Ion Implantation Effects on the Metal-Semiconductor Interfaces.

In this thesis, the effects of ion implantation on metal-semiconductor interfaces are studied. Hydrogen ions have been used as the implanted species. The implantation is carried out on Al/n-Si Schottky contacts. Electrical characterizations, deep level transient spectroscopy measurements, and the ^{15}N hydrogen profiling technique have been used to study the effects of ion implantation. It is demonstrated that the defect centers in the depletion region created by hydrogen implantation have more likely negative or possibly neutral signatures, rather than a positive signature as has been previously speculated. These negatively charged centers compensate for the positive donor resulting in a widening of the depletion region and reduction in the capacitance of the metal-semiconductor contacts. The tendency of hydrogen to passivate its own damage which results in the recovery of electronic transport across the metal-semiconductor junction upon low temperature heat treatment is also demonstrated. In connection with the behavior of hydrogen in silicon, in the second part of this thesis, detailed theoretical calculations on the hydrogen passivation of defects in silicon are carried out. A particular type of defect, namely, a substitutional sulfur in silicon, is chosen and is studied using the modified intermediate neglect of differential overlap (MINDO/3) molecular orbital method. It is found that the sulfur center can be passivated using one or two hydrogen atoms. The calculations indicate that the most stable positions of the hydrogen atoms are between the sulfur and its silicon neighbors. The hydrogens bond to the nearest silicon atoms and only weakly interact with the sulfur. Thermochemistry considerations predict that a single hydrogen passivates the sulfur center, provided these centers are in abundance in the silicon. Hydrogen ion implantation has also been carried out on Schottky contacts having a large difference in metal work function, Ti/p-Si and PtSi/p-Si structures. The aim of the study is to investigate the possibility of producing Fermi level pinning using ion implantation. The results show a dependence of the implantation effects upon metal overlayer work functions. Consequently, the observation does not seem to indicate the occurrence of Fermi level pinning due to a highly damaged near-surface region after ion implantation. This result is in opposition to what has been previously proposed. In general, it is suggested that ion implantation alters the electrical characteristic of the contacts mainly by creating defects in the semiconductor depletion region. All such defects act as defect centers giving rise to a deviation in the electrical characteristics from the normal behavior. The centers do not play a major role in producing a Fermi level pinning.