SiC Wafer Laser Division Method
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Solution Overview
Problem
The high Mohs hardness of SiC substrates leads to excessive wear of abrasive members during grinding, resulting in poor economy and inefficiency in thinning and dividing wafers into device chips.
Innovation Solution
A wafer processing method that forms division start points and separation start points using a laser beam to create modified layers and cracks within the SiC substrate, allowing for wafer separation without grinding the back side, thereby reducing abrasive wear and enabling thinning and division of SiC wafers into individual device chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the back side of an SiC wafer is ground by a grinding wheel having abrasive members, then the wafer thickness is reduced to a predetermined thickness, but the abrasive members wear in an amount 4000 times to 5000 times that in grinding a silicon substrate
Solution Approach 1:
The patent replaces the mechanical grinding system with a laser-based processing system. A laser beam is used to form a modified layer and induce cracks along the division lines of the SiC wafer, enabling separation without mechanical contact. This substitution eliminates the excessive wear of abrasive members while achieving the required wafer thinning and division.
Solution Approach 2:
The patent changes the physical state and properties of the SiC wafer through laser irradiation. The laser beam modifies the crystal structure of the SiC at the division lines, creating a modified layer with different mechanical properties that facilitates clean separation. This parameter change allows the wafer to be divided without mechanical grinding.
2Ease of manufacture
If the back side of an SiC wafer is ground to reduce thickness, then the wafer can be divided into device chips, but the process becomes economically inefficient due to high abrasive wear
Solution Approach 1:
The patent replaces the energy-intensive mechanical grinding process with a laser-based process. The laser beam directly modifies the SiC material at the division lines, requiring significantly less energy input while achieving the same thinning and division results. This improves manufacturing efficiency and reduces energy consumption.
Solution Approach 2:
The patent performs preliminary laser processing to form modified layers and induce cracks along the division lines before final separation. This preliminary action prepares the wafer structure to facilitate easy and clean division, eliminating the need for subsequent mechanical grinding and improving overall process efficiency.
3Loss of substance
If a laser beam with transmission wavelength is applied to form a modified layer, then the wafer can be separated without grinding, but the focal point must be precisely controlled inside the substrate
Solution Approach 1:
The patent uses a protective member as an intermediary between the laser beam and the SiC wafer surface. The protective member helps control and distribute the laser energy, facilitating precise focal point positioning within the substrate. This intermediary element enables accurate modified layer formation while protecting the wafer surface during the process.
Solution Approach 2:
The patent utilizes the optical properties of SiC at different wavelengths. By selecting a laser wavelength that is transmitted by SiC and focusing it inside the substrate, the method creates a modified layer at a specific depth. The optical absorption and transmission characteristics of SiC enable precise control of the modification depth through wavelength selection and focal point adjustment.
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 abrasive wear, allowing for efficient thinning and division of SiC wafers with minimal grinding, achieving a cost-effective process and enabling reuse of the second wafer as an SiC substrate.
Implementation Method 1
a separation start point forming step of setting a focal point of a laser beam inside the SiC substrate at a predetermined depth from the second surface, which depth corresponds to a vertical position near the division start point, after performing the protective member providing step, and then applying the laser beam to the second surface as relatively moving the focal point and the SiC substrate
Implementation Method 2
applying the laser beam to the second surface as relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface and cracks extending from the modified layer along the c-plane
Data Source
AI summary
A wafer formed from an SiC substrate having a first surface and a second surface is divided into individual device chips. A division start point formed by a laser has a depth corresponding to the finished thickness of each device chip along each division line formed on the first surface. The focal point of the laser beam is set inside the SiC substrate at a predetermined depth from the second surface, and the laser beam is applied to the second surface while relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface and cracks extending from the modified layer along a c-plane, thus forming a separation start point. An external force is applied to the wafer, thereby separating the wafer into a first wafer having the first surface and a second wafer having the second surface.