【International Papers】Charge recovery by vacuum annealing in β-Ga₂O₃ multi-fin trench Schottky barrier diodes

      Researchers from the The Ohio State University have published a dissertation titled "Charge recovery by vacuum annealing in β-Ga₂O₃ multi-fin trench Schottky barrier diodes" in APL Electronic Devices.

Background

      β-Ga₂O₃ is an ultra-wide bandgap semiconductor with a bandgap of 4.8 eV and a theoretical breakdown field strength of 8 MV/cm. This gives Ga₂O₃ a high Baliga Figure of Merit (BFOM) compared to Si, SiC, and GaN, making it attractive for high-power electronics. The availability of melt-grown bulk substrates makes β-Ga₂O₃ technology highly scalable and reliable and creates a competitive advantage over SiC and GaN. At this stage, the challenge with β-Ga₂O₃ is the absence of efficient P-type doping. Therefore, realizing devices closer to the theoretical limit is difficult if conventional planar vertical device architectures are used. In this context, the trench architecture is quite useful as it provides engineering flexibility and design scope to enable devices closer to the theoretical limit. Due to this reason, trench Schottky barrier diodes (SBDs) have been extensively explored due to their increased ability to sustain high electric fields. However, this also creates another difficulty: trench SBDs are conventionally fabricated using Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE), which generally utilizes a Cl-based chemistry and results in charge compensation within the etched structure. We observed the effects of this charge compensation and resulting increase in on-resistance in our previous work. In addition, we found that the (010) plane is particularly susceptible to BCl₃/Cl₂-based dry-etch damage as compared to the (100) plane.

Abstract

      In this work, we have demonstrated charge recovery in (001) β-Ga₂O₃ vertical structures after reactive ion etching. The charge recovery is achieved by annealing the etched structures under ultra-high vacuum. Using the same technique, we have further demonstrated multi-fin trench Schottky barrier diodes oriented along [100] and [010] directions with comparable on-resistance. The trench Schottky barrier diodes showed a breakdown voltage as high as 1.85 kV with a punch-through breakdown electric field over 3.2 MV/cm.

Summary

      In summary, we have shown charge recovery in ICP-RIE-etched β-Ga₂O₃ vertical structures using annealing and demonstrated kV-class multi-fin β-Ga₂O₃ trench SBDs with 1.85 kV hard breakdown voltage and a corresponding breakdown electric field of 3.2 MV/cm in the β-Ga₂O₃. By annealing the etched fin structures in ultra-high vacuum, comparable forward conduction was achieved in both [100] and [010] oriented fins. This method can further be implemented to obtain large-area multi-fin devices and can be used to develop β-Ga₂O₃ trench MOSFETs that do not suffer from orientation-dependent on-resistance variation.