Patent Publication Number: US-2005130079-A1

Title: Pattern formation method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority under 35 U.S.C. §119 on Patent Application No. 2003-417836 filed in Japan on Dec. 16, 2003, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to a pattern formation method for use in fabrication process or the like for semiconductor devices.  
      In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for further rapid development of lithography technique. Currently, pattern formation is carried out through photolithography using exposing light of a mercury lamp, KrF excimer laser, ArF excimer laser or the like, and use of F 2  laser lasing at a shorter wavelength is being examined. However, since there remain a large number of problems in exposure systems and resist materials, photolithography using exposing light of a shorter wavelength has not been put to practical use.  
      In these circumstances, immersion lithography has been recently proposed for realizing further refinement of patterns by using conventional exposing light (for example, see M. Switkes and M. Rothschild, “Immersion lithography at 157 nm”, J. Vac. Sci. Technol., Vol. B19, p. 2353 (2001)).  
      In the immersion lithography, a region in an exposure system sandwiched between a projection lens and a resist film formed on a wafer is filled with a liquid having a refractive index n (wherein n&gt;1) and therefore, the NA (numerical aperture) of the exposure system has a value n-NA. As a result, the resolution of the pattern of the resist film can be improved.  
      Now, a conventional pattern formation method employing the immersion lithography will be described with reference to  FIGS. 12A through 12D .  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 12A , the aforementioned chemically amplified resist material is applied on a substrate  1  so as to form a resist film  2  with a thickness of 0.35 nm.  
      Then, as shown in  FIG. 12B , with an immersion liquid (water)  3  provided on the resist film  2 , pattern exposure is carried out by irradiating the resist film  2  with exposing light  4  of ArF excimer laser with NA of 0.68 through a mask  5 .  
      After the pattern exposure, as shown in  FIG. 12C , the resist film  2  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  2   a  made of an unexposed portion of the resist film  2  and having a line width of 0.09 μm is formed as shown in  FIG. 12D .  
      As shown in  FIG. 12D , however, the resist pattern  2   a  formed by the conventional pattern formation method employing the immersion lithography is in a defective shape.  
     SUMMARY OF THE INVENTION  
      The present inventors have variously examined the reason why the resist pattern formed by the conventional immersion lithography is in a defective shape, resulting in finding that it is because the adhesion (wettability) to the resist film  2  of the immersion liquid  3  provided for the immersion lithography on the resist film  2  is poor. Specifically, the immersion liquid  3  provided on the resist film  2  is, for example, not uniformly diffused on the resist film  2  but tends to be present thereon in the form of drops. Therefore, it is difficult to uniformly provide the immersion liquid  3  on an exposure region of the resist film  2 . In other words, it is confirmed that the necessary exposure region of the resist film  2  is not sufficiently covered with the immersion liquid  3 .  
      When a resist pattern in such a defective shape is used for etching a target film, the resultant pattern of the target film is also in a defective shape, which disadvantageously lowers the productivity and the yield in the fabrication process for semiconductor devices.  
      In consideration of the aforementioned conventional problem, an object of the invention is forming a resist pattern in a good shape by employing the immersion lithography.  
      The present inventors have made various examinations for improving the adhesion to a resist film of an immersion liquid provided on the resist film, resulting in finding that it is effective to perform, before the pattern exposure, a surface treatment for exposing the surface of a resist film to an acid solution, a surface active agent or a solution including a compound having a hydrophilic group such as cyclodextrin. Specifically, before the pattern exposure, a solution including a compound having a hydrophilic group is supplied onto the surface of the resist film, thereby lowering the hydrophobic property of the surface of the resist film, namely, reforming the surface of the resist film to be easily interacted with the immersion liquid. As a result, the immersion liquid provided on the reformed resist film can sufficiently cover the exposure region. In other words, a hydrophilic group is coordinated on the surface of the resist film by supplying a compound having the hydrophilic group. Therefore, the surface of the resist film temporarily exhibits a hydrophilic property, and hence, the affinity is improved owing to the ion interaction with the immersion liquid generally including a large number of hydroxyl groups. As a result, it is possible to avoid the state where the immersion liquid is repelled on the surface of the resist film and cannot be easily uniformly diffused.  
