Focus Ring Wear Rate Measurement via Optical Path Ratio
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Solution Overview
Problem
The existing method for measuring the wear rate of a focus ring in a substrate processing apparatus is limited by the need to maintain a preset temperature, which restricts when measurements can be taken, and requires opening the processing chamber, reducing operational efficiency.
Innovation Solution
A method involving thermally coupling a non-consumable part with the focus ring, using low-coherence light beams to measure the wear rate by calculating the ratio of optical path lengths between the consumable and non-consumable parts, allowing for temperature-independent wear rate measurement within the processing chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the wear rate is measured by maintaining a preset temperature, then measurement accuracy is improved, but measurement timing is restricted and operational efficiency deteriorates
Solution Approach 1:
The invention changes the measurement parameter from absolute optical path length to ratio of optical path lengths between consumable and non-consumable parts. This ratio-based measurement eliminates temperature dependency, allowing accurate wear rate measurement during plasma processes without maintaining preset temperature, thereby resolving the contradiction between measurement accuracy and operational efficiency
Solution Approach 2:
The invention introduces a non-consumable part made of the same material as the consumable part as a reference object. By measuring the optical path length ratio between the consumable part and this intermediary non-consumable part, the measurement becomes independent of temperature variations, enabling continuous monitoring during operation
2Measurement precision
If the focus ring is taken out of the processing chamber for measurement, then measurement can be performed, but the processing chamber must be opened and evacuated time is lost
Solution Approach 1:
The invention enables the focus ring to be measured in situ within the processing chamber using optical measurement through the chamber window. The wear rate is determined by comparing optical path lengths during the plasma process itself, eliminating the need to remove the focus ring and lose evacuation time
Solution Approach 2:
The invention replaces mechanical removal and external measurement systems with optical measurement through the chamber window. By using low-coherence light beams to measure optical path lengths during operation, the system eliminates mechanical intervention and associated time losses
3Adaptability or versatility
If temperature varies during plasma process, then operational flexibility is improved, but measurement accuracy deteriorates due to thermal expansion and refractive index changes
Solution Approach 1:
The invention transforms the measurement approach from absolute optical path length measurement to ratio-based measurement between consumable and non-consumable parts. This parameter change makes the measurement invariant to temperature-induced thermal expansion and refractive index changes, enabling accurate measurement during plasma processes with varying temperatures
Solution Approach 2:
The invention creates a reference system using a non-consumable part made of the same material as the consumable part. Both parts experience identical temperature conditions, so their optical path length ratio remains constant with temperature changes, effectively canceling out thermal effects and enabling flexible measurement timing
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 accurate and timely measurement of the focus ring's wear rate without temperature-dependent errors, maintaining operational efficiency by allowing measurements during plasma processes.
Implementation Method 1
an optical path length of the low-coherence light beam that travels forward and backward within the focus ring in a thickness direction is calculated based on interference between a reference light beam and a low-coherence light beam reflected from the bottom surface of the focus ring and interference between the reference light beam and a low-coherence light beam reflected from a top surface of the focus ring
Implementation Method 2
the focus ring is made of silicon and, in general, the silicon thermally expands and its refractive index varies depending on a temperature
Data Source
AI summary
A wear rate measurement method includes thermally coupling a focus ring having a top surface and a bottom surface with a reference piece having a bottom surface facing a susceptor and a top surface facing the focus ring; measuring a first optical path length of a low-coherence light beam that travels forward and backward within the focus ring by irradiating the low-coherence light beam to the focus ring orthogonally to the top surface and the bottom surface thereof; measuring a second optical path length of a low-coherence light beam that travels forward and backward within the reference piece by irradiating the low-coherence light beam to the reference piece orthogonally to the top surface and the bottom surface thereof; and calculating a wear rate of the focus ring based on a ratio between the first optical path length and the second optical path length.