Apparatus and methods for detecting overlay errors using scatterometry

• US 7,876,440 B2
• Filed: 07/17/2009
• Issued: 01/25/2011
• Est. Priority Date: 12/05/2002
• Status: Active Grant

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Fabrikant, Anatoly, Levy, Ady, Friedmann, Michael, Smith, Ian, Mieher, Walter D., Golovanesky, Boris, Adel, Michael E.
• Primary Examiner(s): Chowdhury; Tarifur
• Assistant Examiner(s): Stock, Jr.; Gordon J
• Application Number:
  US12/505,311
• Publication Number:
  US 20090284744A1
• Time in Patent Office: 557 Days
• Field of Search: None
• US Class Current: 356/401
• CPC Class Codes: G01N 2021/213 Spectrometric ellipsometry
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
• CPC Class Codes: G03F 7/70683 Mark designs
• CPC Class Codes: G03F 9/7049 Technique, e.g. interferometric
• CPC Class Codes: G03F 9/7084 Position of mark on substrate, i.e. position in (x, y, z) of mark, e.g. buried or resist covered mark, mark on rearside, at the substrate edge, in the circuit area, latent image mark, marks in plural levels
• CPC Class Codes: G03F 9/7088 Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection

Abstract

Disclosed are apparatus and methods for determining overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample. Targets A, B, C and D that each include a portion of the first and second structures are provided. The target A is designed to have an offset Xa between its first and second structures portions; the target B is designed to have an offset Xb between its first and second structures portions; the target C is designed to have an offset Xc between its first and second structures portions; and the target D is designed to have an offset Xd between its first and second structures portions. Each of the offsets Xa, Xb, Xc and Xd is different from zero, and Xa is an opposite sign and differ from Xb.

Claims

1. A method for determining overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, the method comprising:

providing targets A, B, C and D that each include a portion of the first and second structures,

wherein the target A is designed to have an offset Xa between its first and second structures portions,

wherein the target B is designed to have an offset Xb between its first and second structures portions,

wherein the target C is designed to have an offset Xc between its first and second structures portions,

wherein the target D is designed to have an offset Xd between its first and second structures portions,

wherein each of the offsets Xa, Xb, Xc and Xd is different from zero, Xa has an opposite sign and differs from Xb, and Xc has an opposite sign and differs from Xd,

wherein the offsets Xa, Xb, Xc and Xd are selected so that an overlay error, including the respective offset, is within a linear region of a plurality overlay values, which include pairs of selected offset Xa, Xb, Xc or Xd and any overlay error;

illuminating the targets A, B, C and D with electromagnetic radiation to obtain radiation output signals S_A, S_B, S_c, and S_D from targets A, B, C, and D, respectively; and

determining any overlay error between the first structures and the second structures using a linear or phase based scatterometry technique based on the obtained radiation output signals S_A, S_B, S_C, and S_D,

wherein the offsets Xa, Xb, Xc, and Xd are selected so that a slope of a negative region of the overlay values equals a slope of a positive region of the overlay values.

2. The method of claim 1, wherein the offsets Xa, Xb, Xc and Xd are selected such that the following conditions are met, where P is a pitch of the targets A, B, C, and D:

0.05<

|Xa/P|<

0.45, and

0.05<

|xb/P|<

0.45.

3. The method of claim 1, wherein the targets A, B, C, and D are process robust targets that are minimally affected by process variations for fabricating such targets.

4. The method of claim 1, wherein the targets A, B, C, and D have substantially same characteristics, including film characteristics, structure size, and composition.

5. The method of claim 1, wherein determining any overlay error is further based on a statistical calculation.

6. The method of claim 1, wherein determining any overlay error is further based on an integration or average of the obtained radiation output signals S_A, S_B, S_C, and S_D or an integration or average of difference values of such obtained radiation output signals S_A, S_B, S_C, and S_D.

