Abstract:
A process of forming a fine pattern including forming a first photoresist layer over a first layer of a semiconductor device. Portions of the first photoresist layer are exposed causing a photochemical reaction therein. Prior to developing the first photoresist layer, a second photoresist layer is formed over the first photoresist layer, and wherein at least one of the first photoresist layer and second photoresist layer comprises a photo base generator.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to making patterns using photoresist materials. BACKGROUND OF THE INVENTION  
         [0002]     Referring now to FIGS.  1 A-I, a known method of making a semiconductor device  10  includes providing a first layer  14  to be etched which may overlie a substrate  12  which may be a semiconductor wafer. The substrate  12  may be any material known to those skilled in the art for making semiconductor devices including, but not limited, to silicon, germanium, silicon and germanium, gallium arsenate, silicon carbide and silicon germanium. The first layer  14  to be etched may be an electrically conductive material or a dielectric. The first layer  14  to be etched is a dielectric such as silicon dioxide, or a low dielectric constant material such as SiOC, SiOF, SiC, SiCN. A first sacrificial layer  16  is provided over the first layer  14  to be etched as shown in  FIG. 1A .  
         [0003]     Referring now to  FIG. 1B , a first mask  18  is provided and includes transparent portions  20  for transmitting light therethrough and non-transparent portions  22  for blocking light. Light as indicated by the arrows labeled  21  is shown through the first mask  18  exposing portions of the first sacrificial layer  16 . The first sacrificial layer  16  comprises a photoresist material and includes light exposed portions  24  and unexposed portions  26 .  
         [0004]     Referring now to  FIG. 1C , the sacrificial layer  16  is developed and the exposed portions  24  removed leaving openings  28  extending through the first sacrificial layer  16 .  
         [0005]     Referring now to  FIG. 1D , thereafter the first sacrificial layer  16  is treated to increase the resistance of the first sacrificial layer  16  without intermixing to first resist material  30  coating. The treating of the first sacrificial layer  16  may include at least one of irradiation of the first sacrificial layer  16  with infrared light, broad band ultraviolet light, deep ultraviolet light (for example having a wave length ranging from 193-248 nm) extra ultraviolet light (for example having a wave length of 13.5 nm), e-beam and x-rays. The first sacrificial layer  16  is treated with ion implant hardening to increase resistance to first resist layer  30  from mixing. The first sacrificial layer  16  is treated with a chemical to increase the resistance of the first sacrificial layer from mixing with the first resist layer  30 , such as, but not limited to, exposing the first sacrificial layer  16  to water vapor and then alkoxysilane gas.  
         [0006]     Referring now to  FIG. 1E , thereafter, a first photoresist layer  30  is formed over the first sacrificial layer  16  and fills the openings  28  extending through the first sacrificial layer  16 .  
         [0007]     Referring now to  FIG. 1F , thereafter, a second mask  32  which includes transparent portions  34  for transmitting light therethrough and non-transparent portions  36  for blocking light is positioned over the structure of  FIG. 1E  and light is transmitted through the mask creating exposed portions  38  in the first photoresist and unexposed portions  40  in the first photoresist. As will be appreciated from  FIG. 1F , the transparent portions  34  of the second mask  32  are much larger than the transparent portions  20  of the first mask.  
         [0008]     Referring now to  FIG. 1G , the first photoresist material is developed and the exposed portions removed to provide openings  42  in the first photoresist that communicate with at least one of the openings  28  and the sacrificial layer  16 . If desired, some of the openings  28  in the first sacrificial  16  may be blocked by unexposed portions  40  of the first photoresist layer  30 . As will be appreciated by  FIG. 1G , each opening  42  in the first photoresist layer  30  is vertically aligned with at least one opening  28  in the first sacrificial layer  16 . An opening  42  in the first photoresist layer  30  may span a plurality of adjacent openings  28  in the first sacrificial layer  16 . Further, the width of the opening  42  in the first photoresist layer  30 , generally indicated by arrow B, is greater in all directions than the width of the opening  28  in the first sacrificial layer  16  in all directions. Consequently, the cross-sectional area of the opening  42  in the first photoresist layer  30  is greater than the cross-sectional area of the opening  28  in the first sacrificial layer  16 .  
