Wafer Image Comparison to Prevent Laser Re-Processing
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Solution Overview
Problem
The challenge is to prevent re-processing of already processed wafers in laser processing, as the presence of modified layers formed during initial processing makes it difficult to visually confirm processing status, leading to potential damage from irregular laser reflection.
Innovation Solution
A laser processing apparatus with a control unit that captures and compares reference images of unprocessed wafers with images of wafers to determine processing status, issuing an alarm if a wafer has already been processed, using predetermined agreement values to decide on wafer processing states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a laser beam is applied to a wafer to form modified layers along streets, then the wafer can be divided into individual device chips, but the presence of modified layers cannot be easily confirmed by the naked eye, making it impossible to determine whether the wafer has been processed
Solution Approach 1:
The patent utilizes optical imaging to detect changes in light transmission or reflection properties of the wafer after laser processing. The imaging unit captures images of the wafer, and the control unit compares these images to detect the presence of modified layers along the streets, enabling non-contact visual confirmation of processing status through optical property changes
Solution Approach 2:
The patent replaces manual visual inspection with an automated imaging and image processing system. The imaging unit and control unit work together to automatically detect processing status by analyzing optical images, substituting human sensory limitations with machine-based optical detection and computational analysis
2Reliability
If a processed wafer is subjected to laser processing again, then the laser beam may reflect irregularly from the modified layers, causing damage to devices and considerable loss
Solution Approach 1:
The patent performs image capture and processing status determination before the laser processing operation begins. The control unit decides whether the wafer has already been processed based on image analysis, and only permits laser processing if the wafer is confirmed unprocessed, preventing re-processing damage through advance detection
Solution Approach 2:
The patent implements a feedback control mechanism where the imaging unit continuously monitors wafer processing status, and the control unit uses this information to control whether the laser processing should proceed. This closed-loop control prevents re-processing by using real-time image feedback to inhibit laser operation on already processed 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
Prevents re-processing of processed wafers, thereby avoiding damage from irregular laser reflections and ensuring accurate processing by determining the processing state of wafers through image comparison and agreement calculations.
Implementation Method 1
an imaging unit that images the wafer in a manner of transmission through the wafer
Implementation Method 2
a laser beam applying unit that applies a laser beam of such a wavelength as to be transmitted through the wafer to the wafer held by the chuck table, with a focal point of the laser beam positioned inside the wafer along the streets, to form modified layers
Data Source
AI summary
A control unit of a laser processing apparatus includes: a reference image storage section that images streets before formation of modified layers by an imaging unit and stores the captured image as a reference image; a calculation section that compares the reference image stored in the reference image storage section with an image of a wafer held by a chuck table that is captured by the imaging unit, and calculates the degree of agreement of the two images; and a decision section that decides whether the wafer is an unprocessed wafer not formed with the modified layers in the case where the degree of agreement calculated by the calculation section is more than a first predetermined value, and decides whether the wafer is a processed wafer formed with the modified layers in the case where the degree of agreement is equal to or less than a second predetermined value.