Transformer Coupled Plasma Enhanced Metal Organic Chemical Vapor Deposition of Ta(Si)N Thin Films and Their Cu Diffusion Barrier Properties

Abstract

Ta(Si)N thin films were fabricated by transformer coupled plasma enhanced chemical vapor deposition (TCPECVD) using a pentakisdiethylaminotantalum [PDEAT, Ta(N[C2H5]2)5] metal organic source and SiH4 at 350°C or lower temperatures for various deposition parameters such as H2/(Ar+H2) ratio, working pressure, input power for plasma generation and substrate bias. The plasma parameters such as plasma temperature (Te), plasma potential (Vp), plasma density (Ne), degree of ionization (Di) and hydrogen radical concentration were characterized by a Langmuir probe and optical emission spectroscopy (OES) and they were related to the film properties. The dissociation efficiency of the metal organic source by the plasma had the most significant influence on the composition, structure and resistivity of the film. The residual carbon which existed in the deposited TaN films was in the form of Ta–C and brought about the decrease in the resistivity of the film. As the dissociation of the metal organic source became more pronounced, the carbon content increased and the resistivity decreased. The 30-nm-thick TaN film deposited at 320°C exhibited film resistivity of less than 1,000 µΩcm and an excellent barrier property against the interdiffusion between Cu and Si layers up to 600°C. By applying a negative bias on the substrates during film deposition, the step coverage characteristics as well as the barrier properties were improved. The amorphous Ta–Si–N films were fabricated by adding Si to TaN films. With an appropriate Si content in Ta–Si–N film, the diffusion barrier property can be improved without a significant increase in film resistivity.