S. Karlsson

Mechanisms of reactive sputtering of titanium nitride and titanium carbide II: Morphology and structure

Titanium was reactively r.f. sputtered in mixed ArN2 and ArCH4 discharges onto substrates held at 775 K. The films obtained were characterized by scanning electron microscopy and X-ray diffraction and through measurements of the microhardness and electrical resistivity. The composition of the films was determined by Auger electron spectroscopy. The measurements show that the morphology of the deposits to a large extent influences the properties of the films obtained. For TiN coatings the electrical resistivity reaches the bulk resistivity only if coatings with the full bulk density are obtained. The difference observed in the lattice parameter for TiN thin film and bulk samples is explained using a grain boundary relaxation model. It is also shown that the heat of formation of the compounds plays an important role in the formation of carbide and nitride films. A high heat of formation promotes the development of large grains and dense structures.

Mechanisms of reactive sputtering of titanium nitride and titanium carbide I: Influence of process parameters on film composition

Abstract The reactive sputtering of titanium in mixed ArN 2 and ArCH 4 discharges was studied by measuring the compositions of both the deposited films and the layers formed on the target. The sputtering experiments were performed in a diode r.f. sputtering unit and the compositions were determined by means of Auger electron spectroscopy. The results show that the amount of reactive constituents incorporated into the growing films depends on whether a compound has been formed on the target. At low pressures where no such compound is formed, the incorporation of the reactive gas follows an adsorption isotherm similar to the Langmuir adsorption isotherm, and very low values of the sticking probability are observed. At higher pressures species originating from the target determine the composition of the coatings. The important process parameters were found to be the partial pressures of the reactive and inert working gases, the ion current density and the voltage applied to the target.

Mechanisms of reactive sputtering of titanium nitride and titanium carbide III: Influence of substrate bias on composition and structure

Abstract Films of TiN and TiC were grown by reactive r.f. sputtering of titanium in mixed ArN2 and ArCH4 discharges on negatively biased substrates. The compositions of the films were measured using Auger electron spectroscopy and their structure and morphology studied using X-ray diffraction and scanning electron microscopy respectively. The composition was found to be strongly affected by the bias voltage. An increase in bias both the carbon and the nitrogen contents in substoichiometric films. However, when stoichiometric TiN is formed no further change in the composition occurs. For TiC films an increase in the carbon- to-titanium ratio above 1.0 is possible. The structure is also affected by the bias voltage. For example the grain size of TiN has a maximum at a bias of 200 V. A possible explanation is a double influence of the ion bombardment. At low voltages, the adatom mobility is enhanced and the grain size increases but as the bias increases resputtering of species from the growing film surface becomes increasingly important and the grain size decreases.

Kinetics of nitride formation on titanium targets during reactive sputtering

During reactive sputtering processes formation of surface compounds on the target leads to large reductions in deposition rate. The formation of such layers during the reactive sputtering of titanium with Ar-N 2 ion beams have been studied “in situ” using Auger electron spectroscopy. The kinetics of the process were studied by monitoring the AES nitrogen signal with time. The amount of nitrogen on the target surface was estimated using a simple kinetic model. The time dependence was found to be in agreement with the exponential rate predicted by the model. To explain fully the processes occurring, chemical reactions at the surface, altering, e.g., the sticking probability and penetration of reactive ions into the target lattice have to be taken into account. It is also shown that the stable δ -TiN phase is formed on the target surface. The most important parameter for the formation of the nitride layer on the target was the ratio between the number of Ar and N 2 ions impinging. The total number of N 2 ions at a fixed N 2 -Ar ratio, i.e. the degree of ionization, was also found to be important. The energy, however, was found to have only a minor influence on the formation of the nitride layer. The resulting nitride layers during ion beam sputtering are also compared with layers formed on the target during reactive sputtering of titanium in an ordinary RF sputtering apparatus.

Solubility limit and precipitate formation in Al-doped 4H-SiC epitaxial material

Heavily Al-doped 4H-SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500 degreesC and 2000 degr ...

