Tetrakis Dimethylamino Hafnium Research Articles

Plasma-Enhanced Atomic Layer Deposition of HfO2 with Substrate Biasing: Thin Films for High-Reflective Mirrors.

Tuning ion energies in plasma-enhanced atomic layer deposition (PEALD) processes enables fine control over the material properties of functional coatings. The growth, structural, mechanical, and optical properties of HfO2 thin films are presented in detail toward photonic applications. The influence of the film thickness and bias value on the properties of HfO2 thin films deposited at 100 °C using tetrakis(dimethylamino)hafnium (TDMAH) and oxygen plasma using substrate biasing is systematically analyzed. The HfO2 films deposited without a substrate bias show an amorphous microstructure with a low density, low refractive index, high incorporation of residual hydroxyl (OH) content, and high residual tensile stress. The material properties of HfO2 films significantly improved at a low bias voltage due to the interaction with oxygen ions accelerated to the film. Such HfO2 films have a higher density, higher refractive index, and lower residual OH incorporation than films without bias. The mechanical stress becomes compressive depending on the bias values. Further increasing the ion energies by applying a larger substrate bias results in a decrease of the film density, refractive index, and a higher residual OH incorporation as well as crystalline inclusions. The comparable material properties of the HfO2 films have been reported using tris(dimethylamino)cyclopentadienyl hafnium (TDMACpH) in a different apparatus, indicating that this approach can be transferred to various systems and is highly versatile. Finally, the substrate biasing technique has been introduced to deposit stress-compensated, crack- and delamination-free high-reflective (HR) mirrors at 355 and 532 nm wavelengths using HfO2 and SiO2 as high and low refractive index materials, respectively. Such mirrors could not be obtained without the substrate biasing during the deposition because of the high tensile stress of HfO2, leading to cracks in thick multilayer systems. An HR mirror for 532 nm wavelength shows a high reflectance of 99.93%, a residual transmittance of ∼530 ppm, and a low absorption of ∼11 ppm, as well as low scattering losses of ∼4 ppm, high laser-induced damage threshold, low mechanical stress, and high environmental stability.

Influence of temperature and plasma parameters on the properties of PEALD HfO2

HfO2 has promising applications in semiconductors and optics due to its high dielectric constant and high refractive index. In this work, HfO2 thin films were deposited by plasma enhanced atomic layer deposition (PEALD) using tetrakis-dimethylamino hafnium (TDMAH) and oxygen plasma. The process optimization to obtain high quality HfO2 thin films with excellent uniformity over a 200 mm diameter is thoroughly discussed. The effects of deposition temperature and plasma parameters on the structural, mechanical, and optical properties, and the chemical composition of the films were investigated. Optimized process parameters yielding a high refractive index, high density, low impurities, low OH incorporation, low absorption in the UV spectral range, and high laser-induced damage threshold (LIDT) were selected for antireflection coatings. The HfO2 thin films were incorporated into antireflection coatings designed for the fundamental wavelength at 1064 nm and its higher harmonics up to the 4th order.

The other model antiferroelectric: PbHfO3 thin films from ALD precursors

Antiferroelectric PbHfO3 is grown from atomic layer deposition precursors lead bis(dimethylaminomethylpropanolate) and tetrakis dimethylamino hafnium with H2O and O3 oxidizers in thicknesses from 20 nm to 200 nm at a substrate temperature of 250 °C. X-ray analysis shows an as-grown crystalline PbO phase that diffuses into an amorphous HfO2 matrix upon annealing to form a randomly oriented, orthorhombic PbHfO3 thin film. Electrical characterization reveals characteristic double hysteresis loops with maximum polarizations of around 30 µC/cm2 and transition fields of 350 kV/cm–500 kV/cm depending on the thickness. Temperature-dependent permittivity and polarization testing show a phase transition at 185 °C, most probably to the paraelectric phase, but give no clear evidence for the intermediate phase known from bulk PbHfO3. The energy storage density for the films reaches 16 J/cm3 at 2 MV/cm. A dielectric tunability of 221% is available within 1 V for the thinnest film. These results highlight the unique spectrum of properties available for thin film perovskite antiferroelectrics.

