Abstract:
A structure and a method for forming the same. The method includes providing a structure including (a) a hole layer, and (b) a pattern transfer layer on and in direct physical contact with the hole layer, wherein the pattern transfer layer comprises a pattern transfer layer hole; depositing an acid supply layer on a side wall of the pattern transfer layer hole; transferring acids from the acid supply layer to an acid storage region in the pattern transfer layer abutting the side wall of the pattern transfer layer hole after said depositing is performed; removing the acid supply layer after said transferring is performed; and performing a chemical shrinking process to the pattern transfer layer hole utilizing the acids from the acid storage region after said removing is performed so as to shrink the pattern transfer layer hole.

Description:
TECHNICAL FIELD 
     The present invention relates to lithographic chemical shrink processes, and more specifically, to improvements to lithographic chemical shrink processes. 
     RELATED ART 
     During the fabrication of a semiconductor integrated circuit (IC), contact holes (i.e., openings) are typically formed in a dielectric layer and then filled with metal (e.g., copper) to provide electric accesses to devices of the IC underneath the dielectric layer. In one conventional method, these contact holes can be formed using a traditional photolithographic process. As the contact holes become smaller and smaller in size with, for example, successive technology generations, there is a need for improvements to the traditional photolithographic process for printing (i.e., creating) smaller contact holes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a structure formation method, comprising providing a structure including (a) a hole layer, and (b) a pattern transfer layer on and in direct physical contact with the hole layer, wherein the pattern transfer layer comprises a pattern transfer layer hole such that a top hole layer surface of the hole layer is exposed to a surrounding ambient through the pattern transfer layer hole; depositing an acid supply layer on a side wall of the pattern transfer layer hole; transferring acids from the acid supply layer to an acid storage region in the pattern transfer layer abutting the side wall of the pattern transfer layer hole after said depositing is performed; removing the acid supply layer after said transferring is performed; and performing a chemical shrinking process to the pattern transfer layer hole utilizing the acids from the acid storage region after said removing is performed so as to shrink the pattern transfer layer hole. 
     The present invention also provides a structure formation method, comprising providing a structure including (a) a hole layer, and (b) a pattern transfer layer on and in direct physical contact with the hole layer, wherein the pattern transfer layer comprises a pattern transfer layer hole such that a top hole layer surface of the hole layer is exposed to a surrounding ambient through the pattern transfer layer hole; depositing an acid storage film on a side wall of the pattern transfer layer hole but essentially not on the exposed-to-ambient top hole layer surface; and performing a chemical shrinking process to the pattern transfer layer hole utilizing the acids from the acid storage film after said depositing is performed so as to shrink the pattern transfer layer hole. 
     The present invention also provides a structure, comprising (a) a hole layer, and (b) a pattern transfer layer on and in direct physical contact with the hole layer, wherein the pattern transfer layer comprises a pattern transfer layer hole, and wherein the pattern transfer layer comprises a first material; (c) an acid storage film being (i) on a side wall of the pattern transfer layer hole and (ii) in direct physical contact with the hole layer, wherein the acid storage film comprises a second material different from the first material; and (d) a polymerized hole shrinking region in direct physical contact with the hole layer and the acid storage film, wherein the polymerized hole shrinking region comprises a third material different from the second material, and wherein the acid storage film is sandwiched between and physically isolates the pattern transfer layer and the polymerized hole shrinking region. 
     The present invention provides improvements to the traditional photolithographic process for printing (i.e., creating) smaller contact holes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A–1G  illustrate the steps of a first contact hole printing process, in accordance with embodiments of the present invention. 
         FIGS. 2A–2E  illustrate the steps of a second contact hole printing process, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A–1E  show cross-section views of a structure  100  illustrating the steps of a first contact hole printing process, in accordance with embodiments of the present invention. More specifically, with reference to  FIG. 1A , in one embodiment, the first contact hole printing process starts out with the structure  100  including a contact hole layer  110  (comprising a dielectric material such as SiO 2  in one embodiment) formed on a semiconductor substrate (not shown for simplicity). The structure  100  further comprises (i) a BARC (bottom antireflective coating) layer  120  on top of the contact hole layer  110  and (ii) a photoresist layer  130  on top of the BARC layer  120 . 
