RF Bias Compensation via Capacitive Divider in Plasma Processing
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Solution Overview
Problem
Current methods for measuring wafer DC bias potential in RF driven plasma chambers are inaccurate due to dependence on leakage current and consumable silicon carbide pins, and fail to account for non-linear relationships between RF voltage and wafer potential in multi-frequency plasmas.
Innovation Solution
A capacitive divider network attached to the RF rod near the ESC base plate, combined with signal conditioning and processing, uses a transfer function to filter and condition RF voltage signals from multiple frequencies, deriving wafer bias potential with improved accuracy by accounting for individual frequency contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If leakage current measurement method is used to ascertain wafer DC bias potential, then wafer bias can be monitored, but measurement precision deteriorates due to high dependence on leakage current magnitude and ESC type
Solution Approach 1:
The patent introduces a current sensor as an intermediary device that measures the RF current through the ESC without requiring direct measurement of leakage current. This mediator approach allows accurate wafer bias potential calculation through mathematical relationships while avoiding the unreliable leakage current measurement path, thereby improving both measurement precision and reliability across different ESC types.
Solution Approach 2:
The patent replaces the direct electrical measurement method (measuring leakage current) with a mathematical calculation approach. By measuring RF current and using established relationships between RF current, RF voltage, and wafer bias potential, the system substitutes a reliable electrical measurement with a computational method that is independent of ESC type and leakage current variations.
2Measurement precision
If silicon carbide pins are used to detect wafer bias potential, then direct plasma contact measurement is achieved, but device complexity and maintenance requirements increase due to frequent consumable replacement
Solution Approach 1:
The patent creates a virtual measurement system that copies the measurement function of physical silicon carbide pins through mathematical modeling. By using current sensors and transfer functions to calculate wafer bias potential, the system replicates the measurement capability without requiring physical contact with the plasma, thereby eliminating consumable wear and replacement needs while maintaining measurement accuracy.
Solution Approach 2:
The patent introduces a current sensor and mathematical model as intermediaries between the plasma and the measurement system. This intermediary approach allows accurate wafer bias potential detection without direct plasma contact, eliminating the need for consumable silicon carbide pins and their associated maintenance requirements, thus improving production throughput.
3Device complexity
If linear scaling of RF peak to peak voltage is used to compute wafer DC bias voltage, then simplified measurement is achieved, but measurement precision deteriorates in multi-frequency plasmas due to non-linear relationships
Solution Approach 1:
The patent segments the RF signal processing into distinct frequency components. By separating the multi-frequency RF signal into individual frequency bands and processing each component separately through appropriate transfer functions, the system accurately captures the non-linear relationships at each frequency while maintaining overall system manageability and precision.
Solution Approach 2:
The patent implements dynamic signal processing that adapts to the specific frequency content and characteristics of the plasma. Rather than using a static linear scaling factor, the system dynamically determines appropriate transfer functions based on the measured RF current and voltage characteristics, allowing accurate wafer bias potential calculation across varying plasma conditions and multi-frequency operations.
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 a more accurate measurement of wafer bias potential with an R-squared value closer to one, reducing the need for frequent consumable replacements and improving production throughput by effectively handling non-linear relationships in multi-frequency plasmas.
Implementation Method 1
A voltage probe, consisting of a capacitive divider network, is attached to the RF rod in close proximity to the ESC base plate
Data Source
AI summary
A method and apparatus for compensating a bias voltage at the wafer by measuring RF voltage signals in RF driven plasma including at least an electrostatic, chuck (ESC), a capacitive divider, a signal processing and signal conditioning network is disclosed. The bias compensation device includes a capacitive divider to detect the RF voltage at the ESC, a signal conditioning network for the purpose of filtering specific RF signals of interests, and a signal processing unit for computing the DC wafer potential from the filtered RF signals.