RF Plasma Current Sensing for Multi-Station Frequency Tuning
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Solution Overview
Problem
Current RF current measurement technologies in semiconductor processing tools face challenges such as narrow bandwidth, which affects the control and troubleshooting of semiconductor fabrication tools, leading to variations in deposition and etch rates due to inaccurate tuning of RF power across multiple processing stations.
Innovation Solution
A system and method for plasma-assisted semiconductor processing that includes measuring the voltage across an inductive element in a current sensor, converting it to plasma current using a linear proportionality factor dependent on the RF power frequency, and adjusting the RF power frequency to reduce station-to-station variations, thereby ensuring uniformity and repeatability in semiconductor processing operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional RF current measurement technologies are used, then the measurement system is simple, but the bandwidth is narrow which leads to inaccurate RF power tuning and station-to-station variations
Solution Approach 1:
The current sensor is segmented into multiple functional components: a voltage sensor for measuring voltage across the plasma, an inductor for creating magnetic flux, and a capacitor for tuning the resonant frequency. This segmentation allows each component to be optimized independently, achieving broadband measurement capability while maintaining manageable complexity through modular design.
Solution Approach 2:
The patent introduces an intermediary measurement approach by measuring voltage across a known impedance (the plasma and sensor combination) rather than measuring current directly. This voltage measurement, combined with knowledge of the sensor's impedance characteristics, serves as an indirect but accurate current measurement method that avoids the limitations of traditional direct current sensing.
2Manufacturing precision
If RF power frequency is not tuned, then the processing is simple, but station-to-station variations cause wafer-to-wafer non-uniformity in film characteristics
Solution Approach 1:
The system implements feedback control by measuring the voltage across the plasma at each station, comparing it to reference values, and automatically adjusting the RF power frequency and distribution to compensate for variations. This closed-loop feedback ensures uniform film characteristics across all stations while maintaining efficient processing through automated correction.
Solution Approach 2:
The RF power frequency is made dynamic rather than fixed. The system continuously adjusts the RF frequency based on real-time measurements of plasma conditions at each station. This dynamic adjustment allows the system to adapt to changing conditions and maintain optimal performance, achieving both precision and productivity.
3Adaptability or versatility
If a broadband current sensor is used, then the measurement bandwidth is sufficient for control and troubleshooting, but the sensor design becomes complex with specific inductance and capacitance requirements
Solution Approach 1:
The sensor achieves broadband capability by carefully selecting and tuning specific parameters: the inductor value (L) and capacitor value (C) are chosen to create a resonant circuit with appropriate bandwidth characteristics. By adjusting these parameters, the sensor can be optimized for different frequency ranges while maintaining a relatively simple overall structure.
Solution Approach 2:
The sensor design creates an equipotential measurement approach where the voltage measurement point is positioned such that the measured voltage directly reflects the plasma conditions without being influenced by variations in other parts of the RF circuit. This equipotential positioning simplifies the measurement interpretation while achieving broadband functionality.
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 allows for accurate and efficient control of RF power across multiple stations, reducing wafer-to-wafer non-uniformity in film characteristics and improving the overall consistency of semiconductor processing operations by dynamically responding to changing conditions.
Implementation Method 1
measuring a voltage across an inductive element in a current sensor, the inductive element being electrically parallel to a capacitive element in the current sensor, the inductive element being electrically inline relative to plasma current flow
Data Source
AI summary
A method of plasma-assisted semiconductor processing in multiple stations in a process chamber is provided. The method comprises: a) providing substrates at each of the multiple stations; b) distributing RF power to multiple stations to thereby generate a plasma in the station, wherein the RF power is distributed according to a RF power parameter that is adjusted to reduce station to station variations; c) tuning a frequency of the RF power, wherein tuning the frequency includes: i) measuring a current of the plasma; ii) determining, according to the current measured in (i), a change to the frequency of the RF power, and iii) adjusting the frequency of the RF power; and d) performing a semiconductor processing operation on the substrate at each station.