RADICAL KINETICS IN A FLUOROCARBON ETCHING PLASMA

Neutral free radicals, CF3 and CF2, in a radio-frequency CF4/H-2 discharge were detected using appearance mass spectrometry. The spatial density distributions of these radicals were obtained with the mixing ratio of H-2/CF4 as a key parameter. Adding a 10% H-2 gas to CF4 enhanced the CF2 density by a factor of 50 and flattened the spatial profile. By the injection of the H-2 gas abruptly into the CF4 discharge, the temporal transition to the CF4/H-2 discharge was investigated. When the percentage of H-2 greater-than-or-equal-to 5%, a strange time variation is found for the CF3 radical: its density sharply rises by a factor of 10 and slowly falls to a value close to the initial one. The slow time response was attributed to the H-2-induced polymer deposition. The surface loss probability of CF2 and CF3 Was measured in various conditions which suggested the importance of surface chemistry of radicals.