Polycrystalline silicon is used as a transducing material in pressure microsensors. Its piezoresistive properties are strongly dependent on the processing steps and its properties -which define the sensor characteristics- vary sharply with temperature. LPCVD boron implanted polysilicon thin films have been annealed by RTA at 1100°C or below under conditions ensuring a uniform dopant distribution accross the film thickness. The resistivity as well as the gauge factor have been measured and compared with other authors' results. The gauge factor has been measured using the clamped beam technique between room temperature and 200°C with a specially designed apparatus. Technological parameters such as the Temperature Coefficient of Resistance (TCR) and the Temperature Coefficient of the Gauge Factor (TCK) are deduced as a function of doping. It appears that such coefficients do not satisfactorily describe the resistivity and gauge factor behavior at high temperature.

During low temperature (below 450°C) annealing, the sheet resistance of phosphorus implanted poly-Si thin films (film thickness : 50nm) decreased to lE+3Ω/square. The sheet resistance after annealing decreased with annealing time and became lower when the dosing level was high enough. At the dose of 8E+14 ions/cm2 we obtained a sheet resistance of 1E+3Q/square by annealing at 450°C for 180min. We analyzed ellipsometry data assuming a two-layer model where the surface layer consists of a-Si and the lower layer of poly-Si. This analysis indicated that the surface of implanted films was amorphized by ion implantation and the amorphized layer thickness increased with dosing level. Also, it turned out that the lower poly-Si layer thickness increased from 30nm to 50nm after annealing accompanied by the conversion of a-Si layer to poly-Si layer. During annealing at low temperature, activation of phosphorus ions implanted into poly-Si and recrystallization of a-Si took place simultaneously and the sheet resistance after annealing decreased with the increase in thickness of the recrystallized region.

Polycrystalline silicon thin films have been selectively deposited at a deposition rate of 60–100Å/min and a substrate temperature of 300°C on molybdenum or silicon over silicon dioxide, silicon nitride or Coming 7059 glass substrate in a continuous hot-wire CVD process involving hydrogen and disilane. Excellent selectivity is achieved on features as small as one micrometer spaced molybdenum lines. The crystallinity of the selectively deposited polysilicon films is thickness dependent. The substrate selectivity is sensitive to both silicon content in the gas phase and substrate temperature. Selective deposition shifts to lower Si content in the gas phase when substrate temperature increases. At a certain substrate temperature, for a silicon content above a certain value in the gas phase, films with similar crystallinity are non-selectively deposited on both molybdenum and silicon dioxide.

Low temperature unhydrogenated polysilicon thin film transistors are elaborated through a fourmask gate aluminium process. Temperature process does not exceed 600°C. Active layer is made of undoped polysilicon layer, an in-situ phosphorus polysilicon layer constitutes source and drain windows and a SiO2 APCVD layer ensures gate insulation. The transistors exhibit electrical properties as good as in the case of hydrogenated ones: a low threshold voltage (VT = 4–5 V), an acceptable optimum field effect mobility (≅ 42 cm2/Vs), a high On/Off state switching, and a high On/Off state current ratio (≅ 107) for a drain voltage equal to 1 V.

Phenomena and solving methods for damage of Sb-doped SbO2 thin films deposited by RF magnetron sputtering have been investigated by observing in the main the positional difference of film electrical resistivity. A ring plate mask was used to disperse the energetic particles and sputtering parameters were controlled such a manner that effects by the parameters were compensated each other. By the control, positional differences in resistivity and XRD patterns of the films could be reduced to a minimum value; The films became nearly uniform ones.

Thin-films of indium-tin oxide (ITO) on soda-lime-silicate (SLS) glass were fabricated using an atmospheric RF plasma mist deposition process. Some of the films were deposited at substrate temperatures between 400 C and 500 C, and were subsequently annealed at 400 C and 530 C for 1 hour. Conductivity was improved due to post-annealing. Film thickness, particle size, film morphology and crystallite size were characterized. The structural changes on the glass and the ITO film were investigated by DRIFT spectroscopy.

Bismuth-doped tin oxide films have been deposited using a new spray-pyrolysis deposition system. Among the properties are the possibility of depositing thin films over very large areas with good uniformity and the relatively small cost compared with other types of deposition systems. The apparatus is divided in two major parts, the aerosol chamber and the deposition chamber. The deposition chamber consists of a flat rotating hot plate that can house substrates up to 18 cm in diameter. Deposition temperature ranges from 290 °C to 350 °C. The SEM pictures show a phase transition from amorphous to polycrystalline which also strongly affects the transport properties of the film. The high values of the surface resistivity obtained are consistent with those ones required to develop an analog grey scale ferroelectric liquid crystal display. The sample shows a 20% uniformity in the value of surface resistivity over an area of 140 cm2, and the results obtained until now show a satisfactory reproducibility. Bismuth and Tin concentration versus deposition temperature have been determined by ICP mass spectrometry. Our work is supported by the ESPRIT project “PROFELICITA”.

