Dc Planar Magnetron Sputtering Research Articles

Ion energies at the cathode of the DC planar magnetron sputtering discharge

The energy distribution of the ions striking the cathode of the dc planar magnetron system was measured over a range of the typical sputtering conditions (magnetic field of 0.07–0.13 T, argon pressure of 0.01–10 Pa, discharge voltage of 250–600 V). The results obtained allow us to conclude that the major part of the incident ion flux originates in the cathode fall region. The theoretical model developed in terms of mobility theory makes it possible to evaluate the cathode fall voltage and its dependence on the sputtering conditions. It was found that the normalized integral form of the incident ions, energy spectrum is practically independent of the sputtering discharge parameters.

Epitaxial growth of superconducting YBa2Cu3O7−x thin films by reactive magnetron sputtering

Perfect epitaxial growth of superconducting YBa2Cu3O7−x thin films have been achieved on (100) SrTiO3, (110) SrTiO3, and (100) ZrO2 substrates using a modified planar dc magnetron sputtering system. The films exhibit zero resistances at 87–90 K with transition widths of about 2 K. The critical current density of 1.4×106 A/cm2 at 77 K so far has been measured on the (100) SrTiO3 substrate. The epitaxial orientation of the thin films was influenced by the substrate orientation, the substrate temperature, and the oxygen partial pressure. The quality of growth and the epitaxial orientation of the films were examined by electron channeling, x-ray diffraction, and reflection high-energy electron diffraction techniques. The preferential epitaxial orientation is discussed.

Characterization of sliced multilayer zone plates for hard x rays (invited)

Circular zone plates for hard x rays, fabricated by dc planar magnetron sputtering, have been characterized using monochromatized synchroton x rays. The zone plates consisted of either 5 or 20 pairs of altenating WSi2 and C layers. The minimum focal spot size attained was less than 3 μm× 10 μm in the vertical and horizontal directions, respectively. The efficiency of the zone plate with 20 layer pairs was determined to be about 4.5%. An x-ray transmission image of a No. 2000 mesh Cu grid and an x-ray fluorescence image of a patterned Co thin film were measured, and it was demonstrated that a high-resolution image could be obtained with the present zone plate. The possibility of implementing the phase zone plate in hard x-ray range is considered.

Fully textured growth of Y1Ba2Cu3O7−δ films by sputtering on LiNbO3 substrates

We present details about the deposition of thin Y1Ba2Cu3O7−δ films on single-crystal LiNbO3 substrates by planar dc magnetron sputtering. Among other data, results of transition temperature (Tc(R=0) =88 K) and critical current density (jc >2×109 A/m2 at 77 K) plus some details about film-to-substrate orientation which is present in all three crystallographic directions are reported.

Structure and Properties of C-Axis Oriented AlN Films Reactively Deposited by DC Planar Magnetron Sputtering

AbstractAluminum nitride (AlN) films have been deposited by reactive DC planar magnetron sputtering at a low substrate temperature of 80°C. An Al disk and either N2 or NH3 were used as a target and an ambient gas, respectively. In films deposited in N2, the c-axis of AlN crystallites was perpendicular to the film plane. On the other hand, in NH3, X-ray diffraction peaks from (100), (110) and (200) were observed. The surface and the cross-sectional microstructures of AlN films deposited in N2 were significantly different from that deposited in NH3. The surface of films deposited in NH3 was smoother than that deposited in N2. The transmittivity of films deposited in NH3 was superior to that deposited in N2 in wavelength of 275∼450 nm. Resistivities of films deposited in N2 and in NH3 were 1014sim;1015 Ω · cm. Dielectric constants of films deposited in N2, and of that deposited in NH3, were 9.7, and 9, respectively, in a frequency range of 20 kHz to 20 MHz. The structure and the properties of AlN films deposited by this method depended on kind of ambient gas.

