Abstract:
A method and system is disclosed for selectively forming photoresist patterns for making openings in a substrate. A layer of photoresist is deposited on the substrate which contains one or more types of photoresist dissolving agent generators. A first set of areas of the photoresist is exposed to a first light source through a first mask to activate a photoresist dissolving agent generator of a first type to release a first photoresist dissolving agent in the first set of areas. Then, a second set of areas of the photoresist is also exposed to a second light source through a second mask to activate a photoresist dissolving agent generator of a second type to release a second photoresist dissolving agent in the second set of areas. The second set of areas is a sub set of the first set of areas such that the first and second photoresist dissolving agents in the second set of areas neutralize each other to protect the second set of areas from being used as the patterns for forming the openings.

Description:
BACKGROUND OF INVENTION  
       [0001]     This disclosure relates generally to the field of semiconductor manufacturing and, more specifically, to the use of a single photoresist layer containing both a photoacid generator and a photobase generator, or the use of both a single photoresist layer containing a photoacid generator and a water-soluble film containing a photobase generator to achieve a packing-and-unpacking process.  
         [0002]     A packed-and-unpacked process generally combines a packed contact hole pattern photomask and an unpacked contact hole pattern photomask to produce a quality pattern with well-defined critical dimensions in a photoresist layer and on an etched substrate. The packed pattern is a combination of desired contact holes and also undesired contact holes that are added to densify the first photomask. The packed pattern photomask is utilized to expose and develop the combined pattern of desired and undesired contact holes in a first layer of photoresist. There are two variations that allow the unpacked pattern to achieve the selection of desired contact holes into the final photoresist pattern. The first variation defines islands in the second photoresist layer that are slightly larger than the undesired contact holes in the first photoresist layer and therefore securely cover them. These photoresist islands in the second photoresist layer, in the first variation, are based on the undesired contact holes in the first photoresist layer. The second variation defines larger areas in the second photoresist layer that cover not only the undesired holes in the first photoresist layer, but also the broader areas between the desired contact holes. The remaining openings in the second photoresist layer, over the desired contact holes in the first photoresist layer, are slightly larger than those desired contact holes in the first photoresist layer. The remaining openings in the second photoresist layer, in the second variation, are based on the desired contact holes in the first photoresist layer.  
         [0003]     Photoresists are photosensitive films used for the transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced transformation of the photoresist coating thereby transferring the pattern of the photomask to the photoresist-coated substrate. Following the exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.  
         [0004]     A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less soluble. In general, photoresist compositions comprise at least a resin binder component and a photoactive agent.  
         [0005]     More recently, chemically-amplified-type resists have been increasingly employed, particularly for formation of sub-micron images and other high-performance applications. A chemically-amplified photoresist contains a polymer, which is not photoactive, a solvent, and a photoacid generator and/or a photobase generator. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain “blocking” groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is formed, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer.  
         [0006]     In the case of a chemically-amplified, positive resist, in which a photoacid generator (PAG), which generates acid under ultra-violet (UV) light exposure, is added, protective groups are deprotected by heating after exposure, in a post-exposure bake (PEB). The acid formed during exposure, and activated during PEB, serves as a catalyst which causes the deprotection reaction to proceed along the polymer chain. The acid cleaves the polymer into smaller molecules with considerably different polarity and solubility in developer solution. The developer produces the exposed pattern in the resist layer. If a photobase generator is added, then an exposure by a different UV light wavelength, or an exposure for a different time, can activate formation of a chemical base, which can selectively neutralize the previously generated acid and thereby prevent its reaction with the polymer. What is needed is an improved method for carrying out the packing-and-unpacking process.  
       SUMMARY  
       [0007]     The present invention is directed to a photoresist process for fabricating integrated circuit devices, (ICs). A single photoresist layer is coated onto a substrate and both a photomask with a packed pattern and a photomask with an unpacked pattern are utilized to expose the photoresist layer.  
         [0008]     In one example, a layer of photoresist which contains one or more types of photoresist dissolving agent generators is deposited on a substrate. A first set of areas of the photoresist is exposed to a first light source through a first mask to activate a photoresist dissolving agent generator of a first type to release a first photoresist dissolving agent in the first set of areas. Then, a second set of areas of the photoresist is also exposed to a second light source through a second mask to activate a photoresist dissolving agent generator of a second type to release a second photoresist dissolving agent in the second set of areas. The second set of areas is a sub set of the first set of areas such that the first and second photoresist dissolving agents in the second set of areas neutralize each other to protect the second set of areas from being used as the patterns for forming the openings.  
