摘要:

The silicon integrated‐circuits chip is built by contiguously embedding, butting, and overlaying structural elements of a large variety of materials of different elastic and thermal properties. Stress develops in the thermal cycling of the chip. Furthermore, many structural elements such as CVD (chemical vapor deposition) silicon nitride, silicon dioxide, polycrystalline silicon, etc., by virtue of their formation processes, exhibit intrinsic stresses. Large localized stresses are induced in the silicon substrate near the edges and corners of such structural elements. Oxidation of nonplanar silicon surfaces produces another kind of stress that can be very damaging, especially at low oxidation temperatures. Mismatch of atomic sizes between dopants and the silicon, and heteroepitaxy produce another class of strain that can lead to the formation of misfit dislocations. Here we review the achievements to date in understanding and modeling these diverse stress problems.

ISSN:0021-8979    

DOI:10.1063/1.349282

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

An etch rate equation for the dry etching of silicon in the absence of ion bombardment is derived from a model in which transport of atomic fluorine is rate determining. This equation indicates that the etch rate follows the Arrhenius rule and is proportional to the fluorine‐atom concentration in the gas phase. The theoretical etch rate is shown to be in good agreement with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.349339

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A series of rhodium‐based multilayer structures has been developed for soft x‐ray applications by using ‘‘trilayer’’ structures and low density boron carbide spacing material. The microstructure of the multilayers was investigated by high‐resolution electron microscopy and compared with those of tungsten‐ and nickel‐based multilayers. Rh crystals having fcc structure but with different preferred orientations were identified in Rh‐based layers. It was confirmed that the major limitation on the performance of the multilayer materials was the crystallization of the metal layers. High reflectivity and selectivity for x‐ray mirrors was obtained in the case of W/Rh/C multilayers due to significant improvement in their microstructure, especially the interface roughness.

ISSN:0021-8979    

DOI:10.1063/1.349314

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Convenient and inclusive tables for the demagnetization factors of general ellipsoids are calculated by an APL program using the mathematical framework of Osborn [Phys. Rev.67, 351 (1945)] along with elliptical integral function tables of Spenceley and Spenceley [Smithsonian Elliptic Function Tables,109, 3863 (1947)]. The new demagnetization tables have immediate application to magnetic and superconductor studies of present day prominence. For an ellipsoid of major axesa≥ (R18)b≥ (R18)cthe range of variables is from 1≥ (R18)(c/a)≥ (R18)0.0001, and 1≥ (R18)(b/a)≥ (R18)0.01; appropriate approximations are indicated for smaller values of these ratios. In addition details of the mathematical calculation are included so that those interested may duplicate the procedure. Methods of applying this ‘‘ellipsoidal’’ approximation to other shapes such as parallelopipeds are also indicated.

ISSN:0021-8979    

DOI:10.1063/1.349315

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The spectra of the third‐order nonlinear optical susceptibility, &khgr;(3), of poly(2,5‐thienylenevinylene) thin films were measured with third‐harmonic generation in the fundamental wavelength range of 1475–2100 nm. The effect of increasing the &pgr;‐conjugation length for &khgr;(3)was investigated for both samples with varied extents of conversion and uniaxially stretched sample. The &khgr;(3)values were intensively increased with the progress of conversion. Two &khgr;(3)peaks at the fundamentals of 1600 and 1950 nm were found in the fully converted film. The largest &khgr;(3)value reached 4.5×10−10esu at 1950 nm, and the origin of the peak was ascribed to three‐photon resonance with the lowest &pgr;‐&pgr;* transition band. It was also found that the overall profile of the &khgr;(3)spectrum drastically changed through uniaxial stretching. The reason for the observed change is discussed in terms of the difference in average &pgr;‐conjugation length.

ISSN:0021-8979    

DOI:10.1063/1.349316

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have linearized the equations for propagation of the beam of light in a semiconductor optical amplifier about an operating point and have derived the rate of growth of small sinusoidal perturbations of the phase and modulus of the complex field amplitude. The perturbations grow if the spatial frequency is below a critical value that depends on the intensity of the field at the operating point. For spatial frequencies above the critical value, the perturbations die out. The critical spatial frequency decreases as the intensity increases above a certain value. In other words, the tendency to filament becomes weaker as the intensity increases above a certain value. Computer‐generated solutions of the propagation and gain equations are included to illustrate the growth of filaments as the plane‐wave intensity changes in an amplifier.

