Rising with the Substrate: The Ascendancy of China's SiC Substrate Industrial Chain
1. Introduction to Silicon Carbide
Silicon Carbide (SiC) is a synthetically produced carbide with the chemical formula SiC and a molecular weight of 40. It has a density of 3.22 g/cm³, a high melting point of up to 2700°C, and a Mohs hardness of 9.2–9.8, second only to diamond.
As a third-generation semiconductor material, Silicon Carbide is one of the ideal materials for manufacturing high-temperature, high-frequency, high-power, and high-voltage devices. Compared to traditional silicon (Si), silicon carbide has a bandgap 3 times wider, a thermal conductivity 3 times higher, a breakdown electric field strength 10 times greater, and an electron saturation drift rate 2 times faster than silicon.
Consequently, semiconductor devices based on silicon carbide can not only operate stably at higher temperatures and are suitable for high-voltage and high-frequency application scenarios, but they also achieve higher operational efficiency with lower energy loss. A comparison of key parameters for the three generations of semiconductor materials is shown in the table below.
2. Types of Silicon Carbide Substrates
Substrates serve as the base material for semiconductor chips, primarily providing physical support, heat conduction, and electrical conduction functions.
According to the "Guidance Catalog for the First Application Demonstration of Key New Materials (2019 Edition)" issued by the Ministry of Industry and Information Technology (MIIT), silicon carbide substrates can be divided into two types based on electrical performance: one is semi-insulating silicon carbide substrates with a resistivity ≥ 10⁵ Ω·cm; the other is conductive silicon carbide substrates with a resistivity between 15–30 mΩ·cm. After epitaxial growth, these two types of substrates are used for manufacturing radio frequency (RF) devices and power devices, respectively.
II. Silicon Carbide Material Industry Chain
The industry chain based on silicon carbide material as the substrate mainly includes substrate preparation, epitaxial growth, device manufacturing, and downstream applications.
The substrate is the segment with the highest technical barriers and the largest value share in the silicon carbide industry chain, and it is also the key to driving the future large-scale industrial development of silicon carbide. In the cost structure of Silicon Carbide Devices, substrates account for up to 46%.
Semi-insulating silicon carbide substrates are mainly used for manufacturing Gallium Nitride (GaN) radio frequency devices, ultimately applied in fields such as 5G communication and defense. Growing a gallium nitride epitaxial layer on this substrate yields GaN-on-SiC epitaxial wafers, which are then used to manufacture GaN RF devices.
Conductive silicon carbide substrates are primarily used for manufacturing power devices, with end markets including electric vehicles, new energy, rail transportation, etc.
Different from the process for traditional silicon-based power devices, silicon carbide power devices require first growing a silicon carbide epitaxial layer on the conductive substrate to form a SiC epitaxial wafer, and then manufacturing various power devices on the epitaxial layer.
III. Silicon Carbide Substrate Production Process
The preparation process for silicon carbide substrates is complex and technically challenging, involving specific steps including: raw material synthesis, crystal growth, ingot processing, boule slicing, wafer grinding, wafer polishing, wafer inspection, and wafer cleaning.
1. Raw Material Synthesis
High-purity silicon powder and high-purity carbon powder are uniformly mixed in a certain ratio. They are synthesized into silicon carbide particles with specific crystal structures and particle sizes in a high-temperature reaction chamber exceeding 2000°C. Through processes like crushing, sieving, and cleaning, high-purity silicon carbide powder raw material is produced to meet the requirements for crystal growth.
2. Crystal Growth
Crystal growth is the most technically difficult step in silicon carbide substrate manufacturing, directly determining the electrical properties of the substrate. Mainstream crystal growth methods currently include the Physical Vapor Transport (PVT) method, High-Temperature Chemical Vapor Deposition (HTCVD) method, and Liquid Phase Epitaxy (LPE) method.
Among these, the PVT method is the mainstream process for commercial SiC substrate production, being technologically mature and widely applied in engineering. The LPE method is considered a potential future process direction.
(1) Physical Vapor Transport (PVT)
When growing SiC crystals using the PVT method, high-purity silicon carbide micropowder and a seed crystal are placed at the bottom and top, respectively, of a graphite crucible within a single crystal growth furnace, creating an axial temperature gradient. The silicon carbide micropowder sublimes at high temperatures into gaseous components like Si₂C, SiC₂, and Si, which are transported to the seed crystal under the temperature gradient to nucleate and crystallize, eventually forming a silicon carbide ingot.
The PVT method has relatively low growth costs, but a current major challenge lies in obtaining high-purity SiC raw materials, as trace impurities can significantly affect crystal purity.