Growth of thin film ferroelectric PZT, PHT, and antiferroelectric PHO from atomic layer deposition precursors

AbstractWe present a conformal method of growing ferroelectric lead hafnate‐titanate (PbHfxTi1−xO3, PHT) and lead zirconate‐titanate (PbZrxTi1−xO3, PZT) using atomic layer deposition (ALD) precursors. The 4+ cation precursors consist of tetrakis dimethylamino titanium (TDMAT), tetrakis dimethylamino zirconium (TDMAZ) and tetrakis dimethyl amino hafnium (TDMAH) for Ti, Zr, and Hf, respectively. The Pb (2+) precursor was Lead bis(3‐N,N‐dimethyl‐2‐methyl‐2‐propanoxide) [Pb(DMAMP)2]. PZT was limited to lead titanate (PTO)‐rich compositions, where x <0.25 for PbZrxTi1−xO3, and exhibited a remnant polarization of 26‐27 µC/cm2 with a coercive field between 150 and 170 kV/cm. The 3D‐structure coating capability of PZT was demonstrated by deposition on micromachined trench sidewalls 45 µm deep. We fabricated Microelectromechanical systems (MEMS) cantilever arrays with PZT thin films grown using the present method and demonstrated piezoelectric actuation. Alternatively, PHT was deposited with Ti and Hf compositions within ±1 at.% of the morphotropic phase boundary (MPB). The PHT exhibited a remanent polarization of 7.0‐8.7 µC/cm2 with a coercive field between 84‐100 kV/cm. We applied the same Pb and Hf precursors from the PHT process to grow antiferroelectric lead‐hafnate (PHO), which showed the characteristic electric field‐induced ferroelectric phase transition at approximately ±280 kV/cm and a maximum polarization of approximately ±32.8 µC/cm2.

Microscopic modeling and optimal operation of plasma enhanced atomic layer deposition

Plasma enhanced atomic layer deposition (PEALD) is one of the most widely adopted deposition methods used in the semiconductor industry. It is chosen largely due to its superior ability to produce ultra-thin high-k dielectric films, which are needed for the further miniaturization of microelectronic devices with the pace of Moore's Law. In contrast to the traditional thermal atomic layer deposition (ALD) method, PEALD allows for high deposition growth per cycle (GPC) under low operating temperature with the help of high energy plasma species. Despite the experimental effort in finding new precursors and plasmas, the detailed surface structures and reaction mechanisms in various PEALD processes remain hard to understand because of the limitation of current in-situ monitoring techniques and the deficiency of the first-principles based analysis. Therefore, in this work, an accurate, yet efficient kinetic Monte Carlo (kMC) model and an associated machine learning (ML) analysis are proposed to capture the surface deposition mechanism and to propose optimal operating conditions of the HfO2 thin-film PEALD using tetrakis-dimethylamino-Hafnium (TDMAHf) and oxygen plasma. Density Functional Theory (DFT) calculations are performed to obtain the key kinetic parameters and the structural details, subsequently employed in the kMC model. After the kMC model is validated by experimental data, a database is generated to explore a variety of precursor partial pressure and substrate temperature combinations using the kMC algorithm. A feed-forward Bayesian regularized artificial neural network (BRANN) is then constructed to characterize the input–output relationship and to investigate the optimal operating conditions.

Comparison between thermal and plasma enhanced atomic layer deposition processes for the growth of HfO2 dielectric layers

In this work, hafnium oxide (HfO2) thin films have been grown on (0 0 1)Si substrates by two different Atomic Layer Deposition (ALD) methods, namely thermal and plasma-enhanced modes. Films have been deposited using tetrakis-dimethylamino hafnium as metal precursor, while water vapor was used as an oxygen reactant in the case of the thermal ALD (T-ALD) process, and oxygen plasma was used as oxidant during the plasma enhanced ALD (PE-ALD) process. A systematic study by varying the deposition temperature (200 °C ≤ Tdep ≤ 300 °C) and number of cycles (i.e. film thickness in the 10–100 nm range) has been carried out for both ALD methods, and the influence on their physical properties has been evaluated. In particular, the comparison of the growth rates and refractive indexes has been carried out by spectroscopic ellipsometry. All the collected results provided data to identify the best suited deposition process.

