Hydrogen and helium bubbles in silicon

Hydrogen is a quite common impurity in semiconductor-silicon technology: it is unintentionally but unavoidably added to the silicon after crystal grow th during wafer processing, and continues to be present during wet oxidatio n, film depositions, etching and annealing steps. The effects of hydrogen i n single crystal silicon at low concentration have been the subject of many papers, books and conference proceedings. Much less considered is the case of hydrogen at massive concentration. One Anal effect of heavy hydrogen lo ading is the formation of cavities and bubbles, with size up to 100 nm. Cav ities and bubbles are also observed after helium loading by high-fluence io n implantation. This article reviews the basic mechanisms responsible for t he formation and growth of such structures in single-crystalline silicon. I n particular, starting from the loading (ion implantation) and having in mi nd the formation of the cavities, this paper will cover: the effects of sub strate temperature, the interaction of vacancies and self-interstitials wit h the impurity, the mechanisms of gas segregation inside the cavities, the pressure which arises because of the segregation and the subsequent displac ement field in the crystal, the stability against heat treatments of the ga s in the cavities and of the cavities themselves. The understanding of the physical processes should lead to gain more insight in the processes of cle avage of the Si-Si bond and vacancy agglomeration which can induce not only the formation of cavities and bubbles, but also planar cutting or explosio n. (C) 2000 Published by Elsevier Science S.A. All rights reserved.