GaN LED Singulation via Laser Trenching and Selective Chemical Etching
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Solution Overview
Problem
Conventional methods for singulating dice from a wafer, such as saw dicing and laser cutting, often result in edge defects, micro-cracks, and residue that can impair the operation of optical semiconductor devices like light emitting diodes (LEDs).
Innovation Solution
A method involving the formation of trenches on a substrate using a coherent laser beam, followed by the selective removal of slag material with chemical solutions like potassium hydroxide, potassium ferricyanide, or hydrochloric acid, to enhance the singulation process without altering the trench shape significantly, thereby improving the efficiency and light output of LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If laser cutting is used to form trenches in the wafer, then edge defects and micro-cracks are avoided, but residue is left on the die that impairs optical semiconductor device operation
Solution Approach 1:
The singulation process is divided into two distinct stages: laser cutting to create trenches without complete penetration, followed by a separate chemical etching process. This segmentation allows each process to optimize for its specific function - laser for precise trench formation with minimal mechanical damage, and chemical etching for residue removal without mechanical contact.
Solution Approach 2:
A chemical etching solution acts as an intermediary substance to remove the residue generated by laser cutting. The chemical solution selectively dissolves the residue material without significantly affecting the trench structure or the die itself, thereby eliminating the harmful residue while preserving the benefits of laser cutting.
2Productivity
If conventional cleaving process is used to complete singulation, then die separation is achieved, but residue remains that is problematic for optical semiconductor devices
Solution Approach 1:
The conventional mechanical cleaving process is replaced or supplemented with a chemical etching process. Instead of using mechanical force to separate the die and potentially leave residue, a chemical solution is used to selectively remove material and residue, achieving complete singulation with superior surface quality for optical devices.
3Productivity
If saw dicing is used for singulating dice, then die separation is achieved, but edge defects and micro-cracks are generated
Solution Approach 1:
The mechanical saw dicing process is replaced with a laser-based approach followed by chemical etching. The laser creates precise trenches without mechanical contact, and the chemical etching completes the separation without the vibration and particulate contamination associated with mechanical sawing, thereby eliminating edge defects and micro-cracks.
Solution Approach 2:
The laser cutting process utilizes phase transitions (vaporization/ablation) to remove material and form trenches without mechanical contact. This phase change-based material removal avoids the mechanical stresses and vibrations that cause edge defects and micro-cracks in conventional saw dicing.
4Illumination intensity
If chemical solution is used to remove slag, then light output and efficiency are enhanced, but trench shape may be altered
Solution Approach 1:
The concentration, temperature, and composition of the chemical etching solution are carefully controlled and optimized to achieve selective removal of slag material while minimizing etching of the trench walls. By adjusting these parameters, the process enhances light output through slag removal while maintaining trench shape integrity within acceptable tolerances.
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 method achieves a substantial increase in light output and efficiency, with over 100% improvement in lumens per Watt output and maintains the trench shape to within 98% of its original form, ensuring high brightness and performance of the LEDs.
Implementation Method 1
forming trenches by scanning a coherent beam of energy in a repetitive manner to respective portions of the surface. The scanned coherent beam, preferably derived from a laser, causes ablation of selected materials of the surface.
Implementation Method 2
The method also subjects the trenches and the slag to a chemical solution to selectively remove the slag without significantly changing the cross-section of the trenches. The chemical is preferably a potassium hydroxide solution, a potassium ferricyanide solution, or a hydrochloric acid solution
Data Source
AI summary
A method of fabricating LED devices includes using a laser to form trenches between the LEDs and then using a chemical solution to remove slag creating by the laser.