Applications of XRD and TOF-SIMS in failure analysis of SiGe epi wafer

In a BiCMOS process, interface quality of SiGe base region determines the performance of heterojunction bipolar transistor. At present, in wafer fabrication, the in-line metrology tools cannot determine epitaxial film quality. In this paper, it is shown that high resolution X-ray diffraction (HRXRD) technique can be used to not only measure physical parameters of SiGe epitaxial film but also determine its quality. In a recent case study it was observed that after preventive maintenance (PM) of epi reactor, the quality of SiGe film was compromised due to poor integrity of Si/SiGe interface. HRXRD and TOF-SIMS techniques were used to determine the root cause poor Si/SiGe interface and it was shown that oxygen trapping is the responsible for the poor film quality.