Structure and Properties of The Oxygen Donor
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STRUCTURE AND PROPERTIES OF THE OXYGEN DONOR L. C. KIMERLING AT&T Bell Laboratories, Murray Hill, New Jersey 07974 ABSTRACIT
During aggregation, an assembly of oxygen atoms in silicon produces an electrically active site. The center is an effective mass, helium-like center (double donor) with a wave function of C2v symmetry. The formation reactions of the assembly reveal details of the invisible early stages of aggregation. The donor character of the center controls the aggregation process in heavily doped material. The atomic structure and the source of the electrical activity of the center remain unresolved. INTRODUCTION
During the past five years, more experimental data regarding the nature of the electrical activity of oxygen in silicon has been generated than in the previous twenty-five years. The quality of the data is high and similar results have been obtained in different research laboratories, yet a complete solution of the "problem" is still missing. A complete solution must explain the observed formation kinetics of the oxygen donor, its equilibrium concentrations, its structures, and the electrical and optical properties of the defect state(s) in an integrated model. The detailed knowledge of the behavior of oxygen in silicon is rivaled only by comparable attention to the system of carbon in iron (steel). The fundamental interest arises from the application of detailed spectroscopy studies which reveal the unique structural nature of this center but vail the source of its electrical activity. The technological driving force is based on the need to critically control the state of oxygen aggregation in silicon substrates so that the matrix hardening effects of the oxygen solute are preserved,
while the gettering action of oxygen
precipitate sites is created. If one considers the silicon/oxygen system as a paradigm for all materials systems, the oxygen donor problem presents a unique opportunity to view and understand the early stages of aggregation and precipitation. These stages in which clusters of undetectable size are formed have been, traditionally, treated theoretically, but rarely explored experimentally. The elusive solution is likely contained in knowledge of the behavior of an embryonic assembly of atoms, which is not yet a stable second phase, but acts to relieve conditions of supersaturation. The new spectroscopies being applied to measuring the properties of this assembly present a powerful window to these early phenomena. The complete understanding will certainly yield new, generic insights. This paper will emphasize our contributions during the past five years. The impact of the results will be critically reviewed, and an updated picture of what is and is not understood will be formulated. KINETICS OF FORMATION
Initial attempts to define a structure for the center were based on formation kinetics during heat treatment. The initial rate of increase in electron concentration exhibited an isothermal proportionality to the fourth power of the oxygen concentration [I1. This concentration d
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