Low-temperature Reactive Sputtering Research Articles

Reducing the incorporation of contaminant oxygen in decorative TiN coatings deposited by low temperature reactive sputtering

This paper focuses on the low-temperature deposition and characterization of titanium nitride coatings. It investigates how the deposition conditions influence the incorporation of contaminant oxygen and the functional properties of the coatings. The coatings were reactively sputtered in an Ar + N2 atmosphere under two different substrate conditions: floating and bias modes. The target poisoning process was studied by selecting different N2 flow rates. The Ti/N ratio and the contaminant concentration varied greatly with the N2 flow rate and substrate bias condition. Both the Ti/N ratio and oxygen inclusion produced important modifications in the structural, chemical, optical and electrical properties of the TiN coatings. Samples deposited in floating mode showed oxygen contents up to 25 at.%, and TiN crystals that were preferentially oriented along the [111] and [110] directions. These coatings exhibited dark brownish colorations. Samples deposited in bias mode showed reduced oxygen contents between 6 and 12 at. % and promoted the crystallization of TiN with the [110] preferential orientation. These coatings presented bright yellowish colorations. By sputter depositing TiN coatings at low substrate temperatures, under appropriate deposition conditions, the desired decorative properties can be achieved while preserving the integrity of sensitive substrates, such as polymers.

Realization of low specific-contact-resistance on N-polar GaN surfaces using heavily-Ge-doped n-type GaN films deposited by low-temperature reactive sputtering technique

We developed a low-temperature ohmic contact formation process for N-polar GaN surfaces. Specific-contact-resistances of 9.4 × 10−5 and 2.0 × 10−5 Ω cm2 were obtained using Ti/Al metal stacks on heavily-germanium-doped GaN films, which were deposited at 500 °C and 600 °C using a radical-assisted reactive sputtering method, respectively. The electrode sintering temperature was as low as 475 °C. Carrier concentrations for the 500 °C and 600 °C samples were 2.6 × 1020 and 1.8 × 1020 cm−3, respectively. These results suggest that this method is highly effective in reducing the contact resistance of GaN devices with low thermal budgets.

Kelvin force microscopy studies of work function of transparent conducting ZnO:Al electrodes synthesized under varying oxygen pressures

The ability to controllably tune the work function of transparent conductors is essential for optimizing the efficiency of thin film solar photovoltaics. Here we use Kelvin force microscopy on lithographically patterned ZnO:Al thin films to measure the dependence of the work function on oxygen content during synthesis. Films were synthesized by low temperature reactive sputtering from a Zn:Al 1.2 wt% target. At optimal oxygen content the resistivity is 3×10 −4 Ω cm with nearly 90% optical transmission in the 400–1100 nm wavelength range relevant to solar photovoltaics. We find that the expected relationship between band filling and work function breaks down in the vicinity of optimal oxygen stoichiometry. For oxygen-rich ZnO:Al films we measure large work functions close to 5 eV. Our results suggest a method for fabricating transparent oxide electron conductors with large, tunable work functions that could be of relevance in designing electrodes for solid state energy conversion technologies.

AlN-based sputter-deposited shear mode thin film bulk acoustic resonator (FBAR) for biosensor applications — A review

A new type of biosensor device is here presented which is fabricated using the same processes used for the fabrication of integrated electrical circuits to enable tighter integration and further sensor/biosensor miniaturization. The device is a so-called thin film bulk acoustic resonator (FBAR) operating in shear mode. Here specifically AlN-based shear mode FBAR is addressed but also an overview of the shear mode FBAR development in general is presented. Developments are reported of a low temperature reactive sputtering process for growing wurtzite–AlN thin films with a close to homogenous c-axis inclination over a 4″ substrate wafer. This process enabled fabrication of shear mode FBAR sensors. The sensor operation is described along with how the design parameters influence its performance. Specifically, sensitivity amplification utilizing low acoustic impedance layers in the FBAR structure is demonstrated and explained. The resolution of the AlN shear mode FBAR sensor is demonstrated to already be comparable with the conventional quartz crystal microbalance (QCM) sensor, suggesting that shear mode FBAR may be a competitive and low cost alternative to QCM.

