A model has been developed to describe the chemistry which occurs in CF4 plasmas and the etching of Si both in the plasma and downstream. One very important feature of this model is that for discharge residence times which vary by more than an order of magnitude, the amount of CF4 consumed is low and relatively constant. This is because the gas-phase combination reactions between F and both CF3 and CF2 lead to the rapid reforming of CF4. The model predicts that CF2 is a major species in the gas phase and that the [F] detected as a sample point downstream is a very sensitive function of [CF2]/[F] in the discharge. Even though the calculations show that [F] in the discharge varies only slightly over the wide range of experimental conditions considered, large variations in [F] at the sample point occur because the [CF2]/[F] ratio in the discharge changes. The concentrations of C2F6 and SiF4 are predicted to within a factor of 2 over a very wide range of experimental conditions. This confirms the importance of gas-phase free radical reactions in the etching of Si.
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Ryan, K.R., Plumb, I.C. A model for the etching of Si in CF4 plasmas: Comparison with experimental measurements. Plasma Chem Plasma Process 6, 231–246 (1986). https://doi.org/10.1007/BF00575130
- Plasma etching
- CF4 chemistry
- comparison with experiments