Inductively-coupled-plasma reactive ion etching of ZnO using BCl3-based plasmas and effect of the plasma treatment on Ti/Au ohmic contacts to ZnO

Inductively-coupled-plasma reactive ion etching (ICP-RIE) behaviour of ZnO has been investigated using BCl3-based plasmas; etch rates are studied as a function of plasma chemistry, ICP coil power and r.f. power. It is shown that compared with Cl2/Ar, Ar and CH4/H2-based gas mixtures, pure BCl3 gas results in high etch rates, indicating that B and BCl radicals react with ZnO and form volatile compounds such as BxOy and/or BCl-O bond. It is further shown that the specific contact resistance as low as 1.5x10-5 Ω cm2 is obtained from Ti/Au contacts on the BCl3 plasma pretreated ZnO. Based on X-ray photoelectron spectroscopy results, possible mechanisms for the BCl3-pretreated improvement of ohmic properties are described