Defect detection system

A surface inspection method for detecting anomalies on a surface having a diffracting pattern thereon that scatter radiation, said method comprising:

• causing the surface to be scanned by a beam of radiation;
• collecting radiation scattered from the surface by means of a collector that collects the scattered radiation substantially symmetrically about a line normal to the surface;
• filtering at least a portion of the collected radiation by means of a spatial filter having an angular gap therein of an angle related to the angular separation of expected radiation components scattered by the pattern on the surface;
• and
• determining the presence of anomalies in or on the surface from said filtered collected radiation.

A surface inspection apparatus for detecting anomalies on a surface, comprising:

• a source supplying a beam of radiation scanning the surface;
• a collector collecting radiation scattered from the surface substantially symmetrically about a line normal to the surface;
• optics including optical channels at different azimuthal angles about the line or about a direction corresponding thereto, the collector supplying the collected radiation to the channels so that information related to relative azimuthal positions of the collected radiation about the line is preserved, and the channels are disposed so that radiation scattered by the surface at different azimuthal angles with respect to the line is conveyed by different channels, said optics including separators separating the channels from each other to reduce crosstalk;
• a plurality of detectors converting the collected radiation carried by at least some of the channels into respective signals representative of radiation scattered at different azimuthal angles about the line;
• and
• a processor determining the presence of anomalies in or on the surface from said signals.

A surface inspection apparatus for detecting anomalies on a surface having a diffracting pattern thereon that scatter radiation, said apparatus comprising:

• a source supplying a beam of radiation scanning the surface;
• a collector collecting radiation scattered from the surface substantially symmetrically about a line normal to the surface;
• a spatial filter filtering at least a portion of the collected radiation, said filter having an angular gap therein of an angle related to the angular separation of expected components scattered by the pattern on the surface;
• and
• a processor determining the presence of anomalies in or on the surface from said filtered collected radiation.

A surface inspection method for detecting anomalies on a surface, wherein a beam of radiation is provided to scan the surface, employing an apparatus comprising a first near normal collection system collecting and directing radiation scattered by an area of the surface along directions near a line perpendicular to the surface to a first detector, a second collection system including a curved mirrored surface having an axis of symmetry about said line reflecting and directing radiation scattered from the area of the surface along directions away from said line to a second detector;

• said method comprising:
• obtaining from the first detector a first output signal in response to scattered radiation from the beam and the area of the surface;
• obtaining from the second detector a second output signal in response to scattered radiation from the beam and the area of the surface;
• and
• deriving a ratio of the first and second output signals to determine whether an anomaly on the surface is a micro-scratch or a particle.

A surface inspection method for detecting anomalies on a surface, employing a curved mirrored surface having an axis of symmetry about said line reflecting and directing radiation scattered from the area of the surface along directions away from said line to a second detector;

• said method comprising:
• providing a beam of radiation in an oblique direction to the surface to scan the surface;
• separately collecting radiation scattered by the surface along forward scattering directions from other scattering directions and detecting separately the separately collected radiation to provide a first signal indicative of the collected forward scattered radiation and a second signal indicative of the collected scattered radiation other than forward scattered radiation;
• comparing the two signals to determine whether an anomaly on the surface is a micro-scratch or particle.

A surface inspection method for detecting anomalies on a surface, employing a curved mirrored surface having an axis of symmetry about said line reflecting and directing radiation scattered from an area of the surface along directions away from said line to a second detector;

• said method comprising:
• providing sequentially a radiation beam of a first state of polarization and a beam of a second state of polarization at oblique direction(s) to the surface to scan the surface, said first and second states being different;
• collecting radiation scattered by a defect during the sequential scans and providing a pair of signals:
• a first comprising a signal indicative of the collected scattered radiation when the surface is scanned by radiation in the first state of polarization and a second comprising a signal indicative of the collected scattered radiation when the surface is scanned by radiation in the second state of polarization;
• and
• comparing the two signals to determine whether an anomaly on the surface is a micro-scratch or particle.

A method for determining roughness of a surface, comprising:

• providing a database correlating haze values with surface roughness of thin films;
• measuring haze values of the surface;
• and
• determining a roughness value of the surface from the haze value and the database.