ESC Clamping Voltage Control via RF Self-Bias Feedback
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Solution Overview
Problem
Current plasma etching technologies face challenges in accurately controlling the electrostatic chuck (ESC) clamping voltage, which can lead to insufficient clamping, causing wafer pop-off or excessive current, and pose difficulties in managing wafer temperature due to heat transfer issues.
Innovation Solution
A plasma reactor system that includes an RF match network coupled with a DC power source and measurement instruments to calculate and adjust the wafer voltage, using multiple RF frequencies to enhance control over the ESC clamping voltage and improve heat transfer efficiency through contact-cooling, allowing for precise control of wafer temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ESC clamping voltage is increased to improve heat transfer and maintain wafer temperature, then the heat transfer efficiency is improved, but the risk of excessive current through the wafer increases which may damage circuit features
Solution Approach 1:
The system continuously measures the self-bias voltage of the wafer and feeds this information back to the DC power source controller, which adjusts the ESC clamping voltage in real-time to maintain optimal heat transfer while preventing excessive current conditions
Solution Approach 2:
The patent replaces direct measurement of wafer voltage with an indirect measurement system that uses RF match network parameters to calculate self-bias voltage, eliminating the need for direct electrical contact with the wafer and enabling safer, more accurate control
2Object-affected harmful factors
If the ESC clamping voltage is decreased to reduce current through the wafer, then the risk of circuit damage is reduced, but the heat transfer efficiency decreases making it difficult to maintain wafer temperature under high heat load
Solution Approach 1:
The real-time feedback loop continuously monitors self-bias voltage and dynamically adjusts ESC clamping voltage, enabling the system to operate at higher clamping voltages for improved heat transfer while automatically reducing voltage when current limits are approached
Solution Approach 2:
The system transitions from static ESC clamping voltage control to dynamic control that continuously adapts the clamping voltage based on real-time wafer self-bias voltage measurements, allowing optimal performance across varying process conditions
3Measurement precision
If direct measurement of wafer voltage is used to control clamping voltage, then the control accuracy is improved, but the system complexity and difficulty of implementation increase
Solution Approach 1:
The patent introduces an intermediary calculation system that derives wafer self-bias voltage from RF match network measurements rather than directly measuring wafer voltage, simplifying the measurement system while maintaining accuracy
Solution Approach 2:
The system replaces direct electrical measurement of wafer voltage with an indirect measurement approach using RF network parameters, eliminating the need for complex direct contact measurement systems
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
The system enables accurate real-time control of the ESC clamping voltage and efficient heat transfer, allowing for increased RF bias power levels and improved etch performance while maintaining stable wafer temperature, even at high heat loads.
Implementation Method 1
The voltage drop produces an electrostatic force clamping the wafer to the ESC. The clamping force is determined by the difference between the time-average of the wafer voltage and the D.C. voltage applied to the ESC electrode.
Implementation Method 2
Wafer bias power may be increased beyond previously permitted levels. The heat transfer rate may be so great as the clamping voltage is increased, that the wafer temperature may be maintained under much higher heat load than was formerly possible.
Data Source
AI summary
In a plasma reactor having an electrostatic chuck, wafer voltage may be determined from RF measurements at the bias input using previously determined constants based upon transmission line properties of the bias input, and this wafer voltage may be used to accurately control the DC wafer clamping voltage.