Gold-Induced Climb of Dislocations in Silicon

Abstract

Studies were made of the climb of dislocations in silicon crystals induced by the diffusion of gold in the temperature range from 1000°C to 1300°C. For some studies, dislocations were introduced into previously dislocation‐free crystals by indentation at room temperature and deformation at about 900°C in order to predetermine both Burgers vector and the direction of deformation. It was possible in this way to introduce left‐handed screw dislocations in small concentrations. The left‐handed screw dislocations were found to form right‐handed helices upon the diffusion of gold during subsequent heat treatment at temperatures above 1000°C. This observation is shown to be consistent with the idea that gold diffuses as an interstitial atom and causes a vacancy deficiency in the neighborhood of dislocations. Further evidence of the structure sensitivity of the diffusion of gold is shown by autoradiographic techniques. Studies were made of the effect of heat‐treatment times and quenching rates upon the diameter of helices. The diameter of the helices increases with time at a given temperature, and increases with temperature during a given time of heat treatment. Variation of the cooling time by a factor of 10³ has no apparent effect on the diameter. Therefore, the helices form as a result of a gradient in the concentration of gold rather than by a quenching process. Impurities introduced by heat treatment at 900°C strongly modify climb in crystals which are relatively free from oxygen. Precipitates believed to be formed during this heat treatment act as nucleation sites for the formation of prismatic loops. Crystals grown from quartz crucibles and thus containing about 10⁺⁵ atom fraction of oxygen have complicated climb mechanisms believed to be associated with the pinning effect of the oxygen on the dislocations. Modified Bardeen‐Herring sources have been found in these cases.