Stress-released Si3N4 fabrication process for dispersion-engineered integrated silicon photonics

Opt Express. 2020 Jun 8;28(12):17708-17722. doi: 10.1364/OE.390171.

Abstract

We develop a stress-released stoichiometric silicon nitride (Si3N4) fabrication process for dispersion-engineered integrated silicon photonics. To relax the high tensile stress of a thick Si3N4 film grown by low-pressure chemical vapor deposition (LPCVD) process, we grow the film in two steps and introduce a conventional dense stress-release pattern onto a ∼400nm-thick Si3N4 film in between the two steps. Our pattern helps minimize crack formation by releasing the stress of the film along high-symmetry periodic modulation directions and helps stop cracks from propagating. We demonstrate a nearly crack-free ∼830nm-thick Si3N4 film on a 4" silicon wafer. Our Si3N4 photonic platform enables dispersion-engineered, waveguide-coupled microring and microdisk resonators, with cavity sizes of up to a millimeter. Specifically, our 115µm-radius microring exhibits an intrinsic quality (Q)-factor of ∼2.0×106 for the TM00 mode and our 575µm-radius microdisk demonstrates an intrinsic Q of ∼4.0×106 for TM modes in 1550nm wavelengths.