Recently, consumers have faced rising prices for semiconductor-powered devices, with shortages affecting the availability of products that serve their daily needs. With increased demand for semiconductors in key areas like the automotive industry, healthcare, and within AI-enabled products, manufacturers are vying to remain competitive while making next-generation breakthroughs in order to meet current demand.
So, the question is: how can industrial researchers continue to innovate in order to boost semiconductor production? And how can simulations relieve the pressure for the semiconductor industry to meet ever-growing global demands?
A joint report authored by Boston Consulting Group (BCG) and The Semiconductor Industry Association (SIA) is aimed at combating semiconductor shortages by profiling risks in the current international supply chain and highlighting semiconductors as a central component of shared economic stability across the globe. Central to the report’s findings are a series of statistics that characterize the current issues the world faces in securing a future where semiconductor demands are met as they continue to grow over the next decade.
The Global Semiconductor Supply Chain at a Glance
The current cooperative structure of the global supply chain for semiconductors is as unique as it is complex, with a web of destinations across the globe from the earliest stages of research and design to the final point of sale. Since the 1970s, specialization within these national and regional stages has contributed to the chain’s ability to produce at the speed of demand, while also innovating and improving the capabilities of semiconductors faster than any one country or region could.
Figure 1 below shows the current global semiconductor market share by region as of 2020. South Korea and the United States account for two-thirds of total market production and sales.
In addition to utilizing the specializations offered by each of the six major regions (Europe, Japan, Mainland China, South Korea, Taiwan, and the United States) that contribute to the global supply chain, the roundabout system also makes use of favorable trade conditions among the participating countries to keep production costs and consumer prices affordable. Figure 2 below shows the usage of semiconductors by industry.
Major risks in disruptions to the current supply chain could lead to a sharp rise in the cost of devices to producers and consumers alike. In a hypothetical situation where the global chain is replaced with self-sufficient regions, the report forecasts up to $900 – 1,225B of upfront investment required to maintain current output and meet rising demands, with an overall cost increase of 35% – 65% for consumers if regional and comparative advantages are ignored.
National policies within key regions, most notably Mainland China – which has massive industrial and manufacturing capabilities – have already placed self-sufficiency as a high priority for their future development in semiconductors.
Similar policies in other nations could leave local markets open to unforeseen factors, including greater competition for materials and additional costs in their securing and transportation. Situations like natural disasters and geopolitical conflict could destabilize systems that seek to decouple from the international chain, leading to regional shortages of semiconductors and additional issues with production for critical communications and security sectors.
Researching and Developing Solutions for the Market
In addition to the current issues that the international supply chain faces, SIA’s report highlights the importance of research and development, which is the primary way that producers maintain state-of-the-art techniques and provide security in their devices.
Although the speed of innovation and change in major market devices like consumer electronics is visible from year-to-year, the time for techniques developed at pre-competition research stages to be utilized at a mass scale and included within the global chain can take decades. As a result, original equipment manufacturers (OEMs) and integrated device manufacturers (IDMs) face upfront costs in both R&D and capital expenditure, with years before seeing a return on investment in these areas.
Despite the delayed turnaround for companies investing and participating in pre-competitive and basic research, cooperation at these early stages enables chips to become smaller while increasing performance. Recent innovations like 5G, internet of things (IoT), and autonomous vehicles all began their journey to widespread use at this stage. Figure 3 below illustrates regional spending in R&D among key regions as a percentage of sales.
SIA’s report also cites the need for utilization of emergent technologies in alleviating risks and constraints in the global chain, with modern inventions like augmented and virtual reality (AR/VR) playing a crucial role in enabling operations to continue remotely throughout the pandemic.
Simulation also provides this principle effect of bridging digital and physical worlds by allowing manufacturers to cut material costs and risk of exposure to hazardous materials, all without sacrificing insights that physical experiments and trials offer.
The use of simulation software and digitally based tools to further minimize risks that current global producers face is both economic and modern, and its viability as an industry-wide solution will only become greater as time continues. Simulations offer additional innovation points through applications for commonly used equipment in the semiconductor industry, such as plasma reactors, with details like simulated angular distribution functions deciding process parameters like excitation frequency and excitation voltage.
