Surface materials analysis of defect ring on image sensor

Abstract

CMOS (Complementary Metal—Oxide—Semiconductor) image sensors are commonly used in many modern electrical products such as digital cameras, camera phones, automotive applications, gaming applications, etc. In this paper, we will discuss unusual pinkish rings which are observed in a captured colored image. The image was captured using a CMOS VGA (640H × 480V) SOC (System-On-a-Chip) digital image sensor. The image sensor has a micron-scale thick film of organic polymer fashioned into an array of dome-like structures called micro-lenses. Each micro-lens helps to direct light towards photodiodes. The array of micro-lenses is aligned on top of a color filter layer in a similar array format. This Color Filter Array (CFA) with Bayer pattern only allows one color (red, green, or blue) to pass down below to the corresponding array of photodiodes. [1–3] It was thought that some surface analysis techniques such as AES (Auger Emission Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) would not be appropriate for analyzing this defect due to sensitivity limits, defect size, or charging effects. Therefore, we collected surface information with ToF SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) which has certain advantages for this type of sample. [4–7] We supplemented this data with analysis from the following instruments: light microscopy, FIB (Focused Ion Beam), SEM (Scanning Electron Microscopy), and TEM-EDS (Transmission Electron Microscopy with Energy-dispersive X-ray Spectroscopy). By combining the data from these techniques, we evaluated possible causes of the pinkish ring color.