Wafer/substrate cleaning is done in order to remove the wafer’s surface of all foreign objects, such as dirt, dust, scum and silicon. It takes place in a clean room for optimal cleanliness. This process uses two solutions containing hydrogen peroxide (H2O2) in order to remove the contaminants from the surface of the substrate.

There are several different points at which a wafer must be cleaned. Many of these procedures involve several steps. This is an example of the initial wafer cleaning process. First, if heavy residue, such as fingerprints, is visible on the surface of the wafer, it is cleaned with a TCE-dipped Q-tip (This is not always necessary for new wafers). The wafer then must be immersed in a series of mixtures, starting with TCE, then acetone, methanol, and is finally rinsed off with distilled water.

Residual organic contaminants must then be removed. The wafer is soaked in an ammonia-peroxide solution for a set time. It is carefully washed off with more distilled water to be sure that the contaminants do not return to the wafer through unbroken water surfaces.

Following this, a test must be done to discover whether or not the wafer’s surface is hydrophilic. If it is, the thin oxide layer must be removed using a dilute HF solution. Once again, after it has been soaked in the solution, the wafer must be rinsed off with distilled water.

The process for removing ionic and metallic contaminants is similar. Instead of using an ammonia-peroxide solution, chloride-peroxide is used. The process then continues very much the same as for organic contaminants but adds one extra step. Once the wafer has been rinsed off with distilled water it is then blow dried with filtered nitrogen before continuing on to clear it of its thin oxide layer. This will sufficiently clean the wafer of any contamination.

The wafer will continue to be cleaned throughout its fabrication regardless of how intricately it is cleaned the first time. It must be kept covered as much as possible to prevent the surface from coming into contact with any contaminants. Each process that takes place with microfabrication is reliant on how free of contamination the wafer’s surface is. Even the tiniest contaminant can have a significant effect on the wafer, so cleaning is substantial to it’s over all ability to function.