Atomic force microscope (AFM) measurements are being used increasingly for metrological applications such as semiconductor process development and control. Common types of measurements are those of feature spacing (pitch), feature height (or depth), and feature width (critical dimension). If high accuracy is required, the scales of an AFM should be calibrated. Presently, available standards for this purpose are calibrated using stylus instruments and optical techniques. The effectiveness of this approach, however, is limited by the differences in the full ranges of the various techniques and by questions of methods divergence. As the repeatability of many commercial instruments continues to improve, the importance of accurate calibration standards will increase. In order to calibrate AFM standards using an AFM, we have designed and built a metrology atomic force microscope, called the calibrated AFM (C¿AFM). This instrument has metrology traceable to the wavelength of light for all three axes. To realize this, a flexure translation stage, heterodyne laser interferometers, and a digital-signal-processor based closed-loop feedback system are used 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. Since the design of this instrument has been discussed in more detail elsewhere, we focus here primarily on the results of performance testing of the C¿AFM for pitch, height, and width measurements.
Proceedings Title: Proceedings of American Society for Precision Engineering
Pub Type: Conferences
AFM, linewidth, metrology, pitch, step height