DC Magnetron Sputtering Deposition Research Articles

In-situ optimization of lateral film uniformity in PVD system by using Fiber Bragg grating temperature sensors

Fiber Bragg grating (FBG) based temperature sensing method has been employed in this work for measuring the lateral temperature distribution on substrate plane during pulse DC magnetron sputtering deposition for optimization of lateral film uniformity. The evolution of temperature distribution with the variation of important process parameters like pulse width (496–1616 ns), deposition pressure (3.1 × 10−3–1.9 × 10–2 mbar) and sputtering power (25–250 W) have been measured over 40 mm radial distance on glass substrate horizon. To investigate the effect of substrate height on the temperature distribution, the later has been measured at two different substrate heights (60 mm and 90 mm) for varying sputtering power. Finally, the effect of variation in temperature distribution on uniformity of thickness and optical, morphological and structural properties have been investigated by separately depositing two HfO2 thin films at two representative extreme deposition powers (75 W and 200 W). The correlation of film non-uniformity of the above properties with the temperature distribution suggests that FBG based multipoint temperature sensing can be possibly used as an indicative tool for in situ optimization of the lateral film uniformity. In addition, the fast response and workability in plasma environment of FBG sensors enables precise in situ mapping of temperature distribution in sputtering process.

Effect of Substrate Negative Bias on the Microstructural, Optical, Mechanical, and Laser Damage Resistance Properties of HfO2 Thin Films Grown by DC Reactive Magnetron Sputtering.

Hafnium oxide thin films have attracted great attention as promising materials for applications in the field of optical thin films and microelectronic devices. In this paper, hafnium oxide thin films were prepared via DC magnetron sputtering deposition on a quartz substrate. The influence of various negative biases on the structure, morphology, and mechanical and optical properties of the obtained films were also evaluated. XRD results indicated that (1¯11)-oriented thin films with a monoclinic phase could be obtained under the non-bias applied conditions. Increasing the negative bias could refine the grain size and inhibit the grain preferred orientation of the thin films. Moreover, the surface quality and mechanical and optical properties of the films could be improved significantly along with the increase in the negative bias and then deteriorated as the negative bias voltage arrived at -50 V. It is evident that the negative bias is an effective modulation means to modify the microstructural, mechanical, and optical properties of the films.

Studies on the Platinum Thick Film Sensor Conformally Written by Laser Micro-Cladding: Formability, Microstructure, and Performance

In this paper, laser micro-cladding technology (LMC) was conducted to prepare high-temperature Pt thick film sensors in situ. The formability, microstructure, sintering mechanism, and electrical properties of the LMCed Pt thick films were first studied systematically. Results indicated that with the increase of laser power density, the sintering degree of the Pt thick film increased obviously, improving its adhesion strength and reducing its resistivity. However, when the laser power density exceeded the threshold, holes or grooves were formed in the Pt film, leading to the degeneration of its properties. A Pt thick film with good adhesion strength, excellent conductive networks, and the minimum resistivity (46 ± 2 μΩ·cm) was obtained at a laser power density of 1.37 × 106 W·cm-2. Then, Pt thick film temperature sensors (including Pt thermal resistance temperature (RTD) and Pt-Pt10%Rh thermocouple sensors) were conformally prepared by LMC. Their temperature-sensing performance became stable after the initial high-temperature calibration, with a linearity of 0.9985 for the RTD with a TCR of 2.46 × 10-3/°C (at 920 °C) and a linearity of 0.9905 for the thermocouple with a Seebeck coefficient of 9.7 μV/°C, both of which are better than that made by direct DC magnetron sputtering deposition. Therefore, this work provides a novel feasible way to conformally integrate high-performance Pt film sensors in situ.

