Integrated circuit overlay test patterns and method thereof

1. A method of semiconductor device fabrication, comprising:

performing, by use of an integrated circuit (IC) design system, a placement process to assign locations of a plurality of functional cells on a chip to be fabricated on a wafer;

identifying, by use of the IC design system, at least one gap among the plurality of functional cells;

inserting, by use of the IC design system, a first overlay test pattern cell within the at least one gap, wherein the first overlay test pattern cell includes a first number of patterns disposed along a first direction at a first pitch, wherein the first pitch is smaller than a smallest wavelength on a full spectrum of humanly visible lights;

prior to the inserting of the first overlay test pattern cell, inserting, by use of the IC design system, at least one standard filler cell in the at least one gap;

prior to the inserting of the first overlay test pattern cell, identifying, by use of the IC design system, a standard filler cell out of the at least one standard filler cell within the at least one gap; and

removing, by use of the IC design system, the identified standard filler cell from the at least one gap.

2. The method of claim 1 , further comprising:

forming the first overlay test pattern cell; and

forming a second overlay test pattern cell directly over the first overlay test pattern cell along a direction normal to a top surface of the wafer, wherein the second overlay test pattern cell includes a second number of patterns disposed along the first direction at a second pitch different from the first pitch.

3. The method of claim 2 ,

wherein the forming of the first overlay test pattern cell comprises forming the first number of patterns with a first conductive material and interposing the first number of patterns with a first dielectric material,

wherein the forming of the second overlay test pattern cell comprises forming the second number of patterns with a second conductive material and interposing the second number of patterns with a second dielectric material.

4. The method of claim 3 , wherein the first conductive material and the second conductive material comprise metal, metal oxide, metal nitride, metal oxynitride, silicide, doped dielectric material, doped compound semiconductor, doped semiconductor, or doped polysilicon.

5. The method of claim 2 , further comprising:

inspecting an overlay between the formed first overlay test pattern cell and the formed second overlay test pattern cell using an electron beam (e-Beam) inspection process.

6. The method of claim 5 , wherein the inspecting of the overlay between the formed first overlay test pattern cell and the formed second overlay test pattern cell comprises taking a voltage contrast image of the formed first overlay test pattern cell and the formed second overlay test pattern cell.

7. A method, comprising:

inserting, by use of an integrated circuit (IC) design system, a first overlay test pattern cell in an IC design layer, wherein the first overlay test pattern cell includes a first number of patterns disposed along a first direction at a first pitch, wherein the first pitch is smaller than a smallest wavelength on a full spectrum of humanly visible lights;

forming the first overlay test pattern cell;

after the forming of the first overlay test pattern cell, forming a second overlay test pattern cell directly over the first overlay test pattern cell, wherein the second overlay test pattern cell includes a second number of patterns disposed along the first direction at a second pitch different from the first pitch; and

inspecting an overlay between the formed first overlay test pattern cell and the formed second overlay test pattern cell using an electron beam (e-Beam) inspection process.

8. The method of claim 7 , further comprising:

prior to the inserting of the first overlay test pattern cell, identifying, by use of the IC design system, at least one gap among a plurality of functional cells in the IC design layer,

wherein the inserting comprises inserting the first overlay test pattern cell within the at least one gap.

9. The method of claim 7 ,

wherein the IC design layer comprises at least one standard filler cell,

wherein the inserting comprises replacing the at least one standard filler cell with the first overlay test pattern cell.

10. The method of claim 7 ,

wherein the forming of the first overlay test pattern cell comprises forming the first number of patterns with a first conductive material and interposing the first number of patterns with a first dielectric material,

wherein the forming of the second overlay test pattern cell comprises forming the second number of patterns with a second conductive material and interposing the second number of patterns with a second dielectric material.

11. The method of claim 10 , wherein the first conductive material and the second conductive material comprise metal, metal oxide, metal nitride, metal oxynitride, silicide, doped dielectric material, doped compound semiconductor, doped semiconductor, or doped polysilicon.

12. The method of claim 7 , wherein the inspecting of the overlay between the formed first overlay test pattern cell and the formed second overlay test pattern cell comprises taking a voltage contrast image of the formed first overlay test pattern cell and the formed second overlay test pattern cell.

13. The method of claim 12 , wherein the taking of the voltage contrast image comprises use of a scanning electron microscope (SEM).

14. The method of claim 12 , wherein the voltage contrast image is bright when a first pattern in the first overlay test pattern cell and a second pattern in the second overlay test pattern cell are at least partially aligned.

15. The method of claim 12 , wherein the voltage contrast image is dark when a first pattern in the first overlay test pattern cell and a second pattern in the second overlay test pattern cell are completely misaligned.

16. The method of claim 7 , wherein the IC design layer comprises a standard filler cell.

17. A method, comprising:

inserting a first overlay test pattern cell in an IC design comprising a transistor, wherein the first overlay test pattern cell includes a first number of patterns disposed along a first direction at a first pitch, wherein the first pitch is smaller than a smallest wavelength on a full spectrum of humanly visible lights;

forming the first overlay test pattern cell in a first layer of the IC design;

after the forming of the first overlay test pattern cell, forming a second overlay test pattern cell in a second layer of the IC design, wherein the second layer is directly over the first layer, wherein the second overlay test pattern cell includes a second number of patterns disposed along the first direction at a second pitch different from the first pitch; and

inspecting an overlay between the formed first overlay test pattern cell and the formed second overlay test pattern cell by taking a voltage contrast image of the formed first overlay test pattern cell and the formed second overlay test pattern cell.

18. The method of claim 17 ,

wherein the first pitch and the second pitch comprise a difference,

wherein the transistor comprises a gate having a gate width,

wherein the difference falls within a range between about one-fortieth ( 1/40) and about one-fourth (¼) of the gate width.

19. The method of claim 17 , further comprising:

prior to the inserting of the first overlay test pattern cell, identifying at least one gap among a plurality of functional cells in the first layer,

wherein the inserting comprises inserting the first overlay test pattern cell within the at least one gap.

20. The method of claim 17 ,

wherein the first layer of the IC design comprises at least one standard filler cell,

wherein the inserting comprises replacing the at least one standard filler cell with the first overlay test pattern cell.