Sapphire Substrate Shearing After Laser Lift-Off Adhesion
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Solution Overview
Problem
The challenge in removing sapphire substrates from GaN interfaces during laser lift-off processes is that the sapphire can melt and adhere to the GaN interface, preventing complete separation and leading to discarded wafers or dies.
Innovation Solution
A shearing device with a movable shearing blade, mounted on a stage with carrier holders, applies a force to the sapphire substrate to separate it from the LED device, utilizing a hard material like tungsten carbide or diamond-coated blades to overcome adhesion, and a vacuum suction system collects the removed substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single shot laser beam is used for lift-off, then the process is simple and fast, but the sapphire substrate may melt and adhere to the GaN interface, preventing complete removal
Solution Approach 1:
The laser lift-off process is divided into multiple sequential shots rather than a single shot. The first shot creates initial separation and heating, while subsequent shots complete the removal. This segmentation allows controlled heating that prevents sapphire melting while ensuring complete GaN interface decomposition and substrate release.
Solution Approach 2:
The laser applies periodic pulsed action with specific timing between shots. The first laser shot is followed by a second shot after a controlled time interval, allowing thermal management that prevents sapphire substrate melting while ensuring complete removal of the GaN interface layer and adhesive.
2Strength
If high energy laser is used to decompose GaN, then separation is achieved, but sapphire substrate melts and forms alumina that sticks to GaN and sapphire surfaces
Solution Approach 1:
The first laser shot performs preliminary decomposition of the GaN interface layer and heating of the adhesive before the second shot. This preliminary action weakens the bonding and prepares the interface for complete separation, reducing the need for excessive energy in subsequent shots that would cause sapphire melting and alumina formation.
Solution Approach 2:
The laser energy parameters are changed between shots - the first shot uses specific energy levels for initial decomposition, while the second shot uses adjusted parameters to complete removal without overheating the sapphire substrate. This parameter control prevents alumina adhesion while ensuring complete separation.
3Device complexity
If manual or simple removal methods are used, then equipment complexity is low, but manufacturing yield is reduced due to discarded wafers
Solution Approach 1:
The system incorporates feedback control through a controller that manages the timing and parameters of multiple laser shots based on process conditions. This feedback mechanism ensures optimal energy delivery for complete substrate removal while preventing defects, thereby increasing manufacturing yield without requiring complex mechanical removal equipment.
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
Effectively completes the removal of sapphire substrates that were not fully detached by laser lift-off, reducing waste and increasing manufacturing yield by ensuring complete substrate separation.
Implementation Method 1
The laser source 102 generates a laser beam that is directed towards and passes through the sapphire substrate 104 and is absorbed by the GaN interface 106 at high temperatures
Implementation Method 2
Thermal decomposition of the GaN interface 106 occurs when high energy from the laser source 102 induces local heating on the GaN interface 106 above the critical sublimation temperature of gallium (Ga)
Implementation Method 3
Thermal decomposition of the GaN interface 106 occurs when high energy from the laser source 102 induces local heating on the GaN interface 106 above the critical sublimation temperature of gallium (Ga)
Implementation Method 4
Removal of the sapphire substrate 104 occurs via the instantaneous N2 vaporization pressure generated, which lifts the sapphire substrate 104 from the GaN interface 106
Implementation Method 5
the sapphire substrate 104 melts and forms one or more forms of alumina (aluminum oxide)
Implementation Method 6
These different forms of alumina form at high temperature due to partial transmission and reflection amplitudes when the laser moves from a low (sapphire) to high (GaN) refractive index medium, causing rapid cooling
Implementation Method 7
a vacuum suction device is provided in fluid communication with the stage
Data Source
AI summary
A light emitting diode (LED) device sapphire substrate removal apparatus and method are disclosed. The apparatus and method includes placing the LED device comprising a sapphire substrate and a carrier onto stage sized and shaped to hold the carrier of the LED device and applying a force with a shearing blade to the sapphire substrate to separate the sapphire substrate from the carrier. The apparatus include the stage and a sapphire substrate shearing device.