摘要:

Numerical results are presented on the evolution of thermal stresses in metal interconnects. Finite element analyses are carried out for a series of parallel aluminum lines embedded within silicon dioxide. The effects of line aspect ratio on the longitudinal and hydrostatic stresses in lines are investigated, for various spaces between lines. Comparisons with the results based on an isolated line under passivation are also made. It is shown that, contrary to what was frequently found by employing the single-line approach, maximum stresses in periodically arranged aluminum lines do not occur when the line width and the line height are approximately equal. The variation of stresses with line aspect ratio is affected by the spacing between lines. Implications of the present findings to the modeling of stresses and to the damage evolution through void formation are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365944

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Strain characterization of materials through Raman spectroscopy often requires the optical phonon wave vector to be in directions other than those of the strain-modified phonon eigenvectors. As a result, the observed mode frequencies are mixtures of the strain-modified eigenfrequencies. The selection rules for such generalized scattering configurations are derived here for the strained zincblende-diamond family crystals. The formulation is based on the relative magnitude of the LO-TO and the strain-induced splittings. The results are important for the analysis of strain-modified Raman lineshapes and of “forbidden” lines. Specific examples are worked out in detail for externally stressed bulk crystals (90° scattering geometry), and for [001], [111], and [110] strained heterojunctions (backscattering under oblique incidence and/or detection). ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365958

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article employs a one-dimensional diffusion model to study the phenomenon of electromigration-induced edge drift in a finite, Al–Cu thin-film conductor. Edge drift is caused by the accumulation of vacancies at the negative (upstream) terminal of the conductor as Al diffuses with the electrical current. When the Cu content exceeds its solubility limit, grain boundaries are decorated withAl2Cuprecipitates, which must be dissolved before significant Al diffusion occurs. Assuming one-dimensional flow in a homogeneous, polygranular film, we compute the rate of growth of the precipitate-free zone at the upstream terminal, and estimate the incubation time for the onset of edge drift. The results predict an incubation time that increases with the grain size and the initial Cu content, and decreases with the square of the current density. The incubation time is inversely proportional to the “electromigration diffusivity”,DE=DBCu&dgr;ZCu*,the product of the grain boundary diffusivity of Cu, the effective grain boundary thickness, and the effective valence of the Cu ion. The results are used to compare a number of prior experimental studies, which are shown (with one exception) to produce consistent values forDE.An analysis of the experimental results suggests that edge drift begins almost as soon as the precipitate-free zone length exceeds the “Blech length” for the line, suggesting that the presence ofAl2Cuprecipitates in the grain boundaries is essential to retard Al electromigration.

ISSN:0021-8979    

DOI:10.1063/1.365948

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The relaxation process in InAsP/InGaAsP strained-layer superlattices (SLSs) with interfacial misfit dislocations has been investigated systematically by transmission electron microscopy (TEM) and x-ray analyses. The TEM analysis reveals that dislocations locate a little inside the buffer layer near the interface between the buffer and first well layer in the SLS. The x-ray analysis of (400) azimuthal angle dependence indicates the buffer layer has a large macroscopic tilt. Using a curve fitting analysis of various(hkl)x-ray profiles and reciprocal lattice mapping measurements, residual strain was determined quantitatively, i.e.,&Dgr;a∥and&Dgr;a⊥,in the SLS and buffer layer. These results reveal that the dislocations mainly cause lattice distortion of the buffer layer rather than relaxation of the SLS layer. The most remarkable result is that the change ofa∥is not equal to that ofa⊥in the buffer layer. This phenomenon strongly suggests that microplastic domains are generated in the buffer layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365959

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have calculated the energy of three distinct grain configurations, namely, completely connected, partially connected, and unconnected configurations, evolving during a spheroidization of polycrystalline thin film by extending a geometrical model due to Miller &etal; to the case of spheroidization at both the surface and film-substrate interface. “Stability” diagram defining a stable region of each grain configuration has been established in terms of the ratio of grain size to film thickness versus equilibrium wetting or dihedral angles at various interface energy conditions. The occurrence of spheroidization at the film-substrate interface significantly enlarges the stable region of unconnected grain configuration thereby greatly facilitating the occurrence of agglomeration. Complete separation of grain boundary is increasingly difficult with a reduction of equilibrium wetting angle. The condition for the occurrence of agglomeration differs depending on the equilibrium wetting or dihedral angles. The agglomeration occurs, at low equilibrium angles, via partially connected configuration containing stable holes centered at grain boundary vertices, whereas it occurs directly via completely connected configuration at large equilibrium angles except for the case having small surface and/or film-substrate interface energy. The initiation condition of agglomeration is defined by the equilibrium boundary condition between the partially connected and unconnected configurations for the former case, whereas it can, for the latter case, largely deviate from the equilibrium boundary condition between the completely connected and unconnected configurations because of the presence of a finite energy barrier to overcome to reach the unconnected grain configuration. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365960

