Laser Wafer Slicing Hexagonal SiC Ingot Separation
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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 due to high material loss and prolonged processing times, particularly when using wire saws, and previous laser-based techniques do not adequately improve productivity despite applying laser beams with small pitches.
Innovation Solution
A wafer producing method that involves setting the focal point of a laser beam at a predetermined depth within the ingot, applying it to form a modified layer parallel to the surface and cracks along the c-plane, and then separating wafers by moving the focal point in specific directions to extend the cracks, optimizing the spacing and overlap of laser spots to enhance productivity and reduce material waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
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 and considerable time is required for cutting
Solution Approach 1:
The patent replaces the mechanical wire saw cutting system with a laser-based system. The laser beam forms a modified layer inside the ingot at a predetermined depth, creating a separation plane without mechanical contact. This substitution eliminates the need for wire saw cutting, dramatically reducing material loss and cutting time while enabling precise wafer separation.
Solution Approach 2:
The patent performs preliminary action by forming a modified layer at a predetermined depth inside the ingot before actual separation. The laser beam creates this modified layer in advance, establishing a separation plane that makes subsequent wafer separation easy and efficient, rather than cutting through the entire ingot thickness.
2Manufacturing precision
If laser beam is scanned spirally or linearly with pitch of 1 to 10 μm to form modified layer and cracks, then separation plane is created, but productivity improvement is insufficient due to very small pitch requirement
Solution Approach 1:
The patent changes the laser scanning parameters by moving the focal point in a specific direction perpendicular to the c-axis and controlling the overlap rate between adjacent focused spots. Instead of using extremely small pitches of 1-10 μm, the method optimizes the balance between precision and speed by adjusting focal spot spacing and overlap, achieving effective separation planes with improved productivity.
Solution Approach 2:
The patent introduces a new dimensional approach by moving the focal point in a direction perpendicular to the c-axis (a-axis or m-axis direction) rather than scanning parallel to the c-axis. This dimensional change allows the laser to create extended modified layers and cracks that propagate along the c-plane, achieving effective separation with larger step sizes and improved processing speed.
3Productivity
If focal point is moved in direction perpendicular to c-axis with controlled overlap rate, then modified layer extends and cracks propagate along c-plane, but requires precise control of laser parameters
Solution Approach 1:
The patent implements feedback control by monitoring and adjusting the overlap rate between adjacent focused spots. The overlap rate is controlled within a specific range (0.2 to 2.0 times the focused spot diameter) to ensure proper crack propagation along the c-plane. This feedback mechanism maintains optimal processing conditions and ensures consistent separation quality.
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 extending crack lengths along the c-plane, reducing ingot discard to about 30%, and efficiently producing hexagonal single crystal wafers with improved economic efficiency.
Implementation Method 1
setting a focal point of a laser beam having a transmission wavelength to inside the ingot at a predetermined depth from a first surface
Implementation Method 2
applying the laser beam to the first surface as relatively moving the focal point and the ingot to thereby form a modified layer parallel to the first surface
Implementation Method 3
form a modified layer parallel to the first surface and cracks extending from the modified layer along a c-plane
Data Source
AI summary
A wafer producing method for producing a hexagonal single crystal wafer from a hexagonal single crystal ingot, including a separation start point forming step of setting the focal point of a laser beam inside the ingot at a predetermined depth from the ingot's upper surface, which depth corresponds to the thickness of the wafer to be produced, and next applying the laser beam while relatively moving the focal point and the ingot to thereby form: (i) a modified layer parallel to the ingot's upper surface, and (ii) cracks extending from the modified layer, thus forming a separation start point. The laser beam is applied to form the modified layer in a condition where the relation of −0.3≤(d−x)/d≤0.5 holds, where d is the diameter of a focused spot of the laser beam and x is the spacing between adjacent focused spots of the laser beam.