Distributed Electron Cyclotron Resonance Plasma Research Articles

Effect of magnetic field profile on the uniformity of a distributed electron cyclotron resonance plasma

This study extensively measured the uniformity of an electron cyclotron resonance (ECR) plasma versus the magnetic field distribution. The influence of magnetic field distribution on the generation of uniform ECR plasma was examined. It is suggested that in addition to the uniformity of the magnetic field distribution at ECR zone and at the downstream zone near the substrate, the transition of the magnetic field between these two zones is also crucial. A uniform ECR plasma with the electron density uniformity of ±7.7% over 500 × 500 mm2 was measured at the downstream. The idea of generating uniform ECR plasma can be scaled up to a much larger area by using an n × n microwave input array and a well-designed magnetic system.

Plasma emission diagnostics during fast deposition of microcrystalline silicon thin films in matrix distributed electron cyclotron resonance plasma CVD system

AbstractThe structural and optoelectronic properties of undoped hydrogenated microcrystalline silicon (μ c‐Si:H) films deposited in a matrix distributed electron cyclotron resonance (MDECR) plasma CVD system using pure silane were studied as a function of microwave power (PMW) and gas pressure (Pgas). The analysis of the silane plasma optical emission spectra (OES) shows the effect of the deposition conditions on the plasma chemistry and resulting film microstructure as studied by spectroscopic ellipsometry and atomic force microscopy. The use of the PMW and Pgas as tunable parameters to achieve μ c‐Si:H films with desired microstructure is discussed. Intrinsic μ c‐Si:H films with good phototransport properties were realized at high deposition rate. Our study shows the usefulness of OES as a fast diagnostic tool for controlling and optimizing the μ c‐Si:H deposition process in MDECR reactor. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Microcrystalline silicon films and solar cells deposited at high rate by Matrix Distributed Electron Cyclotron Resonance (MDECR) plasma

AbstractThe latest results obtained in a new promising Matrix Distributed Electron Cyclotron Resonance (MDECR) reactor for the deposition of microcrystalline silicon (μc‐Si:H) films and cells are reported in this article. The reactor is presented with a focus on the importance and the difficulties of temperature measurements. The unique properties of this high density plasma allowed us to demonstrate high deposition rates of 28 Å/s. The chemical composition of the MDECR material has been compared to a standard material and in particular, the effect of the oxygen level will be discussed. The installation of a load‐lock allowed a reduction of the oxygen con‐tamination by a factor of 10. Lower microwave powers helped to improve the electrical properties of the material. So far, the cell performance unfortunately seems decoupled from these successive optimizations of the film quality, and stayed limited (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of ion energy on structural and electrical properties of intrinsic microcrystalline silicon layer deposited in a matrix distributed electron cyclotron resonance plasma reactor

AbstractMicrocrystalline silicon films were deposited in a matrix distributed electron cyclotron resonance (MDECR) plasma enhanced chemical vapor deposition (PECVD) system using pure silane, under varying substrate bias conditions. Microstructural characterization of the films shows a lower void fraction and a preponderance of nanograins in films deposited at negative bias, while in positive bias a thin incubation layer is seen with a higher void fraction. Plasma emission studies reveal higher electron temperature and more atomic H at positive bias, which lead to early onset of crystallization. The microstructural properties of the films are correlated with the dark and phototransport properties. Our study demonstrates the importance of substrate bias in controlling the ion energy and properties of films deposited in the MDECR reactor.

Wettability of hydrogenated tetrahedral amorphous carbon

The wettability and surface energy of hydrogenated amorphous carbon films (a-C:H) elaborated by distributed electron cyclotron resonance plasma were studied by contact angle measurements in relation to composition, structure and topography. Tetrahedral a-C:H (ta-C:H) showed relatively high water contact angle (CA) up to 82.3°, and low surface energy ( E s), down to 25.3 mJ/m 2. Hydrophobicity was found to increase with the intensity of the ion bombardment and with the tetrahedral character. A decrease of the dispersive component is responsible of the decrease of surface energy with substrate bias. Low mass-density polymer-like a-C:H (PLC) presents also a relatively high hydrophobicity with high water CA, up to 76.7°, and low surface energy values, down to 32.1 mJ/m 2. Hydrophobicity is interpreted as resulting from a surface layer rich in sp 2-carbon for ta-C:H and rich in C–H bonds for PLC.

