Laser Wafer Separation for Hexagonal SiC Ingot Wastage Reduction
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Solution Overview
Problem
The existing methods for slicing hexagonal single crystal ingots, such as those made of SiC or GaN, are inefficient, leading to high material wastage and reduced productivity due to the difficulty in cutting these hard materials with wire saws, and previous laser-based techniques do not adequately improve productivity despite using small laser beam pitches.
Innovation Solution
A wafer producing method that involves setting the focal point of a laser beam at a predetermined depth within the ingot, forming a modified layer parallel to the surface and cracks along the c-plane, and using an off-angle to extend the cracks, allowing for efficient separation of wafers with reduced material loss by adjusting the laser beam's polarization and scanning direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If wire saw is used to slice hexagonal single crystal ingot, then wafer can be produced, but 70 to 80% of the ingot is discarded causing poor economy
Solution Approach 1:
The patent replaces the mechanical wire saw cutting system with a laser-based processing system. The laser beam forms a modified layer and induces cracks along the c-plane inside the ingot, enabling separation without mechanical contact. This substitution eliminates the need for extensive material removal and allows precise control of the separation plane, significantly reducing ingot wastage while improving productivity.
Solution Approach 2:
The patent changes the physical state and properties of the ingot material through laser irradiation. By controlling laser parameters (wavelength, power, scanning speed, focal depth) and processing atmosphere (oxygen concentration), the method creates a modified layer with specific thermal and mechanical properties that facilitate crack propagation along the desired c-plane separation path, enabling efficient wafer production with minimal waste.
2Productivity
If wire saw is used to cut hexagonal single crystal ingot, then wafer can be obtained, but considerable time is required causing reduction in productivity
Solution Approach 1:
The patent replaces the slow mechanical wire saw cutting process with rapid laser processing. The laser beam can quickly traverse the ingot and induce cracks along the separation plane at speeds much faster than mechanical cutting, dramatically reducing the time required for wafer production while increasing overall productivity.
Solution Approach 2:
The patent employs periodic laser irradiation with controlled pulse intervals to efficiently propagate cracks along the separation plane. By using pulsed laser operation with optimized duty cycles and scanning speeds, the method achieves rapid material separation without excessive heat accumulation, maintaining high processing speed and productivity.
3Manufacturing precision
If laser beam is scanned spirally or linearly with pitch of 1 to 10 μm, then modified layer and cracks are formed at very high density, but productivity improvement is not yet sufficient
Solution Approach 1:
The patent applies local quality by concentrating laser energy specifically at the focal point inside the ingot to create a modified layer only where needed. By controlling the focal depth and scanning parameters, the method creates high-density cracks precisely along the c-plane separation path without unnecessarily processing the entire ingot volume, thereby improving both precision and productivity.
Solution Approach 2:
The patent transitions from two-dimensional surface scanning to three-dimensional internal processing by focusing the laser beam at a specific depth inside the ingot. This allows the modified layer and cracks to form within the bulk material along the separation plane, enabling more efficient separation with reduced material removal and improved productivity while maintaining high crack density.
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 significantly improves productivity by reducing ingot wastage to about 30% and stabilizing crack formation, enabling more efficient production of hexagonal single crystal wafers with longer crack propagation and improved wafer separation.
Implementation Method 1
applying the laser beam to the ingot as scanning the laser beam on the ingot to thereby form a modified layer and cracks in a separation plane inside the ingot
Implementation Method 2
setting the focal point of a laser beam having a transmission wavelength to SiC inside a hexagonal single crystal ingot, next applying the laser beam to the ingot as scanning the laser beam on the ingot to thereby form a modified layer and cracks
Data Source
AI summary
A hexagonal single crystal wafer is produced from a hexagonal single crystal ingot. A wafer producing method includes a separation start point forming step of applying a laser beam to the ingot to form a modified layer parallel to the upper surface of the ingot and cracks extending from the modified layer, thus forming a separation start point. The focal point of the laser beam is relatively moved in a first direction perpendicular to a second direction where a c-axis in the ingot is inclined by an off angle with respect to a normal to the upper surface. The off angle is formed between the upper surface and a c-plane perpendicular to the c-axis, thereby linearly forming the modified layer extending in the first direction. The laser beam is applied to the ingot with the direction of the polarization plane of the laser beam set to the first direction.