Silicon carbide, how expensive is it?

By orchioo Oct5,2023

Silicon carbide semiconductor is the core material of the newly developed wide bandgap semiconductor. The devices made of it have the characteristics of high temperature resistance, high voltage resistance, high frequency, high power, radiation resistance, etc. It has the advantages of fast switching speed and high efficiency. Significantly reducing product power consumption, improving energy conversion efficiency and reducing product size, it is mainly used in the radio frequency field represented by 5G communications, national defense and military industry, aerospace and power electronics fields represented by new energy vehicles and “new infrastructure”. It has clear and considerable market prospects in both civilian and military fields.

Silicon carbide has obvious advantages in manufacturing radio frequency devices, power devices and other fields. However, in the fields of radio frequency devices and power devices, the bottleneck of silicon carbide substrate market application is its high production cost. The restrictive factors affecting the cost of silicon carbide substrates are slow production rate and low product yield. The main reasons are: the current mainstream commercial PVT method has slow crystal growth speed and difficult defect control. Compared with mature silicon wafer manufacturing processes, silicon carbide substrates are still relatively expensive in the short term. For example, the current price of silicon carbide power devices is still several times that of silicon-based devices. Downstream application fields still need to balance the relationship between the high price of silicon carbide devices and the reduction in overall costs due to the superior performance of silicon carbide devices. In the short term, To a certain extent, it limits the penetration rate of silicon carbide devices. Its high cost limits its application scenarios and market penetration in the lower-end market. So what exactly is silicon carbide expensive?

1. Understanding silicon carbide substrate

(1) Material properties

Silicon carbide substrate is the core material of the newly developed wide bandgap semiconductor. Silicon carbide substrate is mainly used in microwave electronics, power electronics and other fields. It is at the front end of the wide bandgap semiconductor industry chain and is a cutting-edge and basic core key material. 4H-SiC has a bandgap of 3.2 (eV), a saturated electron drift rate of 2.00 (107 cm/s), a breakdown electric field strength of 3.5 (MV/cm), and a thermal conductivity of 4.00 (W·cm-1·K-1 ), which has several times the advantages of silicon-based ones. The forbidden band refers to the energy range in the energy band structure where the density of energy states is zero, often used to represent the energy range between the valence band and the conduction band; the saturation electron drift rate refers to the electron drift rate that after reaching a certain range, it no longer follows the electric field. The limit value that continues to increase due to the action; the electron drift rate refers to the average speed of electrons moving under the action of an electric field; the thermal conductivity refers to the measure of the material’s ability to conduct heat, also known as the thermal conductivity; the breakdown electric field strength refers to the dielectric under the action of a strong enough electric field Will lose its dielectric properties and become a conductor, which is called dielectric breakdown, and the corresponding electric field intensity is called breakdown electric field intensity.

Note 1: Silicon carbide has more than 200 structures

Based on the above excellent material properties, the ultimate performance of silicon carbide substrate is better than that of silicon substrate. It can meet the application needs under high temperature, high pressure, high frequency, high power and other conditions, and has been used in radio frequency devices and power devices.

(2) Classification of silicon carbide substrates

Silicon carbide substrates can be divided into two types: semi-insulating and conductive. Among them, semi-insulating silicon carbide substrates have high resistivity (resistivity ≥105Ω·cm), and semi-insulating substrates plus heterogeneous gallium nitride Epitaxial wafers can be used as materials for radio frequency devices, and are mainly used in the fields of 5G communications, national defense and military industries as mentioned above; the other type is conductive silicon carbide substrate with low resistivity (resistivity range is 15~30mΩ·cm) , conductive silicon carbide substrates combined with silicon carbide homoepitaxy can be used as materials for power devices. The main application scenarios are electric vehicles, energy and other fields. Both have a wide range of application scenarios and affect many industries and markets. Wide scope and other characteristics.

Note 1: Radio frequency devices refer to a type of components formed using radio frequency technology, often used in wireless communications and other fields

Note 2: Power devices refer to discrete devices used in power conversion and control circuits of power equipment, also called power electronic devices.