Tantalum nitride thin film resistors by low temperature reactive sputtering for plastic electronics

AbstractThis article describes the fabrication and characterisation of tantalum nitride (TaN) thin film for applications in plastic electronics. Thin films of comparable thickness (50–60 nm) have been deposited by RF‐magnetron‐reactive sputtering at low temperature (100 °C) and their structure and physical (electrical and mechanical) properties have been correlated by using sheet resistance, stress measurements, atomic force microscopy (AFM), XPS, and SIMS. Different film compositions have been obtained by varying the argon to nitrogen flow ratio in the sputtering chamber. XPS showed that 5:1, 2:1 and 1:1 Ar:N2 ratios gives Ta2 N, TaN and Ta3N5 phases, respectively. Sheet resistance revealed an increase in resistivity ongoing from the Ta2N phase to the Ta3N5 one. The electrical properties of these films are comparable to those obtained by high temperature deposition process already reported in literature. Furthermore, a roughness and grain size modulation of the above films can be obtained by applying an RF negative bias during deposition without affecting the electrical resistivity. Copyright © 2008 John Wiley & Sons, Ltd.

Microscopic investigations of aluminum nitride thin films grown by low-temperature reactive sputtering

Aluminum nitride (AlN) films were grown on sapphire substrates by radio frequency magnetron sputtering in plasma containing a mixture of argon and nitrogen, using a pure aluminum target. Surface morphology dependence of the AlN films on growth conditions such as substrate temperature and nitrogen concentration was investigated. c-axis preferred wurtzite AlN film with surface roughness as small as 2.9 nm was obtained at substrate temperature of 100 °C and nitrogen concentration of 20%. The surface roughness of the AlN films increased with increasing substrate temperature and nitrogen concentration. The correlation between the growth conditions and the film morphology was discussed.

Growth of [111]-Oriented Lead Zirconate Titanate Thin Film with Smooth Surface to Improve Electrical Properties

[111]-Oriented lead zirconate titanate (PZT) films with smooth surfaces were successfully grown on (111)-oriented polycrystalline Pt substrates after in-situ Ar-plasma cleaning by low-temperature reactive sputtering and rapid thermal annealing. The Pb composition was stoichiometrically controlled not only for total composition but also in the depth direction by low-temperature reactive sputtering. A (111)-oriented perovskite-phase PZT film with a very smooth surface was then obtained by rapid thermal annealing. The leakage current of quasi-epitaxial PZT films was markedly reduced to 10-7 A/cm2 and the equivalent SiO2 layer thickness of around 0.4 nm was obtained for the fatigue-free PZT films thinner than 100 nm.

Preparation of aluminum nitride thin films by reactive sputtering and their applications to GHz-band surface acoustic wave devices

Single crystal aluminum nitride (AlN) thin films were prepared by a low-temperature reactive sputtering on basal plane sapphire [(001)Al2O3] at a substrate temperature of less than 315 °C. Surface acoustic wave (SAW) characteristics with an interdigital transducer /(001)AlN/(001)Al2O3 structure were investigated. The phase velocity and temperature coefficient of delay time are 5750–5765 m/s and 55–63 ppm/°C at KH=1.2–1.6, respectively. Resonator-type 1-GHz-band SAW filters with its structure were fabricated. The insertion loss and suppression were 23 dB and more than 20 dB, respectively.

Preparation of c-Axis Oriented AlN Thin Films by Low-Temperature Reactive Sputtering

C-axis oriented aluminum nitride (AlN) thin films on (110) silicon were prepared by reactive RF magnetron sputtering in argon and nitrogen atmosphere without substrate heating. We investigated the dependence of some properties for the AlN thin film on sputtering conditions, especially N2 concentration. It was found that c-axis orientation tended to improve gradually with decreasing N2 concentration. The full width of half the maximum intensity (FWHM) of the rocking curve for a (002) plane of hexagonal AlN was 1∼2 degrees at a 10% N2 concentration. This was a suitable value for surface acoustic wave (SAW) device. IDT/AlN/(110)Si structure SAW resonators were fabricated. It was confirmed that the insertion loss was 14 dB and phase velocity was 4800 m/s, respectively.

Fabrication of Encapsulated Indium Films for Melting Experiments

ABSTRACTWe describe the fabrication of submicron, multiprobe thin indium film conductors for electrical measurments above their melting transition. Problems unique to handling liquid films were overcome by using tri-level Si3N4/In/W structures. Tungsten (W) leads made good electrical contact to, yet did not alloy With the liquid indium (In). A silicon-nitride (Si3N4 ) encapsulating layer deposited over the In/W devices prevented the indium from forming islands when liquid. Indium wires were fabricated using e-beam lithography and liftoff. Low temperature reactive sputtering technique was used to deposit the Si3N4 without melting the indium. The technique could be easily adapted to use with other low melting point materials.