Multilayer optical filters control by multi‐channel kinetic ellipsometry

AbstractThe use of multi‐wavelength kinetic ellipsometry control for the deposition of multilayer filters is presented. Two different control methods are described and their use for the fabrication of different types of optical filters is illustrated. We fit the ellipsometric data with a model and adjust the physical thickness during deposition to ensure the conservation of the optical thickness. In order to illustrate this method and to show its importance in the case of periodic structures or single layer control, a Bragg mirror and a resonator layer in a Fabry‐Perot filter were grown using Matrix Distributed Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (MDECR‐PECVD). The use of fitting both the index and thickness for control of the physical thickness is also shown. The importance of this method for manufacturing non‐periodic multilayer structures is demonstrated by the controlled deposition of an antireflection coating. The different features of these two methods are presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Distributed electron cyclotron resonance plasma: A technology for large area deposition of device-quality a-Si:H at very high rate

Distributed electron cyclotron resonance is a technique that combines low pressure, microwaves and magnetic confinement with a network of antennas to produce large area, remote, high-density plasmas in a simple reactor design. We are optimizing this promising technology for depositing intrinsic and doped a-Si:H layers for thin film solar cells. Operating in depletion mode, the growth rate is proportional to the silane flow rate and the layer quality is affected by the gas residence time, power/gas flow rate ratio, ion energy and substrate temperature. Fast deposition of device-quality hydrogenated amorphous silicon requires short gas residence time and large silane flow rate but also a well-controlled sheath potential, to induce surface re-organization without generating defects, as well as a deposition temperature larger than 250 °C. Rates up to 60 Å/s have been achieved, i.e. at least 5 times the industrial best. 300 nm-thick device-quality layers were produced with a minority carrier diffusion length larger than 150 nm. Using a single-point injection, we achieved an homogeneity of ± 6% (± 3 sigma) for the material bandgap, ± 10% for the dielectric function and ± 12% for the solar cell fill-factor, for an average deposition rate of 24 Å/s on a 20 × 20 cm 2 glass.

A comparative study on the effect of VUV radiation in plasma SiO x-coated polyimide and polypropylene films

Wettability of polyimide (PI) and polypropylene (PP) films have been improved using SiO x -like thin layers deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave distributed electron cyclotron resonance plasma reactor. The films wettability evolution behaviors were evaluated through the results of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The plasma depositions of SiO x thin layers in presence of VUV radiation induce a contact angle decrease to about 7° and 35° for PI and PP films, respectively. XPS data showed that such difference in wettability is attributed to the increase of hydrophilic group's proportion at the surface of coated PI films due to VUV irradiation. AFM images showed that the PI surface topography remains relatively smooth when coated in presence of VUV radiation. However, in the case of PP films, AFM images revealed the growth of irregular structure due to a substrate etching effect supported by VUV radiation. For polymers coated without VUV irradiation, the deconvolution of the C1s peaks showed a significant decrease of C O bonds for both PI and PP substrates.

Nonlinear effects in collision cascades and high energy shock waves during ta-C:H growth

The surface topography of hydrogenated tetrahedral amorphous carbon (ta-C:H) is critical for various applications such as microelectromechanical devices, magnetic and optical storage devices, and medical implants. The surface topography of ta-C:H films deposited by distributed electron cyclotron resonance plasma from C2H2 gas precursor was investigated. The effects of pressure, together with ion flux and energy, are studied by atomic force microscopy in relation to the structural evolution of the films. The results are compared with the predictions of the Edward-Wilkinson model [Proc. R. Soc. London, Ser. A 44, 1039 (1966)] recently proposed to account for ta-C:H growth and with previous interpretations based on hypersonic shock waves. The random hillocks observed on the smooth surfaces of ta-C:H films deposited at high pressure are thought to result from the interference of high energy shock waves triggered by C4Hx+ ions that produce overlapping collision cascades and induce nonlinear effects.

