Interdiffusion of thin Cr and Au films deposited on silicon

The backscattering technique has been used to study the interdiffusion process of Cr and Au films deposited on silicon substrates. The results indicate that Au diffuses in Cr with an effective diffusion coefficient $\text{D =}\text{const. exp}\text{(?0.68/}\text{k}\text{T)}$. The activation energy is consistent with a diffusion process which occurs preferentially through grain boundaries. The high value of the diffusion coefficient justifies the presence of Au at the CrSi interface after a low temperature short-time heat treatment. At temperatures above 370 °C (the eutectic point of the SiAu system) and after a long enough heat treatment the gold is completely mixed with silicon.     

Optical properties of pulse laser deposited AlN thin films on silicon

Aluminium-nitride thin films were deposited on silicon Si(111) substrate with pulsed laser deposition in a Riber LDM-32 system. The optical properties of the films were studied by means of optical spectroscopy with an incoherent light source mainly covering the visible range. It is demonstrated that, in comparison with an aluminium mirror, under certain deposition conditions, the film may behave as a metallic thin film as far as the optical reflection is concerned. In this case, there is an enhanced plasmonic reflection peak in the optical spectrum and the peak may be modified according to the degree of the phase transition. The microscopic structures as well as the surface topographies of the films were also studied with X-ray photoelectron spectroscopy and scanning electron microscopy. It turns out that the density and the size of the microscopic domains in the film determine whether the film remains dielectric or becomes metallic. The diamagnetic effect in the enhanced plasma increases in the process when the sample is smoothed out with the optimized nitrogen gas pressure. The nitrogen pressure is thus identified as the most influential deposition condition to the phase transition.     

Humidity sensing characteristics of hydrotungstite thin films

Thin films of the hydrated phase of tungsten oxide, hydrotungstite (H₂WO₄·H₂O), have been grown on glass substrates using a dip-coating technique. The b-axis oriented films have been characterized by X-ray diffraction and scanning electron microscopy. The electrical conductivity of the films is observed to vary with humidity and selectively show high sensitivity to moisture at room temperature. In order to understand the mechanism of sensing, the films were examined by X-ray diffraction at elevated temperatures and in controlled atmospheres. Based on these observations and on conductivity measurements, a novel sensing mechanism based on protonic conduction within the surface layers adsorbed onto the hydrotungstite film is proposed.     

Characterization of low pressure chemically vapour- deposited thin silicon nitride films

Silicon nitride films prepared on silicon by low pressure chemical vapour deposition (LPCVD) were characterized by electrical measurements (current-voltage and capacitance-voltage), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). The contact current versus contact field characteristics were interpreted in terms of the Fowler-Nordheim tunnelling of holes from silicon into silicon nitride, with the field of charged traps and the effect of changing the triangular shape of the barrier under steady state conditions taken into account and on the assumption of a Poole-Frenkel detrapping mechanism. AES data show that the LPCVD process yields stoichiometric Si₃N₄ films. RHEED data shows that films of thickness more than 10 nm are amorphous. Some crystalline structures of Si₃N₄ and SiO₂ are observed for thicknesses of less than 10 nm.     

VHF-PECVD沉积本征微晶硅薄膜氧污染研究

通过激活能测试装置测量VHF-PECVD高速沉积的本征微晶硅薄膜,并对不同沉积功率、不同沉积压强条件下沉积制备的样品的激活能进行了分析研究。结果表明:在不同功率、不同气压沉积条件下沉积的微晶硅薄膜,激活能偏低,薄膜在沉积过程中被氧杂质污染;随着沉积功率的增大和沉积气压的增大,沉积速率随着提高,样品的激活能升高,通过提高沉积功率和沉积气压可以有效的抑制氧污染。     

Morphological characteristics of carbon/polytetrafluoroethylene films deposited on porous carbon support

The effect of polytetrafluoroethylene (PTFE) content on morphological characteristics of carbon/PTFE films deposited on porous carbon support was investigated by mercury-porosimetry, scanning electron microscopy (SEM) and a.c. impedance spectroscopy. The microstructure of the film was affected by the content of fluoropolymer. The layer has two distinctive pore distributions with a boundary of about 0.35 m. The polymer coated the pores with size higher than 1 m (carbon interagglomerate pores), while the pores with size lower than 1 m were not influenced by the presence of PTFE. Above 40 wt% PTFE, a further supply of polymer did not fill the pores, but increased the thickness of the sample. The presence of cracks, increasing in number and size with PTFE content, was also revealed. © 1998 Chapman & Hall     

