CF4 decomposition in a low-pressure ICP: influence of applied power and O2 content

This paper focuses on the investigation of CF4 decomposition in a low-pressure inductively coupled plasma by means of a global model. The influence of O-2 on the CF4 decomposition process is studied for conditions used in semiconductor manufacturing processes. The model is applied for different powers and O-2 contents ranging between 2% and 98% in the CF4/O-2 gas mixture. The model includes the reaction mechanisms in the gas phase coupled with the surface reactions and sticking probabilities of the species at the walls. The calculation results are first compared with experimental results from the literature (for the electron density, temperature and F atom density) at a specific power, in the entire range of CF4/O-2 gas mixture ratios, and the obtained agreements indicate the validity of the model. The main products of the gas mixture, obtained from this model, include CO, CO2 and COF2 together with a low fraction of F-2. The most effective reactions for the formation and loss of the various species in this process are also determined in detail. Decomposition of CF4 produces mostly CF3 and F radicals. These radicals also contribute to the backward reactions, forming again CF4. This study reveals that the maximum decomposition efficiency of CF4 is achieved at a CF4/O-2 ratio equal to 1, at the applied power of 300 W.