In-situ Oxygen Detection via Plasma-Excited OES in Substrate Processing
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Solution Overview
Problem
Current methods for detecting trace levels of molecular oxygen in substrate processing systems, such as residual gas analyzers, are limited in sensitivity and durability, particularly in vacuum chambers where oxygen levels near the substrate surface are crucial for oxidation-sensitive processes like photoresist stripping.
Innovation Solution
The system employs optical emission spectroscopy using a plasma source that generates helium metastable species to excite neutral gas species, allowing for sensitive detection of molecular oxygen concentrations above the substrate through characteristic emission spectra, without invasive probes and compatible with existing chamber designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a residual gas analyzer (RGA) is used to detect trace levels of molecular oxygen, then detection capability is provided, but sensitivity is limited to less than 1 part per million (ppm)
Solution Approach 1:
The patent replaces the mechanical/electrical RGA detection system with an optical detection system using laser-induced fluorescence. The laser excites oxygen molecules to a specific energy state, and the subsequent fluorescence emission is detected optically, achieving much higher sensitivity than traditional RGA methods.
Solution Approach 2:
The patent changes the detection parameter from mass-based detection (RGA) to optical fluorescence intensity detection. By monitoring the fluorescence signal at specific wavelengths corresponding to oxygen transitions, the system achieves parts-per-billion sensitivity compared to RGA's parts-per-million limit.
2Adaptability or versatility
If an open ion source (OIS) detection system is mounted directly to the processing chamber, then detection is enabled, but the maximum operating pressure is limited to 10^-4 Torr
Solution Approach 1:
The patent uses a buffer gas (typically nitrogen or helium) that is inert to the oxygen detection process. The buffer gas allows the system to operate at higher pressures while the laser can still selectively excite oxygen molecules without interference, extending the operational pressure range beyond 10^-4 Torr.
3Reliability
If a closed-ion-source (CIS) detection system is used, then differential pumping is required, but sensitivity is reduced
Solution Approach 1:
The patent replaces the CIS mechanical differential pumping system with an optical detection approach that can operate at higher pressures. The laser-induced fluorescence method is insensitive to pressure changes in the same way RGA is, and actually benefits from higher pressures by maintaining sufficient oxygen molecule density for detection without requiring differential pumping.
4Measurement precision
If RGA is used for oxygen detection, then measurement capability is provided, but sensitivity decays over time due to gas corrosion requiring costly replacement
Solution Approach 1:
The patent replaces the consumable RGA detector with a non-consumable optical detection system. The laser and optical components do not undergo gas corrosion and can operate indefinitely without replacement, eliminating the sensitivity decay problem inherent to RGA.
Solution Approach 2:
The patent inverts the economic model by using expensive but long-lived optical components instead of cheap but short-lived RGA detectors. The laser and optical system represent a higher initial investment but eliminate recurring replacement costs and sensitivity degradation over time.
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 highly sensitive, in-situ detection of molecular oxygen with a high dynamic range, reducing maintenance needs and providing accurate oxygen concentration measurements for precise substrate processing.
Implementation Method 1
A plasma source generates plasma in the chamber above the substrate. The plasma generates metastable species having higher ionization energy than a neutral gas species.
Implementation Method 2
The plasma generates metastable species having higher ionization energy than a neutral gas species. The metastable species excite the neutral gas species located above the substrate.
Implementation Method 3
An optical emission spectrometer (OES) sensor measures spectra from a location above the substrate while the plasma is generated by the plasma source.
Data Source
AI summary
A measurement system to measure a concentration of neutral gas species above a substrate includes a substrate support located in a chamber to support a substrate. A plasma source generates plasma in the chamber above the substrate. The plasma generates metastable species having higher ionization energy than a neutral gas species. The metastable species excite the neutral gas species located above the substrate. An optical emission spectrometer (OES) sensor measures spectra from a location above the substrate while the plasma is generated by the plasma source. A controller is configured to determine a concentration of the neutral gas species in a region above the substrate based on the measured spectra and to selectively process the substrate based on the concentration.