July 2021 - Esgee Tech

How to Simulate Plasma Discharge in a Meter-scale ICP Reactor?

by esgee-webmaster | Jul 24, 2021 | Blog, VizGlow

Humans took a big leap forward when we learned to control fire and use it for our daily needs. A similar leap happened when we learned to generate and handle plasmas, the fourth and most abundant state of matter found mostly in stars.

Today, every consumer electronic device and computing hardware relies on plasmas in their core manufacturing technology. The semiconductor industry isn’t the only industry to be revolutionized by plasma and its limitless applications; the metallurgical, aerospace, automotive, chemical and medical industries also rely on plasma technologies.

Plasma can be generated in several ways; one of the common forms of plasma used in industrial applications is Inductively Coupled Plasma (ICP). As its name suggests, the energy for producing and sustaining the plasma is provided by induction coils to which high-frequency alternating current is supplied. This type of plasma can be produced at a wide range of operating pressures, flow rates, and feed-gas compositions. As a result of its versatility, ICP’s are especially favored among semiconductor manufacturers to produce high-density plasmas for etching, deposition, and other processes in the fabrication of invisible electronic components embedded in very large-scale integrated circuits that constitute logic, memory, and other types of chips. A similar class of ICP’s discharges, albeit much bigger in size, is also used in the manufacture of flat panel displays and solar panels.

VizGlow™: Simulate Real Physics of Non-equilibrium Plasmas

Plasma discharge, flow, and electromagnetic simulations are challenging on many accounts: transient electromagnetic fields, spatio-temporal variations in electron and ion densities due to chemical reactions, complex circuit configurations for power supply, and a plethora of surface reactions all need to be taken into account. The industrial researchers and product developers desire nothing less than highest fidelity simulations for understanding the plasma behavior at a wide range of length-scales.

Over the past 15 years, at Esgee Tech, we have developed our flagship simulation software VizGlow™ to accomplish the most challenging objectives as desired by the semiconductor industry. VizGlow™ is capable of simulating ICPs at a great fidelity by coupling plasma, electromagnetics, reactive flow, surface chemistry, and circuit dynamics. It supports large-scale 3D unstructured mesh of accurate and complex industrial wafer-processing reactors. In addition, various modifications to the classical ICP are possible such as multiple turn coils (this study), pulsing, multi-frequency input power, RF biasing at select surfaces, application of permanent magnetic fields, and operation in cavity resonant modes. All of these modifications can be simulated using VizGlow™.

In this blog post, we discuss a large-scale multi (dual) coil ICP reactor simulated using VizGlow™.

Large-Scale ICP Reactor: An Industrially-Relevant Problem

An ICP reactor is a workhorse for several semiconductor, flat panel, and solar industrial applications. The advantage of inductive power coupling is that there is low plasma potential drop across sheaths, generation of high-density plasma at lower electron temperature, which leads to higher ion flux and reduced ion bombardment energy at the wafer surfaces. Additionally, multiple spatially distributed inductive coils with multiple turns each helps generate a more uniform plasma covering a wider volume and processing surface area. Using multiple coils also allows for the generation of a complex and deliberately tailored spatial distribution of the electromagnetic fields that in turn enables exploitation of interesting properties of electromagnetic wave interference patterns for generating plasmas. Several parameters such as: position of the coils, coil structure, and current direction, could be altered to optimize the design of an ICP plasma. These are merely a few of the large number of parametric studies that one could explore using VizGlow™.

VizGlow™ enables large-scale reactor simulations such as the reactor discussed here, which measures 2.03m x 1.54m x 0.805m (LxWxH), and is used for processing wide area substrates such as for flat panel displays and solar panels. The computational domain is divided into following regions/sub-domains:

Coils: two spiral excitation coils are operated in-phase at a frequency of 13 MHz and power of 1 kW to generate EM waves.
Coil cage: a Faraday cage which houses two coils
Plasma: the region with an initial pressure of ~1 Torr in which argon plasma is generated
Window: an interface between the coil cage and plasma that isolates plasma and coils
Substrate: the surface that is exposed to the generated plasma for processing

Detailed Insights into Plasma Field

Plasma uniformity across a wide area is essential for generating uniform ion fluxes and radical fluxes at the wafer surface. The figure on the right illustrates that a dense plasma is generated directly underneath the coil and is highest underneath the dielectric window where the electromagnetic waves are introduced. VizGlow™ is able to capture the electromagnetic skin effect, i.e, shielding of the electromagnetic waves by high density plasma. Moreover, power deposition only occurs at a small zone within the skin depth. The active radicals and the ions then diffuse from this generation zone to the substrate usually located at the bottom of the chamber.

The results indicate that this fundamental ICP property is well represented by VizGlow™.

In an electromagnetic field, Poynting Vectors represent the electromagnetic energy flux and its direction. It is particularly important to understand the flow of energy as it is critical to the design and optimization of the plasma devices. Results obtained by VizGlow™ can be viewed in an immersive environment in the figure on top to see how these three-dimensional vectors carry the energy from the coils and deposit it in the plasma field. The color of the vector indicates the strength of the vector. These three-dimensional visualizations allow researchers to comprehend the plasma field in greater detail.

