next up previous
Next: 1.1.4 Diffusion Up: 1.1 Overview of Semiconductor Previous: 1.1.2 Etching and Deposition

1.1.3 Ion Implantation

Ion implantation is the most widely applied doping technique in modern semiconductor technology as it allows for vertically shallow and retrograde as well as laterally well defined dopant profiles. Ionized dopant atoms are accelerated through an electrostatic field, strike the surface and penetrate into the wafer. The dose can be tightly controlled by measuring the ion current. The penetration is adjusted by the acceleration energy. As both, dose and depth, can be monitored electrically ion implantation is highly controllable and reproducible. A subsequent thermal processing step is necessary for two reasons. Firstly, the implanted dopant atoms partly reside on interstitial sites inside the crystal lattice and are, thus, electrically inactive. Secondly, the implanted ions displace silicon atoms and thereby cause implantation damages. A subsequent thermal treatment is necessary to heal as much as possible of the implantation damages and to activate the dopants by moving them on substitutional lattice sites. This so called annealing process limits the possible resolution of the implanted profile. Rapid thermal annealing at a very high temperature allows to repair the damage with minimal dopant movement. When implanting into a single crystal another problem arises due to the anisotropy of the target. Along the major crystal axis the implanted dopants collide with fewer target atoms and can thus penetrate deeper into the crystal. This phenomenon referred to as channeling can be significantly reduced by slightly tilting the ion beam against the preferred orientations [Boh95b] [Puc96b].


next up previous
Next: 1.1.4 Diffusion Up: 1.1 Overview of Semiconductor Previous: 1.1.2 Etching and Deposition
Mustafa Radi
1998-12-11