Lithography process control using scatterometry metrology and semi-physical modeling

Abstract

In this paper, results and analysis are presented from Advanced Micro Devices' (AMD) efforts at calculating lithography dose and focus parameters using scatterometry metrology and semi-physical CD models. The system takes advantage of the accurate and precise top and bottom CD data produced by scatterometry to differentiate dose and focus variation. To build the lithography process model, scatterometry data is generated for each field of a focus-exposure matrix (FEM) wafer, and the resulting top and bottom CD data is used to fit the parameters of series expansions relating CD to dose and focus. When new CD data is generated, the models can be inverted to solve for dose and focus independently. Our methodology employs a flexible modeling and inversion approach in an attempt to make the technique applicable to any production film stack and any line spacing regime. The quality of the inversion results are highly correlated to the degree of focus observability present in the system. Our results will show how a series of litho process with varied film stacks and line/space ratios respond to this technique, and we will report some best practices for a variety of use cases ranging from equipment characterization to focus monitoring on product.