Effect of temperature on microstructure and electrical properties of TaSi2 thin films grown on Si substrates

Tantalum silicide (TaSi2) thin films were deposited on n-type silicon single crystal substrates using a dual electron-gun system and with Ta and Si targets. The thicknesses of TaSi2 thin films considered in this study are in the range 200–500 nm, respectively. The TaSi2/Si samples were annealed at temperature 1173 K for 2 h in a vacuum of 10−8 mbar. The structure of the tantalum silicide thin films was investigated by X-ray diffraction (XRD). X-ray diffraction results show changes in the structure of TaSi2 thin films from amorphous to crystalline after annealing. According to XRD analysis, a complete conversion to single-phase disilicide TaSi2 was achieved from a sample composition of Ta:Si = 1:2. DC conductivity was measured for the TaSi2 thin films in the temperature range 300–900 K before and after annealing. It has been observed that the DC conductivity and activation energy was affected by changing the TaSi2 film thickness and by annealing. The experimental results indicate that, the conduction phenomena of the investigated sample proceeded via two distinct mechanisms. The first one in the low-temperature range T < 500 K can be described by thermally-assisted tunneling of the carriers in the localized states near the band edge. The value of the pre-exponential factor before and after annealing is less than 104 Ω−1 cm−1. The other process appears in the high temperature region T > 500 K, where thermally activated conduction occurs through the extended states. Here the value of the pre-exponential factor before and after annealing is larger than 104 Ω−1 cm−1. The conductivity is greater in the crystalline phase than in the amorphous phase. The activation energy ΔE for our films before and after annealing is increased with increasing film thickness.

Research highlights
► The low resistivity and an excellent chemical stability make Refractory metal silicides one of the attractive materials for interconnections and low resistance contacts in integrated circuits.
► TaSi2 can be directly used as a gate material without need for ploy-Si.
► The electrical and structural properties of stoichiometric TaSi2 films with different thicknesses and at different temperatures have been studied.