Dry etching of n-face GaN using two high-density plasma etch techniques

This paper describes processing of GaN on the on the (000I) N-face surface, using two different high-density plasma etch techniques, inductively coupled plasma (ICP) etch, and electron cyclotron resonance (ECR) etching. ICP experiments used several different conditions employing Cl2-Ar-BCl3 or Cl2-Ar plasmas. The resulting maximum etch rates of 370-390 nm/min are approximately twice as high as etch rates for Ga-face (0001) GaN with the same recipes. ECR etching employed a Cl2-CH4-Ar recipe, which produced an average etch rate of 55 nm/min in a 20-minute etch process on N-face GaN. Both etch techniques increased the roughness of N-face GaN, but could produce surfaces with average roughness values below 3 nm. Selection of conditions with a dominant chemical etch contribution is important to maintain smooth surfaces. The use of both ICP and ECR etching in sequence is advantageous in situations where a GaN substrate several tens of microns in thickness must be thinned from the backside, stopping the etch in a suitable marker layer.