18 August 2000 Automated OPC optimization using in-line CD-SEM
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Optical Proximity Correction (OPC) through assisted features in masks is one of the resolution enhancement techniques in advanced optical lithography. When printing sub-wavelength features on a wafer, OPC becomes necessary. Since OPC is process dependent, it is no easy task to find optimized OPC level for specific lithography process with either rule based or model based OPC application. To benefit from OPC in aggressive gate geometry, the level of correction needs to be optimized. We propose a practical method in OPC optimization using a CD-SEM. During the early process development phase, a test mask can be generated with various levels of OPC correction on a typical feature to be monitored during and after process development. A test wafer is the processed using the test mask using pre-determined photo process. A series of SEM images of the OPC feature on the test wafer will be automatically acquired by a CD-SEM. An OPC optimization algorithm will analyze the acquired images and find contour edges of those images. The contours from those images will be then overlaid on top of each other. With ideal feature shape as a reference, the closest contour to the ideal feature represents the optimized OPC among those tested OPC levels. The selected OPC, not only takes into account of optical effect from scanner optics, but also resist related effects. Production masks can then be produced with the selected level of OPC to maximize the benefit. In this paper, we will demonstrate the above- proposed OPC optimization process.
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Bo Su, Mina Menaker, Nadav Haas, Ramkumar Subramanian, Bhanwar Singh, "Automated OPC optimization using in-line CD-SEM", Proc. SPIE 4181, Challenges in Process Integration and Device Technology, (18 August 2000); doi: 10.1117/12.395714; https://doi.org/10.1117/12.395714

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