Source and mask optimization by changing intensity and shape of the illumination source

• US 7,864,301 B2
• Filed: 08/05/2008
• Issued: 01/04/2011
• 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): Kim; Peter B
• Assistant Examiner(s): LIU, CHIA HOW MICHAEL
• Application Number:
  US12/186,410
• Publication Number:
  US 20090053621A1
• Time in Patent Office: 882 Days
• Field of Search: 355/67, 355/55, 355/77, 355/53, 430/5
• US Class Current: 355/77
• 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 for determining an optimal mask comprising the steps of:

identifying a predetermined range of illumination intensity values based on specifications of an illumination system for illuminating the optimal mask;

determining optimum diffraction orders;

obtaining an optimal transmission mask based on the optimum diffraction orders based on the identified predetermined range; and

determining an optimal mask based on the optimal transmission mask,

wherein the optimum diffraction orders are determined by determining a magnitude and phase of diffraction orders which form an image in an image plane of the illumination system which maximizes the minimum illumination log slope at user selected fragmentation points of the optimal mask while forcing an intensity of illumination at the fragmentation points to be within the predetermined range.

2. The method of claim 1, wherein the step of obtaining the optimal transmission mask includes a step of determining a number of horizontal diffraction orders of the optimum 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 optimal transmission mask includes a step of determining a number of vertical diffraction orders of the optimum 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 determining optimum diffraction orders determines optimum diffraction orders in the spatial frequency domain.

5. The method of claim 1, wherein the step of determining an optimal 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 the optimum diffraction orders,

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

6. A method of optimizing a placement of transmission and phase shifting features on a mask comprising the steps of:

obtaining optimal mask transmission characteristics based on optimum diffraction orders of the mask;

locating areas of maximum transmission and minimum transmission through the mask based on the obtained optimal mask transmission characteristics;

assigning a primitive area in the mask as an area centered on one of the areas of maximum transmission and minimum transmission;

varying edges of primitive area to match the optimum diffraction orders, wherein the primitive area has a minimum size which is substantially equal to a minimum feature size of the mask.

7. The method of claim 6, wherein the step of obtaining optimal mask transmission characteristics includes a step of determining a number of horizontal diffraction orders of an optimum mask to be illuminated by an identified illumination system, wherein the number of horizontal diffraction orders is determined according to the equation:

8. The method of claim 6 wherein the step of obtaining optimal mask transmission characteristics includes a step of determining a number of vertical diffraction orders of an optimum mask to be illuminated by an identified illumination system, wherein the number of vertical diffraction orders is determined according to the equation

9. The method of claim 6, wherein the mask is a CPL mask.

10. A computer readable medium containing instructions stored therein which, when executed by a computer, causes the computer to perform a method for determining an optimal mask comprising the steps of:

identifying a predetermined range of illumination intensity values based on specifications of an illumination system for illuminating the optimal mask;

determining optimum diffraction orders;

obtaining an optimal transmission mask based on the optimum diffraction orders based on the identified predetermined range; and

determining an optimal mask based on the optimal transmission mask,

wherein the optimum diffraction orders are determined by determining a magnitude and phase of diffraction orders which form an image in an image plane of the illumination system which maximizes the minimum illumination log slope at user selected fragmentation points of the optimal mask while forcing an intensity of illumination at the fragmentation points to be within the predetermined range.

11. The computer readable medium of claim 10, wherein the step of obtaining the optimal transmission mask includes a step of determining a number of horizontal diffraction orders of the optimum diffraction orders, wherein the number of horizontal diffraction orders is determined according to the equation:

12. The computer readable medium of claim 10, wherein the step of obtaining the optimal transmission mask includes a step of determining a number of vertical diffraction orders of the optimum diffraction orders, wherein the number of vertical diffraction orders is determined according to the equation

13. The computer readable medium of claim 10, wherein the step of determining optimum diffraction orders determines optimum diffraction orders in the spatial frequency domain.

14. The computer readable medium of claim 10, wherein the step of determining an optimal 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 the optimum diffraction orders,

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

15. A computer readable medium containing instructions stored therein which, when executed by a computer, causes the computer to perform a method of optimizing a placement of transmission and phase shifting features on a mask comprising the steps of:

obtaining optimal mask transmission characteristics based on optimum diffraction orders of the mask;

locating areas of maximum transmission and minimum transmission through the mask based on the obtained optimal mask transmission characteristics;

assigning a primitive area in the mask as an area centered on one of the areas of maximum transmission and minimum transmission;

varying edges of the primitive area to match the optimum diffraction orders, wherein the primitive area has a minimum size which is substantially equal to a minimum feature size of the mask.

16. The computer readable medium of claim 15, wherein the mask is a CPL mask.

17. The computer readable medium of claim 15, wherein the step of obtaining optimal mask transmission characteristics includes a step of determining a number of horizontal diffraction orders of an optimum mask to be illuminated by an identified illumination system, wherein the number of horizontal diffraction orders is determined according to the equation:

18. The computer readable medium of claim 15, wherein the step of obtaining optimal mask transmission characteristics includes a step of determining a number of vertical diffraction orders of an optimum mask to be illuminated by an identified illumination system, wherein the number of vertical diffraction orders is determined according to the equation