摘要:

The theory of electromagnetic flaw detection based on the Lorentz reciprocity theorem has been applied to quantitative modeling of the corrosion buildup problem in PWR steam generators. Formulation of the electromagnetic probe response in spatial Fourier transform domain clarifies the role of the probe as a spatial frequency filter. Examples are given of tailoring the spatial frequency response to achieve specific performance characteristics, such as liftoff noise discrimination and flaw shape characterization. The relationship of spatial frequency response to probe geometry is analyzed for two dimensional inductive and capacitive structures, and the use of signal compression for realizing good spatial resolution and improved signal‐to‐noise ratio in long probes is discussed.

ISSN:0021-8979    

DOI:10.1063/1.332417

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In the dry etching of microelectronic devices, a common side effect is the deposition of material which can inhibit etching and catastrophically contaminate devices. However, simultaneous deposition and etching may be necessary to achieve a desired selectivity and anisotropy. Carbon tetrachloride is one plasma reagent which has been used to etch Al, Si, GaAs, and InP and has shown a propensity to deposit polychlorocarbons. Two variables known to affect both plasma etching and deposition rates are electrode material and oxidant concentration. To understand these effects, we utilize optical emission spectroscopy to measure instantaneous CCl4plasma etching rates of GaAs and InP as a function of O2or Cl2concentration with graphite or stainless steel electrodes. For comparison, HCl plasma etching of InP is also examined. Post‐etch surface analysis by Auger electron spectroscopy in conjunction with time‐resolved, etching‐rate measurements enable a separate assessment to be made of the effects of gas‐phase composition and deposition on etching rates. When stainless steel electrodes are used, oxidant addition to the CCl4feedstock liberates chlorine and enhances the initial etching rate but does not reduce etch inhibition by plasma‐generated deposits. The use of graphite electrodes reduces deposition but does not eliminate it. If an HCl plasma is used with stainless steel electrodes to etch InP, deposition and etch inhibition by iron and nickel chlorides occur. In general, deposition can be minimized by using graphite electrodes and HCl gas. However, faster etching rates can be achieved by using graphite and CCl4. In this case oxidant addition should not only enhance etching rates but also reduce polychlorocarbon formation. The use of stainless steel electrodes with chlorine containing plasmas should generally be avoided.

ISSN:0021-8979    

DOI:10.1063/1.332418

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The gas‐phase reactions of D+2, D+3, SiF+, and SiF+3with SiF4and of SiF+and SiF+3with D2have been studied in the center‐of‐mass energy range of 0.2–7 eV using a tandem mass spectrometer. Only one reaction of a silicon‐containing ion with SiF4was observed, namely the highly endothermic transfer of F−from SiF4to SiF+. Hence the SiF4molecule must be almost unique in showing a virtual absence of gas‐phase ionic chemistry in pure SiF4subjected to ionization. Several ion‐molecule reactions were observed in the SiF4–D2system but of these only the dissociative F−transfer from SiF4to D2+is exothermic. The almost total absence of exothermic ion‐molecule reactions means that the ionic distribution pertinent to the plasma chemistry of the SiF4and SiF4–H2systems will be determined solely by the cross sections of the electron impact ionization processes.

ISSN:0021-8979    

DOI:10.1063/1.332419

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

For the microwave dish antennas, the antenna gain when transmitting can be different, and is usually less, than that of the same antenna when receiving. The theory of the far field transmit and receive antenna gains is developed for the classical dish as well as for the general case. Aperture functions are derived for use in the integral form of the Fraunhofer diffraction equation. Both the aberration effects of the dish and the angular distribution of the feed are taken into account. Calculations of transmit and receive antenna patterns and gains are compared for thef/1 classical dish for various amounts of feed spillover.

