Source and Mask Optimization by Changing Intensity and Shape of the Illumination Source

• US 20090053621A1
• Filed: 08/05/2008
• Published: 02/26/2009
• 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
• Granted Patent: US 7,864,301 B2
• Time in Patent Office: Days
• US Class Current: 430/5
• 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:

determining optimum diffraction orders of an ideal mask;

obtaining an optimal transmission mask based on the optimized diffraction orders of the ideal mask; and

determining an optimal mask based on the optimal transmission mask,

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

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

$m=2<br><br><br><br>\mathrm{floor}<br><br>\left[\frac{P_x<br><br>\left({\mathrm{\sigma <br><br>}}_{\max }+1\right)<br><br>\mathrm{NA}}{\mathrm{\lambda <br><br>}}\right]+1$

where m is the number of horizontal diffraction orders;

P_x is the pitch of the repetitive cell in the x direction;

λ

is a wavelength of the illumination source;

NA is a numerical aperture of the projection optics; and

σ

_max is a radial extent of the distribution of a beam of light from the illumination source.

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

$n=2$



floor 

[ P x 

( σ

max + 1 ) 

NA λ

] + 1

where n is the number of vertical diffraction orders;

P_x is the pitch of the repetitive cell in the y direction;

λ

is a wavelength of the illumination source;

NA is a numerical aperture of the projection optics; and

σ

_max is a radial extent of the distribution of a beam of light from the illumination source.

4. The method of claim 1, wherein the step of determining optimum diffraction orders determines optimum diffraction orders in the special frequency domain.

5. The method of claim 1, wherein the step of determining an optimum 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 each primitive area to match optimal diffraction orders,

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