2.2.1 Contact Etch Stop Liner Technique

In this technique a highly stressed liner is uniformly deposited on top of the wafer after the silicide formation, transferring the stress from the liners to the channel. The stress-transfer depends on the thickness and the material properties of the liner [Ito00]. Tensile liners have been reported to improve the saturated drive current of n-channel and p-channel MOSFETs by 11% and 20%, respectively [Yang04].

If one single liner is used, only one type of stress can be introduced in both the n-channel and the p-channel MOSFET. As a consequence, similar to global strain techniques, just one transistor type is enhanced while the other might even be degraded. In order to achieve performance enhancement in both n-channel- and p-channel MOSFETs, two types of stress liners have to be processed. In a dual stress liner (DSL) process a highly compressive nitride is deposited on top of the p-channel MOSFET, whereas a highly tensile nitride is deposited on top of the n-channel MOSFET [Sheraw05,Yang04].

Si$_3$Ni$_4$ layers with more than 2.0 GPa tensile and 2.5 GPa compressive stress have recently been reported. These films introduce more than 1.0 GPa stress in the MOSFET channel [Arghavani06] being comparable in magnitude to stress-induced by selective epitaxial growth techniques (see Section 2.2.3).

E. Ungersboeck: Advanced Modelling Aspects of Modern Strained CMOS Technology