         [0009]     Referring now to  FIG. 1H , thereafter, the semiconductor device is etched through the openings  42  and  28  to etch openings  44  through the first layer  14 . The first photoresist layer  30  is etched substantially by the etching material as will be appreciated by the position of the upper surface  41  of the photoresist layer  30  as originally deposited and the position of the upper surface  43  of the etched first photoresist layer  30 . However, due to the treatment of the sacrificial layer  16 , the opening pattern  44  is transfer directly from the sacrificial layer  16 . This allows for much narrower features and greater packing density of features in the first layer  14 . The first layer  14  is silicon dioxide and the etching is accomplished using a plasma etch including CF 4  and CHF 3 . The photoresist layer  30  and the sacrificial layer  16  may be exposed in the above embodiments using KrF light as exposure light as well as, G rays, I rays, ArF light and e-beam  
         [0010]     Referring now to FIGS.  2 A-I, a known method of making a semiconductor device includes providing a first sacrificial layer  16  over a first layer  14  to be etched over a semiconductor substrate  12  as described with respect to  FIG. 1A . However, the first sacrificial layer  16  comprises a hard mask such as silicon nitride or silicon oxynitride overlying the first layer  14 . A second sacrificial layer  46  is provided over the first sacrificial layer  16 . The second sacrificial layer  46  comprises a photoresist material.  
         [0011]     Referring now to  FIG. 2B , a first mask  18  is provided which again includes transparent portions  20  transmitting light therethrough and non-transparent portions  22 . Light is transmitted through the first mask  18  creating exposed portions  48  and unexposed portions  50  in the second sacrificial layer  46 . Thereafter, the second sacrificial layer  46  is developed and the exposed portions  48  removed producing openings  52  through the second sacrificial layer  46 . The openings  52  expose a portion of the first sacrificial layer  16 .  
         [0012]     Referring now to  FIG. 2D , the first sacrificial layer  16 , which is a hard mask, is etched to provide openings  28  extending through the first sacrificial layer  16  exposing portions of the first layer  14 . The silicon nitride may be etched with phosphoric acid in the case of a wet etch, or a plasma generated from CF 4  /O 2 . The second sacrificial layer  46  is removed.  
         [0013]     Referring now to  FIG. 2E , a first photoresist layer  30  is formed over the first sacrificial layer  16  so that portions of the photoresist layer fill the openings  28  formed in the first sacrificial layer  16 .  
         [0014]     Referring now to  FIG. 2F , thereafter a second mask  32  is provided including transparent portions  34  for transmitting light therethrough and non-transparent portions  36  for blocking light and light is transmitted through the second mask  32  creating exposed portions  38  in the first photoresist layer  30  and unexposed portions  40  in the first photoresist layer  30 .  
         [0015]     Referring now to  FIG. 2G , thereafter the photoresist layer  30  is developed and the exposed portions  38  removed leaving openings  42  in the first photoresist layer  30 . An opening  42  in the first photoresist layer  30  may span a plurality of adjacent openings  28  in the first sacrificial layer  16 . Further, the width of the opening  42  in the first photoresist layer  30  generally indicated by arrow B is greater in all directions than the width of the opening  28  in the first sacrificial layer  16  in all directions. Consequently, the cross-sectional area of the opening  42  in the first photoresist layer  30  is greater than the cross-sectional area of the opening  28  in the first sacrificial layer  16 .  
         [0016]     Referring now to  FIG. 2H , thereafter the first layer  14  is etched to provide openings  44  therethrough. As will be appreciated from  FIG. 2H , the first photoresist layer  30  is substantially etched as will be appreciated from the location of the upper surface  41  indicated by the dotted line of the first photoresist  30  as originally deposited and the upper surface  43  of the etched first photoresist layer  30 . However, because the first sacrificial layer  16  is a hard mask such as silicon nitride, the first sacrificial layer  16  is substantially unaffected by the etching material. This allows for much narrower and more densely packed features to be formed in the first layer  14 . Thereafter, the first photoresist layer  30  and the sacrificial layer  16  are removed as shown in  FIG. 2I .  
         [0017]     FIGS.  3 A-E illustrate a known method of making a photoresist structure. A first layer  110  is provided and a first photoresist  112  is provided over the first layer  110 . The first layer  10  may be a metallization layer, dielectric layer, or a semiconductor substrate, for example, a silicon wafer. The first photoresist layer  112  is exposed, developed and patterned to produce a plurality of first photoresist features  114 . Each of the first photoresist features  114  has an upper surface  116  and at least a first sidewall  118 , and typically a second opposite sidewall  120  as shown in  FIG. 3B .  
         [0018]     Thereafter, as shown in  FIG. 3C , a second photoresist  122  is applied over the structure of  FIG. 3B . The upper surface  116 , the first sidewall  118  and the second sidewall  120 , are all covered by the second photoresist material  122 .  
