Protection of Silicon Wafers from Alkali Contamination during High-Temperature Processing Using Electric Field

Abstract

A novel method for reducing metallic contamination of silicon wafer surfaces and oxide layers during high temperature processing is described. It involves the application of an electric field across wafers exposed to oxidizing and inert annealing ambients. Secondary ion mass spectrometry, capacitance-voltage, and vapor-phase decomposition/total reflection X-ray fluorescence techniques were used to measure metallic contamination levels in the silicon oxide layers. Results indicate that a positive bias, applied to the silicon at high temperature, provides a significant reduction of Li, Na, and K content in the oxides, compared with conventional wafer processing involving both oxidation and annealing treatments. The results were interpreted within the framework of a developed model that takes into account migration of alkali ions in the presence of an electric field. A thermodynamic approach to alkali metal oxidation was used to explain the similarity of the results in oxygen and argon ambients. © 2000 The Electrochemical Society. All rights reserved.