Plasma Beam Source Research Articles

Plasma atomic layer etching of ruthenium by oxygen adsorption-removal cyclic process

Ruthenium (Ru) is a next-generation metal interconnect material, and the demand for precise etching is on the rise. This study explores anisotropic atomic layer etching (ALE) of Ru, utilizing various oxygen adsorption methods (O radical, oxygen plasma, or O2 molecule) and two types of plasma sources: inductively coupled plasma (ICP) and ion beam source. Through ICP ALE, an etch per cycle (EPC) of ∼ 1.5 Å/cycle was achieved using oxygen plasma for adsorption. For ion beam ALE, EPC values of ∼ 0.8 Å/cycle were obtained using oxygen radical, and ∼ 0.4 Å/cycle through physisorption using oxygen molecule without plasma generation. The higher EPC with the ICP ALE was attributed to spontaneous etching during oxygen adsorption during the oxygen plasma generation. Conversely, the lower EPC with ion beam ALE during oxygen adsorption using O2 molecule without plasma generation resulted from nonuniform oxidation of Ru during the adsorption step. Among the three ALE methods, optimal Ru ALE with 100 % ALE synergy was achieved with ion beam ALE, likely due to the absence of ion bombardment during oxygen adsorption and the precise Ar+ ion energy for removing RuOx formed on the surface.

Influence of process parameters including the confining magnetic field of a plasma beam source on the deposition of N‐doped hydrogenated carbon films

Electrically conductive nitrogen‐doped hydrogenated carbon films (a‐C:H:N) were deposited using a nitrogenacetylene gas mixture by plasma‐assisted chemical vapor deposition (PACVD). A capacitively coupled plasma beam source was used for the depositions. The plasma is excited by a radio‐frequency (RF) discharge and confined by Helmholtz magnetic coils, resulting in an increase in plasma density. The ion energy, as well as the deposition rate, can be controlled by the choice of the size of the coupling electrode, i.e. the ratio of cathode-to‐anode area, the electric current at the Helmholtz magnet coils, the total gas pressure and the RF power. The interdependence of these process parameters on the ion energy and the deposition rate has been studied in detail in this work. Hardness and electrical resistivity were measured on the deposited a‐C:H:N films.

Direct graphene synthesis on Si(1 0 0) by inductively coupled plasma beam source

The graphene was synthesized directly on the Si(100) substrate by an Inductively Coupled Plasma Beam Source without any catalyst. Plasma power, methane gas flow, hydrogen gas flow, temperature and time effects on graphene layers number and flake size, defects density, and surface morphology were studied. Prevailing defects type was considered. Boundary defects dominated in most samples due to the polycrystalline nature of the directly synthesized graphene. However, high methane gas flows, low synthesis times, and low synthesis temperatures were beneficial for the hydrogenation of the growing graphene. On-site defects prevailed in these samples. It was found that synthesis power, temperature, and time should be optimized to avoid out-of-plane graphene growth. An additional hydrogen gas flow effectively controlled graphene layers number. D + D‘ and D + D“ peaks were explored. It was supposed that the D + D‘ peak is mainly related to the on-site defects associated with a hydrogen atom bonded to the carbon atom in the graphene sheet. The line-of-sight graphene deposition was demonstrated. The main graphene growth-related physical and chemical processes were considered. The observed results were explained by a competition between graphene growth, hydrogen etching, hydrogenation, and thermal stress release.

Physical and electrical properties of nitrogen-doped hydrogenated amorphous carbon films

Nitrogen-doped hydrogenated amorphous carbon films (a-C:H:N) have been prepared by a plasma-activated chemical vapor deposition technique (PACVD) by using a plasma beam source (PBS). The properties of the a-C:H:N films were changed by varying the total pressure, the substrate temperature (100 °C, 300 °C) and nitrogen partial pressure p(N2) by adding nitrogen to the precursor acetylene (C2H2). For the investigations, a-C:H:N films have been deposited onto glass slides and doped silicon wafers. The deposition rate decreased with increasing nitrogen content in the N2/C2H2 gas mixture and with decreasing total pressure. The elemental composition of two sample series (300 °C) has been analyzed with Elastic Recoil Detection Analysis (ERDA). The highest N content and N/C ratio was estimated to be 16 at.% and 0.25 at the highest p(N2), respectively. Microhardness measurements showed that the hardness decreased with increasing p(N2). Electrical resistance of the a-C:H:N films was measured by 4-point probe. Electrically conductive coatings have been obtained by nitrogen-doped a-C:H films at higher substrate temperature (300 °C). The electrical resistance of the a-C:H:N films also decreases with decreasing total pressure, with the lowest value being about 1 Ohm cm. The film density was determined by means of X-ray reflectometry (XRR).

