Illumination Optimization

• US 20110116067A1
• Filed: 07/07/2009
• Published: 05/19/2011
• Est. Priority Date: 07/07/2008
• Status: Active Grant

• Current Assignee: Brion Technologies Incorporated (ASML Holding NV)
• Original Assignee: Brion Technologies Incorporated (ASML Holding NV)
• Inventors: Feng, Hanying, Ye, Jun, Cao, Yu
• Granted Patent: US 8,542,340 B2
• Time in Patent Office: Days
• US Class Current: 355/67
• CPC Class Codes: G03F 7/70091 Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA]
• CPC Class Codes: G03F 7/70441 Optical proximity correction [OPC]
• CPC Class Codes: G03F 7/70666 Aerial image, i.e. measuring the image of the patterned exposure light at the image plane of the projection system

Abstract

A method of optimizing an illumination pupil shape for a lithographic process 1 comprises identifying a target pattern (206) to be imaged by said lithographic process. It further comprises identifying at least one optimization point (262) in said target pattern and identifying at least one design for manufacturing metric (270) per optimization point. Additionally it comprises selecting a set of illumination source points (274) based on the identified at least one design for manufacturing metric and determining the illumination pupil shape (284) based on the selected set of illumination source points.

Claims

1. A method of optimizing an illumination pupil shape for a lithographic process, the method comprising the steps of:

identifying a target pattern to be imaged by said lithographic process;

identifying at least one optimization point in said target pattern;

identifying at least one design for manufacturing metric per optimization point;

selecting a set of illumination source points based on the identified at least one design for manufacturing metric; and

determining the illumination pupil shape based on the selected set of illumination source points.

2. The method of optimizing an illumination pupil shape according to claim 1, comprising identifying a design for manufacturing metric based on at least one of an aerial image intensity slope, a mask error enhancement factor and a derivative of a critical dimension versus a value of a process window of the lithographic process.

3. The method of optimizing an illumination pupil shape according to any of the previous claims, further comprising optimizing the target pattern based on the determined illumination pupil shape.

4. Method according to claim 3 wherein optimizing the target pattern results in an optimized target pattern, comprising determining a further set of optimization points based on the optimized target pattern and optimizing the illumination pupil shape based on the optimized target pattern and the further set of optimization points.

5. Method according to any of the claims 1 to 4, comprising

identifying an acceptable range for each the at least one design for manufacturing metric per optimization point;

and

selecting the set of illumination source points for illuminating the target pattern such that the design for manufacturing metric is within the acceptable range for each optimization point and for each design for manufacturing metric.

6. Method according to claim 5, comprising

sorting the illumination points for each combination of design for manufacturing metric and optimization point to provide a sorted order based on the value of the design for manufacturing metric in the combination;

assembling a plurality of further sets of illumination points by selecting a further set of illumination points per combination of design for manufacturing metric and optimization point based on the sorted order;

determining the set of illumination points by selecting illumination points from the intersection of further sets of illumination points.

7. Method according to any of the claims 1 to 4, comprising

defining a cost function based on the at least one design for manufacturing metric

an iteration process comprising

determining the value of the cost function for an illumination source point

optimizing the illumination pupil shape by adding illumination source points to a set of selected illumination source points based on corresponding values of the cost function until an iteration criterion is met.

8. Method according to claim 7, comprising

illumination source points in the set of selected illumination source points are not re-evaluated during a later iteration.

9. Method according to claim 7 or 8, comprising

determining the second order coefficient in a polynomial representation of aerial image intensity (I) as a function of a parameter of a process window of the lithographic process;

identifying at least one design for manufacturing metric to be the magnitude of the second order coefficient.

10. Method according to claim 8, comprising

determining a worst case optimization point by determining which optimization point has the largest minimum value for the magnitude of the second order coefficient associated with an individual illumination source point;

selecting the associated individual illumination source point with the minimum value of the magnitude of the second order coefficient for that optimization point;

selecting a further illumination source point having an opposite effect on the second order coefficient in that optimization point.

11. Method according to any of the claims 7 to 10, comprising

defining interdependency relations between illumination source points based on symmetry in the illumination source;

selecting interdependent illumination source points based on the interdependency relations.

12. Device manufacturing method comprising

patterning a beam of radiation from an illumination source with a patterning device;

exposing a substrate to the patterned beam of radiation;

using an illumination pupil shape for the illumination source determined in any of the claims 1 to 11.

13. Device manufacturing method according to claim 12, comprising using an illumination pupil shape filter.

14. Device manufacturing method according to claim 13, comprising

either using the determined illumination pupil shape to program a programmable device in the pupil plane of the illumination source, or

using a diffractive optical element having a diffractive pattern corresponding to the illumination pupil shape determined according to any of the claims 1 to 11 in the pupil plane of the illuminator source.

15. Method of producing a diffractive optical element, comprising

determining an illumination pupil shape according to any of the claims 1 to 11,

producing a diffractive pattern on the diffractive optical element based on the determined illumination pupil shape.

16. A computer readable medium bearing a computer program for optimizing an illumination pupil shape, the computer program, when executed, causing a computer to perform the steps of any of the claims 1 to 11.