Hf-silicate Layer Research Articles

Oxidation Mechanisms of Hafnium Overlayers Deposited on an Si(111) Substrate.

The oxidation mechanism of hafnium overlayers on an Si(111) substrate [Hf-Si(111), including the outermost metallic Hf overlayers and interfacial Hf silicides (HfSi and HfSi4)] was investigated via high-resolution synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) of Hf 4f5/2,7/2, Si 2p1/2,3/2, and O 1s core levels. The atomic-scale interaction of O2 molecules with Hf-Si(111) is discussed by comparing the results obtained following thermal O2 exposures [translational energy (Et) ≈ 0.03 eV] with those obtained following supersonic O2 molecular beam (SOMB) irradiation (Et ≈ 2.2 eV). Metallic Hf and interfacial HfSi were immediately oxidized to HfO2 and Hf (sub)silicates (Hf-O-Si configurations) via trapping-mediated dissociative adsorption. Upon excessive SOMB irradiation, the other interfacial HfSi4 was oxidized via direct dissociation. When oxidation proceeded at the Si(111) substrate via excess SOMB irradiation, volatile Si atoms were emitted from the interfacial SiO2/Si-strained layers. When the volatile Si atoms were trapped in the overlayers, the HfO2 overlayers were converted into completely oxidized Hf silicate layers. However, when the volatile Si atoms passed through the HfO2 overlayers, they reacted with the impinging O2, and the outermost SiO2 deposition layers were formed on HfO2 (or Hf silicate) layers.

Characterization of the electronic structure and thermal stability of HfO2/SiO2/Si gate dielectric stack

X‐ray photoelectron spectroscopy was used to investigate thermal stability of HfO2 on SiO2/Si substrate prepared by atomic layer deposition, followed by annealing at different temperature. Hf silicate and Hf silicide are formed at the interface of HfO2 and SiO2 during deposition. The Hf silicide disappears, while the amount of the Hf silicate is intensified after post‐deposition annealing treatment at 400 °C. Phase separation of the Hf silicate layer occurs when the annealing temperature is over 400 °C, resulting in the Hf silicate decomposition into Si and Hf oxides. Moreover, crystallization at high temperature leads to grain boundaries formation, which deteriorates the gate leakage current, as observed by the electrical measurements. The similar annealing temperature dependence of both internal electric field and the amount of Hf silicate implies that the Hf silicate plays a key role in building up the internal electric field, which is attributed to generation of oxygen vacancies (Vo) in the Hf silicate layer. Copyright © 2017 John Wiley & Sons, Ltd.

Room temperature formation of Hf-silicate layer by pulsed laser deposition with Hf-Si-O ternary reaction control

We investigated the room temperature growth of HfO2 layers on Si substrates by pulsed laser deposition under ultra-high vacuum conditions. The laser fluence (LF) during HfO2 layer growth was varied as a growth parameter in the experiments. X-ray photoemission spectroscopy (XPS) was used to observe the interface chemical states of the HfO2/Si samples produced by various LFs. The XPS results indicated that an interface Hf-silicate layer formed, even at room temperature, and that the thickness of this layer increased with increasing pulsed LF. Additionally, Hf-Si bonds were increasingly formed at the interface when the LF was more than 2 J/cm2. This bond formation process was related to decomposition of HfO2 to its atomic states of Hf and O by multiphoton photochemical processes for bandgap excitation of the HfO2 polycrystalline target. However, the Hf-Si bond content of the interface Hf-silicate layer is controllable under high LF conditions. The results presented here represent a practical contribution to the development of room temperature processing of Hf-compound based devices.

