Abstract
The carrier mobility of MOSFET with nano-scale is reduced by replacing SiO2 with high-k gate dielectric. Channel material selection and interfacial layer quality are crucial to enhance carrier mobility. In this thesis, SiGe is used as channel material, carrier mobility and electrical properties of FinFET are enhanced by super-lattice (SL) epitaxially. Although EOT can be reduced by IL with CF4 plasma treatment, the leakage and interface trap density are increased. Hence, O2 and N2 plasma are applied to improve the interface quality. In the first part, Si/SiGe buried channel is epitaxially grown in layer-by-layer on SOI substrate. Strained SiGe is an attractive channel material beyond Si due to its higher carrier mobility. Electrical characteristics of FinFETs with SiGe and SiGe super-lattice(SL) buried channel are investigated and compared. The diffusion of GeOx can be suppressed by Si cap in SL structure, and the mobility can be enhanced by the strained Si/SiGe structure. FinFETs with SiGe SL buried channel demonstrate higher drain current of 3.23x10-5A, On/Off ratio of 7 orders and S.S of 71 mV/dec. A very high electron mobility of 452 cm2/V-sec is achieved for FinFET with Si/SiGe SL buried channel. Effects of O2 and N2 plasma treatment on gate leakage and defect passivation in FinFET with CF4 plasma treated interfacial layer are studied in the second part. Higher drain current and mobility in FinFETs are achieved by combining CF4 together with O2 plasma treatments, but the leakage is too large. FinFETs treated by CF4 together with N2 plasma treatments show larger drain current, higher mobility and lower leakage current. A gate leakage current of 2.7x10-5 A/cm2, on/off ratio of 8 orders, S.S of 67.5 mV/dec, mobility of 375 cm2/V-sec in Si n-FinFET are achieved by CF4+N2 plasma treatments.