Comparative study of the metal organic chemical vapor deposition of beta-CoGa thin films from dialkylgallium tetracarbonylcobaltate single-source precursors

The volatile heterodinuclear organometallic compounds L(CO)(3)Co-GaR(2)(Do) and L(CO)(3)Co-Ga[(CH2)(3)NR(2)(1)] (R) (R = H, CH3, C2H5, CH(2)(t)Bu, CH(2)SiMe(3); Do = THF, NMe(3), NC7H13; L = CO, PMe(3), PPh(3); R(1) = CH3; C2H5; 1-10 were studied as single molecule precursors for the deposition of binary Co/Ga alloy thin films by MOCVD using a horizontal hot-walled reactor in the absence of carrier gases in vacuo. The metal concentrations of the thin films were found to depend on the substrate temperature and the type of substituents at the gallium atom. Cobalt-rich films were typically deposited below 250 degrees C. The 1:1 ratio of the metals in the precursor compounds is retained above 300-350 degrees C. Typical growth rates were between 0.1 and 1 mu m h(-1) at similar to 1 Pa total pressure. The best results were obtained with the precursor compound (CO)(4)Co-GaEt(2)(NMe(3)) (5a). The grown films showed impurity levels of C, N, and O close to the detection limit of the used analytical methods (less than or equal to 0.5 at. % by AES). The thin-film resistivities were around 150(+/-30) mu Omega cm in these cases. At substrate temperatures below 300 degrees C, alkyl-transfer reactions are important, which are likely to be surface driven. These processes generate volatile and thermally stable gallium alkyls GaR(3), which pass through the reaction zone. This mechanism explains the gallium deficiency of the Co1Ga1-x films grown at low substrate temperatures. Other byproducts were mainly unsaturated hydrocarbons (e.g., ethene or H2C=CHCH(2)NMe(2)) and nonfragmented donor ligands Do (e.g., THF, NMe(3)). The films were routinely examined ex situ by SEM-EDX and AUGER electron spectroscopy. Films grown on various substrates (quartz, GaAs, silicon) were structurally characterized by X-ray diffraction showing the cubic beta-CoGa as the only detectable crystalline phase in the case of GaAs(100) and quartz substrates (ca. 300 degrees C substrate temperature). At higher deposition temperatures (350-380 degrees C for GaAs and 400-450 degrees C for silicon) interfacial solid-state reactions occurred to give various other phases such as alpha-Co1-deltaGadelta, beta-CoGa, CoGa3, CoAs, and Co2Si.