Tetrakis Ethylmethylamino Hafnium Research Articles

Growth mechanism of HfO2 film on H-terminated Si (100) surface from atomic layer deposition process using tetrakis(ethylmethylamino)hafnium

The deposition of HfO2 on H-terminated Si (100) surfaces presents both interest and challenges due to the complexity of the surface reaction mechanisms. Previous experimental studies reported conflicting results regarding the formation of interfacial layers and the presence of incubation periods during the initial cycles of the HfO2 atomic layer deposition (ALD) process. In this study, we provide a detailed analysis of the surface reaction mechanism of HfO2 ALD on H-terminated Si (100) surfaces using tetrakis(ethylmethylamino)hafnium (TEMAH) and water. Our findings demonstrate that TEMAH chemisorbs onto the H-terminated Si (100) surface through the formation of two N-Si interfacial bonds. Additionally, the remaining ligands of the adsorbed Hf precursor are efficiently removed through hydroxylation during the water pulse, with low energy barriers of +25.9 to +30.0 kJ/mol. Furthermore, the N-Si interfacial bonds can be broken, allowing for the formation of Hf-O-Si interfacial bonds during either the water pulse or post-deposition processes. This work provides valuable insights into the surface reactions of HfO2 ALD and explains the varied interfacial bonding and incubation periods observed in prior studies.

A theoretical study of the atomic layer deposition of HfO2 on Si(1 0 0) surfaces using tetrakis(ethylmethylamino) hafnium and water

The atomic layer deposition (ALD) of hafnium oxide (HfO2) thin film has attracted considerable attention owing to its crucial role in downscaling semiconductor devices. Herein, we theoretically investigated the reaction mechanisms during the ALD of HfO2 thin film (HfO2–ALD) on silicon (Si) surface using tetrakis(ethylmethylamino) hafnium (TEMAH) and water. By using two surface models, fully and partially hydroxylated Si(100) surfaces, we demonstrated that controlling the concentration of hydroxyl groups on the surface is important to enhance the activity for ligand-exchange reactions (LERs) of TEMAH and thereby effectively promote HfO2–ALD. During the precursor pulse, LERs on the fully hydroxylated Si(100) surface easily convert TEMAH into an unsaturated Hf atom with a low energy barrier of 25.8 kJ/mol, while mono(ethylmethylamino) hafnium (MEMAH) is obtained as the final product on the partially hydroxylated Si(100) surface with an energy barrier of 61.3 kJ/mol. The remaining ligand of the adsorbed MEMAH can be removed via LER with water during the water pulse. This work not only provides a better understanding of the conversion of TEMAH into a Hf atom on the hydroxylated Si(100) surface but also offers us more insights into the role of surface hydroxyls in the formation of HfO2 thin films.

Bipolar Resistive Switching in Hafnium Oxide-Based Nanostructures with and without Nickel Nanoparticles

As research into additives and intentionally introduced impurities in dielectric thin film for enhancing the resistive switching based random access memories (RRAM) continues to gain momentum, the aim of the study was to evaluate the effects of chemically presynthesised Ni nanoparticles (NPs) embedded in a dielectric layer to the overall structure and resistive switching properties. HfO2-based thin films embedded with Ni NPs were produced by atomic layer deposition (ALD) from tetrakis(ethylmethylamino)hafnium (TEMAH) and the O2 plasma ALD process onto a TiN/Si substrate. The Ni NPs were separately synthesised through a continuous flow chemistry process and dispersed on the dielectric layer between the two stages of preparing the HfO2 layer. The nanodevices’ morphology and composition were analysed with physical characterisation methods and were found to be uniformly dispersed across the sample, within an amorphous HfO2 layer deposited around them. When comparing the resistive switching properties of otherwise identical samples with and without Ni NPs, the ILRS/IHRS ratio rose from around a 4 to 9 at 0.2 V reading voltage, the switching voltage dropped from ~2 V to ~1.5 V, and a distinct increase in the endurance characteristics could be seen with the addition of the nanoparticles.

