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US 5,864,394 AGranted
Surface inspection system
AssigneeKLA-Tencor Corporation
InventorsJohn R. Jordan, III, Mehrdad Nikoonahad, Keith B. Wells
Life of this patent
Estimating the term…
Abstract
A high throughput surface inspection system with enhanced detection sensitivity is described. The acquired data is processed in real time at a rate of below 50 MHz thereby reducing the cost for data processing. Anomalies are detected and verified by comparing adjacent repeating patterns and the height of the surface is monitored and corrected dynamically to reduce misregistration errors between adjacent repeating patterns. Local thresholds employing neighborhood information are used for detecting and verifying the presence of anomalies. The sampled point spread function of the combined illumination and collection system is exploited for anomaly detection and verification.
Claims113
An inspection system for detecting anomalies on a surface, comprising:
- means for optically scanning the surface;
- means for collecting light scattered by the surface and deriving an intensity value for at least a first pixel location from the collected light;
- means for determining an error threshold for said at least first pixel location from intensity values stored for at least a corresponding second pixel location and its neighboring pixel locations of a reference image of the surface, said error threshold being determined by the difference between an intensity value stored for the second pixel location and a maximum or minimum of intensity values stored for the second pixel location and its neighboring pixel locations in the reference image;
- and
- means for identifying anomalies by comparing the difference between the intensity value for the at least first pixel location and that stored for the second pixel location to said error threshold.
2 more elements
An inspection system for detecting anomalies on a surface, comprising:
- means for optically scanning the surface;
- means for collecting light scattered by the surface and deriving intensity values for said first pixel location and for its adjacent pixel locations from the collected light;
- a memory storing intensity values for a second pixel location of a reference image of the surface, said second pixel location corresponding in position to the at least first pixel location, and for neighboring pixel locations of the second pixel in the reference image corresponding in position to the adjacent pixel locations of the at least first pixel location;
- means for identifying anomalies by ascertaining whether each of some of the intensity values for the first pixel location and its adjacent pixel locations exceeds or is less than that stored for the corresponding pixel location of the second pixel location and its neighboring pixel locations.
1 more element
An inspection system for determining an anomaly on a surface, comprising:
- means for providing the intensity value for at least a first pixel location on the surface;
- a memory storing an intensity value for at least a second pixel location of a reference image of the surface, said second pixel location corresponding in position to the at least first pixel location;
- means for verifying the anomaly by ascertaining whether the intensity value of the at least first pixel location is a multiple of the intensity value of second pixel location, said multiple being in the range of 2 to 16.
An inspection system for determining an anomaly on a surface, comprising:
- means for providing the intensity values for at least a first pixel location and its adjacent pixel locations on the surface;
- a memory storing intensity values for a second pixel location of a reference image of the surface, said second pixel location corresponding in position to the at least first pixel location, and for neighboring pixel locations of the second pixel in the reference image corresponding in position to the adjacent pixel locations of the at least first pixel location;
- means for determining an anomaly by convolving a convolution matrix with the intensity values at said first pixel location and its adjacent pixel locations to obtain a first convolved value, and with the intensity values at said second pixel location and its neighboring pixel locations to obtain a second convolved value, and determining whether the difference between the first and second convolved values exceeds a predetermined convolution threshold.
An inspection method for detecting anomalies on a surface, comprising the steps of:
- optically scanning the surface;
- collecting light scattered by the surface and deriving an intensity value for at least a first pixel location from the collected light;
- determining an error threshold for said at least first pixel location from intensity values stored for at least a corresponding second pixel location and its neighboring pixel locations of a reference image of the surface, said error threshold being determined by the difference between the intensity value stored for the second pixel location and a maximum or minimum of intensity values stored for the second pixel location and its neighboring pixel locations in the reference image;
- and
- identifying anomalies by comparing the difference between the intensity value for the at least first pixel location and that stored for the second pixel location to said error threshold.
