Yz. Hu et al., In situ rapid thermal oxidation and reduction of copper thin films and their applications in ultralarge scale integration, J ELCHEM SO, 148(12), 2001, pp. G669-G675
Copper is widely accepted as a next-generation metallization material for u
ltralarge-scale integration (ULSI) because of its low resistivity and high
electromigration resistance. It is well known that Cu oxidizes easily at lo
w temperatures. This characteristic has impeded the application of Cu in in
tegrated circuits. However, the high oxidation rate of Cu and high reductio
n 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 wer
e performed in dry and wet oxygen at temperatures from 100 to 600 degreesC
for oxidation times from 10 to 718 s. Scanning electron microscopy, Rutherf
ord backscattering spectrometry, spectroscopic ellipsometry and reflectomet
ry, and X-ray photoelectron spectroscopy were used for analyzing the chemic
al composition of the processed material and determining the oxidation/redu
ction kinetics of the films. The results showed that the oxide phase is CuO
at higher temperature and Cu2O at lower temperature (<400C). In situ reduc
tion of copper oxide was studied using secondary ion mass spectroscopy, ind
icating 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 lamp
s is consequently reflected by the Cu surface. An improved process, called
shield-enhanced RTP, results in higher lamp power efficiency and better wit
hin wafer temperature uniformity. (C) 2001 The Electrochemical Society.