Application of advanced hybrid metrology method to nanoimprint lithography

Nanoimprint lithography (NIL) is one alternative lithography solution that is being pursued by the industry. A metrology-related problem specific to NIL is the measurement of the residual layer thickness (RLT), as knowledge of this is key to the monitoring and control of the NIL process and subsequent patterning. Scatterometry is used to measure the RLT due to its ability to measure profile features non-destructively with high throughput. But because scatterometry is sensitive to features unrelated to the parameter of interest, complex geometries throughout the film stack can make the measurement challenging. New methods to reduce the impact of such complex geometries on the measurement parameters of interest are therefore needed. Because of the use of NIL for 3DNAND development, the measurement of the RLT with complex structures underneath becomes necessary. This paper describes the results from a new hybrid metrology method that can combine key information from these complex geometries with scatterometry measurements to reduce the impact on the RLT measurement due to the layers beneath the resist. By reducing this impact, scatterometry measurement noise and cross-correlation of parameters are reduced, resulting in better precision and accuracy in the RLT measurement.