Raghunandan Bhakta

Synthesis of nano-scale TiO2 particles by a nonhydrolytic approach

We describe a convenient nonhydrolytic approach to the preparation of uniform, quantum confined TiO2 nanocrystals using an intramolecularly adduct stabilised alkoxide precursor. In contrast to established aqueous sol–gel techniques the processing in hydrocarbon solvents at high temperatures allows access to very small free standing crystallites, and opens up new possibilities for control over size distribution, surface chemistry and particle agglomeration.

MOCVD of TiO2 thin films and studies on the nature of molecular mechanisms involved in the decomposition of [Ti(OPri)2(tbaoac)2]

A tailored precursor namely bis(isopropoxy)bis(tert-butylacetoacetato)titanium [Ti(OPri)2(tbaoac)2] was developed which showed good promise for depositing TiO2 thin films at reduced substrate temperatures compared to [Ti(OPri)2(thd)2]. Uniform films with high growth rates (∼10 nm min−1) and lower surface roughness (<2 nm) were obtained on SiOx/Si and Pt/ZrOx/SiOx/Si substrates. Electrical properties of the films on Si substrates were studied and lowest equivalent oxide thickness (EOT) was around 2 nm and anatase phase had a dielectric constant around 40. A study on the thermolysis behaviour of [Ti(OPri)2(tbaoac)2] was carried out using matrix-isolation FTIR spectroscopy, to understand the mechanistic details of its thermal decomposition. It was found that the decomposition takes place by the formation of ketene intermediates.

Thin Films of HfO2 for High-k Gate Oxide Applications from Engineered Alkoxide- and Amide-Based MOCVD Precursors

HfO 2 thin films with thickness between 2 and 20 nm were grown by liquid injection metallorganic chemical vapor deposition, LI-MOCVD, on SiO x /Si(100) substrates. Different mononuclear precursors ([Hf(OPr i ) 2 (tbaoac) 2 ], [Hf(NEt 2 ) 2 (guanid) 2 ], and [Hf(OBu t ) 2 (dmae) 2 ] were tested in combination with different solvents. Growth rate, surface morphology, crystal structure, and crystal density of the as-deposited films were analyzed as a function of deposition temperature. The influence of postdeposition annealing on the densification and crystallization was studied. Correlation of the structural properties with the electrical properties of metal insulator semiconductor capacitors with Pt top electrodes is discussed. Fully silicided metal gate stacks are additionally discussed for selected samples.

Mixed amide–malonate compound of hafnium as a novel monomeric precursor for MOCVD of HfO2 thin films

The concept of introducing malonates as chelating ligands in combination with metal amides has yielded a new class of compounds which enable growth of HfO2 thin films at low deposition temperatures by liquid injection metalorganic chemical vapour deposition.

Precursor chemistry for TiO2: titanium complexes with a mixed nitrogen/oxygen ligand sphere

Novel mixed amido-malonato complexes of titanium are reported. The complexes were synthesized by partially replacing the amido groups from the complexes [Ti(NMe2)4] and [Ti(NEt2)4] via Brønstedt acid/base reactions, using the malonate-ligands di-isopropylmalonate (Hdpml) and di-tert-butylmalonate (Hdbml). Four representative complexes were synthesized and fully characterised by 1H NMR, 13C NMR, CHN analysis and mass spectrometry. The crystal structures of the six-coordinated complexes [Ti(NMe2)2(dbml)2] (3) and [Ti(NEt2)2(dbml)2] (4) are presented and discussed. The complexes are solids and the chemical and thermal characteristics of the complexes strongly depend on the substitution at the malonate ligand. While dpml containing complexes show a promising behaviour for classical MOCVD, dbml containing complexes seem to be more suitable for liquid injection-metal-organic chemical vapour deposition (LI-MOCVD). Based on its thermal characteristics, the most promising complex for thermal CVD, [Ti(NEt2)2(dpml)2] (2) was selected for preliminary MOCVD experiments, which indicate a good suitability for the deposition of TiO2 thin films.

High-k dielectric materials by metalorganic chemical vapor deposition : Growth and characterization

Two novel mononuclear mixed alkoxide compounds of Ti and Zr, [Ti(OPr i )2(tbaoac)2] and [Zr(OPr i )2(tbaoac)2], were synthesised and characterised. These complexes are highly soluble and possess superior thermal properties showing promising characteristics as precursors for MOCVD of oxide thin films. Results are presented for thin films, which were deposited in a liquid injection metal-organic chemical vapour deposition production tool. Special emphasis is given to the properties of ZrO2 thin films within MIS structures as proposed for gate oxide applications and to the compatibility of the new Ti precursor with a standard Sr(thd)2 precursor for low temperature deposition of SrTiO3.

Bis(2-butyl-N,N'-diisopropylamidinato)dichlorohafnium(IV).

The title compound, [Hf(C11H23N2)2Cl(2)], is a monomeric hafnium(IV) complex containing two bidentate amidinate ligands and two cis Cl atoms. The crystals are triclinic (space group P-1) and there is one independent six-coordinate monomer with a highly distorted octahedral geometry in the asymmetric unit. The reported structure is the first hafnium-amidinate complex to be characterized successfully by single-crystal X-ray diffraction.