Thermal stability of hafnium silicate dielectric films deposited by a dual source liquid injection MOCVD

The hafnium and silicon precursors, Hf(NMe₂)₄ and Bu^tMe₂SiOH, have been investigated for the MOCVD of high-κ hafnium silicate, (HfO₂)_1–x –(SiO₂) _x films for gate dielectric applications. Control of the silica concentration in the hafnium silicate can be achieved by varying the relative precursor ratios up to a saturation level of 35–40% SiO₂. The thermal stability of the resulting hafnium silicate films in air has been investigated using medium energy ion scattering. Internal oxidation of the underlying silicon substrate is discernable when the films are annealed in dry air for 15 min over the temperature range 800–1000 °C.     

Thermal stability of hafnium silicate dielectric films deposited by a dual source liquid injection MOCVD

The hafnium and silicon precursors, Hf(NMe₂)₄ and Bu^tMe₂SiOH, have been investigated for the MOCVD of high- hafnium silicate, (HfO₂)_1–x –(SiO₂) _x films for gate dielectric applications. Control of the silica concentration in the hafnium silicate can be achieved by varying the relative precursor ratios up to a saturation level of 35–40% SiO₂. The thermal stability of the resulting hafnium silicate films in air has been investigated using medium energy ion scattering. Internal oxidation of the underlying silicon substrate is discernable when the films are annealed in dry air for 15 min over the temperature range 800–1000 °C.     

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.     

Preparation and Properties of Thin HfO<Subscript>2</Subscript> Films

HfO₂ layers were grown on silicon by metalorganic chemical vapor deposition using (C₅H₅)₂Hf(CH₃)₂, (C₅H₅)₂Hf(N(C₂H₅)₂)₂, and Hf(dpm)₄ as volatile precursors and were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and IR spectroscopy. The films were shown to consist of monoclinic HfO₂ and to contain hafnium silicide and silicate at the HfO₂/Si interface. The presence of hafnium silicide was attributed to oxygen deficiency produced by argon ion milling. Hafnium silicate was formed as a result of the reaction between hafnium and silicon oxides during annealing. Current-voltage and capacitance-voltage measurements on Al/HfO₂/Si test structures were used to determine the dielectric permittivity and electrical resistivity of the films: ? = 15–20, ρ ～ 10¹⁵ cm.     

Multi-scale modelling of silicon nanocrystal synthesis by Low Pressure Chemical Vapor Deposition

A multi-scale model has been developed in order to represent the nucleation and growth phenomena taking place during silicon nanocrystal (NC) synthesis on SiO₂ substrates by Low Pressure Chemical Vapor Deposition from pure silane SiH₄. Intrinsic sticking coefficients and H₂ desorption kinetic parameters were established by ab initio modelling for the first three stages of silicon chemisorption on SiO₂ sites, i.e. silanol Si―OH bonds and siloxane Si―O―Si bridges. This ab initio study has revealed that silane cannot directly chemisorb on SiO₂ sites, the first silicon chemisorption proceeds from homogeneously born unsaturated species like silylene SiH₂. These kinetic data were implemented into the Computational Fluid Dynamics Fluent code at the industrial reactor scale, by activating its system of surface site control in transient conditions. NC area densities and radii deduced from Fluent calculations were validated by comparison with experimental data. Information about the deposition mechanisms was then obtained. In particular, hydrogen desorption has been identified as the main limiting step of NC nucleation and growth, and the NC growth rate highly increases with run duration due to the autocatalytic nature of deposition.     

One-step growth of HfSiON films

Hafnium silicate (HfSiO) has been identified as a promising candidate to replace silicon oxide/oxynitride as a high-κ material for gate dielectric applications. Nitrided hafnium silicate has been found to have a number of advantages in film performance. However, two-step processes have been commonly used, i.e. the first step is the deposition of HfSiO film by CVD, ALD or other techniques, and the second step is film nitridation. In this research, HfSiON films (Hafnium silicon oxynitride, or nitrided HfSiO) were directly deposited on Si substrate by Chem. Vap. Depos. using trisilylamine (TSA) and tetrakis(diethylamido)hafnium(IV) (TDEAH) precursors. TSA, a highly volatile and carbon-free precursor, was used as the Si source and was delivered in pure vapor phase without heating. TDEAH was used as the Hf source and delivered by direct liquid injection (vaporizer). HfSiON films were deposited in a single step with no need of a post treatment process for nitrogen incorporation. The HfSiON films can be tuned in wide compositional (Hf, Si, O, N) ranges and high growth rates were achieved. The addition of NH₃ to the reactant gas stream was found to be able to deposit films with high and controllable N content. It was also found that NH₃ had significant impact on film growth rate and composition.     

