The fundamental nature and control of dislocations in single crystal silicon

Abstract

This dissertation considers the influences of thermal cycling on process induced dislocations in single crystal silicon wafers. To determine these influences, a technique for selectively inducing dislocations into silicon wafers during thermal cycling has been developed, and a numerical model for predicting the temperature distribution within the wafers when the dislocations occur has been derived. Based on these experiments and calculations, critical temperature ranges above which dislocations can be expected to occur, upon thermal cycling have been established. Also times within the thermal cycle at which dislocations are induced have been determined and the damage compared. As a result, production techniques by which these process induced imperfections can be reduced or eliminated are proposed and discussed. In addition, a mechanical stressing device used in attempts to simulate the thermal stresses induced in the wafer during thermal cycling is described, and the resulting surface stress patterns revealed upon chemical etching are discussed. Based on the rupture to a dislocation-free sub-surface upon mechanically stressing a previously dislocated wafer, a dipole loop formation of an induced dislocation is proposed. If the dipole loop argument is accepted, then the determination of the penetration depth of the induced dislocations can be made by measurement of the depth of the ruptured sub-surface.