Gettering:  Gettering is the process of trapping unwanted impurities in a place away from the active region. Active region is the region where transistors are created, i.e. it is the region near the front surface. If unwanted impurities are present in Si, then it is desirable to move them to the back of the wafer rather than leave them on the front, active, side. This is achieved by one of the following techniques. The impurities tend to move towards crystal defects. All these techniques involve creating crystal defects of one form or another. In one technique, the back side of the wafer is doped with high concentrations of Phosphorous. In another, argon implantation is performed on the back side, leading to defects. In the third technique, silicon nitride film is deposited on the back side and this leads to stress, which leads to defects. Adding slight amount of oxygen during the Si crystal growth itself is another technique that can help trap the defects. Even if the defects are near the active area, if they are trapped and made immobile, then the life of the chip will be longer.