SiC Laser Wafer Separation with Absorbing Chuck Surface Inspection
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Solution Overview
Problem
The existing methods for producing wafers from silicon carbide (SiC) ingots face inefficiencies due to high material loss during cutting and polishing, and errors in the inspection of separation layers formed during laser processing, particularly when the ingot thickness decreases, affecting the accuracy of the separation layer formation.
Innovation Solution
A laser processing apparatus with a chuck table having a holding surface that absorbs inspection light and a porous plate made of porous glass, which reduces the reflection of inspection light and minimizes errors in the inspection of separation layers, allowing for precise formation and inspection of separation layers in SiC ingots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SiC ingot is held on a conventional chuck table with a reflective holding surface, then the ingot can be securely held during laser processing, but the inspection light is reflected by the chuck table causing errors in separation layer inspection
Solution Approach 1:
The holding surface of the chuck table is changed to a black color that absorbs inspection light instead of reflecting it. This color change eliminates the harmful reflection that interfered with separation layer inspection, allowing accurate detection of the separation layer formation without errors caused by reflected light from the chuck table surface.
Solution Approach 2:
The reflective property of the chuck table holding surface, which originally caused harmful interference with inspection, is converted into a beneficial absorbing surface. By making the holding surface black, the previously harmful reflected light is transformed into absorbed light, eliminating the inspection error and turning the chuck table's holding function into a non-interfering support structure.
2Productivity
If a wire saw is used to cut the SiC ingot, then the ingot can be divided into wafers, but 70% to 80% of the ingot is discarded resulting in low productivity and high cost
Solution Approach 1:
The mechanical wire saw cutting system is replaced with a laser processing system that forms separation layers inside the SiC ingot. This substitution eliminates the need for physical cutting and polishing, allowing wafers to be separated along the formed separation layers without discarding 70-80% of the ingot, thereby dramatically improving productivity and reducing material waste.
Solution Approach 2:
The laser processing method utilizes phase transitions and chemical reactions within the SiC ingot to form separation layers. By irradiating the ingot with laser beams, the SiC undergoes decomposition and phase changes to create separation layers, enabling wafer division without mechanical cutting and minimizing material loss.
3Productivity
If the SiC ingot height decreases due to repeated wafer separation, then more wafers can be produced from the ingot, but the originally-set processing conditions become ineffective for forming proper separation layers
Solution Approach 1:
The laser processing system is designed with dynamic adjustment capabilities that allow processing conditions to be automatically modified based on the remaining ingot height. As wafers are separated and the ingot becomes thinner, the system dynamically adjusts laser parameters such as power, speed, and focal position to maintain effective separation layer formation throughout the entire processing sequence.
Solution Approach 2:
The system incorporates inspection mechanisms that monitor separation layer formation in real-time and provide feedback to the control system. Based on this feedback, the processing conditions are automatically adjusted to compensate for changes in ingot height, ensuring consistent separation layer quality across all wafers produced from a single ingot.
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
The solution effectively suppresses errors in the inspection results of SiC ingots, enhancing the accuracy and efficiency of the wafer separation process by reducing the influence of reflected light from the chuck table, thereby improving the productivity and quality of wafer production.
Implementation Method 1
a beam condenser that positions the focal point of a laser beam with a wavelength having transmissibility with respect to SiC, to a depth equivalent to the thickness of a wafer to be produced from an upper surface of the SiC ingot, and that irradiates the SiC ingot with the laser beam to form the separation layer arising from separation of SiC into Si and carbon (C) and extension of cracks along a c-plane
Implementation Method 2
a separation layer inspecting unit that executes irradiation with inspection light with such a wavelength as to have transmissibility with respect to the SiC ingot and be reflected by the separation layer and that inspects the separation layer from the intensity of reflected light
Implementation Method 3
The holding surface of the chuck table has a color that absorbs the inspection light
Data Source
AI summary
A laser processing apparatus includes a chuck table that holds an SiC ingot on a holding surface, a laser beam irradiation unit that positions the focal point of a laser beam to a depth equivalent to the thickness of a wafer to be produced from a first surface and that irradiates the SiC ingot with the laser beam to form a separation layer arising from separation of SiC into Si and C and extension of cracks along a c-plane. A movement unit relatively moves the chuck table and the laser beam irradiation unit, and a separation layer inspecting unit executes irradiation with inspection light with such a wavelength as to have transmissibility with respect to the SiC ingot and be reflected by the separation layer, and inspects the separation layer from the intensity of reflected light. The holding surface has a color that absorbs the inspection light.