Apparatus for surface inspection

An apparatus for making high-sensitivity measurements of dot-shaped, linear, and platform surface defects during an inspection of a surface., said apparatus comprising:

• a light source producing a light beam;
• a supporting disk on which an object having a surface to be inspected or examined is placed with the surface exposed;
• an objective passing the light beam from the light source perpendicularly onto the surface of the object on the supporting disk;
• drive means connected to the supporting disk for moving the disk and the object thereon rotationally and translationally relative to the light beam so as to permit the light beam to scan the surface of the object along a spiral path;
• a photo detector positioned to receive light reflected by the surface of the object and collected by the objective and having an output providing a signal representative of the reflected light received:
• an astigmatic lens system positioned on the optical path of the light beam between the light source and the objective whereby an intermediate image is formed,
• a dark-field stop assembly positioned in the optical path of the light beam between the astigmatic lens system and the objective and having an adjustable dark-field deflection system whereby the light beam after deflection is directed exactly centered through the objective and at right angles onto the surface of the object,
• the objective, the dark-field stop assembly and at least one diaphragm being placed along an optical axis between the object and the photo detector and making up image-forming optics which are rotationally symmetrical in relation to the optical axis,
• electronic analysis means and a computer unit connected to receive signals from the photo detector and for breaking down the output signal from the photo detector into measured values produced by dot-shaped, linear, and planiform defects in the surface of the object under inspection, and
• means for determining the effective scanning position of the light beam on the object surface at any time connected to the computer unit to associate the scanning positions with the measured values,
• the electronic analysis means further has a signal input connected with the output of the photo detector and to a haze channel having a haze filter and a peak suppressor,
• the signal input is connected to a particle channel which has a subtraction circuit and a peak detector with a digital output,
• a haze-filter output is connected to the input of an analog-digital converter which has an output, and
• the haze filter is connected to a nominal-bandwidth input and the peak detector is connected to a second input of the electronic analysis means,
• so that the measurements due to planiform defects are available at the output of the analog-digital converter, the measurements due to dot-shaped defects (LPDs) and linear defects are available at the output of the peak detector, and all these measurements are then loaded and stored in the computer unit.