Silicon Nitride Waveguide Integration With Ge Photodiode
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Solution Overview
Problem
The current system faces challenges in monolithically integrating a germanium photodiode and a silicon nitride optical waveguide on the same substrate due to the thin core thickness of the silicon nitride waveguide, which results in difficulties in thickness control and increased waveguide loss when using silicon nitride without oxygen, making it hard to achieve satisfactory optical waveguide properties with reproducibility.
Innovation Solution
A method involving the formation of a silicon nitride core using an ECR plasma CVD method with SiD4 and N2 gases, where a silicon oxide layer is used as a selective growth mask to grow germanium, allowing for the integration of a germanium photodiode and silicon nitride optical waveguide on a silicon substrate, ensuring optical connection and minimizing waveguide loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride core with thickness of 0.4 to 0.6 μm is used to achieve single-mode operation, then the optical waveguide can operate in single-mode, but it becomes difficult to control the thickness with sufficient margin and reproducibility
Solution Approach 1:
A silicon oxide layer is introduced as an intermediary between the silicon substrate and the silicon nitride core. This intermediary layer serves as a buffer that compensates for thickness variations, allowing the silicon nitride core to maintain its thin dimension for single-mode operation while providing sufficient manufacturing margin through the oxide layer thickness control.
Solution Approach 2:
The patent changes the material composition parameter by using silicon oxide (with oxygen) instead of pure silicon nitride. This parameter change increases the refractive index contrast and allows for better thickness control margin while maintaining single-mode operation characteristics.
2Volume of moving object
If pure silicon nitride is used as the core material, then the waveguide size can be reduced, but Ge adheres to the exposed portion during selective growth, increasing waveguide loss
Solution Approach 1:
The silicon oxide layer acts as a protective intermediary between the Ge growth process and the silicon nitride core. During selective Ge growth, the oxide layer prevents Ge adhesion to the core, and subsequent removal of the oxide layer does not leave Ge residues on the core, thereby maintaining low waveguide loss.
Solution Approach 2:
The silicon oxide layer is formed preliminarily before the Ge selective growth process. This preliminary protective layer prevents Ge adhesion issues during the growth process, solving the problem before it occurs.
3Volume of moving object
If the core thickness is reduced to 0.4 to 0.6 μm for single-mode operation, then the optical module size can be reduced, but the step difference due to the Si core on the lower side cannot be ignored, degrading waveguide properties
Solution Approach 1:
The silicon oxide layer serves as a leveling intermediary that fills and compensates for the step difference created by the thin silicon nitride core and the underlying silicon core. This intermediary structure provides a flat reference plane for subsequent layer formation, maintaining waveguide properties despite the reduced core thickness.
Solution Approach 2:
The patent addresses the step difference problem by introducing a solution in the vertical dimension - using the oxide layer thickness to compensate for the height variation caused by the thin core, rather than trying to eliminate the step difference in the horizontal plane.
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 enables the monolithic integration of a germanium photodiode and silicon nitride optical waveguide, achieving low loss and high performance in communication wavelength bands, facilitating the development of small-sized, high-performance optical modules.
Implementation Method 1
a silicon nitride layer including silicon nitride is formed on the first silicon oxide layer
Implementation Method 2
a selective growth mask is formed thereon, Ge is caused to selectively grow in this state
Data Source
AI summary
A silicon nitride core is formed on a silicon core via a first silicon oxide layer, and a germanium pattern caused to selectively grow in an opening penetrating through a second silicon oxide layer formed on the silicon nitride core and the first silicon oxide layer is formed on a lower silicon pattern formed to be continuous with the silicon core, thereby constituting a Ge photodiode.