Fiber-Array Endpoint Detection for Low Open-Area Plasma Processing
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Solution Overview
Problem
Existing endpoint detection methods in plasma-assisted wafer processing face challenges with low signal strength due to small open areas on wafers or coupons, making it difficult to detect chemical species effectively, especially when the open area is less than 10% of the wafer area, and current high-resolution spectrometers like Echelle style spectrometers are costly and unsuitable for high-volume manufacturing.
Innovation Solution
A novel spectrographic detector system using ultra-narrow bandwidth filters coupled with photon detection electronics, such as PMT arrays or photodiodes, to collect and analyze optical emissions from plasma processes, providing high selectivity and cost-effectiveness for high-volume manufacturing by customizing filters for specific wavelengths and species detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Echelle style spectrometers are used for high-resolution spectral analysis, then spectral resolution is improved, but device cost and complexity increase significantly making them unsuitable for high-volume manufacturing
Solution Approach 1:
The spectrum is segmented into multiple wavelength bands, with each band detected by a dedicated photodetector element. This segmentation approach allows using simpler detection components instead of a single complex high-resolution spectrometer, resolving the contradiction between spectral resolution and device complexity
Solution Approach 2:
The detector array provides multi-functional capability by simultaneously detecting multiple chemical species across different wavelength ranges. Each detector element serves multiple purposes: wavelength-specific detection, species identification, and endpoint detection, replacing the need for a single complex instrument
2Adaptability or versatility
If coupons or wafers with low open area are processed, then process development and device feature testing are enabled, but optical signal strength decreases making endpoint detection difficult
Solution Approach 1:
The detection system is optimized for local signal characteristics by using multiple photodetector elements tuned to specific wavelength bands where chemical species emit. This local optimization allows detecting weak signals from small open areas by focusing detection sensitivity on relevant spectral regions
Solution Approach 2:
The system changes detection parameters by adjusting which wavelength bands are monitored and how signal integration is performed across multiple detectors. This parameter flexibility enables adapting to low signal strength conditions while maintaining detection accuracy for process development applications
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 reliable endpoint detection in plasma-assisted wafer processing with high selectivity and low cost, suitable for mass production, even in scenarios with low open areas, by amplifying weak optical signals and filtering specific wavelengths, thereby improving signal-to-noise ratio and detection accuracy.
Implementation Method 1
When a photodetector's processing circuitry analyzes those wavelengths, the identity of the chemical species can be detected
Implementation Method 2
A plasma is a superposition of many different chemical species having corresponding wavelengths resulting from transition of a particle from an excited state to a ground state
Implementation Method 3
optical emission generated from many atoms or molecules of a chemical species
Data Source
AI summary
The disclosure describes apparatus and method for detecting an endpoint in plasma-assisted wafer processing in a chamber. A fiber array comprising a plurality of fibers collects optical emission light from the chamber during the plasma-assisted wafer processing. The fiber array is split into two or more sub-arrays of fibers, each group carrying a portion of the light to a segment of a photodetector. Each segment of photodetector has a corresponding narrowband optical filter designed for a specific range of wavelengths. A computer processor analyzes detected signals from the plurality of segments of the photodetector, and determines, based on the analysis of the detected signals, an endpoint of the plasma-assisted wafer processing as indicated by the presence or the absence of the one or more chemical species in the chamber. The photodetector can be based on photomultiplier tubes (PMT), specifically multi-anode PMT.