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

Several methods are presented for the routine ultra-trace analytical monito ring 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. Electr okinetic injection, sample stacking, and electrolyte composition were, ther efore, optimized and made robust. For electrokinetic injection with transie nt isotachophoretic preconcentration a linear range of 0.05 to 0.5 mu mol L -1 was obtained; for sample stacking the linear range was 0.5 to 10 mu mol L-1, even in the presence of up to 750 mu mol L-1 hydrofluoric acid. Inorga nic anions and monovalent carboxylic acids are predominately dissolved in t he aqueous layer on the wafer surface whereas dicarboxylic acids are chemic ally bonded to the silanol groups and form esters.