Sub-12nm Optical Lithography with 4x Pitch Division and SMO-Lite

摘要

The CMOS logic 22nm node is being done with single patterning and a highly regular layout style using Gridded Design Rules (GDR). Smaller nodes will require the same regular layout style but with multiple patterning for critical layers. A "lines & cuts" approach is being used to achieve good pattern fidelity and process margin, with extendibility to ～7nm. In previous work, Design-Source-Mask Optimization (DSMO) has been demonstrated to be effective down to the 16nm node. The transition from single- to double- and in some cases triple- patterning was evaluated for different layout styles, with highly regular layouts delaying the need for multiple-patterning compared to complex layouts. To address mask complexity and cost, OPC for the "cut" patterns was studied and relatively simple OPC was found to provide good quality metrics such as MEEF and DOF. This is significant since mask data volumes of ＞500GB per layer are projected for pixelated masks created by complex OPC or inverse lithography; writing times for such masks are nearly prohibitive. In this study, we extend the scaling using SMO with simplified OPC in a technique called "SMO-Lite" beyond 16nm. The same "cut" pattern is used for each set of simulations, with "x" and "y" locations for the cuts scaled for each node. The test block is a reasonably complex logic function with ~100k gates of combinatorial logic and flip-flops. Another approach for scaling the "cut" pattern has also been studied. This involves the use of a hole pitch division process to create a grid template combined with a relatively large "selection" pattern to create cuts at the desired grid locations. Experimental demonstration of the cut approach using SMO-Lite and a grid template will be presented. Wafer results have been obtained at a line half-pitch of 20nm, which corresponds to the gate pitch at the 10nm node.