Improved selectivity in dry etching of lithium niobate with thermal annealed hydrogen silsesquioxane mask

Thin-film lithium niobate (TFLN) plays a critical role in the field of photonic device engineering due to its unique optical properties inherited from LN. These properties encompass robust electro-optic (EO) coefficients and extensive spectral transparency. As a consequence, TFLN facilitates the production of various crucial devices such as EO modulators, acoustic-optic modulators, EO frequency combs, and nonlinear wavelength converters. However, a key fabrication challenge persists in the low dry etching selectivity between TFLN and hydrogen silsesquioxane (HSQ) resist. Here, we propose that the selectivity of LN/HSQ dry etching can be improved by thermal annealing of HSQ masks before dry etching processing. The LN/HSQ etching selectivity increases from 0.55 to ∼1 when the developed HSQ masks are annealed, while the microring quality factor (Q) tests reflect that the optical losses remain unaltered.