Patent ID: 8423922

Claim:
A photomask designing method for creating a pattern layout having an assist pattern placed around a design pattern, the method, implemented by at least one processor, comprising: placing a plurality of evaluation points around the design pattern; setting an evaluation index for imaging properties of the design pattern on an imaging surface; combining a light intensity distribution of the design pattern with light intensity distributions of the evaluation points to obtain a light intensity distribution of the design pattern on the imaging surface; evaluating the light intensity distribution of the design pattern on the imaging surface using the evaluation index to determine a region having an effective evaluation point placed; determining a placement condition for the assist pattern based on the region where the effective evaluation point is placed; and placing the assist pattern around the design pattern based on the placement condition to create the pattern layout, wherein the evaluation index is at least one selected from the group consisting of light intensity for the design pattern, an integrated value of the light intensity for the design pattern, and a gradient of the light intensity distribution of the design pattern, the following formula is used as an evaluation formula for the light intensity for the design pattern, ∑ m ⁢ σ m ⁡ ( E ij ( m ) · E main * ( m ) + E main ( m ) · E ij * ( m ) ) , the following formula is used as an evaluation formula for the integrated value of the light intensity for the design pattern, ∑ m ⁢ σ m ⁡ [ ∫ ∫ ( x , y ) ≤ S ⁢ E ij ( m ) ⁡ ( x , y ) · E main * ( m ) ⁡ ( x , y ) + E main ( m ) ⁡ ( x , y ) · E ij * ( m ) ⁡ ( x , y ) ⁢ ⅆ x ⁢ ⅆ y ] , and the following formula is used as an evaluation formula for the gradient of the light intensity distribution of the design pattern, ( ⅆ I ⅆ x ) x = edge ∝ ⁢ ∑ m ⁢ σ m ⁢ ⁢ E main ( m ) · ⁢ E main * ( m ) ' + ⁢ ⁢ ∑ i , j ≠ main ⁢ [ ∑ m ⁢ σ m ( ⁢ E main ( m ) · ⁢ E ij * ( m ) ' ⁢ + ⁢ E ij ( m ) · ⁢ E main * ( m ) ' ⁢ ) ⁢ ] + c . c .