Contour metrology accuracy assessment using TMU analysis

In semiconductor fabs, top-down critical dimension scanning electron microscopes (CD-SEMs) are key enablers for metrology and process control, and in order to continue to address the increasing metrology requirements of the semiconductor industry, additional applications that exploit the potential of CD-SEM equipment have being developed. More recently, the uses of contour extraction have expanded to encompass other applications that serve newer technologies, such as ILT (Inverse Lithography Technology), photonics, and DSA (Directed Self Assembly), where the characteristics of the 2D curvilinear patterns are such that standard measurement solutions are no longer an option. The applications for these newer technologies have driven the need for highly accurate contour metrology algorithms. In turn, the need for standardization of what is meant by “accurate” contour metrology has emerged. This paper explores the concept of accuracy as it relates to contour metrology and applies the fundamental methodologies of TMU analysis to the problem of finding the best methods of determining contour metrology accuracy. During the development of this methodology, it was discovered that the application of TMU analysis to contour metrology reveals unexpected conceptual challenges that force a deeper understanding of accuracy and how it pertains to contour metrology. The paper resolves these challenges and proposes a standardization for contour metrology accuracy assessment. Results from analysis of the extracted contours validates the usefulness of the proposed accuracy methodology and establishes the quality of the accuracy of the extracted contours.