STRUCTURAL PROPERTIES AND STRESS ANALYSIS OF SIO_2 THIN FILMS

摘要

Wet and dry oxidations of (111) crystalline silicon wafers were performed at temperatures between 900℃ and 1150℃ and subsequently annealed at 700℃. Process parameters such as the withdrawal rate from the furnace and annealing time were varied and the effect on the oxide layer is discussed. The magnitude and nature of the stress in the wafers after thermal oxidation was analysed using micro-Raman spectroscopy. The Full Width at Half Maximum (FWHM) of the Raman peak at ～ 520 cm~(-1) was also analysed to extract information relating to crystal disorder and defect density caused by the oxidation process. The results obtained from the Raman technique are compared with FTIR results and theoretical predictions from bow measurements using surface profilometry. It was found that the stress is lower if the wafer is cooled slowly in the furnace tube. The addition of chlorine to the ambient during oxide growth, or increasing the annealing time, reduces the wafer bow and the consequent stress. FTIR and ellipsometry data indicate that the wafer oxidised at 900℃ shows the highest density and refractive index. These results are consistent with results obtained recently by Martinet and Devine (1) for (100) silicon wafers. The densification process exhibits two distinct temperature regimes, viz. a low-temperature regime and a high temperature regime, in accordance with the atomic model predictions described in Lukovsky et al (2).