Optical Wafer Thickness Measurement Without Spectral Dispersion
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Solution Overview
Problem
Existing non-contact measuring units for wafer thickness measurement are inefficient as they require spectral dispersion of return light by a diffraction grating and subsequent Fourier transform to calculate light intensity for each wavelength, making it difficult to measure thickness in a short period of time.
Innovation Solution
A measuring apparatus that includes a light source, a condenser lens, a collimating lens, a transmission filter, and a sensor to measure the thickness or height of a plate-shaped workpiece by detecting interference light and determining the coordinate position of high light intensity without the need for spectral dispersion or Fourier transform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a non-contact type measuring unit uses spectral dispersion by a diffraction grating to measure thickness, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent extracts only the necessary wavelength information directly at the measurement point using a spectrally selective detector, eliminating the need for full spectral dispersion and Fourier transform processing. This selective extraction of information reduces processing time while maintaining measurement accuracy.
Solution Approach 2:
The patent replaces the mechanical spectral dispersion system (diffraction grating) with an optical filtering approach using interference filters or tunable filters that can selectively transmit specific wavelengths. This substitution eliminates moving parts and complex optical paths while achieving the same measurement objective more rapidly.
2Productivity
If a contact type measuring unit is used to measure wafer thickness, then measurement speed is improved, but the ground surface may be damaged
Solution Approach 1:
The patent introduces light as an intermediary medium to perform thickness measurement without physical contact. The light interacts with the wafer to provide measurement information, eliminating direct mechanical contact that could damage the ground surface while maintaining measurement capability.
Solution Approach 2:
The patent replaces the mechanical contact measurement system with an optical measurement system. By using light reflection and interference phenomena, the system achieves thickness measurement without physical contact, thereby preventing ground surface damage while maintaining productivity.
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 wafer thickness or height without the need for spectral dispersion or Fourier transform, improving efficiency and reducing measurement time, which enhances the efficiency of laser processing and grinding.
Implementation Method 1
light reflected from the ground surface (upper surface) of the wafer and light transmitted through the wafer and reflected from a reflection surface (lower surface) of the wafer
Implementation Method 2
spectral interference waveform of light reflected from the ground surface (upper surface) of the wafer and light transmitted through the wafer and reflected from a reflection surface (lower surface) of the wafer
Data Source
AI summary
A measuring unit of a measuring apparatus includes a light source that emits light in a predetermined wavelength region, a condenser lens that applies the light emitted by the light source, to a plate-shaped workpiece held by a chuck table, a collimating lens that forms return light reflected by the plate-shaped workpiece into parallel light, a transmission filter that transmits interference light of the return light formed into the parallel light, a sensor that has coordinates for receiving the interference light transmitted through the transmission filter and detecting light intensity, and a controller that determines a coordinate position at which the light intensity detected by the sensor is high, as the thickness or height of the plate-shaped workpiece.