     Next, in one embodiment, the photoresist layer  130  is exposed to light through a mask (not shown, but typically placed on top of the photoresist layer  130 ) containing clear and opaque features such that a region  131  of the photoresist layer  130  is exposed to light while other regions of the photoresist layer  130  are not exposed to light, in this case drawn to reflect a positive-tone photoresist. The BARC layer  120  optimizes the image quality by suppressing reflections within the photoresist layer  130 . More specifically, the BARC layer  120  ensures that a substantial portion of light that passes through the photoresist layer  130  is absorbed by the BARC layer  120  without being reflected back to the photoresist layer  130  by any layer(s) beneath the BARC layer  120  (including the contact hole layer  110 ). 
     In one embodiment, assume that positive-tone optical lithography is used. In other words, the photoresist layer  130  comprises a positive-tone photoresist material such that regions of the photoresist layer  130  exposed to light change from originally insoluble to soluble in a photoresist developer (a solvent) while other regions of the photoresist layer  130  not exposed to light remain insoluble in the photoresist developer. As a result, with reference to  FIG. 1B , in one embodiment, the photoresist developer is used to develop away (remove) the exposed-to-light region  131  ( FIG. 1A ) of the photoresist layer  130  (called development process) resulting in a photoresist hole  132  in the photoresist layer  130 . 
     It should be noted that when the photoresist layer  130  is exposed to light, the intensity of energy reaching the photoresist layer  130  is at its highest at the center of the region  131  ( FIG. 1A ) and decays at the perimeter of the region  131  ( FIG. 1A ). As a result, a region  139  abutting the region  131  ( FIG. 1A ) does not attain an acid concentration level required for inducing photoresist development. Therefore, when the region  131  ( FIG. 1A ) is later removed, the region  139  remains and contains some photo acids (called residual photo acids). 
     Next, in one embodiment, the patterned photoresist layer  130  is used as a blocking mask for directionally (vertically) etching the BARC layer  120  through the photoresist hole  132  so as to extend the photoresist hole  132  further down until a top surface  112  of the SiO 2  contact hole layer  110  is exposed to the surrounding ambient through the extended photoresist hole  132  as shown in  FIG. 1C . As a result, the extended photoresist hole  132  has a side wall  133 , 123  comprising the photoresist side wall portion  133  and a BARC side wall portion  123 . In one embodiment, the directional etching of the BARC layer  120  is a RIE (reactive ion etching) process. 
     Next, with reference to  FIG. 1D , in one embodiment, an acid supply layer  140  is deposited on top of the entire structure  100  of  FIG. 1C  (by spin-apply in one embodiment) such that the acid supply layer  140  is in direct physical contact with the photoresist side wall portion  133  and the BARC side wall portion  123  of the extended photoresist hole  132 . 
     In one embodiment, the acid supply layer  140  comprises a material that contains acidic species (such as proton H+) that diffuse into regions  134  and  124  of the photoresist layer  130  and the BARC layer  120 , respectively. Originally, acid concentrations in the regions  134  and  124  may be different. However, the acid diffusions from the acid supply layer  140  into the regions  134  and  124  tend to equalize the acid concentrations in the regions  134  and  124 . 
     In one embodiment, the entire structure  100  of  FIG. 1D  is raised to a pre-determined temperature so as to speed up the acid diffusion process such that the acid concentrations in the regions  134  and  124  are essentially equal in a time period less than 60 seconds. 
     In one embodiment, the acid supply layer  140  comprises a weak water-based (or alcohol-based) solvent of a polymer which has an acid concentration high enough to allow for acid diffusion into the regions  134  and  124  but weak enough so as to not dissolve the photoresist layer  130  and the BARC layer  120 . 
     Next, in one embodiment, the acid supply layer  140  is removed by, illustratively, a water rinsing step. As a result, the extended photoresist hole  132  is reopened and the top surface  112  of the contact hole layer  110  is again exposed to the surrounding ambient through the extended photoresist hole  132 . 
     Next, with reference to  FIG. 1E , in one embodiment, a hole shrinking film  150  is formed on top of the entire structure  100  by, illustratively, a spin-on process such that the hole shrinking film  150  comes into direct physical contact with the regions  134  and  124 . 
     In one embodiment, the hole shrinking film  150  comprises a material which, when coming into direct contact with acids (like the acids in the regions  134  and  124 ) at an elevated temperature, becomes (i) insoluble in a first post-shrink rinse chemical (e.g., water) and (ii) capable of withstanding a subsequent etching of the contact hole layer  110  during the formation of a contact hole  114  ( FIG. 1G ) in the contact hole layer  110 . More specifically, in one embodiment, the hole shrinking film  150  comprises a water-soluble (or alcohol-soluble) polymer and can be formed by spin-applying the water-soluble polymer on top of the entire structure  100 . 
