Room Temperature Atomic Layer Deposition of Gallium Oxide Investigated by IR Absorption Spectroscopy

Low-Temperature As-Grown Crystalline β-Ga2O3 Films via Plasma-Enhanced Atomic Layer Deposition

“…The O 1s core level spectrum is well fitted with two major components at binding energies (BEs) of 530.5 and 531.6 eV for in situ Ar annealed and 530.8 and 532.1 eV for 200 W as-deposited samples. The lower BEs at 530.5 and 530.8 eV for both samples (Figure b,e) match well with the lattice oxide (in the form of O–Ga bonding state) in the Ga 2 O 3 films. ,,− , Aside from this, some prior studies have attributed the additional O peaks that appear at slightly higher BEs such as 531.3 and 531.1 eV to oxygen vacancies, 532.7, 532.3, 532.0, 533.3, and 532.8 eV to hydroxyl (−OH) types of bonding state, and 533.2, 532.8, and 531.6 eV to the carbonyl type of bonding structure (in the form OC). Similar features are also seen here for these PEALD grown Ga 2 O 3 films: the subpeak at 531.6 eV for in situ Ar annealing sample (Figure b) can be assigned to oxygen vacancies, whereas the subpeak at 532.1 eV for the 200 W as-deposited film can be attributed to hydroxyl (−OH) and/or carbonyl (OC) bonding states.…”

“…We propose two possible reasons behind this: (i) In our recent AlN growth efforts with the same PEALD system, we have observed that such abrupt thickness gains (kinks) arise due to plasma-induced artifacts at elevated rf powers (≥75 W). , (ii) As the rate of post-plasma thickness gains at 100 and 200 W (Figure a) appears to be more gradual rather than abrupt jumps as was the case in our previous works, , it might be that the possible ligand redeposition process still remains active slightly into early stages of the purge, whereafter it stops as no new energetic plasma species are generated and the plasma-generated (ligand) byproducts are fully pumped out. Although, there are almost no prior in-depth studies on real-time in situ dynamic growth monitoring − ,− of ALD grown Ga 2 O 3 , in a relatively recent work, similar film thickness gains during post-plasma purge periods were observed where the authors have attributed it to the potentially trapped Ga precursor in the delivery line getting adsorbed even before their next precursor was pulsed …”

“…To date, Ga 2 O 3 films have been grown by using deposition techniques such as sputtering, pulsed laser deposition (PLD), the sol–gel method, molecular beam epitaxy (MBE), , metal–organic chemical vapor deposition (MOCVD), and atomic layer deposition (ALD). ,,− Although Ga 2 O 3 layers can be deposited at relatively low substrate temperatures via sputtering and PLD, these techniques significantly lack from high crystal quality, large-area uniformity, and 3D conformality on high-aspect-ratio device structures . On the other hand, device quality epitaxial Ga 2 O 3 thin films are mainly produced on non-Si substrates by using MBE and MOCVD, which require substantially higher substrate temperatures (700–1000 °C). ,− However, such high-temperature harsh processing environments limit the application space of high-quality Ga 2 O 3 layers, particularly its direct monolithic integration on temperature-sensitive CMOS and flexible platforms (Si and amorphous glass/polymeric substrates), which necessitate low-temperature, conformal, and precisely controlled film growth with high crystallinity …”

“…Compared to conventional thermal ALD, plasma-enhanced atomic layer deposition (PEALD) offers additional benefits, where energetic plasma-generated neutral radicals and charged ions further facilitate ALD surface reactions to take place at lower substrate temperatures, while promoting improved film properties including film density and crystal order. − Ga 2 O 3 films have been successfully grown via both thermal and plasma-enhanced ALD by utilizing a number of Ga precursors. However, the vast majority of the reported ALD-grown Ga 2 O 3 films are amorphous which require an extra high-temperature (>700 °C) post-deposition thermal annealing process to achieve crystallization. − ,− There are only a handful of recent reports (published in 2019–2020) on the as-grown crystalline Ga 2 O 3 at reduced substrate temperatures. ,− In the work done by Roberts et al, crystalline films of metastable α-Ga 2 O 3 phase have been successfully grown on sapphire (α-Al 2 O 3 ) at 250 °C, where the films partially included amorphous phases as well. More recently, Wheeler et al have shown high-quality heteroepitaxial Ga 2 O 3 films grown on c -plane sapphire via PEALD at 295 °C, where tuning the substrate temperature, plasma gas composition, and reactor pressure enabled selectivity between different Ga 2 O 3 phases (α, β, and ε) .…”

Low Thermal Budget Heteroepitaxial Gallium Oxide Thin Films Enabled by Atomic Layer Deposition

“…There are only a few literature reports of gallium oxide grown by ALD. − ,− They mostly result in amorphous films that require high-temperature annealing to crystallize. However, there are very few reports ,,,,, of ALD growth of crystalline gallium oxide.…”