Process variation in silicon photonic devices

Area of Science:

• Photonics and Materials Science
• Integrated Optics and Semiconductor Fabrication

Background:

• Foundry-fabricated silicon-on-insulator (SOI) wafers contain arrays of passive optical devices like microrings, racetrack resonators, and directional couplers.
• Characterization reveals significant variations in the optical responses of these devices, impacting their performance and uniformity.

Purpose of the Study:

• To quantify the process variation in passive SOI optical devices.
• To understand the spatial correlation of these variations across fabricated wafers.
• To establish a metric for process variation relevant to integrated photonic circuit design.

Main Methods:

• Fabrication of four wafers with repeating patterns of SOI optical devices.
• Physical and optical characterization of microrings, racetrack resonators, and directional couplers.
• Device-heating experiments to assess thermal effects and their spatial independence.
• Statistical analysis of optical response variations (peak wavelength) across devices at varying spatial extents.

Main Results:

• Optical responses of SOI devices exhibit significant, location-independent thermal effects.
• Room-temperature optical response variations demonstrate a spatial correlation consistent with a "random walk" pattern.
• Process variation is quantified as approximately 1 nm²/cm, aligning with existing literature values.

Conclusions:

• Spatial process variations in SOI optical devices follow a predictable "random walk" model.
• The quantified process variation (1 nm²/cm) provides a crucial parameter for designing robust integrated photonic circuits.
• Understanding and quantifying these variations are essential for achieving reliable performance in foundry-fabricated photonic devices.