Nitridation of aluminum particles and formation process of aluminum nitride coatings by reactive RF plasma spraying

Nitridation of aluminum particles and formation process of aluminum nitride coatings by reactive RF plasma spraying was investigated by collecting splat and depositions and fabrication of the coating. Nitriding reaction of aluminum particles during flight in the plasma and after deposit on the substrate was confirmed by the observation of splats and the deposition morphologies, respectively. However, as nitriding reaction of aluminum particles easily forms brittle agglomerates on the substrate, the formation of sound coating was difficult. Though the coating was fabricated with the spraying condition of RF power of 5 kW, it was impossible to fabricate the coatings with RF power of 6 kW. In order to fabricate aluminum nitride coatings by reactive RF plasma spraying, it is necessary to control the plasma and the substrate temperature for the suitable conditions with changing RF power and nitrogen gas flow rate.     

Optimization of ion energy spread in inductively coupled plasma source designed for focused ion beam applications

The ion energy distribution of inductively coupled plasma ion source for focused ion beam application is measured using a four grid retarding field energy analyzer. Without using any Faraday shield, ion energy spread is found to be 50 eV or more. Moreover, the ion energy distribution is found to have double peaks showing that the power coupling to the plasma is not purely inductive, but a strong parasitic capacitive coupling is also present. By optimizing the various source parameters and Faraday shield, ion energy distribution having a single peak, well separated from zero energy and with ion energy spread of 4 eV is achieved. A novel plasma chamber, with proper Faraday shield is designed to ignite the plasma at low RF powers which otherwise would require 300-400 W of RF power. Optimization of various parameters of the ion source to achieve ions with very low energy spread and the experimental results are presented in this article.     

Carbon incorporation in silicon-carbon films grown at different substrate temperatures

Hydrogenated microcrystalline silicon-carbon thin films have been deposited by plasma enhanced chemical vapour deposition technique at the substrate temperatures of 250 °C and 400 °C varying the radio frequency (RF) power in the 10-100 W range. The effects of substrate temperature and RF power on the structural, compositional, optical, and electrical properties have been investigated. The increase of substrate temperature or RF power leads to a decrease of crystallinity degree and an enhancement of carbon content. Optical absorption in the UV-visible region and electrical conductivity are affected in a different way by the RF power and substrate temperature variations. Silicon grain nucleation of films deposited at the temperature of 250 °C on commercial doped tin oxide substrate has been explored, for different RF power, by means of X-ray diffraction measurements.     

Studies of radiofrequency plasma deposition of hexamethyldisiloxane films and their thermal stability and corrosion resistance behavior

Hexamethyldisiloxane (HMDSO) films (thickness: 282-929 nm) are prepared by the radiofrequency plasma assisted chemical vapour deposition (RF-PACVD) method using an Ar/HMDSO/O₂ gas mixture. The deposition process is carried out in an RF reactor at a working pressure of 1.2 × 10⁻¹ mbar and an RF power range of 20-100 W. From the studies on Ar/O₂ and Ar/HMDSO/O₂ discharge characteristics using a self-compensated emissive probe, it is revealed that electrons play an important role in the plasma polymerization of HMDSO monomers. Optical emission spectroscopy (OES) and Fourier transform infrared (FT-IR) spectroscopy show that the plasma deposited HMDSO films tend to be more inorganic in nature at higher RF powers. A film prepared at an RF power of 100 W exhibits more thermal stability and corrosion resistance behavior in comparison to films deposited at lower powers (20-80 W). A correlation of the results obtained from OES and FT-IR analyses with the thermal stability and corrosion resistance behavior of the films has been attempted.     