Influence of substrate shape on TiN films prepared by reactive sputtering

Abstract TiN films were prepared by reactive sputtering in ArN 2 discharges, using both r.f. sputtering and d.c. planar magnetron sputtering. The films were grown on differently shaped molybdenum substrates which were negatively biased during deposition. When a bias voltage of −200 V or more was used an increased rate of resputtering was observed close to sharp edges on some substrates. In some cases the rate of resputtering was so high that it caused complete resputtering of the deposited material. The amount of resputtering is measured and discussed in terms of the bias potential, the gas scattering and the balance between the deposition rate and ion bombardment. The increased rate of resputtering close to sharp edges is explained as due to an increased ion current density around the edges.

Organic matter chlorination rates in different boreal soils: the role of soil organic matter content.

Transformation of chloride (Cl(-)) to organic chlorine (Cl(org)) occurs naturally in soil but it is poorly understood how and why transformation rates vary among environments. There are still few measurements of chlorination rates in soils, even though formation of Cl(org) has been known for two decades. In the present study, we compare organic matter (OM) chlorination rates, measured by (36)Cl tracer experiments, in soils from eleven different locations (coniferous forest soils, pasture soils and agricultural soils) and discuss how various environmental factors effect chlorination. Chlorination rates were highest in the forest soils and strong correlations were seen with environmental variables such as soil OM content and Cl(-) concentration. Data presented support the hypothesis that OM levels give the framework for the soil chlorine cycling and that chlorination in more organic soils over time leads to a larger Cl(org) pool and in turn to a high internal supply of Cl(-) upon dechlorination. This provides unexpected indications that pore water Cl(-) levels may be controlled by supply from dechlorination processes and can explain why soil Cl(-) locally can be more closely related to soil OM content and the amount organically bound chlorine than to Cl(-) deposition.

Hydrogen dissociation on clean and contaminated Pd studied with a Pd-MOS structure and photoelectron spectroscopy

We show how a new combination of methods can be used in order to gain information on hydrogen dissociation on Pd and on its dependence on the electronic structure. With this method we can also detect changes in hydrogen pressure of about 1×10−11 Torr H2 corresponding to hydrogen coverages on the Pd surface of about 0.001 of a monolayer.

Surface Reactions on Pd Studied With a Hydrogen Sensitive MOS-Structure and Photoelectron Spectroscopy

During the last couple of years catalytic reactions on Pd surfaces have been studied at our department by means of a hydrogen sensitive Pd-MOS structure and work function measurements. These studies have been performed at atmospheric pressures with Ar and O2 as carrier gases. We have now extended this type of measurements to the ultra-high vacuum (UHV) region and also combined them with both UV and, in certain cases, X-ray photoelectron spectroscopy (UPS, XPS) studies. With this technique we are able to detect about 0.001 of a monolayer of hydrogen, and changes in rate or equilibrium constants corresponding to changes in an energy coordinate of less than 10 meV. Furthermore, results from a Cd contaminated Pd-MOS structure indicates that the ability of Pd to dissociate H2 is related to a microscopic parameter and not to any general metal-like parameter.

UV-light induced mineralization of organic matter bound chlorine in Lake Bjän, Sweden––a laboratory study

Surface water and aqueous solutions of isolated organic matter from a humic rich lake in southern Sweden were exposed to artificial UV radiation to investigate the UV light induced influence on organic matter bound chlorine in natural systems. It was found that the photodegradation of organic matter bound chlorine was more pronounced than the photodegradation of organic carbon. After 120 h of irradiation of the isolated organic matter, only 35% of the initial organochlorine was still in the solution compared to about 70% of the dissolved organic carbon (DOC). A similar result was obtained for unfractionated surface water. Furthermore, our results indicate that the loss of organic chlorine was mainly due to a mineralization of organic chlorine into chloride ions. The total decrease of organic chlorine after 120 h was 32 microg Cl(org) l(-1), of which the major part disappeared in the initial irradiation phase. A similar increase was observed in the chloride concentration (34 microg Cl(-) l(-1)).