Optical Endpoint Detection for Low Open Area Plasma Etching
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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 photomultiplier tube arrays or photodiodes, to collect and analyze optical emissions from plasma processes, providing high selectivity and cost-effectiveness for endpoint detection in plasma-assisted wafer processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Echelle style spectrometers are used for high-resolution spectrographic detection, then spectral resolution is improved, but device cost and complexity increase significantly making them unsuitable for high-volume manufacturing
Solution Approach 1:
The spectrometer is segmented into multiple photodetector elements (e.g., 64 or more pixels) arranged in an array, where each element detects a specific wavelength range. This segmentation allows the system to achieve high spectral resolution by distributing the detection function across multiple simpler photodetector elements rather than using a single complex Echelle spectrometer, thereby reducing overall device complexity and cost while maintaining measurement precision.
Solution Approach 2:
The patent replaces the complex mechanical Echelle spectrometer system with an optical fiber-based system coupled to a photodetector array. This substitution eliminates the need for complex mechanical scanning and diffraction elements, using instead a more compact and manufacturable configuration that achieves comparable or superior spectral resolution through the arrayed photodetectors, thus reducing device complexity for high-volume manufacturing.
2Reliability
If conventional spectrometers are used for endpoint detection, then detection capability is provided, but signal strength is insufficient when open area is less than 10% of wafer area
Solution Approach 1:
Multiple optical fibers are bundled together to form a fiber bundle that collects optical emissions from the plasma process. By merging the light collection capability of many individual fibers into a single bundle, the system significantly increases the total optical signal strength collected from the wafer surface, enabling reliable endpoint detection even when the open area is less than 10% of the total wafer area.
Solution Approach 2:
The patent transitions from point-by-point spectral analysis to a multi-dimensional approach by using an array of photodetectors that simultaneously detect multiple wavelength ranges across different spatial positions. This dimensional expansion in the detection space allows the system to collect and analyze optical emissions from multiple locations concurrently, thereby increasing the effective signal strength and improving endpoint detection reliability for small open areas.
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
The system achieves reliable endpoint detection with high selectivity and low cost, suitable for high-volume manufacturing, by amplifying weak optical signals and customizing filter configurations for specific wavelength ranges, enabling accurate detection of chemical species even in low open area scenarios.
Implementation Method 1
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. When a photodetector's processing circuitry analyzes those wavelengths, the identity of the chemical species can be detected.
Implementation Method 2
a photodetector having a plurality of segments, each segment having a corresponding narrowband optical filter designed for a specific range of wavelengths
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 groups 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 tube (PMT) array or based on photodiodes (e.g., avalanche photodiodes (APDs)).