Ion Energy Analyzer Grid Segmentation for Plasma Measurement
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Solution Overview
Problem
Conventional ion energy analyzers in plasma processing systems perturb the plasma, fail to operate at large electric potentials, and suffer from noise due to secondary electron emission, making them ineffective for accurately measuring ion energy distribution.
Innovation Solution
An ion energy analyzer with an entrance grid, an ion selection grid, an electron rejection grid, and an ion current collector, designed to be electrically floating on an RF-powered electrode, using high capacitance and RF filters to minimize perturbations and noise, allowing in-situ measurement of ion energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ion energy analyzers are used to measure ion energy distribution, then measurement capability is provided, but the plasma is perturbed and measurement accuracy deteriorates
Solution Approach 1:
The analyzer is segmented into multiple independently controllable grids (entrance grid, ion selection grid, electron rejection grid, exit grid) rather than using a single grid structure. This segmentation allows each grid to perform a specific function (ion transmission, energy selection, electron rejection) thereby achieving accurate IED measurement while minimizing overall plasma perturbation through optimized individual grid potentials
Solution Approach 2:
The ion selection grid acts as an intermediary element between the plasma and the ion collector. By introducing this intermediate grid with可调 positive bias, the system can select ions of specific energies without requiring the collector itself to be deeply embedded in the plasma, thereby reducing plasma perturbation while maintaining measurement capability
2Measurement precision
If conventional ion energy analyzers operate at large electric potentials, then ion energy selection capability is improved, but the analyzers fail to function properly
Solution Approach 1:
The analyzer employs dynamic voltage control of the ion selection grid, allowing the bias potential to be adjusted in real-time according to the specific measurement requirements. This dynamic adjustment capability enables the system to operate reliably across a wide range of potentials (from low to high) by optimizing the grid voltage for each measurement condition, thereby achieving both broad energy selection range and operational reliability
Solution Approach 2:
The system changes the electrical parameters (voltage and polarity) of different grids independently and adaptively. The ion selection grid can be biased positively to transmit ions, while the electron rejection grid is biased negatively to block electrons. This parameter flexibility allows the analyzer to maintain reliable operation across large potential ranges by adjusting grid voltages to match the specific ion energy distribution being measured
3Measurement precision
If conventional ion energy analyzers are used, then ion current measurement is enabled, but substantive noise from secondary electron emission occurs
Solution Approach 1:
The electron rejection grid, biased negatively, converts the harmful secondary electron emission into a beneficial filtering mechanism. Secondary electrons generated in the plasma are naturally attracted to the positively biased ion selection grid, but the negatively biased electron rejection grid repels them back, preventing them from reaching the ion collector. This transforms the harmful electron emission into a controllable factor that actually helps distinguish ions from electrons
Solution Approach 2:
The electron rejection grid extracts and removes secondary electrons from the ion beam path before they can reach the ion collector. By placing this dedicated electron removal element in the beam path and biasing it negatively, the system selectively removes the harmful electron component while allowing ions to pass through to the collector, thereby achieving noise-free ion current measurement
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, non-perturbing measurement of ion energy distribution in plasma processing systems, reducing noise and extending operational range to large electric potentials.
Implementation Method 1
only the ions in the beam of ions having sufficient energy to overcome the potential barrier imposed by the grid will pass through the grid
Implementation Method 2
an electron rejection grid disposed proximate to the ion selection grid, wherein the electron rejection grid is coupled to an electron rejection voltage source configured to negatively bias the electron rejection grid
Implementation Method 3
an ion current collector disposed proximate to the electron rejection grid and configured to receive a selected ion current
Data Source
AI summary
An ion energy analyzer is described for use in diagnosing the ion energy distribution (IED) of ions incident on a radio frequency (RF) biased substrate immersed in plasma. The ion energy analyzer comprises an entrance grid exposed to the plasma, an ion selection grid disposed proximate to the entrance grid, an electron rejection grid disposed proximate to the ion selection grid, and an ion current collector disposed proximate to the electron rejection grid. The ion selection grid is coupled to an ion selection voltage source configured to positively bias the ion selection grid by an ion selection voltage, and the electron rejection grid is coupled to an electron rejection voltage source configured to negatively bias the electron rejection grid by an electron rejection voltage. Furthermore, an ion current meter is coupled to the ion current collector to measure the ion current.