Effect of Oxygen on the Temperature Dependence of Electrical Properties of Reactively Sputtered Tantalum Films

Abstract

The negative temperature coefficient of resistivity (TCR) displayed by p-Ta, which has thus far not been satisfactorily explained, has been examined by measuring the variation of electrical resistivity with temperature, from -2S300 OK, and by measuring the Hall coefficients, at room temperature and a t 77 OK, of films containing up to -60 at.% oxygen. The Hall measurements indicate carrier concentrations of -loz2 ~m -~ and mobilities of -1 cm2/V s. The analysis of the results has considered the granular structure of the films and has subsequently compared these results with an 'activated tunneling' model of conduction. Theoretical calculations which assume the film to be comprised of cubic grains separated by T a 2 0 5 agree well with the experimental measurements.Metallic conduction still appears to be contributing to the film properties even at the highest oxygen concentrations of the present investigation.Le coefficient negatif de variation de resistivite en fonction de la temperature (TCR) du p-Ta, qui n'a pas encore ete expliquk de f a~o n satisfaisante, a etC examine en mesurant la resistivite Clectrique en fonction de la temperature de 20 a 300 "K et en mesurant, a temperature ambiante et a 77 OK, les coefficients de Hall de films contenant jusqu'a 60% d'oxygene atomique. Les mesures d'effet Hall indiquent des concentrations de porteurs de cm-3 et des mobilites de -1 cm2/V s. Lors de I'analyse des resultats on a tenu compte de la structure granulaire des films et on a subsequemment compare ces resultats avec un modele "d'effet tunnel active" de la conduction. Des calculs theoriques, faits en supposant que le film est compose de grains cubiques sCparCs par Ta205, concordent tres bien avec les mesures expirimentales.La conduction metallique contribue aux proprietes du film mCme avec les plus fortes concentrations en oxygene utilisees au cours de cette investigation.

Tantalum Suboxide Films with Tunable Composition and Electrical Resistivity Deposited by Reactive Magnetron Sputtering

“…The first region for O content of 50 at.% is characterized by a weak dependence of ρ on O content. This corresponds to the so-called "plateau" region wherein ρ is approximately linear with O content, which has previously been observed for TaO x films made by the "triode" sputtering technique [13,14]. The dependence becomes strong, close-to-exponential in the second region of O content within ∼50-70 at.%, consistent with previous reports [13,28,29].…”

“…Tantalum oxides are, therefore, attractive candidates as alternative hohlraum materials due to their tunable electrical resistivity and good oxidation and corrosion resistance. Prior work on the Ta-O system has mostly focused on stoichiometric Ta 2 O 5 films [10][11][12] or else films with oxygen content in the range of 0-60 at.% [13,14]. Films with composition corresponding to the transition from metallic conduction to insulating behavior remain comparatively unexplored.…”

Electron microprobe analysis of the Ta-O system

“…Standard samples with oxygen contents between 8.3 and 60.7 at % were obtained in this way. For oxygen contents above 10 at %, the P-Ta phase (Read and Altman 1965) was the only phase observed, although it has been postulated that amorphous Taz05 is present between the P-Ta grains (Waterhouse and Westwood 1971). The film thicknesses of these standard samples were between 2000 and 6200 A.…”

“…The thin film standards were sections of films prepared by triode sputtering tantalum onto glass (Corning 7059) substrates in oxygen-argon mixtures (Waterhouse et a2 1971), and were taken from areas whose properties were already known Westwood 1971, Waterhouse et al 1971). The oxygen concentrations of these films were determined with an accuracy of better than t 2 at % from anodization efficiency measurements (Wilcox and Westwood 1971).…”

“…The broken line in figure 2 is based on the assumption that the total correction factor is unity, and there is good agreement between this line and the experimental values, at least for W/ WO > 0.2. Waterhouse and Westwood (1971) showed that the sputtered films probably consisted of small (2: 100 A) grains of p-Ta in a matrix of Taz05. Thus the ratios R/Ro andf(x)/fo(x) were expected to be close to unity.…”