Selective gas phase pulsed etching of oxides with NbCl5

Abstract

Ta₂O₅ films were etched with NbCl₅ using a chemical vapor etching method known as gas-phase pulsed etching (GPPE) where the etchant is delivered in short pulses with inert gas purging in between the pulses. Arrhenius type dependence of etch per cycle (EPC) on temperature was found at 275–375 °C and the activation energy of the etching reaction is estimated at 120 kJ mol⁻¹. Length of the etchant pulse had a linear effect on EPC and increasing the purge length also increased EPC. Roughnesses of the partially etched films increased from 0.2 to 1.4 nm, as measured by atomic force microscopy. No residual Nb or Cl was detected in the films by energy-dispersive X-ray spectroscopy, but a small amount of Cl residue was seen with in vacuo X-ray photoelectron spectroscopy. Etching of TiO₂ and ZrO₂ was also observed but HfO₂ was not etched by NbCl₅ at 300–400 °C. Selectivity with respect of SiO₂, Al₂O₃, and TiN was also proven at the same temperature range. EPC up to 2.8, 1.1, and 4.0 Å were observed for Ta₂O₅, ZrO₂, and TiO₂, respectively.