IMPROVEMENT OF CZOCHRALSKI SILICON-WAFERS BY HIGH-TEMPERATURE ANNEALING

High-temperature annealing in hydrogen, argon, and oxygen ambients improves the electrical performance of Czochralski Si wafers considerably. The gate oxide integrity of such wafers can approach values close to 100% yield after annealing for 1 to 2 h at 1200 degrees C in argon and hydrogen ambient which is related to a significant reduction of near-surface crystal defects as compared to nonannealed polished wafers. The perfection of epitaxial wafers is, however, not obtained. The high-temperature treatment deteriorates the surface of polished wafers depending on the ambient used. A protective oxide layer grown during annealing in an oxygen ambient prevents roughening due to desorption of SiO. A more pronounced roughening occurs by annealing in hydrogen or argon which is tightly connected to the chemical composition of the surface. A hydrogen terminated 2 x 1 reconstructed Si (100) surface is observed after annealing in hydrogen. An oxygen-denuded zone is formed close to the surface during high-temperature annealing preventing oxygen precipitation in this region of the wafer. The oxygen precipitation in the bulk of the wafers depends significantly on the details of the annealing process. A precipitation behavior similar to nonannealed Si wafers can be obtained by appropriate process parameters.