Plasma etching selectivity of ZrO2 to Si in BCl3/Cl2 plasmas

To improve the etching selectivity of ZrO2, a promising high-k dielectric material on silicon, BCl3 was added to a Cl2 plasma to enhance the ZrO2 etch rate while suppressing the silicon etch rate. The electron temperature, ion density, and gas-phase composition in BCl3/Cl2 plasmas were characterized by Langmuir probe, optical emission spectroscopy, and quadrupole mass spectrometry. The maximum ZrO2 etch rate coincides with the highest ion density obtained at 40% of BCl3 in BCl3/Cl2 plasmas. In etching ZrO2, oxygen was removed as boron-oxygen-chlorine compounds, in contrast to its removal as ClO+ in a pure Cl2 plasma. Boron passivation of silicon forming B–Si bonds was confirmed by x-ray photoelectron spectroscopy. The threshold energies for etching ZrO2 and Si in pure BCl3 plasmas were determined to be 21 and 28 eV, respectively. At an ion energy of 75 eV, the etching selectivity between ZrO2 and Si was ∼0.01 in a pure Cl2 plasma to ∼1.5 in a pure BCl3 plasma. The etching selectivity was increased to be greater than 10 at ion energies near and above the ZrO2 etching threshold.