Chemomechanical polishing of silica and silicon by fluoride- and oxide-based reagents: identification of a reaction intermediate

Abstract

The effect of added hydrogendifluoride anion on the chemomechanical polishing of silica and silicon wafers by aqueous suspensions of cerium(IV) or silicon(IV) oxides has been investigated over a range of solution pH. The effect on silica is marked at very low pH; an intermediate under these conditions has been identified as K₂SiF₆ coated with a thin silica-like layer. The [HF₂]^– anion is ineffective for silica polishing above pH 7 and for silicon under all conditions examined. The most effective reagent for the latter substrate is a mixture of cerium(IV) oxide and alkaline silica sol. An explanation for the role of [HF₂]^– is offered.