In-house SiN process development for integrated photonic applications

Abstract

Over the last decade, silicon nitride (SiN) based integrated photonics has become popular due to its CMOS com-patibility, low loss, wide spectral operation band and tolerance to high optical power. It has great potential in different application areas like quantum information processing, microwave photonics, spectroscopy, etc. However, the growth of an optical grade oxide layer (for bottom cladding) and subsequent deposition of SiN device layer on the surface of a handle silicon wafer are the most important aspects for the realization of large- scale photonic integrated circuits with an acceptable waveguide losses and fabrication yields. In this paper, we report the in- house technology development of SiN waveguide devices starting from a 4- inch silicon wafer. Both the thermally grown buried oxide (BOX) and the LPCVD deposited SiN device layer show excellent uniformities in terms of their thickness <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(1900\pm 20nm, 400\pm 4nm$</tex> , respectively) as well as refractive indices <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(n_{SiO_{2}}= 1.45\pm 0.001, n_{SiN}=2.024\pm 0.003$</tex> at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda\sim 1.55\mu m)$</tex> across the full wafer. We have discussed the design and characterization of the grating coupler, single mode waveguides operating at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda\sim 1.55\mu m$</tex> and their fabrication flow as well. The fabricated single mode waveguides (TE polarized) with input/output grating couplers exhibit a 3-dB bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 50nm$</tex> with a peak transmission efficiency at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda\sim 1570nm$</tex> . The SiN waveguides fabricated out of in-house processed SiN wafer exhibit reasonable third order non-linearity; confirmed by stimulated four wave mixing experiment.