Plasma Etching with Tetrafluoromethane and Nitrous Oxide: The Role of Oxygen in the Etching of Silicon Materials

Abstract

The effects of gas additives in tetrafluoromethane plasma on the etching characteristics with or without the assistance of ion bombardment were studied. Both mass spectrometry and optical emission spectroscopy techniques were applied to analyze the plasma species. The concentrations of F, O, and in plasma with some percentage of , , and were measured. Interpretation of the etch rate variation with gas additives is given based on these measurements. By adding some percentage of to , higher silicon etch rate and lower photoresist etch rate were achieved compared with adding to . The silicon etch rate with also outperforms that with . The competition of O and with F in reaching the silicon etch sites is believed to be responsible for the result that the plasma etches silicon even slower than the plasma, which has lower F, much lower O, and very little concentrations in the plasma compared to those in plasma. The effect of oxygen in retarding silicon etching was observed to be reduced by bombarding the silicon surface with energetic ions. When ion bombardment with sufficient ion energy was added to the etching process, the silicon etch rate with plasma exceeded that with plasma due to higher F concentration existing in the plasma. In contrast to silicon etching, plasma etches photoresist faster than plasma due to higher oxygen concentration existing in the plasma. Therefore, plasma can achieve better silicon‐to‐photoresist etching selectivity when the effect of energetic ion bombardment is not significant. As a comparison, silicon dioxide etch rate was also found to be slightly higher when was used to replace as a gas additive in plasma. This also results in higher silicon‐to‐silicon dioxide etching selectivity.