     Next, in one embodiment, the structure  100  is baked to an elevated temperature (i.e., higher than room temperature) such that the acids in the regions  134  and  124  diffuse into a hole shrinking region  152  of the hole shrinking film  150 . At the elevated temperature, the diffused acids in the hole shrinking region  152  catalyze cross-linking reactions (i.e., polymerization) in the hole shrinking region  152  causing the hole shrinking region  152  to change from originally soluble to insoluble in the first post-shrink rinse chemical. 
     Next, the first post-shrink rinse chemical is used to the remove the entire hole shrinking film  150  except the insoluble hole shrinking region  152  such that the extended photoresist hole  132  is reopened (but shrunk) and such that the top surface  112  of the contact hole layer  110  is again exposed to the surrounding ambient through the shrunk photoresist hole  132  as shown in  FIG. 1F . This process can be referred to as the first post-shrink rinse. 
     Next, with reference to  FIG. 1G , in one embodiment, the contact hole  114  is formed in the contact hole layer  110  directly beneath and aligned with the shrunk photoresist hole  132 . Illustratively, the contact hole  142  is formed by directionally etching (e.g., RIE in one embodiment) the contact hole layer  110  through the shrunk photoresist hole  132 . In one embodiment, the contact hole  114  is then filled with an electrically conducting material (not shown) such as copper to provide electric access to device(s) (not shown) underneath the contact hole layer  110 . 
     In summary, with reference to  FIGS. 1A–1G , the first contact hole printing process comprises forming a pattern transfer layer  120 , 130  (i.e., the BARC layer  120  and the photoresist layer  130 ) on top of the contact hole layer  110  in which the contact hole  114  is to be printed. Next, a pattern transfer layer hole  132  (also called the photoresist hole  132 ) is formed in the pattern transfer layer  120 , 130 . Next, the acid supply layer  140  is deposited to supply acids to the acid storage region  134 , 124  abutting the side wall  133 , 123  of the pattern transfer layer hole  132 . Next, the acid supply layer  140  is removed. Next, a chemical shrink process is performed to the pattern transfer layer hole  132  utilizing the acids in the acid storage region  134 , 124  so as to shrink the pattern transfer layer hole  132 . More specifically, the chemical shrink process comprises (i) depositing the hole shrinking film  150 , (ii) polymerizing the hole shrinking region  152  of the hole shrinking film  150  utilizing the acids from the acid storage region  134 , 124 , and (iii) removing the hole shrinking film  150  except the polymerized hole shrinking region  152  which in effect shrinks the pattern transfer layer hole  132 . Finally, the contact hole  114  is formed in the contact hole layer  110  aligned with the shrunk pattern transfer layer hole  132 . 
       FIGS. 2A–2E  show cross-section views of a structure  200  illustrating the steps of a second contact hole printing process, in accordance with embodiments of the present invention. More specifically, with reference to  FIG. 2A , in one embodiment, the second contact hole printing process starts out with the structure  200  similar to the structure  100  of  FIG. 1B . For simplicity, all reference numerals herein have three numeric digits starting with the numeric figure number. In addition, similar regions have the identical reference numerals except for the first digit which is used to indicate the numeric figure number. 
     More specifically, the structure  200  comprises a contact hole layer  210  (comprising a dielectric material such as SiO 2  in one embodiment) formed on a semiconductor substrate (not shown for simplicity). The structure  200  further comprises (i) a BARC (bottom antireflective coating) layer  220  on top of the contact hole layer  210  and (ii) a photoresist layer  230  on top of the BARC layer  220 . The photoresist layer  230  and the BARC layer  220  comprise a photoresist hole  232  such that a top surface  212  of the SiO 2  contact hole layer  210  is exposed to the surrounding ambient through the photoresist hole  232 . 
     Next, with reference to  FIG. 2B , in one embodiment, an acid storage film  236  is conformably formed (by chemical vapor deposition or CVD in one embodiment) on all organic surfaces that are exposed to the surrounding ambient but essentially not on non-organic surfaces of the structure  200  of  FIG. 2A . The organic surfaces include (i) a top surface  234  of the photoresist layer  230  and (ii) a side wall  233 , 223  of the photoresist hole  232 . The side wall  233 , 223  comprises a photoresist side wall portion  233  and a BARC side wall portion  223 . 