Industry leaders like Dr. Peter Ventzek and Dr. Alok Ranjan of Tokyo Electron Ltd. – a global supplier of equipment used to fabricate integrated circuits- have already taken advantage of high-fidelity plasma simulation and processing to develop new techniques with a wide array of applications for the semiconductor industry, using the insights offered by numerical simulations using VizGlow™. Here are a few examples of patented methods and techniques using simulations that are contributing to the semiconductors of today and tomorrow:
· Mode-switching plasma systems and methods that allow manufacturers to reduce minimum-required features and the cost of ICs, while also increasing packing density of components. Manufacturers working at the atomic scale are able to continue scaling semiconductor devices with consideration for constraints like equipment configurability, equipment cost, and wafer throughput.
· Techniques that include formation, patterning, and removal of materials in order to achieve physical and electrical specifications for the current and next generation of semiconductor. Plasma etching and deposition are prone to issues with decoupling source power (SP) and bias power (BP) effects, resulting in reduced control and precision. Decoupling these effects helps reduce cross-talk between a source and bias and in turn enhances control while decreasing complexity.
· Utilizing pulsed electron beams to create new plasma processing methods, which enable reduction of feature size while maintaining structural integrity. As device structures continue to densify and develop vertically, these methods which produce atomic-level precision in plasma processes will be useful for profile control, particularly in controlling deposition and etching processes at timescales associated with growth of a single monolayer of film.
Processes in plasma-assisted etching or deposition rely on the accurate determination of the distribution of the ion energy and angle close to the substrate surface. Precise control over these parameters could be used to manipulate the bombardment of the process surface. However, from a process engineer’s perspective, the incremental changes in geometric design, voltage, power, feed gas composition, and flow rates must be correlated with IEADF (Ion Energy and Angular Distribution functions).
The engineering team at Tokyo Electron Ltd. uses our non-equilibrium plasma solver, VizGlow™, and particle solver, VizGrain™, to understand underlying physics and find the best operating conditions for Tokyo Electron Ltd. products. In a paper published in the Journal of Physics D: Applied Physics, Dr. Rochan Upadhyay, and Dr. Kenta Suzuki, Esgee Technologies along with researchers at The University of Texas at Austin validated the VizGlow™ simulations used to obtain IEADF in a capacitively coupled plasma reactor.
Esgee Technologies uses software products, databases, and consulting projects to solve challenges faced by industrial manufacturers. We are dedicated to the development of plasma and physics simulations for manufacturing applications across a wide range of manufacturing industries, including semiconductors, with a legacy of support for analyzing existing equipment, improving processes, and developing new equipment concepts through the use of our software.
Thanks for reading! If you’re still curious about the topics discussed in this article, check out the following journal papers (and ask us for a free copy!):
Upadhyay R., K. Suzuki, L. L. Raja, P.L.G. Ventzek, and A. Ranjan. (2020). Experimentally Validated Computations of Simultaneous Ion and Fast Neutral Energy and Angular Distributions in a Capacitively Coupled Plasma Reactor. Journal of Physics D: Applied Physics. 53. 10.1088/1361-6463/aba068.
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The inquisitive mind of mankind permitted spaceflight to grow in the last century and exponentiate in recent years. Thanks to the technologies that drive this rapid deployment of spacecrafts. Statistics show that the year 2020 had seen a record breaking 114 launches which placed over 1000 satellites in orbit. This number increased further in 2021 – in a span of 9 months over 1600 satellites were launched.
Launching satellites to orbit is arduous. Maintaining their orbits throughout their lifetime to accomplish their mission is a tough problem, as well. Gravitational effects combined with possible aero-drag can deorbit satellites.
Small orbital thrusters keep the satellites in their desired track by firing periodically to account for gradual changes in orbit, an effect known as orbital decay. With an ever-growing number of satellites orbiting with tight tolerances, maintaining precise orbits and controlled deorbiting upon reaching end-of-life is also critical.
Development of highly efficient and reliable thrusters is carried out by various agencies around the world. Different types of orbital thrusters exist. They are broadly classified as chemical thrusters and non-chemical thrusters such as ion thrusters – which is the topic of this blog.
