Bipolar-type Plasma Based Ion Implantation Research Articles

Positron annihilation spectroscopy of thermally annealed hydrogenated amorphous carbon films

Hydrogenated amorphous carbon (a-C:H) films are prepared using a bipolar-type plasma-based ion implantation and deposition system, followed by thermal annealing of the films at 200 °C-800 °C. The structural and compositional changes are examined by Raman spectroscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis (ERDA). Positron annihilation spectroscopy (PAS) is also conducted to investigate the behavior of voids in the films. The results of Raman and ERDA measurement clearly show that the sp2 ring clusters increase, and hydrogen content apparently decreases at temperatures between 400 °C and 800 °C. Uncorrelated behaviors between positron lifetimes and line-shape parameters are observed in the PAS results, which can be attributed to several competing effects, such as hydrogen release, bond reconstruction, and electronic-state change of voids. Furthermore, it is suggested that the graphitization of the films begins from the surface to the inside, accompanied by the hydrogen release that is related to the void behavior.

Effect of Water Adsorption Layers on the Friction Properties of Fluorinated Amorphous Carbon Films in Ambient Air.

Fluorinated amorphous carbon (a-C:F) films with different microstructures were prepared with bipolar-type plasma-based ion implantation and deposition method by changing the negative bias voltage, and the tribological properties were investigated in ambient air. Their surface chemistry and water adsorption properties were investigated to determine their friction properties. Microstructural analysis results showed that, as the negative bias voltage increased, the density of the films decreased with the promotion of graphitization. The water adsorption properties evaluated using a quartz crystal microbalance showed that a large adsorbed water weight was observed for the films deposited at high negative bias voltages. In contrast, these films exhibited thin water adsorption layers from the measurements with an ellipsometer. These results indicate that water molecules are adsorbed on the film surface and permeate into the films, particularly for the films deposited at high negative bias voltages. The friction properties in ambient air depend significantly on their microstructure and relative humidity (RH). Regardless of the RH, the higher the negative bias voltage during film deposition, the lower the friction coefficient. Since several water molecules existed on the surface of the film deposited with a low negative bias voltage, its surface was oxidized during sliding, which increased the friction coefficient. In addition, the friction coefficient of the films increased at high RH. The number of water molecules adsorbed on the film increased as the RH increased, causing a high shear force owing to many hydrogen bonds and/or high capillary force at the friction interface.

Effect of precursor gas on the structure and mechanical properties of hydrogenated amorphous carbon films deposited on a trench sidewall

Hydrogenated amorphous carbon (a-C:H) films were deposited on a trench-shaped target (20-mm pitch and 10-mm depth) using a bipolar-type plasma-based ion implantation and deposition (bipolar PBII&D) technique. The thickness uniformity, microstructure, and mechanical properties of the a-C:H films deposited on the top, sidewall, and bottom surfaces of the trench were investigated. In our previous study, toluene gas was used for coating a trench target using the bipolar PBII&D technique; the thickness and hardness of the a-C:H films on the sidewall of the trench were smaller and the film structure was more graphite-like than those on the top and bottom surfaces. Because the film properties of the a-C:H film are related to the incident energy per carbon atom, in this study, methane (CH4), which has a lighter mass and fewer carbon atoms (one carbon atom) in a molecule than toluene, was used as a precursor gas to enhance the incident energy per carbon atom and suppress the inertia in the vertical direction. The structure and mechanical properties of the a-C:H films were evaluated by Raman spectroscopy, XPS, AFM, and a nanoindentation test. In addition, a plasma simulation was conducted to determine the effect of the precursor gas on the ion and radical behavior and the coating mechanism. As a result, the use of the methane precursor gas leads to increasing the indentation hardness, to lowering the surface roughness, and to changing its structure from graphite-like to diamond-like as compared to the use of the toluene precursor gas.

