Automatic Optical Inspection and Laser Cleaning of Image Sensors

A new dry cleaning methodology named laser shock cleaning and optical inspection technique has been applied not only to remove the particles from the surfaces of image sensors but also to inspect the surfaces automatically before or after the cleaning. In the packaging of CMOS and CCD image sensing modules, the particles generated during the assembly process should be removed from the surfaces of image sensors in order to ensure clear image as well as to enhance the yield. The different kinds of particles were removed from the surfaces by the laser shock cleaning technique which utilizes the airborne shock wave induced by intense laser pulse. For the quantitative evaluation of cleaning performance, number, shape and size of the particles on the surfaces of image sensors were measured by vision inspection technique before and after cleaning. It was found that most particles on the surfaces were successfully removed after the treatment of laser-induced shock waves. The average removal efficiency of the particles was over 95 %. It is interestingly found that the remaining particles after the cleaning are based on organics, which are probably attached during the bonding process.