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 fr om low doses (10(12)/cm2), where the radiation damage can be neglected , to high doses (10(15)/cm2) where the damage influences the depth dis tribution. At low doses the profile results from the superimposition o f the channeled and of the random component. So the maximum penetratio n of the channeled particles along the different channels can be easil y experimentally determined. The maximum penetration of ions and the e xtracted electronic stopping are reported for [100], [110] axial chann eling and for implants in thick amorphous Si targets. Increasing the d ose a third component is necessary to describe the dopant profile. Thi s contribution is related to the fraction of dechanneled particles tha t depends on the number of displaced silicon atoms. In this case the p rofiles can be determined as a convolution of three gaussian curves. C hanneling tails are present also for implants performed in a random eq uivalent 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 profil es at low doses. The lateral spread of channeled implants under the ma sk is quite small also at relatively high doses. This lateral spread h as been studied by means of two dimensional spreading resistance and a comparison with random implant is presented. In channeling implants t he radiation damage is also reduced and the amount of extended defects generated after thermal annealing is reduced too. All these effects a re presented and discussed.