Patent Publication Number: US-2003224254-A1

Title: Method for reducing dimensions between patterns on a photomask

Description:
RELATED APPLICATION  
     [0001] This application is a continuation-in-part application of U.S. application Ser. No. 09/978,546, entitled “Method for Reducing Dimensions Between Patterns on a Photoresist,” filed on Oct. 18, 2001, and claims priority to U.S. Provisional Application Serial No. 60/390,183, entitled “Sub-90 nm Space and Hole Patterning Using 248 nm Lithography with Plasma-Polymerization Coating,” filed on Jun. 21, 2002. This application is also related to concurrently-filed U.S. application Ser. No. ______ (Attorney Docket No. 08409.0002-01000), entitled “Method for Reducing Dimensions Between Patterns on a Hardmask,” and U.S. application Ser. No. ______ (Attorney Docket No. 08409.0002-03000), entitled “Method for Reducing Dimensions Between Patterns on a Photoresist.” These related applications are expressly incorporated herein by reference. 
    
    
     
       DESCRIPTION OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] This invention relates in general to a photomask manufacturing process and, more particularly, to a photomask manufacturing method having reduced dimensions between patterns on a photomask.  
       [0004] 2. Background of the Invention  
       [0005] With sub-micron semiconductor manufacturing process being the prevalent technology, the demand for a high-resolution photolithographic process has increased. The resolution of a conventional photolithographic method is primarily dependent upon the wavelength of a light source, which dictates that there be a certain fixed distance between patterns on a photoresist. Distance separating patterns smaller than the wavelength of the light source could not be accurately patterned and defined.  
       [0006] Prior art light sources with lower wavelengths are normally used in a high-resolution photolithographic process. In addition, the depth of focus of a high-resolution photolithographic process is shallower compared to a relative low-resolution photolithographic process. As a result, a photoresist layer having a lower thickness is required for conventional photolithographic methods. However, a photoresist layer having a lower thickness is susceptible to the subsequent etching steps in a semiconductor manufacturing process. This relative ineffective resistance to etching reduces the precision of patterning and defining of a photoresist. These limitations prevent the dimensions of patterns on a photoresist from being reduced.  
       [0007] Furthermore, a photomask is commonly used in the photolithography process, during which a pattern on the photomask is transferred to the photoresist on a substrate. A photomask usually has a transparent substrate with a layer of masking material that blocks light in the photolithography process. A feature size of the photomask determines the feature size of the photoresist patterns. Therefore, reducing the feature size of photomask helps reducing a semiconductor device size.  
       [0008] A conventional method of manufacturing a photomask includes forming the layer of masking material on the transparent substrate, forming a resist layer on the layer of masking material, patterning and defining the resist layer, etching the masking material, and removing the patterned and defined resist layer.  
       SUMMARY OF THE INVENTION  
       [0009] In accordance with the present invention, there is provided a method for manufacturing a photomask that includes providing a transparent substrate, forming a mask layer over the substrate, providing a resist layer over the mask layer, patterning and defining the resist layer to define a critical dimension of the photomask, depositing a third layer over the patterned and defined resist layer to decrease the critical dimension of the photomask, etching the third layer, and etching the mask layer.  
       [0010] Also in accordance with the present invention, there is provided a method for manufacturing a photomask that includes providing a transparent substrate, forming a mask layer over the substrate, providing a resist layer over the mask layer, patterning and defining the resist layer to form at least two resist structures, each having a substantially horizontal top and at least one substantially vertical sidewall, and wherein the at least two resist structures are separated by a first space, depositing a layer of photo-insensitive material on the tops and sidewalls of the at least two resist structures, etching the layer of photo-insensitive material, and etching the mask layer.  
       [0011] In one aspect, the step of depositing a layer of photo-insensitive material is performed at a temperature lower than a stability temperature of the patterned and defined resist layer.  
       [0012] Further in accordance with the present invention, there is provided a method for manufacturing a photomask that includes providing a transparent substrate, forming a mask layer over the substrate, providing a resist layer over the mask layer, patterning and defining the resist layer to form at least one resist structure, each having a substantially horizontal top and at least one substantially vertical sidewall, depositing a photo-insensitive material over the at least one resist structure, wherein a first amount of the photo-insensitive material is deposited on the top of the resist structure and a second amount of the photo-insensitive material is deposited on the at least one sidewall of the resist structure, etching the photo-insensitive material and the mask layer, and removing the at least one resist structure.  
