cross-sectional view, respectively, of an embodiment of a photomask with a wavelength reducing medium and pellicle.
a and 11b illustrate a top view and a cross-sectional view , respectively, of another embodiment of a photomask with a wavelength reducing medium and pellicle.
a and 12b illustrate a top view and a cross-sectional view, respectively, of an embodiment of a photomask during a manufacturing stage.
a and 13b illustrate a top view and a cross-sectional view, respectively, of an embodiment of a photomask during a manufacturing stage.
The present disclosure relates generally to photolithography and, more particularly, to using a wave-length reducing medium with a photomask. It is understood, however, that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Referring to
The absorption layer 104 may be formed using a number of different processes and materials, such as depositing of a metal film made with Chromium (Cr) and iron oxide, or an inorganic film made with MoSi, ZrSiO, and SiN. The absorption layer 104 may be patterned to have one or more openings 108 through which light may travel without being absorbed by the absorption layer. In some embodiments, the absorption layer 104 may have a multi-layer structure, which may further include an antireflection (ARC) layer and/or other layers. In addition, some of these layers may be formed multiple times to achieve a desired composition of the absorption layer 104.
The absorption layer 104 may be tuned to achieve a predetermined transmittance and an amount of phase shifting, enabling the absorption layer 104 to shift the phase of light passing through the absorption layer, for improved imaging resolution. For example, the transmittance of the absorption layer 104 may be tuned to between approximately three percent and thirty percent, while the phase shift is tuned to approximately 180 degrees. This type of photomask is sometimes referred to as an attenuated phase-shifting photomask. In another example, the transmittance of the absorption layer 104 may be extremely high (e.g., 95%), and the phase shift may be approximately 180 degrees. This type of photomask is sometimes referred to as a chromeless phase-shifting photomask.
The WRM 106 may be used to fill in the one or more openings 108 of the absorption layer 104. The surface of the WRM 106 may be substantially co-planar with the surface of the absorption layer 104, but may be fine tuned to be slightly higher or lower with the plane of the surface of the absorption layer 104. Both materials may be planarized using known planarization techniques, such as chemical-mechanical planarization (CMP) to form a planar surface. The thickness of the WRM 106 may vary from less than to about the thickness of the absorption layer 104 (e.g., if the surface of the WRM is aligned with the surface of the absorber), to up to about ten times the wavelength of light passing through the WRM 106 during photolithographic processing. The WRM material used for the WRM 106 may be chosen based on a desired level of transparency and a desired refractive index. The WRM 106 preferably has a refractive index different from that of the absorption layer. In the present example, the WRM material is selected to provide both a high level of transparency and a high refractive index. Exemplary WRM materials include photoresist materials, polymer materials, and dielectric materials. For example, the material may include polyimide, SiO2, indium tin oxide (ITO), polyvinyl alcohol (PVA), or silicone.
During a photolithography process, the photomask 100 is disposed above a semiconductor formation. Typically, the photomask 100 does not come into contact with the surface of the semiconductor formation. Due to the relatively high refractive index (“n”) of the WRM 106, the wavelength of the light passing through the WRM 106 during photolithography processing may be reduced by a factor of n from the wavelength of the light in a vacuum. Since the physical size of the opening 108 in the absorption layer 104 remains the same, but the size of the opening 108 relative to the wavelength of the light is enlarged by the factor of n, optical diffraction is reduced accordingly and the resolution of imaging of the photomask 100 on a wafer may be enhanced.
Referring now to
In step 154 (
In step 156 and with additional reference to
Referring now to
For purposes of illustration, the ARC layers may include an ARC layer 210 on an underside (relative to the absorption layer 204) of the substrate 202, an ARC layer 212 between the substrate 202 and the absorption layer 204, an ARC layer 214 between the absorption layer 204 and the WRM 206, and/or an ARC layer 216 above the WRM 206. It is understood that the ARC layer 214 may not cover the sidewall of the patterned absorption layer 204, depending on a particular processing sequence or processing method used to form the photomask 100.
The ARC layers 210, 212, 214, 216 may be used at an interface to reduce stray light introduced by the photomask. Such interfaces may include an interface between the substrate 202 and the absorption layer 204 (using the ARC layer 212), an interface between the absorption layer 204 and the WRM 206 (using the ARC layer 214), and an interface between the substrate 202 and the WRM 206 (using the ARC layer 212), even though these ARC layers may function differently. For example, the ARC layer 214 on the absorption layer 204 may eliminate stray light contributed by the high reflectivity of the absorption layer. The ARC layer 216 on the WRM 206 may reduce multiple reflections between the outer face of the WRM 206 and the absorption layer 204. It may also reduce the reflection between the WRM 206 and the space outside. The ARC layer 212 on the substrate may reduce flare back into an illumination system used during photolithography and may provide a smooth transition between the substrate 202 and the WRM 206 to eliminate mismatch of the refractive index.
