Secondary ion mass spectroscopic characterization of silver and aluminum diffusion in parylene

Aluminum and silver on parylene‐n (PA‐n) were explored as metallization options. The low resistivity of silver (1.6 μΩ cm) makes it suitable for interconnection applications. Al is a well studied and utilized metal. Al and Ag diffusion have been compared to that of Cu. The Al, Ag, and Cu were deposited by partially ionized beam (PIB) technique. PA‐n, a low dielectric constant polymer, was vapor deposited. Diffusion of the metals was studied at anneal temperatures/time of 573–623 K/0.5 Hr using secondary ion mass spectrometry and Rutherford backscattering techniques. The metal diffusion in the PA‐n was found to be very small. The Cu diffusion profiles were of low concentration but fairly deep. It was observed that the Ag diffused less than the Al, both in atomic concentration and diffusion depth. For these annealing temperatures and time, it was estimated that the diffusion coefficients for Al was about 0.4 × 10⁻¹³ cm²/s; for Ag was about 0.8 × 10⁻¹⁴ cm²/s at 573 K; and for Cu was about 0.6 × 10⁻¹³ cm²/s at 623 K. The diffusion coefficient of Cu in PA‐n was found to be comparable to the diffusion coefficient in polyimides. A substantial reduction of diffusion due to higher ion acceleration (1–3 kV) during PIB metal deposition was observed. It was found that there was significant diffusion when Ag/Pa‐n was annealed at 648 K.