Halogen etching of group 13–15 (3–5) semiconductors and its relevance to chemical–mechanical polishing. The reactions of dibromine, dichlorine and sodium hypochlorite with gallium arsenide and related materials

Abstract

Room-temperature etching of gallium arsenide, gallium antimonide, indium phosphide, indium arsenide and indium antimonide by dibromine or dichlorine has been studied under anhydrous conditions using Raman spectroscopy to identify the primary products and radiotracers, [⁸²Br] or [³⁶Cl], to probe interactions among the species formed. Comparisons are drawn with etching behaviour in solution particularly with sodium hypochlorite towards GaAs for which the reactive species at pH<8.0 is shown to be Cl₂ . Under anhydrous conditions the GaAs surface is passivated rapidly owing to the formation of an involatile liquid layer, believed to be a solution of Ga₂Cl₆ in AsCl₃ . Above pH=8.0, where the dominant etchant is believed to be [OCl]^– , an active surface, in which considerable reconstruction has occurred, is formed. The etching behaviour has enabled the chemomechanical polishing of 13–15 semiconductors by Br₂ and NaOCl based reagents to be rationalised. In particular, it is shown that the alumina component of a NaOCl-based polishing reagent has a minimal chemical role.