Selected high thermal novolaks and positive-working radiation-sensitive compositions

A positive-working photoresist composition, comprising the admixture of:

• (a) a high thermal alkali-soluble novolak binder resin comprising the addition-condensation reaction product of a phenolic mixture with at least one aldehyde source, the feedstock said phenolic mixture for said reaction comprising:
• (1) about 25 to about 40 weight percent of said phenolic mixture being a monomer selected from meta-cresol, 2,5-xylenol and the combination thereof;
• (2) about 40 to about 70 weight percent of said phenolic mixture being para-cresol;
• and
• (3) about 3 to about 20 weight percent of said phenolic mixture being acetamidophenol;
• all percentages based on the weight of the total phenolic monomer feedstock;
• (b) at least one o-quinone photoactive compound, the amount of said photoactive compound or compounds being 10 to 60 percent by weight of said novolak binder resin;
• and
• (c) at least one solvent;
• the high thermal property of the novolak binder resin being obtained without the necessity for fractionation of the novolak binder resin.