A method for generating masks for manufacturing of a semiconductor structure comprises the following steps. A design pattern for features to be formed on a substrate is divided into a first set of patterns and a second set of patterns. The first set of patterns comprises a first pattern corresponding to a first feature, the second set of patterns comprises two second patterns corresponding to two second features, and the first feature will be arranged between the two second features when the features are formed on a substrate. Two assist feature patterns are added into the first set of patterns. The two assist feature patterns are arranged in locations corresponding to the two second features, respectively. A first mask is generated based on the first set of patterns with the assist feature patterns. A second mask is generated based on the second set of patterns.