SiC Wafer Separation Using Laser-Induced Breakable Layers
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Solution Overview
Problem
The existing methods for producing SiC wafers from single crystal ingots are inefficient due to high ingot discard rates and low productivity, primarily because of the difficulty in cutting the hard SiC ingot using wire saws and the need for dense laser-modified layers, which reduce productivity.
Innovation Solution
A method involving the formation of a breakable layer inside the SiC ingot using a pulsed laser beam with a specific energy density and movement pattern, creating cracks that allow for efficient separation of wafers without forming damage layers above or below the breakable layer, thereby reducing ingot discard and improving productivity.
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 the cutting time is excessively long and productivity is reduced due to the high hardness of SiC
Solution Approach 1:
The patent replaces the mechanical wire saw cutting system with a laser-based system. The laser beam forms modified layers inside the SiC ingot through optical-thermal interaction, and the ingot is then broken along these modified layers to obtain wafers. This substitution of mechanical cutting with laser processing dramatically reduces cutting time and improves productivity while dealing with the high hardness of SiC.
2Manufacturing precision
If both sides of the sliced wafer are polished to mirror finish, then the wafer quality is improved, but 70% to 80% of the ingot is discarded causing poor economy
Solution Approach 1:
The patent performs preliminary action by forming modified layers at precise depths inside the SiC ingot before cutting. These modified layers are created at the exact wafer thickness position, allowing the ingot to be broken cleanly at the desired depth. This preliminary positioning eliminates the need for extensive material removal and polishing, significantly reducing ingot discard while maintaining wafer quality.
Solution Approach 2:
The patent changes the physical state and properties of the SiC ingot by creating modified layers through laser processing. The modified layers have different physical properties than the original SiC, creating a separation plane that allows clean breaking. This parameter change enables precise thickness control without requiring large amounts of material to be removed and re-polished.
3Manufacturing precision
If the laser beam is applied to form modified layers densely with pitch of approximately 10 μm, then the separation quality is improved, but productivity is reduced
Solution Approach 1:
The patent optimizes the laser processing parameters, specifically the pitch between modified layers. Instead of using a dense pitch of 10 μm, the patent determines an optimal pitch range of 1-5 μm that maintains sufficient separation quality while dramatically reducing processing time. This parameter optimization balances separation precision with productivity improvement.
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 enhances productivity by minimizing ingot discard and maintaining wafer quality, as it allows for efficient separation of SiC wafers without forming damage layers, thus reducing the need for grinding and increasing the efficiency of the wafer production process.
Implementation Method 1
SiC is decomposed into Si and C by the pulsed laser beam first applied
Implementation Method 2
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 3
cracks extending from the modified layer in opposite directions along the c-plane
Data Source
AI summary
An SiC wafer is produced from a single crystal SiC ingot by a method that includes forming a plurality of breakable layers constituting a separation surface in the SiC ingot, each breakable layer including a modified layer and cracks extending from the modified layer along a c-plane, and separating part of the SiC ingot along the separation surface as an interface to thereby produce the SiC wafer. In forming the separation surface, the energy density of a pulsed laser beam is set to an energy density not causing the formation of an upper damage layer above the breakable layer previously formed due to the reflection of the pulsed laser beam from the breakable layer and not causing the formation of a lower damage layer below the breakable layer previously formed due to the transmission of the pulsed laser beam through the breakable layer.