Room-temperature and high-quality HfO2/SiO2 gate stacked film grown by neutral beam enhanced atomic layer deposition

This study reports the fabrication of the high-quality hafnium dioxide (HfO2) film at room temperature (20–30 °C) using the neutral beam enhanced atomic layer deposition (NBEALD) we developed. The HfO2 film was fabricated using tetrakis(ethylmethylamino)hafnium (TEMAH) as the Hf precursor and O2 NB as the oxidant. Argon gas was used for the carrier and purge gases. The HfO2 film-deposition process consists of 5-s TEMAH feed, 5-s Ar purge, 5-s O2 gas injection, 20-s O2 neutral beam irradiation, and 5-s Ar purge. The HfO2 film exhibited a saturated growth per cycle of 0.18 nm/cycle and a high-quality film with low C contamination (2.7%), N contamination (3.9%), and a good O/Hf ratio (2.0) was achieved. The film also had an ideal refractive index of 1.9. Additionally, continuously grown high-quality HfO2 and silicon dioxide (SiO2) gate oxide films (stacked HfO2/SiO2 gate oxide film) were successfully fabricated at room temperature. This film has the potential to decrease the thermal budget, thus enabling high flexibility when designing semiconductor structures. These findings demonstrate the effectiveness of our NBEALD in forming high-k gate stack structures.

Impact of Hf and Al Co-Incorporation into the Atomic-Layer-Deposited ZnO Active Channel for the Thin-Film Transistor Applications

ZnO-based oxide semiconductors have attracted much attention as active layer for thin film transistors (TFTs) due to their special features such as low-temperature process compatibility, high transparency, and wide bandgap (~3.37 eV). However, the instability and difficulty in controlling the electrical conductivity of ZnO still remain as critical issues. To solve these problems, various metal atoms have been introduced in ZnO, such as In, Ga, Sn, Al, and Hf. Among them, Hf and Al can be acted as stability enhancer by suppressing oxygen vacancies formation and as conductivity modulator by adjusting doping concentration, respectively. To effectively exploit their advantages, the composition control is one of the important parameters to be carefully adjusted. Furthermore, the active channel layer should have homogenous and smooth surface for forming good interface between Hf-Al-Zn-O (HAZO) active and Al2O3 gate insulator layers. From these viewpoints, atomic layer deposition (ALD) can be an optimum method to deposit the HAZO thin films because of such benefits as excellent conformality and good controllability for composition and film thickness. Thus, in this work, we fabricated top-gate transparent oxide TFTs using newly presented HAZO active channels deposited by ALD method and investigated the effects of Hf and Al concentration on the device performance including basic characteristics such as carrier mobility, subthreshold swing (SS), and turn-on voltage (Von), and reliability characteristics. The ALD temperature of HAZO was fixed at 100 oC. Tetrakis(ethylmethylamino)hafnium (TEMAHf), trimethylaluminium (TMA), diethylzinc (DEZ), and H2O were used as Hf, Al, Zn, and O2 sources, respectively. In this work, the composition control of Hf and Al was selected as main strategy to modulate device property. The atomic composition of 20-nm-thick HAZO thin films was controlled by adding TEMAHf and TMA cycles among a total 100 cycles. Total ALD cycles were designed so that the HfO2 and Al2O3 were located in the intervals of ZnO. For the HAZO thin film with 2-at%-Hf and 2-at%-Al, the position of two TEMAHf cycles were placed on 40th and 80th cycles, and two TMA cycles were placed on 20th and 60th cycles of total 100 cycles, separately. The incorporated amounts of Hf and Al were modulated into 2, 4, 6, 8, and 10 at% and 2 and 4 at%, respectively. The data figure shows the comparisons in transfer characteristics for the fabricated top-gate TFTs using HAZO active layers with various amounts of incorporated Hf when the incorporated Al amount was fixed at 2 at%. The fabricated devices show distinct differences in device characteristics depending on the incorporated Hf and Al compositions. When the Hf amounts were varied from 2 to 10 at%, the Von’s shifted to positive direction from negative side toward 0 V and SS values were improved from 1.12 to 0.37 V/dec. In contrast, the carrier mobility was slightly decreased from 2.97 to 1.24 cm2/Vs. The post-annealing effects were also investigated. The fabricated TFTs were thermally treated at the temperature range from 150 to 250 oC for 1 h in oxygen atmosphere. The Von shifted toward positive direction and SS were improved as the increase in annealing temperature, although the on-current and carrier mobility showed decreasing trend. In conclusion, we successfully confirmed that the new composition of oxide semiconductor, HAZO, can be utilized as an active layer for the oxide TFT, and that the electronic natures of the HAZO channel layers can be well controlled by adjusting the ALD conditions. The top-gate TFT using the HAZO channel with 10-at%-Hf and 2-at%-Al showed the best device characteristics such as low SS value of 370 mV/dec, low-voltage operation at around 0 V, and comparable carrier mobility of 1.24 cm2/Vs. It was also found that thermal treatment in oxygen atmosphere markedly influenced on the transfer characteristics including the location of Von. Here, we believe that the device performance can be far improved by simultaneously optimizing the Hf and Al incorporating amounts and the post annealing process condition. Optimum ALD conditions for preparing the HAZO channel layers will also be important for better device performance for the HAZO TFTs. Furthermore, we have plans to investigate the device reliability, which is one of the most important factor in evaluating device characteristics, such as positive bias temperature stress stability (PBTS), and negative bias illumination stability (NBIS). As results, highly-stable TFTs will be implemented with practical value of carrier mobility by employing HAZO channel with appropriate incorporating amounts of Hf and Al at optimum ALD conditions. Figure 1

