SEM Based Data Extraction for Model Calibration
The model calibration process in a resolution-enhancement technique (RET) flow is one of the most critical steps towards building an accurate OPC recipe. RET simulation platforms use models for predicting latent images in the wafer due to exposure of different design layouts. Accurate models can precisely capture the proximity effects for the lithographic process and help RET engineers build the proper recipes to obtain high yield.
In this paper, we present an approach to extracting the EPE (edge placement error – the displacement between the polygon and resist edge) information from both SEM images and contours extracted by the metrology tools for structures on test wafers, and directly use them in the calibration of a 55-nm poly process. These new EPE structures would now mimic the complexity of real 2D designs. Each of these structures can be individually weighed according to the data variance. Model accuracy is then compared to the conventional method of calibration using symmetrical data only. The paper also illustrates the ability of the new flow to extract more accurate measurement out of wafer data that are more immune to errors compared to the conventional method.
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