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

Area of Science:

• Materials Science
• Photonics Engineering
• Integrated Optics

Background:

• Thick silicon nitride films are crucial for integrated silicon photonics but suffer from high tensile stress, leading to cracking.
• Existing fabrication methods struggle to produce thick, high-quality silicon nitride films without defects.
• Stress management is critical for realizing advanced photonic devices like microring and microdisk resonators.

Purpose of the Study:

• To develop a novel stress-released fabrication process for stoichiometric silicon nitride (Si3N4).
• To enable the creation of dispersion-engineered photonic devices with enhanced performance.
• To demonstrate a scalable process for producing thick, crack-free Si3N4 films on silicon wafers.

Main Methods:

• A two-step growth process for Si3N4 films using low-pressure chemical vapor deposition (LPCVD).
• Introduction of a stress-release pattern during the intermediate growth step to mitigate tensile stress.
• Fabrication of waveguide-coupled microring and microdisk resonators on the stress-managed Si3N4 platform.

Main Results:

• Demonstration of a nearly crack-free, approximately 830nm-thick Si3N4 film on a 4-inch silicon wafer.
• Achieved high intrinsic quality (Q)-factors: ~2.0x10^6 for a 115µm-radius microring (TM00 mode) and ~4.0x10^6 for a 575µm-radius microdisk (TM modes) at 1550nm.
• Successful integration of dispersion-engineered resonators with cavity sizes up to a millimeter.

Conclusions:

• The developed stress-released Si3N4 fabrication process effectively minimizes film cracking.
• The platform supports high-Q factor microring and microdisk resonators, crucial for advanced photonic applications.
• This advancement paves the way for high-performance, dispersion-engineered integrated silicon photonics.