Surface Layer Of Substrate Research Articles

Electrochemical deposition of metal layers and structures for Si-based microsystems

This work reports the study of the electrochemical (EC) deposition of Ni metallic layers and Ni/Cu multilayer structures on Si based substrates. The structural analysis of the processed samples has been performed by X-ray diffraction (XRD) and these data have been correlated with the characterisation of their surface morphology by atomic force microscope (AFM) measurements. The results obtained show the strong dependence of the structural parameters of the deposited films on the substrate surface layer and growth current density, for Ni layers grown onto EC deposited Cu sacrifical ones a strong (2 2 0) preferred orientation evolves with deposition time. This is likely related to a textured structure of the Cu film. Direct deposition onto Au coated oxidised Si wafer allows to avoid this preferential orientation, but a strong decrease in the Ni growth rate is observed. Texturing of the Ni film can also be controlled by the current density during growth.

Some features of the ion-beam mixing during simultaneous ion implantation and metal deposition

Experimental results on the ion implantation of Ta and Cu ions into an Al substrate, accompanied by the deposition of these ions in the form of a surface coating are reported. The coatings composed of the implant elements exhibit a complicated structure and lead to an increase in the microhardness, adhesion properties, and corrosion resistance of the substrate. An analysis of data on the energy distribution of secondary ions shows that the surface layer of ion-implanted substrates contains intermetallic phases.

Phase structure and mechanical and adhesion properties of epoxy/silica hybrids

Organic/inorganic hybrids containing 4– to 19.8 wt% of silica were synthesized from an epoxy resin diglycidyl ether of bisphenol-A (DGEBA) and a γ-glycidoxypropyltrimethoxysilane (GPTMS) or a tetramethylorthosilicate (TMOS) by utilizing a sol/gel process. In the DGEBA/GPTMS hybrids, the storage modulus in the rubbery region increased and the peak area of the tan δ curves in the glass transition region decreased, respectively, with the hybrization of small amounts of silica. This may result from the suppression of the epoxy network moiety with the incorporation of the silica network. Observation using transmission electron microscopy (TEM) revealed that the silica networks are uniformity dispersed in the hybrids. Furthermore, the hybrids with GPTMS showed a very high adhesion strength for the silicone rubber. Results from the X-ray microanalysis show that the silica networks are concentrated in the interfacial area of the adhesive joints with silicone rubber. In the swelling test of silicone rubber with the epoxy resin containing GPTMS, the degree of swelling increased with increasing GPTMS content. The high adhesion strength observed in the DGEBA/GPTMS hybrids was caused by the immersion of the adhesives into the surface layer of the silicone rubber substrate, which was attributed to the good affinity between GPTMS and the silicone rubber.

Metal-semiconductor transitions induced by adsorption of alkali metals on the Si(001) surface

The changes in the electronic structure of the surface layer of a semiconductor substrate have been studied with allowance made for the indirect and dipole-dipole interactions between adatoms. The conditions for the formation and suppression of gaps in the energy band of surface states of the substrate are determined as a function of the adatom coverage of the surface. The results obtained are used in the interpretation of the metal-semiconductor transitions upon adsorption of cesium and sodium atoms on the Si(001) surface.

Magneto-optical observation of surface currents in microelectronic circuits

A magneto-optical method is applied to observe surface electrical currents in microelectronic devices. We describe here the opportunity of direct experimental localization of latchup effect in complementary metal-oxide-semiconductor integrated circuits (ICs) by visualization of latchup current path in surface layer of ICs substrate. To observe currents greater than 10 mA the garnet films with both uniaxial and in-plane anisotropy are utilized. Optimal polarization geometry providing maximal visual contrast is calculated. Topologies of both solitary and two neighboring electrical currents are experimentally investigated. The sensitivity limit (minimal current surface density) of this method of magneto-optic visualization is estimated to be 0.1 mA/μm.

