SiC Wafer Laser Separation via Modified Layer
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Solution Overview
Problem
The existing methods for producing SiC wafers from single crystal ingots are inefficient due to high discarding rates and low productivity, particularly because of the difficulty in cutting and polishing high-hardness SiC ingots, and the need for densely formed modified layers with a pitch of approximately 10 μm, which reduces productivity.
Innovation Solution
An SiC wafer producing method that involves forming linear modified layers inside the ingot using a pulsed laser beam, creating cracks that propagate along the c-plane, and multiple layers connected by these cracks to form a separation surface, allowing for efficient separation of wafers with reduced ingot discard and improved productivity, along with a chamfering step to remove burrs before grinding for stable processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a wire saw is used to cut the SiC 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 modified layer forming system. The laser beam creates modified layers inside the ingot that guide crack propagation, enabling separation without mechanical contact. This substitution eliminates the need for extensive material removal and reduces cutting time significantly.
Solution Approach 2:
The patent forms modified layers in advance within the ingot at predetermined depths before separation. These pre-formed modified layers serve as guides for crack propagation during the separation process, enabling precise wafer extraction with minimal material loss and reduced processing time.
2Manufacturing precision
If both sides of the wafer are polished to a mirror finish after cutting, then the product quality is improved, but the already reduced ingot utilization is further worsened
Solution Approach 1:
The patent performs preliminary processing by forming modified layers and inducing cracks along the separation plane before actual separation. This pre-positioning of separation paths ensures that wafers are extracted with minimal additional material removal needed, improving overall ingot utilization while maintaining surface quality requirements.
3Manufacturing precision
If the modified layers are densely formed with a pitch of approximately 10 μm, then the separation precision is improved, but the productivity is reduced
Solution Approach 1:
The patent applies partial action by forming modified layers only at specific predetermined depths where separation is needed, rather than densely throughout the entire ingot. The crack propagation mechanism extends the effect of sparsely distributed modified layers to achieve precise separation without requiring dense modification at every location.
Solution Approach 2:
The patent segments the modification process by creating discrete modified layers at specific depths rather than continuous dense modification. Each modified layer acts as an independent initiation point for crack propagation, and the cumulative effect of these segmented modifications achieves the desired separation precision with reduced overall processing time.
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 discard to approximately 30% and ensures stable processing quality by removing burrs before grinding, thus enhancing the efficiency of SiC wafer production.
Implementation Method 1
SiC is decomposed into Si and C by the pulsed laser beam first applied, and the pulsed laser beam next applied is absorbed by C previously produced to continue the decomposition of SiC into Si and C in a chain reaction manner
Implementation Method 2
applying the pulsed laser beam to the SiC ingot as relatively moving the SiC ingot and the focal point in a first direction perpendicular to a second direction where the off angle is formed, thereby forming a linear modified layer inside the SiC ingot at the predetermined depth
Data Source
AI summary
A SiC wafer is produced from a single crystal SiC ingot. A modified layer is formed by setting a focal point of a pulsed laser beam inside the ingot at a predetermined depth from the upper surface of the ingot, the predetermined depth corresponding to the thickness of the wafer to be produced. The pulsed laser beam is applied to the ingot while moving the ingot in a first direction perpendicular to a second direction where an off angle is formed, thereby forming a modified layer in the first direction inside the ingot and cracks propagating from the modified layer along a c-plane. A separation surface is formed by indexing the ingot in the second direction and applying the laser beam plural times to thereby form a separation surface inside the ingot. Part of the ingot is separated along the separation surface to thereby produce the wafer.