Apparatus and method for measuring wafers

A method for measuring wafers, the method comprising the steps of:

• a) generating a measuring light beam with an optical coherence tomograph, wherein a wavelength range of the measuring light beam is selected such that a wafer is at least partially transparent to the measuring light beam;
• b) directing the measuring light beam at the wafer with an optical system;
• c) deflecting the measuring light beam in two spatial directions with a scanning device, which is controlled in such a way that the measuring beam scans the surface of the wafer successively at a plurality of measuring points;
• d) calculating distance values and/or thickness values based on interference signals provided by the optical coherence tomograph;
• and
• e) calculating at least one characteristic quantity of the wafer from the distance values and/or thickness values.

A device for measuring wafers, the device comprising:

• an optical coherence tomograph configured to generate a measuring light beam and to direct the measuring light beam onto a wafer via an optical system, wherein a wavelength range of the measuring light beam is selected such that the wafer is at least partially transparent for the measuring light beam;
• a scanning device configured to deflect the measuring light beam in two spatial directions;
• a control unit configured to control the scanning device in such a way that the measuring light beam scans the surface of the wafer successively at a plurality of measuring points, wherein two measuring points have a distance dmax of 140 mm≤dmax≤600 mm;
• and
• an evaluation unit configured to calculate
• distance values A of a surface of the wafer facing the scanning device,
• thickness values TW from interference signals provided by the optical coherence tomograph and obtained by an interference of light reflected from the surface of the wafer facing the scanning device with light reflected from a surface of the wafer facing away from the scanning device, and
• a median area M according to M=A+½ TW.