Kinetics of the thermal oxidation of WSi2

Abstract

The thermal oxidation WSi₂ films has been studied. Thin films of WSi₂ were deposited by sputtering on (100) silicon and on oxidized silicon, and then oxidized in dry O₂ and in steam atmospheres at 1000, 1100, and 1200 °C for times up to 30 min. In all cases the dry O₂ oxidation resulted in films of poor quality. The films had rough surfaces, with WO₃ present in powder form. However, steam oxidation gave SiO₂ films of good quality. For WSi₂/Si as well as WSi₂/SiO₂/Si samples, as the oxidation proceeded, WSi₂ reacted with steam to form SiO₂ and W₅Si₃. The rate of oxidation and activation energy were different for the two types of substrates. For WSi₂ films deposited directly on Si, the oxidation process was significantly modified because Si atoms rapidly diffused through the silicides and took part in the oxidation process, and thus affected the conversion of WSi₂ to W₅Si₃. However, with WSi₂ films deposited on oxidized Si, the absence of free Si atoms resulted in the faster transformation of WSi₂ into W₅Si₃.