ISSN:0021-8979    

DOI:10.1063/1.350349

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Experiments are described in which a high‐purity, high‐power (0.15 TW, 1 MeV) proton beam is generated from an ion source consisting of H2gas frozen onto a liquid‐helium‐cooled copper anode at 4.2 K in a series‐field‐coil extraction diode on the 0.7 TW HydraMITE‐II accelerator. Peak anode proton current densities of 2 kA/cm2were measured. This current density is a factor of 100 higher than those obtained in previous liquid‐helium‐cooled cryogenic diode experiments on small accelerators and is in the range required for high‐power ion beam applications. Thomson parabola, Faraday cup, and carbon activation measurements indicate an ion beam proton fraction close to 100% for the cryogenic source, compared to 50–70% for the standard hydrocarbon anode tested. The cryogenic proton source is believed to consist of no more than a few monolayers of molecular hydrogen. The hydrogen‐coated cryogenic anode shows a faster initial anode turn‐on than other materials. However, source‐limited emission from the thin hydrogen layer results in a somewhat longer current risetime, reduced ion diode efficiency, lower proton current enhancement over the Child–Langmuir limit, and a proton spectrum of lower average energy than for the hydrocarbon anode. Techniques to overcome these limitations are discussed. Cryogenic ion sources consisting of frozen N2, CH4, and Ne have also been studied. In each case, high intensity beams consisting predominantly of components of the refrigerated gas were produced.

ISSN:0021-8979    

DOI:10.1063/1.349317

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Electron and negative ion densities in the afterglow and in the plasma initiation phase of a 13.56‐MHz rf discharge in CF4were measured by using a microwave cavity method and a laser photodetachment technique. Measurements were carried out at low rf powers (≲10 W) and in the pressure range from 100 to 300 mTorr. The electron density in the afterglow showed an enhanced decay rate due to the presence of negative ions. Electrons originating from negative ions through associative collisional detachment with neutral radicals were also detected in the afterglow. Decay curve analysis of the negative ion density gave an ion–ion (presumably CF+3−F−) recombination rate constant of (5±2)×10−13m3 s−1, and showed that, in the active plasma, the negative ion loss rates by associative detachment and ion–ion recombination are of the same order of magnitude. The behavior of the electron and negative ion densities in the plasma initiation phase indicates that molecules and radicals that slowly accumulate in the plasma do not play a significant role in the production of negative ions.

ISSN:0021-8979    

DOI:10.1063/1.349318

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Dislocation pileups between a finite crack tip and a grain boundary with a dislocation‐free zone is investigated by the method of continuous dislocation modeling. Analytic solutions of both the dislocation distributions inside the crack and plastic zone and the stress field in the space are obtained. The stress intensity factor at the crack tip and the stress concentration at the grain boundary are derived. When the applied stress exceeds &tgr;&Lgr;0 [cos−1(c/a),k], the dislocations emitted from the crack tip pile up on the grain boundary. Note that &Lgr;0is the Heuman lambda function and &tgr; is the lattice friction stress.aandcare the grain size and surface crack length, respectively.Kis defined as (c/b)<rl>(a2−b2)/(a2−c2)<rlx,>, where (b−c) is the dislocation‐free zone. The stress concentration at the grain boundary increases with increasing grain size but decreases with increasing dislocation‐free zone. In contrast, if the applied stress is less than or equal to &tgr;&Lgr;0 [cos−1(c/a),k], no stress concentration exists at the grain boundary. The stress intensity factor at the crack tip increases with increasing size of dislocation‐free zone but decreases with increasing grain size. Our results are reduced to several special cases.

ISSN:0021-8979    

DOI:10.1063/1.349319

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Subsurface boron doping reconstructs the Si(111) surface and alters the electronic character of the surface Si atoms. The interaction of atomic hydrogen with the boron‐modified Si(111)‐(&sqrt;3×&sqrt;3)‐R30° surface was studied using temperature programmed desorption (TPD), high‐resolution electron energy‐loss spectroscopy (HREELS), and low‐energy electron diffraction. In comparison to the Si(111)‐(7×7) surface, we observe a significantly reduced hydrogen saturation coverage, measured by TPD and HREELS, and the absence of silane production. The ordered (1/3 ML) subsurface boron atoms passivate the surface Si atoms and reduce their reactivity with atomic hydrogen. This leads to a surface condition causing suppression of silicon etching by atomic hydrogen, compared to the unmodified Si(111)‐(7×7) surface.

ISSN:0021-8979    

DOI:10.1063/1.349320

出版商:AIP    

年代:1991

数据来源: AIP