Correcting 3D effects in phase shifting masks using sub-resolution features
View Patent ↗Using phase shifting on a mask can advantageously improve printed feature resolution on a wafer, thereby allowing greater feature density on an integrated circuit. Phase shifting can create an intensity imbalance between 0 degree and 180 degree phase shifters on the mask. An improved method of designing an alternating PSM to minimize this intensity imbalance is provided. Sub-resolution features, called “blockers”, can be incorporated in the alternating PSM design. Specifically, blockers can be formed in the 0 degree phase shifters. In this configuration, the intensity associated with the 0 degree phase shifters approximates the intensity associated with the corresponding 180 degree phase shifters. Intensity balancing using blockers retains image contrast, thereby ensuring printed feature quality.
1. A method of designing an alternating phase shifting mask (PSM), the method comprising:
converting a layout to an alternating PSM design including 0 degree phase shifters and 180 degree phase shifters; and
incorporating blockers in the alternating PSM design, wherein a blocker is formed in a 0 degree phase shifter to minimize an intensity imbalance with the corresponding 180 degree phase shifter.
2. The method of claim 1 , wherein incorporating blockers includes growing a length of the blocker.
3. The method of claim 1 , wherein incorporating blockers includes forming a plurality of blockers in the 0 degree phase shifter.
4. The method of claim 1 , wherein if a 180 degree phase shifter includes a sub-resolution feature, then sizing the blocker in the 0 degree phase shifter to be larger than the sub-resolution feature.
5. The method of claim 1 , wherein incorporating blockers creates a substantially uniform intensity imbalance error on the alternating PSM.
6. The method of claim 1 , further including performing optical proximity correction (OPC) on the alternating PSM design.
7. The method of claim 6 , wherein performing OPC is done after incorporating blockers in the alternating PSM design.
8. The method of claim 6 , wherein performing OPC is done before incorporating blockers in the alternating PSM design.
9. A method of generating an alternating phase shifting mask (PSM) design including 0 degree phase shifters and 180 degree phase shifters, the method comprising:
minimizing an intensity imbalance between a 0 degree phase shifter and a 180 degree phase shifter corresponding to the 0 degree phase shifter by incorporating a first sub-resolution feature in the 0 degree phase shifter.
10. The method of claim 9 , wherein incorporating the first sub-resolution feature includes growing a single dimension of the first sub-resolution feature.
11. The method of claim 9 , wherein incorporating the first sub-resolution feature includes forming a plurality of sub-resolution features in the 0 degree phase shifter.
12. The method of claim 9 , wherein if the 180 degree phase shifter includes a second sub-resolution feature, then sizing the first sub-resolution feature to be larger than the second sub-resolution feature.
13. The method of claim 9 , wherein incorporating the first sub-resolution feature for each 0 degree phase shifter and 180 degree phase shifter of the alternating PSM creates a substantially uniform intensity imbalance error on the alternating PSM.
14. The method of claim 9 , further including performing optical proximity correction (OPC) on the alternating PSM design.
15. The method of claim 14 , wherein performing OPC is done after incorporating minimizing intensity imbalance.
16. The method of claim 14 , wherein performing OPC is done before incorporating minimizing intensity imbalance.
17. An alternating phase shifting mask (PSM) comprising:
a 180 degree phase shifter;
a 0 degree phase shifter corresponding to the 180 degree phase shifter; and
at least one sub-resolution feature formed in the 0 degree phase shifter to minimize an intensity imbalance with the 180 degree phase shifter.
18. The alternating PSM of claim 17 , further including an undercut in the 180 degree phase shifter.
19. The alternating PSM of claim 17 , further including a bias in the 180 degree phase shifter.
20. The alternating PSM of claim 17 , further including a sub-resolution feature formed in the 180 degree phase shifter, wherein the sub-resolution feature formed in the 0 degree phase shifter is larger than the sub-resolution feature formed in the 180 degree phase shifter.
21. A computer-implemented system for generating an alternating phase shifting mask (PSM) design, the alternating PSM design including 0 degree phase shifters and 180 degree phase shifters, the system comprising:
an input interface for receiving a layout;
means for converting the layout to the alternating PSM design, wherein the alternating PSM design includes a blocker formed in a 0 degree phase shifter to minimize an intensity imbalance with a corresponding 180 degree phase shifter; and
an output interface for outputting the alternating PSM design.
22. The computer-implemented system of claim 21 , wherein the means for converting includes software code for increasing a dimension of the blocker to improve the intensity imbalance.
23. The computer-implemented system of claim 21 , wherein the means for converting includes software code for creating a uniform intensity imbalance error on the alternating PSM using a plurality of blockers.
24. The computer-implemented system of claim 21 , wherein the means for converting includes software code for performing optical proximity correction (OPC) on he alternating PSM design.