Oxide Atomic Layer Deposition Research Articles

Characterization of Polymetal Gate Transistors With Low-Temperature Atomic-Layer-Deposition-Grown Oxide Spacer

In this letter, W/WNx/poly-Si gate DRAM transistors with oxide spacers grown by low-temperature atomic layer deposition (ALD) have been fabricated, and the electrical characteristics are analyzed. The low-temperature ALD oxide effectively prevents the oxidation of exposed tungsten, and the fabricated devices show superior electrical properties to those with nitride/oxide spacer. The data retention time is improved by 30%, and the hot-carrier degradation characteristics are also enhanced. The threshold voltage of the fabricated W/WNx/poly-Si gate n-channel transistors with ALD oxide spacer is increased due to the suppression of boron deactivation by hydrogen. In particular, the transconductance of n-channel transistors in core/peripheral circuits was found to be enhanced by less-compressive stress in ALD oxide spacers.

Atomic Layer Deposition of MgO Using Bis(ethylcyclopentadienyl)magnesium and H2O

Magnesium oxide (MgO) atomic layer deposition (ALD) was performed using sequential exposures of bis(ethylcyclopentadienyl)magnesium (Mg(CpEt)2) and H2O. Quartz crystal microbalance (QCM) measurements monitored the mass deposition during MgO ALD and verified self-limiting reactions for each reactant. Extremely efficient reactions were observed that required reactant exposures of only ∼1 × 104 L (1 L = 1 × 10−6 Torr s). X-ray reflectivity (XRR) studies were used to confirm the QCM measurements and determine the film density and film thicknesses. The MgO ALD film density was 3.07 g/cm3. The largest MgO ALD growth per cycle was 1.42 A/cycle at 150 °C and the growth per cycle decreased for temperatures >150 °C. Fourier transform infrared spectroscopy was used to study the CpEt* and OH* surface species during MgO ALD and also to monitor the bulk vibrational modes of the growing MgO films. Transmission electron microscopy of MgO ALD on ZrO2 nanoparticles revealed the conformality of the MgO films and confirmed t...

The effect of aluminum oxide incorporation on the material and electrical properties of hafnium oxide on Ge

Hafnium aluminate thin films were synthesized by atomic layer deposition (ALD) to assess the effect of aluminum oxide incorporation on the dielectric/Ge interfacial properties. In these HfxAlyOz thin films, the Hf to Al cation ratio was effectively controlled by changing the ratio of hafnium oxide to aluminum oxide ALD cycles, while their short range order was changed upon increasing aluminum oxide incorporation, as observed by extended x-ray absorption fine structure analysis. The incorporation of aluminum oxide was shown to improve the electrical characteristics of hafnium oxide/Ge devices, including lower interface state densities and leakage current densities.

The reaction pathways of the oxygen plasma pulse in the hafnium oxide atomic layer deposition process

The plasma enhanced atomic layer deposition process for the HfO2 thin film is modeled as simple reactions between Hf(OH)3NH2 and reactive oxygen species. The density functional theory calculation was performed for plausible reaction pathways to construct the reaction profile. While the triplet molecular oxygen is unlikely to form a reactive complex, the singlet molecular oxygen forms the stable adduct that goes through the transition state and completes the reaction pathway to the products. Either two singlet or two triplet oxygen atoms make the singlet adduct complex, which follows the same pathway to the product as the singlet molecular oxygen reacts.

Selective-Area Atomic Layer Deposition Using Poly(methyl methacrylate) Films as Mask Layers

Selective-area atomic layer deposition (ALD) was achieved using poly(methyl methacrylate) (PMMA) films as growth inhibiting mask layers. The PMMA films were prepared from PMMA−toluene solution by spin-coating and patterned by UV lithography through a mechanical mask. The patterned PMMA films were tested in several ALD processes, both noble metals and oxides. The tested noble metal processes were iridium, platinum, and ruthenium, and the oxide processes were Al2O3 and TiO2. Al2O3 was deposited using AlCl3 and H2O and trimethylaluminum (TMA) and H2O. TiO2 was deposited using Ti(OMe)4 and H2O. The growth temperatures were 250−350 °C.

Surface Reaction Mechanisms during Ozone-Based Atomic Layer Deposition of Titanium Dioxide

We have investigated the surface reaction mechanisms during the atomic layer deposition (ALD) of TiO2 using titanium tetraisopropoxide (TTIP) and ozone using in situ attenuated total reflection Fourier transform infrared spectroscopy. The ozone reaction mechanism is fundamentally different than water-based ALD of metal oxides, where −OH groups are the reactive sites for metal alkoxides. In ozone-based ALD, the isopropoxy-ligand-terminated surface, generated after TTIP exposure, reacts with ozone, forming different surface carbonates. Upon subsequent TTIP exposure, the isopropoxy ligands chemisorb on the surface carbonates, releasing CO2. The growth rate, ∼0.52 A/cycle, is almost independent of the substrate temperature between 150 and 250 °C.

