On the etching mechanism of ZrO2 thin films in inductively coupled BCl3/Ar plasma

The etching mechanism of ZrO₂ thin films in BCl₃/Ar plasma was investigated using a combination of experimental and modeling methods. It was found that an increase in the Ar mixing ratio causes the non-monotonic behavior of the ZrO₂ etch rate which reaches a maximum of 41.4 nm/min at about 30-35% Ar. Langmuir probe measurements and plasma modeling indicated the noticeable influence of a BCl₃/Ar mixture composition on plasma parameters and active species kinetics that results in non-linear changes of both densities and fluxes for Cl, BCl₂ and . From the model-based analysis of surface kinetics, it was shown that the non-monotonic behavior of the ZrO₂ etch rate can be associated with the concurrence of chemical and physical pathways in ion-assisted chemical reaction.     

Electrical properties of thin RF sputtered Ta2O5 films after constant current stress

Stress-induced leakage currents (SILCs) in thin Ta₂O₅ films after short- and long-term constant current stress (CCS) at both gate polarities at different levels of injected current were investigated. The behavior of the SILCs and the change of quasistatic C–V characteristics after the degradation confirmed the variations of gate voltage with time during CCS necessary to maintain the injected current density through the oxide.The conduction mechanisms were also investigated. Initially, normal Poole–Frenkel (PF) mechanism dominates in the oxide at medium fields (0.4– 1.7 MV/cm) independently of the deposition temperature or annealing steps. After the degradation modified PF with different compensation factors appears. After long-term degradation conduction mechanism goes back to PF.     

Pre-breakdown in thin SiO2 films

The on-off fluctuations of the tunnel current in 5.6 nm SiO₂ films before dielectric breakdown are analyzed in detail. For this purpose, a low noise measurement system has been realized which allows detection of pre-breakdown phenomena and interruption of the stress before catastrophic failure occurs. A spectral analysis of these fluctuations is presented along with preliminary results of the experiments made possible, for the first time, by the new measurement system     

Comparison of transformation to low-resistivity phase andagglomeration of TiSi2 and CoSi2

The phase transformation and stability of TiSi₂ on n ⁺ diffusions are investigated. Narrower n⁺ diffusions require higher anneal temperatures, or longer anneal times, than wider diffusions for complete transitions from the high-resistivity C49 phase to the low-resistivity C54 phase. A model is presented which explains this in terms of the probability of forming C54 nuclei on narrow diffusions and the influence of diffusion width on C54 grain size. The results are that more C49 and C54 nucleation events are required to completely transform narrow lines. For thin TiSi₂ (40 nm), there is a narrow process window for achieving complete transformation without causing agglomeration of the TiSi₂. The process window decreases with decreasing silicide thickness. A significantly larger process window is achieved with short-time rapid annealing. Similar studies are performed for CoSi₂ on n⁺ and p⁺ diffusions. No linewidth dependence is observed for the transformation from CoSi_x to CoSi₂. There is a broad process window from 575°C to 850°C using furnace annealing, for which the low-resistivity phase is obtained without causing agglomeration     

Post deposition UV-induced O2 annealing of HfO2 thin films

UV-assisted annealing processes for thin oxide films is an alternative to conventional thermal annealing and has shown many advantages such as low annealing temperature, reducing annealing time and easy to control. We report in this work the deposition of ultra-thin HfO₂ films on silicon substrate by two CVD techniques, namely thermal CVD and photo-induced CVD using 222 nm excimer lamps at 400 °C. As-deposited films of around 10 nm in thickness with refractive indices from 1.72 to 1.80 were grown. The deposition rate measured by ellipsometry was found to be about 2 nm/min by UV-CVD, while the deposition rate by thermal CVD is 20% less than that by UV-CVD. XRD showed that the as-deposited HfO₂ films were amorphous. This work focuses on the effect of post deposition UV annealing in oxygen on the structural, optical and electrical properties of the HfO₂ films at low temperature (400 °C). Investigation of the interfacial layer by FTIR revealed that thickness of the interfacial SiO₂ layer slightly increases with the UV-annealing time and UV annealing can convert sub-oxides at the interface into stoichiometric SiO₂, leading to improved interfacial qualities. The permittivity ranges in 8–16, are lower than theoretical values. However, the post deposition UV O₂ annealing results in an improvement in effective breakdown field and calculated permittivity, and a reduction in leakage current density for the HfO₂ films.     

