摘要:

Ion beam sputter‐deposition is one of the techniques used for synthesizing high Tcsuperconducting films in laboratory experiments. However, the scaling‐up of this method for technological applications, such as in microelectronics, will require a better understanding of basic phenomena occurring during the deposition process. First results are presented here from experimental and computer simulation studies on ion scattering and sputtering processes. It is demonstrated that scattering of neutralized ions from the targets can result in undesirable erosion of, and inert gas incorporation in, the growing films, depending on the ion/target atom mass ratio and ion beam angle of incidence/target/substrate geometry. The studies indicate that sputtering by Kr+or Xe+ions is preferable to the most commonly used Ar+ions, since the undesirable phenomena mentioned above are minimized for the first two ions. These results are used to determine optimum sputter deposition geometry and ions beam parameters for growing high Tcfilms.

ISSN:0094-243X    

DOI:10.1063/1.39032

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The self‐bias voltage on the rf electrode is used to obtain information concerning negative ion current in rf magnetron sputtering from a single ceramic target. Measurement is made as a function of rf power for YBaCuO and other perovskite targets in an Ar+O2mixture plasma. The self‐bias voltage initially increases with increasing rf power, and then passes through a maximum and decreases. This abnormal relation between self‐bias voltage and rf power is enhanced with increasing O2/Ar ratio in the Ar‐O2mixture plasma and also for Ba‐containing targets. The bias voltage drop is consistent with the composition deviation of on‐axis deposited films and is attributed to negative ion formation at the target. Therefore negative ion formation can be indirectly monitored by the target self‐bias voltage.

ISSN:0094-243X    

DOI:10.1063/1.39033

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ion beam sputtering is presently used to deposit films from single phase YBa2Cu3O7−&dgr;targets. Generally, Ar+ion beams (∼1500 eV) produced by Kaufman‐type ion sources are used for this purpose. It has been observed that these ion beams induce compositional and morphological changes on the polycrystalline ceramic target surface, which results in the composition of sputtered flux displaying a time‐dependent behavior. This in turn may lead to undesirably long times for reaching steady state conditions in the sputtering process.From the literature, it appears that only incomplete studies of these effects have been performed during experiments directed mainly at producing and characterizing high Tc films.Therefore, the stuides reported in this paper have been directed at examining in some detail the effects mentioned above as a function of two important parameters, i.e., ion beam energy and dose deposited in the targets during the sputtering process.The analysis techniques used to characterize the target changes include electron microscopy scanning Auger microprobe, and X‐ray diffraction techniques. Correlations between target initial conditions and ion‐induced changes and film compositions are discussed.The results indicate copper depletion in the sputtered targets and copper enrichment in the deposited films. The sputter conditions play a critical role in determining the surface topography evolution. No correlations between surface microstructure and film compositions were observed.

ISSN:0094-243X    

DOI:10.1063/1.39034

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have investigated the effects of low energy bombardment on the microstructural, compositional, and electrical characteristics of ion beam sputtered thin films of Y1Ba2Cu3Ox. During deposition, secondary bombardment of the growing film was performed using a Kaufman or ECR type ion source with energy ranging up to 125 eV. Microstructural changes have been characterized by TEM and XRD. Ion channeling has been performed to characterize the degree of orientation of the films. The effects of bombardment on the composition of the films were studied by RBS. It has been found that the use of an ECR microwave oxygen ion source trained on the growing films induces as‐deposited superconductivity and also play a role in the texturing of the films. The effects of ion bombardment on the critical current (Jc) and temperature (Tc) are also reported.

ISSN:0094-243X    

DOI:10.1063/1.39062

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thin films of 1‐2‐3 high Tcsuperconductors were fabricated by RF magnetron sputtering from a several compound oxide target. Film composition was studied as a function of oxygen content of the target, power density, temperature, and pressure. Compositional analysis was performed by Rutherford backscattering spectroscopy and energy dispersive x‐ray analysis before and after annealing treatment. The resulting film compositions were then related to the aforementioned sputtering parameters so that optimal sputtering conditions for achieving consistent 1‐2‐3 film stoichiometry could be established.

