Methods, apparatus, and systems for minimizing defectivity in top-coat-free lithography and improving reticle CD uniformity

1. A method, comprising:

forming a photomask for a lithographic process comprising a lithographic exposure and a developing step, the forming comprising:

defining a first pattern in the photomask, the first pattern comprising a main functional pattern, the main functional pattern comprising structures; and

defining a second pattern in the photomask, the second pattern comprising a sub-resolution fill pattern in one or more areas between structures of the first pattern or within one or more structures of the first pattern, the sub-resolution fill pattern comprising sub-resolution structures that do not substantially modify a locally complete resist removal in the developing step, the sub-resolution fill pattern having a pitch or range of pitches smaller than a minimum resolved pitch of the lithographic exposure and/or at least a part of the sub-resolution structures of the sub-resolution fill pattern not substantially modifying an imaging of any structure of the main functional pattern in the lithographic exposure.

2. The method according to claim 1 , comprising:

defining the sub-resolution fill pattern to comprise a regular pattern in an area of the sub-resolution fill pattern, the regular pattern comprising alternating lines and spaces, or contact-like structures, or a combination thereof.

3. The method according to claim 2 , comprising:

defining the sub-resolution fill pattern to comprise a combination of dark and clear patterns.

4. The method according to claim 2 , comprising:

defining a pitch or a range of pitches of the regular pattern of the sub-resolution fill pattern, the pitch or range of pitches being smaller than a minimum resolved pitch of the lithographic exposure.

5. The method according to claim 4 , comprising:

defining the pitch or range of pitches to be smaller than 80 nanometers (nm).

6. The method according to claim 4 , comprising:

defining a direction of the regular pattern, the direction being a direction for which the minimum resolved pitch of the lithographic exposure has a maximum value.

7. The method according to claim 1 , comprising:

adjusting a size of the sub-resolution structures of the sub-resolution fill pattern to correspond to a predetermined background intensity in the lithographic exposure, and/or to a predetermined pattern density of the sub-resolution fill pattern.

8. The method according to claim 1 , comprising:

adjusting a size, a shape, and/or a position of one or more sub-resolution structures of the sub-resolution fill pattern in a border region of the sub-resolution fill pattern to optimize, in the lithographic exposure, a depth of focus and/or contrast of one or more structures of the main functional pattern in a vicinity of the one or more sub-resolution structures of the sub-resolution fill pattern.

9. The method according to claim 1 , the forming of the photomask further comprising:

writing the sub-resolution fill pattern with a reduced number and/or complexity of optical proximity corrections, a reduced number of writing passes, a reduced writing dose, a faster writing time, and/or a less advanced photomask writing tool compared to a number and/or complexity of optical proximity corrections, a number of writing passes, a writing dose, a writing time, and/or a photomask writing tool, respectively, used for a writing of the main functional pattern.

10. The method according to claim 1 , the forming of the photomask further comprising:

omitting an inspection or a part of an inspection for the sub-resolution fill pattern, or inspecting the sub-resolution fill pattern with a lower accuracy, a lower resolution, a faster inspection speed, a lower number of scans, and/or a less advanced inspection tool, compared to an accuracy, a resolution, an inspection speed, a number of scans, and/or an inspection tool, respectively, used for an inspection of the main functional pattern.

11. The method according to claim 1 , the forming of the photomask further comprising:

detecting a defect in the sub-resolution fill pattern, and omitting a repair process for the defect in the sub-resolution fill pattern, or repairing the defect in the sub-resolution fill pattern with a lower accuracy, a faster repair speed, a lower number of iterations, and/or a less advanced repair tool, compared to an accuracy, a repair speed, a number of iterations, and/or a repair tool, respectively, used for a repair process for the main functional pattern.

12. The method according to claim 1 , comprising:

providing a substrate coated with a photoresist without a top coat;

exposing the substrate in the lithographic exposure; and

developing the photoresist in the developing step.

13. A device, comprising:

a photomask for a lithographic process comprising a lithographic exposure and a developing step, the photomask comprising:

a first pattern, the first pattern comprising a functional pattern, the functional pattern comprising a main functional pattern, the main functional pattern comprising structures; and

a second pattern, the second pattern comprising a sub-resolution fill pattern defined in the photomask in one or more areas between structures of the first pattern or within one or a plurality of the structures of the first pattern, the sub-resolution fill pattern comprising sub-resolution structures, the presence of which does not substantially modify a locally complete resist removal in the developing step, the sub-resolution fill pattern having a pitch or range of pitches smaller than a minimum resolved pitch of the lithographic exposure and/or at least a part of the sub-resolution structures of the sub-resolution fill pattern not influencing an imaging of any structure of the main functional pattern in the lithographic exposure.

14. The device according to claim 13 , wherein the sub-resolution fill pattern comprises a regular pattern, the regular pattern comprising alternating lines and spaces or contact-like structures or a combination thereof.

15. The device according to claim 13 , wherein the sub-resolution fill pattern comprises a combination of dark and clear patterns.

16. The device according to claim 14 , wherein the regular pattern of the sub-resolution fill pattern comprises a pitch or range of pitches smaller than a minimum resolved pitch of the lithographic exposure.

17. The device according to claim 14 , wherein a direction of the regular pattern of the sub-resolution fill pattern is a direction for which the minimum resolved pitch of the lithographic exposure has a maximum value.

18. The device according to claim 13 , wherein a size of sub-resolution structures of the sub-resolution fill pattern corresponds to a predetermined background intensity in the lithographic exposure and/or a predetermined pattern density of the sub-resolution fill pattern.

19. The device according to claim 13 , wherein a size and/or shape and/or position of one or more sub-resolution structures of the sub-resolution fill pattern in a border region of the sub-resolution fill pattern is adjusted to optimize, in the lithographic exposure, a depth of focus or contrast of one or more structures of the main functional pattern.

20. A system comprising:

a processor or a plurality of processors, the processor or the plurality of processors configured to design a layout for a photomask for a chip layer and a lithography process for an exposure of a substrate with the photomask, the layout comprising a main functional pattern comprising structures, the processor or the plurality of processors configured to:

define a fill area in the layout of the photomask and calculate a desired background illumination intensity for a substrate area corresponding to the fill area, the background illumination intensity being calculated to not cause a printing in the lithography process;

select a fill pattern type for the one or more fill areas;

define a pitch or range of pitches for the fill pattern types;

define a fill pattern comprising sub-resolution structures, the fill pattern comprising the fill pattern type and the pitch or range of pitches in the fill area;

calculate a size of the sub-resolution structures to correspond to desired background illumination intensity;

adjust a size, a shape, or a position of one of more sub-resolution structures in a border region of the fill areas to

optimize a depth of focus and/or contrast in the exposure of the structure of the main functional pattern in a vicinity of the sub-resolution structures or optimize an illumination intensity for a substrate area corresponding to the sub-resolution structures, and

calculate an optical proximity correction for structures of the main functional pattern of the layout for the photomask.