Polarization-enhanced imaging of photoresist gratings in the real-time scanning optical microscope

A method of imaging sub-0.5-µm-dense photoresist lines with the real-time scanning optical microscope by the use of elliptically polarized light is developed. The imaging method takes advantage of the fact that polarized light undergoes a change in polarization when reflected from a grating structure. A confocal scanning optical microscope is modified to image this light. The resulting images show an increase in the detected intensity of the light reflected from the substrate region of the grating. Increasing this signal level improves the ability of the microscope to make linewidth measurements on photoresist structures as small as 0.3 µm. Results from several different semiconductor substrates are presented. A brief review of the grating theory is presented to suggest possible origins for the increase in light intensity.