We have studied grain growth and electrical properties of polycrystalline tin oxide (SnO2) thin films prepared by vacuum-evaporation with a two-step process: evaporation of tin metal films and then oxidation of these metal films. Surface morphology of the SnO2 thin films was observed by atomic force microscopy. The grain size of the SnO2 thin films is found to increase with the film thickness and oxidation temperature. Kinetics of the grain growth is discussed in terms of a 3-dimensional diffusion limited process. The diode current-voltage (I-V) characteristic of the SnO2/Si heterojunctions (isotype and anisotype) was measured in the temperature range of 14K-383K. Changes in the diode ideality factor and threshold voltage with temperature are discussed. In addition, we present ambient tunnelling I-V results measured from individual SnO2 grains.

Chemically deposited thin films have multiple applications, in particular for low cost solar cells production. However, due to their inhomogeneous structure, it is very difficult to predict their physical properties. In this work we present a mean field approximation to model the effective electrical conductivity of the polycrystalline ZnO chemical deposited thin films. Our model considers elliptical inclusions randomly distributed in a matrix. We compare with the experimental results of two different deposition methods: spray pyrolysis [1] and successive ion layer adsorption and reaction (SILAR) [2]. Supported by the structural information of these samples, we select the elliptical geometrical parameters. We obtain a good fit of the experimental measurements with our calculation.

In the present contribution an X-ray diffraction (XRD) study of thin films in the Mo-Bi-O system is reported. The samples were grown by MOCVD on A12O3 substrates. Several thin films have been grown starting from a Mo:Bi ratio in the two metallorganic precursors ranging from 6:1 to 1:1, thus obtaining films constituted by MoO3 and Mo-Bi-O layers with different thicknesses. The effect of the underlying Mo-Bi-O layer on the preferred orientation of the MoO3 layer, which is found in the samples with a high Mo:Bi ratio in the precursors, is discussed. Moreover, an equation is proposed relating the percentage of the phase constituting the film, as given by the Rietveld leastsquares procedure, and the film thickness. Thus it is shown that the growth rate of the pure MoO3 film is much higher than that of the Mo-Bi-O oxide film. A tentative explanation can be given by considering a possible growth inhibiting action by Bi in this system.

The oxygen-ion conducting Aurivillius phases Bi2Cu0.1V0.9O5.35 and Bi2Nb0.3V0.7O5.5 were synthesized as bulk powders by the sol-gel method, and gave single-phase powder X-ray diffraction patterns at calcination temperatures as low as 450 °C. Crack-free films of both materials were spin-coated onto quartz, platinum, and silver substrates and heat-treated in a twostep firing process. The effects of different process parameters were investigated.

The interactions between thin films of Zn and (100)InP were analysed with secondary ion mass spectrometry, X-ray diffraction and transmission electron microscopy. Zn was found to penetrate the native oxide on InP surface during deposition, and to form an ohmic contact when deposited on n-type InP. Under heat treatment Zn protrudes into InP, and beneath Zn/InP interface a tetragonal Zn3P2 phase lattice matched to InP grows.

Amorphous and microcrystalline silicon-germanium alloys, a-SixGel-x:H and μc-SixGel-x:H, respectively, have been prepared by reactive magnetron sputtering (RMS) from pure crystalline Si and Ge targets in a hydrogen ambient using argon as the sputtering gas. We have investigated the structural, optical, and electronic properties of the as-deposited films. The optical and electrical properties, e.g., the ambipolar diffusion length, photoconductivity, and photosensitivity, were found to be comparable to those of device-grade a-SixGe1-x:H alloys, e.g., films with x ∼ 0.5, and band-gaps ∼ 1.3–1.4 eV. In contrast to the behavior of the a-SixGel-x:H alloys, the μc-SixGe1-x:H alloys do not display a Staebler-Wronski effect, as manifested by a decay of the photoconductivity under intense illumination.

One of the most important problems to solve in order to improve the CdTe solar cell performance is the deposition of stable ohmic contacts. W and Mo with their high work function, high temperature stability and good mechanical properties are prospective materials for contacts to p-CdTe. This paper presents data for the electrophysical characteristics of W or Mo/CdTe and W or Mo/ CdS-CdTe heterostructure systems. W and Mo films are deposited by a W(CO)6 based CVD process at atmospheric pressure and low temperatures (250–300)°C. We emphasize the improvment of the contact properties by developing a transitional layer heavily doped with acceptors. The defects arrangement in the layer should promote the diffusion of such impurities as Cu, P, As etc. A proper balance between the impurities and the defects could be achieved by suitable thermal treatment. Rapid thermal or traditional annealing in different gas atmospheres – N2, Ar or air were applied, followed by chemical or electrochemical treatment. Electrical characteristics measurements and structural studies were performed for CdTe layers as well as for the SnO2 - CdS - CdTe structures

The characterization of MOCVD-grown GaAs-AlGaAs materials and GaAs p+n junctions on poly-Ge substrates is presented. Minority carrier lifetime in GaAs-AIGaAs double-hetero (DH) structures grown on these substrates and the variation of lifetimes across different grainstructures are discussed. Minority-carrier diffusion lengths in polycrystalline GaAs p+-n junctions were evaluated by cross-sectional electron-beam induced current (EBIC) scans. The junctions were also studied by plan-view EBIC imaging. Optimization studies of GaAs solar cell on poly-Ge are discussed briefly. The effect of various polycrystalline substrate-induced defects on performance of GaAs solar cells are presented.

