THERMAL-OXIDATION IN WET OXYGEN OF REACTIVE ION-BEAM SPUTTER-DEPOSITED SILICON-NITRIDE FILMS

Oxidation kinetics of silicon nitride films in wet oxygen at 900 and 1000-degrees-C, deposited at room temperature by ion-beam sputtering is studied. Two compositions of Si(x)N(y) were used: quasistoichiometric (N/Si = 1.4) and silicon-rich (N/Si = 0.8). The results are compared with similar experiments on low-pressure chemical vapor deposited silicon nitride and bare silicon substrates. The optical properties of silicon nitride bulk and the thickness of the layer formed during oxidation were measured by ellipsometry and characterized in depth by Auger profiles. Refractive index of ion-beam sputter-deposited films decreased during oxidation. This variation is explained by a reduction of disorder in the layer. The Auger analysis of oxidized silicon nitride films shows a three-layer system, SiO2/Si(x)N(y)O(z)/Si3N4, for the two compositions used. The intermediate oxynitride layer, of homogeneous composition in the case of stoichiometric films, is thicker for the silicon-rich films and its composition is variable with depth. However, the oxidation rate remains the same for the two compositions used. The experimental data are analyzed by using published oxidation models.