Study on Ge/Si ratio, silicidation, and strain relaxation of high temperature sputtered Co/Si1−xGex structures

Abstract

As the transistors continue to scale down, the characteristics of high-temperature-sputtered Co/Si1−xGex junction have received lots of attention because of its potential applications to heterojunction bipolar transistors. In this study, we have fabricated Co/Si1−xGex junction using room-temperature and high-temperature (i.e., at 450 °C) sputtered Co on top of strained Si0.86Ge0.14 and Si0.91Ge0.09 layers prepared by ultrahigh vacuum chemical molecular epitaxy. The relative composition of Ge in Ge-rich Si1−zGez precipitate and the solid solution of ternary phase silicide of Co–Si–Ge system were compared between room-temperature and high-temperature sputtered samples. We found that the high-temperature-sputtered samples are more effective in inhibiting lattice relaxation, which would be beneficial for manufacturing metal silicide/Si1−xGex structure devices. Mechanisms were proposed to explain the large difference between the room-temperature and high-temperature sputtered samples. It is believed that the mixed Co–Si–Ge solution on high-temperature-sputtered samples is responsible for the different silicidation behaviors.