Residual stress characterization of diamond-like carbon coatings by an X-ray diffraction method

Abstract This paper presents residual stress measurements of amorphous diamond-like carbon (DLC) coatings obtained by studying the stress conditions of the substrate surface layer immediately adjacent to the coating via X-ray diffraction (XRD) with a thin film attachment. In such a set-up, the incidence angle α at which the primary beam strikes the specimen is fixed at a glancing angle (2° in our experiments) relative to the sample surface while the detector rotates to collect the diffracted X-rays. The amorphous carbon coatings were deposited on single-crystal silicon wafers and on polycrystalline KBr substrates in an unbalanced magnetron sputtering system. The effects of substrate material and deposition parameters on the internal stresses of the coatings are discussed in detail. XRD with thin film attachment provides a new and more precise way to determine the residual stresses in amorphous coatings. Increasing the relative nitrogen flow reduces the compressive stress level of the hydrogenated amorphous carbon coatings. Under the experimental conditions studied, higher substrate bias power and sputter power densities both increased the compressive stress level.

Characterization of the Post Dry‐Etch Cleaning of Silicon for Ti‐Self‐Aligned Silicide Technology

The Si surface after reactive ion etching (RIE) and different cleaning procedures was characterized by angle resolved X‐ray photoelectron spectroscopy, high‐resolution transmission microscopy, and atomic force microscopy. It was shown that polymers, silicon carbides (Si‒C bonds), and chemisorbed fluorine (Si‒F), cover the silicon surface after RIE in a mixture. The last two residues penetrate the surface layer of a silicon substrate. polymers are removed by oxygen plasma but Si‒C and Si‒F bonds related residues cannot be removed by “oxygen plasma/diluted HF” treatment. These compounds can be removed only by additional etching of the silicon surface layer. According to our experimental conditions a silicon consumption of 2.8 nm was enough to eliminate these compounds. By comparing different cleaning recipes and conditions it was found that ‐plasma/HF/APM (ammonia‐hydrogen peroxide mixture) provides the best cleaning characteristics. APM removes fluorine and carbon contamination by precise, controlled etching of silicon with high etch selectivity toward an spacer. The silicon surface after the cleaning is quite smooth. It was demonstrated that the post spacer‐etch cleaning of ‐plasma/HF/APM is a robust process for Ti‐salicide technology with respect to the reduction of the leakage current between poly‐Si and source/drain. © 1999 The Electrochemical Society. All rights reserved.

Can core/shell nanocrystals be formed by sequential ion implantation? Predictions from kinetic lattice Monte Carlo simulations

High-dose ion implantation has proven to be a powerful technique to form a large variety of nanocrystals in the near surface layer of substrates. However, core/shell nanocrystals, which possess some unique physical properties, have been synthesized up to now only by colloid chemistry. A kinetic 3D lattice Monte Carlo (KLMC) model is used for the study of the diffusion, precipitation and interaction kinetics of the sequentially implanted atom types X and Y in a chemically neutral matrix. Applying a simplified model of collisional mixing, the coating behavior of previously nucleated precipitates of atom type X by atoms of type Y has been simulated.

The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates

The sputter-induced epitaxy change of in-plane orientation occurring in YBa2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a BaxMg1-xO buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45° oriented growth to the 0° oriented growth.

Diamond deposition on titanium and iron substrates pretreated in N 2–C 2H 2 plasma

Diamond deposition on pure titanium and iron substrates pretreated in N 2–C 2H 2 plasma without any mechanical surface pretreatment was studied. High quality diamond film was deposited on such pretreated substrates by CVD using combustion flame. After the pretreatment, a C–C bond was detected on the modified substrate, and graphitic carbon formation on the substrate was suppressed during diamond deposition. The surface of the modified substrate also became slightly rough, so the anchor effect between the film and the substrate was expected. This suppression and the anchor effect would indicate a remarkable improvement of adhesion of the film to the substrate. In particular, the diamond deposition process on the plasma-pretreated iron substrate was compared in detail with that on the substrate scratched with diamond powder. It was found that diamond was directly grown from the carbonitrided surface layer of the plasma pretreated substrate.

Treatment of various surface treated layers by plasma immersion ion implantation

In this paper we present our preliminary results of the plasma immersion ion implantation (PI 3) treatment of boronised and laser surface treated layers. The substrate treatment was followed by the PI 3 treatment. The structural changes in the surface layers of pretreated substrates due to PI 3 treatments at various temperatures will also be discussed. In addition, the property changes characterised by microhardness and wear tests are presented.

