Photolithographic mask having half tone main features and perpendicular half tone assist features

A photolithographic mask for the exposure of a radiation-sensitive resist layer on a semiconductor substrate, the photolithographic mask comprising:

• at least one radiation-transmissive substrate, at least one radiation-opaque layer, and at least one half tone layer,
• the radiation-opaque layer and the at least one half-tone layer being used to provide main features, the main features being formed in such a way that the pattern formed by the main features is transferred into the resist layer when irradiated;
• and
• the radiation-opaque layer and the at least one half-tone layer are used to provide assist features, the assist features being formed in such a way that the pattern formed by the assist features is not transferred into the resist layer when irradiated,
• wherein for one main feature, which is oriented in a first direction at least in the region of a partial piece, there are at least two assist features, which, adjacent to the partial piece, are oriented in a second direction which is substantially perpendicular to the first direction,
• wherein a distance x of the assist features from the main features lies in the range λ/(5 NA)<x<2λ/(3 NA).