Papers by Keyword: Epitaxial Layer

Abstract: We have investigated a conversion of basal plane dislocation (BPD) to threading edge dislocation (TED) in growth of epitaxial layers (epi-layers) on 4H-SiC vicinal substrates with an off-angle of 0.85° at low C/Si ratio of 0.7 by using deep KOH etching and X-ray topography observations. Deep KOH etching indicated that BPDs in the substrates converted to TEDs in the epi-layers. X-ray topography observations suggested that the conversion occurred during epitaxial growth when the thickness of epi-layers was less than 1.5 μm. We found that the conversion ratio obtained from counting deep KOH etch pits was over 99%.

Abstract: The effect of process parameters such as growth temperature, C/Si ratio, etching time, and Si/H₂ ratio on dislocation density was investigated by performing KOH etching on 100 μm thick epitaxial layers grown on 4° off axis 4H-SiC substrates at various growth conditions by a chemical vapor deposition (CVD) process using a chloride-based chemistry to achieve growth rates exceeding 100 μm/h. We observe that the growth temperature and the growth rate have no significant influence on the dislocation density in the grown epitaxial layers. A low C/Si ratio increases the density of threading screw dislocations (TSD) markedly. The basal plane dislocation (BPD) density was reduced by using a proper in-situ etch prior to growth.

Abstract: 4H-SiC epitaxial films grown on 4H-SiC in CVD reactor VP508GFR are investigated using FTIR, X-Ray diffraction, C-V measurements, stylus profiler and DIC optical microscopy.

Abstract: 4H-SiC homoepitaxial layers with different thicknesses from 12.5 µm up to 50 µm were investigated by microwave-detected photoconductivity decay (µ-PCD), deep level transient spectroscopy (DLTS) and defect selective etching (DSE) to shed light on the influence of the epilayer thickness and structural defects on the effective minority carrier lifetime. It is shown that the effective lifetime, resulting directly from the µ-PCD measurement, is significantly influenced by the surface recombination lifetime. Therefore, an adequate correction of the measured data is necessary to determine the bulk lifetime. The bulk lifetime of these epilayers is in the order of several microseconds. Furthermore, areas with high dislocation density are correlated to areas with locally reduced effective lifetime.

Abstract: Morphologies of basal plane dislocations (BPDs) in 4H-SiC epilayers doped with nitrogen or aluminum are explained in detail. While BPDs in low N-doped or Al-doped epilayers show the morphology of gliding dislocations responding to stresses, BPDs in highly N-doped (≥1.0×10¹⁸ cm^-3) epilayers appear different. Some of them are parallel to [11-20] while others are straight and tilt from [11-20]. Tilt BPDs were also studied by TEM. Factors that relate to such morphology are discussed.

Abstract: A new method for the separation of threading screw dislocations (TSD) and threading edge dislocations (TED) in a 4H-SiC epitaxial layer is proposed by measurement of the etch pit angles. The etch pit angles of the TSDs and TEDs were 28±3 and 18±3°, respectively. In the case of etch pit depths within the epitaxial layer, the values were almost constant. Almost all of the TSDs were converted from basal plane dislocations (BPDs) at the epitaxial layer/substrate interface.

Abstract: Two types of in-grown stacking faults in 4H-SiC epitaxial layers (SFs) were investigated using a new photoluminescence (PL) topographic imaging system, macro/micro PL mapping system, TEM and molten KOH etch pit observation. Shockley type SFs (SSFs) of 3C and 8H inclusion were identified as two different types of triangular PL emission patterns with corner angle of 60° and 30° spreading to the <11-20> down step direction. The peak wavelengths are 423nm and 465nm, respectively. The 60° triangular SSFs are 3C inclusion related with threading edge dislocations. The 30° triangular SSFs are 8H inclusions related with basal plane dislocations. Such SFs are caused by dislocation- related disturbance of the step flow growth resulting in insertion of new cubic sites in between the 4H hexagonal turns. The substrate surface roughness at the early stage of the epitaxial growth and the growth rate may correlate with the might be deeply related in the SFs formation of SFmight be deeply related in the SFs.

Abstract: In this paper we present results on the growth of low-doped thick epitaxial layers on 4° off-oriented 4H-SiC using a commercially available hot-wall multi-wafer CVD system. For the first time we show results of a low-doped full-loaded 73” run on 4° off-oriented substrates with a layer thickness of more than 70 µm. The target doping concentration of 1.2×1015 cm-3 is suitable for blocking voltages > 6 kV. Results on doping, thickness and wafer-to-wafer homogeneities are shown. The surface quality of the grown layers was characterized by AFM. The density of different types of dislocations was determined by Defect Selective Etching.

Abstract: We investigated the expansion of single Shockley stacking faults (SSFs) in a 4H-SiC epitaxial layer under high-intensity scanning laser beam during room temperature photoluminescence mapping, which is similar to the degradation of bipolar pin diodes during forward current injection. In an epitaxial layer on an 8 off-axis (0001) substrate, the SSF-related intensity patterns induced by scanning high-intensity laser beam were classified into two types. The first one was a triangular pattern and the second a pattern which expanded in accordance with the motion of the scanning laser beam. The origins of the SSFs responsible for both patterns are presumably due to the preexisting basal plane dislocations and the dislocation-loops on the basal plane in the epitaxial layer, respectively. On the other hand, most of the SSF-expansion in on-axis (11 2 0) epitaxial layers were similar to the second type in the (0001) epitaxial layer. We, therefore, suggest that the dislocation-loops, which were located close to the surface, were dominant nucleation-sites of the SSFs in the (11 2 0) epitaxial layers.

Abstract: In this paper, we present results of epitaxial layer deposition for production needs using our hot-wall CVD multi-wafer system VP2000HW from Epigress with a capability of processing 7×3” or 6×100mm wafers per run in a new 100mm setup. Intra-wafer and wafer-to-wafer homogeneities of doping and thickness for full-loaded 6×100mm and 7×3” runs will be shown. Results on Schottky Barrier Diodes (SBD) processed in the multi-wafer system will be given. Furthermore, we show results for n- and p-type SiC homoepitaxial growth on 3”, 4° off-oriented substrates using a single-wafer hot-wall reactor VP508GFR from Epigress for the development of PiN-diodes with blocking voltages above 6.5 kV. Characteristics of n- and p-type epilayers and doping memory effects are discussed. 6.5 kV PiN-diodes were fabricated and electrically characterized. Results on reverse blocking behaviour, forward characteristics and drift stability will be presented.