6.1 Range Concepts

As discussed in Chap. 5, the implanted ion loses energy by means of both nuclear and electronic interactions with the substrate atoms. The former interaction consists of individual elastic collisions between the ion and target-atom nuclei, whereas the electronic interactions can be viewed more as a continuous viscous drag phenomenon between the injected ions and the sea of electrons surrounding the target nuclei. For the energy regime normally used in heavy-ion implantation (i.e., tens to hundreds of kilo-electron-volts), the nuclear contribution to the stopping process normally dominates, and this is reflected in the particular ion trajectories as the ion comes to rest within the solid.

In Fig. 6.1 we see a two-dimensional schematic view of an individual ion's path in the ion implantation process as it comes to rest in a material. As this figure shows, the ion does not travel to its resting place in a straight path due to collisions with target atoms The actual integrated distance traveled by the ion is called the range, R. The ion's net penetration into the material, measured along the vector of the ion's incident trajectory, which is perpendicular to the surface in this example, is called the projected range, R _P.

Figure 6.1: An ion incident on a semiconductor penetrates with a total path length R, which gives a projected range R _P, along the direction parallel to that of the incident ion (Mayer et al. 1970)

In Fig. 6.2, a more general three-dimensional...