High performance metal-insulator-metal capacitors with atomic vapor deposited HfO2 dielectrics

Thin HfO₂ films were grown as high-k dielectrics for Metal-Insulator-Metal applications by Atomic Vapor Deposition on 8 inch TiN/Si substrates using pure tetrakis(ethylmethylamido)hafnium precursor. Influence of deposition temperature (320-400 °C) and process pressure (2-10 mbar) on the structural and electrical properties of HfO₂ was investigated. X-ray diffraction analysis showed that HfO₂ layers, grown at 320 °C were amorphous, while at 400 °C the films crystallized in cubic phase. Electrical properties, such as capacitance density, capacitance-voltage linearity, dielectric constant, leakage current density and breakdown voltage are also affected by the deposition temperature. Finally, TiN/HfO₂/TiN stacks, integrated in the Back-End-of-Line process, possess 3 times higher capacitance density compared to standard TiN/Si₃N₄/TiN capacitors. Good step coverage (> 90%) is achieved on structured wafers with aspect ratio of 2 when HfO₂ layers are deposited at 320 °C and 4 mbar.     

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.     

Conformal growth and characterization of hafnium silicate thin film by MOCVD using HTB (hafnium tertra-tert-butoxide) and TDEAS (tetrakis-diethylamino silane)

Hafnium silicate (HfSi _x O _y ) films were deposited by metal-organic chemical vapor deposition (MOCVD) using hafnium tetra-tert-butoxide [HTB, Hf(OC(CH₃)₃)₄] and tetrakis-diethylamino silane [TDEAS, Si(N(C₂H₅)₂)₄]. The grown Hf-silicate films showed Hf-rich composition and impurity concentrations less than 1 atomic % (below detection limits). Uniformly deposited films with good step-coverage were obtained on hole-patterned SiO₂ substrates. Hafnium silicate films had stable amorphous crystalline structure up to 800 °C annealing and above 900 °C, a tetragonal HfO₂ crystal phase was observed. Dielectric constant (k) of the Hf-silicate films was about 15 and flat band voltage (V _fb) and hysteresis were very low.     

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} .     

Atomic layer deposition of hafnium oxide dielectrics on silicon and germanium substrates

Hafnium oxide films have been deposited at 250 °C on silicon and germanium substrates by atomic layer deposition (ALD), using tetrakis-ethylmethylamino hafnium (TEMAH) and water vapour as precursors in a modified Oxford Instruments PECVD system. Self-limiting monolayer growth has been verified, characterised by a growth rate of 0.082 nm/cycle. Layer uniformity is approximately within ±1% of the mean value. MOS capacitors have been fabricated by evaporating aluminium electrodes. CV analysis has been used to determine the bulk and interface properties of the HfO₂, and their dependence on pre-clean schedule, deposition conditions and post-deposition annealing. The dielectric constant of the HfO₂ is typically 18. On silicon, best results are obtained when the HfO₂ is deposited on a chemically oxidised hydrophilic surface. On germanium, best results are obtained when the substrate is nitrided before HfO₂ deposition, using an in-situ nitrogen plasma treatment.     

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.     

Annealing optimization of silicon nitride film for solar cell application

Hydrogenated films of silicon nitride (SiNx:H) is commonly used as an antireflection coating as well as passivation layer in crystalline silicon solar cell. SiNx:H films deposited at different conditions in Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor were investigated by varying annealing condition in infrared (IR) heated belt furnace to find the optimized condition for the application in silicon solar cells. By varying the gases ratio (R = NH₃/SiH₄ + NH₃) during deposition, the SiNx:H films of refractive indices 1.85-2.45 were obtained. Despite the poor deposition rate, the silicon wafer with SiNx:H film deposited at 450 °C showed the best effective minority carrier lifetime. The film deposited with the gases ratio of 0.57 shows the best peak of carrier lifetime at the annealing temperature of 800 °C. The single crystalline silicon solar cells fabricated in conventional industrial production line applying the optimized film deposition and annealing conditions on large area substrates (125 mm × 125 mm) were found to have the conversion efficiencies as high as 17.05 %. Low cost and high efficiency single crystalline silicon solar cells fabrication sequence employed in this study has also been reported in this paper.     

Effect of rapid thermal annealing time on Au/SiOx film prepared by hot wire assisted plasma enhanced chemical vapour deposition technique

In this study, nanocomposite material consisting of silicon suboxide (SiO_x) film embedded with gold nanoparticles (Au NPs) was synthesized using hybrid technique combining hot wire evaporation and plasma enhanced chemical vapour deposition (PECVD) method. As prepared Au/SiO_x films were rapid thermal annealed at constant temperature of 800 °C for different annealing times from 30 to 120 s. The use of tungsten filament for Au evaporation allowed the effective reduction of the silicon content. Depth profiling analysis confirmed the embedded in structure of Au/SiO_x film. FESEM, UV/VIS/NIR and PL spectroscopy were utilized to study the structural and optical properties of annealed Au/SiO_x film for different times. Embedded Au NPs diffused towards the surface of SiO_x film agglomerate and increased in size with an increase in annealing time. Localized surface plasmon resonance (LSPR) peak induced by Au NPs in SiO_x, which is dependent on annealing time, was clearly observed in optical spectra. Intensity and position of the PL peak located at 580 nm experienced a decrease and red-shift, as annealing time increased.     