Synthesis of Al Thin Films with High Optical Transmittance by DC Magnetron Sputtering Process Parameter Optimization

Nanostructured Al thin film with higher optical transmittance and electrical conductivity has intensive applications in solar cells and optical and microelectronic devices. This experimental-based research study has optimized the DC magnetron sputtering deposition parameters (sputtering power, sputtering current, voltage, and working gas pressure) for Al thin film deposition to obtain the highest optical transmittance and lower sheet resistance. Optical transmittance, surface roughness, film thickness, sheet resistance, grain size, and surface morphology were characterized using UV-vis-NIR spectroscopy, surface profiler, spectroscopic ellipsometry, four-point probe, and FE-SEM, respectively to determine the effects of sputtering process parameters on Al films’ different properties. Experimental investigations reveal that electrical conductivity, surface roughness, grain size, and deposition rate increase with increasing of sputtering power at certain working gas pressure. At the optimized condition (sputtering power 80 W, working gas pressure 5 mTorr, deposition time 5 min and ambient temperature), the relatively higher optical transmittance in visible region 96%, moderate sheet resistance 0.196 ohm/square and lowest average surface roughness 2.86 nm were obtained for Al thin film. After all, this research study will help to understand the best Al film deposition parameters in terms of optical transmittance and electrical conductivity for future research and industrial applications.

Suppression of substrate temperature in DC magnetron sputtering deposition by magnetic mirror-type magnetron cathode

Magnetron sputtering generally increases the temperature of the substrate placed to face the sputtering target above 40 °C because the plasmas are transported through unbalanced magnetic field lines from the sputtering target to the substrate surface. However, by using a magnetic mirror-type magnetron cathode, we were able to suppress the temperature of the substrate temperature to the environmental temperature of less than 40 °C at a target–substrate distance of ≥50 mm with a DC input power of ≤30 W and an Ar gas pressure of ≤0.15 Pa. This was possible because the balanced magnetic field lines confined the plasmas near the sputtering target. By enabling film deposition on low heat-resistant substrates, this deposition technique for suppressing the substrate temperature may have uses in various application fields.

Huge giant-magnetoresistance of Co/Ru/L11-CoPt multi-layer pseudo-spin valve

Co/Ru/L11-CoPt based thin film as pseudo spin valve prepared by DC magnetron sputtering deposition. The magnetic and magnetoresistance properties with the thickness change of L11-CoPt layer were investigated. The resulting spin valve exhibited well-different out-of-plane and in-plane hysteresis loops. The coercivities changed unpredictably at different thicknesses of L11-CoPt layer. A perpendicular giant magnetoresistance ratio is obtained about 59.70 % and 160 % with current-out-of-plane measurements for the pattern and cross-linking structures of Pt(20 nm)/Co(2.5 nm)/Ru(1.5 nm)/[L11-CoPt]8/Pt(20 nm)/glass substrate, respectively. It was ascribed this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Co free layer and L11-CoPt reference layer through Ru spacer layer, and considered as the ferromagnetic interlayer exchange coupling.

MEMS-based resistive hydrogen sensor with high performance using a palladium-gold alloy thin film

Hydrogen sensors have been widely used in several fields for monitoring the concentration of hydrogen and for its alarming leakage. In this study, a microelectromechanical systems (MEMS)-based resistive hydrogen sensor using a palladium-gold (Pd-Au) alloy thin film was developed, which has the advantages of low power consumption, mass production, and high performance. A sensitive alloy film was prepared by DC magnetron sputtering deposition and annealed at various temperatures. It was integrated on a patterned silicon substrate with heating and temperature detection resistances and fabricated by MEMS processes. This film exhibited the best response performance to hydrogen at annealing and working temperatures of 200 and 60 °C, respectively. The sensor exhibited a good response to hydrogen from 5 ppm to 3%. The response attained a value of 3.3%, and the response and recovery times were 22 and 160 s, respectively, for a hydrogen concentration of 3%. The sensor also indicated good repeatability, long-term stability, and high selectivity for hydrogen over other gases (sulfur dioxide, ethanol, methane, ammonia, carbon monoxide, nitrogen dioxide, and formaldehyde). Thus, it has good potential for the detection of hydrogen leakage in new energy vehicles.

