摘要:

A comparison of experimental measurements and numerical calculations of temporal and spatial sheath evolution is presented. Spherical targets of copper and stainless steel (radius=2 cm) and a cylindrical target (radius=0.95 cm, height=18 cm) were immersed in an argon plasma with plasma densities of 2×108–8×109cm−3and biased negatively (20–50 kV). A Langmuir probe was used to detect the propagating sheath edge. Experimental measurements of sheath edge position were in good agreement with those determined by numerical calculations.

ISSN:0021-8979    

DOI:10.1063/1.348600

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The distribution of ion energies and the temporal modulation of ion and electron currents were measured at the cathode of an asymmetric, capacitively coupled rf discharge system operated at 13.56 MHz. The ion energy distributions (IEDs) were found to exhibit pronounced features, namely a characteristic series of peaks and double peaks, their position and intensity depending strongly on process parameters such as self‐bias voltage and pressure. Those structured IEDs have been observed for a variety of gases including argon, oxygen, hydrogen, and benzene. The IED features are explained by the rf modulation of the sheath potential in combination with the creation of thermal ions by charge‐exchange processes in the sheath. A model for the ion transport through collisional rf sheaths is presented which satisfactorily explains the observed IEDs. It will be shown that the observed features are an inherent property of capacitively coupled rf discharges. By analyzing these structures detailed information about the spatial field distribution in the sheath and the transport of ions through rf plasma sheaths is obtained. The time‐resolved measurements revealed that the ion current behind the cathode is strongly modulated. This temporal modulation has been described by the same theory confirming the applicability of the present model. Finally the electron current was found to be confined to short periodic pulses of 2–3 ns width.

ISSN:0021-8979    

DOI:10.1063/1.348601

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A numerical study on the ion and neutral angular impact energy distribution at the rf‐driven electrode of a reactive ion etcher is presented. The calculations for the ions are performed using a Monte Carlo method that includes charge exchange and elastic scattering. The contribution of both collision processes to the angular ion impact energy distribution is studied. For the case that charge exchange is the only collision process, the Monte Carlo results can be checked against those of a method based on a spatially uniform and time independent collision rate. In that case, both methods yield the same ion impact energy distribution. The position, velocity, and propagation angle of the energetic neutrals created in collisions of ions with the background gas are stored. These are used as input data for a separate code that follows the evolution of the angular neutral energy distribution, taking into account (multiple) neutral elastic scattering. From the ion and neutral distributions, the number of neutrals per ion, the average impact energy, and the energy‐weighted average impact angle have been derived. It is shown that these parameters are well described by simple expressions. Finally, the sputter yield is calculated. The results show that the contribution of the angular distributions of both ions and neutrals to the yield can be neglected.

ISSN:0021-8979    

DOI:10.1063/1.348602

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A study of the effect of Ge+implantation energy, dose, and temperature on the concentration of atoms bound by the extrinsic end‐of‐range dislocation loops in Si ⟨100⟩ wafers is presented. Plan‐view and cross‐sectional transmission electron microscopy observations of both the as‐implanted and annealed (900 °C, 30 min) morphology were made. The implant energy was varied from 30 to 150 keV, the dose varied from 2×1014to 1×1016/cm2, and the temperature was varied by using three different wafer‐cooling methods during the implantation. Increasing the implant energy, dose, or wafer temperature all resulted in significant increases (as much as two orders of magnitude) in the concentration of atoms bound by the end‐of‐range loops. Recent models have suggested that the concentration of end‐of‐range defects is related to the integrated recoil concentration beyond the amorphous/crystalline (a/c) interface. Correlation oftrim‐88 calculations with measureda/cdepths show that the integrated recoil concentration beyond thea/cinterface can explain both qualitatively and quantitatively the dependence of the ‘‘trapped interstitials’’ on the implant energy. However, this model can only qualitatively explain the temperature dependence of the defects, and it fails to account for the strong dose dependence when wafer heating is suppressed.

ISSN:0021-8979    

DOI:10.1063/1.348603

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The growth of Fe films on ZnSe(001) epilayers and bulk GaAs(001) substrates has been studied to determine the mode of film growth, the formation of the interface, and the structure of the overlayer at the 1–10 monolayer level. Auger electron diffraction (AED), x‐ray photoelectron spectroscopy (XPS), and reflection high‐energy electron diffraction data are obtained for incremental deposition of the Fe(001) overlayer. The coverage dependence of the AED forward scattering peaks reveals a predominantly layer‐by‐layer mode of film growth at 175 °C on ZnSe, while a more three‐dimensional growth mode occurs on the oxide‐desorbed GaAs(001) substrate. XPS studies of the semiconductor 3dlevels indicate that the Fe/ZnSe interface is less reactive than the Fe/GaAs interface.

