Plasma OES Endpoint Detection Using Short Power Pulses
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Solution Overview
Problem
Current optical emission spectroscopy (OES) systems face challenges in accurately detecting endpoint detection (EPD) during plasma etching processes, particularly in conditions with low plasma discharge or low open ratio etching, leading to insufficient excitation for optical emissions and limited sensitivity.
Innovation Solution
Implementing short duty power spikes and excitation power modulation during OES data collection to enhance signal intensity, using power pulsing techniques that minimize interference with the plasma process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous low power is applied to sustain plasma during etching, then plasma process stability is maintained, but OES signal intensity becomes insufficient for accurate endpoint detection
Solution Approach 1:
The patent applies periodic power pulsing to the plasma chamber during etching processes. By delivering short bursts of elevated power periodically (e.g., pulse width modulation with duty cycles between 1-50%), the system temporarily enhances plasma excitation and OES signal intensity during specific measurement windows, while maintaining overall plasma stability through controlled averaging. This periodic action resolves the contradiction by providing high signal intensity only when needed for detection, rather than requiring continuous high power that would disrupt process stability.
2Measurement precision
If high power is applied continuously to enhance OES signal, then optical emission intensity increases, but interference with the plasma etching process increases
Solution Approach 1:
The system uses periodic power pulsing with controlled duty cycles to deliver enhanced power only during brief measurement windows. This temporal separation ensures that high power is applied only when OES measurement is needed, rather than continuously during the entire etch process. The duty cycle is optimized so that the average power remains within process specifications, minimizing interference with etch rate and plasma chemistry while providing sufficient signal intensity during detection phases.
Solution Approach 2:
The patent implements preliminary power pulsing sequences before and during endpoint detection phases. By preparing the plasma with controlled power bursts in advance of the critical measurement moment, the system ensures optimal excitation conditions are established without applying continuous high power that would interfere with the actual etching process. This preliminary action allows the plasma to be primed for detection while maintaining process integrity.
3Measurement precision
If power pulsing is used to enhance OES detection, then endpoint detection sensitivity improves, but system complexity increases
Solution Approach 1:
The power control system implements periodic pulsing using standard pulse width modulation techniques that leverage existing RF power supply capabilities. By utilizing conventional PWM controllers and timing circuits already present in plasma processing equipment, the system achieves enhanced detection sensitivity without requiring complex custom hardware. The periodic nature of the pulsing allows synchronization with the etch process cycle, enabling simple timing-based control logic rather than complex real-time adjustments.
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
Enhances OES signal intensity, allowing for more robust endpoint detection (EPD) in challenging etch process conditions, providing accurate characterization of plasma processes.
Implementation Method 1
exposing the substrate in a plasma processing chamber to a plasma powered by applying a first power to a first electrode
Implementation Method 2
obtaining an optical emission spectrum (OES) from the plasma while applying the second power to the second electrode
Data Source
AI summary
A method of processing a substrate that includes: exposing the substrate in a plasma processing chamber to a plasma powered by applying a first power to a first electrode of the plasma processing chamber for a first time duration; and after the first time duration, determining a process endpoint by: while exposing the substrate to the plasma by applying the first power to the first electrode, applying a second power to a second electrode of the plasma processing chamber for a second time duration that is shorter than the first time duration; and obtaining an optical emission spectrum (OES) from the plasma while applying the second power to the second electrode, where an energy of the second power over the second time duration is less than an energy of the first power over a sum of the first and the second time durations by a factor of at least 2.