Mask pattern correction method
The main mask pattern of a photomask is corrected by adding serifs of one type (inner or outer) to a pair of mutually adjacent corners in the pattern, and adding a serif of the opposite type (outer or inner) to the edge between the corners. When the photomask is used to create a resist pattern by photolithography in the fabrication of a semiconductor device, the serifs combine to produce an optical proximity correction that reduces corner rounding and increases edge straightness in the resist pattern.
1. A method of correcting a main mask pattern used to create a resist pattern by photolithography, to improve corner morphology of the resist pattern, comprising:
adding first serifs to two adjacent corners of a part of the main mask pattern; and
adding a second serif to an edge of said part of the main mask pattern disposed between said two adjacent corners, the second serif extending inward from said edge if the first serifs extend outward from the two adjacent corners, or extending outward from said edge if the first serifs extend inward from the two adjacent corners.
2. The method of claim 1 , wherein said part of the main mask pattern is transparent, said first serifs are inner serifs, and said second serif is an outer serif.
3. The method of claim 2 , wherein said corners have interior angles less than one hundred eighty degrees.
4. The method of claim 3 , wherein said corners have interior angles of from forty-five degrees to one hundred thirty-five degrees.
5. The method of claim 1 , wherein said part of the main mask pattern is opaque, said first serifs are outer serifs, and said second serif is an inner serif.
6. The method of claim 5 , wherein said corners have interior angles less than one hundred eighty degrees.
7. The method of claim 6 , wherein said corners have interior angles of from forty-five degrees to one hundred thirty-five degrees.
8. The method of claim 5 , wherein said main mask pattern has another opaque part with a side facing said edge, the method further comprising adding an inner serif to said side, facing the inner serif added to said edge.
9. The method of claim 1 , wherein said edge is shorter than other edges of said part of said main mask pattern adjacent to said corners.
10. The method of claim 1 , wherein said first serifs are multi-step serifs.
11. The method of claim 1 , wherein said second serif is a multi-step serif.
12. The method of claim 10 , wherein said second serif is a multi-step serif.
13. The method of claim 1 , wherein said part of the main mask pattern is opaque, said first serifs are outer serifs, and said second serif is an inner serif, said corners have interior angles less than one hundred eighty degrees, and said main mask pattern has another opaque part with a side facing said edge, the method further comprising adding an inner serif to said side, facing the inner serif added to said edge.
14. The method of claim 1 , wherein said part of the main mask pattern has an opaque meandering shape deviating alternately to one side and another side of a longitudinal axis, said two adjacent corners being disposed at points where one of said part of the main mask pattern deviates toward the longitudinal axis, said edge being parallel to the longitudinal axis and displaced toward the longitudinal axis, said first serifs being inner serifs, said second serif being an outer serif.
15. The method of claim 1 , wherein said part of the main mask pattern has a transparent meandering shape deviating alternately to one side and another side of a longitudinal axis, said two adjacent corners being disposed at points where one of said part of the mask pattern deviates toward the longitudinal axis, said edge being parallel to the longitudinal axis and displaced toward the longitudinal axis, said first serifs being outer serifs, said second serif being an inner serif.