Selective Monomer 150mm 4H-SiC Homoepitaxy Via Chemical Potential Modification

4H-silicon carbide(4H-SiC)is a very promising wide band-gap semiconductor for the new generation power electronics due to its excellent properties.Currently,4H-SiC power devices with high breakdown voltages have been widely studied and developed.The drift layer(epitaxial)thickness is gradually increased for the demond of high breakdown voltage devices.Meanwhile,in order to reduce the manufacturing cost of 4H-SiC power devices,increasing the wafer size is an effective method.At present,the wafer diameter of 4H-SiC has been gradually inceased from 100 mm to 150 mm.However,during the epitaxial growth,the temperature gradient in the wafer is larger as the wafer size increasing,the structure and roughness of the epitaxial film are not easily to control,and the suppression of defects is more difficult.The uniformity of the thickness and concentration distribution in the wafer is difficult to guarantee.In order to solve these problems,the homoepitaxial growth of 150 mm 4H-SiC thick films has been studied in this paper.The specific research contents and results are as follows:1)Based on the step-growth modle,the variation of grown step height with the gorwth atmosphere has been studied by first-principles calculation,and theexperimental verification was carried out.Four kinds of C-Si diatomic step structure models of 4H-SiC substrate with Si polar surface were established.The monomers such as C/Si atoms,SiC molecule and SimCn clusters were adsorbed on the step to form atom,molecule and cluster growth structure.The formation energies of thesegrowth structures have been evaluated by performing first principles total-energy calculations wihin density functional theory(DFT),and vary with the chemical potential of silicon.Compared with the clean step surface,the results show that Si atom,SiC molecule and Si2C cluster can be adsorbed stably at the step boundary.The results showed that the step surface adsorbs Si atoms preferentially in the Si-rich condition with the growth step height of 1/4c,and the step surface adsorbs SiC preferentially in the C-rich condition with the growth step height of 1/2c or lc.Chemical Vapor Phase Epitaxy(CVPE)experiments were carried out to verify the relationship between the theoretical results,even the C/Si ratio changing and the growth step height.The direction of the key process for 150 mm 4H-SiC epitaxital growth was pointed out as follows:Low growth rate and Si-rich condition(Si/HZ=0.26‰,C/Si=0.8)for buffer layer can obtained the step growth height of 1/4c and realized complete replication of substrate lattice,which is conducive to reduce the epi-defects and obtain high doping level for buffer layer.High growth rate and C-rich condition(Si/H2=0.97‰,C/Si=1.55)for drift layer can realized the preferential adsorption of SiC molecule and obtained the step growth height of 1/2c or lc,which can result in the good surface roughness and low concentration for epi-layer.2)The formation mechanism of new basal plane dislocation(BPD')and its gliding generated internal dislocations(IDs)and half-loop arrays(HLAs)during 150 mm 4H-SiC epitaxial growth have been studied.By increasing in-situ etching time to 10 minutes,the substrate strain can be fully released and BPD' gliding can be effectively avoided.The number of BPD'defects in Si-rich buffer layer,C-rich drift layer and unstable ramping layer were observed.The results showed that the ramping layer is the decisive factor for BPD'defect formation due to its growth rate and growth condition.In order to reduce the diffusion of excess C atoms into the buffer layer with a large number of C vacancies/voids during the growth of ramping layer,the effects of accelerating the growth of ramping layer and reducing the diffusion time of C atoms on BPD'defects were investigated.Finally,by optimizing the Si and C source flows to Si/H2=1.94‰,C/H2=2.60‰(C/Si=1.34)for drift layer,the growth rate of ramping layer is increased and the excess C atoms is reduced.At the same time,increasing C/Si from 0.8 to 1.3 at the initial growth of ramping layer ensures that the whole ramping layer grows in C-rich condition.150 mm 4H-SiC epitaxial layer with BPD'free has been obtained.It is confirmed that chemical potential controlled growth monomers can not only grow buffer layers for replicating lattice information of substrates and repairing surface defects,but also can grow high quality epitaxial layers with good roughness.More importantly,it can also be used to guide the adjustment of the growth atmosphere of ramping layer and obtains 150 mm 4H-SiC homoepitaxial layer with zero basal plane dislocation.3)Linear depletion fo source gases have been obtained by epitaxial growth with disc no-rotation.It's found that the adjustment of the three H2 flux is helpful to improve the thickness uniformity,which resulted in uniformity reducing from 1.07%to 0.30%.And the concentration uniformity has been reduced from 8.55%to 4.52%by adjusting the ratio of the N2 in three zones.With the modified process,150mm 4H-SiC epitaxial wafers with-60 ?m thick and?1 × 1016 cm-3 concentration has been grown.The CS920 PL mapping showed that no BPD'or its gliding has been found in the epi-layer.The surface defect density is 0.31 cm-2,and resulting in the 2mm×2mm die yield of 98.7%.The thickness and doping uniformity were 0.26%and 4.49%,respectively.The roughnesses of the obtained wafer is around 0.35 nm scanned by AFM on 20×20 ?m2 areas,showing step bunchings free on the surface.Continuous growth experiments showed that the 150 mm 4H-SiC thich film epitaxial process has good stability and repeatability.