       [0013] In one aspect, the first amount is greater than the second amount.  
       [0014] In another aspect, the first amount is less than the second amount.  
       [0015] Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.  
       [0016] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.  
       [0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018] FIGS.  1 - 3 B are cross-sectional views of the semiconductor manufacturing process steps of the present invention; and  
     [0019] FIGS.  4 A- 4 D show cross-sectional views of the photomask manufacturing process steps of the present invention. 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
     [0020] Reference will now be made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
     [0021] FIGS.  1 - 3 B are cross-sectional views of the semiconductor manufacturing process steps of the present invention. Referring to FIG. 1, the method of the present invention begins by defining a wafer substrate  100 . Wafer substrate  100  may be of any known semiconductor substrate material, such as silicon. A first layer  110  is then provided over wafer substrate  100 . In one embodiment, first layer  110  is a semiconductor material, such as polysilicon. First layer  110  may also be a dielectric layer or a metal layer. First layer  110  may be deposited over wafer substrate  100  by any known deposition process. In another embodiment, first layer  110  is a dielectric material, in which case first layer  110  may be deposited or grown over wafer substrate  100 .  
     [0022] An anti-reflection coating (ARC) layer  120  may optionally be provided over first layer  110  to decrease the reflection from first layer  110  in subsequent manufacturing steps. A photoresist layer  130  is then provided over ARC layer  120 . In an embodiment in which an ARC layer is not provided, photoresist layer  130  is deposited overfirst layer  110 . Photoresist layer  130  is then patterned and defined using a known photolithographic process to form a patterned and defined photoresist layer having a plurality of photoresist structures  130 . Photoresist structures  130  include substantially vertical sidewalls  132  and substantially horizontal tops  134 . When first layer  110  is a semiconductor material, photoresist structures  130  functions to form conductors from first layer  110 .  
     [0023] Referring to FIG. 2, a second layer  150  is deposited over the patterned and defined photoresist layer  130  by a known chemical vapor deposition apparatus  140 . Known chemical vapor deposition processes include plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD). Second layer  150  may be organic or inorganic, and is photo-insensitive. In one embodiment, second layer  150  is a polymer layer. In another embodiment, second layer  150  is substantially conformal, covering both tops  134  and sidewalls  132  of photoresist structures  130 . In one embodiment, an amount of second layer  150  deposited on tops  134  of photoresist structures  130  is substantially greater than an amount adhered to the sidewalls  132 . Having a substantially more of second layer  150  deposited on tops  134 , photoresist structures  130  become more resistive to subsequent etching steps, thereby preserving the precision of the photolithographic process. In addition, the step of depositing second layer  150  is performed at a temperature lower than a stability temperature of photoresist structures  130 . In other words, second layer  150  is deposited at a temperature not affecting the structural stability of photoresist structures  130 .  
     [0024] After the deposition of second layer  150 , the space between photoresist structures  130  is decreased, for example, from 0.22 microns to 0.02 microns.  
     [0025] In the PECVD process, the pressure used is in the range of approximately 5 mTorr to 30 mTorr. The source power ranges from approximately 900 watts to 1800 watts and the bias power ranges from 0 to 1300 W. The deposition rate is between approximately 3,000 Å per minute and 6,000 Å per minute. In addition, polymer layer  150  comprises at least one hydrocarbon partially substituted by fluorine, the source for forming polymers. The partially-substituted hydrocarbons may be chosen from difluoromethane (CH 2 F 2 ), a mixture of difluoromethane and octafluorobutene (C 4 F 8 ), and a mixture of difluoromethane and trifluoromethane (CHF 3 ). In one embodiment, when the partially-substituted hydrocarbons include CH 2 F 2  only, the thickness “a” of a portion of polymer layer  150  is the same as the thickness “b” of another portion of polymer layer  150 .  
     [0026] Moreover, argon (Ar) and carbon monoxide (CO) may be mixed with the gases introduced during the PECVD process. Argon acts as a carrier to enhance etch uniformity of photoresist layer  130  and ARC layer  120 . The function of carbon monoxide is to capture fluorine radicals and fluoride ions generated by the fluoro-substituted hydrocarbons. As such, etching of the polymers during the deposition process is prevented, thereby enhancing the deposition rate of polymer layer  150 . Oxygen (O 2 ) and nitrogen (N 2 ) gases also can be added to the PECVD process. Contrary to the function of the carbon monoxide, the presence of oxygen serves to etch polymer layer  150 . Therefore, the deposition rate of polymer layer  150  can be controlled. Also, perfluorohydrocarbons, such as hexafluoroethane (C 2 F 6 ) and tetrafluoromethane (CF 4 ), can be mixed with the gases combined with the plasma during deposition because these gases, similar to the oxygen gas, etch polymer layer  150 .  