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.     

Physico-chemical, structural and physical properties of hydrogenated silicon oxinitride films elaborated by pulsed radiofrequency discharge

Films prepared by radiofrequency pulsed plasma enhanced chemical vapor deposition from a mixture of silane (SiH₄) and nitrous oxide (N₂O) were studied. Variation of operating conditions (flow rate, deposition temperature ...) resulted in films with chemical compositions changing from hydrogenated silicon oxynitride (SiO_xN_y:H) to silicon oxide (SiO_x:H). Infrared and Rutherford backscattering spectroscopy studies of the as-deposited films revealed different SiO_x arrangements disturbed by Si-N bonds and H-Si ≡ Si_(3 − x)O_x clusters depending on the substrate temperature and the N₂O/SiH₄ ratio. For films obtained using low N₂O/SiH₄ rations and annealed at temperature higher than 1273 K, Raman spectroscopy and microscopy analyses revealed the presence of silicon nanocrystals embedded in a matrix containing Si, O, and N. Spectroscopic ellipsometry revealed the presence of silicon nanocrystals along with two other amorphous phases (SiO_xN_y and SiO₂) in annealed samples. The electrical characteristics of annealed films obtained from capacitance-voltage measurements indicated a stable charge trapping in ultra-thin SiO_xN_y layers. These preliminary results suggest that Si-nc containing silicon oxynitride layers can be potential candidates to be used in the floating gate fabrication of memory devices.     

A simple approach of preparing amorphous SiOx film on aluminum substrate

A kind of silicon oxide (SiO_x) film was grown on aluminum substrate by low temperature-atmospheric pressure chemical vapor deposition (CVD). The film thickness, changed with the procession temperature and time, and source gaseous ratio, were studied. The optimized procession parameters were determined. The film section morphology was investigated by the scanning electronic microscopy (SEM) and result shows that the SiO_x film is bound firmly to the aluminum substrate without any crack or gap. The reason of the excellent combination was also discussed. The X-ray diffraction technology (XRD) and transmission electronic diffraction technology (TED) demonstrate that the SiO_x film is basically amorphous with a little crystalline area in it.     

Formation of gas barrier films by Cat-CVD method using organic silicon compounds

Silicon nitride (SiN_x) and silicon oxynitride (SiO_xN_y) films have been formed by catalytic chemical vapor deposition (Cat-CVD) method using hexamethyldisilazane (HMDS). Addition of NH₃ gas and increase in gas pressure can prevent carbonization of tungsten (W) catalyzer. These SiO_xN_y films have high gas barrier ability compare to the case of SiO_xN_y films using SiH₄ and thus are expected for novel sealing films.     

Optical and dielectric properties of thin SiOx films of variable composition

The effect of the composition of amorphous SiO_x films produced by the vacuum evaporation of SiO, on their optical and dielectric properties was investigated. The variation in the composition of the films was achieved by changing the deposition rate and the pressure of the residual gases.The optical band gap was observed to increase from 2.2 to 3.1 eV as the deposition rate was decreased from 50 to 5 Å s^-1 and simultaneously the refractive index, the permittiviity and the dielectric loss factor were found to decrease. The composition and structure of the films were determined from the optical absorption and IR spectroscopy.The experimental results revealed that SiO_x films produced by vacuum evaporation do not comprise a simple mixture of silicon and SiO₂ phases but they have a single-phase structure.     

Effect of the oxygen fraction on the structure and optical properties of HfOxNy thin films

The main purpose of this work was to prepare hafnium oxynitride (HfO_xN_y) thin films. HfO_xN_y thin films were deposited by radio frequency reactive magnetron sputtering from a pure Hf target onto Quartz and ZnS substrates at room temperature. The depositions were carried out under an oxygen-nitrogen-argon atmosphere by varying the flow rate of the reactive gases (oxygen/nitrogen ratio). The variation of the flow rate of the reactive gases changed the structure and properties of the films. Glancing incidence X-ray diffraction (GIXRD) was used to study the structural changes of as-deposited films; a new crystalline hafnium oxynitride phase was formed in a region of oxygen/nitrogen ratio. Cross-section of the films observed by SEM revealed that the films grew with a columnar-type structure, and surface observation with AFM showed values of surface roughness changed with the flow rate of the reactive gases, higher oxygen fraction had lower surface roughness than lower oxygen fraction. Visible spectra, infrared spectra, refractive index, absorption coefficient also changed with the variation of the oxygen fraction.