RF Blocking Filter for Plasma Reactor Heated Electrostatic Chuck
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Commercially available RF filters used in plasma reactors for semiconductor fabrication fail to block RF bias power effectively due to high RF voltage causing overheating, and alternative designs with air core chokes require excessive windings leading to capacitive reactance and RF leakage.
Innovation Solution
An RF blocking filter using low-permeability fused iron powder toroids and moderate winding turns to provide sufficient inductive reactance at 13.56 MHz, coupled with capacitors for resonance above the HF frequency, effectively isolating RF bias power from the heating element while allowing 60 Hz AC power to the resistive heating element without overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high permeability magnetic core is used in the RF filter choke, then the RF impedance at 13.56 MHz is sufficiently high to block RF bias power, but the high magnetic flux causes extreme heating and destruction of the filter
Solution Approach 1:
The patent changes the permeability parameter of the magnetic core from high (3000-7000) to low (10-100), and adjusts the number of windings parameter accordingly (16-24 turns) to achieve the required inductive reactance without excessive magnetic flux that would cause overheating
Solution Approach 2:
The patent uses a composite structure combining low-permeability magnetic core material with specific wire gauge (3-3.5 mm diameter) and winding configuration, creating a filter design that balances RF blocking capability with thermal management
2Temperature
If an air core choke is used to avoid overheating, then the magnetic core heating problem is eliminated, but over forty or more windings are required which creates high capacitive reactance and allows RF leakage
Solution Approach 1:
The patent introduces a magnetic core with low but non-zero permeability (10-100), which reduces the required number of windings to 16-24 turns, thereby reducing capacitive reactance while avoiding the overheating issues of high-permeability cores
3Reliability
If the number of windings in the choke is increased to provide sufficient inductive reactance, then the RF impedance increases to block RF bias power, but the capacitive reactance increases allowing RF leakage
Solution Approach 1:
The patent optimizes the number of windings parameter to 16-24 turns, which provides sufficient inductive reactance for RF blocking while keeping capacitive reactance low enough to prevent RF leakage, achieving a balance between the two opposing requirements
4Reliability
If a high impedance filter is placed between the heating element and RF bias source, then RF bias power is blocked from the heater circuit, but the filter overheats and fails due to high RF voltage
Solution Approach 1:
The patent changes the magnetic core permeability parameter to a low value (10-100), which reduces magnetic flux and associated heating, allowing the filter to maintain its RF blocking capability while withstanding high RF voltages (2 kV peak-to-peak) without overheating or failure
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 solution provides over 60 dB of RF attenuation at 13.56 MHz, preventing RF leakage and maintaining stable plasma control with negligible impedance changes, while safely handling several kW of AC power and high RF voltages without overheating.
Implementation Method 1
provide sufficient inductive reactance at 13.56 MHz
Implementation Method 2
each of the capacitors having a capacitance that forms a resonance with the inductance of the corresponding one of the inductors at a resonant frequency at least several MHz above the HF frequency
Implementation Method 3
an electrical heating element is provided within an insulating layer of the ESC as an electrically resistive element underlying the wafer support surface
Implementation Method 4
respective pluralities of fused iron powder toroids of magnetic permeability on the order of about 10 stacked coaxially within respective ones of the pair of cylindrical envelopes
Data Source
AI summary
An RF blocking filter isolates a two-phase AC power supply from at least 2 kV p-p of power of an HF frequency that is reactively coupled to a resistive heating element, while conducting several kW of 60 Hz AC power from the two-phase AC power supply to the resistive heating element without overheating, the two-phase AC power supply having a pair of terminals and the resistive heating element having a pair of terminals. The filter includes a pair of cylindrical non-conductive envelopes each having an interior diameter between about one and two inches and respective pluralities of fused iron powder toroids of magnetic permeability on the order of about 10 stacked coaxially within respective ones of the pair of cylindrical envelopes, the exterior diameter of the toroids being about the same as the interior diameter of each of the envelopes. A pair of wire conductors of diameter between 3 mm and 3.5 mm are helically wound around corresponding ones of the pair of envelopes to form respective inductor windings in the range of about 16 to 24 turns for each the envelope, each of the conductors having an input end and an output end. The input end of each one of the conductors is coupled to a corresponding one of the pair of terminals of the two-phase AC power supply, and the output end of each one of the conductors is coupled to a corresponding one of the pair of terminals of the resistive heating element.