Laser-induced fluorescence spectroscopy and imaging of semiconductor wafers

Fluorescence spectra of selected films used in microelectronic fabrication have been recorded. We have used a 0.125-m focal length spectrophotometer and a 400-line/mm grating resulting in 4.2-nm spectral resolution. The optical setup employs a laser at 364 nm for excitation and a dark-field collection configuration-a geometry that we routinely use for laser scanning for inspection purposes. A simple, though thorough, analysis and methodology for the removal of the system spectral response is presented. Results show that films used in microelectronic fabrication, in general, yield a broadband fluorescence spectrum under 364-nm excitation. Further, a scanning system that bases the image contrast on laser-induced fluorescence from the wafer surface is described and demonstrated. It is shown that this is a particularly useful inspection/review modality when the wafer is at poly/metal process level and the contaminant is a fall-on or residue of an organic material