Silicon-Germanium Interdiffusion and Its Impacts on Enhanced Mobility MOSFETs

As complementary metal-oxide-semiconductor field-effect transistors (MOSFETs) scale, strained Si and SiGe technology have received more attention as a means of enhancing performance via improved carrier mobility. One of the biggest challenges for strained Si and SiGe technology is Si-Ge interdiffusion during thermal processing. Two different aspects of Si-Ge interdiffusion are explored in this work. The first part of this work demonstrates that Si-Ge interdiffusion and ion implantation damage during the fabrication of strained Si MOSFETs have significant impact on electron mobility and thus device performance. Long channel n-MOSFETs with different thermal processing and implant conditions were fabricated on both CZ Si wafers and strained Si/relaxed Si0.8Ge0.2 heterostructures. In order to avoid scattering by ionized dopant impurities, neutral Si and Ge were implanted into the channel at six different doses ranging from 4 x 10 cm to 1 x 10 atoms/cm. It is shown that the mobility enhancement factor is degraded by RTA and ion implantation. For each RTA condition, there is a threshold implantation dose, above which the strained Si mobility starts to degrade significantly. The degradation is larger for devices with higher thermal budgets or implantation doses. Si-Ge interdiffusion at the strained Si/relaxed Si0.8Ge0.2 interface was found to be the major mobility degradation mechanism for devices with higher thermal budget, while for devices with lower thermal budget, residual ion implantation damage in the strained Si channel is considered to be the key degradation mechanism.