Characterization of diamond-like carbon films prepared using various source gases by plasma-based ion implantation and deposition

Diamond-like carbon (DLC) films are prepared by bipolar-type plasma-based ion implantation and deposition (PBIID) using the combination of toluene (C7H8), tetramethylsilane (TMS: Si(CH3)4) and nitrogen (N2) as a source gas. The characteristics and mechanical properties of the films are examined by Raman spectroscopy and nanoindentation measurement, respectively. The film composition is evaluated by X-ray photoelectron spectroscopy (XPS). Raman analysis reveals that polymer-like structure is formed and increases with increasing Si content. The hardness and Young's modulus decrease with increasing Si content. The ratio of Si to C (Si:C) in the films is almost equal to that in the source gases. The addition of N2 together with TMS causes a slight increase of sp2 ring clusters and improvement of the mechanical properties probably due to the formation of SiN bonds. Moreover, the Si:C ratio in the films is enhanced by the N2 addition.

Analysis of microstructure and surface morphology of a-C:H films deposited on a trench target

The bipolar-type plasma-based ion implantation and deposition (bipolar PBII&D) is beneficial in coating a hydrogenated amorphous carbon film (a-C:H film) on a 3-dimensional coating target. In this study, a trench (pitch: 20 mm, aspect ratio: 1.0) was prepared as a coating target and evaluated the microstructure and surface morphologies of a-C:H films. Although the a-C:H films were coated successfully in all trench surfaces, the sidewall surface showed quite different properties as compared to that of coated on the top or bottom surface. It is because of the conformal ion sheath cannot be formed around the sidewall surface, which in turn leads to the decrease of incidence ion flux to the sidewall. The structural properties and surface morphology are investigated using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). From the Raman measurements of a-C:H films on the sidewall surface, it is observed that the Raman G-peak position shifts to a higher wave number. The Full Width at Half Maximum of G-peak (FWHM(G)) decreases to a smaller value compared to those of the films on the top and bottom surfaces. These results indicate that the structure of a-C:H films on the sidewall surface is graphitized compared to those on top and bottom surfaces, which results in the reduction of hardness.

Effect of Ar+ ion assist on the properties of a-C:H films deposited on a trench

In this study, a precursor gas mixture of toluene and Ar was used for the deposition of a-C:H films on a trench (20-mm pitch and 10-mm depth), and the effect of the Ar flow ratio on the film properties was investigated. The a-C:H films were deposited using a bipolar-type plasma based ion implantation and deposition technique under a negative pulse voltage of −2kV. The mechanical properties of the prepared a-C:H films, including internal stress, hardness and adhesion strength, were measured by means of surface profilometry, nanoindentation and a microscratch test, respectively. Furthermore, the microstructure of a-C:H films was evaluated by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results showed that the thickness uniformity across the trench surface is improved by the addition of Ar, in particular, at an Ar flow ratio of 80%. The film on the top and bottom surfaces of the trench tends to change from a PLC to DLC structure with increasing Ar flow ratio, resulting in a significant improvement of mechanical properties. In the case of the sidewall, the film tends to change to a more GLC structure with increasing Ar flow ratio due to the Ar+ ion bombardment and sputtering effect.

Structure and mechanical properties of a-C:H films deposited on a 3D target: comparative study on target scale and aspect ratio