7. The method of claim 1, wherein a portion of at least one of the radiation output signals S_A, S_B, S_C, and S_D is spatially filtered so as to obtain a spatial portion of each of the at least one radiation output signals S_A, S_B, S_C, and S_D so that the spatial portion corresponds to one or more pixel lines selected from a plurality of pixel lines that form a whole image of the corresponding target A, B, C, or D.

8. The method of claim 1, wherein each offset is a combination of F and f0, wherein F is selected to provide a maximum sensitivity to overlay errors and f0 is selected to be outside a specification limit for overlay errors.

9. The method of claim 1, wherein illuminating each of the targets A, B, C and D includes modulating through multiple wavelengths and determining any overlay error is further based on a Fourier Transform process that represents each radiation output signals S_A, S_B, S_Cand S_D by a Fourier series expansion having a plurality of known parameters and a plurality of unknown parameters, including an unknown overlay error.

10. The method of claim 8, wherein F equals P/4, where P is a pitch of the targets A, B, C, and D.

11. The method of claim 9, wherein the number of unknown parameters equals four and any overlay error is determined by analyzing the Fourier series expansion to solve for the unknown overlay error.

12. A system for determining overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, comprising:

a scatterometry module for illuminating the targets A, B, C and D with electromagnetic radiation to obtain spectra S_A, S_B, S_C, and S_D from targets A, B, C, and D, respectively; and

a processor operable for determining any overlay error between the first structures and the second structures using a linear or phase based scatterometry technique based on the obtained spectra S_A, S_B, S_C, and S_D,

wherein targets A, B, C and D each include a portion of the first and second structures,

wherein the target A is designed to have an offset Xa between its first and second structures portions,

wherein the target B is designed to have an offset Xb between its first and second structures portions,

wherein the target C is designed to have an offset Xc between its first and second structures portions,

wherein the target D is designed to have an offset Xd between its first and second structures portions, and

wherein each of the offsets Xa, Xb, Xc and Xd is different from zero, Xa has an opposite sign and differs from Xb, and Xc has an opposite sign and differs from Xd

wherein the offsets Xa, Xb, Xc and Xd are selected so that an overlay error, including the respective offset, is within a linear region of a plurality overlay values, which include pairs of selected offset Xa, Xb, Xc or Xd and any overlay error;

wherein the offsets Xa, Xb, Xc, and Xd are selected so that a slope of a negative region of the overlay values equals a slope of a positive region of the overlay values.

13. The system of claim 12, wherein the offsets Xa, Xb, Xc and Xd are selected such that the following conditions are met, where P is a pitch of the targets A, B, C, and D:

0.05<

|Xa/P|<

0.45, and

0.05<

|xb/P|<

0.45.

14. The system of claim 12, wherein determining any overlay error is further based on an integration or average of the obtained radiation output S_A, S_B, S_C, and S_D or an integration or average of difference values of such obtained radiation output signals S_A, S_B, S_C, and S_D.

15. The system of claim 12, wherein a portion of at least one of the radiation output signals S_A, S_B, S_C, and S_D is spatially filtered so as to obtain a spatial portion of each of the at least one radiation output signals S_A, S_B, S_C, and S_D so that the spatial portion corresponds to one or more pixel lines selected from a plurality of pixel lines that form a whole image of the corresponding target A, B, C, or D.

16. The system of claim 12, wherein illuminating the targets A, B, C, and D includes modulating through multiple wavelengths and determining any overlay error is further based on a Fourier Transform process that represents each radiation output signals S_A, S_B, Sc, and S_D by a Fourier series expansion having a plurality of known parameters and a plurality of unknown parameters, including an unknown overlay error and wherein the number of unknown parameters equals four and any overlay error is determined by analyzing the Fourier series expansion to solve for the unknown overlay error.

17. The system of claim 12, wherein each offset is a combination of F and f0, wherein F is selected to provide a maximum sensitivity to overlay errors and f0 is selected to be outside a specification limit for overlay errors.

18. The system of claim 17, wherein F equals P/4, where P is a pitch of the targets A, B, C, and D.