Interlevel Dielectric Processes Using PECVD Silicon Nitride, Polyimide, and Polybenzoxazole for GaAs HBT Technology

Abstract

Multiple factors need to be considered when selecting an interlevel dielectric material for GaAs semiconductor device fabrication including what the electrical, mechanical, chemical, thermal, and cost requirements are and whether the material and the process are compatible with GaAs processing. In this study, we evaluated several interlevel dielectric materials for GaAs heterojunction bipolar transistor (HBT) technology. This technology requires the material to have good gapfill and planarizing characteristics, as the various device and interconnect structures can have significant topography. Additionally, the process typically can only have a maximum temperature of , as device degradation can occur at higher temperatures. The dielectric materials evaluated are plasma-enhanced chemical vapor deposition (PECVD), silicon nitride , polyimide, and photodefinable polybenzoxazole (PBO). The PECVD is mostly conformal when deposited. However, it has a high dielectric constant, cannot be used as gapfill material, and does not planarize the underlying topography, which makes multilevel metallization challenging. Polyimide and PBO, both of which need to be thermally cured, have a lower dielectric constant than PECVD . However, the polyimide in this study has to be dry-etched, unlike the photosensitive PBO. Furthermore, the PBO has better gapfill and planarization capabilities than polyimide.