Same Requirements, two different approaches:
Thrust can be quantified as the amount of force produced by expelling a certain mass flow rate at some exhaust velocity. This gives flexibility to attain the desired thrust at the expense of a large mass flow rate expelled at low velocity or a small mass flow rate at high velocity.
Chemical thrusters eject byproducts at a large mass flow rate but at a relatively low velocity. Powerful thrusters are fed by large fuel tanks during the initial stages of space flight to reach orbit. These thrusters have low specific impulse.
Unlike traditional chemical thrusters, ion thrusters function by Coulombic acceleration ions (typically xenon) in an electrostatic field to high velocity. This results in high specific impulse upwards of 2000 s with electrical efficiencies reaching as high as 80%. Along with fast response times, ion thrusters can be precisely controlled, thus reducing the need for large propellant tanks. Therefore, ion thrusters are highly sought for long-term interplanetary and deep space missions.
Iodine thrusters, a possible alternative to more expensive xenon thrusters:
While xenon-based ion thrusters are great alternatives to chemical thrusters, operational cost is high due to the rarity of xenon. Novel propellants such as water, krypton, bismuth, are being researched. Costly experiments are being conducted worldwide to study these novel propellants. In this blog we explore the possibility of iodine as an alternative. Main advantages of using iodine are: larger ionization cross-section compared to xenon and a small volumetric footprint for storing iodine as it is solid under standard temperature and pressure.
High fidelity numerical models using VizGlow™:
Prototyping ion thrusters for experimentation and iterative design is time consuming and difficult which are associated with large expenses. Replicating operating conditions of these thrusters in laboratories is difficult. Therefore, researchers often rely on numerical models to optimize their designs. Modelling of ion thrusters is a multiple physics problem which encompasses a broad spectrum of physics. Fluid dynamics, reactive flow, plasma, electromagnetics, surface physics have to be accounted for to model ion thrusters at highest fidelity. Coupling between these individual physics is not straightforward in many cases. As a result, approximations have to be made to simplify the mathematics. Such reduced models may not always represent the behavior of ion thrusters. In fact, the literature pertaining to simplified computational studies of ion thrusters is scarce.
VizGlow™ – a non-equilibrium plasma solver that is fully coupled, self-consistent, and allows accurate numerical simulation of plasma thrusters. VizGlow™ allows coupling of multispecies chemically reactive plasma dynamics with Maxwell’s equation for the electromagnetic waves. Our tool also supports hybrid models that combine traditional Navier-Stokes (CFD) equations and particle-in-cell (PIC). This, for example, can be used to describe the behavior of ejected plasma plume into vacuum.
Our team at Esgee Tech along with collaborators have simulated an ion thruster that utilizes iodine.
Simulation setup and discussion:
Here the computational domain consists of a 6 cm x 10 cm plasma chamber within which iodine plasma is generated by a four-turn metal coil antenna that is driven at 13.56 MHz and deposits a power of 100 W. A dielectric quartz layer interfaces between the coil antenna and the plasma chamber. A comparison of the plasma properties at two different pressures, 1.0 Pa and 2.5 Pa is performed in this study.
The simulation has captured non-equilibrium effects such as disparate electron and heavy particle temperatures. We also resolved electrostatic sheaths. The electrostatic Joule heating is negligible compared to the wave power deposited into the plasma. The dielectric quartz wall attains a potential to balance the flux of positive and negative species.
Results from VizGlow™ indicate that for both pressures, almost all of the molecular iodine dissociates into I+ ions which dominate the mixture. The concentration of molecular iodine ion, i.e., I2+ is about one order of magnitude smaller than that of the dominant singly-ionized atomic iodine.
The pressure has an effect on the composition of the generated plasma. The plasma is electropositive with electrons as dominant negatively-charged species for the chamber pressure of 1.0 Pa. This, however, changes with increase in pressure, as plasma formed at 2.5 Pa is electronegative, where atomic iodine anions (I-) are the dominant negatively-charged species.
An interesting feature that VizGlow™ captured is the presence of vortex-like structures surrounding the plasma bulk. This effect is a result of transport of electron and anion species in the electronegative plasma.
Future of iodine thruster modelling:
VizGlow™ is constantly evolving with new features, a growing database of chemistries, fast and accurate solvers. One can perform trade studies to understand the effects of chamber pressure and temperature. Future work in this area could also focus on the reactivity of iodine with the surface of the thruster and spacecraft to estimate the lifetime of the thrusters.