The effects of process temperature on the work function modulation of ALD HfO2 MOS device with plasma enhanced ALD TiN metal gate using TDMAT precursor

We have investigated the effects of metal gate process temperature on the effective work function (Weff) of MOS devices with all ALD HfO2/TiN gate stack and its correlation with grain size of PEALD TiN metal gate is presented with other electrical characteristics. Ti precursor and reactant were used with tetrakis-dimethyl-amino titanium (TDMAT) and H2/N2 mixture for TiN while tetrakis-ethylmethyl-amino hafnium (TEMA-Hf) and H2O were used for HfO2. With increasing TiN deposition temperature, the Weff of TiN electrode is positively shifted up to ~200meV while EOT is kept as 1.2nm. These findings could be attributed to the combining effects from crystal structure change (i.e., increased grain size) and different chemical composition. Unlike PVD TiN system, in ALD TiN system, higher VFB is observed with increasing Ti ratio in the film, ascribed to the small amount of carbon residue (6–9at%) within the TDMAT precursor.

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.

Correcting "static" measurements of vapor pressure for time dependence due to diffusion and decomposition.

The static method for measuring vapor pressure assumes that the sample is pure and that its temperature is steady and uniform. In practice, the measured pressure may be time dependent due to evaporative cooling after pumping on the sample, transpiration of the sample in a temperature gradient, or diffusion of an impurity out of the sample. An impurity cannot be avoided if the sample is decomposing. This article identifies and quantifies various causes of time dependence, and it includes an analysis that can obtain the vapor pressure from the time-dependent pressure of a decomposing sample. The analysis was applied to measurements of TEMAH (tetrakisethylmethylaminohafnium), whose decomposition continuously generated a volatile impurity. The corrected vapor pressures obtained for three TEMAH samples at 39 °C agreed to within ±1 %, even though the partial pressure of the impurity was as much as 7 times larger.

Apparatus to measure the vapor pressure of slowly decomposing compounds from 1 Pa to 105 Pa.

This article describes an apparatus and method for measuring vapor pressures in the range from 1 Pa to 105 Pa. Its three distinctive elements are : (1) the static pressure measurements were made with only a small temperature difference between the vapor and the condensed phase, (2) the sample was degassed in situ, and (3) the temperature range extended up to 200 °C. The apparatus was designed to measure metal-organic precursors, which often are toxic, pyrophoric, or unstable. Vapor pressures are presented for naphthalene, ferrocene, diethyl phthalate, and TEMAH (tetrakisethylmethylaminohafnium). Also presented are data for the temperature-dependent decomposition rate of TEMAH.

Deposition temperature dependent optical and electrical properties of ALD HfO2 gate dielectrics pretreated with tetrakisethylmethylamino hafnium

The effect of deposition temperature on the growth rate, band gap energy and electrical properties of HfO2 thin film deposited by atomic layer deposition (ALD) has been investigated. By means of characterization of spectroscopy ellipsometry and ultraviolet–visible spectroscopy, the growth rate and optical constant of ALD-derived HfO2 gate dielectrics are determined precisely. The deposition temperature dependent electrical properties of HfO2 films were determined by capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements. The leakage current mechanism for different deposition temperature has been discussed systematically. As a result, the optimized deposition temperature has been obtained to achieve HfO2 thin film with high quality.

