Reactive Mid-frequency Magnetron Sputtering Research Articles

Control of optical properties of TiN_xO_y films and application for high performance solar selective absorbing coatings

TiNxOy films with controllable optical properties have been fabricated by reactive mid-frequency magnetron sputtering from titanium nitride target. The optical and electrical properties were studied as a function of the reactive gas flow and were correlated with the film stoichiometry. The results showed that the behavior of TiNxOy films can be adjusted from metallic to dielectric by increasing oxygen content, which is of great significance to their extensive applications. Owing to the accurate control of optical properties, a TiNxOy based solar selective absorbing coating has been designed and prepared with the aid of TiO2/Si3N4/SiO2 antireflection layers. Its solar absorbance is as high as 97.5% and thermal emissivity is 4.3% with total thickness of 230 nm. The solar absorbance can maintain above 90% for a broad incident angle range from 0° to 65°.

Influence of oxygen partial pressure on the growth of Al-doped zinc oxide films by reactive MF magnetron sputtering

Abstract Aluminum-doped zinc oxide thin films have been fabricated by reactive mid-frequency magnetron sputtering from Zn/Al metallic targets (Al 2 wt.%) with a dual magnetron (TwinMag™) configuration. The dependence of the structure, composition, electrical and optical properties of the films on the oxygen partial pressure has been investigated. It is shown that films with low resistivity and high optical transmittance could only be deposited under a narrow range of oxygen partial pressure. The film prepared at a partial pressure of 25 mPa exhibited highly c-axis oriented growth and a lowest resistivity of 4.6 · 10−4 Ω cm.

ZnO:Al Films Prepared by Reactive Mid-frequency Magnetron Sputtering with Rotating Cathode

Al-doped zinc oxide (ZnO:Al, AZO) films were deposited on glass substrates using a reactive mid-frequency (MF) magnetron sputtering process with rotating cathodes. The influence of deposition parameters on structural, electrical and optical properties of AZO films is investigated. It is observed that the rotating magnetron targets exhibited a sputtered metallic surface over a wider range, and there is no re-deposition zone between the racetracks. The films deposited at static deposition mode demonstrate more homogenous in thickness and resistivity across the target surface compared with conventional rectangular targets. The films deposited under the proper conditions show a regular cone-shaped grain surface and densely packed columnar structure. The minimum resistivity of 3.16 × 10 −4 Ω·cm was obtained for the film prepared at substrate temperature of 150°C, gas pressure of 640 MPa and oxygen partial pressure of 34 MPa.

Microstructure evolution of Al-doped zinc oxide films prepared by in-line reactive mid-frequency magnetron sputtering

Aluminium-doped zinc oxide (ZnO:Al or AZO) thin films were deposited on glass substrates by reactive mid-frequency (MF) magnetron sputtering from Zn/Al metallic targets. Strong (002) preferred orientation was detected by X-ray diffraction (XRD). It was observed by plan-view transmission electron microscopy (TEM) that an AZO film deposited at low substrate temperature was composed of irregular large grains; but the film prepared at high temperature was composed of moderate sized grains with a regular shape. A secondary phase of ZnO2 was also observed for the film deposited at low substrate temperature. The cross-sectional TEM study of the AZO film showed that prior to the well-aligned columnar growth an initial interfacial zone with nano crystallites were formed. The nano crystallites formed initially with a large tilt angle normal to the substrate surface and during the growth of the transition zone, the tilt angle decreased until it vanished. The evolution of the film structure is discussed in terms of evolutionary selection model and the dynamic deposition process.

Material study on reactively sputtered zinc oxide for thin film silicon solar cells

Aluminum doped zinc oxide (ZnO:Al, AZO) films were prepared by reactive mid frequency magnetron sputtering. We characterized the electrical and optical properties as well as the surface morphology obtained after wet chemical etching. The carrier mobility could be increased up to 42 cm 2/Vs and the transmission between 400 and 1100 nm was enhanced by the reduction of aluminum content in the targets. The working point of the reactive sputtering process strongly influences the etching behavior and was used to optimize the light scattering properties of the ZnO:Al films after wet chemical etching. Finally, the texture-etched ZnO:Al films were successfully applied as substrates for silicon thin film solar cells.

Spectrally selective reflecting thin-film filters for laser display technology

To provide a contrast improvement for projection screens used with the laser display technology, a thin selective reflecting filter was designed. To overcome the problem of unknown starting designs and permit a new evaluation technique, an evolutionary algorithm was implemented. Due to the lack of known target spectra rather than known features of the target spectra, a novel evaluation procedure using color metrics was implemented. Different selective reflecting filters were deposited on glass as well as on plastic substrates by reactive mid-frequency magnetron sputtering. In-situ ellipsometry was used for process control and in-situ re-design of the filter.

