Influence of the carrier wafer during GaN etching in Cl2 plasma

Abstract

In this study we have performed a thorough characterization of GaN surface after etching up to 100 nm in Cl 2 plasma under various bias voltage and according to the carrier wafer used (Si, SiO 2 , Si 3 N 4 , photoresist). The objective of this article is to evaluate the etch damage and contamination of the GaN surface when materials with other chemical nature are present during the etching. The effects of etching conditions on surface morphology and chemical compositions of etched GaN films are studied in detail using XPS and AFM measurements. To this aim, an universal methodology is proposed to estimate accurately by XPS the stoichiometry of GaN surface exposed to reactive plasmas when only a Al Kα X-ray source is available. The results indicate that the GaN etching mechanisms are very sensitive to the chlorine radical density present in the plasma, the latter being strongly influenced by the carrier wafer. Substrates that are more chemically reactive with Cl 2 plasma such as silicon or photoresist compared to SiO 2 or Si 3 N 4 will lead to a greater loading of atomic chlorine, which in turn will lead to lower GaN etch rates. Moreover, the GaN surface contamination will depend on the etch byproducts ejected by the carrier wafer.