Infrared study on room-temperature atomic layer deposition of HfO2 using tetrakis(ethylmethylamino)hafnium and remote plasma-excited oxidizing agents

Room-temperature atomic layer deposition (ALD) of HfO2 was examined using tetrakis (ethylmethylamino)hafnium (TEMAH) and remote plasma-excited water and oxygen. A growth rate of 0.26 nm/cycle at room temperature was achieved, and the TEMAH adsorption and its oxidization on HfO2 were investigated by multiple internal reflection infrared absorption spectroscopy. It was observed that saturated adsorption of TEMAH occurs at exposures of ∼1 × 105 L (1 L = 1 × 10−6 Torr s) at room temperature, and the use of remote plasma-excited water and oxygen vapor is effective in oxidizing the TEMAH molecules on the HfO2 surface, to produce OH sites. The infrared study suggested that Hf–OH plays a role as an adsorption site for TEMAH. The reaction mechanism of room temperature HfO2 ALD is discussed in this paper.

Characterization of Chemical Bonding Features and Interfacial Reactions in Ge-MIS Structure with HfO2/TaGexOy Dielectric Stack

As means to control interface reactions between HfO2 and Ge(100), chemical vapor deposition (CVD) of ultrathin Ta-rich oxide using tris(tert-butoxy)(tert-butylimido)tantalum (Ta-TTT) on chemically-cleaned Ge(100) has been conducted prior to atomic-layer controlled CVD of HfO2 using tetrakis (ethylmethylamino) hafnium (TEMA-Hf) and O3. An impact of post metallization annealing (PMA) in N2 ambience on chemical structure and electrical properties for TiN-gate Ge-MIS structure has been investigated. Hard x-ray photo-emission spectroscopy (HAXPES) measurements under synchrotron radiation with the excitation energy of 7939 eV show that good thermal stability of MIS structure against PMA at temperature of 400 °C. Diffusion of Ge atoms into stack dielectrics and TiN was observed after PMA at temperatures over 500 °C. As for the electrical properties of MIS capacitors, PMA at 300 °C was found to be effective to reduce the hysteresis due to charge trap and gate leakage current through the dielectrics. It was also found that the relative dielectric constant of interfacial TaGexOy thin layer was ~ 9, and calculated equivalent SiO2 thickness (CET) of 1.0 nm can be achieved for the sample with 3 nm thick HfO2/1nm-thick TaGexOy stack dielectrics.

Room-Temperature Atomic Layer Deposition of HfO2 By Using Remote Plasma Source

The sizes of integrated semiconductor devices such as metal oxide semiconductor (MOS), have reached to submicron range where the gate oxide films are needed to fabricate at a nanometer scale. Atomic layer deposition (ALD) is a potential technique for depositing dielectric films with monolayer precision by repeating adsorption of a source gas on a substrate that is subsequently reactivated for further adsorption [1]. HfO2 is believed to be a candidate as the high-k gate oxide material [2]. The growth temperature for the HfO2 deposition has been desired to be decreased to near room temperature because the interfacial layer is formed by the solid phase reaction with heating processes [3]. We developed a room-temperature (RT) atomic layer deposition technique for HfO2 deposition by using tetrakis(ethylmethylamino)-hafnium (TEMAH) as a precursor and a remote-plasma excited oxidizing gas.A p-type Si(100) substrate with a resistivity of 8-12 Ωcm was used as a sample. Prior to the experiment, the sample was cleaned with buffered HF acid solution and sulfuric acid-hydrogen peroxide mixture solution. As a hafnium source, TEMAH precursor was introduced in a variable leak valve. A remote-plasma system generating excited oxidizing gas was installed to the ALD chamber as shown in Fig.1. The source gas for the oxidizing gas is a mixture of H2O vapor and a carrier gas. The plasma was generated in a glass tube with an induction coil with a frequency of 13.56MHz and a RF power of 30 W. Before the ALD process, the substrate surface was treated with the plasma excited oxidizing gas for 5 min to be terminated with OH groups. For the HfO2 deposition, we repeated the cycle of TEMAH saturation and the oxidizing gas treatment at RT. The TEMAH exposure was set to 1.67×10-3 Torr×60 s. The saturation of TEMAH on the hydroxylated Si surface has been confirmed by IR absorption spectroscopy. The plasma excited oxidizing gas was injected for 2 min. The oxidization state of HfO2 film was evaluated by X-ray photoelectron spectroscopy (XPS). The thickness of the grown film was measured by spectroscopic ellipsometry. Fig.2 shows XPS spectra for Hf4f of HfO2 film grown on Si by the present ALD technique. The peak position of 16eV indicates the growth of HfO2 on Si. It is found that with the increase in the ALD cycles, the intensity of Hf 4f7/2 peak increases. We also checked the composition of HfO2 using XPS analysis. The ratio of Hf and O was calculated to be 1:2.06. The small amount of N as the impurity was detected as an impurity in the film (data not shown). We are now evaluating the concentration of the residual carbon in the film.Fig.3 shows the HfO2 thicknesses as a function of the ALD cycle. The linear increase in the HfO2 thickness with the ALD cycles indicates that the HfO2 is grown on Si with a constant rate in the ALD mode. The growth rate is estimated to be 0.26 nm/cycle. This value is comparable with those reported in previous ALD studies [4].To conclude, we successfully developed a non-heating ALD technique for HfO2 deposition at room temperature using a remote-plasma source. We are now investigating the electrical characteristics of HfO2 grown on Si and Ge as a MOS device. Moreover, the RT grown HfO2 films might be applicable in acid proof coatings on plastic materials. Detail will be presented at the conference.

