Laser Wafer Slicing Control for Uniform SiC Separation Depth
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Solution Overview
Problem
The existing methods for slicing wafers from ingots, particularly those made of silicon carbide, face challenges such as non-uniform impurity distribution leading to inconsistent separation layer formation and high kerf loss due to variations in impurity concentrations within the ingot.
Innovation Solution
A laser processing apparatus and method that uses a fluorescence detection unit to determine impurity concentrations on the ingot surface, adjusting laser beam irradiation conditions such as output power, condenser lens height, and overlap rate based on detected photon numbers to form a uniform separation layer at a consistent depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a laser beam is irradiated to a SiC single crystal ingot including a facet region with higher impurity concentration, then a separation layer is formed, but the separation layer is not formed at a uniform position and kerf loss increases
Solution Approach 1:
The patent applies local quality by detecting impurity concentration variations at different locations on the ingot surface using fluorescence detection, and then adjusting laser irradiation conditions (power, speed, focal point) according to the specific impurity concentration at each location. This ensures uniform separation layer formation despite spatial variations in impurity distribution.
Solution Approach 2:
The patent changes laser irradiation parameters (output power, irradiation speed, focal point position) based on detected impurity concentrations. By dynamically adjusting these parameters according to local impurity levels, the separation layer is formed at a uniform depth across regions with varying impurity concentrations, preventing kerf loss.
2Productivity
If a laser beam is irradiated to form a separation layer in an ingot with non-uniform impurity distribution, then wafer slicing is achieved, but variations occur in the position at which the separation layer is formed
Solution Approach 1:
The patent implements feedback control by detecting fluorescence intensity (which correlates with impurity concentration) at each location before laser irradiation, storing this information, and using it to adjust laser parameters during subsequent processing. This feedback mechanism ensures consistent separation layer positioning despite impurity variations.
Solution Approach 2:
The patent performs preliminary fluorescence detection and stores impurity concentration information for each location before laser irradiation. This preliminary characterization of the ingot allows for optimized laser parameter selection that compensates for impurity variations, ensuring uniform separation layer formation.
3Manufacturing precision
If different irradiation conditions are applied to facet and non-facet regions, then separation layer formation is improved, but variations in impurity concentration within each region still cause position inconsistencies
Solution Approach 1:
The patent dynamically adjusts laser irradiation parameters (power, speed, focal point) based on real-time fluorescence detection results. Instead of using fixed conditions for entire regions, the system continuously adapts parameters to match local impurity concentrations, achieving uniform separation layer formation while managing complexity through automated control.
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 approach allows for reduced kerf loss and consistent separation layer formation across the ingot, even with regions of different impurity concentrations, enhancing the efficiency of wafer slicing.
Implementation Method 1
a fluorescence detection unit configured to irradiate excitation light of a predetermined wavelength to the ingot from above the ingot, and to detect fluorescence occurring from the ingot
Implementation Method 2
a laser beam irradiation unit configured to irradiate a laser beam of a wavelength, which has transmissivity through the ingot, to the ingot with a focal point of the laser beam positioned at a depth from an upper surface of the ingot
Data Source
AI summary
Irradiation conditions for a laser beam to respective ones of a plurality of regions included in the upper surface of an ingot are set according to the numbers of photons of fluorescence occurring when excitation light is irradiated to the respective regions. Here, it is to be understood that the number of the photons of the fluorescence occurring from a region of an ingot depends on the concentration of an impurity doped in the ingot. A separation layer can therefore be formed at a uniform depth from the upper surface of the ingot even if regions of different impurity concentrations are included in the ingot. It is hence possible to reduce a kerf loss when wafers are sliced from an ingot.