The results of atomic layer deposition of Ta 2 O 5 on silicon using the precursors TaF 5 and H 2 O are reported. The films are stoichiometric Ta 2 O 5 at the surface, becoming Ta-rich as the interface is approached. For deposition temperatures from 400 to 450°C and chamber pressures from 0.5 to 5 Torr, the deposition rate exhibits two growth regimes, postulated to be due to differences in the densities of hydroxyl species on the chemically cleaned Si substrates and on the deposited Ta 2 O 5 layer. Growth rate in the "converged" regime, in which Ta 2 O 5 has completely covered the substrate, is more strongly affected by the partial pressure of the TaF 5 than by that of the H 2 O. A comparison is made between the growth rate and the surface coverage of TaF 5 calculated with a simple Langmuir model. The deposited phase changes from amorphous to crystalline ͑hexagonal͒ in the same interval of pressure and temperature. The controlling factor for formation of the hexagonal polymorph is the partial pressure of the TaF 5 precursor. The extent of surface coverage of TaF 5 alone does not adequately account for the dependence of the extent of crystallization on pressure and temperature, and it is likely that there are additional important surface reaction components.High-dielectric-constant materials, including Ta 2 O 5 , have been investigated intensively for many years. Interest in these materials is driven primarily by requirements of the microelectronics industry for higher charge storage capacity in semiconductor memories and lower leakage in thin transistor gate oxides. The usefulness of a given material for these applications depends strongly on the particular phases present and their chemical and thermal stability. For example, the hexagonal ͑␦͒ polymorph of Ta 2 O 5 has been reported to have a significantly higher dielectric constant than the amorphous phase. 1,2 While formation of the desired phase often requires hightemperature annealing of the as-deposited film, it is useful to be able to deposit the material in the desired form without conversion at high temperature, as this provides an additional degree of freedom for postdeposition processing. An equally important requirement for semiconductor applications is the ability to deposit the material in the 1-10 nm thickness range with a high degree of repeatability and uniformity across substrates as large as 300 mm diameter.Ta 2 O 5 films have been reported to have a variety of electrical and material properties, depending upon substrate, precursor chemistry, method of film growth, deposition conditions, and postdeposition treatment. It has been found, generally, that tantalum oxide films grown using organometallic Ta precursors are amorphous as-deposited. 3,4 The most commonly used organometallic precursor for Ta 2 O 5 is tantalum pentaethoxide ͓Ta͑OC 2 H 5 ͒ 5 ͔, and films deposited with this compound are amorphous for both atomic layer deposition ͑ALD͒ 5,6 and chemical vapor deposition ͑CVD͒. 1,7,8 The amorphous films can be crystallized at high temperature. U...
We characterized thin Al2O3 dielectrics with TiN electrodes in a three-dimensional, high-aspect-ratio, metal–insulator–metal capacitor structure. Transmission electron microscopy images did not reveal any interfacial layer(s) or intermixing of the films. This was confirmed by series capacitance analysis. Extensive electrical characterization indicated a well-behaved dielectric response. Time and frequency domain measurements did not show any significant dielectric relaxation. Charge transport was controlled by a direct tunneling mechanism in the field range of 1.5 to 6 MV/cm for a 50 Å film. The Fowler–Nordheim tunneling mechanism dominated the high field range (>6 MV/cm for a 50 Å film), and the leakage currents became independent of dielectric thickness. The electron tunneling effective mass was found to be 0.2 me.
Epitaxial (110) orthorhombic KNbO, thin films were prepared using alkoxide solutions. Single-phase films were produced with stoichiometric sols while slight variations in stoichiometry (52/48 Nb/K or 48/52 NWK) created residual second phases. Nucleation and growth of KNbO, as a function of process conditions were monitored by observing the KNbO, rosettes produced from niobium-rich solutions. Methanolic solutions produced films with the highest rosette density and the highest amount of KNbO,. Hydrolysis of the sol aided the crystallization of the KNb03 phase but also promoted the formation of second phases. Hydrolysis at 0°C reduced second-phase formation.
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