         [0009]     In one example, the photoresist layer contains both a photoacid generator and a photobase generator, and the photoacid generator is activated first. In another example, the photoresist layer contains a photoacid generator and a water-soluble film containing a photobase generator is coated onto the photoresist layer. In yet another example, the photoresist layer contains both a photobase generator and a photoacid generator and the photobase generator is activated first.  
         [0010]     Various aspects of the disclosure will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIGS. 1A-1F  are partial sectional views of semiconductor structures for illustrating the processing steps according to the first example of the present disclosure.  
         [0012]      FIGS. 2A-2G  are partial sectional views of semiconductor structures for illustrating the processing steps according to the second example of the present disclosure.  
         [0013]      FIGS. 3A-3F  are partial sectional views of semiconductor structures for illustrating the processing steps according to the third example of the present disclosure.  
         [0014]      FIG. 4  presents a flowchart explaining processing steps according to the first example of the present disclosure.  
         [0015]      FIG. 5  presents a flowchart explaining processing steps according to the second example of the present disclosure.  
         [0016]      FIG. 6  presents a flowchart explaining processing steps according to the third example of the present disclosure.  
     
    
     DESCRIPTION  
       [0017]     In the present disclosure, a packed pattern and an unpacked pattern are utilized to define a photoresist layer pattern. The final pattern has the critically defined dimensions of the packed pattern. A photoresist dissolving agent generator such as a photoacid generator and/or a photobase generator are incorporated into either a single photoresist layer or into a photoresist layer and a water-soluble film. Acid produced by the photoacid generator in the exposed areas is activated during a post-exposure bake. In this disclosure, the undesired holes in the packed pattern are not covered by patterned areas of a second photoresist layer. Instead, the undesired holes in the first photoresist layer are given another different exposure via a second photomask. Chemical base produced by the photobase generator in undesired hole patterns neutralizes acid produced during the previous exposure. The acid, in areas selected to be retained in the final pattern, cleaves the photoresist polymer into smaller and more soluble moieties. These soluble areas are dissolved away by the developer, subsequently producing the final desired pattern.  
         [0018]     In a first example,  FIG. 1A  illustrates a substrate  102  coated by a chemically-amplified photoresist  104  containing both a photoacid generator and a photobase generator. In  FIG. 1B , ultraviolet (UV) light is utilized to expose areas  106  of the photoresist layer  104 , via the photomask  108  with a packed pattern (i.e., the packing mask). Opaque areas  110  of the photomask  108  leave part of the photoresist  104  that are directly underneath unexposed. Clear areas  112  of the photomask  108  expose and activate the photoacid generator in the photoresist layer  104  to generate acid in areas  106 , that are directly underneath.  
         [0019]      FIG. 1C  illustrates the exposure of the same photoresist layer  104  by UV light of either a different wavelength or a longer exposure time via the photomask  114  with an unpacked pattern (i.e., an unpacking mask). Opaque areas  116  of the photomask  114 , with an unpacked pattern, leave some areas of the photoresist  104  unexposed. Clear areas  118  of the photomask  114  expose and activate the photobase generator in the photoresist layer  104  to generate a chemical base in areas  120 . This base neutralizes the acid that was previously generated. It is noted that areas  120  are a subset of areas  106 .  
         [0020]      FIG. 1D  illustrates the effects of the post-exposure bake. In the photoresist layer  104 , areas  122  contain only acid generated from the first exposure via the photomask  108 . Areas  124  contain both acid generated from the first exposure via the photomask  108 , and also base generated from the second exposure via the photomask  114 . In areas  124 , the base neutralizes the acid and therefore there is no net effect on the photoresist layer  104  in areas  124  and no pattern is developed there.  FIG. 1E  illustrates the development of the photoresist layer  104  through which areas  122  are dissolved away in the desired holes  126  only. Areas  124  are undeveloped and therefore photoresist remains there as shown as areas  128 . The developed pattern yields open holes in locations defined by the packed pattern of the first photomask  108  minus the locations defined by the unpacked pattern of the second mask  114 , but with the critical dimensions of the packed pattern of the first mask  108 .  FIG. 1F  illustrates the etched substrate  130 . The desired pattern developed and shown in  FIG. 1E  is accurately defined in the etched pattern  132  in the substrate.  
