CVD Chamber Heater Stray Radiation Control
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Solution Overview
Problem
Radiation thermometers in MOCVD processes face significant bias errors due to stray radiation from peripheral heating elements, which can overwhelm the radiation emitted from the target, especially when using resistance heating elements operating at higher temperatures than the crystalline growth layers.
Innovation Solution
The reactor chamber is configured to reduce stray radiation by incorporating a low heat flux portion on the peripheral heating element, a radiation trap, or a deflection surface to minimize radiation contribution at the target area, thereby reducing the bias error caused by stray radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If resistance heating elements are used to heat the wafer carrier, then heating efficiency is improved, but stray radiation increases causing measurement bias
Solution Approach 1:
The heating system is segmented into multiple heating zones with different power levels. The peripheral heating element is divided into a first portion (higher power) and a second portion (lower power), allowing differential heating that reduces stray radiation in the measurement direction while maintaining overall heating efficiency
Solution Approach 2:
Different regions of the heating system are assigned different functional qualities. The peripheral heating element's second portion operates at lower power specifically to reduce stray radiation in the radiation thermometer's line of sight, while the first portion maintains higher power for effective heating, creating local quality variations that simultaneously address heating efficiency and measurement accuracy
2Temperature
If peripheral heating elements operate at high temperature, then heating performance is improved, but stray radiation contribution to the target increases
Solution Approach 1:
The peripheral heating element is segmented into portions with different operating temperatures. The second portion operates at a lower temperature than the first portion, reducing its blackbody radiation intensity at the measurement wavelength while maintaining sufficient heating capability through the higher-temperature first portion
Solution Approach 2:
The operating temperature parameter of the peripheral heating element is changed across different portions. By operating the second portion at a lower temperature, the blackbody radiation intensity is reduced according to Planck's law, thereby reducing stray radiation contribution while the first portion maintains higher temperature for effective heating
3Measurement precision
If radiation thermometer detects radiation at 410 nm, then temperature measurement capability is improved, but stray radiation from heating elements overwhelms the signal
Solution Approach 1:
The heating element is segmented to create a radiation minimum zone in the peripheral region where the radiation thermometer operates. This segmentation allows the measurement system to detect radiation from the wafer carrier at 410 nm without being overwhelmed by stray radiation from the heating elements
Solution Approach 2:
The design converts the potentially harmful stray radiation from heating elements into a beneficial configuration by positioning the radiation minimum zone of the peripheral heating element aligned with the radiation thermometer's measurement direction. This creates a natural radiation shield that enhances measurement capability
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 configuration significantly reduces the bias error in temperature measurements by minimizing stray radiation detected by the radiation thermometer, improving the accuracy of temperature readings for crystalline growth materials during high-temperature processes.
Implementation Method 1
The components operating at the elevated temperature, such as the wafer carrier and wafers, will emit radiation in all directions, causing radiation to inter-reflect within the chamber
Implementation Method 2
the blackbody intensity of the radiation in the infrared portion of the electromagnetic spectrum is about 9 orders of magnitude higher than in the primary band pass
Implementation Method 3
radiation thermometers or pyrometers... that detect radiation at wavelengths shorter than 450 nm
Implementation Method 4
the low heat flux portion configured to operate at a temperature that is at least 300° C. less than any other portion of the heating element when operating at a maximum operating temperature
Data Source
AI summary
An apparatus and method for controlling stray radiation within a CVD chamber. A heater array disposed beneath a wafer carrier for radiatively heating of the wafer carrier includes a peripheral or outermost heating element or elements. Scattered radiation originating from a designated segment of the peripheral heating element(s) can be reduced locally by one of several mechanisms, including reducing the emission (e.g., operating temperature) of the designated segment, or capturing or deflecting a portion of the radiation originating from the designated segment. In one embodiment, an electrical connector on a resistance heating element provides the reduced emission from the designated segment. It has been found that radiation thermometers fixed proximate an axis that extends from the center of the wafer carrier and across the designated segment is subject to less stray radiation, thus providing a more reliable temperature reading in the optical wavelengths.