Study On Defect Characterization And Formation Mechanism Of 4H Silicon Carbide Synthesized By PVT Method

Wide band gap,high breakdown electric field,high thermal conductivity and high saturation electron drift speed are the characteristics of 4H-type silicon carbide（4H-SiC）,and its performance in the manufacture of high-power,high-frequency,and high-temperature semiconductor electronic devices far exceeds that of silicon crystals.The invention of the physical vapor transport method（PVT method）commercialized large-diameter silicon carbide wafers.However,the silicon carbide crystal contains many defects,which will reduce the quality of the wafer and even make it unusable.In this paper,conventional gemological methods are used to test the gemological parameters of4H-SiC synthesized by PVT method,and through KOH corrosion,scanning electron microscope,atomic force microscope,Fourier infrared spectrometer,ultraviolet-visible spectrophotometer and micro-Raman spectrometer were used to characterize 4H-SiC defects.This paper identifies two types of defects,including material type defects（carbon inclusions）,and inlaid structures,mosaic structure,polytypes,micropipes,threading screw dislocations（TSD）,threading edge dislocations（TED）,and basal plane dislocation（BPD）.Under the microscope,the mosaic structure has the crystallographic morphology of the crystal body;different polytypes and colors have a certain corresponding relationship,4H polytype is yellowish brown,6H polytype is blue-green,15R polytype is yellow;while carbon inclusions have an adverse effect on the spiral growth path.In the off-axis growth of single crystal substrates,the dislocation defects displayed after KOH etching are mostly TSD,TED,BPD,and the center point of the corrosion pit is biased to the（112"0）direction.The predecessors have relatively shallow research on the morphology of the corrosion pit,which is used in this article.Scanning electron microscopy conducted contrast analysis on the corrosion pits of dislocation defects.It was found that the TSD corrosion pits were six-sided single cones and had three different styles.Three TSD dislocation models were established correspondingly,and the TED corrosion pits were tested by atomic force microscopy,the 3D view is an oblique cone,and the apex of the corrosion pit points to the（11 2"0）direction,which is the same as the TED dislocation in the scanning electron microscope,but there is no obvious difference in Raman shift for different dislocation defects in the Raman test.The Raman spectrum is useless for the detection of dislocation defects.In addition,atomic force microscopy testing also found that the 4H-SiC synthesized by PVT has a spiral growth mechanism.The smaller the surface roughness of the sample,the worse the crystal quality and the more defects.Select polytypes in typical samples for spectroscopy,the peak of 798～866cm^-1 in the infrared reflectance spectrum is caused by carrier absorption,and infrared spectroscopy has no significance for polytype identification;the 4H polytype absorption peak in the ultraviolet absorption spectrum is 462nm,the 6H polytype absorption peak is 630nm,the 15R polytype absorption peak is 437nm,and the higher the doping concentration of the wafer,the stronger the ultraviolet absorption intensity;Raman spectroscopy can accurately identify different polytypes and is an effective detection method to identify polytype defects.Defects are related to the growth mechanism of 4H-SiC synthesized by PVT method.To improve the growth quality of silicon carbide crystals and reduce defects,we should start with the growth mechanism.Based on this research,the author suggests to use zero micropipes and single polytype seed crystals in the crystal growth process to improve the surface quality of the seed crystals and avoid scratches and CMP scratch defects;further more control the stress of the thermal field by optimizing the temperature field distribution in the PVT method;use a silicon carbide source of fine raw materials to reduce impurities.