Real-Time Substrate Temperature Measurement via Optical Absorption Edge
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Solution Overview
Problem
Existing methods for precise temperature measurement during semiconductor wafer processing, such as thermocouples and optical pyrometry, are inadequate due to slow response times, accuracy issues, and susceptibility to coating and mechanical failures, making real-time and spatially resolved measurements challenging.
Innovation Solution
An optical method using a single small core optical fiber connected to a solid-state array spectrometer, which operates in diffuse scattering reflectance, transmission, or transmission modes with a feedback-controlled light source, allowing for fast and accurate temperature measurement by analyzing the interband optical absorption edge without mechanical choppers or intra-chamber optics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermocouples are used for temperature measurement, then temperature monitoring is achieved, but response time is slow and accuracy deteriorates due to coating and mechanical failures
Solution Approach 1:
The patent replaces mechanical thermocouples with an optical measurement system that uses light reflection and absorption properties to determine temperature. The system employs a light source, optical fiber, and detector to measure the wavelength of light reflected from or transmitted through the wafer, eliminating mechanical contact and its associated reliability issues such as coating accumulation and physical failure.
Solution Approach 2:
The patent introduces optical fiber as an intermediary to transmit light between the measurement system and the wafer surface. This intermediary allows temperature measurement without direct mechanical contact, preventing the thermocouple issues of coating accumulation and mechanical failure while maintaining measurement capability through optical properties that change with temperature.
2Reliability
If optical pyrometry is used for temperature measurement, then non-contact measurement is achieved, but measurement precision deteriorates due to emissivity variations and limited temperature range
Solution Approach 1:
The patent changes the measurement parameter from thermal radiation emission (pyrometry) to optical absorption and reflection characteristics. By measuring how the wafer absorbs or reflects light at different wavelengths, the system determines temperature based on changes in optical properties rather than emitted radiation, overcoming the limitations of emissivity variations and extending the measurable temperature range.
Solution Approach 2:
The patent measures light properties at specific wavelengths corresponding to the wafer's bandgap energy, where the optical absorption coefficient changes most sensitively with temperature. This focused wavelength selection provides superior temperature measurement precision compared to broadband pyrometric methods that must account for varying emissivity across the entire spectrum.
3Measurement precision
If conventional thermocouples are used, then temperature monitoring is achieved, but response speed deteriorates due to thermal mass and contact requirements
Solution Approach 1:
The patent replaces mechanical thermocouples with an optical measurement system that uses light reflection and absorption properties to determine temperature. The system employs a light source, optical fiber, and detector to measure the wavelength of light reflected from or transmitted through the wafer, eliminating mechanical contact and its associated reliability issues such as coating accumulation and physical failure.
4Measurement precision
If thermocouples are placed in direct contact with substrate, then temperature measurement is achieved, but manufacturing precision deteriorates due to spot thermal distortion
Solution Approach 1:
The patent replaces mechanical thermocouples with an optical measurement system that uses light reflection and absorption properties to determine temperature. The system employs a light source, optical fiber, and detector to measure the wavelength of light reflected from or transmitted through the wafer, eliminating mechanical contact and its associated reliability issues such as coating accumulation and physical failure.
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
Enables real-time, precise temperature control across a wide range of temperatures (ambient to 700°C) with high data sampling rates, overcoming limitations of existing technologies by maintaining accuracy and speed, even in multi-wafer deposition systems.
Implementation Method 1
utilizing a fiber coupled solid state array spectrometer
Implementation Method 2
based on the nearly linear dependence of the interband optical absorption edge on temperature
Implementation Method 3
operates in diffuse scattering reflectance, transmission, or transmission modes
Implementation Method 4
fiber coupled solid state array spectrometer
Data Source
AI summary
The invention is an optical method and apparatus for measuring the temperature of semiconductor substrates in real-time, during thin film growth and wafer processing. Utilizing the nearly linear dependence of the interband optical absorption edge on temperature, the present method and apparatus result in highly accurate measurement of the absorption edge in diffuse reflectance and transmission geometry, in real time, with sufficient accuracy and sensitivity to enable closed loop temperature control of wafers during film growth and processing. The apparatus operates across a wide range of temperatures covering all of the required range for common semiconductor substrates.