Effect of trench spacer etch on PMOS threshold voltage

Sacrificial oxide growth depends on previous etch conditions of trench spacer. When etch process is not optimized, the variation in the thickness of the sacrificial oxide, through which threshold-adjust implant for PMOS transistors is performed, becomes large. By improving the etch process, the variation of sacrificial oxide thickness is reduced and the variation of PMOS threshold voltages is lessened. In this paper, we describe the improved etch condition and compare the results of 0.7 μm PMOS threshold voltages using different etch processes