Dopant enhanced in nickel silicide formation for high-<Emphasis Type="Italic">k</Emphasis> dielectric applications

The thermal stability of fully silicided NiSi with arsenic doping on silicon was investigated. The combination of full nickel silicidation gate electrodes and hafnium based high-k gate dielectrics is one of the most promising gate stacks to replace poly-Si/SiO₂/Si gate stacks in the future complementary metal–oxide–semiconductor (CMOS) sub-45 nm technology node. The aims of the work were to investigate the Ni silicide phase-related issues associated with arsenic dopant and thermal annealing on Ni–FUSI/HfO₂/Si and Ni–FUSI/HfSiO/Si gate stacks. It was found that arsenic-incorporation demonstrated some improvement in both morphology and phase stability of nickel silicided films at high processing temperatures regardless underlying gate dielectrics. The correlations of Ni–Si phase transformation and arsenic doapnt with their electrical and physical changes were established by sheet resistance measurements, X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, the modulation of the work function (WF) of Ni fully silicided gates by arsenic impurity is presented, comparing the effects of dopant (As) on the WF and silicide phases (NiSi and NiSi₂). It confirmed that the work function of NiSi can be tuned by implanting arsenic dopant, but it ineffective for NiSi₂ phase.     

Control of oxidation on NiSix during etching and ashing processes

The oxidation on nickel silicide (NiSi_x) during plasma etching and oxygen ashing is investigated for stable contact resistance on NiSi_x. NiSi_x exposed by various processes is observed by X-ray photoelectron spectroscopy. The oxidation on NiSi_x is promoted by the fluorine that remains during etching and the oxide thickness on n⁺ NiSi_x is greater than that on p⁺ NiSi_x. The remaining fluorine after etching can be decreased by in-situ nitrogen plasma treatment during the post-etching process. Therefore, the oxidation progress with exposure to air and the difference in oxidation on NiSi_x between n⁺ and p⁺ can be suppressed.     

Effect of ultraviolet light exposure on a HfOx RRAM device

This paper studies the effect of ultraviolet (UV) light exposure on the resistive switching characteristics of an ITO/HfO_x/TiN structure. Unstable and unreliable switching properties are generally observed on the ITO/HfO_x/TiN sample. Under the appropriate exposure time, the samples were able to achieve the superior electrical characteristics and reduced resistance dispersion. We suggest that the improvement of switching characteristics and resistance dispersion is related to the oxygen-rich HfO₂ layer formed at the M/O interface caused by UV light. This indicates that UV laser exposure is a critical issue in the electrical characteristics of RRAM devices.     

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.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Ni silicide formation on epitaxial Si1 − yCy/(001) layers

The formation of Ni silicides on Si_1 − yC_y (y = 0.01 and 0.018) epilayers grown on Si(001) has been investigated. The presence of C atoms was found to significantly retard the growth kinetics of NiSi and enhances the thermal stability of thin NiSi films. For Ni(11 nm)/Si_0.982C_0.018 samples, the process window of NiSi was shifted and extended to 450-700 °C. Moreover, there was an additional strain introduced into the Si_1 − yC_y epilayers during Ni silicidation. This work shows the potential of Ni silicidation on Si_1yC_y for device applications.     

Formation of NiSi2/SiNX compound nanocrystal for nonvolatile memory application

In this paper, the NiSi₂/SiN_X compound NCs (CNCs) structure is studied to further improve the retention. To introduce the nitride based traps, NiSi₂ was also sputtered in the mixture gas of Ar (50 sccm) and NH₃ (10 sccm) at room temperature, and the NiSi₂/SiN_X CNCs can be easily formed after rapid thermal annealing. In addition, standard memory devices with single and double NiSi₂ nanocrystal were also prepared for comparison. By XPS analyses, the nanocrystals fabricated in the ambiance of NH₃ can be confirmed to be composited of NiSi₂ and SiN_X compound. According to memory characteristics results, better retention characteristic of device with single-layer NiSi₂/SiN_X compound nanocrystal NVMs can be observed after 10⁴ s, raises from 50% to 72% in comparison with the control sample, even better than the double-layer NiSi₂ nanocrystal, 58%. Indeed, the formation of NiSi₂/SiN_X CNCs can improve the retention characteristics remarkably due to the additional tunnel barrier and deep traps in the nitride.     

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.     

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.     