Effect of processing conditions on residual stress in sputtered transition metal nitrides (TiN, ZrN and TaN): Experiments and modeling

Stress evolution during reactive DC magnetron sputtering deposition in TiN, ZrN and TaN films at different growth rates, pressures and relative gas flow rates was measured by a wafer curvature technique. The results indicate that, for a given growth rate, the stress in each material is tensile at higher pressures and becomes more compressive with lower pressures. At lower pressures, the stress tends to become more compressive with increasing growth rate. Increasing the gas flow rate of N2 relative to Ar is observed to enhance compressive stress generation in TaN but has a weaker effect on TiN and ZrN. At lower pressure, the compressive stress magnitude scales with TiN < ZrN < TaN. The stress at different processing conditions was analyzed in terms of a kinetic model that includes the effects of growth kinetics and energetic bombardment. The resulting parameters are compared with calculations from binary collision Monte-Carlo simulation codes.

Pulse frequency effect on the NiTi plasmas characteristics and thin film properties and fabrication of NiTi micro-comb structures

Nickel-titanium (NiTi) is a thermal shape memory alloy (SMA) widely used in the actuator domain in miniaturized systems. With a titanium nitride (TiN) capping layer, NiTi exhibits better mechanical properties and enhances biocompatibility in biomedical applications. In addition, TiN can be efficiently heated to a higher temperature than induce the phase transformation in NiTi MEMS structures. This could be easily achieved by fabricating a TiN heater pattern over or alongside the NiTi MEMS structures. The subject of this work is the NiTi thin films deposited utilizing the pulsed DC magnetron sputter (PDCMS) deposition process at various pulse frequencies (50–350 kHz). The TiN capping layer was also grown on the Si/NiTi stack by the same process. The NiTi micro-comb and TiN micro-heater MEMS structures were fabricated using bulk laser micromachining. Freestanding MEMS structures of NiTi and TiN thin films were realized by etching the bottom silicon with an etch rate of 600 nm/Sec using chemical wet etch by tetramethylammonium hydroxide TMAH.

Sputter Deposited Magnetostrictive Layers for SAW Magnetic Field Sensors.

For the best possible limit of detection of any thin film-based magnetic field sensor, the functional magnetic film properties are an essential parameter. For sensors based on magnetostrictive layers, the chemical composition, morphology and intrinsic stresses of the layer have to be controlled during film deposition to further control magnetic influences such as crystallographic effects, pinning effects and stress anisotropies. For the application in magnetic surface acoustic wave sensors, the magnetostrictive layers are deposited on rotated piezoelectric single crystal substrates. The thermomechanical properties of quartz can lead to undesirable layer stresses and associated magnetic anisotropies if the temperature increases during deposition. With this in mind, we compare amorphous, magnetostrictive FeCoSiB films prepared by RF and DC magnetron sputter deposition. The chemical, structural and magnetic properties determined by elastic recoil detection, X-ray diffraction, and magneto-optical magnetometry and magnetic domain analysis are correlated with the resulting surface acoustic wave sensor properties such as phase noise level and limit of detection. To confirm the material properties, SAW sensors with magnetostrictive layers deposited with RF and DC deposition have been prepared and characterized, showing comparable detection limits below 200 pT/Hz1/2 at 10 Hz. The main benefit of the DC deposition is achieving higher deposition rates while maintaining similar low substrate temperatures.

Development of titanium nitride thin film microheaters using laser micromachining

In this paper, we report the fabrication and characterization of titanium nitride (TiN) thin-film-based microheaters. TiN thin films have been optimized on Si and SiO2 substrates for their optimum electrical resistivities by controlling the process parameters, including argon:nitrogen (Ar:N2) ratio in reactive pulsed DC magnetron sputter (PDCMS) deposition technique. An optical emission spectroscope (OES) was used for monitoring the plasma characteristics at various nitrogen flow rates. The microstructural and surface properties of the TiN films have been investigated and correlated with the electrical properties. It has been observed that the amount of nitrogen flux in the TiN plasma plays an essential role in the microstructural, surface, and electrical properties of the TiN thin films. Micro-heaters have been fabricated with TiN thin films with low electrical resistivity using laser engraving techniques instead of conventional lithographic and micromachining techniques. The TiN microheater has shown excellent performance. A temperature of 406 °C has been achieved by applying an input power of 8 W. This work paves the path for developing scalable and economic TiN microheaters using laser micromachining techniques.