Recently, the bipolar-type plasma-based ion implantation and deposition (bipolar PBII&D) method has attracted large attention owing to its non-line-of-sight coating technique. In particular, bipolar PBII&D is beneficial in coating a hydrogenated amorphous carbon (a-C:H) film on a 3D target. Therefore, in this study, a-C:H films were prepared onto a complex-shaped 3D target such as macrotrench (pitch: 20 mm, aspect ratio: 1.0), microchannel (width: 100 µm, aspect ratio: 20), microtrench (pitch: 4 µm, aspect ratio: 2.0), or nanotrench (pitch: 300 nm, aspect ratio: 2.0) using bipolar PBII&D, and the film properties were evaluated. With regard to the mechanical properties, the film thickness and hardness were evaluated using a scanning electron microscope (SEM) and nanoindentation measurements, respectively. With regard to the structural properties, the microstructure of the films was evaluated by Raman spectroscopy. Subsequently, the structural and mechanical properties were compared with each other to reveal the target scale- and aspect ratio-dependence on the film properties. Furthermore, the coating mechanism was elucidated by analyzing the plasma behavior around the target using a plasma simulation method. The particle-in-cell/Monte Carlo collision (PIC-MCC) and the direct simulation Monte Carlo (DSMC) methods were simultaneously used as the plasma simulation method. Each of these is a calculation method that analyzes the behavior of ions and radicals, respectively. As a result, the a-C:H films were successfully coated onto any scale and any shape of the target. In contrast, the results of the hardness and those from the Raman spectroscopy on the sidewall surface indicated non-uniformity of the film structure and depended on the scale and aspect ratio of a target, i.e. the hardness and Raman data show different values depending on the target scale and aspect ratio. The result of the plasma simulation suggested that such non-uniform mechanical or structural properties were strongly related to the non-uniform behavior of the plasma particle incident to the sidewall depending on the scale and aspect ratio of the target. Moreover, with regard to the a-C:H films on a nanotrench, their film properties were predicted by presenting comparative discussions of the experimental measurement and plasma simulation analysis for the macrotrench, microchannel, and microtrench.

Deposition of a-C:H films on inner surface of high-aspect-ratio microchannel

Hydrogenated amorphous carbon (a-C:H) films were prepared on inner surface of 100-μm-width microchannel by using a bipolar-type plasma based ion implantation and deposition. The microchannel was fabricated using a silicon plate, and two kinds of microchannels were prepared, namely, with a bottom layer (open at one end) and without a bottom layer (open at both ends). The distribution of thickness and hardness of films was evaluated by SEM and nanoindentation measurements, respectively, and the microstructures of films were evaluated by Raman spectroscopy. Furthermore, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision and Direct Simulation Monte Carlo to investigate the coating mechanism for the microchannel. It was found that the film thickness decreased as the depth of the coating position increased in the microchannels where it is open at one end. The uniformity of the film thickness improved by increasing the negative pulse voltage because ions can arrive at the deeper part of the microchannel. In addition, the hardness increased as the depth of the coating position increased. This is because the radicals do not arrive at the deeper part of the microchannel, and the incident proportion of ions relative to that of radicals increases, resulting in a high hardness due to the amorphization of the film. The opening area of the microchannel where the aspect ratio is very small, radicals dominate the incident flux, whereas ions prevail over radicals above an aspect ratio of about 7.5. On the other hand, in the microchannels that are open at both ends, there were great improvements in uniformity of the film thickness, hardness, and the film structure. The a-C:H films were successfully deposited on the entire inner surface of a microchannel with an aspect ratio of 20.

Deposition of a-C:H films on a nanotrench pattern by bipolar PBII&D

In this study, hydrogenated amorphous carbon (a-C:H) films were deposited on a nanotrench pattern (300 nm pitch, aspect ratio: 2.0) by bipolar-type plasma based ion implantation and deposition technique (bipolar PBII&D), and the effects of bipolar pulse on the film properties were investigated. Moreover, the behaviour of ions and radicals surrounding the nanotrench was analyzed to clarify the coating mechanism and properties of the a-C:H films on the nanotrench. Further, thermal nanoimprint lithography was carried out using the nanotrench pattern coated with a-C:H films as the mold, and the mold release properties were evaluated. All nanotrench surfaces were successfully coated with the a-C:H films, but the film thickness on the top, sidewall, and bottom surfaces of the trench were not uniform. The surface roughness of the a-C:H films was found to decrease at a higher positive voltage; this happens due to the higher electron temperature around the nanotrench because of the surface migration of plasma particles arrived on the trench. The effects of the negative voltage on the behaviour of ions and radicals near the sidewall of the nanotrench are quite similar to those near the microtrench reported previously (Park et al 2014 J. Phys. D: Appl. Phys. 47 335306). However, the positive pulse voltage was also found to affect the behaviour of ions and radicals near the sidewall surface. The incident angles of ions on the sidewall surface increased with the positive pulse voltage because the energy of incoming ions on the trench decreases with increasing positive voltage. Moreover, the incident ion flux on the sidewall is affected by the positive voltage history. Further, the radical flux decreases with increasing positive voltage. It can be concluded that a higher positive voltage at a lower negative voltage condition is good to obtain better film properties and higher film thickness on the sidewall surface. Pattern transfer properties for the nanoimprint formed by using nanotrench molds were greatly improved by the a-C:H films owing to the resultant reduction in the mold release force.

