Rapid Thermal Annealing Treatment of Electroplated Cu Films

Abstract

Cu seed layers for copper electroplating were deposited by magnetron sputtering on silicon wafers using TaN as diffusion barriers between the seed layer and silicon. The Cu seed layer was cleaned with a H2 plasma prior to electroplating the copper film, and the effects of the H2 plasma pretreatment were investigated. After thin copper films were grown by electrodeposition on the copper seed layers which had been cleaned with the H2 plasma, they 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. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and resistivity measurements were done to ascertain the optimum heat treatment conditions for obtaining films with minimum resistivity and with smooth, predominantly (111)-oriented surfaces. The as-deposited film had a resistivity of ∼6.3 μΩ-cm and a relatively small intensity ratio of the (111) to the (200) peak. With heat treatment, the resistivity decreased and the (111) peak became dominant. In addition, the surface smoothness of the copper film was improved. The optimal condition (with a resistivity of 1.98 μΩ-cm) is suggested to be rapid thermal nitriding at 400 ◦C.