Dependence of electron channel mobility on Si-SiO2interface microroughness

The effect of the Si-SiO₂ interface microroughness on the electron channel mobility of n-MOSFETs was investigated. The surface microroughness was controlled by changing the mixing ratio of NH₄ OH in the NH₄OH-H₂O₂-H₂O solution in the RCA cleaning procedure. The gate oxide was etched, following the evaluation of the electrical characteristics of MOS transistors, to measure the microroughness of the Si-SiO₂ interface with scanning tunneling microscopy (STM). As the interface microroughness increases, the electron channel mobility, which can be obtained from the current-voltage characteristics of the MOSFET, gets lower. The channel mobility is around 360 cm²/V-s when the average interface microroughness is 0.2 nm, where the substrate impurity concentration is 4.5×10¹⁷ cm^-3, i.e. the electron bulk mobility is 400 cm²/V-s. It goes down to 100 cm²/V-s when the interface microroughness exceeds 1 nm     

Dependence of surface morphology of CVD diamond films on deposition conditions

The diamond films have been deposited by the hot filament CVD method on molybdenum substrates from the mixture reactant gas of acetone and hy-drogen.The surface morphologies of the obtained diamond films under various de-position conditions have been observed by scanning electron microscope (SEM).The experimental results strongly indicate that the surface morphologies of the re-sulting films have closely related to the deposition conditions,i.e.,reaction pres-sure.For molybdenum substrates,under the lower reaction pressure the surface morphologies of the grains comprising the resulting films mainly display the small single crystal cubo-octahedron and double small crystal cubo-octahedron;under the higher reaction pressure ,the surface morphologies mainly display the large cauliflower-like .These results show that there are various crystal habits for CVD diamond under various deposition conditions .     

Dependence of surface morphology of CVD diamond films on deposition conditions

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Dependence of the surface morphology of ultrathin bismuth films on mica substrates on the film thickness

The results of studying the surface of 15- to 100-nm-thick bismuth films by atomic-force microscopy are reported. The near-linear character of the dependences of the average surface roughness and the average height of growth patterns on the film thickness is established. It is found that the average crystallite size increases, as the film thickness is increased. A slight dependence of the crystallite size on the film thickness is observed at thicknesses in the range of 27–70 nm.     

Characterization of thin-oxide MNOS memory transistors

A direct tunneling theory is formulated and applied to high-speed thin-oxide complementary metal-nitride-oxide-silicon (MNOS) memory transistors. Charge transport in the erase/write mode of operation is interpreted in terms of the device threshold voltage shift. The threshold voltage shift in the erase/write mode is related to the amplitude and time duration of the applied gate voltage over the full range of switching times. MNOS memory devices (X_{o}=25 Aring, X_{N} = 335 Aring) exhibit aDelta V_{th} = plusmn3V for an erase/writet_{p} = 100ns, which corresponds to an initial oxide field strengthE_{ox}= 1.2 times 10^{7}V/cm. The direct tunneling theory is applied to the charge retention or memory mode in which charge is transported to and from the Si-SiO2interface states. The rate of charge loss to interface states is influenced by electrical stress which alters the interface state characteristics. We discuss the fabrication of complementary high-speed MNOS memory transistors and the experimental test procedures to measure charge transport and storage in these devices.     

Estimation of thin-oxide reliability using proportional hazardsmodels

Proportional hazards models for estimating thin-oxide dielectric reliability and time-dependent dielectric-breakdown hazard rates are developed. Two groups of models are considered: group one ignores interactions between temperature and electric field, while group two considers several forms of interactions. The inclusion of interaction is not statistically significant at the 1% level. An analysis of the Hokari time-dependent dielectric-breakdown data, in terms of the form of the electric-field acceleration factor, shows that the approach of I.C. Chen et al. (1985) is more appropriate than the approach of D.L. Crook (1979)     

Endurance of thin-oxide nonvolatile MNOS memory transistors

A discussion of the factors which determine the endurance of thin-oxide MNOS memory transistors is presented. Si-SiO2interface states are influential in the early stages of erase/write cycling, while charge movement into the nitride controls the long term cycling characteristics. Other important variables include the method of preparation of the thin-oxide region, its composition, dielectric properties and thickness; the high density of spatially localized traps near the nitride-oxide interface; the low conductivity Si3N4dielectric, and electric field strengths. Optimizing these variables permits MNOS memory transistors to be operated with high endurance, reliably to beyond 10¹⁰erase/write cycles with ±20-V, 100-µs pulses and demonstrate a minimum 2-V memory window at 2900 h retention time.     

