Microlithographic structures and method of fabrication
View Patent ↗A method of formulating and fabricating a mask pattern and resulting mask for forming isolated or closely spaced contact holes in an integrated circuit. The mask has a transparent mask substrate and patterned regions of attenuating phase shift material and opaque, partially transmissive or transparent material arranged to reduce the effect of side lobes and improve depth of focus. The rims, frames and outrigger patterns for the attenuating phase shift material and opaque, partially transmissive or transparent material are determined according to calculations performed on a processor with imaging software for various optical conditions and exposed feature criteria.
1. A microlithographic mask for forming a sub-resolution feature in photoresist with an acceptable process latitude, said mask comprising:
a layer of transparent material;
a layer of light-obstructing material; and
a layer of attenuating phase shifting material located between said layer of transparent material and said layer of light-obstructing material; and
wherein said layer of light-obstructing material and said layer of attenuating phase shifting material are patterned to form a transparent hole, a partially transmissive assist feature, and a light-obstructing frame located between said transparent hole and said partially transmissive assist feature.
2. The mask of claim 1 , wherein said transparent hole is a rectangle.
3. The mask of claim 2 , wherein said light-obstructing frame includes an opaque frame, and wherein said opaque frame surrounds said transparent hole.
4. The mask of claim 3 , wherein said partially transmissive feature includes a partially transmissive frame surrounding said opaque frame.
5. The mask of claim 4 , wherein said layer of light-obstructing material includes a layer of opaque material, and wherein said layer of opaque material includes an opaque background surrounding said partially transmissive frame.
6. The mask of claim 1 , wherein said layer of transparent material includes quartz.
7. The mask of claim 6 , wherein said layer of attenuating phase shifting material includes a material selected from the group consisting of MoSi, chromium fluoride, silicon nitride, titanium nitride, tantalum silicide and zirconium silicon oxide.
8. The mask of claim 7 , wherein said attenuating phase shifting material is deposited on said quartz.
9. The mask of claim 7 , wherein the transmissivity of said layer of attenuating phase shifting material relative to said layer of transparent material is in the range of from about 6% to 100%.
10. The mask of claim 7 , wherein said layer of light-obstructing material includes chrome.
11. The mask of claim 1 , further comprising a partially transmissive frame, said layer of phase-shifting material being located between said transparent hole and partially transmissive frame.
12. A microlithographic mask, comprising:
transparent material; and
patterned opaque material and phase shifting material, said patterned materials defining an opening, an opaque frame surrounding said opening, sub-resolution bars surrounding said frame, and opaque corners located between sub-resolution bars.
13. The mask of claim 12 , wherein said transparent material includes quartz.
14. The mask of claim 13 , wherein said phase shifting material is partially transmissive relative to said transparent material.
15. The mask of claim 14 , wherein said opaque material includes metal deposited on said phase shifting material.
16. A mask for forming an array of sub-resolution features, said mask comprising:
a layer of transparent material;
a layer of light-obstructing material; and
a layer of attenuating phase shifting material located between said layer of transparent material and said layer of light-obstructing material; and
wherein said layer of light-obstructing material and said layer of attenuating phase shifting material are patterned to form transparent holes and light-obstructing frames surrounding said transparent holes.
17. The mask of claim 16 , further comprising partially transmissive features surrounding said light-obstructing frames.
18. The mask of claim 17 , further comprising opaque corners on said partially transmissive features.
19. A multi-tone mask for forming sub-resolution features, said mask comprising:
a first layer of attenuating phase shifting material, said layer defining openings corresponding to said sub-resolution features; and
a second layer of material for preventing incident light from propagating through said first layer, said second layer including frames surrounding said openings, and wherein said second layer defines bar-shaped partially transmissive assist features.
20. The mask of claim 19 , wherein phase-shifted light transmitted through one of said bar-shaped partially transmissive assist features operatively interacts with light transmitted through said openings.
21. A mask for forming an elliptical feature in photoresist, said mask comprising:
a layer of transparent material;
a layer of opaque material; and
a layer of attenuating phase shifting material located between said layer of transparent material and said layer of opaque material; and
wherein said layer of opaque material and said layer of attenuating phase shifting material are patterned to form transparent holes and opaque frames surrounding said transparent holes.
22. The mask of claim 21 , further comprising an array of rectangular openings, and attenuating phase shifting bars located between said rectangular openings.
23. The mask of claim 22 , further comprising a patterned layer of opaque material for defining said attenuating phase shifting bars.
24. The mask of claim 23 , further comprising a transparent substrate for supporting said attenuating phase shifting bars and said patterned layer of opaque material.
25. A method of making a multi-tone microlithographic mask, said method comprising:
providing sets of dimension data representative of mask patterns;
for each set of dimension data, calculating feature dimension data as a function of optical conditions; and
for a desired optical condition, identifying the sets of dimension data that have feature dimension data within desired limits.
26. The method of claim 25 , further comprising the step of selecting the one set of dimension data that achieves the smallest change in critical dimension between a zero defocus condition and a maximum considered defocus condition.
27. The method of claim 26 , wherein said dimension data includes the widths of transparent openings in said patterns.
28. The method of claim 25 , wherein said feature dimension data define opaque corner structures.
29. The method of claim 25 , wherein said feature dimension data define partially transmissive corner structures.