Plasma Sputtering Process for Micron-Scale Particle Production
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Solution Overview
Problem
Existing plasma sputtering processes for producing small particles have low pick-up probabilities of atoms on particle surfaces, leading to slow growth rates and low production rates, making them unsuitable for particles in the range of a few micrometers.
Innovation Solution
A plasma sputtering process with a high-density plasma is achieved by controlling the process gas number density, plasma electron number density, and plasma electron temperature to ionize a significant portion of sputtered target atoms, increasing the pick-up flux of ionized atoms on grain surfaces, and using a pulsed power supply to maximize power without overheating the cathode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional plasma sputtering process is used, then particles can be formed from solid target material, but the pick-up probability of atoms on particle surfaces is low leading to slow growth rates
Solution Approach 1:
The patent applies parameter changes by optimizing the plasma gas pressure to a specific range (0.1-10 Pa) and controlling the plasma power density to enhance the ionization fraction of sputtered atoms. This increases the concentration of ionized species in the plasma, thereby improving the pick-up probability on particle surfaces and increasing the particle production rate while maintaining the advantage of using solid target materials.
2Productivity
If plasma energy is increased to ionize more sputtered atoms, then pick-up flux of ionized atoms increases, but cathode overheating occurs
Solution Approach 1:
The patent employs periodic pulsed plasma discharge instead of continuous DC discharge. The plasma is switched on and off in cycles, allowing the cathode to cool down during the off-period while still achieving sufficient ionization during the on-period. This periodic action enables high pick-up flux of ionized atoms without causing cathode overheating, thus resolving the contradiction between productivity and temperature control.
3Quantity of substance
If process gas pressure is increased to increase plasma density, then ionization of sputtered atoms improves, but mean free path of atoms decreases
Solution Approach 1:
The patent optimizes the process gas pressure to a specific window (0.1-10 Pa) where the plasma electron number density is sufficiently high to ensure good ionization of sputtered atoms, while the mean free path remains long enough to allow sputtered atoms to reach the plasma region and be ionized effectively. This balanced parameter selection resolves the contradiction between increasing plasma density and maintaining adequate atomic transport.
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 process significantly increases the production rate of small particles by enhancing the pick-up probability and efficiency of ionized sputtered target atoms, allowing for the production of particles with sizes up to 10 µm, including nanoparticles, with improved productivity and control over particle properties.
Implementation Method 1
The plasma electron number density and the plasma electron temperature are sufficient to ionize at least a part of the sputtered target atoms
Implementation Method 2
Atoms are sputtered from the target by means of the plasma
Implementation Method 3
A plasma is created and the energy provided to the plasma is controlled such that a predetermined plasma electron number density ne and a predetermined plasma electron temperature Te are obtained
Data Source
Figure 1
Figure 2a~2b
Figure 2c
AI summary
A high production rate plasma sputtering process for producing particles having a size of 10 µm or less is disclosed. The process causes ionization of at least a part of the sputtered target atoms and is performed at such parameters that the pick-up probability of ionized sputtered target atoms on the surface of grains is high.