Engineering a Unified Dielectric Solution for AlGaN/GaN MOS-HFET Gate and Access Regions

Typically GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) have used two separate dielectrics for the gate and access regions. However, as this article shows, with proper gate-stack engineering, a unified dielectric solution can be achieved for the transistor. HfO2 dielectrics were deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H2O) and ozone (O3). It was found that MOS-HFETs with O3 oxidant yielded lower threshold voltage ( ${V}_{\text {TH}}$ ) shifts, higher maximum drain current ( ${I}_{\text {DS,max}}$ ) of 340 mA/mm, 20% lower ON-resistance ( ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ ), higher peak transconductance at 112.66 mS/mm, lower hysteresis, and lower gate leakage ( ${5.4} \times {10}^{-{6}}$ A/cm2) compared to water oxidant based MOS-HFETs with ${I}_{\text {DS},\text {max}}$ of 240 mA/mm, 81.38 mS/mm peak transconductance, and ${1.7} \times {10}^{-{4}}$ A/cm2 gate leakage. DC/RF dispersion tests showed MOS-HFETs with O3 oxidant had ~200 $\times $ better current collapse recovery. Temperature characterization and reliability test results, such as high-temperature reverse bias (HTRB), are published for the first time on ALD-HfO2/AlGaN/GaN MOS-HFETs using tetrakis(dimethylamino)hafnium (TDMAH) and O3 precursor. Using an ozone oxidant provided more stability (i.e., less variability in ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ and ${V}_{\text {TH}}$ ) as a function of temperature. Finally, when devices were electrically stressed in the OFF-state, the HTRB test showed minimal ${V}_{\text {TH}}$ drift ( ${V}_{\text {TH}}$ drift (2.5 V) in the case of H2O oxidant.

A correlation study of layer growth rate, thickness uniformity, stoichiometry, and hydrogen impurity level in HfO2 thin films grown by ALD between [formula omitted] and [formula omitted]

Hafnium oxide was deposited from tetrakis(dimethylamino)hafnium (TDMAHf) and water by atomic layer deposition (ALD) on heated 4″ Si wafers covered with native oxide in the temperature range from 100°C to 350°C. Optimized self-limiting ALD reaction and smallest hydrogen impurity level have been realized for a substrate temperature of 300°C. The stoichiometry of deposited films and hydrogen impurity level were measured by elastic recoil detection analysis. The hafnium to oxygen ratio showed the expected 1:2 value. Besides hydrogen, no other impurities could be detected. Furthermore, a strong correlation between the growth rate per cycle (GPC), film uniformity and level of hydrogen impurities was observed.In addition, the characterization of the crystal structure showed the appearance of some crystallites in an amorphous matrix already for a growth temperature of 250°C and a pure crystalline layer at a growth temperature of 350°C. The increased crystallinity with increasing growth temperature was attributed to a higher seed concentration and a nearly constant crystal size.

Resistive switching characteristics of MIM structures based on oxygen-variable ultra-thin HfO2 and fabricated at low temperature

We report the resistive switching characteristics of Metal-Insulator-Metal (MIM) structures fabricated at low temperature and having different concentrations of oxygen vacancies in the insulator. The oxygen modulation in HfO2 is promoted by a very simple variation of standard thermal Atomic-Layer Deposition (ALD), so that different exposure times to H2O during each half-cycle of the hafnium oxide deposition are used (being Tetrakis Dimethylamino Hafnium–TDMAH the other precursor). We show the correlation of the stoichiometry with the forming voltage, conduction mechanisms and resistance windows of memory devices. All structures present a bipolar operation mode in which the resistive switching mechanism is related to the migration of oxygen vacancies inside the dielectric. These MIM devices have a simple structure, low power consumption and they are fabricated using a very low thermal budget of only 250°C, thus enabling their integration at the Back-End of Line (BEOL) stage of an integrated circuit in order to increase the density of memory arrays in at least one order of magnitude.

