PREDEPOSITION CHEMISTRY UNDERLYING THE FORMATION OF GERMANIUM FILMS BY CVD OF TETRAVINYLGERMANE

The predeposition chemistry involved in the formation of elemental ger manium films by MOCVD using tetravinylgermane as the precursor has bee n investigated under both static and dynamic conditions. Decomposition of the neat germane under static conditions has been studied using Fo urier transform infrared spectroscopy in the temperature range 613-683 K, and is found to be second order with respect to loss of Ge(CH=CH2) (4). Second-order rate constants vary from 30.4 l mol(-1) at 613 K to 128 l mol(-1) at 683 K, from which Arrhenius analysis yields a value o f the activation energy of 186.5 kJ mol(-1). Observed products are eth ene, ethyne, and butadiene. These data are interpreted in terms of a g as-phase free-radical chain mechanism involving addition of vinyl radi cals at the a-carbon of a vinyl group of Ge(CH=CH2)(4) followed by eli mination of butadiene, and subsequent loss of vinyl radicals from tran sient Ge(CH=CH2)(n) (n = 1-3) species. Under dynamic flow conditions u sing helium as the carrier gas, decomposition of TVG does not commence until ca. 670 K and conversions of >90% are not achieved until ca. 97 0 K. Under these conditions decomposition is probably an unimolecular process involving successive loss of vinyl radicals from germanium. Et hene, ethyne, and butadiene are again formed together with small amoun ts of other hydrocarbons. When hydrogen is employed as the carrier gas , the decomposition is more facile and ethene is by far the major hydr ocarbon product. The behavior of triethylvinylgermane under flow condi tions is similar.