Noel Hoilien

Chemical vapour deposition of the oxides of titanium, zirconium and hafnium for use as high-k materials in microelectronic devices. A carbon-free precursor for the synthesis of hafnium dioxide

A brief survey of the precursors used for the chemical vapour deposition of the dioxides of titanium, zirconium and hafnium is presented. The review covers precursors used for the closely related process known as atomic layer chemical vapour deposition (ALCVD or ALD). Precursors delivered by standard carrier gas transport and by direct liquid injection (DLI) methods are included. The complexes fall into four classes based upon the ligands: halides, alkoxides, acetylacetonates (acac) and nitrates. Compounds bearing a mixture of ligand types have also found application in this area. The impact of the ligand on the microstructure of the metal oxide film is greatest at lower temperatures where the deposition rate is limited by the surface reactivity. The first use of anhydrous hafnium nitrate, Hf(NO3)4, to deposit films of hafnium oxide on silicon is reported. The films are characterized by Rutherford backscattering and X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. Copyright

Group IVB metal oxides high permittivity gate insulators deposited from anhydrous metal nitrates

The electrical performance of column IVB metal oxide thin films deposited from their respective anhydrous metal nitrate precursors show significant differences. Titanium dioxide has a high permittivity, but shows a large positive fixed charge and low inversion layer mobility. The amorphous interfacial layer is compositionally graded and contains a high concentration of Si-Ti bonds. In contrast, ZrO/sub 2/ and HfO/sub 2/ form well defined oxynitride interfacial layers and a good interface with silicon with much less fixed charge. The electron inversion layer mobility for an HfO/sub 2//SiO/sub x/N/sub y//Si stack appears comparable to that of a conventional SiO/sub 2//Si interface.

Low Temperature Chemical Vapor Deposition of ZrO2 on Si(100) Using Anhydrous Zirconium (IV) Nitrate

Anhydrous zirconium(IV) nitrate was used as a volatile, carbon-free precursor for the low pressure chemical vapor deposition of thin ZrO 2 films on silicon (100) substrates. Depositions were performed at substrate temperatures between 300 and 500°C at total reactor pressures between 0.25 and 1.1 Torr. During deposition the N 2 carrier gas (flow rates = 20 or 100 sccm) was diverted through the precursor vessel which was maintained between 80 and 95°C. Under these conditions typical growth rates reached 10.0 nm/min. The polycrystalline films were predominantly monoclinic ZrO 2 with compositions very near the ideal value. Cross-sectional transmission electron microscopy and medium energy ion scattering established that an interfacial layer of SiO 2 separates the silicon substrate from the ZrO 2 . Electrical measurements made on capacitors constructed of 58 nm thick films of ZrO 2 with a platinum top electrode suggest that charge trapping occurs in the Si/ZrO 2 interfacial region.

Amorphous Mixed TiO 2 and SiO 2 Films on Si(100) by Chemical Vapor Deposition

Amorphous thin films of composition Ti x Si 1-x O 2 have been grown by low pressure chemical vapor deposition on silicon (100) substrates using Si(O-Et) 4 and either Ti(O- i Pr) 4 or anhydrous Ti(NO 3 ) 4 as the sources of SiO 2 and TiO 2 , respectively. The substrate temperature was varied between 300 and 535°C, and the precursor flow rates ranged from 5 to 100 sccm. Under these conditions growth rates ranging from 0.6 to 90.0 nm/min were observed. As-deposited films were amorphous to X-rays and SEM micrographs showed smooth, featureless film surfaces. Cross-sectional TEM showed no compositional inhomogeneity. RBS revealed that x (from the formula Ti x Si 1-x O 2 ) was dependent upon the choice of TiO 2 precursor. For films grown using TTIP-TEOS x could be varied by systematic variation of the deposition conditions. For the case of TN-TEOS x remained close to 0.5 under all conditions studied. One explanation is the existence of a specific chemical reaction between TN and TEOS prior to film deposition. TEOS was mixed with a CCl 4 solution of TN at room temperature to produce an amorphous white powder (Ti/Si = 1.09) and 1 HNMR of the CCl 4 solution indicated resonances attributable to ethyl nitrate.

Group IVB Oxides as High Permittivity Gate Insulators

Increasing MOSFET performance requires scaling, the systematic reduction in device dimensions. Tunneling leakage, however, provides an absolute scaling limit for SiO 2 of about 1.5 nm. Power limitations and device reliability are likely to pose softer limits slightly above 2 nm. We have investigated the use of high permittivity materials such as TiO 2 , ZrO 2 , and their silicates as potential replacements for SiO 2 . We have synthesized titanium nitrate (Ti(NO 3 ) 4 or TN), zirconium nitrate (Zr(NO 3 ) 4 or ZrN), and hafnium nitrate (Hf(NO 3 ) 4 or HfN) as hydrogen and carbon free deposition precursors. Several problems arise in the use of these films including the formation of an amorphous low permittivity interfacial layer. For TiO 2 this layer is formed by silicon up diffusion. Surface nitridation retards the formation of the interfacial layer. We discuss the effects of both thermal and remote plasma surface nitridation treatments on the properties of the film stack. ZrO 2 and HfO 2 appear to form a thermal layer of silicon oxide between the high permittivity film and the silicon and have excess oxygen in the bulk of the film.

Chemical Vapor Deposition of Titania/Silica and Zirconia Films

Amorphous thin films of composition Ti x Si 1−x O 2 have been grown by low pressure chemical vapor deposition on silicon (100) substrates using Si(OEt) 4 and either Ti(O i Pr) 4 or anhydrous Ti(NO 3 ) 4 as the sources of SiO 2 and TiO 2 , respectively. The substrate temperature was varied between 300 and 535°C, and the precursor flow rates ranged from 5 to 100 sccm. Under these conditions growth rates ranging from 0.6 to 90.0 nm/min were observed. Films were amorphous to X-rays as deposited and SEM micrographs showed smooth, featureless film surfaces. Cross-sectional TEM showed no compositional inhomogeneity. RBS revealed that x (from the formula Ti x Si 1−x O 2 ) was dependent upon the choice of TiO 2 precursor. For films grown using TTIP-TEOS x could be varied by systematic variation of the flow of N 2 through the precursor vessels or the deposition temperature. For the case of TN-TEOS x remained close to 0.5. The results suggested the existence of a specific chemical reaction between TN and TEOS prior to film deposition. The CVD of zirconium dioxide (ZrO 2 ) films from zirconium tetra- tert -butoxide {Zr[OC(CH 3 ) 3 ] 4 } is also described. The films, which were deposited on Si(100), were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ellipsometry, X-ray diffraction (XRD), and Rutherford backscattering spectroscopy (RBS). Deposition was studied between ∼380 and 825 °C, and at precursor pressures between 4 × 10 −5 and 1 × 10 −4 Torr. The kinetics for steady-state growth were studied as functions of temperature and precursor pressure. Results were fit to a two-step kinetic model involving reversible precursor adsorption followed by irreversible decomposition to ZrO 2 .