Electron Beam Exciter for Plasma Etch Endpoint Detection
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Solution Overview
Problem
Traditional Optical Emission Spectroscopy (OES) endpoint detection methods fail in new plasma etch processes, particularly 'remote plasma' and low energy plasma processes, due to lack of fluorescence in the reaction chamber, and secondary plasma units suffer from instability and polymer formation on observation windows, leading to inaccurate process monitoring.
Innovation Solution
An electron beam exciter system that uses a variable density electron source and energy extractor to independently control electron density and energy, stabilizing electron beams for consistent light emission monitoring, and incorporates an electron collector and counter for feedback-controlled adjustments to maintain optimal excitation conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a secondary plasma unit is used to excite effluent gases for OES endpoint detection, then fluorescence signal can be produced in processes that otherwise lack it, but polymer forms on the observation window attenuating the light signal
Solution Approach 1:
The patent introduces an electron beam as an intermediary excitation mechanism between the plasma process and the OES detection system. Instead of using a secondary plasma unit that directly contacts the effluent gases near the observation window, the electron beam excites the gases remotely, eliminating the harmful polymer deposition on the window while maintaining fluorescence signal generation.
Solution Approach 2:
The patent replaces the mechanical/plasma-based excitation system (secondary plasma unit) with an electron beam-based excitation system. This substitution eliminates the need for physical plasma generation near the observation window, thereby preventing polymer formation while maintaining the ability to excite effluent gases for endpoint detection.
2Reliability
If a secondary plasma unit is used for effluent gas excitation, then endpoint detection becomes possible, but the plasma excitation becomes unstable over long periods causing signal fluctuations
Solution Approach 1:
The patent replaces the unstable secondary plasma unit with an electron beam excitation system. The electron beam provides stable, controllable excitation of effluent gases without the inherent instability of maintaining a secondary plasma discharge, thereby improving long-term signal stability while maintaining endpoint detection capability.
Solution Approach 2:
The patent changes the excitation mechanism from plasma-based to electron beam-based, fundamentally altering the physical parameters of the excitation process. This parameter change eliminates the instability issues associated with plasma maintenance while preserving the ability to detect endpoint changes through fluorescence monitoring.
3Device complexity
If traditional OES monitoring is used in remote plasma processes, then process monitoring is simple, but no fluorescence is produced because reactive species are not excited to high enough energy states
Solution Approach 1:
The patent introduces an electron beam as an intermediary excitation source that bridges the gap between remote plasma processes and OES detection. The electron beam directly excites the effluent gases to high energy states, producing fluorescence signals even when the primary plasma process does not generate sufficient excitation, thereby maintaining monitoring simplicity while enabling signal detection.
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 detection of endpoint changes in plasma etch processes by stabilizing electron beam density and energy, reducing polymer formation, and improving the accuracy and longevity of process monitoring systems.
Implementation Method 1
An electron beam (E-beam) is used for exciting gas particles in an effluent stream
Implementation Method 2
the reactant gases and reaction gas products are excited by the plasma causing fluorescence of light at wavelengths characteristic of those species
Data Source
AI summary
The present invention is directed to a gas line electron beam exciter, gas line electron beam excitation system and method for exciting a gas using an electron beam exciter. The electron beam exciter generally comprises a variable density electron source for generating a cloud of electrons in an electron chamber and a variable energy electron extractor for accelerating electrons from the electron chamber as an electron beam and into an effluent stream for fluorescing species in the effluent. The electron density of the electron beam is variably controlled by adjusting the excitation power applied to the variable density electron source. The electrons in the electron chamber reside at a reference electrical potential of the chamber, typically near ground electrical potential. The electron energy of the electron beam is variably controlled by adjusting an electrical potential across the variable energy electron extractor, which energizes the electrons through an extraction hole of the chamber and toward the extractor. The greater the difference in the electrical potential between the electron extractor and the electron source, the higher the energy imparted to the electrons in the electron beam. The excitation power applied to the electron source can be adjusted independently from the electron energy of the electron beam, thereby altering the electron density of the electron beam without changing the energy level of the electrons of the electron beam.