Because atomic force microscopes (AFMs) are capable of generating three dimensional images with nanometer level resolution, these instruments are being increasingly used in many industries as tools for dimensional metrology at sub- micrometer length scales. To achieve high accuracy, the scales of an AFM must be calibrated. Presently available standards for this purpose are commonly calibrated using stylus instruments and optical techniques. We have developed the calibrated AFM (C-AFM) in order to calibrate pitch and height standards using an AFM. Our instrument has metrology traceable to the wavelength of light for all three axes. This is accomplished through the integration of a flexure x-y translation stage, heterodyne laser interferometers, and a digital-signal-processor based closed-loop feedback system to control the x-y scan motion. The z-axis translation is accomplished using a piezoelectric actuator with an integrated capacitance sensor, which is calibrated using a heterodyne laser interferometer. When fully developed, this instrument will be a calibration tool for pitch and height standards for scanning probe microscopes. We have recently completed a reevaluation of the titling motions of the C-AFM scanner. This has allowed a refinement in our estimate of the Abbe error contribution to our measurement uncertainty. Our most recent pitch measurements are consistent with this new estimate and thus support our refined uncertainty budget. We have recently completed measurements of pitch on several samples, including both grid type and linear scale patterns, for an industrial user. We are also working toward the development of linewidth standards through the comparison of C-AFM width measurements with values obtained from other methods, including an electrical resistance techniques. In this paper, we will describe the current status of the C-AFM, discuss the use of the instrument for measurements of pitch and width, and describe our plans for future measurements.
Proceedings Title: Proceedings of SPIE, Metrology, Inspection, and Process Control for Microlithography XII, Bhanwar Singh, Editor
Conference Dates: February 23, 1998
Conference Location: Santa Clara, CA
Conference Title: Linewidth Calibration Metrology
Pub Type: Conferences
AFM, linewidth, metrology, pitch, scale calibration, SPM, standards