In situ rapid thermal oxidation and reduction of copper thin films and their applications in ultralarge scale integration

Copper is widely accepted as a next-generation metallization material for ultralarge-scale integration (ULSI) because of its low resistivity and high electromigration resistance. It is well known that Cu oxidizes easily at low temperatures. This characteristic has impeded the application of Cu in integrated circuits. However, the high oxidation rate of Cu and high reduction rate of its oxides at low temperature can be exploited for some potential applications. This paper presents the kinetic studies of Cu film oxidation and in situ reduction of its oxide films. The Cu oxidation experiments were performed in dry and wet oxygen at temperatures from 100 to 600 degreesC for oxidation times from 10 to 718 s. Scanning electron microscopy, Rutherford backscattering spectrometry, spectroscopic ellipsometry and reflectometry, and X-ray photoelectron spectroscopy were used for analyzing the chemical composition of the processed material and determining the oxidation/reduction kinetics of the films. The results showed that the oxide phase is CuO at higher temperature and Cu2O at lower temperature (<400C). In situ reduction of copper oxide was studied using secondary ion mass spectroscopy, indicating that the reduction of Cu oxides proceeds from the interface to the surface with a high reduction rate. The infrared reflectivity of Cu surface is over 99%. This is a problem when the Cu process is performed in a rapid thermal processing (RTP) system, since most of the radiation from the lamps is consequently reflected by the Cu surface. An improved process, called shield-enhanced RTP, results in higher lamp power efficiency and better within wafer temperature uniformity. (C) 2001 The Electrochemical Society.