Lithographic process for reducing the lateral chromium structure loss in photomask production using chemically amplified resists

A process for producing photomasks for optical lithography, which comprises the steps of:

• providing a transparent substrate;
• applying a layer of a mask material on the transparent substrate;
• applying a layer of photoresist on the layer of the mask material, the photoresist comprising:
• a film-forming polymer containing acid-labile groups to be cleaved under action of acid for liberating groups resulting in an increase in solubility of the film-forming polymer in aqueous alkaline developers, and further containing anchor groups for linkage of amplification agents;
• a photo acid generator;
• and
• a solvent;
• heating the layer of the photoresist to remove the solvent resulting in a photoresist film being obtained;
• writing a structure in the photoresist film using a focused electron beam resulting in an exposed photoresist film having exposed parts, in which a strong acid is liberated from the photo acid generator, and unexposed parts, in which no acid has been liberated;
• heating the exposed phototresist film so that, in the exposed parts, acid-labile groups on the film-forming polymer are cleaved and polar groups are liberated resulting in a contrasted resist film being obtained;
• developing the contrasted resist film using a developer resulting in a structured resist having lands and trenches disposed between the lands and in which the mask material is bare;
• adding an amplification agent to the structured resist, the amplification agent having at least one reactive group which can react with the anchor groups of the film-forming polymer resulting in the amplification agent bonding to the film- forming polymer contained in the lands, so that an amplified resist is obtained;
• removing any excess amplification agent;
• and
• etching away bare mask material resulting in the structure being transferred to the layer of the mask material.