Patent Document

This application is a Divisional of Ser. No. 11/160,670, filed Jul. 5, 2005, now U.S. Pat. No. 7,288,478, issue date Oct. 30, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to lithographic chemical shrink processes, and more specifically, to improvements to lithographic chemical shrink processes. 
     2. 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. 
     Therefore, there is a need for contact hole printing processes that allow printing contact holes relatively smaller than those of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a structure formation method, comprising providing a structure including (a) a hole layer having a top hole layer surface, (b) a BARC (bottom antireflective coating) layer on the top hole layer surface, and (c) a patterned photoresist layer on top of the BARC layer, wherein the patterned photoresist layer comprises a photoresist hole such that a top BARC surface of the BARC layer is exposed to the surrounding ambient at a bottom wall of the photoresist hole; extending the photoresist hole by removing a portion of the BARC layer directly beneath the bottom wall of the photoresist hole such that an area of the top hole layer surface is exposed to the surrounding ambient via the extended photoresist hole, wherein said extending the photoresist hole is performed before any deposition of any layer on the patterned photoresist layer; and depositing a hole shrinking film (i) on the patterned photoresist layer, (ii) on a side wall of the extended photoresist hole, and (iii) on the bottom wall of the extended photoresist hole after said extending the photoresist hole is performed. 
     The present invention also provides structure formation method, comprising providing a structure including (a) a hole layer having a top hole layer surface, (b) an acid containing layer on the top hole layer surface, wherein the acid containing layer comprises acids necessary for a chemical shrink process, and (c) a patterned photoresist layer on top of the acid containing layer, wherein the patterned photoresist layer comprises a photoresist hole such that a top acid containing layer surface of the acid containing layer is exposed to the surrounding ambient at a bottom wall of the photoresist hole; extending the photoresist hole by removing a portion of the acid containing layer directly beneath the bottom wall of the photoresist hole such that an area of the top hole layer surface is exposed to the surrounding ambient via the extended photoresist hole, wherein said extending the photoresist hole is performed before any deposition of any layer on the patterned photoresist layer, and wherein said extending the photoresist hole undercuts the patterned photoresist layer; and depositing a hole shrinking film (i) on the patterned photoresist layer, (ii) on a side wall of the extended photoresist hole, and (iii) on the bottom wall of the extended photoresist hole after said extending the photoresist hole is performed. 
     The present invention also provides a structure, comprising (a) a hole layer including a top hole layer surface; (b) a BARC (bottom antireflective coating) layer being on the top hole layer surface and comprising a BARC hole in the BARC layer; (c) a photoresist layer being on top of the BARC layer and being in direct physical contact with the BARC layer via a first common interfacing surface, wherein the photoresist layer comprises a photoresist hole directly above the BARC hole; and (d) a polymerized hole shrinking region in the photoresist hole and the BARC hole, wherein the polymerized hole shrinking region is in direct physical contact with the hole layer. 
     The present invention provides contact hole printing processes that allow printing contact holes relatively smaller than those of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1F  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. 
         FIGS. 3A-3F  illustrate the steps of a third contact hole printing process, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A-1F  illustrate 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 a structure  100  including a contact hole layer  110  (comprising a dielectric material such as SiO 2  in one embodiment) to be patterned with contact holes. The contact hole layer  110  is 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 over 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  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 first photoresist developer (a solvent) while other regions of the photoresist layer  130  not exposed to light remain insoluble in the first photoresist developer. As a result, with reference to  FIG. 1B , in one embodiment, the first 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 patterned photoresist layer  130  which exposes a top BARC surface  121  of the BARC layer  120  to the surrounding ambient light. 
     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 hole layer surface  112  of the SiO 2  contact hole layer  110  is exposed to the surrounding ambient through the photoresist hole  132  as shown in  FIG. 1C . In one embodiment, the directional etching of the BARC layer  120  is a RIE (reactive ion etching) process. As depicted in  FIG. 1B , the top BARC surface  121  and the top hole layer surface  112  are in different planes and are parallel to each other. 
     Next, with reference to  FIG. 1D , in one embodiment, a hole shrinking film  140  is formed on top of the entire structure  100  of  FIG. 1C  by, illustratively, a spin-on process such that the hole shrinking film  140  completely fills the photoresist hole  132  and such that the hole shrinking film  140  and the BARC layer  120  have a common surface  135 . 
