[Rh(η-C3H5)(CO)2] has high volatility; it decomposes to Rh at moderate temperatures and, in the presence of H2, and gives Rh films having high purity and adhering well to a Si substrate.
[Rh(η-C3H5)(CO)2] was studied by the thermolysis reactions (in a crude approximation of the CVD conditions): the
precursor was heated to 140°C in a vessel sealed under vacuum; the gaseous products of thermolysis were analyzed by GC, MS, or GC/MS whereas the residual Rh complexes present after partial pyrolysis were extracted and examined by MS, IR, and NMR
techniques. It was found by GC/MS that pyrolysis of [Rh(C3H5)(CO)2] produces 1,5-hexadiene and propene as main products.[i]
[i] R. Kumar, R.J. Puddephatt, Canad. J. Chem, 1991 , « New precursors for organometallic chemical vapor deposition of rhodium », http://www.nrcresearchpress.com/doi/abs/10.1139/v91-017
Rhodium allyl bis(carbonyl) Rh(allyl)(CO)2 complex is less investigated as precursor for the deposition of Rh layers.
Rh films containing about 6 mass% of C and absence of any O impurity were produced by thermal CVD of this complex at 180°C in H2 on Si substrates, with growth rates ~5-10 nm/s. In the absence of H2, the carbon content in the Rh layers significantly increased (up to 40 mass% C), as well 12% O contamination was found. Addition of only 10-3 Torr H2 was sufficient to reduce the C, O impurities in the deposited Rh layers.
Addition of H2 did not reduce minimal CVD temperature for the [Rh(η-C3H5)(CO)2] precursor (same as observed for [RhCp(CO)2] precursor, but opposite to the [RhCp(cod)] and [Rh(η-allyl)3], for which the rusiction in required CVD was observed upon addition H2). Thus, H2 effect on the Rh layer purity and in the required CVD temperature are independent.
Deposited Rh layers adhered well to the Si substrates.(scotch tape/scratch tests). The resistivity of Rh samples grown using H2 was ~28 µΩ·cm, whereas layers grown without H2 had ~60 µΩ·cm (for comparison , bulk Rh has resistivity 4.51 Ω·cm at 20°C). Thus, lower conductivity is is partially caused by the residual C in the Rh films grown by CVD. Rh films were smooth, composed of crystallites with dimensions of ca. 200 Å across, according to the scanning electron microscopy (SEM).
CVD experiments were performed in the vertical CVD reactor; Si substrates were heated to the growth temperature (130-270°C), there was either no carrier gas, or a small H2 flow was passed over the Rh(allyl)(CO)2 precursor. If higher growth rate was
needed, the precursor was warmed (to max 50°C vaporisation temperature). Rh-contaning coatings up to 2 µm in thickness were obtained in 0.5-1 h. The temperatures 130, 180, 230, and 270°C were checked for the growth; the minimum CVD temperature
was determined when most rhodium precursor decomposed to give growth of Rh metal rather than simply subliming in the equipment. Rh layers grown at 270°C were studied analytically [i]
[i] R. Kumar, R.J. Puddephatt, Canad. J. Chem, 1991 , « New precursors for organometallic chemical vapor deposition of rhodium », http://www.nrcresearchpress.com/doi/abs/10.1139/v91-017