Method and system for inspecting wafers for electronics, optics or optoelectronics

A method for the inspection of a wafer for electronics, optics or optoelectronics, comprising:

• rotating the wafer about an axis of symmetry perpendicular to a main surface of said wafer;
• emitting, from at least one light source coupled with an interferometric device, at least two pairs of incident coherent light beams, each pair being arranged in order to form, at the intersection between the two beams, a respective measurement volume containing interference fringes having an inter-fringe distance different from that of another measurement volume;
• at least a portion of the main surface of the wafer passing through each of said measurement volumes during the rotation of the wafer;
• collecting at least a portion of the light scattered by said part of the surface of the wafer;
• capturing the collected light and emitting an electrical signal representing the variation in the light intensity of the collected light as a function of time;
• detecting, in said signal, a frequency component in the variation of the light intensity of said collected light, said frequency being the time signature of the passage of a defect through a respective measurement volume;
• for each detected signature, determining a parameter, called visibility of the defect, dependent on the inter-fringe distance of the respective measurement volume and the size of the defect and given by the following formula, determined on the basis of a Doppler signal due to a defect passing through the measurement volume and expressed in the form of an electrical voltage as a function of time:
• I
• max
• -
• I
• min
• I
• max
• +
• I
• m
• ⁢
• in
• -
• 2
• ⋆
• Offset
• where Imax and Imin define the minimum electrical voltage and the maximum electrical voltage defining the peak of said Doppler signal and Offset is that between the mean value of the Doppler signal and an axis corresponding to a zero electrical voltage;
• on the basis of the visibility determined for each measurement volume, obtaining a respective item of information on the size of said defect;
• and
• cross-checking the information obtained for each measurement volume in order to determine the size of the defect.