GaN LED Laser Lift-Off Sacrificial Layer
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Solution Overview
Problem
The existing manufacturing methods for GaN-based light emitting diodes on sapphire substrates face issues with high-pressure N2 gas generation during laser lift-off, which can destroy the semiconductor layer, and subsequent metal sputtering from the bonding layer causing short circuits and leakage.
Innovation Solution
A method involving a two-step isolation process to form a sacrificial layer around each semiconductor element, followed by laser removal of the sapphire substrate with an irradiation area covering each element within the outline of the sacrificial layer, preventing metal sputtering and reducing the risk of short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sapphire substrate is removed by irradiating a laser from a side of the sapphire substrate, then the sapphire substrate can be removed, but high-pressure N2 gas is generated which may destruct the GaN based semiconductor layer
Solution Approach 1:
The patent divides the semiconductor layer into chip regions separated by street regions, and further segments each chip region by forming a sacrificial layer around its perimeter. This segmentation prevents high-pressure N2 gas from being sealed locally across the entire semiconductor layer, thereby reducing the risk of destruction while maintaining layer integrity.
Solution Approach 2:
The patent introduces a sacrificial layer as an intermediary component between the semiconductor layer and the laser irradiation process. This sacrificial layer acts as a buffer that absorbs or redirects the high-pressure N2 gas generation, protecting the semiconductor layer from direct damage during substrate removal.
2Reliability
If the semiconductor lamination is removed from the street region before LLO process, then the sapphire substrate can be removed, but the laser irradiates the bonding metal layer causing metal sputtering which deposits on chip sides and causes short circuit and leakage
Solution Approach 1:
The patent performs preliminary etching to form a sacrificial layer around each chip region before the laser lift-off process. This preliminary action creates a protective boundary that prevents laser irradiation from directly contacting the bonding metal layer, thereby preventing metal sputtering and subsequent short circuits.
Solution Approach 2:
The sacrificial layer serves as an intermediary barrier between the laser beam and the bonding metal layer. By positioning this layer at the perimeter of each chip region, it intercepts the laser energy and prevents it from reaching the metal layer, thus eliminating the harmful sputtering effect.
3Reliability
If a wide isolation trench is formed by etching a half of the thickness of the semiconductor lamination, then metal sputtering is prevented, but the process complexity increases
Solution Approach 1:
The patent segments the semiconductor layer into discrete chip regions with street regions between them, and further segments each region by forming a sacrificial layer. This segmentation approach achieves effective isolation and protection while maintaining a relatively simple process compared to forming deep wide isolation trenches through the entire semiconductor lamination.
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 increases yields by preventing semiconductor layer destruction and short circuits, allowing for efficient removal of the sapphire substrate without damaging the semiconductor elements.
Implementation Method 1
the sapphire substrate is removed by irradiating a laser from a side of the sapphire substrate. By the irradiation of the laser, the GaN based semiconductor is decomposed at an interface between the sapphire substrate and the GaN based semiconductor layer, and Ga metal and N2 gas are generated.
Implementation Method 2
the laser is irradiated to the bonding metal layer (AuSn, etc.) on the supporting substrate at the LLO process. The light of 248 nm wavelength almost completely passes through the sapphire substrate; therefore, a region (street region) without the GaN layers is irradiated by the laser and so metal is sputtered from the bonding metal layer in the street region and adheres to side walls of the element
Data Source
AI summary
A manufacturing method of a semiconductor element comprises the steps of (a) preparing a growth substrate, (b) forming a semiconductor layer on the growth substrate, (c) dividing the semiconductor layer into a plurality of elements while leaving at least a part of the semiconductor layer between each element to form a sacrificial layer around each element, (d) forming a metal layer on the semiconductor layer, (e) bonding a supporting substrate to the semiconductor layer via the metal layer, and (f) removing the growth substrate from the semiconductor layer by irradiating a laser whose area of irradiation covers each element within an outline of the sacrificial layer of each element.