Each ARC layer may have multi-level structure that provides each ARC layer with multiple layers having different refractive indices. For example, the ARC layers may have a graded structure where the refractive index of each ARC layer changes gradually to match the refractive indexes of neighboring materials in the photomask 100. The ARC layers may comprise an organic material containing hydrogen, carbon, or oxygen; compound materials such as Cr2O3, ITO, SiO2, SiN, TaO5, Al2O3, TiN, and ZrO; metal materials such as Al, Ag, Au, and In; or combination thereof.
Referring now to
As previously described, materials used for the absorption layer 204 may include metal film such as Chromium (Cr) and iron oxide, or inorganic films such as MoSi, ZrSiO, and SiN. The absorption layer 204 may be formed using CVD, plating, or PVD processes. In the present example, sputtering deposition may be preferred to provide the absorption layer 204 with thickness uniformity, relatively few defects, and better adhesion.
The ARC layers may use an organic material containing hydrogen, carbon, or oxygen; compound materials including Cr2O3, ITO, SiO2, SiN, TaO5, Al2O3, TiN, and ZrO; metal materials such as Al, Ag, Au, and In; or combination thereof. Methods used to form the ARC layers include spin-on coating, CVD, plating, or PVD.
In step 254, the absorption layer 204 and the ARC layer 214 may be patterned to have a predefined arrangement of openings as previously described with respect to the method 150 of
Referring now to
For purposes of illustration, the ARC layers may include an ARC layer 310 on an underside (relative to the absorption layer 304) of the substrate 302, an ARC layer 312 between the substrate 302 and the absorption layer 304, an ARC layer 314 between the absorption layer 304 and the WRM 306, and/or an ARC layer 316 above the WRM 306. These ARC layers are similar to those described with respect to
Referring now to
In step 354, the absorption layer 304 may be patterned to have a predefined arrangement of openings as previously described and, in step 356, the ARC layer 314 is formed. Since the ARC layer 314 is formed after the absorption layer 304 is formed and patterned, the ARC layer 314 conforms to the shape of the absorption layer 304. This enables the ARC layer 314 to be formed over the sidewalls of the absorption layer 304 (
a and 10b illustrate a top view and a cross-sectional view, respectively, of an embodiment of a photomask having a wavelength-reducing material (WRM) layer and a pellicle. The photomask 400 comprises a transparent substrate 402, an absorption layer 404, and a wavelength-reducing material (WRM) 406. The transparent substrate 402, absorption layer 404, and wavelength-reducing material (WRM) 406 are substantially similar to the transparent substrate 102, absorption layer 104, and wavelength-reducing material (WRM) 106, respectively, in composition, formation, and structure. The photomask 400 may further comprise anti-reflective coating (ARC) layers adjacent the transparent substrate 402, absorption layer 404, and/or wavelength-reducing material (WRM) 406, similar to the photomask 200, or photomask 300 in configuration, composition, and formation. The photomask 400 further comprises a pellicle 408 mounted on the WRM layer. The pellicle 408 may comprise a frame 408a and a film 408b. The frame 408a is attached to the WRM layer 406 at edges thereof by a techniques such as glue for adhesion. The film 408b is configured to have a space from the WRM layer 406 and the absorption layer 402 and substantially covers the both. The pellicle 408 or a second pellicle may be alternatively mounted on the non-patterned side of the transparent substrate.
a and 11b illustrate a top view and a cross-sectional view, respectively, of another embodiment of a photomask having a wavelength-reducing material (WRM) layer and a pellicle. The photomask 450 comprises a transparent substrate 402, an absorption layer 404, and a wavelength-reducing material (WRM) 406 substantially similar to the photomask 400 of
Methods of fabricating the photomask 450 of
a and 12b illustrate a top view and a cross-sectional view, respectively, of a photomask during a manufacturing stage. The absorption layer 404 and the WRM layer 406 are formed on the transparent substrate 402 similar to the method 150. The ARC layers may also be formed thereon similar to the method 250 or the method 350. Then the protective cover 409 is mounted on the WRM layer 406 to cover the absorption layer and substantially covers the WRM layer leaving edges of the WRM layer exposed. The edges have a dimension large enough to hold a pellicle frame but not too large to being over the absorption features 404.
