Materials Science Forum Vols. 600-603

Abstract: In order to demonstrate the formation of 3C-SiC film on Si (111) at low substrate temperature, the effects of C3H8 on the crystallinity of the films on Si (111) have been investigated by changing the flow rate of C3H8 at the substrate temperature of 950 °C. Nearly single-crystalline 3C-SiC film grew under the ratio of the flow rate of C3H8 to the flow rate of SiH4 (C/Si) of 2 - 2.5. From these results, it is suggested that C/Si shifts into higher with decreasing the substrate temperature. The crystallinity has been investigated by a reflection electron diffraction (RED) and a X-ray diffraction (XRD). The thickness and the surface roughness of the films were investigated by an ellipsometric measurement.

Abstract: One of the main challenging tasks in the prospective technology is the buckling suppression of the 3C-SiC film due to the melting and solidification process and the stress relief as a consequence of the short time Si melting during the Flash Lamp Annealing. To overcome this effect and to stabilize a flat surface morphology an alternative i-FlASiC process was developed. This work refers to the influence of the layer stack modifications by doping and meltstop formation by ion implantation on the wafer buckling. The samples were studied by transmission electron microscopy, high resolution x-ray diffraction and infrared ellipsometry. The aim was to optimize the doping and flash lamp annealing conditions in relation to the i-FLASiC layer stack modification.

Abstract: The aim of this work is to improve the heteroepitaxial growth process of 3C-SiC on Si substrates using Trichlorosilane (SiHCl3) as the silicon growth precursor. With this precursor it has been shown that it is possible to simultaneously increase the growth rate of the process and avoid the nucleation of silicon droplets in the gas phase. Growth experiments were conducted on three (3) Si substrate orientations in order to assess the impact of the Si substrate on the resulting 3C-SiC film. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis show the important role of the substrate orientation for the growth process. The different orientation of the substrate modifies the morphology of the 3C-SiC crystalline structure, mostly by changing the density of micro-twins and stacking faults inside the film.

Abstract: The carbonization conditions (acetylene pressure and heating rate) to obtain close carbonized layer covered on Si(001) substrate without thermal pits is studied. Subsequent hetero-epitaxial 3C-SiC with smooth surface have been grown by low-pressure CVD. Single-crystalline carbonized layers could be grown at 1050°C by using suitable carbonization processes. The surfaces of Si were covered with single-crystalline 3C-SiC layers at an early stage of carbonization, preventing out-diffusion of Si atoms from Si substrates. 3C-SiC epi-film have RMS = 0.4nm but no single domain. The protrusion density of the film was an order of 1000 cm-2.

Abstract: Using AlN as a buffer layer, 3C-SiC film has been grown on Si substrate by low pressure chemical vapor deposition (LPCVD). Firstly growth of AlN thin films on Si substrates under varied V/III ratios at 1100oC was investigated and the (002) preferred orientational growth with good crystallinity was obtained at the V/III ratio of 10000. Annealing at 1300oC indicated the surface morphology and crystallinity stability of AlN film. Secondly the 3C-SiC film was grown on Si substrate with AlN buffer layer. Compared to that without AlN buffer layer, the crystal quality of the 3C-SiC film was improved on the AlN/Si substrate, characterized by X-ray diffraction (XRD) and Raman measurements.

Abstract: This paper describes the characteristics of poly (Polycrystalline) 3C-SiC grown on SiO2 and AlN buffers, respectively. The crystallinity and the bonding structure of poly 3C-SiC grown on each buffer layer were investigated according to various growth temperatures. The crystalline quality of poly 3C-SiC was improved from resulting in decrease of FWHM (Full width half maximum) of XRD and FT-IR by increasing the growth temperature. The minimum growth temperature of poly 3C-SiC was 1100 °C. The surface chemical composition and the electron mobility of poly 3C-SiC grown on each buffer layer were investigated by XPS and Hall Effect. The chemical compositions of surface of poly 3C-SiC grown on SiO2 and AlN were not different. However, their electron mobilities were 7.65 ㎝2/V.s and 14.8 ㎝2/V.s, respectively. Therefore, since the electron mobility of 3C-SiC/AlN was two times higher than that of 3C-SiC/SiO2, AlN is a suitable material, as buffer layer, for SiC growth with excellent crystalline quality.

Abstract: A review is presented of the current understanding of the dislocation configurations observed in PVT-grown 4H- and 6H-SiC boules and CVD-grown 4H-SiC homoepitaxial layers. In both PVT-grown boules and CVD-grown epilayers, dislocation configurations are classified according to whether they are growth dislocations, i.e., formed during growth via the replication of dislocations which thread the moving crystal growth front, or result from deformation processes (under either mechanical or electrical stress) immediately following growth, during post growth cooling, i.e., behind the crystal growth front or during device operation. Possible formation mechanisms of growth defects in the PVT grown boules, such as axial screw dislocations and threading edge dislocation walls are proposed. Similarly, possible origins of growth defect configurations in CVD-grown epilayers, such as Frank faults bounded by Frank partials, BPDs and TEDs, are also discussed. In a similar way, the origins of BPD configurations resulting from relaxation of thermal stresses during post-growth cooling of the PVT boules are discussed. Finally, the susceptibility of BPD configurations replicated into CVD grown epilayers from the substrate towards Recombination Enhanced Dislocation Glide (REDG) is discussed.

Abstract: Defect formation in 4H-SiC(0001) and (000-1) epitaxy is investigated by grazing incidence synchrotron reflection X-ray topography and transmission electron microscopy. Frank-type faults, which are terminated by four Frank partials with a 1/4[0001] type Burgers vector with the same sign on four different basal planes, are confirmed to be formed by conversion of a 1c threading edge dislocation (TSD) in the substrate as well as simultaneous generation of a 1c TSD during epitaxy. The collation between the topography appearance and the microscopic structure and the variety of Frank faults are shown. Formation of carrot defects and threading dislocation clusters are also investigated.

Abstract: The nucleation and expansion of Shockley stacking faults (SSFs) in 4H-SiC is known to induce an increase in the forward voltage drop (Vf) of bipolar devices such as pin diodes. However, recent annealing experiments have shown that SSFs can not only expand, but that low temperature annealing (210-7000C) induces a contraction of the SSFs that is coupled with a full and repeatable recovery of the Vf drift. Here we report that following extended periods of forward bias operation that the Vf drift of 10kV 4H-SiC pin diodes saturates, with the saturation Vf drift dropping with increasing stressing temperature. Upon reaching saturation, increases in temperature during forward bias operation at the same injection conditions also lead to a partial recovery of the Vf drift. Furthermore, the magnitude of this current-induced recovery is dependent upon the injection current, as reductions in the current cause a slower, but larger overall Vf drift recovery. All of these results clearly indicate that the current driving force models for SSF expansion are either incomplete or incorrect and that further efforts are required for a more complete understanding of SSF dynamics to be obtained.

Abstract: In EPR (electron paramagnetic resonance) identification of point defects, hyperfine (HF) interaction is decisive information not only for chemical identity but also for the local geometry and the electronic state. In some intrinsic defects in SiC, the wave function of the unpaired electron extends quite unevenly among major atoms comprising the defects. In such a case, the determination of the number of equivalent atoms and the chemical identity (Si or C) of those atoms even with weak HF splitting are useful to compare with HF parameters obtained theoretically. For vacancy-related defects of relatively deep levels, the sum of the spin densities on the nearest-neighbor shell is found to be 60-68%.