         [0019]     Thereafter, as shown in  FIG. 3D , the structure of  FIG. 3C  is heated to release an acid in the plurality of individual photoresist features  114 . The second photoresist material  122  may be crosslinked upon exposure to the acid released from the plurality of photoresist features  114 . The acid diffuses from the upper surface  116 , first sidewall  118  and second sidewall  120  outwardly into the second photoresist material  122 . Thereafter, the uncrosslinked portions of the second photoresist layer  122  are removed by, for example, developing using a liquid chemical developer to dissolve the soluble regions of the photoresist. The above-described process may be utilized to produce photoresist structures having a relatively narrow gap  148  between structures caused by the crosslinked portion  124  of the first photoresist  112  that extends along each of the first sidewall  118  and the second sidewall  120  from the upper face  16  down to the first layer  110 .  
         [0020]     Sugino et al., U.S. Pat. No. 6,566,040, issued May 20, 2003, discloses a hole pattern or separation pattern of a first resist that is capable of supplying acid formed on a semiconductor substrate. A crosslinking film is formed on the sidewall of the first substrate pattern to obtain a resist pattern having a reduced hole diameter or separation width. Then, the hole diameter or the separation width is further reduced by causing thermal reflow of the crosslinked film. The semiconductor substrate is etched by using a resulting resist pattern as a mask. The water-soluble crosslinking agents used as the second resist include urea crosslinking agents such as urea, alkoxymethylene ureas, N-alkoxymethylene ureas, ethyleneurea, ethylene urea carboxylates and the like, melamine crosslinking agents such as melamine, alkoxymethylene melamines and the like, and amino crosslinking agents such as benzoguanamine, glycoluril and the like. Examples of water-soluble resist materials usable as the second resist include, aside from the water-soluble crosslinking agents used singly or in combination, the mixtures of these resins and crosslinking agents. The material for the first photoresist may be one which makes use of a mechanism capable of generating an acidic component inside the photoresist by an appropriate thermal treatment, and may be either a positive or negative photoresist. Examples of photoresist include novolac resin and a naphthoquinonediazide photosensitive agent. A chemically amplified resist making use of an acid generating mechanism may also be used as the first photoresist.  
         [0021]     Ishibashi et al., U.S. Pat. No. 6,319,853, issued Nov. 20, 2001, discloses a method of producing a pure resist pattern having superior topography smaller than the limit of wavelength of exposure light. A first photoresist pattern containing material capable of producing an acid on exposure to light is coated with a second resist containing material which causes a crosslinking reaction in the presence of an acid. An acid is produced in the photoresist pattern by exposing the pattern to light, thus forming a crosslinked layer along the boundary surface between the first resist pattern and the second resist pattern. As a result, the second resist pattern which is greater than the first resist pattern is formed.  
         [0022]     Tanaka et al., U.S. Pat. No. 6,593,063, issued Jul. 15, 2003, discloses a first resist layer capable of generating an acid formed on a semiconductor base and is developed in a shortened development time than usual. The first resist pattern is covered with a second resist layer containing a material capable of crosslinking in the presence of an acid. The acid is generated in the first resist pattern by application of heat or by exposure to light, and a crosslinked layer is formed in the second resist pattern at the interface with the first resist pattern as a cover layer for the first resist pattern, thereby the first resist pattern is caused to be thickened. The non-crosslinked portion of the second resist pattern is removed and the fine resist pattern is formed. The hole diameter of the resist pattern can be reduced, or the isolation width of a resist pattern may be produced utilizing this method.  
       SUMMARY OF THE INVENTION  
       [0023]     A process of forming a fine pattern comprising:  
         [0024]     forming a first photoresist layer over a first layer of a semiconductor device;  
         [0025]     exposing portions of the first photoresist layer causing a photochemical reaction therein;  
         [0026]     prior to developing the first photoresist layer, forming a second photoresist layer over the first photoresist layer;  
         [0027]     and wherein at least one of the first photoresist layer and second photoresist layer comprises a photo base generator.  
         [0028]     Other embodiments of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0030]      FIG. 1A  illustrates a known method of making a semiconductor device including providing a first sacrificial layer over a first layer to be etched.  
         [0031]      FIG. 1B  illustrates a known method of making a semiconductor device including selectively exposing portions of the first sacrificial layer.  
         [0032]      FIG. 1C  illustrates a known method of making a semiconductor device including removing the exposed portion of the first sacrificial layer providing openings therein.  
         [0033]      FIG. 1D  illustrates a known method of making a semiconductor device including treating the first sacrificial layer.  
         [0034]      FIG. 1E  illustrates a known method of making a semiconductor device including forming a first photoresist layer over the first sacrificial layer.  
         [0035]      FIG. 1F  illustrates a known method of making a semiconductor device exposing portions of the first photoresist layer.  
