Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films

HfO₂ thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O₂/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO₂ grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO_x suboxide layer at the HfO₂/Si interface is unavoidable. The HfO₂ thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O₂/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO₂, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO₂ to form HfO₂, leaving Si-Si bonds behind.     

Effect of inner oxygen on the interfacial layer formation for HfO<Subscript>2</Subscript> gate dielectric

The interfacial layer (IL) formed at the HfO₂/Si interface was investigated by using Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Differently with the previous reports, it is concluded that the inner oxygen from bulk film predominates the oxidation process in interface region rather than the oxygen introduced from outer environment. First, from FT-IR, it is found that the formation of the IL strongly relies on the annealing temperature but does not obviously rely on the HfO₂ thickness and the annealing atmosphere. Second, the contradistinctive images of Hf/Si annealed in oxygen ambient and Hf/SiO₂ annealed in vacuum were investigated by TEM, which confirms the conclusion obtained from FT-IR data that the IL is formed not by a diffusion of the oxygen from the annealing atmosphere, but by a reaction within the interface region. Third, the Hf 4f, O 1s, and Si 2p core-level energy states of Hf/SiO₂ stack annealed in vacuum were investigated by XPS using two ways, one is investigating the samples annealed in vacuum for varied time and the other is investigating the fully oxidized sample in different depth. Based on the experiments, it is concluded that the inner oxygen from bulk films (HfO₂ or SiO₂) has greater influence on the IL formation comparing with the outer oxygen from environment.     

Modulation of the structural and optical properties of sputtering-derived HfO2 films by deposition power

High-k gate dielectric HfO₂ thin films have been deposited on Si and quartz substrate by radio frequency magnetron sputtering. The structural and optical properties of HfO₂ thin films related to deposition power are investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), ultraviolet–visible spectroscopy (UV–Vis), and spectroscopic ellipsometry (SE). Results confirmed by XRD have shown that the as-deposited HfO₂ thin films are not amorphous state but in monoclinic phase, regardless of deposition power. Analysis from FTIR indicates that an interfacial layer has been formed between the Si substrate and the HfO₂ thin film during deposition. AFM measurements illustrate that the root mean square (RMS) of the as-deposited HfO₂ thin films’ surface demonstrates an apparent reduction with the increase of deposition. Combined with UV–Vis and SE measurements, it can be noted reduction in band gap with an increase in power has been observed. Additionally, increase in refractive index (n) has been confirmed by SE.     

Synthesis and characterization of HfO2 and ZrO2 thin films deposited by plasma assisted reactive pulsed laser deposition at low temperature

A plasma assisted reactive pulsed laser deposition process was demonstrated for low-temperature deposition of thin hafnia (HfO₂) and zirconia (ZrO₂) films from metallic hafnium or zirconium with assistance of an oxygen plasma generated by electron cyclotron resonance microwave discharge. The structure and the interface of the deposited films on silicon were characterized by means of Fourier transform infrared spectroscopy, which reveals the monoclinic phases of HfO₂ and ZrO₂ in the films with no interfacial SiO_x layer between the oxide film and the Si substrate. The optical properties of the deposited films were investigated by measuring the refractive indexes and extinction coefficients with the aid of spectroscopic ellipsometry technique. The films deposited on fused silica plates show excellent transparency from the ultraviolet to near infrared with sharp ultraviolet absorption edges corresponding to direct band gap.     

Surface treatment for high-quality Al2O3 and HfO2 layers deposited on HF-dipped surface by atomic layer deposition

Al₂O₃ and HfO₂ thin layers were deposited on either 0.7-nm chemical SiO₂ surface layers, HF-dipped Si surfaces or on HF-dipped Si surfaces with an innovative Cl₂ surface treatment. This chemical treatment leads to the formation of one mono-layer of –OH groups on the silicon surface without any SiO _x growth. Thicknesses, composition, and structure of the high-k layers as well as the nature of their interfaces with silicon were studied using spectrometric ellipsometry, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). While deposition on a HF-dipped Si surface led to a nucleation retardation and to a 3-dimensional growth mode, high-quality, uniform Al₂O₃ layers were obtained on a Cl₂-treated Si surface. XPS and ATR analyses showed a very small SiO _x regrowth, less than 0.26 nm during deposition.     

