Realization of high performance dual gate DRAMs without boron penetration by application of tetrachlorosilane silicon nitride films

Abstract

It is well known that conventional SiN films accelerate boron penetration due to hydrogen desorption during a high temperature annealing process after SiN deposition (Pfiester et al, 1990). The boron penetration causes depletion of the gate electrodes and threshold voltage deviations, and degrades the PMOSFETs. In the case of next generation DRAMs, thick SiN films are necessary as a hard mask for a self-aligned contact (SAC) process to increase the density. Simultaneously, dual gate CMOS systems should be applied to realize high performance. Therefore, SiN films without boron penetration must be developed for realization of dual gate CMOS systems with a SAC process. Conventional silicon nitride (SiN) films accelerate boron penetration, which causes the degradation of PMOSFETs. It was found that boron penetration becomes worse in proportion to SiH content incorporated in SiN LPCVD films. Applications of SiH-less SiN films, formed from tetrachlorosilane (TCS) and ammonia, have successfully realized the high performance of PMOSFETs in dual gate system DRAMs.