GaN LED Wafer Bonding for Thermal Management
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Solution Overview
Problem
Traditional methods for manufacturing GaN LED devices using sapphire substrates suffer from low thermal conductivity, leading to reliability issues such as bending or peeling due to differences in thermal expansion coefficients between the substrate and semiconductor materials.
Innovation Solution
The method employs aligned wafer bonding technology to bond a provisional sapphire substrate with a permanent substrate having better thermal conductivity, forming metal pattern areas on both substrates before bonding, which allows for efficient heat dissipation and prevents peeling during the cutting process of LED devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire substrate is used for GaN LED manufacturing, then the LED can be grown steadily on the substrate, but the thermal conductivity is low causing reliability issues
Solution Approach 1:
The manufacturing process is segmented into two phases: growth phase using sapphire substrate and operation phase using metallic substrate. The LED epitaxial layer is first grown on sapphire, then transferred to metallic substrate through aligned wafer bonding, separating the growth function from the heat dissipation function.
Solution Approach 2:
Sapphire substrate serves as an intermediary medium that enables GaN growth but is later removed. The metallic substrate acts as a permanent intermediary for heat dissipation. Aligned wafer bonding technology serves as the intermediary process enabling the transfer from temporary to permanent substrate.
2Temperature
If metallic permanent substrate is formed by electroplating to improve thermal conductivity, then heat dissipation improves, but the difference in thermal expansion coefficient causes bending or peeling
Solution Approach 1:
The bonding process parameters are precisely controlled including temperature (80-150°C), pressure (1-10 atm), and time to achieve optimal bonding without causing deformation. The metal layer thickness (1-10 μm) is optimized to provide sufficient bonding strength while minimizing thermal expansion stress.
Solution Approach 2:
A composite structure is created with multiple layers: LED epitaxial layer, metal layer (Al, Cu, or alloy), and metallic substrate. This composite structure is designed to balance thermal conductivity, mechanical strength, and thermal expansion compatibility, preventing peeling while maintaining heat dissipation performance.
3Reliability
If aligned wafer bonding is used to bond provisional and permanent substrates, then thermal conductivity improves without peeling, but the manufacturing process complexity increases
Solution Approach 1:
Metal layers and bonding layers are pre-formed on both provisional and permanent substrates before bonding. Alignment marks are pre-defined to guide the bonding process. This preliminary preparation simplifies the actual bonding operation and ensures high precision alignment without requiring complex real-time adjustment systems.
4Strength
If metal layers are formed on both substrates before bonding, then bonding strength improves, but the manufacturing steps increase
Solution Approach 1:
The formation of metal layers, bonding layers, and alignment marks are merged into a single integrated process step performed on both substrates simultaneously using sputtering or evaporation. This combining of operations reduces the total number of separate manufacturing steps while achieving multiple functions: structural support, thermal conduction, and bonding capability.
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 enhances the thermal conductivity and reliability of GaN LED devices by minimizing stress and damage during the cutting process, ensuring effective heat dissipation and preventing peeling, while maintaining the structural integrity of the LED devices.
Implementation Method 1
the provisional substrate and the permanent substrate are bonded together by aligned wafer bonding method
Data Source
AI summary
A method for manufacturing GaN LED devices is disclosed herein. First, a LED epitaxial layer is formed on a provisional substrate. Part of the LED epitaxial layer is removed to form a plurality of LED epitaxial areas. Then, a first transparent conductive layer, a metal reflective layer, and a first metal bonding layer are sequentially formed on the plurality of LED epitaxial areas and then part of the first transparent conductive layer, the metal reflective layer, and the first metal bonding layer are removed. Next, a permanent substrate is provided. At least a metal layer and a second metal bonding layer are formed on the permanent substrate. Then, part of at least the metal layer and the second metal bonding layer are removed. Next, the provisional substrate is bonded to the permanent substrate by aligned wafer bonding method. Then, the provisional substrate is removed to expose a surface of the LED epitaxial layer and then an n-type electrode is formed on the surface. Next, the permanent substrate is cut to form a plurality of LED devices.