     [0027] In one embodiment, when the gases used during deposition of second layer  150  include approximately 10 to 30 sccm of C 4 F 8 , 10 to 30 sccm of CH 2 F 2 , 50 to 150 sccm of CO, and 100 to 300 sccm of argon (Ar), the amount of second layer  150  deposited on tops  134  of photoresist structures  130  is substantially greater than the amount adhered to sidewalls  132 . In another embodiment, when the gases used during deposition of second layer  150  include approximately 10 to 30 sccm of C 4 F 8 , 0 to 15 sccm of CH 2 F 2 , 0 to 50 sccm of CO, and 100 to 300 sccm of argon (Ar), and the bias power is greater than approximately 400 W, the amount of second layer  150  deposited on tops  134  of photoresist structures  130  is substantially less than the amount adhered to sidewalls  132 .  
     [0028] Referring to FIGS. 3A and 3B, second layer  150 , photoresist structures  130 , ARC layer  120 , and first layer  110  are etched anisotropically with a plasma-based dry etching process. The dry etching process uses plasma  160  as etchant. In an embodiment in which “a” is thicker than “b,” the thickness of second layer  150  changes from “a” to “a-b” after second layer  150  deposited over ARC layer  120  is completely etched away. This shows that second layer  150  provides excellent resistance to the plasma etch process and therefore enhances the etching resistance of photoresist structures  130 .  
     [0029] As shown in FIG. 3B, when the anisotropic dry etching process continues, second layer  150  acts as an etch stop and remains on the sidewalls of photoresist structures  130 . Thus, the dimensions between the patterned photoresist and underlying patterned first layer  110  are reduced. Photoresist structures  130  may be removed using any conventional process.  
     [0030] FIGS.  4 A- 4 D show a manufacturing method of a photomask consistent with one embodiment of the present invention. Unless otherwise described hereinafter, the method shown and described in FIGS.  1 - 3 B, including the results and advantages thereof, are the same as the method shown in FIGS.  4 A- 4 D.  
     [0031] Referring to FIG. 4A, a transparent substrate  400  is provided. Substrate  400  may be comprised of glass, such as soda lime glass, borosilicate glass, quartz glass, sapphire, or the like, having a smooth surface. A mask layer  410  is formed on substrate  400 . Mask layer  410  may comprise chromium, molyddenum silicide, or other conventional masking material. Referring to FIG. 4B, a resist layer  420  is formed over mask layer  410  and patterned and defined using an electron beam to expose predetermined parts of mask layer  410 . One or more resist structures  420  are formed during this step, each of which has a substantially horizontal top and one or more substantially vertical sidewalls.  
     [0032] Referring to FIG. 4C, a third layer material  430  is deposited over the entire surface of the resulted structure including the tops and sidewalls of resist structures  420  and the exposed surface of mask layer  410 . Third layer  430  may be deposited with any known chemical vapor deposition process, include plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD). Third layer  430  may be organic or inorganic, and is photo-insensitive. In one embodiment, third layer  430  is a polymer layer, and may be substantially conformal. An anisotropic etching of third layer  430  is performed to remove the inorganic material deposited on the exposed surface of mask layer  410 , as shown in FIG. 4D. Third layer  430  deposited on the sidewalls is not removed or is only partially removed. The resulted resist structures  420  with third layer material  430  on the sidewalls narrows the critical dimension defined as the minimal feature size of the photomask.  
     [0033] In one embodiment, the one or more resist structures  420  comprise at least two resist structures separated by a space. As shown in FIG. 4D, the space between the at least two resist structures is reduced by the inorganic material deposited on the sidewalls of the structures.  
     [0034] In another embodiment, an amount of the inorganic material deposited on the tops of resist structures  420  is substantially greater than an amount of the inorganic material deposited on the sidewalls of resist structures  420 . In yet another embodiment, an amount of the inorganic material deposited on the tops of resist structures  420  is substantially less than an amount of the inorganic material deposited on the sidewalls of resist structures  420 .  
     [0035] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.