Nitride Semiconductor Film Laser Flaw Patterning
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Solution Overview
Problem
GaN-based light-emitting diodes (LEDs) face performance limitations due to poor electrical and thermal conductivity of sapphire substrates, and ultraviolet (UV) laser lift-off (LLO) technology struggles with incomplete decomposition at chip edges and substrate separation, leading to film damage and cracking.
Innovation Solution
A method and apparatus that selectively form flaws in a pre-determined pattern within a thin film layer using a focused laser to concentrate stress, allowing for controlled fracture during a stress-inducing operation, such as LLO, without requiring photolithography and enabling arbitrary pattern formation and penetration depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If UV laser lift-off technology is used to transfer GaN LED thin films from sapphire substrate, then the crystal quality is maintained, but incomplete decomposition at chip edges occurs leading to film damage and cracking
Solution Approach 1:
The patent applies preliminary action by performing stress-inducing operations (such as heating or mechanical stress) on the thin film structure before the laser lift-off decomposition process. This pre-stressing creates controlled flaws that guide the decomposition front, ensuring complete and uniform separation from the sapphire substrate without edge-related incomplete decomposition or film damage.
Solution Approach 2:
The patent utilizes parameter changes by modifying the stress state of the thin film structure through controlled heating or mechanical loading before laser irradiation. These parameter changes induce specific flaw patterns that enhance the uniformity of laser-induced decomposition, preventing edge effects and ensuring complete film separation while maintaining crystal quality.
2Adaptability or versatility
If photolithography and wet or plasma etching are used to partition LLO regions, then the LLO regions can be patterned, but the process complexity increases and pre-etching is required
Solution Approach 1:
The patent extracts and eliminates the photolithography and etching steps from the conventional process by directly using laser-induced stress cracking to create the desired patterns. The stress-inducing operation followed by controlled decomposition achieves region partitioning without requiring photoresist coating, patterning, or chemical etching, thereby reducing process complexity while maintaining pattern flexibility.
Solution Approach 2:
The patent replaces the mechanical and chemical processes of photolithography and etching with a combined thermal-mechanical-laser process. By applying stress (thermal or mechanical) followed by selective laser decomposition, the desired patterning is achieved through physical stress-induced flaws rather than chemical etching, simplifying the overall process while enabling arbitrary pattern formation.
3Ease of manufacture
If sapphire substrate is used for GaN LED epitaxy growth, then the substrate availability is high, but the electrical and thermal conductivity is poor limiting device performance
Solution Approach 1:
The patent applies segmentation by separating the GaN thin film from the sapphire substrate through controlled laser-induced decomposition. This segmentation allows the GaN film to be transferred to alternative substrates with better electrical and thermal conductivity, while the sapphire substrate can be reused or discarded, thus resolving the contradiction between substrate availability and device performance.
Solution Approach 2:
The patent uses a sacrificial intermediate layer or stress-induced flaw pattern as a mediator between the GaN film and sapphire substrate. This intermediary structure enables controlled separation and film transfer to high-performance substrates, allowing the benefits of easy sapphire fabrication to be combined with the superior electrical and thermal properties of alternative substrates like SiC or diamond.
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 prevents stress propagation and film damage, allows for flexible partitioning of LLO regions, and eliminates the need for pre-etching, enhancing the reliability and process flexibility of substrate and film separation in GaN-based LEDs.
Implementation Method 1
Regions of a thin film structure are selectively decomposed within a thin film layer to form flaws in a pre-determined pattern
Implementation Method 2
The flaws locally concentrate stress in the pre-determined pattern during a stress-inducing operation
Implementation Method 3
The flaws locally concentrate stress in the pre-determined pattern during a stress-inducing operation. The stress-inducing operation causes the thin film layer to fracture at the pre-determined pattern
Data Source
AI summary
An embodiment is a method to induce flaw formation in nitride semiconductors. Regions of a thin film structure are selectively decomposed within a thin film layer at an interface with a substrate to form flaws in a pre-determined pattern within the thin film structure. The flaws locally concentrate stress in the pre-determined pattern during a stress-inducing operation. The stress-inducing operation is performed. The stress-inducing operation causes the thin film layer to fracture at the pre-determined pattern.