Wafer cleaning is an essential part of the wafer fabrication process. It ensures that the wafers produced are defect-free, particle-free, and contaminant-free so that the wafers are of premium quality. It also helps create thin silicon wafers. There are various wafer cleaning techniques. In this article, we will discuss to you the most common methods of cleaning wafer:
Chemically bonded film contaminants can be removed on the surface of the wafer through chemical cleaning. The process involves a series of acid and rinses baths. It begins with preliminary cleaning, then the elimination of residual organic contaminants and some metals, after that will be the removal of the hydrous oxide film that is produced from the previous step, then, before the final step, which is drying, atomic and ionic contaminants will go through desorption. It's better to refrain from storing cleaned wafers, but if needed, it must be done in closed glass containers inside a nitrogen dry box.
Native oxide films can sometimes be found on thin silicon wafers where they shouldn't be. They can trigger adverse effects, like higher contact resistance or restricted interfacial reactions. Sputter etching or plasma etching is the techniques commonly used to get rid of these native oxide films. It is performed in the same vacuum environment where the overlying layer will be done.
Wafers are also commonly contaminated with insoluble particulates. The two techniques used to remove these particulate contaminants are ultrasonic scrubbing and a combination of high-pressure spraying and mechanical scrubbing. Ultrasonic scrubbing involves immersing wafers in a liquid medium which is equipped with ultrasonic energy. The shockwaves created in this process loosens and displaces the particulates. The particles will then be filtered.
This process involves using a rotating brush that hydroplanes over a solvent applied on the surface of the wafer. The rotating brush doesn’t touch the actual wafer, but the solvent moved by the brush removes the particles from the wafer’s surface. A high-pressure jet will then be used to spray over the wafer surface to get rid of the particulate contaminants.
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