Optical inspection method and optical inspection apparatus
In the conventional contaminant particle/defect inspection method, if the illuminance of the illumination beam is held at not more than a predetermined upper limit value not to give thermal damage to the sample, the detection sensitivity and the inspection speed being in the tradeoff relation with each other, it is very difficult to improve one of the detection sensitivity and the inspection speed without sacrificing the other or improve both at the same time. The invention provides an improved optical inspection method and an improved optical inspection apparatus, in which a pulse laser is used as a light source, and a laser beam flux is split into a plurality of laser beam fluxes which are given different time delay to form a plurality of illumination spots. The scattered light signal from each illumination spot is isolated and detected by using a light emission start timing signal for each illumination spot.
1. An inspection apparatus for inspecting an anomaly of a substrate, the apparatus comprising:
a moving unit for moving the substrate;
an illumination unit for emitting first and second optical beams, the illumination unit including a pulse light source for generating a plurality of illumination areas on the substrate, the illumination areas being formed in relation to a moving direction of the moving unit;
a first photo-detector arranged in an optical path of the first optical beam emitted from the illumination unit, the first photo-detector configured to output a first illumination timing signal;
a second photo-detector arranged in an optical path of the second optical beam emitted from the illumination unit, the second photo-detector configured to output a second illumination timing signal;
a detection unit for detecting scattered light from the substrate, wherein the detection unit isolates outputs of the illumination areas from each other based on the first illumination timing signal and the second illumination timing signal; and
a processing unit configured to determine the anomaly based on the isolated outputs.
2. The inspection apparatus according to claim 1 , wherein the first photo-detector and the second photo-detector are arranged at a same distance optically.
3. The inspection apparatus according to claim 1 , further comprising:
a waveform shaper which shapes at least one of the first illumination timing signal and the second illumination timing signal.
4. The inspection apparatus according to claim 3 , wherein the waveform shaper provides a first time-delay to the first illumination timing signal.
5. The inspection apparatus according to claim 4 , wherein the waveform shaper provides a second time-delay to the second illumination timing signal.
6. The inspection apparatus according to claim 3 , wherein the waveform shaper provides a first continuous time to the first illumination timing signal.
7. The inspection apparatus according to claim 3 , wherein the waveform shaper provides a second continuous time to the second illumination timing signal.
8. A method for inspecting an anomaly of a substrate, the method comprising steps of:
moving the substrate;
generating pulse light emissions to form first and second optical beams;
forming a plurality of illumination areas on the substrate with the first and second optical beams, the illumination areas being formed in relation to a moving direction of the substrate;
by way of a plurality of photo-detectors arranged in an optical path of the first and second optical beams, outputting first and second illumination timing signals based on timing of the first and second optical beams reaching their respective illumination areas;
detecting scattered light from the substrate;
responsive to the detected scattered light, isolating outputs of the illumination areas from each other based on the first illumination timing signal and the second illumination timing signal; and
determining the anomaly based on the isolated outputs.
9. The method according to claim 8 , further comprising:
providing a first time-delay to the first illumination timing signal.
10. The method according to claim 9 , further comprising:
providing a second time-delay to the second illumination timing signal.
11. The method according to claim 8 , further comprising:
providing a first continuous time to the first illumination timing signal.
12. The method according to claim 11 , further comprising:
providing a second continuous time to the second illumination timing signal.