Plasma Processing Apparatus RF Bias Control
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Solution Overview
Problem
Conventional capacitively coupled plasma processing apparatuses using a single RF frequency for ion attraction face difficulties in controlling ion energy distribution, limiting the controllability of the RF bias function and leading to tradeoffs in etching rate, selection ratio, and etched shape in high aspect ratio contact plasma etching.
Innovation Solution
A plasma processing apparatus employing three RF powers with different frequencies (100 kHz to 300 MHz) applied to the first electrode, along with a filter circuit configured to prevent unwanted resonance on the RF transmission line, allowing independent control of minimum and maximum ion energies and optimizing ion energy distribution for various process characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single RF frequency is used for ion attraction, then the device complexity is reduced, but the controllability of ion energy distribution deteriorates
Solution Approach 1:
The patent segments the RF power supply into three independent frequency sources (first RF: 100 kHz to 6 MHz, second RF: 6 MHz to 40 MHz, third RF: 40 MHz to 300 MHz). Each frequency component can be independently controlled to apply different energies to ions, enabling fine-grained control over the ion energy distribution without requiring a single complex adjustable RF system.
Solution Approach 2:
The patent changes the frequency parameter of the RF power supply from a single value to multiple discrete values. By selecting different frequency combinations from the three RF power supplies, the system can adjust the ion energy distribution characteristics (minimum energy, maximum energy, and energy width) to optimize for different process requirements such as etching rate, selection ratio, and anisotropy.
2Adaptability or versatility
If multiple RF frequencies are applied to control ion energy distribution, then the controllability of RF bias function is improved, but unwanted resonance may occur on the RF transmission line
Solution Approach 1:
The patent introduces a filter circuit as an intermediary component between the three RF power supplies and the first electrode. This filter circuit selectively passes the desired RF frequencies while attenuating unwanted frequencies and harmonics, preventing resonance conditions on the RF transmission line. The filter acts as a mediator that enables multi-frequency operation while maintaining system stability and reliability.
3Productivity
If RF power is increased to accelerate ions, then the etching rate is improved, but the maximum ion energy increases leading to loss of process control
Solution Approach 1:
The patent creates a dynamic ion energy distribution by combining three different RF frequencies. The lower frequency (first RF) contributes to higher maximum ion energies that drive etching rate, while the higher frequencies (second and third RF) add smaller energy increments that broaden the energy distribution. This dynamic combination allows the system to achieve high productivity through increased ion energy while maintaining precision control over the energy distribution shape, enabling independent optimization of etching rate and selectivity.
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
Enhances the controllability of the RF bias function, prevents unwanted resonance, and improves the reliability of the plasma process by allowing flexible control of ion energy distribution, thereby optimizing process characteristics and preventing circuit damage from high currents.
Implementation Method 1
a first RF power supply that applies a first RF power having a first frequency f1 to the first electrode; a second RF power supply that applies a second RF power having a second frequency f2 to the first electrode; a third RF power supply that applies a third RF power having a third frequency f3 to the first electrode
Implementation Method 2
a filter circuit connected between the second electrode and a member having a ground potential... configured such that, in a case where 3f23, assuming that (f1+f2) is A and the lower one of 2f2 and (f3−f2) is B, no resonant frequency is present in the frequency range of f13
Implementation Method 3
Electrons are accelerated by the electric field generated between the electrodes facing each other due to an application of the RF power
Implementation Method 4
plasma is generated by the collision and ionization between electrons and the process gas
Implementation Method 5
ions contained in the plasma are accelerated and attracted on the substrate by a negative bias voltage or sheath voltage generated on the lower electrode
Data Source
AI summary
Provided is a capacitively coupled plasma processing apparatus which improves a controllability of the RF bias function and reliably prevents unwanted resonance from being generated on a RF transmission line between a counter electrode and ground potential to enhance reliability of the plasma process. In the capacitive coupled type plasma processing apparatus, three kinds of RF powers from a first, second and third RF power supplies (35, 36, 38) are superimposed and applied to susceptor (lower electrode) (16). In such a three-frequency superimposing and applying application scheme, the frequency-impedance characteristic around upper electrode (48) is considered to prevent a serial resonance from occurring on an RF transmission line around upper electrode (48) in consideration of all the low order frequencies of the IMD relevant to and affecting the plasma process. Since the fluorocarbon layer by itself functions as an antireflective film and a harm mask, the reliability of processing can be improved, while reducing the cost.