Capacitance-voltage characterization of silicon oxide and silicon nitride coatings as passivation layers for crystalline silicon solar cells and investigation of their stability against x-radiation

In this work capacitance-voltage measurements of three different dielectric layers, thermal silicon oxide, plasma enhanced chemical vapor deposited (PECVD) silicon oxide, and PECVD silicon nitride, on p-type silicon have been performed in order to obtain characteristics as the energy distribution of the interface trap density and the density of fixed charges. Spatially resolved capacitance-voltage, ellipsometry and lifetime measurements revealed the homogeneity of layer and passivation properties and their interrelation. Additionally lifetime measurements were used to evaluate x-radiation induced defects emerged during electron beam evaporation for sample metallization.     

Bonding mechanism and stress distribution of a glass frit free thick film metallization for AlN-ceramic

Typical thick film pastes applied for the metallization of AlN-ceramics are glass bonding systems. The glass phase responsible for adhesion onto the ceramic unfortunately also acts as a heat barrier and impairs the excellent thermal conductivity of AlN. A new glass frit free conductor paste has been especially developed for the metallization of AlN. A numerical analysis of the stress distribution within the metallized ceramic induced by a continuous as well as a pulsed mode operating heat source has been conducted for this new metallization paste and, for comparison purpose, also for a standard thick film paste by means of a finite element program. In order to determine the physical property data of the phases occurring at the interface between metallization and substrate required for numerical simulation the relevant intermetallic samples have been synthesized.     

Development of Glass Frit Free Metallization Systems for AIN

Currently only glass bonding thick film conductor systems are commercially available for metallizing AlN-ceramic. The glass phase formed between metallization and ceramic impairs the high thermal conductivity of AlN. A new glass frit free metallization system has been developed utilizing the bonding mechanism of active brazing to provide the adhesion of metallization onto the ceramic. Aspects of paste preparation range from the derivation of the metallic powder to the selection of an appropriate printing vehicle which must decompose completely during the firing process under an inert atmosphere. The adhesion strength of the new paste system with the alternative bonding mechanism has been evaluated and contrasted with that of standard thick film pastes.     

Energy Transfer in Dye Mixtures Studied by Laser Fluorimetry

Radiationless energy transfer in the laser dye mixture consisting of rhodamine 6G (donor) and rhodamine B (acceptor) has been studied using fluorescence lifetime measurements. The main aim was to observe directly the effect of energy transfer on the excited-state lifetime of the donor. Estimates of the energy transfer parameters are in agreement with predictions of the Forster theory for resonance transfer based on long-range dipole-dipole interactions.     

Diffusion barrier properties of AlMoNbSiTaTiVZr high-entropy alloy layer between copper and silicon

The application of an AlMoNbSiTaTiVZr high-entropy alloy film as diffusion barrier for copper metallization has been investigated. The AlMoNbSiTaTiVZr and copper layers are deposited sequentially, without breaking vacuum, onto silicon substrates by DC magnetron sputtering. The AlMoNbSiTaTiVZr films are found to possess a stable amorphous structure due to their high-entropy and limited diffusion kinetics. The AlMoNbSiTaTiVZr high entropy alloy film is determined to prevent copper-silicide formation up to 700 °C for 30 min. Thus, HEAs appear to have potential use as effective diffusion barriers for copper metallization.     

Determining oxygen diffusion coefficients in polymer films by lifetimes of luminescent complexes measured in the frequency domain

Polymer films doped with luminescent ruthenium complexes are proving to be important oxygen sensors. We describe a technique using lifetime measurements in the frequency domain for determining the diffusion coefficient of oxygen through various polymer supports. These fundamental measurements will allow for more rational design of improved sensors. Three types of polymers were doped with [Ru(4,7-diphenyl-1,10-phenanthroline)3]Cl2. We monitored the luminescence versus time after applying a step increase in the oxygen pressure at the surface of the film. We modeled the decrease in apparent lifetime as a function of time using the diffusion coefficient of oxygen in the polymer as the only adjustable parameter. The model accurately predicted the lifetime versus time curves, and diffusion coefficients agreed well with those obtained from intensity measurements. The advantages and disadvantages of the lifetime technique to those used earlier are discussed.     

