Application of near-field optics to critical dimension metrology

Scanned-probe microscopes often have difficulty measuring absolute lengths due to nonlinearities in the piezo elements used to scan the tip. We have developed a method which allows for calibrated scanning of a near-field optical aperture. This method allows for point-by-paint correction for piezo nonlinearities such as hysteresis and creep by imaging the light emanating from a near-field probe onto a position sensitive detector. We have used this principle to fabricate a microscope with 20 nm accuracy in tip position. With further improvements, we believe single nanometer accuracy is possible. (C) 1997 American Institute of Physics.