ISSN:0021-8979    

DOI:10.1063/1.348604

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present a detailed study of the effects of ion bombardment on the optoelectronic properties ofa‐Si:H films. Two series of samples were deposited from a rf glow discharge at 30 and 100 mTorr of silane pressure, corresponding to two different deposition conditions. The energy of the ions impinging on the substrate was increased by applying a negative dc bias in steps of 25 V to the substrate holder. The increase of the substrate bias from 0 to −100 V had no effect on the deposition rate ofa‐Si:H at 30 mTorr, whereas a factor of 2 decrease was observed for deposition at 100 mTorr. The density of states of thea‐Si:H films, determined by photothermal deflection spectroscopy and by the constant‐photocurrent method, decreased as the substrate bias was increased up to −50 V, especially for the series deposited at 100 mTorr. At the same time the valence‐band tail became sharper. These observations are consistent with the improvement of the electron drift‐mobility deep‐trapping‐lifetime (&mgr;d&tgr;d)eproduct, determined by time‐of‐flight, and of the hole‐mobility recombination‐lifetime (&mgr;&tgr;r)hproduct determined from the voltage dependence of the photocurrent collection efficiency. For both series of samples, the films with the best electronic properties were obtained at a negative substrate bias of 50 V. No correlation was found between the substrate bias and the light‐induced degradation behavior of these films. The saturated density of light‐induced defects shows a direct correlation with the optical gap.

ISSN:0021-8979    

DOI:10.1063/1.348605

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The influence of deposition conditions on the molecular structure of thin films deposited from tetramethylsilane through plasma enhanced chemical vapor deposition was investigated using infrared spectroscopy, ultraviolet–visible absorption spectroscopy, and sputtered neutral atom mass spectrometry (SNAMS). The infrared spectra revealed a strong dependence of film structure on the deposition pressure, with high pressures (>50 mTorr) producing linear, polymeric films, and low pressures (<50 mTorr) producing amorphous, crosslinked films. The structure of the polymeric films was dominated by carbon atoms incorporated as intact, chain terminating methyl groups. The crosslinked films contained fewer methyl groups and proportionately more bridging methylene and branching methylidyne groups. SNAMS measurements revealed that the carbon‐to‐silicon ratio was inversely dependent on deposition pressure, with carbon content increasing as deposition pressures decrease. UV–visible measurements indicated that the optical properties of the films were strongly dependent on deposition pressure, particularly at pressures below 100 mTorr. Films prepared in these experiments exhibited optical gaps ranging from 2.1 to 3.9 eV. From these results, a film structure evolution model is postulated, stressing the interactions between precursor structure, fragment structure, and plasma energetics.

ISSN:0021-8979    

DOI:10.1063/1.348606

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The changes in resistivity for niobium and tantalum wires, which had been loaded with 5.37% (atom ratio) and 6.24% tritium respectively, was measured over a 1‐year period. After an initial rapid increase corresponding to roughly 5 &mgr;&OHgr; m for He interstitials, the resistivity reached a local maximum. It then continued to increase at a rate expected for the development of insulating He bubbles and material swelling. The local maximum corresponds to the point at which active acoustic emission is taking place and is indicative of dislocation loop punching at the bubbles. The stabilization of the resistivity after this local maximum is thought to be due to the general lattice relaxation and the formation of a complex and well‐developed dislocation network.

ISSN:0021-8979    

DOI:10.1063/1.348607

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A detailed study of the influence of substrate temperature on the radiation‐induced lattice strain field and crystalline‐to‐amorphous (c–a) phase transition in MeV oxygen ion implanted GaAs crystals has been made using channeling Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the x‐ray rocking curve technique. A comparison has been made between the cases of room temperature (RT) and low temperature (LT) (about 100 K) implantation. A stronginsitudynamic annealing process is found in RT implantation at a moderate beam current, resulting in a uniform positive strain field in the implanted layer. LT implantation introduces a freeze‐in effect which impedes the recombination and diffusion of initial radiation‐created lattice damage and defects, and in turn drives more efficiently thec–atransition as well as strain saturation and relaxation. The results are interpreted with a spike damage model in which the defect production process is described in terms of the competition between defect generation by nuclear spikes and defect diffusion and recombination stimulated by electronic spikes. It is also suggested that the excess population of vacancies and their complexes is responsible for lattice spacing expansion in ion‐implanted GaAs crystals.

ISSN:0021-8979    

DOI:10.1063/1.348608

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Nanometer‐scale structures as small as 1 nm were fabricated on graphite surfaces using a scanning tunneling microscope in the presence of low‐pressure (10−4Torr) trimethylaluminum. The studies were performed under controlled conditions of gas purity and gas pressure, allowing systematic measurements. We studied the voltage threshold and other features of the fabrication process as a function of the tip‐surface biasing voltage and the tunneling current. The studies lead us to believe that the structures were formed by bombardment of the graphite surface by ions produced by electron‐assisted field ionization localized in the region of the tunneling gap.

ISSN:0021-8979    

DOI:10.1063/1.348609

出版商:AIP    

年代:1991

数据来源: AIP