Plasma Table Bias Control to Prevent Workpiece Discharge
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Solution Overview
Problem
In plasma processing apparatuses, the cyclic application of negative DC voltage to the placement table can lead to a lowering of plasma potential, causing voltage fluctuations in the workpiece, which may result in discharge between the placement table and the workpiece, degrading the quality of the workpiece and reducing yield.
Innovation Solution
A plasma processing apparatus with a DC power supply that alternately generates positive and negative DC voltages, where a controller measures the workpiece voltage and adjusts the negative DC voltage to match the workpiece voltage, thereby reducing the potential difference and preventing discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If negative DC voltage is applied to the placement table to draw ions into the workpiece, then ion bombardment efficiency is improved, but plasma potential lowers causing voltage fluctuations and discharge between placement table and workpiece
Solution Approach 1:
The control unit continuously monitors the voltage between the placement table and workpiece, and dynamically adjusts the negative DC voltage magnitude based on real-time voltage measurements. This feedback mechanism ensures that the voltage difference remains within a safe range while maintaining effective ion bombardment, thereby preventing discharge while preserving productivity.
Solution Approach 2:
The system transitions from a static DC voltage application to a dynamic control approach where the negative DC voltage magnitude is continuously adjusted based on real-time voltage measurements. This dynamic adjustment allows the system to adapt to changing plasma conditions, maintaining optimal ion bombardment efficiency while preventing voltage fluctuations that could cause discharge.
2Productivity
If negative DC voltage is applied to the placement table, then ion drawing into workpiece is enhanced, but workpiece voltage fluctuates leading to quality degradation
Solution Approach 1:
The control unit uses real-time voltage measurements to dynamically adjust the negative DC voltage, ensuring that ion bombardment remains effective while preventing excessive voltage fluctuations that would degrade workpiece quality. This feedback-controlled approach maintains manufacturing precision while preserving ion drawing efficiency.
Solution Approach 2:
The system changes the magnitude of negative DC voltage dynamically based on measured voltage conditions. By adjusting this parameter in real-time, the system maintains optimal ion drawing efficiency while preventing voltage conditions that would lead to discharge and quality degradation.
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 solution effectively suppresses discharge between the placement table and the workpiece, maintaining the quality and yield of the processed workpiece by ensuring the potential difference does not exceed a threshold.
Implementation Method 1
By applying radio-frequency power to the placement table for bias purpose, the ions in the plasma are drawn into the workpiece
Implementation Method 2
The controller is configured to measure a voltage of the workpiece placed on the placement table
Data Source
AI summary
A plasma processing apparatus includes: a placement table serving as a lower electrode and configured to place thereon a workpiece to be subjected to a plasma processing; a DC power supply configured to alternately generate a positive DC voltage and a negative DC voltage to be applied to the placement table; and a controller configured to control an overall operation of the plasma processing apparatus. The controller is configured to: measure a voltage of the workpiece placed on the placement table; calculate, based on the measured voltage of the workpiece, a potential difference between the placement table and the workpiece in a period during which the negative DC voltage is applied to the placement table; and control the DC power supply such that a value of the negative DC voltage applied to the placement table is shifted by a shift amount that decreases the calculated potential difference.