Process optimizations to recessed e-SiGe source/drain for performance enhancement in 22 nm all-last high-k/metal-gate pMOSFETs

摘要

In this paper, the technology of recessed embedded SiGe (e-SiGe) source/drain (S/D) module is optimized for the performance enhancement in 22 nm all-last high-k/metal-gate (HK/MG) pMOSFETs. Different Si recess-etch techniques were applied in S/D regions to increase the strain in the channel and subsequently, improve the performance of transistors. A new recess-etch method consists of a two-step etch method is proposed. This process is an initial anisotropic etch for the formation of shallow trench followed by a final isotropic etch. By introducing the definition of the upper edge distance (D) between the recessed S/D region and the channel region, the process advantage of the new approach is clearly presented. It decreases the value of D than those by conventional one-step isotropic or anisotropic etch of Si. Therefore, the series resistance is reduced and the channel strain is increased, which confirmed by the simulation results. The physical reason of D reducing is analyzed in brief. Applying this recess design, the implant conditions for S/D extension (SDE) are also optimized by using a two-step implantation of BF2 in SiGe layers. The overlap space between doping junction and channel region has great effect on the device's performance. The designed implantation profile decreases the overlap space while keeps a shallow junction depth for a controllable short channel effect. The channel resistance as well as the transfer ID-VG curves varying with different process conditions are demonstrated. It shows the drive current of the device with the optimized SDE implant condition and Si recess-etch process is obviously improved. The change trend of on-off current distributions extracted from a series of devices confirmed the conclusions. This study provides a useful guideline for developing high performance strained PMOS SiGe technology. (C) 2016 Elsevier Ltd. All rights reserved.