Showing papers on "Pulsed laser deposition published in 1989"

Anisotropic deposition of silicon dioxide

Abstract: In a radio-frequency plasma deposition reactor (10), SiO 2 is deposited from a source (16) of tetraethoxysilane (TEOS). The deposition is made to be anisotropic, that is, to be deposited preferentially on horizontal surfaces, by use in the deposition atmosphere of a constituency such as NH 3 or NF 3 which inhibits SiO 2 deposition, along with a radio-frequency power in excess of 100 watts, which preferentially removes the inhibiting gas from horizontal surfaces through ion impact.

High-performance TFTs fabricated by XeCl excimer laser annealing of hydrogenated amorphous-silicon film

Abstract: High-performance staggered a-Si:H and poly-Si thin-film transistors (TFTs) fabricated by XeCl excimer laser annealing of a-Si:H films are discussed. The field-effect mobility of poly-Si TFT is 102 cm/sup 2//V-s, and that of a-Si:H TFT is 0.23 cm/sup 2//V-s. Their drain current on/off ratios are over 10/sup 6/. Except for the crystallization, the fabrication process was the same for both of them. This process appears extremely promising for the integration of matrix elements and peripheral drivers in a single substrate. >

High‐temperature superconductivity in ultrathin films of Y1Ba2Cu3O7−x

Abstract: We have grown ultrathin films of Y1Ba2Cu3O7−x in situ on (001) SrTiO3 by pulsed laser deposition The zero resistance transition temperature (Tc0) is >90 K for films >300 A thick The critical current density (Jc at 77 K) is 08×106 A/cm2 for a 300 A film and 4–5×106 A/cm2 for a 1000 A film The Tc0 and Jc deteriorate rapidly below 300 A, reaching values of 82 K and 300 A/cm2 at 77 K, respectively, for a 100 A film Films only 50 A thick exhibit metallic behavior and possible evidence of superconductivity without showing zero resistance to 10 K These results are understood on the basis of the defects formed at the film‐substrate interface, the density of which rapidly decreases over a thickness of 100 A We have studied these defects by ion channeling measurements and cross‐section transmission electron microscopy Our results suggest that the superconducting transport in these films is likely to be two dimensional in nature, consistent with the short coherence length along the c axis of the crystals

Low temperature organometallic deposition of metals

Abstract: A process for coating metal on a substrate. The process uses organometallic compounds such as (trimethyl)(cyclopentadienyl) platinum in the presence of a reducing fluid such as hydrogen gas to produce high purity films capable of selective deposition on substrates containing, for example, tungsten and silicon. The films are deposited using chemical vapor deposition (CVD) or gas phase laser deposition. The invention also comprises devices made from the process of the invention.

Optical spectroscopy: An in situ diagnostic for pulsed laser deposition of high Tc superconducting thin films

Abstract: High oxygen partial pressure has been found to be an important parameter for the pulsed laser deposition of as‐deposited superconducting thin films with high Tc and Jc. The optical emissions from both elemental and oxide species ejected from the target of YBa2Cu3O7−x during the pulsed laser deposition process increase with the oxygen pressure, with the oxide emission showing a stronger pressure dependence than the elemental emission. The dynamics of the interaction between the oxygen atoms and the species in the laser‐produced plume were studied by a wavelength and time‐resolved measurement. The results are qualitatively explained using a simple model based on optical emission arising from inelastic and recombination collision between the elemental species and electronically excited oxygen atoms. The formation of oxides in the plume is shown to be essential for the production of higher quality superconducting films, indicating the value of optical spectroscopy as a diagnostic tool.

