One of the most important properties of semiconductor materials is that their conductivity can be controlled by adding dopants. Semiconductor materials such as silicon, germanium, and III–VI compounds (e.g., gallium arsenate) are doped with either n- or p-type dopants in IC fabrication. There are two methods used to dope semiconductors: diffusion or ion implantation. Before 1970, a diffusion process was used in IC fabrication. Currently, doping processes are mainly performed by ion implantation.
Ion implantation is an adding process in which dopant atoms are forcefully added into a semiconductor substrate by means of energetic ion beam injection. It is the dominant doping method in the semiconductor industry and is commonly used for various doping processes in IC fabrication. Figure 8.1 shows the relationship of the ion implantation process to other processes in IC manufacturing flow.