Using Higher Diffraction Orders to Improve the Accuracy and Robustness of Overlay Measurements

TL;DR

This paper presents a new method to improve overlay measurements by using higher diffraction orders, enhancing accuracy and robustness in semiconductor manufacturing.

Contribution

The novel approach introduces specially designed markers to enhance higher diffraction orders, improving overlay error detection.

Findings

The method corrects measurement errors using higher diffraction orders, improving accuracy.

Specially designed markers increase diffraction efficiency, making higher orders more usable.

The proposed design is compatible with current systems and suitable for advanced manufacturing processes.

Abstract

This paper introduces a method for improving the measurement performance of single wavelength overlay errors by incorporating higher diffraction orders. In this method, to enhance the accuracy and robustness of overlay error detection between layers, the measurement errors introduced by empirical formulas are corrected by incorporating higher diffraction orders, based on the differences in the light intensity difference curves for different diffraction orders. This method also expands the range of available wavelengths for selection. The introduction of specially designed overlay error measurement markers enhances the diffraction efficiency of higher diffraction orders to overcome the issue of their weak light intensity, making them difficult to utilize effectively. This paper first conducts a theoretical analysis using scalar diffraction theory, and then demonstrates the feasibility of the design through vector diffraction simulations and optical path simulations. The resulting two-layer marker structure is simple and compatible with existing measurement systems, showing tremendous potential for application at advanced process nodes.

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