Technical note: Cryogenic vacuum pump characteristics in reactive d.c. magnetron sputtering processes

Abstract

Cryogenic vacuum pumping has become an accomplished fact in reactive d.c. magnetically enhanced sputtering processes. Thin film requirements have become more stringent with respect to deposition parameter control and reproducibility focusing attention on the operating characteristics of the vacuum pumps commonly used on modern sputtering systems. TiOx films reactively sputtered from a metal target have been deposited in an argon-oxygen mixture by varying the O2 partial pressure. The purpose of this study is to investigate the effect of pumping system characteristics using a standard CVI TM150 size cryogenic pump on the profile of the cathode discharge with respect to O2 percentage. TiOx films were deposited reactively at discharge power levels of 1.0 kW, 2.0 kW and 4.0 kW respectively for Ptot levels of 1.0 mTorr and 2.0 mTorr. A direct comparison with oil diffusion pumping was obtained by replacing the cryogenic pump with a Varian VHS6 oil diffusion pump and repeating the test depositions at the previously stated discharge power levels.Other ancillary pumping system parameters for both the cryogenic pump and the oil diffusion pump were obtained. They include pumpdown characteristics, argon flow rate with respect to chamber pressure, residual gas spectra with respect to argon partial pressure and chamber variation with respect to oxygen percentage with constant argon flow rates.