Origin of the implantation and annealing effects on the residual stress release in a silicon-on-sapphire system

In semiconductor industry, a thin hetero-epitaxial film layer is normally deposited onto a dissimilar substrate, which inevitably leads to residual stresses and microstructural defects. Ion implantation and subsequent annealing have been used to mitigate such stresses and defects, but the microstructural origin is unclear. This paper carries out an in-depth investigation into the effects of these processes on the stress and microstructure variations in silicon-on-sapphire (SOS) thin film systems undergone Si+ implantation and 600 °C to 1,000 °C annealing. The residual stresses were measured by Raman Scattering, whereas the microstructures of the samples were examined by cross-sectional TEM. It was found that the release of the as-grown residual stress after high-energy implantation was more remarkable, and that the increase of ion density leads to more significant stress relief. Under an extreme condition, however, a large number of ions will result in a significant expansion of substrate, causing tension in the silicon film. A higher annealing temperature renders a greater residual stress recovery, an improved crystalline quality, and a clear-cut interface with periodical misfit dislocations. The study concluded that the sapphire lattice expansion caused by ion penetration can hardly be altered by annealing, and as such, the residual stress in the silicon film can be effectively reduced after annealing and an ideal crystal quality can be obtained at the same time.