摘要:

A novel resistometric technique enables the investigation of single void nucleation and growth induced by electromigration (EM) for aluminum (Al) lines having a perfect bamboo structure in comparison with single‐crystal Al lines. Fine tungsten (W) voltage probes were fabricated at every 4 &mgr;m along the Al line with grain sizes of 10 &mgr;m or more. Local electrical resistance changes have confirmed that a void nucleated only at the grain boundary and no damage appeared within the grains. The measured values of the local electrical resistance changes were converted to EM‐induced void growth rates. The vacancy flux was deduced from the void growth rate under the assumption that a vacancy volume is equal to the atomic volume. It has been clarified that the vacancy fluxes for a bamboo‐structured Al line were about one order magnitude smaller than the ideal vacancy fluxes in the Al lattice derived from the Nernst–Einstein relation. The vacancy fluxes for single‐crystal Al lines were also quantified under an accelerated test at a high electric current density with a temperature gradient. These results suggest that the bamboo grain boundaries have a blocking effect on vacancy flow. This blocking produces vacancy supersaturation near the grain boundary, and the reduction in vacancy flux is well explained by the back‐diffusion due to the corresponding concentration gradient.

ISSN:0021-8979    

DOI:10.1063/1.354413

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The structure of GaN films grown by electron‐cyclotron‐resonance‐assisted molecular beam epitaxy on Si(111), Si(001), basal‐plane sapphire,a‐plane sapphire, andr‐plane sapphire substrates was studied with four‐circle x‐ray diffractometry. Phase content, domain size, inhomogeneous strain, and in‐plane and out‐of‐plane domain misorientations were measured and compared for films grown on each type of substrate. Wurtzite and zinc blende polymorphs were found to coexist in films grown on Si(111). The two structures grow in the (0002) and (111) orientations, respectively, so that they may transform into each other via stacking faults on close‐packed planes. Smaller amounts of zinc blende material were also found in predominately (0002) wurtzitic films ona‐plane sapphire and (112¯0) wurtzitic films onr‐plane sapphire.

ISSN:0021-8979    

DOI:10.1063/1.354414

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Mechanism of SiC heteroepitaxial growth by the carbonization of the Si(001) surface was studied at the atomic scale using molecular dynamics (MD) simulations and molecular beam epitaxy (MBE) experiments. Heteroepitaxial growth of single crystal 3c‐SiC on the Si(001) surface (3c‐SiC[001]∥Si[001] and 3c‐SiC[110]∥Si[110]) was observed in both the MD simulations and MBE experiments. Breaking of the Si—Si bonds and shrinkage of the [110] Si rows with C atoms are possible mechanisms for the heteroepitaxial growth of SiC on Si(001). Microscopic structures and mechanisms of the twin formations and pit formations are discussed. Ultraviolet light irradiation is proposed and confirmed to enhance the epitaxial growth of SiC in the MBE experiments.

ISSN:0021-8979    

DOI:10.1063/1.354385

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Reciprocating sliding friction experiments in humid air and in dry nitrogen and unidirectional sliding friction experiments in ultrahigh vacuum were conducted with a natural diamond pin in contact with microwave‐plasma‐deposited diamond films. Diamond films with a surface roughness (Rrms) ranging from 15 to 160 nm were produced by microwave‐plasma‐assisted chemical vapor deposition. In humid air and in dry nitrogen, abrasion occurred when the diamond pin made grooves in the surfaces of diamond films, and thus, the initial coefficients of friction increased with increasing initial surface roughness. The equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. In vacuum the friction for diamond films contacting a diamond pin arose primarily from adhesion between the sliding surfaces. In these cases, the initial and equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. The equilibrium coefficients of friction were 0.02–0.04 in humid air and in dry nitrogen, but 1.5–1.8 in vacuum. The wear factor of the diamond films depended on the initial surface roughness, regardless of environment; it increased with increasing initial surface roughness. The wear factors were considerably higher in vacuum than in humid air and in dry nitrogen.

