Silicon Technologies: Ion Implantation and Thermal Treatment

Chapter 2

Ion Implantation ¹

2.1. Introduction

Ion implantation consists of introducing charged atoms (projectiles) into a material (the target), by communicating to them sufficient energy so that they enter beyond the surface area. The projectiles’ energy is thus clearly different from those of techniques aiming for a surface process or deposition (plasma, molecular beam). Moreover, the implantation is distinguished from these other methods by the purity of the beam, selected at the isotopic level.

It is essentially thanks to the semiconductor industry that implantation technology could spread. Ion implantation is indeed the most common method of semiconductors doping¹. Nowadays, there are thousands of ion implantation machines functioning in this industry. Most of them are devoted to the production of integrated circuits based on silicon. The method, which in the 1970s definitively led to ion implantation supplanting diffusion in the manufacturing technology of microelectronics devices, is the adjustment of the threshold voltage of MOS transistors.

Once incorporated in the process and because of its advantages, implantation quickly imposes itself into all the other doping stages, and even in processes of insulation or purification of the silicon: formation of drain and source areas and the deep n- or p-wells of CMOS circuits, the realization of burred collectors, emitter and base doping in bipolar technology, impurity gettering, realization of buried insulating silica layers ...