Patent Publication Number: US-2003235998-A1

Title: Method for eliminating standing waves in a photoresist profile

Description:
DESCRIPTION OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates in general to a semiconductor manufacturing process and, more particularly, to a novel manufacturing process to improve conventional photolithographic methods.  
       [0003] 2. Background of the Invention  
       [0004] 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. In addition, conventional photolithographic methods often leave a rough profile on vertical surfaces of an etched photoresist due to the characteristics of conventional etching processes. A photoresist having a rough profile often presents itself in the shape of a “standing wave” on the photoresist surfaces. The lack of uniformity on the photoresist surfaces may additionally hinder reduction in the critical dimensions of the semiconductor manufacturing process, and presents an additional obstacle to accurate definition of desired patterns during subsequent manufacturing steps, resulting in decreased process yield.  
       [0005] It is accordingly a primary object of the invention to provide a method to eliminate the standing waves on an etched photoresist surface.  
       SUMMARY OF THE INVENTION  
       [0006] In accordance with the invention, there is provided a semiconductor manufacturing method that includes defining a semiconductor substrate, depositing a layer of first material over the semiconductor substrate, providing a layer of photoresist over the layer of first material, patterning and defining the photoresist layer to form at least one substantially vertical sidewall having a surface and one substantially horizontal sidewall, and depositing a layer of polymer over the patterned and defined photoresist layer, wherein the polymer layer is substantially conformal and covers the at least one substantially vertical sidewall of the photoresist layer to form a substantially smooth profile.  
       [0007] In one aspect, the layer of polymer is deposited with plasma enhanced chemical vapor deposition at a pressure of between approximately 7 mTorr and 30 mTorr.  
       [0008] In another aspect, the layer of first material comprises one of polysilicon, dielectric material or metallic material.  
       [0009] Also in accordance with the present invention, there is provided a semiconductor manufacturing method that includes defining a substrate, depositing a first layer over the substrate, providing a layer of photoresist over the first layer, patterning and defining the photoresist layer to form at least one photoresist structure having at least one substantially vertical sidewall and one substantially horizontal surface, wherein a surface of the at least one substantially vertical sidewall is rough, and depositing a layer of polymer over the patterned and defined photoresist layer, wherein the polymer layer is substantially conformal and covers the at least one substantially vertical sidewall and one substantially horizontal surface, and wherein the polymer layer covers the rough surface of the at least one substantially vertical sidewall to form a substantially smooth profile.  
       [0010] Further in accordance with the present invention, there is provided a semiconductor manufacturing method that includes defining a semiconductor substrate, depositing a layer of first material over the semiconductor substrate, providing a layer of photoresist over the layer of first material, patterning and defining the photoresist layer to form at least one substantially vertical sidewall having a surface and one substantially horizontal sidewall, wherein the surface of the at least one substantially vertical sidewall includes a plurality of concave and a plurality of convex portions, and modifying the surface of the at least one substantially vertical sidewall with a layer of polymer for a predetermined deposition and etching ratio to form a substantially smooth profile, wherein the polymer layer is substantially conformal.  
       [0011] 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.  
       [0012] 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  
     [0013]FIGS. 1 and 2 are a cross-sectional views of the semiconductor manufacturing process steps of the present invention.  
    
    
     DESCRIPTION OF THE EMBODIMENTS  
     [0014] 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.  
     [0015] FIGS.  1 - 2  are cross-sectional views of the semiconductor manufacturing process steps of the present invention. Referring to FIG. 1, a semiconductor structure  10  is formed by first defining a wafer substrate  12 . The wafer substrate  12  may be of any known semiconductor substrate material, such as silicon. A first layer  14  is then provided over the wafer substrate  12 . In one embodiment, the first layer  14  is a semiconductor material, such as polysilicon. The first layer  14  may also be a dielectric layer or a metal layer. The first layer  14  may be deposited over the wafer substrate  12  by any known deposition process. In another embodiment, the first layer  14  is a dielectric material, in which case the first layer  14  may be deposited or grown over the wafer substrate  12 .  
     [0016] An anti-reflection coating (ARC) layer  16  may optionally be provided over the first layer  14  to decrease the reflection from the first layer  14  in the subsequent manufacturing steps. A photoresist layer  18  is then provided over the ARC layer  16 . In an embodiment in which an ARC layer is not provided, the photoresist layer  18  is deposited over the first layer  14 .  
     [0017] After the photoresist layer  18  has been provided, it is patterned and defined using any known photolithographic process to form a patterned and defined photoresist layer  18 . The patterned and defined photoresist layer  18  includes substantially vertical sidewalls  18 - 1  and  18 - 2 . As shown in FIG. 1, the surfaces of the sidewalls  18 - 1  and  18 - 2  are rough in the shape of “standing waves,” having a plurality of concave and convex portions.  
     [0018] Referring to FIG. 2, a second layer  20  may be deposited over the patterned and defined photoresist layer  18  by any known chemical vapor deposition process. A known chemical vapor deposition process includes plasma enhanced chemical vapor deposition (PECVD) and low pressure chemical vapor deposition (LPCVD). The second layer  20  comprises a polymer, and is substantially conformal, such that the second layer  20  covers both the horizontal surfaces (not numbered) and vertical sidewalls  18 - 1  and  18 - 2  of the photoresist  18 . The deposition process, especially the chemical vapor deposition processes that simultaneously provide both deposition and etching functionalities, may be adjusted such that the second layer  20  covers the entire vertical sidewalls  18 - 1  and  18 - 2  of the photoresist  18 , or covers only the concave portions of the vertical sidewalls  18 - 1  and  18 - 2  of the photoresist  18  wherein the second layer  20  deposited on the convex portions is etched. The material characteristics of the second layer  20  enables the rough surfaces of the vertical sidewalls  18 - 1  and  18 - 2  to be covered with the second layer  20 , presenting a substantially smooth and uniform vertical profile of the photoresist  18 .  
     [0019] In one embodiment, the step of depositing the second layer  20  is performed with the PECVD process. The pressure used for forming the second layer  18  is in the range of approximately 7 mTorr to 30 mTorr. The upper source power ranges from approximately 600 wafts to 1300 watts, and the lower source power ranges from approximately 150 watts to 700 watts. The gas used may include one of difluoromethane (CH 2 F 2 ), a mixture of difluoromethane and octafluorobutene (C 4 F 8 ), and a mixture of difluoromethane and trifluoromethane (CHF 3 ). Moreover, argon (Ar), nitrogen (N 2 ), and carbon monoxide (CO) may be mixed with the gases introduced during the PECVD process. The carbon monoxide functions to capture fluorine radicals and fluoride ions generated by the fluoro-substituted hydrocarbons.  
     [0020] 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.