Optimization of 28NM Sige Sigma Shape Trench Depth Loading Effect

Since CMOS technology moved to 28nm node and beyond, selective epitaxial embedded SiGe (e-SiGe) is widely used for Source/Drain for introducing compressive strain to PMOS channel to improve the hole mobility. Studies have shown, the depth loading (or range) of sigma-shaped silicon trench at different opening CD area has influence on device performance, and device performance can be significantly improved by depth loading reduction. In this paper, influence of chuck speed of TMAH process to improve sigma-shaped silicon trench depth loading effect was investigated. It was shown that higher chuck speed process mode has more superiority than lower chuck speed mode. The depth range can be reduced 10A with such high chuck speed mode. And no negative impact was observed on sigma-shaped trench physical profile.