Modeling of wafer alignment marks using geometrical theory of diffraction (GTD)

Chin Boon Tan; Swee Hock Yeo; Andrew Khoh

doi:10.1117/12.599252

10 May 2005 Modeling of wafer alignment marks using geometrical theory of diffraction (GTD)

Chin Boon Tan, Swee Hock Yeo, Andrew Khoh

Proceedings Volume 5752, Metrology, Inspection, and Process Control for Microlithography XIX; (2005) https://doi.org/10.1117/12.599252
Event: Microlithography 2005, 2005, San Jose, California, United States

Abstract

In photolithography, alignment is a critical step prior to exposure of wafers in the scanner. When the alignment light strikes onto the wafer alignment marks, the backward diffracted waves are collected and analyzed as alignment signal. In this case, robustness of the marks is very important as it determines the quality of the signal. Poor alignment signal results in unacceptable overlay which requires rework of the wafers. Wafer alignment marks are usually grating on the substrates which are formed during different masking layers. In this paper, modeling of wafer alignment mark is performed using Geometrical Theory of Diffraction (GTD). The model is developed to investigate light scattering problem in alignment marks particularly at the sidewall. GTD can be extended and applied in such a study due to the existing of wave-like properties of the diffracted components. The main interest here is to find diffraction coefficient that can be fit into the model to determine the backward diffracted waves. With this, different arbitrary angle of the mark sidewall can be studied besides a perfect step grating. The results also look into different consequences of marks, such as grating depth.

Citation Download Citation

Chin Boon Tan, Swee Hock Yeo, and Andrew Khoh "Modeling of wafer alignment marks using geometrical theory of diffraction (GTD)", Proc. SPIE 5752, Metrology, Inspection, and Process Control for Microlithography XIX, (10 May 2005); https://doi.org/10.1117/12.599252

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