         [0036]      FIG. 1G  illustrates a known method of making a semiconductor device including forming openings in the first photoresist layer that communicate with at least one opening in the first sacrificial layer.  
         [0037]      FIG. 1H  illustrates a known method of making a semiconductor device including etching openings in the first layer.  
         [0038]      FIG. 1I  illustrates a known method of making a semiconductor device including removing the first photoresist layer and the first sacrificial layer.  
         [0039]      FIG. 2A  illustrates a known method of making a semiconductor device including providing a first layer to be etched, a first sacrificial layer over the first layer, and a second sacrificial layer over the first sacrificial layer.  
         [0040]      FIG. 2B  illustrates a known method of making a semiconductor device including selectively exposing portions of the second sacrificial layer.  
         [0041]      FIG. 2C  illustrates a known method of making a semiconductor device including removing the exposed portion of the second sacrificial layer providing openings therein.  
         [0042]      FIG. 2D  illustrates a known method of making a semiconductor device including etching openings through the first sacrificial layer.  
         [0043]      FIG. 2E  illustrates a known method of making a semiconductor device including forming a first photoresist layer over the first sacrificial layer.  
         [0044]      FIG. 2F  illustrate a known method of making a semiconductor device including forming a first photoresist layer over the first sacrificial layer.  
         [0045]      FIG. 2G  illustrates a known method of making a semiconductor device including forming openings in the first photoresist layer that communicate with at least one opening in the first sacrificial layer.  
         [0046]      FIG. 2H  illustrates a known method of making a semiconductor device including etching openings in the first layer.  
         [0047]      FIG. 2I  illustrates a known method of making a semiconductor device including removing the first photoresist layer and the first sacrificial layer.  
         [0048]      FIG. 3A  illustrates a prior art method of forming a photoresist structure including depositing a first photoresist layer on a first layer.  
         [0049]      FIG. 3B  illustrates a prior art method including exposing, developing and patterning portions of the first photoresist layer.  
         [0050]      FIG. 3C  illustrates a prior art method including depositing a second photoresist layer over the structure of  FIG. 3B .  
         [0051]      FIG. 3D  illustrates a prior art method including heating features formed by the first photoresist layer to cause an acid to be diffused from the features and crosslinked with the second photoresist layer along the boundary surfaces of the first photoresist features.  
         [0052]      FIG. 3E  illustrates a step in a prior art method including developing a second photoresist layer to remove uncrosslinked portions and to produce a photoresist structure having a relatively narrow gap between adjacent photoresist.  
         [0053]      FIG. 4A  illustrates one embodiment according to the present invention including forming a first photoresist layer over a first layer of a semiconductor device.  
         [0054]      FIG. 4B  illustrates one embodiment according to the present invention exposing portions of the first photoresist layer.  
         [0055]      FIG. 4C  illustrates one embodiment according to the present invention including forming a second photoresist layer over the first photoresist layer.  
         [0056]      FIG. 4D  illustrates one embodiment according to the present invention including exposing portions of the second photoresist layer.  
         [0057]      FIG. 4E  illustrates one embodiment according to the present invention including baking the semiconductor device.  
         [0058]      FIG. 4F  illustrates one embodiment according to the present invention including developing the first photoresist layer and the second photoresist layer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0059]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0060]     Referring now to FIGS.  4 A-F, a known method of making a semiconductor device  210  includes providing a first layer  214  to be etched or otherwise further treated or further processed which may overlie a substrate  212  which may be a semiconductor wafer. Alternatively, the first layer  214  may be a semiconductor wafer. The substrate  212  may be any material known to those skilled in the art for making semiconductor devices including, but not limited, to silicon, germanium, silicon and germanium, gallium arsenate, silicon carbide and silicon germanium. The first layer  214  to be etched treated or treated may be an electrically conductive material, a dielectric or a semiconductor substrate. The first layer  214  to be etched, treated or further processed may be a dielectric such as silicon dioxide, or a low dielectric constant material such as SiOC, SiOF, SiC, SiCN. A first photoresist layer  216  is provided over the first layer  214  to be etched as shown in  FIG. 4A . The first photoresist layer  216  may be a negative photoresist wherein exposed parts of the negative photoresist become cross-linked and polymerized due to the photochemical reaction, which hardens and remains after development, whereas the unexposed parts are dissolved by the developer solution. Alternatively, the first photoresist layer  216  may be a positive photoresist material, for example, wherein the main component is a novolac resin, and wherein the exposed parts&#39; cross-links break down and become softened due to the photochemical reaction known as photosolubilization and are dissolved by the developer solution and the unexposed parts remain. The first photoresist layer  216  may include a photo acid generator that produces an acid upon exposure to heat or certain light, or the first photoresist layer  216  may include a photo base generator that produces a base upon exposure to heat or certain light.  
