The Low Pressure Homoepitaxial Growth Of 4H-SiC And Device Verification

Silicon carbide?SiC?is a very desirable semiconductor material for applications of high power electronic devices due to its superior physical properties such as wide bandgap,high thermal conductivity and high critical breakdown electric field strength.After near 30years of development,SiC electronic devices have been widely used in the military area such as warship,aircraft,radar,communication and navigation,etc.and in civil area,such as photovoltaic inverter,high-speed train,smart grid and electric vehicles,etc.For high power SiC devices,high-quality and thick 4H-SiC epilayers with low defects density,low doping concentration and good morphology are required.However,there still have many problems unsolved in some areas,such as defects and uniformity controlling in the growth of thick epitaxial layers on lager diameter substrate,which restrict the performance improvement of 4H-SiC device and the wide range application in power electronic system.In this work,studies are performed to obtain high quality 4-inch thick 4H-SiC homoepitaxial layers.The main contents and highlights are as follows:1)Study was put on the mechanism for the morphology,structure and origination of new type triangular defects.Zigzag like triangular defect?ZLTD?and inverted pyramid related triangular defect?IPRTD?are studied by optical microscope,Raman,electron back scattered diffraction?EBSD?,transmission electron microscope?TEM?and laser scanning confocal microscope.It is found that 3C-SiC crustalline inclusions are present in both defects of ZLTD and IPRTD.Different morphologies and structures are attributed to the difference of growth mechanism.ZLTD originates from spontaneous 3C-SiC nucleation on terrace.The main growth mode of ZLTD is step flow growth of 3C which accompanied by2D nucleation growth along with[0001].The origination of IRPTD is attributed to2D nucleation on defect sites.The main reason to form invert pyramid structure results from the difference in growth rate between step-flow growth and lateral growth along with the directions of[1-100]and[1-100]and H₂ etching.2)The growth of 4H-SiC epilayers on 4°off-axis substrates were performed using horizontal hot wall chemical vapor deposition?HWCVD?with a standard chemistry of silane-propane-hydrogen under low pressure condition,which focuses on the effects of growth pressure on morphology,basal plane dislocations?BPDs?and crystalline quality.It is found that morphological defects reduce with the decreasing of growth pressure,since the surface diffusion length of absorbed adatoms increases under low growth pressure,so as to suppres the nucleation of adatoms on terraces and the formation of morphological defects.However,as the surface diffusion length increasing under low growth pressure,the difference of growth velocity atsteps enhances,leading to the extension of steps width and the formation of step-bunching.Besides variation of surface diffusion length,the phenomenon described above can be correlated with the dominant mode for minimizing surface energy atthe varied growth pressure.Step-bunching is reduced by the optimization of etching process during growth.High quality homoepitaxial layer of 10?m thickness is obtained with a thickness uniformity of 1.66%and a doping uniformity of 3.52%on100mm substrate.3)Study has focoused on the effect of growth pressure on the instrinsic defects in unintentionally doped 4H-SiC homoepitaxial epilayers grown by horizontal hot wall chemical vapor deposition system with a standard chemistryof silane-propane-hydrogen using the techniques of low temperature photoluminescence?PL?and electron spin resonance?ESR?.Itrevealsthat the mainintrinsic defects in 4H-SiC epitaxial layers grown in different pressures are carbon vacancies and related complexes.In addition,point defects concentration reduces with the decrease of growth pressure.Based on the calculation of the equivalent paramagnetic center corresponding the intrinsic defects in different samples with the Brillouin fitting,the effect of growth pressure on the intrinsic defects in theunintentionally doped 4H-SiC homoepitaxial epilayers shows the same tendency as the experimental results obtained from PL and ESR.Comparing with the growth in normal pressure,the carbon vacancies in the epilayers grown with low pressure are reduced by 60%,which may be attributed to the increase of effective C/Si ratio on the growth surface at lower pressure,resulting in the reduction of intrinsic defects.Besides,step-flow growth mode is enhanced by lowering growth pressure.It is reasonable to believe that the enhancement of step-flow growth increases the possibility of incorporationof carbon atoms and suppresses the formation of intrinsic defects.It is indicated that growth pressure plays a significant role in the formation of intrinsic defects and deep levels and provides a strategy for the reduction of intrinsic defects and deep levels.4)4H-SiC JBSs were farbricated on 4 inch epilayer wafers,which were grown under optimized grow condition,in order to study the electrical impact of surface defects on high voltage SiC Schottky barrier diode.It is found that Comets are determental to a Schottky barrier diode.Carrots have small effect on reverse breakdownand degrade the leakage current at low reverse bias.Growth pits show no direct impact on the leakage current and breakedown voltage.Triangular defects have strong effect on reverse breakdownand degrade the leakage current.A 50%reduction of reverse breakdown of Schottky barrier diode with triangular defects is observed and the leakage current increases by four orders of magnitude.