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.

Characterization of defects in Si and SiO2−Si using positrons

The metal-oxide-semiconductor transistor has become the dominant device for very large-scale integrated circuits. The performance and reliability of an MOS device are heavily influenced by the quality and properties of the interface between the oxide and the Si region directly beneath. Inherent, process-related, and operationally and environmentally generated interface states or traps are exceedingly harmful or disabling when present. Although controlled successfully by semiempirical design, fabrication and operational regimens, ever-smaller device size-approaching the scale in which a single trap can be important-makes further extension of knowledge on the basic physical and chemical aspects of interface states essential for confident technological progress. In addition, Si/SiO2 interface states continue to merit research in their own right. This paper briefly highlights selected topics from past and present interface-state research and describes some essential physical and chemical properties.

https://iopscience.iop.org/article/10.1088/0268-1242/4/12/001/pdf

MOS interface states: overview and physicochemical perspective

Positrons in Surface Physics

As a result of considerable progress in microfabrication technology for ultra-large scale integration (ULSI), it has become necessary to control oxide formation on an atomic scale in order to produce defect-free SiO2/Si interfaces. However, the possibility of forming an atomically flat interface by oxidizing an atomically flat silicon surface without introducing structural defects is not yet clarified. In this article the present understanding of chemical structures of SiO2/Si interfaces and initial stage of oxidation of silicon surfaces are reviewed.

Chemical Structures of the SiO2Si Interface

The plastic slip process in crystals is described by a continuum mechanics technique using models for the behaviour of dislocations. Some new models are established for the mean glide path distance of dislocations during single slip and multiple slips and comparisons are made for the strain-hardening characteristics accompanying those models. The spontaneous transition in the deformation curve of single crystals from stage I to stage II is naturally introduced through models of the mean glide path distance.

Numerical modelling of plastic multislip in metal crystals of f.c.c. type

The annihilation characteristics of a monoenergetic beam of positrons, after implantation in Si with a 350‐nm overlayer of SiO2, were measured as a function of mean implantation depth. Positrons implanted overlapping the SiO2/Si interface were observed to decay from a state with properties distinctively different from the state in bulk Si and the thermally grown SiO2, i.e., a positron interface state. The momentum distribution of the annihilating positron‐electron pair, as observed in the Doppler broadening of the annihilation line, is much broader for this state than for either bulk Si or SiO2, in contrast to previously observed localized positron states in solids and at surfaces which show a narrower distribution.

SiO2/Si interface probed with a variable‐energy positron beam

Monoenergetic positrons with incident energies of less than 25 eV were employed as a nondestructive surface and near-surface sensitive probe. Positron reflectivity and the positronium emission were measured as a function of incident energy for various oxygen coverages ranging from submonolayer to 3500 A of SiO/sub 2/ on Si. The characteristics of these spectra change systematically with oxidation and are in good agreement with the known development of the surface electronic structure. Different oxidation stages are identified.

Y. Chen

Papers

SiO2/Si interface probed with a variable‐energy positron beam

Monitoring the surface oxidation process with an energy-tunable monoenergetic positron beam

Introduction; Success of the Technique

Technology of Positron Analysis

Monoenergetic Positron Beam Facilities and Proposals