High critical currents in epitaxial YBa2Cu3O7−x thin films on silicon with buffer layers

Abstract: As‐deposited superconducting thin films (∼0.1 μm) of YBa2Cu3O7−x have been prepared by pulsed laser deposition on (100) Si with buffer layers of BaTiO3/MgAl2O4. X‐ray diffraction studies reveal that the films grow epitaxially with the c axis preferentially oriented normal to the substrate surface. This is confirmed by ion channeling measurements along the (100) (normal to the surface) and (110) directions of the Si substrate showing a minimum yield of 54% along the (100), and 78% along the (110) axes using 2.8 MeV He++. Preliminary transmission electron microscopy study also supports these results. The as‐deposited films have zero resistance temperatures of 86–87 K, and critical current densities of 6×104 A/cm2 at 77 K and 1.2×105 A/cm2 at 73 K. Our results indicate that the superconducting properties of the films are limited primarily by the quality and degree of epitaxal growth of the buffer layers on the silicon substrate.

Observation of the early stages of growth of superconducting thin films by transmission electron microscopy

Abstract: A method for the direct observation of the early stages of growth of superconducting films by transmission electron microscopy (TEM) is reported. The technique uses well‐characterized, single‐crystal TEM foils as substrates for the deposition process. Ultrathin films of YBa2Cu3O6+x (YBCO) were prepared by pulsed laser deposition from stoichiometric bulk samples directly onto (001) oriented MgO thin‐foil substrates. Observation of the film by TEM is possible without any post‐deposition specimen preparation. The epitactic nature of the film growth is shown by analysis of the moire fringe pattern and by selected area diffraction. In addition to an interconnected film, copper oxide particles and stoichiometric ablated clusters were observed.

Physical Vapor Deposition

Abstract: In the early days of microelectronics, physical vapor deposition was simply applied to the evaporation of Al to form the high conductivity connections to transistors. With the ever-increasing complexity of silicon integrated circuits and the development of GaAs circuits, a much wider range of materials must be deposited to fulfill special needs for patterning, electromigration, diffusion barriers, Schottky contacts, air bridges, etc. (Table 1); alloys and compounds must be deposited as well as elemental metals. Sputter deposition has been used increasingly and other specialized techniques have also been applied; reactive evaporation, activated reactive evaporation, ion plating, and cluster ion deposition have been developed to meet special needs. However, evaporative and sputter deposition techniques are still the primary physical vapor deposition methods used for microcircuit fabrication and this review chapter will focus on their similarities and differences as they apply to microcircuit fabrication in both Si and GaAs.

Microstructure of in situ epitaxially grown superconducting Y‐Ba‐Cu‐O thin films

Abstract: The microstructure of in situ epitaxially grown Y‐Ba‐Cu‐O thin films on (001) SrTiO3 substrates was studied using cross‐sectional transmission electron microscopy. The films, prepared by pulsed laser deposition at substrate holder temperature of 650 °C without post‐annealing, exhibit zero resistivity above 90 K and critical currents exceeding 106 A/cm2 at 77 K. The films are of heavily faulted single crystalline structure with the c axis approximately perpendicular to the substrate (001) surface. We suggest that, due to the fast quenching and low substrate temperature, crystalline defects and chemical fluctuations are locked into a faulted structure after each laser pulse. Despite their rather imperfect microstructure, the films are free from macroscopic grain boundaries and secondary phases and possess superb superconducting properties.

Low magnetic flux noise observed in laser-deposited in situ films of YB2Cu3Oy and implications for high- Tc SQUIDs

Abstract: THE first device made from a thin film of a high-transition-temperature (high-Tc) superconductor was a d.c. SQUID (superconducting quantum interference device)1. Many applications of SQUIDs demand high sensitivity at low frequencies f( ≤1 Hz), and thus require films with low intrinsic '1/f magnetic flux noise2, 3. Although the level of 1/f noise in T2Ba2Ca2Cu3Ox SQUIDs4 is significantly lower than that in earlier YBa2Cu3O3, (YBCO) SQUIDs1, it remains higher than that in low-Tc devices. In post-annealed films of YBCO, the magnitude of the 1/f noise has been shown5 to decrease dramatically as the quality of the films is improved. Here we report measurements of flux noise in a film of YBCO grown in situ by pulsed laser deposition (but not patterned into a SQUID). The 1/f noise level was two orders of magnitude lower than in our best post-annealed film. Provided that it proves possible to fabricate suitable low-noise Josephson junctions, a d.c. SQUID made from a film of this quality and operated at liquid-nitrogen temperature (77 K) should approach the low-frequency performance currently achieved in commerically available Iow-Tc SQUIDs.