Ion mass and energy selective hyperthermal ion-beam assisted deposition setup.

For the synthesis of high-quality thin films, ion-beam assisted deposition (IBAD) is a frequently used technique providing precise control over several substantial film properties. IBAD typically relies on the use of a broad-beam ion source. Such ion sources suffer from the limitation that they deliver a blend of ions with different ion masses, each of them possessing a certain distribution of kinetic energy. In this paper, a compact experimental setup is presented that enables the separate control of ion mass and ion kinetic energy in the region of hyperthermal energies (few 1 eV - few 100 eV). This ion energy region is of increasing interest not only for ion-assisted film growth but also for the wide field of preparative mass spectrometry. The setup consists of a constricted glow-discharge plasma beam source and a tailor-made, compact quadrupole system equipped with entry and exit ion optics. It is demonstrated that the separation of monoatomic and polyatomic nitrogen ions (N+ and N2+) is accomplished. For both ion species, the kinetic energy is shown to be selectable in the region of hyperthermal energies. At the sample position, ion current densities are found to be in the order of 1 μA/cm2 and the full width at half maximum of the ion beam profile is in the order of 10 mm. Thus, the requirements for homogeneous deposition processes in sufficiently short periods of time are fulfilled. Finally, employing the described setup, for the first time in practice epitaxial GaN films were deposited. This opens up the opportunity to fundamentally study the influence of the simultaneous irradiation with hyperthermal ions on the thin film growth in IBAD processes and to increase the flexibility of the technique.

Silicon nitride and silicon etching by CH3F/O2 and CH3F/CO2 plasma beams

Silicon nitride (SiN, where Si:N ≠ 1:1) films low pressure-chemical vapor deposited on Si substrates, Si films on Ge on Si substrates, and p-Si samples were exposed to plasma beams emanating from CH3F/O2 or CH3F/CO2 inductively coupled plasmas. Conditions within the plasma beam source were maintained at power of 300 W (1.9 W/cm3), pressure of 10 mTorr, and total gas flow rate of 10 sccm. X-ray photoelectron spectroscopy was used to determine the thicknesses of Si/Ge in addition to hydrofluorocarbon polymer films formed at low %O2 or %CO2 addition on p-Si and SiN. Polymer film thickness decreased sharply as a function of increasing %O2 or %CO2 addition and dropped to monolayer thickness above the transition point (∼48% O2 or ∼75% CO2) at which the polymer etchants (O and F) number densities in the plasma increased abruptly. The C(1s) spectra for the polymer films deposited on p-Si substrates appeared similar to those on SiN. Spectroscopic ellipsometry was used to measure the thickness of SiN films etched using the CH3F/O2 and CH3F/CO2 plasma beams. SiN etching rates peaked near 50% O2 addition and 73% CO2 addition. Faster etching rates were measured in CH3F/CO2 than CH3F/O2 plasmas above 70% O2 or CO2 addition. The etching of Si stopped after a loss of ∼3 nm, regardless of beam exposure time and %O2 or %CO2 addition, apparently due to plasma assisted oxidation of Si. An additional GeOxFy peak was observed at 32.5 eV in the Ge(3d) region, suggesting deep penetration of F into Si, under the conditions investigated.

Fringe structures and tunable bandgap width of 2D boron nitride nanosheets.

We report studies of the surface fringe structures and tunable bandgap width of atomic-thin boron nitride nanosheets (BNNSs). BNNSs are synthesized by using digitally controlled pulse deposition techniques. The nanoscale morphologies of BNNSs are characterized by using scanning electron microscope (SEM), and transmission electron microscopy (TEM). In general, the BNNSs appear microscopically flat in the case of low temperature synthesis, whereas at high temperature conditions, it yields various curved structures. Experimental data reveal the evolutions of fringe structures. Functionalization of the BNNSs is completed with hydrogen plasma beam source in order to efficiently control bandgap width. The characterizations are based on Raman scattering spectroscopy, X-ray diffraction (XRD), and FTIR transmittance spectra. Red shifts of spectral lines are clearly visible after the functionalization, indicating the bandgap width of the BNNSs has been changed. However, simple treatments with hydrogen gas do not affect the bandgap width of the BNNSs.

