The Cu film was deposited on sputter deposited TiN/Ti/Si-substrate and TiN/Ti/$SiO_2$/Si-substrate in a low-pressure reactor using Cu(hfac)(tmvs) as the precursor. The deposited films were subjected to annealing at various annealing temperatures(350-550℃),methods(post anneal, in-situ anneal),and ambients(Ar,$H_2$(10%)/Ar). The changes of the microstructures and the electrical properties of the Cu film was observed and its grain growth mechanism was investigated.
The mechanism of Cu diffusion in the TiN was investigated to analyse the diffusion barrier properties of TiN against Cu in respect to its thickness and the composition. The improvement of the Cu diffusion barrier properties through the extension and the densification of grain boundary by varying the deposition method and by stuffing was investigated using various characterization methods(SEM, XRD, 4-point probe, AES, and C-V plot).
The in-situ annealing was more effective than the post annealing in regard to the suppression of Cu oxide formation, and $H_2$(10%) /Ar was more effective than Ar as an ambient gas for the post annealing of Cu films because $H_2$ enables the reduction of Cu oxide on the Cu surface and in the grain boundary, causing greater grain size, smoother surface, hence resulting in smaller electrical resistivity of the annealed film. With increase of the annealing temperature, the surface roughness and the resistivity of the annealed film decreased, and grain size increased.
Upon annealing at 450℃, for 30min in an $H_2$(10%)/Ar ambient, the grain size of the Cu film deposited at 180℃ under 0.5 torr with the deposition rate of 53 nm/min increased from 122 nm to 271 nm and the resistivity decreased from 2.35μΩㆍcm to 2.07μΩㆍcm, and the activation energy of the grain growth of Cu was 12.2 kcal/mol.
The Cu diffusion barrier property of TiN was found to be affected not only by the TiN thickness, that is the diffusion distance, but also by the microstructure of the TiN, which changes with the thickness of TiN film. The density of TiN was more important than the atomic ratio of TiN in regard to the Cu diffusion barrier property, because TiN with high density had lower defect density than the TiN with low density. From the view point of the microstructure of TiN, the Cu diffusion barrier property of TiN improved when the grain boundary of TiN was lengthened and densified, which was confirmed by increase of the breakdown temperature of the TiN diffusion barrier observed through various characterization methods. The 40nm thick TiN with double deposition(the expending of the grain boundary of TiN), stuffing (the densification of the grain boundary of TiN) by RTP treatment ($NH_3$, 600℃, 1 minute) was found to be stable up to 575℃ for 2 hours by the C-V characterization method.
The C-V characterization method was most sensitive among the various characterization methods for the observation of the breakdown of the TiN diffusion barrier,and then the sensitivity decreased in the order of AES, SEM, 4-point probe, and XRD. When the annealing temperature was increased, the beginning of the TiN diffusion barrier breakdown started in very small regions of the TiN film. Considering that 40nm thick TiN had grain size of below 40nm, it can be concluded that the Cu diffusion in the TiN started only through the weak grain boundary of the TiN film.