VizGlow™ can simulate actual designs of ion thrusters that are meant to propel next generation efficient spacecraft and expand the horizon of understanding of the cosmos.
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Moore’s Law, a traditional benchmark in the semiconductor industry, has led to miniaturization, speed and efficiency improvements in modern microelectronics. The primary approach to keep up with the trend is to shrink the size of various features within an integrated circuit (IC). In recent years, however, engineers have extended fabrication techniques to sub-10 nm scales and layering circuitry on top of one another to develop 3D circuits and thereby adhering to Moore’s Law.
There are several benefits of modern 3D semiconductor architectures including small footprint, improved performance, reduced power, and integration of diverse circuits in a single package. However, disadvantages such as design and manufacturing complexity along with poor fabrication yield which directly affect the cost of these chips. With research accelerating the means of producing cheap mainstream 3D IC structures, atomic layer deposition (ALD) has emerged as a critical fabrication technique.
Atomic Layer Deposition: advantages and disadvantages
Atomic Layer Deposition (ALD) is a technique for sequentially depositing thin films of gaseous reactants (called precursors) onto a substrate. The advantage of ALD over other chemical vapor deposition techniques is that gas-to-surface depositions that occur in ALD processes are intrinsically self-limited. Each ALD cycle starts with the introduction of a specific mixture of precursors followed by deposition which terminates when all the sites on the wafer have reacted. Therefore, ALD can achieve atomic layer precision as deposition occurs one layer at a time. Repeated cycles of different precursors result in the formation of a desired chemical deposition on a substrate which is ready for next stages of fabrication. The self-limiting nature of ALD processes is beneficial for chemically processing high aspect ratio via, trenches, etc. in next generation high-capacity flash memory devices.
The main drawback of depositing one-layer at a time comes with low throughput – ALD processes are slow. Novel reactor designs are needed to achieve faster processing times while maintaining quality of deposition. Processing a batch of 10s – 100s of stacked wafers inside a reactor is one viable method of increasing throughput. Several configurations of batch processors exist – these designs focus on the arrangement, orientation and number of wafers of a stack.
Numerical modelling: a high fidelity and low cost alternative to experiments
Optimization of reactor design and chemistry is critical to achieve high yields and lower costs of manufacturing semiconductors. Experimental prototyping of large reactors with complex geometries is tedious and expensive. Some overheads that are associated with every experiment are high cost of precursor gases, reactor prototyping, long experiment cycle times, and needless human exposure to toxic chemicals. These undesirable factors prompt engineers to resort to design and development using high fidelity numerical software tools such as Esgee Tech’s suite of multiphysics simulators.
Wafer processing typically occurs in high vacuum (~ milli-Torr) regimes. At such low pressures, the mean free path of participating gas species becomes significant and comparable to the size of the reactor, resulting in high Knudsen number slip flows. Results obtained using traditional CFD models raise several uncertainties in these cases. A true physics-based approach such as gas kinetic modeling is required to capture physics across very different length scales – from the meter-scale reactor scale dynamics to nanometer-scale mechanisms. Moreover, modelling ALD processes using numerical methods requires comprehensive coupling of physics: gas dynamics, multispecies reactive mechanisms in gas and surface phases, magnetohydrodynamics, electromagnetics and dust/macro-particle dynamics.
VizGlow™: Simulate Real Physics
Our flagship solver, VizGlow™ has particle simulation capabilities (in addition to a host of other modeling features) that allows fully-coupled 3D particle-based simulations, representing conditions observed in industrial reactors with high accuracy. VizGlow™ is capable of simulating reactive gas dynamics of semiconductor wafer processing devices using both direct-simulation-Monte-Carlo (DSMC), particle-in-cell (PIC), and hybrid coupled plasma-fluid simulations. Example applications of VizGlow™ include: simulation of capacitively coupled plasma (CCP) reactors, inductively coupled plasma (ICP) reactors, feature-scale etching/deposition simulations and magnetron sputtering. With VizGlow™ computational models, researchers gather a complete picture of the mechanisms of a wafer processing reactor occurring in macroscale and microscale for a fraction of cost compared to long, complex and costly experimental setups and analyses.