ISSN:0021-8979    

DOI:10.1063/1.354386

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Phase transitions that involve solid‐state reactions between cobalt and thin films of germanium have been investigated. Germanides are formed by reacting Co (300 A˚ thick) with thin layers of Ge (∼2000 A˚ thick) deposited on silicon substrates. Germanium was deposited on Si by rapid thermal chemical‐vapor deposition and cobalt was deposited onto Ge by evaporation. The Co/Ge/Si stacked structure samples were then rapid thermally annealed at atmospheric pressure in an inert ambient consisting of Ar. Using x‐ray‐diffraction spectroscopy, Co5Ge7and CoGe2are identified as the phases which form at 300 and 425 °C respectively. The sheet resistance was found to be a strong function of the annealing temperature and a minimum resistivity of approximately 35 &mgr;&OHgr; cm is obtained after annealing at 425 °C. The minimum resistivity material corresponds to the CoGe2phase with an orthorhombic crystal structure. Above 600 °C, the resistivity increases due to an instability of the solid‐phase reaction between Co and thin Ge layers deposited on Si. This instability is attributed to rapid Co diffusion at the temperatures which are required to form CoGe2along with structural defects in the Ge layer.

ISSN:0021-8979    

DOI:10.1063/1.354387

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In order to understand the physical principles which underlie the formation of metal/semiconductor interfaces, epitaxial Al films are grown by molecular beam epitaxy on As‐stabilized and Al‐stabilized AlAs(001) surfaces some of which were coated with a single monolayer (1 ML) of Ga or In. Reflection high‐energy electron diffraction and x‐ray diffraction measurements reveal that the growth direction and epitaxial relationship of the Al films are drastically changed by the surface modification by 1 ML Ga or In. A variety of Al film configurations are obtained, of which the Al(001)/Ga(or In)/AlAs(001) heterostructure is technologically important because it has an ideally lattice matched metal/semiconductor heterostructure. We propose structural models for three Al phases, i.e., Al(001) and two kinds of Al(110), and discuss the physical origin of the variation of Al phases. It is shown that the changes observed in the epitaxial relationships of Al films can be systematically explained in terms of bond strengths at the interface. In the growth of metals on semiconductors, interface modification is shown to be effective for controlling the growth.

ISSN:0021-8979    

DOI:10.1063/1.354362

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Intrinsic stresses in sputter‐deposited thin films are studied via a two‐dimensional molecular‐dynamics model. Two‐body potential functions, periodic boundary conditions, and a generalized Langevin equation are applied to determine the microstructure of the film. The intrinsic stresses are then calculated using a stress method. 12 layers of substrate atoms are arranged in the (111) plane at the beginning of the film growth simulation. The molecular‐dynamics simulations using the constant pressure and constant temperature ensemble are first carried out to obtain the zero stress state of the substrate. A thin film of Ni atoms is deposited in the presence of a background of argon and energetic ions in order to obtain a reasonable representation of the film structure. After the deposition process is completed, the film and the substrate are allowed to contract or expand in accordance with the elastic energies. It is found that the microstructure and intrinsic stresses of the film depend upon the incident energy of incoming particles, the ion bombardment, and the amount of trapped gas impurity. The model strongly suggests that the argon impurities trapped into the deposited film are the primary cause of the state of compressive stress. It also shows that in sputter‐deposited films the magnitude of the compressive stress depends more strongly on the film structure than on the quantity of the argon gas trapped in the film. A tight packing of film atoms around argon atoms is likely to lead to higher compressive stresses in the film.

