One of the most important cleaning steps in the processing of silicon wafers is post-lap, or post-grind, cleaning. If a wafer is not cleaned of all particles and organics prior to either caustic or acid etch, defects, staining and non-uniformity will occur.
Although lapping debris should be removed in a post-lap rinse cycle, cleaning lines are designed to handle a significant amount of particulate matter and a variety of organic materials and metals. Typically, two to three ultrasonic cleaning tanks are used in succession, with aggressive chemistry in the first tank, and milder chemistry – often simply a DI water rinse – in the last. For increased effectiveness, operating temperatures for the ultrasonic tanks range from 50°C to 70°C, just below the cloud point of most detergents. An amount as small as <.5% caustic can be added to the detergent tanks to increase cleaning efficacy. Intersurface Dynamics ultrasonic detergents are utilized by major wafer manufacturers worldwide to ensure the cleanest possible post-lap results and hence the highest possible yield.