Profile Measurement of Polished Surface with Respect to a Lattice Plane of a Silicon Crystal Using a Self-Referenced Lattice Comparator

A method is proposed for performing surface profile measurements with respect to a reference plane defined by the lattice plane of a silicon single crystal. In this method, a surface normal to a polished plane is detected using an optical autocollimator and the direction normal to the lattice plane is sensed by X-ray diffraction. The relationship between these planes can be determined if the polished plane is connected to the single crystal. In the measurement system, the mirror and the silicon single crystal are attached backto-back. A monochromatized synchrotron radiation X-ray beam is incident on the single crystal and two detectors are used to measure diffracted X-rays. An optical autocollimator placed near the mirror is used to monitor the inclination of the mirror. The normal direction of the crystal lattice plane is obtained from two diffractions from equivalent reciprocal lattice points. The normal to the mirror is taken to be the angle measured by the autocollimator when the two diffractions are observed. Test experiments have been performed using the self-referenced lattice comparator established at beamline BL3C of the Photon Factory, KEK. The proposed method is discussed by comparing the surface profile of the mirror measured with this system with that measured using a Fizeau interferometer.