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This article relates to the measurement of the periodicity (pitch) of grating samples used as test sites for the purpose of monitoring critical sub-micron dimensions.
English (United States)
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Spectroscopic Pitch Measurement Technique
This article relates to the measurement of the periodicity (pitch) of grating
samples used as test sites for the purpose of monitoring critical sub-micron
State-of-the-art optical equipment is falling behind semiconductor
manufacturing requirements for measurement of critical dimensions below 1
micron. These optical measurement tools rely on high resolution imaging
capabilities to produce images of the semiconductor devices which can be
calibrated and measured. The best broad band optical microscopes have a
optical resolution which limits measurements to 0.7 to 0.9 micron. The newest
confocal laser microscopes may be limited to measurements in the 0.3 to 0.5
micron range and are difficult to operate. Scanning electron microscopes have a
resolution in the nanometer range using energetic electron beams which pose
sample damage concerns. A new technique makes use of the reflected intensity
of light as a function of wavelength to make pitch measurements.
Spectroscopic pitch measurements, utilizing characteristics of light reflected
from an area of regular lines and spaces, can be made with a high degree of
accuracy on sub-micron diffraction gratings. A
light microscope equipped with a spectrophotometer can measure the reflected
light intensity from an area of uniformly spaced lines. The spectral signal is
comprised of intensities at discrete wavelengths which, when analyzed, provides