Ultra-trace analytical monitoring of silicon wafer surfaces by capillary electrophoresis

Abstract

Several methods are presented for the routine ultra-trace analytical monitoring of inorganic and organic anions and cations on the surface and in the native oxide of silicon wafers – the wafer-surface water-extraction method, the vapor-phase-decomposition method, and the re-dissolving method. Electrokinetic injection, sample stacking, and electrolyte composition were, therefore, optimized and made robust. For electrokinetic injection with transient isotachophoretic preconcentration a linear range of 0.05 to 0.5 µmol L^–1 was obtained; for sample stacking the linear range was 0.5 to 10 µmol L^–1, even in the presence of up to 750 µmol L^–1 hydrofluoric acid. Inorganic anions and monovalent carboxylic acids are predominately dissolved in the aqueous layer on the wafer surface whereas dicarboxylic acids are chemically bonded to the silanol groups and form esters.