Inductively coupled plasma etch damage in (-201) Ga2O3 Schottky diodes

Bulk, single-crystal Ga2O3 was etched in BCl3/Ar inductively coupled plasmas as a function of ion impact energy. For pure Ar, the etch rate (R) was found to increase with ion energy (E) as predicted from a model of ion enhanced sputtering by a collision-cascade process, R ∝(E0.5 – ETH0.5), where the threshold energy for Ga2O3, ETH, was experimentally determined to be ∼75 eV. When BCl3 was added, the complexity of the ion energy distribution precluded, obtaining an equivalent threshold. Electrically active damage introduced during etching was quantified using Schottky barrier height and diode ideality factor measurements obtained by evaporating Ni/Au rectifying contacts through stencil masks onto the etched surfaces. For low etch rate conditions (∼120 Å min−1) at low powers (150 W of the 2 MHz ICP source power and 15 W rf of 13.56 MHz chuck power), there was only a small decrease in reverse breakdown voltage (∼6%), while the 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 (∼700 Å min−1) and power (400 W ICP and 200 W rf) 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. This shows that there is a trade-off between the etch rate and near-surface damage.