Our users at The University of Texas at Austin in collaboration with researchers at Samsung Electronics have modelled multispecies gas dynamics of an industrially relevant multi-wafer ALD batch reactor. Their work published recently in the Journal of Vacuum Science and Technology A, has also been featured as an editor’s pick for the journal’s September issue (https://doi.org/10.1116/6.0000993).
An in-depth look inside the ALD batch reactor:
The problem consists of a large industrial thermal ALD batch reactor that houses 25 wafers. A specific mixture of carrier gas N2 and silicon precursor Si2Cl6 (hexachlorodisilane, commonly referred to as HCD) are fed into the reactor at a rate of 5 SLPM through the central and lateral inlets. Three chamber pressure is achieved by controlling inlet flow rates. The walls of the reactor are treated as isothermal boundaries at 873 K.
The mesh contains 1.2 million tetrahedral elements and simulated over 15 million particles using the DSMC solver in VizGlow™.
The kinetic particle model in VizGlow™ is able to accurately simulate the gas dynamics in the flow inlet feed pipes, expansion through micronozzles, across the inter-wafer zones and the outlet. A particular region of interest among design engineers is the geometry of the spray nozzles and vicinity past nozzles. In this study, VizGlow™ captures the viscous dominating effects in the nozzle region due to the low pressure, high temperature, and small dimensions, the flow remains subsonic through the nozzle.
An important outcome of this simulation is significant non-uniformities recorded in the precursor distribution within a particular wafer and across different wafers. This is critical to understanding the process yield in these reactors.
Analyse your reactor designs using VizGlow™:
The studies, designs and resulting improvements surrounding wafer processing reactors are endless. This study paves a path to future studies on a variety of reactor configurations using VizGlow™.
Process engineers can optimise their reactor design by studying the effect of important parameters such as precursor flow rates, gas composition, nozzle designs, layout of the nozzles, orientation of wafers, size of wafers, pressure and thermal conditions – everything about a batch reactor can be accurately described with truly and fully coupled multiphysics with VizGlow™. Research to improve reactor efficiency through rapid trade studies can be performed using results from VizGlow™ at a much faster pace and a much cheaper budget than traditional experimentation.
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The future of transportation seems to be increasingly electric. In its latest report on electric vehicles (EV), the International Energy Agency (IEA) highlights a 40% increase in EV demand despite a 16% dip in the global car sales. Moving towards electrified vehicles has also pushed a shift in the vehicle design where the mechanical components are being replaced with electronic-based automotive components. Relays play a critical role in such electrified systems.
A relay is a switch that is operated electrically and is used to control a high power circuit with a low power signal circuit. The most common type of relay is an electromechanical relay that consists of terminals for the signal and the terminals where the supply and load are connected. Upon receiving a signal, an electromagnetically operated armature closes or opens the gap between the supply and the load terminals. Traditional electromechanical relays dominate the market, over solid state relays, because of their advantages in a wide operating range of voltages and currents and the low cost to manufacture due to the simplicity in design. However, the main problem that affects the lifetime of electromechanical relays is arcing.
The primary undesirable effect of arcing is sudden load surge in a circuit. This delays the signal to the primary circuit breaker to isolate the load device, which may fail due to overcurrent. Further, arcing leads to high surface temperature which can erode the terminals and contactors or even weld the contactors to the terminals. Both of these undesirable phenomena cause a great deal of reliability and safety issues. The strength and duration of the arc have a significant impact on the safety of electric vehicles as well as on relay contactor erosion, therefore the lifetime of the relay.
Therefore, it is crucial to study the formation of arcs within relays and explore designs that suppress the arc formation. At Esgee Tech, we delve further into how this disengagement happens and what could be done to improve it further. An insight into these phenomena could allow faster mitigation of arcs and thus quicker response times.
Arc – The Most Energetic Type of Plasma Discharge
A gaseous medium that experiences a sufficiently high electric field results in ionization of the medium which causes the medium to become conductive. We call this an electrical discharge. The characteristics of an electrical discharge depends on the voltage and current as shown in the figure on the left. Discharges carrying large currents, such as illustrated in this blog post, are classified as arcs. Arc is self-sustaining, i.e., it does not require an external ionization source to maintain discharge – the internal electron and gaseous processes maintain structure of the arc.
