Efficient isotropic modeling approach to incorporate electromagnetic effects into lithographic process simulations

A method for designing a lithographic process employing a computer system by simulating an image of a topographic mask under an illumination having an associated electric field, said method comprising:

• providing a design of the topographic mask, the mask design including a mask feature having two-dimensional polygon feature edges in a horizontal plane of the mask, wherein the feature edges have a finite thickness along a non-horizontal direction of the mask;
• determining, employing a computer system including a central processing unit, a thin mask representation of the electric field on the mask plane corresponding to said mask feature;
• determining, employing said computer system, a first field difference between the electric field on the mask plane along an extended edge of an elementary pattern unit having said finite thickness and the electric field on the mask plane along the corresponding extended edge of a thin mask elementary pattern unit under illumination of a first component of the electric field and a second field difference between the electric field on the mask plane along said extended edge of said elementary pattern unit having said finite thickness and the electric field on the mask plane along said corresponding extended edge of said thin mask elementary pattern unit under illumination of a second component of the electric field orthogonal to said first component of the electric field;
• forming, employing said computer system, an isotropic field perturbation (IsoField Perturbation) to the thin mask electric field on the mask plane corresponding to said extended edge of said elementary pattern unit having said finite thickness comprising a weighted coherent combination of said first and second field differences;
• providing, employing said computer system, an imaging model for simulating an image on a wafer plane, the imaging model comprising a representation of the electric fields on the mask plane responsive to illumination from an imaging system, wherein said representation of the electric fields on the mask plane comprises said thin mask representation combined with said Isofield Perturbation;
• and
• simulating an image on the wafer plane corresponding to said mask feature under the illumination using said imaging model.

A non-transitory computer usable medium having a computer readable program embodied therein for designing a lithographic process by simulating an image of a topographic mask under an illumination having associated electric field, wherein said computer readable program is configured to run on a computer to operate on a design of the topographic mask, the mask design including a mask feature having two-dimensional polygon feature edges in a horizontal plane of the mask, wherein the feature edges have a finite thickness along a non-horizontal direction of the mask, wherein the computer readable program when executed on the computer causes the computer to perform the method steps of:

• determining a thin mask representation of the electric field on the mask plane corresponding to said mask feature;
• determining a first field difference between the electric field on the mask plane along a first edge of said mask feature and the electric field on the mask plane along the corresponding edge of a thin mask representation of said mask feature under illumination of a first component of the electric field and a second field difference between the electric field on the mask plane along said first edge of said mask feature and the electric field on the mask plane along said corresponding first edge of said thin mask representation of said mask feature under illumination of a second component of the electric field orthogonal to said first component of the electric field;
• forming an isotropic field perturbation (IsoField Perturbation IsoΔM) to the thin mask electric field on the mask plane corresponding to said first edge of said mask feature comprising a weighted coherent combination of said first and second field differences;
• providing an imaging model for simulating an image on a wafer plane, the imaging model comprising a representation of the electric fields on the mask plane responsive to illumination from an imaging system, wherein said representation of the electric fields on the mask plane comprises said thin mask representation combined with said Isofield Perturbation;
• and
• simulating an image on the wafer plane corresponding to said mask feature under the illumination using said imaging model.

A non-transitory computer usable medium having a computer readable program embodied therein for designing a lithographic process by simulating an image of a topographic mask under an illumination having associated electric field, wherein said computer readable program is configured to run on a computer to operate on a design of the topographic mask, the mask design including a mask feature having two-dimensional polygon feature edges in a horizontal plane of the mask, wherein the feature edges have a finite thickness along a non-horizontal direction of the mask, wherein the computer readable program when executed on the computer causes the computer to perform the method steps of:

• determining a thin mask representation of the electric field on the mask plane corresponding to said mask feature;
• determining a first field difference between the electric field on the mask plane along an extended edge of an elementary pattern unit having said finite thickness and the electric field on the mask plane along the corresponding extended edge of a thin mask elementary pattern unit under illumination of a first component of the electric field and a second field difference between the electric field on the mask plane along said extended edge of said elementary pattern unit having said finite thickness and the electric field on the mask plane along said corresponding extended edge of said thin mask elementary pattern unit under illumination of a second component of the electric field orthogonal to said first component of the electric field;
• forming an isotropic field perturbation (IsoField Perturbation) to the thin mask electric field on the mask plane corresponding to said extended edge of said elementary pattern unit having said finite thickness comprising a weighted coherent combination of said first and second field differences;
• providing an imaging model for simulating an image on a wafer plane, the imaging model comprising a representation of the electric fields on the mask plane responsive to illumination from an imaging system, wherein said representation of the electric fields on the mask plane comprises said thin mask representation combined with said Isofield Perturbation;
• and
• simulating an image on the wafer plane corresponding to said mask feature under the illumination using said imaging model.