Materials Science Forum Vols. 600-603

Abstract: The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall CVD reactor, with growth rates as high as 170 µm/h at 1600°C. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor up to about 100 µm/h. The growth rate dropped for C/Si < 1 but was constant for C/Si > 1. Further, the growth rate decreased with lower Cl/Si ratio.

Abstract: We have developed a new chemical vapor deposition (CVD) system that is capable of a high growth rate of over 100 µm/h with good uniformities of thickness and carrier concentration. In this CVD system, the process gases contribute efficiently to epitaxial growth. In a demonstration of the abilities of the CVD system, we achieved an average growth rate of 140 µm/h, a thickness uniformity of 3.9%, and a carrier concentration uniformity of 8.9% in a 2-inch wafer, without degradation of the crystallinity.

Abstract: The growth rate of 4H-SiC epi layers has been increased up to 100 µm/h with the use of trichlorosilane instead of silane as silicon precursor. The epitaxial layers grown with this process have been characterized by electrical, optical and structural characterization methods. Schottky diodes, manufactured on the epitaxial layer grown with trichlorosilane at 1600 °C, have higher yield and lower defect density in comparison to diodes realized on epilayers grown with the standard epitaxial process.

Abstract: A process has been developed to grow multi-epy high doped structure. Trichlorosilane (TCS) and Ethylene have been used as precursor; Nitrogen (N2) and trimethylaluminum (TMA) as doping source. The SIMS and SCM analysis show that using this silicon precursor very abrupt N++/P+/N+ junctions (40-60 nm) can be obtained with low background doping concentration in a single epitaxial growth run.

Abstract: The mechanism of layer growth as well as defect formation in the SiC crystal is fundamentally important to derive its appropriate performance. The purpose of the present study is to investigate competitive adsorption properties of growth species on the various 4H-SiC polytype surfaces. Adsorption structure and binding energy of growth species in the experimentally condition on various SiC surfaces were investigated by density functional theory. For the SiC(000-1) and SiC(0001) surfaces, the adsorption energy by DFT follows the orders C > H > Si > SiC2 > Si2C > C2H2. Furthermore, based on the DFT results, amount of adsorption of each species in the experimental pressure condition were evaluated by grand canonical Monte Carlo method. H and Si are main adsorbed species on SiC(0001) and SiC(000-1) surfaces, respectively. The ratio of amount of adsorption of Si to H was depending on the surface structure that might explain different growth rate of the surfaces.

Abstract: A novel Monte Carlo kinetic model has been developed and implemented to predict growth rate regimes and defect formation for the homo-epitaxial growth of various SiC polytypes on different substrates. Using this model we have studied the generation of both point like and extended defects in terms of the growth rate and off-cut angle, finding qualitative agreement with both electrical and optical characterization and analytical results.

Abstract: Triangular defects and inverted pyramid type defects formed during homoepitaxial growth on 4H-SiC Si face, 4° off-cut towards [11-20] direction have been investigated. Growth parameters responsible for triangular defect formation were identified and optimized for its reduction in this study. It was found that although the high temperature reduces the density of inverted pyramid type defects, it is not the only remedy for reducing their density and cleanliness of susceptor along with the initial growth condition plays a major role in the formation of these defects.

Abstract: Basal Plane Dislocations (BPD) in SiC are thought to cause degradation of bipolar devices as they can trigger the formation and expansion of stacking faults during device operation. Therefore, epilayers without any BPD are strongly recommended for the achievement of long-term reliable bipolar devices. Such epilayers can be achieved by supporting the conversion of BPD into Threading Dislocations (TD), which depends on the epitaxial growth mode (as described in literature). In this work, the influence of several pre-treatments of the SiC substrate prior to epitaxial growth and different epitaxial growth parameters on the reduction of the BPDs in the SiC epilayers was investigated on 4° off-axis substrates. The dislocation content in substrates and epilayers was determined by Defect Selective Etching (DSE) in molten KOH. The averaged BPD density in epitaxial layers can be reduced to < 100 cm-2 for substrate preparation techniques and to < 30 cm-2 for well-suited epitaxial growth parameters. A certain combination of epitaxial growth parameters leads to < 3 BPD/cm2 in the epitaxial layer.

Abstract: The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52×1020 cm-3 with Hall mobility of about 1 cm2/Vs and resistivity of 1.6~2.2×10-2 Wcm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Wcm for resistivity, 5.3×1018 cm-3 for hole carrier concentration, and 7 cm2/Vs for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.

Abstract: Homoepitaxial growth of 4H-SiC epilayer by hot-wall chemical vapor deposition using bis-trimethylsilylmethane (BTMSM, C7H20Si2) precursor was investigated. The growth rate of 4H-SiC was investigated as a function of the growth temperature and source flow rate. The FWHM values of epilayers as the growth temperature and source flow rate also investigated. The growth rate of 4H-SiC epilayer grown by hot-wall CVD was 3.0 μm/h and the background doping level of 4H-SiC epilayer was mid 1015/cm3.