EFFECTS OF A THIN CVD-Si LAYER ON THE OXIDATION BEHAVIOR OF Si_3N_4

摘要

Si_3N_4 (SN282) shows classical features of severe oxidation degradation such as formation of blisters in its thermally grown oxide (TGO), extensive cracking, and spallation of the TGO upon oxidation in oxygen at 1200℃. This study has revealed that SN282 coated with chemically vapor deposited (CVD) polycrystalline Si layers exhibits much improved oxidation behavior in terms of TGO growth rate as well as morphological characteristics of the TGO. Specifically, TGO growth on SN282 coated with CVD Si is reduced by a factor of four compared with uncoated samples. The TGO on the coated samples is glassy in appearance and uniform in thickness. The improved oxidation resistance of SN282 can be attributed to the role of the CVD-Si layer as a diffusion barrier to mitigate the incorporation of impurity cations from SN282 to the TGO.