Effect of Oxygen on the Electrical and Structural Properties of Triode-Sputtered Tantalum Films

Abstract

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.

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].…”

“…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]. The third region is for O content of 70 at.%, when the film composition approaches that of stoichiometric Ta 2 O 5 and ρ experiences a rapid increase, where most films with O content above ∼70 at.% had ρ values that were too high to be measured with our (direct-current) setup.…”

“…These observations of the dependence of O content on the deposition rate (influenced by both the chamber pressure and the position of the substrate within the chamber) and chamber pressure indicate that film stoichiometry is determined by the availability of oxygen-containing molecules at the growing film surface, which can also be noted in the data of Waterhouse et al [13] The impingement rate of Ta atoms onto the substrate can be determined by RBS areal density measurements, while the flux of oxygen-containing molecules onto the substrate is determined by their partial pressure and can be estimated with the Knudsen-Langmuir equation [24]:…”

“…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.…”

Effect of arc suppression on the physical properties of low temperature dc magnetron sputtered tantalum thin films

“…[3][4][5][6][7][8][9][10][11] This work, for the first time, reports the physical properties of tantalum thin films prepared at different substrate temperatures in the range of 300-673 K by the continuous dc magnetron sputtering technique in normal and arcsuppression modes. ␤-phase films have high hardness and are quite brittle; 3 these films were used as resistors ͑ = 160-250 ⍀ cm͒.…”