ISSN:0094-243X    

DOI:10.1063/1.39051

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The use of a radio frequency (RF) excited oxygen plasma for cleaning and oxygenation of high Tcsuperconducting films at room temperature is studied by photoemission spectroscopy. Plasma oxidation at ∼10 mT pressure, removes comtaminants like carbon and causes the Ba 5p and 4d and the 0 ls corelevels to shift to lower binding energy. Valence band spectra for an epitaxial Y2Ba4Cu8O15+xfilm on SrTiO3(001) show a Fermi edge and resemble spectra presented by other groups for YBa2Cu3O7single crystals and epitaxial films. These films also show a sharp 0 ls corelevel near 528 eV. Possible reactive ion etching of a degraded YBCO film surface is demonstrated in a series of spectra taken after successive oxygen plasma treatments. A surface contaminated with BaCO3becomes barium deficient after the initial plasma treatment but a second plasma treatment of a substrate biased to −200 V to promote sputtering produces photoemission features typical of an YBa2Cu3O7surface.

ISSN:0094-243X    

DOI:10.1063/1.39052

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Gd‐Ba‐Cu‐O superconducting thin films were oxidized by an ion doping technique using a microwave electron‐cyclotron‐resonance (ECR) plasma with AC(20kHz) substrate bias at a substrate temperature of 330 °C. Under conditions with the lowest emission intensity ratio of molecular oxygen ions(O2+) to oxygen atoms(O) observed by optical emission from O2plasma, superconducting films did not exhibit superconductivity after treatment. X‐ray diffraction indicated that bonded oxygen atoms were removed from the films by oxygen radical. Under conditions with high O2+/O ratio, the superconducting thin films were not remarkably changed. The effect of oxygen ion doping could be observed.

ISSN:0094-243X    

DOI:10.1063/1.39053

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thin‐film preparation of Bi‐Sr‐Ca‐Cu‐O system has been studied by layer‐by‐layer method using multitarget sputtering. Targets of Bi metal, SrCu and CaCu aloys were used and reactive dc sputtering was carried out in argon and oxygen mixed atmosphere. Oxide thin layers were sequentially deposited in the order of Bi, SrCu, CaCu and SrCu onto MgO(100) substrates heated at 600–700 °C. By adjusting the thickness of each layer to the ideal value, Bi‐based thin films of various crystal structure with different numbers of CuO2planes between Bi‐O bilayers were selectively prepared. As‐grown films with three CuO2planes showed the highest superconducting onset temperature (Tc) of 110 K and the highest zero‐resistance temperature of 45 K. Films with two and four CuO2planes showed Tc’s of 95 K and 85 K, respectively. Films with five CuO2planes showed high resistivity and exhibited semiconductor‐like behavior. Furthermore, by using this method new Bi‐based multilayer films with different numbers of CuO2planes were successfully prepared.

ISSN:0094-243X    

DOI:10.1063/1.39054

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconducing YBa2Cu3O7−xfilms were prepared by pulsed CO2laser deposition. Correlations between target composition and microstructure, and film composition, morphology, and uniformity were made in order to understand the process by which film growth occurs. Auger spectroscopy of the molten globules produced by laser deposition showed the globules to be compositionally nonuniform with Y depletion at the surface, and enrichment inside the globule. Evaporated Cu and Ba were detected in the films. After annealing the films, both Cu rich and Ba rich surface areas were detected, but the overall composition of the film was YBa2Cu3O7−x.

ISSN:0094-243X    

DOI:10.1063/1.39035

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Metal organic chemical vapor deposition (MOCVD) has the potential of emerging as a major technique for the deposition of thin films of high temperature superconductors and related materials. In this paper, we present preliminary results ofin‐situpreparation of Y‐Ba‐Cu‐O on yttria‐stabilized zirconia (YSZ) and silicon substrates.

ISSN:0094-243X    

DOI:10.1063/1.39036

出版商:AIP    

年代:1990

数据来源: AIP