FOURIER-TRANSFORM INFRARED-ABSORPTION SPECTROMETRY MEASUREMENTS OF A CF4 DISCHARGE IN AN ELECTRON-CYCLOTRON-RESONANCE REACTOR

Knowledge of the neutral gas composition in a discharge is important f or understanding the chemical processes involved in both etching and d eposition environments. We have performed Fourier-transform infrared a bsorption spectrometry measurements of a CF4 plasma in an electron cyc lotron etching tool. Spectral bands from both CF4 and CF3 were observe d. The densities of these species were calculated from the strength of the measured absorption. It was found for typical discharge powers th at the CF4 density was approximately 20% of the total density and depe nded only on the plasma density. This data is used to show that recycl ing of the daughter species (C, CFx, F-x, etc.) on the chamber walls i s the major source of the CF4 observed. Thus one finds that wall condi tions play a very important role in determining the plasma chemistry i n this high density, >10(11) cm(-3), and low neutral pressure, <10 mTo rr, discharge. Additionally, it was found that the CF3 density was app roximately 20% of the total density and depended on the product of the plasma density and the CF4 density. This implies that the CF3 is prod uced primarily through an e(-)+CF4-->e(-)+CF3+F type of reaction. Fina lly, it was found that the upper limit of CF2 density was 1.6x10(13) c m(-3) over the entire parameter range explored.