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Nanoscopy is a term that we use to describe optical techniques using digital image processing that are capable of nanometric
observation and measurement. Laser Scanning Tomography (LST) is used for defect analysis in the bulk of semiconductor
wafers for revealing particles as small as mm and for measuring densities of uptolO13 cm3 The unusually high contrast of
the system allows us to observe submicron particles which are more than three orders of magnitude smaller than the Rayleigh
criterion for the optical system. Recent work using deconvolution of point image functions enables us to perform sub-micron
optical serial sectioning, for determining the depth of defects.
The best conditions for classical LST (using laser illumination perpendicular to the viewing direction) are when operating
further than a few microns below the surface in semiconductor wafers; ie it is ideal for bulk defect studies. The study of
imperfections inside epilayers in the top ijim layer requires a modified technique. Instead of illuminating at 900 the
viewing direction, the infra red laser beam is introduced obliquely to the front suffe to illuminate the defects in the epilayer
while still in the dark-field mode. Combining this method with high resolution sectioning will be the basis for a technique of
three dimensional submicron defect analysis in epilayers.
Results are given of defect studies in annealed GaAs and silicon to demonstrate the capabilities of LST for naiiometer analysis
in bulk materials. Sub-micron depth measurement is shown for single particles using the PSF of the system for the out-offocus
case. Some initial results are given of studies of defects in a highly lattice mismatched epilayer using IR transmission
microscopy, phase stepping microscopy (PSM, used in surface profiling) and the new dark field oblique laser illumination
technique.
LST, and the new nanoscopy techniques are non-destructive, operate under normal room conditions, and give sub-micron
observation and distance measurement of defects over large areas with the possibility of 3D image synthesis for defect
analysis.
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