Getter pumping to allow economical sputtering with xenon

Abstract

Increases in sputter rate, under equivalent commercial operating conditions, can often be achieved by using inert gases heavier than Ar. High atomic weight targets and high sputter voltages result in Kr and Xe having higher sputter yields than Ar. The larger ionization cross sections of Kr and Xe also result in a plasma enhancement. The high consumption rate of sputter gas has previously prevented the economical utilization of Kr and Xe. A d.c.-powered Ti sputter target was added to an r.f. planar diode sputtering system. The sputtered titanium was deposited directly on the vacuum chamber walls to form a large room temperature getter pumping surface. Calculations showed an increase of two orders of magnitude in the pumping speeds of O 2, N 2, H 2O and H 2 over that of a conventional throttled 10 cm diffusion pump. This pumping speed allowed improved sputter cleaning of substrates and the deposition of higher purity films. Operating the Ti getter pump with the diffusion pump closed allowed sputtering with very little inert gas consumption. R.f. sputtering of a Ti target with 750 W at 8 mTorr gas pressure resulted in a sputter gas consumption rate of 3 × 10 -3 cm 3 min -1 for both Ar and Xe. This consumption rate corresponds to a Xe cost of less than 1 ¢ h -1.