Noble gas control of diamond-like content and compressive stress in carbon films by arc-mixed mode high power impulse magnetron sputtering

Conventional DC magnetron sputter deposition from a carbon target with argon as the sputtering gas is limited by a low deposition rate, and the resultant coatings have low diamond-like sp 3 content. Here we study arc-mixed mode high power impulse magnetron sputtering (HiPIMS) of carbon using He, Ne, Ar, Xe and Kr gases and show an increase in deposition rate is achieved by using noble gases heavier than argon. On the other hand, a higher sp 3 fraction is achieved by using noble gases lighter than argon. The higher deposition rate of the heavier noble gases is attributed to the higher sputtering yield and an earlier arc onset owing to their lower ionization potential . The higher sp 3 fraction achieved by lighter noble gases is attributed to stress generation by knock-on collisions at the surface of the depositing film, in the absence of stress relief created by large thermal spike volumes. When neon was used as the sputtering gas, the inert gas content was higher than for any other noble gas. Our results lead to opportunities for grading the sp 3 content with depth simply by changing the gas composition, allowing fabrication of buried conductive channels in ta-C, Metal-Insulator-Metal (MIM) (low sp 3 /high sp 3 /low sp 3 ) structures and biosensor films (high sp 3 /low sp 3 ). • Arc-mixed mode HiPIMS deposition of carbon films with He, Ne, Ar, Xe, and Kr noble gases. • The highest sp 3 fraction is achieved by He-Ne mixtures, attributed to effective momentum transfer. • The density and compressive stress in the films decrease with increasing size of noble gas atoms. • The results suggest creating buried conduction channels by changing the sputter gas composition.

Amorphous SiSn Alloy: Another Candidate Material for Temperature Sensing Layers in Uncooled Microbolometers

Herein, the prospect of using amorphous Si1–x Sn x alloys as alternative temperature‐sensing active materials in microbolometers is evaluated by studying their temperature‐dependent resistive properties along with their infrared optical properties. Si1–x Sn x thin films (200 nm thick), with varying Sn concentrations, are prepared at room temperature by cosputtering from Si and Sn targets using simultaneous radio frequency and DC magnetron sputter deposition. Low beam energy X‐ray microanalysis is used to estimate the atomic concentrations of the prepared films. Atomic force microscopy analysis shows an increase in the root‐mean‐square surface roughness of the prepared Si1–x Sn x thin films, with increasing Sn content. Sheet resistance versus temperature measurements are performed yielding temperature coefficients of resistance of 3.25, 2.65, and 1.72% K−1 at resistivity values of 116.18, 27.36, and 2.34 Ω cm for Sn concentrations of 35%, 44%, and 48%, respectively. Infrared ellipsometry measurements are performed to extract the optical properties of the Si1–x Sn x thin films and optical simulations confirm that a Fabry–Pérot cavity microbolometer configuration containing an Si1–x Sn x thin film can achieve high absorptance in the 8–12 μm band. This study shows that Si1–x Sn x alloys are a suitable, simple, and low‐cost replacement for thermometer layers used in uncooled infrared microbolometers.

A combined molecular dynamics/Monte Carlo simulation of Cu thin film growth on TiN substrates: Illustration of growth mechanisms and comparison with experiments

