CHANNELING IMPLANTS IN SILICON-CRYSTALS

Boron and phosphorus channeling implants in silicon at medium and high energies are reviewed. A wide range of doses has been investigated from low doses (10(12)/cm2), where the radiation damage can be neglected, to high doses (10(15)/cm2) where the damage influences the depth distribution. At low doses the profile results from the superimposition of the channeled and of the random component. So the maximum penetration of the channeled particles along the different channels can be easily experimentally determined. The maximum penetration of ions and the extracted electronic stopping are reported for [100], [110] axial channeling and for implants in thick amorphous Si targets. Increasing the dose a third component is necessary to describe the dopant profile. This contribution is related to the fraction of dechanneled particles that depends on the number of displaced silicon atoms. In this case the profiles can be determined as a convolution of three gaussian curves. Channeling tails are present also for implants performed in a random equivalent direction. These tails can be reduced but cannot be avoided. Monte Carlo simulations. based on a simple treatment of the electronic energy loss within different channels, describe quite well the profiles at low doses. The lateral spread of channeled implants under the mask is quite small also at relatively high doses. This lateral spread has been studied by means of two dimensional spreading resistance and a comparison with random implant is presented. In channeling implants the radiation damage is also reduced and the amount of extended defects generated after thermal annealing is reduced too. All these effects are presented and discussed.