SiC Wafer Planarization via Laser Separation and Optical Flatness Feedback
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Solution Overview
Problem
The separation surface of silicon carbide (SiC) ingots becomes rough after wafer separation, leading to inefficient grinding processes due to difficulty in detecting flatness, resulting in excessive grinding and low productivity.
Innovation Solution
A planarization method involving the formation of a separation layer within the SiC ingot using a laser beam to generate isotropic cracks, followed by a grinding step with a rotatable chuck table and ring-patterned grinding wheel, and a flatness detection process using light reflection to determine when the surface is flat, thereby ending the grinding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the separation surface is ground to make it flat, then the flatness is improved, but the grinding time is extended and excessive grinding occurs
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the reflected light intensity during grinding. The light emitting unit irradiates the separation surface, and the light receiving unit detects the reflected light. When the surface becomes flat, the reflected light intensity changes characteristically, providing real-time feedback to automatically terminate the grinding process, thus preventing excessive grinding while ensuring adequate flatness
Solution Approach 2:
The patent replaces manual or conventional mechanical flatness detection methods with an optical detection system. By using light emission and reflection detection, the system automatically determines when the separation surface has achieved sufficient flatness, eliminating the need for prolonged mechanical grinding and manual inspection
2Ease of manufacture
If conventional wire saw cutting is used to generate wafers from SiC ingot, then the wafer can be produced, but the cutting time is considerable and productivity is low
Solution Approach 1:
The patent replaces the mechanical wire saw cutting process with a laser-based separation method. By irradiating the SiC ingot with a laser beam having a specific wavelength that transmits through SiC, a separation layer is formed at the planned cutting plane, and the wafer is separated along this layer. This optical method eliminates the time-consuming mechanical cutting process while maintaining wafer production capability
Solution Approach 2:
The laser irradiation induces localized phase changes and thermal effects within the SiC ingot at the focal point, creating a separation layer through controlled material modification. This allows separation without mechanical contact, dramatically reducing cutting time while preserving the integrity of the generated wafers
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 prevents excessive grinding and shortens the grinding time by accurately detecting the flatness of the separation surface, enhancing the efficiency of the SiC ingot planarization process.
Implementation Method 1
the focal point of a laser beam with such a wavelength as to be transmitted through SiC is positioned inside an SiC ingot and the SiC ingot is irradiated with the laser beam to form a separation layer
Implementation Method 2
the SiC ingot is irradiated with the laser beam to form a separation layer in which SiC is separated into Si and C
Implementation Method 3
grinding is carried out by a grinding wheel having plural grinding abrasives disposed in a ring manner, and the separation surface of the ingot is made flat
Implementation Method 4
irradiating the separation surface of the SiC ingot exposed from the grinding wheel with light and detecting reflected light to detect the degree of flatness
Data Source
AI summary
A planarization method includes a grinding step of holding the opposite side to a separation surface in an SiC ingot by a rotatable chuck table and rotating a grinding wheel having plural grinding abrasives disposed in a ring manner to grind the separation surface of the SiC ingot held by the chuck table, and a flatness detection step of irradiating the separation surface of the SiC ingot exposed from the grinding wheel with light and detecting reflected light to detect the degree of flatness. The grinding step is ended when that the separation surface of the SiC ingot has become flat is detected in the flatness detection step.