Laser-scanning tomography: a survey of recent investigations in semiconductor materials

Abstract

Laser-scanning tomography (LST) was proposed by Moriya and Ogawa in 1983 as a non-destructive and non-invasive method for imaging small grown-in precipitates in the bulk of semiconductor materials. It has been shown that particles as small as 1 nm can be revealed by this method. The geometrical location of these defects has been obtained with 1 mu m precision in the (x,y) plane and with 0.1 mu m precision in the z direction. Extrapolations have also been performed in order to analyse implanted layers, epilayers and completed structures. Gallium arsenide has been the material studied most extensively by the method of LST, although InP and silicon have also been profitably investigated. Microprecipitates (MPS) contribute to an internal 3D structure which is typical of the material and also of its previous thermal history. It has been shown that annealing is able to render the electrical behaviour of SI GaAs ingots uniform and also to induce nucleation and growth of silica gettering centres in silicon wafers which are initially doped with oxygen. These MP structures are observed and quantitatively evaluated in such materials in a way which is far more convenient than traditional destructive etching. In this survey the authors recall the basis of the LST method and its metrological applications. Recent results in materials knowledge will be developed, especially in the field of GaAs, InP and silicon wafer technology.