Ion implantation is a crucial part of silicon wafer fabrication. It is a low-temperature process where ions of one element are increased into a solid material, which changes the chemical, physical, or electrical property of the material. Ion implantation has slowly but steadily replaced thermal diffusion for doping in wafer manufacturing because of its profuse advantages. The most important advantage of ion implant over diffusion is its ability to precisely control the depositing of dopant atoms into the substrate. In this article, we will discuss the process of ion implantation.
The main purpose of ion implantation is to alter the type and level of conductivity of semiconductor materials. It is utilized to create bases, resistors, and emitters in bipolar devices, including drains and sources in MOS devices. Ion implantation is also used to dope polysilicon layers.
Impurity atoms are vaporized and accelerated towards the silicon wafer during ion implantation. These high-energy atoms penetrate the crystal lattice and lose their energy by slamming into silicon atoms before ultimately coming to rest to some extent. Altering the acceleration energy regulates the typical depth of depositing the impurity atoms. Heat treatment is utilized to restore and strengthen the crystal lattice disturbances caused by the atomic collisions.
Collisions are expected, as every implanted ion collides with various target atoms before it comes to a halt. Stopping power refers to the energy that is lost from the ion per unit path length of the ion. The damage caused by these atomic collisions during ion implantation modifies the electrical properties of the target. It also causes deep electron and hole traps that apprehend mobile carriers and boost resistivity. This means that annealing plays an important role. It is needed to restore lattice damage and place dopant atoms in vicarious sites that allow them to be electrically active once more.
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