Methods for critical dimension and focus mapping using critical dimension test marks

• US 20030211700A1
• Filed: 12/04/2002
• Published: 11/13/2003
• Est. Priority Date: 04/19/2002
• Status: Active Grant

• Current Assignee: Nikon Precision Incorporated (Nikon Corporation)
• Original Assignee: Nikon Precision Incorporated (Nikon Corporation)
• Inventors: Morita, Etsuya, Magoon, Holly H., Pierce, Ronald A., Leung, Frank C., Putnam, Christopher Howard, Roberts, Norman E.
• Granted Patent: US 6,974,653 B2
• Time in Patent Office: Days
• US Class Current: 438/401
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70641 Focus
• CPC Class Codes: G03F 7/70683 Mark designs

Abstract

Methods for using critical dimension test marks (test marks) for the rapid determination of the best focus position of lithographic processing equipment and critical dimension measurement analysis across a wafer'"'"'s surface are described. In a first embodiment, a plurality of test mark arrays are distributed across the surface of a wafer, a different plurality being created at a plurality of focus positions. Measurement of the length or area of the resultant test marks allows for the determination of the best focus position of the processing equipment. Critical dimension measurements at multiple points on a wafer with test marks allow for the determination of process accuracy and repeatability and further allows for the real-time detection of process degradation. Using test marks which require only a relatively simple optical scanner and sensor to measure their length or area, it is possible to measure hundreds of measurement values across a wafer in thirty minutes. Comparable measurements with a Scanning Electron Microscope (SEM) require at least five hours.

Claims

1. A method comprising:

repeatedly exposing a wafer with a lithography tool to form a plurality of test marks on the surface of the wafer;

measuring a focus component of the test marks;

mapping the wafer from the measured focus component of the test marks;

characterizing the lithography tool based on the mapped wafer; and

adjusting the lithography tool to improve focusing based on the characterization.

2. The method of claim 1, wherein the focus component comprises one of the following:

curvature within one of the test mark exposures;

curvature across the wafer;

tilt within one of the test mark exposures;

tilt across the wafer;

variation of tilt and focus within one of the exposures along the scanning direction of the lithography tool; and

comparison of the scanning of selected test marks on the wafer versus the scanning of second test marks off the wafer.

3. The method of claim 1, wherein the test marks are formed at the periphery of the wafer and the interior regions of the wafer.

4. The method of claim 1, wherein each of the test marks comprises a test mark pattern, the test mark pattern including an array of overlapping exposure lines having a width substantially equal to a critical dimension of interest.

5. The method of claim 1, wherein the test mark pattern is formed by scanning in one of the following directions;

the plus only direction;

the minus only direction;

or

the plus and minus direction

6. A method for determining the performance of semiconductor wafer processing equipment, the method comprising:

creating a plurality of test marks on the surface of the semiconductor wafer during a processing step, the test marks being made by an imaging pattern with known critical dimensions;

measuring the test marks after the processing step is complete; and

adjusting the equipment if the test marks are not measured to have at least a predefined value.

7. The method of claim 6 wherein the test marks are created on scribe lines which denote the boundary between the plurality of active semiconductor dies being fabricated on the semiconductor wafer.

8. The method of claim 6 wherein the plurality of test marks comprises a plurality of matrices of test marks, at least some of the matrices being created on interior areas of the semiconductor wafer and at least some of the matrices being created on the outer edge of the semiconductor wafer.

9. The method of claim 6 wherein an optical scanning device measures a length of the test marks, the equipment being adjusted if the length measured is not at least as great as a first predefined length.

10. The method of claim 6 wherein an optical scanning device measures the area of the test marks, the equipment being adjusted if the area measured is not at least as great as a first predefined area.

11. The method of claim 6 wherein the test marks are placed on production semiconductor wafers.

12. The method of claim 6 wherein the test marks are placed on test semiconductor wafers.

13. A method as recited in claim 6 wherein the test marks are created on areas of the semiconductor wafer that will not be part of functional finished semiconductor devices.

14. A method for using test marks generated by a lithographic process, the method comprising the steps of:

selecting areas of a semiconductor wafer, the wafer having a top surface upon which areas test marks will be generated;

generating the test marks on the selected areas by using a lithographic process;

measuring at least a first predefined parameter of the test marks; and

altering at least one parameter of the lithographic process depending on the results of the measuring step.

