Tiezhong Ma

Titanium dioxide (TiO 2 )-based gate insulators

Titanium dioxide has been deposited on silicon for use as a high-permittivity gate insulator in an effort to produce low-leakage films with oxide equivalent thicknesses below 2.0 nm. Excellent electrical characteristics can be achieved, but TEM and electrical measurements have shown the presence of a low-resistivity interfacial layer that we take to be SiO2. The leakage current follows several mechanisms depending on the bias voltage. Reasonably good agreement has been seen between current-voltage measurements and a 1D quantum transport model.

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.

High mobility HfO2 n- and p-channel transistors

Abstract High permittivity HfO 2 films have been deposited directly on silicon using the thermal decomposition of the hafnium nitrato precursor Hf(NO 3 ) 4 . These films were then used to build n- and p-channel field effect transistors. N+ poly, P+ poly, and Pt have been used as gate electrodes. The mobility of the poly gate devices is comparable to that of SiO 2 /Si, however, these devices show a thicker equivalent oxide thickness than the Pt devices. The effect of the composition of the films on their electrical performance is discussed.

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.

A 1.1 nm oxide equivalent gate insulator formed using TiO/sub 2/ on nitrided silicon

Tunneling leakage limits the scaling of SiO/sub 2/ to about 1.5 nm. Well behaved transistors have previously been made with MOCVD-deposited TiO/sub 2/ using the thermal decomposition of titanium tetrakis isopropoxide. However, after the required O/sub 2/ anneal, these devices have a 2.5 nm amorphous interfacial layer which severely limits the capacitance. We have synthesized nitrato titanium (Ti(NO/sub 3/)/sub 4/ or NT) as a hydrogen and carbon free deposition. In an effort to obtain low leakage, /spl sim/1.0 nm GOE slacks, we have used NT to deposit progressively thinner TiO/sub 2/ layers on silicon that has been thermally nitrided at 850/spl deg/C in NH/sub 3/ at 10 torr. The article shows film morphology representative of device deposition (500/spl deg/C). TiO/sub 2/ deposition rates were /spl sim/0.8 nm/min. A post deposition anneal of 700/spl deg/C was done in N/sub 2/. These anatase films are stable up to approximately 850/spl deg/C. Capacitors were made by Pt sputtering, photolithography, and ion milling. A final 450/spl deg/C H/sub 2/ anneal was done on all samples.

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.