Comparison of the ZnO:Al films deposited in static and dynamic modes by reactive mid-frequency magnetron sputtering

Al-doped zinc oxide (ZnO:Al or AZO) films were deposited on glass substrates by sputtering Zn–Al metallic targets (Al 2 wt%) with an in-line reactive MF magnetron sputtering in both static and dynamic deposition modes. The lateral distribution of the crystalline structure, composition, electrical and optical properties of the films prepared in a static mode were investigated. The films obtained at a central region show cone-shaped grain surface and columnar structure with a lateral grain size of 40–80 nm. In contrast, the film structure obtained at a side region is porous with a grain size of around 30–50 nm. As a result of this lateral structure variation, the carrier concentrations of the film decreased from the target centre to the edge and, inversely, the sheet resistance increased. No significant effect of the erosion craters of the targets on the structure and properties of the film are observed. The lateral inhomogeneity of the properties can be improved by increasing the working gas pressure. The structural, electrical and optical properties for the film deposited in a dynamic mode were comparable with those of the films obtained at central region in the static mode. The conduction mechanism of carrier transport in AZO films is discussed.

Studies on ZnO:Al thin films deposited by in-line reactive mid-frequency magnetron sputtering

Al-doped ZnO (ZnO:Al or AZO) films were deposited on glass substrates using an in-line reactive mid-frequency (MF) magnetron sputtering process. The influence of the deposition parameters including oxygen partial pressure and substrate temperature on the surface morphology and electrical, optical and mechanical properties of the films were investigated. The film hardness as determined by a nano-indenter indicate that the crystallinity of the ZnO:Al films was improved with increasing substrate temperature. The films with minimum resistivity could only be deposited under a narrow range of oxygen partial pressure. The carrier concentration, Hall mobility and optical band gap of the ZnO:Al films increased when the substrate temperature was raised from room temperature to 150 °C, and then decreased when the temperature was higher than 150 °C. The film prepared at the substrate temperature of 150 °C exhibited columnar structure with a RMS roughness of 4.4 nm and a lowest resistivity of 4.6×10 −4 Ω cm. The transmittance and reflectance spectra with the ellipsometric data were analyzed by using a Drude–Lorentz–Gauss model.

Growth behaviours and properties of the ZnO:Al films prepared by reactive mid-frequency magnetron sputtering

Al-doped zinc oxide (ZnO:Al) films were prepared on float glass substrates by in-line reactive mid-frequency (MF) magnetron sputtering from a Zn–Al metallic target (Al 2 wt%). The influences of working gas pressure and substrate temperature on the crystallization behaviours as well as on the electrical and optical properties of the films were investigated. The films prepared at substrate temperature from 100°C to 200°C exhibit columnar structure, having high carrier concentration, high Hall mobility and good conductivity. The crystallinity of the films was improved and the columnar film growth became more dominant as the working gas pressure increased. The grains of the film prepared at a working gas pressure of 970 mPa and a substrate temperature of 170°C are facetted on the film surface and the grain columns are grown through the entire film. Optical transmittance up to 87% in the visible range and electrical resistivity as low as 2.86×10 −4 Ω cm were obtained under these optimal deposition conditions.

Design and manufacture of spectrally selective reflecting coatings for the use with laser display projection screens.

To provide screens for laser projection that improve contrast, a spectrally selective reflecting filter was designed by using genetic algorithms to overcome the problem of unknown starting values. Colormetrics rather than fixed targets were used for evaluation. Various selective filters were deposited upon glass as well as upon solid and flexible plastic substrates by reactive mid-frequency magnetron sputtering. For process control, in situ spectroscopic ellipsometry was applied.

Uniformity in large area ZnO:Al films prepared by reactive midfrequency magnetron sputtering

Al-doped zinc oxide (ZnO:Al) films were deposited on glass substrates using a reactive midfrequency magnetron sputtering process. The optical transmission and reflection as well as the electrical resistivity of the films prepared on an area of 1000×600 mm2 were determined at different locations. Films with a uniform distribution of resistivity between 2.9×10−4 and 3.6×10−4 Ω cm and transmittance up to 88% in the visible spectral range were obtained. The ellipsometric spectra of the films were also analyzed using the Drude–Lorentz model. The calculated thicknesses of the films agreed well with those measured by a step profilometer. Secondary neutral mass spectrometry depth profiling showed uniform contents of Zn and O elements, while a slight periodic variation of the Al content was observed at different depths inside the film. A transition zone of 35–55 nm in width between the films and glass substrates due to the interdiffusion was also observed.