化学气相沉积铝掺杂碳化硅的微波介电特性

Dielectric properties of aluminum-doped silcion carbide using chemical vapor deposition

以三氯甲基硅烷(CH3SiCl3,MTS)为原料,三甲基铝(Al(CH3)3,TMA)为掺杂源,氢气和氩气分别作为两者的载气,氩气同时作为稀释气以常压化学气相沉积在石墨基体上沉积碳化硅涂层。采用XRD、EDS和介电性能测试,结果表明铝已经进入碳化硅晶格中并占据硅的位置,同时引起介电常数实部和虚部有不同程度的增大,这可能是由于SiC中固溶了Al原子,在掺杂后的SiC中形成大量的带电缺陷,这些带电缺陷在电磁波交变电场作用下产生极化耗散电流和强烈的极化弛豫。

Silicon carbide coatings have been grown onto graphite substrates by normal pressure chemical vapor deposition using methyltriehlorosilane（MTS, CH3 SiCl3 ） and trimethylaluminum （TMA, Al （CH3）3 ） as source precursors, H2 as carrier gas and Ar as carrier and diluent gas in the horizontal cold-wall CVD reactor. The coatings phase and chemical composition were studied. The SiC coating consisted of β-SiC with very little free carbon. The Al doped coating was composed of massive β-SiC, a little amount of Al4SiC, and certain free carbon. The dielectric properties of both coatings after removing excessive free carbon and SiO2 were measured in a frequency range of 8.2-12.4GHz. The results show that real part and imaginary part of permittivity of undoped SiC are lower than those of Al doped SiC coating. The reason is probably the SiC coatings dissolve a great deal of aluminum. So the charged defects and quasi-free electrons move in the response to the electric field, and a diffusion or polarization current results from the field propagation. The higher imaginary part （ε″） is due to the dieleetrieal relaxation.