The influence of silicon heat treatments on the minority carrier generation and the dielectric breakdown in MOS structures

Abstract

The minority carrier lifetime of Si and the dielectric breakdown of SiO2 on Si has been investigated as a function of various high temperature treatments preceding the formation of the SiO2 layer. Annealing wafers in H2 or certain H2 -containing ambients prior to oxidation lea to a dramatic decrease in the number of breakdown defects found in capacitors. The higher the temperature the more effective is the defect removal. Using this process the defect density could be reproducibly controlled at ≤10 defects/cm, and in some cases wafers with no defects were found. The defects appear to be related to some airborn contamination and can be increased by exposure to air and to certain aqueous cleaning steps. By "soaking≓ the Si wafers in an equilibrium gas mixture containing SiH4 as well as HCl, it was possible to prevent etching of the Si but yet expose the wafer to approximately 4% HC1 for longer times and at higher temperatures, 12 75‡C, than is possible with the well known HCl-oxidation process. It was found that this treatment will remove Au, Fe, and Cu from intentionally contaminated wafers but at rates much slower than would be expected from bulk-diffusion, rate-limited transport. Soaking at 1275‡C led to minority carrier lifetimes comparable but not significantly better than for HCl-oxidized wafers. © 1974 American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.