SOI Device Layer Transfer to High-Thermal-Conductivity Substrates
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Solution Overview
Problem
Current methods for manufacturing substrates with high thermal conductivity face challenges such as metal impurity diffusion, inefficient heat dissipation, and high-frequency loss, particularly in silicon-on-insulator (SOI) wafers, which require high-temperature processes and are expensive, and existing thinning techniques leave machining marks and are not suitable for high-frequency applications.
Innovation Solution
A method involving the transfer of a device layer from an SOI wafer to a high-thermal-conductivity transfer substrate using a temporary bonding adhesive, followed by thermal curing and peeling, which allows for the removal of the silicon layer without inverting the device layer, utilizing a low-stress adhesive with acid resistance to prevent peeling and maintain high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a sapphire substrate is used for high thermal conductivity and low high-frequency loss, then thermal conductivity and high-frequency performance are improved, but the substrate becomes transparent to visible light making it unresponsive to photosensors and expensive for large diameters
Solution Approach 1:
The patent introduces a temporary bonding adhesive as an intermediary layer between the silicon layer and the sapphire substrate. This adhesive layer enables the transfer process while allowing the final device to use an opaque ceramic substrate instead of transparent sapphire, thus maintaining high-frequency performance while improving manufacturability and photosensor compatibility
Solution Approach 2:
The patent creates a copy of the device structure by transferring the silicon device layer onto a different substrate type. The device layer is separated from its original silicon substrate and replicated onto a ceramic substrate, allowing the functional device to be preserved while changing the substrate properties for better manufacturability
2Loss of energy
If ceramic sintered bodies are used as substrates, then thermal conductivity is improved and they are inexpensive and opaque, but metal impurities from the sintering process diffuse during manufacturing causing contamination and device characteristic degradation
Solution Approach 1:
The patent performs the device fabrication and layer stacking on a silicon substrate first, before transferring to the ceramic substrate. This preliminary action on the silicon substrate avoids exposure to high temperatures that would cause metal impurity diffusion from the ceramic sintered body, thus preventing contamination while still benefiting from the ceramic substrate's thermal conductivity
Solution Approach 2:
The temporary bonding adhesive acts as an intermediary that enables the transfer of the device layer from the silicon substrate to the ceramic substrate without requiring high-temperature processing on the ceramic substrate itself, thus preventing metal impurity diffusion while achieving the thermal conductivity benefits
3Temperature
If the silicon back surface is thinned to improve heat dissipation, then heat dissipation efficiency is improved, but the device region acts as heat pools and efficiency remains unfavorable
Solution Approach 1:
The patent extracts the device layer from the thick silicon substrate and transfers it to a thin ceramic substrate. This extraction removes the heat pool regions (the bulk silicon) while preserving the device region, allowing for efficient heat dissipation through the highly thermal conductive ceramic substrate without the detrimental heat pooling effects of thick silicon
4Ease of manufacture
If SiO2 insulating layer is used in SOI wafers, then device fabrication is enabled, but the low thermal conductivity of SiO2 prevents efficient heat dissipation
Solution Approach 1:
The patent creates a composite structure where the silicon device layer with SiO2 insulating layer is combined with a ceramic substrate having high thermal conductivity. This composite material approach maintains the device fabrication capabilities provided by SiO2 while compensating for its low thermal conductivity through the high thermal conductivity ceramic substrate
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 method enables efficient heat dissipation, reduces high-frequency loss, and prevents metal impurity diffusion, resulting in a substrate with improved thermal conductivity and manufacturing efficiency without the need for high-temperature processes.
Implementation Method 1
a step of temporarily bonding a surface on which the device layer is formed of the SOI wafer to a supporting substrate using an adhesive for temporary bonding
Implementation Method 2
bonding the insulator layer in the thinned device wafer to the transfer substrate via the adhesive for transfer
Implementation Method 3
a step of thermally curing the adhesive for transfer under a load at the same time as or after bonding
Data Source
AI summary
A highly thermal conductive substrate formed by bonding a device layer formed on a silicon on insulator (SOI) wafer and a buried oxide film to an insulator substrate having a thermal conductivity of 40 W/m·K or more via a low-stress adhesive, wherein a thickness of the buried oxide film is 50 to 500 nm and a thickness of the adhesive is 0.1 to 10 μm.