Photomask and methods for manufacturing and correcting photomask

A manufacturing method of a photomask using an ArF excimer laser as an exposing source, being used for a projection exposure by an off axis illumination, and comprising on a principal plane of a transparent substrate a main pattern transferred to a transfer-target surface by the projection exposure and an assist pattern formed nearby the main pattern and not transferred to the transfer-target surface;

• wherein the manufacturing method comprises steps of:
• (a) forming a semi-transparent film and a light shielding film sequentially on the principal plane of the transparent substrate, in which the semi-transparent film is a two-layer semi-transparent film and a lower-layer semi-transparent film on the transparent substrate side serves also as an etch stop layer of an upper-layer semi-transparent film, to obtain a film thickness for allowing a retardation of approximately 180° between a light transmitting through the two-layer semi-transparent film and a light transmitting through a transparent region of the transparent substrate;
• (b) forming a first resist pattern on the light shielding film to form a main pattern part and an assist pattern part by sequentially dry-etching the light shielding film and the two-layer semi-transparent film;
• (c) peeling off the first resist pattern to subsequently form a second resist pattern on the light shielding film and remove the light shielding film of the assist pattern part by etching;
• (d) peeling off the second resist pattern to subsequently dry-etch the whole principal plane of the transparent substrate and form the assist pattern by dry-etching the semi-transparent film of the assist pattern part until a film thickness for allowing a predetermined retardation within a scope of 70° to 115° between a light transmitting through the assist pattern and the light transmitting through the transparent region of the transparent substrate is obtained;
• and
• (e) removing the light shielding film of the main pattern part by etching to form the main pattern and generate a retardation of 180° between a light transmitting through the main pattern and the light transmitting through the transparent region of the transparent substrate.