Reducing variations in energy reflected from a sample due to thin film interference

• US 20060268265A1
• Filed: 09/09/2005
• Published: 11/30/2006
• Est. Priority Date: 05/31/2005
• Status: Active Grant

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Chuang, Yung-Ho, Armstrong, J. Joseph
• Granted Patent: US 7,609,373 B2
• Time in Patent Office: Days
• US Class Current: 356/237.200
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection
• CPC Class Codes: G01N 2021/8809 Adjustment for highlighting flaws
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/95607 using a comparative method

Abstract

A system and method for inspecting a multi-layer sample, such as a silicon wafer, is disclosed. The design reduces variations in total reflected energy due to thin film interference. The design includes illuminating the sample at two incident angle ranges, where the two incident angle ranges are such that variation in total reflected energy at a first incident angle range may be employed to balance variation in total reflected energy at a second incident angle range. Defects are detected using die-to-die subtraction of the sample illuminated at the two incident angle ranges.

Claims

1. A method to reduce variations in total reflected energy due to thin film interference when inspecting a sample, comprising:

producing p-polarized light based on at least one from a group comprising linear, circular, and random polarized light; and

illuminating the sample at an incident angle similar to Brewster'"'"'s angle for a top most film, wherein said illuminating uses p-polarized light from said producing;

wherein the p-polarized light is p-polarized relative to the sample.

2. The method of claim 1 where the illuminating is quatrupole illumination.

3. The method of claim 1 wherein illumination from said illuminating comprises a ring with a range of incident angles both greater than and less than Brewster'"'"'s angle.

4. The method of claim 3 where the variation in total reflected energy at incident angles less than Brewster'"'"'s angle is used to balance the variation in the total reflected energy at angles greater than Brewster'"'"'s angle.

5. The method of claim 1 where p-polarization is obtained by using a mosaic of waveplates.

6. The method of claim 1 where p-polarization is obtained directly from a laser.

7. The method of claim 1 where p-polarization is obtained using an axicon.

8. The method of claim 1 where p-polarization is obtained using form birefringence.

9. The method of claim 1 where p-polarization is obtained using a diffractive element.

10. The method of claim 1 where p-polarization is obtained using a plastic sheet polarizer.

11. A method to reduce variations in total reflected energy due to thin film interference when inspecting a sample, comprising:

illuminating the sample using ring illumination provided at a plurality of incident angles, wherein the plurality of incident angles provide variation in total reflected energy at a first incident angle range to balance variation in total reflected energy at a second incident angle range.

12. The method of claim 11 where each incident angle uses azimuthal ring illumination.

13. The method of claim 12 where each incident angle includes a range of incident angles.

14. The method of claim 13 where one range of incident angles is p-polarized and another range is s-polarized.

15. The method of claim 13 where both ranges of incident angles are s-polarized.

16. The method of claim 13 where both ranges of incident angles are p-polarized.

17. The method of claim 14 where s-polarized light comes from a first laser pulse and p-polarized light comes from a second laser pulse.

18. The method of claim 11, wherein said illuminating employs light energy comprising at least one from a group comprising linearly, circularly, or randomly polarized light transformed into one from a group comprising p polarization and s polarization.

19. A method to reduce variations in total reflected energy due to thin film interference for inspection of a sample, comprising:

choosing two incident angle ranges such that variation in total reflected energy at a first incident angle range may be employed to balance variation in total reflected energy at a second incident angle range;

illuminating the sample at both of the two incident angle ranges; and

detecting defects on the sample using die-to-die subtraction of the sample from a reference sample, where the sample and reference sample are both illuminated at the two incident angle ranges.

20. The method of claim 19 where the sample comprises a semiconductor wafer.

21. The method of claim 19 where the thin film comprises one from a group comprising polysilicon, silicon, oxide, low-k dielectric, high k dielectric, photoresist, spin on glass, and nitride.

22. The method of claim 19 where a layer under the thin film is predominantly a metal.

23. The method of claim 19 where the layer under the thin film is silicon.