Papers by Author: Jacques Dazord

Abstract: Starting from 3C-SiC(111) layers grown by Vapour-Liquid-Solid mechanism, homoepitaxial growth by Chemical Vapour Deposition was carried out on top of these seeds. The effect of the growth temperature and of the C/Si ratio in the gas phase was investigated on the surface morphology, the roughness and the defect density. It was found that the initial highly step-bunched surface of the VLS seeds could be greatly smoothen using appropriate conditions. These conditions were also found to reduce significantly the defect size and/or density at the surface.

Abstract: Like on 6H-SiC substrates, 3C-SiC islands precipitation was found to be the initial stage of the VLS growth of 3C-SiC layers on 4H-SiC surfaces. This precipitation happens between 1100 and 1200°C with a heating rate of 2.8°C.s-1, without addition of propane. The islands size increases in a similar manner whether the final temperature increases (for a given heating rate) or the heating rate decreases (for a given final temperature). This enlargement can give rise to a complete cubic layer for the highest temperatures or the slowest heating rates. It is suggested that the carbon atoms involved in the enlargement process (after the nucleation) come from the graphite crucible.

Abstract: The formation of dots by CVD in the hetero-system SiC-Si was studied in the two possible ways : Si dots on SiC substrate and SiC dots on Si substrate. The substrates underwent special surface treatment to reveal a network of parallel steps before deposition of the dots. In the Si on SiC case, the dots density on the 8°off 4H-SiC substrate varied in the range 107 – 7x108 cm-2 and mainly depends on the SiH4 flux and the deposition time. The Si dots are in majority aligned along the step edges of the substrate. In the other hetero-system, only propane was introduced in the reactor to performed a localised carbonisation of the Si(111) 1.5°off substrate. The SiC dots obtained at 1200°C have similar density the Si ones but with smaller size.

Abstract: We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS) mechanism on Si face 6H-SiC substrates, on-axis and 3.5° off. The Si-Ge melts, which Si content was varied from 10 to 50 at%, were fed by 3 sccm of propane. The growth temperature was varied from 1200 to 1600°C. It was found that 3C-SiC layers (either twinned or twinned free) form at low temperature while homoepitaxy is achieved at high temperature. The proposed growth mechanism involves the initial formation of 3C islands during the heating ramp (below 1200°C) and the dissolution of these islands when temperature increases. Geometrical aspects, such as the step density at the surface and the vertical component of the growth, are also considered to explain the difference observed between the on and off axis substrates.

Abstract: 6H and 4H–SiC epilayers were Al-implanted at room temperature with multiple energies (ranging from 25 to 300 keV) in order to form p-type layers with an Al plateau concentration of 4.5×1019 cm-3 and 9×1019 cm-3. Post-implantation annealing were performed at 1700 or 1800 °C up to 30 min in Ar ambient. During this process, some samples were encapsulated with a graphite (C) cap obtained by thermal conversion of a spin-coated AZ5214E photoresist. From Atomic Force Microscope measurements, the roughness is found to increase drastically with annealing temperature for unprotected samples while the C capped samples show a preservation of their surface states even for the highest annealing temperature. After 1800°C/30 min annealing, the RMS roughness is 0.46 nm for the lower fluence implanted samples, slightly higher than for unimplanted samples (0.31 nm). Secondary Ion Mass Spectroscopy measurements confirm that the C cap was totally removed from the SiC surface. The total Al-implanted fluence is preserved during postimplantation annealing. A redistribution of the Al dopants is observed at the surface which might be attributed to Si vacancy-enhanced diffusion. An accumulation peak is also observed after annealing at 0.29 9m, depth corresponding to the amorphous/crystalline interface that was determined on the as-implanted samples by Rutherford Backscattering Spectroscopy in channeling mode. The redistribution of the dopants has an impact on their electrical activation. A lower sheet resistance (Rsh= 8 k
) is obtained for samples annealed without capping than for samples annealed with C capping (Rsh= 15 k
).