Comparison of HfCl4, HfI4, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO2 films deposited by ALD: A DFT study

The final structure of HfO2 films grown by atomic layer deposition (ALD) after reaction with OH− ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl4 (hafnium tetrachloride), HfI4 (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO–H was studied employing the B3LYP (Becke 3-parameter, Lee–Yang–Parr) hybrid functional and the PBE (Perdew–Burke–Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.

Nucleation and Growth of the HfO2 Dielectric Layer for Graphene-Based Devices

We investigated nucleation and growth characteristics of atomic layer deposition (ALD) HfO2 on exfoliated and chemical vapor deposition (CVD) graphene by using two Hf precursors, tetrakis(dimethylamino)hafnium (TDMAH) and hafnium tetrachloride (HfCl4). Experimental results and theoretical calculations indicate that HfO2 nucleation is more favorable on CVD graphene than on exfoliated graphene due to the existence of defect sites. Also, the TDMAH precursor showed much more unfavorable nucleation and growth than HfCl4 due to different initial adsorption mechanisms, affecting lower leakage currents and breakdown electric field. ALD growth characteristics of HfO2 will be fundamentally and practically significant for realizing the fabrication of graphene-based electronic devices.

Influence of Substrate on Hafnium Silicate Metal-Insulator-Metal Capacitors Grown by Atomic Layer Deposition

Metal insulator metal (MIM) capacitors are fundamental components of the electronic circuitry commonly found in many devices in areas such as analogue to digital conversion, micro-electromechanical systems, medical, automotive and memory applications [1-4]. Current MIMCAPS generally employ optimised low dielectric constant (k) materials (k~3.9 - 7) to attain the target electrical properties of high breakdown field and low current leakage. However, device scaling is limited due to the low k value of these materials and this presents a significant challenge to the future development of these technologies [5]. Many high k materials are under investigation to replace these lower k dielectrics to substantially increase the maximum capacitance density and reduce the area associated with the integration of MIM structures. In this work we investigate the growth of hafnium silicate films by plasma assisted atomic layer deposition on a metal electrode. The hafnium silicate film was deposited using Tetrakis(dimethylamino)hafnium (TDMAHf) and Tetrakis(dimethylamino)silane (TDMASi) precursors at 250oC with a remote oxygen plasma (300 W). From HR-TEM analysis and Raman spectroscopy it has been observed that the main crystalline phase is monoclinic HfO2. This crystallographic phase appears to be templated by the underlying titanium adhesion (10 nm) layer through the platinum electrode (200 nm). The HR TEM analysis also reveals the presence of nanoparticles, located primarily towards the lower platinum metal layer. Based on electron energy loss spectroscopy (EELS) analysis the nanoparticles are consistent with silicon oxide inclusions, located at HfO2 grain boundaries. In addition, the presence of additional phases was detected; these included a super-cell structure within the bulk and an amorphous phase. No hysteresis was observed in the capacitance voltage measurements and the material was observed to exhibit a k value of ~18.

Aperture-time of oxygen-precursor for minimum silicon incorporation into the interface-layer in atomic layer deposition-grown HfO2/Si nanofilms

Hafnium oxide nanofilms were grown with atomic layer deposition on H-terminated Si (001) wafers employing tetrakis dimethyl amino hafnium (TDMA-Hf) and water as precursors. While the number of cycles (30) and the aperture-time for TDMA-Hf (0.08 s) were kept constant, the aperture-time (τH2O) for the oxidant-agent (H2O) was varied from 0 to 0.10 s. The structure of the films was characterized with robust analysis employing angle-resolved x-ray photoelectron spectroscopy. In addition to a ∼1 nm hafnium oxide layer, a hafnium silicate interface layer, also ∼1 nm thick, is formed for τH2O > 0. The incorporation degree of silicon into the interface layer (i.e., the value of 1 − x in HfxSi1−xOy) shows a minimum of 0.32 for τH2O = 0.04 s. By employing the simultaneous method during peak-fitting analysis, it was possible to clearly resolve the contribution from the silicate and from oxide to the O 1s spectra, allowing for the assessment of the oxygen composition of each layer as a function of oxidant aperture time. The uncertainties of the peak areas and on the thickness and composition of the layers were calculated employing a rigorous approach.