Characteristics of capacitively coupled helium plasma driven by various frequencies under constant power conditions

The influence of excitation frequency (13.56–96 MHz) on the characteristics of capacitively coupled helium plasma is investigated by means of Langumir probe and CCD camera. Measurements are performed in helium pressure of 10.66 and 33.3 Pascal (Pa) under fixed dissipated power of 10 W. With increasing the driving frequency, the RF/HF voltage and dc-self bias markedly decrease. Meanwhile, the plasma density and electron temperature peak in the frequency range 27–56 MHz, beyond which they decrease as exciting frequency increase. A different feature of the electron energy probability function EEPF is observed with exciting frequency; Maxwellian type EEPF at low frequency of 13.56 MHz evolves into a bi-Maxwellian type with a hump/beamlike in the frequency range 27–56 and eventually comes back to Maxwellian distribution at frequency ≥76 MHz. The observed results are explained in terms of electromagnetic wave effect and capacitive to inductive heating transition induced by exciting frequency.     

Optical characterisation of radio frequency plasma polymerised Lavandula angustifolia essential oil thin films

Optically transparent RF plasma polymerised thin films were fabricated from Lavandula angustifolia essential oil under varying RF power levels and their optical properties investigated. The refractive index, extinction coefficient, absorption and optical band gap of the thin films in addition to their thickness and roughness were investigated using the spectroscopic ellipsometry and UV-Vis spectroscopy in the wavelength range 200-1000 nm (6.199-1.239 eV). For films fabricated under the RF power from 10 W to 75 W, the refractive index values vary from 1.530 to 1.543 at 500 nm. Even though the refractive index is unaffected by the RF power, the optical band gap tends to decrease with increasing RF power, with 2.75 at 10 W and 2.34 at 75 W.     

Investigation of the plasma uniformity in an internal linear antenna-type inductively coupled plasma source by applying dual frequency

A large area inductively coupled plasma source with an internal linear-type antenna was operated in dual frequency mode (2 MHz/13.56 MHz), and the electrical/plasma characteristics of the ICP source were examined as a function of the relative rf power ratio. When the source was operated in single frequency mode (13.56 MHz only), approximately 8.5% plasma uniformity was observed at 5 kW of 13.56 MHz rf power for the substrate size of 880 mm × 660 mm. The plasma uniformity improved with increasing rf power. However, a further improvement in plasma uniformity to approximately 6.3% could be obtained using the dual frequency mode by applying 0.9 kW of 2 MHz rf power in addition to 5 kW of 13.56 MHz. For 15 mTorr Ar, the plasma density at a dual frequency rf power of 0.9 kW 2 MHz/5 kW 13.56 MHz was 1.6 × 10¹¹/cm³ and the electron temperature was approximately 3 eV. The addition and increase in 2 MHz rf power to the 13.56 MHz power increased the plasma density without increasing the electron temperature.     

Structural and optical properties of amorphous oxygenated iron boron nitride thin films produced by reactive co-sputtering

Amorphous oxygenated iron boron nitride (a-FeBN:O) thin films were prepared by reactive radio-frequency (RF) sputtering, from hexagonal boron nitride chips placed on iron target, under a total pressure of a gas mixture of argon and oxygen maintained at 1 Pa. The films were deposited onto silicon and glass substrates, at room temperature. The power of the generator RF was varied from 150 to 350 W. The chemical and structural analyses were investigated using X-ray photoelectron spectroscopy (XPS), energy dispersive of X-ray and X-ray reflectometry (XRR). The optical properties of the films were obtained from the optical transmittance and reflectance measurements in the ultraviolet-visible-near infrared wavelengths range. XPS reveals the presence of boron, nitrogen, iron and oxygen atoms and also the formation of different chemical bonds such as Fe-O, B-N, B-O and the ternary BNO phase. This latter phase is predominant in the deposited films as observed in the B 1s and N 1s core level spectra. As the RF power increases, the contribution of N-B bonds in the as-deposited films decreases. The XRR results show that the mass density of a-FeBN:O thin films increases from 2.6 to 4.12 g/cm³ with increasing the RF power from 150 to 350 W. This behavior is more important for films deposited at RF power higher than 150 W, and has been associated with the enhancement of iron atoms in the film structure. The optical band gap decreases from 3.74 to 3.12 eV with increasing the RF power from 150 to 350 W.     

