The Role of Hydrides in the Equilibrium of Aluminum in Aqueous Solutions

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Abstract
Magnesium aluminum spinel is commonly used as a substrate for the heteroepitaxial chemical vapor deposition of silicon. Hydrogen is usually used as a carrier gas, and a high‐temperature pretreatment in hydrogen is typically performed on the substrate with the idea that abrasion polishing damage will either be annealed or removed. In this paper the rate of material removal in hydrogen of stoichiometric spinel is presented as a function of crystallo‐graphic orientation, time, and temperature. For example, at 1000°C the rate is ∼1 Aå/min; at 1300°C,∼100 Aå/min. However, it was found that such a hydrogen ambient promotes crazing of the substrate surface, thus degrading its suitability for heteroepitaxy. This phenomenon was studied, and it is suggested that the cause is due to a preferential out‐diffusion of magnesium from the surface, which induces a strain large enough to result in brittle fracture. It has been shown that the crazing is obviated by the use of helium as a carrier gas.

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