Method and device for the contactless assessment of the surface quality of a wafer

A device for the contactless assessment of the surface quality of a disk-shaped, fine-machined workpiece, in particular a wafer, according to the angle-resolved scattering light measuring technology, comprising

• an optical sensor which emits a beam of rays with defined intensity distribution onto the surface of the workpiece to be assessed and illuminates a measuring spot,
• wherein the reflected intensity of the radiation is detected by means of a line sensor with a discrete number of photodetectors in a defined angular range and at least one characteristic value is determined therefrom,
• a rotary device which rotatably mounts the workpiece, wherein a rotation angle sensor detects the rotation angle,
• a positioning device which orients the sensor relative to the surface of the workpiece such that its measuring axis is perpendicular to the surface, wherein the positioning device mounts the sensor movably in radial direction relative to the surface of the workpiece and rotatably about its measuring axis by an angle,
• wherein in a set-up mode, the sensor is rotated at a predetermined measuring position about its measuring axis and an initial rotary position with associated initial rotation angle is determined in which the intensity characteristic value is at a maximum,
• and wherein in a measuring mode, a control, taking into account this initial rotation angle, calculates from the detected intensity of the photodetectors at least one characteristic value for the surface quality.