Preparation of BaF2 films by metalorganic chemical vapor deposition

Abstract: To date thin films of II(a) fluorides (CaF2, BaF2, SrF2, and their mixtures) have only been deposited by physical vapor deposition techniques. We report for the first time the deposition of BaF2 films on silicon and yttrium‐stabilized zirconia substrates by metalorganic chemical vapor deposition at a substrate temperature as low as 400 °C.

Optical emission and mass spectroscopic studies of the gas phase during the deposition of SiO2 and a‐Si:H by remote plasma‐enhanced chemical vapor deposition

Abstract: This paper will present mass spectrometric and optical emission spectroscopic studies of the deposition process of amorphous hydrogenated silicon (a‐Si:H) and silicon dioxide (SiO2) by remote plasma‐enhanced chemical vapor deposition (remote PECVD). We have established that the silane reactant, which is not directly exposed to a rf plasma in either of the deposition processes, is not fragmented or chemically combined in the gas phase. Specifically there is no evidence for the formation of disilane, Si2H6, or siloxanes or silanols in the gas phase, as in the direct PECVD process. In the case of the a‐Si:H depositions, the silane is excited in the gas phase and the excited species, SiH*4 , is the deposition precursor. In the case of the SiO2 depositions, the active species promoting deposition is an O2 metastable neutral molecule. The by‐products of the respective reactions are H2 and H2O.

Method and apparatus for rapidly growing films on substrates using pulsed supersonic jets

Abstract: A method and apparatus for the rapid and economical deposition of uniform and high quality films upon a substrate for subsequent use in producing electronic devices, for example. The resultant films are either epitaxial (crystalline) or amorphous depending upon the incidence rate and the temperature and structure of the substrate. The deposition is carried out in a chamber maintained at about 10 -6 Torr. A gaseous source of the material for forming the deposit is injected into the deposition chamber in the form of a pulsed supersonic jet so as to obtain a high incidence rate. The supersonic jet is produced by a pulsed valve between a relatively high presure reservoir, containing the source gaseous molecules, and the deposition chamber; the valve has a small nozzle orifice (e.g., 0.1-1.0 mm diameter). The type of deposit (crystalline amorphous) is then dependent upon the temperature and structure of the substrate. Very high deposition rates are achieved, and the deposit is very smooth and of uniform thickness. Typically the deposition rate is about 100 times that of much more expensive conventional molecular beam methods for deposition, and comparable to certain expensive plasma-assisted CVD methods of the art. The high growth rate of this method results in a reduced contamination of the deposit from other elements in the environment. The method is illustrated by the deposition of epitaxial and amorphour germanium films upon GaAs substrates.

Reactive deposition of hard coatings

Abstract: The reactive deposition of thin films is analyzed by means of a microphysical model. This model shows the way in which to (i) eliminate the hysteresis effect and (ii) control the deposition process. Special attention is devoted to physical parameters, such as fluxes of ions v i , metallic particles v m and reactive gas particles v r , the energy of particles bombarding the growing film and the substrate temperature which play a fundamental role in the deposition process, and to deposition systems with enhanced ionization. A correlation between (i) process parameters, (ii) microstructure, texture, phase and chemical composition of films, and (iii) resulting film properties is discussed in detail for Ti−N films. A comparison of arc evaporation and magnetron sputtering is also given. The need for equipment providing independent control of the deposition rate and ion bombardment of films is emphasized.