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

It is demonstrated that plate-shaped crystals of Yb:LuPO₄, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr⁴⁺:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.     

Effects of surface treatments using PECVD-grown hexamethyldisiloxane on the performance of organic thin-film transistor

Hexamethyldisiloxane (HMDSO) was deposited on a gate dielectric surface by plasma enhanced chemical vapor deposition for surface treatment, and its effects on the microstructure of pentacene and the transistor characteristics were examined. HMDSO films were deposited at room temperature at various RF powers (10 W to 120 W). Atomic force microscopy analysis of the pentacene films showed a significant increase in the grain size of the samples treated under the optimum RF power (10 W), which in turn led to a significant improvement in the electrical mobility. These results show that PECVD-grown HMDSO can be used as an effective surface treatment and warrants further investigation for process optimization.     

Advanced Power Supplies designed for Plasma Deposition and Etching

Plasma deposition and etching processes are used for a wide range of applications as for example the production of semiconductor circuits, flat panel displays, solar cells, architectural glass and data storage media. To fulfill the special needs of each single process stable DC, MF and RF process power ranging from 50W to 200kW is needed. All generators need a high precision process control and a supreme arc management with adaptable parameters to provide minimal disturbances in the plasma process and to obtain optimized results in terms of film quality, homogeneity and uniformity over the whole substrate. The fast and flexible arc handling leads to an improvement in the film quality by minimizing flaws and defects and enables the use of very high sputter rates. To fit DC process demands a new concept for a modular DC system has been realized where up to four 30kW modules can be combined using master slave concept. The arc management and control of the DC module has an intelligent control enabling arc detection times of less than 1μs and a residual energy delivered to the process of only 6 mJ per kW. For MF processes a fast and effective arc management is an even more important tool for keeping reactive processes stable. The new generation of MF power supplies enables arc detection and shut off times of 5μs with a residual energy delivered to the process of only 5 mJ per kilowatt. This yields the additional advantage that even when the cathode material is almost used up and consequently the arc probability increases, the low residual energy values contribute to an extended service life of the cathode and to better utilization of the target material. Essentially, the outstanding feature of effective arc management is an undisturbed plasma during the whole operation time. The fast arc suppression minimizes the interruption in the sputtering process to negligibly small values. However, because arcs also serve to remove unwanted materials on the cathode, power supplies must be able to control and regulate the arc energy precisely. MF power supplies are available for process power up to 200kW. RF systems are based on two different concepts to fit the broad power range between 50W and 50kW. For the low energy range a fully transistorized and μC‐controlled RF generator was developed. This generator has been designed for a max. power of 3kW. Important features are the compact size, robustness, reliability and easy maintenance To have a cost effective design for a high power RF generator in this power range an oscillator ‐ amplifier concept has been chosen with a solid state driver in combination with a tube type end stage amplifier. To fit todays demands for advanced etching a dual frequency system consisting of a 13.6 MHz and a 3.4 MHz unit was developed. This enables the possibility to separately control plasma density and ion energy of the discharge.     

Studies of medium frequency high power density magnetron sputtering discharges

Optical emission spectroscopy and Langmuir probe have been used to study the power dependence of medium frequency, 100 kHz, pulsed magnetron sputtering discharge. Copper target was sputtered in the argon atmosphere. The examined power ranged from 0.5 to 4.5 kW which gave an average power density on target surface from 25 to 115 W/cm². Optical spectroscopy did not reveal any significant changes of copper ion contribution to the sputtering process. The electron temperature and plasma potential changed a little with applied power. The electron density depended linearly on the sputtering power.     