The mycorrhizal status of plants colonizing a calamine spoil mound in southern Poland

The arbuscular mycorrhizal (AM) status of two plant communities on a calamine spoil mound (rich in cadmium, lead and zinc) in southern Poland was surveyed: an undisturbed grassland community and an early succession community that developed after complete removal of the surface layer of the calamine substrate about 10 years earlier. The undisturbed site harbored 40 herbaceous species making up 87% of the absolute cover. AM colonization was recorded in 25 species accounting for 77% of the relative cover. Species with 51–75% AM root colonization such as Festuca ovina and Leontodon hispidus dominated the undisturbed turf, contributing 45% to the relative cover. Carex ssp. were the most abundant nonmycorrhizal plants and accounted for 9% of the relative cover. Spores of Glomus aggregatum, G. constrictum, G. fasciculatum, G. pansihalos, Glomus sp. and Entrophospora sp. averaged 25 per 100 g dry substrate at the undisturbed site. The disturbed site was colonized by 25 species accounting for 17% of the absolute cover. Among the AM plants, most abundant were the species with up to 20% AM root colonization, such as Agrostis stolonifera and Thymus pulegioides, wich accounted for 24% of the relative cover. Nonmycorrhizal species, such as Biscutella laevigata,Cardaminopsis arenosa, Gypsophila fastigiata and Silene vulgaris, dominated the early succession community and contributed 64% to the relative cover. Spores of G. fasciculatum and Entrophospora sp. averaged 20 per 100 g dry substrate at the disturbed site.

Impurity dependence of oxide defects in Czochralski silicon

Octahedral cavities have recently been found in the Czochralski silicon (CZ-Si) substrate surface layer just under oxide defects. We investigate the effect that adding HCl to oxygen during oxidation has on the oxide defect density. The effect of intentionally introducing impurities onto a Si surface on the oxide defect density is also examined. Our experimental results suggest that impurities are closely related to the generation of oxide defects. A model is presented in which impurities are incorporated into the growing octahedral cavities during Si crystal growth, and then introduced into the growing oxides during thermal oxidation. These impurities in the oxides then act as a conductive path (oxide defects) in the insulator on the CZ-Si.

X-Ray Truncation Rod Analysis Of Cu Thin Films on C-Plane Sapphire

AbstractThe interfacial structure of room-temperature MBE-grown Cu thin film on c-plane sapphire has been studied by measuring the substrate crystal truncation rod (CTR) using synchrotron radiation. One substrate was annealed in air at 1500°C for 3 hours followed by an anneal in UHV at 1200°C for 30 minutes prior to Cu deposition. CTR from a clean sapphire substrate without Cu coverage was measured as a reference. The annealed substrate showed higher diffracted intensity along the CTR due to changes in surface structure. The terminating sequence of the substrate surface layers have been obtained from intensity profile analysis.

Investigation of the adhesive strength of PMMA structures on substrates obtained by deep X-ray lithography

The adhesive strength of PMMA structures obtained by deep X-ray lithography with synchrotron radiation is a decisive factor for effective structure replication in subsequent electroforming processes. The adhesion depends on various factors, in particular on the interaction of radiation and secondary electrons at the boundary resist/substrate. We have determined the adhesion strength of PMMA microcolumns as a function of the dose deposited below the mask absorber by breaking tension measurements applying a new experimental method. Care has been taken to separate degradation effects in the resist due to the primary photon beam from the loss of adhesion at the boundary substrate/resist caused by secondary electrons. This has been studied quantitatively by utilizing different substrate materials like glassy carbon, wet oxidized titanium, copper and gold.Monte Carlo simulations have been carried out to simulate the deposited dose at the surface layer of different substrates. The corresponding results are supplemented by deep lithography experiments, which may be used as a means to directly conclude the deposited resist dose from secondary electrons emitted from the substrate surface.All the irradiation experiments have been performed with specially designed masks for deep X-ray lithography at the storage ring DCI (Orsay/France).

The composition of octahedron structures that act as an origin of defects in thermal SiO2 on Czochralski silicon

Recently, octahedron structures have been found in the Czochralski-silicon substrate surface layer just under the oxide defects. An attempt is made to characterize these structures by analysis with transmission electron microscopy and energy-dispersive x-ray spectroscopy. Several results indicate that the structure is full of vacancies. This is contrary to previously reported results suggesting that the octahedron structures found in Si bulk are filled with amorphous SiO2. A model for the formation of an octahedron structure with many vacancies is proposed.

