Photodefinable Polybenzoxazole Interlevel Dielectric for GaAs HBT Applications

Jiro Yota, Hoa Ly, Dragana Barone, Mike Sun, and Ravi Ramanathan
Skyworks Solutions, Inc.
GaAs Technology
2427 W. Hillcrest Dr., Newbury Park, CA 91320
Keywords: GaAs, HBT, polybenzoxazole, interlevel dielectric, photodefinable, photosensitive

We have developed and characterized polybenzoxazole (PBO) as interlevel dielectric for GaAs heterojunction bipolar transistor (HBT) applications. The film is applied by spin-coating and is photosensitive and photodefinable. These characteristics allow the simplification of the process flow and allow the elimination of various steps, including resist coat, dry-etch and resist strip processes that are typically used to define the vias. Additionally, the film can be cured at lower temperature (250oC or higher) than the typical polyimide 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 also show that device wafers fabricated with this film as interlevel dielectric, does not result in any significant difference in the electrical characteristics, when compared to those fabricated using dry-etch polyimide interlevel dielectric. All the above characteristics make this photodefinable PBO film to be well-suited as interlevel dielectric for and compatible with GaAs HBT processing. The use of this film will allow significant reduction in capital and consumable cost, in addition to reduction in cycle time of wafers manufactured using GaAs HBT technology.
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