Laser Wafer Separation with Undulation Compensation
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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 long processing times, with wire saws requiring significant discarding of material and laser cutting methods not adequately improving productivity despite small pitch scanning.
Innovation Solution
A wafer producing method that involves measuring end surface undulation, setting a laser beam focal point at a predetermined depth within the ingot, and controlling the objective lens height to form a flat separation plane, allowing for efficient wafer separation without being affected by undulations, using a laser processing apparatus with precise control over the laser beam's direction and power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If wire saw is used to slice the ingot, then the 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 beam processing system. The laser beam forms a modified layer and cracks inside the ingot along the separation plane, enabling separation without mechanical contact. This substitution eliminates the need for extensive material removal while maintaining cutting capability, directly addressing the high material loss issue.
Solution Approach 2:
The patent changes the physical state and properties of the ingot material through laser heating. By controlling the laser beam parameters (power, scanning speed, focal point depth), the material undergoes localized phase changes and thermal stress, forming modified layers and cracks that enable separation. This parameter-based control allows precise separation with minimal material waste.
2Productivity
If wire saw is used to cut the hexagonal single crystal ingot, then the ingot can be sliced, but considerable time is required reducing productivity
Solution Approach 1:
The laser processing system operates at much higher speeds compared to mechanical wire saw cutting. The laser beam can rapidly scan and process the ingot surface, forming modified layers and cracks quickly. This non-contact optical processing method eliminates the slow mechanical cutting process, directly improving productivity and reducing processing time.
Solution Approach 2:
The laser beam is scanned in a periodic manner across the ingot surface, systematically creating modified layers and cracks along the separation plane. This periodic scanning action allows continuous processing at high speed, maintaining productivity while reducing overall processing time compared to sequential mechanical cutting.
3Manufacturing precision
If laser beam is scanned with small pitch (1 to 10 μm), then modified layer and cracks are formed at high density, but the improvement in productivity is not yet sufficient
Solution Approach 1:
The laser beam first forms a modified layer as a preliminary structure before creating cracks. This modified layer serves as a precursor that guides crack propagation and ensures high-density crack formation. By preparing this modified layer in advance through controlled laser scanning, the process achieves high precision crack density while maintaining reasonable processing speed.
Solution Approach 2:
The patent dynamically adjusts the laser beam scanning parameters including pitch, speed, and power during processing. By optimizing these dynamic parameters, the system achieves high-density modified layer and crack formation without excessively slowing down the process, balancing manufacturing precision with productivity improvement.
4Manufacturing precision
If undulation is present on the end surface of the ingot, then modified layers follow the undulation, but extensive polishing is required increasing material loss
Solution Approach 1:
The laser beam processing is performed as a preliminary action before separation. By forming the modified layer and cracks while the ingot is in its original state with undulations, the subsequent separation process naturally follows the laser-created path. This preliminary laser processing eliminates the need for post-separation polishing to remove undulations, preventing material loss that would otherwise occur during polishing.
Solution Approach 2:
Instead of treating the undulation on the end surface as a defect requiring correction through polishing, the patent utilizes the undulation as part of the natural separation path. The laser beam follows the undulated surface profile, and the resulting separation plane naturally accommodates the surface geometry, converting what would be a harmful factor (requiring material removal) into a beneficial feature (natural separation path).
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 enables the efficient production of wafers with reduced material loss and improved productivity by forming a flat separation plane within the ingot, allowing for the effective separation of wafers without the need for extensive polishing, thus enhancing the economic viability of the process.
Implementation Method 1
applying the laser beam to the end surface of the ingot as relatively moving the focal point and the ingot to thereby form a separation plane containing a modified layer and cracks
Implementation Method 2
form a separation plane containing a modified layer and cracks extending from the modified layer
Data Source
AI summary
A wafer is produced from an ingot having an end surface. The method includes an end surface measuring step of measuring undulation present on the end surface, and a separation plane forming step of setting the focal point of a laser beam inside the ingot at a predetermined depth from the end surface, which depth corresponds to the thickness of the wafer to be produced, and next applying the laser beam to the end surface to thereby form a separation plane containing a modified layer and cracks extending from the modified layer. The height of an objective lens for forming the focal point of the laser beam is controlled so that the focal point is set in the same plane to form the separation plane, according to the numerical aperture NA of the lens, the refractive index N of the ingot, and the undulation present on the end surface.