Vertical GaN LED Chip Stress Distribution via Rounded Corners
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Solution Overview
Problem
The production of vertically structured Group III nitride semiconductor LED chips is hindered by the formation of cracks during the lift-off process from sapphire substrates, leading to defective products and reduced yield, due to stress concentration at the corners of the light emitting structures.
Innovation Solution
The method involves forming light emitting structures with a top view shape of a circle or 4n-gon having rounded corners and incorporating through grooves or holes in the conductive support to distribute stress, thereby reducing crack incidence and improving the quality and yield of vertical LED chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If light emitting structures with sharp corners are used during lift-off, then the manufacturing process is simpler, but stress concentration occurs at corners leading to crack formation and reduced yield
Solution Approach 1:
The patent applies curvature by forming light emitting structures with rounded corners instead of sharp corners. This curvature eliminates stress concentration points that would otherwise occur at sharp corners during the lift-off process, preventing crack formation and improving yield of defect-free LED chips while maintaining manufacturing simplicity.
2Reliability
If through grooves or holes are added to conductive support, then stress distribution is improved reducing cracks, but device complexity increases
Solution Approach 1:
The patent applies segmentation by introducing through grooves or holes in the conductive support structure. These segmented features divide the continuous conductive support into regions that allow stress to distribute more evenly during lift-off, preventing stress concentration and crack formation in the light emitting structures, while adding only moderate complexity to the overall device.
3Ease of manufacture
If conventional lateral structure is used with sapphire substrate, then manufacturing is easier, but heat dissipation is insufficient causing heat saturation
Solution Approach 1:
The patent applies inversion by transitioning from the conventional lateral current flow structure to a vertical current flow structure. In this inverted architecture, electric current flows vertically through the light emitting structure from bottom to top, enabling efficient heat dissipation through the conductive support while maintaining ease of manufacture on sapphire substrates.
Data Source
AI summary
A method for manufacturing vertically structured Group III nitride semiconductor LED chips includes a step of forming a light emitting laminate on a growth substrate; a step of forming a plurality of separate light emitting structures by partially removing the light emitting laminate to partially expose the growth substrate; a step of forming a conductive support on the plurality of light emitting structures; a step of lifting off the growth substrate from the plurality of light emitting structures; and a step of cutting the conductive support thereby singulating a plurality of LED chips each having the light emitting structure. The step of partially removing the light emitting laminate is performed such that each of the plurality of light emitting structures has a top view shape of a circle or a 4n-gon (“n” is a positive integer) having rounded corners.