Positive resist composition

Abstract

Disclosed is an improved, chemically-amplifying positive resist composition for radiations, especially UV rays, deep-UV rays, excimer laser beams, X-rays, electron beams. The composition comprises (A) a resin component whose solubility in an alkaline aqueous solution is increased by the action of acids, (B) a chemical compound which generates an acid when exposed to radiations, and (C) an organic carboxylic acid compound and (D) an amine, in which said resin component (A) is a mixture comprising (a) a polyhydroxystyrene having a weight-average molecular weight of from 8,000 to 25,000 and a molecular weight distribution (M w /M n ) of 1.5 or less where from 10 to 60 mol % of the hydroxyl groups have been substituted by residues of a general formula (I): wherein R 1 represents a hydrogen atom or a methyl group, R 2 represents a methyl group or an ethyl group, and R 3 represents a lower alkyl group having 1 to 4 carbon atoms; and (b) a polyhydroxystyrene having a weight-average molecular weight of from 8,000 to 25,000 and a molecular weight distribution (M w /M n ) of 1.5 or less where from 10 to 60 mol % of the hydroxyl groups have been substituted by tert-butoxycarbonyloxy groups. The composition has a high sensitivity, a high resolution, high heat resistance, good width characteristic in focus depth and good post-exposure storage stability, has good storage stability as a resist solution, and gives resist patterns with good profiles, without depending on the substrate to which it is applied. The composition is useful for forming fine patterns in producing ultra-LSIs.

What is claimed is:  
     
       1. A positive resist composition comprising a mixture of (A) a resin component whose solubility in an alkaline aqueous solution is increased by the action of acids, (B) a chemical compound which generates an acid when exposed to radiations, (C) an organic carboxylic acid compound and (D) an amine, in which said resin component (A) is a mixture comprising (a) polyhydroxystyrene having a weight-average molecular weight of from 8,000 to 25,000 and a molecular weight distribution (M w /M n ) of 1.5 or less where from 10 to 60 mol % of the hydroxyl groups have been substituted by residues of a general formula (I):                    
       wherein R 1  represents a hydrogen atom or a methyl group, R 2  represents a methyl group or an ethyl group, and R 3  represents a lower alkyl group having 1 to 4 carbon atoms;  
       and (b) a polyhydroxystyrene having a weight-average molecular weight of from 8,000 to 25,000 and a molecular weight distribution (M w /M n ) of 1.5 or less where from 10 to 60 mol % of the hydroxyl groups have been substituted by tert-butoxy-carbonyloxy groups. 
     
     
       2. The positive resist composition as claimed in  claim 1 , in which said component (D) is an aliphatic amine. 
     
     
       3. The positive resist composition as claimed in  claim 1 , in which the proportion of said component (D) is from 0.01 to 1% by weight relative to the component (A). 
     
     
       4. A positive resist composition comprising a mixture of (A) a resin component whose solubility in an alkaline aqueous solution is increased by the action of acids, (B) a chemical compound which generates an acid when exposed to radiations, (C) an organic carboxylic acid compound and (E) an N,N-dialkylcarbarboxyl acid amide in which said resin component (A) is a mixture comprising (a) a polyhydroxystyrene having a weight-average molecular weight of form 8,000 to 25,000 and a molecular weight distribution (M w /M n ) of 1.5 or less where from 10 to 60 mol % of the hydroxyl groups have been substituted by residues of a general formula (I):                    
       wherein R 1  represents a hydrogen atom or a methyl group, R 2  represents a methyl group or an ethyl group, and R 3  represents a lower alkyl group having 1 to 4 carbon atoms;  
       and (b) a polyhydroxystyrene having a weight-average molecular weight of from 8,000 to 25,000 and a molecular weight distribution (M w /M n ) of 1.5 or less where from 10 to 60 mol % of the hydroxyl groups have been substituted by tert-butoxycarbonyloxy groups. 
     
     
       5. The positive resist composition as claimed in  claim 4 , in which said component (E) is dimethylacetamide. 
     
     
       6. The positive resist composition as claimed in  claim 4 , in which the proportion of said component (E) is from 0.1 to 5% by weight relative to the component (A). 
     
     
       7. The positive resist composition as claimed in  claim 1 , which further contains (E) an N,N-dialkylcarbarboxyl acid amide in addition to components (A), (B), (C) and (D). 
     
     
       8. The positive resist composition as claimed in  claim 7 , in which said component (D) is an aliphatic amine and said component (E) is dimethylacetamide. 
     
     
       9. The positive resist composition as claimed in  claim 7 , in which the proportion of said component (D) is from 0.01 to 1% by weight and that of said component (E) is from 0.01 to 5% by weight relative to the component (A). 
     
     
       10. A substituted polyhydroxystyrene resin comprising ( a )  polyhydroxystyrene having a weight - average molecular weight of from  8 , 000  to  25 , 000  and a molecular weight distribution  ( M   w   /M   n )  of  1 . 5  or less where from  10  to  60  mol  %  of the hydroxyl groups have been substituted by residues of a general formula  ( I ):                    
       
         wherein R 
         1  
         represents a hydrogen atom or a methyl group, R 
         2  
         represents a methyl group or an ethyl group, and R 
         3  
         represents a lower alkyl group having  1  to  4  carbon atoms. 
       
     
     
       11. The substituted polyhydroxystyrene resin as claimed in  claim 10  wherein the hydroxyl groups are substituted by  1 - ethoxy - ethoxy groups or  1   - methoxy - n - propoxy groups.   
     
     
       12. A mixture of substituted polyhydroxystyrene resins comprising a mixture of the substituted polyhydroxystyrene ( a )  of    claim 10    and  ( b )  a polyhydroxystyrene having a weight - average molecular weight of from  8 , 000  to  25 , 000  and a molecular weight distribution  ( M   w   /M   n )  of  1 . 5  or less where from  10  to  60  mol  %  of the hydroxyl groups have been substituted by tert - butoxy - carbonyloxy groups.   
     
     
       13. The mixture of substituted polyhydroxystyrene resins ( a )  and  ( b )  as claimed in    claim 12    in which the mixing proportion of the resin  ( a )  to resin  ( b )  is in the range from  30 : 70  to  90 : 10  by weight.   
     
     
       14. The mixture of substituted polyhydroxystyrene resins ( a )  and  ( b )  as claimed in    claim 13    in which the mixing proportion of the resin  ( a )  to resin  ( b )  is in the range from  50 : 50  to  80 : 20  by weight.