Laser Spot Trajectory Control for Elliptical Wafer Drilling
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Solution Overview
Problem
The shape of the laser beam spot is often distorted, such as elliptical, leading to irregular processing shapes and reduced quality of device chips during laser processing, particularly when forming small holes on electrode pads.
Innovation Solution
A laser processing apparatus with a chuck table and a laser beam irradiation unit that includes an X-axis and Y-axis optical scanner, controlled by a controller which adjusts the position of the laser beam spot to match the desired processing shape coordinates, ensuring the spot's contour aligns with the processing shape even when the spot is elliptical.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser beam irradiation is executed using a conventional spot shape assumption (circular), then the processing speed and simplicity are maintained, but the actual processing shape becomes distorted when the spot is elliptical, reducing manufacturing precision
Solution Approach 1:
The system performs preliminary measurement of the actual laser spot shape using a camera before processing, and pre-calculates the corrected irradiation trajectory. This preliminary action allows the system to compensate for spot distortion without adding complexity during the actual processing phase, as the correction parameters are prepared in advance based on measured spot characteristics
Solution Approach 2:
The system implements feedback by measuring the actual laser spot shape with a camera and using this information to adjust the irradiation trajectory. The measured spot dimensions and orientation feed into the control system, which automatically calculates and applies the necessary trajectory corrections to achieve accurate processing shapes despite spot distortion
2Productivity
If the laser spot shape is not corrected for distortion, then the processing procedure remains simple and fast, but the processed shape deviates from the desired shape, reducing product quality
Solution Approach 1:
The system performs self-characterization by automatically measuring its own laser spot shape using an integrated camera and computational algorithms. This self-service approach eliminates the need for external calibration equipment or manual measurement, allowing the system to autonomously determine and compensate for its spot distortion while maintaining processing efficiency
Solution Approach 2:
The system dynamically changes the irradiation trajectory parameters based on the measured spot characteristics. By adjusting the trajectory coordinates and orientation according to the actual spot shape and orientation, the system compensates for distortion effects while maintaining high processing speed through automated real-time parameter adjustment
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 precise formation of desired processing shapes, preventing distortion and improving the quality of device chips by accurately positioning the laser beam spot within or outside the processing shape, regardless of its elliptical shape.
Implementation Method 1
irradiating the back surface of a device chip corresponding to an electrode pad with a laser beam and properly forming a small hole
Implementation Method 2
a small hole is formed in the back surface of an electrode pad formed on a device chip
Implementation Method 3
an X-axis optical scanner that is disposed between the laser oscillator and the fθ lens and induces the laser beam emitted by the laser oscillator in the X-axis direction, a Y-axis optical scanner that is disposed between the laser oscillator and the fθ lens and induces the laser beam emitted by the laser oscillator in the Y-axis direction
Implementation Method 4
an fθ lens that focuses the laser beam emitted by the laser oscillator on the workpiece held by the chuck table
Data Source
AI summary
A controller includes a spot shape storing section that stores the shape of a spot of a laser beam with which a wafer held by a chuck table is irradiated, and a processing shape storing section that stores X-coordinates and Y-coordinates on a processing shape to be formed in the wafer. When the wafer is irradiated with the spot of the laser beam, an X-axis optical scanner and a Y-axis optical scanner are controlled on the basis of the shape of the spot, and the X-coordinates and Y-coordinates on the processing shape and irradiation with the laser beam is executed so that that the contour of the shape of the spot is positioned to an X-coordinate and Y-coordinate on the processing shape, and that a tangent line to the spot and a tangent line to the processing shape at the X-coordinate and Y-coordinate correspond with each other.