Photodefinable Polybenzoxazole as Interlevel Dielectric and Buffer Layer for GaAs HBT Technology

Abstract

Polybenzoxazole (PBO) has been investigated and used as interlevel dielectric and buffer layer for GaAs hetero-junction bipolar transistor (HBT) technology. The polymer film is applied by spin-coating, and is photosensitive and photodefinable. These film characteristics allow the simplification of the process flow and allow the elimination of various steps that are typically used to define the vias, streets, and bonding pads. Additionally, this PBO film can be cured at low temperature (>250oC) and the resulting film has good characteristics against moisture absorption and is stable thermally. Furthermore, the film has good planarity and gapfill characteristics, and has excellent mechanical properties. Results show that GaAs device wafers fabricated with this film as interlevel dielectric has good electrical characteristics. When used as buffer layer, the PBO film is shown to be effective in mechanically protecting the underlying devices and interconnections. The use of photodefinable PBO will result in improvement in device quality and reliability, in addition to in significant reduction in capital and consumable cost, and reduction in cycle time of wafers manufactured. All the above characteristics make this PBO film to be well-suited as interlevel dielectric and buffer layer for and compatible with GaAs HBT technology.