Hot Plasma Etching of Gallium Nitride

Sara Harrison | 19-FS-005

Project Overview

The goal of this study was to demonstrate the feasibility of hot plasma etching of gallium nitride (GaN) for fabricating ultra-smooth, three-dimensional (3D) structures in an inductively coupled plasma (ICP) etch system. Deep etching of GaN, with precise control over the etch profile and surface morphology, is important for several applications in electronics, optoelectronics, and photonic devices. In this project, we demonstrated that high-temperature etching conditions can be generated using modern ICP etch technology by installing a custom variable temperature heating stage and performing a parametric study of etch conditions. We investigated the substrate temperature, radio-frequency power, ICP power, and substrate carrier to determine their effects on GaN micropillar etch characteristics. Substrate temperature was shown to improve the sidewall etch morphology and nanometer-scale sidewall roughness was achieved. Selectivities greater than 40:1 were achieved with aluminum nitride carrier wafers, which is 6 to10 times higher than values typically reported for etching GaN with an oxide hard mask.

This capability enables deeper GaN etching without the use of a metal hard mask, which can be a source of contamination. We also achieved vertical profiles with aluminum carrier wafers, demonstrating the importance of sidewall passivation during GaN etching for profile control. This work provided significant insight into the etch parameter requirements needed to achieve ultra-smooth, high-quality, deep etching of GaN.

Mission Impact

This project supports Lawrence Livermore National Laboratory's mission focus area of energy security and climate resilience by providing improved capabilities for applications in high-efficiency power switching, radioisotope batteries, and optoelectronic devices. It is also in line with the Laboratory's core competency of advanced materials and manufacturing because it will improve the manufacturability of 3D wide bandgap semiconductor structures beyond what is currently achievable using conventional approaches.

Publications, Presentations, and Patents

Frye, C. D., et al. 2020. "Ultrahigh GaN:SiO2 Etch Selectivity by Addition of Al to a Cl2/Ar ICP Plasma," 62nd Electronic Materials Conference, The Ohio State University, OH, June 2020. LLNL-ABS-803641