ERDA and Structural Characterization of Oriented Multiwalled Carbon Nanotubes

Oriented multiwalled carbon nanotubes have been synthesized by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition. Elastic recoil detection analysis measurements on multiwalled carbon nanotubes are reported here for the first time. On the basis of the recorded depth profiles, we have developed a simple model to estimate the surface densities of as-grown nanotubes. Besides, nitrogen and hydrogen contents into MWNT, typically less than 6.5 and 8 atom %, respectively, have been characterized as a function of the chemical nature of the catalyst, the synthesis temperature, and the hydrogen carrying diluent gas. These results are discussed with respect to the structural characterization performed by electron energy loss spectroscopy measurements, transmission electron microscopy and X-ray photoelectron spectroscopy.

Comparison between continuous and microwave oxygen plasma post-treatment on organosilicon plasma deposited layers: Effects on structure and properties

The aim of this work is to characterize and understand the effects of oxygen plasma post-treatments on plasma polymerized hexamethyldisiloxane (ppHMDSO) layers, as these post-treatments on plasma polymerized layers are an alternative way to produce SiO x ( x ≈ 2) films. Oxygen discharges on ppHMDSO films in continuous plasma (DC) and microwave multipolar plasma excited by distributed electron cyclotron resonance plasma (MW) are compared by studying their effect s on the post-treated layer thickness, chemical composition, film structure and functional properties. Fourier Transform Infra-Red and X-ray Photoelectron Spectroscopies have been used to determine the film structure and composition of the initial ppHMDSO films and the post-treated layers. The oxygen post-treatment etches the end bonds and leads to a cross-linking of the polymer chains (formation of SiOC bonds). Oxidation process is strongly linked to the plasma type. A pre-existing model for the oxide growth has been applied, showing that the MW process is more effective than the DC. The main conclusion is that the structure of the resulting films is different for each process and that the oxygen diffusion coefficient is linked to the film structure. Higher oxygen diffusion is achieved in MW films, which are less dense than the films obtained by using the DC technique. It is also shown that the film properties (such as wettability, hardness and electrical and optical properties) are modified after the oxygen post-treatment. Finally, we briefly discuss on the most appropriate process to obtain these films according to the final application of the coatings.

Characterization of carbon nanotubes and carbon nitride nanofibres synthesized by PECVD

This paper presents a novel dual plasma enhanced chemical vapor deposition (PECVD) process developed to grow carbon nitride nanofibres (CN-NFs) at room temperature (RT) and its basic version used to grow multi-walled carbon nanotubes (MWCNTs) at temperatures as low as 550 °C. The dual process alternates two low pressure-high density plasmas, one inductively coupled (ICP) and the other one excited by distributed electron cyclotron resonance (DECR). MWCNTs can be synthesized using only the DECR plasma source. The paper focuses on the comparison between CN-NFs and MWCNTs detailing their structure as revealed by transmission electron microscopy (TEM), X-ray photo electron spectroscopy (XPS) and Raman spectroscopy.

Growth and Modification of Organosilicon Films in PECVD and Remote Afterglow Reactors