      Furthermore, the present inventors have confirmed that the hydrophilic property of the surface of the resist film can be improved not only through the surface treatment of the resist film with the hydrophilic solution but also by adding a compound having a hydrophilic group to the resist film so as to make part of the compound having a hydrophilic group coordinate on the resist film.  
      The present invention was devised on the basis of the aforementioned findings, and according to the invention, the adhesion to a resist film of an immersion liquid provided on the resist film is improved by exposing the surface of the resist film to a solution including a compound having a hydrophilic group or by adding the compound to the resist film or the immersion liquid. Specifically, the present invention is practiced as follows:  
      The first pattern formation method of this invention includes the steps of forming a resist film on a substrate; exposing the resist film to a solution including a compound having a hydrophilic group; performing pattern exposure by selectively irradiating the resist film with exposing light with an immersion liquid provided on the resist film after exposing the resist film to the solution; and developing the resist film after the pattern exposure.  
      In the first pattern formation method, the hydrophilic property of the surface of the resist film is improved owing to the compound having a hydrophilic group, and therefore, the adhesion to the resist film of the immersion liquid provided on the resist film in the pattern exposure is improved. Therefore, since a necessary exposure region is sufficiently covered with the immersion liquid provided on the resist film, the immersion liquid definitely transmits the exposing light. As a result, abnormal exposure can be prevented, so that a resist pattern can be formed in a good shape by the immersion lithography.  
      The second pattern formation method of this invention includes the steps of forming, on a substrate, a resist film including a compound having a hydrophilic group; performing pattern exposure by selectively irradiating the resist film with exposing light with an immersion liquid provided on the resist film; and developing the resist film after the pattern exposure.  
      In the second pattern formation method, when the immersion liquid is provided on the resist film, part of the compound having a hydrophilic group is coordinated on the surface of the resist film, so that the hydrophilic property of the surface of the resist film can be improved, and therefore, the adhesion to the resist film of the immersion liquid is improved. Therefore, since a necessary exposure region is sufficiently covered with the immersion liquid provided on the resist film, the immersion liquid definitely transmits the exposing light. As a result, abnormal exposure can be prevented, so that a resist pattern can be formed in a good shape by the immersion lithography.  
      The second pattern formation method preferably further includes, between the step of forming a resist film and the step of performing pattern exposure, a step of exposing the resist film to a solution including a compound having a hydrophilic group. Thus, the hydrophilic property of the surface of the resist film can be further improved, and hence, the adhesion to the resist film of the immersion liquid can be further improved.  
      In the first or second pattern formation method, the compound having a hydrophilic group is preferably an acid compound, a surface active agent or cyclodextrin. At this point, it is known that cyclodextrin is a cyclic oligosaccharide and has a plurality of hydroxyl groups (—OH) around.  
      Furthermore, the surface active agent is preferably a cationic surface active agent or a nonionic surface active agent.  
      In the first or second pattern formation method, the immersion liquid is preferably water.  
      In the first or second pattern formation method, a puddle method, a dip method or a spray method may be employed in the step of exposing the resist film to a solution including a compound having a hydrophilic group.  
      The third pattern formation method of this invention includes the steps of forming a resist film on a substrate; performing pattern exposure by selectively irradiating the resist film with exposing light with an immersion liquid including cyclodextrin provided on the resist film; and developing the resist film after the pattern exposure.  
      In the third pattern formation method, since the immersion liquid provided on the resist film includes cyclodextrin, the hydrophilic property of the surface of the resist film is improved owing to a hydrophilic group of the cyclodextrin, and therefore, the adhesion to the resist film of the immersion liquid is improved. Therefore, since a necessary exposure region is sufficiently covered with the immersion liquid provided on the resist film, the immersion liquid definitely transmits the exposing light. As a result, abnormal exposure can be prevented, so that a resist pattern can be formed in a good shape by the immersion lithography. In the third pattern formation method, the immersion liquid preferably includes water.  
      The concentration of the acid compound or the surface active agent is appropriately approximately 10 −4  wt % or more and 10 −2  wt % or less, which does not limit the invention.  