2 more elements
An inspection method for detecting anomalies on a surface, comprising the steps of:
- optically scanning the surface;
- collecting light scattered by the surface and deriving intensity values for said first pixel location and for its adjacent pixel locations from the collected light;
- storing intensity values for a second pixel location of a reference image of the surface, said second pixel location corresponding in position to the at least first pixel location, and for neighboring pixel locations of the second pixel in the reference image corresponding in position to the adjacent pixel locations of the at least first pixel location;
- identifying anomalies by ascertaining whether each of some of the intensity values for the first pixel location and its adjacent pixel locations exceeds or is less than that stored for the corresponding pixel location of the second pixel location and its neighboring pixel locations.
1 more element
An inspection method for determining an anomaly on a surface, comprising the steps of:
- providing the intensity value for at least a first pixel location on the surface;
- storing an intensity value for at least a second pixel location of a reference image of the surface, said second pixel location corresponding in position to the at least first pixel location;
- verifying the anomaly by ascertaining whether the intensity value of the at least first pixel location is a multiple of the intensity value of second pixel location, said multiple being in the range of 2 to 16.
An inspection method for determining an anomaly on a surface, comprising the steps of:
- providing the intensity values for at least a first pixel location and its adjacent pixel locations on the surface;
- storing intensity values for a second pixel location of a reference image of the surface, said second pixel location corresponding in position to the at least first pixel location, and for neighboring pixel locations of the second pixel in the reference image corresponding in position to the adjacent pixel locations of the at least first pixel location;
- determining an anomaly by convolving a convolution matrix with the intensity values at said first pixel location and its adjacent pixel locations to obtain a first convolved value, and with the intensity values at said second pixel location and its neighboring pixel locations to obtain a second convolved value, and determining whether the difference between the first and second convolved values exceeds a predetermined convolution threshold.
A system for detecting anomalies on a surface;
- comprising:
- means for directing a focused beam of light at a grazing angle toward said surface;
- means for causing relative motion between the beam and the surface so that the entire surface is scanned with said beam;
- means for detecting the specular reflection from the said surface and dynamically measuring the height of the said surface during scan;
- means for dynamically correcting the height of said surface during scan;
- means for collecting light scattered from the surface and converting such light into an electrical signal;
- means for digitally processing said electrical signal for detecting anomalies, said digital processing means detecting anomalies by comparing the difference between the intensity value for at least a first pixel location and that stored for at least a second pixel location of a reference image of the surface to an error threshold, said error threshold being determined by the digitally processing means from the difference between the intensity value stored for the second pixel location and a maximum or minimum of intensity values stored for the second pixel location and its neighboring pixel locations of the reference image.
4 more elements
A method for detecting anomalies on a surface;
- comprising the steps of:
- directing a focused beam of light at a grazing angle toward said surface;
- causing relative motion between the beam and the surface so that the entire surface is scanned with said beam;
- detecting the specular reflection from the said surface and dynamically measuring the height of the said surface during scan;
- dynamically correcting the height of said surface during scan;
- collecting light scattered from the surface and converting such light into an electrical signal;
- and
- digitally processing said electrical signal for detecting anomalies, said digitally processing step detecting anomalies by comparing the difference between the intensity value for at least a first pixel location and that stored or at least second pixel location of a reference image of the surface to an error threshold, said error threshold being determined in the digitally processing step by the difference between the intensity value stored for the second pixel location and a maximum or minimum of intensity values stored for the second pixel location and its neighboring pixel locations of the reference image.
5 more elements
A method for detecting anomalies on a surface of a semiconductor wafer;
- comprising:
- directing a focused beam of light towards said surface to illuminate an area of the surface defining a spot;
- causing relative motion between the beam and the wafer so that the beam scans a serpentine path covering substantially the entire surface;
- collecting light scattered along said path for detecting anomalies and converting the collected light to an electrical signal;
- wherein the spot size and said directing and causing steps are such that the beam substantially inspects the entire surface of the wafer at a throughput in excess of about 40 wafers per hour for 150 mm diameter wafers, at a throughput in excess of about 20 wafers per hour for 200 mm diameter wafers, and at a throughput in excess of about 10 wafers per hour for 300 mm diameter wafers;
- and
- digitally processing said electrical signal for detecting anomalies at a data clock rate less than 50 MHz.