Dependence of electrical and optical properties of ZnO films on substrate temperature

ZnO films were prepared by filtered cathodic vacuum arc technique with Zn target at different substrate temperatures. The crystallinity is enhanced with increasing substrate temperature and preferably oriented at (1 0 3) direction when the substrate temperature is higher than 230°C. The PL emission corresponding to the exciton transition at 3.37 eV can be observed at room temperature, which indicates that high-quality films have been obtained by this technique. The Hall mobility, which increases with substrate temperature, is dominated by grain boundary scattering.     

Dependence of field-effect hole mobility of PPV-based polymer films on the spin-casting solvent

We present field-effect mobility measurements on a conjugated polymer poly(2-methoxy-5-(3^′,7^′-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) that was spin-cast from different solvents. The organic field-effect transistors were fabricated using an Al/p⁺-Si/SiO₂/TiW/Au/MDMO-PPV configuration. The hole field-effect mobilities for MDMO-PPV deposited from a toluene and chlorobenzene solution were found to be 5×10⁻⁶ and 3×10⁻⁵ cm²/(V s), respectively, as calculated from the saturation regime. These results are explained on the basis of a modification of the polymer morphology caused by using different solvents, as evidenced by light scattering experiments on the MDMO-PPV solutions.     

Impact of cooling condition on the crystal structure and surface quality of preferred c-axis-oriented AlN films for SAW devices

AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency(RF) magnetron sputtering method.The post-processing is carried out under the cooling conditions including high vacuum,low vacuum under deposition gas ambient and low vacuum under dynamic N2 ambient.Structures and morphologies of the films are analyzed by X-ray diffraction(XRD) and atomic force microscopy(AFM).The hardness and Young’s modulus are investigated by the nanoindenter.The experimental results indicate that the(100) and(110) peak intensities decrease in the XRD spectra and the root-mean-square of roughness(Rrms) of the film decreases gradually with the increase of the cooling rate.The maximum values of the hardness and Young modulus are obtained by cooling in low vacuum under deposition gas ambient.The reason for orientation variation of the films is explained from the perspective of the Al-N bond formation.     

Hydrogen sensitivity of palladium?thin-oxide?silicon Schottky barriers

It is shown that current transport through Schottky barriers formed by Pd on n-type silicon with a thin thermally grown oxide is sensitive to hydrogen in the ambient. It is shown that a transition from minority- to majority-carrier dominated current occurs with increasing hydrogen pressure.     

Radiation effects on thin-oxide MOS capacitors caused by electron beam evaporation of aluminum

The effects of electron-beam evaporation of Al on fast surface states, oxide charges and generation lifetime in MOS capacitors were studied. Fast surface states were increased when the thickness of the oxide was reduced to less than 400 Å. Negative charges were induced near the A1/SiO₂ interface. Both negative charges and fast surface states were reduced by using higher deposition temperatures, even though deposition temperatures were lower than post-metallization-annealing temperatures.Generation centers were also induced by electron beam evaporation. However, such generation centers were removed completely by the cleaning of furnace tubes with HCl.     

Pulsed laser deposition of carbon films: Dependence of film properties on laser wavelength

We have grown thin carbon films by pulsed laser deposition and have investigated the extent to which the properties of such films, as well as the processes responsible for these properties, are laser wavelength dependent. Films were grown by ablating material from a graphite target onto room temperature Si(100) substrates with 1064 and 248 nm laser radiation. The films were analyzed byin situ electron energy loss spectroscopy and byex situ Raman spectroscopy. The results indicated that films grown with 1064 nm ablation were graphitic, while those grown with 248 nm radiation were diamond-like. We have also examined the mass and kinetic energy distributions of the particles ejected from graphite by the two laser wavelengths. The results indicated that irradiation of graphite with 1064 nm laser radiation results in the ejection of a series of carbon cluster ions C _n ⁺ (1 ≤ n ≤ 30) with mean kinetic energies less than 5 eV. Ablation of graphite with 248 nm radiation results in the ejection of primarily C ₂ ⁺ and C ₃ ⁺ with mean kinetic energies of 60 and 18 eV, respectively. These results suggest that large, low energy clusters produce graphitic films, while small, high energy clusters produce films of diamond-like carbon.     

Effect of surface treatment on electromigration in aluminum films

Surface treatment methods for educing aluminum electromigration are studied. Simple methods for reducing aluminum electromigration have been found. Oxygen-plasma treatment and a H₂O₂ dip after aluminum patterning are shown to improve conductor life with respect to electromigration. By the oxygen-plasma treatment, the mean times to failure is improved more than two time over that for the current method. This improvement of life is a function of the oxygen-plasma treatment time and is affected by aluminum annealing and the material used for passivation. By H₂O₂ dip treatment, the mean time to failure is improved more than three times over that obtained using the current method. This improvement of life depends on the aluminum area exposed to the H₂O₂ dip. The improvement of conductor life due to surface treatments can be explained by suppression of the aluminum surface and/or grain diffusivity due to oxidation of the aluminum surface     

