Surface blistering of low-temperature annealed hydrogen and helium co-implanted silicon and its application to splitting of bonded wafer substrates

Abstract

Applications involving transfer of pre-processed silicon layers to substrates of different material often requires a restricted thermal budget. In the case of thermal splitting of hydrogen and helium implanted bonded wafer substrates this can mean restricting temperatures within the range 250–400 °C depending on application. The present study investigates the phenomenon of blistering of implanted substrates as a precursor to thermal splitting following annealing over this temperature range. Optical microscopy was used to detect blister initiation temperature and TEM to show details of sub-surface processes. Results showed that plots of Ln(time) v. blister initiation temperature consisted of several straight-line regions yielding an activation energy for each region. TEM showed strain lines extending to the surface and the development of voiding at the platelet line and between the platelet line and sample surface. The results suggest that the movement of He and its interaction with vacancy complexes plays an important role during annealing. Hydrogen and helium co-implanted silicon wafers bonded to oxide-coated silicon wafers were thermally split at a temperatures between 280 and 300 °C yielding a pinhole-free silicon-on-oxide (SOI), layer of about 460 nm with an RMS roughness measured by AFM in the range 3–6 nm rms.