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.
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.
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.
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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