GaP Window Layer Thickness for Crack-Resistant Micro-LED Lift-Off
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Solution Overview
Problem
The manufacturing of bonded wafers for AlGaInP-based micro-LEDs faces challenges due to the low mechanical strength of these LEDs, leading to cracking during the laser lift-off (LLO) process, which results in a decreased yield.
Innovation Solution
A method involving epitaxial growth of AlGaInP-based layers on a GaAs substrate, followed by the growth of a GaP window layer, bonding this layer to a transparent substrate via a thermosetting bonding member, and performing laser lift-off to isolate micro-LED devices. The GaP window layer is crucial, with a thickness of 6 µm or more to prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser lift-off treatment is performed on AlGaInP-based micro-LEDs with conventional thin window layers, then the LLO process can be completed, but the micro-LED devices crack and yield decreases
Solution Approach 1:
The patent changes the thickness parameter of the GaP window layer from conventional thin layers (typically 1-2 µm) to a thicker layer of 6 µm or more. This parameter change provides sufficient mechanical strength to prevent cracking during LLO while maintaining the laser lift-off functionality, thereby resolving the contradiction between yield improvement and mechanical strength requirements
Solution Approach 2:
The thick GaP window layer acts as a cushioning layer that absorbs and distributes the mechanical stress generated during the laser lift-off process. By providing this protective cushion beforehand, the micro-LED devices are prevented from cracking, thus improving yield without compromising the LLO process
2Reliability
If the GaP window layer thickness is increased to 6 µm or more, then cracking during LLO is prevented, but the manufacturing process complexity increases
Solution Approach 1:
The patent modifies the window layer thickness parameter to 6 µm or more, which fundamentally changes the mechanical properties of the structure. This single parameter change provides inherent crack prevention during LLO, achieving reliability improvement without requiring additional complex manufacturing steps or process modifications
3Adaptability or versatility
If AlGaInP-based LEDs are used instead of GaN-based LEDs, then different material properties are achieved, but the mechanical strength is lower causing cracking during transfer
Solution Approach 1:
The patent creates a composite structure where the AlGaInP-based micro-LED is combined with a thick GaP window layer. This composite structure leverages the superior mechanical strength of the GaP window layer to protect the more fragile AlGaInP micro-LED during the laser lift-off process, enabling the use of AlGaInP materials while preventing cracking through the reinforcing composite design
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 effectively improves the yield of micro-LED devices by preventing cracking during the LLO process, even for devices with small dimensions, by ensuring the GaP window layer has sufficient thickness.
Implementation Method 1
The GaP window layer has a thickness of 6 µm or more, which provides sufficient mechanical support to prevent cracking of the micro-LED device during the laser lift-off process
Implementation Method 2
bonding the GaP window layer to a transparent substrate via a thermosetting bonding member
Implementation Method 3
irradiating a laser from the transparent substrate side and sublimating the thermosetting bonding member through laser lift-off treatment
Implementation Method 4
sublimating the thermosetting bonding member in contact with the transparent substrate through laser lift-off treatment
Implementation Method 5
epitaxially growing an AlGaInP-based first cladding layer, an AlGaInP-based non-doped active layer, and an AlGaInP-based second cladding layer on a GaAs substrate
Data Source
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AI summary
The present invention is a method for manufacturing a bonded wafer for a micro-LED, the method includes the steps of epitaxially growing an AlGaInP-based first cladding layer, non-doped active layer, and second cladding layer on a GaAs substrate to form an epitaxial layer, growing a GaP window layer on the second cladding layer, bonding the GaP window layer to a transparent substrate via a thermosetting bonding member, separating the GaAs substrate, isolating the epitaxial layer into micro-LED devices, exposing the second cladding layer or the GaP window layer of the micro-LED device, forming electrodes, adhering the electrodes to a transfer substrate, and irradiating a laser from the transparent substrate side to isolate the micro-LED device from the transparent substrate, in which the GaP window layer has a thickness of 6 µm or more. This provides a method for manufacturing a bonded wafer for an AlGaInP-based micro-LED which improves a yield decrease caused by a crack in a micro-LED device during a LLO step.