Microscopic structure of the discommensurate phases in Ge(111)/Ga. II. Domain superstructure and discommensurations.

We present atomically resolved scanning tunneling microscope (STM) images of two of the discommensurate phases---\ensuremath{\gamma} and \ensuremath{\beta}---occurring in the system Ge(111)/Ga. In both phases Ga atoms substitute the Ge atoms of the substrate surface layer, resulting in a local (1\ifmmode\times\else\texttimes\fi{}1) structure within domains. In the \ensuremath{\beta} phase, which occurs at slightly higher Ga coverages than the \ensuremath{\gamma} phase, a stacking fault is visible in half of the domains. The domains are separated by elementary discommensurations, so-called domain walls. In the present study we focus on the microscopic structure of these walls---a problem that is hard to access with methods other than STM. From the STM data we deduce a microscopic model of the walls of the \ensuremath{\beta} phase, where virtually all dangling bonds are saturated---in contrast to the situation in the \ensuremath{\gamma} phase. This energetically favorable situation is enabled by the presence of the stacking fault. We propose that the gain in energy due to the removal of all dangling bonds in the walls of the \ensuremath{\beta} phase exceeds the loss in energy associated with the stacking fault, driving the transition from the \ensuremath{\gamma} to the \ensuremath{\beta} phase.

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

First principles calculations of clean and adsorbate-covered surfaces of Si(001) and Ge(001) are reported. Chemical trends in the adsorption of ordered Na, K, Ge, As, Sb, S, Se and Cl overlayers are discussed. The calculations are based on the local-density approximation and employ non-local, norm-conserving pseudopotentials together with Gaussian orbital basis sets. The semi-infinite geometry of the substrate is properly taken into account by employing our scattering theoretical method. From total-energy minimization calculations we obtain optimal surface reconstructions which show asymmetric dimers for Si(001), Ge(001) and Ge:Si(001). For As:Si(001), Sb:Si(001) and Sb:Ge(001), we find symmetric adatom dimers in the equilibrium geometries. S or Se adlayers are found to be adsorbed in bridge positions forming a (1×1) unit cell with a geometry very close to the configuration of a terminated bulk lattice. Cl atoms adsorb on top of the dangling bonds of symmetric Si dimers residing in the first substrate-surface layer. Our calculations for Na:Si(001) and K:Si(001) confirm valley-bridge site adsorption for half monolayer coverage. For full monolayer alkali-metal coverage, adsorption in pedestal and valley-bridge positions is found to be energetically most favourable. The calculated optimal adsorption configurations are in excellent agreement with a whole body of recent experimental data on surface-structure determination. For these structural models, we obtain electronic surface band structures which agree very good with a wealth of data from angle-resolved photoemission spectroscopy investigations.

Peculiarities and application perspectives of metal-ion implants in glasses

Ion implantation in insulators causes modifications in the refractive index as a result of radiation damage, phase separation, or compound formation. As a consequence, light waveguides may be formed with interesting applications in the field of optoelectronics. recently implantation of metals ions (e.g. silver, copper, gold, lead, etc.) showed the possibility of small radii colloidal particles formation in a thin surface layer of the glass substrate. These particles exhibit an electron plasmon resonance which depends on the optical constants of the implanted metal and on the refractive index of the glass host. The non-linear optical properties of such colloids, in particular the enhancement of optical Kerr susceptibility, suggest that the ion implantation technique may play an important role for the production of all-optical switching devices. In this paper an analysis of the state-of-the-art of the research in this field will be presented in the framework of ion implantation in glass physics and chemistry.

Photoemission study of the growth of the LaF3/Si (111) interface

Photoemission spectroscopy with synchrotron radiation was used to study the LaF3/Si (111) interface as a function of annealing temperature for LaF3 films. These films range in thickness from 0.7–11 monolayers and have been deposited at room temperature. The La/Si photoemission intensity ratio at surface sensitive and bulk sensitive experimental conditions shows that island formation occurs at 420 °C. The stoichiometry of the LaF3 films is conserved until desorption begins at approximately 580 °C, where fluorine desorbs from the surface completely and lanthanum remains on the silicon substrate. From a line shape analysis of the Si 2p and La 4d core levels it is apparent that the interface is dominated by La–Si bonds. Changes in the surface Fermi level are induced by the penetration of lanthanum into the surface layers of the silicon substrate upon annealing.