Measurement of Fluorocarbon Radicals Generated from C4F8/H2 Inductively Coupled Plasma: Study on SiO2 Selective Etching Kinetics

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Abstract
The kinetics of highly selective SiO2 etching were studied on the basis of appearance mass spectroscopy (AMS) measurement of fluorocarbon radicals generated from C4F8/H2 inductlvely coupled plasma (ICP). Results obtained by varying of H2 concentration in C4F8, total pressure and RF power implied that CF1 radical played a major role in the polymer film deposition. In particular, radical measurements carried out by varying the length of a quartz tube which was set in front of an inlet of radicals effusing into AMS revealed that CF2 radical might not contribute to the polymer deposition and that the sticking probability of CF1 radical was reduced considerably in the presence of hydrogen. It was also observed that in etching using a capillary plate as a high-aspect-ratio mask, the carbon-rich polymer film is deposited on the Si bottom surface in the presence of hydrogen at high CF1/CF2 radical density ratio. Accordingly, CF1 radicals whose surface loss is suppressed in the presence of hydrogen are likely to arrive at deep the bottom surface, forming the carbon-rich polymer by reaction of hydrogen with fluorine from CF1 radicals.