Patent ID: 7781125

Claim:
A halftone phase shift mask blank used as a material for manufacturing a halftone phase shift mask comprising: a substrate, a light-semitransmissive film having a required transmittance and phase shift amount and formed on said substrate, said light-semitransmissive film being one of (1) a single-layer structure containing a metal, silicon and nitrogen or (2) a multi-layer structure having an upper layer in a direction away from said substrate that contains a metal, silicon and nitrogen, and an ammonium ion production preventing layer for preventing production of ammonium ions, which is formed with an oxidation of one of (1) a surface portion of said light-semitransmissive film of the single-layer structure or (2) a surface portion of said upper layer in said light-semitransmissive film of the multi-layer structure, respectively, so as to contain a metal, silicon, nitrogen and oxygen and which is exposed on the surface of said mask after said mask is manufactured, said ammonium ion production preventing layer being less in nitrogen content (1) relative to said light-semitransmissive film other than the surface portion in said single-layer structure or (2) relative to said upper layer other than the surface portion in said multi-layer structure, respectively.