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.

Date Published: 1 January 1991
PDF: 8 pages
Proc. SPIE 1332, Optical Testing and Metrology III: Recent Advances in Industrial Optical Inspection, (1 January 1991); doi: 10.1117/12.51106

Published in SPIE Proceedings Vol. 1332:
Optical Testing and Metrology III: Recent Advances in Industrial Optical Inspection
Chander Prakash Grover, Editor(s)