A lithographic
mask having a
mask substrate (3) and a patterned
mask layer (4) which includes mask structures (5) and can be transferred by
lithography to a further substrate is disclosed. With masks of this type, it is customary for a protective layer to be provided in the form of a membrane positioned at a distance from the
mask layer (4), in order to keep
impurity particles or other impurities away from the focal plane of the
mask layer (4). According to the invention, the protective layer (6) is applied in liquid form directly to the mask structures (5) and fills up spaces between the mask structures (4). Then, the protective layer (6), while it is still in the
liquid state, is covered with a plane-
parallel plate. The continuously dense protective layer (6) which is formed in accordance with the invention is even more reliable in preventing
impurity particles or impurities (20) from penetrating into spacers between the structures (5) of the
mask layer (4). The
impurity particles or impurities (20) can only be deposited on the outer side (16) of the protective layer (6), at a still greater distance from the focal plane.