DRASTIC CHANGE IN CF-2 AND CF-3 KINETICS INDUCED BY HYDROGEN ADDITION INTO CF-4 ETCHING PLASMA

CF2 and CF3 radical in a CF4/H-2 etching system were directly measured by means of threshold-ionization mass spectrometry. Addition of 10% H-2 to CF4 increased the CF2 density by two orders of magnitude, flattened the spatial profile, while it doubled the CF3 density. After the abrupt addition of H-2, the temporal transition to steady CF4/H-2 discharge was investigated on reactive species such as CF(x), F, H, HF and CHF3. In particular, an anomalous time variation was found on the CF3 radical: its density sharply rises by a factor of 20 and slowly falls to a value close to the initial one. The slow time response was attributed to fluorocarbon film deposition induced by H-2 addition. A good correlation was obtained between the CF(x) density and the surface loss probability measured.