Multi-level scanning method for defect inspection

• US 6,484,306 B1
• Filed: 12/17/1999
• Issued: 11/19/2002
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: EUV LLC (Intel Corporation)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Jeong, Seongtae, Bokor, Jeffrey
• Primary Examiner(s): Siek, Vuthe
• Assistant Examiner(s): Kik, Phallaka
• Application Number:
  US09/466,730
• Time in Patent Office: 1,068 Days
• Field of Search: 716/1-21, 430/4-5, 378/34-35, 382/144, 382/145, 382/149, 700/105, 700/108-110, 700/115-121
• US Class Current: 716/52
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/0006 using a design-rule based approach

Abstract

A method for performing scanned defect inspection of a collection of contiguous areas using a specified false-alarm-rate and capture-rate within an inspection system that has characteristic seek times between inspection locations. The multi-stage method involves setting an increased false-alarm-rate for a first stage of scanning, wherein subsequent stages of scanning inspect only the detected areas of probable defects at lowered values for the false-alarm-rate. For scanning inspection operations wherein the seek time and area uncertainty is favorable, the method can substantially increase inspection throughput.

Claims

1. A defect inspection method, comprising the steps of:

(a) performing a first stage inspection of a surface of an object using a first defect identification threshold;

(b) using said first stage inspection, identifying a plurality of first defect areas on said object;

(c) performing a second stage inspection of said first defect areas using a second defect identification threshold that provides a reduced level of false alarms as compared with the first defect identification threshold; and

(d) using said second stage inspection, identifying a plurality of second defect areas as a subset of the first defect areas.

2. A method as recited in claim 1, wherein each of said defect thresholds are calculated to provide a given signal-to-noise ratio for the inspection that corresponds to a specific maximum false-alarm ratio.

3. A method as recited in claim 1, wherein said object comprises a mask blank to be inspected.

4. A method as recited in claim 3, wherein said mask blank comprises an Extreme UltraViolet Lithography mask blank.

5. A method as recited in claim 1, wherein said defect identification thresholds are determined based upon seek times and area uncertainty of a scanning inspection system.

6. A defect inspection method, comprising the steps of:

inspecting a surface of an object for defects using a defect identification threshold and identifying a defect region on said object;

inspecting said defect region using a lower defect identification threshold and identifying a new defect region that is smaller in size than the previously identified defect region; and

successively inspecting each subsequently identified defect region using a lower defect identification threshold than the previous defect identification threshold until a final defect identification threshold is reached.

7. A method as recited in claim 6, wherein a two stage inspection is performed by setting said defect inspection threshold to said final defect identification threshold.

8. A method as recited in claim 6, wherein said object comprises a mask blank to be inspected.

9. A method as recited in claim 8, wherein the mask blank comprises an Extreme UltraViolet Lithography mask blank.

10. A method as recited in claim 6, wherein said defect identification thresholds are determined based upon seek times and area uncertainty of a scanning inspection system.

11. A method for inspecting a first area of a surface of an object for defects by scanning said first area, said first area comprising a plurality of second areas, said method comprising the steps of:

(a) measuring a characteristic from each of said second areas, comparing each said measured characteristic against a threshold value X during the scan, and saving location information for each failed comparison and designating the location as a probable defect;

(b) altering the threshold value X to a value closer to a final threshold which characterizes a final stage of inspection;

(c) measuring a characteristic of each probable defect location, comparing each said measured characteristic against the altered threshold value X from step (b), and saving location information for each of said second areas which still fails the comparison;

(d) designating probable defects as actual defects when the threshold value X is set to a value equal to the final threshold value; and

(e) returning to step (b) to perform another inspection stage if the threshold value X is not set to a value equal to the final threshold value.

12. A method as recited in claim 11, wherein a two stage inspection is performed by setting said threshold value X to the final threshold value upon a first entry and singular entry to step (b).

13. A method as recited in claim 11, wherein said first area is contained upon a mask blank to be inspected.

14. A method as recited in claim 13, wherein said mask blank comprises an Extreme UltraViolet Lithography mask blank.

15. A method as recited in claim 11, wherein said threshold values are computed based upon seek times and area uncertainty of a scanning inspection system.