      Also, the concentration of cyclodextrin is appropriately approximately 10 −3  wt % or more and 1 wt % or less, which does not limit the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1A, 1B  and  1 C are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 1 of the invention;  
       FIGS. 2A and 2B  are cross-sectional views for showing other procedures in the pattern formation method of Embodiment 1;  
       FIGS. 3A and 3B  are diagrams for showing the adhesion between a resist film and an immersion liquid, and specifically,  FIG. 3A  is a cross-sectional view obtained when the adhesion is low and  FIG. 3B  is a cross-sectional view obtained when the adhesion is high;  
       FIGS. 4A, 4B  and  4 C are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 2 of the invention;  
       FIGS. 5A and 5B  are cross-sectional views for showing other procedures in the pattern formation method of Embodiment 2;  
       FIGS. 6A, 6B  and  6 C are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 3 of the invention;  
       FIGS. 7A and 7B  are cross-sectional views for showing other procedures in the pattern formation method of Embodiment 3;  
       FIGS. 8A, 8B ,  8 C and  8 D are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 4 of the invention;  
       FIGS. 9A, 9B ,  9 C and  9 D are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 5 of the invention;  
       FIGS. 10A, 10B ,  10 C and  10 D are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 6 of the invention;  
       FIGS. 11A, 11B ,  11 C and  11 D are cross-sectional views for showing procedures in a pattern formation method according to Embodiment 7 of the invention; and  
       FIGS. 12A, 12B ,  12 C and  12 D are cross-sectional views for showing procedures in a conventional pattern formation method. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     EMBODIMENT 1  
      A pattern formation method according to Embodiment 1 of the invention will now be described with reference to  FIGS. 1A through 1C ,  2 A and  2 B.  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 1A , the aforementioned chemically amplified resist material is applied on a substrate  101  so as to form a resist film  102  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 1B , a surface reforming treatment for improving the hydrophilic property of the surface of the resist film  102  is performed by exposing the surface of the resist film  102  to an aqueous solution  103  of acetic acid with a concentration of approximately 3×10 −3  wt % for 15 seconds by, for example, a puddle method.  
      Next, as shown in  FIG. 1C , with an immersion liquid  104  of water provided between the resist film  102  and a projection lens  106 , pattern exposure is carried out by irradiating the resist film  102  with exposing light  105  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 2A , the resist film  102  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  102   a  made of an unexposed portion of the resist film  102  and having a line width of 0.09 μm is formed as shown in  FIG. 2B .  
      In this manner, according to the pattern formation method of Embodiment 1, the surface of the resist film  102  is exposed to the aqueous solution  103  of acetic acid having a carboxyl group (—COOH), that is, a hydrophilic group, before the pattern exposure, and hence, the hydrophilic property of the surface of the resist film  102  is improved by the carboxyl group. Therefore, the adhesion to the resist film  102  of the immersion liquid  104  provided on the resist film  102  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  104  provided on the resist film  102 , and hence, the immersion liquid  104  definitely transmits the exposing light  105 . As a result, the resist pattern  102   a  made of the resist film  102  can be formed in a good shape by the immersion lithography.  
      The acid compound included in the aqueous solution  103  is not limited to acetic acid but may be trifluoromethylsulfonic acid, nonafluorobutylsulfonic acid, perfluorooctylsulfonic acid or the like.  
       FIG. 3A  shows a contact angle θ 1  of an immersion liquid  104  against a first resist film  102 A on the first resist film  102 A having comparatively low affinity against the immersion liquid  104 , and  FIG. 3B  shows a contact angle θ 2  of an immersion liquid  104  against a second resist film  102 B on the second resist film  102 B having affinity against the immersion liquid  104  higher than the first resist film  102 A. In this case, a contact angle θ means an angle between the surface of a resist film and the liquid surface of an immersion liquid at the boundary therebetween.  
      As shown in  FIGS. 3A and 3B , as the affinity between the immersion liquid  104  and the second resist film  102 B is higher, the contact angle θ of the immersion liquid against the surface of the resist film is larger (i.e., θ 2 &gt;&gt;θ 1 ). Thus, a difference in the contact angle θ corresponds to a difference in the affinity between the immersion liquid and the resist film.  