A refined thernodynamic analysis of the reaction between molen Al and SiC is presented. The calculations indicate much higher Si concentrations for saturation with respect to AkC 3 formation than previously reported. Preliminary microstructural studies confirm the formation of interfacial A14C3 for pure Al thin films on SiC reacted at 9000C. The implications of the calculations and experimental observations for the production of ohmic contacts to p-type SiC are discussed.

In advanced ULSI devices, Ti (titanium)/TiN (titanium nitride) film stack is commonly used as liner materials. Ti is used to reduce contact/via resistance while TiN is utilized as an adhesion/diffusion barrier layer. Ti/TiN liner with optimized thickness combinations should be used for progressively advanced ULSI devices with features of reduced dimensions and increased aspect ratios in order to effectively reduce contact/via resistance, ensure barrier quality, and maximize cross section of metal conductors with low electrical resistivities. This study evaluates the film properties such as sheet resistance, density, stress, grain structures, and reflectance of individual Ti and TiN, and composite Ti/TiN films manufactured by collimated physical vapor deposition (PVD). The film thickness ranges from 5 to 60nm. The dependence of these properties on the film thickness will be discussed.

Cu has two advantages over Al for sub-quarter micron interconnect application: (1) higher conductivity and (2) improved electromigration reliability. However, Cu diffuses quickly in SiO2and Si, and must be encapsulated. Polycrystalline films of Physical Vapor Deposition (PVD) Ta, W, Mo, TiN, and Metal-Organo Chemical Vapor Deposition (MOCVD) TiN and Ti-Si-N have been evaluated as Cu diffusion barriers using electrically biased-thermal-stressing tests. Barrier effectiveness of these thin films were correlated with their physical properties from Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Secondary Electron Microscopy (SEM), and Auger Electron Spectroscopy (AES) analysis. The barrier failure is dominated by “micro-defects” in the barrier film that serve as easy pathways for Cu diffusion. An ideal barrier system should be free of such micro-defects (e.g., amorphous Ti-Si-N and annealed Ta). The median-time-to-failure (MTTF) of a Ta barrier (30 nm) has been measured at different bias electrical fields and stressing temperatures, and the extrapolated MTTF of such a barrier is > 100 year at an operating condition of 200C and 0.1 MV/cm.

We have investigated the effects of Cu and Si dopants on electromigration mass transport in Al interconnects for VLSI technology. Four Al alloys with different Cu and Si dopant concentrations (AI-1.5%Cu, AI-1.5%Cu-I.5%Si, AI-0.5%Cu-I.0%Si, and AI-I.O%Cu-I.0%Si) were sputter deposited onto Si substrates covered with 0.55 pRm of Si02 (tetraethylorthosilicate). All metal films were deposited using an MRC903 sputter deposition system to a thickness of 6800Å. Deposition parameters were held constant for each metallurgy, with a base pressure of 7x 10−2 torr, deposition pressure of 102 torr, forward power of 7 Kwatts, and substrate bias of 125 volts. Test structures designed according to National Institute of Standards design guidelines were fabricated in each metallurgy using conventional photolithography and reactive ion etching methods for line widths of 1.0, 1.8, 3.0, 5.0 and 10.0 μm. Accelerated test conditions of T=200°C and DC current density of 2x106 A/cm−2 were used. The results show that electromigration resistance increases with increasing Cu content and decreases as Si content increases. These results are explained in terms of precipitate, grain size distribution, orientation and stress by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). Our results provide a general guideline relating Cu and Si dopant concentrations, film microstructure and the intrinsic reliability of the metallization system.

The Solid Phase Crystallization (SPC) of amorphous silicon films deposited by Low Pressure Chemical Vapor phase Deposition (LPCVD) using pure silane at 550'C was studied by in-situ monitoring the film conductance. The saturation of the conductance at the end of the crystallization process is found transient. The conductance decreases slowly after the onset of the saturation. This degradation is also observed from other analyses such as ellipsometry spectra, optical transmission and Arrhenius plots of the conductivity between 250 and 570K. Hall effect measurements show that the degradation is due to a decrease of the free carrier concentration n and not to a decrease of the mobility. This indicates a constant barrier height at the grain boundaries. The decrease of n is then due to a defect creation in the grain. Hence, whatever the substrate used, an optimum crystallization time exists. It depends on the amorphous quality film which is determined by the deposition techniques and conditions and on the crystallization parameters.