Ion implantation: A new method of doping semiconductors—II

Abstract

A novel method for doping semiconductors is ion implantation where impurities are injected in the form of high-energy ions. The range of these ions is well defined and is a function of ion energy and mass, the nature of the crystal and its orientation to the beam. In addition t o its application to semiconductor device manufacture, ion implantation involves a good deal of interesting physics over a wide field, and in order to include the important aspects the article has been divided into two parts. In Part I the current theory for the range of heavy ions in amorphous and crystalline materials was summarized with the aid of a simple model that demonstrated some of the important features. Some experimental results for the ranges of particles in semi- conductors were given and the various methods used to obtain them were reviewed. In addition, typical apparatus used for ion implantation was described with particular reference to ion sources. In Part II some of the interesting techniques used to study the properties of implanted layers are described. In particular, the location of dopant atoms in the crystal and the disorder of the lattice after bombardment can be investigated by studying the back- scattered yield from crystals bombarded with ‘probe’ beams of, for example, He+ ions. This method is described and typical results are presented together with electrical measurements such as the mobility of carriers in the implanted layers. Damage in the crystal can also be studied using electron diffraction and electron microscopy, and some of the work in this field is described. In addition, the potential advantages and uses of ion implantation are outlined with reference to some of the semiconductor devices that have already been made using this technique.