Mask error enhancement factor variation with pattern density for 65 nm and 90 nm line widths

Mask error enhancement factor (MEEF) minimization is much emphasized due to the reduction of the device technology node. The MEEF is defined as the ratio of the critical dimension (CD) obtained on wafer-level imaging to the target CD on the mask. We found that the pattern density influenced that the MEEF and that the MEEF changed with the pattern density. We also tried to obtain the 65 nm and 90 nm CD value by using the optimized diffusion length of a chemically amplified resist. It turned out that a very small diffusion length had to used to get the desired 90 nm line width at 193 nm. We used dense line and space (L/S) bars, 3 L/S bars only, and an isolated line pattern to obtain the pattern density dependency and to obtain different MEEFs. In order to determine the MEEFs for various pattern densities, we used a commercial simulation tool, Solid-E, and could obtain the minimum MEEF values for the different pattern densities.