Synchrotron radiation photoemission study of interfacial electronic structure of HfO2 on In0.53Ga0.47As(001)-4 × 2 from atomic layer deposition

The growth of a passivating layer on a In0.53Ga0.47As(001)-4 × 2 surface by atomic-layer deposition of tetrakis[ethylmethylamino]Hafnium (TEMAHf)) followed by the water pulse was investigated by synchrotron radiation photoemission. The Hf atoms maintain four-fold coordination, both after the initial TEMAHf deposition and the subsequent water pulse. The Hf atoms initially bond to the As dangling bonds of the surface As atom located on the edges of the raised ridges. One EMA ligand is removed in this process. Subsequent water exposure substitutes OH ligand for one or more remaining EMA ligands. These in turn react with TEMAHf to form Hf-O-Hf bonds allowing the hafnium oxides to grow. The surface In atoms on the terrace of the raised ridges were partially removed, but none bonded of the precursor atoms. Correlations between the interfacial electronic structure and the electric performance are discussed.

Effects of trimethylaluminium and tetrakis(ethylmethylamino) hafnium in the early stages of the atomic-layer-deposition of aluminum oxide and hafnium oxide on hydroxylated GaN nanoclusters

We calculate the interactions of two atomic layer deposition (ALD) reactants, trimethylaluminium (TMA) and tetrakis(ethylmethylamino) hafnium (TEMAH) with the hydroxylated Ga-face of GaN clusters when aluminum oxide and hafnium oxide, respectively, are being deposited. The GaN clusters are suitable as testbeds for the actual Ga-face on practical GaN nanocrystals of importance not only in electronics but for several other applications in nanotechnology. We find that TMA spontaneously interacts with hydroxylated GaN; however it does not follow the atomic layer deposition reaction path unless there is an excess in potential energy introduced in the clusters at the beginning of the optimization, for instance, using larger bond lengths of various bonds in the initial structures. TEMAH also does not interact with hydroxylated GaN, unless there is an excess in potential energy. The formation of a Ga-N(CH3)(CH2CH3) bond during the ALD of HfO2 using TEMAH as the reactant without breaking the Hf-N bond could be the key part of the mechanism behind the formation of an interface layer at the HfO2/GaN interface.

Evidence of GeO volatilization and its effect on the characteristics of HfO2 grown on a Ge substrate

HfO2 films are deposited by atomic layer deposition (ALD) using tetrakis ethylmethylamino hafnium (TEMAH) as the hafnium precursor, while O3 or H2O is used as the oxygen precursor. After annealing at 500 °C in nitrogen, the thickness of Ge oxide's interfacial layer decreases, and the presence of GeO is observed at the H2O-based HfO2 interface due to GeO volatilization, while it is not observed for the O3-based HfO2. The difference is attributed to the residue hydroxyl groups or H2O molecules in H2O-based HfO2 hydrolyzing GeO2 and forming GeO, whereas GeO is only formed by the typical reaction mechanism between GeO2 and the Ge substrate for O3-based HfO2 after annealing. The volatilization of GeO deteriorates the characteristics of the high-κ films after annealing, which has effects on the variation of valence band offset and the C—V characteristics of HfO2/Ge after annealing. The results are confirmed by X-ray photoelectron spectroscopy (XPS) and electrical measurements.

