Pulsed RF Plasma Timing for Uniform Density and Hot Spot Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing plasma processing methods face challenges in maintaining plasma density and uniformity due to overlapping RF power pulses, which can lead to hot spots and difficulties in applying uniform plasma processing.
Innovation Solution
A plasma processing method and apparatus that apply pulsed RF power with a controlled phase difference between two RF frequencies, ensuring the on-periods of the lower-frequency RF power do not overlap with the higher-frequency RF power, promoting plasma ignition and maintaining density while improving ion energy distribution and controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulsed RF power is applied to generate plasma and control ion energy, then plasma ignition and ion energy distribution are improved, but plasma density maintenance becomes difficult when on-periods overlap
Solution Approach 1:
The patent applies periodic pulsed RF power with carefully controlled timing. The lower-frequency RF power (ion energy control) and higher-frequency RF power (plasma generation) are both pulsed with specific duty cycles and phase differences. This periodic action ensures that ionization occurs during the higher-frequency power on-periods while ion energy is controlled during lower-frequency power on-periods, preventing overlap that would cause hot spots and maintain stable plasma density.
Solution Approach 2:
The patent employs preliminary action by controlling the lower-frequency RF power on-period to end just before the higher-frequency RF power on-period begins. This timing arrangement prepares the plasma for efficient ionization by the higher-frequency power while avoiding simultaneous application that would cause density fluctuations. The phase difference control ensures proper sequencing of these preliminary actions.
2Manufacturing precision
If lower-frequency RF power is applied for ion energy control, then ion energy distribution is improved, but hot spots occur when on-periods overlap with higher-frequency RF power
Solution Approach 1:
The patent uses periodic pulsed power with specific duty cycles (e.g., 30-70% for lower-frequency, 70-30% for higher-frequency) and frequency ratios (e.g., 1:4 or 1:10). This periodic application with controlled timing separates the functions: lower-frequency power controls ion energy when plasma is present, while higher-frequency power regenerates plasma density, preventing overlapping that causes hot spots.
Solution Approach 2:
The patent changes key parameters including RF power frequency (lower vs. higher), duty cycle (asymmetric values), and phase difference (controlled time offset). By adjusting these parameters, the system achieves uniform ion energy distribution without hot spots, as the lower-frequency power does not overlap with higher-frequency power on-periods, preventing excessive localized heating.
3Reliability
If asymmetric duty cycles are used for plasma generation and ion control, then plasma density and ion energy control are improved, but phase difference control becomes more complex
Solution Approach 1:
The patent implements periodic pulsed RF power with asymmetric duty cycles where the lower-frequency power (ion energy control) and higher-frequency power (plasma generation) have complementary duty cycle values. This periodic structure with fixed phase difference simplifies control compared to continuous asymmetric application, as the timing relationships are established through regular pulse sequences rather than continuous variable adjustment.
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 approach allows for reliable plasma ignition and maintenance of plasma density, preventing hot spots and enabling uniform plasma processing by controlling the timing of RF power pulses, thereby enhancing processing quality and accuracy.
Implementation Method 1
a pulse wave of radio frequency power for generating a plasma... the radio frequency power for plasma generation
Implementation Method 2
a pulse wave of radio frequency power for biasing... controlling the pulse wave of radio frequency power for plasma generation and the pulse wave of radio frequency power for biasing, such that a predetermined phase difference occurs
Data Source
AI summary
A method performed by a plasma processing apparatus including a first electrode and a second electrode is provided. The method includes applying a pulsed wave of first radio frequency (RF) power to the first electrode or the second electrode; and applying a pulsed wave of second RF power having a lower frequency than the first RF power, to the first electrode with a given phase difference relative to the pulsed wave of the first RF power. A first on-period of the second RF power and a second on-period of the second RF power are controlled such that the first on-period and the second on-period do not overlap with a period of time while the first RF power is turned on. Also, the first on-period is controlled such that the first on-period ends just before the first RF power is turned on.