Light intensity modulation method

1. A light intensity modulation method implemented by using a mask, comprising the steps of:

1) calculating a transmittance distribution of the mask for modulating an initial light intensity distribution into a target light intensity distribution, based on a circle of confusion (CoC) function of an illumination system, the initial light intensity distribution of an illumination field of view (FOV) and the target light intensity distribution of the illumination FOV;

2) meshing the mask according to a desired accuracy of the target light intensity distribution and determining a distribution of opaque dots in each of cells resulting from the meshing based on the transmittance distribution of the mask and a desired accuracy of the transmittance distribution; and

3) fabricating the mask based on the determined distribution of the opaque dots, and then deploying the mask in the illumination system.

2. The light intensity modulation method according to claim 1 , wherein in step 1), the transmittance distribution of the mask is derived by a deconvolution according to the following formula:

( K*N )×Fun= M,

where,

K denotes the initial light intensity distribution;

M denotes the target light intensity distribution;

N denotes the transmittance distribution of the mask;

Fun denotes the CoC function;

* denotes a multiplication operation; and

× denotes a convolution operation,

and wherein, the CoC function is:

Fun

⁡

(

x

,

y

)

=

e

(

-

x

2

+

y

2

2

⁢

σ

2

)

2

⁢

π

·

σ

,

⁢

3

⁢

σ

=

R

=

L

*

tan

⁡

(

θ

)

,

where,

R denotes a radius of an optical spot formed in the illumination FOV by a corresponding one of the opaque dots on the mask;

x and y denote coordinates of a certain point in the illumination FOV;

L denotes a distance between the mask and the illumination FOV; and

θ denotes an angle of divergence of the illumination system.

3. The light intensity modulation method according to claim 1 , wherein meshing the mask according to the desired accuracy of the target light intensity distribution in step 2) comprises: initially meshing the mask; and interpolating the resulting cells so that a greatest value, after interpolation, out of light intensity gradients between adjacent cells is smaller than the desired accuracy of the target light intensity distribution.

4. The light intensity modulation method according to claim 1 , wherein determining the distribution of the opaque dots in each of the cells based on the transmittance distribution of the mask and the desired accuracy of the transmittance distribution in step 2) comprises: calculating an area of opaque dots based on a criterion that a ratio of the area of opaque dots to an area of a corresponding one of the cells is not greater than the desired accuracy of the target light intensity distribution; and determining, by fitting, a number of the opaque dots and a pitch of the opaque dots in a corresponding one of the cells based on the transmittance distribution of the mask and on the area of the opaque dots.

5. The light intensity modulation method according to claim 1 , wherein the opaque dots are implemented as chrome dots.

6. The light intensity modulation method according to claim 1 , wherein the mask is formed of fused silica.