Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences


UC Berkeley


2008 Research Summary

Optical System Characterization through Scatterometry

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Yu Ben, Jing Xue and Costas J. Spanos

Efficient metrology is needed for timely parameter extraction in support of Design for Manufacturing (DFM) models. This is particularly important in order to determine the existence of so-called "hot spots" in IC layouts [1]. Effective hot spot identification depends on accurate lithography simulation, which requires accurate estimation of key optical system aberrations. Among various metrology techniques, optical digital profilometry (ODP, also known as scatterometry) is considered superior in light of its high throughput, sub-nanometer resolution and non-invasive nature [2].

In this project, an ODP-based approach is introduced for lithography parameter extraction. First-principle simulation verifies the capability of extracting the first 34 Zernike coefficients, not including piston, x-tilt, and y-tilt. The feasibility of the extraction is confirmed by a commercial ODP platform. Promising results have been achieved to date with simulated state-of-the-art optical systems with partial coherence of 0.3 and Strehl ratio of about 0.97. This approach can be further customized in conjunction with hot spot detection, where the optimization scheme will be tailored to maximize the sensitivities of those aberrations that exert particular influence to specific patterns.

Figure 1
Figure 1: Scatterometry-based characterization flow

M. Cote and P. Hurat, "Standard Cell Printability Grading and Hot Spot Detection," International Symposium on Quality of Electronic Design (ISQED), 2005, pp. 264-269.
C. J. Spanos, X. Niu, N. Jakatdar, and J. Bao, "Specular Spectroscopic Scatterometry," IEEE Trans. Semiconductor Manufacturing, Vol. 14, No. 2, May 2001.