Method of fabricating an integrated circuit with non-printable dummy features

1. A method comprising:

determining an optimized block dummy density ratio r 0 of an IC design layout, the IC design layout including a subdivisional area having a plurality of main features and a plurality of space blocks, the optimized block dummy density ratio r 0 being calculated from a total pattern density associated with the subdivisional area of the IC design layout;

determining a target block dummy density ratio R of the IC design layout according to the optimized block dummy density ratio r 0 ;

choosing dummy features according to an associated maximum intensity that is less than an exposure threshold dose of at least one of the main features;

generating a pattern of the dummy features according to the target block dummy density ratio R;

generating a modified IC design layout by adding the dummy features to the IC design layout; and

fabricating an integrated circuit according to the modified IC design layout.

2. The method of claim 1 , wherein the dummy features include an optical proximity correction feature that enhances imaging resolution.

3. The method of claim 1 , wherein the determining of the target block dummy density ratio R of the IC design layout is further according to process window and throughput.

4. The method of claim 1 , determining a size and pitch of at lone of the dummy features.

5. The method of claim 1 , wherein the dummy features are not printable in a lithography process.

6. The method of claim 1 , wherein the optimized block dummy density ratio r 0 is calculated by a formula r 0 =( PD 0 · PD S − PD 0 ·PD S )/σ S 2 wherein:

PD 0 is an average of a main pattern density;

PD S is an average of a block dummy pattern density;

PD 0 · PD S is an average of a product of the main pattern density and the block dummy pattern density; and

σ is defined by a formula σ 2 =PD 2 − PD 2 , where PD is a total pattern density defined in a formula PD=PD 0 +rPD S and r is a block dummy density ratio, σ S is defined by a formula σ S 2 = PD S 2 − PD S 2 .

7. The method of claim 1 , wherein the pattern of the dummy features is a matrix selected from the group consisting of matrix of squares, matrix of rectangles and a matrix of irregular dummy arrays.

8. An integrated circuit fabrication method comprising:

reading, by a computing system, an integrated circuit (IC) design layout file having an IC design layout that includes a plurality of main features and space blocks;

calculating, by the computing system, an optimized block dummy density ratio r 0 of the IC design layout;

determining, by the computing system, a target block dummy density ratio R of the IC design layout according to the optimized block dummy density ratio r 0 , process window, and throughput;

determining, by the computing system, a pattern of a dummy feature according to the target block dummy density ratio R; and

adding, by the computing system, the pattern in the space blocks to form a modified IC design layout.

9. The method of claim 8 , wherein the calculating of the optimized block dummy density ratio includes determining the optimized block dummy density ratio r 0 by a formula r 0 =( PD 0 · PD S − PD 0 ·PD S )/σ S 2 wherein:

PD 0 is an average of the main pattern density;

PD S is an average of a block dummy pattern density;

PD 0 · PD S is an average of a product of the main pattern density and the block dummy pattern density; and

σ is defined by a formula σ 2 = PD 2 − PD 2 , where PD is a total pattern density defined in a formula PD=PD 0 +rPD S and r is a block dummy density ratio, as is defined by a formula σ S 2 = PD S 2 − PD S 2 .

10. The method of claim 8 , wherein adding the pattern in the space blocks to form a modified IC design layout comprises adding the pattern to a polysilicon design layer included in the modified IC design layout.

11. The method of claim 8 , wherein the dummy feature is an optical proximity correction feature that enhances imaging resolution.

12. The method of claim 8 , wherein the pattern includes an irregular dummy array, the irregular dummy array having the dummy feature, such that a total dummy area/space block area is equal to the target block dummy density ratio R.

13. A method comprising:

determining an optimized block dummy density ratio r 0 of an IC design layout, the IC design layout including a subdivisional area having a plurality of main features and a plurality of space blocks, the optimized block dummy density ratio r 0 being calculated from a total pattern density associated with the subdivisional area of the IC design layout;

determining a target block dummy density ratio R of the IC design layout according to the optimized block dummy density ratio r 0 ;

generating a pattern of dummy features according to the target block dummy density ratio R;

generating a modified IC design layout by adding the dummy features to the IC design layout; and

fabricating an integrated circuit according to the modified IC design layout.

14. The method of claim 13 , further comprising choosing the dummy features according to an associated intensity that is less than an exposure threshold dose of at least one of the main features.

15. The method of claim 13 , wherein the dummy features are optical proximity correction (OPC) features.

16. The method of claim 13 , wherein each of the dummy feature has a first side length A and a second side length B and the pattern of the dummy features has an x-direction pitch p x and a y-direction pitch p y such that AB/p x p y =R.

17. The method of claim 13 , wherein the dummy features have a cross-sectional profile selected from the group consisting of a square shaped cross-sectional profile and a rectangular shaped cross-sectional profile.

18. The method of claim 13 , wherein the total pattern density includes a main feature density and a block dummy pattern density weighted by a block dummy density ratio, the block dummy density ratio being between 0 and 1.

19. The method of claim 13 , wherein the determining of the optimized block dummy density ratio r 0 of the IC design layout, includes determining based on a statistical measure of the total pattern density.

20. The method of claim 13 , wherein the determining of the optimized block dummy density ratio r 0 includes calculating a formula

r 0 =( PD 0 · PD S − PD 0 ·PD S )/σ S 2   (2)

wherein:

PD 0 is an average of a main pattern density;

PD S is an average of a block dummy pattern density;

PD 0 · PD S is an average of a product of the main pattern density and the block dummy pattern d; and

σ is defined by a formula σ 2 = PD 2 − PD 2 , where PD is a total pattern density defined in a formula PD=PD 0 +rPD S and r is a block dummy density ratio, σ S is defined by a formula σ S 2 = PD S 2 − PD S 2 .