Paper AP+PS+TF-ThM11
Thermal Atomic Layer Etching of GaN and Ga₂O₃ Using Sequential Fluorination and Ligand-Exchange Reactions

Thursday, October 24, 2019, 11:20 am, Room B130

Atomic layer etching (ALE) of GaN and Ga₂O₃ is important for the fabrication of power electronics devices. Thermal ALE of GaN and Ga₂O₃ was performed using sequential, self-limiting surface reactions. The thermal ALE was accomplished using fluorination and ligand-exchange reactions. XeF₂ and HF were used as the fluorination reactants. BCl₃ was the main metal precursor for ligand-exchange. Ga₂O₃ was also etched using Al(CH₃)₃, AlCl(CH₃)₂, TiCl₄ or Ga(N(CH₃)₂)₃ as the metal precursors for ligand-exchange.

Crystalline GaN samples prepared using MOCVD techniques at the US Naval Research Laboratory were etched with sequential XeF₂ and BCl₃ exposures. GaN etch rates varied from 0.18 to 0.72 Å/cycle at temperatures from 170 to 300°C, respectively (see Supplemental Figure 1). Because the GaN etch rates were self-limiting versus BCl₃ exposure and BCl₃ pressure, the GaN etching mechanism is believed to involve XeF₂ fluorination of GaN to GaF₃ and then ligand-exchange between BCl₃ and GaF₃ to yield volatile BCl_wF_x and GaF_yCl_z species. GaN fluorination using a NF₃ plasma was also successful for etching crystalline GaN at 250°C.

Ga₂O₃ samples deposited using ALD techniques were etched with sequential HF and BCl₃ exposures. Ga₂O₃ etch rates varied from 0.59 to 1.35 Å/cycle at temperatures from 150 to 200°C, respectively. The Ga₂O₃ etch rates were self-limiting versus HF and BCl₃ exposure. Ga₂O₃ ALE was also performed using HF for fluorination and a variety of metal precursors for ligand-exchange. Ga₂O₃ etch rates at 250°C were 0.2, 0.8, 1.1 and 1.2 Å/cycle for Ga(N(CH₃)₂)₃, TiCl₄, Al(CH₃)₃ and AlCl(CH₃)₂ as the metal precursors, respectively (see Supplemental Figure 2). The wide range of metal precursors that can etch Ga₂O₃ argues that the ligand-exchange reaction with GaF₃ is facile.