Etch characteristics of optical waveguides using inductively coupled plasmas with multidipole magnets

Abstract

In this study, silica glass etch characteristics of inductively coupled plasmas with and without the multidipole magnets were investigated using CF4 and SF6 as the etch gases. A Langmuir probe and optical emission spectroscopy were used to investigate the characteristics of the plasmas. When the silica glass was etched with the multidipole magnets, a significant increase in etch rate was obtained with the magnets for both CF4 and SF6 together with an increase in ion saturation current as measured by the Langmuir probe. F radicals estimated by Ar actinometry also increased with the addition of the magnets. When the etch characteristics of CF4 and SF6 with magnets were compared at the same etch conditions, SF6 showed the higher etch rates (>800 nm/min) while CF4 showed the higher etch selectivity (>70:1) over the Cr mask material used in the study. With the magnets, a vertical etch profile was obtained with CF4 while the etch profile with SF6 was a little re-entrant. A 10 μm deep anisotropic silica glass etch profile with a smooth sidewall could be obtained using CF4 and with the magnets at 7.5 mTorr of operational pressure, 1000 W of inductive power, and −100 V of dc self-bias voltage. The silica glass etch rate and the etch selectivity over Cr under these etch conditions were 700 nm/min and 70, respectively.