         [0061]     Optionally, the first photoresist layer  216  may be baked to evaporate solvents and to densify the photoresist. Referring now to  FIG. 4B , a first mask  218  is provided and includes transparent portions  220  for transmitting light therethrough and non-transparent portions  222  for blocking light. Light as indicated by the arrows labeled  221  is shown through the first mask  218  exposing portions of the first photoresist layer  216 . The first photoresist layer  216  now includes light exposed portions  224  and unexposed portions  226 .  
         [0062]     Thereafter, without developing the first photoresist layer  216 , a second photoresist layer  230  is formed over the first photoresist layer  216  as shown in  FIG. 4C . The second photoresist layer  230  may be a negative photoresist wherein exposed parts of the negative photoresist become cross-linked and polymerized due to the photochemical reaction, which hardens and remains after development, whereas the unexposed parts are dissolved by the developer solution. Alternatively, the second photoresist layer  230  may be a positive photoresist material, for example wherein the main component is a novolac resin, and wherein the exposed parts&#39; cross-links break down and become softened due to the photochemical reaction known as photosolubilization and are dissolved by the developer solution and the unexposed parts remain. The second photoresist layer  230  may include a photo acid generator that produces an acid upon exposure to heat or certain light, or the second photoresist layer  230  may include a photo base generator that produces a base upon exposure to heat or certain light. The first photoresist layer  216  may include the opposite photo generator from the second photoresist layer  230 . Furthermore, the photoresist layer  216  and  230  also include a cross-linking agent that cross links the photoresist material upon exposure to an acid or a base. For example, the first photoresist layer  216  may include a photo acid generator and a cross-linking agent activated by a base, and the second photoresist layer  230  may include a photo base generator or a cross-linking agent activated by an acid; and conversely, the first photoresist layer  216  may include a photo base generator and a cross-linking agent activated by an acid, and the second photoresist layer  230  may include an photo acid generator or a cross-linking agent activated by a base. The second photoresist layer  230  may be water soluble or with different solvent than first photoresist layer  216 . The second photoresist layer  230  may also produce a base on exposure to heat or light, wherein the base neutralizes the acid produced upon expose of a first photoresist that is a positive photoresist.  
         [0063]     Referring now to  FIG. 4D , thereafter, a second mask  232  which includes transparent portions  234  for transmitting light therethrough and non-transparent portions  236  for blocking light is positioned over the structure of  FIG. 4C  and light is transmitted through the mask creating exposed portions  238  in the first photoresist and unexposed portions  240  in the first photoresist. As will be appreciated from  FIG. 4D , at least one of the transparent portions  234  of the second mask  232  or at least one of the light blocking portions  400  of the second mask  232  extends across two adjacent exposed portions of the first photoresist layer  216  or across two adjacent unexposed portion of the first photoresist layer  216 . .  
         [0064]     Referring now to  FIG. 4E , thereafter, the semiconductor device  210  of  FIG. 4D  is exposed to heat, for example in a post exposure bake process causing a base to be released from the second photoresist layer  230 , wherein the base reacts with acid produced in the exposed portion of the first photoresist layer  216  causing at least an upper portion  500  of the exposed portion of the first photoresist layer  216  to be neutrally without cleavage by acid. The un-cleavage positive polymer is not soluble in the developer so that the upper portions  500  are not soluble in the developer.  
         [0065]     Thereafter, as shown in  FIG. 4F , the semiconductor device is devolved in a water based developer that removes the second photoresist layer  230 . The developer also removes unprotected, unpolymerized portions  502  (exposed portions in the case of a negative photoresist) of the first photoresist layer, but does not remove the upper portions  500 , unpolymerized portion  224  and polymerized portions  226  (unexposed portions in the case of a negative photoresist) of the first photoresist layer  216 . An opening  502  may be provided through the first photoresist layer  216  after developing.  
         [0066]     In another embodiment as also shown in  FIG. 4F , the semiconductor device is devolved in a water based developer that removes the second photoresist layer  230 . The developer also removes unprotected, unpolymerized (polarized, developer soluble) portions  502  (exposed portions in the case of a positive photoresist) of the first photoresist layer, but does not remove the upper polymerized(non polarized, non-soluble to developer) portions  500 , unpolymerized portion  224  and polymerized portions  226  (unexposed portions in the case of a positive photoresist) of the first photoresist layer  216 . An opening  502  may be provided through the first photoresist layer  216  after developing.  
         [0067]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.