Nucleation and Growth of CVD Cu Films
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a metallization method for high aspect ratio features. It also provides the low process temperatures required for the utilization of low-K dielectric materials. Between Cu and dielectric a diffusion barrier layer is necessary that can consist of Ta, Ti or their compounds preferably deposited by highly conformal CVD processes. It is known that the adhesion and orientation of CVD Cu depend strongly on the nature of the underlying substrate [2-4]. Without annealing the CVD Cu films deposited directly on the diffusion barrier show a poor adhesion and the crystal orientation is found to be random [6,7]. These observations make it necessary to achieve a better understanding of the microstructure development during nucleation and the interfacial structure between the CVD Cu and the diffusion barrier. Furthermore, it was found that a PVD seed layer deposited on top of the diffusion barrier prior to the CVD Cu deposition leads to a significant improvement of film adhesion and a preferred texture of the Cu layer [3]. A comparison between this system and the stack barrier/CVD Cu is thus helpful to understand the mechanism of adhesion and orientation. EXPERIMENT The main focus of this work was to study nucleation and growth of CVD Cu and its dependence on the underlying material. The Cu deposition as well as the deposition of the barrier layer were performed in high vacuum cluster tools (Endura TM and CenturaTM based). 237 Mat. Res. Soc. Symp. Proc. Vol. 564 © 1999 Materials Research Society
(tmvs)Cu(I)(hfac) was used as precursor for the CVD Cu deposition with a deposition temperature of 180 'C. The Ta PVD barrier was deposited using the ionized metal plasma (IMP) technique (nominal thickness 200 A), whereas the CVD TiN barrier was produced by a combination of CVD TiCN deposition (using TDMAT as precursor) and subsequent crystallization and carbon etching by a N2/H2 plasma [8]. The CVD TiN was deposited in two steps leading to an approximate barrier thickness of 2x50A. The PVD Cu seed layers were also produced using the IMP technique. Morphology and microstructure were studied by means of high-resolution transmission electron microscopy (HRTEM). Film orientation was investigated by X-ray diffraction (XRD) measurements. Atomic Force Microscopy in tapping mode was used to investigate the surface topography. RESULTS AND DISCUSSION In order to study the nucleation stage we investigated CVD Cu and PVD Cu films after short deposition times of 90 s for the CVD Cu (nominal thickness: 100 A) and 2 s (60 A) and 20 s (200 A) for the PVD Cu. The surface topography of these films as measured by AFM is displayed in Fig. I a, l b and I c. The PVD Cu films show a smooth surface with a very low rms value of 2.4 A for the 60 A PVD Cu film and 3.4 A for the 200 A PVD Cu film. The CVD Cu film gives a much higher value of about 36 A for a nominal film thickness of about 100 A.
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Fig. 1: AFM images of IMP Cu films deposited for a) 2s and b) 20s and c) CVD Cu film after 90s deposition time.
HRTEM cross sectional images of the 100 A CVD
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