Transmission Thermometry with Laser Decorrelation for Noise Reduction
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Solution Overview
Problem
Current temperature measurement techniques using laser radiation in thermal processing chambers face significant noise due to interference effects and varying refractive indices of substrates, which reduces the accuracy of thermal state detection.
Innovation Solution
Incorporating a decorrelator, such as a broadband amplifier or mode scrambler, in the optical path to broaden the spectrum and reduce coherency of the radiation, thereby minimizing noise and improving the accuracy of temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high power laser radiation is used to detect thermal state, then the radiation can be differentiated from background radiation, but noise is generated due to interference effects and wavelength variations
Solution Approach 1:
A decorrelator device is introduced as an intermediary component in the optical path between the laser source and substrate. This decorrelator broadens the spectral width of the laser radiation and reduces temporal coherence, thereby eliminating interference effects while maintaining the high power needed for background differentiation. The decorrelator acts as a mediator that transforms the laser output into optimized measurement radiation.
Solution Approach 2:
The spectral parameters of the laser radiation are changed by passing it through a decorrelator. The decorrelator increases the spectral width from a narrow laser line to a broader spectrum, and modifies the temporal coherence properties. This parameter transformation maintains the radiance needed for detection while eliminating the harmful interference effects caused by narrow spectral width and high coherence.
2Stability of the object's composition
If temperature-controlled lasers are used, then wavelength stability is improved, but mode-hopping noise remains
Solution Approach 1:
The decorrelator serves as an intermediary that processes the laser output to eliminate mode-hopping effects. By broadening the spectrum and reducing coherence, the decorrelator transforms the unstable narrow-line laser radiation into stable broad-band radiation suitable for accurate transmission measurement.
3Power
If narrow spectral width laser radiation is used, then high power is achieved, but interference effects are produced when radiation reflects between substrate surfaces
Solution Approach 1:
The decorrelator is positioned in the optical path as an intermediary device that modifies the laser radiation properties. It broadens the spectral width and reduces temporal coherence, thereby eliminating the interference effects generated by reflections between substrate surfaces while preserving the high power characteristics needed for effective measurement.
Solution Approach 2:
The spectral and coherence parameters of the laser radiation are transformed by the decorrelator. The narrow spectral width is broadened, and the high temporal coherence is reduced, converting the radiation into a form that maintains high power but eliminates interference effects caused by substrate reflections.
4Temperature
If substrate temperature changes occur, then thermal state information is available, but refractive index and thickness changes alter interference patterns
Solution Approach 1:
By changing the spectral parameters of the measurement radiation through the decorrelator, the system becomes insensitive to the refractive index and thickness variations that occur with temperature changes. The broadened spectrum and reduced coherence eliminate the formation of temperature-dependent interference patterns, allowing direct correlation of transmitted radiation intensity with substrate thermal state.
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
The use of a decorrelator significantly reduces noise in the detected radiation, allowing for more precise correlation of transmitted radiation with the thermal state of the substrate, enhancing the accuracy of temperature measurement.
Implementation Method 1
The decorrelator may be a broadband amplifier and/or a mode scrambler. A broadband amplifier may be a broadband laser, Bragg grating, a fiber Bragg grating, a Raman amplifier, a Brillouin amplifier, or combinations thereof.
Implementation Method 2
The decorrelator may be a broadband amplifier and/or a mode scrambler.
Implementation Method 3
Lasers are typically used because they offer high power, and because they afford the opportunity to select a particular wavelength best suited to the substrate. Lasers produce coherent radiation that, when transmitted through a substrate, can indicate a thermal state of the substrate
Implementation Method 4
As this varying radiation impacts a substrate, some of the radiation reflects between the opposite surfaces of the substrate, producing an interference effect.
Implementation Method 5
As the substrate temperature changes, its refractive index may change, and its thickness may change, altering the interference patterns observed.
Data Source
AI summary
Apparatus and methods for measuring the temperature of a substrate are disclosed. The apparatus includes a source of temperature-indicating radiation, a detector for the temperature-indicating radiation, and a decorrelator disposed in an optical path between the source of temperature-indicating radiation and the detector for the temperature-indicating radiation. The decorrelator may be a broadband amplifier and/or a mode scrambler. A broadband amplifier may be a broadband laser, Bragg grating, a fiber Bragg grating, a Raman amplifier, a Brillouin amplifier, or combinations thereof. The decorrelator is selected to emit radiation that is transmitted, at least in part, by the substrate being monitored. The source is matched to the decorrelator such that the emission spectrum of the source is within the gain bandwidth of the decorrelator, if the decorrelator is a gain-driven device.