Effect of P addition on the thermal stability and electrical characteristics of NiSi films

Immersion Ni-P deposition is undoubtedly one of the most important catalytic deposition process, due to its simplicity in operation and low equipment cost. In this study, immersion deposited Ni-P films were used to form Ni-silicide films. Ni-P films with a thickness of 100 nm were fabricated by immersing Si(100) substrates in an aqueous deposition solution. Ni-silicide films were then formed by annealing the samples in a furnace at temperatures ranging from 400 °C to 900 °C for 1 h in an argon ambient. Experimental results indicate that a phosphor addition in Ni films increased the transformation temperature of NiSi to NiSi₂ to 900 °C. Moreover, the feasibility of enhancing the thermal stability of NiSi by varying the interface energy at the NiSi₂/Si interface and the surface energy of a Ni-P-Si capping layer on the NiSi surface is discussed.     

Thermal and ion-induced dissociation of NiSi and NiSi2 in contact with nickel

The interaction of nickel with NiSi and NiSi₂ was investigated using backscattering spectrometry and glancing angle X-ray diffraction. With nickel films deposited onto NiSi or NiSi₂, Ni₂Si was formed at the original compound-nickel interface by the dissociation of the compounds on annealing at temperatures of about 300 °C. The dissociation of NiSi and NiSi₂ into Ni₂Si has also been observed when the samples were irradiated with argon ions. We attribute similarities in the two processes to the presence of thermodynamic forces in ion-induced reactions and the dependence of the radiation-enhanced migration on the intrinsic diffusion properties in the system.     

Chemical vapor deposition of NiSi using Ni(PF3)4 and Si3H8

NiSi_x films were deposited using chemical vapor deposition (CVD) with a Ni(PF₃)₄ and Si₃H₈/H₂ gas system. The step coverage quality of deposited NiSi_x was investigated using a horizontal type of hot-wall low pressure CVD reactor, which maintained a constant temperature throughout the deposition area. The step coverage quality improved as a function of the position of the gas flow direction, where PF₃ gas from decomposition of Ni(PF₃)₄ increased. By injecting PF₃ gas into the Ni(PF₃)₄ and Si₃H₈/H₂ gas system, the step coverage quality markedly improved. This improvement in step coverage quality naturally occurred when PF₃ gas was present, indicating a strong relationship. The Si/Ni deposit ratio at 250 °C is larger than at 180 °C. It caused a decreasing relative deposition rate of Ni to Si. PF₃ molecules appear to be adsorbed on the surface of the deposited film and interfere with faster deposition of active Ni deposition species.     

Combining grazing incidence X-ray diffraction and X-ray reflectivity for the evaluation of the structural evolution of HfO2 thin films with annealing

Metal oxides of high dielectric constant are candidates to substitute SiO₂ as gate dielectric in complementary metal-oxide-semiconductor technology. In this contribution we present the application of X-ray techniques to the study of thermal stability of 5-, 10- and 20-nm-thick HfO₂ deposited by atomic layer deposition. Grazing incidence X-ray diffraction spectra are refined by Rietveld analysis. X-Ray reflectivity (XRR) data are fitted in order to evaluate the thickness, the surface roughness and the interface stability upon thermal processing between 300 and 1050 °C. The electronic density values obtained from the scattering coefficients of the crystallographic phase are compared to the values related to the critical angle of the XRR spectra. The thickness and the electronic density of the as grown layer are slightly affected by the thermal treatment. The surface and interfacial roughness are also very stable. The crystallographic ordering evolves starting from the amorphous structure of the as-deposited film towards the polycrystalline monoclinic HfO₂ films obtained by annealing at high temperatures. The results are discussed and compared to plan view and cross-sectional transmission electron microscopy images.     

Fabrication and electrical properties of metal-oxide semiconductor capacitors based on polycrystalline p-CuxO and HfO2/SiO2 high-κ stack gate dielectrics

Polycrystalline p-type Cu_xO films were deposited after the growth of HfO₂ dielectric on Si substrate by pulsed laser deposition, and Cu_xO metal-oxide-semiconductor (MOS) capacitors with HfO₂/SiO₂ stack gate dielectric were primarily fabricated and investigated. X-ray diffraction and X-ray photoelectron spectroscopy were applied to analyze crystalline structure and Cu⁺/Cu²⁺ ratios of Cu_xO films respectively. SiO₂ interlayer formed between the high-κ dielectric and substrate was estimated by the transmission electron microscope. Results of electrical characteristic measurement indicate that the permittivity of HfO₂ is about 22, and the gate leakage current density of MOS capacitor with 11.3 nm HfO₂/SiO₂ stack dielectrics is ∼ 10⁻⁴ A/cm². Results also show that the annealing in N₂ can improve the quality of Cu_xO/HfO₂ interface and thus reduce the gate leakage density.     

