Advanced phase shift inspection method

• US 20020131052A1
• Filed: 11/09/2001
• Published: 09/19/2002
• Est. Priority Date: 11/13/2000
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation
• Original Assignee: KLA-Tencor Corporation
• Inventors: Emery, David G.
• Granted Patent: US 6,836,560 B2
• Time in Patent Office: Days
• US Class Current: 356/511
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G03F 1/26 Phase shift masks [PSM]; PSM blanks; Preparation thereof
• CPC Class Codes: G03F 1/72 Repair or correction of mask defects
• CPC Class Codes: G03F 1/84 Inspecting

Abstract

A method and apparatus for inspecting patterned transmissive substrates, such as photomasks, for unwanted particles and features occurring on the transmissive as well as pattern defects. A transmissive substrate is illuminated by a laser through an optical system comprised of a laser scanning system, individual transmitted and reflected light collection optics and detectors collect and generate signals representative of the light transmitted and reflected by the substrate. The defect identification of the substrate is performed using only those transmitted and reflected light signals, and other signals derived from them, such as greyscale representations and image features. Defect identification is performed using a pattern inspection algorithm by comparing image feature representations of the present substrate with an idealized representation thereof, and using an advanced phase shift algorithm that accounts for particular types of expected anomalies.

Claims

1. A method for inspecting a specimen having at least one feature located thereon, comprising:

performing a transmitted energy inspection and a reflected energy inspection of said specimen;

submitting results from said transmitted energy inspection and said reflected energy inspection to a transmitted-reflected look up table, wherein said transmitted-reflected look up table comprises transmitted and reflected modification parameters dependent upon predetermined characteristics of said feature; and

outputting modified combined transmitted energy data and reflected energy data based on modified results determined by said transmitted-reflected look up table.

2. The method of claim 1, wherein boundaries of said specimen are remapped to optimize sensitivity on edges located on said specimen having predetermined compositions.

3. The method of claim 1, wherein said submitting step results in a transmitted representation and a reflected representation, further comprising applying shifting, stretching, and shaping functions to at least one of the transmitted representation and the reflected representation.

4. The method of claim 1, wherein said submitting step results in a transmitted representation and a reflected representation, further comprising normalizing at least one of said transmitted representation and said reflected representation.

5. The method of claim 1, wherein said submitting step results in a transmitted representation and a reflected representation, further comprising applying curve fitting to at least one of said transmitted representation and said reflected representation.

6. The method of claim 1, wherein said submitting step results in a transmitted representation and a reflected representation, further comprising selectively ignoring at least one of the transmitted representation and the reflected representation.

7. A method for inspecting a specimen, comprising:

performing a transmitted energy inspection and a reflected energy inspection of said specimen, thereby producing a transmitted representation and a reflected representation of said specimen; and

modifying at least one of the transmitted representation and the reflected representation based on an expected received transmitted/received signal dependent upon predetermined knowledge associated with specimen composition.

8. The method of claim 7, wherein said modifying utilizes a transmitted-reflected look up table having coefficients based upon known characteristics of previously inspected specimens.

9. The method of claim 8, wherein boundaries of said specimen are remapped to optimize sensitivity on edges having predetermined compositions.

10. The method of claim 8, further comprising applying shifting, stretching, and shaping functions to at least one of the transmitted representation and the reflected representation.

11. The method of claim 8, further comprising normalizing at least one of said transmitted representation and said reflected representation.

12. The method of claim 8, further comprising applying curve fitting to at least one of said transmitted representation and said reflected representation.

13. The method of claim 8, further comprising selectively ignoring at least one of the transmitted representation and the reflected representation.

15. The method of claim 14, wherein said modifying utilizes a transmitted-reflected look up table having coefficients based upon known characteristics of previously inspected specimens.

16. The method of claim 14, wherein boundaries of said specimen are remapped to optimize sensitivity on edges having predetermined compositions.

17. The method of claim 14, further comprising applying shifting, stretching, and shaping functions to at least one of the transmitted representation and the reflected representation.

18. The method of claim 14, further comprising normalizing at least one of said transmitted representation and said reflected representation.

19. The method of claim 14, further comprising applying curve fitting to at least one of said transmitted representation and said reflected representation.

20. The method of claim 14, further comprising selectively ignoring at least one of the transmitted representation and the reflected representation.

14. A method for inspecting a specimen, comprising:

performing a transmitted energy inspection and a reflected energy inspection of said specimen, thereby producing a transmitted representation and a reflected representation of said specimen; and

modifying said transmitted representation and said reflected representation based on predetermined known transmitted/reflected characteristics of previously inspected specimens having physical feature compositions similar to those of the specimen.

21. A method for inspecting a specimen, comprising:

performing a calibration function, capturing transmitted and reflected images and quantifying extreme values for transmitted and reflected images;

performing a transmitted-reflected map calibration function, producing a transmitted-reflected map function;

loading the transmitted-reflected map function into a lookup table, producing a set of inspection parameters; and

inspecting the specimen based on the inspection parameters.