Drastic Change in CF2 and CF3 Kinetics Induced by Hydrogen Addition into CF4 Etching Plasma

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Abstract
CF2 and CF3 radical in a CF4/H2 etching system were directly measured by means of threshold-ionization mass spectrometry. Addition of 10% H2 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 H2, the temporal transition to steady CF4/H2 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 H2 addition. A good correlation was obtained between the CF x density and the surface loss probability measured.