(2) High-Temperature Chemical Vapor Deposition (HTCVD)
The HTCVD method involves introducing high-purity gases such as silane, ethane/propane, and hydrogen from the bottom of the reactor. They first react in the high-temperature zone to form silicon carbide precursors, which then follow the gas flow into the low-temperature zone to deposit onto the seed crystal, forming the silicon carbide crystal.
The advantage of this method is the precise control of the Si/C ratio, enabling continuous growth of high-purity, high-quality crystals. Although equipment costs are higher than the PVT method and its application is not yet widespread, crystals produced by HTCVD have fewer defects, high quality, and low impurity content, garnering increasing attention.
(3) Liquid Phase Epitaxy (LPE)
In the LPE method, a silicon carbide seed crystal is fixed to the front end of a seed rod. The graphite crucible contains silicon raw material and a small amount of doping elements, heated above the melting point of silicon (1500–1700°C) to melt it. Rotation of the seed crystal or counter-rotation of the crucible ensures uniform distribution of carbon and doping elements in the melt. Then, through slow cooling, the solution becomes supersaturated, leading to the growth of silicon carbide crystals on the seed crystal.
The LPE method allows for controllable radial growth and can produce crystals free of micropipe defects, but the growth cost is relatively high.
3. Ingot Processing
Using an X-ray single crystal orienter, the silicon carbide ingot is oriented. It is then ground flat and rounded through precision mechanical processing to become a standard diameter and angle silicon carbide boule. All boules undergo dimensional and angular inspection.
4. Boule Slicing
While reserving allowances for subsequent processing, the boule is sliced into wafers of different thicknesses using diamond wire saws. Fully automatic testing equipment is used to inspect surface shape parameters such as Warp, Bow, and Total Thickness Variation (TTV).
5. Sliced Wafer Grinding
The sliced wafers are thinned to a specified thickness using specialized grinding slurry, removing surface wire marks and damage. All sliced wafers are inspected for surface shape and electrical properties using fully automatic testing equipment and non-contact resistivity testers.
6. Lapped Wafer Polishing
Specific polishing slurries are used for mechanical polishing and chemical polishing of the lapped wafers to eliminate surface scratches, reduce roughness, and remove processing stress, achieving a nano-level surface flatness.
Parameters are inspected using equipment such as X-ray diffractometers, atomic force microscopes, surface flatness testers, and comprehensive surface defect testers. The quality grade of the polished wafers is determined based on these measurements.
7. Polished Wafer Cleaning
Within a Class 100 cleanroom, the polished wafers are cleaned using specific chemical reagents and deionized water to remove surface particles, metal ions, and organic contaminants. After spin-drying, they are packaged in clean wafer boxes, finally forming the silicon carbide substrates.
IV. Rapidly Growing Market Size of Silicon Carbide Substrates
According to data from Gongyan Wang, the global silicon carbide substrate market size reached $754 million in 2022, a year-on-year increase of 27.8%. It is projected to grow to $1.6 billion by 2025.
In 2022, the global conductive silicon carbide substrate market size was $512 million, accounting for 67.9%; the semi-insulating silicon carbide substrate market size was $242 million, accounting for 32.1%, as shown in the figure below.
V. Competitive Landscape of the Silicon Carbide Substrate Market
Currently, the global conductive silicon carbide substrate market is primarily dominated by foreign manufacturers.
In 2020, Wolfspeed held a 62% share in the global conductive silicon carbide substrate market, with the top three companies (CR3) holding 89%. Among domestic Chinese companies, Tianke HeDa held a 4% market share. Conductive silicon carbide substrates are currently a key area for import substitution in China, with broad market potential.
According to incomplete statistics, domestic companies that have achieved industrialization of silicon carbide substrates include Tianyue Advanced, Beijing Tianke HeDa Semiconductor Co., Ltd., Shanxi Shuoke Crystal Co., Ltd., Hebei Tongguang Semiconductor Co., Ltd., etc.
VI. Future Development Trends of Silicon Carbide Substrates
Improving production efficiency and reducing costs are the core directions for the technological development of silicon carbide substrates, with increasing substrate size being a key path. Larger substrate sizes allow for more chips to be manufactured per unit area, thereby reducing the average chip cost.
Currently, 4-inch (100mm) is the mainstream specification for semi-insulating silicon carbide substrates, while 6-inch (150mm) is mainstream for conductive silicon carbide substrates. Considering cost and downstream application trends, 6-inch semi-insulating and 8-inch conductive silicon carbide substrates will become the key development directions for the industry in the future.