Vertical GaN LED Microwave-Assisted Wafer Bonding
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Solution Overview
Problem
The existing manufacturing processes for vertical structure GaN LEDs face challenges such as stress, defects, and reduced yield due to high temperature and pressure requirements in wafer bonding, which lead to substrate bending and crystal defects, and limit the improvement of ohmic characteristics of the n-side electrode.
Innovation Solution
A method involving microwave-assisted bonding at low temperatures (200°C or less) using a metal bonding layer with a high melting point or eutectic metals, where microwaves are applied to partially heat the bonding interface while bringing the metal bonding layers into contact, reducing thermal stress and enabling improved ohmic characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional wafer bonding is performed at high temperature and pressure, then bonding strength is achieved, but substrate bending and crystal defects occur
Solution Approach 1:
The patent replaces conventional thermal-pressure bonding (mechanical/thermal system) with microwave-assisted bonding (electromagnetic field system). Microwaves directly heat the metal bonding layer at the bonding interface, achieving strong bonding without requiring high overall temperature and pressure, thus preventing substrate bending and crystal defects while maintaining bonding strength.
Solution Approach 2:
The patent changes the bonding parameters by using microwave radiation to selectively heat the metal bonding layer to its melting point while keeping the overall process temperature low (200°C or less). This parameter change allows bonding to occur without the high temperature and pressure conditions that cause substrate deformation and defects.
2Reliability
If high temperature bonding is used, then bonding is achieved, but ohmic characteristics of n-side electrode cannot be improved
Solution Approach 1:
The patent segments the heating process by using microwaves to selectively heat only the metal bonding layer at the bonding interface, while keeping the n-type semiconductor layer and electrode contact area at low temperature (200°C or less). This segmented heating allows bonding to proceed without degrading the ohmic characteristics of the n-side electrode contact.
3Temperature
If low melting point eutectic metals are used for bonding, then bonding temperature is reduced, but bonding strength and reliability decrease
Solution Approach 1:
The patent uses microwave energy to directly heat the metal bonding layer to its melting point, replacing the need for high overall temperature processing. This allows the use of low melting point eutectic metals (such as Au-Sn, Au-In, Pd-In with melting points ≤330°C) while still achieving strong bonding, because the microwaves concentrate energy at the bonding interface rather than heating the entire substrate.
4Reliability
If conventional thermal bonding is used, then bonding is achieved, but process time is long and yield is reduced
Solution Approach 1:
The patent replaces slow thermal diffusion heating with rapid microwave heating, which directly energizes the metal bonding layer at the bonding interface. This electromagnetic field-based heating method significantly reduces process time and enables low temperature bonding (200°C or less), thereby increasing production efficiency and yield while maintaining bonding reliability.
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 significantly reduces defects and cracks, enhances ohmic characteristics, and increases the process yield by allowing the use of materials with high thermal expansion coefficients, while maintaining a low process temperature and shortening the bonding time.
Implementation Method 1
bonding a conductive substrate includes partially heating a metal bonding layer by applying microwaves to a bonding interface while bringing the metal bonding layer into contact with the bonding interface
Data Source
AI summary
A method of manufacturing a vertical structure light emitting diode device, the method including: sequentially forming a first conductivity type III-V group compound semiconductor layer, an active layer, and a second conductivity type III-V group compound semiconductor layer on a substrate for growth; bonding a conductive substrate to the second conductivity type III-V group compound semiconductor layer; removing the substrate for growth from the first conductivity type III-V group compound semiconductor layer; and forming an electrode on an exposed portion of the first conductive III-V group compound semiconductor layer due to the removing the substrate for growth, wherein the bonding a conductive substrate comprises partially heating a metal bonding layer by applying microwaves to a bonding interface while bringing the metal bonding layer into contact with the bonding interface.