     EMBODIMENT 2  
      A pattern formation method according to Embodiment 2 of the invention will now be described with reference to  FIGS. 4A through 4C ,  5 A and  5 B.  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 4A , the aforementioned chemically amplified resist material is applied on a substrate  201  so as to form a resist film  202  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 4B , the surface reforming treatment for improving the hydrophilic property of the surface of the resist film  202  is performed by exposing the surface of the resist film  202  to an aqueous solution  203  of benzylmethylammonium chloride, that is, a surface active agent, with a concentration of approximately 7×10 −3  wt % for 30 seconds by, for example, the puddle method.  
      Next, as shown in  FIG. 4C , with an immersion liquid  204  of water provided between the resist film  202  and a projection lens  206 , pattern exposure is carried out by irradiating the resist film  202  with exposing light  205  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 5A , the resist film  202  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  202   a  made of an unexposed portion of the resist film  202  and having a line width of 0.09 μm is formed as shown in  FIG. 5B .  
      In this manner, according to the pattern formation method of Embodiment 2, the surface of the resist film  202  is exposed to the aqueous solution  203  of benzylmethylammonium chloride, that is, a surface active agent, before the pattern exposure, and hence, the hydrophilic property of the surface of the resist film  202  is improved by a hydrophilic group of the surface active agent. Therefore, the adhesion to the resist film  202  of the immersion liquid  204  provided on the resist film  202  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  204  provided on the resist film  202 , and hence, the immersion liquid  204  definitely transmits the exposing light  205 . As a result, the resist pattern  202   a  made of the resist film  202  can be formed in a good shape by the immersion lithography.  
      The surface active agent included in the aqueous solution  203  may be a nonionic surface active agent instead of benzylmethylammonium chloride, that is, a cationic surface active agent.  
      Examples of the cationic surface active agent are, apart from benzylmethylammonium chloride, cetylmethylammonium chloride, stearylmethylammonium chloride, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, distearyldimethylammonium chloride, stearyldimethylbenzylammonium chloride, dodecylmethylammonium chloride, dodecyltrimethylammonium chloride, benzyltrimethylammonium chloride, and benzalkonium chloride.  
      Also, examples of the nonionic surface active agent are nonyl phenol ethoxylate, octylphenyl polyoxyethylene ether, lauryl polyoxyethylene ether, cetyl polyoxyethylene ether, sucrose fatty ester, polyoxyethylene lanolin fatty ester, polyoxyethylene sorbitan fatty ester, polyoxyethylene glycol mono fatty ester, fatty monoethanolamide, fatty diethanolamide and fatty triethanolamide.  
     EMBODIMENT 3  
      A pattern formation method according to Embodiment 3 of the invention will now be described with reference to  FIGS. 6A through 6C ,  7 A and  7 B.  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 6A , the aforementioned chemically amplified resist material is applied on a substrate  301  so as to form a resist film  302  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 6B , the surface reforming treatment for improving the hydrophilic property of the surface of the resist film  302  is performed by exposing the surface of the resist film  302  to an aqueous solution  303  of α-cyclodextrin with a concentration of approximately 5×10 −3  wt % for 25 seconds by, for example, the puddle method.  
      Next, as shown in  FIG. 6C , with an immersion liquid  304  of water provided between the resist film  302  and a projection lens  306 , pattern exposure is carried out by irradiating the resist film  302  with exposing light  305  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 7A , the resist film  302  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  302   a  made of an unexposed portion of the resist film  302  and having a line width of 0.09 μm is formed as shown in  FIG. 7B .  
      In this manner, according to the pattern formation method of Embodiment 3, the surface of the resist film  302  is exposed to the aqueous solution  303  of cyclodextrin having a hydroxyl group (—OH) before the pattern exposure, and hence, the hydrophilic property of the surface of the resist film  302  is improved owing to the hydroxyl group of the cyclodextrin. Therefore, the adhesion to the resist film  302  of the immersion liquid  304  provided on the resist film  302  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  304  provided on the resist film  302 , and hence, the immersion liquid  304  definitely transmits the exposing light  305 . As a result, the resist pattern  302   a  made of the resist film  302  can be formed in a good shape by the immersion lithography.  
