USE OF MAXIMUM-ENTROPY DECONVOLUTION FOR THE STUDY OF SILICON DELTA-LAYERS IN GAAS

Semiconductor layer structures with sharply changing concentration, an d more especially delta-doped (single atomic plane) structures, provid e an ideal environment for the study of the more subtle mass transport phenomena such as concentration-dependent diffusion and localized mix ing caused by ion bombardment. However, to be able to extract meaningf ul parameters from such experiments, accurate depth profiles must be o btained with extremely high depth resolution and good sensitivity. Sec ondary ion mass spectrometry (SIMS) provides one of. the most sensitiv e methods for acquiring such profiles. To obtain high depth resolution , a number of criteria must be satisfied, not the least of which is th e reduction of redistribution by the probe; thus it is essential to em ploy a low energy primary beam. It is also vital that the crater floor recedes parallel to the original surface of the specimen. This necess itates accurate scanning of a stable ion beam, so as to ensure a const ant flux across the entire sampled area. If this is not the case, dept h resolution will degrade as a function of depth, and important inform ation will be lost. However, even if probes of the order of 1-2 keV ar e used, together with a precision scan system, beam-induced redistribu tion is still a significant limit to the sharpness of the recorded pro files. To further improve upon the data, the effects of the analysis m ust be removed from the profile. In this article we demonstrate the us e of the maximum entropy deconvolution technique, applying it to a SIM S depth profile of a multilayer silicon in gallium arsenide structure containing alternating layers of high and low areal density. The impor tant issue of data validity is discussed and the deconvolved results a re used to calculate a diffusion constant for the denser layers, the l ess dense layers show no diffusion at the growth temperature of 450 de grees C. (C) 1996 American Vacuum Society.