Annealing temperature modulated interfacial chemistry and electrical characteristics of sputtering-derived HfO2/Si gate stack

Sputtering-derived HfO2 high-k gate dielectric thin films have been deposited on Si substrate by means of high vacuum physics vapor deposition method. Via characterization from x-ray photoelectron spectroscopy (XPS) and electrical measurements, the effect of post-deposition annealing temperature on the interfacial and electrical properties of HfO2/Si gate stack has been investigated. XPS analyses show that an interfacial layer between HfO2 and silicon substrate has been found in the post-deposition annealing process. Increase in Hf-silicate layer and reduction in SiO2 low-k interface layer have been detected. Electrical measurements of MOS capacitor based on Al/HfO2/Si gate stacks indicate that annealing HfO2 sample at 300 °C demonstrated the improved electrical performance. As a result, the leakage current of 3.60 × 10−5 A/cm2 at applied substrate voltage of 2 V, which is much lower than those samples annealed at other temperature, has been obtained. The leakage current mechanism for different annealing temperature has been discussed systematically.

Oxygen vacancy formation and the induced defect states in HfO2 and Hf-silicates – A first principles hybrid functional study

O vacancy formation and the associated electronic defect states in Hf-based oxides have been investigated over a wide range of compositions using first-principles hybrid density functional calculations. Based on the generated structure models, we have identified the most probable O coordination structures in amorphous HfO2 and in Hf-silicates, respectively. Our calculations showed that the formation energies of O vacancy and the positions of the induced defect states in the band gap are largely dependent on the local structures of the vacancy site rather than on the compositions of Hf-silicates. Considering the measured valence band offset between Si and Hf-silicates, a considerable amount of O vacancies are likely to stay in the charge neutral state in Hf-silicates when the Fermi level lies in the band gap region of Si. Furthermore, the concentration of O vacancy in Hf-silicates was found to be much lower than that in HfO2 when the Fermi level lies in/below the mid-gap region of Si. Consequently, the flat band voltage shift and the transient threshold voltage instability can be significantly reduced in Hf-silicates in comparison to that in HfO2, indicating that the presence of a Hf-silicate layer in between the gate oxides and the Si substrate could be beneficial to the performance of the CMOS device.

Interfacial Dead-Layer Effects in Hf-Silicate Films with Pt or RuO2 Gates

The interfacial dead-layer (DL) effects at the interfaces between Hf-silicate films and Pt or RuO2 gate metals are examined. The Si content in the Hf-silicate film was controlled to vary the dielectric constant (k). The DL effect was strongly dependent on the k value of the Hf-silicate layer, and was suppressed when the Si content was increased to ∼80% (k ≈ 6). This Si content also coincides with the Fermi level pinning-free composition. Therefore, the optimum high-k gate dielectric structure could be a higher-k layer HfO2 capped with a lower-k layer (k ≈ 6) with minimum thickness (∼1 nm) for the best dielectric performance.

Effects of the Interfacial Layer on Electrical Properties of TiO2-based High-k Dielectric Composite Films

Effects of interfacial layer on the electrical properties of TiO2 based dielectric thin films prepared by atomic layer deposition are investigated. It was confirmed from XPS data that the Hf-silicate and La-silicate interfacial layers including SiOx were formed in the interface of the HfO2/TiO2/Al2O3 (HTA) and La2O3/TiO2/Al2O3 (LTA) gate stack structures, respectively. In addition, the dielectric constants and leakage currents of HTA and LTA structures were affected by the formation of Hf-silicate and La-silicate layer in the interface and crystallization of TiO2 thin film, respectively. It was also found that the LTA thin film annealed at 600 °C showed the low equivalent oxide thickness of 0.91 nm and the low leakage current of 4.16×10-6 A/cm2 at 4 MV/cm.

