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BCl 3 is an attractive plasma etchant for oxides because it is a Lewis acid used to scavenge native oxides on many semiconductors due to the strong B–O bonding. We investigated BCl 3 -based dry etching of the NiO/Ga 2 O 3 heterojunction system. BCl 3 /Ar Inductively Coupled Plasmas produced maximum etch rates for NiO up to 300 Å.min −1 and 800 Å.min −1 for β -Ga 2 O 3 under moderate plasma power conditions suitable for low damage pattern transfer. The selectivity for NiO: Ga 2 O 3 was <1 under all conditions. The ion energy threshold for initiation of etching of NiO was between 35–60 eV, depending on the condition and the etch mechanism was ion-driven, as determined by the linear dependence of etch rate on the square root of ion energy incident on the surface. By sharp contrast, the etching of Ga 2 O 3 had a stronger chemical component, without a well-defined ion energy threshold. The as-etched NiO and Ga 2 O 3 surfaces show chlorine residues, which can be removed on both materials by the standard 1NH 4 OH: 10H 2 O or 1HCl: 10H 2 O rinses used for native oxide removal. According to the location of the Cl 2p 3/2 peak, the Cl is ionically bonded.
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Selective Wet and Dry Etching of NiO over β-Ga 2 O 3
Patterning of NiO/Ga 2 O 3 heterojunctions requires development of selective wet and dry etch processes. Solutions of 1:4 HNO 3 :H 2 O exhibited measurable etch rates for NiO above 40 °C and activation energy for wet etching of 172.9 kJ.mol −1 (41.3 kCal.mol −1 , 1.8 eV atom −1 ), which is firmly in the reaction-limited regime. The selectivity over β -Ga 2 O 3 was infinite for temperatures up to 55 °C. The strong negative enthalpy for producing the etch product Ga(OH) 4 suggests HNO 3 -based wet etching of NiO occurs via formation and dissolution of hydroxides. For dry etching, Cl 2 /Ar Inductively Coupled Plasmas produced etch rates for NiO up to 800 Å.min −1 , with maximum selectivities of <1 over β -Ga 2 O 3 . The ion energy threshold for initiation of etching of NiO was ∼55 eV and the etch mechanism was ion-driven, as determined the linear dependence of etch rate on the square root of ion energy incident on the surface.
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- Award ID(s):
- 1856662
- PAR ID:
- 10362785
- Date Published:
- Journal Name:
- ECS Journal of Solid State Science and Technology
- Volume:
- 11
- Issue:
- 10
- ISSN:
- 2162-8769
- Page Range / eLocation ID:
- 104001
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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We report the dry etching characteristics of Cr2MnO4thin films using Cl2-based inductively coupled plasmas (ICP) for applications in Ga2O3-based power electronics, where p-n heterojunctions offer advantages over Schottky diodes. Cr2MnO4, a thermally stable p-type oxide, was deposited via RF sputter beam epitaxy and etched using Cl2/Ar and BCl3/Ar plasmas, with the latter producing much lower etch rates. The etch rates and surface roughness were investigated as functions of Cl2flow rate, RF power, and gas composition. Results reveal that increasing the Cl2flow rate enhances etch rates but degrades surface roughness due to non-volatile chloride formation and redeposition. Higher RF power improves surface smoothness by increasing ion bombardment energy, promoting physical sputtering, and enabling uniform etching. The etch process is ion-flux limited, with threshold energies comparable to NiO. Post-etch X-ray photoelectron spectroscopy analysis confirms that NH4OH rinsing effectively removes chlorine residues by dissolving metal chlorides and neutralizing acidic species, ensuring a clean surface. These findings underscore the importance of optimizing plasma parameters and post-etch cleaning for fabricating high-quality Cr2MnO4/Ga2O3heterojunctions, which hold promise for high-temperature, high-power electronic applications.more » « less
