Optimization of hydrogen silsesquioxane planarization for multilayer photonic platforms

Le résumé fourni par la source

Multilayer photonic platforms enable large-scale photonic integrated circuits with compact, sophisticated routing and densely integrated components, but their fabrication requires flat intermediate surfaces to ensure high-quality layer deposition and avoid scattering losses. Chemical mechanical polishing (CMP) is the standard planarization technique but demands costly dedicated equipment and is incompatible with polymer-based interlayers. Contact planarization using hydrogen silsesquioxane (HSQ) offers a low-cost alternative, yet prior demonstrations have been limited to etch depths below 150 nm and minimum feature sizes of 100 nm, well short of the requirements of standard silicon photonic processes. In this work, we present a bilayer HSQ deposition process that achieves effective planarization over a substantially broader dimensional range, covering trench widths from 75 nm to 1 µm and inter-structure spacings from 50 nm to 3 µm, for silicon etch depths of both 220 nm and 300 nm. Residual thickness variations of approximately 1 nm are obtained for narrow features with spacings between 50 nm and 500 nm, rising to approximately 7 nm for large 3 µm trenches. Inter-layer optical transitions between silicon and silicon nitride single-mode waveguides exhibit insertion losses as low as 0.3 dB per interface, confirming the optical quality of the planarized layers. These results establish bilayer HSQ contact planarization as a practical, high-performance alternative to CMP for Si-SiN multilayer photonic platforms.

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