Effect of polyimide processing on multichip glass ceramic module fabrications

This paper discusses the yield analysis of the thin film wiring layers fabricated on the 127 mm multichip glass ceramic modules (MCM-D), currently used on the IBM Enterprise System/9000/sup TM/ family of computer processors. To select a suitable polyimide (PI) for the thin film wiring layer, modules were fabricated with either the BTDA-APB or the PMDA-ODA polyimide. By keeping all other processing parameters and structures the same, the wiring layers fabricated with the PMDA-ODA polyimide exhibited significantly better yield than those made of the BTDA-APB PI. The yield loss in the modules fabricated with the BTDA-APB PI occurred during thermal processing, where some of the transmission lines fabricated atop the PI were found cracked. Further investigations indicate that, during lift-off processing, the presence of a small contaminant, such as a fiber, metal flake, a particle, or polishing scratches can expose the PI to the hot N-methylpyrollidinone (NMP) solvent. Depending on the polyimide used for thin film processing, the diffusion and swelling of the PI by the low molecular weight organic solvent can potentially produce significant damage to the polyimide/Cu wiring structure and the consequent yield loss of the modules due to line opens. The magnitude of the damage was found to depend on the rate of solvent diffusion, process temperature, lift-off time and the amount of PI swelling during processing.