Semiconductor Ingot Wafer Peeling Using Sidewall Laser Crack Initiation
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Solution Overview
Problem
The existing methods for forming wafers from semiconductor ingots, particularly those made of hard materials like SiC and GaN, are inefficient, leading to high material wastage and increased production costs due to the difficulty in cutting and processing these ingots with wire saws, and previous laser-based methods are time-consuming and poor in productivity.
Innovation Solution
A wafer forming method that involves applying a laser beam with a focal point inside the ingot to create a modified layer on the side surface, followed by applying an external force to develop a crack from the side surface inward, allowing for efficient peeling off of wafers using a peeling-off layer, which can be formed using various methods such as laser beams or ultrasonic waves, to reduce material wastage and enhance productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wire saw cutting is used to form wafers from semiconductor ingot, then wafers can be formed with finished surfaces, but 70% to 80% of the semiconductor ingot is thrown away and productivity is low
Solution Approach 1:
The patent applies laser beams to pre-form modified layers at predetermined depths within the semiconductor ingot before the actual wafer separation process. This preliminary action creates predetermined separation planes that facilitate subsequent easy peeling, thereby improving productivity while maintaining manufacturing precision.
Solution Approach 2:
The patent replaces the traditional mechanical wire saw cutting system with a laser-based modified layer formation system. By using laser energy to create modified layers that enable easy separation, the method eliminates the need for time-consuming mechanical cutting while achieving both high precision and improved productivity.
2Manufacturing precision
If laser beam is applied densely at 10 μm intervals to form modified layer over whole region, then modified layer can be formed for wafer separation, but the process takes considerable time and productivity is poor
Solution Approach 1:
The patent applies laser beams at strategically selected positions rather than densely across the entire surface. By forming modified layers at key locations and utilizing crack propagation mechanisms, the method achieves effective wafer separation with significantly reduced laser application time compared to full-surface treatment.
Solution Approach 2:
The patent divides the modified layer formation process into discrete focal points positioned at specific depths and locations within the ingot. Instead of treating the entire surface uniformly, the laser is applied at segmented positions that are sufficient to initiate crack propagation and enable separation, thereby reducing total processing time.
3Manufacturing precision
If hexagonal single crystal ingot of SiC or GaN is cut by wire saw, then wafers can be formed, but the hardness of the material makes cutting difficult and time-consuming
Solution Approach 1:
The patent replaces mechanical wire saw cutting with a laser-based approach that forms modified layers within the hard semiconductor ingot material. This substitution eliminates the difficulty of mechanically cutting hard materials like SiC and GaN while maintaining precise wafer formation capability.
Solution Approach 2:
The patent changes the physical state and properties of the semiconductor material by using laser energy to create modified layers with altered structural characteristics. These modified layers have different properties that enable easy separation, transforming the difficulty of cutting hard materials into an easily achievable peeling process.
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 the amount of semiconductor ingot wasted during wafer formation and improves the efficiency of the process, allowing for the cost-effective production of wafers by efficiently developing cracks and peeling off wafers from the ingot.
Implementation Method 1
applying a laser beam of such a wavelength as to be transmitted through the semiconductor ingot to the semiconductor ingot, with a focal point of the laser beam positioned inside from the side surface
Implementation Method 2
exerting an external force from the upper surface of the semiconductor ingot and concentrating a stress on a crack extending from the modified layer to the inside to cause the crack to develop from the side surface side toward the inside
Implementation Method 3
a laser beam of such a wavelength as to be absorbed in the semiconductor ingot is applied while being positioned inside the wafer to be formed, to thereby partially expand the wafer to be formed and cause the crack to develop from the side surface to the inside
Implementation Method 4
a pulsed laser beam of such a wavelength as to be absorbed in the semiconductor ingot is applied to the upper surface of the semiconductor ingot to generate a stress wave by heating
Implementation Method 5
an ultrasonic wave is applied from the upper surface of the semiconductor ingot to cause the crack to develop from the side surface toward the inside
Data Source
AI summary
A wafer forming method includes a modified layer forming step of applying a laser beam of such a wavelength as to be transmitted through an ingot to the ingot with a focal point of the laser beam positioned inside from a side surface at a position corresponding to the thickness of a wafer to be formed, to form a modified layer over the whole circumference of the side surface, a peeling-off layer forming step of exerting an external force from an upper surface of the ingot and concentrating a stress on a crack extending from the modified layer to the inside, to cause the crack to develop from the side surface side toward the inside and form a peeling-off layer, and a wafer forming step of peeling off a wafer to be formed, from the ingot, with the peeling-off layer as a start point, to form the wafer.