Looking to know more? Let’s connect!

If you are someone as excited about plasma flow simulations as we are, feel free to follow us at LinkedIn or reach out to us at info@esgeetech.com.

Meanwhile, if you are curious about the latest developments in plasma flow simulations, feel free to go through the following journal papers (do ask us for a free copy!):

D. Levko, C. Shukla, R.R. Upadhyay, L.L. Raja, Computational study of plasma dynamics and reactive chemistry in a low-pressure inductively coupled CF₄/O₂ plasma, Journal of Vacuum Science & Technology B 39, 042202 (2021), https://doi.org/10.1116/6.0001028
T. Iwao, P.L.G. Ventzek, R.R. Upadhyay, L. L. Raja, H. Ueda, & K. Ishibashi, “Measurements and modeling of the impact of radical recombination on silicon nitride growth in microwave plasma assisted atomic layer deposition”, Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 36(1), pp. 03DB01, 2018, https://doi.org/10.1116/1.5003403
L. L. Raja, S. Mahadevan, P.L.G. Ventzek, and J. Yoshikawa, “Computational modeling study of the radial line slot antenna microwave plasma source with comparisons to experiments,” Journal of Vacuum Science &Technology A, vol. 31, no. 3, p. 031304, 2013, https://doi.org/10.1116/1.4798362

Why Do Combustion Engines Always Tell Terrible Knock-Knock Jokes?

by esgee-webmaster | Jul 10, 2021 | Blog, VizSpark

Automobiles have significantly improved the lives of humans – nothing is too far these days with a car. In our vehicle, we set off to drive for work, make a short spree to the local grocery store, cruise on a long road trip, get our packages delivered, and what-have-you.

We almost never notice the complex mechanisms of a car that reliably get us from point to point (until it breaks down…). Every time we start our car to carry out our business on the road and until we turn it off, there are, on average, a few thousand explosions per minute inside the engines of our car that set us in motion. That is almost 20 times every second for each cylinder!

Hidden Consequences of the “Bang” Part of Combustion

Spark plug ignites fuel-air mixtures by inducing a dielectric breakdown in the spark gap. In order to initiate the breakdown, sufficient voltage difference across the electrodes is supplied until the breakdown happens. This phenomenon leads to formation of a spark – a form of plasma and is akin to formation of lightning, but on a much smaller scale.

At such intense continuous operating conditions, every stroke of the engine causes the electrodes on the spark plug to undergo various phenomena such as melting, vaporization, sputtering, and oxidation. These processes cause electrodes to erode which leads to degraded performance of the engine. More often than not, when you are trying to start the engine – and it fails or if your car is sluggish, it is likely due to eroded electrodes which are causing this nuisance. Electrode erosion affects formation of spark between the electrodes.

The Issue…

Spark plug erosion is a complex multi-physics transient phenomena which involves coupling of surface physics (electrode depletion), thermal plasma physics (spark formation), circuit dynamics (ignition coils), turbulent chemical interactions (combustion) and heat transfer.

The spark between the electrodes lasts only for a few milliseconds, depending on the ignition system. On the other hand, the erosion of the electrodes could take up to years. Modelling misfires and erosion are arduous as the model needs to accurately capture multi-physics phenomena that occur in completely different time scales.

This poses a problem: how do you simulate physics of spark plugs which occur at different time scales, with highest possible fidelity, simultaneously, within a matter of hours?

The Solution…

Here is where multiphysics capabilities of VizSpark opens new dimensions of understanding erosion – our thermal equilibrium plasma solver developed at Esgee Technologies, has been successfully used by major automotive companies to understand the spark formation and erosion behavior of the electrodes.

VizSpark provides multiphysics tools for mixing and matching electromagnetics, plasma, fluid dynamics, chemistry, circuit dynamics and many more, in a single easy-to-use framework.

Here’s How…

For example, our CircuitLib module in VizSpark allows for flexibility in a variety of configurations which power the electrode. The circuit parameters are coupled with the fluid dynamics module. This means you could generate a spark in a realistic manner as it would happen in an engine.

The figure on the left, captures variations in the spark properties which are reflected in the results generated by the coupling of physics. Industrial researchers rely on the highly resolved current and voltage readings to understand the misfires that lead to erosion. Using VizSpark simulation, they have developed a predictive ability to design high-efficiency spark plugs by optimizing electrode geometry.

Next comes the massively scalable multi-processor, multi-node capability of VizSpark which is implemented at all stages of the simulation: mesh partitioning and simulation. The video on the right shows our high fidelity 3D representation of the geometry involved in this study. Here the top electrode is grounded, while the bottom electrode is connected to a current source to power the spark plug. Here, the geometry is an accurate representation of a J-type spark plug. Using partitioned mesh, Vizspark takes advantage of parallel processing and speeds up the simulation by many folds.

Stay Tuned for More Details

In the meantime, feel free to check out the whitepaper and other ground breaking simulations. Follow us on LinkedIn!