Correction for flare effects in lithography system

• US 8,887,104 B2
• Filed: 09/01/2011
• Issued: 11/11/2014
• Est. Priority Date: 09/14/2010
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Liu, Hua-Yu, Li, Jiangwei, Chen, Luoqi, Liu, Wei, Jiang, Jiong
• Primary Examiner(s): NGUYEN, NHA T
• Application Number:
  US13/823,685
• Publication Number:
  US 20130185681A1
• Time in Patent Office: 1,167 Days
• Field of Search: 716 50- 56, 430/5, 430/30
• US Class Current: 716/51
• 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 7/70941 Stray fields and charges, e.g. stray light, scattered light, flare, transmission loss
• CPC Class Codes: G06F 30/20 Design optimisation, verification or simulation optimisation, verification or simulation of circuit designs G06F30/30
• CPC Class Codes: G06F 30/30 Circuit design

Abstract

A method for reducing an effect of flare produced by a lithographic apparatus for imaging a design layout onto a substrate is described. A flare map in an exposure field of the lithographic apparatus is simulated by mathematically combining a density map of the design layout at the exposure field with a point spread function (PSF), wherein system-specific effects on the flare map may be incorporated in the simulation. Location-dependent flare corrections for the design layout are calculated by using the determined flare map, thereby reducing the effect of flare. Some of the system-specific effects included in the simulation are: a flare effect due to reflection from black border of a mask, a flare effect due to reflection from one or more reticle-masking blades defining an exposure slit, a flare effect due to overscan, a flare effect due reflections from a gas-lock sub-aperture of a dynamic gas lock (DGL) mechanism, and a flare effect due to contribution from neighboring exposure fields.

Claims

1. A method implemented by a computer for reducing an effect of flare produced by a lithographic system for imaging a design layout onto a substrate, the method comprising:

adjusting a point spread function (PSF) to account for system-specific effects on flare due to identified characteristics of the lithographic system;

simulating, using the computer, a flare map in an exposure field of the lithographic system by mathematically combining a density map of the design layout at the exposure field with the adjusted PSF, such that the system-specific effects on the flare map are incorporated in the simulation; and

calculating location-dependent flare corrections for the design layout by using the determined flare map, thereby reducing the effect of flare.

2. The method of claim 1, wherein the system-specific effects include one or more of:

a flare effect due to reflection from black border of a mask, a flare effect due to reflection from one or more reticle-masking blades defining an exposure slit, a flare effect due to overscan, a flare effect due reflections from a gas-lock sub-aperture of a dynamic gas lock (DGL) mechanism, and a flare effect within a specific exposure field due to contribution from other neighbouring exposure fields.

3. The method of claim 1, wherein the adjusted PSF is anisotropic to simulate one or more of the following effects:

a flare effect due to reflection from black border of a mask, a flare effect due to reflection from one or more reticle-masking blades defining an exposure slit, a flare effect due to overscan, a flare effect due reflections from a gas-lock sub-aperture of a dynamic gas lock (DGL) mechanism, and a flare effect within a specific exposure field due to contribution from other neighbouring exposure fields.

4. The method of claim 1, wherein the density map comprises a representation of the design layout after being modified by optical enhancement features (OEF).

5. The method of claim 4, wherein the method further comprises:

updating the post-OEF design layout with the location-dependent flare corrections to create an improved post-OEF flare-corrected design layout; and

using the improved post-OEF flare-corrected design layout to improve an accuracy of a full-field computational lithography model for the lithographic system.

6. The method of claim 1, wherein the density map is created by:

obtaining a design layout of a single chip, wherein a total design layout at the exposure field includes the design layouts of one or more substantially identical single chips;

obtaining a location database having information about each single chip'"'"'s location within the exposure field; and

repeating the design layout of the single chip within the exposure field using the location database.

7. The method of claim 1, wherein the method further comprises:

using a relatively coarse grid to approximate the density map of the design layout at the exposure field to determine the flare map.

8. The method of claim 1, wherein the step of calculating the location-dependent corrections for the design layout comprises:

creating a reference image of the design layout with a zero-flare or a known reference-flare condition; and

comparing the determined flare map with the reference image to calculate the location-dependent flare corrections.

9. The method of claim 8, wherein the reference image is an aerial image or a density map of the design layout at the exposure field using a relatively fine grid.

10. The method of claim 1, wherein the radiation beam in the lithographic system has an extreme ultra-violet (EUV) wavelength and is projected using reflective optics.

11. The method of claim 1, wherein the method further includes:

additionally compensating for shadowing effects at the exposure field.

12. The method of claim 11, wherein the method further includes:

calculating and applying mask proximity correction (MPC) to the design layout after OEF, flare and shadow correction.

13. The method of claim 1, wherein the adjusted PSF is expressed in a fractal form in frequency domain, or, in a tabulated form in spatial domain, relating PSF values with corresponding discrete distances.

14. A computer program product comprising a computer-readable medium having instructions recorded therein, which when executed, cause the computer to generate files corresponding to a design layout, wherein the design layout is modified such that it reduces an effect of flare produced by a lithographic system in accordance to claim 1.

15. The method of claim 1, further comprising, before the step of determining the flare map, obtaining a reference flare value from an EUV system model of the lithographic system, wherein the step of determining the flare map includes using the obtained reference flare value.

16. A method implemented by a computer for reducing an effect of flare produced by a lithographic system for imaging a design layout onto a substrate, the method comprising:

determining, using the computer, a flare map in an exposure field of the lithographic system by mathematically combining a density map of the design layout at the exposure field with a point spread function (PSF), wherein the density map comprises a representation of the design layout after being modified by optical enhancement features (OEF);

modifying the determined flare map to account for system-specific effects on flare due to identified characteristics of the lithographic system; and

calculating location-dependent flare corrections for the post-OEF design layout by using the determined flare map, thereby reducing the effect of flare.