Silicon Photonics Wafer Substrate Removal for Low-Loss Waveguides
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Solution Overview
Problem
Standard silicon-on-insulator processes face challenges in fabricating silicon photonics wafers due to high light transmission loss caused by the high-optical refractive index of the silicon substrate, which is not compatible with low-loss silicon optical waveguide structures, and require custom thick buried oxide layers that increase complexity and cost.
Innovation Solution
The method involves removing the high-optical refractive index silicon substrate from the silicon photonics wafer after fabrication, allowing the use of standard thin buried oxide layers and enabling low-loss silicon optical waveguide structures by flip chip bonding the active silicon photonics layer to an electrical CMOS wafer, and optionally adding a low-optical refractive index backing wafer to the exposed buried oxide layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a silicon substrate is used in standard silicon-on-insulator processes, then the wafer structure is simple and manufacturing is easier, but high light transmission loss occurs due to the high-optical refractive index of the silicon substrate
Solution Approach 1:
The patent extracts and removes the silicon substrate from the wafer structure after the active silicon photonics layer and thin buried oxide layer are fabricated. This extraction eliminates the harmful high-optical refractive index silicon substrate that causes light transmission loss, while preserving the beneficial thin buried oxide layer structure that enables low-loss optical waveguide operation.
Solution Approach 2:
The patent segments the wafer into separate functional layers: the active silicon photonics layer containing optical waveguides, a thin buried oxide layer for optical isolation, and removes the silicon substrate. This segmentation allows each layer to perform its optimal function without the interference of the high-index silicon substrate.
2Loss of energy
If custom thick buried oxide layers are used to reduce light transmission loss, then optical performance improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the thickness parameter of the buried oxide layer from thick (custom) to thin (standard), achieving low-loss optical waveguide operation with a thin buried oxide layer of 2-10 micrometers. This parameter change simplifies the manufacturing process while maintaining optimal optical performance.
Solution Approach 2:
The thin buried oxide layer serves multiple functions: it provides optical isolation between the active silicon photonics layer and the substrate, enables low-loss optical waveguide operation, and is compatible with standard silicon-on-insulator manufacturing processes. This multi-functionality eliminates the need for custom thick buried oxide layers.
3Reliability
If custom thick buried oxide layers are fabricated, then optical waveguide performance improves, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent performs preliminary fabrication of the active silicon photonics layer and thin buried oxide layer using standard silicon-on-insulator processes before removing the silicon substrate. This preliminary action allows the use of well-established, cost-effective manufacturing processes while achieving the desired optical performance.
Solution Approach 2:
The silicon substrate is treated as a disposable temporary support structure that is removed after serving its purpose during fabrication. This allows the use of standard, inexpensive silicon substrate manufacturing processes while achieving the final low-loss optical waveguide structure without the substrate.
4Device complexity
If standard thin buried oxide layers are used, then manufacturing complexity is reduced, but high light transmission loss occurs due to the silicon substrate
Solution Approach 1:
The patent extracts and removes the harmful silicon substrate that causes high light transmission loss when used with thin buried oxide layers. This extraction allows the use of simple, standard thin buried oxide layers while eliminating the optical loss problem that would otherwise occur.
Solution Approach 2:
The thin buried oxide layer acts as an intermediary between the active silicon photonics layer and the removed silicon substrate, providing optical isolation and enabling low-loss waveguide operation. This intermediary layer allows the use of standard thin oxide processes while achieving optimal optical performance.
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 functionality of low-loss silicon optical waveguide structures using standard silicon-on-insulator processes, reducing complexity and cost by eliminating the need for custom thick buried oxide layers and avoiding issues like wafer bowing, while allowing for standard CMOS processing and integration with low-optical refractive index materials.
Implementation Method 1
light at the silicon-silica interface undergoes internal reflection and, therefore, remains in the silicon photonic components
Implementation Method 2
A low-optical refractive index backing wafer is then added to the exposed backside surface of the thin buried oxide layer
Data Source
AI summary
Processing for a silicon photonics wafer is provided. A silicon photonics wafer that includes an active silicon photonics layer, a thin buried oxide layer, and a silicon substrate is received. The thin buried oxide layer is located between the active silicon photonics layer and the silicon substrate. An electrical CMOS wafer that includes an active electrical layer is also received. The active silicon photonics layer of the silicon photonics wafer is flip chip bonded to the active electrical layer of the electrical CMOS wafer. The silicon substrate is removed exposing a backside surface of the thin buried oxide layer. A low-optical refractive index backing wafer is added to the exposed backside surface of the thin buried oxide layer. The low-optical refractive index backing wafer is a glass substrate or silicon substrate wafer. The silicon substrate wafer includes a thick oxide layer that is attached to the thin buried oxide layer.