Epitaxial Growth and Superconducting Properties of Yba2Cu3O7 Thin Films and Yba2Cu3O7/Dy(Pr)Yba2Cu3O7 Superlattices

AbstractWe have prepared in situ REBa2Cu3O7 (REBCO) (RE= Y, Pr, Dy) thin films and YBC0/Dy(Pr)BC0 superlattices by single target dc planar magnetron sputtering. YBCO/DyBCO superlattices have been realized with modulation wavelength as short as 24Å, i.e., a unit cell of YBCO alternates with a unit cell of DyBCO, on average. The superconducting properties of such superlattices are indistinguishable from those of single layers. Tco's (zero resistance) are between 85 and 89K, and the residual resistivity ratios are between 2.5 and 3. In contrast to these results, when YBCO is layered with PrBCO, which is insulating, a dramatic change in the superconducting properties is observed. We have been able to artificially vary the coupling between single 12Å unit cell of YBCO by interposing insulating planes of PrBCO. As the YBCO layer separation increases, T is reduced and the transition broadens showing evidence of 2‐D superconducting fluctuations.

Characterization of Pb(Zr,Ti)O3 thin films deposited from multielement metal targets

Lead zirconate titanate [Pb(Zr,Ti)O3 or PZT] thin films have been grown by sputtering a multi-element metal target in oxygen using dc planar magnetron sputtering. Growth parameters and annealing conditions have been optimized. The kinetics of reactive sputtering and the implications of sputtering parameters on film composition have been studied. The studies reveal the requirement for operation at low substrate temperatures (200 °C), high sputtering pressures (4–5 Pa), and a large substrate-to-target distance (10 cm) for obtaining good control over composition. The structural and electrical properties of films were found to depend on the compositional ratio of Zr/Ti, similar to that observed in bulk PZT ceramics. Films having a resistivity of 1010 Ω cm and a dielectric constant ε′∼820 at room temperature (300 K) have been achieved. Ferroelectric hysteresis loop measurements indicated a remanent polarization of 30.0 μC/cm2 and coercive field of 25 kV/cm for the rhombohedral phase composition (Zr/Ti=58/42). Piezoelectric activity in the films is reported for the first time, through the fabrication of a surface-acoustic-wave delay line on a poled polycrystalline PZT thin film.

Effect of radio‐frequency‐induced substrate biasing on the microstructure of palladium films

Palladium films were deposited by dc planar magnetron sputtering while biasing the film substrate. The pseudodielectric function of the films was measured by spectroscopic ellipsometry in the spectral range 1.5–6.0 eV. The films were best described by the two‐dimensionally isotropic Sen, Scala, and Cohen effective medium theory. With increasing rf‐induced substrate biasing the Pd film microstructure was modified in a manner similar to that obtained by varying the film–substrate temperature alone.

The effects of oxygen contamination on the properties of reactively sputtered indium nitride films

Thin films of InN, a direct band gap semiconductor, were deposited by dc planar magnetron sputtering of an indium target in a pure nitrogen atmosphere. Rutherford backscattering analysis of the film stoichiometry showed oxygen contamination of at least 11 at. % throughout the film thickness. In spite of this bulk contamination, the crystal structure showed no evidence of In2O3 or of an indium oxynitride. The band gap also was indicative of InN (1.89 eV), not In2O3 (3.6 eV). We propose that the oxygen forms an amorphous indium oxynitride that exists in an InN polycrystalline matrix, and that this amorphous oxynitride decreases the electron mobility of the films.

Columnar Structure in Continuously Sputtered Co-Cr Films

Co-Cr films were continuously formed on a substrate film in motion by DC planar magnetron sputtering, and the effect on the columnar microstructure of films was investigated. Columnar grains were bow-shaped owing to the change in angle of incidence ? of sputtered particles, in contrast with films formed on a stationary substrate; but the extent of change in ? had little effect. These results can be approximated using a vector sum representing sputtering from two line sources.

