摘要:

Plate impact and split Hopkinson pressure bar (SHPB) experiments have been conducted on three grades of silicon carbide produced by different routes. Data are presented which indicate that the failure of the materials was delayed for some time after the maximum stress had been achieved. In particular, the measured lateral component of the stress in plate impact was found to increase across a front which traveled behind the shock. This phenomenon is akin to the failure wave which has been observed to occur in glasses but has not previously been reported in polycrystalline materials. Hopkinson bar experiments have revealed significant differences in the behaviors between the three materials. These may be related to the effects observed in the plate impact experiments. These results explain the anomalous ballistic phenomena that have been reported for the penetration behavior of SiC. Additionally the Hugoniot elastic limit (HEL) and shear strength were found to vary with the production route used. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364450

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Amorphous metallic alloys, frequently observed to occur in systems with large negative heats of mixing, are much less common in systems which are immiscible in the equilibrium solid state, such as Nb–Cu. However, amorphous Nb–Cu alloys can be produced over a wide composition range by sputtering. Using isothermal and nonisothermal differential scanning calorimetry, both the kinetics and the thermodynamics of these amorphous Nb–Cu alloys were characterized quantitatively. It was found that the formation enthalpies of the amorphous alloys amounted to only 4.5–7.6 kJ/g atom. These data were combined with a modeling of the thermodynamic functions of the system. The unexpected low enthalpies and Gibbs energies of the amorphous phase demonstrate the thermodynamic stabilization of the liquid phase which develops with undercooling. This is connected with a change of sign in the heat of mixing of the liquid phase, which is positive at high temperatures and negative at low temperatures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364451

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy (MBE). Damage from nonamorphizing Si implants at doses ranging from 5×1012to 1×1014/cm2evolves into a distribution of {311} interstitial agglomerates during the initial annealing stages at 670–815 °C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of {311} defects during Ostwald ripening with an activation energy of 3.8±0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ∼3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ∼1019/cm3prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364452

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Si wafers were preamorphized by eitherSi+orGe+ions at temperatures between 5 and 40 °C. The diffusion of low energy (4 keV)B+implants into the preamorphized Si was studied in order to monitor the flux of interstitials from the end of range (EOR) region toward the surface. Transient enhanced diffusion (TED) in the regrown silicon was observed for all implants. Increasing the implantation temperature of theSi+implant by as little as 15 °C can result in a marked decrease in the magnitude of the interstitial flux flowing from the EOR region toward the surface. This sensitivity to implant temperature appears to be even greater forGe+implants. In order to better understand this effect, detailed transmission electron microscopy (TEM) studies were conducted. As-implanted cross-sectional TEM micrographs indicate a measurable decrease in the thickness of the amorphous layer (up to 300 Å) occurs when the implantation temperature increases from 5 to 40 °C as a result of ion beam induced epitaxial recrystallization. Upon 800 °C annealing, two types of defects are observed in the EOR region: {311} defects and dislocation loops. The {311} defects are unstable and the comparison of secondary ion mass spectroscopy and TEM data for annealed samples indicating the dissolution of these {311} defects is at least one of the sources of interstitials for TED in the regrown Si at 800 °C. The EOR dislocation loops are stable for the annealing conditions used in this study (800 °C for 15 min) and there appears to be an exponential dependence of the TED that occurs in regrown Si on the density of the EOR dislocation loops. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364391

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Interdiffusion coefficients on the group V sublattice of GaAs were determined in GaAsP/GaAs and GaAsSb/GaAs superlattices. Strained GaAs0.86P0.14/GaAs, GaAs0.8P0.2/GaAs0.975P0.025and GaAs0.98Sb0.02/GaAs superlattices were annealed between 850 °C and 1100 °C under different arsenic vapor pressures. The diffusion coefficient was measured by secondary ion mass spectroscopy and cathodoluminescence spectroscopy. The interdiffusion coefficient was higher under arsenic-rich conditions than under gallium-rich conditions, pointing to an interstitial-substitutional type of diffusion mechanism. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364453

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Passivated and unpassivated Al single-crystal lines with (110), (133), and (111) planes parallel to the substrate have been fabricated and electromigration tests have been performed to study transgranular failure mechanisms. Both erosion voids and slitlike voids with {111} facets were observed in single-crystal lines. The slitlike voids lie along the in-plane direction, which leads to minimum-surface-area voids among the crystallographically possible directions for the {111}-faceted voids. Voids that nucleate in the lines appear to be mobile and can move toward the cathode end and sometimes accumulate in the cathode pad. (110)-textured lines fail due to erosion voids, slitlike voids, and pad voids, with roughly equal probability. However, (111)- and (133)-textured lines failed predominantly due to pad voids. In both passivated and unpassivated single-crystal lines, the median time to failure,t50,is texture dependent, witht50(111)>t50(133)>t50(110),and witht50(111)⩾10×t50(110).The activation energy for failure for (110) single-crystal lines is about 1 eV, suggesting that Al/oxide interface diffusion may be the dominant mechanism in these lines, and by inference, in bamboo grains in lines with near-bamboo or fully bamboo microstructures. The current density exponent for failure times of single-crystal lines is about 2.5, which is close to that of polycrystalline lines. Based on the results of this study, coupled with results from an earlier model for calculation of lifetimes due to polygranular failure mechanisms, an improved scaling methodology for projection of lifetimes from test conditions to service conditions for near-bamboo interconnects is proposed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364454

