Energy resolved ion mass spectroscopy of the plasma during reactive magnetron sputtering

Abstract

The energy distribution and composition of the ion flux on a substrate during reactive magnetron sputtering of TiN and TiWN films were studied by the energy resolved mass spectroscopy. The entrance flange of the probe Hiden EQP500 was positioned in a distance of 50 mm from the Ti or WTi (70:30 at.%) target 100 mm in diameter. The sputtering was carried out in a mixture of argon and nitrogen of various compositions at pressures from 0.05 to 10 Pa and discharge currents from 0.5 to 7 A. The energy spectra of ions at low pressures were characterized by extended high-energy tails. The high energy of sputtered (metal) atoms follows from their distribution at the cathode after being sputtered. The high-energy gas ions (Ar +, N 2 +, N +) stem from two sources. One is the transfer of energy in the collisions with the sputtered metal atoms. The other is the reflection of the energetic ions from heavy elements in the target. A strong reduction of the ion energy at the substrate was found when the pressure was increased from 0.5 to 10 Pa. As a consequence of a loss of energy in many collisions the high-energy portion of the ion energy spectra diminished and the energy spectra of various kinds of ions became similar. Nevertheless, the reflected ions were still apparent, albeit at lower intensity. The TRIM Monte-Carlo simulation showed that the flux of the fast reflected ions and flux of sputtered atoms are of the same order of magnitude, indicating thus the important role of the former species in forming the film properties at low pressures. The analysis of the composition of the ion flux during sputtering in a mixture of nitrogen and argon revealed that the ratio of ion fluxes TiN +/Ti + reached maximum of approximately 0.13, while WN +/W + was up to 0.3.