Oxide formed in semiconductor substrate by implantation of substrate

Abstract

A process and resulting product is described for forming an oxide in a semiconductor substrate which comprises initially implanting the substrate with atoms of a noble gas, then oxidizing the implanted substrate at a reduced temperature, e.g., less than 900.degree. C., to form oxide in the implanted region of the substrate, and then etching the oxidized substrate to remove a portion of the oxide. The resulting oxidation produces a dual layer of oxide in the substrate. The upper layer is an extremely porous and frothy layer of oxide, while the lower layer is a more dense oxide. The upper porous layer of oxide can be selectively removed from the substrate by a mild etch, leaving the more dense oxide layer in the substrate. Further oxide can then be formed adjacent the dense layer of oxide in the substrate, either by oxide deposition over the dense oxide or by growing further oxide beneath the dense oxide layer. The initial oxide formed by the process appears to be temperature independent, at temperatures of 900.degree. C. or less, with oxide formation apparently dependent upon the extent of the implanted regions of the substrate, rather than upon temperature, resulting in thermal savings. Furthermore, the excess implanted noble gas in the substrate adjacent the oxide formed therein can have beneficial effects in inhibiting the formation of parasitic field transistors and in greater control over field thresholds.