Using a sequential molecular dynamics (MD)/time-stamped force-bias Monte Carlo (tfMC) algorithm to simulate the deposition of Cu species onto a TiN(001) substrate at 600 K, it is shown for the first time that at the very early stage of growth, BCC-Cu grows pseudomorphically on the TiN(001) substrate as a very thin continuous film with the BCC-Cu[001]//TiN[001] growth direction. By increasing the thickness of the Cu thin film, however, the film transforms through the Nishiyama-Wasserman mechanism from BCC into predominantly FCC-Cu with abundant nanotwins, which is the same type of structure obtained in the experiment conducted here via a dc magnetron sputter deposition technique to grow Cu on TiN(001) at 105 °C. In agreement with the experimental observations in the literature, the devised MD/tfMC is employed further to reveal that on the N-terminated TiN(111), Cu shows a very poor wettability, and FCC-Cu(111) grows vertically in the form of tall 3D islands. On Ti-terminated TiN(111) surface, however, FCC-Cu(111) initially grows in the form of 2D islands with high wettability. With additional Cu deposition, a triangular misfit dislocation network is generated at the Cu(111)//Ti-terminated TiN(111) interface with subsequent formation of a two-layer nanotwin with its twinning plane parallel to the surface substrate.

Optimization of low resistivity molybdenum thin films for high-temperature microheater applications

In this paper, we discuss the optimal DC magnetron sputtering deposition conditions needed to obtain low resistivity Molybdenum (Mo) thin films for high-temperature (800 °C) microheater applications. The influence of Ar gas pressure (2–10 mTorr), sputtering power (80–160 W), and annealing temperature (200–1000 °C) on the resistivity and adhesive properties of Mo thin films were investigated. The structural, morphological, and electrical properties of as-deposited and annealed Mo thin films were characterized by X-ray diffraction, Scanning Electron Microscopy, Atomic Force Microscopy, and four-point probe techniques. The thin films deposited at 120 W, 6 mTorr, and annealed at 1000 °C showed low resistivity (18 μΩ-cm) and good adhesive properties. Suspended-membrane microheaters were fabricated using as-deposited and annealed Mo thin films, and their performance characteristics were compared. The impact of thin-film resistivity on power consumption and on the maximum operating temperature of Mo microheater was also investigated.

Structural and magnetic properties of CoTi thin films deposited by magnetron sputtering method

ABSTRACT Co1–xTix (x = 0.3, 0.5 and 0.7) thin films were prepared on Si (100) substrate using DC-magnetron sputtering deposition technique. A structural phase transition occurs from hexagonal to cubic crystal structure when the Ti composition is above 30 percentage. The thickness of the films obtained from X-ray Reflectivity data is about 30 nm. The average particle size of the CoTi thin films was calculated using the Atomic Force Microscopy image. The Magneto-Optic Kerr Effect measurements suggest that only Co0.7Ti0.3 thin film exhibits soft magnetic behaviour whereas the other thin films have no magnetic properties because of small grain size and reduction of inter-grain exchange interaction. Co0.7Ti0.3 thin film has twofold magnetic anisotropy. The angle-dependent coercivity (H c) is numerically fitted with a two-phase model of magnetization reversal, which confirms the presence of magnetic anisotropy. The magnetization reversal occurs via coherent rotation of spins along the hard axis.

Reactive pulsed DC magnetron sputtering deposition of vanadium oxide thin films: Role of pulse frequency on the film growth and properties

In this study, vanadium oxide (VOx) thin films were prepared by reactive pulsed DC magnetron sputtering (PDMS). The influence of pulse frequency (Fp) on the deposition process and properties of VOx films was investigated. The obtained results indicate that with the increase of Fp, which not only can enhance the oxidation of vanadium but also can facilitate the formation of a denser microstructure and smoother surface morphology in the films. More importantly, films with composition from metal-rich to maximum stoichiometry can be accessed by tuning the Fp, without varying any other parameters, especially, the flow rate of reactive gas. And temperature dependent electrical properties of the VOx films can also be tailored via the Fp to fall in the desirable range for microbolometer applications. The impacts of Fp on the reaction between V and O, thin film growth and some dynamic processes occurring during reactive PDMS were analyzed. The corresponding underlying mechanisms were discussed in detail. Our present work may provide a practical and effective way to develop the reactive sputtering towards hysteresis-free, and also paves the way for optimizing the reactive sputtered VOx films with desirable properties via Fp.