Measurement and control of a residual oxide layer on TiSi2 films employed in ohmic contact structures

An inadvertent oxide layer is formed on a titanium disilicide (TiSi₂) film following various wet and dry processes in a manufacturing environment. The use of H₂SO₄:H₂O₂:H₂O (1:1:5) as a wet etch for excess Ti metal, prior to the high temperature anneal used to form a subsequent TiSi₂ layer, is identified as the source of the undesired oxide via multiwavelength spectroscopic ellipsometry and Auger electron spectrometry studies. This inadvertent oxide layer on TiSi₂ is shown to form bad electrical contacts and is a contributing source to large standby currents in polysilicon gate shunts. Spectroscopic ellipsometry is shown herein as a unique analytical tool to determine both the thickness and structure of this poorly structured oxide during process development. A single wavelength ellipsometer monitoring scheme for both the appearance as well as the thickness of this inadvertent oxide layer is proposed for use in high-volume manufacturing     

Effect of ytterbium doping on the optical and electrical properties of intrinsic In2O3 thin films

Ytterbium doped In₂O₃ thin films (0.5%, 1.0%, 1.4%, 1.7% and 8.5 wt.%) have been prepared by a vacuum evaporation method on glass and silicon-wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV-VIS-NIR absorption spectroscopy, and electrical (ac and dc) measurements. Experimental data indicate that Yb³⁺ doping slightly stress the In₂O₃ crystalline structure and change the optical and electrical properties. The electrical and optical behaviours of the Yb-doped In₂O₃ films show that they are wide-band semiconductors with band gap 3.67-3.7 eV and insulating properties. The ac and dc-electrical measurements show that it is possible to use Yb-doped In₂O₃ as an optical-sensitive high-k insulator for metal-insulator-silicon configurations.     

Microstructure and electrical characteristics of Ba0.65Sr0.35TiO3 thin films etched in CF4/Ar/O2 plasma

Radio frequency magnetron sputtered Ba_0.65Sr_0.35TiO₃ (BST) thin films were etched in CF₄/Ar/O₂ plasma by magnetically enhanced reactive ion etching technique. The etching characteristics of BST films were characterized in terms of microstructure and electrical properties. Atomic force microscopy and X-ray diffraction results indicate that the microstructure of the etched BST film is degraded because of the rugged surface and lowered intensities of BST (1 0 0), (1 1 0), (1 1 1) and (2 0 0) peaks compared to the unetched counterparts. Dielectric constant and dielectric dissipation of the unetched, etched and postannealed-after-etched BST film capacitors are 419, 346, 371, 0.018, 0.039 and 0.031 at 100 kHz, respectively. The corresponding dielectric tunability, figure of merit and remnant polarization are 19.57%, 11.56%, 17.25%, 10.87, 2.96, 5.56, 3.62 μC/cm², 2.32 and 2.81 μC/cm² at 25 V, respectively. The leakage current density of 1.75 × 10⁻⁴ A/cm² at 15 V for the etched BST capacitor is over two orders of magnitude higher than 1.28 × 10⁻⁶ A/cm² for the unetched capacitor, while leakage current density of the postannealed-after-etched capacitor decreases slightly. It means that the electrical properties of the etched BST film are deteriorated due to the CF₄/Ar/O₂ plasma-induced damage. Furthermore, the damage is alleviated, and the degraded microstructure and electrical properties are partially recovered after the etched BST film is postannealed at 923 K for 20 min under a flowing O₂ ambience.     

Structural properties of fluorinated SiO2 thin films

Fluorinated SiO₂ (SiOF) films, prepared by plasma enhanced chemical vapour deposition from SiH₄, N₂O and CF₄ precursors, have been analysed by infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to extract chemical and structural information. Notwithstanding XPS reveals that fluorine concentrations are quite low (less than 4 at.%), the analysis of the Si–O–Si vibration modes in the IR spectra indicates that CF₄ addition involves a deeper modification of the film structure, than the simple formation of Si–F bonds. In particular, by increasing the F concentration in the oxides, the stretching frequency of the Si–O–Si bonds increases, while the bending frequency decreases. On the basis of the central force model, both observations are consistent with the occurrence of a Si–O–Si bond angle relaxation phenomenon, the importance of which increases with the fluorine concentration in the films.     

Molecular dynamics characterization of crystalline and amorphous TiSi2 phases

Molecular dynamics simulations by a tight binding potential provide new interesting information on the ground state properties of the TiSi₂ phases. In particular, we have compared some structural, elastic, thermodynamic and electronic properties of the C49, the C54 and the amorphous phases. It turns out that the C49 structure is much softer than the C54, also displaying a melting temperature some 300–400 K below the one for the C54, in agreement to very recent experimental results. The amorphous phase is energetically and structurally more akin to the C49 than to the C54 phase. On the basis of these results we suggest the higher formation kinetics of the former to be related to an intrinsic advantage in the growth stage.     

Preparation of n-type semiconductor SnO2 thin films

We studied fluorine-doped tin oxide on a glass substrate at 350℃using an ultrasonic spray technique. Tin（Ⅱ） chloride dehydrate,ammonium fluoride dehydrate,ethanol and NaOH were used as the starting material, dopant source,solvent and stabilizer,respectively.The SnO₂:F thin films were deposited at 350℃and a pending time of 60 and 90 s.The as-grown films exhibit a hexagonal wurtzite structure and have（101） orientation.The G = 31.82 nm value of the grain size is attained from SnO₂:F film grown at 90 s,and the transmittance is greater than 80%in the visible region.The optical gap energy is found to measure 4.05 eV for the film prepared at 90 s, and the increase in the electrical conductivity of the film with the temperature of the sample is up to a maximum value of 265.58（Ω·cm）^-1,with the maximum activation energy value of the films being found to measure 22.85 meV,indicating that the films exhibit an n-type semiconducting nature.     