Plasma-parameter dependence of thin-oxide damage from wafercharging during electron-cyclotron-resonance plasma processing

In this work, the effects of plasma-parameter variations on the charging damage of polysilicon-gate MOS capacitor test structures exposed to O₂ electron-cyclotron-resonance (ECR) plasmas are investigated. The results show that charging damage is generated when large potential differences exist across the gate-oxide layers of the MOS capacitor test structures and that these potential differences can only occur in the presence of plasma nonuniformities. These results demonstrate the critical need for plasma uniformity during processing, in particular as device dimensions shrink and gate-oxide thicknesses decrease. The plasma parameters were varied by adjusting the neutral gas pressure and by independently biasing a circular grid and a ring electrode located above the wafer. The damage induced in the test wafers during the plasma exposure was characterized with ramp-voltage breakdown measurements. Radial profiles of the floating potential measured with a Langmuir probe were found to vary nonuniformly when the grid electrode was positively biased due to preferential depletion of electrons relative to ions beneath the grid electrode. An equivalent-circuit model of the test wafer and the wafer-stage electrode predicts that the silicon substrate acquires a potential equal to the average of the wafer surface potential. Comparisons of the calculated profiles of the potential difference across the gate-oxide layers of the test structures and whole-wafer maps of the breakdown-voltage measurements show that the majority of the damage occurs where the oxide potential difference is largest and that the damage only occurs in the presence of plasma nonuniformities     

Experimental study and modeling of band-to-band tunneling leakage current in thin-oxide MOSFETs

The band-to-band tunneling current in MOS transistors is studied by measuring and simulating the leakage characteristics of devices with an oxide thickness in the range 100–250 Å and different source-drain junctions. In case of conventional As implanted junctions a simple physically based expression for the tunneling leakage current as a function of applied voltage and oxide thickness with empirically matched parameters is derived. A 2-D process and device simulation approach has been used for analysis and reduction of the band-to-band tunneling leakage in conventional DDD and GGO transistors.     

衬底表面处理对原子层沉积方式生长铂金薄膜的影响

在这篇文章中,我们利用原子层沉积(ALD)的方式在硅衬底上生长铂金(反应源是(CH₃C₅H₄Pt(CH₃)₃)和氧气)。将经过氢氟酸处理和氧气处理的两种类型硅衬底进行生长对比实验来探究衬底表面处理对原子层沉积方式生长铂金薄膜的影响。相对于经氧化处理的硅衬底来说,在氢氟酸处理的硅衬底上淀积铂金薄膜有较长的滞后时间且生长过程不同。此外,即使在原子层沉积铂金薄膜实验之前利用氢氟酸处理硅衬底以去除天然氧化层,淀积实验完成后在铂金和硅衬底界面处仍有一层中间氧化层。文章解释了导致这种差异性的原因。     

Dependence of resistivity and photoconductivity in evaporated cadmium sulphide thin films on deposition and annealing conditions

The resistivity of evaporated thin films of CdS has been measured as a function of deposition and annealing conditions. Resistivity was found to be thermally activated with a high temperature activation energy of approximately 0-5?eV, which was identified with the height of the inter-crystalline barrier in the Petritz model. Resistivity decreased with increasing film thickness and annealing temperature and increased with increasing deposition rate and substrate temperature during deposition. It is proposed that these variations are related to previously reported changes in the microcrystallite grain size and the degree of preferential orientation in the [002] direction. In addition resistivity is also dependent on compositional changes during the deposition process and mobility variations due to surface scattering. Preliminary results indicate that the films are weakly photoconductive, with lower photosensitivity for the thicker films.     

Investigation of the surface silica layer on porous poly-Si thin films

The surface properties of porous poly-Si (PPS) have profound effects on the characteristics of optoelectronic devices and PPS-based gas and bio-chemical sensors. In this work, the effects of plasma dry etching on the surface structures and optical characteristics of PPS film are investigated. Experimental results show that a thin crystalline silica layer is formed on the anodically etched rough surface of the PPS films. When this layer is removed, the photoluminescence intensity decreases sharply, whereas the micro-Raman resonance peak (near 517 cm⁻¹) does not shift but its intensity increases significantly. The mechanisms for these observations are discussed in detail.     

High-frequency reactive diode sputtering of magnetite films on the sapphire surface

The conditions (oxygen partial pressure and growth rate) for the deposition of magnetite (iron oxide) Fe₃O₄ on the r plane of the single-crystalline sapphire using the high-frequency reactive diode sputtering of the Fe target are determined. The resulting ferromagnetic layers exhibit polycrystalline structure with a typical block size of 100–200 nm. The X-ray analysis is used to demonstrate that the textured phase of magnetite that is normally oriented with respect to the substrate dominates in the blocks and Fe and Fe₂O₃ impurities are almost absent.