CORRELATION BETWEEN COPPER DIFFUSION AND PHASE-CHANGE IN PARYLENE

The parylene family of polymeric insulating materials is of interest in electronics because of its low dielectric constant and good sticking properties. It is vapor depositable at low temperatures. Copper is a good conductor and a suitable metal for an interconnection system. Consequently, the Cu/parylene system is a promising combination for multilayer interconnections and thin film packaging. To investigate one aspect of the feasibility of using these two materials for an interconnection scheme, the diffusion of copper into parylene at elevated temperatures has been investigated using the Rutherford back scattering technique. The chief findings of this paper are: 1. Detectable (RBS) Cu diffusion starts at > 573 K. Higher temperature causes more diffusion as expected. 2. The alpha --> beta-phase change is not the main source of the diffusion. 3. The copper deposited on the alpha-parylene does not diffuse even after extended anneals of six hours at 573 K. Thus, the copper-alpha-parylene interconnect system can have thermal budget allowance of more than six hour 4. The starting phase of the PA-n affects its diffusion resistant properties. Furthermore a thermal processing window showing a safe half hour of vacuum annealing at soldering temperatures has been demonstrated.