A comparison of failure predictions by strength and fracture mechanics techniques

Predictions of lifetime under load were made for five ceramic materials using strength and fracture mechanics techniques. The double-torsion technique was used to obtain fracture mechanics data, while the stressing-rate technique was used to obtain strength data. An error analysis based on the error propagation law was performed to determine confidence limits for the failure predictions. Agreement of lifetime predictions by the stressing-rate and fracture mechanics techniques were obtained for only two of the materials. The implications of these results with regard to microstructural effects on crack propagation and design applications are discussed.     

Titanium nitride diffusion barrier for copper metallization on gallium arsenide

The diffusion properties of Cu, Cu/titanium nitride (TiN) and Cu/TiN/Ti metallization on GaAs, including as-deposited film and others annealed at 350-550 °C, were investigated and compared. Data obtained from X-ray diffractometry, resistivity measurements, scanning electron microscopy, energy dispersive spectrometer and Auger electron spectroscopy indicated that in the as-deposited Cu/GaAs structure, copper diffused into GaAs substrate, and a diffusion barrier was required to block the fast diffusion. For the Cu/TiN/GaAs structure, the columnar grain structure of TiN films provided paths for diffusion at higher temperatures above 450 °C. The Cu/TiN/Ti films on GaAs substrate were very stable up to 550 °C without any interfacial interaction. These results show that a TiN/Ti composite film forms a good diffusion barrier for copper metallization with GaAs.     

Pore formation in aluminum films on macroporous silicon during high-temperature annealing

The surface of an aluminum metallization coating applied on a macroporous silicon layer and annealed for 10–60 min at 550°C has been studied by atomic-force and electron microscopy techniques. It is established that the annealing results in the formation of through (open) macropores with lateral dimensions within 400–1300 nm in the aluminum film and in the growth of large hillocks with heights of up to 1.2μ m on the surface, which are located at the edges of these macropores. The geometric parameters of large hillocks are independent of the duration of annealing.     

Investigation of high power effects on Ti/Al and Ta-Si-N/Cu/Ta-Si-N electrodes for SAW devices

Damage behavior of two different metallization systems (Ti/Al bilayer and Ta-Si-N/Cu/Ta-Si-N multilayer) as finger electrodes in surface acoustic waves (SAW) devices was investigated. A special test structure was developed for this reason. The samples were loaded with traveling SAWs varying input power and loading time. Simultaneously during these experiments, the electric behavior of the SAW structure was measured and damage development by voids and hillock formation was observed using optical microscopy, too. The damaged structures were investigated by means of different microscopy techniques. Results show that the Cu-based metallization system has a significantly higher acoustomigration resistance and power durability in comparison with the Al thin film system.     

Thickness measurements of unsaturated superfluid 4He films under driven and persistent flow

Third-sound techniques have been used to measure the thickness of an unsaturated superfluid ⁴He film as a function of flow velocity. Under the conditions of persistent flow the film thins according to the predictions of Kontorovich. In situations in which a heater is used to continuously drive a film current the measured thinning is in disagreement with the predictions of Kontorovich. A possible explanation for these results is presented. We conclude that the film thinning problem presents no fundamental discrepancy with the Bernoulli equation.Work supported by the National Science Foundation through grants DMR76-08260, 78-07762, and 79-09248.     

Photophysics of laser dye-doped polymer membranes for laser-induced fluorescence photogrammetry

Laser-induced fluorescence target generation in dye-doped polymer films has recently been introduced as a promising alternative to more traditional photogrammetric targeting techniques for surface profiling of highly transparent or reflective membrane structures. We investigate the photophysics of these dye-doped polymers to help determine their long-term durability and suitability for laser-induced fluorescence photogrammetric targeting. These investigations included experimental analysis of the fluorescence emission pattern, spectral content, temporal lifetime, linearity, and half-life. Results are presented that reveal an emission pattern wider than normal Lambertian diffuse surface scatter, a fluorescence time constant of 6.6 ns, a pump saturation level of approximately 20 microJ/mm2, and a useful lifetime of more than 300,000 measurements. Furthermore, two demonstrations of photogrammetric measurements by laser-induced fluorescence targeting are presented, showing agreement between photogrammetric and physically measured dimensions within the measurement scatter of 100 microm.     

Experimental determination of the thermal conductivity of thin films

Two techniques have been developed to determine experimentally the thermal conductivity of thin solid films of thickness 500 Å or more at low and high temperatures. The first technique is a steady state and is suitable for measurements above room temperature. The method enables the thermal conductivity of eight film specimens to be measured simultaneously. The second technique is a transient one (an adaptation of Ioffe's method for bulk materials) and is suitable for measurements in the temperature range 100–260 K. The two techniques have been used to make measurements of thin films of copper and various crystalline and amorphous semiconductors. The values of the thermal conductivity for thick copper films by both techniques agree quite well with the bulk values.     

