Plasma influence in tantalum sputtering

Abstract

The angular distribution function (ADF) and the sputtering yield have been measured in a triode sputtering system where a dense ionic current (35 mA/cm2) drawn from an argon plasma confined by a magnetic field impinges upon a tantalum target biased at 1.8 keV. The system was placed in a vacuum chamber at a pressure on the order of 10−4 Torr. The results are the following for the two phases of Ta deposited. For α-Ta the ADF is Lambertian but the associated yield is lower than the theoretical one; for β-Ta the ADF curve lies below the Lambertian cosine curve. We suggest the following interpretation based on the influence of impurities. For α-Ta there are many impurities which can be ionized and contribute to the current. Also, these ions destroy the Ar* metastables and, therefore, lower the Ta-Ar* collision probability. For β-Ta there are no impurities. The current is due only to ionized argon and Ar* metastables are not destroyed (i.e., the collision probability is much higher). In such a way, we are able to explain the discrepancies observed in these two cases in terms of both the sputtering yield and the ADF.

The structure and stability of β-Ta thin films

“…Moreover, our simulations have shown this structure to be stable up to 400 K (the substrate temperature during deposition of h-Ta is normally below~400 K [46]). This suggests that the formation of h-phase tantalum in thin films may not be impurity stabilized [47][48][49] or substrate stabilized [50,51], as previously suggested. In addition, a phase transformation to bcc was never observed for the extended h-Ta solid in the simulation work by Klaver [52].…”

“…a-Ta is considered an attractive coating material in many applications for its high toughness, ductility, low electrical resistivity (15-60 AV cm), and corrosion resistance [1,2]. Hard and brittle h-Ta is less desirable in most applications with the exception of thin film resistors because of its high resistivity (170-210 AV cm) [3][4][5][6]. The structure of Ta films deposited by sputtering is usually the metastable h-phase or a mixture of the two phases.…”

“…The mechanism of the preferential growth of h-phase is not well understood. It is not even clear that this phase has a unique structure as various lattice constants of h-Ta films [8,9] and a broad range of resistivity [4][5][6] has been reported. The study presented in this paper addresses these issues.…”

Theory of the structural phases of group 5B–6B metals and their transport properties

“…The room temperature resistivities of β-Ta thin films with thicknesses ranging from 100 -20,000 Å have been measured by the four-point probe method 23,24,30,45,46,53 and the values obtained fall in the range 170 -220 µΩ cm. The value of the bcc Ta room temperature resistivity is 13.6 µΩ cm, 24 1200 -1600 % less than the range of values that have been reported for β-Ta.…”

Structural and Electronic Properties of Pure Ta, TaNO, and TaZrNO with Ab Initio Calculations

“…The discoverers of the tetragonal tantalum β-Ta (a metastable phase), in 1965 are Read and Altman [1]. It has been attracting much interest in most applications because of its high resistivity (170-210 μΩ cm) [2][3][4][5]. It is preferred for fabricating capacitors and resistors.…”