Interfacial oxide and other species in trimethylaluminum-pretreated atomic layer deposition-Al₂O₃/GaN characterized by sputter-assisted ToF-SIMS

Deposition techniques, like atomic layer deposition (ALD), are used to form high-quality dielectrics for GaN-based metal–oxide–semiconductor (MOS) gate structures due to the lack of a reliable thermal oxide in GaN. Moreover, interfacial GaO_x from pre-existing native oxides is thought to adversely impact channel carrier dynamics and induce undesired threshold voltage shifts in GaN-based MOS gate structures. Exposure of the GaN surface to the trimethylaluminum (TMA) precursor prior to standard alumina ALD decreases the native oxide layer on GaN, but the extent of chemical modification has not been well studied in the context of interface composition in a MOS gate structure. Herein, we compare annealed 55 nm Al₂O₃ dielectric films on GaN grown using either a water-first ALD process or a process including sequential pulses of TMA immediately before the initiation of Al₂O₃ ALD. Time-of-Flight Secondary Ion Mass Spectrometry measures differences in the interfacial GaO_x content between each ALD film. Here, it also detects surface contaminant species like Si, F, S, and C. Furthermore, we report the formation of an AlN species at the Al₂O₃/GaN interface, which is more prominent for the film grown using the TMA pre-pulse step. In general, this work demonstrates that the TMA pre-pulse step is an effective strategy for cleaning substrate surfaces prior to ALD.. Authors: Rummel, Brian Douglas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)] (ORCID:0000000201615774); Klesko, J. P. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)] (ORCID:0000000339898009); Meyerson, M. L. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)] (ORCID:000000019327442X); Ohlhausen, J. A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)]; Glaser, C. E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)] (ORCID:0009000496632674). DOE Contract: NA0003525. Subjects: Atomic layer deposition; Depth profiling techniques; Dielectric materials; Interface defects; MOS devices; Secondary ion mass spectrometry; X-ray photoelectron spectroscopy