Bandgap yield loss due to dislocations on RFSiGe transceiver ICs: failure analysis, design improvements and process solutions

Abstract

New design and layout methods were developed to overcome yield loss from dislocation defects, which are omnipresent in SiGe technologies as a penalty for the higher speed compared to pure Si. This paper presents the failure analysis on bandgap malfunctions in a RF-SiGe transceiver device which is currently ramped to production. The resulting yieldloss was significant. In-circuit fault analysis identified collector-emitter leakage of the SiGe-HBT's as the electrical root cause. All existing failure patterns were explained with SPICE circuit simulation. Isolation and characterization of the bipolar transistor and high resolution TEM showed dislocations originating from the high strain at the STI-moat edge. Design and layout improvements were applied to reduce the sensitivity of the bandgap reference circuit to the defects: a 5V HBT with superior yield performance was introduced, and variations in the sizing of the matched npn were investigated. With these improvements, the bandgap fails were drastically reduced.