Laser Lift-Off Overlap Pulsing for Crack-Reduced GaN Separation
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Solution Overview
Problem
Laser lift off techniques for separating GaN layers from sapphire substrates in LED manufacturing face challenges such as low productivity due to high residual stresses and localized issues like cracking and uneven material removal, which affect the yield and quality of the resulting devices.
Innovation Solution
The implementation of a laser lift off system that overlaps irradiation zones with multiple pulses of laser irradiation per location using a non-homogeneous laser beam with a smooth spatial distribution of energy, allowing for stepwise relative movement between the laser beam and the workpiece to achieve self-homogenization and minimize stress during the separation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher laser exposure is applied in certain areas to ensure complete separation, then separation effectiveness is improved, but material removal increases and pressure rises causing epi cracking and device degradation
Solution Approach 1:
The patent applies local quality by using a non-homogeneous laser beam with a smooth spatial distribution of energy across the beam profile. Different regions of the beam deliver different energy densities, with the central region providing higher exposure for complete separation while the peripheral regions provide lower exposure to avoid excessive material removal and pressure buildup that causes cracking. This spatial variation in energy distribution allows simultaneous achievement of effective separation and crack prevention in different areas of the irradiation zone.
Solution Approach 2:
The patent changes the energy distribution parameter of the laser beam from homogeneous to non-homogeneous with a smooth spatial distribution. This parameter change allows the system to deliver varying energy densities across different regions of the workpiece, optimizing both separation effectiveness in high-energy regions and crack prevention in low-energy regions, thereby resolving the contradiction between complete separation and avoiding epi cracking.
2Ease of manufacture
If uniform laser exposure is applied across the workpiece, then manufacturing simplicity is maintained, but localized high exposures cause uneven material removal and cracking
Solution Approach 1:
The patent implements local quality through a non-homogeneous laser beam with smooth spatial energy distribution, where the central region delivers higher energy for complete separation and peripheral regions deliver lower energy to prevent excessive material removal. This creates a gradient energy distribution that naturally compensates for localized variations in material properties and thickness, achieving uniform material removal without complex process adjustments.
Solution Approach 2:
The non-homogeneous beam profile with smooth spatial energy distribution provides self-homogenization across the workpiece. The varying energy densities automatically compensate for local variations in material absorption and thickness, with higher energy regions ensuring complete separation and lower energy regions preventing over-processing, thereby achieving uniform results without external intervention or complex control systems.
3Reliability
If multiple pulses of laser irradiation are applied per location, then separation quality is improved by minimizing stress, but processing time increases
Solution Approach 1:
The patent applies periodic action by using multiple pulsed laser irradiations at each location rather than a single continuous exposure. The pulsed delivery allows stress to dissipate between pulses, preventing cumulative stress buildup that causes cracking. The non-homogeneous beam profile ensures each pulse delivers optimized energy distribution, and the repeated pulsing gradually achieves complete separation while maintaining material integrity, balancing separation quality with acceptable processing time.
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 effectively separates layers while minimizing cracking and stress, thereby improving the yield and quality of semiconductor devices by ensuring consistent exposure and reducing the impact of localized high exposures.
Implementation Method 1
generating pulses of laser irradiation by a non-homogenous laser beam with a smooth spatial distribution of energy
Implementation Method 2
The multiple pulses of laser irradiation from the non-homogeneous beam may irradiate the overlapping irradiation zones
Implementation Method 3
The pulses of laser irradiation may be sufficient to separate the layers of material
Data Source
AI summary
Laser lift off systems and methods overlap irradiation zones to provide multiple pulses of laser irradiation per location at the interface between layers of material to be separated. To overlap irradiation zones, the laser lift off systems and methods provide stepwise relative movement between a pulsed laser beam and a workpiece. The laser irradiation may be provided by a non-homogeneous laser beam with a smooth spatial distribution of energy across the beam profile. The pulses of laser irradiation from the non-homogenous beam may irradiate the overlapping irradiation zones such that each of the locations at the interface is exposed to different portions of the non-homogeneous beam for each of the multiple pulses of the laser irradiation, thereby resulting in self-homogenization. Thus, the number of the multiple pulses of laser irradiation per location is generally sufficient to provide the self-homogenization and to separate the layers of material.