15. The method of claim 14 wherein the first predefined parameter of the test marks is the length of the test marks.

16. The method of claim 14 wherein the first predefined parameter of the test marks is the area of the test marks.

17. The method of claim 14, wherein the areas selected on the semiconductor wafer include the scribe lines, the scribe lines being cut when the wafer is diced.

18. The method of claim 14 wherein the parameter of the lithographic process being altered is the focus of the lithographic process.

19. The method of claim 14 wherein the test marks are generated as matrixes of test marks.

20. A method for determining the best focus position of a lithographic production device, the method comprising the steps of:

creating a plurality of test fields in a resist, wherein each test field has a multiplicity of test marks that are stepped through focus;

measuring each of the test marks, thereby generating test mark data;

using the test mark data to select a best focus profile for future operation of the lithographic production device that created test marks.

21. The method of claim 20 wherein the area of the test marks is measured to generate the test mark data.

22. The method of claim 20 wherein the length of the test marks is measured to generate the test mark data.

23. The method of claim 20 wherein the test fields are created on a test wafer prior to using the lithographic device to produce a production wafer.

24. The method of claim 20 wherein the test fields are created on production wafers selected on a predefined schedule, the test mark data from test field on production wafers being used to adjust the focus of the lithographic production device during manufacturing operations.

25. An apparatus for determining the best focus position of a lithographic production device, the apparatus comprising:

the lithographic production device for creating a plurality of test fields in a resist formed on a wafer, wherein each test field has a multiplicity of test marks that are formed using incrementally different focuses of the lithographic device such that the marks within each field are stepped through focus, the test fields being distributed at different locations about the wafer with some test fields being located at the edge of a useful portion of the wafer and some of the test fields being located at interior positions on the wafer;

a measuring system for measuring each of the test marks at each of the plurality of focus steps; and

a data collection device coupled to the measuring system for storing the results of the measurement of the test marks and for calculating from the stored measurements the best focus position of the lithographic production device.

26. The apparatus of claim 25 wherein the data collection device selects the best focus position of the lithographic production device based upon the position that created test marks having the largest measured value.

27. The apparatus of claim 25 wherein the test fields are formed on a test wafer, the apparatus determining the best focus position for the device prior to the device'"'"'s use in production.

28. The apparatus of claim 25 wherein test fields are formed on production wafers selected on a first predefined schedule, the test fields on the production wafer allowing the apparatus to repeatedly determine the best focus position of the device during production, the device being recalibrated after measurement of the test marks formed on the production wafer are measured.

29. The apparatus of claim 25 wherein the test fields are formed in the scribe lines that separate the individual integrated circuit dies that are being formed on the wafer.

30. The apparatus of claim 25 wherein the test fields are formed in areas of the individual integrated circuit dies that will comprise at least part of the completed integrated circuit die.

31. The apparatus of claim 25 wherein the measuring system and lithographic production device are completely separate devices.

32. A method for determining the best focus position of a lithographic production device, the method comprising the steps of:

creating a plurality of test marks across a surface of a wafer at a first focus position;

stepping the focus position to a successive focus position;

repeating the creating and stepping operations until a plurality of test marks has been created on the wafer at a predefined plurality of focus steps;

measuring each plurality of test marks at each f the plurality of focus steps;

selecting the focus step for future operation of the lithographic production device that created test marks having the largest measure value.

33. The method of claim 32 wherein an optical apparatus measures the length of the test marks and the selected focus step creates the longest measured test mark.

34. The method of claim 32 wherein an optical apparatus measures the area of the test marks and the selected focus step creates the largest measured test mark.

35. The method of claim 32 wherein each plurality of test marks comprises an array of test marks.

36. The method of claim 35 wherein each array of test marks comprises a 3×

5 rectangular matrix of test marks.

37. The method of claim 32 wherein a scanning apparatus creates the test marks and further wherein at least some of the test marks are created on an outer edge of the wafer as the scanning apparatus scans from across the surface of the wafer to a position where the scanner is not over the wafer and at least some of the test marks are created on an outer edge of the wafer as the scanning apparatus scans from a position where the scanner is not over the wafer to a position where the scanner scans across the surface of the wafer.

38. The method of claim 32 wherein the selected focus step is determined by averaging the measured values of the test marks created on interior portions of the wafer and test marks created on the outer edge of the wafer.