Silicon Ingot Separation Layer Inspection by Transmitted Light
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Solution Overview
Problem
Existing methods for determining a separation layer inside a silicon ingot for wafer separation are prone to productivity loss and are influenced by saw marks, leading to incomplete separation and material waste.
Innovation Solution
An inspection method and apparatus that utilize laser beam irradiation to form a separation layer within a silicon ingot, followed by light reflection analysis to determine the state of cracks and connectivity, allowing for efficient wafer separation without productivity loss and saw mark interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a collecting lens and separation layer detecting unit are disposed adjacent to each other along the processing feed direction, then the detection timing coincides with the end of laser processing, but a region becomes undetectable requiring overrun of the lens and detecting unit, which lowers productivity
Solution Approach 1:
The patent changes the spatial arrangement from a linear configuration (along the processing feed direction) to a configuration where the light source and light receiving unit are positioned on opposite sides of the workpiece. This dimensional change allows light to pass through the workpiece and detect the separation layer without requiring overrun movements, thereby maintaining full detection coverage while improving productivity.
2Measurement precision
If the separation layer state is determined using the magic mirror principle, then the separation layer can be detected, but the determination is susceptible to influence from saw marks on the ingot surface
Solution Approach 1:
The patent extracts the harmful factor (saw marks on the surface) from the detection process by using transmitted light that passes through the workpiece rather than reflected light from the surface. This allows detection of the internal separation layer while eliminating interference from surface defects like saw marks, thereby improving both detection capability and reliability.
3Ease of manufacture
If wire saw cutting is used to cut wafers from silicon ingot, then cutting can be performed, but the cutting allowance is large (approximately 300 μm) and additional processing (lapping, etching, polishing) is required, resulting in low productivity
Solution Approach 1:
The patent applies preliminary action by forming a separation layer inside the silicon ingot before the actual cutting process. This internal separation layer serves as a pre-prepared fracture line that guides subsequent breaking, eliminating the need for large cutting allowances and additional surface processing steps, thereby significantly improving productivity.
4Loss of substance
If laser beam irradiation is used to form separation layer inside ingot, then material loss is significantly reduced, but there is risk of insufficient separation layer formation or incomplete separation
Solution Approach 1:
The patent implements feedback by using a light receiving unit to detect the separation layer formed by laser irradiation. The detected information provides feedback on the quality and completeness of separation layer formation, allowing for verification and adjustment to ensure reliable separation while maintaining the advantage of reduced material loss.
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
Enables rapid and accurate determination of separation layer formation and connectivity, ensuring efficient wafer separation with minimal material loss and improved productivity.
Implementation Method 1
positioning the focal point of a laser beam with a wavelength having transmissibility with respect to the workpiece to a depth equivalent to a thickness of a wafer to be manufactured from the upper surface of the workpiece and executing irradiation with the laser beam
Implementation Method 2
forming a separation layer including a modified layer parallel to the upper surface and cracks that extend from the modified layer inside the workpiece
Implementation Method 3
irradiating the whole of the upper surface of the workpiece in which the separation layer has been formed with light having such a wavelength as to be transmitted through the workpiece and reflect at the crack of the separation layer
Implementation Method 4
receiving reflected light resulting from the irradiation in the irradiation step and reflection by the crack
Data Source
AI summary
An inspection method of a workpiece includes a separation layer forming step of forming a separation layer composed of a modified layer parallel to an upper surface and cracks that extend from the modified layer inside the workpiece, an irradiation step of irradiating the whole of the upper surface of the workpiece in which the separation layer has been formed with light with such a wavelength as to be transmitted through the workpiece and reflect at the crack of the separation layer after the separation layer forming step is executed, a light reception step of receiving reflected light resulting from the irradiation in the irradiation step and reflection by the crack, and a determination step of determining the state of the separation layer on the basis of the intensity of the reflected light received in the light reception step.