SiC is a binary compound formed by Si element and C element in 1:1 ratio, that is, 50% silicon (Si) and 50% carbon (C), and its basic structural unit is SI-C tetrahedron.
For example, Si atoms are large in diameter, equivalent to an apple, and C atoms are small in diameter, equivalent to an orange, and an equal number of oranges and apples are piled together to form a SiC crystal.
SiC is A binary compound, in which the Si-Si bond atom spacing is 3.89 A, how to understand this spacing? At present, the most excellent lithography machine on the market has a lithography accuracy of 3nm, which is a distance of 30A, and the lithography accuracy is 8 times that of the atomic distance.
The Si-Si bond energy is 310 kJ/mol, so you can understand that the bond energy is the force that pulls these two atoms apart, and the greater the bond energy, the greater the force that you need to pull apart.
The Si-C bond atomic spacing is 1.89 A and the bond energy size is 447 kJ/mol.
Compared with traditional silicon-based semiconductor materials, it can be seen from the bond energy that the chemical properties of silicon-based semiconductor materials are more stable.
It can be seen that any C atom is connected to the four nearest Si atoms, and conversely, any Si atom is connected to the four nearest C atoms.
The SiC crystal structure can also be described by the layered structure method. As shown in the figure, several C atoms in the crystal occupy six grid sites on the same plane, forming a close-packed layer of C atoms, while Si atoms also occupy six grid sites on the same plane and form a close-packed layer of Si atoms.
Each C in a close-packed layer of C atoms is connected to its nearest Si, and vice versa. Every two adjacent layers of C and Si atoms form a carbon-silicon diatomic layer.
The arrangement and combination of SiC crystals are very rich, and more than 200 SiC crystal types have been discovered.
This is similar to Tetris, although the smallest unit blocks are the same, but when the blocks are put together, they form different shapes.
The spatial structure of SiC is slightly more complex than Tetris, and its smallest unit changes from a small square to a small tetrahedron, a tetrahedron composed of C and Si atoms.
In order to distinguish the different crystal forms of SiC, the Ramsdell method is mainly used for labeling at present. The method uses the combination of letters and numbers to represent the different crystal forms of SiC.
Letters are placed at the back to indicate the cell type of the crystal. C stands for Cubic (first letter of the English cubic), H stands for Hexagonal (first letter of the English), R stands for Rhombus (first letter of the English rhombus). Numbers are placed first to represent the number of layers of the Si-C diatomic layer of the basic repeating unit.
In addition to 2H-SiC and 3C-SiC, other crystalline forms can be regarded as a mixture of sphalerite and wurtzite structure, that is, close-packed hexagonal structure.
The C-plane refers to the (000-1) crystal face of the silicon carbide wafer, that is, the surface on which the crystal is cut along the negative direction of the C-axis, and the terminating atom of the surface is the carbon atom.
The silicon surface refers to the (0001) crystal face of the silicon carbide wafer, that is, the surface on which the crystal is cut along the positive direction of the C-axis, and the terminating atom of the surface is the silicon atom.
The difference between C-plane and silicon plane will affect the physical and electrical properties of silicon carbide wafer, such as thermal conductivity, electrical conductivity, carrier mobility, interfacial state density and so on.
The choice of C-plane and silicon plane will also affect the manufacturing process and performance of silicon carbide devices, such as epitaxial growth, ion implantation, oxidation, metal deposition, contact resistance, etc.
