Integration of Photodefinable Polybenzoxazole as Intermetal Dielectric for GaAs HBT Technology

Abstract

Photodefinable polybenzoxazole (PBO) has been integrated as intermetal dielectric in GaAs hetero-junction bipolar transistor (HBT) technology. Process module optimization and integration studies were performed and the results and process flow were compared to those of dry-etch polyimide. The photodefinable PBO is shown to allow the intermetal dielectric process flow to be simplified and the number of processes and equipment to be reduced. Results show that PBO has more planarity than polyimide, when coated on GaAs HBT wafers, which typically have significant topography. The photolithography coat, expose, and develop processes were optimized to obtain the desired dielectric thickness and the required via dimension and sidewall profile, in addition the removal of the PBO from the die street. The PBO thermal curing process was performed at 300oC, while plasma ashing was performed to remove any PBO residue from the bottom of the vias. These results show that the photodefinable PBO film is compatible with, is suitable for, and can be integrated as intermetal dielectric in GaAs HBT technology.