Laser Wafer Separation for Hexagonal SiC Ingots
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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 low productivity, as they require significant time and result in 70-80% of the ingot being discarded during the cutting process with wire saws, and previous laser-based techniques do not adequately improve productivity due to small laser beam pitch.
Innovation Solution
A wafer producing method that involves setting the focal point of a laser beam at a predetermined depth within the ingot to form a modified layer and cracks parallel to the c-plane, with the laser beam applied multiple times to extend cracks from the modified layer, allowing for efficient separation of wafers by applying an external force along the formed separation start point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a wire saw is used to cut the hexagonal single crystal ingot, then the 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 and creates cracks along the c-plane, enabling separation without mechanical contact. This substitution eliminates the material loss associated with wire saw cutting while maintaining wafer production capability.
Solution Approach 2:
The patent changes the physical state and properties of the ingot material through laser heating. By controlling the laser parameters (wavelength, power, scanning speed), the material undergoes localized modification forming a modified layer that facilitates clean separation. This parameter control enables precise separation with minimal material loss.
2Manufacturing precision
If the laser beam is scanned spirally or linearly with a pitch of 1 to 10 μm to form modified layer and cracks, then separation can be achieved, but the productivity improvement is not yet sufficient due to the very small pitch required
Solution Approach 1:
The patent performs preliminary action by first forming a modified layer at a specific depth inside the ingot before creating cracks. This pre-formed modified layer acts as a guide and initiator for crack propagation, allowing cracks to extend along the c-plane more efficiently. This preliminary modification enables subsequent cracking with less stringent pitch requirements, improving productivity.
Solution Approach 2:
The patent transitions from two-dimensional surface scanning to three-dimensional internal modification by focusing the laser beam inside the ingot at a predetermined depth. This volumetric approach allows the modified layer to be formed throughout the thickness of the future wafer, enabling crack propagation along the entire separation plane simultaneously, thereby reducing the required scanning pitch and improving processing speed.
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 reduces material loss to about 30% and improves productivity by allowing for easier separation of wafers, as the cracks formed along the c-plane can be connected to efficiently produce hexagonal single crystal wafers from the ingot.
Implementation Method 1
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 2
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 producing method for producing a hexagonal single crystal wafer from a hexagonal single crystal ingot includes a separation start point forming step of setting the focal point of a laser beam inside the ingot at a predetermined depth from the upper surface of the ingot, which depth corresponds to the thickness of the wafer to be produced, and next applying the laser beam to the upper surface of the ingot while relatively moving the focal point and the ingot to thereby 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. In the separation start point forming step, the laser beam is applied to the ingot plural times with the focal point of the laser beam set at the modified layer previously formed, thereby separating the cracks from the modified layer.