Phenol novolak resin, production process thereof, and positive photoresist composition using the same

Abstract

A phenol novolak resin has a peak intensity ratio of ortho-ortho bond (o-o)/ortho-para bond (o-p)/para-para bond (p-p) in a resin structure not substantially varying in each molecular weight fraction and has a weight average molecular weight (Mw) of 3000 to 20000 in terms of polystyrene, which peak intensity ratio is detected by 13 C-NMR analysis. The phenol novolak resin can form both dense pattern and isolation pattern with good shapes in the formation of a fine resist pattern of not more than 0.35 μm and has satisfactory sensitivity, definition, and focal depth range properties, and has a resin composition being uniform in each molecular weight fraction. A process for producing the phenol novolak resin, and a positive photoresist composition using the resin are also provided.

What is claimed is:  
     
         1 . A phenol novolak resin: 
 having a peak intensity ratio of ortho-ortho bond (o-o)/ortho-para bond (o-p)/para-para bond (p-p) not substantially varying in each molecular weight fraction, said peak intensity ratio being detected in a resin structure by  13 C-NMR analysis; and    having a weight average molecular weight (Mw) of 3000 to 20000 in terms of polystyrene.    
     
     
         2 . A phenol novolak resin according to    claim 1   , comprising at least two selected from phenol constitutional units represented by the following formulae (I) to (IV):  
                   
     
     
         3 . A phenol novolak resin: 
 having a peak intensity ratio of ortho-ortho bond (o-o)/ortho-para bond (o-p)/para-para bond (p-p) in a range of 3.0-5.0/2.0-3.5/1, said peak intensity ratio being detected in a resin structure by  13 C-NMR analysis and not substantially varying in each molecular weight fraction;    comprising phenol constitutional units represented by the formulae (I) and (III) as defined in    claim 1    and the following formula (V); and    having a weight average molecular weight (Mw) of 3000 to 20000 in terms of polystyrene.  
                 
   
     
     
         4 . A phenol novolak resin: 
 having a peak intensity ratio of ortho-ortho bond (o-o)/ortho-para bond (o-p)/para-para bond (p-p) in a range of 5.0-8.5/2.5-4.5/1, said peak intensity ratio being detected in a resin structure by  13 C-NMR analysis;    comprising phenol constitutional units represented by the formulae (I) and (II) as defined in    claim 1    and the following formula (VI); and    having a weight average molecular weight (Mw) of 3000 to 20000 in terms of polystyrene.  
                 
   
     
     
         5 . A phenol novolak resin according to any one of    claims 1    to    3   , wherein a ratio of the peak intensities of para-para bond (p-p) to the total of the peak intensities of ortho-ortho bond, ortho-para bond, and para-para bond [(o-o)+(o-p)+(p-p)] is in a range of 10% to 20%.  
     
     
         6 . A phenol novolak resin according to    claim 4   , wherein a ratio of the peak intensities of para-para bond (p-p) to the total of the peak intensities of ortho-ortho bond, ortho-para bond, and para-para bond [(o-o)+(o-p)+(p-p)] is in a range of 5% to 15%.  
     
     
         7 . A phenol novolak resin according to any one of    claims 1    to    6   , wherein a resin film formed by the use of the phenol novolak resin dissolves in a 2.38% by weight aqueous tetramethylammonium hydroxide solution at 25° C. at a rate of 0.01 to 0.001 μm/s.  
     
     
         8 . A process for producing a phenol novolak resin, comprising the steps of: 
 (a) subjecting a phenol to a polycondensation reaction in the presence of an acid catalyst;    (b) removing water from a reaction system;    (c) decomposing, in the presence of an acid catalyst, the polycondensation product obtained in the step (a); and    (d) subjecting the resulting product to a polycondensation reaction with an aldehyde or a ketone.    
     
     
         9 . A positive photoresist composition comprising a phenol novolak resin according to any one of    claims 1    to    7   , and a 1,2-naphthoquinonediazide-group-containing compound.