A spectroellipsometric investigation of the effect of argon partial pressure on sputtered palladium films

The microstructure of palladium thin films prepared by dc planar magnetron sputtering at low deposition temperatures was investigated as a function of the argon partial pressure. The films were characterized by spectroellipsometry, electron microscopy, and x-ray diffraction. Below a transition pressure Pt≂15 mTorr, the films consisted of densely packed grains, corresponding to the zone T region in Thornton’s structure zone model. Above this transition pressure the films developed into a more voided columnar structure, characteristic of a zone 1 region. A microstructural analysis of the spectroellipsometric data indicated a general trend to increased porosity and microroughness of the films with higher argon pressures. Furthermore, the effective medium theory of Sen, Scala, and Cohen (SSC), relevant for a random coated-particle microstructure where the grains are optically isolated from each other, was required to describe the films prepared with argon pressures above Pt. The zone 1 region was therefore best described optically as a random coated-particle microstructure where the microroughness and porosity varied with the argon pressure. Spectroellipsometry, which is sensitive to the film microstructure, was able to identify the zone T/zone 1 transition through the changes in the pseudodielectric function of the Pd films. Electron microscopy confirmed that for the thin films prepared at argon pressures higher than Pt, the grains became isolated by void boundaries, thus further supporting the random coated-particle basis of the SSC theory.

NbN film deposition using optical emission spectroscopy

NbN films were deposited on unheated Si substrates by dc and rf reactive planar magnetron sputtering of Nb in an Ar and N 2 gas mixture. The optical emission spectrum of the plasma was recorded for different sputtering conditions and the target sputtering rate was found to be proportional to the intensity of any Nb emission line. A model for the reactive sputtering mechanism was developed and the optimum sputtering parameters were selected by observing the change in the Nb emission line intensity as a function of the partial pressure of nitrogen. The critical temperatures of the films were in the 13 to 15.8 K range.

C-axis orientation of Co-Cr thin films by facing targets sputtering

Sputtered Co-Cr thin films have been extensively investigated as one of the most promising media for the perpendicular magnetic recording. In this study, the dependence of the c-axis dispersion ΔΘ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> on the film thickness δ has been investigated using the Facing Targets Sputtering (FTS) apparatus and the conventional DC planar magnetron sputtering (DCM) one. The films deposited by DCM exhibited a considerable dependence of ΔΘ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> on δ below 4,000 Å. This was mainly attributed to the bombardment of γ-electrons ejected from the central area of the target where the magnetic field is not so strong as to confine them. However, the films deposited by FTS did not show the significant dependence of ΔΘ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> on δ and it was less than 5 degrees even at δ as thin as 200 Å. This result indicates that the FTS system developed by the authors may be very suitable to prepare Co-Cr thin films for high density perpendicular magnetic recording media.

High rate sputtering deposition of nickel using dc magnetron mode

High rate sputtering of nickel using dc planar magnetron was successfully developed in East Fishkill for high throughput requirement. Rates in excess of 10 kA/min from targets up to 3/8 in. thick were achieved. Magnetic field strength was found to be the key parameter in depositing nickel at high rates, which has not been very successful in the coating industry. A minimal or sufficient magnetic field strength (mfs) about 300 G at Ni target surface is crucial in forming a stable plasma in dc magnetron sputtering. This minimal mfs can be generated with a strong magnet in the cathode assembly. Upon reaching this mfs, the I–V characteristics in Ni sputtering process follow the normal I=KVn relationship of dc planar magnetron sputtering. Nickel target thickness ranging from 1/8 to 3/8 in. with magnetic field strength ranging from 300 to 800 G were investigated in developing this process. The process can only be controlled well with a fine mfs adjustment. The sputtering equipment for magnetic material deposition must contain an adjustment mechanism in its cathode design in order to control mfs. Nickel film quality also seems to be affected by mfs due to the electron heating of the substrate and low angle incident atoms. A desired quality film of magnetic material such as Ni can be achieved with an optimal sputtering process that has a constant magnetic field strength at the target surface.

Crystalographic Orientation of Continuously Sputtered Co-Cr Films

The dependence of film crystal orientation on film thickness for several Co-Cr films formed by dc planar magnetron sputtering with a variety of deposition mask arrangements was investigated. Special attention was paid to the initial layer. The dependence of magnetic properties on film thickness was found to be strongly influenced by the mask arrangement, especially by the distance between the mask edge and the roll, and by the initial incidence angle for the sputtered atoms. It was found that controlling these parameters properly is extremely important in continuous sputtering.