Sputter deposition and surface treatment of TiO2 films for dye-sensitized solar cells using reactive RF plasma

Sputter deposition followed by surface treatment was studied using reactive RF plasma as a method for preparing titanium oxide (TiO₂) films on indium tin oxide (ITO) coated glass substrate for dye-sensitized solar cells (DSCs). Anatase structure TiO₂ films deposited by reactive RF magnetron sputtering under the conditions of Ar/O₂(5%) mixtures, RF power of 600 W and substrate temperature of 400 °C were surface-treated by inductive coupled plasma (ICP) with Ar/O₂ mixtures at substrate temperature of 400 °C, and thus the films were applied to the DSCs. The TiO₂ films made on these experimental bases exhibited the BET specific surface area of 95 m²/g, the pore volume of 0.3 cm²/g and the TEM particle size of ∼ 25 nm. The DSCs made of this TiO₂ material exhibited an energy conversion efficiency of about 2.25% at 100 mW/cm² light intensity.     

Low temperature electric transport properties in hydrogenated microcrystalline silicon films

The dark conductivity of microcrystalline silicon (μc-Si:H) films, deposited in a RF-PECVD system varying the RF power in the 15-100 W range, has been investigated as a function of the temperature. Under low electric field condition (10³ V/cm), the conductivity of the samples as a function of the exponential of T^− 1/4 presents a linear behaviour in the measured temperature range. The density of states near the Fermi level, the range of hopping and the activation energy for hopping have been evaluated using the diffusion model. A correlation between the hopping parameters and the crystallinity degree has been found.     

Electrical properties of ultra-thin oxynitrided layer using N2O plasma in inductively coupled plasma chemical vapor deposition for non-volatile memory on glass

In this work, the silicon oxynitride layer was studied as a tunneling layer for non-volatile memory application by fabricating low temperature polysilicon thin film transistors on glass. Silicon wafers were oxynitrided by only nitrous oxide plasma under different radio frequency powers and plasma treatment times. Plasma oxynitridation was performed in RF plasma using inductively coupled plasma chemical vapor deposition. The X-ray energy dispersive spectroscopy was employed to analyze the atomic concentration ratio of nitrogen/oxygen in oxynitride layer. The oxynitrided layer formed under radio frequency power of 150 W and substrate temperature of 623 K was found to contain the atomic concentration ratio of nitrogen/oxygen as high as 1.57. The advantage of high nitrogen concentration in silicon oxide layer formed by using nitrous oxide plasma was investigated by capacitance-voltage measurement. The analysis of capacitance-voltage characteristics demonstrated that the ultra-thin oxynitride layers of 2 nm thickness formed by only nitrous oxide plasma have good properties as tunneling layer for non-volatile memory device.     

Spatially resolved thermal probe measurement for the investigation of the energy influx in an rf-plasma

The total energy influx for a typical radiofrequency process plasma has been measured by means of a simple thermal probe. The procedure is based on the measurement of temporal slope of the substrate temperature during the plasma process. A substrate dummy which is thermally isolated and inserted into the plasma at substrate position served as thermal probe. It can be moved in vertical and horizontal directions in order to measure the different energy influxes and their topology in the reactor vessel. The knowledge of the spatial distribution is important for coating or sputtering processes.Different contributions to the total energy influx can be identified by different orientation of the thermal probe. If the thermal probe is orientated to the rf-electrode (“down”) the energy influx is much higher than in the opposite direction. This difference can be explained by an additional influx due to the secondary electron emission from the powered rf-electrode.     

Supermagnetron plasma CVD of highly effective a-CNx:H electron-transport and hole-blocking films suited to Au/a-CNx:H/p-Si photovoltaic cells

Hydrogenated carbon nitride (a-CN_x:H) films (0-500 nm) were deposited on p-Si wafers to make Au/a-CN_x:H/p-Si photovoltaic cells using i-C₄H₁₀/N₂ supermagnetron plasma chemical vapor deposition. At a lower electrode RF power (LORF) of 50 W and an upper electrode RF power (UPRF) of 50-800 W, hard a-CN_x:H films with optical band gaps of 0.7-1.0 eV were formed. At a film thickness of 25 nm (UPRF of 500 W), the open circuit voltage and short circuit current density were 247 mV and 2.62 mA/cm², respectively. The highest energy conversion efficiency was 0.29%. The appearance of the photovoltaic phenomenon was found to be due to the electron-transport and hole-blocking effect of thin a-CN_x:H film.     