Structural changes of hydrogenated amorphous carbon films deposited on steel rods

In this study, hydrogenated amorphous carbon (a-C:H) films were deposited on steel rods of various radii by using bipolar-type plasma based ion implantation and deposition, and the film structure and mechanical properties have been investigated. Furthermore, the behavior of plasma surrounding the steel rods (i.e., flux and energy of incident ions and electrons) was investigated using the particle-in-cell Monte Carlo collision (PIC-MCC) method to examine the mechanism behind the structural changes of the a-C:H films. Three kinds of amorphous carbon films with different microstructures were prepared by changing the negative pulse voltages from −1kV to −5kV: one polymer-like carbon film and two diamond-like carbon films that possess the maximum FWHM(G) (full width at half maximum of Raman G-peak) and maximum hardness. The structure of the a-C:H films was evaluated through Raman spectroscopy, and the hardness of the films was measured using nanoindentation. It was found that the structures of a-C:H films deposited on the steel-rod surfaces are quite different from those on flat surfaces, and the film structures are directly affected by the curvature of the rod. It was also determined from the plasma simulation that the incident electron flux and ion flux become more intense as the curvature increases, resulting in the structural changes of the a-C:H films due to hydrogen evolution and thermal relaxation in the films.

Microstructure of a-C:H films prepared on a microtrench and analysis of ions and radicals behavior

Amorphous carbon films (a-C:H) were prepared on a microtrench (4-μm pitch and 4-μm depth), and the uniformity of film thickness and microstructure of the films on the top, sidewall, and bottom surfaces of the microtrench were evaluated by scanning electron microscopy and Raman spectroscopy. The a-C:H films were prepared by bipolar-type plasma based ion implantation and deposition (bipolar PBII&D), and the negative pulse voltage, which is the main parameter dominating the film structure, was changed from −1.0 to −15 kV. Moreover, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision (PIC-MCC) and Direct Simulation Monte Carlo (DSMC) to investigate the coating mechanism for the microtrench. The results reveal that the thickness uniformity of a-C:H films improves with decreasing negative pulse voltage due to the decreasing inertia of incoming ions from the trench mouth, although the film thickness on the sidewall tends to be much smaller than that on the top and bottom surfaces of the trench. The normalized flux and the film thickness show similar behavior, i.e., the normalized flux or thickness at the bottom surface increases at low negative pulse voltages and then saturates at a certain value, whereas at the sidewall it monotonically decreases with increasing negative voltage. The microstructure of a-C:H films on the sidewall surface is very different from that on the top and bottom surfaces. The film structure at a low negative pulse voltage shifts to more of a polymer-like carbon (PLC) structure due to the lower incident energy of ions. Although the radical flux on the sidewall increases slightly, the overall film structure is not significantly changed because this film formation at a low negative voltage is originally dominated by radicals. On the other hand, the flux of radicals is dominant on the sidewall in the case of high negative pulse voltage, resulting in a deviation from the Raman behavior of a-C:H films deposited by bipolar PBII&D. This tendency intensifies as the negative voltage becomes greater. Also, the energy of incident ions on the sidewall of the trench increases with increasing negative voltage, which causes a shift in the Raman data of the sidewall to the bottom right corner on the figure depicting the relationship of the FWHM(G) and the G-peak position, indicating increased graphitization of a-C:H film.

