In-Situ Pyrometer for Silicon Carbide Wafer Temperature Accuracy
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Solution Overview
Problem
Conventional pyrometry techniques suffer from inaccuracies in measuring silicon carbide wafer temperatures due to changing emissivity and background radiation at elevated temperatures, especially during epitaxial growth and wafer transfers, which are typically above 1400-1700°C and 800-1100°C, respectively.
Innovation Solution
A dual-channel pyrometer system using wavelengths of 444-484 nm for high temperatures and 940-960 nm for lower temperatures, combined with a reflectometer to correct for emissivity changes, minimizes stray radiation and provides accurate temperature measurements by employing silicon photodiodes and collimators to enhance precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional emissivity-corrected pyrometry at 949 nm is used, then temperature measurement is feasible in the 1000-1100°C range, but measurement accuracy deteriorates significantly at elevated temperatures of 1400-1700°C
Solution Approach 1:
The patent changes the operating wavelength parameter from conventional 949 nm to a shorter wavelength range of 444-484 nm. This parameter change enables accurate temperature measurement at elevated temperatures (1400-1700°C) where conventional pyrometry fails, as the shorter wavelength is less affected by the temperature-dependent emissivity changes and background radiation that plague longer wavelength measurements at high temperatures.
Solution Approach 2:
The patent introduces a reflectometer as an intermediary measurement device that works in conjunction with the pyrometer. The reflectometer measures the reflectivity of the wafer surface, which is then used to calculate emissivity. This intermediary measurement allows for real-time correction of emissivity changes during the growth process, thereby maintaining temperature measurement accuracy across a wide temperature range.
2Adaptability or versatility
If a single wavelength pyrometer is used, then the device is simple, but it cannot accurately measure temperatures across both low (800-1100°C) and high (1400-1700°C) temperature ranges
Solution Approach 1:
The patent segments the temperature measurement function by implementing a dual-channel pyrometer system. One channel operates at 444-484 nm for high temperature measurements (1400-1700°C) during epitaxial growth, while the other channel operates at 940-960 nm for lower temperature measurements (800-1100°C) during wafer transfers. This segmentation allows each channel to be optimized for its specific temperature range, achieving versatility without requiring excessive complexity in a single universal channel.
Solution Approach 2:
The patent creates a multi-functional pyrometer system that can measure temperatures across both low (800-1100°C) and high (1400-1700°C) ranges using two wavelength channels. The system also integrates a reflectometer for emissivity correction, making the entire apparatus universally applicable to different process stages (epitaxial growth and wafer transfers) without requiring separate measurement systems.
3Measurement precision
If wafer emissivity is assumed constant, then measurement process is simple, but temperature determination becomes inaccurate as emissivity changes during growth
Solution Approach 1:
The patent implements a feedback mechanism where the reflectometer continuously measures the wafer surface reflectivity, which is then used to calculate the current emissivity value. This real-time emissivity information feeds back to the temperature calculation algorithm, allowing the system to dynamically adjust for emissivity changes during the growth process. This feedback loop maintains accurate temperature determination without requiring manual intervention or complex pre-programming.
Solution Approach 2:
The system performs self-correction for emissivity changes by using the reflectometer to automatically determine the wafer's optical properties during measurement. Rather than requiring external calibration or manual emissivity input, the system serves itself by deriving the necessary correction factors from its own reflectivity measurements, thereby maintaining measurement accuracy while keeping the operation simple.
4Measurement precision
If 949 nm pyrometer is used for partially opaque wafers, then measurement is possible, but the reading becomes a weighted average of wafer and carrier temperatures introducing uncertainty
Solution Approach 1:
The patent changes the measurement wavelength from 949 nm to a shorter range of 444-484 nm. At this shorter wavelength, the silicon carbide wafer material is more absorptive and less transparent, even at elevated temperatures. This parameter change ensures that the pyrometer measures primarily the wafer surface temperature rather than a weighted average that includes carrier temperature, thereby eliminating the background radiation interference problem.
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 system achieves improved accuracy in measuring silicon carbide wafer temperatures by reducing temperature measurement errors by a factor of two compared to conventional methods, ensuring precise temperature determination during epitaxial growth and wafer transfers.
Implementation Method 1
A body's temperature can be computed given its emissivity (E) and emitted radiation power (P) according to Planck's equation
Implementation Method 2
Reflectometry measurements can aid in this real-time determination according to the relation: E = 1 - R in which E is the emissivity and R is the reflectivity of the target
Data Source
AI summary
A chemical vapor deposition system (CVD) adapted to capture a temperature of a silicon carbide layer grown on a wafer includes a reaction chamber adapted to grow a silicon carbide layer epitaxially on wafers present within the chamber, a wafer carrier having a platform for carrying at least one wafer, a light source that emits radiation of a prescribed wavelength toward the wafer carrier, a first pyrometer coupled to the reaction chamber and configured to receive radiation emitted or reflected from the wafer and to measure radiation intensity of the prescribed wavelength, a reflectometer coupled to the pyrometer configured to receive and measure radiation of the prescribed wavelength reflected from the wafer in response to the radiation emitted by the light source, and an electronic controller configured to determine a temperature of the silicon carbide layer grown on the wafer using measurements of the first pyrometer and reflectometer.