Back-End Optical Waveguides in Metal Stack for Reduced Substrate Loss
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Solution Overview
Problem
Current integrated silicon photonic devices face challenges in optical packaging due to high confinement, misalignment intolerance, and substrate coupling losses, particularly when trying to match large optical modes and align different chip thicknesses and geometries, which increases costs and complexity.
Innovation Solution
Fabricating integrated optical devices within the vertical span of a metal stack during the back end of line process using doped waveguides and deposition of materials like silicon nitride, poly-silicon, and silicate glass, which allows for greater flexibility and reduces substrate loss, enabling better alignment and material interfacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If integrated silicon photonic devices are fabricated using conventional front-end processes, then device integration is achieved, but optical packaging complexity and cost increase due to high confinement and misalignment intolerance
Solution Approach 1:
The patent transitions optical device fabrication from the conventional front-end process (two-dimensional planar fabrication) to the back-end process (three-dimensional vertical fabrication within the metal stack span). This dimensional shift allows optical waveguides to be formed vertically between metal layers, decoupling optical fabrication from planar semiconductor processing and enabling better alignment tolerance and reduced substrate coupling losses.
Solution Approach 2:
The patent introduces the metal stack structure as an intermediary medium that provides both mechanical support and optical isolation. By forming optical waveguides within the vertical span of the metal stack, the metal layers serve as shielding barriers that reduce substrate coupling losses and provide a stable reference framework for alignment, thereby simplifying optical packaging while maintaining precision.
2Reliability
If optical devices are fabricated to match large optical modes, then coupling efficiency improves, but chip thickness and geometry alignment becomes more difficult
Solution Approach 1:
The patent utilizes the vertical dimension within the metal stack to form optical waveguides at different heights, allowing independent optimization of waveguide geometry for coupling efficiency without being constrained by planar chip thickness variations. This vertical positioning freedom enables better mode matching while simplifying alignment procedures.
Solution Approach 2:
The patent changes the fabrication parameters by performing optical device formation at back-end processing temperatures and conditions, allowing greater flexibility in waveguide geometry and material composition. This enables optimization of waveguide dimensions for large optical modes while maintaining compatibility with existing chip structures, thereby improving coupling efficiency without increasing alignment complexity.
3Ease of manufacture
If conventional fabrication processes are used, then standard manufacturing is maintained, but substrate coupling losses increase
Solution Approach 1:
The patent introduces the metal stack as an intermediary shielding structure that blocks substrate coupling losses. By forming optical waveguides within the vertical span of the metal stack, the metal layers act as optical barriers that prevent energy loss to the substrate, thereby reducing coupling losses while maintaining compatibility with standard manufacturing processes.
Solution Approach 2:
The patent extracts the optical device fabrication step from the conventional front-end process and relocates it to the back-end process within the metal stack. This separation allows the optical waveguides to be formed in an environment that inherently provides better optical isolation from the substrate, reducing coupling losses while maintaining manufacturing standardization through integration with existing back-end processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces costs and complexity, improves optical performance, and increases integration scale by decoupling modulator design, allowing for more efficient coupling and alignment of optical devices, while avoiding coherence length issues and substrate losses.
Implementation Method 1
forming the waveguide portion of a material having a first index of refraction greater than a second index of refraction of an oxide material surrounding the waveguide portion
Implementation Method 2
doping utilizing at least one of ion implantation and diffusion
Implementation Method 3
doping utilizing at least one of ion implantation and diffusion
Implementation Method 4
material deposition includes deposition of at least one of silicon nitride, amorphous silicon, poly-silicon, silicon oxynitride (SiON), silicon-germanium (SiGe), SiO2, silicate glass, and germanium (Ge)
Data Source
AI summary
An integrated optical device fabricated in the back end of line process located within the vertical span of the metal stack and having one or more advantages over a corresponding integrated optical device fabricated in the silicon on insulator layer.