Development and Characterization of Photodefinable Polybenzoxazole
Buffer Layer for InGaP/GaAs HBT Applications

Dragana Barone, Jiro Yota, Hoa Ly, Stanley Mui, Shiban Tiku, and Steve Canale
Skyworks Solutions, Inc.
2427 W. Hillcrest Dr., Newbury Park, CA 91320
Keywords: InGaP/GaAs, HBT, polybenzoxazole, buffer layer, photodefinable, photosensitive
Mechanical damage to the final passivation layer and underlying devices and interconnections is occasionally observed during semiconductor fabrication. This damage can occur during handling, wafer backside processing, and during assembly. Damage can be in the form of scratches, embedded defects, cracks, chip-outs, delamination, which can affect the circuit performance and can lead to lower yield, poor quality and reliability, and higher customer return. We have developed a process for InGaP/GaAs HBT technology using a photodefinable polybenzoxazole (PBO) as buffer layer that is coated on top of the final passivation layer, for effective protection against mechanical damage. The PBO process is manufacturable, is compatible with existing process and tool sets, with minimal additional steps, and uses no additional mask layer. Furthermore, the material has excellent material characteristics and also functions as resist and hardmask during street and bondpad opening etch. Additionally, InGaP/GaAs HBT wafers with MIM capacitors, and with PBO as buffer layer that have been intentionally damaged, have been shown to have minimal capacitor failures even after wafer exposure to high temperature, high pressure, and high humidity autoclave test conditions, compared to the many failures observed on wafers with no PBO buffer layer.
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