DOPING OF NANO-SIZED DIAMOND LIKE CARBON FILMS AND THEIR CHARACTERIZATION BY MICRO RAMAN SPECTROSCOPY

Capabilities of the rf plasma beam source in deposition of ultra thin diamond like carbon for the hard disk drive applications have been studied. Nano-sized films were doped by nitrogen, hydrogen and silicon and characterized by micro Raman spectroscopy. Projected ranges of incident carbon ions into the magnetic layer as well as growing film were calculated by Monte Carlo simulation. Ion ranges at 100 eV incident energy were around 0.5 nm. With micro Raman spectroscopy is possible to qualitatively determine optimal deposition parameters and to follow changes in the film properties and carbon binding structure in amorphous matrix with hydrogen, nitrogen and silicon doping elements.

DOPING OF NANO-SIZED DIAMOND LIKE CARBON FILMS AND THEIR CHARACTERIZATION BY MICRO RAMAN SPECTROSCOPY

Capabilities of the rf plasma beam source in deposition of ultra thin diamond like carbon for the hard disk drive applications have been studied. Nano-sized films were doped by nitrogen, hydrogen and silicon and characterized by micro Raman spectroscopy. Projected ranges of incident carbon ions into the magnetic layer as well as growing film were calculated by Monte Carlo simulation. Ion ranges at 100 eV incident energy were around 0.5 nm. With micro Raman spectroscopy is possible to qualitatively determine optimal deposition parameters and to follow changes in the film properties and carbon binding structure in amorphous matrix with hydrogen, nitrogen and silicon doping elements.

Modelling and Simulation of the Advanced Plasma Source

Plasma ion assisted-deposition (PIAD) is a combination of conventional thermal evaporation deposition and plasma-beam surface modification; it serves as a well-established technology for the creation of high quality coatings on mirrors, lenses, and other optical devices. It is closely related to ion-assisted deposition to the extent that electrons preserve quasineutrality of the ion beam. This paper investigates the Advanced Plasma Source (APS), a plasma beam source employed for PIAD. A field enhanced glow discharge generates a radially expanding plasma flow with an ion energy of about 80-120 eV. Charge exchange collisions with the neutral background gas (pressure 0.1 Pa and below) produce a cold secondary plasma, which expands as well. A model is developed which describes the primary ions by a simplified Boltzmann equation, the secondary ions by the equations of continuity and momentum balance, and the electrons by the condition of Boltzmann equilibrium. Additionally, quasineutrality is assumed. The model can be reduced to a single nonlinear differential equation for the velocity of the secondary ions, which has several removable singularities and one essential singularity, identified as the Bohm singularity. Solving the model yields macroscopic plasma features, such as fluxes, densities, and the electrical field. An add-on Monte-Carlo simulation is employed to calculate the ion energy distribution function at the substrate. All results compare well to experiments conducted at a commercial APS system.

Latest innovations in large area web coating technology via plasma enhanced chemical vapor deposition source technology

In this article, the authors discuss the latest results of our development of large area plasma enhanced chemical vapor deposition (PECVD) source technologies for flexible substrates. A significant challenge is the economical application of thin films for use as vapor barriers, transparent conductive oxides, and optical interference thin films. Here at General Plasma the authors have developed two innovative PECVD source technologies that provide an economical alternative to low temperature sputtering technologies and enable some thin film materials not accessible by sputtering. The Penning Discharge Plasma (PDP™) source is designed for high rate direct PECVD deposition on insulating, temperature sensitive web [J. Modocks, Proceedings of the Society of Vacuum Coaters, 2003 (unpublished), p. 187]. This technology has been utilized to deposit SiO2 and SiC:H for barrier applications [V. Shamamian et al. Proceedings of the Flexible Displays and Manufacturing Conferrence, 2006 (unpublished)]. The Plasma Beam Source (PBS™) is a remote plasma source that is more versatile for deposition on not only insulating flexible substrates but also conductive or rigid substrates for deposition of thin films that are sensitive to the high ion bombardment flux inherent to the PDP™ technology. The authors have developed PBS thin film processes in our laboratory for deposition of SiO2, SiC:O, SiN:C, SiN:H, ZnO, FeOx, and Al2O3. [M. A. George, Conference Proceedings of the Association of Industrial Metallizers, Coaters, and Laminators (AIMCAL), 2007 (unpublished)]. The authors discuss the design of the patented sources, plasma physics, and chemistry of the deposited thin films.

