The paper consists of three parts. In the first part we review the basic experimental and theoretical results which shaped our present knowledge on point defects and diffusion processes in silicon. These results concern on one side oxidation effects which established that silicon self-interstitials and vacancies coexist in silicon and on the other side diffusion of gold into dislocation-free silicon which allowed to determine the self-interstitial contribution to silicon self-diffusion and to estimate the corresponding vacancy contribution. In the second part we discuss topics for which an understanding is just emerging within the framework of coexisting self-interstitials and vacancies: reaching of local dynamical equilibrium between self-interstitials and vacancies; rough estimates of the thermal equilibrium concentrations of self-interstitials and vacancies and their respective diffusivities, and finally, various possibilities to generate an undersaturation of self-interstitials. In the third part we examine swirl defect formation in silicon in terms of vacancies and self-interstitials.

Point defects, diffusion processes, and swirl defect formation in silicon

Vacancy-type microdefect formation in Czochralski silicon

Taking into account a wide variety of recent results from studies of silicon crystal growth and high temperature wafer heat treatments, a consistent picture of intrinsic point defect behavior is produced. The relevant point defect parameters: diffusivities, equilibrium concentrations and the details of the interaction of vacancies with oxygen are deduced. This set of parameters successfully explains a very wide array of experimental observations covering the temperature range 900–1410 °C. These experimental observations, which are reviewed here, include the properties of grown-in microdefects and vacancy-controlled oxygen precipitation effects in rapidly cooled wafers. The analysis of point defect behavior from observations of high temperature phenomena such as these has the great advantage of relative simplicity and transparency.

On the Properties of the Intrinsic Point Defects in Silicon: A Perspective from Crystal Growth and Wafer Processing

A novel crystal growth method has been developed for the production of ingots, bricks and wafers for solar cells. Monocrystallinity is achievable over large volumes with minimal dislocation incorporation. The resulting defect types, densities and interactions are described both microscopically for wafers and macroscopically for the ingot, looking closely at the impact of the defects on minority carrier lifetime. Solar cells of 156 cm2 size have been produced ranging up to 17% in efficiency using industrial screen print processes.

V.V. Voronkov

Papers

The mechanism of swirl defects formation in silicon