Patent ID: 7761837

Claim:
A method of designing a phase shift mask, wherein the mask comprises at least a trench and light blocking parts, the mask being suitable for lithographic processing of a device using a predetermined illumination dose, the method comprising: selecting, by one or more computing devices, at least one set of mask parameters, the mask parameters comprising at least a trench bias, a light blocking part bias and an etching depth of the trench, taking into account the illumination dose, wherein the selecting at least one set of mask parameters comprises: selecting a plurality of sets of mask parameters suitable for using the phase shift mask substantially in focus, wherein the selecting a plurality of sets of mask parameters suitable for using the phase shift mask substantially in focus comprises adjusting the light blocking part bias to correct a feature size and adjusting the trench bias to correct a feature position; and selecting from the plurality of sets of mask parameters at least one set of mask parameters suitable for using the phase shift mask with the illumination dose in a predetermined out of focus range.