Some aspects of blistering and exfoliation of helium-hydrogen coimplanted (100) silicon

A Si(He,H) system, produced by ion implantation and suitable for SOI fabrication, is studied during and after the thermal treatment which induces surface blistering and exfoliation. The attention is focused on the influence of storage time between the implantation stage and the annealing stage, since it is expected that even at low temperatures the phenomena taking part in the blistering and exfoliation process are active. Three different storage environments are selected: (1) liquid nitrogen, (2) room temperature and (3) 100 °C in air. The main result is that long time sample storage has the effect of decrease the exfoliation efficiency. Moreover, optimum conditions for exfoliation are met at storage time around 24 h at 100 °C, where the maximum fraction (1) of the sample surface (about 16%) results exfoliated and (2) of He atoms (about 80%) are desorbed. The discussion evidences that He desorbtion during annealing and exfoliation efficiency are strictly correlated. Moreover, a phenomenological model explaining the observed storage effect is sketched, deduced from the present knowledge of the Si(H), Si(He) and Si(He,H) systems.