Lithographic mask, and method for covering a mask layer

A method for making a mask, the method comprising:

• providing a mask that includes a patterned mask layer, the mask comprising mask structures that can be transferred by lithography;
• forming a protective layer over a surface of a mask substrate on which the patterned mask layer is arranged, the protective layer being formed by applying a material in a liquid state directly onto the mask structures and into spaces between the mask structures;
• and
• covering the protective layer, in the liquid state, with a plane-parallel plate in contact with the protective layer,
• wherein the protective layer has a layer thickness that is at least double a layer thickness of the patterned mask layer.

A method of forming a semiconductor device, the method comprising:

• providing a mask that comprises mask structures arranged on a surface of a mask substrate and a protective layer that overlies and directly contacts the mask structures and fills up spaces between the mask structures, wherein providing the mask comprises forming the mask, the forming comprising covering a protective layer, in a liquid state, with a plane-parallel plate in contact with the protective layer;
• directing electromagnetic radiation toward the mask;
• and
• directing the electromagnetic radiation from the mask toward a semiconductor wafer such that a pattern of the mask structures is transferred to a layer of the semiconductor wafer,
• wherein the protective layer has a layer thickness that is at least double a layer thickness of the patterned mask layer.