Influences of different oxidants on the characteristics of HfAlOx films deposited by atomic layer deposition

A comparative study of two kinds of oxidants (H2O and O3) with the combinations of two metal precursors [trimethylaluminum (TMA) and tetrakis(ethylmethylamino) hafnium (TEMAH)] for atomic layer deposition (ALD) hafnium aluminum oxide (HfAlOx) films is carried out. The effects of different oxidants on the physical properties and electrical characteristics of HfAlOx films are studied. The preliminary testing results indicate that the impurity level of HfAlOx films grown with both H2O and O3 used as oxidants can be well controlled, which has significant effects on the dielectric constant, valence band, electrical properties, and stability of HfAlOx film. Additional thermal annealing effects on the properties of HfAlOx films grown with different oxidants are also investigated.

Control of Interfacial Reaction of HfO<sub>2</sub>/Ge Structure by Insertion of Ta Oxide Layer

As means to control interface reactions between HfO2 and Ge(100), chemical vapor deposition (CVD) of ultrathin Ta-rich oxide using Tri (tert-butoxy) (tert-butylimido) tantalum (Ta-TTT) on chemically-cleaned Ge(100) has been conducted prior to atomic-layer controlled CVD of HfO2 using tetrakis (ethylmethylamino) hafnium (TEMA-Hf) and O3. The XPS analysis of chemical bonding features of the samples after the post deposition N2 annealing at 300°C confirms the formation of TaGexOy and the suppression of the interfacial GeO2 layer growth. The energy band structure of HfO2/TaGexOy/Ge was determined by the combination of the energy bandgaps of HfO2 and TaGexOy measured from energy loss signals of O 1s photoelectrons and from optical absorption spectra and the valence band offsets at each interface measured from valence band spectra. From the capacitance-voltage (C-V) curves of Pt-gate MIS capacitors with different HfO2 thicknesses, the thickness reduction of TaGexOy with a relative dielectric constant of 9 is a key to obtain an equivalent SiO2 thickness (EOT) below 0.7nm.

IR study of fundamental chemical reactions in atomic layer deposition of HfO2 with tetrakis(ethylmethylamino)hafnium (TEMAH), ozone, and water vapor

The fundamental reactions in HfO2 atomic layer deposition (ALD) with the precursors tetrakis(ethylmethylamino)hafnium (TEMAH), ozone, and water vapor on Si (100) surfaces at room temperature (RT) were studied by infrared absorption spectroscopy (IRAS) with a multiple internal reflection geometry. The IRAS results indicated that TEMAH can be adsorbed at OH sites on Si surfaces at RT. Ozone irradiation on the TEMAH-adsorbed Si surface at RT effectively removes hydroaminocarbon adsorbates introduced in the course of TEMAH adsorption, although this treatment provides no OH-group adsorption sites for TEMAH on the Si surface at RT. For further adsorption, water–vapor treatment at around 160°C is effective in restoring the adsorption sites. The IR study suggests that the cyclic process of TEMAH adsorption and ozone treatment at RT followed by OH restoration with water vapor at a temperature of 160°C allows continuous HfO2 deposition.

Evaluation of high thermal stability cyclopentadienyl Hf precursors with H2O as a co-reactant for advanced gate logic applications

For the purpose of extending the upper temperature limit of metallorganic atomic layer deposition, mixed ligand precursors containing cyclopentadienyl (Cp, C5H5) ligands have been shown to exhibitsuperior thermal stability compared to the widely adopted tetrakis(ethylmethylamino)hafnium (TEMAH) precursor while also possessing adequate vapor pressure characteristics for use in atomic layer deposition (ALD) processing. In order to prevent the deleterious oxidation of the underlying Si from O3 the use of a milder oxidant such as H2O is preferred. Accordingly in this study, we investigated ALD using the liquid precursors CpHf(NMe2)3 and (CpMe)2Hf(OMe)Me in the temperature range 305 – 410 °C with H2O as a co-reactant and compared the film growth and electrical properties with films deposited using a conventional TEMAH/H2O process at 305 °C as well as the same process with an optimized annealing scheme. The CpHf(NMe2)3/H2O process was observed toexhibit a growth-per-cycle (GPC) in the range 0.23 – 0.36 Å/cycle which is roughly half that of the TEMAH/H2O process (∼0.6 Å/cycle). In the 340 – 375 °C range this process is comparable toTEMAH/H2O in terms of equivalent oxide thickness but with slightly higher leakage. Even thoughthis process allows for higher processing temperatures it is not able to scale to the level of theTEMAH/H2O process using an optimized annealing scheme. For (CpMe)2Hf(OMe)Me withH2O,in the process space investigated in this study this process was unable to afford a viable growth rate (<0.03 Å/cycle) for device testing although a GPC of 0.33 Å/cycle was obtained using O3.