Temperature-Dependent Physical and Memory Characteristics of Atomic-Layer-DepositedRuOxMetal Nanocrystal Capacitors

Physical and memory characteristics of the atomic-layer-depositedRuOxmetal nanocrystal capacitors in an n-Si/SiO2/HfO2/RuOx/Al2O3/Pt structure with different postdeposition annealing temperatures from 850–1000°C have been investigated. TheRuOxmetal nanocrystals with an average diameter of 7 nm and a highdensity of 0.7 × 1012/cm2are observed by high-resolution transmission electron microscopy after a postdeposition annealing temperature at 1000°C. The density ofRuOxnanocrystal is decreased (slightly) by increasing the annealing temperatures, due to agglomeration of multiple nanocrystals. The RuO3nanocrystals and Hf-silicate layer at the SiO2/HfO2interface are confirmed by X-ray photoelectron spectroscopy. For post-deposition annealing temperature of 1000°C, the memory capacitors with a small equivalent oxide thickness of ~9 nm possess a large hysteresis memory window of >5 V at a small sweeping gate voltage of ±5 V. A promising memory window under a small sweeping gate voltage of ~3 V is also observed due to charge trapping in theRuOxmetal nanocrystals. The program/erase mechanism is modified Fowler-Nordheim (F-N) tunneling of the electrons and holes from Si substrate. The electrons and holes are trapped in theRuOxnanocrystals. Excellent program/erase endurance of 106cycles and a large memory window of 4.3 V with a small charge loss of ~23% at 85°C are observed after 10 years of data retention time, due to the deep-level traps in theRuOxnanocrystals. The memory structure is very promising for future nanoscale nonvolatile memory applications.

Interface Study of SiO2/ HfO2/SiO2 Stacks Used as InterPoly Dielectric for Future Generations of Embedded Flash Memories

AbstractWe have investigated the integration of Hf-based material as Inter Poly Dielectric in flash memories devices. Electrical measurements showed the good properties of SiO2/HfO2/SiO2 stacks. We then interested to the impact of the thermal budget on this specific stack which induces changes in the electrical properties. XPS measurements suggests those changes are due to the presence of an Hf-silicate layer at the SiO2/HfO2 interface.

Effect of thermal treatment on the band offsets and interfacial properties of HfOxNy gate dielectrics

Band offsets and interfacial properties of HfOxNy films grown on Si(1 0 0) through radio-frequency reactive magnetron sputtering were investigated by x-ray photoelectron spectroscopy. The changes in the conduction band offset, the valence band offset, as well as in the interfacial properties were obtained as a function of the annealing temperature. The interfacial layer is unavoidably formed for the deposited films and the composition of the interfacial layer is most likely Hf-silicate and SiOx. With the increase in the annealing temperature, it is confirmed that the reaction between SiOx and HfOxNy films formed more Hf-silicate interfacial layer. The valence band offset (ΔEv) shifts upwards gradually with the increase in annealing temperature due to the decrease in N elements. After thermal treatment, the obtained conduction band offset (ΔEc) increased from 1.20 eV at 500 °C to 1.25 eV at 800 °C.

Characteristics of Hf-silicate Interfacial Layers Formed by WetEtching

Interfacial layers of Hf-silicate films grown on Si substrates by using atomic layer deposition and wet etched with buered hydrogen fluoride were investigated. After etching the Hf-silicate film, the remaining gate dielectric is an interfacial layer, composed mainly of SiO2. By etching, the thickness of the Hf-silicate films was reduced and the C-V curves exhibited an increasing hysteresis window, as compared to as-deposited samples, due to charges trapped at the interface and to etching impurities. Also, we found that an increase in the capacitance was obtained after etching. The dielectric constant after an etching time of 20 seconds was lower than that of the unetched sample and this value was calculated as 7.97. However, a large leakage current density was the result of direct tunneling in the thinned films.

Enhancement in thermal stability of atomic layer deposited HfO 2 films by using top Hf metal layer

A thin (∼ 0.5 nm) layer of Hf metal was deposited on an atomic layer deposited (ALD) HfO 2 film by the DC sputtering method. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses showed that the Hf metal layer transformed into HfO 2 during the post-deposition annealing process. It appears that the HfO 2 layer formed by the oxidation of Hf metal provided the underlying ALD HfO 2 layer with the nucleation sites necessary to decrease the grain-boundary density of the crystallized HfO 2 film. The decrease in the grain-boundary density resulted in a reduction in the Hf-silicate formation and interfacial layer growth during post deposition annealing. This eventually resulted in a smaller increase in the capacitance equivalent thickness (CET) and high-k characteristics in the CET vs. leakage current density curve even after post deposition annealing at 1000 °C.

