Dual-stage wet oxidation process utilizing varying h2/o2 ratios

Abstract

A method for forming silicon oxide layers on silicon wafers by a wet oxidation process that utilizes a dual-stage pyrolysis is described. The process can be carried out by flowing a first H /O mixture that has a first H /O gas mixture ratio into a torch and then feeding water vapor generated into the wet oxidation chamber to form a first layer of silicon oxide, and then flowing a second H /O mixture that has a second H /O gas mixture ratio into the torch and feeding water vapor generated into the wet oxidation chamber for forming a second thickness of the silicon oxide layer. The second H /O ratio is smaller than the first H /O ratio by at least of the value of the first H /O ratio. For instance, when the first H /O ratio used is large than 1.5, the second H /O ratio used is less than 1.2. In one example, the first H /O gas mixture ratio utilized is 1.8, while the second H /O gas mixture ratio utilized is 1.0. It has been found that by reducing the hydrogen content, i.e. by decreasing the H /O gas mixture ratio, the partial pressure of the water vapor generated is reduced which minimizes the loading effect in the furnace tube during the wet oxidation process and improves the uniformity of the silicon oxide layers deposited.