REACTIVE ION ETCHING OF GALLIUM NITRIDE IN SILICON TETRACHLORIDE PLASMAS

The reactive ion etching characteristics of gallium nitride (GaN) in silicon tetrachloride plasmas (SiCl4, 1:1/SiCl4:Ar, and 1:1/SiCl4:SiF4) in the pressure range between 20 and 80 mTorr have been investigated. For the pressure range investigated, etch rates are found to be essentially identical for the different gas mixtures and also invariant with pressure. However for all gas mixtures, etch rates increased monotonically with increasing plasma self-bias voltage exceeding 50 nm/min at 400 V. This is one of the highest etch rate ever reported for GaN. Smooth and anisotropic etch profiles are demonstrated for structures of submicrometer dimensions. The slight overcut observed in the etch profiles is attributed to the significant role of physical ion bombardment in the etching mechanism. Auger electron spectroscopy show that a wet etch in dilute HF is needed to clear the Si (in the form of SiOx) embedded in the near surface of GaN during etching thereby restoring etched surfaces to their virgin state.