Laser irradiation effects in Si+-implanted SiO2

Shimizu, Itoh, Matsunami and Fujita have reported experimental results on fused SiO2 which was implanted with Si+ and then either laser or furnace annealed. In view of the importance of this work to the laser processing of SiO2, we here present a physically consistent interpretation of what was found. Considering the laser annealings, the shift of the profiles towards the surface, as well as the detailed shapes of the profiles, can be understood in terms of the Soret effect. Re-emission of Si from the surface suggests a role for the well known reaction Si(l) + SiO2(l) = 2SiO(g). Considering the furnace annealings the outstanding result is the shift of the profiles away from the surface combined with a persisting re-emission of Si. By analogy with results of Arnold and Peercy for Li-bombarded fused SiO2 and of Matzke for Xe-bombarded alpha-quartz, we suggest a role for bombardment-induced nucleation followed by crystal growth during the annealing. This causes the Si impurity atoms to be dragged in part towards the surface and the reaction Si(l) + SiO2(l) = 2SiO(g) again to play a role. At the same time the remaining Si impurity atoms are found at a greater depth.