HfO2 gate insulator formed by atomic layer deposition for thin-film-transistors

We have investigated the effects of annealing temperature on the physical and electrical properties of the HfO₂ film deposited by an atomic layer deposition (ALD) method for high-k gate oxides in thin-film-transistors (TFTs). The ALD deposition of HfO₂ directly on the Si substrate at 300 °C results in the formation of thin HfSi_xO_y interfacial layer between Si and HfO₂. The subsequent low temperature N₂-annealing of HfO₂ films (i.e., 300 °C) using a rapid thermal processor (RTP) improves the overall electrical characteristics of HfSi_xO_y-HfO₂ films. Based on the current work, we suggest that HfO₂ film deposited by the ALD method is suitable for high-k gate oxides in TFTs, which have to be fabricated at low temperature.     

Modelization of hafnium silicate chemical vapor deposition using tetrakis-diethyl-amino-hafnium and tetrakis-dimethyl-amino-silane

The Chemical Vapor Deposition growth mechanism of a hafnium silicate film deposited by means of the co-flow of two precursors, TDEAH (tetrakis-diethyl-amino-hafnium) and 4DMAS (tetrakis-dimethyl-amino-silane), is characterized. Typical growth kinetics demand that the deposition rate increases and the silicon concentration remain stable with increasing reactor pressure. Though the deposition rate follows the expected growth kinetics, the silicon concentration in the silicate does not and exhibits an abnormal increase with increasing reactor pressure. To understand this atypical behavior the formation of pure HfO₂ from TDEAH and pure SiO_x from 4DMAS is first studied. Experimental results show that whereas the HfO₂ deposition is well behaved and fits a diffusion-based model defined by assuming diffusion of TDEAH through a boundary layer, the deposition of SiO_x with 4DMAS requires Hf-O nucleation sites and self-saturates after a single Si―O monolayer is formed. Based on these observations, a model is developed for hafnium silicate formation. The Atomic Layer Deposition like behavior of 4DMAS decomposition results in a deposition rate and film stoichiometry that are weakly sensitive to the 4DMAS partial pressure, and instead are driven by the TDEAH reaction. Since TDEAH operates within a transport-limited regime, the deposition rate is insensitive to substrate temperature, and is only controlled by the TDEAH partial pressure and the gas phase kinematics, rendering the process robust and easily controllable with excellent reproducibility.     

In situ studies of the atomic layer deposition of thin HfO2 dielectrics by ultra high vacuum atomic force microscope

We studied in situ the initial stages of atomic layer deposition (ALD) of HfO₂ by an ultra high vacuum atomic force microscope working in frequency-modulation mode. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf and water as precursors, were performed on the Si(001)/SiO₂ substrate maintained at 230 °C. After each ALD cycle we studied the influence of the HfO₂ growth on the surface height histogram, the root mean square roughness, the surface fractal dimension and the autocorrelation function. This detailed analysis of the surface topography allowed us to confirm the completion of the first HfO₂ layer after four ALD cycles.     

Rutile-type TiO2 thin film for high-k gate insulator

We investigated rutile-type titanium dioxide (TiO₂) films for possible use as a high-k gate insulator. The TiO₂ thin films were directly deposited on Si substrates using a RF magnetron sputtering method with a sintered oxide target. A single phase of rutile-type TiO₂ whose dielectric constant of approximately 75 was obtained when the film was deposited in an inert gas atmosphere and annealed at 800 °C in an oxidizing gas atmosphere. The oxygen ions were deficient in the as-deposited film, and consequently, a sufficient oxygen supply was needed to crystallize the film to a single phase of rutile during the post-annealing. However, the interfacial SiO₂ layer between the TiO₂ and the Si substrate simultaneously grew thicker than 2 nm. As the interfacial SiO₂ grew, the leakage current was decreased and the equivalent oxide thickness was increased, in the Au/rutile-type TiO₂/Si capacitor. Therefore, we concluded that the growth of the interfacial SiO₂ layer thicker than 2 nm is inevitable to form the single phase of rutile-type TiO₂ and to decrease the leakage.     

Electron energy-loss spectroscopy investigation of Y2O3 films on Si (001) substrate

Electron energy -loss spectroscopy has been used to investigate the interface between a Y₂O₃ film and the silicon substrate. The chemical composition of the interface layer is revealed to be nearly pure amorphous SiO₂. Yttrium silicates are found at the Y₂O₃/SiO₂ interface region. The formation of the interfacial yttrium silicates has been interpreted by the direct chemical reaction between the deposited Y₂O₃ film and the SiO₂ interface layer. The Si L₂₃ and O K edges of yttrium silicates (Y₂SiO₅ and Y₂Si₂O₇) have been calculated by the first-principle full multiple - scattering method. The theoretical results are consistent with the experimental spectra, which confirms the formation of yttrium silicates.     

