What is High-purity porous graphite ? - Vetek

In recent years, the performance requirements for power electronic devices in terms of energy consumption, volume, efficiency, etc. have become increasingly higher. SiC has a larger bandgap, higher breakdown field strength, higher thermal conductivity, higher saturated electron mobility, and higher chemical stability, which makes up for the shortcomings of traditional semiconductor materials. How to grow SiC crystals efficiently and on a large scale has always been a difficult problem, and the introduction of high-purity porous graphite in recent years has effectively improved the quality of SiC single crystal growth.

Typical physical properties of VeTek Semiconductor porous graphite:

High-purity porous graphite for SiC single crystal growth by PVT method

Ⅰ. PVT method

PVT method is the main process for growing SiC single crystals. The basic process of SiC crystal growth is divided into sublimation decomposition of raw materials at high temperature, transportation of gas phase substances under the action of temperature gradient, and recrystallization growth of gas phase substances at the seed crystal. Based on this, the inside of the crucible is divided into three parts: raw material area, growth cavity and seed crystal. In the raw material area, heat is transferred in the form of thermal radiation and heat conduction. After being heated, SiC raw materials are mainly decomposed by the following reactions:

SiC(s) = Si(g) + C(s)

2SiC(s) = Si(g) + SiC₂ (g)

2SiC(s) = C(s) + Si₂C(g)

In the raw material area, the temperature decreases from the vicinity of the crucible wall to the raw material surface, that is, the raw material edge temperature > raw material internal temperature > raw material surface temperature, resulting in axial and radial temperature gradients, the size of which will have a greater impact on crystal growth. Under the action of the above temperature gradient, the raw material will begin to graphitize near the crucible wall, resulting in changes in material flow and porosity. In the growth chamber, the gaseous substances generated in the raw material area are transported to the seed crystal position driven by the axial temperature gradient. When the surface of the graphite crucible is not covered with a special coating, the gaseous substances will react with the crucible surface, corroding the graphite crucible while changing the C/Si ratio in the growth chamber. Heat in this area is mainly transferred in the form of thermal radiation. At the seed crystal position, the gaseous substances Si, Si2C, SiC2, etc. in the growth chamber are in an oversaturated state due to the low temperature at the seed crystal, and deposition and growth occur on the seed crystal surface. The main reactions are as follows:

Si₂C (g) + SiC₂ (g) = 3SiC (s)

Si (g) + SiC₂ (g) = 2SiC (s)

Application scenarios of high-purity porous graphite in single crystal SiC growth furnaces in vacuum or inert gas environments up to 2650°C:

According to literature research, high-purity porous graphite is very helpful in the growth of SiC single crystal. We compared the growth environment of SiC single crystal with and without high-purity porous graphite.

Temperature variation along the center line of the crucible for two structures with and without porous graphite

In the raw material area, the top and bottom temperature differences of the two structures are 64.0 and 48.0 ℃ respectively. The top and bottom temperature difference of the high-purity porous graphite is relatively small, and the axial temperature is more uniform. In summary, high-purity porous graphite first plays a role of heat insulation, which increases the overall temperature of the raw materials and reduces the temperature in the growth chamber, which is conducive to the full sublimation and decomposition of the raw materials. At the same time, the axial and radial temperature differences in the raw material area are reduced, and the uniformity of the internal temperature distribution is enhanced. It helps SiC crystals grow quickly and evenly.

In addition to the temperature effect, high-purity porous graphite will also change the gas flow rate in the SiC single crystal furnace. This is mainly reflected in the fact that high-purity porous graphite will slow down the material flow rate at the edge, thereby stabilizing the gas flow rate during the growth of SiC single crystals.

Ⅱ. The role of high-purity porous graphite in SIC single crystal growth furnace

In the SIC single crystal growth furnace with high-purity porous graphite, the transport of materials is restricted by high-purity porous graphite, the interface is very uniform, and there is no edge warping at the growth interface. However, the growth of SiC crystals in the SIC single crystal growth furnace with high-purity porous graphite is relatively slow. Therefore, for the crystal interface, the introduction of high-purity porous graphite effectively suppresses the high material flow rate caused by edge graphitization, thereby making the SiC crystal grow uniformly.

Interface changes over time during SiC single crystal growth with and without high-purity porous graphite

Therefore, high-purity porous graphite is an effective means to improve the growth environment of SiC crystals and optimize crystal quality.

Porous graphite plate is a typical use form of porous graphite

Schematic diagram of SiC single crystal preparation using porous graphite plate and the PVT method of CVD SiC raw material from VeTek Semiconductor

VeTek Semiconductor's advantage lies in its strong technical team and excellent service team. According to your needs, we can tailor suitable high-purity porous graphite products for you to help you make great progress and advantages in the SiC single crystal growth industry.