Mass and energy resolved detection of ions and neutral sputtered species incident at the substrate during reactive magnetron sputtering of Ti in mixed Ar+N2 mixtures

Abstract

The fluxes of ions and neutral sputtered particles incident at the growth surface during the deposition of TiN by reactive magnetron sputtering from a Ti target in mixed Ar+N2 discharges were determined using a combination of in situ double-modulation mass spectrometry, Langmuir probe, discharge, deposition rate, and film composition measurements. The N2 fraction fN2 in the discharge was varied from 0 to 1 with the total pressure maintained at 3 mTorr (0.4 Pa). Target nitridation, observed directly through the detection of sputter-ejected TiN molecules, was found to occur over the narrow fN2 range between ≂0.035 and 0.06. With fN2<0.1, more than 94% of the ion flux incident at the substrate is Ar+ while for pure N2 discharges, N+2 accounts for more than 95% of the incident ions. Both the incident Ar+ and N+2 ion fluxes are highly monoenergetic with energies corresponding to eVs, where Vs is the applied negative substrate bias with respect to the plasma potential. However, the energy distributions of incident Ti+ and N+ ions are extended due to the high-energy tails in their sputter-ejection energy distributions. The primary sputter-ejected particles are Ti and N atoms. TiN, TiN+, and Ti+ do not contribute significantly to film growth kinetics.