Analysis of sputtering discharge by optical and mass spectrometry. I. Platinum and tantalum sputtered in argon

Abstract

Optical emission and mass spectrometry techniques have been used to investigate the gas composition during the sputtering of platinum and tantalum in an argon discharge in a dc diode system. The optical emission technique shows that hydrogen is always present in the discharge although the mass spectrometer only detects hydrogen in the case of tantalum. For both metals, the hydrogen is due to dissociation of water vapor, either in the discharge or in the tantalum case by reaction with the tantalum, and its concentration depends on the sputtering conditions and duration and also on the sputtering and vacuum procedures used. The deposition rates of both metals increase as the hydrogen concentration decreases because a greater percentage of the discharge current is due to argon instead of hydrogen ions; changes of 20% in the deposition rate are observed due to this effect. The resistivity of the tantalum films increases with the hydrogen concentration in the discharge, if the hydrogen is due to dissociation of water vapor; no increase is observed when hydrogen is leaked into the sputtering system to increase the hydrogen concentration. It is proposed that the increase in resistivity is due to an increase in the oxygen concentration in the tantalum films, water vapor produced by outgassing being the source of oxygen. At 4.0 kV, changes in resistivity from 210 to 257 μΩ cm were observed and, at 3.0 kV, the resistivity changed from 382 to 560 μΩ cm. The optical emission technique shows promise as a tool for investigating processes taking place in a sputtering discharge without disturbing the system.