PROPERTIES OF PLANAR-MAGNETRON-SPUTTERED TANTALUM FILMS

The effects of sputter conditions on the physical properties of tantalum films deposited from a planar magnetron cathode were investigated using voltages between 250 and 600 V. The films were deposited onto glass and Al2O3 ceramic substrates at a rate of 2000 Å min-1 in argon-nitrogen mixtures, which resulted in a variation of the nitrogen content in the tantalum between zero and 34 at.%. In contrast to the results reported for films sputtered at 200 Å min-1 and at several kilovolts without a magnetic field only two crystalline phases were observed. Films sputtered without nitrogen had the structure of β-tantalum and the crystallographic properties and temperature coefficient of resistance were found to depend on the sputter voltage and/or argon pressure. A change in film structure from β-tantalum to α-tantalum (body-centred cubic) was observed at about 5 at.% nitrogen. No further change in crystalline structure occurred as the nitrogen content increased to 34 at.% with increasing flow rate. It appears that the magnetron-sputtered tantalum films can accommodate much larger quantities of nitrogen interstitially that films sputtered by conventional high voltage techniques which form the hexagonal close-packed Ta2N phase above 25 at.% nitrogen. © 1979.