Reactive ion etching of quartz and silica-based glasses in CF 4/CHF 3 plasmas

Abstract

The reactive ion etching (RIE) of quartz and of silica-based glasses (Suprasil 2, Herasil 2, BK7, LE, NA and soda-lime) has been examined in CF 4/CHF 3 plasmas. The etch rate was shown to reduce strongly with an increasing percentage of non-volatile elements in the composition of the glass. The etching of the quartz and the Suprasil 2 and Herasil 2 glasses was consistent with a process of ion-enhanced chemical reaction as identified by Steinbruchel et al. J Electrochem Soc 1985; 132 (1): 180 [1]. For these substrates, the etch rate was directly dependent on the square root of bias voltage in the RIE and increased with the ratio of CF 4 : CHF 3 in the gas mixture. The comparatively low etch rates of the LE (low expansion), soda-lime and NA (non-alkali) glasses were equivalent in both the CHF 3/CF 4 and Ar plasmas, indicating a process of sputter etching. The BK7 glass has shown intermediate characteristics with a higher etch rate in CF 4/CHF 3 than in an Ar plasma, indicating ion-enhanced chemical etching but with little dependence on the CF 4 : CHF 3 gas ratio. These results have been applied in the fabrication of grating patterns.