Effect of the post-deposition annealing on electrical characteristics of MIS structures with HfO2/SiO2 gate dielectric stacks

In this work, we report on effects of post-deposition annealing on electrical characteristics of metal–insulator–semiconductor (MIS) structures with HfO₂/SiO₂ double gate dielectric stacks. Obtained results have shown the deterioration of electro-physical properties of MIS structures, e.g. higher interface traps density in the middle of silicon forbidden band (D_itmb), as well as non-uniform distribution and decrease of breakdown voltage (U_br) values, after annealing above 400 °C. Two potential hypothesis of such behavior were proposed: the formation of interfacial layer between hafnia and silicon dioxide and the increase of crystallinity of HfO₂ due to the high temperature treatment. Furthermore, the analysis of conduction mechanisms in investigated stacks revealed Poole–Frenkel (P–F) tunneling at broad range of electric field intensity.     

Interfacial layer growth of ZrO2 films on silicon

In this work, the interfacial layer growth for both as-deposited and annealed ZrO₂ thin films on silicon is analyzed in detail by the high-resolution cross-sectional transmission electron microscope and spectroscopic ellipsometry. For as-deposited ZrO₂/SiO₂/Si, the thickness of a SiO₂-like layer at the silicon interface was found to depend on the oxygen partial pressure during deposition. At oxygen partial pressure ratio of above 50% the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO₂ film and silicon consumption at the interface. At oxygen partial pressure ratio in the range 7-50%, the visible growth of interfacial silicon oxide layer was not present. The interfacial layer for ZrO₂/Si with optimal partial pressure (15%) during annealing at 600 °C was found to be the two-layer structure composed of the ZrSi_xO_y overlayer and the SiO_x downlayer. The formation of the interfacial layer is well accounted for diffusion mechanisms involving Si indiffusion and grain-boundary diffusion.     

Effects of (NH4)2Sx treatment on the electrical and optical properties of indium tin oxide/conducting polymer electrodes

In this study, the effects of (NH₄)₂S_x treatment on the electrical and optical properties of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) electrodes were researched. The authors found that (NH₄)₂S_x treatment could result in suppressing the hysteresis-type current-voltage characteristics related to the interfacial capacitance variation and a reduction in the equivalent refractive index of the ITO/PEDOT:PSS electrodes, owing to the improvement in the interfacial stability of the ITO/PEDOT:PSS electrodes and a reduction in the interface trap-states related charge store at the ITO/PEDOT:PSS interface. This implies that the ITO/PEDOT:PSS electrodes fabricated using the (NH₄)₂S_x-treated ITO may produce a higher extraction efficiency for ITO/PEDOT:PSS-based optoelectronic devices.     

Interface roughness effect between gate oxide and metal gate on dielectric property

We report a simple theoretical model based on experimental data about the interface roughness effect between gate oxide and metal gate on dielectric. From the analytic approach, we confirm that the increase in interface roughness generates the decrease in the dielectric constant as well as the increase in the leakage current. We checked the interface roughness effect between high-κ HfO₂ gate oxides and Ru gates by atomic layer deposition (ALD) and physical vapor deposition (PVD). The ALD Ru gate showed better dielectric properties (high dielectric constant and low leakage current) and lower interface roughness than the PVD Ru metal gate.     

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.     

Hysteresis in metal insulator semiconductor structures with high temperature annealed ZrO2/SiOx layers

Hysteresis behaviour in sandwich structure — zirconium oxide/chemical silicon oxide, annealed at temperature of 850 °C in oxygen ambient, was studied. Formation of thin ZrSi_xO_y layer due to the high temperature annealing was found. Metal-insulator-semiconductor (MIS) capacitors using ZrO₂/ZrSi_xO_y/SiO_x insulator were studied. High-frequency capacitance-voltage (HF C-V), current-voltage (I-V) and current-time (I-t) measurements were carried out on the Al/ZrO₂/ZrSi_xO_y/SiO_x/Si capacitors.Two leakage current components were identified — tunneling current component at high electric fields and transient current component at low fields. The transient leakage currents are due to charge trapping phenomena. The measured I-t characteristics are related with charging/discharging and dielectric relaxation phenomena. A counter-clockwise HF C-V hysteresis, larger than 2 V at thickness of the stack structure of about 50 nm was observed.Metal-insulator-semiconductor field effect transistors (MISFETs) using ZrO₂/ZrSi_xO_y/SiO_x-gate insulator were studied. P-channel MISFETs with aluminum gate electrode were fabricated on standard n-type silicon substrates. Due to charging/discharging phenomena in the gate dielectric the transistors can be switched between On- and Off-state with the polarity of applied stress voltage.