The physics of arcs is very complex. Ambient pressure, ambient temperature, geometry of the electrodes, gas composition, electromagnetic fields, external circuit parameters and surface properties all dynamically affect the formation and quenching of arcs. Industrial designs of relays need to account for all of these tightly coupled phenomena.
Our engineers at Esgee Tech have developed VizSpark™, a robust and accurate thermalized plasma simulator. VizSpark™ allows coupling of reactive plasma mechanics, fluid dynamics, transient electromagnetics, radiative mechanisms, surface erosion physics, circuit dynamics and continuously morphing boundaries. VizSpark™ also supports complex 3D industrial geometries.
Using VizSpark™ the industrial problem of understanding arcs and optimizing design and safety of EV relays can be effectively addressed at high fidelity.
EV Relay Computational Model and Results:
The electric vehicle relay geometry described in this blog comprises a stationary anode (left terminal), a stationary ground (right terminal) and a movable contactor that disengages to break the circuit. The circuit coupled with this domain is a 220 V DC supply via a load resistor as shown in the figure below. The gas composition in the relay is hydrogen which is kept at a pressure of 1 bar and 300 K. An external magnetic field of 1T is imposed in the z-direction (into the screen).
VizSpark™ captures breakdown of arc between the electrodes accurately as shown in the illustration below. Initially, about 35A flows through the arc, upon ignition. The Arc stretches outwards due to Lorentz force generated by the interaction of the arc with the external magnetic field. The total resistance of the arc increases as it stretches. This decreases the current and cools down the arc as temperature decreases due to reduction in joule heating. The partially extinguished arc reignites several times, around 400 µs, before finally extinguishing, in a phenomenon called restrike. VizSpark™ accurately simulates the stretching of the arc and formation of a new filament during restrikes. This is seen as a “saw-tooth” waveform in both transient voltage and current graphs.
As the gap between the contactor and terminals increases, the conditions are unfavorable for restrikes and fewer restrikes are seen in the later stages of the simulation. The potential across the gap increases to 220V and the current drops to 0A which marks a completely extinguished arc and the relay circuit is open.
Trade Studies with VizSpark™
A variety of methods can be applied to ensure faster quenching of the arc, which reduces the electrical cutoff time. A few techniques to extinguish the arc quickly are: stretching the arc through external magnetic fields, increasing the speed of the moving contactor, using gas mixtures that absorb electrons such as SF6, using gas mixtures with high thermal conductivities such as hydrogen, and using an arc chute/splitter plates to divide the main arc into smaller faster dissipating arcs. Further, use of external circuits such as snubber circuits which consist of a series configuration capacitor and resistor connected in parallel across the relay suppresses the spike in current as the voltage starts to fluctuate during arc quenching. All of these configurations can be simulated at fidelity using VizSpark™.
The computational model shown here is capable of incorporating comprehensive arc physics necessary to study quenching behavior in high-voltage EV relays. The model can be used to perform design/parametric studies on EV relays in reasonable computational time. Future work should involve detailed validation of the model with existing experimental data. Other avenues of research include incorporating eroded metal vapor, the inclusion of arc chute or splitter plates, and electrode deformation due to erosion.
We hope you are someone who is as fascinated about plasma flow simulations as we are, feel free to follow us at LinkedIn or reach out to us at firstname.lastname@example.org.
In the meantime, explore the following journal articles (do ask us for a free copy!):
Karpatne, A., Breden, D., and Raja, L., “Simulation of Arc Quenching in Hermetically Sealed Electric Vehicle Relays,” SAE Int. J. Passeng. Cars – Electron. Electr. Syst. 11(3):149-157, 2018, https://doi.org/10.4271/2018-01-0765.
N. Ben Jemaa, L. Doublet, L. Morin and D. Jeannot, “Break arc study for the new electrical level of 42 V in automotive applications,” Proceedings of the Forth-Seventh IEEE Holm Conference on Electrical Contacts (IEEE Cat. No.01CH37192), 2001, pp. 50-55, https://www.doi.org/10.1109/HOLM.2001.953189