Characterization of defects in Si and SiO2−Si using positrons

Abstract

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.

Positron confinement in embedded lithium nanoclusters

“…This phenomenon is observed, e.g., for the SiʈSiO 2 interface. 27 Open volume defects or lattice mismatch at the interface can induce positron trapping. No evidence of positronium formation was found in the analysis of the 2D-ACAR distribution, showing that large vacancy-type defects are not present.…”

“…In the case of, e.g., a SiʈSiO 2 interface, there is evidence of preferential trapping at this interface. 27 Usually, the positron affinity is determined experimentally by measuring the electron and positron work functions 28 ͓see Eq. ͑3͔͒.…”

Experimental and theoretical aspects of electric-field-assisted positron kinetics in metal-oxide-silicon systems

“…48 in Ref. 11 shows two distinct peaks in the S parameter, associated with the Al/SiO 2 and the SiO 2 /Si interfaces. In case of enhanced positron mobility in the oxide, these two peaks cannot be clearly separated ͑Fig.…”

“…The results for positive bias are comprised of SiO 2 , SiO 2 /Si, and Si contributions, with the latter one remaining constant. As the SiO 2 and SiO 2 /Si signatures are drastically different, [10][11][12]16,17,25 any change of the experimentally measured parameters is directly related to a positron drift from the oxide into the SiO 2 /Si interface. Fortunately, numerous publications contain such data.…”

“…After PAS was first applied to study MOS devices, 9 a wealth of information about the SiO 2 and SiO 2 /Si structure and properties was obtained by two groups: one at Brookhaven National Laboratory 10,11 and the other at Delft University of Technology. 12 Although their efforts led to a general understanding of the positron behavior in MOS, differences in the experimental results led to discrepancies in the interpretation of some key characteristics of the SiO 2 and SiO 2 /Si.…”