Method and system for inspecting boards for microelectronics or optics by laser doppler effect

A system for inspecting wafers for microelectronics or optics, comprising:

• a device for driving a wafer in rotation about an axis (X) of symmetry perpendicular to a main surface (S) of said wafer;
• a light source suitable for emitting a light beam;
• an interferometric device coupled with the light source in order to split the beam emitted by said source into two beams and in order to form, at the intersection between the two beams, a measurement volume (V) containing interference fringes, the dimension (Dy) of said measurement volume in a radial direction of the wafer being comprised between 5 and 100 μm, the interferometric device and the drive device being arranged in relation to one another so that a region of the main surface of the wafer in rotation passes through at least one fringe of the measurement volume;
• a device for collecting light scattered by the wafer;
• a device for acquiring collected light configured in order to emit an electrical signal representing the variation in the light intensity of the collected light as a function of time;
• and
• a processing device configured in order to detect, in said signal, a frequency component in said collected light, said frequency being the time signature of the passage of a defect through a respective measurement volume and in order to determine, based on said frequency, the position of the defect in the radial direction and/or in the thickness of the wafer.