EFFECTS OF RAPID THERMAL NITRIDING TREATMENT OF ELECTROPLATED CU FILMS

초록

The electromigration performance of metal lines in ultralarge scale integrated circuits (ULSI) technology has now become a primary focus of the scientific community because of the increasing current density in miniaturized devices. Due to its lower resistivity (~1.7μΩ-cm) and high resistance to electromigration compared with aluminum and its alloys, electroplated copper (Cu) has been widely accepted as a new interconnect material for ULSI applications1-4). It is well known that the nucleation of copper is very sensitive to the surface condition of the seed layer5). We have previously studied the effects of pretreatment of the copper seed layer surface on the subsequent copper electroplating4). In the present communication, we focus on different post deposition heat treatments to find out how they affect the properties of the copper films deposited on ECR plasma cleaned copper seed layers. Thin copper films were grown by electroplating on copper seed layers deposited 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 (VA), 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. Also XPS and AES analysis were performed to investigate the binding properties of the Cu-N bonds and the compositional change of the surface region of the copper film by the RTN treatment. 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 -cm) is suggested as the rapid thermal nitriding at 400℃ for 120 sec.