The structural and electrical properties of nitrogen-doped tantalum films, sputtered in a dc triode system, have been investigated. For constant sputtering voltage and current, the tantalum deposition rate decreased with increasing nitrogen flow rate; at a flow rate of 12 cm3 min−1, the deposition rate was 75% of the rate obtained without the addition of nitrogen. The density of the films decreased from 15.4 to 9.8 g cm−3 as the nitrogen flow increased from 0 to 12 cm3 min−1. The net effect on the film thickness is an increase from 2700 to 3800 Å for films on glass substrates. Films were also deposited on ceramic substrates at the same time. Both x-ray diffractometer and powder camera analysis showed that the films consisted of the bcc Ta phase at nitrogen flows up to 3 cm3 min−1 but the lattice was approximately 3% larger than for bulk Ta. The hcp Ta2N phase appeared at flow rates above 3 cm3 min−1 and the change from bcc Ta to hcp Ta2N was accompanied by an increase in the room-temperature coefficient of resistance from positive to negative values. For films on glass, the resistivity was approximately 250 μΩ cm as the nitrogen flow increased from 4 to 8 cm3 min−1 but the resistivity had a monotonic increase for films on ceramic substrates. The hcp Ta2N phase was replaced by the fcc TaN phase as the flow rate increased in this range; the latter phase had a preferred (111) orientation on the substrate. As the flow rate increased from 8 to 12 cm3 min−1, the resistivity increased rapidly for both types of substrates and the temperature coefficients became rapidly more negative. It is suggested that this behavior is due to the presence of an insulating nitride phase in the film.

The structural and electrical properties of oxygen-doped tantalum films, sputtered in a triode system, have been investigated. X-ray diffraction traces from films with a low oxygen content indicate the presence of bcc Ta with a strained lattice. The intensity of the (110) bcc Ta diffraction peak decreases with increasing oxygen content and is interpreted as a decrease in the amount of bcc Ta phase present. Over this same range the appearance and rise in intensity of the β-Ta (200) peak indicates the formation of β-Ta. As the oxygen content is further increased, the structural data indicate a reorientation of the tetragonal β-Ta (200) to the (202) planes with respect to the film surface, an effect which has been previously observed in diode-sputtered tantalum; further increase in oxygen content produces a stretching of the β-Ta lattice by as much as 10% of the value reported by Read and Altman. The room-temperature resistivity increases with increasing oxygen content until a ``plateau'' region is reached at ∼ 210 μΩ cm corresponding to 12 at. % oxygen, and together with the x-ray data the electrical measurements indicate a change of phase from bcc to β-Ta. Above approximately 40 at. % oxygen the resistivity increases rapidly suggesting the formation of tantalum oxide.

Effect of arc suppression on the physical properties of low temperature dc magnetron sputtered tantalum thin films Low target power wafer sputtering regime identified during magnetron tantalum barrier physical vapor deposition J. Appl. Phys. 98, 024904 (2005); 10.1063/1.1980532Ultraviolet emission from argon water-vapor mixtures excited with low-energy electron beams

Tantalum films have been deposited in a triode sputtering system operating at a total pressure of 5×10−4 Torr that was maintained by continuously adding an argon-water vapor mixture. Because of the low operating pressure, a mass spectrometer mounted directly in the chamber was used, without any differential pumping, to monitor mass spectra before, during, and after sputtering. The mass spectra show that the water vapor is dissociated in the discharge, and the resultant oxygen is gettered into the film. The oxygen content of the films was determined from the anodization efficiency, and it increased linearly with the inlet rate of water vapor. Measurements of the electrical properties show that the oxygen is incorporated in the films in the same way for water vapor and oxygen doping. The resistivity is increased from 50 to 1014μΩ cm with increasing oxygen content. The rapid increase in resistivity from 50 to 200 μΩ cm between 4 and 11 at.% is due to the change from bcc to the β-Ta structure. These results show that very low outgassing rates of water vapor may be sufficient to produce β-Ta in many sputtering systems.