         [0021]     In a second example,  FIG. 2A  illustrates a substrate  202  coated by a chemically amplified photoresist  204  containing a photoacid generator. In  FIG. 2B , UV light is utilized to expose areas  206  of the photoresist layer  204  via the photomask  208  with a packed pattern. Opaque areas  210  of the photomask  208  leave the areas  204  that are directly underneath unexposed. Clear areas  212  of the photomask  208  expose and activate the photoacid generator in the photoresist layer  204  to generate acid in areas  206  that are directly underneath.  FIG. 2C  illustrates the coating of the undeveloped photoresist layer  204  by a water-soluble film  214  containing a photobase generator (PBG).  FIG. 2D  illustrates the exposure of the water-soluble film  214  containing a PBG by UV light via photomask  216  with an unpacked pattern. Opaque areas  218  of the photomask  216  leave the water-soluble film  214  unexposed in areas  204 . Clear areas  220  of the photomask  216  expose and activate the photobase generator in the water-soluble film to generate a chemical base in areas  222  that diffuses into the areas  224  of the underlying photoresist layer  204 . Areas  224  are only the undesired holes in the packed pattern. The chemical base diffuses most heavily into the top of areas  224  producing areas  226 . This base neutralizes the acid that was previously generated in the same areas of  206 .  
         [0022]      FIG. 2E  illustrates the effect of a post-exposure bake. In the photoresist layer  204 , areas  206  contain only acid generated from the first exposure via the photomask  208 . Areas  226  contain both acid generated from the first exposure and also base generated from the second exposure. In areas  226 , the base neutralizes the acid and therefore there is no net effect on the photoresist layer  204  in areas  226  and no pattern is developed there. Areas  228  are the only areas of the photoresist layer that contained acid after the first exposure with the photomask with the packed pattern. Post-exposure bake causes the acid to break up the polymer of the photoresist layer into smaller moieties that will be soluble in the aqueous basic develop solution.  
         [0023]      FIG. 2F  illustrates the dissolution of the water-soluble film and the development of the photoresist layer  204 . Areas  228  are dissolved away in the desired holes  230  only. Areas  226  are undeveloped and therefore photoresist remains there as areas  232 . The developed pattern yields open holes in locations defined by the packed pattern of the first photomask  208  minus the locations defined by the unpacked pattern of the second photomask  216 , but with the critical dimensions of the packed pattern of the first photomask  208 .  FIG. 2G  illustrates the etched substrate  234 . The desired pattern developed and shown in  FIG. 2F  is accurately defined in the etched openings  236  in the substrate  234 .  
         [0024]     In a third example,  FIG. 3A  illustrates a substrate  302  coated by a chemically-amplified photoresist  304  containing both a photobase generator and a photoacid generator. In  FIG. 3B , UV light, either of a chosen wavelength or with an extended exposure time, is utilized to expose areas  306  of the photoresist layer  304  via the photomask  308  with an unpacked pattern. Opaque areas  310  of the photomask  308  leave the photoresist areas  304 , that are directly underneath, unexposed. Clear areas  312  of the photomask  308  expose and activate the photobase generator in the photoresist layer  304 , with a chosen UV wavelength or an extended exposure time, to generate a chemical base in areas  306  that are directly underneath.  FIG. 3C  illustrates the exposure of areas  314  and  316  of the same photoresist layer  304  by UV light via the photomask  318  with a packed pattern. Opaque areas  320  of the photomask  318 , with a packed pattern, leave the photoresist  304  unexposed. Clear areas  322  of the photomask  318  expose and activate the photoacid generator in the photoresist layer  304  to generate acid in the areas  314  and  316 . In areas  316 , the acid is neutralized by the chemical base previously generated there by the exposure shown in  FIG.3B . It is understood that areas  316  may be subsets of areas  314 .  FIG. 3D  illustrates the effects of the post-exposure bake. In the photoresist layer  304 , areas  324  contain only acid generated from the second exposure via the photomask  318 . Areas  326  contain both acid generated from the second exposure via photomask  318 , and also chemical base generated from the first exposure via photomask  308 . In areas  326 , the base neutralizes the acid and therefore there is no net effect on the photoresist layer  304  in areas  326  and no pattern is developed there.  