2. The cost is high in the following aspects: (1) The proportion of consumables with high one-time prices

(1) Judging from the overall amount of raw material expenditures, the company’s raw material expenditures increased from 32.5 million yuan in 2018 to 199.269 million yuan in 2021. This shows the market popularity and market development prospects of silicon carbide, from 32.5 million yuan to 199.269 million yuan in 2021. The compound growth rate from RMB 10,000 to 19926.9 is as high as more than 6%, which shows the market’s recognition of silicon carbide and the market popularity of silicon carbide;

(2) Among the raw materials for the preparation of silicon carbide substrates, taking 2021 as an example, graphite parts accounted for 45.21% of the cost, and graphite felt accounted for 41.32%, accounting for 86.53% of the raw material cost. Compared with carbon powder, There is a huge difference between the proportions of silicon powder at 0.97% and 1.99%. Compared with other polishing liquids with 2.01%, polishing pads with 1.75%, diamond powder with 2.34%, and others with proportions of 4.18%, there is also a huge difference. Among them, the largest proportion of raw materials It is graphite parts 45.21%, and the raw material with the lowest proportion is cutting steel wire 0.22%;

(3) Among the raw materials for silicon carbide substrate preparation from 2018 to 2021, the raw materials can be divided into three categories according to the fluctuation trend of their cost proportions: The first category is that the proportion shows an upward trend, such as graphite parts rising from 32.98% to 45.21% %, graphite felt increased from 37.06% to 41.32%; the second category is raw materials whose proportion has remained basically stable, such as cutting steel wire, the proportion has been maintained at 0.25 (within ±0.5), and the proportion of polishing fluid has been maintained at 1% (± About 1%) and the proportion of polishing pads has remained at 2% (within ±0.5%); the third category is raw materials that show a downward trend in proportion, such as toner, which dropped from 5.71% in 2018 to 0.97% in 2021. The proportion of silicon powder in 2018 increased from 5.47% to 1.99% in 2021, and the proportion of others decreased from 8.75% in 2018 to 4.18% in 2021;

Based on the above analysis, it can be seen that in the preparation process of silicon carbide, the excessive proportion of disposable high-priced consumables is one of the reasons for the high production cost of silicon carbide substrates. Crucible (graphite parts) refers to a vessel made of graphite powder of a certain particle size, pressed under high pressure and calcined at high temperature for a long time. It has the characteristics of high temperature resistance, strong thermal conductivity, good corrosion resistance, and long life. It is an important part of the growth process of silicon carbide crystals. One of the consumables, its proportion in the raw materials for silicon carbide substrate production will reach more than 45% by 2021, and its proportion is also showing an upward trend. This is a big reason for the high cost of silicon carbide preparation.

(2) High requirements for preparation process conditions

The PVT method refers to Physical Vapor Transportation, a common silicon carbide crystal growth method. Silicon carbide powder is heated at a high temperature above 2,300°C and at a low pressure close to vacuum, so that it sublimates to produce Si, Si2C, and SiC2. and other reaction gases with different gas phase components; due to the different gas phase partial pressures of Si and C components formed by the solid phase sublimation reaction, the Si/C stoichiometric ratio varies with the thermal field distribution, and it is necessary to make the gas phase components according to the designed thermal field and The temperature gradient distributes and transports the components to the established crystallization position in the growth chamber; in order to avoid disordered gas phase crystallization to form polycrystalline silicon carbide, a silicon carbide seed crystal (seed) is set at the top of the growth chamber, and the The gas phase components transported to the seed crystal are atomically deposited on the surface of the seed crystal driven by the supersaturation of the gas phase components, and grow into a silicon carbide single crystal.
The entire solid-gas-solid reaction process of the above silicon carbide single crystal preparation is in a complete and sealed growth chamber. The various parameters of the reaction system are coupled with each other. Any fluctuation in growth conditions will cause changes in the entire single crystal growth system, affecting The stability of silicon carbide crystal growth; in addition, silicon carbide single crystals have a variety of atomic connection and bonding methods in different close-packed structures in their crystal orientation, thus forming more than 200 crystal forms of silicon carbide isomeric structures, and The energy conversion barrier between different crystal forms is extremely low. Therefore, the transformation of different crystal forms is very easy to occur in the PVT single crystal growth system, leading to serious quality problems such as disorder of the target crystal form and various crystal defects. Therefore, special testing equipment is needed to detect the crystal form and various defects of the crystal ingot.

