A cleanroom is an environment that has a controlled level of contamination and allows in a very low level of pollutants like dust or chemical vapors. They are used mostly in biotechnology, life sciences, and of course semiconductor manufacturing, as well as other fields that cannot have environmental contamination in their products.
The air that enters a cleanroom from the outside is filtered and constantly recirculated though different filters to avoid any internally generated contaminants. The staff whom work within the cleanroom must enter and leave through airlocks and wear appropriate clothing to be sure not to contaminate the room. To be sure that organic contamination is reduced at all costs, materials made from natural fibers, such as paper and pencils, are excluded from entry to the cleanroom. These somewhat extreme measures assure that the wafer experiences minimal contamination.
Contamination comes from several different factors and any sort of interaction with those contaminants can ruin a substrate. The first aspect that can contribute to contamination is the facility. Sheet rock, paint, and air conditioning pollutants provide problems to a wafer being manufactured. The cleanroom eliminates the worry of any such dangers. Another detriment is people. Skin flakes and hair are abundant but unwanted organic materials. These can be eliminated by wearing protective clothing and through the use of airshowers that remove further contaminants from such clothing.
Once past the possibility of outside contaminants, cleanrooms also need to be able to remove any contamination created within itself. Tool generated pollutants, such as those emitted by anything from friction and vibration to mops and dusters, are protected against through the use of specialized tools that create very little contamination. Fluids, like coatings or particles in the air, must be eliminated through the constant recirculation of cleanroom air throughout filters.
Finally, contamination can come from the product itself that the cleanroom attempts to protect. Silicon chips, quartz flakes, and even cleanroom debris must be avoided through special means and constantly cleaning the wafer over and over again through wafer/substrate cleaning.
Cleanrooms are classified by the number and size of particles permitted per volume of air. They can range anywhere from ISO 1 to ISO 9 and can contain from as little as .1 micrometer of a particle to 5 micrometers of a particle.