The protective cover 408 may comprise quartz, metal such as aluminum and stainless steel, and/or polymer such as polyimide. The protective cover may have a wall thickness to be self-sustained. The protective cover may include a rim and a top portion. The rim may be in contact with the WRM layer. The top portion may be designed and configured to have no contact with the WRM layer and the absorption features at any point. The protective cover may be held to the photomask by a method such as vacuum technique as illustrated in
a and 13b illustrate a top view and a cross-sectional view, respectively, of the photomask during another manufacturing stage. The edges of the WRM layer are removed when the absorption features and the rest of the WRM layer are protected by the protective layer. The removal of the edges of the WRM layer may be implemented by a dry etching as shown in
The edges of the WRM layer may be removed without using the protective cover. For example, the photomask may be held vertical and have its edge dipped in an etching solution tank 434 such that only the edge of the WRM layer is removed, as shown in
In another example as illustrated in
In a another example as illustrated in
Thus the present disclosure provides a photomask comprising a transparent substrate and an absorption layer proximate to the transparent substrate. The absorption layer has at least one opening formed therein. The photomask also comprises a wavelength-reducing material (WRM) layer disposed in the at least one opening, wherein the wavelength-reducing material and the absorption layer form a generally planar surface, and a pellicle mounted proximate to the transparent substrate. The pellicle may comprise a frame proximate to the transparent substrate and a film to cover the transparent substrate. The frame may be attached on the WRM layer at edges and the film substantially covers the absorption layer and the WRM layer. The frame may be attached on a patterned side of the transparent substrate at edges such that the film covers the absorption layer and the WRM layer. The frame may be attached onto a non-patterned side of the transparent substrate. The WRM layer may comprise a transparent polymer material, a photoresist material, or a transparent dielectric material. The WRM layer may have a refractive index different from that of the absorption layer.
The present disclosure also provides a method for fabricating a photomask comprising forming an absorption layer proximate to a transparent substrate, patterning the absorption layer, forming at least one opening in the absorption layer, forming a wavelength-reducing material (WRM) layer in the at least one opening of the absorption layer, and mounting a pellicle proximate to the transparent substrate. The mounting a pellicle may comprise attaching a frame of the pellicle on the WRM layer, substantially covers the absorption layer and the WRM layer. The mounting a pellicle may comprise attaching a frame of the pellicle on a non-patterned side of the transparent substrate. The mounting a pellicle may comprise mounting a frame of the pellicle on a patterned side of the transparent substrate such that the pellicle covers the absorption layer and the WRM layer. The mounting a pellicle may comprise: removing edges of the WRM layer to expose edges of the transparent substrate on the patterned side; and attaching the pellicle by gluing the frame of the pellicle on the edges of the transparent substrate. The method may further comprise: covering the WRM layer and the absorption layer using a protective cover, leaving edges of the WRM layer exposed before the removing edges; and taking away the protective cover after the removing edges. The protective cover may comprise a material selected from the group consisting of metal, quartz, and polymer. The protective cover may have a wall thickness to be self-sustained. The protective cover may include a rim and a top portion. The protective cover may include a valve for vacuuming and releasing. The WRM layer may be covered by the protective layer leaving a space between the WRM layer and a top of the protective layer. The WRM layer may be covered by holding the protective cover by vacuum and/or pressure. The edges of the WRM layer may be removed by methods such as dry etching, wet etching, liquid nozzle etching, and/or a lithography process. The pellicle may mounted comprise using glue for adhesion.
The present disclosure also provides a photolithography method comprising positioning a photomask above a semiconductor formation and exposing the photomask and semiconductor formation to light. The photomask includes a transparent substrate, an absorption layer proximate to the transparent substrate and defining at least one opening therein, a high refractive index layer disposed in the at least one opening of the absorption layer and operable to reduce a wavelength of light passing therethrough during photolithography, and a pellicle attached on the transparent substrate.
The present disclosure has been described relative to a preferred embodiment. Improvements or modifications that become apparent to persons of ordinary skill in the art only after reading this disclosure are deemed within the spirit and scope of the application. It is understood that several modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. For example, one or more of the illustrated ARC layers may be excluded or additional ARC layers may be used. Materials used for the transparent substrate, absorption layer, wavelength reducing material, and ARC layers may vary, as may the method by which the various layers are formed. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.
This application is a continuation-in-part of U.S. Utility Patent Application Serial No. 10/964,842, filed on Oct. 13, 2004 and entitled “A Device and Method for Providing Wavelength Reduction with a Photomask”, which claims priority to U.S. Provisional Patent Application Ser. No. 60/511,503, filed on Oct. 15, 2003 and entitled the same.
Number | Date | Country | |
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60511503 | Oct 2003 | US |
Number | Date | Country | |
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Parent | 10964842 | Oct 2004 | US |
Child | 11248070 | Oct 2005 | US |