Etching, Insertion, and Abstraction Reactions of Atomic Deuterium with Amorphous Silicon Hydride Films

Abstract

We report structural and kinetic studies of the reactions of hydride species in Si thin films with atomic deuterium (Dat). Infrared (IR) spectroscopy is used to obtain Si−H bonding information, and direct recoiling methods are used to measure reaction rates. Two kinds of films are prepared by filament-assisted growth from Si2H6 and are characterized by IR spectroscopy. A film containing only monohydride hydrogen is grown at 200 °C, and a polymer containing tri-, di-, and monohydride is grown at −110 °C. Rates of H abstraction by Dat, and of Dat insertion into Si−Si bonds, are reported. The abstraction rate of H by Dat in both films is similar to the abstraction rate on H-terminated crystal Si surfaces. The insertion rate into Si−Si bonds in both films is about one-tenth the rate of abstraction. A qualitative study of the etching reaction of Dat with the polymeric film is reported, and a strong temperature dependence is observed.

In situ probing of surface hydrides on hydrogenated amorphous silicon using attenuated total reflection infrared spectroscopy

“…The surface spectra cannot directly be compared with those of Toyoshima 40 because the Ar-D 2 plasma treatment can also induce other changes in the bulk and at the surface, such as deuterium insertion in Si-Si bonds and a-Si:H etching. 16 For the present purpose, which is to compare different methods for obtaining the surface composition, the effect of these changes is made irrelevant. This is done by comparing the surface spectrum obtained by the above mentioned method with a spectrum obtained by ion assisted desorption of deuterium from an a-Si:D film prepared by Ar-D 2 plasma treatment as well.…”

“…On the other hand, the increased absorbance due to the newly created surface deuterides does not give a good indication of the surface composition because atomic deuterium can also induce other changes at the surface. 16 This has no implications for the absorbance corresponding to the disappearing hydrides as this region of the spectrum shows only what has been removed from the surface. However, the fact that this technique does not work out properly can be seen in Fig.…”

“…11,12,15 This method also reveals the interactions of atomic deuterium ͑hydrogen͒ with a-Si:H films, which are not limited only to hydrogen substitution at the surface. 16 A method recently applied to study the surface hydrides on amorphous and nanocrystalline silicon films 17 is the removal of the surface hydrides by low-energy ͑ϳ20 eV͒ ion bombardment using a low ion density Ar plasma. The absorption by the hydrides before and after this Ar plasma was measured by attenuated total reflection Fourier transform infrared spectroscopy ͑ATR-FTIR͒.…”

“…32 Thus a 10 s Ar plasma exposure corresponds to an ion dose of 2ϫ10 16 cm Ϫ2 , which is in the expected order of magnitude to remove approximately 1 monolayer of adsorbates.…”

Abstraction of atomic hydrogen by atomic deuterium from an amorphous hydrogenated silicon surface

“…The difficulty arises from the fact that H can insert into Si-Si bonds at a comparable rate on the a-Si:H surface due to the presence of strained Si-Si bonds 21,22 and, hence, it is difficult to quantitatively deconvolute the effects of the two reactions on the surface H coverage. Using sensitive infrared reflection absorption spectroscopy and 20 nm thick a-Si:H films, von Keudell et al were the first to separate the insertion and exchange reactions of H in the bulk.…”