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The characteristics of sputtered NiO for use in pn heterojunctions with Ga 2 O 3 were investigated as a function of sputtering parameters and postdeposition annealing temperature. The oxygen/ nickel and Ni 2 O 3 /NiO ratios, as well as the bandgap and resistivity, increased as a function of O 2 /Ar gas flow ratio. For example, the bandgap increased from 3.7 to 3.9 eV and the resistivity increased from 0.1 to 2.9 Ω cm for the O 2 /Ar ratio increasing from 1/30 to 1/3. By sharp contrast, the bandgap and Ni 2 O 3 /NiO ratio decreased monotonically with postdeposition annealing temperatures up to 600 °C, but the density of films increased due to a higher fraction of NiO being present. Hydrogen is readily incorporated into NiO during exposure to plasmas, as delineated by secondary ion mass spectrometry measurements on deuterated films. The band alignments of NiO films were type II-staggered gaps with both α- and β-Ga 2 O 3 . The breakdown voltage of NiO/β-Ga 2 O 3 heterojunction rectifiers was also a strong function of the O 2 /Ar flow ratio during deposition, with values of 1350 V for 1/3 and 830 V for 1/30.more » « less
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There is increasing interest in the alpha polytype of Ga 2 O 3 because of its even larger bandgap than the more studied beta polytype, but in common with the latter, there is no viable p-type doping technology. One option is to use p-type oxides to realize heterojunctions and NiO is one of the candidate oxides. The band alignment of sputtered NiO on α-Ga 2 O 3 remains type II, staggered gap for annealing temperatures up to 600 °C, showing that this is a viable approach for hole injection in power electronic devices based on the alpha polytype of Ga 2 O 3 . The magnitude of both the conduction and valence band offsets increases with temperature up to 500 °C, but then is stable to 600 °C. For the as-deposited NiO/α-Ga 2 O 3 heterojunction, ΔE V = −2.8 and ΔE C = 1.6 eV, while after 600 °C annealing the corresponding values are ΔE V = −4.4 and ΔE C = 3.02 eV. These values are 1−2 eV larger than for the NiO/β-Ga 2 O 3 heterojunction.more » « less
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This work demonstrates an in situ etching technique for β-Ga2O3 using solid-source metallic gallium (Ga) in a low-pressure chemical vapor deposition (LPCVD) system, enabling clean, anisotropic, plasma damage-free etching. Etching behavior was systematically studied on (2¯01) β-Ga2O3 films and patterned (010) β-Ga2O3 substrates as a function of temperature (1000–1100 °C), Ar carrier gas flow (80–400 sccm) and Ga source-to-substrate distance (1–5 cm). The process exhibits vapor transport- and surface-reaction-limited behavior, with etch rates reaching a maximum of ∼2.25 µm/h on (010) substrates at 1050 °C and 2 cm spacing. Etch rates decrease sharply with increasing source-to-substrate distance due to reduced Ga vapor availability, while elevated temperatures enhance surface reaction kinetics through increased Ga reactivity and suboxide formation, leading to enhanced etch rates. In-plane anisotropy studies using radial trench patterns reveal that the (100) orientation produces the most stable etch front, characterized by smooth, vertical sidewalls and minimal lateral etching, consistent with its lowest surface free energy. In contrast, orientations such as (101), which possess higher surface energy, exhibit pronounced lateral etching and micro-faceting. As the trench orientation progressively deviates from (100), lateral etching increases. Facet evolution is observed between (100) and (1¯02), where stepped sidewalls composed of alternating (100) and (1¯02) segments progressively transition into a single inclined facet, which stabilizes along (100) or (1¯02) depending on the trench orientation. The (100)-aligned fins exhibit minimal bottom curvature, while (201)-aligned structures display increased under-etching and trench rounding. Collectively, these findings establish LPCVD-based in situ etching as a scalable, damage-free, and orientation-selective technique for fabricating high-aspect-ratio β-Ga2O3 3D structures in next-generation power devices.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1149/2162-8777/ac94a0
