Three-dimensional mask model for photolithography simulation

1. A method implemented by a computer for creating a three-dimensional mask model, the method comprising:

identifying features to include in a mask for which the three-dimensional mask model is to be created;

simulating the effect of light passing through the mask having the identified features using three-dimensional mask topography information to produce a theoretical image;

determining initial filtering kernels for the three-dimensional mask model using the theoretical image; and

modifying the initial filtering kernels until a total difference between the theoretical image and a simulated image is minimized or below a threshold to produce final filtering kernels,

wherein the final filtering kernels are configured to be convolved with one or more mask transmission functions to produce a near-field image, and wherein the simulating, determining and modifying steps are implemented using the computer.

2. The method of claim 1 , wherein the mask transmission functions include one or more of a standard thin-mask transmission function and derivatives of the standard thin-mask transmission function.

3. The method of claim 1 , wherein the final filtering kernels include a linear filtering kernel and at least one bilinear filtering kernel.

4. The method of claim 1 , wherein the three-dimensional mask topography information was produced by inspecting a manufactured calibration mask having the identified features.

5. The method of claim 1 , wherein simulating the effect of light passing through a mask includes simulating a plane wave of light and oblique waves of light passing through the mask.

6. A method implemented by a computer for creating a three-dimensional mask model, the method comprising:

identifying features to include in a mask for which the three-dimensional mask model is to be created;

simulating the effect of light passing through the mask having the identified features using three-dimensional mask topography information to produce a theoretical image;

determining initial correction factors for the three-dimensional mask model using the theoretical image; and

modifying the initial correction factors until a total difference between the theoretical image and a simulated image is minimized to produce final correction factors,

wherein the final correction factors are configured to be multiplied by a Fourier transform of one or more mask transmission functions to produce a near-field image, and wherein the simulating, determining and modifying steps are implemented using the computer.

7. The method of claim 6 , wherein the three-dimensional mask topography information was produced by inspecting a manufactured calibration mask having the identified features.

8. The method of claim 6 , wherein simulating the effect of light passing through a mask includes simulating a plane wave of light and oblique waves of light passing through the mask, and one or more of the final correction factors models oblique incidence effects.

9. A photolithography simulation system implemented by a computer, the system comprising:

a three-dimensional mask model of a type of photolithography mask, the three-dimensional mask model comprising one or more of:

a correction factor configured to modify a mathematical transform of a mask transmission function of a mask;

a correction factor configured to modify a mathematical transform of a first mask-edge function corresponding to a first angle of orientation associated with the mask;

a correction factor configured to modify a mathematical transform of a second mask-edge function corresponding to a second angle of orientation associated with the mask; and

a correction factor configured to modify a mathematical transform of a mask-corner function of the mask,

wherein the correction factors represent one or more effects of the topography of the type of photolithography mask on light passing through a mask of that type; and

a software tool executed by the computer using the three-dimensional mask model to simulate a near-field image expected to be produced by a photolithographic tool using the type of photolithography mask.

10. The system of claim 9 , wherein one or more of the correction factors is a function of polarization and incident angle of light.

11. The system of claim 9 , wherein one or more of the correction factors is independent of the layout of a particular photolithography mask.

12. The system of claim 9 , wherein one or more of the correction factors is calibrated to a theoretical simulated image such that a total difference between the theoretical simulated image and a simulated image produced using mask layout data and the three-dimensional mask model is minimized or below a threshold.

13. The system of claim 12 , wherein the theoretical simulated image was produced by rigorously simulating the effects of a plane wave of light and oblique waves of light passing through a mask, such that each of the correction factors models oblique incidence effects.

14. The system of claim 9 , wherein the type of photolithography mask is one of a group consisting of a binary mask and a phase-shifting mask.

15. The system of claim 9 , wherein the three-dimensional mask model comprises a frequency-domain model.

16. The system of claim 9 , wherein existing symmetry properties of one or more correction factors of the three-dimensional mask model are used to improve computational efficiency.