Three-Wavelengths Interferometric Measuring Device And Method

An interferometric measuring device for measuring a surface or profile of an object, the measuring device comprising:

• a beam generating unit comprising at least a first light source, wherein the beam generating unit is operable to generate a measurement beam with a spectral component at a wavelength smaller than 550 nm,
• a splitter to branch off an object beam and a reference beam from the measurement beam,
• a measurement probe coupled to the beam generating unit in a light transmitting way and configured to direct the object beam onto the surface and to capture a portion of the object beam reflected from the surface as a signal beam,
• an optical beam recombiner operable to recombine the signal beam and the reference beam in an analysis beam,
• a beam divider unit coupled to the recombiner, the beam divider unit being operable to extract a first partial beam of a first center wavelength λ1 from the analysis beam and to extract a second partial beam of a second center wavelength λ2 from the analysis beam, wherein the second center wavelength λ2 is different from the first center wavelength λ1,
• a detector unit coupled to the beam divider unit and comprising at least a first detector to detect the first partial beam and comprising at least a second detector to detect the second partial beam,
• a signal analyzer connected to the detector unit and operable to derive a distance between the measurement probe and the surface on the basis of signals obtained from the at least first detector and the at least second detector.

A method of measuring a surface or profile of an object, the method comprising the steps of:

• providing the object, wherein the object comprises a surface material,
• generating a measurement beam with a beam generating unit,
• branching off an object beam and a reference beam from the measurement beam and directing the measurement beam onto the surface of the object by an optical probe, wherein the surface material comprises an optical penetration depth of less than 100 μm, less than 50 μm, less than 20 μm, 10 μm, less than 5 μm, less than 2 μm, less than 1 μm, less than 0.5 μm or less than 0.1 μm for one of the object beam and the measurement beam,
• capturing a portion of the measurement beam reflected by the surface as a signal beam,
• recombining the signal beam and the reference beam in an analysis beam and
• detecting an interference of the analysis beam by a detector unit and deriving a distance between the optical probe and the surface by analyzing signals of the detector unit.