As new, advanced high-k dielectrics are being developed to replace SiO2 in future generations of microelectronics devices, understanding their etch characteristics becomes vital for integration into the manufacturing process. We report on the etch rates and possible mechanisms for one such dielectric, Zr1-xAlxOy (x approximate to0.2), in plasmas containing a mixture of Cl-2 and BCl3, as a function of gas composition and ion impact energy. Higher concentrations of BCl3 enhance the etch rate as well as selectivity of Zr1-xAlxOy etching as compared to the etching of a-Si, whereas increasing ion energy increases the etching rates but decreases selectivity. In a high density helical resonator plasma, etching rates on the order of 700 Angstrom /min and 1:1 selectivity are typical. Angle-resolved x-ray photoelectron spectroscopy was used to study the composition of the upper similar to 30 Angstrom of the film, before and at the end of the etching process. We found that the etching rate of Zr1-xAlxOy does not change with time for the range of Cl-2/BCl3 ratios and ion energies investigated, whereas the a-Si etching rate in pure BCl3 plasma and at zero substrate bias decreases with time, due to the formation of a B-Si film on the surface.