Stray Light Compensation in Substrate Temperature Measurement
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Solution Overview
Problem
Existing non-contact optical temperature measurement techniques for semiconductor substrates in plasma processing chambers face inaccuracies due to the reliance on unknown emissivity values and the inability to distinguish between blackbody radiation from the substrate and stray blackbody radiation, leading to unreliable temperature readings.
Innovation Solution
A method and system that involve measuring the temperature of a reference target and stray blackbody radiation, calculating the reflectance of both, and using these values to determine the temperature of the target, while accounting for stray blackbody radiation through additional photocurrent terms in the Planck Radiation Equation, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If brightness pyrometry is used to measure substrate temperature, then non-contact measurement is achieved, but measurement precision deteriorates due to unknown emissivity
Solution Approach 1:
The patent introduces a reference target with known reflectance properties as an intermediary standard. By measuring the reference target's reflected radiation and comparing it with the substrate's radiation, the system creates a reference framework that eliminates the need to know the substrate's emissivity, thereby resolving the precision problem while maintaining non-contact measurement
Solution Approach 2:
The patent changes the measurement parameter from direct temperature measurement (which requires emissivity knowledge) to reflectance measurement. By measuring the reflectance of both the reference target and substrate at the same wavelength, and using the known reflectance of the reference target, the system calculates the substrate temperature without needing to know its emissivity
2Loss of information
If pyrometry measures radiation from the substrate, then temperature information is obtained, but measurement precision deteriorates due to stray blackbody radiation interference
Solution Approach 1:
The patent segments the total measured radiation into two distinct components: reflected radiation from the substrate and stray blackbody radiation from chamber walls. By separately measuring and calculating each component's contribution to the total photocurrent, the system can isolate and eliminate the stray radiation interference, thereby improving measurement precision
Solution Approach 2:
The patent implements a feedback mechanism where the measured reflectance of the substrate and the known reflectance of the reference target are used to calculate the expected reflected radiation. This calculated value is then fed back into the temperature calculation to compensate for and remove the stray blackbody radiation component from the total measurement
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 approach enables accurate non-contact temperature measurements of semiconductor substrates by accounting for stray blackbody radiation, enhancing the reliability and precision of temperature readings in plasma processing environments.
Implementation Method 1
The Planck Radiation Equation for spectral radiation emitted from an ideal blackbody
Implementation Method 2
Equation 3, which describes the photocurrent detected by a pyrometer
Implementation Method 3
a first reflected intensity from the light beam reflecting off a reference target
Data Source
AI summary
This disclosure describes systems, methods, and apparatuses for making a non-contact measurement of a substrate in a plasma processing chamber that accounts for stray blackbody radiation. In particular, a photocurrent is calculated that can be attributed to the stray blackbody radiation based upon a temperature of the stray blackbody radiation, a reflectance of a target substrate, and a temperature of the substrate. Knowing the photocurrent attributable to the stray blackbody radiation, a non-contact temperature measurement can be made, and the photocurrent attributable to the stray blackbody radiation can be subtracted out to arrive at a more accurate non-contact substrate temperature measurement.