Effects of chemical and electrochemical etching on polycrystalline thin films of CuGaSe2

Electrochemical and, especially, chemical oxidative etching drastically improves the photoresponse of liquid electrolyte/CuGaSe₂-on-Mo junctions. This is expressed in decreased effective doping levels and increased effective minority carrier diffusion lengths. It is accounted for by removal of highly defective surface layers, which also leads to an increase in the barrier height, as judged from a positive shift of the flat band potential (on the electrochemical scale). The etching effects are seen clearly in Zn/CuGaSe₂ devices, by electron beam-induced current. This last method also reveals a supra-grain structure, which is tentatively explained by thermal stress-induced strain at the Mo-CuGaSe₂ interface.     

Thermoelectric power of SnO2 anisotropic thin films

A calculation of thermoelectric power in fluorine-doped SnO₂ thin films is carried out using the Boltzmann transport theory and including anisotropic effects over material as well as the degeneracy grade of the samples. Curves of thermoelectric power in dependence of the temperature and concentration of F-impurities are reported. Finally, the computed values are compared with those obtained experimentally.     

具有SiO2/SiNX/SiO2 复合绝缘层的有机薄膜晶体管

We have investigated a SiO_2/SiN_x/SiO_2 composite insulation layer structured gate dielectric for an organic thin film transistor(OTFT) with the purpose of improving the performance of the SiO_2 gate insulator. The SiO_2/SiN_x/SiO_2 composite insulation layer was prepared by magnetron sputtering.Compared with the same thickness of a SiO_2 insulation layer device,the SiO_2/SiN_x/SiO_2 composite insulation layer is an effective method of fabricating OTFT with improved electric characteristics and decrease...     

Photo-CVD process for ultra thin SiO2 films

In this paper we first report the use of very low deposition rate photo-induced chemical vapor deposition process, (below 0.05 nm/min). This photo-CVD process is adequate to grow very thin and ultra thin layers of SiO₂. Details on the design of the reaction chamber, reactive gases and process parameters to obtain the desired deposition regime are presented. Dependence of deposition rate on pressure in the chamber and gas flow ratio is discussed. Deposited layers were characterized using I–V and C–V techniques.     

Contact potential measurements on thin SiO2 films

Contact potential measurements by the Kelvin method were performed in vacuum on silicon wafers whose thermal oxide film was etched into the shape of a wedge. A given position along the oxide corresponded directly to a given depth and by scanning a reference electrode stripe across the wafer, information about the distribution of the oxide charge through the thickness was obtained. It was found that the oxide charge was positive and concentrated within a few hundred angstroms of the SiSiO₂ interface.     

Spin synthesis of monolayer of SiO2 thin films

The highly ordered monolayer of submicron size silica (SiO₂) particles (235 nm) is developed on p-silicon by using three-step spin-coating in colloidal suspension, which has significant potential in various applications. The influence of three-step spin speeds, spinning time, acceleration time between different steps, concentration of SiO₂ particles in the solution, solution quantity, and the ambient humidity (relative humidity) on the properties of monolayer SiO₂ are studied in order to achieve a large area monolayer film. A relatively high surface coverage and uniform monolayer film of SiO₂ particles in the range of 85%-90% are achieved by appropriate control of the preparative parameters. We conclude that this method can be useful in industrial applications, because of the fabrication speed, surface coverage and cost of the process.     

Structural and electrical characterization of gold nanoclusters in thin SiO2 films: Realization of a nanoscale tunnel rectifier

Conductive atomic force microscopy has been used to measure the I-V characteristics of nanometric Au clusters embedded in a SiO₂ film prepared by sputter deposition and low temperature annealing. Highly local asymmetric rectifier I-V characteristics were evidenced and modelled in terms of electrical transport through an asymmetric double barrier tunnel junction SiO₂/Au cluster/SiO₂. The threshold voltage depends strongly on the cluster size and barrier thickness according to the model given.     

Characterization of CuGaSe2 thin films grown by MOCVD

CuGaSe₂ thin films have been grown by metalorganic chemical vapor deposition (MOCVD), from three organometallic precursors. Samples of about 1-2 μm thick are codeposited onto Pyrex and Mo-coated soda lime glass. A large range of compositions was investigated and characterized. Stoichiometric CuGaSe₂ thin films are single-phased and their optical bandgap is about 1.68 eV. The features of the films are presented in relation with their composition. XRD spectra always exhibit a preferential orientation along the (112) plane. Secondary phases have been observed: Cu₂Se for Cu-rich films, CuGa₃Se₅ for Ca-rich films. Observation of the morphology reveals larger polyhedral grains for Cu-rich films becoming platelet-shaped and tilted for Ga-rich compounds. The optical properties are also sensitive to the compositional changes and related to the eventual presence of binary phases. The gap increases with the Ga-content. The CuGa₃Se₅, phase exhibit a gap of about 1.85 eV. All the samples have a p-type conductivity