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Significant ion irradiation is needed during growth to synthesize cubic boron nitride(cBN)films. This results in large film stresses, which have limitedcBNfilm thicknesses to only a few hundred nm and represents a significant barrier in the development ofcBNfilm technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 &mgr;m) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a highcBNcontent were synthesized. ThickercBNfilms enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60–70 GPa, which are greater than values measured for bulkcBN.The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN films are discussed with reference to other ultrahard thin films such as diamond and diamondlike carbon. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365961

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In recent years, many investigators have reported visible photoluminescence from structures that consist of Ge or Si nanocrystals embedded in aSiO2matrix deposited or grown on various substrates. We have developed a rapid technique for studying the through-thickness microstructure of this class of materials via atomic force microscopy (AFM) and, using this technique, we report on the precipitation and growth of Ge crystallites formed via a two-step process of hydrothermal oxidation ofSi1−xGexO2(x=0.15) at 450–500 °C and subsequent chemical reduction in forming gas (85/15:N2/H2; 800 °C). The Ge-particle distributions obtained with this AFM cross-sectional technique are consistent with those previously reported using other techniques. The utility of cross-sectional AFM for the evaluation of nanoscale features in the thickness of a thin film is evaluated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365962

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

X-ray photoelectron spectroscopy (XPS) has been used to characterize the thin thermal oxide film grown on single crystal CdSe(0001) and polycrystalline CdSe by exposure to O2(dry air) at 350 °C. SeOxspecies, wherex=2,3, are clearly identified by a 5 eV shift of the Se 3d3/2,5/2peaks to higher binding energy. A very weak shift to lower binding energy is observed for the Cd peaks. The positions of the Cd and O peaks do not match those found for the known cadmium oxides, CdO and CdO2. Instead, it is proposed that the Cd bound oxygen atoms occupy substitutional Se sites. The presence of Cd bound oxygen can also be inferred from the intensities of theSeOx,Cd, and O peaks. Raman spectroscopy confirms the existence of O in Se substitutional sites. Angle-resolved XPS is used to determine the thickness of the oxide and the relative amount of SeOxand Cd bound oxygen. The XPS data are consistent with an 8–9 Å thick oxide where∼60&percent; of the oxygen is bound to Se and∼40 is bound to Cd. The data show that the oxide structure contains two layers; a passivation layer made of the SeOxspecies and, underneath, a layer containing oxygen in Se substitutional sites. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366263

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A formulation is proposed to estimate the charge transfer&Dgr;qCufrom Cu to some anions in metal-oxide crystals, using Auger electron spectroscopy. In the formulation, a parameter, the Auger transition probability&ohgr;, is introduced, which is defined as the ratio of Auger intensity due to a certain transition to the total Auger intensity due to other transitions when the same core electrons are primarily excited. By applying the formulation to vacuum-cleaved surfaces of YBa2Cu3O7−&dgr;(YBCO) and Ba2Cu3O4Cl2(BCOC) crystals, we obtained the following results: (1) YBCO cleaves between CuO2and BaO layers, and the amount of&Dgr;qCuis 2.3 in units of elementary electric charge. The deviation of&Dgr;qCufrom 2.0 suggests the existence of Cu3+-like atoms; (2) for BCOC,&Dgr;qCuvaries from 3.3 to 1.7 depending on the Ar ion beam sputtering time. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366262

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present velocity-field simulations ofn-doped, wurtzite-phase GaN for temperatures between 77 and 1000 K using an ensemble Monte Carlo technique. A three-valley model of the band structure is assumed, and the ionized impurity, polar optical phonon, acoustic phonon, piezoelectric, and intervally scattering mechanisms are considered. Electron degeneracy and heating are also accounted for. Properties of the two dimensional electron gas in AlGaN/GaN heterostructures are also estimated by performing simulations on bulk GaN in which the electron concentration exceeds the ionized donor concentration by factors of ten to one hundred. The simulations predict that peak steady-state drift velocities ranging from3.3×107to2.1×107 cm/sfor temperatures between 77 and 1000 K can be achieved in both the two dimensional electron gas and in the bulk material with an ionized donor concentration of1016 cm−3.Furthermore, the simulations predict that the two-dimensional electron gas in GaN will exhibit a low-field mobility an order of magnitude greater than the bulk material, in agreement with experimental results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365963

出版商:AIP    

年代:1997

数据来源: AIP