Ge1-xSix on Ge-based n-type metal-oxide semiconductor field-effect transistors by device simulation combined with high-order stress-piezoresistive relationships

摘要

The considerably high carrier mobility of Ge makes Ge-based channels a promising candidate for enhancing the performance of next-generation devices. The n-type metal-oxide semiconductor field-effect transistor (nMOSFET) is fabricated by introducing the epitaxial growth of high-quality Ge-rich Ge1-xSix alloys in source/drain (S/D) regions. However, the short channel effect is rarely considered in the performance analysis of Ge-based devices. In this study, the gate-width dependence of a 20 nm Ge-based nMOSFET on electron mobility is investigated. This investigation uses simulated fabrication procedures combined with the relationship of the interaction between stress components and piezoresistive coefficients at high-order terms. Ge1-xSix alloys, namely, Ge0.96Si0.04, Ge0.93Si0.07, and Ge0.86Si0.14, are individually tested and embedded into the S/D region of the proposed device layout and are used in the model of stress estimation. Moreover, a 1.0 GPa tensile contact etching stop layer (CESL) is induced to explore the effect of bi-axial stress on device geometry and subsequent mobility variation. Gate widths ranging from 30 nm to 4 mu m are examined. Results show a significant change in stress when the width is <300 nm. This phenomenon becomes notable when the Si in the Ge1-xSix alloy is increased. The stress contours of the Ge channel confirm the high stress components induced by the Ge0.86Si0.14 stressor within the device channel. Furthermore, the stresses (S-yy) of the channel in the transverse direction become tensile when CESL is introduced. Furthermore, when pure S/D Ge1-xSix alloys are used, a maximum mobility gain of 28.6% occurswith an similar to 70 nm gate width. A 58.4% increase in mobility gain is obtained when a 1.0 GPa CESL is loaded. However, results indicate that gate width is extended to 200 nm at this point. (C) 2015 Elsevier B.V. All rights reserved.