Chemical structure and electrical properties of sputtered HfO2 films on Si substrates annealed by rapid thermal annealing

The chemical structure and electrical properties of HfO₂ thin film grown by rf reactive magnetron sputtering after rapid thermal annealing (RTA) were investigated. The chemical composition of HfO₂ films and interfacial chemical structure of HfO₂/Si in relation to the RTA process were examined by X-ray photoelectron spectroscopy. Hf 4f and O 1s core level spectra suggest that the as-deposited HfO₂ film is nonstoichiometric and the peaks shift towards lower binding energy after RTA. The Hf-Si bonds at the HfO₂/Si interface can be broken after RTA to form Hf-Si-O bonds. The electrical characteristics of HfO₂ films were determined by capacitance-voltage (C-V) and current density-voltage (J-V) measurements. The results showed that the density of fixed charge and leakage current density of HfO₂ film were decreased after the RTA process in N₂ atmosphere.     

Evolution of SiO2/Ge/HfO2(Ge) multilayer structure during high temperature annealing

Use of germanium as a storage medium combined with a high-k dielectric tunneling oxide is of interest for non-volatile memory applications. The device structure consists of a thin HfO₂ tunneling oxide with a Ge layer either in the form of continuous layer or discrete nanocrystals and relatively thicker SiO₂ layer functioning as a control oxide. In this work, we studied interface properties and formation kinetics in SiO₂/Ge/HfO₂(Ge) multilayer structure during deposition and annealing. This material structure was fabricated by magnetron sputtering and studied by depth profiling with XPS and by Raman spectroscopy. It was observed that Ge atoms penetrate into HfO₂ layer during the deposition and segregate out with annealing. This is related to the low solubility of Ge in HfO₂ which is observed in other oxides as well. Therefore, Ge out diffusion might be an advantage in forming well controlled floating gate on top of HfO₂. In addition we observed the Ge oxidation at the interfaces, where HfSiO_x formation is also detected.     

Characteristics of high-k gate oxide prepared by oxidation of multi-layered Hf/Zr/Hf/Zr/Hf metal films

We investigated the physical and electrical properties of Hf-Zr mixed high-k oxide films obtained by the oxidation and annealing of multi-layered metal films (i.e., Hf/Zr/Hf/Zr/Hf, ∼ 5 nm). We demonstrated that the oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf-Zr mixed oxide film was formed on the top of silicate film due to inter-diffusion between Hf and Zr layer. This film shows the improved dielectric constant (k) and the raised crystallization temperature. Compared with HfO₂ and ZrO₂ gate dielectric, the crystallization temperature of Hf-Zr mixed oxides was raised by more than 200 °C. Using AES and XPS, we observed that Zr oxide has more fully oxidized stoichiometry than Hf oxide, irrespective of annealing temperatures. We also found that the thickness of an interfacial layer located between Hf-Zr mixed oxide and Si substrate also increases as annealing temperature increases. Especially, the thin SiO_x interfacial layer starts to form if annealing temperature increases over 700 °C, deteriorating the equivalent oxide thickness.     

Composition and structure of hafnia films on silicon

Ellipsometry, electron microscopy, and x-ray photoelectron spectroscopy data indicate that, during HfO₂ deposition onto silicon, the native oxide reacts with the HfO₂ deposit to form an amorphous intermediate layer which differs in refractive index (?1.6) from both HfO₂ (1.9–2.0) and SiO₂ (1.46). Thermodynamic analysis of the Si-SiO₂-HfO₂-Hf system shows that Si is in equilibrium with Si/HfO_{2 ? y} only at low oxygen pressures. Starting at a certain oxygen pressure (equivalent to the formation of a native oxide layer), the equilibrium phase assemblage is Si/HfSiO₄/HfO_{2 ? y} .     

Investigation of the aluminum oxide/Si(1 0 0) interface formed by chemical vapor deposition

Thin films of aluminum oxide were deposited using trimethylaluminum and oxygen. The deposition rate was found to decrease with increasing temperature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the film/substrate interface. When dry O₂ was used during deposition, the film/substrate interface was free of any silicon dioxide or aluminum silicate phase. On annealing the as-deposited films in Ar, a layer of silicon dioxide film formed at the interface. XPS results indicated that the O/Al ratio in the as-deposited films was higher than that in stoichiometric Al₂O₃. However, the ratio was found to decrease in the annealed samples suggesting that excess oxygen present in the deposited films is responsible for the formation of interfacial silicon dioxide layer. Interfacial phase formation was observed in the as-deposited samples, when small amounts of ozone along with oxygen were used as the oxygen precursor.     

