Apparatus and methods for combined brightfield, darkfield, and photothermal inspection
Disclosed are methods and apparatus for detecting defects or reviewing defects in a semiconductor sample. The system has a brightfield (BF) module for directing a BF illumination beam onto a sample and detecting an output beam reflected from the sample in response to the BF illumination beam. The system has a modulated optical reflectance (MOR) module for directing a pump and probe beam to the sample and detecting a MOR output beam from the probe spot in response to the pump beam and the probe beam. The system includes a processor for analyzing the BF output beam from a plurality of BF spots to detect defects on a surface or near the surface of the sample and analyzing the MOR output beam from a plurality of probe spots to detect defects that are below the surface of the sample.
1. A method of detecting defects or reviewing defects in a semiconductor sample, the method comprising:
scanning a sample portion with a brightfield (BF) illumination beam;
detecting a BF output beam reflected from the sample portion as the BF beam scans over the sample portion;
determining surface or near-surface characteristics of the sample portion based on the detected BF output beam;
finding candidate locations within the sample portion that are likely to have additional defects below a surface of the sample based on the determined surface or near-surface characteristics of the sample portion that were determined based on the detected BF output beam;
directing a modulated pump beam and a probe beam at each candidate location;
detecting a modulated optical reflectivity signal from each candidate location in response to each probe beam being directed to each candidate location; and
determining a feature characteristic that is below the surface at each candidate location based on the modulated optical reflectivity signal detected from such candidate location.
2. The method of claim 1 , further comprising:
detecting a darkfield (DF) output beam scattered from the sample portion as the BF beam scans over the sample portion or in response to scanning a darkfield beam over the sample portion;
determining surface or near-surface characteristics of the sample portion based on the detected DF output beam; and
finding a second plurality of candidate locations based on the surface or near-surface characteristics of the sample portion based on the detected DF output beam;
detecting a modulated optical reflectivity signal from each second candidate location in response to each probe beam being directed to each second candidate location; and
determining a feature characteristic that is below the surface at each second candidate location based on the modulated optical reflectivity signal detected from such second candidate location.
3. The method of claim 2 , wherein the first and second candidate locations are found by correlating surface or near-surface characteristics with a presence of sub-surface defects.
4. The method of claim 3 wherein the first and second candidate locations are each associated with a sub-area of the sample portion that has one or more surface or near-surface characteristics that deviate by a predefined amount from an average of the sample portion.
5. The method of claim 4 , wherein at least one of the first and second candidate locations has through-silicon vias (TSV's).
6. The method of claim 4 , wherein the first and second candidate locations are selected to be distributed across its associated sub-area.
7. The method of claim 1 , further comprising:
determining whether the surface or near-surface characteristics indicate a presence of oxidation on the surface; and
removing the oxidation prior to directing the modulated pump beam and the probe beam at each candidate location.
8. The method of claim 1 , wherein at least some of the candidate locations are each selected to be centered on a structure based on an image of such structure that is generated based on the BF output beam.
9. The method of claim 1 , wherein at least some of the candidate locations are further selected to be distributed across a structure based on an image of such structure that is generated based on the BF output beam.