Infrared spectroscopy of chemically bonded hydrogen at voids and defects in silicon

Abstract

Chemical bonding of H to displacement defects and internal surfaces in Si has been investigated by infrared-absorption and nuclear reaction analysis techniques. A He implantation/anneal sequence was used to produce faceted voids which are retained to at least 800 °C in a buried layer as revealed by transmission electron microscopy. Hydrogen was injected into void layers by three different methods: ion implantation, plasma exposure, and H2 gas exposure. Infrared absorption by Si-H stretch modes with frequencies characteristic of monohydrides on (100) and (111) surfaces are observed for all methods of H injection, consistent with bonding on faceted void surfaces. Thermal stability of Si-H is higher on void surfaces than on other trapping sites. Displacement defects produced by H-ion implantation trap H but release it upon annealing for retrapping on voids. The Si-H absorption bands with frequencies characteristic of monohydrides on (100) and (111) surfaces anneal in parallel between 600 and 800 °C and in coincidence with the loss of total H measured by nuclear reaction analysis. Moreover, densities comparable to the total H density are estimated for void surface states and for Si—H bonds on void surfaces. It is inferred from these results that bonding of H on the void surfaces is energetically favored over H2 formation in the voids, and it is concluded that the 2.5±0.2 eV determined in a separate study of H release from buried voids is the Si—H bond energy descriptive of both (111) and (100) surfaces.