Low loss poly-silicon for high performance capacitive silicon modulators.

Area of Science:

• Materials Science
• Photonics Engineering
• Semiconductor Physics

Background:

• Silicon photonics is a rapidly growing field for integrated optical circuits.
• Polycrystalline silicon (polysilicon) is being explored as a cost-effective alternative to crystalline silicon for photonic applications.
• Capacitive modulators and other silicon photonic devices require materials with well-defined optical properties.

Purpose of the Study:

• To investigate the optical properties of polycrystalline silicon for silicon photonics.
• To optimize the fabrication process for polysilicon rib waveguides.
• To characterize optical propagation losses and identify their origins.

Main Methods:

• Deposition of amorphous silicon layers using Low-Pressure Chemical Vapor Deposition (LPCVD) on a 300 mm wafer.
• Solid phase crystallization annealing to convert amorphous silicon to polycrystalline silicon.
• Fabrication of rib waveguides and measurement of optical propagation losses at 1.31 µm.
• Physical analysis using Transmission Electron Microscopy with Astigmatism Correction (TEM ASTAR), Atomic Force Microscopy (AFM), and Secondary Ion Mass Spectrometry (SIMS).

Main Results:

• Optimal deposition and annealing conditions were determined for polysilicon fabrication.
• Fabricated 400 nm-wide rib waveguides exhibited low optical propagation losses.
• Losses were measured to be in the range of 9.2–10 dB/cm at 1.31 µm.
• Physical analysis provided insights into the sources of optical losses.

Conclusions:

• Polycrystalline silicon is a viable material for silicon photonics applications.
• The optimized fabrication process yields high-quality rib waveguides with low optical losses.
• Further integration of polysilicon into devices like capacitive modulators is feasible.