Threshold determination in an inspection system

• US 8,260,035 B2
• Filed: 09/22/2006
• Issued: 09/04/2012
• Est. Priority Date: 09/22/2006
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation (KLA Corporation)
• Original Assignee: KLA-Tencor Corporation (KLA Corporation)
• Inventors: Tek, Mehmet, Tiemeyer, Timothy, Vertikov, Andrey
• Primary Examiner(s): Park, Chan S
• Assistant Examiner(s): Yentrapati, Avinash J
• Application Number:
  US11/525,527
• Publication Number:
  US 20080075353A1
• Time in Patent Office: 2,174 Days
• Field of Search: None
• US Class Current: 382/152
• CPC Class Codes: G01N 2021/4711 Multiangle measurement
• CPC Class Codes: G01N 2021/4735 Solid samples, e.g. paper, glass
• CPC Class Codes: G01N 2021/8861 Determining coordinates of flaws
• CPC Class Codes: G01N 21/4738 Diffuse reflection precedence is given to G01N21/55 - G01N21/57 if specular component is taken into consideration, e.g. also for testing fluids, fibrous materials
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G06F 18/2415 based on parametric or probabilistic models, e.g. based on likelihood ratio or false acceptance rate versus a false rejection rate
• CPC Class Codes: G06V 10/145 Illumination specially adapted for pattern recognition, e.g. using gratings
• CPC Class Codes: G06V 10/30 Noise filtering
• CPC Class Codes: G06V 10/98 Detection or correction of errors, e.g. by rescanning the pattern or by human intervention; Evaluation of the quality of the acquired patterns

Abstract

A method and system for inspecting a surface of a semiconductor workpiece comprises providing a surface inspection system and using the surface inspection apparatus to cause laser light to impinge upon a test location on the workpiece surface and thereby cause the laser light to emerge from the surface as returned light comprising at least one of reflected light and scatter light; collecting the returned light and generating a signal from the returned and collected light, the signal comprising a signal value representative of a characteristic of the workpiece surface at the test location; providing a plurality of threshold candidates and causing the surface inspection system to select a threshold from among the plurality of threshold candidates; comparing the threshold to the signal value to obtain a difference value; using the difference value to assess the characteristic of the workpiece surface at the test location; and using the surface inspection system to automatically cause the method to be repeated for a plurality of test locations on the workpiece surface.

Claims

1. A method for inspecting a surface of a semiconductor workpiece, the method comprising:

providing a surface inspection system and using the surface inspection apparatus to cause laser light to impinge upon a test location on the workpiece surface and thereby cause the laser light to emerge from the surface as returned light comprising at least one of reflected light and scattered light;

collecting the returned light and generating a signal from the returned and collected light, the signal comprising a signal value representative of a characteristic of the workpiece surface at the test location;

providing a plurality of defect threshold candidates, the violation of which indicates the presence of a preexisting defect on the workpiece,

receiving with the surface inspection system an input from a user, where the input represents a desired sensitivity for the inspection of the workpiece,

causing the surface inspection system to automatically select a threshold from among the plurality of defect threshold candidates based on the input from the user and a plurality of prior signal values from secondary test locations, such that the threshold selected for the test location is different from the threshold selected for a different test location on the workpiece;

comparing the threshold to the signal value to obtain a difference value;

using the difference value to assess the characteristic of the workpiece surface at the test location; and

using the surface inspection system to automatically cause the method to be repeated for a plurality of test locations on the workpiece surface.

2. A method as recited in claim 1, wherein the collected and returned light consists of scattered light.

3. A method as recited in claim 1, wherein the collected and returned light consists of reflected light.

4. A method as recited in claim 1, wherein the plurality of threshold candidates comprises an estimate of the signal value.

5. A method as recited in claim 1, wherein the plurality of threshold candidates comprises a statistical value based upon a plurality of signal values for a corresponding plurality of test locations on the workpiece surface.

6. A method as recited in claim 1, wherein the plurality of threshold candidates comprises a value that is representative of a minimum size expected for the characteristic that is detectable given the sensitivity of the surface inspection system.

7. A method as recited in claim 6, further comprising using a constant sensitivity value to comprise the plurality of threshold candidates.

8. A method as recited in claim 1, wherein the plurality of threshold candidates comprises a false alarm-based threshold that is representative of a minimum size expected for the characteristic that is detectable given the sensitivity of the surface inspection system and a desired maximum probability of false identifications of the characteristic in the signal value for the surface inspection system.

9. A method as recited in claim 1, wherein the plurality of threshold candidates comprises a false alarm-based threshold that is representative of a maximum acceptable probability of false defect detection for the surface inspection system.

10. A system for inspecting a surface of a semiconductor workpiece, the system comprising:

a laser source that causes a laser light to impinge upon a test location on the workpiece surface and thereby cause the laser light to emerge from the surface as returned light comprising at least one of reflected light and scattered light;

a collection subsystem that collects the returned light and generates a signal from the returned and collected light, the signal comprising a signal value representative of a characteristic of the workpiece surface at the test location;

a processing device that,

receives an input from a user, where the input represents a desired sensitivity for the inspection of the workpiece,

causes the system to automatically select a threshold from among a plurality of defect threshold candidates, the violation of which indicates the presence of a preexisting defect on the workpiece, based on the input from the user and a plurality of prior signal values from secondary test locations, such that the threshold selected for the test location is different from the threshold selected for a different test location on the workpiece,

compares the signal value to the threshold to obtain a difference value, that uses the threshold using the difference value to assess the characteristic of the workpiece surface at the test location; and

uses the surface inspection system to automatically analyze the workpiece surface at a plurality of test locations.