Thickness Measuring Apparatus Using Zero-Crossing Differential Waveform Analysis
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Solution Overview
Problem
Existing thickness measuring apparatuses face challenges in accurately measuring the thickness of thin wafers and composite materials with multiple layers, as they require precise waveform analysis and are material-specific, leading to difficulties in detecting individual layer thicknesses without damaging the surface.
Innovation Solution
A thickness measuring apparatus that uses a light source to emit white light, a diffraction grating to separate wavelengths, and an image sensor to generate spectral interference waveforms, with a reference waveform recording section to determine thickness based on material-specific reference waveforms, allowing for accurate measurement of single and multi-layered materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If waveform analysis based on Fourier transform is used to measure thickness, then noncontact measurement is achieved, but measurement precision decreases as wafer becomes thinner
Solution Approach 1:
The patent changes the measurement parameter from peak value detection to zero-crossing point detection in the differential waveform. This parameter change enables accurate thickness measurement of thin wafers by identifying the point where the differential waveform crosses zero, which corresponds to the thickness information, rather than relying on peak values that become less distinct for thinner samples.
Solution Approach 2:
The patent replaces the conventional Fourier transform-based thickness extraction method with a differential waveform analysis method. By differentiating the spectral interference waveform and detecting zero-crossing points, the system achieves better precision for thin wafer measurement without contact, substituting a more sensitive signal processing approach.
2Reliability
If spectral interference waveform analysis is used, then noncontact thickness measurement is achieved, but difficulty in detecting individual layer thicknesses in composite wafers increases
Solution Approach 1:
The patent applies segmentation by dividing the composite wafer measurement into individual layer measurements. By scanning the wafer surface and detecting zero-crossing points at different positions, the system separates and measures the thickness of each layer independently, even in multi-material composite structures.
Solution Approach 2:
The patent uses the differential waveform as an intermediary to extract thickness information from the spectral interference waveform. The zero-crossing points in the differential waveform serve as a clear marker that facilitates the detection of individual layer thicknesses in composite wafers, making the measurement process more reliable.
3Measurement precision
If material-specific waveform analysis is required, then measurement precision for specific materials is improved, but adaptability to different materials decreases
Solution Approach 1:
The patent achieves universality by developing a measurement method that works across different materials through the common physical phenomenon of spectral interference. The differential waveform analysis and zero-crossing point detection approach is material-agnostic, allowing the same system to accurately measure thickness of various materials without requiring material-specific calibration or analysis methods.
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 high-accuracy thickness measurement of wafers, including those with multiple layers, by matching spectral interference waveforms with material-specific reference waveforms, improving precision and applicability across different materials.
Implementation Method 1
measures the thickness by obtaining spectral interference waveforms of light reflected from the grinding surface of the wafer and light passing through the wafer and reflected from an opposite surface
Implementation Method 2
a diffraction grating disposed in the second optical path; an image sensor configured to detect an optical intensity signal of light separated into each wavelength by the diffraction grating
Data Source
AI summary
A thickness measuring apparatus for measuring the thickness of a workpiece held on a chuck table includes the followings: a light source configured to emit white light; an optical branching unit configured to branch, to a second optical path, reflected light applied from the light source to the workpiece held on the chuck table via a first optical path and reflected from the workpiece; a diffraction grating disposed in the second optical path; an image sensor configured to detect an optical intensity signal of light separated into each wavelength by the diffraction grating; and a thickness output unit configured to generate a spectral interference waveform on the basis of the optical intensity signal detected by the image sensor, determine the thickness on the basis of the spectral interference waveform, and output the thickness.