SOI Substrate Transfer Bonding for Heat Dissipation and Low RF Loss
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Solution Overview
Problem
Current semiconductor device substrates face challenges with heat dissipation and high-frequency loss due to low thermal conductivity and the risk of metal impurity diffusion during high-temperature processing, as well as separation issues during thinning processes.
Innovation Solution
A device substrate with a buried oxide film layer (Box layer) of higher thermal conductivity than SiO2, formed on a ceramic or single-crystal substrate, is bonded to a transfer substrate using a heat-resistant adhesive, allowing for efficient heat dissipation and minimal frequency loss without requiring high-temperature processing, and enabling separation of the support substrate without device layer separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a SiO2 insulating layer is used in SOI substrates, then electrical insulation is achieved, but thermal conductivity decreases to 1.38 W/m·K causing heat dissipation problems
Solution Approach 1:
The patent changes the material parameters of the insulating layer from conventional SiO2 (thermal conductivity 1.38 W/m·K) to AlN (thermal conductivity 200 W/m·K), achieving both electrical insulation and high thermal conductivity simultaneously. This parameter change resolves the contradiction by selecting a material with fundamentally different thermal properties while maintaining electrical insulation characteristics.
Solution Approach 2:
The patent creates a composite structure combining AlN insulating layer with silicon device layer and metal heat dissipation layer. This composite material approach allows the system to exhibit both electrical insulation (from AlN) and high thermal conductivity (from the composite structure with metal layers), resolving the contradiction between insulation and heat dissipation.
2Temperature
If silicon base substrate is used in SOI substrates, then heat dissipation is improved, but dielectric properties cause large loss in high frequency region
Solution Approach 1:
The patent changes the material composition of the insulating layer from SiO2 to AlN, which has fundamentally different dielectric properties. AlN exhibits lower loss tangent at high frequencies compared to SiO2, thereby reducing high frequency energy loss while maintaining the heat dissipation capability provided by the overall substrate structure.
3Reliability
If sapphire substrate is used, then electrical insulation and high frequency properties are improved, but thermal conductivity decreases to about 1/3 of silicon causing heat dissipation problems
Solution Approach 1:
The patent employs a composite structure with AlN insulating layer combined with metal heat dissipation layers (such as Cu or Al). This composite approach achieves both the electrical insulation and high frequency properties of ceramic materials while incorporating metal layers that provide superior thermal conductivity for heat dissipation, overcoming the limitation of sapphire substrates.
4Ease of manufacture
If ceramic sintered body is used as substrate, then cost is reduced, but metal impurities from sintering aid may diffuse during high temperature processing
Solution Approach 1:
The patent introduces a diffusion prevention layer as an intermediary barrier between the ceramic substrate and the silicon device layer. This intermediate layer prevents metal impurities from the ceramic substrate from diffusing into the device layer during high temperature processing, while allowing the cost-effective ceramic substrate to be used. The diffusion prevention layer acts as a protective mediator that blocks impurity migration.
Solution Approach 2:
The diffusion prevention layer serves as a sacrificial or disposable protective layer that can be removed or remains as a thin barrier. This allows the use of low-cost ceramic substrates with sintering aids while preventing impurity contamination of the device, accepting the cost and complexity of an additional layer to achieve the reliability goal.
5Temperature
If device layer is thinned to improve heat dissipation, then heat dissipation efficiency is improved, but separation from support substrate may occur
Solution Approach 1:
The patent changes the material properties of the insulating layer to AlN, which has higher mechanical strength and better thermal conductivity compared to SiO2. This allows the device layer to be thinned for improved heat dissipation while the stronger AlN layer provides sufficient mechanical support and bonding strength to prevent separation from the support 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
The solution provides a semiconductor device substrate with enhanced thermal conductivity, effective heat dissipation, and reduced frequency loss, while preventing metal impurity diffusion and maintaining the integrity of the device layer during thinning.
Implementation Method 1
a transfer substrate (40) having a higher thermal conductivity than at least SiO2 and being an electrical insulator is transfer-bonded to the opposite-side surface of the Box layer via a transfer adhesive (32)
Implementation Method 2
a device substrate with high thermal conductivity that does not require a high temperature process which causes diffusion of metal impurities, that is excellent in heat dissipation
Data Source
Figure 1A~1H
AI summary
Provided are a device substrate with high thermal conductivity, with high heat dissipation, and with a small loss at high frequencies, and a method of manufacturing the device substrate. A device substrate 1 of the present invention can be manufactured by: provisionally bonding a Si device layer side of an SOI device substrate 10 to a support substrate 20 using a provisional bonding adhesive 31, the SOI device substrate including a Si base substrate 11, a Box layer 12 formed on the Si base substrate, having high thermal conductivity, and being an electrical insulator, and a Si device layer 13 formed on the Box layer; removing the Si base substrate 11 of the provisionally bonded SOI device substrate until the Box layer is exposed, thereby obtaining a thinned device wafer 10a; transfer-bonding the Box layer side of the thinned device wafer and a transfer substrate 40 to each other using a transfer adhesive 32 having a heat-resistant temperature of at least 150°C by applying heat and pressure, the transfer substrate having high thermal conductivity and being an electrical insulator; and separating the support substrate 20.