The use of etchants in assessment of semiconductor crystal properties

In addition to the use of chemical etching techniques to discover the density of dislocations in silicon and germanium and to reveal p-n junctions in semiconductor devices, certain etching methods are capable of revealing a number of other features of fundamental interest. Close examination of etched specimens is often highly informative and rewarding. The shapes of some etch pits can give surface orientations to within one or two degrees. Impurity anomalies giving rise to localized regions of opposite conductivity to that of the bulk may be detected, and striations due to fluctuations of impurity density can sometimes be revealed in material which is nominally of one type and homogeneous. These etching methods can be used, in particular, to examine the effect of dislocations and other defects on the redistribution of impurities during heat treatment of silicon. The motion of dislocations during annealing of germanium may be studied qualitatively, and polygonization and the formation of tilt boundaries and other arrays of minimum energy have been observed.