     In one embodiment, the acid storage film  236  comprises a material that contains acids that are needed for a subsequent chemical shrinking process (described below). In addition, the material of the acid storage film  236  also contains functional units that chemically react with acrylic or other polymer functional groups present on organic surfaces but not present on non-organic surfaces so as to form durable bonds only between the acid storage film  236  and these organic surfaces. 
     Next, with reference to  FIG. 2C , in one embodiment, a hole shrinking film  250  is formed on top of the entire structure  200  of  FIG. 2B  by, illustratively, a spin-on process such that the hole shrinking film  250  completely fills the photoresist hole  232 . 
     In one embodiment, the hole shrinking film  250  comprises a material which, when coming into direct contact with acids (like the acids in the acid storage film  236 ) at an elevated temperature, becomes (i) insoluble in a second post-shrink rinse chemical (e.g., water) and (ii) capable of withstanding a subsequent etching of the contact hole layer  210  during the formation of a contact hole  214  ( FIG. 2E ) in the contact hole layer  210 . More specifically, in one embodiment, the hole shrinking film  250  comprises a water-soluble (or alcohol-soluble) polymer and can be formed by spin-applying the water-soluble polymer on top of the entire structure  200  of  FIG. 2B . 
     Next, the structure  200  is baked to an elevated temperature such that (i) the acids in the acid storage film  236  diffuse into a hole shrinking region  252  of the hole shrinking film  250 . At the elevated temperature, the diffused acids in the hole shrinking region  252  catalyze cross-linking reactions (i.e., polymerization) in the hole shrinking region  252  causing the hole shrinking region  252  to change from originally soluble to insoluble in the second post-shrink rinse chemical. 
     Next, the second post-shrink rinse chemical is used to develop away (i.e., remove) the entire hole shrinking film  250  except the insoluble hole shrinking region  252  such that the photoresist hole  232  is reopened (but shrunk) and such that the top surface  212  of the contact hole layer  210  is again exposed to the surrounding ambient through the shrunk photoresist hole  232  as shown in  FIG. 2D . This process can be referred to as the second post-shrink rinse. 
     Next, with reference to  FIG. 2E , in one embodiment, the contact hole  214  is formed in the contact hole layer  210  directly beneath and aligned with the shrunk photoresist hole  232 . Illustratively, the contact hole  214  is formed by directionally etching (e.g., RIE in one embodiment) the contact hole layer  210  through the shrunk photoresist hole  232 . In one embodiment, the contact hole  214  is then filled with an electrically conducting material (not shown) such as copper to provide electric access to device(s) (not shown) underneath the contact hole layer  210 . 
     In summary, with reference to  FIGS. 2A–2E , the second contact hole printing process comprises forming a pattern transfer layer  220 , 230  (i.e., the BARC layer  220  and the photoresist layer  230 ) on top of the contact hole layer  210  in which the contact hole  214  is to be printed (i.e., formed). Next, a pattern transfer layer hole  232  (also called the photoresist hole  232 ) is formed in the pattern transfer layer  220 , 230 . Next, the acid storage film  236  is deposited to supply acids for a subsequent chemical shrink process. Next, the chemical shrink process is performed to the pattern transfer layer hole  232  utilizing the acids from the acid storage film  236  so as to shrink the pattern transfer layer hole  232 . More specifically, the chemical shrink process comprises (i) depositing the hole shrinking film  250 , (ii) polymerizing the hole shrinking region  252  of the hole shrinking film  250  with the help of the acids from the acid storage film  236 , and (iii) removing the hole shrinking film  250  except the polymerized hole shrinking region  252  which in effect shrinks the pattern transfer layer hole  232 . Finally, the contact hole  214  is formed in the contact hole layer  210  aligned with the shrunk pattern transfer layer hole  232 . 
     In the embodiments described above, the first and contact hole printing processes are used to print contact holes  114  and  214  of  FIGS. 1G and 2E , respectively. In general, any hole (not just contact holes) of any size and shape can be printed in the layers  110  and  210  of  FIGS. 1G and 2E , using the first and second contact hole printing processes, respectively. For instance, with reference to  FIGS. 1A–1G , if a the hole  114  having a shape of a long trench needs to be printed in the layer  110 , the photoresist hole  132  needs to have the shape of a long trench. 
     While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.