Doping, Surface Modifications and Metal Contacts
This chapter discusses several processes related to the introduction of controlled impurities in semiconductors, implantation and related process such as exfoliation, and metal–semiconductor electrical contacts. In thermal diffusion, the wafers are placed in a hot furnace along with the dopant sources to allow the impurity atoms to diffuse through the substrate. During doping by thermal diffusion, the wafers are stacked vertically in a wafer carrier and placed in a quartz tube, and heated using infrared lamps or resistive heaters from outside the tube. One of the major disadvantages of doping by thermal diffusion is the isotropic nature of the doped profile. A metal film deposited on a semiconductor surface can produce different results depending on the type of metal, type of semiconductor, surface conditions, and annealing. Metal-semiconductor contacts are often annealed at elevated temperatures to improve their properties. This causes the atoms from both sides of the interface to diffuse and fill the voids and dangling bonds at interface.