SiC Polarity Effects on Reaction, Doping and Epitaxy

Due to the differences in atomic structure and lattice parameters, SiC crystals have different physical and chemical properties on their surfaces, resulting in polarity. The two non equivalent surfaces in the direction of the polarity axis are called the Si surface and the C surface. The polarity of SiC crystals is an important factor affecting their material growth, mechanical processing, epitaxy, and device performance. Choosing a suitable polarity surface is crucial for optimizing device performance and reliability. PAM-XIAMEN can offer double side CMP SiC substrate for epitaxy.

1. Chemical Reaction Behavior of SiC Polar Surface

In SiC crystals, there are significant differences in the oxidation and doping behavior between the Si and C surfaces, mainly attributed to their different atomic arrangements, electronic structures, and surface properties. Due to the need for Si atoms to overcome higher energy barriers during the oxidation process, such as the higher activation energy for Si atoms to form Si-O bonds with O atoms, the oxidation rate of the Si surface is slower than that of the C surface. On the contrary, the oxidation rate of the C surface is faster than that of the Si surface because C atoms are more easily bound to O atoms. In addition, the surface structure of the C surface may be more prone to form unstable oxides, thereby accelerating the oxidation process.

Fig. 1 (a) The functional relationship between the thickness of Si-surface oxide and time and temperature; (b) The thickness of C-surface oxide as a function of time and temperature. (Solid line: Song model calculation result; Scatters: 4H-SiC oxidation experimental results)

In terms of doping behavior, the binding site of impurity atoms is controlled by the relative size of the covalent radius between the doping atom and the replaced atom. N atoms are more easily doped on the Si surface because their radius is similar to that of C atoms, which can replace C atoms in the lattice. And Al atoms are more easily doped on the C plane because the radius of Al atoms is similar to that of Si atoms, which can replace Si atoms into the lattice. On the C-plane step, N atoms can bond with several Si atoms in the lower layer, while on the Si plane step, N only bonds with one Si atom, resulting in a lower reverse desorption rate of N on the C-plane and a higher doping concentration on the C-plane. The doping of Al atoms is opposite to that of N atoms.

Fig. 2 The surface vacancy-induced incorporation doping for N and Al

2. Influence of SiC Polarity on Heteroepitaxy

2.1 Homoepitaxy

In the field of high-power devices, Si-surface SiC is still mainly used for epitaxial preparation. The latest research shows that due to the low oxidation rate of the silicon surface, it can promote the formation of high-quality gate oxide layers, such as MOSFET gate oxide; A lower surface roughness is very advantageous for obtaining a smooth surface morphology. However, the epitaxial growth rate on the silicon surface is slow, which limits the production capacity. Usually, it has a higher defect density in the epitaxial layer and requires stricter process control. In contrast, carbon face SiC exhibits an epitaxial growth rate of up to 50 µm/hr, which greatly improves production efficiency. By optimizing chemical mechanical polishing (CMP) and etching processes, extremely low defect density can be achieved, even approaching defect free levels, which is crucial for improving device performance. Its longer surface diffusion length is conducive to the dominant step flow growth mode, which helps to further reduce defects. However, the main challenges it faces are the faster oxidation rate of the carbon surface and the easier formation of 4H SiC multi type inclusion defects that penetrate the wafer.

2.2 Heteroepitaxy

When researchers used SiC substrates to grow graphene, they found that in the layer growth mode, a (6 √ 3 × 6 √ 3) R30 ° buffer layer is usually formed when graphene is grown on the Si surface, and then graphene grows in a layered mode. This growth mode makes the number of graphene layers controllable, but the buffer layer may cause defects. When graphene is grown on the C-plane, no buffer layer is formed, and the surface reconstruction process is more complex. Graphene is more likely to nucleate at defect sites and grow in a polycrystalline form, with independent layers and lower electron mobility.

In terms of film polarity, AlN films grown on the Si surface usually have Al polarity, while AlN films grown on the C surface usually have N polarity. Similarly, GaN films grown on the Si surface typically have Ga polarity, while GaN films grown on the C surface typically have N polarity.

Whether you need SiC substrate  for research or for industrial applications, please contact us email at [email protected] and [email protected].

 

Reference

1. ZHAO, C. Y., WANG, E. H., & HOU, X. M. (2021). Research progress on the oxidation mechanism and kinetics of a SiC semiconductor with different crystal surfaces. Chinese Journal of Engineering, 43(5), 594-602.

2. Huang, Y., Lin, H., Zhang, X., & Xiang, G. (2025). Polarity-dependent effects in silicon carbide crystals: from fundamentals to applications. Journal of Physics D: Applied Physics, 58(18), 183003.