ECR-PECVD制备氮化硅薄膜的键态结构

用红外光谱和拉曼光谱分析了用低温电子回旋共振等离子体CVD技术制备的Si3N4薄膜的键态结构。结果表明Si3N4薄膜主要由Si-N键结构组成，还含有Si-H和Si-O-Si键结构。随着沉积温度的提高，Si3N4薄膜中的Si-H键减少，氢含量降低。可利用提高沉积温度来减少Si3N4薄膜中的氢含量。在沉积温度为420℃时Si3N4薄膜的Raman光谱在短波方向出现一新的展宽的拉曼散射峰。     

Nanoindentation stress-strain curves of plasma-enhanced chemical vapor deposited silicon oxide thin films

Plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiO_x) thin films have been widely used in Micro/Nano Electro Mechanical Systems to form electrical and mechanical components. In this paper, we explore the use of nanoindentation techniques as a method of measuring equivalent stress-strain curves of the PECVD SiO_x thin films. Four indenter tips with different geometries were adopted in our experiments, enabling us to probe the elastic, elasto-plastic, and fully plastic deformation regimes of the PECVD SiO_x thin films. The initial yielding point (σ_I) and stationary yielding point (σ_II) are separately identified for the as-deposited and annealed PECVD SiO_x thin films, as well as a standard fused quartz sample. Based on the experimental results, a shear transformation zone based amorphous plasticity theory is applied to depict the plastic deformation mechanism in the PECVD SiO_x.     

AC impedance spectroscopy of porous silicon thin films containing metallic cations

Thin porous silicon (PS) films were prepared by HF/HNO₃ vapor etching on silicon wafers. The infiltration of metallic cations inside the porous silicon matrix followed by slow heating in air leads to an interesting electrical and optical physical phenomena. Al³⁺, Cu⁺, K⁺, Li⁺ metallic cations as chloride or as nitrate solutions are infiltrated inside the silicon porous matrix. After annealing in air at 500 °C during 2 h a structure was achieved in order to measure the Nyquist diagram corresponding to the cations embedded in PS/silicon. The real and imaginary parts of the whole structure depend on the voltage bias and on the frequency. Those signify that the junction is a Schotky-barrier junction.

From the variation of Ln(σT) versus absolute temperature T, where σ is the conductivity, we have deduced the activation energy of the metallic impurities in the [100 °C–400 °C] temperature range. We have found that the activation energies are of about 0.19 eV, 0.25 eV, 0.49 eV and 0.71 eV for Cu⁺, K⁺, Al³⁺ and Li⁺ cations respectively. These kinds of structures are suitable for gas sensing, optical sensing or for the fabrication of fuel cell membranes.     

X-ray determination of the residual stresses in thin aluminum films deposited on silicon substrates

Results of x-ray strees measurements on highly [111] textured thin aluminum films deposited on [100] silicon wafers were reported. Due to the texturing the conventional sin²ϕ technique for polycrystalline materials was found to be difficult to use. X-ray stress measurements were thus made as if the thin films were single crystals with [111] planes parallel to the substrate. The calculated stresses for unannealed specimens were found to be compressive and small, approximately -20 to -30 MPa. The calculated stresses for specimens annealed at 450°C were found, after a waiting time of 34 days, to be tensile and larger, approximately 120 to 140 MPa.     

Characterization of yttria-stabilized zirconia thin films deposited by electron beam evaporation on silicon substrates

Structure, phase composition and electrical conductivity of thin yttria-stabilized zirconia (YSZ) films deposited by electron beam evaporation on a silicon (1 0 0) substrate at different temperatures i.e. room temperature (r.t.), 700 and 830°C, as well as the quality of the YSZ–Si interface have been investigated. The phase composition was verified by Raman spectroscopy and by infrared (i.r.) transmission measurements. The structure of films changed in agreement with their electrical conductivity depending on the deposition temperature. Both structure and thereby electrical conductivity were influenced by the high concentration of Y2O3 stabilizer used and by the post-deposition thermal treatment of films. The deposition temperature was also important in determining the quality of the YSZ–Si interface and hence the accessible sweep of the surface potential. The capacitance–voltage characteristics of the metal–insulator–semiconductor (MIS) structures incorporating YSZ films measured at r.t. showed hysteresis and positive shifts of the flat-band voltages. © 1998 Chapman & Hall     

Residual stress in piezoelectric poly(vinylidene-fluoride-co-trifluoroethylene) thin films deposited on silicon substrates