ISSN:0021-8979    

DOI:10.1063/1.354363

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A negative effect on the quality of diamond film because of the addition of hydrogen to carbon‐dioxide–hydrocarbon gases was investigated. To elucidate the role of hydrogen and oxygen in diamond synthesis using microwave plasma chemical‐vapor deposition, diamond films were deposited by adding hydrogen and oxygen to carbon‐dioxide–methane‐gas mixtures. Improvements in the quality of diamond film and extensions of the diamond‐forming region were obtained, due to the addition of oxygen to the carbon‐dioxide–methane‐gas mixtures. The nucleation density of deposits increased when the amount of hydrogen was increased but decreased when the amount of oxygen was increased. The results of optical emission spectroscopy indicate that the amount of atomic hydrogen in the ground state remained nearly the same, respectively, with increasing amounts of hydrogen and oxygen. However, the amount of electronically excited atomic hydrogen and C2emissions increased with an increase in the amount of added hydrogen; this means that the electronically excited atomic hydrogen did not benefit diamond growth and the C2radicals facilitated the formation of amorphous or graphitic carbon. In contrast to the addition of hydrogen, when oxygen was added, the electronically excited atomic hydrogen and C2radicals decreased, and a larger amount of oxygen‐containing species such as atomic oxygen and OH radicals was in the plasma, so the quality of the diamond film improved. In summary, adding hydrogen to the carbon‐dioxide–methane‐gas mixtures had a negative effect on diamond growth, whereas adding oxygen had a beneficial effect.

ISSN:0021-8979    

DOI:10.1063/1.354364

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Micro‐Raman spectroscopy is used to study mechanical stress in local isolation structures on silicon substrates (poly‐buffered local oxidation of silicon, called PBLOCOS or LOPOS). The influence of processing parameters such as nitride film thickness and width, pad oxide thickness, and field oxide thickness is studied. Also the change of the local stress during the successive processing steps of the isolation is investigated: deposition of the nitride mask, field oxidation, and removal of the nitride mask. The results are explained using a simple analytical model. It is found that stress varies very much during the different processing stages. After deposition of the nitride film, the stress is compressive under the mask lines and tensile outside the lines, close to the line border. The stress magnitude is highly dependent on the thickness of the nitride film. It can be described by edge forces. During field oxidation, this edge‐force‐induced stress nearly completely relaxes. In LOPOS structures with field oxide, the magnitude and distribution of the mechanical stress is mainly determined by the compressive forces exerted by the field oxide and the bird’s beak on the silicon, and tensile forces which are related to the bending of the nitride film at the edges. The influence of nitride film thickness on the stress at the center of the lines, &ohgr;c, is much smaller after field oxidation. For wide lines &ohgr;cis compressive and much higher than before field oxidation. For small widths &ohgr;cbecomes tensile due to the influence of the vertical forces acting at the bird’s beak edge. The tensile stress due to the bending of the nitride film edge is much larger than the field‐oxide‐induced compressive stress, and dominates the stress picture at the bird’s beak. Only when very thick field oxides and thin nitride films are used, the field‐oxide‐induced compressive stress becomes visible. This becomes more clear when, in a further process stage, the nitride film is removed. The stress picture is then completely determined by the field oxide and the stress in the active area is always compressive.

ISSN:0021-8979    

DOI:10.1063/1.354365

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Polycrystalline Fe‐Mo‐Si‐B alloys with grain sizes of 15–200 nm were synthesized via crystallization of the amorphous alloy. Positron lifetime results show that there are two existing types of interfacial defects in nanocrystalline Fe‐Mo‐Si‐B alloys, namely free‐volume‐sized defects and nanovoids. The free‐volume‐sized defect shows almost no change in size or density during grain growth, and has a mean lifetime smaller than that of its amorphous counterpart as a result of structural relaxation in the process of crystallization. However, abnormal changes in size and density of nanovoids with grain growth were noticed. It is of great interest that the variations of intermediate lifetime &tgr;2and intensity ratioI1/I2with the average grain sizeD¯ are exactly compatible with those of microhardness. A lower density of nanovoids corresponds to a larger microhardness in the case of the present alloy system.

ISSN:0021-8979    

DOI:10.1063/1.354366

出版商:AIP    

年代:1993

数据来源: AIP