Highly sensitive positive photoresist compositions

Abstract

Positive resists sensitive to UV, electron beam, and x-ray radiation which are alkaline developable are formulated from a polymer material comprising recurrent structures having alkaline soluble groups pendent to the polymer backbone, a portion of which groups are substituted with acid labile groups.

We claim:  
     
         1 . An improved positive working resist composition comprising a polymeric material having functional groups pendent thereto which contribute to the solubility of the polymer in alkaline developers and a portion of which functional groups are substituted with acid labile groups which inhibit the alkaline solubility of the polymer, and a photoinitiator which generates a strong acid upon radiolysis to remove the acid labile groups from the functional groups in the exposed areas of the polymer.  
     
     
         2 . The resist composition of    claim 1    wherein the polymeric material comprises an aromatic polymer.  
     
     
         3 . The resist composition of    claim 2    wherein the aromatic material is a polystyrene.  
     
     
         4 . The resist composition of    claim 1    wherein the alkaline soluble functional groups are selected from the group consisting of hydroxyl, amine, carboxyl, and imide NH.  
     
     
         5 . The resist composition of    claim 4    wherein the alkaline soluble functional group is hydroxyl.  
     
     
         6 . The resist composition of    claim 1    wherein the acid labile group is selected from the group of alkyloxycarbonyl, aryloxycarbonyloxy, and alkyloxycarbonyloxy.  
     
     
         7 . The resist composition of    claim 6    wherein the alkyl portion of the acid labile group has an available hydrogen on an a carbon atom.  
     
     
         8 . The resist composition of    claim 7    where the alkyl portion of the acid labile group is secondary alkyl or tertiary alkyl.  
     
     
         9 . The resist composition of    claim 1    wherein from about 20% to about 50% of the pendent groups are substituted with acid labile groups.  
     
     
         10 . The resist composition of    claim 1    wherein the polymer is a polystyrene, the functional group is hydroxyl, and the acid labile group is a secondary or tertiary alkyloxy carbonyloxy group.  
     
     
         11 . The resist composition of    claim 11    wherein the polymer is a p-hydroxystyrene and the acid labile group is t-butyloxycarbonyloxy.  
     
     
         12 . The method of making a substituted polymeric material for use in resist compositions, comprising the steps of: 
 (a) dissolving a polymer having acid labile groups pendent to the polymer backbone thereof in an acid stable solvent,    (b) heating the solution with stirring under an unreactive atmosphere to a temperature in the range 20 to 70° C.,    (c) adding concentrated mineral acid to the stirred solution in an amount sufficient to remove acid labile groups from the polymer,    (d) continuing the reaction until the desired degree of substitution is achieved,    (e) quenching the reaction with base, and    (f) precipitating the substituted polymeric material.    
     
     
         13 . The method of    claim 12    wherein the polymer is polystyrene.  
     
     
         14 . The method of    claim 12    wherein the acid labile groups are selected from the group consisting of alkyloxycarbonyl, aryloxycarbonyloxy and alkyloxycarbonyloxy.  
     
     
         15 . The method of    claim 14    wherein the alkyl portion of the acid labile group has an available hydrogen on an α carbon atom.  
     
     
         16 . The method of    claim 15    wherein the alkyl portion of the acid labile group is secondary alkyl or tertiary alkyl.  
     
     
         17 . The method of    claim 16    wherein the acid labile group is t-butyloxycarbonyloxy.  
     
     
         18 . The method fo    claim 12    wherein the pKa of the acid is less than about 4.  
     
     
         19 . The method of    claim 18    wherein the mineral acid is sulfuric acid.  
     
     
         20 . The method of    claim 12    wherein the reaction temperature is in the range of 50-60° C.  
     
     
         21 . The method of    claim 12    wherein the reaction is quenched with ammonium hydroxide.  
     
     
         22 . The method of    claim 12    wherein the substituted polymeric material is precipitated in ammonium acetate.