A Novel CMOS Image Sensor Package Cover Glass White Stain Material Identification Metrology by TOF-SIMS

The demand of CMOS Image Sensor (CIS) in consumer electronics and automotive industries is increasing from day to day in the era of Internet of Things (IoT). The search for lower production cost, shorter production lead time, higher yield of CIS package has becoming more and more challenging. Quality assurance and failure analysis play an important role to ensure high yield production. Typical CIS package failure modes are non-stick on pad (NSOP), lifted CIS die, foreign material on micro lenses, epoxy under cured and stain on cover glass. Most of these failure modes are commonly found in other packages, in this work we highlight on cover glass stain issue which may alter the incoming light intensity and refract its direction and hence producing wrong output signal which is critical when safety of user come into picture especially for automotive industry. The stain observed on cover glass is in white colour with small size, thin layer, low concentration which it difficult to be detected by most of the conventional analysis tools such as Energy Dispersive X-ray (EDX) and Fourier Transform Infrared (FTIR). Top surface analysis tools, X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) were used for the white stain failure analysis. XPS analysis was performed to analyse what is the additional elements present on the white stain as compared to a reference sample, higher Carbon (C) and Oxygen (O) were detected implying that the white stain is likely an organic based material. TOF-SIMS analysis was performed to examine the molecular information of the white stain, fatty acid compound was detected based on 267.3u, 283.3u and 285.3u fragments. Fatty acid is commonly used in die attach epoxy, the white stain on cover glass is likely formed during epoxy process that causes outgassing of volatile fragments.