Sapphire Wafer Dividing Method for Light Extraction
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Solution Overview
Problem
The refractive index difference between sapphire substrates and air leads to inefficient light emission from light emitting devices, as light is totally reflected when the angle of incidence exceeds the critical angle, causing confinement of light within the substrate.
Innovation Solution
A method involving the formation of modified layers inside a sapphire wafer using a laser beam with a transmission wavelength, followed by chamfering and dividing with a cutting blade to create cut grooves, allowing light to be emitted efficiently by reducing the angle of incidence to below the critical angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire substrate is used for light emitting devices, then the substrate provides high thermal conductivity and chemical stability, but the high refractive index difference between sapphire and air causes total internal reflection and confines light inside the substrate, reducing light emission efficiency
Solution Approach 1:
The patent divides the sapphire substrate surface into multiple regions by forming grooves that segment the continuous surface. This segmentation creates multiple reflection interfaces and reduces the effective area for total internal reflection, allowing light to escape more efficiently while maintaining the substrate's inherent stability properties
Solution Approach 2:
The patent applies local quality changes by creating grooves with specific depth and width parameters in certain regions of the sapphire substrate. These localized structural modifications alter the optical properties only in the groove regions, enabling light extraction without affecting the overall substrate stability and thermal conductivity
2Productivity
If the sapphire wafer is divided into individual devices along division lines, then individual light emitting devices are obtained, but the division process may damage the light emitting layer or result in poor division precision
Solution Approach 1:
The patent performs preliminary action by forming grooves along the intended division lines before actually separating the wafer. These pre-formed grooves serve as guides and stress concentration points that enable precise and clean separation along the desired paths, protecting the light emitting layer from damage during the division process
Solution Approach 2:
The patent replaces direct mechanical cutting with a groove-forming process followed by controlled separation. Instead of applying high mechanical force directly to cut through the hard sapphire substrate, the process uses localized material removal to create grooves, then applies minimal force to complete the separation along these pre-defined paths, improving both precision and protection of the light emitting layer
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 method enhances the luminance of light emitting devices by facilitating the escape of light from the sapphire substrate, improving the efficiency of light emission and reducing the number of steps in the wafer division process.
Implementation Method 1
applying a laser beam having a transmission wavelength to the sapphire wafer from the back side of the sapphire wafer along the division lines in a condition where the focal point of the laser beam is set inside the sapphire wafer, thereby forming a plurality of modified layers inside the sapphire wafer along the division lines
Implementation Method 2
an external force is applied to the modified layers reduced in strength to divide the wafer
Implementation Method 3
since the refractive index of sapphire is remarkably larger than that of air, there is a problem such that the light is not efficiently emerged from the sapphire substrate. This is due to the fact that when the angle of incidence of light upon the interface between the sapphire substrate and the air is greater than a critical angle (34.5°) total reflection occurs on this interface
Data Source
AI summary
A sapphire wafer dividing method including a modified layer forming step of forming a plurality of modified layers inside a sapphire wafer along a plurality of crossing division lines formed on the front side where a light emitting layer is formed, and a chamfering and dividing step of forming a plurality of cut grooves on the back side of the sapphire wafer along the division lines, thereby dividing the sapphire wafer into individual light emitting devices along the modified layers as a division start point, wherein the corners of the back side of each light emitting device are chamfered by the formation of the cut grooves in the chamfering and dividing step.