Investigation of enhanced 2D field-stitching method as a simulation-tool for line-edge roughness in scatterometry

Scatterometry is a method commonly used in semiconductor metrology for measuring critical dimension (CD). It relies on measurement of light diffracted on a periodic structure and using it to derive the actual profile by running complex simulations. As CD is getting smaller with next lithography nodes, the Line-Edge Roughness/Line Width Roughness (LER/LWR) are becoming significant fraction of its overall size - therefore there is a need to include them in the simulations. Simulation of the LER/LWR's influence, in its random nature, calls for simulating relatively large fields. These large fields, if treated with rigorous electromagnetic simulations, are either very time-extensive or impossible to conduct, therefore computationally bearable, approximate approach needs to be applied. Our approximate method is "Field-Stitching Method" (FSM). We present its 2D version with varying parameter called "overlap region". We simulate the line grating structure with CD disturbed by LER/LWR and apply Rigorous Coupled Wave Analysis (RCWA) supported by the 2D FSM. We also generate the results obtained exclusively by RCWA, to which we compare the results of the approximate approach. Based on the comparison we discuss the benefits FSM brings and its limitations.

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