Silicon Carbide

The next generation of semiconductor devices

 european flag This project “Scanner for early stage quality control  in silicon carbide crystals” has received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No 953549.

Why is Silicon Carbide important?

Silicon Carbide (SiC) is a surging semiconductor. Among different semiconductors, the most commonly used today are industrially grown Silicon (Si) and Gallium Arsenide (GaAs). However, recently there has been a shift in the market—silicon carbide is attracting more and more investment due to its superior properties. Compared to conventional silicon-based devices, SiC offers almost 10X the breakdown field strength (2.8MV/cm vs 0.3MV/cm) and 3X the thermal conductivity, making it ideal for high-voltage applications: electric cars, power supplies, solar inverters, trains and wind turbines. Its superior conductive properties are increasingly necessary for automotive and power generation devices operating at higher voltages, higher temperatures, and higher frequencies than ever before.

Another benefit is that a SiC epitaxial layer deposited on a substrate could be much thinner, down to one-tenth of a traditional Si epitaxial layer. For example, the SiC epitaxy on SiC substrates provides a range of available layer thicknesses from sub-micron to more than 200µm. In comparison, this is is about one-tenth of that of Si epitaxial layers. 

Additionally, SiC devices reduce the amount of energy lost in a system, improve performance, reliability, and cut operating costs. For instance, in hybrid and electric vehicles SiC power solutions contribute to increased fuel economy and a larger cabin area, while in solar power generation applications they improve power loss by approximately 50%, contributing to reduced global warming.

Due to these advantages, SiC is expected to become the standard material used for power electronics applications over the next few years.

Crystal growth and defectiveness

SiC boules are typically crystallised by one of the two processes:

1. Sublimation method (often called “Rayleigh’s method”) that sublimates SiC powder, transports sublimated gas to the surface of the seed crystal by a heat gradient, and recrystallises it under cold temperatures. Compared with conventional Si ingots which are crystallised in the liquid phase from Si melt, the growth rate using the sublimation method is slow, making crystal defects likely to occur, and therefore requires advanced technology for crystal control.

2. High-Temperature Chemical Vapour Deposition (HTCVD). The method feeds precursor gases upwards through heating zone in vertical graphite crucible to the seed crystal placed at the top. The precursor gases are SiH4 and a hydrocarbon. The growth temperature is ~2100–2300°C, the growth rate is 0.1-1mm/h.

Crystal growth is the most difficult step in the material value chain.The growth is a completely blind process – there is no way to see or directly measure what is growing. As a result, compared with Silicon, SiC is a highly defective material. Typical defects are micropipes and dislocations within the atomic lattice. Each defect degrades the manufacturing yield and reliability for SiC power devices. The micropipes reduce blocking voltage and gate oxide reliability. The dislocations do the same, and also reduce local carrier lifetime.

Scientific Visual is working to create such an early-stage inspection system to visualise defects in raw SiC crystals. We will publish project news on this page. Our expert staff is happy to test your samples and to apply early-stage inspection technology to your production. Please contact us at your earliest convenience at welcome@scientificvisual.ch.

What is Sic_Scope, the Scanner for Early-Stage Quality Control in Silicon Carbide Crystals?

SiC_Scope is an innovative quality control system that maps the internal defects in raw, un-processed SiC crystals. The innovation combines index-matching liquids with confocal tomography & specialized software to automate the inspection of the raw crystals. Before extending to the SiC, the company has applied the proprietary immersion tomography inspection to sapphire, ruby, and fluorite industrial crystals.

The traditional methods of SiC inspection require slicing the crystal to wafers to visualize defects in each wafer by chemical etching. It was impossible to know the location defects without pre-processing.

The new SiC_Scope visualizes the defects before slicing. There is no more need for the crystal to be cut or polished. It ensures that only high-quality material enters the costly wafering stage. The data gathered by the SiC_Scope are objective (human-independent) and help growers establish the relationship between the SiC furnace parameters and the number, location, and type of crystal defects. Shortly speaking, SiC_Scope allows crystal growers and furnace manufacturers to adapt their processes, driving down the number of defective crystals.

Scientific Visual is a leader in automated quality control equipment for industrial crystals. We established our name first in the sapphire industry and, more recently, in the semiconductor crystals. The objective now is to upgrade the current SiC_Scope prototype to work on a complete range of industrially important SiC crystals. It required a significant investment to finalize the technological developments and bring SiC_Scope to the market. It is also necessary to build industrial prototypes for onsite testing with prospects and product communication.

Silicon Carbide vs Gallium Nitride
Gallium Nitride (GaN) is another semiconductor showing great promise for the future. There is a great deal of ongoing discussions and questions about GaN versus SiC crystals, and which device / material is best suited for a specific application. This table presents a short summary of both material properties.

Property SiC GaN
Band Gap (eV) 3.2 3.4
Critical Field 10e6 V/cm 3 3.5
Electron Mobility (cm2/V-sec) 900 2000
Electron Saturation mobility (106 cm/sec) 22 25
Thermal Conductivity (Watts/cm2 K) 5 1.3

Given its higher electron mobility, GaN is more suitable for lower power/voltage, high frequency applications while SiC stands for high power and high voltage switching power applications.
With a thermal conductivity of 1.3 W/cm2K, GaN is worse at transferring thermal loads. It is also easier to manufacture large and uniform wafers from SiC than from GaN.

Ultimately, both SiC and GaN will play important roles but each will settle into its own niche.

To learn more about SiC vs GaN competition, refer, for example, to https://www.powerelectronics.com/technologies/power-management/article/21864289/the-great-semi-debate-sic-or-gan

Silicon Carbide market
The global SiC market size is estimated to grow from $749 million in 2020 to $1,812 million by 2025. The market of SiC substrate separately is estimated at $310 million now (2020) and is forecasted to reach $USD 1B in 2027, providing a CAGR of 21.4% during 2022-2027. The key factor fuelling the growth is the growing demand for SiC devices in the power electronics industry.

In the last decade, 75% of the SiC wafer business was generated by USA-based companies, namely CREE, II-VI and Dow Corning, 20% in Europe and 5% in Japan.

In recent years, the Asia-Pacific region (APAC) has begun to gain traction as multiple SiC suppliers and growers.

* RoW stands for Rest of the World: Middle East, Africa and South America. 

 

References
  • Dhanaraj G, Raghothamachar B, Dudley M, editors. Handbook of crystal growth-Chap 23- and Characterization of Silicon Carbide Crystals. In: Handbook of crystal growth- Heidelberg ; New York: Springer; 2010.
  • Wellmann PJ. Review of SiC crystal growth technology. Semiconductor Science and Technology. 2018 Oct 1;33(10):103001.
  • Kimoto T, Cooper JA. Fundamentals of silicon carbide technology: growth, characterization, devices and applications. Singapore: John Wiley & Sons Singapore Pte. Ltd; 2014. 538 p.
  • Lapedus M. SiC Demand Growing Faster Than Supply. 2019 May 23 ; Available from: https://semiengineering.com/sic-demand-growing-faster-than-supply/

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