Laser Processing Apparatus Focal Point Deviation Correction
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Solution Overview
Problem
Laser processing apparatuses face challenges in maintaining accuracy due to focal point deviation of the laser beam along wafer division lines, especially when forming modified layers, as the expansion caused by the laser beam makes it difficult to detect and correct the focal position, leading to inaccurate processing.
Innovation Solution
A laser processing apparatus with a chuck table, laser beam applying means, imaging means, X and Y moving means, and control means that includes a deviation detecting section to correct the index amount by detecting the deviation of the focal point from the center of each division line, allowing for high-precision processing without needing to visually recognize the modified layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a laser beam is applied to the wafer to form a modified layer inside the wafer along each division line, then the laser processing capability is improved, but the focal point deviates in the Y direction due to wafer expansion, causing loss of manufacturing precision
Solution Approach 1:
The patent implements a feedback mechanism where the imaging means detects the position of characteristic points on the wafer before and after laser processing. The control means calculates the deviation of the focal point from the division line based on the displacement of these characteristic points, and automatically corrects the indexing amount to compensate for this deviation, thereby maintaining manufacturing precision despite wafer expansion.
Solution Approach 2:
The patent replaces direct visual recognition of the modified layer with an imaging system that detects characteristic points on the wafer surface. This optical detection system substitutes for mechanical or visual inspection methods, enabling non-contact, high-precision measurement of focal point deviation without interfering with the laser processing.
2Reliability
If the focal point is set inside the wafer to form a modified layer, then the laser processing effectiveness is improved, but the modified layer cannot be visually recognized, making it difficult to detect focal position deviation
Solution Approach 1:
The patent introduces characteristic points as intermediary markers on the wafer surface. These characteristic points serve as mediators between the invisible modified layer and the detection system. By tracking the displacement of these visible characteristic points, the system can indirectly measure the focal point deviation caused by wafer expansion without needing to directly observe the modified layer.
Solution Approach 2:
The patent creates an optical copy or image of the wafer surface using the imaging means. This optical copy allows the control means to analyze the positions of characteristic points and calculate focal point deviation without physical contact with the wafer or interference with the laser processing, solving the detection difficulty while maintaining processing effectiveness.
3Productivity
If laser processing is performed along multiple division lines, then the productivity is improved, but the cumulative expansion causes increasing focal point deviation, reducing manufacturing precision
Solution Approach 1:
The patent performs preliminary detection of characteristic point positions before laser processing begins. The control means stores these initial positions and uses them as a reference to calculate cumulative deviation as processing progresses along multiple division lines. This allows the system to proactively adjust indexing amounts to compensate for anticipated cumulative expansion effects.
Solution Approach 2:
The patent implements dynamic correction of the indexing amount during the laser processing sequence. Rather than using a fixed indexing value, the control means continuously updates the indexing amount based on real-time deviation detection from characteristic points, allowing the system to adapt to cumulative wafer expansion and maintain precision throughout high-volume processing.
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 immediate correction of index amounts to maintain high-precision processing, even when the focal position deviates, ensuring accurate laser processing along wafer division lines without requiring detection of the modified layer formed inside the wafer.
Implementation Method 1
When the laser beam is applied to the wafer along each division line, a portion of the wafer irradiated with the laser beam is minutely expanded.
Implementation Method 2
imaging means for imaging the wafer held on the chuck table
Data Source
AI summary
A laser processing apparatus includes a controller having (a) a section for storing the Y coordinate of a characteristic point having a predetermined positional relation to each division line formed on a wafer as a reference value with respect to a reference position where the focal point of a laser beam coincides with a predetermined position on each division line, (b) a section for detecting the amount of deviation of the Y coordinate of the characteristic point after indexing each division line of the wafer in the Y direction by the operation of a Y moving unit, from the Y coordinate stored as the reference value, and (c) a section for determining whether or not the amount of deviation detected is greater than an allowable value.