Size and shape effect of SiC source/drain on strained Si

Strained Si is used to enhance carrier mobility in MOSFET devices. Epi-grown Si(1-x)C(x) as a source/drain induces strain on a channel because its lattice constant is smaller than Si. The distribution of stress varies with the layout of the device and can involve gate length, source/drain width, elevation height, etc. In this work, we report on how these parameters effect channel strain by employing the Finite Element Method. A 3-dimensional model and anisotropic properties such as the elastic constant and Poisson's ratio were adopted for high accuracy. Si0.983C0.017 was used as the source/drain on a Si substrate. The lateral channel strain was calculated based on a 30-90 nm gate length, a 30-90 nm source/drain width and 0-30 nm elevated source/drain shapes. The results showed that, when the gate length is longer, the channel strain is lower. On the other hand, source/drain width affects channel strain in a reverse manner. For models with the same gate length and source/drain width: 30, 60, 90 nm, the average channel strain is lower when the gate length and source/drain width are shorter. An additional parameter, namely, source/drain elevation height, was also studied. Interestingly, the effect of elevated shape is dependent on gate length and source/drain width.