Development of a 30-kW Plasma Gun System With a Long Lifetime

A hollow cathode that has extremely stable discharge characteristics has been developed. It is composed of two separated lanthanum hexaboride (LaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ) disks in the tube as the electron emitters. The design accomplishes great advantages by extending the surface discharge area of LaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , an extension that is also useful for optimal fixing of LaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . The hollow cathode is capable of producing 30 kW (100 V and 300 A) of power continuously. The plasma beam generated by the hollow cathode passes through holes in the centers of two intermediate electrodes covered with tungsten, which is water cooled due to the high plasma temperature entailed (greater than 3000 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C ). The combination of the hollow cathode and the two intermediate electrodes is practically useful for an ion plating plasma beam source.

Magnetotransport properties and thermal stability of magnetic tunnel junctions with wave resonance plasma oxidized barrier

AlO x tunnel barriers prepared by oxidizing ultra-thin Al films of various thickness by means of a Rf wave resonance plasma beam source were investigated to understand the influence of the plasma oxidation conditions on the junction resistance R j, the magnetoresistance ratio (MR) and the switching characteristics of exchange-biased magnetic tunnel junctions (MTJs) with NiMn pinning layer. The junction properties were characterized as a function of oxidation time, plasma power and distance between plasma source and sample. The MR of the as-deposited junction was about 15%. The highest exchange bias fields (17 mT) and pinned layer coercivities (23 mT) can be achieved with extended annealing at low temperatures T ≅ 32 0 ∘ C or with a rapid annealing at T ≅ 40 0 ∘ C , respectively. Short-time annealing (1 min) at intermediate temperatures (350 °C) and field cooling at 1 T leads to the highest MR effect of 35% at room temperature and 55% at 4.2 K.

Hydrogen content estimation of hydrogenated amorphous carbon by visible Raman spectroscopy

In the present study, we report the hydrogen content estimation of the hydrogenated amorphous carbon (a-C:H) films using visible Raman spectroscopy in a fast and nondestructive way. Hydrogenated diamondlike carbon films were deposited by the plasma enhanced chemical vapor deposition, plasma beam source, and integrated distributed electron cyclotron resonance techniques. Methane and acetylene were used as source gases resulting in different hydrogen content and sp2∕sp3 fraction. Ultraviolet-visible (UV-Vis) spectroscopic ellipsometry (1.5–5eV) as well as UV-Vis spectroscopy were provided with the optical band gap (Tauc gap). The sp2∕sp3 fraction and the hydrogen content were independently estimated by electron energy loss spectroscopy and elastic recoil detection analysis-Rutherford back scattering, respectively. The Raman spectra that were acquired in the visible region using the 488nm line shows the superposition of Raman features on a photoluminescence (PL) background. The direct relationship of the sp2 content and the optical band gap has been confirmed. The difference in the PL background for samples of the same optical band gap (sp2 content) and different hydrogen content was demonstrated and an empirical relationship between the visible Raman spectra PL background slope and the corresponding hydrogen content was extracted.

Effect of Thickness of Ion Beam Deposited Molybdenum Trioxide Thin Films on Gas Sensing Properties

ABSTRACTThis paper documents the study of thickness effects of ion beam deposited molybdenum trioxide thin films on their gas sensing properties. For processing the films, the primary plasma beam source was used to sputter material from the target, while the secondary beam was used as an ion assist source. The deposited material was annealed at 500°C for 8 hours. The microstructural characterization of the films was done using Scanning Electron Microscopy and X-ray diffraction. Sensing tests were performed in the temperature range of 350–500°C under varying and constant concentration levels of ammonia. The recorded data have been qualitatively and quantitatively analyzed and significant trends according to different parameters (thickness, sensing temperature, gas concentration) have been identified. These suggest a relation existing between processing conditions, the microstructure of the material and its response to gases at different concentration, and the optimum working temperature regime.