     In one embodiment, the hole shrinking film  140  comprises a material which, when coming into direct contact with the residual photo acids at a high temperature, becomes solid and capable of withstanding a subsequent etching of the BARC layer  120  and the contact hole layer  110  during the formation of a contact hole  114  ( FIG. 1F ) in the contact hole layer  110 . More specifically, in one embodiment, the hole shrinking film  140  comprises a water-soluble polymer (or alcohol-soluble polymer) and can be formed by spin-applying the water-soluble polymer on top of the entire structure  100  of  FIG. 1C . Next, the structure  100  is baked to an elevated temperature such that (i) the residual photo acids in the region  139  diffuse into a region  143  of the hole shrinking film  140  via the side wall  133  and (ii) BARC acids in the BARC layer  120  diffuse into a region  145  of the hole shrinking film  140  via the common surface  135 . 
     In one embodiment, the acid concentration in the region  139  is smaller than the acid concentration in the BARC layer  120 . As a result, the acid diffusion from the region  139  into the region  143  is at a lower rate than the acid diffusion from the BARC layer  120  into the region  145  resulting in a thickness  143 ′ of the region  143  being smaller than a thickness  145 ′ of the region  145 . In other words, different acid concentrations in the region  139  and the BARC layer  120  results in different acid diffusion rates from the region  139  and the BARC layer  120  into the regions  143  and  145 , respectively. However, it should also be noted that temperature also affects the acid diffusion rates from the region  139  and the BARC layer  120  into the regions  143  and  145 , respectively. For instance, the acids in the region  139  may be more mobile than the acids in the BARC layer  120  upon heating above the glass transition temperature (Tg). Since the BARC is conventionally cross-linked, there is no such transition point in the BARC. In one embodiment, the thicknesses  143 ′ and  145 ′ are controlled by (i) the bake temperature at which the structure  100  is baked and (ii) the duration of the bake step. The higher the bake temperature and the longer the structure  100  is baked, the larger the thicknesses  143 ′ and  145 ′. 
     At the elevated temperature, the diffused residual photo acids in the region  143  catalyze cross-linking reactions (i.e., polymerization) in the region  143  causing the region  143  to change from originally soluble to insoluble in a first post-shrink rinse chemical (e.g., water). 
     Similarly, at the elevated temperature, the diffused BARC acids in the region  145  catalyze cross-linking reactions (i.e., polymerization) in the region  145  causing the region  145  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  140  except the insoluble regions  143  and  145  (also referred to as the region  143 , 145 ) such that the photoresist hole  132  is reopened and such that the top hole layer surface  112  of the contact hole layer  110  is again exposed to the surrounding ambient through the reopened photoresist hole  132  as shown in  FIG. 1E . This process can be referred to as the first post-shrink rinse. 
     Next, with reference to  FIG. 1F , in one embodiment, the contact hole  114  is formed in the contact hole layer  110  directly beneath and aligned with the reopened photoresist hole  132 . Illustratively, the contact hole  142  is formed by directionally etching (e.g., RIE etching in one embodiment) the contact hole layer  110  through the 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 . 
       FIGS. 2A-2E  illustrate 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 a structure  200  including 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 . 
     For simplicity, all reference numerals herein have three numeric digits starting with the numeric figure number. In addition, similar regions have identical reference numerals except for the first digit which is used to indicate the numeric figure number. For example, the BARC layer  120  ( FIG. 1A ) and the BARC layer  220  ( FIG. 2A ) are similar. 
     Next, in one embodiment, the photoresist layer  230  is exposed to light through a mask (not shown, but typically projected onto the photoresist layer  230 ) containing clear and opaque features such that a region  231  of the photoresist layer  130  is exposed to light while other regions of the photoresist layer  230  are not exposed to light. The BARC layer  230  optimizes the image quality by suppressing reflections within the resist. 
     In one embodiment, assume that positive-tone optical lithography is used. As a result, with reference to  FIG. 2B , a second photoresist developer is used to develop away (remove) the exposed-to-light region  231  ( FIG. 2A ) of the photoresist layer  230  (called development process) resulting in a photoresist hole  232  in the patterned photoresist layer  230 . 
     It should be noted that when the photoresist layer  230  is exposed to light, the intensity of energy reaching the photoresist layer  230  is at its highest at the center of the region  231  ( FIG. 2A ) and decays at the perimeter of the region  231  ( FIG. 2A ). As a result, a region  239  abutting the region  231  ( FIG. 2A ) does not attain an acid concentration level required for inducing photoresist development. Therefore, when the region  231  ( FIG. 2A ) is later removed, the region  239  remains and contains some photo acids (called residual photo acids). 
