Improvement of field effect mobility with dual-work function gate in n-LDMOST by using ni-silicidation of poly-Si gate

Abstract

A lateral double diffused metal-oxide-semiconductor transistor (LDMOST) with double work function gate (DWG) structure was fabricated by utilizing silicidation of poly-Si layer. The n+ poly-Si gate in the source side was step-etched and the whole surface of the poly-Si gate was covered with Ni film, followed by self-aligned silicide (salicide) process. The step-etched poly-Si layer in the source side was totally converted to Ni-rich silicide which resulted in a higher work function. On the other hand, in the drain side, only the upper part of thick poly-Si layer was silicided and the non-silicided lower part of the poly-Si layer was considered to be a gate with a lower work function. In DWG structure, the average electric field in the channel is enhanced, which increases electron velocity and thus improves the overall carrier transport efficiency. The fabricated DWG-LDMOST exhibited better device performances, such as 16.4 % improvement in field effect mobility and 3.3 % improvement in sub-threshold slope.