Thermodynamic properties and interfacial layer characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition

The thermodynamic properties and interfacial characteristics of HfO2 thin films that were deposited by the direct plasma atomic layer deposition (DPALD) method are investigated. The as-deposited HfO2 films that were deposited by the DPALD method show crystallization of the HfO2 layers, which initiates at approximately the 35th cycle (about 2.8nm) of the DPALD process. Medium-energy ion scattering analysis reveals that the direct O2 plasma causes a compositional change in the interfacial layer as the process progresses. With an increase in the number of process cycles, the Si content decreases and the O content increases at that position, so that the HfO2-like Hf-silicate layer is formed on top of the interfacial layer. The enhanced physical reactivity of the oxygen ions in the direct plasma and the Hf-silicate layer may be the driving forces that accelerate the early crystallization of the HfO2 layer in the DPALD process in the as-deposited state.

Interface Engineering by PVD-Based In-Situ Fabrication Method for Advanced Metal/High-k Gate Stacks

We fabricated high-quality silicate gate dielectrics by utilizing a solid phase interface reaction (SPIR) between ultrathin metal layers and SiO2 underlayers. Metal diffusion to the SiO2 underlayer forms a high-quality silicate interlayer, and preserving the initial SiO2/Si bottom interface ensures good electrical properties. The Hf silicate dielectrics were fabricated by the SPIR method using Hf layers less than 0.5-nm-thick that were fully consumed by interface reactions, resulting in Hf silicate layers that remained amorphous after activation annealing. The superior electrical properties of the poly-Si/HfSixOy/SiO2/Si MOSFETs were demonstrated through low leakage current and high electron mobility. We also recently proposed a novel in-situ fabrication method that continuously fabricates high-k dielectrics using SPIR and metal electrodes with a low-damage sputtering system. We investigated structural and electrical properties of metal/high-k gate stacks and demonstrated the effectiveness of the in-situ method in improving electrical properties.

Characterization of the Ultrathin $\hbox{HfO}_{2}$ and Hf-Silicate Films Grown by Atomic Layer Deposition

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The physical properties of <formula formulatype="inline"><tex>$\hbox{HfO}_{2}$</tex> </formula> and Hf-silicate layers grown by the atomic layer chemical vapor deposition are characterized as a function of the Hf concentration and the annealing temperature. The peaks of Fourier transform infrared spectra at 960, 900, and 820 <formula formulatype="inline"><tex>$\hbox{cm}^{-1}$</tex> </formula> originate from Hf–O–Si chemical bonds, revealing that a Hf-silicate interfacial layer began to form at the <formula formulatype="inline"> <tex>$ \hbox{HfO}_{2}/\hbox{SiO}_{2}$</tex></formula> interface after postdeposition annealing process at 600 <formula formulatype="inline"><tex>$^{\circ}\hbox{C}$</tex> </formula> for 1 min. Moreover, the intensity of the peak at 750 <formula formulatype="inline"><tex>$\hbox{cm}^{-1}$</tex></formula> can indicate the degree of crystallization of <formula formulatype="inline"><tex>$\hbox{HfO}_{2}$</tex> </formula>. The formed Hf-silicate layer between <formula formulatype="inline"> <tex>$\hbox{HfO}_{2}$</tex></formula> and <formula formulatype="inline"><tex>$ \hbox{SiO}_{2}$</tex></formula> is also confirmed by X-ray photoelectron spectroscopy. </para>

Polarity asymmetry of stress and charge trapping behavior of thin Hf- and Zr-silicate layers

In this paper, reliability aspects of thin Zr- and Hf-silicate layers are addressed by analyzing the stress induced leakage current (SILC) and charge trapping during constant voltage stress (CVS) and constant current stress (CCS). Voltage polarity and temperature effects on the degradation of the layers are also studied. SILC in silicate layers is found to be strongly polarity dependent and it is suggested that the damage causing it is near silicate/Si interface. SILC has a transient component and its recovery is explained by the trapping/detrapping of traps participating in Poole–Frenkel conduction. Unlike SiO 2, hot carrier induced damage is not the main mechanism for SILC creation. Therefore, the origin of SILC in silicate layers is distinctly different to SiO 2.

