Semiconductor Optical Waveguide Backside Cavity Design
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Solution Overview
Problem
Existing semiconductor devices with air-layer cavities around optical waveguides face reliability issues due to the need for forming wiring layers above the waveguide, which complicates the manufacturing process and can lead to optical losses and scattering of light.
Innovation Solution
A semiconductor device design featuring a substrate with a first opening on its back surface that overlaps the optical waveguide, allowing for improved light confinement and reduced optical losses, along with a cover to maintain air pressure and prevent oxidation, enhancing mechanical strength and modulation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cavity covering the lower surface and both side surfaces of the optical waveguide is formed to enhance light confinement, then light confinement effect is improved, but device complexity and manufacturing difficulty increase due to the need to form wiring layers above the waveguide
Solution Approach 1:
The patent forms the cavity on the back surface (lower surface) of the substrate rather than removing material from the front surface. This dimensional change allows the cavity to be formed independently of the wiring layer formation process on the front surface, eliminating the conflict between cavity formation and wiring layer deposition. The cavity is created by removing a portion of the lower surface of the substrate, while wiring layers are formed on the upper surface, thus resolving the manufacturing complexity issue.
2Reliability
If the cavity covering the optical waveguide is formed early in the manufacturing process, then light confinement is enhanced, but reliability decreases due to potential optical losses and scattering during subsequent wiring layer formation
Solution Approach 1:
The manufacturing process is segmented into independent stages: (1) forming the cavity on the back surface of the substrate, (2) forming the optical waveguide on the front surface, and (3) forming wiring layers on the front surface above the waveguide. This segmentation allows each process to be completed independently without interfering with the others, ensuring both optical signal stability and manufacturing feasibility.
Solution Approach 2:
The substrate acts as an intermediary structure that separates the cavity formation process on the back surface from the waveguide and wiring layer formation on the front surface. This spatial separation through the substrate medium allows the cavity to provide light confinement while the front surface structures can be formed without causing optical losses or scattering.
3Ease of manufacture
If insulating layers are used to cover the optical waveguide, then manufacturing is easier, but light confinement effect is reduced compared to using an air-layer cavity
Solution Approach 1:
The patent applies different materials with different properties to different locations: insulating layers cover the side surfaces of the optical waveguide for easy manufacturing and protection, while a portion of the lower surface of the substrate is removed to form an air-layer cavity for superior light confinement. This local differentiation of material properties optimizes both manufacturing ease and light confinement effect.
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
The design enhances the reliability and modulation efficiency of the semiconductor device by reducing light scattering and oxidation risks, while allowing for stable manufacturing of the wiring layers without compromising the device's performance.
Implementation Method 1
The refractive index of the material constituting the optical waveguide is greater than the refractive indices of the materials constituting the first insulating layer and the second insulating layer. This allows light to travel along the optical waveguide while substantially confined inside the optical waveguide.
Implementation Method 2
A semiconductor device having an optical waveguide covered with an air-layer instead of an insulating film such as silicon oxide is known from the viewpoint of enhancing the effects of confining light inside the optical waveguide.
Data Source
AI summary
A semiconductor device includes a substrate having a first surface and a second surface that have top and back relation, an insulating layer formed on the first surface of the substrate, and an optical waveguide formed on the insulating layer and formed of a semiconducting layer. A first opening is formed on the second surface of the substrate. The first opening overlaps the optical waveguide in plan view.