The effect of Ge condensation on channel strain during the post annealing process of recessed source/drain Si _1-xGe _x

This study reports on Ni germanosilicide formation on recessed Si _0.82Ge _0.18 source/drain structures and its effects on channel strain. A combination of transmission electron microscopy techniques,including nanobeam diffraction, shed some light on a previously unrecognized factor in the channel strain evolution during silicidation: a Ge accumulation layer produced at the bottom of the germanosilicide layer. The formation of such a Ge rich layer added an additional compressive strain to the channel strain upon moderate silicidation, while the contribution of thermal strain arising from the cooling cycle became dominant in an excessively silicided sample, which turned the channel strain into a tensile value.