CHARACTERIZATION OF DEFECTS IN SI AND SIO2-SI USING POSITRONS

In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open-volume-type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional. defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si-based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2-Si interface trap centers, variations of interface trap density, hole trapping at SiO2-Si interfaces, and radiation damage in SiO2-Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.