Effect of RF Plasma on Silicon Nitride Deposition from SiF 4 /NH 3 Gas Mixtures in a Hot Wall Reactor
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EFFECT OF RF PLASMA ON SILICON NITRIDE DEPOSITION FROM SiF4/NH 3 GAS MIXTURES IN A HOT WALL REACTOR
C.GOMEZ-ALEIXANDRE,O.SANCHEZ AND J.M.ALBELLA Instituto Ciencia de Materiales, CSIC, Universidad Aut6noma,C12. Cantoblanco, 28049 Madrid.Spain ABSTRACT Si3N4 films have been deposited on silicon substrates at high temperatures (800-l0000 C) in a plasma CVD hot wall reactor using SiF4 and NH3 as primary reactant gases. In this range ofI temperatures the activation energy is 35.9 Kcal mol grad . The effect of an RF plasma induced either in the up or in the down stream configuration has been evaluated. The results show that in the 200-400 w range the reaction rate increases linearly with the RF power. The addition of hydrogen to the above gas mixture also produces an enhancement of the deposition reaction, probably as a consequence of the inhibition of the etching effect of the fluorine atoms on the Si3N4 deposited layers. INTRODUCTION silicon nitride obtained by chemical vapor deposition (CVD) techniques has been extensively investigated for different applications, including microelectronic devices and ceramic hard coatings. The gases used as silicon precursors are generally silane (SiH4), dichlorosilane (SiCI2H2), silicon tetrachloride (SiC14) or silicon tetrafluoride (SiF4). Among them, silane is the most widely used although it is known that in this case the films may incorporate large amounts of hydrogen during deposition [1,7]. The -SiH radicals included in this type of films may act as charge traps, thus producing a great instability in the electrical characteristics.From the ceramic point of view, the presence of hydrogen in the films may produce also harmful effects when the material is cycled to very high temperatures. In order to circumvent these problems, several attempts have been made using a fluorine source in the reactant gases [3]. The fluorine atoms are able to substitute the hydrogen atoms in the films, resulting -in Si-F bonds with much greater stability (128.4 Kcal mol compared to 70.4 Kcal mol-I ). For these reasons we have investigated alternative routes for obtaining silicon nitride films by CVD methods. Although some authors have obtained pyrolytic silicon nitride by CVD starting from SiF4 and NH3 gas mixtures [4,5,6] the reaction is still not well understood. In this paper we have followed this route, i.e. the reaction of SiF4+ NH3 in a hot wall reactor heated at high temperatures (800-1000" C). In this range of temperature, the reaction produces very pure films,i.e. practically hydrogen-free. The effect of an RF plasma, as well as the addition of hydrogen to the reactant
Mat. Res. Soc. Symp. Proc. Vol. 190. @1991 Materials Research Society
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EXPERIMENTAL Si3N4 films were deposited onto (111) p-type silicon substrates by the CVD technique using a tubular hot-wall reactor. The reactor consisted in a quartz tube of about 100 cm long and 6cm diameter heated by an external furnace up to 10000
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