12 March 2008 Study of SRAF placement for contact at 45 nm and 32 nm node
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Abstract
At 45 and 32 nm nodes, one of the most critical layers is the Contact one. Due to the use of hyper NA imaging, the depth of focus starts to be very limited. Moreover the OPC is rapidly limited because of the increase of the pattern density. The limited surface in the dark field region of a Contact layer mask enforces the edges movement to stop very quickly. The use of SRAF (Sub Resolution Assist Feature) has been widely use for DOF enhancement of line and space layers since many technology node. Recently, SRAF generated using inverse lithography have shown interesting DOF improvement1. However, the advantage of the ideal mask generated by inverse lithography is lost when switching to a manufacturable mask with Manhattan structures. For SRAF placed in rule based as well as Manhattan SRAF generated after inverse lithography, it is important to know what their behavior is, in term of size and placement. In this article we propose to study the placement of scatter-trenches assist features for the contact layer. For this we have performed process window simulation with different SRAF sizes and distance to the main OPC. These results permit us to establish the trends for size and placement of the SRAF. Moreover we have also take a look of the advantages of using 8 surrounding SRAF (4 in vertical - horizontal and 4 at 45°) versus 4 surrounding SRAF. Based on these studies we have seen that there is no real gain of increasing the complexity by adding additional SRAF.
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V. Farys, V. Farys, F. Robert, F. Robert, C. Martinelli, C. Martinelli, Y. Trouiller, Y. Trouiller, F. Sundermann, F. Sundermann, C. Gardin, C. Gardin, J. Planchot, J. Planchot, G. Kerrien, G. Kerrien, F. Vautrin, F. Vautrin, M. Saied, M. Saied, E. Yesilada, E. Yesilada, F. Foussadier, F. Foussadier, A. Villaret, A. Villaret, L. Perraud, L. Perraud, B. Vandewalle, B. Vandewalle, J. C. Le Denmat, J. C. Le Denmat, M. K. Top, M. K. Top, } "Study of SRAF placement for contact at 45 nm and 32 nm node", Proc. SPIE 6924, Optical Microlithography XXI, 69242Z (12 March 2008); doi: 10.1117/12.774091; https://doi.org/10.1117/12.774091
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