Papers by Keyword: PVT Growth

Abstract: We have investigated the applicability of a new type of 3C-SiC powder source material during PVT growth which consist of a particle size of ca. 10 µm (aggregates up to ca. 150 µm). In-situ X-ray visualization of 75 mm and 100 mm PVT growth runs showed a smooth SiC powder consumption during growth. Using Raman spectroscopy, we have found a high 4H-SiC polytype stability and a low residual stress distribution in the intentionally n-type doped grown crystals.

Abstract: The fabrication of n-channel IGBTs is constrained by the low conductivity as well as poor quality of the p-type SiC substrate. This paper reports 6-inch high quality p-type 4H-SiC wafers achieved by PVT method. The wafers were examined by synchrotron X-ray topography indicating average defect densities are on par or better than commercial 6-inch n-type wafers. Large areas of the wafer, especially the middle region of the wafer is characterized by very low density of BPDs. The extent of prismatic slip due to radial thermal gradients is also vastly reduced compared to typical n-type wafers.

Abstract: Prismatic slip systems are the secondary slip systems in Silicon carbide (4H-SiC) crystals. The previously proposed radial thermal model of the PVT growth process for SiC crystals, which predicts the occurrence of slip in different prismatic planes as a function of the radial position in the boule, has been shown to generally work well. Recent observations of growth interface nucleation of prismatic slip necessitated updating the thermal model to incorporate the effects of the curvature of the growth interface. A 3D finite element model has been developed to include the growth interface curvature complexity. The model predicts high dislocation densities due to prismatic slip near the peripheral regions dropping to zero near the center for wafers from sections of the boule grown with a flatter interface and a less dense distribution of prismatic slip dislocations that extends to the center for wafers from boule sections grown with a more convex interface. Additionally, due to such an interface-initiated prismatic slip, , the asymmetrical step configuration produced by off-axis growth results in an asymmetrical distribution of prismatic slip. The studies suggest that a reduced surface curvature is necessary to suppress the prevalence of interface-related prismatic slip generation.

Abstract: The carbon inclusions in SiC bulk crystals were studied by using optical microscope. The carbon inclusions were classified into three types, namely Type Ⅰ (100~1000 μm), Type Ⅱ (20~50 μm), Type Ⅲ (~5 μm) carbon inclusions based on their different morphologies. In addition, the evolution of these three type carbon inclusions with crystal growth process was traced. It was found that the number of Type Ⅰ and Type Ⅱ carbon inclusions showed declined tendency with crystal growth, while the number of Type Ⅲ carbon inclusions exhibited less dependence on crystal growth. Furthermore, the formation mechanism of carbon inclusions was clarified. This study would give out a better understanding of carbon inclusions, thus contribute to reducing or eliminating carbon inclusions in SiC crystals.

Abstract: Dislocation behavior during the early stages of physical vapor transport (PVT) growth of 6-inch diameter 4H-SiC crystals has been investigated by synchrotron monochromatic beam X-ray topography (SMBXT) in conjunction with ray tracing simulations of dislocation images. Our studies reveal that most of the TSDs/TMDs are replicated into the newly grown layer while most TEDs are generated by either nucleation in pairs at the growth interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown layer are of screw type with and this has been verified by comparison with ray tracing simulated images. TEDs with same and opposite sign of Burgers vector are found to be deflected on to the same basal plane by the overgrowth of macro-steps and they glide in the same and opposite directions respectively. TMDs deflected on to the basal plane by macro-steps get dissociated into c and a components, with the a segment undergoing glide to form V-shaped configurations.

Abstract: We have developed the bulk growth technique to reduce threading screw dislocations (TSDs) by combining solution growth and PVT growth methods. More than 80 % of TSDs in original seed crystals were successfully converted to Frank defects on basal planes by the solution growth on 4° off C-face with Si-5at.% Ti solvent. After PVT growth on the as-grown surface of the conversion layer, TSDs in the original seed were successfully reduced. The presence of micrometer-size macrosteps in the initial stage of PVT growth is important to continue to propagate the converted Frank defects on basal planes during PVT bulk growth.

Abstract: The cubic polytype of SiC (3C-SiC) is the only one that can be grown on silicon substrate with the thickness required for targeted applications. Possibility to grow such layers has remained for a long period a real advantage in terms of scalability. Even the relatively narrow band-gap of 3C-SiC (2.3eV), which is often regarded as detrimental in comparison with other polytypes, can in fact be an advantage. However, the crystalline quality of 3C-SiC on silicon has to be improved in order to benefit from the intrinsic 3C-SiC properties. In this project new approaches for the reduction of defects will be used and new compliance substrates that can help to reduce the stress and the defect density at the same time will be explored. Numerical simulations will be applied to optimize growth conditions and reduce stress in the material. The structure of the final devices will be simulated using the appropriated numerical tools where new numerical model will be introduced to take into account the properties of the new material. Thanks to these simulations tools and the new material with low defect density, several devices that can work at high power and with low power consumption will be realized within the project.

Abstract: Structural transformation from threading screw dislocations (TSDs) to stacking faults (SFs) has been investigated for PVT-grown 4H-SiC single crystals using X-ray topography and transmission electron microscopy (TEM). The transformation of TSDs is induced by the structural interference with bunched surface macrosteps over 100 nm in height. The stacking sequence of a SF was determined to be (433) in Zadanov's notation by using high-resolution TEM. Our detailed analyses revealed that the (433) stacking structure can be constructed by a combination of five faults including both four Frank type faults and one Shockley type fault.

Abstract: The electronic quality of a Physical Vapour Transport (PVT) grown 15R-SiC crystal at different stages of growth was assessed by time-resolved optical pump-probe techniques. The measured differential transmittivity (DT) kinetics for the layers corresponding to the initial, middle and final stages of growth revealed clear differences in the decay of the DT signal, indicating a decreasing concentration of traps at the later stages of the crystal growth. The estimated trap concentration in the initial layer was N_T ≈ 10¹⁹ cm^-3, while it decreased down to less than 2×10¹⁸ cm^-3 in the top layer. The injection dependence of the diffusion coefficient at room temperature confirmed the gradual decrease of N_T in the layers corresponding to later stages of growth. Accordingly, the bipolar diffusion coefficient in the middle and the top layer was D_a ≈ 2 cm²/s, while D_a = 0.9 cm²/s was measured in the layer closest to the seed.

Abstract: Iron (Fe) impurity concentrations in a SiC bulk crystal and source powders used for the bulk crystal growth are analyzed by means of secondary ion mass spectrometry and the validity of the obtained data are discussed. The secondary ion signal of ⁵⁶Fe is found to be affected significantly by the mass interference of ²⁸Si₂, and therefore measurements of ⁵⁴Fe instead of ⁵⁶Fe offer a better detection limit for the analysis. A high concentration of Fe is found at proximity of the SiC bulk crystal surface. Possible sources of the Fe contamination are discussed based on the depth profile data of Fe in both the bulk crystal and the source powders.