Patent ID: 8289525

Claim:
An optical surface measuring apparatus, comprising: an interferometer for radiating laser light onto a surface of an object to be measured, receiving laser light reflected from the surface, and outputting an interference signal based on distance to the surface; an object lens for transmitting the laser light radiated by the interferometer, and forming a focal point at a point of measurement on the surface of the object to be measured; an electric-powered stage for adjusting a location of the object to be measured; a beam splitter for separating the laser light reflected from the surface of the object to be measured; a collimator lens for focusing the laser light separated by the beam splitter; an astigmatic lens for transmitting the laser light focused by the collimator lens, thereby generating astigmatism; a Focus Error (FE) signal output unit for receiving the laser light transmitted through the astigmatic lens, and outputting an FE signal based on the distance to the surface of the object to be measured; and a control unit for receiving the interference signal from the interferometer and the focus error signal from the FE signal output unit, calculating variation in the distance based on these signals, and acquiring surface status information, including height difference on the surface, from the calculated variation, wherein the control unit overlaps a periodic distance variation signal obtained from the interference signal from the interferometer and the FE signal, and acquires overlapping values of the two signal values as the reference data.