For future generations of non-volatile memory applications, the replacement of the interpoly dielectric by a suitable high-k material is required. Rare-earth aluminates are potential candidates because they are predicted to combine a high dielectric permittivity with a large band gap. We demonstrate the atomic layer deposition (ALD) of Gd x Al 2-x O 3 layers using Gd(

GdxHf1−xnormalOy thin films were deposited by atomic layer deposition (ALD) using tris(isopropyl-cyclopentadienyl) gadolinium [Gd(normalPirCp)3] and HfCl4 in combination with normalH2O as an oxidizer. Growth curves showed a nearly ideal ALD behavior. The growth per individual Gd(normalPirCp)3/normalH2O or HfCl4/normalH2O cycle was 0.55 Å, independent of the Gd/(Gd+Hf) composition x in the studied range. This indicates that the amount of HfO2 deposited during a HfCl4/normalH2O cycle was essentially identical to the amount of Gd2normalO3 deposited during a Gd(normalPirCp)3/normalH2O cycle, assuming identical atomic densities of the films independent of composition. The crystallization of GdxHf1−xnormalOy with Gd/(Gd+Hf) contents x between 7 and 30% was studied. Films with x≳10% crystallized into a cubic/tetragonal HfO2 -like phase during spike or laser annealing up to 1300°C , demonstrating that the cubic/tetragonal phase is thermally stable in this temperature range. A maximum dielectric constant of κ∼36 was found for a Gd/(Gd+Hf) concentration of x∼11% .

An aqueous deposition process for V(6)O(13) films is developed whereby the vanadium oxidation state is continuously controlled throughout the entire process. In the precursor stage, a controlled wet chemical reduction of the vanadium(V) source with oxalic acid is achieved and monitored by (51)Vanadium Nuclear Magnetic Resonance ((51)V-NMR) and Ultraviolet-Visible (UV-Vis) spectroscopy. The resulting vanadium(IV) species in the aqueous solution are identified as mononuclear citrato-oxovanadate(IV) complexes by Electron Paramagnetic Resonance (EPR) and Fourier Transform Infra-Red (FTIR) spectroscopy. This precursor is successfully employed for the deposition of uniform, thin films. The optimal deposition and annealing conditions for the formation of crystalline V(6)O(13), including the control of the vanadium oxidation state, are determined through an elaborate study of processing temperature and O(2) partial pressure. To ensure a sub 100 nm adjustable film thickness, a non-oxidative intermediate thermal treatment is carried out at the end of each deposition cycle, allowing maximal precursor decomposition while still avoiding V(IV) oxidation. The resulting surface hydrophilicity, indispensable for the homogeneous deposition of the next layer, is explained by an increased surface roughness and the increased availability of surface vanadyl groups. Crystalline V(6)O(13) with a preferential (002) orientation is obtained after a post deposition annealing in a 0.1% O(2) ambient for thin films with a thickness of 20 nm.

Although the next generation high-k gate dielectrics has been defined for the 45nm complementary metal oxide semiconductor technology node, threshold voltage control and equivalent oxide thickness (EOT) scaling remain concerns for future devices. Therefore, the authors explored the effect of incorporating dysprosium in the gate stack. Results suggest that improved EOT-leakage scaling is possible by adding Dy to the interfacial SiO2 layer in a 1:1 ratio or by adding 10% Dy to bulk HfO2. The deposition of a 1nm Dy2O3 cap layer lowered the threshold voltage by ∼250mV. In addition, for future dynamic random access memory capacitor applications, dielectrics with ε of 50–130 are projected by the International Technology Roadmap for Semiconductors, unachievable with standard high-k dielectrics. Theoretical modeling can help direct the experimental work needed for extensive screening of alternative dielectrics. Moreover, materials such as perovskites only exhibit a sufficiently high-k value when properly crystallized. Therefore, control over the crystalline phase of the material might become a necessity to obtain the proper material characteristics as shown for SrTiOx. After crystallization, the permittivity was observed to increase from 20 to 135. In addition, material and gate stack optimization to limit leakage current densities for these higher-k dielectrics will be needed.

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Articles you may be interested inEffect of annealing and electrical properties of high-κ thin films grown by atomic layer deposition using carboxylic acids as oxygen source

Ultrathin (normalNb1−xnormalTax)2normalO5 films, with thicknesses from ∼3to∼25nm , were deposited by chemical solution deposition starting from aqueous precursor solutions. The film’s dielectric properties were characterized by capacitance–voltage and current–voltage measurements. Permittivities ranged from 20 to 31 after annealing at 600°C , with the highest value obtained for pure normalNb2normalO5 . With increasing Nb content, increasing leakage currents were observed. The crystallization temperature was determined by in situ X-ray diffraction measurement for films with ∼15nm thickness: normalNb2normalO5 was crystalline as deposited (600°C) , while the crystallization temperature of solid solutions increased with increasing Ta content, up to 875°C for pure normalTa2normalO5 . NbTanormalO5 showed a marked increase in permittivity from 27 to 38 after crystallization anneal at 600 and 800°C , respectively. For normalNb2normalO5 , no significant difference in permittivity was observed between amorphous and crystalline layers.