Laser Machining Height Detection via Interferometric and Confocal Fusion
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Solution Overview
Problem
The challenge in laser machining semiconductor and optical device wafers is the difficulty in achieving uniform modified layer formation due to variations in wafer thickness, which disrupts the interference between light reflected from the wafer and reference light, making it hard to accurately measure the height position of the workpiece.
Innovation Solution
A laser machining apparatus incorporating both interferometric and confocal optical height position detection systems, where the difference in height measurements from both methods is used to correct the position of the condensing point, ensuring accurate height positioning even with disturbances in interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an interferometric height position detector is used to achieve wide measurement range and high detection speed, then detection speed and measurement range are improved, but measurement accuracy deteriorates when interference is disturbed by DBR films on optical device wafers
Solution Approach 1:
The patent combines both interferometric height position detection and confocal optical height position detection systems in the laser machining apparatus. The interferometric system provides fast detection speed and wide measurement range, while the confocal system ensures accurate height position measurement even when interference is disturbed by DBR films. The control unit integrates data from both systems to achieve reliable height position detection for laser machining.
2Adaptability or versatility
If wafer thickness varies due to undulations, then adaptability to different wafer conditions is improved, but manufacturing precision deteriorates because uniform modified layer formation becomes difficult
Solution Approach 1:
The patent performs height position detection of the wafer surface before laser machining using both interferometric and confocal optical detection systems. This preliminary detection allows the control unit to determine accurate height positions and adjust laser beam irradiation parameters in advance, ensuring uniform modified layer formation despite variations in wafer thickness caused by undulations.
Solution Approach 2:
The patent dynamically adjusts the laser beam irradiation conditions based on real-time height position detection results. The control unit modifies laser parameters such as power, pulse duration, and scanning speed according to the detected wafer surface topography, enabling consistent modified layer formation across areas with varying thickness while maintaining adaptability to different wafer conditions.
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
This approach allows for precise and accurate measurement of the workpiece height, enabling uniform modified layer formation despite wafer thickness variations and interference issues.
Implementation Method 1
The interferometric height position detection means detects the height position of the upper face of the workpiece held by the chuck table based on the interference between light reflected from the upper face of the workpiece and reference light
Implementation Method 2
The confocal optical height position detection means detects the height position of the upper face of the workpiece held by the chuck table
Implementation Method 3
The laser beam irradiation means has an objective condenser lens adapted to condense and irradiate a laser beam onto the workpiece held by the chuck table
Data Source
AI summary
A laser machining apparatus that includes an interferometric height position detection unit, a condensing point position adjustment unit, and a confocal optical height position detection unit. A controller of the laser machining apparatus specifies, as a correction value, the difference between the two height positions of the upper face of the workpiece, one detected by the confocal optical height position detection unit and the other detected by the interferometric height position detection unit. The controller controls the condensing point position adjustment unit based on the height position obtained by correcting the height position of the upper face of the workpiece detected by the interferometric height position detection unit using the correction value.