Cleaning and rinsing steps occur at different times within the processes that convert mono-crystalline ingots and polycrystalline silicon slabs into individual wafers.
Ingots and slabs that have been cropped should be rinsed with the filtered coolant/lubricant used in the cropping saw. This ensures that the silicon is transferred and mounted on the squaring saw with no inherent particles or defects that can cause problems during squaring.
Once the ingot or slab is squared it should also be rinsed with the filtered coolant/lubricant used in the squaring saw. After squaring, the silicon blocks should be cleaned in an ultrasonic tank or rinsed with a high pressure spray prior to mounting on a beam. Once mounted on a beam the block is secured to the wire saw for wafering. The cleaning or rinsing of the blocks should include a detergent designed to clean silicon without staining.
Once the blocks are mounted on a beam and fixture to the slurry fed wire saw they are converted into individual wafers. Once the wafers are cut they should be rinsed prior to demount. The rinsing should be performed using a low foaming detergent. After demount the wafers should be stored in wet-storage as they await cleaning. The wet storage should contain an inhibitor which prevents staining and additionally loosens particles left from the sawing process.
Stored wafers are then cleaned using either ultrasonic cleaning or spray cleaning, or, a combination of both. Ultrasonic cleaning using a temperature of about 45 degrees C with a detergent designed for silicon can remove most if not all of the contaminating process particles. High pressure spraying can also perform much the same function as ultrasonic but requires an ultra-low foam detergent designed for silicon. In some instances, for complete cleaning, a combination of both ultrasonic and spray cleaning is used. In this case an ultra-low foaming detergent should be used in both processes since carry over from the ultrasonic tank can cause foaming in the spray wash system.
Once the wafers are cleaned they are dried, stacked and ready for sale or further processing.