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The things about silicon carbide

2023/09/06

Speaking of silicon carbide, it can be said that in today's hard technology investment circle, everyone knows it. Especially investors who invest in semiconductors, as if they have not invested in silicon carbide, are embarrassed to say that they are investors in the semiconductor industry. But many people may wonder, what is the role of silicon carbide? Where are the areas of application and scope? Can silicon carbide allow China to overtake in the semiconductor industry? Let's reveal them one by one.

What is a third-generation semiconductor?

When it comes to silicon carbide, we must first understand what the third generation semiconductor is.

The first generation of semiconductor materials mainly refers to silicon (Si), germanium (Ge) as the representative of element semiconductor materials, applications are extremely common, including integrated circuits, electronic information network engineering, computers, mobile phones, etc. Silicon-based semiconductor materials are currently the largest and most widely used semiconductor materials, and more than 90% of semiconductor products are made of silicon-based materials. However, the physical properties of silicon materials limit their application in optoelectronics and high-frequency electronic devices, such as its indirect bandgap characteristics, which determines that it cannot obtain high electro-optical conversion efficiency; And its band gap width is narrow, saturated electron mobility is low, which is not conducive to the development of high-frequency and high-power electronic devices, silicon-based devices reach the limit of their performance in high-voltage and high-power occasions above 600V.

The second generation of semiconductor materials are mainly compound materials represented by gallium arsenide (GaAs) and indium phosphide (InP), and the key communication chips currently used in mobile phones are made of similar materials. Due to the insufficient band gap of second-generation semiconductor materials, the breakdown electric field is low, which limits their application in the field of high temperature, high frequency and high power devices. In addition, due to the toxicity of gallium arsenide materials, it may cause environmental pollution problems and pose a potential threat to human health.

The third generation of semiconductor materials refers to wide bandgap semiconductor materials represented by silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), diamond, aluminum nitride (AlN), which are mostly used in communications, new energy vehicles, high-speed rail, satellite communications, aerospace and other scenarios, among which the research and development of silicon carbide and gallium nitride are relatively mature. Compared with the previous two generations of semiconductor materials, the third generation of semiconductor materials has a large band gap, high breakdown electric field, high thermal conductivity, high electron saturation rate, strong radiation resistance and other advantages, therefore, semiconductor devices prepared by the third generation semiconductor materials can not only operate stably at higher temperatures, but are suitable for high voltage and high frequency scenarios. In addition, higher operating capacity can be achieved with less electrical energy consumption.

What is good about silicon carbide?

Silicon carbide is a group IV.-IV compound semiconductor material composed of carbon and silicon, with a variety of allotrope types, so there are many different types in the silicon carbide group, of which 4H-SiC and 6H-SiC are mostly used in the industry, and 4H-SiC saturated electron speed is twice that of Si, thus providing higher current density and higher voltage for SiC components, often used as silicon carbide power devices. At the same time, the electron mobility of 4H-SiC is twice that of 6H-SiC because 4H-SiC has a higher horizontal axis (a-aixs) mobility. In the growth process of silicon carbide crystals, it is necessary to accurately control the parameters such as silicon-carbon ratio, growth temperature gradient, crystal growth rate and air flow pressure, otherwise polymorphic inclusions are easy to occur, resulting in unqualified crystals.

The main form of silicon carbide in semiconductors is as a substrate material, based on its excellent characteristics, the limit performance of silicon carbide substrate is better than that of silicon substrate, which can meet the application needs under high temperature, high pressure, high frequency, high power and other conditions, and the current silicon carbide substrate has been used in RF devices and power devices.

What is the difficulty of industrialization of silicon carbide?

From a technical point of view, the preparation and epitaxy of silicon carbide substrate is very difficult and long. Silicon carbide single crystal is composed of two elements, carbon and silicon, with a stoichiometric ratio of 1:1. But these two elements can be combined in many ways when growing in three-dimensional space.

Single crystal means that the arrangement of atomic layers is periodic. The atomic layer growth process of each layer lasts a very long time, tens of hours or even hundreds of hours. During the long-term crystal growth process, if the temperature, pressure, supersaturation and other environmental factors inside the crystal growth chamber change, it will not necessarily grow according to this structure. This can lead to physical uniformity in the epitaxial layer, which can lead to device failure. Therefore, from the perspective of the substrate, it is necessary to try to ensure the uniformity of the substrate material. Through precise control, we can create an environment suitable for 4H structure. The inside of the crucible is a high temperature of more than 2000 degrees, and it is impossible to observe the inside of the crucible. We can only detect the temperature point on the back of the crucible, the temperature of the circulating water, the flow rate, and the current intensity. The means of direct control are very limited, and can only be detected indirectly. After the substrate is finished, it is long epitaxy, and after epitaxy, it is a series of lithography, etching, glue, deposition, cleaning, ion implantation and other processes, which are basically the same as the silicon process, and then the back-end wafer cutting, packaging and testing, etc., the basic process is similar to silicon. Among them, long epitaxy, photoresist, backside annealing, etching, and oxide gate process differences, ohmic contact and silicon process differences are very large.

