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 hori zontal hot-walled reactor in the absence of carrier gases in vacuo. Th e metal concentrations of the thin films were found to depend on the s ubstrate 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 30 0-350 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 wi th the precursor compound (CO)(4)Co-GaEt(2)(NMe(3)) (5a). The grown fi lms 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 AE S). The thin-film resistivities were around 150(+/-30) mu Omega cm in these cases. At substrate temperatures below 300 degrees C, alkyl-tran sfer reactions are important, which are likely to be surface driven. T hese processes generate volatile and thermally stable gallium alkyls G aR(3), which pass through the reaction zone. This mechanism explains t he gallium deficiency of the Co1Ga1-x films grown at low substrate tem peratures. 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 (qu artz, GaAs, silicon) were structurally characterized by X-ray diffract ion showing the cubic beta-CoGa as the only detectable crystalline pha se in the case of GaAs(100) and quartz substrates (ca. 300 degrees C s ubstrate temperature). At higher deposition temperatures (350-380 degr ees C for GaAs and 400-450 degrees C for silicon) interfacial solid-st ate reactions occurred to give various other phases such as alpha-Co1- deltaGadelta, beta-CoGa, CoGa3, CoAs, and Co2Si.