Large area deposition of hydrogenated amorphous carbon films for optical storage disks

Homogenous wear resistant carbon coatings with an optical gap of 3 eV but low stress are needed to increase the storage density in optical storage disks in order to reach 100 GB in 12-cm diameter disks. Here, hydrogenated amorphous carbon (a-C:H) films are deposited at room temperature using a large area electron cyclotron wave resonance plasma beam source of 14.2-inch diameter. Methane is used as the precursor. The ion flux and energy, plasma pressure, distance between the extraction grid and the substrate were varied. The films are characterized in terms of hydrogen content, stress, optical gap, refractive index, wear resistance, surface roughness and homogeneity by a variety of characterization techniques. Resonant Raman spectroscopy is used in order to non-destructively monitor the disk quality. We show how it is possible to produce homogenous, wear resistant a-C:H coatings with an optical gap of 3 eV and low stress (<500 MPa), without damaging the plastic disks.

Effect of N doping on structure and properties of DLC films produced by plasma beam deposition

A novel plasma beam source for the deposition of DLC films is described. Wide ranges of ion energy (130-250 eV) and C/sub 2/H/sub 2//N/sub 2/ flow conditions have been used to investigate the effect of N doping an the structure and properties of DLC films. The resulting films are characterized by their chemical composition, Raman spectra, electron spin density, mass density, and hardness, which critically depend on the N content. The addition of N causes the sp/sup 2/ carbon content in the DLC films to increase and results in lower density and hardness. The film density also decreases with increasing ion energy at high N concentrations. Carbon films with maximum density and hardness of 2.1 g/cm/sup 3/ and 25 GPa, respectively, can be produced using the plasma beam source.

Maximized sp3 bonding in carbon nitride phases

Carbon nitride films were deposited using a low pressure, dual ion beam system consisting of a filtered cathodic vacuum arc and a plasma beam source for carbon and nitrogen ions, respectively. This system maintains highly ionized beams even at high nitrogen fluxes, unlike in single beam systems. Film composition and bonding were measured by electron energy loss spectroscopy. Films with nitrogen to carbon atom ratios (N/C) up to 0.5 are produced. The carbon bonding is found to change gradually from sp3 to sp2, rather than sharply above a critical N content, as found previously. This indicates that N atoms form individual C=N bonds rather than causing a reversion of the entire C network to sp2. This allows us to maintain C sp3 bonding to the highest N contents so far achieved.

Defect and disorder reduction by annealing in hydrogenated tetrahedral amorphous carbon

Hydrogenated tetrahedral amorphous carbon (ta-C:H) is a form of diamond-like carbon with a high sp3 content (>60%), grown here using a plasma beam source. Information on the behaviour of hydrogen upon annealing is obtained from effusion measurements, which show that hydrogen does not effuse significantly at temperatures less than 500°C in films grown using methane and 700°C in films grown using acetylene. Raman measurements show no significant structural changes at temperatures up to 300°C. At higher temperatures, corresponding to the onset of effusion, the Raman spectra show a clustering of the sp2 phase. The density of states of ta-C:H is directly measured using scanning tunnelling spectroscopy. The measured gradients of the conduction and valence band tails increase up to 300°C, confirming the occurrence of band tail sharpening. Examination of the photoluminescence background in the Raman spectra shows an increase in photoluminescence intensity with decreasing defect density, providing evidence that paramagnetic defects are the dominant non-radiative recombination centres in ta-C:H.

The Preparation, Characterization and Tribological Properties of TA-C:H Deposited Using an Electron Cyclotron Wave Resonance Plasma Beam Source

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 900 Å/min over a 4″ diameter and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized in terms of its sp3 content, mass density, intrinsic stress, hydrogen content, C–H bonding, Raman spectra, optical gap, surface roughness and friction coefficient. The results obtained indicated that the film properties were maximized at an ion energy of approximately 167 eV, corresponding to an energy per daughter carbon ion of 76 eV. The relationship between the incident ion energy and film densification was also explained in terms of the subsurface implantation of carbon ions into the growing film.