R.F. sputtered β-tantalum and b.c.c. tantalum films

Tantalum films have been deposited on both glass and Ta₂O₅-coated substrates by r.f. sputtering. The structure, resistivity ρ and temperature coefficient of resistance TCR of films sputtered in pure argon or reactively in Ar-O₂ or Ar-N₂ have been determined. In pure argon on sufficiently preheated substrates a very pure b.c.c. Ta phase (α^∗-Ta), with ρ∼25 μΩ cm and TCR∼1500 ppm/°C, is formed. Sputtering on substrates which are only slightly preheated or are heated solely by the sputtering process yields a tetragonal Ta phase (β-Ta) with ρ∼165 μΩ cm and TCR∼-160 ppm/°C. With added oxygen the β−Ta phase is produced over the whole partial pressure range investigated. Low partial pressures of nitrogen lead to β-Ta. At higher nitrogen partial pressures b.c.c. Ta (α-Ta) with ρ∼50 μΩ cm and TCR∼650 ppm/°C is formed and finally the plateau region is observed.