DLC coating on a trench-shaped target by bipolar PBII

Bipolar-type plasma based ion implantation (bipolar PBII) and deposition is a promising coating technique, especially for the complex-shaped target surface. In this study, diamond-like carbon (DLC) films were prepared by a bipolar PBII technique to a trench-shaped target (20mm pitch and 10mm depth), and the uniformity, structural and mechanical properties of DLC films coated on the top, inside wall and bottom surfaces of the trench were evaluated by surface profilometer, Raman spectroscopy and nanoindentation hardness tests. Moreover, plasma simulation was conducted to reveal the DLC coating mechanism for finding the optimum coating conditions. Particle-In-Cell with Monte Carlo Collision (PIC–MCC) method and Direct Simulation Monte Carlo (DSMC) method were used for computing the plasma behavior. As a result, thickness uniformity of DLC films was improved with decreasing negative pulse voltage. On the other hand, the thickness of DLC films on the inside wall of the trench was much smaller than those of the top and bottom surfaces of the trench. This is because the conformal ion sheath cannot be formed around the inside wall, which in turn leads to the decrease of incidence ion flux to the inside wall, and the idea has been verified through the simulation of plasma behavior. From the Raman measurements of DLC coatings on the inside wall, it is observed that the Raman G-peak position shifts to a higher wave number and the Full Width at Half Maximum of G-peak (FWHM(G)) decreases to a smaller value compared to those of the films on the top and bottom surfaces. These indicate that the structure of DLC coatings on the inside wall surface has changed compared to those on top and bottom surfaces, i.e., graphitized, which results in the reduction of hardness.

Effects of electrical conductivity of substrate materials on microstructure of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma based ion implantation, and the structural differences between DLC films deposited on different electrical conductive substrates, i.e., conductive Si wafers and insulating glass plates are examined by Raman spectroscopy and x-ray photo emission spectroscopy (XPS). In the Raman measurements, graphite (G) and disorder (D) peaks are observed for both samples. However, the additional photo luminescence is overlapped on the spectra in the case of on-glass sample. To elucidate the structural difference, the intensity ratio of D to G peak (I(D)/I(G)), G peak position and full width at half maximum (FWHM) are obtained by curve fitting using Gaussian function and linear baseline. It is found that the I(D)/I(G) is lower, G peak position is higher and FWHM of G peak is narrower for on-glass sample than for on-Si sample. According to Robertson [1], lower I(D)/I(G) seems more sp3 C-C bonding in amount for on-glass sample. In contrast, higher G peak position and narrower FWHM of G peak suggest less sp3 C-C bonding in amount for on-glass sample. The results of XPS analysis with C1s spectra reveal that sp3 ratio, i.e., the intensity ratio of sp3/(sp3+sp2) is smaller for on-glass sample than for on-Si sample. The inconsistency of the trend between I(D)/I(G) and other parameters (G peak position and FWHM of G peak) might be caused by the overlap of photo luminescence signal on Raman spectrum as to on-glass sample. From these results, it is considered that sp3 C-C bonding is reduced in amount when using insulating substrate in comparison with conductive substrate.

Nitrogen implantation into diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Different type of diamond-like carbon (DLC) films, such as electrically insulating and conductive ones are, prepared by bipolar-type plasma based ion implantation. They are implanted using 80keV N2+ ions at a dose of 5×1016N2+/cm2. And the changes in surface morphology and the microstructure are examined by atomic force microscopy (AFM) and Raman measurements. Elementary composition of the samples is checked by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). The results of RBS measurements indicate that the areal density of N is approximately 1×1017atoms/cm2 in the samples. The results of ERDA measurements also show that H decreases in concentration near the surface region of the films. Smooth and rough granular surfaces are observed for insulating and conductive DLC films, respectively. The results of Raman measurements reveal that the conductive DLC films are mainly composed of graphite-like structure. After N implantation, the surface morphology and the microstructure of the insulating DLC films are not changed significantly. However, for the conductive DLC films, the surfaces become smoothening due to amorphization by N implantation. In the case of the Si containing conductive DLC films, the surface smoothening effect is weakened.

