Reverse-Synchronized RF Coils for Uniform Plasma Sheath Control
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Solution Overview
Problem
Existing plasma processing systems fail to achieve uniform ion density and flux distribution across a semiconductor wafer, leading to non-uniform etch profiles due to tilted ion directions and non-uniform plasma sheath thickness.
Innovation Solution
Implementing reverse synchronization pulsing of RF coils, where one RF coil is turned on while the other is off during specific time periods, to minimize interference and enhance plasma sheath uniformity and ion tilt.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If both RF coils are operated simultaneously, then plasma generation is maintained, but plasma density uniformity deteriorates due to interference between coils
Solution Approach 1:
The patent applies periodic pulsed operation of RF coils in reverse synchronization, where coils are alternately activated and deactivated in periodic cycles. This temporal modulation allows each coil to generate plasma independently during its active phase, eliminating continuous interference while maintaining overall plasma generation through sequential operation.
Solution Approach 2:
The system dynamically switches between different coil configurations by controlling the timing and duration of each coil's operation. The pulse width, duty cycle, and synchronization phase are dynamically adjusted to optimize plasma uniformity while maintaining sufficient plasma density for processing.
2Area of stationary object
If both RF coils are operated simultaneously, then plasma coverage is maintained, but sheath thickness uniformity deteriorates
Solution Approach 1:
By periodically pulsing the RF coils in reverse synchronization, the system creates alternating plasma generation zones. During each pulse cycle, one coil generates plasma while the other is off, allowing independent control of plasma parameters in different spatial regions. This temporal separation translates to improved spatial uniformity of sheath thickness across the substrate.
3Quantity of substance
If both RF coils are operated simultaneously, then plasma flux is maintained, but ion direction uniformity deteriorates due to tilted ion directions
Solution Approach 1:
The periodic pulsed operation with reverse synchronization ensures that ions are accelerated primarily by one coil at a time during each cycle. This eliminates the competing electric fields that would otherwise cause ion trajectory tilting. The cumulative effect over many cycles maintains sufficient plasma flux while achieving uniform ion direction perpendicular to the substrate.
4Manufacturing precision
If RF coils are pulsed in reverse synchronization, then plasma uniformity improves, but plasma generation continuity may be affected
Solution Approach 1:
The pulse frequency and duty cycle are carefully selected so that the sum of plasma generation from alternating coils maintains continuous average plasma density. The off-time of one coil coincides with the on-time of the other, creating overlapping plasma tails that ensure continuity while allowing each coil to operate independently for improved uniformity.
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 method achieves a more uniform plasma sheath thickness and ion flux distribution, reducing ion tilt and ensuring uniform processing of semiconductor wafers.
Implementation Method 1
separately pulsed radio frequency (RF) coils... When a first one of the two RF coils is on during a pulsing cycle
Implementation Method 2
If density or flux of ions of plasma formed above a semiconductor wafer is nonuniform, a thickness of a sheath of the plasma is also nonuniform. Because the ions enter the sheath perpendicular to a boundary of the sheath
Data Source
AI summary
Systems and methods for pulsing radio frequency (RF) coils are described. One of the methods includes supplying a first RF signal to a first impedance matching circuit coupled to a first RF coil, supplying a second RF signal to a second impedance matching circuit coupled to a second RF coil, and pulsing the first RF signal between a first parameter level and a second parameter level. The method includes pulsing the second RF signal between a third parameter level and a fourth parameter level in reverse synchronization with the pulsing of the first RF signal.