Wafer Thickness Measurement Using Spectral Interference Waveforms
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Solution Overview
Problem
Existing thickness measuring apparatuses face challenges in accurately measuring the thickness of thin wafers, especially those with multiple layers, due to interference from diffraction gratings and varying material properties, leading to difficulties in detecting individual layer thicknesses and achieving high accuracy.
Innovation Solution
A thickness measuring apparatus that uses white light, fθ lenses, and diffraction gratings to generate spectral interference waveforms, with image sensors detecting light intensity and a reference waveform recording section to compare and decide thickness based on material-specific reference waveforms, allowing for accurate measurement of composite wafers with multiple layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If spectral interference waveform is formed by light reflected from ground surface and transmitted light reflected from opposite surface, then non-contact measurement is achieved, but it becomes difficult to detect thickness of individual layers in composite wafers
Solution Approach 1:
The patent segments the spectral interference waveform into multiple wavelength components using a diffraction grating and multiple image sensors. Each image sensor detects spectral interference waveforms at different wavelengths, allowing the system to separate and analyze interference patterns from different layers independently. This segmentation enables identification of individual layer thicknesses in composite wafers by analyzing wavelength-specific interference characteristics
Solution Approach 2:
The patent adds the wavelength dimension to the measurement by using spectral interference waveforms at multiple wavelengths. Instead of analyzing a single interference waveform, the system captures spectral information across different wavelengths, creating a two-dimensional measurement space (position and wavelength) that enables differentiation between layers with different optical properties and thicknesses
2Measurement precision
If multiple diffraction gratings are used to form interfering light, then spectral interference waveform is generated, but thickness information of individual layers is synthesized and cannot be detected separately
Solution Approach 1:
The patent creates multiple copies of the interference measurement at different wavelengths using multiple image sensors. Each sensor captures a spectral interference waveform that is a copy of the overall interference pattern but at a specific wavelength range. By comparing these wavelength-specific copies, the system can identify which layers contribute to which interference patterns, thereby recovering individual layer thickness information that would otherwise be lost in the synthesized waveform
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 easy and high-accuracy thickness measurement of wafers, even those with multiple layers, by distinguishing between different materials and layers, improving processing efficiency into desired thicknesses.
Implementation Method 1
a light source that emits white light
Implementation Method 2
a plurality of fθ lenses disposed to share a measurement region of the workpiece
Implementation Method 3
a plurality of diffraction gratings each disposed on the plurality of second optical paths
Implementation Method 4
a plurality of image sensors that detect intensity of light spectrally split on each wavelength basis by the plurality of diffraction gratings and generate a spectral interference waveform
Implementation Method 5
measures the thickness by a spectral interference waveform formed by light reflected from the ground surface of the wafer and light that has been transmitted through the wafer and been reflected from the opposite surface
Data Source
AI summary
A thickness measuring apparatus that measures a thickness of a workpiece held by a chuck table. The thickness measuring apparatus includes plural image sensors that detect intensity of light spectrally split on each wavelength basis by plural diffraction gratings and generate a spectral interference waveform and a thickness output unit that outputs thickness information from the spectral interference waveform generated by the plural image sensors. The thickness output unit includes a reference waveform recording section in which spectral interference waveforms corresponding to plural thicknesses are recorded as reference waveforms and a thickness deciding section that compares plural spectral interference waveforms generated by the plural image sensors with the reference waveforms recorded in the reference waveform recording section and decides the thickness corresponding to each spectral interference waveform from the reference waveform that corresponds to the spectral interference waveform in the waveform shape.