Effects of H2 gas addition into process and H ion implantation on the microstructure of hydrogenated amorphous carbon films prepared by bipolar-type plasma based ion implantation

Hydrogenated amorphous carbon films are deposited on Si(100) and SiO2 glass substrates by a bipolar-type plasma based ion implantation system. The films are prepared using toluene gas at a constant flow rate of 2sccm. The effects of H2 gas addition during deposition on the microstructure of the films are examined by electrical conductivity measurements, Raman spectroscopy, elastic recoil detection analysis (ERDA) and optical spectroscopy. In addition, H implantation is also carried out using H2 plasma discharge. Thickness of the films is approximately 60nm for all samples. It is found that electrical conductivity slightly increases with increasing additive H2 flow rate. However, the conductivity drastically decreases after H implantation. Raman analysis reveals that H2 gas addition slightly causes the film graphitization, but the H implantation does it amorphization. The results of ERDA show that the H concentration in the films slightly decreases with increasing H2 gas addition, but increases by H implantation. In spite of H2 gas addition, the optical band gap is not changed and kept approximately 0.7eV. However, H implantation makes it increase up to approximately 1.0eV.

6PM1-C-1 バイポーラPBII法によるマイクロトレンチへのDLCコーティング(6PM1-C OS6 マイクロナノトライボロジー(2))

Diamond-Like Carbon (DLC) film is carbon-based hard thin film in amorphous state having an intermediate structure of graphite and diamond. DLC has excellent characteristics as a coating material such as high hardness, low friction, abrasion resistance, and chemical stability. Further, in recent years, with the development of nanotechnology, DLC film has been expected as a protective coating for a fine three-dimensional structure. So optimization of DLC film deposition technique to a fine three-dimensional structure are necessary. In the present study, DLC films were prepared using a bipolar-type plasma based ion implantation and deposition (bipolar PBII&D) system on the micro-scale trench patterns and uniformity of film thickness deposited on each trench surface was evaluated.

Optical and Electrical Properties of Nitrogen-Doped Diamond-Like Carbon Films Prepared by a Bipolar-Type Plasma-Based Ion Implantation

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma-based ion implantation (PBII) technique using toluene and nitrogen gases (N2), and the optical and electrical properties are examined as a function of N2 flow rate. The N concentration in the films and structural changes are also examined by Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), and Raman spectroscopy. It is found that the deposition rate decreases, but N concentration linearly increases with increasing N2 flow rate. Granular surfaces are observed and the grains decreases in size as N2 flow rate increases. In addition, Raman analysis suggests that aromatic ring clusters and the amorphous structure increase in amount. The optical band gap and conductivity increase with increasing N concentration up to about 11 at. %, and then decrease with further increase in N concentration.

Optical and Electrical Properties of Nitrogen-Doped Diamond-Like Carbon Films Prepared by a Bipolar-Type Plasma-Based Ion Implantation

Optical and Electrical Properties of Nitrogen-Doped Diamond-Like Carbon Films Prepared by a Bipolar-Type Plasma-Based Ion Implantation

Wear test and Raman analysis of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Wear test and Raman analysis of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Effects of working pressure on the deposition of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma based ion implantation (PBII), and the deposition rate and the microstructure of the films are examined as a function of working pressure (P) in the range of 0.08–0.5Pa. The positive and negative pulse voltages are fixed at +2kV and −5kV, respectively. The optical emission spectra on the bipolar pulse plasma are also examined. It is found that the deposition rate is increased with increasing P. Raman analysis shows that the intensity ratio of D peak to G peak, ID/IG, suggesting the amount of graphite-like structure, is not significantly changed in this pressure range. However, ion beam analysis reveals that the density of the films is slightly decreased with increasing P, probably due to the increase of H concentration in the films. In addition, the hardness and elastic modulus of the films are also gradually decreased with increasing P. On the other hand, optical emission peaks from H, CH and C radicals are clearly observed. These peaks, especially CH radical, are increased in intensity with increasing P, indicating that the plasma density is increased. This result in the increase of the deposition rate and the results suggest that the rapid increase of CH radicals (and CH ion flux) at higher P presumably causes the slight reduction of the density and mechanical properties of DLC films due to the increase of H concentration.