The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE) (72/28)) piezoelectric polymer thin films deposited on silicon wafers were investigated using the wafer curvature method. Double-side polished silicon wafers with minimized initial wafer warpage were used to replace single-side polished silicon wafers to obtain significantly improved reliability for the measurement of the low residual stress in the P(VDF-TrFE) polymer thin films. Our measurement results showed that all the P(VDF-TrFE) films possessed a tensile residual stress, and the residual stress slowly decreased with time. Our analysis further indicates that the tensile stress could arise from the thermal mismatch between the P(VDF-TrFE) film and the silicon substrate. Besides possible viscoelastic creep mechanism in thermoplastic P(VDF-TrFE) films, microcracks with widths in the range of tens of nanometers appeared to release the tensile residual stress.     

Vacuum deposited polyimide thin films

Vacuum deposition as an attractive alternative for polyimide (PI) layers formation is discussed. PI thin films can be formed by vapour co-deposition of the precursor monomers pyromellitic dianhydride and 4,4′-oxydianiline following a thermal treatment at a temperature of over 150°C. The effects of the dynamic state of the substrate, dose stoichiometry and thermal treatment on the surface morphology and imidization rate of PI films were investigated using scanning electron microscopy, thermogravimetric, differential thermal analyses and Fourier transform infrared spectroscopy and microscopy. The results showed that the solid state reaction between the precursors starts at about 175°C. The imidization finishes in the temperature interval of 342–365°C. The destruction of PI is observed at 520°C. The surface morphology of the layers depends only on the monomer ratio. The resulting vacuum deposited PI films are smooth, uniformly thick and form without shrinkage.     

Size dependent optical characteristics of chemically deposited nanostructured ZnS thin films

ZnS thin films of different thicknesses were prepared by chemical bath deposition using thiourea and zinc acetate as S²⁻ and Zn²⁺ source. The effect of film thickness on the optical and structural properties was studied. The optical absorption studies in the wavelength range 250–750 nm show that band gap energy of ZnS increases from 3·68–4·10 eV as thickness varied from 332–76 nm. The structural estimation shows variation in grain size from 6·9–17·8 nm with thickness. The thermoemf measurement indicates that films prepared by this method are of n-type.     

Influence of surface Pd doping on gas sensing characteristics of SnO2 thin films deposited by spray pirolysis

In this article the analysis of steady state and transient gas sensing characteristics of undoped and Pd surface doped SnO₂ films, deposited by spray pyrolysis, is described. The influence of parameters such as air humidity (2-50% RH), operation temperature (25-500 °C) and Pd surface concentration (0-1% ML Pd) on gas response to CO and H₂ (0.1-0.5%), response time, shape of sensitivity S(T) curves and activation energy of τ(1/kT) dependencies are discussed. A mechanism based on a chemisorption model is proposed to explain how Pd influences the gas sensing characteristics of SnO₂ films.     

Characterization of pyrolytically deposited V2O3 thin films

V₂O₃ films were deposited using the pyrolysis technique. The surface composition and structure of the deposited V₂O₃ films were investigated using scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Electronic conductivity measurements of the films were also carried out as a function of temperature from room temperature to about 430 K.The SEM analysis showed a smooth film surface which on exposure at high intensity showed some form of restructuring. The AES, however, indicated the presence of carbon in the deposited film while the RHEED showed a streaked pattern which could result from the restructing observed in the SEM analysis.The electrical conductivity measurements showed metallic-type behaviour in the region investigated. A smooth second-order transition was observed at about 400 K.     

Platinum thin films deposited on silicon oxide by focused ion beam: characterization and application

Focused ion beam system was used for deposition of platinum (Pt) thin films on thermally oxidized silicon (Si). Various test patterns (squares and lines) were deposited for electrical characterization of the films, using 2- and 4-terminal measurements. Tests with parallel Pt lines were also carried out, and considerable leakage was detected for the interline distances in the sub-micron range. We investigated two ways to decrease the leakage current: inducing surfaces roughness and using an oxygen plasma after patterns deposition. A method of dielectrophoresis with an AC electric field was applied to align and deposit metallic multi-wall carbon nanotubes (CNT) between pre-fabricated metal, gold, and palladium electrodes with a micron-scale separation. Further, using focused electron and ion beam-deposited Pt contacts in two different configurations (“Pt-on-CNT” and “CNT-on-Pt”), 4-terminal measurements have been performed to evaluate intrinsic nanotube resistances.