     In one embodiment, the BARC layer  220  comprises a wet-developable material such that the second photoresist developer which is used to develop the photoresist layer  230  also isotropically etches the BARC layer  220  stopping at the SiO 2  contact hole layer  210 . Alternatively, an isotropic etching of the BARC layer  220  separate from the development of the photoresist layer  230  (i.e., using etchants other than the second photoresist developer) is performed. As a result of the development of the photoresist layer  230  and the subsequent isotropic etching of the BARC layer  220 , a top surface  212  of the contact hole layer  210  is exposed to the surrounding ambient through the photoresist hole  232 . In one embodiment, the isotropic etching of the BARC layer  220  undercuts the photoresist layer  230  as shown in  FIG. 2B . 
     Next, with reference to  FIG. 2C , in one embodiment, a hole shrinking film  240  is formed on top of the entire structure  200  of  FIG. 2B  by, illustratively, a spin-on process such that the hole shrinking film  240  completely fills the photoresist hole  232 . In one embodiment, the hole shrinking film  240  comprises a water-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 residual photo acids in the region  239  diffuse into a region  243  of the hole shrinking film  240  via the side wall  233  and (ii) BARC acids in the BARC layer  220  diffuse into a region  245  of the hole shrinking film  240  via the common surface  235 . 
     In one embodiment, the acid concentration in the region  239  is smaller than the acid concentration in the BARC layer  220 . As a result, the acid diffusion from the region  239  into the region  243  is at a lower rate than the acid diffusion from the BARC layer  220  into the region  245  resulting in a thickness  243 ′ of the region  243  being smaller than a thickness  245 ′ of the region  245 . In one embodiment, the thicknesses  243 ′ and  245 ′ are controlled by (i) the bake temperature at which the structure  200  is baked and (ii) the duration of the bake step. The higher the bake temperature and the longer the structure  200  is baked, the larger the thicknesses  243 ′ and  245 ′. 
     In one embodiment, the bake temperature and the duration of the bake step for the structure  200  of  FIG. 2B  are such that the difference of thicknesses  243 ′ and  245 ′ is equal to the undercut degree  238  ( FIG. 2B ). 
     At the elevated temperature, the diffused residual photo acids in the region  243  catalyze cross-linking reactions (i.e., polymerization) in the region  243  causing the region  243  to change from originally soluble to insoluble in a second post-shrink rinse chemical (e.g., water). 
     Similarly, at the elevated temperature, the diffused BARC acids in the region  245  catalyze cross-linking reactions (i.e., polymerization) in the region  245  causing the region  245  to change from originally soluble to insoluble in the second post-shrink rinse chemical. 
     Next, the second post-shrink rinse chemical is used to the remove the entire hole shrinking film  240  except the insoluble regions  243  and  245  (also referred to as the region  243 , 245 ) such that the top surface  212  of the contact hole layer  210  is again exposed to the surrounding ambient as shown in  FIG. 2D . This process can be referred to as the second post-shrink rinse. 
     Because the difference of thicknesses  243 ′ and  245 ′ is equal to the undercut degree  238  ( FIG. 2B ), the side wall  234  of the reopened photoresist hole  232  is vertical through out the photoresist layer  230  and the BARC layer  220 . 
     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 photoresist hole  232 . Illustratively, the contact hole  242  is formed by directionally etching (e.g., RIE etching in one embodiment) the contact hole layer  210  through the photoresist hole  232 . In one embodiment, the contact hole  214  is then filled with a electrically conducting material (not shown) such as copper to provide electric access to device(s) (not shown) underneath the contact hole layer  210 . 
       FIGS. 3A-3F  illustrate the steps of a third contact hole printing process, in accordance with embodiments of the present invention. More specifically, with reference to  FIG. 3A , in one embodiment, the second contact hole printing process starts out with a structure  300  including a contact hole layer  310  (comprising a dielectric material such as SiO 2  in one embodiment) formed on a semiconductor substrate (not shown for simplicity). The structure  300  further comprises (i) a BARC (bottom antireflective coating) layer  320  on top of the contact hole layer  310  and (ii) a photoresist layer  330  on top of the BARC layer  320 . 
     Next, in one embodiment, the photoresist layer  330  is exposed to light through a mask (not shown, but typically formed on top of the photoresist layer  330 ) containing clear and opaque features such that a region  331  of the photoresist layer  330  is exposed to light while other regions of the photoresist layer  330  are not exposed to light. The BARC layer  330  ensures that a substantial portion of light that passes through the photoresist layer  330  is absorbed by the BARC layer  330  without being reflected back to the photoresist layer  330  by any layer(s) beneath the BARC layer  330  (including the contact hole layer  310 . 
