Inductively Coupled Plasma Etching and Electrically Active Damage of Bulk, Single-Crystal Ga2O3
Authors: Yang Jiancheng , Ahn Shihyun , Ren Fan , Pearton Stephen J. , Khanna Rohit , Bevlin Kristen , Geerpuram Dwarakanath , Tung Li-Chun , Lin Jingyu , Jiang Hongxing , Kuramata Akito 
Published: February 2020

Monoclinic β phase Ga2O3 is attracting great attention for high power electronics, military applications, and solar blind photodetectors for deep-UV detection, all because of its large direct bandgap (~4.9 eV) and theoretical critical electric field (EC) strength of 8 MV/cm. [1,2,3] There has been a tremendous achievement in both bulk and epitaxial growth of β-Ga2O3. The large bulk β-Ga2O3 is commercially available, and n-type epistructures are also coming onto the market in limited quantities.[4] Record high Vertical diode fabricated on β -Ga2O3 with a reverse breakdown voltage of 1600 V was demonstrated[5], and Ga2O3 based variety of electronic devices have also been reported including metal-semiconductor field-effect transistors, depletion-mode metal-oxide-semiconductor field-effect transistors, and finfets fabricated on either bulk or thin films.[6,7,8,9] It is quite clear that more organized study of etching is needed for intradevice isolation or for exposing layers in gate recess processing for subsequent Schottky gate formation. While numerous wet etchants have been reported for Ga2O3, including HNO3/HCl, H2SO4, H3PO4 and HF-based solutions,[10,11] not too much is known about its dry etching characteristics and the associated mechanisms and effects on the optical properties of the material.

In this study, we will report the effect of dry etching conditions on etching rates and damage induced by the ion bombardment on vertical β-Ga2O3 rectifiers. A Plasma Therm 760 Inductively Coupled Plasma (ICP) system was employed for dry etching by varying the ICP power ranging from 100 to 800W, chuck power (15-400 W) with either Cl2/Ar or BCl3/Ar discharges. The highest etch rate achieved was ~130 nm/min using 800 W ICP source power and 200 W chuck power (13.56 MHz). The etched Ga2O3 surfaces become oxygen-deficient under strong ion-bombardment conditions, and the electrically active damage introduced during etching was quantified using Schottky barrier height and diode ideality factor measurements. For low etch rate conditions (~12 nm/min) at low powers (150 W ICP source power at 2 MHz and 15 W rf chuck power at 13.56 MHz). There was only a small decrease in reverse breakdown voltage (~6%) while the Schottky barrier height decreased from 1.2 eV to 1.01 eV and the ideality factor increased from 1.00 to 1.06. Under higher etch rate (~70 nm/min) and power (400 W ICP and 200 W rf power) conditions, the damage was more significant, with the reverse breakdown voltage decreasing by ~35%, the barrier height was reduced to 0.86 eV and the ideality factor increased to 1.2. By annealing the etched samples at 450°C, the Schottky barrier height, diode ideality factor and reverse breakdown voltage were restored as compared to the reference sample.

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