The Study On Low-pressure Homoepitaxial Growth Of 4H-SiC

The research of Si C power devices is an increasing concern in recent years. Since Si C power devices are fabricated on the epilayer, the quality of Si C epilayer is very important to the performance of Si C power devices. In order to produce Si C power devices, a 50-micron-thick Si C epilayer with high quality is essential, but the epitaxial growth rate available is so slow that growth time becomes longer. Thus it is necessary to improve the rate.In this dissertation, the low-pressure homoepitaxial growth of 4H-Si C have been studied. The influence of growth pressure, source flow rate and growth time on growth rate was studied. And the thickness uniformity, surface defect, surface morphology and crystal quality of samples have also been studied. The main studies and contributions of this dissertation are as follows.1) When the growth pressure reduced from 100 mbar to 40 mbar, the growth rate of epilayer remains between 10 μm/h and 10.5 μm/h. The density of triangular defects decreases from 71.4 cm-2 to 13.4 cm-2 and the density of carrot defects decreases from 44.6 cm-2 to 17.9 cm-2. The main reason for this phenomenon is that low pressure may decrease surface free energy and inhibit abnormal nucleation in the early phase. As the growth pressure decreases, the opposite trend that the surface roughness increases is observed. The RMS increases from 0.331 nm to 0.69 nm.This phenomenon may have relations with the increase of adatom surface mobility or the decrease of surface free energy. In addition, with the decrease of growth pressure, the crystal quality of samples becomes better. The FWHM decreases from 86.4468 arcsec to 58.4282 arcsec.2)When growth pressure is 40 mbar and silane flow rate increases from 10.5 sccm to 50 sccm, the growth rate of samples almost increases linearly, up to 12.5 μm/h, and the growth rate is not saturated. The increase of the density of surface defects and the degradation of crystal quality are caused by the increase of silane flow rate. The density of triangular defects increases from 4.5 cm-2 to 102.6 cm-2, the density of carrot defects increases from 0 cm-2 to 75.9 cm-2, and the FWHM increases from 27.3135 arcsec to 84.3121 arcsec. This may be because the increase of growth rate results in the increaseof rate of abnormal nucleation. In addition, the increase of silane flow rate doesn’t cause obvious degradation in the surface morphology of samples. The RMS of samples remain at 0.60 nm.3) When growth pressure is 40 mbar and growth time increases from 1 hour to 4 hours, the growth rate of epilayer remains above 10 μm/h stably. The crystal quality has no obvious change in at least 3 hours. The FWHM increases from 55.0412 arcsec to 60.2635 arcsec. When growth time is 4 hours, the FWHM will increase to 98.0071 arcsec. The density of surface defect increases when growth time increases. The density of triangular defects increases from 8.9 cm-2 to 111.6 cm-2 and the density of carrot defects increases from 40.2 cm-2 to 67.0 cm-2. This may be for temperature fluctuation after long time operation of CVD reactor. In addition, the increase of growth time doesn’t cause obvious degradation in the surface morphology of samples. The RMS of samples remain at 0.38 nm.