Source and mask optimization by changing intensity and shape of the illumination source and magnitude and phase of mask diffraction orders

• US 8,730,452 B2
• Filed: 12/07/2010
• Issued: 05/20/2014
• Est. Priority Date: 03/31/2003
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Masktools B.V. (ASML Holding NV)
• Inventors: Socha, Robert
• Primary Examiner(s): LIU, CHIA HOW MICHAEL
• Application Number:
  US12/962,522
• Publication Number:
  US 20110075124A1
• Time in Patent Office: 1,260 Days
• Field of Search: 355/67, 355/55, 355/53, 430/5
• US Class Current: 355/55
• 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 7/70125 Use of illumination settings tailored to particular mask patterns details of setting means G03F7/70091
• CPC Class Codes: G03F 7/70425 Imaging strategies, e.g. for increasing throughput or resolution, printing product fields larger than the image field or compensating lithography- or non-lithography errors, e.g. proximity correction, mix-and-match, stitching or double patterning
• CPC Class Codes: G03F 7/70433 Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors
• 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: G06T 7/001 using an image reference approach

Abstract

An illumination source is optimized by changing the intensity and shape of the illumination source to form an image in the image plane that maximizes the minimum ILS at user selected fragmentation points while forcing the intensity at the fragmentation points to be within a small intensity range. An optimum mask may be determined by changing the magnitude and phase of the diffraction orders to form an image in the image plane that maximizes the minimum ILS at user selected fragmentation points while forcing the intensity at the fragmentation points to be within a small intensity range. Primitive rectangles having a size set to a minimum feature size of a mask maker are assigned to the located minimum and maximum transmission areas ad centered at a desired location. The edges of the primitive rectangle are varied to match optimal diffraction orders O(m,n). The optimal CPL mask O_CPL(x,y) is then formed.

Claims

1. A method of obtaining a target source and a target mask comprising the steps of:

determining how an illumination is provided from an illumination source included with an illumination system to a plurality of source points and a mask corresponding to a predetermined mask pattern;

selecting fragmentation points in an image plane of an image formed by the illumination provided to the predetermined mask pattern;

determining an intensity and image log slope of illumination at each fragmentation point;

calculating a predetermined intensity range based on the illumination system'"'"'s specifications; and

changing the intensity and shape of the illumination source and the magnitude and phase of diffraction orders of the mask to form an image in the image plane that maximizes the minimum image log slope at the fragmentation points while forcing the intensity at the fragmentation points to be within the predetermined intensity range, thereby obtaining the target source and the target mask from the changed illumination source and mask, respectively.

2. The method of claim 1, wherein the step of obtaining the target mask includes a step of determining a number of horizontal diffraction orders, wherein the number of horizontal diffraction orders is determined according to the equation:

3. The method of claim 1, wherein the step of obtaining the target mask includes a step of determining a number of vertical diffraction orders, wherein the number of vertical diffraction orders is determined according to the equation

4. The method of claim 1, wherein the step of obtaining the target mask includes determining optimum diffraction orders in the spatial frequency domain.

5. The method of claim 1, wherein the step of obtaining the target mask comprises the steps of:

locating areas of maximum transmission and minimum transmission;

assigning a primitive area as an area centered on an area of maximum transmission or minimum transmission;

varying edges of the primitive area to match optimum diffraction orders,

wherein the primitive area has a minimum size which is substantially equal to a minimum feature size of the target mask.

6. The method of claim 1, wherein obtaining the target mask comprises:

performing a non-linear optimization to find optimal diffraction orders; and

performing a linear optimization by selecting quantized mask transmission to match the optimal diffraction orders.

7. The method of claim 1, wherein the target mask is implemented on a chromeless phase lithography (CPL) mask.

8. The method of claim 1, wherein the target mask is implemented on an attenuated phase shifted (PSM) mask.

9. The method of claim 1, wherein obtaining the target mask comprises:

initially providing a reference dark field transmission mask whose patterns are converted into the target mask by simultaneously changing the intensity and shape of the illumination source and the magnitude and phase of the diffraction orders.

10. A non-transitory computer readable storage medium containing instructions stored therein which, when executed by a computer, causes the computer to perform a method of obtaining a target source and a target mask comprising the steps of:

determining how an illumination is provided from an illumination source included with an illumination system to a plurality of source points and a mask corresponding to a predetermined mask pattern;

selecting fragmentation points in an image plane of an image formed by the illumination provided to the predetermined mask pattern;

determining an intensity and image log slope of illumination at each fragmentation point;

calculating a predetermined intensity range based on the illumination system'"'"'s specifications; and

changing the intensity and shape of the illumination source and the magnitude and phase of diffraction orders of the mask to form an image in the image plane that maximizes the minimum image log slope at the fragmentation points while forcing the intensity at the fragmentation points to be within the predetermined intensity range, thereby obtaining the target source and the target mask from the changed illumination source and mask, respectively.

11. The non-transitory computer-readable storage medium of claim 10, wherein the step of obtaining the target mask includes a step of determining a number of horizontal diffraction orders, wherein the number of horizontal diffraction orders is determined according to the equation:

12. The non-transitory computer-readable storage medium of claim 10, wherein the step of obtaining the target mask includes a step of determining a number of vertical diffraction orders, wherein the number of vertical diffraction orders is determined according to the equation

13. The non-transitory computer-readable storage medium of claim 10, wherein the step of obtaining the target mask includes determining optimum diffraction orders in the spatial frequency domain.

14. The non-transitory computer-readable storage medium of claim 10, wherein the step of obtaining the target mask comprises the steps of:

locating areas of maximum transmission and minimum transmission;

assigning a primitive area as an area centered on an area of maximum transmission or minimum transmission;

varying edges of the primitive area to match optimum diffraction orders,

wherein the primitive area has a minimum size which is substantially equal to a minimum feature size of the target mask.

15. The non-transitory computer-readable storage medium of claim 10, wherein obtaining the target mask comprises the steps of:

performing a non-linear optimization to find optimal diffraction orders; and

performing a linear optimization by selecting quantized mask transmission to match the optimal diffraction orders.

16. The non-transitory computer-readable storage medium of claim 10, wherein the target mask is implemented on a chromeless phase lithography (CPL) mask.

17. The non-transitory computer-readable storage medium of claim 10, wherein the target mask is implemented on an attenuated phase shifted (PSM) mask.

18. The non-transitory computer-readable storage medium of claim 10, wherein obtaining the target mask comprises:

initially providing a reference dark field transmission mask whose patterns are converted into the target mask by simultaneously changing the intensity and shape of the illumination source and the magnitude and phase of the diffraction orders.