The process conditions for silicon carbide preparation are extremely demanding and include the following points:

(1) There are many environmental impurities in the synthesis process of silicon carbide powder, making it difficult to obtain high-purity powder; incomplete reaction between silicon powder and carbon powder as the reaction source can easily cause Si/C ratio imbalance; after the synthesis of silicon carbide powder, The crystal form and particle size are difficult to control;
(2) The “solid-gas-solid” conversion and recrystallization process is completed in a closed graphite chamber at high temperatures above 2,300°C and close to vacuum. The growth cycle is long, control is difficult, and defects such as microtubes and inclusions are prone to occur;
(3) Silicon carbide includes more than 200 different crystal forms, but production generally requires only one crystal form. Crystal form transformation is prone to occur during the growth process, resulting in multi-type inclusion defects. During the preparation process, a single specific crystal form is difficult to stably control, and different The extremely low energy conversion barrier between crystal forms makes control more difficult. Parameter control and related research during the period require huge R&D costs, which is another major reason for the high cost of compliant silicon carbide.

(3) Pollution treatment

As we all know, in an environment where the country is strengthening ecological construction, carbon neutrality, and carbon peaking, the pollution problem of material preparation will undoubtedly add a hidden investment to the cost of materials. The main processes of silicon carbide substrate materials involve raw material synthesis, crystal growth, ingot processing, ingot cutting, cutting disc grinding, grinding disc polishing, polishing disc cleaning, etc. It is not a heavily polluting industry; the main pollutant generated is waste water. (Mainly including pickling cleaning wastewater, exhaust gas purification wastewater, chamfering cleaning wastewater, grinding cleaning wastewater, mechanical polishing cleaning wastewater, domestic sewage, etc.), general solid waste (mainly including purified impurities, processing scraps, domestic waste, etc.), hazardous Waste (mainly including waste grinding fluid, waste cutting fluid, waste polishing fluid, etc.), waste gas (mainly including pickling waste gas, ethanol cleaning waste gas, organic waste gas, etc.), noise, etc. The main methods of pollutant treatment are: wastewater is discharged into the city’s water purification plant for further treatment after being treated at the sewage treatment station to meet standards; domestic waste in general solid waste is entrusted to the environmental sanitation department, and other resources are reused through recycling units; hazardous waste is entrusted to have Qualified third-party agencies handle it; exhaust gas is discharged through sewage discharge devices in compliance with regulations; noise is handled through vehicle soundproofing measures and other methods.

Although silicon carbide manufacturing companies are not heavy polluters, China’s high-quality economic development is undoubtedly accompanied by the country’s strengthening of ecological construction, carbon neutrality, and carbon peaking. Therefore, the pollution treatment of preparation materials is an indispensable issue. important factors ignored. Although the cost of pollution treatment is an indirect cost in the material preparation process, as a new type of material, the treatment of pollution problems has always been the focus of everyone’s attention. The treatment of pollutants is undoubtedly a boost to the high cost of silicon carbide. one of those.

(4) Taking microscopic density as an example to explain the low yield

The core technical parameters of silicon carbide include diameter, microtube density, polytype area, resistivity range, total thickness change, curvature, warpage, and surface roughness. The specific meanings of the above technical parameters are as follows:

Table 2. Specific meaning of technical parameter indicators

One of the most important crystallographic defects in silicon carbide crystals are micropipes, which is another contributor to low product yields and the high cost of compliant silicon carbide. Microtubules are hollow tubes that extend throughout the crystal rod. The existence of microtubes is fatal to the application of devices. The density of microtubes in the substrate will directly determine the crystal quality of the epitaxial layer. The presence of microtubes in the device area will lead to excessive device leakage current or even device breakdown, resulting in Device failure. Therefore, reducing the density of microtubes is an important technical direction for the industrial application of silicon carbide. With the continuous advancement of microtube defect improvement technology, the world’s leading silicon carbide companies can stably control the microtube density below 1cm-2. This is just one of the evaluation indicators. It is conceivable that it is difficult to control costs to produce high-quality substrates within the nanometer range of many of the above core indicators.

Based on the above information, it can be seen that in the silicon carbide preparation process, the high proportion of one-time expensive consumables, the difficulty of realizing the preparation process conditions, the high cost of preparation pollution treatment, and the high density of crystal microtubes are all important reasons for the high cost of silicon carbide. . Since the above points have high technical and financial barriers, breakthroughs require huge R&D investment and long-term talent training. Therefore, for the specific market penetration of silicon carbide, it is necessary to reduce costs, expand size, and increase market penetration. Rates still have a long way to go!

By orchioo

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