ISSN:0021-8979    

DOI:10.1063/1.332420

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Experimentally, it has been established that negative ions cross the anode‐cathode gap in transmission lines operating at sufficiently high currents that electrons emitted from the cathode would be magnetically insulated (i.e., deflected back to the cathode by the Lorentz force before reaching the anode). In this paper, a one‐dimensional analysis of electron and negative ion emission from a cathode shows that electron emission decreases monotonically to zero as the ion emission increases to the maximum space charge limited value. A second one‐dimensional calculation shows that in high current lines, neglecting electron emission, monopolar emission of ions is inhibited by the self‐magnetic fields in the line, while bipolar emission is enhanced. Finally, a section is devoted to the approximate solution of several two‐dimensional problems using some of the earlier results of this paper, as well as an empirical scaling law derived by other researchers relating the negative ion current densityjnto the current per unit width in a line,J:jn=KJ3. In particular, fractional current loss as a function of distance from a load drawing a fixed current is found. An interesting byproduct of this calculation is the demonstration that the empirical scaling law leads to infinite line currents in a finite distance along a planar line, while such a divergence occurs only for certain parameter ranges on radial disk feed lines.

ISSN:0021-8979    

DOI:10.1063/1.332421

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We present a technique for orienting a superconductive magnetic gradiometer, formed by two coplanar pickup loops, to suppress gradient fluctuations originating from nearby magnetic objects. We developed the technique to quiet fluctuations coming from the steel structure of an oceanographic research tower that impressed gradients of about 200 nT/m at the gradiometer. Facing the loops nearly edgewise to the tower quiets noise to the level of inherent instrument noise, ∼0.1 (pT/m)/(Hz)1/2, at frequencies from 1 to 25 Hz. It also quiets noise nearly to inherent instrument noise at frequencies from 0.1 to 10 mHz. Comparison of the empirical result with the quieting expected from a formulation of gradiometer response shows that gradient fluctuations coming from a nearby magnetic object appear to a gradiometer to come from fluctuations in location and moment of a magnetic dipole near the magnetic centroid of the object, whatever the magnetic structure of the object.

ISSN:0021-8979    

DOI:10.1063/1.332422

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Transmission electron microscopy has been employed to characterize GaAs permeable base transistor structures. Submicrometer‐period tungsten base gratings fabricated on GaAs substrates by using either liftoff or etching techniques have been studied. Fabrication‐related problems such as electrically isolated tungsten debris and poor tungsten adhesion to GaAs have been identified. The crystal quality of GaAs layers grown by vapor phase epitaxy over the tungsten base gratings has also been investigated. Both stacking faults and voids have been found in these layers. The concentration of voids, which have an elongated‐bubble shape, depends on the orientation of the base grating on the GaAs surface. The effect of these structural imperfections on device performance is discussed.

ISSN:0021-8979    

DOI:10.1063/1.332423

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The dielectric breakdown strength of CO2laser‐grown oxides is measured and compared with other SiO2films grown by well‐established techniques. For the first time, the successful application of laser technology with existing Integrated Circuit preparation techniques to manufacture simple Metal‐Oxide‐Silicon devices is reported. Optimum processing conditions for CO2laser oxidation of Si are described which eliminate such common laser‐induced faults as slip dislocation and wafer warpage. The average field strength exhibited by thefirstcapacitor to break down from several batches of 100 incorporating a laser‐grown oxide layer was found to be 8.3 MV cm−1.

ISSN:0021-8979    

DOI:10.1063/1.332424

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Voltage–current characteristics have been measured for varistors that have been heated in reducing or oxidizing gases. Reducing environments produced large decreases in the leakage resistance. However, the original varistor characteristics could be restored by subsequent heating in oxidizing ambients. The oxygen partial pressure below which degradation occurred is 100 Pa at 800 °C. Degradation by reducing ambients occurred at much lower temperatures (150–500 °C) than did restoration of the varistor characteristics by oxidizing ambients (500–700 °C). An explanation of the observed behavior is proposed.

ISSN:0021-8979    

DOI:10.1063/1.332425

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Compensation for the proximity effect in electron lithography can be achieved by equalization of the backscattered dose received by all pattern points. This is accomplished by exposing the reverse tone of the required pattern with a beam diameterdc=2&sgr;b×(1+&eegr;e)−1/4and doseQc=Qe×[&eegr;e/(1+&eegr;e)], where &sgr;bis the radius of the Gaussian spatial distribution function of backscattered electrons at normally exposed pixels, &eegr;eis the ratio of backscattered to forwardscattered energy, andQeis the dose delivered to normally exposed pixels. This correction method has been confirmed to work for 500‐nm features by computer simulation of electron beam exposure and development and by experiment on a raster scan electron beam lithography system.

ISSN:0021-8979    

DOI:10.1063/1.332426

出版商:AIP    

年代:1983

数据来源: AIP