Diffusion in silicon of elements from columns III and V of the Periodic Table is reviewed in theory and experiment. The emphasis is on the interactions of these substitutional dopants with point defects (vacancies and interstitials) as part of their diffusion mechanisms. The goal of this paper is to unify available experimental observations within the framework of a set of physical models that can be utilized in computer simulations to predict diffusion processes in silicon. The authors assess the present state of experimental data for basic parameters such as point-defect diffusivities and equilibrium concentrations and address a number of questions regarding the mechanisms of dopant diffusion. They offer illustrative examples of ways that diffusion may be modeled in one and two dimensions by solving continuity equations for point defects and dopants. Outstanding questions and inadequacies in existing formulations are identified by comparing computer simulations with experimental results. A summary of the progress made in this field in recent years and of directions future research may take is presented.

Point defects and dopant diffusion in silicon

The method of obtaining pure polycrystalline silicon is described, followed by short accounts of how this material is converted into single-crystal form either by the Czochralski (CZ) pulling method or the float-zone (FZ) method. It is shown that the silicon contains various impurities including oxygen, carbon, boron and possibly hydrogen. The defects and impurities often show a nonhomogeneous distribution in the form of helical swirls. Heat treatment of silicon-containing oxygen leads to the clustering of this impurity. At 450 degrees C there is formation of small complexes that act as shallow donors. Investigations using IR and ESR spectroscopy have so far failed to determine the atomic configuration of the defects. Heating at higher temperatures causes wide-scale precipitation of oxygen. There are interactions with carbon and there can be formation of silicon carbide precipitates. Contamination from Cu, Au, Fe, etc., can occur during these treatments and methods for gettering these metals are discussed, involving dislocations and silica precipitates. Low-temperature irradiations produce vacancies and self-interstitials which combine with impurities to form complexes on heating from 4K to 300K. Evidence is presented to illustrate the possible charge states of self-interstitials. Damage produced by fast neutrons is discussed next, followed by a brief account of neutron transmutation doping whereby neutrally occurring 30Si is converted to 31P by the capture of thermal neutrons. Some aspects of high-temperature diffusion are discussed and attempts are made to correlate the data with that derived from the irradiation studies.

https://iopscience.iop.org/article/10.1088/0034-4885/45/10/003/pdf

Defects in silicon

Publisher Summary The chapter presents a discussion on electronic structure of three-dimensional (3d) transition-atom impurities in semiconductors. The effects of 3d impurities in semiconductors have preoccupied the field since the invention of the transistor. Reliable experimental data for germanium and silicon became available quite early. The chapter presents an in-depth review of the present status of the field. This review contains a most careful and detailed exposition of various aspects of the subject, presented, as the author states using “the combined points of view of theoretical solid-state physics, semiconductor physics, and classical inorganic chemistry.” The chapter discusses the great progress that has been made. The chapter presents a review on the recent developments vis a vis the new experimental methodologies and the classical phenomenological approaches used earlier to understand deep 3d impurities. The author attempts to present a coherent picture of the understanding of isolated 3d impurities in cubic semiconductors from the combined points of view of theoretical solid-state physics, semiconductor physics, and classical inorganic chemistry.

Electronic Structure of 3d Transition-Atom Impurities in Semiconductors

Characterization of Si/SiO2 interface defects by electron spin resonance

The properties of amorphous materials determined by the presence of localized atomic and electronic states are reviewed. Experimental data on atomic dynamics in glasses are described. The two-level-system (TLS) model is presented, and the limits of its applicability analysed. The concept of soft atomic potentials, allowing generalization of the TLS model to higher energies, is introduced. Atomic dynamics in soft potentials, as well as soft-potential coupling with phonons and thermal expansion of glasses, are described. Localized electronic states in glasses are investigated and different theoretical models of such states in glassy semiconductors are reviewed. The connection between localized electronic states and soft potentials is studied. Particular attention is paid to low-relaxation processes in glasses controlled by two-well soft potentials; specifically, low-frequency noise in disordered conductors is considered. The possibility of investigating the localized states in question with the hel...

Localized states in glasses

Experimental evidence is presented in support of a recent suggestion by Baraff, Kane, and Schl\"uter that the isolated lattice vacancy in silicon is an Anderson negative-$U$ system The second donor level (+/++) (of charge state + if defect level is occupied by an electron; ++, if unoccupied) is located at ${E}_{v}+013$ eV, above a first donor level (0/+) at ${E}_{v}+005$ eV Evidence is presented that interstitial boron has negative-$U$ properties with a single donor level (0/+) at ${E}_{c}\ensuremath{-}013$ eV, above a single acceptor level (-/0) at ${E}_{c}\ensuremath{-}045$ eV

J. R. Troxell

Papers

Negative-U Properties for Point Defects in Silicon