X-ray photoelectron spectroscopic characterization of the adhesion behavior of chemical vapor deposited copper films

Abstract

Adhesion behavior of chemical vapor deposited (CVD) copper (Cu) films on various barrier substrates was studied using a pull-off test. The mean adhesion strength of Cu films on air-exposed physical vapor deposition (PVD) Ta, air-exposed CVD TiN, in situ PVD TiN, and in situ CVD TiN were determined to be 3.42, 4.74, 4.64, and 10.24 MPa, respectively. The adhesion of Cu films on the in situ PVD TiN exhibited almost the same strength as the adhesion on the air-exposed CVD TiN. Root-mean-squared (rms) roughness values for air-exposed CVD TiN and in situ PVD TiN are 8.06 and 1.18 nm, respectively. The rougher surface morphology of the air-exposed CVD TiN films was considered to improve adhesion due to mechanical anchoring. The adhesion strength of the Cu film on the in situ CVD TiN was two times higher than that on the air-exposed CVD TiN. In order to examine the adhesion difference, x-ray photoelectron spectroscopy (XPS) measurement was performed on the exposed interface after pulling off the Cu film. The XPS results showed that on the in situ barrier Cu(OH)2 was formed at the surface, but on the air-exposed barrier Cu(OH)2 was not formed. Consideration of the Ti 2p spectra and the Cu 2p spectra indicated that the native oxide composition of the barrier surface affects the adhesion characteristics in the same way as the oxidation resistance of the Cu atoms. Since the amount of residual F was only 3 to 4 at. % at the interface, the effect of F on the adhesion was not as important as that of the native oxide.