Inductively Coupled Plasma Etching of III-N Semiconductors

Abstract

The principal focus of this research was the employment of an in-house designed and constructed inductively coupled plasma (ICP) system for integrated studies pertaining to the etching rates and etching selectivity among AlN, GaN, and Al(x)Ga(1-x)N. An (ICP) system was chosen because of its high plasma density and low cost relative to other high-density plasma etching systems. The etch rates were studied as a function of ICP power, pressure, DC bias, and gas composition. The use of a mixture of 2 sccm BCl3 and 18 sccm Cl2 resulted in a maximum etch rate of 2.2 microns/min for GaN as well as nearly vertical sidewalls with proper masking. A selectivity value, i.e. the ratio of the etch rates between two materials, as high as 48 was achieved between GaN and AlN with the addition of low concentrations of O2 to a Cl2/Ar chemistry. The use of another selectivity technique, namely, low DC biases resulted in a maximum selectivity of 38. The mechanisms responsible for the GaN etching were determined by monitoring both the ion density with a Langmuir probe and the relative Cl radical density with an optical emission spectrometer. Increasing the ion density resulted in a non-linear increase in the etch rates; increasing the Cl radical density had a minim al affect on etch rate.