Three-Coil ICP Source with Current Divider for Plasma Uniformity
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Solution Overview
Problem
The challenge in plasma processing for larger semiconductor wafers is achieving uniformity of plasma process rates across the treated surface, which is complicated by internal resonances and mutual inductances among multiple RF coils, leading to unpredictable impedance matching and potential plasma instabilities.
Innovation Solution
A plasma reactor system with three coil antennas and a current apportionment controller that uses variable impedance elements and a user interface to control current distribution, employing a look-up table and processor to define impedance values for optimal current apportionment among the coils, thereby stabilizing plasma processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If three separately powered RF coils are used to improve uniformity control for 450 mm wafers, then plasma uniformity control is improved, but system complexity and unpredictability increase due to internal resonances and mutual inductances
Solution Approach 1:
The patent combines three separately powered RF coils into a single RF power system with a unified impedance match. The current divider network distributes power from one RF source to three coil antennas, eliminating the complexity of three independent impedance matching systems while maintaining the ability to control current distribution among the coils for plasma uniformity.
Solution Approach 2:
The patent introduces a current divider network as an intermediary component between the single RF power source and the three coil antennas. This current divider with variable impedance elements acts as a mediator that enables independent current control to each coil, resolving the complexity of direct separate powering while achieving the desired plasma uniformity control.
2Manufacturing precision
If RF power levels are adjusted to counteract non-uniformities, then plasma uniformity is improved, but resonant modes are excited causing plasma instabilities and high RF voltages
Solution Approach 1:
The patent employs variable impedance elements in the current divider network that can be dynamically adjusted to optimize current distribution among the coils. This dynamic control allows the system to achieve plasma uniformity while avoiding resonant modes by continuously adapting the impedance matching conditions, thereby preventing plasma instabilities and excessive RF voltages.
Solution Approach 2:
The patent changes the impedance parameters of the current divider branches to control the current apportionment to each coil. By adjusting the variable impedance elements, the system optimizes the current distribution to achieve uniform plasma processing while avoiding resonant conditions that would cause instabilities and high voltages.
3Power
If impedance matching is required for all three coils, then power delivery is optimized, but control of power levels becomes unpredictable and complicated
Solution Approach 1:
The patent creates a universal impedance matching system where a single RF power source with one impedance match serves all three coil antennas. The current divider network provides multi-functionality by simultaneously delivering power to three coils and enabling independent current control, eliminating the need for three separate impedance matching systems and simplifying operation.
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 enables precise control of current distribution among the RF coils, improving plasma uniformity and stability by minimizing resonant modes and high RF voltages, thus enhancing the consistency of plasma processing for larger wafers.
Implementation Method 1
An RF source power generator 150 has an output terminal coupled through a RF impedance match 152
Implementation Method 2
three coil antennas 120, 122, 124 having respective driven ends and return ends... to control uniformity of radial distribution of process rate
Implementation Method 3
A current apportionment controller controls impedances of the variable impedance elements of the pair of current divider branches
Implementation Method 4
The RF power levels applied to the different coils are selected to counteract non-uniformities
Data Source
AI summary
An inductively coupled plasma reactor has three concentric coil antennas and a current divider circuit individually controlling currents in each of the three coil antennas by varying two variable impedance elements in the current divider circuit in response to a desired current apportionment among the coil antennas received from a user interface.