Growth Principle of SiC Silicon Carbide Single Crystal
Mar 06,2023
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Enray
Silicon carbide single crystal substrate material (Silicon Carbide Single Crystal Substrate Materials, hereinafter referred toSiCSubstrate) is also a kind of crystal material, belongs to the wide band gap semiconductor material, with high pressure resistance, high temperature resistance, high frequency, low loss and other advantages, is the preparation of high-power power electronic devices and microwave RF devices of the basic material.
Crystal structure of SiC
SiCThe single crystal is composedSiandCTwo elements according1:1stoichiometric compositionⅣ-ⅣGroup compound semiconductor materials, hardness second only to diamond.
CAtomic andSiatoms have.4Valence electrons can be formed.4covalent bond, compositionSiCBasic structural unit--Si-Ctetrahedron,SiAtomic andCThe coordination numbers of the atoms are4, that is, eachCAll around the atom.4OneSiatoms, eachSiAll around the atom.4OneCThe atom.
SiCAs a crystal material, the substrate also has the characteristics of periodic stacking of atomic layers.Si-Cdouble atomic layer along[0001]direction of stacking, due to the small difference in bond energy between layers, it is easy to produce different connections between atomic layers, which leadsSiCThere are many kinds of crystal forms. Common crystal forms are2H-SiC,3C-SiC,4H-SiC,6H-SiC,15R-SiCWait. The arrangement of the atomic layers is different, which makes the constituent atoms different,2HAll atoms in the crystal form are hexagonal. And3CThe atoms in the crystal form are all cubic. Different occupancy ratios affect the band gap and carrier properties of the crystal. As the proportion of hexagonal positions increases, the width of the forbidden band gradually increases from3Ccrystal band gap2.4eVTo2Hcrystal form3.2eV.
Among them, according“ABCB”The structure of sequential stacking is called4HCrystal form. Although different crystal formsSiCCrystals have the same chemical composition, but their physical properties, especially the band gap, carrier mobility and other characteristics are quite different. From a theoretical point of view,2HAll crystal forms are hexagonal stacking mode--The band gap is the largest and should be the most suitable material for high-power devices. However, from the following phase diagram, it can be seen that the preparation conditions are difficult to achieve in the actual operation process. Therefore, in the real situation, the choice4HCrystal form. Its performance in manufacturing and various aspects is more suitable for applications in the semiconductor field.
The above figure can also be seen4HThe area of the crystal form in the phase diagram is not large, so the difficulty coefficient of manufacturing is also very high. Growth temperature, pressure and other factors will affectSiCTherefore, in order to obtain a single crystal material with high quality and uniform crystal form, various process parameters such as growth temperature, growth pressure and growth rate must be accurately controlled in the preparation process.
SiC preparation method: physical vapor sublimation method (PVT method)
CurrentlySiCCrystal growth methods are mainly physical vapor transport method(Physical Vapor Transport Method, PVTLaw)High Temperature Chemical Vapor Deposition(High Temperature Chemical Vapor Deposition, HTCVDLaw)Liquid phase method(Liquid Phase Method)Wait. among them,PVTThe method is more mature and more suitable for industrial mass production.
so-calledPVTThe law means thatSiCThe seed crystal is placed on the top of the crucible, andSiCPowder as raw material placed at the bottom of the crucible, in a closed environment of high temperature and low pressure,SiCA method in which the powder sublimates and is transported upward to the vicinity of the seed crystal under the action of temperature gradient and concentration difference, and then recrystallizes after reaching a supersaturated state. This method can implementSiCControlled growth of crystal size and specific crystal forms.
However, the usePVTgrowth methodSiCCrystals need to be grown for a long time, always maintain appropriate growth conditions, otherwise it will lead to lattice disorder, thereby affecting the quality of the crystal. But...SiCCrystal growth is completed in a confined space, effective monitoring means less, more variables, so the difficulty of process control.
The main mechanism of stable growth of single crystal form: step flow growth mode
InPVTgrowth methodSiCIn the process of crystal, step flow growth mode (Step Flow Growth) is considered to be the main mechanism for the stable growth of a single crystal form.
after gasificationSiAtomic andCThe atom will have priority inkinkThe spot locations are bonded to the crystal surface atoms, where nucleation grows so that the individual steps flow forward in parallel. When the step width of the crystal surface is far more than the diffusion free path of the adsorbed atoms, a large number of adsorbed atoms may be agglomerated, and the two-dimensional island growth mode formed will destroy the step flow growth mode, resulting in4HCrystal structure information is lost, resulting in polytype defects. Therefore, the adjustment of process parameters should realize the regulation of the surface step structure, so as to inhibit the generation of polytype defects, achieve the purpose of obtaining a single crystal form, and finally prepare a high quality crystal.
Of course, the preparation of high qualitySiCThe substrate and crystal growth are only the first step. Before the product finally meets the requirements, it needs to go through a series of processes such as cutting, grinding, chamfering, polishing, cleaning, and testing.SiCSingle crystal as a hard and brittle material, the technical requirements for the processing link is also very high, the damage produced in each production link may have a certain hereditary, passed to the next process, and ultimately affect the quality of the product, so efficient processing.SiCThe technology of substrate has also attracted the attention of industry and academia.
Article Source: Silicon CarbideSiCsemiconductor material
Hunan enrui silicon carbide deposition furnace (professional custom factory)
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