Atomic layer deposition of CeO2/HfO2 gate dielectrics on Ge substrate

We systematically investigated atomic layer deposition (ALD) of HfO2, CeO2 and Ce-doped HfO2 thin films on Ge substrates by using tetrakis dimethylamino hafnium (TDMAH) and tris(isopropyl-cyclopentadienyl)cerium [Ce(iPrCp)3] precursors with H2O. The growth characteristics, chemical and electrical properties were comparatively characterized. On the basis of X-ray photoemission spectroscopy analyses, it was confirmed that the ALD CeO2 on Ge can form a stable interfacial layer composed of Ge1+ and Ge3+, leading to improved interfacial properties. In addition, Ce-doped HfO2 films with various Ce compositions (Ce:Hf=1:1, 1:2, 1:4 and 1:8) were prepared by an ALD supercycle process on Ge substrates. Thereby, we demonstrated that overall electrical properties including dielectric constant, interface state density, hysteresis and leakage current density are significantly improved.

The combination self-cleaning effect of trimethylaluminium and tetrakis (dimethyl-amino) hafnium pretreatments on GaAs

The self-cleaning effect of trimethylaluminium (TMA) and tetrakis (dimethyl-amino) hafnium (TDMAH) pretreatments on GaAs substrates was investigated deeply. The chemical states were carefully characterized by the X-ray photoelectron spectroscopy, which demonstrates that the pretreatment before ALD of dielectric films can suppress the formation of native oxides on GaAs substrates effectively. It is found that the combination of TMA and TDMAH pretreatments has better self-cleaning effect than single TMA pretreatment based on a ligand-exchange reaction mechanism between TMA/TDMAH and the native oxide. The transmission electron microscopy images also show a thinnest interlayer thickness of ∼0.2nm for the TMA+TDMAH pretreated sample. TMA+TDMAH pretreated samples exhibit significantly improved interfacial and electrical properties such as the highest accumulation capacitance, the least stretch-out of capacitance–voltage curves, and the lowest interface trap density. These results indicate that the surface pretreatment by using the combination of TMA and TDMAH pulses may be a promising approach for the realization of high quality GaAs-based transistor devices.

Interface layer in hafnia/Si films as a function of ALD cycles

A systematic angle resolved x-ray photoelectron spectroscopy study of the structure of hafnia films grown on silicon with atomic layer deposition (ALD) is presented. The hafnium precursor employed was tetrakis dimethyl amino hafnium with water as the oxidant agent. The number of ALD cycles ranged from 3 to 25. The Hf 4f spectrum shows two components 0.47 eV apart, one associated with hafnia (17.6 eV) and the other (18.1 eV) with a hafnium silicate interface layer. The composition of the interface layer, HfxSi1-xOy, evolves continuously from silicon-rich (x = 0.1 for 3 ALD cycles) to hafnium rich (x = 0.75 for 25 ALD cycles). The binding energy difference between the Hf 4f components associated with the silicate and hafnia changes very little with the silicate composition. The binding energy of the Si4+ component, which is associated with the silicate, varies from 3.25 to 2.85 eV (referenced to the Si0+ component) with the number of ALD cycles. The oxygen stoichiometric coefficient of the silicate is close to the expected value of 2 for all the samples. However, the hafnia shows an excess of oxygen for some of the samples.

