Rapid thermal annealing :  After ion implantation, the Si crystal will have a lot of defects and will have stress. The stress must be relieved and the defects reduced. This process is called ‘repair’. If the wafer is heated and cooled, then these goals can be achieved. However, the dopants will diffuse at high temperature and hence the profile will change significantly.

If the wafer is heated quickly, the dopant diffusion is minimized, but the defect and stress levels will reduce. This process is called Rapid Thermal Annealing (RTA).  The typical activation energy for repair (5 eV) is more than the typical activation energy for diffusion (3 or 4 eV). Hence, high temperatures favor repair over diffusion. 

The rapid increase in temperature is achieved by using lamps or lasers, but furnace can be used for relatively low temperatures (<500 ˚C).  Heating rates in the range of 100 to 1000 ˚C/s can be achieved. The high temperatures are measured using pyrometers. In case of lamps, tungsten halogen bulbs or arc lamps are used. These operations are conducted in high vacuum. Otherwise, the silicon wafer surface will get oxidized quickly.