Shallow Trench Isolation Stress Effect on NMOS Transistor Leakage, SRAM Standby Current and VCCMIN

Abstract

Three key process steps in shallow trench isolation (STI) technology: STI liner oxide, STI to AA step height, and annealing temperature. Their impacts on NMOS devices leakage, SRAM standby current and Vccmin have been studied. MOSFET transistors off state current (Ioff) and body current (IB) were measured at varied length of diffusion (LOD) for STI stress effect analysis. For low power NMOSFET transistors, IB is seen to be the main part of Ioff and has a strong correlation to the processes that modulates STI stress. The experiment results show that the STI stress level can be much reduced by decreasing STI oxide RTA temperature and liner ox thickness, hence leading to lower IB and SRAM standby current. It is also demonstrated that SRAM Vccmin can be improved ~10% by STI stress reduction.