Properties of hydrogen induced voids in silicon

Abstract

After heat treatment, silicon samples implanted with high doses of hydrogenexhibit blistering and defoliation of thin silicon layers. The process is usedcommercially in the fabrication of thin silicon-on-insulator layers (SmartCut®). In the present study we investigate the behaviour of hydrogen after different processingsteps, which lead to thin Si layers bonded to glass substrates. A set of hydrogenimplanted samples is studied by means of low temperature photoluminescence, Ramanspectroscopy, x-ray diffraction and optical microscopy (visible and infrared). Theformation of Si–H bonds is detected after implantation together with a build-up ofinternal strain. After annealing, the relaxation of the implanted layers is found to beconnected with the formation of hydrogen saturated vacancies and the formation ofH2 molecules filling up larger voids. A comparison is made with hydrogen plasma treatedsamples, where well defined platelets on {111} planes are found to trap hydrogen molecules.No direct evidence of the role of {111} and {100} platelets in the blistering process is found inthe implanted layers from our study. We determine considerable compressive stressesin the bonded Si layers on glass substrates. The photoluminescence is stronglyenhanced in these bonded layers but red-shifted due to a strain reduced band gap.