Surface chemistry of plasma-assisted atomic layer deposition of Al2O3 studied by infrared spectroscopy

The surface groups created during plasma-assisted atomic layer deposition (ALD) of Al2O3 were studied by infrared spectroscopy. For temperatures in the range of 25–150°C, –CH3 and –OH were unveiled as dominant surface groups after the Al(CH3)3 precursor and O2 plasma half-cycles, respectively. At lower temperatures more –OH and C-related impurities were found to be incorporated in the Al2O3 film, but the impurity level could be reduced by prolonging the plasma exposure. The results demonstrate that –OH surface groups rule the surface chemistry of the Al2O3 process and likely that of plasma-assisted ALD of metal oxides from organometallic precursors in general.

In Situ Gas Phase Diagnostics for Hafnium Oxide Atomic Layer Deposition

Atomic layer deposition (ALD) is an important method for depositing the nanometer-scale, conformal high k dielectric layers required for many nanoelectronics applications. In situ monitoring of ALD processes has the potential to yield insights that will enable efficiencies in film growth, in the development of deposition recipes, and in the design and qualification of reactors. This report will describe the status of a project to develop in situ diagnostics for hafnium oxide ALD processes. The focus is on an examination of the utility of Fourier transform infrared spectroscopy and diode laser spectroscopy for optimizing deposition conditions, rather than simply monitoring precursor delivery. Measurements were performed in a single-wafer, warm-wall, horizontal-flow reactor during hafnium oxide ALD involving tetrakis(ethylmethylamino) hafnium and water. Measurements were performed near the wafer surface under a range of deposition conditions in an effort to correlate gas phase measurements with surface processes.

Mechanism for zirconium oxide atomic layer deposition using bis(methylcyclopentadienyl)methoxymethyl zirconium

The mechanism for zirconium oxide atomic layer deposition using bis(methylcyclopentadienyl)methoxymethyl zirconium and H2O was examined using ab initio calculations of hydrolysis energies to predict the order of ligand loss. These predictions were tested using in situ mass spectrometric measurements which revealed that the methyl ligand, and 65% of the methylcyclopentadienyl ligands are lost during the zirconium precursor adsorption. The remaining 35% of the methylcyclopentadienyl ligands and the methoxy ligand are lost during the subsequent H2O exposure. These measurements agree very well with the predictions, demonstrating that thermodynamic calculations are a simple and accurate predictor for the reactivities of these compounds.

Atomic Layer Deposition of Hafnium Based Gate Dielectric Layers for CMOS Applications

To increase CMOS device performance, new materials are introduced in the gate stack (high-k dielectrics, metal gates) and the transistor channel (Ge, III-V). In this work, we study the Atomic Layer Deposition (ALD) of hafnium based gate dielectric oxides. Depositing by means of surface controlled reactions implies that the chemical sites at the surface can determine the growth behavior. First, the starting surface effect is analyzed for HfO2 ALD on Ge and GaAs substrates. Either substrate inhibition or enhancement occurs, both associated with an initial regime of island growth. The presence of oxygen enhances the GPC in the first reaction cycle. Second, the steady ALD of ternary oxides (hafnium silicate, aluminate, zirconate) is discussed. HfCl4 (and ZrCl4) chemisorption are much less affected by the composition of ternary oxides than by the starting surface. On the other hand, the SiCl4 chemisorption rate is significantly affected by the Hf-content of hafnium silicates.

Precursors for MOCVD and ALD of Rare Earth Oxides−Complexes of the Early Lanthanides with a Donor-Functionalized Alkoxide Ligand

