Optical proximity correction using chamfers and rounding at corners

1. A method of optimizing a design to be formed on a substrate, comprising the steps of:

(a) determining approximate rounding of at least one corner of an image of the design based on a derivation of a predefined rule concerning a sub-lithographic assist feature for sharpening the corner of the design to be formed on the substrate when positioned on a mask at a position corresponding to the at least one corner;

(b) generating a representation of the design further to the approximate rounding of the at least one corner;

(c) generating an initial representation of a mask utilized to image the design based on the representation; and

(d) performing Optical Proximity Correction (OPC) further to the initial representation of the mask.

2. The method of optimizing the design, according to claim 1 , wherein step (d) further comprises the steps of:

(e) generating an image of the design further to the initial representation of the mask;

(f) evaluating deviation between the representation generated in Step (b) and the image generated in Step (e);

(g) determining whether a result of the evaluation of Step (f) satisfies predefined constraints;

(h) in the event the result does not satisfy predefined constraints, generating a next representation of the mask in accordance with the results; and

(i) repeating Steps (f)-(h) until the deviation meets predefined constraints.

3. The method, according to claim 1 , further comprising the steps of:

(i) determining the approximate rounding based on a derivation of predefined rules;

(ii) selecting a size of a cutout from a chamfer based on the approximate rounding; and

(iii) chamfering the at least one corner to approximate rounding in accordance with the size of the cutout.

4. The method, according to claim 3 , wherein the predefined rules define dimensions of a serif.

5. The method, according to claim 3 , further comprising the step of selecting a shape of the cutout from the chamfer.

6. The method, according to claim 5 , wherein at least two angles of the shape of the cutout are equal.

7. The method, according to claim 3 , wherein the size of the cutout from the chamfer is based on the chamfer forming angles in increments of a predetermined size.

8. The method, according to claim 7 , wherein the predetermined size is 45 degrees.

9. The method, according to claim 1 , further comprising the step of chamfering the at least one corner of the design to approximate the rounding.

10. The method, according to claim 1 , wherein the approximate of the rounding corresponds to minimal rounding based on a set of predetermined processing factors.

11. The method, according to claim 9 , wherein the chamfer corresponds to a first chamfer corresponding to a first corner of the design, further comprising the steps of:

(i) determining a size of a second cutout from a second chamfer for a second corner adjacent to the first corner; and

(ii) reducing the size of at least one of the first chamfer and the second chamfer so that the first chamfer and the second chamfer do not intersect.

12. The method, according to claim 9 , wherein the chamfer corresponds to a first chamfer corresponding to a first corner of the design, further comprising the steps of:

(i) determining a size of a second cutout from a second chamfer for a second corner adjacent to the first corner; and

(ii) reducing the size of the first chamfer and the second chamfer proportionally so that the first chamfer and the second chamfer do not intersect.

13. The method, according to claim of claim 3 , wherein the predefined rules concern serif selection, further comprising the step of:

selecting the size of the chamfer based on the overlap values of a serif selected using the predefined rules.

14. The method of optimizing the design, according to claim 2 , further comprises the steps of:

(i) determining rounding of corners of the initial representation of the mask based on mask manufacturing constraints; and

(ii) generating a modified mask representation based on the initial representation in which corner rounding is applied.

15. The method of optimizing the design, according to claim 14 , wherein rounding at each corner has a predetermined radius.

16. A computer readable medium having executable code thereon, wherein execution of the code by at least one programmable computer causes the at least one programmable computer to perform a sequence of steps as in any one of claims 1 - 15 for optimizing the design to be formed on the substrate.