Fabrication and Alignment of Hybrid Gratings

As device complexity grows, multiple patterning techniques are used in the fabrication of combination pattern. Holographic lithography provides a cost-effective solution for periodic nanometers-level structures with high efficiency and scalability, while mask lithography is commonly employed for non-periodic structures with microns-level linewidth. Achieving precise alignment between these two regions is a significant technical challenge, as any misalignment can impact the overall device performance. To address this, advanced alignment techniques and optimized lithographic processes are required to ensure that the different patterns are properly coordinated, minimizing errors and enhancing the reliability and functionality of the final device.
In this paper, we present a novel fabrication process for hybrid gratings that integrates holographic lithography and masked lithography within a unified optical path. This process incorporates advanced alignment techniques to ensure accurate positioning of the two distinct patterned regions. The alignment signal is generated from the diffraction of a reference grating, which is integrated into the mask used for fabricating the codes. This reference grating, placed within the interference optical path, produces reference fringes recorded by a CCD camera. By analyzing and precisely adjusting these reference fringes, the alignment between the grating and encoding regions is optimized, thereby significantly increasing the performance.

Keywords: Hybrid gratings, Absolute encoding, Reference grating, Precision grating measurement, Lithography.

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