An Investigation of Two-Step Oxidation in Dry Oxygen and the Effect of Oxide Thermal History on Its Growth Properties

Gate oxide growth in ultralarge scale complementary metal oxide semiconductor technologies involves exposure to various oxidizing conditions during temperature ramp-up and stabilization steps. These conditions are significantly differ-ent from that of the main oxidation interval. Previous tudies dealing with thick oxides having different preoxidation treatments have indicated that thermal history has a significant impact on subsequent oxide growth rate of the initial oxide. However, these trends are unclear for ultrathin oxides. In this paper, we report the results of our study on two-step oxidation in the thin (accelerated) regime. We have used initial oxides of different hicknesses, grown under various processing conditions prior to growing the second oxide film. The results indicate that, in contrast to the case of thick oxides, the thermal history from the first step oxidation (i.e., during temperature ramp-up and stabilization or initial oxidation) has no impact on subsequent oxide growth rate. Furthermore, we have extended the accelerated growth model by Massoud to account for two-step oxidations. Recently, the process of growing thermal SiO2 on silicon substrates having an initial thermal oxide layer has re-ceived renewed attention. The reason for this is three-fold: first, in growing SiO2 films, the effect of oxide thermal his