Method of removing resist mask and a method of manufacturing semiconductor device

A method of removing a resist mask on a substrate comprising the steps of:

• (a) forming a mask comprising organic material on a surface layer of a substrate;
• (b) implanting impurity ions into the surface layer through openings in the mask as well as into a surface layer of said mask thereby reacting said impurity ions with a surface portion of said mask and thereby forming a hard layer on a surface of said mask while leaving a substantially unreacted layer of said mask under said hard layer;
• and
• (c) removing the mask by sequentially:
• (1) exposing the mask to a plasma activated gas containing hydrogen under conditions sufficient to vaporize said hard layer and thereby initiate removal of said mask,
• (2) after removal of said hard layer, exposing the mask to a plasma activated gas containing oxygen under conditions sufficient to remove said unreacted layer;
• and
• wherein, after said unreacted layer has been removed by said plasma activated gas containing oxygen to thereby completely remove said mask, aluminum oxide residues are left,
• (3) after removal of said mask by said oxygen, exposing said remaining aluminum oxide residues to a wet solution comprising an etchant consisting essentially of nitric acid under conditions sufficient to cause said nitric acid to remove said aluminum oxide residues.