Low Temperature Deposition of Silicon Nitride by the Catalytic Chemical Vapor Deposition Method

Abstract: A new low temperature deposition method named "catalytic chemical vapor deposition (Cat-CVD or CTL-CVD)" is applied to obtain silicon nitride films. In the method, a N2H4, N2, and SiH4 gas mixture is decomposed by the catalytic or pyrolytic reaction with a heated catalyzer placed near substrates, so that silicon nitride films are deposited at substrate temperatures as low as 300°C with deposition rates near 1000 A/min, without plasma nor photochemical excitation. It is found that the resistivity, breakdown electric field and hydrogen content of the films are almost equivalent to those of thermal CVD films deposited at about 700°C, and that the diffusivity of depositing species appears large enough to obtain good stepcoverage.

Deposition of Thin Rhodium Films by Plasma-Enhanced Chemical Vapor Deposition

Abstract: Thin films of rhodium have been prepared starting from dicarbonyl-2.4-pentadionato-rhodium(I), Rh(CO)2C5H7O2, by plasma enhanced CVD. The dependence of the deposition rate and film properties on substrate temperature, partial pressure of the organometallic and on hydrogen has been studied. Metal contents of ≈ 100% and thin-film resistivities as low as 5 times the bulk resistivity of rhodium have been achieved.

High temperature superconducting thin films: The physics of pulsed laser ablation

Abstract: A study of the interaction of pulsed coherent radiation from a Nd:YAG laser (wavelength 1064 nm) with solid targets used in the deposition of YBa2Cu3O7−x superconducting thin films is presented. Electron microscopy, time-of-flight mass spectroscopy, laser induced fluorescence spectroscopy, precise target weight loss measurements, and wet chemical analysis of collected films were employed. The photon-target interaction, the gas phase ablated particle beam, and the collected film were each probed. Conclusions concerning the physics of the ablation process and important practical considerations for the production of high quality superconducting films were obtained.

Evaporating and sputtering: Substrate heating dependence on deposition rate

Abstract: The deposition of copper into the through holes and vias of printed wiring boards (PWB’s) has been done using vacuum processing techniques such as evaporation and sputtering. One of the most important limiting factors for any deposition process is the substrate heating. The temperature of epoxy‐glass PWB’s should not exceed 180 °C (350 °F). For evaporation, there are two major contributions, the heat of condensation and radiant heating, with the heat of condensation dominating at deposition rates >2 μm/min. The radiant heating is very dependent on α e, the product of the substrate absorptivity and the source emissivity. Sputter deposition has two main sources of substrate heating: the heat of condensation and the kinetic energy of the incident atoms and ions. The experimental apparatus used to measure the power absorbed by a PWB substrate is described. Data are presented for the power absorbed by the substrate as a function of deposition rate for sputtered copper. These data are compared with the results ...

Deposition of diamond films

Abstract: Diamond films are deposited at substrates below temperatures of 400° C. by chemical vapor deposition using a high powered pulsed laser and a vapor which is an aliphatic carboxylic acid or an aromatic carboxylic anhydride.

Laser CVD and plasma CVD of CrO2 films and cobalt doped CrO2 films using organometallic precursors

Abstract: Chromium dioxide is deposited as a ferromagnetic layer onto selected portions of a substrate or over the entire substrate. Chromium hexacarbonyl vapor is introduced into a vacuum deposition chamber at e.g. 10 milliTorr and oxygen is introduced at e.g. 15 to 100 milliTorr. A UV laser beam is focused onto the substrate to form the CrO2 layer photolytically. The CrO2 layer can also be deposited by RF plasma deposition. This technique can also be employed for depositing MoC2, WC2, Mo2 φ3, MoO2 or WO2. Magnetic recording or memory devices are produced without the high failure rate typical of the prior art sputtering technique.

Aluminum selective area deposition on Si using diethylaluminumchloride

Abstract: Aluminum deposition on Si was studied using diethylaluminumchloride (DEAlCl) as a new Al chemical vapor deposition source. Selective area deposition was successfully achieved at substrate temperatures of 313–380 °C. The deposition rate was higher than 370 A/min. Reflectance and resistivity of the deposited films were comparable to those of the evaporated ones. Decomposition experiments suggest that DEAlCl catalytically decomposes on the Al surface, which would explain the high selectivity observed.

