SiC Wafer Thinning via Laser Modified Layer
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Solution Overview
Problem
The high Mohs hardness of SiC substrates leads to excessive wear of abrasive members during grinding, resulting in poor economy and inefficiency in wafer processing compared to silicon substrates.
Innovation Solution
A wafer processing method that uses a laser beam to form modified layers and cracks inside the SiC substrate, allowing for separation into individual device chips without grinding the back side, thereby reducing abrasive wear and achieving efficient thickness reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the back side of SiC wafer is ground by a grinding wheel having abrasive members, then the thickness of the wafer is reduced to a predetermined thickness, but the abrasive members wear in an amount approximately 4 times to 5 times the grinding amount of the wafer, causing very poor economy
Solution Approach 1:
The patent replaces the mechanical grinding system with a laser-based system. A laser beam is used to form a modified layer inside the SiC wafer at a predetermined depth, which then serves as a separation start point. This substitution eliminates the need for abrasive members and mechanical contact, thereby preventing abrasive wear entirely while achieving precise thickness control through the laser-modified layer depth.
Solution Approach 2:
The patent performs preliminary laser processing to create a modified layer and separation start point before any separation or thinning operation. By pre-forming the modified layer at the desired finished thickness depth, the subsequent separation process becomes straightforward and does not require aggressive grinding that would cause abrasive wear.
2Productivity
If the back side of SiC wafer is ground by a grinding wheel, then the wafer thickness is reduced, but the grinding process causes excessive abrasive member wear compared to silicon substrate grinding
Solution Approach 1:
The patent replaces the mechanical grinding system with a laser-based system. A laser beam is used to form a modified layer inside the SiC wafer at a predetermined depth, which then serves as a separation start point. This substitution eliminates the need for abrasive members and mechanical contact, thereby preventing abrasive wear entirely while achieving precise thickness control through the laser-modified layer depth.
Solution Approach 2:
The patent changes the physical state and properties of the SiC wafer through laser irradiation. The laser beam modifies the crystalline structure and physical properties of the SiC at the focal point, creating a modified layer with different characteristics that facilitate easy separation. This parameter change allows thickness reduction without mechanical grinding and associated abrasive wear.
3Loss of substance
If a laser beam is applied to form a modified layer inside the SiC substrate, then separation start points are formed without abrasive wear, but the process requires precise focal point positioning and movement control
Solution Approach 1:
The patent replaces the mechanical grinding system with a laser-based system. A laser beam is used to form a modified layer inside the SiC wafer at a predetermined depth, which then serves as a separation start point. This substitution eliminates the need for abrasive members and mechanical contact, thereby preventing abrasive wear entirely while achieving precise thickness control through the laser-modified layer depth.
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 method effectively thins and divides SiC wafers into device chips with minimal abrasive wear, allowing for the reuse of the second wafer as a substrate and significantly improving processing economy.
Implementation Method 1
setting the focal point of a laser beam having a transmission wavelength to the SiC substrate inside the SiC substrate at a predetermined depth from the first surface or the second surface... and next applying the laser beam to the first surface or the second surface as relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface and cracks extending from the modified layer along the c-plane
Data Source
AI summary
A wafer formed from an SiC substrate having a first surface and a second surface is divided into individual device chips. A division start point formed by a cutting blade has a depth corresponding to the finished thickness of each device chip along division lines formed on the first surface. A separation start point is formed by a laser beam having a focal point set inside the SiC substrate at a predetermined depth from the second surface, and the laser beam is applied to the second surface while relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface and cracks extending from the modified layer along a c-plane. An external force is applied to the wafer, thereby separating the wafer into a first wafer having the first surface and a second wafer having the second surface.