      The cyclodextrin included in the aqueous solution  303  is not limited to α-cyclodextrin but may be β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin or the like.  
     EMBODIMENT 4  
      A pattern formation method according to Embodiment 4 of the invention will now be described with reference to  FIGS. 8A through 8D .  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Acid compound: acetic acid   0.05 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 8A , the aforementioned chemically amplified resist material is applied on a substrate  401  so as to form a resist film  402  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 8B , with an immersion liquid  404  of water provided between the resist film  402  and a projection lens  406 , pattern exposure is carried out by irradiating the resist film  402  with exposing light  405  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 8C , the resist film  402  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  402   a  made of an unexposed portion of the resist film  402  and having a line width of 0.09 μm is formed as shown in  FIG. 8D .  
      In this manner, according to the pattern formation method of Embodiment 4, the resist film  402  includes acetic acid, and hence, the hydrophilic property of the surface of the resist film  402  is improved owing to a carboxyl group of the included acetic acid. Therefore, the adhesion to the resist film  402  of the immersion liquid  404  provided on the resist film  402  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  404  provided on the resist film  402 , and hence, the immersion liquid  404  definitely transmits the exposing light  405 . As a result, the resist pattern  402   a  made of the resist film  402  can be formed in a good shape by the immersion lithography.  
      The acid compound included in the resist film  402  is not limited to acetic acid but may be trifluoromethylsulfonic acid, nonafluorobutylsulfonic acid, perfluorooctylsulfonic acid or the like.  
     EMBODIMENT 5  
      A pattern formation method according to Embodiment 5 of the invention will now be described with reference to  FIGS. 9A through 9D .  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Surface active agent: octylphenyl polyoxyethylene ether   0.07 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 9A , the aforementioned chemically amplified resist material is applied on a substrate  501  so as to form a resist film  502  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 9B , with an immersion liquid  504  of water provided between the resist film  502  and a projection lens  506 , pattern exposure is carried out by irradiating the resist film  502  with exposing light  505  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 9C , the resist film  502  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  502   a  made of an unexposed portion of the resist film  502  and having a line width of 0.09 μm is formed as shown in  FIG. 9D .  
      In this manner, according to the pattern formation method of Embodiment 5, the resist film  502  includes octylphenyl polyoxyethylene ether, that is, a nonionic surface active agent, and hence, the hydrophilic property of the surface of the resist film  502  is improved owing to a hydrophilic group of the included surface active agent. Therefore, the adhesion to the resist film  502  of the immersion liquid  504  provided on the resist film  502  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  504  provided on the resist film  502 , and hence, the immersion liquid  504  definitely transmits the exposing light  505 . As a result, the resist pattern  502   a  made of the resist film  502  can be formed in a good shape by the immersion lithography.  
      The surface active agent included in the resist film  502  is not limited to octylphenyl polyoxyethylene ether but may be any of the cationic surface active agents and the nonionic surface active agents described in Embodiment 2.  
     EMBODIMENT 6  
      A pattern formation method according to Embodiment 6 of the invention will now be described with reference to  FIGS. 10A through 10D .  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Compound having hydrophilic group: β-cyclodextrin   0.05 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 10A , the aforementioned chemically amplified resist material is applied on a substrate  601  so as to form a resist film  602  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 10B , with an immersion liquid  604  of water provided between the resist film  602  and a projection lens  606 , pattern exposure is carried out by irradiating the resist film  602  with exposing light  605  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 10C , the resist film  602  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  602   a  made of an unexposed portion of the resist film  602  and having a line width of 0.09 μm is formed as shown in  FIG. 10D .  
      In this manner, according to the pattern formation method of Embodiment 6, the resist film  602  includes cyclodextrin having a hydroxyl group, and hence, the hydrophilic property of the surface of the resist film  602  is improved owing to the hydroxyl group of the cyclodextrin. Therefore, the adhesion to the resist film  602  of the immersion liquid  604  provided on the resist film  602  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  604  provided on the resist film  602 , and hence, the immersion liquid  604  definitely transmits the exposing light  605 . As a result, the resist pattern  602   a  made of the resist film  602  can be formed in a good shape by the immersion lithography.  
      The cyclodextrin included in the resist film  602  is not limited to β-cyclodextrin but may be α-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin or the like.  
