Size tolerance of sub-resolution assist features for sub-50 nm node device

摘要

Sub-resolution assist features (SRAFs) have been used to enhance lithographic process window of main features. As the device is scaled down, the SRAF size decreases drastically and the distance between main features and SRAF closes up. The variation of main feature CD and SRAF size from mask production process influences destructively on gate CD control and it makes the device performance degraded. Fabrication of small and uniform-sized SRAFs is one of the key mask technologies because mean-to-target (MTT) and CD uniformity of SRAFs are more difficult to be controlled than those of main features. In addition, for sub-50 nm design nodes, mask topography effects can not be neglected because exposure wavelength is similar to a mask pitch from main feature to SRAF or SRAF to SRAF. In order to consider mask topography effects, all lithographic simulations were performed with a rigorous coupled wave analysis (RCWA) electromagnetic field calculation. In this study, we will demonstrate that SRAF size tolerance is deduced from the effects of SRAF size deviation from the mask production on a main feature CD. To define the SRAF size deviation effects, main feature CD variation is simulated for different SRAF sizes. We will explore SRAF size tolerances for sub-50 nm design nodes. It can be suggested as one of the mask requirements.