Study of copper diffusion into tantalum nitride (Ta/sub 2/N) by rapid thermal annealing (RTA)

Abstract

We have carried out direct diffusion measurements of Cu into Ta 2 N. Thin films of 50nm thickness of Cu were grown onto a thick Ta 2 N layer of 1µm deposited by Ionized Metal Plasma (IMP). Samples were annealed in a rapid thermal system from temperatures ranging from 400°C to 750°C for periods of 180s. Results based on sheet resistance measurements, x-ray diffraction analyses, atomic force microscopy measurements and secondary ion mass spectroscopy analyses consistently follow a transformation of amorphous Ta 2 N to a crystalline phase and finally forming Cu-Ta-O compounds at higher annealing temperatures. The copper and tantalum nitride diffusion profile was performed using Secondary Ion Mass Spectroscopy. The Cu diffusion coefficients in Ta 2 N can be described by 1.5778 × 10 -12 exp (-0.4066 eV/kT) cm 2 /s. To assure reliability, the extent of both diffusions should be considered in device design and processing.