Sapphire Wafer Dividing with Laser Chamfering
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Solution Overview
Problem
Light emitted from sapphire light emitting devices is not efficiently emitted into ambient air due to total reflection at the interface between the sapphire layer and air, caused by the higher refractive index of sapphire compared to air, leading to confinement of light within the sapphire layer.
Innovation Solution
A dividing method for sapphire wafers that involves forming modified layers and cut grooves along division lines using laser processing and cutting, respectively, to chamfer the corners of the light emitting devices, allowing light to be emitted at angles less than or equal to the critical angle, thereby improving luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a sapphire wafer is divided into individual light emitting devices using conventional laser processing methods, then the wafer can be divided along division lines, but the luminance of the light emitting devices is reduced due to total reflection at the sapphire-air interface
Solution Approach 1:
The patent applies preliminary chamfering processing to the back surface of the sapphire wafer before dividing it into individual light emitting devices. By forming chamfered surfaces at the corners and edges of each device through laser processing or mechanical cutting, the patent modifies the geometry in advance to enable light extracted from the light emitting layer to escape more efficiently. This preliminary geometric modification prevents total reflection by ensuring light rays incident on the sapphire-air interface do so at angles less than the critical angle, thereby improving luminance before the actual division occurs.
2Illumination intensity
If the sapphire wafer is divided without chamfering, then the division process is simpler, but light is confined inside the sapphire layer due to total reflection
Solution Approach 1:
The patent employs laser processing to create chamfered surfaces on the back side of the sapphire wafer, replacing traditional mechanical chamfering methods. The laser beam selectively removes material along the division lines to form precise chamfered geometries without requiring complex mechanical tooling or multiple machining steps. This substitution of mechanical processing with optical processing simplifies the overall device complexity while achieving the same light extraction enhancement through chamfering.
3Productivity
If conventional laser processing is used to form grooves and divide the wafer, then the division can be achieved, but the light extraction efficiency remains poor
Solution Approach 1:
The patent merges two functions into a single laser processing step: creating division grooves for wafer separation and simultaneously forming chamfered surfaces for light extraction enhancement. By optimizing the laser processing parameters, the chamfered surfaces are created along the division lines where the laser both cuts the sapphire to define individual devices and angles the cut surfaces to facilitate light escape. This merging of division and chamfering operations maintains high productivity while significantly improving luminance compared to conventional separate processing steps.
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 chamfering of light emitting device corners enables efficient emission of light from the sapphire layer to the outside, enhancing the luminance of each device by reducing total reflection and increasing the escape cone of emitted light.
Implementation Method 1
a pulsed laser beam is applied to the wafer to form a plurality of laser processed grooves on the front side of the wafer
Implementation Method 2
forming modified layers inside the sapphire wafer along the division lines
Implementation Method 3
cutting the sapphire wafer from the back side thereof by using a cutting blade to thereby form a plurality of cut grooves
Implementation Method 4
when the angle of incidence of light upon the interface between the sapphire layer and the air is greater than a critical angle (34.5°), total reflection occurs on this interface, causing confinement of the light inside the sapphire layer
Implementation Method 5
performing ablation by applying a laser beam having an absorption wavelength to the sapphire wafer to thereby form a plurality of preliminary grooves
Data Source
AI summary
A sapphire wafer dividing method including a cut groove forming step of forming a plurality of cut grooves on the back side of a sapphire wafer along a plurality of crossing division lines formed on the front side where a light emitting layer is formed, a modified layer forming step of forming a plurality of modified layers inside the sapphire wafer along the division lines, and a dividing step of dividing the sapphire wafer into individual light emitting devices along the modified layers as a division start point, thereby chamfering the corners of the back side of each light emitting device owing to the formation of the cut grooves in the cut groove forming step.