Stress induced leakage current mechanism in thin Hf-silicate layers

Stress induced leakage current (SILC) in thin Hf-silicate layers and the mechanisms of its creation are examined. A very strong polarity and thickness dependence as well as partial recovery of SILC are observed. It is suggested that the trapping in preexisting sites influences SILC by two ways: (1) it could be the first stage of defect generation mechanism leading to the permanent component of SILC and (2) it is fully responsible for the partial recovery of SILC. Therefore, the origin of SILC in Hf silicate is distinctly different from that of SiO2. The physical origin of the preexisting sites is also discussed.

Silicate layer formation at HfO2/SiO2/Si interface determined by x-ray photoelectron spectroscopy and infrared spectroscopy

A high-k Hf-silicate interfacial layer grown by the solid phase reaction between sputtered metallic Hf films and an underlying SiO2/Si substrate through in situ vacuum annealing and subsequent thermal oxidation has been investigated. By means of the chemical shifts of Si 2p, Hf 4f, and O 1s core-level spectra determined by x-ray photoelectron spectroscopy (XPS), the formation of an interfacial Si-O-Si bond as the dominant reaction during in situ thermal oxidation of the Hf/SiO2/Si gate stack has been confirmed. In situ vacuum anneals without air exposure at 700 °C accelerates the interface reaction and results in the formation of Si-rich Hf-silicate interfacial layer. Analysis by Fourier transform infrared spectroscopy (FTIR) has indicated that vacuum annealed samples containing the silicate interface layer effectively suppresses the growth of the interfacial SiOx layer compared to unannealed samples during postdeposition annealing.

Physical and electrical characterizations of ultrathin Si-rich Hf-silicate film and Hf-silicate/SiO2 bilayer deposited by atomic layer chemical vapor deposition

Hf-silicate films and Hf-silicate/SiO2 bilayers were fabricated on Si(100) to study SiO2 buffer layer effects. Hf-silicate layers were grown by atomic layer chemical vapor deposition using alternate supply of tetrakis-diethylamido-hafnium (Hf[N(C2H5)2]4) and tetra-n-butyl-orthosilicate [Si(OnBu)4] precursors. Ultrathin SiO2 buffer layers effectively suppressed Hf-rich phases and dislocations found at Hf-silicate/Si interfaces in Hf-silicate samples. These effects resulted in the significantly improved electrical properties of bilayers, compared to Hf-silicate films, such as low leakage current density (Jg), low flatband voltage (Vfb) shift, and high breakdown voltage (VBD).

Characteristics of the HfO2 Thin Films Grown by Remote Plasma Atomic Layer Deposition Method on the Plasma Oxidized Si Substrate

We investigated the electrical and physical characteristics of HfO2/SiO2/Si structure grown by remote plasma atomic layer deposition (RPALD) method. The surface preparation of Si (100) substrate was performed on HF-cleaned Si substrate by remote plasma oxidation (RPO) process and yielded about 0.5-nm-thick SiO2 layer. HfO2 films were deposited on both HF-cleaned and RPO-treated Si substrates by the RPALD method, respectively. Results show that the RPO-treated substrate effectively suppressed the diffusion of oxygen or/and silicon into the film during film deposition. Therefore, the RPO-treated samples have thinner initial Hf silicate layers than those without RPO treated substrate. And we have also observed a decreasing of the hysteresis and effective charge density (Qeff) as well as an improvement of the equivalent oxide thickness (EOT) in RPO treated samples.