The deposition rate and properties of the deposit in plasma enhanced chemical vapor deposition of TiN

Abstract: Titanium nitride (TiN) films were deposited onto tool steels and cemented carbide cutting tools by plasma enhanced chemical vapor deposition (PECVD) using a gaseous mixture of TiCl4, N2, H2, and Ar in order to find out the effects of the deposition temperature and rf power density on the deposition rate and properties of deposited TiN. The deposition rate and crystallinity of the deposited TiN was affected by the deposition temperature as well as the plasma power density. The deposition rate was decreased with an increase in deposition temperature between 270 and 430 °C. The crystallinity of deposited TiN was improved by an increase in deposition temperature as well as rf power density. Crystalline TiN was obtained above 300 °C and showed a strong crystallographic preferred orientation of 〈200〉. TiN layers deposited by PECVD using TiCl4 as a reactant contained chlorine, the content of which was increased with a decrease in deposition temperature. Oxygen at the interface between the TiN deposited layer and the substrate excluded nitrogen and chlorine. The surface morphology of the deposited TiN is a dome‐shaped cluster composed of many fine grains.

Ferrimagnetic rare-earth orthoferrites: a new, magnetic substrate for the growth of epitaxial Y-Ba-Cu-O thin films

Abstract: We report, for the first time, growth of thin films of Y‐Ba‐Cu‐O by pulsed laser deposition onto [001] YbFeO3 single‐crystal substrates. A Tc,0 of 88 K was obtained along with a critical current greater than 105 A/cm2 at 77 K. X‐ray diffraction shows epitaxial growth of the 1‐2‐3 phase with the c axis oriented normal to the substrate plane. Rocking curve measurements show a 0.5° full width at half maximum, indicating good alignment of the layered structure. The composition was verified by Rutherford backscattering, while channeling results reveal a 17% yield, consistent with the rocking curve measurements. Growth of thin films of 1‐2‐3 on a magnetic substrate may open the way for potentially new applications.

Focused Ion Beam Induced Deposition

Abstract: Ion induced deposition is a novel method of thin film growth in which a local gas ambient is created near an ion bombarded surface. The ion bombardment causes the gas molecules to break up and some of the gas constituents to deposit on the surface. If a focused ion beam is used, then this becomes a technique for maskless, resistless, patterned deposition. Depositions of films from gases of Al(CH3)3, WF6 and Ta(OC2H5)2 have been reported. The films for the most part have contained high (approaching 50%) concentrations of impurities such as O or C, presumably due to the lack of ultrahigh vacuum conditions. Gold deposition has been observed from dimethyl gold hexa fluoroacetylacetonate (C7 H7F6 O2 Au), with both focused ion beams and broad beams. In many cases, the gold films are much purer (less than 5% C or O) and have exhibited resistivities from 20 to 1000µΩcm (Bulk gold resistivity is 2.5µΩcm.) Deposition yields (atoms deposited per incident ion) of 4 to 100 have been observed. But the higher yields correlate with higher resistivity and higher impurity content. Preliminary transmission electron microscope examination shows the gold films to start out as unconnected islands of 40 to 60nm dimensions. The mechanisms for the deposition is at present not well understood. Some hypotheses will be discussed. Ion-induced deposition appears to be a promising technique for in-situ deposition of metals or insulators with submicrometer resolution.

Sum frequency mixing of copper vapor laser output in KDP and beta -BBO

Abstract: Generation at 271 nm by frequency summing the two copper vapor laser (CVL) output wavelengths (at 511 and 578 nm) in beta -BBO and KDP is reported. A maximum sum frequency output of 100 mW was obtained for 6.8 W total pump power from a CVL operating with a fully unstable (M=16) confocal cavity. >