Optical Film Thickness Meter Double-Substrate Measurement
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Solution Overview
Problem
Existing optical film thickness meters face challenges in accurately measuring film thickness and spectroscopic characteristics due to measurement errors caused by differences in transmission positions and the need for an anti-reflective film, especially when measuring substrates with low refraction indices like SiO2, leading to instability and control errors in the film forming process.
Innovation Solution
An optical film thickness meter that measures light passing through an actual substrate twice, using a reflection mirror to reflect the light and ensure it passes through the same spot, eliminating measurement errors by inclining the substrate relative to the optical system, thereby increasing transmissivity and improving control accuracy without requiring an anti-reflective film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a corner cube prism is used to reflect the outgoing light, then the film thickness can be measured, but measurement errors occur due to different transmission positions and multiple reflections
Solution Approach 1:
The patent extracts the harmful multiple reflection components from the measurement system by using a beam splitter to separate the direct reflection light from the corner cube prism from the transmitted light path, eliminating measurement errors caused by substrate surface reflections
Solution Approach 2:
The patent introduces a beam splitter as an intermediary component that mediates between the corner cube prism and the detector, allowing the system to distinguish and separately measure the useful transmitted light from the harmful multiple reflection light
2Measurement precision
If a transmission type optical film thickness meter is used, then high measurement accuracy can be achieved, but control is difficult for substrates with low refraction index difference
Solution Approach 1:
The patent employs periodic modulation of the light source intensity and synchronous detection to amplify the small signal changes caused by thin film deposition, making the measurement controllable and detectable even for substrates with low refraction index difference
Solution Approach 2:
The patent changes the measurement parameter from direct transmissivity to the rate of change of transmissivity over time, allowing detection of small film thickness changes by measuring the derivative signal rather than the absolute value
3Measurement precision
If an anti-reflective film is formed on each surface, then accurate measurement can be made, but the device complexity and manufacturing process increase
Solution Approach 1:
The patent extracts and removes the harmful multiple reflection components from the measurement signal using a beam splitter, eliminating the need for anti-reflective films on the substrate surfaces
Solution Approach 2:
The patent converts the harmful multiple reflection effect into a separate measurable signal that can be subtracted from the total signal, allowing accurate film thickness measurement without requiring anti-reflective film treatment
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 minimizes measurement errors, enhances the accuracy of film thickness control, and allows for precise measurement of optical film thickness and spectroscopic characteristics, particularly for substrates with low refraction indices, by ensuring consistent light paths and increased light amount changes.
Implementation Method 1
light projecting means which emits outgoing light L1 as measurement light toward the actual substrate S... light receiving means which receives the measurement light which has passed through the actual substrate, been reflected by the reflection mirror and passed through the actual substrate
Implementation Method 2
a reflection mirror which reflects the outgoing light at a position on the side opposite to the light projecting means relative to the actual substrate S
Data Source
AI summary
An optical film thickness meter capable of measuring an optical film thickness and spectroscopic characteristics highly accurately, and a thin film forming apparatus with the optical film thickness meter are provided. The optical film thickness meter includes a light projector, a light receiver, a monochromator, and a reflection mirror having a reflection surface substantially perpendicularly to the optical axis of measurement light on the side opposite to an actual substrate. The actual substrate is disposed having a predetermined angle to the optical axis. The measurement light passes through the actual substrate twice, whereby a change in transmissivity can be increased, and control accuracy of thickness measurement is improved. Measurement errors caused by a difference in transmission positions is prevented. Since the measurement light which has not passed through the measurement substrate twice is not detected by the light receiver, the optical film thickness and spectroscopic characteristics is measured highly accurately.