Impact of ozone concentration on atomic layer deposited HfO 2 on GaAs

Effect of ozone (O 3) concentration (90, 300 g/Nm 3) on atomic layer deposition of HfO 2 thin films on GaAs wafers using tetrakis (dimethylamino)hafnium (TDMAHf) as Hf precursor was systematically studied including MISCAP performance and related microstructure. High-resolution transmission electron microscopy analyses show that oxidation of the GaAs substrate enhances with O 3 concentration which leads to an increase in interfacial layer (IL) thickness between the high-k dielectric and the substrate. The thin IL was maintained after PDA, while the high-k (HfO 2) layer experienced shrinkage of ∼12% due to densification. However HfO 2 film deposited using O 3 concentration of 300 g/Nm 3 produced relatively thicker IL and thinner high-k layer which both did not show a noticeable change after PDA. This led to C max variations depending on the different O 3 concentration. In the case of O 3 concentration of 90 g/Nm 3, increase of leakage current density by an order was observed and corresponding micro-structural change is discussed.

Effect of Ozone Concentration on Atomic Layer Deposited HfO2 on Si

Effect of ozone concentration (200-400 g/Nm3) on atomic layer deposition of HfO2 thin films on Si wafers using tetrakis (dimethylamino)hafnium (TDMAHf) as Hf precursor was systematically studied. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy analyses show that oxidation of the Si substrate enhances with ozone concentration which leads to an increase in interfacial layer (IL) thickness between the high-k dielectric and the substrate. The relatively thicker IL successfully suppresses additional growth of itself and Si out-diffusion into the dielectric during post deposition annealing (PDA). Corresponding electrical characteristics such as capacitance-voltage, leakage current density and time zero dielectric breakdown display significant improvement for HfO2 film prepared using higher ozone concentration after PDA.

Properties of atomic layer deposited HfO 2 thin films

The growth, composition and morphology of HfO 2 films that have been deposited by atomic layer deposition (ALD) are examined in this article. The films are deposited using two different ALD chemistries: i) tetrakis ethylmethyl amino hafnium and H 2O at 250° and ii) tetrakis dimethyl amino hafnium and H 2O at 275 °C. The growth rates are 1.2 Å/cycle and 1.0 Å/cycle respectively. The main impurities detected both by X-ray Photoelectron Spectroscopy and Fourier transform infrared spectroscopy (FTIR) are bonded carbon (~ 3 at.%) and both bulk and terminal OH species that are partially desorbed after high temperature inert anneals up to 900 °C. Atomic Force Microscopy reveals increasing surface roughness as a function of increasing film thickness. X-ray diffraction shows that the morphology of the as-deposited films is thickness dependent; films with thickness around 30 nm for both processes are amorphous while ~ 70 nm films show the existence of crystallites. These results are correlated with FTIR measurements in the far IR region where the HfO 2 peaks are found to provide an easy and reliable technique for the determination of the crystallinity of relatively thick HfO 2 films. The index of refraction for all films is very close to that for bulk crystalline HfO 2.

Nucleation Studies of HfO2 Thin Films Produced by Atomic Layer Deposition

AbstractA hot wall Atomic Layer Deposition (ALD) flow reactor equipped with a Quartz Crystal Microbalance (QCM) has been used for the deposition of HfO2 thin films with tetrakis (dimethylamino) hafnium (TDMAH) and H2O as precursors. HfO2 films were deposited on H-terminated Si and SC1 chemical oxide starting surfaces. Spectroscopic ellipsometry (SE) and QCM measurements confirm linear growth of the films at a substrate temperature of 275°C. FTIR spectra indicate the films are amorphous as-deposited. Two distinct growth regimes are observed: from 1-50 cycles, both surfaces display similar growth rates of about 1.0Å/cycle; from 50-200 cycles, HfO2 growth is decreased by about 15% to ~0.87Å/cycle on both surfaces. Nucleation and initial growth behavior of the films on Si-H were examined using X-ray photoelectron spectroscopy (XPS). Angle-resolved XPS, at take-off angles of θ=0, 15, 30, 45 and 60° measured from the normal to the sample surface, is used to probe the interfacial region of thin films (4, 7, 10, 15 and 25 cycles) on H-terminated samples. Initially, an interfacial layer comprised of a SiOx/HfSiOx mixture is grown between 1-10 ALD cycles. We observe that the Si/HfO2 interface is unstable, and oxidation continues up to the 25th ALD cycle, reaching a thickness of ~18Å.