From the cost point of view, the value of the entire silicon carbide device basically accounts for 50% of the substrate and 20% of the extension. There are roughly three types of silicon carbide growth technology, PVT physical vapor phase transport method, HT-CVD high temperature vapor deposition method, and LPE solution method. Among them, PVT is more mainstream, the advantages are simple, reliable and controllable. CVD has too high requirements for equipment, the price is very expensive (tens of millions of yuan), only high-quality semi-insulating substrates will use this method; The LPE solution method can make a natural P-type substrate, but the defects are difficult to control, and it takes time to accumulate, and many Japanese companies focus on this route. The epitaxy of silicon carbide generally uses a special MOCVD/HT-CVD, the price is very expensive, basically more than 1500 million yuan, and the production capacity is very low, a furnace a month production capacity is 30 pieces. Therefore, the silicon carbide 6-inch substrate is as high as $1000,6, while the 23-inch silicon wafer is $150 (<> yuan), which is too far different. The lack of high-efficiency long-crystal technology leads to the cost of the substrate is too high, the second device process is not very perfect, and the special equipment is not very perfect, expensive and few, resulting in the FAB plant capacity has not been fully expanded, in short, the amount is too small, the substrate price is high, the process is not mature, resulting in silicon carbide devices are too expensive, restricting large-scale applications.

Illustration: Silicon carbide growth process

Will China be able to overtake in corners through silicon carbide?

It's not so much about overtaking in corners, but about the gap between us and foreign countries on silicon carbide.

First of all, silicon carbide belongs to the mature process range, from materials to equipment to processes can be done in our country, does not involve the neck of the process equipment, but there is still a gap of at least 5-8 years between China and foreign countries. This gap is embodied in: 1) optimization of silicon carbide crystal structure; 2) Yield rate; 3) Cost reduction.

The first point has actually been mentioned earlier, long crystal and epitaxy is an extremely long but very important process, and the subtle process or control differences in this process will lead to structural changes, resulting in different properties of silicon carbide, and even affect the entire yield rate.

The second point is that in order to improve the yield rate, there will be an extension step to make up for the shortcomings in the substrate preparation process.

The third point of cost reduction is to allow the industry to use it on a large scale, but cost reduction is the result of the joint efforts of the entire upstream and downstream industry chain, which needs to be jointly promoted from materials and equipment to the consumer side, which carries more time costs.

Demand flashpoint for silicon carbide

In the next few years, the SiC market will benefit from vehicle electrification, electric vehicle supporting equipment construction, 5G base station and data center construction. Fuel vehicles have shifted to electric vehicles, and the use of power semiconductors has increased dramatically. Automotive applications are the fastest growing segment of the power semiconductor market. In addition, the demand for charging stations and charging piles will also increase. The EU CO2 emission standards and China's new infrastructure will bring new increments to photovoltaic and wind power in the new energy market. According to the report, the global SiC power semiconductor market size was about $2019 million in 4 and is expected to increase to more than $2022 billion by 10, with an annual growth rate of 40%.

Source: Yole, Infineon

Vehicle electrification will form the largest downstream market for SiC. The value of automotive semiconductors is increasing, and SiC applications are the future trend. At present, the main drive inverter in xEV vehicles is still dominated by IGBT+Si FRD solutions, considering that future electric vehicles require longer driving range, shorter charging time and higher battery capacity, SiC MOSFET components will be the general trend, and the time node is about 2023 or 2024. SiC is expected to improve the efficiency of SiC inverters by 3%-5%, thereby reducing battery costs. Inverters and generators grew more, with an increase of nearly 100% in full hybrid electric vehicles and plug-in hybrids. The fastest growing mild hybrid electric vehicles bring a greater increase in the value of semiconductors.

The hard technology team of New Value Capital believes that no one can ignore the established fact that the US war to restrict China's high-performance chips has begun and will not stop in the short term. Power semiconductor devices and automotive chips, many times do not use advanced processes at all, many processes are concentrated in about 65 nanometers, which is the field where China can establish a safe and controllable supply chain。 In the supply chain in this area, the demand for some domestic alternatives is also increasing. At present, some car companies will also have the index of choosing domestic suppliers, and select domestic core components in some terminal products, from top to bottom, layer by layer penetration, and gradually achieve domestic substitution. Although automotive electronic devices such as power semiconductors have higher market access thresholds, longer production line return cycles, and lower gross profits than consumer electronics, from the current situation, the establishment of controllable automotive electronics and new energy production lines is a road that must be taken. The most fundamental thing is that China can have controllable capabilities, which is a difficult but brightest road.

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