Photomask blank, resist pattern forming process, and photomask preparation process

Abstract

A photomask blank has a resist film comprising (A) a base resin, (B) an acid generator, and (C) a basic compound. The resist film further comprises (D) a polymer comprising recurring units having a side chain having a fluorinated hydrocarbon group which contains a carbon atom to which a hydroxyl group is bonded and vicinal carbon atoms bonded thereto, the vicinal carbon atoms having in total at least two fluorine atoms bonded thereto. Addition of polymer (D) ensures uniform development throughout the resist film, enabling to form a resist pattern having high CD uniformity.

1 . A photomask blank comprising a resist film deposited thereon, said resist film comprising
 (A) a base resin which is insoluble in an aqueous alkaline solution, but turns to be soluble in an aqueous alkaline developer under the action of an acid,   (B) an acid generator,   (C) a basic compound, and   (D) a polymer comprising first recurring units having a side chain having a first fluorinated hydrocarbon group bearing a hydroxyl group which contains the carbon atom to which the hydroxyl group is bonded and vicinal carbon atoms bonded thereto, the vicinal carbon atoms having in total at least two fluorine atoms bonded thereto.   
   
   
       2 . The photomask blank of  claim 1  wherein the polymer (D) functions such that the contact angle with neutral water of a resist film comprising components (A) to (D) is larger than the contact angle of a resist film comprising components (A) to (C) and free of component (D). 
   
   
       3 . The photomask blank of  claim 1  wherein the base resin (A) comprises recurring units having an aromatic structure. 
   
   
       4 . The photomask blank of  claim 1  wherein the polymer (D) includes main recurring units in which atoms forming the polymerized main chain are not part of a cyclic structure. 
   
   
       5 . The photomask blank of  claim 1  wherein the first recurring units of the polymer (D) have the general formula (1) or (2): 
     
       
         
         
             
             
         
       
     
     wherein R 1  and R 2  are each independently hydrogen or a straight, branched or cyclic C 1 -C 6  alkyl group, or R 1  and R 2  may bond together to form a ring, a combination of R 1  and R 2  standing for a divalent organic group of 2 to 12 carbon atoms in total,
 R 3  and R 4  are each independently hydrogen or methyl, 
 R 5  is a straight, branched or cyclic C 1 -C 6  alkylene group in which at least one hydrogen atom may be substituted by a fluorine atom, R 6  is independently a straight or branched C 1 -C 10  alkyl group in which at least one hydrogen atom is substituted by a fluorine atom, or R 5  and R 6  may bond together to form a ring, a combination of R 5  and R 6  standing for a trivalent organic group of 2 to 12 carbon atoms in total, and 
 X 1  is —C(═O)—, —C(═O)—O—, —O—, —C(═O)—R 7 —C(═O)—, or —C(═O)—O—R 7 —C(═O)—O— wherein R 7  is a straight, branched or cyclic C 1 -C 10  alkylene group. 
 
   
   
       6 . The photomask blank of  claim 1  wherein the polymer (D) further comprises second recurring units having a side chain having a second fluorinated hydrocarbon group different from the first fluorinated hydrocarbon group and free of the first fluorinated hydrocarbon group. 
   
   
       7 . The photomask blank of  claim 6  wherein the second recurring units of the polymer (D) have the general formula (3): 
     
       
         
         
             
             
         
       
     
     wherein R 8  is independently hydrogen or methyl, R 9  is a straight, branched or cyclic C 1 -C 10  alkyl group in which at least one hydrogen atom is substituted by a fluorine atom, and X 2  is —C(═O)—, —C(═O)—O—, —O—, —C(═O)—R 10 —C(═O)—, or —C(═O)—O—R 10 —C(═O)—O— wherein R 10  is a straight, branched or cyclic C 1 -C 10  alkylene group. 
   
   
       8 . The photomask blank of  claim 1  wherein a pattern is written on the resist film by electron beam lithography. 
   
   
       9 . A process for forming a resist pattern using a workpiece having a resist film deposited thereon,
 said resist film comprising   (A) a base resin which is insoluble in an aqueous alkaline solution, but turns to be soluble in an aqueous alkaline developer under the action of an acid,   (B) an acid generator,   (C) a basic compound, and   (D) a polymer comprising first recurring units having a side chain having a first fluorinated hydrocarbon group bearing a hydroxyl group which contains the carbon atom to which the hydroxyl group is bonded and vicinal carbon atoms bonded thereto, the vicinal carbon atoms having in total at least two fluorine atoms bonded thereto,   said process comprising the steps of irradiating high-energy radiation to the resist film in the absence of a liquid, and developing the resist film with an aqueous alkaline developer.   
   
   
       10 . The process of  claim 9  wherein the polymer (D) functions such that the contact angle with neutral water of a resist film comprising components (A) to (D) is larger than the contact angle of a resist film comprising components (A) to (C) and free of component (D). 
   
   
       11 . The process of  claim 9  wherein the high-energy radiation is a high-energy beam. 
   
   
       12 . The process of  claim 11  wherein the high-energy radiation is an electron beam. 
   
   
       13 . A process for preparing a photomask, comprising the steps of forming a resist pattern in accordance with the process of  claim 9  wherein the workpiece is a photomask blank, and etching the photomask blank through the resist pattern as an etching mask.