Nanoscale strained-Si MOSFET physics and modeling approaches: a review

Abstract

An attempt has been made to give a detailed review of strained silicon technology. Various device models have been studied that consider the effect of strain on the devices, and comparisons have been drawn. A review of some modeling issues in strained silicon technology has also been outlined. The review indicates that this technology is very much required in nanoscale MOSFETs due to its several potential benefits, and there is a strong need for an analytical model which describes the complete physics of the strain technology.

An Analytical Model for the Threshold Voltage of Short-Channel Double-Material-Gate (DMG) MOSFETs with a Strained-Silicon (s-Si) Channel on Silicon-Germanium (SiGe) Substrates

“…In strained Si film, the 6-fold degenerate valley in the conduction band splits into a 2-fold non planar and a 4-fold planar degenerate valleys [9]. In the same way, the valence band also splits into two band each consisting of light and heavy holes [9].…”

“…In strained Si film, the 6-fold degenerate valley in the conduction band splits into a 2-fold non planar and a 4-fold planar degenerate valleys [9]. In the same way, the valence band also splits into two band each consisting of light and heavy holes [9]. The carriers then prefer the lower energy valley while occupying them resulting in the reduction of intervalley scattering and effective mass of the carrier [9].…”

“…which results in lattice mismatch and tensile biaxial strain in the silicon epitaxial layer [9]. In strained Si film, the 6-fold degenerate valley in the conduction band splits into a 2-fold non planar and a 4-fold planar degenerate valleys [9].…”

“…In the same way, the valence band also splits into two band each consisting of light and heavy holes [9]. The carriers then prefer the lower energy valley while occupying them resulting in the reduction of intervalley scattering and effective mass of the carrier [9]. To sum it all, the benefits achieved are firstly a modified lattice constant of the material; second a modified energy band structure to trap carriers through well formation and finally an enhanced mobility [10].…”

“…However, as the Ge content is increased, the critical thickness; which is the thickness to which the strained silicon can be grown without inducing misfit dislocations to alleviate strain; is reduced [12]. When strain is included in the Si channel of the MOSFET it offers better performance than the conventional MOSFETs due to its higher electron and hole mobility, high field velocity and velocity overshoot of carriers as discussed in literature [9][10][11][12]. However, the enhanced carrier mobility when coupled with high fields as in further scaled strained bulk MOSFET results in highly energetic and accelerated carriers known as the "Hot Carriers" [13,14].…”