4 more elements
A method for detecting anomalies on a surface, comprising the steps of:
- directing a focused beam of light towards said surface to illuminate an area of the surface defining a spot;
- causing relative motion between the beam and the surface so that the beam scans a serpentine path covering substantially the entire surface;
- collecting light scattered along said path for detecting anomalies and converting the collected light to an electrical signal;
- wherein the spot size and said directing and causing steps are such that the surface is inspected at a speed not less than about 1.5 cm.sup.2 /s;
- and
- digitally processing said electrical signal for detecting anomalies at a data clock rate of less than 50 MHz.
3 more elements
A method for detecting anomalies on a surface, comprising the steps of:
- directing a beam of light towards said surface to illuminate an area of the surface defining a spot;
- causing relative motion between the beam and the surface so that the beam scans a serpentine path covering substantially the entire surface;
- and
- collecting light scattered along said path for detecting anomalies and converting the collected light to an electrical signal;
- said surface having dimensions of not less than 200 mm in any direction along the surface, wherein said directing and causing steps are such that the beam scans substantially the entire surface in about 50 to 90 seconds;
- and
- digitally processing said electrical signal for detecting anomalies at a data clock rate of less than 50 MHz.
4 more elements
A method for detecting anomalies on a surface, comprising the steps of:
- directing a focused beam of light towards said surface to illuminate an area of the surface defining a spot whose size is in the range of about 5 to 15 micrometers;
- causing relative motion between the beam and the surface so that the beam scans a serpentine path covering substantially the entire surface, said surface having dimensions of not less than 200 mm in any direction along the surface, wherein said directing and causing steps are such that the beam scans substantially the entire surface in about 50 to 90 seconds;
- collecting light scattered along said path for detecting anomalies and converting the collected light to an electrical signal;
- and
- digitally processing said electrical signal for detecting anomalies at a data clock rate of less than 50 MHz.
2 more elements
A system for detecting anomalies on a surface, comprising:
- means for directing a focused beam of light towards said surface at an oblique angle of .theta. from the normal direction to the surface to illuminate a plurality of areas on the surface during the scan, each such illuminated area on the surface defining a spot of size w, said collecting and converting step converting the collected light into electrical signals representing light collected from N pixels within each spot;
- means for causing relative motion between the beam and the surface so that the beam scans a serpentine path covering substantially the entire surface, said path including a plurality of strips of sweeps of effective length l shorter than the dimensions of the surface, wherein the beam scans each sweep in time T;
- means for collecting light scattered along said path for detecting anomalies and converting the collected light to an electrical signal;
- and
- means for digitally processing said electrical signal for detecting anomalies, at a data clock rate substantially proportional to Nl/wT.
2 more elements
An inspection system for detecting anomalies on a surface, comprising:
- means for optically scanning the surface;
- means for collecting light scattered by the surface and deriving an intensity value for at least a first pixel location from the collected light;
- means for determining an error threshold for said at least first pixel location from intensity values stored for at least a corresponding second pixel location and its neighboring pixel locations of a reference image of the surface, said error threshold being determined by the difference between two intensity values stored for the second pixel location and its neighboring pixel locations in the reference image;
- and
- means for identifying anomalies by comparing the difference between the intensity value for the at least first pixel location and that stored for the second pixel location to said error threshold.
2 more elements
An inspection method for detecting anomalies on a surface, comprising the steps of:
- optically scanning the surface;
- collecting light scattered by the surface and deriving an intensity value for at least a first pixel location from the collected light;
- determining an error threshold for said at least first pixel location from intensity values stored for at least a corresponding second pixel location and its neighboring pixel locations of a reference image of the surface, said error threshold being determined by the difference between two intensity values stored for the second pixel location and its neighboring pixel locations in the reference image;
- and
- identifying anomalies by comparing the difference between the intensity value for the at least first pixel location and that stored for the second pixel location to said error threshold.
2 more elements
Dependencies are inferred from the claim text.