Titanium film deposition by high-power impulse magnetron sputtering: Influence of pulse duration

Surface modification with high-power glow discharges is a promising physical vapor deposition (PVD) technology for industrial usage. A metal ion density higher than 10¹⁸ m⁻³ can be obtained due to a high-power input in the plasma. In the present paper, titanium films were deposited on Si (100) substrates using high-power impulse magnetron sputtering (HIPIMS). The pulse duration was varied to investigate the deposition rate and the titanium film structure. The plasma source was an unbalanced magnetron sputtering (UBMS) discharge generation system. The deposition rate was correlated to the electrical characteristics. There was an instantaneous power threshold of approximately 36 kW to significantly increase the deposition rate by 4-5 times. The deposition rate increased linearly with respect to the average power until the average power reached 5.6 kW (about 30 W/cm² for a total area of the target), and an 83% increase of the deposition rate from the linear relationship was observed. The increase of the deposition rate was possibly closely related to the so-called thermal spike, where the target temperature increases due to a high power input to the target. The surface morphology and the crystalline structure of the films were studied for a variety of pulse durations, and the results were compared to the case of the direct-current magnetron sputtering (dcMS) process. The titanium films at an average power of 1.2 kW and a pulse duration of 50 μs have a smaller crystalline size and a smoother surface than those at an average power of 825 W by dcMS. The crystal orientation (101) was dominated when the pulse duration was lengthened to 180 μs, although the (002) orientation was dominant in dcMS. The crystal size and the surface roughness increased significantly when the pulse duration was increased from 50 μs to 180 μs in HIPIMS. The consumed power in the plasma by HIPIMS can be an important parameter for the crystal size and the structure.     

Improvements in the angular current density of inductively coupled plasma ion source for focused heavy ion beams

A compact inductively coupled plasma ion source (ICPIS) is developed for producing high current micron size beams for high speed micromachining applications. Angular current density (J_Ω) of the beam extracted from ICPIS is measured and found to be three orders higher than that of the conventional liquid metal ion sources. An improvement in J_Ω by >30% is achieved through the increase of RF power density in the plasma by reducing the plasma volume instead of operating ion source at high RF power. Studies on J_Ω show that heavier ions have maximum J_Ω at lower power and vice versa for the lighter ions. Ion beams of Neon, Argon, Krypton and Xenon extracted at 5 kV, have J_Ω of 57, 51, 37 and 30 mA/Sr respectively at RF power in the range of 75 W–200 W. Measurements on proton beam which is very important for imaging applications show J_Ω of 45 mA/Sr at 200 W.     

Synthesis and characterization of plasma-polymerized tert-butylacrylate films

Plasma polymerized tert-butylacrylate (pp-t-BA) film was prepared using tert-butylacrylate monomer under 100 Pa of vapor pressure with varying RF power of 10-250 W and continuous wave RF power of 13.56 MHz. The deposition rates of pp-t-BA films were determined using quartz crystal microbalance (QCM) method. The chemical structure of pp-t-BA films was characterized using FT-IR, contact angle and XPS techniques. The gas sorption properties of pp-t-BA were measured using a QCM sensor array. Results showed that deposition rates of pp-t-BA film were proportional to the polymerization time at 100 Pa of monomer pressure under the same RF power. The deposition amount of pp-t-BA films increased gradually with increasing RF power of 30-150 W. Increasing the RF power on plasma polymerization decreased the amount of ester group in pp-t-BA films. Sensitivity of gas sorption on pp-t-BA films is related to the RF power of polymerization.