Fourier-Transform Thickness Measurement For Plate-Shaped Workpieces
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Solution Overview
Problem
Existing thickness measurement methods for plate-shaped workpieces, such as wafers, are time-consuming due to the need to change irradiation positions to detect thickness across an entire area.
Innovation Solution
A thickness measuring apparatus with a chuck table and scanning mirror system that uses a light source, diffusing film, and light detector to measure thickness at multiple coordinates simultaneously by emitting light at specified wavelengths and performing Fourier transforms on detected light intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a noncontact type measuring instrument using spectral interference waveform is used to measure the entire area of the wafer, then measurement precision is improved, but measurement time increases due to the need to change irradiation positions
Solution Approach 1:
The patent transitions from one-dimensional sequential point measurement to two-dimensional simultaneous area measurement by projecting the spectral interference waveform across the entire wafer surface using a diffraction grating and line sensor, enabling parallel measurement of multiple positions
Solution Approach 2:
The patent creates an optical copy of the spectral interference information from the entire wafer surface and projects it onto a diffusing film where a line sensor can simultaneously detect the waveform at multiple positions, replacing physical sequential scanning
2Loss of time
If a contact type measuring instrument is used to measure wafer thickness, then measurement time is reduced, but the grinding surface of the wafer is damaged
Solution Approach 1:
The patent replaces the mechanical contact measurement system with an optical measurement system that uses light to detect thickness, eliminating mechanical contact and its associated surface damage while maintaining measurement capability
Solution Approach 2:
The patent introduces light as an intermediary between the measurement instrument and the wafer surface, allowing thickness measurement without direct contact through optical interference phenomena
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 rapid measurement of thickness at multiple positions on a plate-shaped workpiece, improving productivity in grinding, polishing, and laser processing by reducing measurement time.
Implementation Method 1
reflected light forming a spectral interference waveform by being reflected from a top surface and an undersurface of the plate-shaped workpiece
Implementation Method 2
spectral interference waveform between light reflected from the grinding surface of the wafer and light transmitted through the wafer and reflected from an opposite surface
Implementation Method 3
disperses return light reflected from the upper surface and the lower surface of the wafer by a diffraction grating
Data Source
AI summary
A measuring instrument includes a light source, a scanning mirror configured to position the light emitted by the light source at coordinates specified by an X-coordinate and a Y-coordinate on a plate-shaped workpiece held on a chuck table, a diffusing film onto which reflected light is projected, the reflected light forming a spectral interference waveform by being reflected from a top surface and an undersurface of the plate-shaped workpiece held on the chuck table, a light detector configured to detect light intensities corresponding to wavelengths of the spectral interference waveform projected onto the diffusing film, a memory configured to store, for each coordinate, the light intensities corresponding to the wavelengths and being detected by the light detector, and a calculating section configured to calculate a thickness at each coordinate by performing a Fourier transform of the light intensities corresponding to the wavelengths and being stored in the memory.