Impact of ion implantation damage and thermal budget on mobility enhancement in strained-Si N-channel MOSFETs

The impact of processing factors such as ion implantation and rapid thermal annealing on mobility enhancement in strained-Si n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) has been investigated. Long-channel strained-Si and bulk n-MOSFETs were fabricated with various channel-region implant doses and thermal budgets. Neutral Si and Ge species were used to study the impact of the implant damage on mobility separately from ionized impurity scattering effects. Electron mobility enhancement is shown to degrade considerably when the implant dose is above a critical dose for a given thermal budget. Transmission electron microscopy, secondary ion mass spectrometry and Raman spectroscopy were used to investigate the mobility degradation mechanisms. Residual implant damage and implant damage enhanced Ge up-diffusion into the Si are shown to be responsible for the mobility degradation. Two-dimensional damage simulations of 30-nm scale MOSFETs are used to examine potential technological implications of these findings.