Mass Spectrometry Radical Detection for Plasma Etch Control
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Solution Overview
Problem
Current methods for detecting radicals during semiconductor fabrication are inefficient, leading to unpredictable etch rates and poor wafer reproducibility due to difficulties in continuously monitoring radical density in plasma processing, which is affected by power drifts and changes in process gases.
Innovation Solution
A method using a mass spectrometer with an electron impact ion source that allows for low and variable electron energies to measure radical density by differentiating between plasma-on and plasma-off conditions, enabling real-time adjustments to the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If test wafers are inserted periodically to test radical reaction, then process adjustments can be made, but continuous monitoring of radical density is not achieved, leading to etch rate changes and poor wafer reproducibility
Solution Approach 1:
The patent replaces the mechanical test wafer insertion method with a mass spectrometer-based detection system that continuously monitors radical density in the plasma chamber, enabling real-time process control without interrupting production
Solution Approach 2:
The mass spectrometer acts as an intermediary device that indirectly measures radical density by detecting radical concentrations in the process chamber, providing continuous data without direct contact with the wafer or plasma
2Quantity of substance
If mass spectrometer measures process gases at high electron energies, then all gas components are ionized, but radicals and neutral particles cannot be distinguished
Solution Approach 1:
The patent changes the electron energy parameter from high to low levels, creating an appearance potential measurement system where only specific radical species are ionized at given masses, enabling differentiation between radicals and neutral particles based on their distinct ionization thresholds
Solution Approach 2:
The mass spectrometer is configured to measure at specific low electron energies tailored to each radical's appearance potential, creating localized measurement conditions that selectively ionize only the target radical species while leaving others unaffected
3Reliability
If grids are used to filter ions from radicals, then ion rejection is achieved, but grids wear out and change electrical characteristics, leading to loss of filter efficiency
Solution Approach 1:
The system uses the plasma process itself to generate the measurement signal, eliminating the need for separate filtering components that would require maintenance and replacement
Solution Approach 2:
The patent replaces the mechanical grid filtering system with a field-free measurement approach where the mass spectrometer directly samples the plasma, avoiding physical components that would degrade 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 provides continuous, real-time monitoring of radical density, allowing for improved etch rate control and enhanced wafer reproducibility by distinguishing between radical and neutral gas components, leading to better process optimization.
Implementation Method 1
uses a mass spectrometer with an electron impact ion source that allows for low and variable electron energies enabling 'appearance potential' measurements to be performed on the process gases
Implementation Method 2
The etching, especially the etching of extremely thin layers of semiconductor material (e.g., semiconductors with structures that are ≤5 nm in size) is efficiently performed using radicals. Radicals are uncharged molecules that have an unpaired valence electron and are therefore, highly reactive and short-lived.
Data Source
AI summary
A method for detecting radicals in process gases in a semiconductor fabrication assembly is provided where the semiconductor fabrication includes a plasma source and a mass spectrometer with an ion source. The method includes separating ions from the process gases and determining a fixed electron energy in which to measure the process gases. Process gases in the semiconductor fabrication assembly are continuously sampled. A first measurement is performed on the sampled process gases at the electron energy using the mass spectrometer, where the first measurement is performed with the plasma source off. A second measurement of the sampled process gases is performed at the fixed electron energy using the mass spectrometer, where the second measurement is performed with the plasma source on. An amount of a radical present in the sampled process gases is determined as a difference between the second measurement and the first measurement.