Papers by Author: Yves Monteil

Abstract: Al-Si patterns were formed on n-type 4H-SiC substrate by a photolithographic process including wet Al etching and Si/SiC reactive ion etching (RIE) process. RF 1000°C annealing under C3H8 flow was performed to obtain p+ SiC layers by a Vapour-Liquid-Solid (VLS) process. This method enables to grow layers with different width (up to 800 µm) and various shapes. Nevertheless the remaining Al-based droplets on the largest patterns are indicators of crack defects, going through the p+ layer down to the substrate. SIMS analyses have shown an Al profile with high doping concentration near the surface, high N compensation and Si/C stoechiometry variation between the substrate and the VLS layer. The hydrogen profile follows the Al profile in the VLS layer with an overshoot at the VLS/substrate interface. I-V measurements performed directly on the semiconductor layers have confirmed the formed p-n junction and allowed to measure a sheet resistance of 5.5 kW/ı

Abstract: The effect of the temperature at which the carbon source is introduced in the reactor on the early stages of the carbonization process is analyzed here. Three samples heated up to 1150°C with propane introduction temperatures (Tintro) of 725, 1030 and 1100°C are analyzed by transmission electron microscopy and attenuated total reflectance. The size of the SiC nuclei increases with Tintro. There is also an effect on the strain of the resulting carbonization layer. The electron diffraction pattern of the sample with the highest Tintro shows a fully relaxed 3C-SiC layer, while no evidence of SiC relaxation is present in low Tintro samples where the SiC islands seems to be pseudomorphic.

Abstract: An approach for the defect density reduction in 3C-SiC epitaxially grown on Si is to improve the quality of the carbonized layer during the early stage of growth. For this reason the conventional carbonization process was replaced by a slower and nearer equilibrium carbonization method. Carbon is introduced by implantation into oxide of an oxidized Si substrate, near the SiO2/Si interface, and then it is transferred to the Si surface by annealing. Good quality 3C-SiC grains are formed embedded into the Si substrate, which are absolutely flat at the SiO2/Si interface. Another advantage of the new carbonization process is the elimination of the cavities due to the suppression of Si out-diffusion.

Abstract: The evolution of defects versus thickness has been investigated in three different freestanding 3C-SiC samples, using TEM (Transmission Electron Microscopy) and LTPL (Low Temperature Photo-Luminescence) spectroscopy. In all samples, the stacking fault density reduces rapidly within the first 20 µm of the growth. Then it remains constant, at about 5x103 cm-1 up to the end. This behavior is attributed to the easy generation of stacking faults, even under a very low thermal stress, as in-situ experiments reveal. On the opposite the elimination of inversion domains, by bending boundaries during the growth, is found to be sample dependant. This is in good agreement with LTPL results.

Abstract: The so-called VLS (Vapour-Liquid-Solid) mechanism in an Al-Si melt has recently demonstrated the capability to grow at low temperature single crystalline 4H-SiC layers, with a high Al content. Using the newly developed VLS technique, we have deposited several 4H-SiC layers and determined the incorporated Al level by SIMS (Secondary Ion Mass Spectroscopy). Depending on the sample, we have found that the SIMS doping level ranges from 5x1019 to 1x1021 at.cm-3. This last value is the highest one reported so far for in-situ doped SiC:Al. From TEM (Transmission Electron Microscopy) analyses we show that the layers are single crystals, with a high density of defects located only at the lower interface and no foreign phase inclusion. These results compare well with the ones obtained in previous works using alternative doping techniques, like ion implantation, chemical vapour deposition or sublimation. It thus suggests that Al solubility limit in SiC is rather temperature independent.

Abstract: One of the problems with Si(001)/3C-SiC templates is that they involve highly defective interfaces due to the presence of misfit dislocations, voids and planar defects that degrade the SiC layer quality. A way to accommodate the high lattice mismatch between these materials and reduce the voids density is to carbonize the Si substrate before the epitaxial growth. In this contribution an alternative way to reduce planar defects density is presented by analyzing the relationship between planar defects and voids. Planar view and cross section transmission electron microscopy micrographs show a diminution of planar defects in the regions surrounding the voids. Due to the lower elastic energy over the voids and/or to a lateral growth in these regions, the generation of planar defects is partially deactivated, improving locally the crystalline quality of the SiC layer. The introduction of such cavities can be thus seen as a new parameter of Si/SiC templates design.

Abstract: We report on the study of the p-type doping of 4H-SiC material using HexaMethylDiSilane/TriMethylAluminium/Propane (HMDS/TMA/P) system in place of the usual Silane/TriMethylAluminium/Propane (S/TMA/P) precursors. The influence of growth parameters such as TMA flow, growth rate or C/Si ratio is investigated. The aluminium incorporation level is deduced from both by C(V) (mercury probe) and SIMS measurements. The presence of aluminium in the layers is confirmed by non-destructive optical micro-Raman experiments. Good quality p-type, aluminium doped 4H-SiC layers can be grown using HMDS/TMA/P system. The amount of aluminium in the layers can be controlled by choosing the growth conditions and an aluminium concentration as high as 2x1019 at.cm-3 has been reached.Finally, comparing the two HMDS/TMA/P and S/TMA/P systems, no difference in aluminium incorporation has been found.

Abstract: We report an experimental investigation of the residual (n-type) and intentional (p-type) doping level of <11-20> epitaxial layers grown on a-cut 4H-SiC substrates. Using SIMS, C(V) measurements, low temperature photoluminescence and Hall effect investigations, we show that nitrogen incorporates 3 times more than usually found for <0001> surfaces. Conversely, aluminum incorporates 8 times less. Altogether, this is in excellent agreement with previous results from stepcontrolled epitaxy.

Abstract: Thin 3C-SiC films epitaxially grown on Si-substrate are substantially improved by the FLASIC process, which involves irradiation with flash lamps with pulse duration of 20ms. The disadvantages of the standard FLASIC process are the undulations introduced in the SiC film due to melting of the Si-substrate and the Si mass transport near the SiC/Si interface during the flash. An improved structure was realised in order to minimize the undulations of the SiC, improving also the quality of the film. This structure involves the deposition of a silicon overlayer (SOL) on the initial SiC layer, followed by an additional SiC capping layer acting as a source for SiC transfer by liquid phase epitaxy to the lower SiC layer. Significant mass SiC transport from the upper to the lower SiC layer through the SOL occurs during the flash. The new structure is characterized as inverse - FLASiC. The structural characteristics of the new structure were studied by transmission electron microscopy and atomic force microscopy.