Magnetic anisotropy and magnetization reversal in cobalt-iron thin film

Cobalt-iron thin film was deposited on rotating silicon (100) substrate using the DC-magnetron sputtering deposition unit. The structure is examined by Grazing Incidence X-ray Diffraction and results reveal that the sample has a bcc crystal structure with lattice constant 2.65 Å. The X-ray Reflectivity data analysis confirms that the thickness of the thin film alloy is about 33 nm. The Energy Dispersive X-ray Analysis confirms the presence of 30.56% of cobalt and 69.44% of iron in cobalt-iron thin film. The study of magnetic properties by Magneto-Optic Kerr Effect technique suggests that sample exhibits soft magnetic behavior. The M–H loop study shows that the coercive field decreases with the increase of rotation of the substrate which may be due to reduced grain size or crystal orientation. The study of remanence magnetization (Mr/Ms) confirms that the sample has a twofold magnetic structure and cubic magnetic anisotropy. The occurrence of the magnetization reversal in the sample is due to the formation of the ripples and change in the contrast in the color of domain images along the easy axis and through coherent rotation of spins along the hard axis. This confirms that the sample has uniaxial nature and found very useful applications in the magnetic sensors, memory storage devices and spintronics.

Multi-tube tantalum membrane reactor for HIx processing section of IS thermochemical process

HIx processing section of Iodine-Sulphur (IS) thermochemical cycle dictates the overall efficiency of the cycle, which poses extremely corrosive HI–H2O–I2 environment, coupled with a very low equilibrium conversion (~22%) of HI to hydrogen at 450 °C. Here, we report the fabrication, characterization and operation of a 4-tube packed bed catalytic tantalum (Ta) membrane reactor (MR) for enhanced HI decomposition. Gamma coated clay-alumina tubes were used as supports for fabrication of Ta membranes. Clay-alumina base support was fabricated with 92% alumina (~8 μm particle size) and 8% clay (~10 μm particle size), sintered at a temperature of 1400 °C. An intermediate gamma alumina coating was provided with 4% polyvinyl butyral as binder for a 10% solid loading. Composite alumina tubes were coated with thin films of Ta metal of thickness <1 μm using DC magnetron sputter deposition technique. The 4-tube Ta MR assembly was designed and fabricated with integration of Pt-alumina catalyst for carrying out the HI decomposition studies, which offered >80% single-pass conversion of HI to hydrogen at 450 °C. The hydrogen throughput of the reactor was ~30 LPH at a 2 bar trans-membrane pressure, with >99.95% purity. This is the first time a muti-tube MR is reported for HIx processing section of IS process.

Linearization of Patterned Pinning Spin Valve Devices for Low-Field Applications

In spin valve sensors, the bias point caused by the interlayer coupling between the pinned layer and the free layer is a crucial issue encountered in the design process, which degrades the responsivity and the weak-field detection feature. In tackling this issue, we present the magnetic bias technique for efficient control of the bias point of the pinned spin valve (PSV). Specifically, the magnetic field that creates a shift of the bias point is generated by a coil being wrapped around the PSV devices. The PSV multilayer structure, Ta(5 nm)/NiFe(3 nm)/CoFe(4.5 nm)/Cu(1.5 nm)/CoFe(2.4 nm)/IrMn(10 nm)/Ta(5 nm), was fabricated using DC magnetron sputtering deposition. The PSV devices patterned by using a simple lift-off technique have a dimension of 1.5 µm × 200 µm. The bias magnetic field was tuned between ± 5 mT by changing an external DC current. Our experimental results indicate that the bias point can be efficiently controlled via a simple adjustment of the current in the bias coil. Consequently, the device responsivity was remarkably enhanced by a factor of 6.75, from 0.8 V/T to 5.4 V/T, leading to a decrease of the detectivity (field noise) from 366 nT/√Hz@1 Hz to 108 nT/√Hz@1 Hz. Additionally, the field noise was further suppressed by a factor of 5 from 363 nT/√Hz@1 Hz to 72 nT/√Hz@1 Hz by applying the AC-driven mode in the half-bridge PSV. The simplicity of our proposed technique makes it particularly pertinent to PSV sensor designs for low-field applications.