Effects of Post-Deposition Annealing on the Copper Films Electrodeposited on the ECR Plasma Cleaned Copper Seed Layer

Abstract

Thin copper films were grown by electrodeposition on copper seed layers which were grown by sputtering of an ultra-pure copper target on tantalum nitride-coated silicon wafers and subsequently, cleaned in ECR plasma. The copper films were then subjected to i) vacuum annealing, ii) rapid thermal annealing (RTA) and iii) rapid thermal nitriding (RTN) at various temperatures over different periods of time. XRD, SEM, AFM and resistivity measurements were done to ascertain the optimum heat treatment condition for obtaining film with minimum resistivity, predominantly (111)-oriented and smoother surface morphology. The as-deposited film has a resistivity of ∼6.3 µΩ·cm and a relatively small intensity ratio of (111) and (200) peaks. With heat treatment, the resistivity decreases and the (111) peak becomes dominant, along with improved smoothness of the copper film. The optimum condition (with a resistivity of 1.98 µΩ·cm) is suggested as the rapid thermal nitriding at 400°C for 120 s.