Abstract:
A method for etching a semiconductor device suitable for forming micron contact hole having a size of less than limit resolution power of exposure equipments is disclosed, including coating a layer for an etch mask on an etched object layer; selectively patterning the layer to form an open area; and swelling side part of the patterned layer and forming the etch mask.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for fabricating a semiconductor device and, more particularly, to a method for etching a semiconductor device suitable for forming micron contact hole having a size of less than limit resolution power of exposure equipments. 
     2. Discussion of the Related Art 
     when photoresist is exposed to light, radiation, heat, and various energies, its inner feature is changed. Polymer, solvent and sensitizer are three main elements constituting photoresist. 
     A background method for patterning photoresist will be described with reference to the attached drawings. 
     FIGS. 1A to  1 E are cross-sectional views showing process steps of a background method for patterning photoresist. 
     First a photoresist film  2  is coated on an etched object  1 , as shown in FIG.  1 A. Then the photoresist film  2  is selectively patterned with an exposure process, as shown in FIG.  1 B. The exposure process causes chemical change of the photoresist film  2 . Due to the chemical change, the exposed part and the unexposed part of the photoresist film  2  have different speeds of development. Using the different development speeds, the photoresist film  2  is patterned with a wet development process, as shown in FIG.  1 C. 
     Subsequently, the etched object  1  is selectively etched by using the patterned photoresist film  2  as a mask, as shown in FIG.  1 D. Next, the photoresist film  2  is all removed as shown in FIG.  1 E. 
     Such a background method for etching semiconductor device has disadvantage that it is impossible to etch photoresist having a pattern size of less than the limit resolution power of an exposure equipment. It is the resolution power of an exposure equipment that sizes of patterned areas such as contact holes depend on. That is to say, it is hard to realize patterned areas having a pattern size of less than the limit resolution power of an exposure equipment that patterns photoresist. Further, since opening area of a mask is small, contrast and intensity of aerial image are small. Thus it is hard to pattern a photoresist film having a high aspect ratio. Besides, etch bias is seriously generated because the patterned part of photoresist is slope. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention is directed to a method for etching a semiconductor device that substantially obviates one or more of problems due to limitations and disadvantages of the related art. 
     An object of the invention is to provide a method for fabricating a semiconductor device in which micron contact holes having sizes of less than the limit resolution power of an exposure equipment. 
     Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for etching a semiconductor device includes the steps of coating an etch mask; selectively patterning the etch mask on the etched object layer to form an open area; and swelling side part of the patterned etch mask. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and various other objects, features, and advantages of the present invention will be readily understood with reference to the following detailed description read in conjunction with the accompanying drawings, in which: 
     FIGS. 1A to  1 E are cross-sectional views showing process steps of a background method for patterning photoresist; 
     FIGS. 2A to  2 F are cross-sectional views showing process steps of a method for patterning photoresist in accordance with an embodiment of the present invention; 
     FIG. 3 is a chemical reaction diagram showing the silylation process in accordance with the present invention; 
     FIG. 4 shows swelling in accordance with the present invention; and 
     FIG. 5 is a graph showing swollen thickness vs pressure silylation press in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIGS. 2A to  2 F are cross-sectional views showing process steps of a method for patterning photoresist in accordance with an embodiment of the present invention, FIG. 3 is a chemical reaction diagram showing the silylation process, and FIG. 4 shows swelling. 
     According to the present invention, a photoresist film is patterned to have a resolution power of as much as the limit resolution power of an exposure equipment or of less than the limit resolution power. Next, the patterned photoresist film is swollen with a silylation process, thereby forming micro patterns. 
     First a photoresist film  21   a , as shown in FIG. 2A, is coated on a thin film  20  that is an etched object. Next, the photoresist film  21   a  is subjected to a partial exposure as shown in FIG.  2 B. As a result, this exposure causes chemical change to happens to the exposed part of the photoresist film  21   a . Thus, the exposed part and the non-exposed part  21   b  of the photoresist film  21   a  have different speeds in development. 
     Thereafter, a wet development process is performed to pattern the exposed photoresist film  21   b , as shown in FIG.  2   c . Next, a silylation process is performed over the side of the patterned photoresist film  21   c  so as to generate swelling as shown in FIG.  2 D. As a result, the opening area is reduced. 
     With the patterned photoresist film  21   c  having the swelling layer  22 , the thin film  20  is selectively etched, as shown in FIG.  2 E. Next, the photoresist film  21   c  is removed. 
     As aforementioned, the opening area of the photoresist film is reduced so that formed is a micro pattern having a size of less than limit resolution power of an exposure equipment. 
     The silylation process used herein will be described with reference to FIG.  3 . Using as a medium an organic chemical compound such as HMDS (hexamethylendislazane) or DMSDEA (dimethylsilyldiethylamine) containing Si, Si is penetrated into Novolak polymer or PHS (poly hydroxy styrene) high polymer constituting photoresist. Some radicals (—OH) of the high polymer are substituted with radicals (—OSiMex). As the result of the substitution, the polymer in the photoresist film where silylation reaction happens has strong etch resistance when an etch process is carried out using the patterned photoresist film as a mask. In addition, the volume of the polymer is swelled. 
     The swollen volume occupies 30% of the total silylated part, as shown in FIG.  4 . 
     The swollen amount can be adjustable according to a medium and process conditions such as temperature, pressure, and time, etc. 
     In the method of the present invention, a photoresist film is patterned so that a predetermined area of the photoresist film is opened. At this time, the opening area is as large as the limit resolution power or less than the limit resolution power to increase process tolerance. A silylation process is carried out over the side of the patterned photoresist film to cause swelling. Accordingly, the opening area is reduced. Using this photoresist film having the reduced opening area as a mask, an etched object is etched to obtain a micro pattern. 
     FIG. 5 shows the characteristic of swelling according to process conditions. Herein, a silylation process is carried out at 70° C., using DMSDEA. When pressure is 30 torr, the swollen thickness is 208 Angstroms. When it is 50 torr, the swollen thickness is 335 Angstroms. When it is 70 torr, the swollen thickness is 407 Angstroms. At this time, the photoresist used is SAL 601, SHIPLEY Ltd. USA. 
     In this way, it is possible to form micro patterns of sizes desired by users by adjusting conditions of silylation process. 
     A method for etching a semiconductor device has the following advantages. It is possible to form etching photo masks having opening areas of higher than limit resolution of an exposure equipment, so that high packing density of semiconductor devices can be obtained. Further, it is possible to adjust an opening area of an etching mask in spite of the resolution power of an exposure equipment and a swollen layer has a strong etch resistance. Thus process tolerance can be heightened. 
     It will be apparent to those skilled in the art that various modification and variations can be made in the method for etching a semiconductor device of the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.