Symmetric target design in scatterometry overlay metrology

Patent metadata

Field	Value
Publication number	US-9739702-B2
Application number	US-201414161398-A
Country	US
Kind code	B2
Filing date	Jan 22, 2014
Priority date	Oct 18, 2012
Publication date	Aug 22, 2017
Grant date	Aug 22, 2017

Abstract

Metrology methods, systems and targets are provided, which implement a side by side paradigm. Adjacent cells with periodic structures are used to extract the overlay error, e.g., by introducing controllable phase shifts or image shifts which enable algorithmic computation of the overlay. The periodic structures are designed to exhibit a rotational symmetry to support the computation and reduce errors.

First claim

What is claimed is:

1. A method of estimating an overlay error between at least two layers, the method comprising:
illuminating a metrology target that comprises at least two periodic structures which are at different layers, are along a direction parallel to the target and have a same pitch, such that at least two of the at least two periodic structures are arranged such that they at least partly share a same border or line with each other when observed from a perspective perpendicular to the target and do not overlap in a direction perpendicular to the target, wherein the metrology target is symmetric with respect to a 180° rotation about an axis that is perpendicular to the target, and wherein the illumination is carried out simultaneously with respect to the at least two periodic structures in order to effect a result selected from the group of:
eliminating an algorithmic inaccuracy which is inversely proportional to a size of the target;
reducing a sensitivity to an illumination asymmetry;
improving an overlay symmetry;
reducing a sensitivity to a target asymmetry;
reducing a sensitivity to a target noise;
eliminating a sensitivity to intra-target process variations;
reducing a size of the target required to be used at a given sensitivity;
reducing a sensitivity to a fully correlated noise; and
increasing an optimization potential by increasing a space of system parameters to be optimized over;

measuring interference of at least one diffraction order from the at least two periodic structures; and
extracting the overlay error from the measured interference.

2. The method of claim 1 , wherein the rotational symmetry satisfies ψ n (a) ({right arrow over (k)})=ψ −n (a) (−{right arrow over (k)}), where a is a layer, k is a position in a pupil plane, n is a diffraction order number, and Ψ is a phase function of an electric field.

3. The method of claim 1 , further comprising introducing a controlled variable that affects at least one of the illumination and collection beams from at least one of the periodic structures, and extracting the overlay error from the measured interference with respect to the introduced controlled variable.

4. The method of claim 1 , further comprising:
setting the illumination beams to exhibit no phase differences;
illuminating separately each periodic structure to measure respective diffracted intensities;
illuminating simultaneously the periodic structures to measure an interference term; and
extracting an overlay from the interference term for ±1 diffraction orders and opposite locations ±k.

5. The method of claim 4 , further comprising choosing a programmed offset between the periodic structures to simplify the overlay extraction.

6. The method of claim 4 , further comprising using three periodic structures, a first structure in one layer and two structures in another layer with different programmed offsets with respect to the first structure and extracting the overlay from the interference terms for ±1 diffraction orders of the two structures in the same layer and the two structures in the same layer.

7. The method of claim 1 , further comprising:
taking multiple measurements with different illumination intensities to extract the overlay; and
extracting the overlay from the interference measurements for ±1 diffraction orders and the different illumination intensities.

8. The method of claim 1 , further comprising:
imaging the metrology target to a field conjugate plane;
performing image shifting at the field conjugate plane;
compensating for the image shifting; and
extracting the overlay algorithmically from the compensated image shifts.

9. The method of claim 1 , further comprising:
imaging the metrology target to a field conjugate plane;
performing image shifting at the field conjugate plane;
processing uncompensated shifted images with respect to phases which are dependent of pupil coordinates; and
extracting the overlay algorithmically from the processing uncompensated shifted images.

10. The method of claim 9 , further comprising calibrating the pupil to calculate the phases and extract the overlay therefrom.

11. The method of claim 9 , further comprising measuring pupil images corresponding to several values of illumination phases.

12. The method of claim 1 , further comprising shifting a phase of at least one of the illumination and collection beams from at least one of the periodic structures, and extracting the overlay error from the measured interference with respect to the shifted phase.

13. The method of claim 12 , further comprising:
using mutually orthogonal polarized illumination beams;
configuring a collection field stop to have respective polarizers to separate the illumination beams; and
shifting phases of the reflected beams in the collection arm with respect to the polarization of the beams.

14. A metrology system comprising:
an illumination arm arranged to illuminate a metrology target that comprises at least two periodic structures which are at different layers, are along a direction parallel to the target and have a same pitch, such that at least two of the at least two periodic structures are arranged such that they at least partly share a same border or line with each other when observed from a perspective perpendicular to the target and do not overlap in a direction perpendicular to the target, wherein the metrology target is symmetric with respect to a 180° rotation about an axis that is perpendicular to the target, and wherein the illumination is carried out simultaneously with respect to the at least two periodic structures in order to effect a result selected from the group of:
eliminating an algorithmic inaccuracy which is inversely proportional to a size of the target;
reducing a sensitivity to an illumination asymmetry;
improving an overlay symmetry;
reducing a sensitivity to a target asymmetry;
reducing a sensitivity to a target noise;
eliminating a sensitivity to intra-target process variations;
reducing a size of the target required to be used at a given sensitivity;
reducing a sensitivity to a fully correlated noise; and
increasing an optimization potential by increasing a space of system parameters to be optimized over;

a collection arm arranged to measure interference of at least one diffraction order from the at least two periodic structures; and
a processor arranged to extract an overlay error from the measured interference.

15. The metrology system of claim 14 , wherein the rotational symmetry satisfies ψ n (a) ({right arrow over (k)})=ψ −n (a) (−{right arrow over (k)}), where a is a layer, k is a position in a pupil plane, n is a diffraction order number, and is a phase function of an electric field.

16. The metrology system of claim 14 , wherein at least one of the illumination arm and the collection arm comprises an introduced controlled variable that affects beams from at least one of the periodic structures, and the processor is arranged to extract the overlay error from the measured interference with respect to the introduced controlled variable.

17. The metrology system of claim 16 , wherein the controlled variable is at least one of: a phase, a polarization, and an intensity of the effected beam.

18. The metrology system of claim 14 , wherein the illumination arm is arranged to:
set illumination beam to exhibit no phase differences;
illuminate separately each periodic structure to measure respective diffracted intensities; and
illuminate simultaneously the periodic structures to measure an interference t

Assignees

• Kla Tencor Corp

Inventors

• Bringoltz Barak
• Kandel Daniel
• Feler Yoel
• Sapiens Noam
• Paykin Irina
• Svizher Alexander
• Aloni Meir
• Ben Dov Guy
• Shalmoni Hadar
• Levinski Vladimir

Classifications

• G01N2201/068

  Optics, miscellaneous · CPC title

• G01N21/01 Primary

  Arrangements or apparatus for facilitating the optical investigation · CPC title

• G01N21/956

  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 H10P74/20)} · CPC title

• G01N21/4788

  Diffraction (for sizing particles G01N15/0205) · CPC title

• G03F7/70683

  Mark designs · CPC title