Complexes of the early lanthanides with the donor-functionalized alkoxide ligand mmp (Hmmp = HOCMe(2)CH(2)OMe, 1-methoxy-2-methylpropan-2-ol) are excellent precursors for Metal Organic Chemical Vapor Deposition (MOCVD) and Atomic Layer Deposition (ALD) of lanthanide oxides; however, their coordination chemistry, which is the subject of this paper, is rather complex. Precursors for MOCVD and ALD of lanthanide oxides are prepared by the reaction of [Ln{N(SiMe(3))(2)}(3)] with 3 equiv of the alcohol Hmmp in toluene in the presence of 1 equiv of tetraglyme and are indefinitely stable in solution. Reaction of [Ln{N(SiMe(3))(2)}(3)] with 3 equiv of Hmmp in the absence of stabilizing Lewis bases gives complex condensed products with empirical formula [{Ln(mmp)(3-n)}(2)O(n)]. These condensed products show poor volatility and are unsatisfactory precursors for MOCVD or ALD of oxides. The cluster complex [La(3)(mu(3),kappa(2)-mmp)(2)(mu(2),kappa(2)-mmp)(3)(mmp)(4)] has been prepared by careful reaction of [La{N(SiMe(3))(2)}(3)] with 4 equiv of Hmmp and has been characterized by single-crystal X-ray diffraction. Salt metathesis reactions using M(mmp) (M = Li or Na) are unreliable routes to [Ln(mmp)(3)]. Crystals of the heterometallic cluster complex [NaLa(3)(mu(3)-OH)(mu(3),kappa(2)-mmp)(2)(mu(2),kappa(2)-mmp)(4)(mmp)(3)] were isolated from the reaction of [La(NO(3))(3)(tetraglyme)] with 3 equiv of Na(mmp), and crystals of [Li(kappa(2)-Hmmp)Pr(mu(2),eta(2)-mmp)(4))LiCl] were isolated from the reaction of PrCl(3) with 3 equiv of Li(mmp); both of these complexes have been characterized by single-crystal X-ray diffraction.

Crystallization of Amorphous Silicon Thin Films Using Self-Limiting ALD of Nickel Oxide

The crystallization of amorphous Si (a-Si) thin films was performed using atomic layer deposition (ALD) of nickel oxide. Nickel oxide layers were deposited using nickel aminoalkoxide as a precursor in Ni and water as a precursor in oxygen. The presence of nickel oxide caused significant crystallization to occur in a-Si at 575 °C under a reducing atmosphere. Even one single ALD layer of nickel oxide was high enough to crystallize the a-Si thin films. Self-limiting layer controllability in ALD is useful in providing a catalytic layer for formation of polycrystalline Si thin films for application to large-scale flat panel displays. © 2007 The Electrochemical Society. [DOI: 10.1149/1.2666721] All rights reserved.

In situ reaction mechanism studies of plasma-assisted atomic layer deposition of Al2O3

Reaction mechanisms during plasma-assisted atomic layer deposition (ALD) of Al2O3 from Al(CH3)3 and O2 plasma were studied by time-resolved quartz crystal microbalance measurements, mass spectrometry, and optical emission spectroscopy. Al(CH3)3 chemisorption on the oxide surface after the plasma pulse releases CH4 products while from the detection of CO, CO2, and H2O in the O2 plasma it is established that surface –CH3 groups are predominantly removed by O radical-driven combustionlike reactions. Also a second pathway exists for –CH3 removal driven by H2O generated in this plasma step. These reaction pathways are expected to be generic for plasma-assisted ALD of oxides from metal organic precursors.

ALD and Characterization of Aluminum Oxide Deposited on Si ( 100 ) using Tris(diethylamino) Aluminum and Water Vapor

A nonpyrophoric, oxygen-free, halogen-free tris(diethylamino) aluminum (TDEAA) precursor was used for atomic layer deposition (ALD) of aluminum oxide on . ALD of aluminum oxide using TDEAA and water was found to be self-limiting with respect to both reactants. The temperature window for ALD in the hotwall reactor used was found to be between 200 and . The ALD rate was at optimum conditions. Fourier transform infrared (FTIR) analyses indicated negligible interfacial growth during deposition. Both FTIR spectra and transmission electron micrographs showed the ALD aluminum oxide to be amorphous. Also, FTIR and X-ray photoelectron spectral (XPS) analyses showed negligible carbon and nitrogen ( atomic) contamination in the film. Z-contrast images and electron energy loss spectra showed uniform aluminum oxide film with an abrupt interface with Si. XPS analysis revealed aluminum oxide film to be stoichiometric with no detectable cluster formation. Also, XP spectra showed no silicate formation at the interface of as-deposited alumina films.

Liquid-Injection Atomic Layer Deposition of TiOx and Pb–Ti–O Films

Pb–Ti–O films were prepared by liquid-injection atomic layer deposition (ALD) using as oxygen source after evaluating Ti precursors with different β-diketonate type ligands, and , dissolved in ethylcyclohexane. For both Ti precursors, the apparent thermal activation energy of the deposition rate of films increased at a deposition temperature of about , and the deposition rate of films grown at saturated against the volume of injected Ti precursors. was selected for the subsequent Pb–Ti–O film deposition because of its high precursor efficiency and the low temperature dependence of the deposition rate. Pb–Ti–O films were prepared using and at deposition temperatures of 240 and . The deposition rates of Pb and Ti in the Pb–Ti–O process were higher than those in binary PbO and processes under the same deposition conditions. The deposition rate of Pb in the Pb–Ti–O process showed a linear increase in response to the injected Pb precursor volume, which was different from the saturated deposition rate of the PbO process. The interface chemistry between the precursors and predeposited cation layers has critical impact on the self-regulated growth mechanism in the multicomponent oxide ALD.

