Patent ID: 7998642

Claim:
A mask pattern data creation method for creating assist pattern feature data of a plurality of assist pattern features to be formed on a mask along with a plurality of main pattern features transferrable to a transfer destination by an exposure, the assist pattern features being not transferrable to the transfer destination, the method comprising: classifying the main pattern features into at least two groups in accordance with a minimum pitch between adjacent main pattern features; determining, for a group having a smallest minimum pitch, whether a spacing between adjacent assist pattern features corresponding to main pattern features in the group is not more than a prescribed spacing, the determination being performed based on: initial positions of the adjacent assist pattern features determined based on an illumination condition; and initial sizes of the adjacent assist pattern features satisfying a size condition such that the adjacent assist pattern features are not transferrable to the transfer destination; and adjusting, when it is determined that the spacing between the adjacent assist pattern features is not more than the prescribed spacing, at least one of the adjacent assist pattern features by at least one of changing its position or reducing its size, so as to increase the spacing between the adjacent assist pattern features to exceed the prescribed spacing.