Double Wafer Bonding for Nitride Waveguide Fabrication
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Solution Overview
Problem
The existing double wafer bonding processes for photonic devices face challenges in achieving high precision optical elements with low optical loss and improved lithography resolution, as the formation of nitride layers is constrained by the conventional CMOS front-end of line (FEOL) process integration, limiting thickness distribution and optical properties.
Innovation Solution
A double wafer bonding process is employed where high precision optical elements, such as nitride layers, are formed in a separate wafer from the active surface layer, allowing for improved thickness distribution, low optical loss, and greater lithography resolution, and additional backend features like through silicon via and electrical circuitry can be added post-bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If nitride layers are formed during conventional CMOS FEOL process integration, then the optical elements can be integrated with the active surface layer, but the thickness distribution and optical properties are limited
Solution Approach 1:
The patent divides the fabrication process into two separate wafer bonding steps: first bonding the nitride layer wafer to the active surface layer wafer, then bonding the carrier wafer to the combined structure. This segmentation allows the nitride layer to be formed independently with optimized thickness distribution before integration, resolving the contradiction between manufacturing precision and process integration constraints.
Solution Approach 2:
The nitride layer is formed on a separate wafer before bonding to the active surface layer. This preliminary action allows the nitride layer to be fabricated with optimized thickness and optical properties using dedicated processes, rather than being constrained by the CMOS FEOL process integration timeline.
2Measurement precision
If high precision optical elements are formed in a separate wafer, then lithography resolution and optical loss are improved, but the fabrication process complexity increases
Solution Approach 1:
The patent segments the fabrication into independent wafer preparations followed by bonding steps. The high precision optical elements are formed on a separate wafer with dedicated lithography processes, achieving improved resolution without constraining the active surface layer fabrication. The separate wafer approach allows each component to be optimized independently.
3Reliability
If double wafer bonding is performed, then optical coupling between devices and elements is achieved, but the process steps increase
Solution Approach 1:
The nitride layer wafer is prepared with pre-formed optical elements before bonding to the active surface layer. This preliminary preparation allows the optical coupling interface to be established with high precision in a single bonding step, rather than requiring multiple alignment and bonding operations, thus maintaining productivity while achieving reliable optical coupling.
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 formation of high precision optical elements with enhanced optical power capacity and reduced thermal dependence, improving the overall performance and design of photonic devices by decoupling the fabrication processes of the optical device and the optical element.
Implementation Method 1
wafer bonding the first and second wafers to form a combined wafer
Implementation Method 2
a third wafer comprising a substrate on a first side and an insulative material on a second side where the second side of the third wafer is wafer bonded to the second wafer
Data Source
AI summary
Embodiments herein describe using a double wafer bonding process to form a photonic device. In one embodiment, during the bonding process, an optical element (e.g., a high precision optical element) is optically coupled to an optical device in an active surface layer. In one example, the optical element comprises a nitride layer which can be patterned to form a nitride waveguide, passive optical multiplexer or demultiplexer, or an optical coupler.