      Furthermore, also in each of Embodiments 4 through 6, not only the compound having a hydrophilic group is included in the resist material but also a surface reforming treatment for further improving the hydrophilic property between the surface of the resist film and the immersion liquid may be performed by exposing the surface of the obtained resist film to an aqueous solution including a compound having a hydrophilic group, namely, an aqueous solution including an acid compound, a surface active agent or cyclodextrin.  
     EMBODIMENT 7  
      A pattern formation method according to Embodiment 7 of the invention will now be described with reference to  FIGS. 11A through 11D .  
      First, a positive chemically amplified resist material having the following composition is prepared:  
                                      Base polymer: poly((norbornene-5-methylene-t-     2 g       butylcarboxylate) (50 mol %) - (maleic anhydride) (50 mol %))       Acid generator: triphenylsulfonium triflate   0.06 g       Solvent: propylene glycol monomethyl ether acetate     20 g                  
 
      Next, as shown in  FIG. 11A , the aforementioned chemically amplified resist material is applied on a substrate  701  so as to form a resist film  702  with a thickness of 0.35 μm.  
      Then, as shown in  FIG. 11B , with an immersion liquid  704  of an aqueous solution including γ-cyclodextrin with a concentration of approximately 3×10 −2  wt % provided between the resist film  702  and a projection lens  706 , pattern exposure is carried out by irradiating the resist film  702  with exposing light  705  of ArF excimer laser with NA of 0.68 through a mask (not shown).  
      After the pattern exposure, as shown in  FIG. 11C , the resist film  702  is baked with a hot plate at a temperature of 110° C. for 60 seconds, and the resultant resist film is developed with a 2.38 wt % tetramethylammonium hydroxide aqueous solution (alkaline developer). In this manner, a resist pattern  702   a  made of an unexposed portion of the resist film  702  and having a line width of 0.09 μm is formed as shown in  FIG. 11D .  
      In this manner, according to the pattern formation method of Embodiment 7, the immersion liquid  704  includes cyclodextrin having a hydroxyl group, and hence, the cyclodextrin is coordinated on the surface of the resist film  702  so as to improve the hydrophilic property of the surface of the resist film  702  owing to the hydroxyl group. Therefore, the adhesion to the resist film  702  of the immersion liquid  704  provided on the resist film  702  in the pattern exposure can be improved. Accordingly, a necessary exposure region can be sufficiently covered with the immersion liquid  704  provided on the resist film  702 , and hence, the immersion liquid  704  definitely transmits the exposing light  705 . As a result, the resist pattern  702   a  made of the resist film  702  can be formed in a good shape by the immersion lithography.  
      The cyclodextrin included in the immersion liquid  704  is not limited to γ-cyclodextrin but may be α-cyclodextrin, β-cyclodextrin, δ-cyclodextrin or the like.  
      Also in Embodiment 7, not only the cyclodextrin is included in the immersion liquid  704  but also the hydrophilic property between the surface of the resist film and the immersion liquid may be further improved by exposing, before the pattern exposure, the surface of the resist film to an aqueous solution including a compound having a hydrophilic group, namely, an aqueous solution including an acid compound, a surface active agent or cyclodextrin, or by adding such a compound having a hydrophilic group to the resist material.  
      On the contrary, also in each of Embodiments 1 through 6, a compound having a hydrophilic group may be included in the immersion liquid.  
      The method employed for exposing the surface of the resist film to the aqueous solution including the compound having a hydrophilic group is not limited to the puddle method but may be a dip method or a spray method.  
      A positive chemically amplified resist is used as the resist material in each embodiment, which does not limit invention, and it goes without saying that the invention is applicable to a negative resist material.  
      Also, the exposing light used in the pattern exposure is not limited to the ArF excimer laser but may be KrF excimer laser, F 2  laser, KrAr laser or Ar 2  laser.  
      As described so far, in the pattern formation method of this invention, the adhesion to a resist film of an immersion liquid provided on the resist film is improved so as to prevent abnormal exposure, resulting in forming a resist pattern in a good shape. Therefore, the invention is useful as a pattern formation method for use in fabrication process for semiconductor devices.