Removing defects from sputter damage on InGaP surfaces using thermal atomic layer etching

Thermal atomic layer etching (ALE) was utilized to remove sputter damage from InGaP samples. Removal of sputter damage from InGaP surfaces was measured using x-ray photoelectron spectroscopy (XPS). Damage was identified by the shifted doublets in the P 2p region of the XPS spectrum. Density functional theory identified the damage as corresponding to the undercoordinated atoms in the InGaP lattice. InGaP substrates were sputtered with Ar+ ions at 500 eV or 2 keV as a model system to simulate the exposure of InGaP to energetic species during plasma processing. The InGaP thermal ALE process used sequential exposures of hydrogen fluoride for fluorination and either trimethylaluminum or dimethylaluminum chloride for ligand exchange at 300 °C. The XPS spectra revealed that InGaP thermal ALE successfully removed damage from sputtering. The area of the shifted doublets in the P 2p region was progressively reduced versus the number of ALE cycles. After ALE, the resulting XPS spectra were equivalent to the spectrum of an InGaP sample with no sputter damage. A bulklike XPS spectrum showing minimal damage was recovered after 50 ALE cycles for a sample initially exposed to 500 eV sputtering. Sputtering at 2 keV required 100 ALE cycles to largely remove the surface defects. The etch depth consistent with 100 ALE cycles indicated a damaged material depth of ∼5–6 nm. In addition, Auger electron spectroscopy (AES) revealed that the Ar AES signal from implanted Ar in InGaP after sputtering was also progressively removed versus the number of ALE cycles.