Polycrystalline Silicon Waveguide Grain Orientation
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Solution Overview
Problem
Optical waveguides made of polycrystalline silicon films face challenges with light scattering due to grain and surface morphology, leading to degradation of optical properties, particularly when formed using LPCVD methods or thermal treatment of amorphous silicon films.
Innovation Solution
A semiconductor device is manufactured with an optical waveguide made of polycrystalline silicon, where crystal grains on the surface are processed to have flat surfaces parallel to the substrate and side surfaces perpendicular to the substrate, reducing surface morphology and scattering, achieved through thermal treatment and planarization techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polycrystalline silicon film is formed by LPCVD method or thermal treatment on amorphous silicon film, then the cost is reduced and multi-layering is enabled, but light scattering occurs due to grain interface and surface morphology, degrading optical properties
Solution Approach 1:
The patent applies parameter changes by controlling the crystal grain size and orientation of polycrystalline silicon through specific thermal treatment conditions. By adjusting temperature, time, and atmosphere parameters during thermal processing, the crystal grains are oriented perpendicular to the film surface, creating flat surfaces that minimize light scattering while maintaining the cost-effective polycrystalline structure
Solution Approach 2:
The patent creates a composite structure where polycrystalline silicon layers with specific crystal orientations are integrated with insulating films and other functional layers. This composite approach allows the optical waveguide to benefit from the low-cost polycrystalline silicon while the overall structure compensates for potential scattering through careful design of interfaces and layer configurations
2Device complexity
If thermal treatment is performed on amorphous silicon film to form polycrystalline silicon, then manufacturing complexity is reduced, but surface roughness increases causing light scattering
Solution Approach 1:
The patent controls surface morphology by precisely adjusting thermal treatment parameters including temperature gradients, treatment duration, and atmospheric composition. These parameter changes promote uniform crystal grain growth with perpendicular orientation, producing flat surfaces that reduce scattering while maintaining process simplicity
Solution Approach 2:
The patent performs preliminary thermal treatment on the amorphous silicon film before final waveguide formation to pre-establish the desired crystal grain structure and surface flatness. This preliminary action ensures that subsequent processing steps work with an optimized substrate, reducing the need for additional surface correction steps
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 results in improved optical properties by minimizing grain and surface scattering, enhancing the performance of the optical waveguide.
Implementation Method 1
performing thermal treatment at a temperature higher than a growth temperature of the polycrystalline silicon film
Implementation Method 2
planarizing an upper surface of first polycrystalline silicon film
Implementation Method 3
an optical waveguide formed on an upper surface of the first insulating film
Data Source
AI summary
Good optical properties can be achieved in an optical waveguide made of polycrystalline silicon.A semiconductor layer that constitutes each of a first optical signal line, a second optical signal line, a grating coupler, an optical modulator, and a p-type layer of a germanium optical receiver is formed by a polycrystalline silicon film. Crystal grains of polycrystalline silicon exposed on an upper surface of the semiconductor layer include crystal grains having flat surfaces parallel to a first main surface of a semiconductor substrate, and crystal grains of polycrystalline silicon exposed on side surfaces (including side surfaces of a protrusion of a protruding portion) of the semiconductor layer include crystal grains having flat surfaces perpendicular to the first main surface of the semiconductor substrate.