Influence of Energetic Oxygen Bombardment on Conductive ZnO Films

Conductive ZnO films were prepared by DC planar magnetron sputtering and DC diode sputtering, and the reason for the high resistivity shown by the films at the substrate positions facing the eroded area of the target was investigated. It was found that bombardment of the film by energetic O atoms or O- ions is responsible for the high film resistivity, since this results in a decrease in both the carrier mobility and the carrier concentration. The arrival of excess O atoms and O- ions with relatively lower energies also induces an increase in the film resistivity as a result of a decrease in carrier concentration. The positional dependence of the film resistivity is explained by considering the above two factors.

Fourfold to threefold transition in diamondlike amorphous carbon films: A study of optical and electrical properties

Hard, diamond-like amorphous carbon films (a-C) were prepared as a function of sputtering power density by employing dc planar magnetron sputtering of a graphite target in pure argon. Films deposited at 300 K and at increasing sputtering power density in the range 0.25–25 W cm−2 show a transition of optical and electrical properties, with the room temperature electrical conductivity increasing from 5×10−4 to 5 Ω−1 cm−1 and the optical gap decreasing from 0.74 to 0.40 eV. The imaginary part ε2 of the complex dielectric function is determined in the photon energy range 0.5–7 eV and shows a clear dependence on sputtering power density. The ε2 spectra for a a-C films possess features typical of amorphous semiconductors. neff, the effective number of valence electrons per carbon atom taking part in optical transitions, is determined via a sum rule operation on ε2. Comparisons of neff for each a-C film with that for crystalline graphite allow the average coordination of the carbon atom to be determined. We observe a systematic four-fold to three-fold transition, with the ratio of carbon atoms having four-fold sp3 configuration (diamond-like) to carbon atoms with three-fold sp2 configuration (graphite) varying from 3:1 to 1:1.

Stoichiometry control mechanisms for bias-sputtered zinc-oxide thin films

We have deposited transparent, conducting ZnO thin films of resistivity 3 × 10−3 Ω∙cm by the technique of DC planar-magnetron sputtering in a reactive Ar–O2 atmosphere, incorporating a reactive gas baffle and substrate RF discharge. The substrate discharge was found to increase the oxygen content of the growing film. Films at low values of the RF-induced substrate self-bias voltage were characterized by a brown colour, resistivities of about 4 × 10−2 Ω∙cm, and composition ZnO0.8. Films at higher bias voltages of −80 V were clear with resistivities of 3 × 10−3 Ω∙cm and a composition approaching stoichiometric ZnO. The oxidation of the films by the RF discharge was shown to occur through preferential resputtering and re-evaporation of excess zinc and by activation and ion-plating of oxygen species. Resputtering and re-evaporation rates were found to be enhanced above that expected for bulk Zn, owing to the loosely bound nature of surface adatoms during film growth.

Energy Distribution of Energetic Oxygen Atoms in the Sputtering of ZnO

Energetic neutral oxygen atoms bombarding the substrate in DC diode sputtering and DC planar magnetron sputtering were detected by a time-of-flight apparatus. In analyzing the time-of-flight spectrum, the energy distribution of the energetic oxygen atoms was computed by the fast Fourier transformation (FFT) method. The energy of the oxygen atoms bombarding the substrate was found to be distributed from 300 to eVT electron volts, the maximum energy which negative oxygen ions gain in the cathode fall in DC diode sputtering. The mean energy of the energetic oxygen atoms was estimated to be nearly eVT/2 electron volts. In planar magnetron sputtering, the flux of the energetic oxygen atoms showed a nearly monochromatic energy distribution.

High-Energy Oxygen Atoms in ZnO Film Preparation by Reactive Sputtering of Zn

Using Zn metal disk target, ZnO films were prepared in Ar+O2 mixed gas by both DC planar magnetron sputtering and RF diode sputtering. The dependence of c-axis orientation of ZnO film on O2 partial pressure was examined from the view point of the bombardment of film by energetic oxygen atoms. For DC planar magnetron sputtering, the c-axis orientation of film does not depend on the O2 partial pressure, but for RF diode sputtering, the c-axis orientation becomes high at r=10–20%, where r is the percent ratio of O2 partial pressure to total pressure. It is found that there exists a correlation between the dependence of c-axis orientation on O2 partial pressure and the film bombardment by energetic O atoms.