         [0025]      FIG. 3E  illustrates the development of photoresist layer  304 . Areas  324  are dissolved away in the desired holes  328  only. Areas  326  are undeveloped and therefore photoresist remains there as areas  330 . The developed pattern yields open holes in locations defined by the packed pattern of the second photomask  318  minus certain locations defined by the unpacked pattern of the first photomask  308 , but with the critical dimensions of the packed pattern of the second photomask  318 .  FIG. 3F  illustrates the etched substrate. The desired pattern developed and shown in  FIG. 3E  is accurately defined in the substrate  332  with opened areas  334 .  
         [0026]      FIG. 4  is a flow chart  400  illustrating the processes according to the first example. In  FIG. 4  the coating of a substrate by a chemically-amplified photoresist containing both a photoacid generator (PAG) and a photobase generator (PBG) is done in step  402 .  
         [0027]     The first exposure, by ultraviolet (UV) light, via a photomask with a packed pattern, of the photoresist layer is done in step  404 . The packed pattern contains both the desired holes and the padding or undesired holes. Acid is generated in the exposed hole patterns.  
         [0028]     The second exposure by ultraviolet (UV) light, via a photomask with an unpacked pattern, of the same photoresist layer is done in step  406 . The unpacked pattern contains only the undesired holes. Chemical base is generated in the exposed hole pattern.  
         [0029]     The post-exposure bake of the photoresist layer, the development of the photoresist layer, and the etching of the substrate are all processed in step  408 . The bake activates the acid in the desired hole patterns, and so those areas become soluble in the developer solution. In the undesired hole patterns, the acid is neutralized by the chemical base and therefore there is no net effect on those photoresist areas and no patterns are developed there. The etch process produces the desired hole pattern in the substrate.  
         [0030]      FIG. 5  is another flow chart  500  representing the processes of the second example. In step  502 , the coating of a substrate by a chemically-amplified photoresist containing a photoacid generator (PAG) is done.  
         [0031]     The first exposure, by ultraviolet (UV) light, via a photomask with a packed pattern, of the photoresist layer is done on step  504 . The packed pattern contains both the desired holes and the padding or undesired holes. Acid is generated in the exposed hole patterns.  
         [0032]     The coating of the undeveloped photoresist layer by a water-soluble film that contains a photobase generator is completed in step  506 .  
         [0033]     The second exposure, by UV light, via a photomask with an unpacked pattern, of the water-soluble film is carried out in step  508 . The unpacked pattern contains only the undesired hole patterns. Chemical base is generated in the exposed hole pattern.  
         [0034]     The post-exposure bake, dissolution of the water-soluble film, development of the photoresist layer, and the etching of the substrate are all processed in step  510 . Post-exposure bake activates the acid only in the desired hole pattern. In the undesired hole pattern, the acid is neutralized by the chemical base so that no pattern is produced there.  
         [0035]      FIG. 6  is another flow chart  600  corresponding to the third example. In step  602 , the coating of a substrate by a chemically-amplified photoresist containing both a photobase generator (PBG) and a photoacid generator (PAG) is completed.  
         [0036]     The first exposure, by ultraviolet (UV) light, via a photomask with an unpacked pattern, of the photoresist layer is done in step  604 . The unpacked pattern contains only the undesired holes. Chemical base is generated in the exposed hole pattern.  
         [0037]     The second exposure, by ultraviolet (UV) light, via a photomask with a packed pattern, of the same photoresist layer is done on step  606 . The packed pattern contains both the desired holes and the padding or undesired holes. Acid is generated in the exposed hole patterns.  
         [0038]     The post-exposure bake of the photoresist layer, the development of the photoresist layer, and the etching of the substrate are done in step  608 . The bake activates the acid in the desired hole patterns and so those areas become soluble in the developer solution. In the undesired hole patterns, the acid is neutralized by the chemical base and therefore there is no net effect on those photoresist areas and no patterns are developed there. The etch process produces the desired hole patterns in the substrate.  
         [0039]     The above disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components, and processes are described to help clarify the disclosure. These are, of course, merely examples and are not intended to limit the disclosure from that described in the claims.  
         [0040]     Although illustrative embodiments of the disclosure have been shown and described, other modifications, changes, and substitutions are intended in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure, as set forth in the following claims.