Faraday Shield Current Control for Plasma Uniformity
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Solution Overview
Problem
Existing inductively coupled plasma processing apparatuses face challenges in achieving uniform plasma distribution due to stray capacitance and current variations along the inductive antenna, which complicates mass production and requires frequent adjustments of annular conductors based on varying process conditions.
Innovation Solution
A plasma processing apparatus with a Faraday shield that supplies radio frequency power and includes a monitoring unit to control the current flowing through it, using variable capacitors to optimize the electrostatic capacity and minimize current variations, thereby improving the azimuthal distribution of plasma.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a current of a certain ampere or more is required to flow in an inductive antenna to generate high density plasma, then plasma density is improved, but ununiform voltage of a certain kilovolt or more is generated along the antenna causing azimuthal distribution of plasma
Solution Approach 1:
A Faraday shield is introduced as an intermediary component between the inductive antenna and the plasma. The shield is equipped with an annular conductor that acts as a mediator to redistribute the electromagnetic field and compensate for the ununiform voltage distribution along the antenna, thereby reducing azimuthal plasma distribution while maintaining high plasma density
Solution Approach 2:
The shape parameters of the annular conductor on the Faraday shield are optimized to specific dimensional ratios (inner diameter to outer diameter between 0.3-0.7, width to outer diameter between 0.05-0.2) to change the electromagnetic field distribution parameters, which compensates for the ununiform voltage and current distribution caused by stray capacitance
2Manufacturing precision
If an annular conductor is placed on a Faraday shield to suppress azimuthal distribution of plasma, then plasma uniformity is improved, but frequent replacement of annular conductors with different shapes is required for different process conditions
Solution Approach 1:
The system transitions from static fixed-shaped annular conductors to a dynamic adjustable system using variable capacitors. The variable capacitors can be electrically adjusted to change the effective electrical characteristics of the annular conductor system, allowing adaptation to different process conditions without physical replacement, thus improving productivity while maintaining plasma uniformity
Solution Approach 2:
Instead of changing the physical shape parameters of the annular conductor for different process conditions, the electrical parameters (capacitance) of the variable capacitors connected to the annular conductor are adjusted. This allows the same physical structure to adapt to different plasma densities, pressures, and gas types, eliminating frequent replacements and enabling mass production
3Quantity of substance
If stray capacitance exists between the inductive antenna and the plasma, then plasma generation is enabled, but current in the antenna does not become a constant value causing azimuthal distribution
Solution Approach 1:
The Faraday shield with annular conductor and variable capacitors serves as an intermediary that stabilizes the electrical connection between the antenna and plasma. The variable capacitors compensate for the destabilizing effect of stray capacitance by providing adjustable capacitive coupling, which maintains constant current flow while still enabling plasma generation
Solution Approach 2:
A monitoring unit measures the actual current flowing through the Faraday shield and provides feedback to a control unit. The control unit adjusts the variable capacitors based on this feedback to maintain constant current, thereby compensating for the instability introduced by stray capacitance and eliminating azimuthal plasma distribution
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 allows for consistent plasma distribution across the plasma processing apparatus, reducing the need for frequent adjustments and enabling mass production by monitoring and controlling the current to maintain optimal plasma uniformity, even with changing process conditions.
Implementation Method 1
an inductive antenna with several turns is disposed outside a vacuum chamber. When a radio frequency current flows to the inductive antenna, plasma is generated in the vacuum chamber by an induction magnetic field.
Implementation Method 2
it is known that stray capacitance exists between this inductive antenna and the plasma. Because the current in the inductive antenna flows in or out the plasma through this stray capacitance, the current in the antenna does not become a constant value.
Data Source
AI summary
The features of the present invention are that a plasma processing apparatus includes: a process chamber in which a sample is plasma-processed; a dielectric window which airtightly seals an upper part of the process chamber; an inductive antenna which is disposed at an upper part of the dielectric window and forms an induction magnetic field; a radio frequency power source which supplies radio frequency power to the inductive antenna; and a Faraday shield to which radio frequency power is supplied from the radio frequency power source and which is disposed between the dielectric window and the inductive antenna, and the plasma processing apparatus further includes a monitoring unit which monitors a current flowing in the Faraday shield and a control unit which controls the monitored current.