Transition metal CVD precursors

Thus, for every transition metal CVD precursor, its vapour pressure, its thermal behaviour, which means its reactivity at a given temperature with regard to the substrate and/or to any additional reagent, and its toxicity should be carefully examined. The ultimate objective is for the chemist to finely tune the rates of nucleation and growth of the deposit, for any given apphcation. 

The atomic structure of the transition metals is such that the J shell is only partly filled. The first transition series (3d) comprises Sc, Ti, V, Cr, Mn, Fe, Co, and Ni the second (4d), Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag the third (5d), Hf, Ta, W, Re, Os, Ir, Pt, and Au. Carbonyl derivatives of at least one type are found for all these metals. Although only a few are presently used in CVD, many are being investigated as they constitute an interesting and potentially valuable group of precursor materials. 

Transition metal-silicon compounds are thought to be precursors in metal silicide CVD processes. The main advantage compared with common precursors is the defined silicon to metal ratio. 

The wide use of p-block and early transition metal chalcogenide materials for electronics applications (semiconductors, semi-metals, battery materials, etc.) has resulted in a large amount of work concerned with CVD using mixtures of metal halides and chalcogenoethers as dual source precursors and preformed complexes as single sources.166... 

CVD is an established method for the synthesis of CNTs [59, 60]. Supported transition metals that catalyze the growth of CNTs, such as iron, nickel, or cobalt, are situated in a tubular reactor, and CNTs are grown at elevated temperature on the surface of the catalyst particles by decomposition of a carbon-containing precursor. The catalyst particles have to be removed by chemical treatment /washing in order to obtain a metal-free final product. 

This chapter is intended to cover major aspects of the deposition of metals and metal oxides and the growth of nanosized materials from metal enolate precursors. Included are most types of materials which have been deposited by gas-phase processes, such as chemical vapor deposition (CVD) and atomic layer deposition(ALD), or liquid-phase processes, such as spin-coating, electrochemical deposition and sol-gel techniques. Mononuclear main group, transition metal and rare earth metal complexes with diverse /3-diketonate or /3-ketoiminate ligands were used mainly as metal enolate precursors. The controlled decomposition of these compounds lead to a high variety of metal and metal oxide materials such as dense or porous thin films and nanoparticles. Based on special properties (reactivity, transparency, conductivity, magnetism etc.) a large number of applications are mentioned and discussed. Where appropriate, similarities and difference in file decomposition mechanism that are common for certain precursors will be pointed out. 

The alkoxyalkyl-substituted /3-diketone ButCOCH2CO(CH2)3OMe (21), with an ethereal scorpion tail, has been synthesized in order to avoid polymerization by saturating all the possible coordination sites of transition-metal and heavier alkaline earth-metal ions.112 The crystallographically studied Cu2+ compound shows a five-coordinate metal environment, where the ethereal tail is bonded to the copper atom of another molecular unit through a weak intermolecular interaction. A new liquid monomeric Ba derivative has been successfully prepared this is a potential molecular precursor in CVD for HTSC mixed metal oxides.112 The... 

For the direct injection of the catalyst or one of its precursors, the choice of compounds is naturally limited to vaporizable substances. The respective transition metal carbonyls and metallocenes proved their worth here. They decompose upon heating in the CVD apparatus and release the elemental metal in the shape of small, catalytically active clusters. 

Transition metal carbonyl is important in laser chemistry as sources of metal atoms or as precursors for chemical vapor deposition (CVD) [104]. Ni(CO)4 shows a typical photofragmentation reaction initiated by the XeCl laser (308 nm, 4.03 eV), and the knowledge on the mechanism is valuable for the design and control of the laser-induced CVD. The SAC-Cl method was applied to the excitation spectrum and the potential energy curves relevant to the photofragmentation reaction [105]. 

---