     In one embodiment, assume that positive-tone optical lithography is used. As a result, with reference to  FIG. 3B , a third photoresist developer is used to develop away (remove) the exposed-to-light region  331  ( FIG. 3A ) of the photoresist layer  330  (called development process) resulting in a photoresist hole  332  in the patterned photoresist layer  330 . 
     It should be noted that when the photoresist layer  330  is exposed to light, the intensity of energy reaching the photoresist layer  330  is at its highest at the center of the region  331  ( FIG. 3A ) and decays at the perimeter of the region  331  ( FIG. 3A ). As a result, a region  339  abutting the region  331  ( FIG. 3A ) does not attain an acid concentration level required for inducing photoresist development. Therefore, when the region  331  ( FIG. 3A ) is later removed, the region  339  remains and contains some photo acids (called residual photo acids). 
     In one embodiment, the BARC layer  320  comprises a wet-developable material such that the second photoresist developer which is used to develop the photoresist layer  330  also isotropically etches the BARC layer  320  stopping at the SiO 2  contact hole layer  310 . Alternatively, an isotropic etching of the BARC layer  320  separate from the development of the photoresist layer  330  (i.e., using etchants other than the third photoresist developer) is performed. As a result of the development of the photoresist layer  330  and the subsequent isotropic etching of the BARC layer  320 , a top surface  312  of the contact hole layer  310  is exposed to the surrounding ambient through the photoresist hole  332 . In one embodiment, the isotropic etching of the BARC layer  320  undercuts the photoresist layer  330  as shown in  FIG. 3B . 
     Next, with reference to  FIG. 3C , in one embodiment, the photoresist layer  330  is thermally reflowed at a reflow temperature in a range of 100-200° C. in a duration in a range of 60-90 seconds such that some material of the photoresist layer  330  flows down under the force of gravity and covers the BARC layer  320 . The heat of the flow process not only generates acids through out the patterned photoresist layer  330  but also uniformly redistributes the residual photo acids from the region  339  ( FIG. 3B ) throughout the patterned photoresist layer  330 . 
     Next, with reference to  FIG. 3D , in one embodiment, a hole shrinking film  340  is formed on top of the entire structure  300  of  FIG. 3C  by, illustratively, a spin-on process such that the hole shrinking film  340  completely fills the photoresist hole  332 . In one embodiment, the hole shrinking film  340  comprises a water-soluble polymer and can be formed by spin-applying the water-soluble polymer on top of the entire structure  300  of  FIG. 3C . 
     Next, the structure  300  is baked to an elevated temperature such that the acids in the region  339  diffuse into a region  343  of the hole shrinking film  340  via the side wall  333  and such that BARC. At the elevated temperature, the diffused acids in the region  343  catalyze cross-linking reactions (i.e., polymerization) in the region  343  causing the region  343  to change from originally soluble to insoluble in a third post-shrink rinse chemical (e.g., water). 
     Next, the third post-shrink rinse chemical is used to the remove the entire hole shrinking film  340  except the insoluble regions  343  such that the photoresist hole  332  is reopened and such that the top surface  312  of the contact hole layer  310  is again exposed to the surrounding ambient through the reopened photoresist hole  332  as shown in  FIG. 3E . This process can be referred to as the third post-shrink rinse. 
     Next, with reference to  FIG. 3F , in one embodiment, the contact hole  314  is formed in the contact hole layer  310  directly beneath and aligned with the photoresist hole  332 . Illustratively, the contact hole  314  is formed by directionally etching (e.g., RIE etching in one embodiment) the contact hole layer  310  through the photoresist hole  332 . It should be noted that the region  343  not only covers the side wall of the photoresist hole  332  but also covers the top surface of the photoresist layer  330 . As a result, the photoresist layer  330  is better protected from the etching of the contact hole layer  310  during the formation of the contact hole  314 . In one embodiment, the contact hole  314  is then filled with a electrically conducting material (not shown) such as copper to provide electric access to device(s) (not shown) underneath the contact hole layer  310 . 
     In the embodiments described above, the first, second, and third contact hole printing processes are used to print contact holes  114 ,  214 , and  314  of  FIGS. 1F ,  2 E, and  3 F, respectively. In general, any hole (not just contact holes) of any size and shape can be printed in the layers  110 ,  210 , and  310  of  FIGS. 1F ,  2 E, and  3 F, using the first, second, and third contact hole printing processes, respectively. For instance, with reference to  FIGS. 1A-1F , 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.

Technology Category: 4