Patent ID: 9115973
Filing Date: 2015-08-25
Classification: G01B

Abstract:
1. A profile measuring instrument, comprising: a fixed member of which position is fixed relative to a workpiece having a surface of which profile to be measured; a scanning member supported by the fixed member, the scanning member being movable in a scan direction along the surface of the workpiece relative to the fixed member; and an interferometer provided to the fixed member, the interferometer detecting a displacement of the surface of the workpiece along the scan direction, wherein the interferometer comprises: a light source; a beam splitter provided to the scanning member, the beam splitter dividing a beam from the light source into a reference beam and a measurement beam; a reference mirror fixed to the fixed member; a measurement optical path in a form of an optical path of the measurement beam, the measurement optical path extending from the beam splitter to the workpiece; and a reference optical path in a form of an optical path of the reference beam, the reference optical path extending from the beam splitter to the reference mirror, and wherein an optical path length of the measurement optical path and an optical path length of the reference optical path are substantially equal such that a difference between the optical path length of the measurement optical path and the optical path length of the reference optical path becomes a predetermined tolerable error or less, wherein the predetermined tolerable error is defined as a value equal to a measurement accuracy required for the measurement instrument divided by frequency stability of the light source.