Etalon Thermometry for Non-Contact Plasma Temperature Sensing
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Solution Overview
Problem
Current temperature measurement technologies in semiconductor processing chambers face challenges such as limited accuracy and reliability, especially at low temperatures and in environments with plasma, due to emissivity variability and interference from radiation sources.
Innovation Solution
The method involves using etalon-objects, such as semiconductor substrates, to perform non-contact temperature measurements by heterodyning coherent radiation, which allows for precise temperature determination based on fringe spacing analysis, minimizing interference from background radiation and emissivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pyrometers are used for temperature measurement, then non-contact measurement is achieved, but measurement accuracy deteriorates due to emissivity variability and plasma interference
Solution Approach 1:
The patent introduces an etalon (a precise optical reference element with known thickness and refractive index) as an intermediary between the light source and the substrate. The etalon creates a reference interference pattern that serves as a stable benchmark, allowing the system to measure substrate temperature through fringe spacing changes without being affected by substrate emissivity variations or plasma interference. This intermediary reference standard enables accurate measurements while maintaining non-contact operation.
2Measurement precision
If contact temperature sensors are used, then measurement accuracy improves, but response time deteriorates and plasma interference increases
Solution Approach 1:
The patent replaces the mechanical contact-based temperature sensing system with an optical measurement system. Instead of using physical temperature sensors that require thermal contact and have slow response times, the system uses light interference patterns to measure temperature optically. This substitution enables rapid, real-time temperature measurements without mechanical contact, eliminating both the slow response time and plasma interference issues associated with contact sensors.
3Ease of operation
If radiation pyrometers are used for low temperature processes, then non-contact measurement is maintained, but measurement accuracy deteriorates below 380°C
Solution Approach 1:
The patent changes the measurement parameter from detecting thermal radiation intensity (which becomes unreliable at low temperatures) to measuring optical interference fringe spacing. The etalon-based interferometric system measures changes in the optical path length caused by temperature-induced refractive index changes and thermal expansion, rather than relying on thermal radiation. This parameter change enables accurate non-contact temperature measurements across a broad range including low temperatures below 380°C.
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 and reliable temperature measurements over a broad range, from -200°C to 700°C, with improved temperature uniformity and control, even in high-background-radiation environments, enhancing semiconductor processing precision and efficiency.
Implementation Method 1
A fringe spacing is determined from an interference pattern of one of the reflected second beam or the transmitted second beam
Implementation Method 2
temperature measurements by heterodyning coherent radiation between two etalon-objects within or associated with the processing chamber
Implementation Method 3
One of the first etalon or the second etalon generates a reflected second beam and a transmitted second beam from the first light beam
Implementation Method 4
passing the first light beam through a substrate disposed in the processing chamber
Data Source
AI summary
A method and apparatus for determining the temperature of a substrate within a processing chamber are described herein. The methods and apparatus described herein utilize an etalon assembly and a heterodyning effect to determine a first temperature of a substrate. The first temperature of the substrate is determined without physically contacting the substrate. A separate temperature sensor also measures a second temperature of the substrate and/or the substrate support at a similar location. The first temperature and the second temperature are utilized to calibrate one of the temperature sensors disposed within the substrate support, a model of the processes performed within the processing chamber, or to adjust a process parameter of the process performed within the processing chamber.