Modification of Opal Photonic Crystals Using Al2O3 Atomic Layer Deposition

Aluminum oxide (Al2O3) atomic layer deposition (ALD) on synthetic opal was explored as a model system to understand the growth of ALD films on photonic crystals. Al2O3 ALD was used to coat the sili...

ALD of Scandium Oxide from Scandium Tris(N,N[sup ʹ]-diisopropylacetamidinate) and Water

Sc 2 O 3 films were deposited by atomic layer deposition (ALD) from a new precursor scandium tris(N,N'-diisopropylacetamidinate) and water. The precursor is thermally stable (>350°C), volatile, with good reactivity to HF-last silicon. A growth rate of 0.3 A/cycle was obtained at 290°C. The films were pure (C,N < 0.5 atom %) and had a refractive index of 1.8. Reactive ion etching tests on ALD scandia showed an etch rate 18 times slower than ALD hafnia. Electrical measurements showed a high permittivity of ∼17, and a leakage current density of <3 × 10 -3 A/cm 2 for an equivalent oxide thickness of 1.8 nm at 1.0 V.

Low-Frequency Noise Performance of HfO2-Based Gate Stacks

The low-frequency noise characteristics of -based dielectrics have been investigated. Attention is given to the deposition technique (metal oxide chemical vapor deposition or atomic layer deposition) used, the film thickness, and the use of a interface layer. n-Type metal oxide semiconductor devices with equivalent oxide thicknesses (EOTs) of 1.5, 2, 3, and 5.5 nm were studied. It is shown that the LF noise of such high- transistors is like. The behavior of the normalized current spectral density vs the drain current points out that for relative thin interfacial layers and at high gate voltages carrier trapping in the layer governs the current fluctuations. The trap densities extracted from the noise are up to 200 times higher than in a thermal oxide reference wafer (5.5 nm EOT). The deposition technique has no strong impact on the density of traps in the high- layer, which is in the range of . However, a strong difference was observed in the noise contribution, which is dominated by carrier scattering at charged traps. For , the scattering coefficient derived from the noise is smaller than for , which can be interpreted in terms of the suppression of the coulomb scattering by the high dielectric constant.

In situ examination of tin oxide atomic layer deposition using quartz crystal microbalance and Fourier transform infrared techniques

The atomic layer deposition (ALD) of tin oxide thin films has been examined using in situ quartz crystal microbalance (QCM) and Fourier transform infrared (FTIR) techniques. The SnOx films were deposited using sequential exposures of SnCl4 and H2O2 at temperatures from 150 to 430 °C. The linear growth of the tin oxide ALD films was observed by both the mass gain during QCM measurements and the background infrared absorbance increase during FTIR investigations. The FTIR spectra revealed the loss and gain of the O–H stretching vibrations of the hydroxyl group for the SnCl4 and H2O2 exposures, respectively. The background infrared absorbance also oscillated after each SnCl4 and H2O2 exposure. The background absorbance increased after SnCl4 exposure and decreased after H2O2 exposure. QCM measurements were consistent with a tin oxide ALD growth rate of ∼60ngcm−2 per cycle. This mass change corresponds to a growth rate of ∼0.7Å∕cycle at 325 °C assuming a SnO2 density of 6.9gcm−3. Additional ex situ surface analysis using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) revealed that the SnOx films grown at 325 °C were defined by x&amp;lt;2. Atomic force microscope (AFM) results also showed that the SnOxALD films deposited on Si(100) wafers have a very rough surface. Understanding and controlling the growth of tin oxide ALD films should be useful to enhance the sensitivity of SnOx gas sensors.

Recent developments in the MOCVD and ALD of rare earth oxides and silicates

Lanthanide, or rare-earth oxides are currently being investigated as alternatives to SiO 2 as the dielectric insulating layer in sub-0.1 μm CMOS technology. Metalorganic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) are promising techniques for the deposition of these high- κ dielectric oxides and in this paper some of our recent research into the MOCVD and ALD of PrO x , La 2O 3, Gd 2O 3, Nd 2O 3 and their related silicates are reviewed.