超高分子量聚乙烯表面金属化及类金刚石薄膜沉积复合处理研究

采用超高分子量聚乙烯(UHMWPE)表面金属化及类金刚石薄膜沉积复合处理工艺,提高超高分子量聚乙烯的耐磨性.首先采用磁过滤阴极真空弧源沉积技术(FCVA)在UHMWPE表面制备约30nm钛金属层,使UHMWPE表面金属化,然后再沉积DLC薄膜,研究结果表明,UHMWPE表面金属化后,DLC薄膜沉积过程中,电荷累积效应消...     

Static characterization of magnetic bubble films

A.C. susceptibility and optical interference are combined to determine the material length, saturation magnetization and thickness of garnet bubble films on GGG substrates. These measurements have been automated to provide precisions of better than 1% and throughputs of more than sixty wafers per hour. Derived values of material length and saturation magnetization agree to better than ±3% with those from visual measurements of stripe width and bubble collapse field for a single film composition. Disagreement between results from two film compositions possibly points up a fundamental difference between the measurement techniques.     

Influence of deposition conditions on optical properties of aluminum nitride (AlN) thin films prepared by DC-reactive magnetron sputtering

Aluminum nitride (AlN) films have been prepared by DC-reactive magnetron sputtering technique. The optical properties of the films have been studied by optical spectroscopy with an incoherent light source. For the first time, it is demonstrated that for certain deposition conditions, the film may behave as a metallic thin film. In this case, there are strongly enhanced reflection peaks in the optical spectrum and the peaks may red-shift according to the degree of the metallization. The microscopic structures of the films have also been studied with scanning electron microscopy (SEM) and X-ray diffraction (XRD). It turns out that the orientation of the crystallites in the film determines whether the film remains dielectric or becomes metallic. It is found that the degree of the metallization depends on the proportion of (1000) preferred orientation in the film. In the deposition process, various deposition parameters have been experimented and a close relation between the deposition parameters and the status of the films is established. The most influential deposition conditions are as follows: the substrate temperature in a range from 200 to 700 °C, the gas composition ratio of Ar/N₂ from 20/80 to 60/40 and the plasma current from 0.2 to 0.45 A.     

Thermal wave measurement of wet paint film thickness

Thermal wave phase measurements are reported on the drying of wet paint films on aluminium substrates. Measurements of the change in thickness as the paint dries have also been obtained using a differential focussing technique on an optical microscope. By including the optical microscope measurements of the drying paint film thickness together with estimates for the density and thermal properties of the drying and cured paint, predictions have been made of the thermal phase/thickness relationships for the wet, dry, curing and cured paints. It is concluded that a phase measurement on the wet paints could be used to predict a final cured paint thickness with an accuracy of approximately ±2 μm. Errors in predicting cured film thickness from a wet film thermal phase measurement arises principally from uncertainty over the solvent content of the wet paint film, the state of cure, and the consequent uncertainty over the paint density and thermal properties.     

Analysis of fatigue data for lifetime predictions for ceramic materials

Accuracy in data analysis is of utmost importance because lifetime predictions are extremely sensitive to experimental uncertainty in the crack growth parameters. The limitations of the conventional data reduction techniques used for analysing static and dynamic fatigue data are reviewed and new, statistical methods of data reduction that offer advantages over the conventional techniques are discussed.     

Characterization of sputter deposited Au/Ni/Al multilayers on Si substrates

Multilayered Au/Ni/Al thin film metallization deposited by DC sputtering on n⁺Si substrates has been investigated. AES depth profiling was performed to reveal the concentration depth profiles of the Au/Ni/Al multilayers before and after annealing at different temperatures in the range 623-723 K. It was found that Ni aluminide layers begin to form during heat treatments at temperatures above 623 K. In addition to this process, Ni was found to diffuse significantly through the Au layer and segregates at the surface, proportionally to the increased annealing temperature. Consequently, the Ni oxidation process was found to take place thus causing the degradation of electrical contact. On the other hand Ni diffuses faster as well toward the Si/Al interface. No contamination traces at interfaces were observed. Electrical measurements of the metallized diode forward characteristics showed minor influence of the metallization heat treatment on the series resistance. Degradations were observed only in the reverse characteristics if the annealing was performed above 723 K.