Method for managing the stress due to the strained nitride capping layer in MOS transistors

Since the 90-nm CMOS technology node, the strained nitride capping layer (i.e., the contact etch stop layer, CESL) is used as a stress-engineering booster that enables transistor improvement. This paper presents a complete mechanical simulation work explaining how the CESL transmits its intrinsic stress to the Si channel. First, it is demonstrated that the CESL stress transmission is the outcome of several CESL parts acting separately (direct effect) or in association (indirect effect) without neglecting the corner effects for small transistors. Then, all the different contributions of these CESL parts on the stress transfer way for long and short channels are explained.. Finally, some guidelines are given for an optimization of the usage of CESL.