Investigation Of The Key Technology For Low Dislocation Density In 4H-SiC Epitaxial Material

Silicon Carbide (SiC), the third generation wide band gap semiconductor material, has outstanding properties such as wide bandgap, high critical breakdown field, higher thermal conductivity, and high electron saturation drift velocity, and it is particularly suitable for fabrication of devices operated in high temperature, high voltage, high power, and high radiation environment. With excellent figure of merits compared with other types of SiC,4H-SiC make it an attractive semiconductor. However, a large number of crystal defects still exist in 4H-SiC crystals. These defects include threading screw dislocations (TSDs), threading edge dislocations (TEDs), basal plane dislocations (BPDs) and stacking faults (SFs)). They affect device performance in different degrees. In these defects, BPDs is the most significant effect on device performance.The foreign researchers have been studied how to reduce the BPDs density in 4H-SiC epilayers, and made certain progresses in this field. But, there are still different opinions for the mechanism of conversion and propagation of dislocations in 4H-SiC epitaxy. Although it has made has made some achievements in epitaxial growth of 4H-SiC material, the related researches are just in beginning in mainland China. Defect characterization of 4H-SiC Material has been reported, but for the method of the growth of epilayer with low BPDs density is not reported. In this dissertation, The mechanism of conversion and propagation of dislocations in 4H-SiC epitaxy is studied. Nondestructive defect characterization for 4H-SiC homoepitaxial layer is presented. The main studies and contributions of this dissertation are as follows:(1) Nondestructive defect characterization for 4H-SiC homoepitaxial layer with the techniques of cathodoluminescence (CL) and scanning electron microscope (SEM) are investigated. The results show that there are some trianglular defects and carrot detects on the surface of epitaxy, a largel amount of TEDs and a small amount of TSDs in epitaxy. A largel amount of BPDs and SFs distribute along basal plane in epitaxy in certain direction. The reason of this distribute feature is the step flow growth caused atoms slip along <1120> Luminescence properties of dislocations in 4H-SiC are studied by means of cathodoluminescence(CL) and defect selective etching. The deduction of green band luminescence contained BPD in 4H-SiC epitaxy is approved by CL. (2) The mechanism of conversion and propagation of dislocations in 4H-SiC epitaxy is dicussed. The results indicate that BPD can t conversed to TED, but TSD can not. The reason is that the former meets the conditions of the lowest energy and the burgers vector conservation, but the latter meets the one condition.It not only explains the mechanism of conversion and propagation of dislocations, but also provides a guide for the growth of epilayer with low BPDs density.(3) Unintentionally doped low BPDs density n type 4H-SiC homoepitaxial layer has been obtained using a low pressure, hot wall CVD reactor on the substrate by molten KOH etching. The defects in epilayer are observed and analyzed, and it is found that the BPDs density in epilayer(5.3×103/cm2) by this method is lower than conventional growth method (1.7×104/cm2).(4) The conversion and propagation of BPDs in epilayer are investigated. It shows that the BPDs along <1120> conversed to TEDs from substrate to epilayer. However, not all BPDs along <1100> in substrate are conversed to TEDs in epilayer. Some of them are propagated into epilayer and the vector of these dislocation line is conversed to <1120>. It is interpreted that step-flow mechanism causes the difference of the vector of dislocation line between substrate and epilayer. The reason of propagation of BPDs along <1100> from substrate to epilayer may be result from stress concentration. It is found that the new BPDs generation is due to the defects on the polished surface of substrate.(5) Intrinsic SFs in 4H-SiC epilayers are investigated. It is found that the nucleation site of intrinsic SFs lies in the interface of substrate and epilayer. It shows that the density of intrinsic SFs in epilayer grown on the etched substrate(5.0×103/cm2) is lower than that on the no-etched substrate, which can be ascribed that the number of nucleation site on the surface of substrate is reduced by molton KOH etching. It provides a guide for the growth of epilayer with low SFs density.