Disclosed is a positive-working chemical-amplification photoresist
composition used in the patterning works in the manufacture of
semiconductor devices, with which quite satisfactory patterning of a
photoresist layer can be accomplished even on a substrate surface
provided with an undercoating film of silicon nitride, phosphosilicate
glass, borosilicate glass and the like in contrast to the prior art using
a conventional photoresist composition with which satisfactory patterning
can hardly be accomplished on such an undercoating film. The photoresist
composition comprises, besides a film-forming resin capable of being
imparted with increased solubility in an alkaline solution by interacting
with an acid and a radiation-sensitive acid-generating compound, a
phosphorus-containing oxo acid such as phosphoric acid and phosphonic
acid or an ester thereof.