Monocrystalline Quartz ICP Etching: Road to High-Temperature Dry Etching

Abstract

In this study, the dry plasma-chemical etching process of monocrystalline SiO2 (quartz) in a fluoride-based (sulfur hexafluoride, SF6) inductively coupled plasma (ICP) was investigated. The etching rate (Vetch) dependencies from the power of the ICP source, bias voltage, distances between the sample holder surface and plasma zone, and pressure in the processing chamber were determined. Additionally, the dependence of the Vetch on the sample holder temperature in a relatively large temperature range (T = 323–598 K) was investigated. The highest Vetch of greater than 1.7 μm/min was achieved at T = 450 K. The optimal process parameters were found in terms of the highest etching rate. Based on the obtained results, the basic process of a high-rate, deep (dozens of μm) anisotropic dry etching of quartz was developed with the usage of a low-powered (< 1000 W) high-frequency ICP source and relatively low bias voltages. During the deep etching process (40 μm), a Vetch = 1 μm/min was achieved. The etching selectivity ratio of the quartz substrate to the mask was approximately 50, and the side-wall inclination of the etched profiles was nearly 85°.