Pyrometer Calibration Using Reflectance Ratios
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing pyrometer calibration methods for semiconducting wafers are inaccurate due to variations in geometry and optical transmission characteristics within processing chambers, leading to temperature measurement errors up to 30 K, and require a calibration sample that can only be used once.
Innovation Solution
A method involving a calibration sample with a transparent layer on a semiconducting wafer, where thermal radiation is measured at different wavelengths to determine reflectance ratios, allowing for accurate temperature assignment and calibration of the pyrometer, enabling precise temperature measurement across a wide range without damaging the calibration sample.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional calibration method using a single-wavelength pyrometer measurement is used, then the calibration process is simple, but the temperature measurement precision deteriorates due to variations in geometry and optical transmission characteristics
Solution Approach 1:
The calibration process is segmented into multiple measurement steps at different wavelengths (first wavelength and second wavelength), allowing independent characterization of reflectance and thermal radiation properties. This segmentation enables precise temperature determination by separating geometric/optical variations from intrinsic material properties.
Solution Approach 2:
The measurement approach transitions from single-wavelength to multi-wavelength measurement, adding the wavelength dimension to the calibration process. By measuring at multiple wavelengths, the system gains additional degrees of freedom to compensate for geometric and optical transmission variations, thereby improving temperature measurement precision.
2Temperature
If a calibration sample with a thin aluminium layer is used, then the calibration can be performed at lower temperatures, but the calibration sample can only be used once due to material damage at high temperatures
Solution Approach 1:
The calibration sample structure is changed by adding a transparent calibration layer with specific optical properties (transparency in the infrared range). This parameter change allows the sample to withstand high temperatures without material degradation, enabling multiple reuse cycles while maintaining calibration accuracy across extended temperature ranges.
Solution Approach 2:
The calibration sample becomes a composite structure combining the semiconducting wafer substrate with a transparent calibration layer. This composite structure leverages the high-temperature stability of the wafer and the optical properties of the transparent layer, creating a durable calibration sample that can be reused multiple times at high temperatures.
3Device complexity
If the pyrometer is located outside the processing chamber, then the measurement system is simpler and the chamber geometry can be optimized, but the optical transmission characteristics of the window may change due to process related coating
Solution Approach 1:
The calibration process incorporates feedback by measuring thermal radiation at multiple wavelengths and using these measurements to determine and compensate for the optical transmission characteristics of the processing chamber window. This feedback mechanism allows the system to adapt to window coating changes and maintain measurement reliability despite the pyrometer being positioned outside the chamber.
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 method provides a more accurate, reliable, and cost-effective calibration process for pyrometers, reducing temperature measurement errors and allowing multiple uses of the calibration sample, thereby improving the precision of semiconducting wafer temperature determination.
Implementation Method 1
the pyrometer is adapted to intercept and measure the thermal radiation which is emitted by the semiconducting wafer
Implementation Method 2
measuring a first reflection signal resulting from reflection of the first radiation on the calibration sample
Data Source
AI summary
A method for calibrating a pyrometer a temperature of a calibration sample is determined from the ratio of a first reflectance and a second reflectance and the pyrometer is calibrated by assigning the determined temperature of the calibration sample with a thermal radiation signal measured by the pyrometer.