System and method for modifying a data set of a photomask
The present invention provides a method for compensating infidelities of a process that transfers a pattern to a layer of an integrated circuit, by minimizing, with respect to a photomask pattern, a cost function that quantifies the deviation between designed and simulated values of circuit parameters of the pattern formed on a semiconductor wafer.
1. A method for optical compensation comprising:
using a computer system to create a simulated circuit pattern using a lithography process, wherein the lithography process uses a photomask defined by a data set having a plurality of polygons that define patterns on the photomask;
calculating a cost function based on an electrical parameter of the simulated circuit pattern, wherein the cost function comprises terms defined by at least one of:
(a) a sum of squares of normalized differences between simulated and designed values of electrical parameters for a multitude of circuit components,
(b) an amount by which the simulated value of the electrical parameter exceeds a maximum allowable value,
(c) an amount by which the simulated value of the electrical parameter falls below a minimum allowable value,
(d) the difference of simulated values of a first and a second electrical parameter of a simulated circuit pattern,
(e) a change in the simulated value of the electrical parameter in response to a change in a condition of the lithography process, and
(f) a restricted simulated value of the electrical parameter that is not larger than a maximum allowable value or not smaller than a minimum allowable value,
and wherein the electrical parameter describes an electrical operational characteristic of the simulated circuit pattern; and
adjusting the polygons based on the calculated cost function in order to reduce the value of the cost function.
2. The method of claim 1 , wherein adjusting the polygons comprises at least one of: segmenting an edge of a polygon, altering a polygon by moving a segment of its edge, moving a polygon, adding a polygon to the data set, and removing a polygon from the data set.
3. The method of claim 1 , wherein the electrical parameter comprises one or more parameters from the group consisting of saturation current, leakage current, threshold voltage, gain, resistance, capacitance, and inductance.
4. The method of claim 1 , wherein calculating the cost function further comprises using geometric variables derived from comparing the simulated circuit pattern with a target circuit pattern.
5. The method of claim 1 , further comprising adjusting distribution or polarization variables of the illumination in a pupil of an optical projector in a way to reduce the value of the cost function.
6. The method of claim 1 , wherein the method is performed using a computer program product having computer readable program code functions embedded in a non-transitory computer useable medium.
7. A computer system configured for optical compensation, comprising:
a processor;
a memory connected to the processor; and
a computer-readable medium having instructions embedded therein, the instructions configured to cause the processor to perform the operations of:
creating a simulated circuit pattern using a lithography process, wherein the lithography process uses a photomask defined by a data set having a plurality of polygons that define patterns on the photomask;
calculating a cost function based on an electrical parameter of the simulated circuit pattern, wherein the cost function comprises terms defined by at least one of:
(a) a sum of squares of normalized differences between simulated and designed values of electrical parameters for a multitude of circuit components,
(b) an amount by which the simulated value of the electrical parameter exceeds a maximum permissible value,
(c) an amount by which the simulated value of the electrical parameter falls below a minimum allowable value,
(d) the difference of simulated values of a first and a second electrical parameter of a simulated circuit pattern,
(e) a change in the simulated value of the electrical parameter in response to a change in a condition of the lithography process, and
(f) a restricted simulated value of the electrical parameter that is not larger than a maximum allowable value or not smaller than a minimum allowable value,
and wherein the electrical parameter describes an electrical operational characteristic of the simulated circuit pattern; and
adjusting the polygons based on the calculated cost function in order to reduce the value of the cost function.
8. The system of claim 7 , wherein adjusting the polygons comprises at least one of: segmenting an edge of a polygon, altering a polygon by moving a segment of its edge, moving a polygon, adding a polygon to the data set, and removing a polygon from the data set.
9. The system of claim 7 , wherein the electrical parameter comprises one or more parameters from the group consisting of saturation current, leakage current, threshold voltage, gain, resistance, capacitance, and inductance.
10. The system of claim 7 , wherein calculating the cost function further comprises using geometric variables derived from comparing the simulated circuit pattern with a target circuit pattern.
11. The system of claim 7 , wherein the instructions are further configured to cause the processor to perform the operation of adjusting distribution or polarization variables of the illumination in a pupil of an optical projector in a way to reduce the value of the cost function.