Fast illumination simulator based on a calibrated flexible point-spread function

• US 9,091,941 B2
• Filed: 04/01/2014
• Issued: 07/28/2015
• Est. Priority Date: 02/21/2011
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Smith, Daniel Gene, Flagello, Donis G.
• Primary Examiner(s): NGUYEN, HUNG
• Application Number:
  US14/242,571
• Publication Number:
  US 20140211186A1
• Time in Patent Office: 483 Days
• Field of Search: 355/52, 355/53, 355/55, 355 67- 71, 356399-401
• US Class Current: 1/1
• CPC Class Codes: G03F 7/70083 Non-homogeneous intensity distribution in the mask plane
• CPC Class Codes: G03F 7/705 Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions
• CPC Class Codes: G03F 7/7055 Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption

Abstract

Method of predicting a distribution of light in an illumination pupil of an illumination system includes identifying component(s) of the illumination system the adjustment of which affects this distribution and simulating the distribution based on a point spread function defined in part by the identified components. The point spread function has functional relationship with configurable setting of the illumination settings.

Claims

1. A method for obtaining a distribution of light at an illumination pupil of an illuminator, which illuminator is configured to distribute light from a light source at the illumination pupil via a distributing optical element, and which illuminator is configured to illuminate a target surface with the distributed light, the method comprising:

preparing a far field distribution of the distributing optical element; and

calculating the distribution of light at the illumination pupil with the use of a plurality of point spread functions of a partial optical system, which point spread functions represent a plurality of positions at the illumination pupil,

wherein the partial optical system is positioned between the distributing optical element and the illumination pupil,

wherein the evaluating the distribution of light at the illumination pupil is effectuated according to

A_reticle(x_mn,y_mn)≈

Σ

_iΣ

_jA_s(α

_ij,β

_ij)psf(x_mn,y_mn,α

_ij,β

_ij,IU_setting),

wherein the far field distribution of light, corresponding to the distributing element configured to scatter light, is represented by As and is a function of coordinates α

_ij and β

_ij of an entrance pupil of the illumination system,

wherein subscripts i and j correspond to a discrete sum across a two dimensional array of pixels in the entrance pupil such that each pixel (i,j) has a pair of pupil coordinates (α

, β

),

wherein a distribution of light in an exit pupil of the illumination system, corresponding to an optical far field incident at the reticle, is represented by A_reticle which is a function of exit pupil coordinates (x_m,n, y_m,n),

wherein psf represents a point spread function, and

wherein IU_setting includes an array of values that determine adjustable parameters of the illumination system.

2. The method of claim 1, wherein

the calculating includes convolving the plurality of point spread functions and the far field distribution.

3. The method of claim 2, wherein

the plurality of point spread functions that represent the plurality of positions expresses a function of a position in the illumination pupil.

4. The method of claim 1, further comprising:

preparing the plurality of point spread functions of a partial optical system.

5. The method of claim 4, wherein

the preparing the plurality of point spread functions includes measuring a distribution of light at the illumination pupil.

6. The method of claim 4, wherein

the preparing the plurality of point spread functions includes simulating the partial optical system by ray tracing.

7. The method of claim 1, wherein

the distributing optical element comprises at least one of a diffracting element, a scattering element, and a micro mirror array.

8. An illuminator that is configured to distribute light from a light source at an illumination pupil via a distributing optical element and that is configured to illuminate a target surface with light distributed at the illumination pupil, the illuminator comprising:

a partial optical system arranged between the distributing optical element and the illumination pupil; and

a pupil distribution calculator configured to calculate a distribution of light at the illumination pupil,

wherein the pupil distribution calculator is configured to calculate the distribution of light at the illumination pupil using a far field distribution of the distributing optical element and a plurality of point spread functions of a partial optical system that represent a plurality of positions at the illumination pupil,

wherein the pupil distribution calculator is configured to calculate the distribution of light at the illumination pupil according to

A_reticle(x_mn,y_mn)≈

Σ

_iΣ

_jA_s(α

_ij,β

_ij)psf(x_mn,y_mn,α

_ij,β

_ij,IU_setting),

wherein the far field distribution of light, corresponding to the distributing optical element configured to scatter light, is represented by As and is a function of coordinates α

_ij and β

_ij of an entrance pupil of the illumination system,

wherein subscripts i and j correspond to a discrete sum across a two dimensional array of pixels in the entrance pupil such that each pixel (i,j) has a pair of pupil coordinates (α

, β

),

wherein a distribution of light in an exit pupil of the illumination system, corresponding to an optical far field incident at the reticle, is represented by A_reticle, which is a function of exit pupil coordinates (x_m,n, y_m,n),

wherein psf represents a point spread function, and

wherein IU_setting includes an array of values that determine adjustable parameters of the illumination system.

9. The illuminator of claim 8, wherein

the pupil distribution calculator is configured to convolve the plurality of point spread functions and the far field distribution.

10. The illuminator of claim 9, wherein

the plurality of point spread function representing the plurality of positions expresses a function of a position in the illumination pupil.

11. The illuminator of claim 8, wherein

the plurality of point spread functions is obtained by measuring a distribution of light at the illumination pupil.

12. The illuminator of claim 8, wherein

the plurality of point spread functions is obtained as a result of a ray tracing simulation of the partial optical system.

13. The illuminator of claim 8, wherein

the distributing optical element comprises at least one of a scattering element and a micro mirror array.

14. A process for enabling a computer to simulate a distribution of light at an illumination pupil of an illuminator, which illuminator is configured to distribute light from a light source at the illumination pupil via a distributing optical element, and which illuminator is configured to illuminate a target surface with light distributed at the illumination pupil, the process comprising:

forming a far field distribution of the distributing optical element; and

calculating the distribution of light at the illumination pupil with the use of a plurality of point spread functions of a partial optical system, which plurality relates to a plurality of positions at the illumination pupil,

wherein the partial optical system is positioned between the distributing optical element and the illumination pupil,

wherein the calculating is effectuated according to

A_reticle(x_mn,y_mn)≈

Σ

_iΣ

_jA_s(α

_ij,β

_ij)psf(x_mn,y_mn,α

_ij,β

_ij,IU_setting),

wherein the far field distribution of light, which corresponds to a diffracting element that is configured to scatter light, is represented by A_s and is a function of coordinates α

_ij and β

_ij of an entrance pupil of the illumination system,

wherein subscripts i and j correspond to a discrete sum across a two dimensional array of pixels in the entrance pupil such that each pixel (i,j) has a pair of pupil coordinates (α

, β

),

wherein a distribution of light in an exit pupil of the illumination system, corresponding to an optical far field incident at the reticle, is represented by A_reticle, which is a function of exit pupil coordinates x_m,n, y_m,n),

wherein psf represents a point spread function, and

wherein IU_setting includes an array of values that determine adjustable parameters of the illumination system.

15. The process of claim 14, wherein

the calculating including convolving the plurality of point spread functions and the far field distribution.

16. The process of claim 15, wherein

the plurality of point spread functions expresses a function of a position in the illumination pupil.

17. The process of claim 14, further comprising:

determining the plurality of point spread functions of the partial optical system.

18. The process of claim 17, wherein

the determining the plurality of point spread functions includes measuring a distribution of light at the illumination pupil.

19. The process of claim 17, wherein

the determining the plurality of point spread functions includes simulating the partial optical system by ray tracing.

20. The process of claim 14, wherein

the distributing optical element comprises at least one of a diffracting element, a scattering element and a micro mirror array.