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electromigration-induced failure of on-chip interconnects continues to be a problem for the microelectronics industry. The electromigration failure rate of a population of similar lines is sensitive to statistical variation in the microstructural characteristics from line to line. These microstructural details depend upon the process and thermal history of the line as well as on the feature size (line length and width). Moreover, as the widths of interconnect lines have fallen below the median grain size of the films from which they are patterned, two distinct types of failure mechanisms have been observed. Determining which failure mechanism(s) will be observed, and in what proportion, is a crucial concern of reliability engineers. This article investigates the complex dependence of the dominant failure mechanism and overall reliability on process history, minimum feature size, line type, line microstructure, and line test conditions. A grain growth simulator has been used to model the microstructural evolution of a film during processing, both prior to and after patterning. In this fashion, large populations of lines with realistic microstructures have been generated in order to observe statistical differences in microstructure and failure rate. An electromigration model is then used to calculate stress evolution. By assuming a critical stress at which the line fails, the failure distributions and overall reliability of the interconnects are obtained, and the conditions under which a transition-in-failure mechanism will occur are predicted. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364446

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A combined analytical and computational model is developed to study the mechanics of strained epitaxial island growth in typical semiconductor systems. Under certain growth conditions in systems with a film/substrate lattice mismatch, deposited material is known to aggregate into islandlike shapes with geometries having arc shaped cross-sections. A two-dimensional model assuming linear elastic behavior is used to analyze an isolated arc shaped island with elastic properties similar to those of the substrate. The substrate is assumed to be much larger than the island. Finite element analysis shows that in order to minimize the total energy, which consists of strain energy, surface energy, and film/substrate interface energy, a coherent island will adopt a particular height-to-width aspect ratio that is a function of only the island volume. It is then shown that for an island with volume greater than a certain critical size, the inclusion of a mismatch strain relieving edge dislocation is favorable. The criterion for the critical size is based on a comparison of the configurational forces acting on the edge of the island in the presence of an edge dislocation. Finally, a finite element calculation combined with an analytical treatment of the singular dislocation fields is used to determine the minimum energy island aspect ratio for the dislocated island/substrate system. The combination of the minimum energy morphology studies for the coherent and dislocated systems with the dislocation nucleation criterion gives a complete model for strained epitaxial island growth which can serve as a basis for interpretation of experiments. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364357

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Holes formed in a solid film during annealing can grow and lead to the formation of many isolated islands. The morphological evolution of holes is thus of primary importance in the production of planar films. This work studies the linear instability of a stationary axisymmetric hole in a film with zero surface mean curvature. At the hole, the film forms a contact angle &agr; with the substrate at a circular contact line of radiusa0.The film is bounded by an outer wall at a distancea0Lfrom the center. An infinitesimal disturbance in the form of a normal mode is applied and its stability analyzed for0⩽&agr;⩽180°and1⩽L<∞.Capillarity-driven surface diffusion is taken to dominate the mass transport. AsL→1,the film is a ring that is unstable to periodic disturbances along the ring. For an unbounded film withL→∞,only axisymmetric disturbances can grow, and the growth rates become independent ofLor the boundary conditions at the outer wall. This instability persists even when the film is “flat” in the limit&agr;→0,in contrast to the stability results of a uniform film without a hole. The growth rates agree qualitatively with those observed in experiments. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364358

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The microstructure of (112) oriented CuInSe2 heteroepitaxial layers grown with molecular beam epitaxy on (111) oriented Si wafers was investigated by transmission electron microscopy. Experimental and calculated diffraction patterns of different zone axes were compared. Extra spots are caused by rotational twins on (112) growth planes. Six twin variants rotated by±120°,±60° and 180° about the [221] axis were identified in the layers. The tetragonal chalcopyrite structure of CuInSe2,the crystal symmetry of the substrate and variations of the growth conditions during the growth are responsible for the formation of these rotational twins. Coherent twin boundaries as well as partly coherent boundaries of twin variants rotated by±60° and 180°were imaged by high resolution transmission electron microscopy. The boundaries can be formed by inserting partial dislocations with Burgers vectorsa/6⟨111¯⟩ into the CuInSe2 structure. This suggests that the annealing of the samples induces the annihilation of these partial dislocations and consequently reduces the density of twins in the CuInSe2 layers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364359

出版商:AIP    

年代:1997

数据来源: AIP