Height Detection Using Chromatic Aberration Lens
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Solution Overview
Problem
Variations in the thickness of semiconductor wafers cause challenges in uniform laser processing, as existing height detecting apparatuses struggle to accurately detect the height of the workpiece, leading to deviations in laser application and incomplete or uneven modified layer formation.
Innovation Solution
A height detecting apparatus utilizing a light source with a predetermined wavelength band, a Fabry-Perot tunable filter, and a chromatic aberration lens to sweep light wavelengths and detect return light intensity, allowing for precise determination of the workpiece height by correlating wavelength and intensity with pre-set values, enabling accurate positioning and uniform processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If oblique light application method is used for height detection, then height detection can be performed, but light application position deviates from division line and detection accuracy deteriorates
Solution Approach 1:
Instead of applying light obliquely and detecting reflected light at an angle, the present invention applies light perpendicularly (orthogonally) to the workpiece upper surface and detects the reflected light along the same perpendicular path. This inversion of the detection geometry eliminates position deviation and ensures accurate height measurement at the intended location.
2Measurement precision
If perpendicular light application is used, then accurate height detection is achieved, but existing apparatus cannot detect height at proper position
Solution Approach 1:
The present invention replaces complex mechanical positioning systems with an optical field-based height detection system. By using a perpendicular light application method with optical field control, the system achieves accurate height detection without requiring complex mechanical adjustments or positioning mechanisms.
3Adaptability or versatility
If variations in wafer thickness are present, then workpiece must be held on chuck table, but uniform laser processing becomes difficult
Solution Approach 1:
The present invention performs height detection of the workpiece upper surface before laser processing. By measuring and storing the height information at each position in advance, the system can compensate for thickness variations during subsequent laser processing, ensuring uniform modified layer formation despite variations in wafer thickness.
Solution Approach 2:
The height detection apparatus provides feedback information about the workpiece surface topography to the control system. This feedback enables real-time adjustment of laser processing parameters or focal position to maintain uniform processing quality across areas with varying thickness.
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 solution ensures accurate detection of the workpiece height, preventing deviations in laser application and allowing for uniform formation of modified layers or grooves, even on wafers with thickness variations, thereby enhancing the precision and consistency of laser processing.
Implementation Method 1
a Fabry-Perot tunable filter connected to the first single-mode fiber between the light source and the fiber coupler for sequentially sweeping light having a single wavelength from the wavelength band at predetermined cycles
Implementation Method 2
a chromatic aberration lens for focusing the light transmitted from the Fabry-Perot tunable filter and applying this light to the workpiece held on the workpiece holding means
Implementation Method 3
a photodetector for detecting the return light emerging from the second single-mode fiber and outputting a signal corresponding to the intensity of the return light detected above
Data Source
AI summary
A height detecting apparatus for detecting the height of a workpiece held on a chuck table. The height detecting apparatus includes a single-mode fiber for transmitting return light reflected from the workpiece and next branched by a fiber coupler, a photodetector for detecting the return light emerging from the single-mode fiber and outputting a signal corresponding to the intensity of the return light detected above, and a controller having a memory for storing a table setting the relation between wavelength and height. The controller determines the wavelength corresponding to the highest light intensity from the wavelengths detected by the photodetector in synchronism with the predetermined cycles of sweeping of light having a single wavelength by a Fabry-Perot tunable filter, and then checks this determined wavelength against the wavelength and height set in the table, thereby determining the height of the workpiece held on the chuck table.