Depth redistribution of components of SiOx layers prepared by magnetron sputtering in the process of their decomposition

The process of thermal decomposition of SiO_x layers prepared by magnetron co-sputtering of Si and SiO₂ on Si and quartz substrates is studied by Auger and secondary ion mass spectroscopies. It is found that high temperature annealing of the layers causes a Si-depleted region near the layer/substrate interface. It is shown that the formation of this region does not depend on the type of substrate but depends on the content of excess Si and is observed at high content of excess Si. When the excess Si content decreases, the Si-depleted region at first smears and then disappears. The mechanism of SiO_x decomposition and possible reasons for the appearance of the Si-depleted region are discussed.     

Atomic layer deposition of HfO2 on self-assembled monolayer-passivated Ge surfaces

HfO₂ films are not easily deposited on hydrophobic self-assembled monolayer (SAM)-passivated surfaces. However, in this study, we deposited HfO₂ films on a tetradecyl-modified SAM with a Ge surface using atomic layer deposition at 350 °C. A slightly thinner HfO₂ film thickness was obtained on the tetradecyl-modified SAM passivated samples than that typically obtained on GeO_x-passivated samples. The resulting electrical properties are explained by the physical thickness and stoichiometry of the interfacial layer.     

Atomic layer deposition of HfO2 thin films and nanolayered HfO2–Al2O3–Nb2O5 dielectrics

Smooth, 4–6-nm thick hafnium oxide films were grown by atomic layer deposition from HfI₄ or HfCl₄ and H₂O on SiO₂/Si(1 0 0) substrates at 300 °C. Non-uniform films were obtained on hydrogen-terminated Si(1 0 0). The stoichiometry of the films corresponded to that of HfO₂. The films contained small amounts of residual chlorine and iodine. The films deposited on SiO₂/Si(1 0 0) were amorphous, but crystallized upon annealing at 1000 °C. In order to decrease the conductivity, the HfO₂ films were mixed with Al₂O₃, and to increase the capacitance, the films were mixed with Nb₂O₅. The capacitance–voltage curves of the Hf–Al–O mixture films showed hysteresis. The capacitance–voltage curves of HfO₂ films and mixtures of Hf–Al–Nb–O were hysteresis free.     

Electric field induced interfacial reaction of Au-Ag bimetal film on SiO2 surface

Interface evolution of nanometer scale Au-Ag bimetal film on SiO₂ substrate surface during electromigration was investigated by angle resolved X-ray photoelectronspectroscopy (ARXPS). ARXPS spectra showed that a chemical reaction between Au-Ag filmand SiO₂ layer occurred at interface, which caused Au, Ag and Si having differentdistribution and chemical states across the film. This result as well as previousobservation by atomic force microscopy (AFM) demonstrate that electromigration of Au-Agbimetal film on SiO₂ surface is accompanied with strong interfacial chemicalreaction rather than a simple lateral physical diffusion process.     

Interfacial adhesion energies of Ru–Mn direct plateable diffusion barriers prepared by atomic layer deposition for advanced Cu interconnects

The effects of Mn addition and post-annealing on the interfacial decohesion energies of Ru direct plateable diffusion barrier layer prepared by atomic layer deposited (ALD) for advanced Cu interconnect applications were systematically evaluated using a four-point bending test. The interfacial decohesion energy increased with the addition of Mn to the Ru thin films and further increased after post-annealing at 500 °C for 30 min in a hydrogen atmosphere, and the interfacial decohesion energies were 3.63, 6.74, and 20.09 J/m² for the as-deposited Cu/Ru/SiO₂, as-deposited Cu/Ru-4.2 at.%Mn/SiO₂, and annealed Cu/Ru-4.2 at.%Mn/SiO₂, respectively. The scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) analysis results clearly indicated that the Mn in the annealed ALD Ru–Mn film diffused toward a Ru/SiO₂ interface and Mn silicate was formed at the Ru/SiO₂ interface. Additionally, the results of the X-ray photoelectron spectroscopy (XPS) analysis clearly showed that MnSiO₃ and MnSi were formed at the Ru/SiO₂ interface. Consequently, the findings of the XPS and STEM/EDS study revealed that there was an adequate correlation between the interfacial decohesion energy and the MnSi and MnSiO₃ bond formed at the Ru–Mn /SiO₂ interface. Therefore, a properly annealed ALD Ru-4.2Mn thin film appears to be a hopeful diffusion barrier layer candidate with strong interfacial reliability for advanced Cu interconnects.