Influence of Seed Crystal on SiC Crystal Growth

Influence of Seed Crystal on SiC Crystal Growth

PAM-XIAMEN can supply SiC seed crystal for single crystal growth, specific parameters can be found in:

Seed crystals have a significant influence on the initial nucleation of crystals. The surface morphology of the crystal nucleation stage can to some extent reflect the rich information of crystal growth mechanism and crystal defect distribution, and the quality of nucleation plays a crucial role in the single crystal growth process. The PVT method for growing 4H SiC single crystals usually uses 4H SiC seed crystals with C-plane normal orientation or slightly skewed angles. The researchers investigated the effect of different seed crystal orientations on the growth of SiC crystals, as follows:

1. Effect of Seed Crystal Treatment Process on Growth of SiC Single Crystal

Studied the effect of different treatment processes on seed crystal for SiC single crystal growth. The SiC wafers cut from the bulk SiC single crystal are treated with different processes such as grinding, polishing, and corrosion. Then, the seed crystals are used to grow SiC crystals by physical vapor transport method with a growth time of 10 minutes. Observing the morphology of the wafer before and after growth using an optical microscope, the results show that:

The pits and scratches generated by cutting SiC crystals can be processed through processes such as grinding, polishing, and corrosion. The processing metamorphic layer generated by grinding on the wafer surface has high energy, and when used for high-temperature crystal growth, the wafer surface undergoes significant carbonization;

Polishing can remove scratches generated during grinding, but it cannot completely remove the grinding deterioration layer or the thinner mechanical damage layer produced by polishing. It can induce SiC polycrystalline nucleation in polished wafers during high-temperature crystal growth;

Corrosion not only reveals structural defects in wafers, but also removes surface mechanical damage layers generated during grinding and polishing. The corroded wafers serves as a seed crystal, and the growth crystal can effectively replicate the structure of the seed crystal, with a smooth surface.

2. Effect of Seed Crystal Polarity on the Stability of 4H-SiC Crystal Structure

The polar axis of SiC crystals belonging to the hexagonal crystal system is the c-axis. When cutting the crystal along the (0001) plane, the SiC wafer has two polar planes, namely the C-plane (0001) and the Si plane (0001). The main difference lies in the different free surface energies, with the C-plane having a lower free surface energy and the Si plane having a higher free surface energy.

In order to investigate the effect of seed crystal polarity on stable crystal growth, SiC crystals were grown on both the C and Si planes of the seed crystals. The results showed that in over 300 experiments, the crystals grown on the C plane were all 4H crystal forms, while only 6H could be grown on the Si plane, and this result was independent of the seed crystal form (4H, 6H, or 15R). Even if 6H SiC was chosen as the seed crystal, 4H-SiC crystals could be successfully grown. The reason for the above phenomenon is related to the free surface energy of the growth surface and the enthalpy of crystal formation.

Usually, 4H crystal forms with higher formation enthalpy tend to grow on the C plane with lower surface energy, while Si planes with higher surface energy are more prone to grow and form 6H crystal forms with lower enthalpy. The researchers further investigated the above viewpoint by splicing the Si and C planes of the 6H SiC crystal form in half and bonding them onto a graphite cover to obtain specific seed crystals, which also proved that the C plane is more conducive to the growth of the 4H SiC crystal form. But there is a transition layer for crystal transformation, which contains both 15R, 4H, and 6H SiC polytype mixtures. The polytype transformation process can be accelerated by introducing Sn vapor into the growth atmosphere.

In order to obtain a single 4H SiC crystal form, it is recommended to choose the C-plane of the 4H SiC crystal form as the seed crystal, providing lower nucleation free energy and maintaining stable crystal growth.


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