Source and mask optimization by changing intensity and shape of the illumination source and magnitude and phase of mask diffraction orders
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.
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:
m
=
2
floor
[
P
x
(
σ
max
+
1
)
NA
λ
]
+
1
where m is the number of horizontal diffraction orders;
P x is the pitch of a repetitive cell in the x direction of the target mask;
λ is a wavelength of the illumination source of a target illumination system;
NA is a numerical aperture of projection optics of the target illumination system; 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 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
n
=
2
floor
[
P
y
(
σ
max
+
1
)
NA
λ
]
+
1
where n is the number of vertical diffraction orders;
P y is the pitch of a repetitive cell in the y direction of the target mask;
λ is a wavelength of the illumination source of a target illumination system;
NA is a numerical aperture of projection optics of the target illumination system; 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 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:
m
=
2
floor
[
P
x
(
σ
max
+
1
)
NA
λ
]
+
1
where m is the number of horizontal diffraction orders;
P x is the pitch of a repetitive cell in the x direction of the target mask;
λ is a wavelength of the illumination source of a target illumination system;
NA is a numerical aperture of projection optics of the target illumination system; and
σ max is a radial extent of the distribution of a beam of light from the illumination source.
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
n
=
2
floor
[
P
y
(
σ
max
+
1
)
NA
λ
]
+
1
where n is the number of vertical diffraction orders;
P y is the pitch of a repetitive cell in the y direction of the target mask;
λ is a wavelength of the illumination source of a target illumination system;
NA is a numerical aperture of projection optics of the target illumination system; and
σ max is a radial extent of the distribution of a beam of light from the illumination source.
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.