Image sensors are electronic integrated circuits that can be used to produce still or video images. Solid state image sensors can be either of the charge coupled device (CCD) type or the complimentary metal oxide semiconductor (CMOS) type. In either type of image sensor, a light gathering pixel is formed in a substrate and arranged in a two-dimensional array. Modern image sensors typically contain millions of pixels to provide a high resolution image. Formed atop each pixel is typically a micro-lens that serve to focus the incident light onto the pixels, and thus to improve the fill factor of each pixel.
In general, the manufacturing process of integrated circuit (IC) image sensors is similar to that of the vast majority of ICs. A relatively large semiconductor wafer (for example, 300 mm diameter) proceeds through a number of deposition, etching, masking, cleaning, and other steps in order to form devices onto the wafer. Moreover, it is not uncommon for hundreds, if not thousands, of discrete IC die to be formed on a single wafer. When the IC die have been fully formed, the wafer is sliced (referred to as dicing) along scribe lines formed in the wafer to separate the individual IC die from one another. After the individual IC die have been separated, the IC die are then mounted onto a package using a die bonding process.
The process of dicing the wafer invariably will result in some amount of particulate matter to be generated that is undesirably deposited onto the micro-lens surface of the IC die. While a cleaning step (using a gas or liquid) is typically performed to remove the particulates, this is still not sufficient to remove all of the particulates. This results in a reduced yield. Further, the cleaning process increases complexity and cost.