Synthesis of SiC on Si by Seeded Supersonic Beams of Fullerenes
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rresponding author: tel.: ++43 0461 314 251, e-mail: [email protected] 257 Mat. Res. Soc. Symp. Proc. Vol. 585 © 2000 Materials Research Society
Via seeding them in a supersonic beam the reactant species can be well controlled in energy and flux distributions [ 12]. The nature of the expansion coupled with differential pumping allows generation of highly collimated intense beams which are uniquely suitable for studying the effects of the beam energy and the incidence angle on the growth. In the synthesis of Si and GaN it has already been shown that the probability of dissociative adsorption of precursors is very sensitive to these parameters [9,13,14]. We therefore use a supersonic seeded beam of C60 that we previously developed [15] to explore moderate (below the thermal reaction threshold of 850900'C) substrate temperature for the synthesis of SiC and assess the control on structure and morphology that can be achieved. EXPERIMENTAL The experimental
apparatus consists essentially of three separately pumped vacuum
chambers. An 8 litres stainless-steel-chamber could simultaneously house three different sources,
so that co-deposition experiments can also be carried out, involving different species such as fullerenes, organic molecules [16] and metals. The first two of them are for hyperthermal supersonic beams (HSB). The C60 supersonic source allows the seeding in different gases and is resistively heated by a shielded tantalum foil. The source calibration in energy as a function of seeding buffer gas pressure (Pseed) and temperature (T.ource) has been presented elsewhere[15]. Among the various buffer gases tested (H, He, Ar, Xe, SF 6, etc.) we choose He for all the experiments reported here. The third source is a Pulsed Arc Gas Aggregation Cluster Source (PAGACS) [12] uniquely suitable for the synthesis of carbon and metal clusters. The beam after the expansion is skimmed by a sharp edged conical collimator of 0.3 mm in diameter and enters the UHV deposition chamber impinging on an area of 10mm in diameter on the substrate. Here a five degrees of freedom manipulator and a fast load lock entry are used to handle the samples. The set-up is equipped with different electron spectroscopies for in-situ characterisation (AES, SEM, LEED, UPS, XPS). A VG 100-mm mean radius hemispherical analyser (CLAM2) with 1 eV resolution collects the electron spectra. Supersonic beams, being highly directional, offer also the advantage that they are more compatible with delicate in-situ characterisation methods. The substrates used (Si(1 11), 0.0120 0-cm of resistivity) etched and oxidised by the Shiraki method [ 17] are rinsed in deionized water and then inserted, through the separately pumped loadlock chamber, into the deposition chamber at a base pressure lower than 1.10-0 Torr. The samples were then annealed with several thermal cycles and "conditioned" to reach 600 'C at a pressure lower than 5. 10-l Torr. The cleaning procedure ends up with a final annealing at 785°C for 15 min at a background pressure lower than 5-10-9 Torr.
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