AbstractSummary: Five hundred nanometer thick organosilicon coatings are prepared on Si substrates in parallel by the plasma‐assisted polymerisation of hexamethyldisiloxane (HMDSO) in an RF‐inductively coupled plasma (RFICP) and distributed electron cyclotron resonance plasma (DECRP) at low pressure (0.27 Pa) and of tetramethyldisiloxane (TMDSO) premixed with oxygen in an N2 microwave induced remote afterglow (MIRA) at 560 Pa. The structure of these different films is analyzed by different techniques, such as Fourier‐transform infrared spectroscopy, Rutherford backscattering spectrometry, atomic force microscopy, ellipsometry, and contact angle measurements. Results of the film composition (at least 30% carbon content), optical properties, and morphology indicate a low cross‐linking degree accompanied by short chain length for RFICP and DECRP films, in contrast to a high‐molecular‐weight structure observed for the MIRA film. Carbon removal is achieved within the same plasma reactors by further oxygen‐containing plasma treatment performed in the RF‐ICP (3.33 Pa), DECRP (0.27 Pa, −200 V biased substrate), and MIRA (N2/O2 (98.7:1.3, 560 Pa)) reactors. The same measurements are carried out on the treated samples in order to detect the main changes in film composition, optical properties, and morphology. The evolution of surface energy is also studied. The results are discussed according to film structure and process specificity.O/Si and C/Si elemental ratios calculated from RBS analysis for an as‐deposited RF‐inductively coupled plasma coating (RFICP) and films post‐treated by N2/O2 microwave induced remote afterglow (MIRA), O2 RFICP and O2 distributed electron cyclotron resonance plasma (DECRP, biased sample) processes.imageO/Si and C/Si elemental ratios calculated from RBS analysis for an as‐deposited RF‐inductively coupled plasma coating (RFICP) and films post‐treated by N2/O2 microwave induced remote afterglow (MIRA), O2 RFICP and O2 distributed electron cyclotron resonance plasma (DECRP, biased sample) processes.

Wettability of polypropylene films coated with SiO x plasma deposited layers

Surface wettability of polypropylene (PP) films has been significantly improved by the deposition of thin SiO x layers, elaborated from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave DECR (distributed electron cyclotron resonance) plasma reactor (2.45 GHz, 400 W). Contact angle measurements, Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to study, respectively, the change in surface free energy, surface topography and chemical composition due to the deposition of thin SiO x layers. Contact angle measurements revealed that the water contact angle value is reduced from about 99° for untreated PP surface to nearly 30° for coated PP film. The polar component of the surface energy is considerably increased from 0.5 to 35 mJ/m 2. For films deposited in the presence of VUV photons, AFM images showed the growth of irregular structure due to substrate etching effect and the deconvolution results of the Si 2p XPS peaks indicated that the proportion of the partly oxidized silicon environment was the major component. However, for films deposited without the presence of VUV radiation, typical SiO 2 agglomerates can clearly be seen on PP surface at a thickness of about 29 nm and the proportion of the silicon dioxide was the major component.

Hard-hydrogenated tetrahedral amorphous carbon films by distributed electron cyclotron resonance plasma

Hard-hydrogenated tetrahedral amorphous carbon films (ta-C:H) are deposited from acetylene-fed distributed electron cyclotron resonance (DECR) plasma over large area (300 mm diameter disk) at near room temperature (below 140 °C). The effects of the ion flux and energy on the structure and physical properties are investigated. For a constant substrate bias V 0 of −150 V, the mass–density, Young’s modulus and hardness reach a maximum value of ∼2.5 g/cm 3, ∼280 GPa, and ∼45 GPa, respectively, and the hydrogen content reaches a minimum of 26 at.% at the maximum ion flux ϕ + of ∼6.3 × 10 15 ions cm −2 s −1. For a constant ion flux and pressure, the mass–density and Young’s modulus reach a maximum at a substrate bias of −300 V, and the hydrogen content is minimised. Electron diffraction, and Raman spectra show that the films grown at the maximum ion flux and a negative substrate bias ranging between 150 and 500 V are ta-C:H. The films contain sp 2-carbon clusters and chains. sp 2-carbon clustering increases with the increase of the substrate bias and decreases with the increase of the ion flux. The disorder increases with the ion flux and decreases with the bias. The optical band-gap decreases with disorder and with sp 2-carbon clustering. It depends primarily on disorder rather than on clustering.

Improvement of the Polyimide Surface Wettability Using SiOx Films Deposited in a DECR Reactor from HMDSO/O2 Mixtures

AbstractSummary: Polyimide (PI) foils were coated with thin SiOx films for surface wettability improvement. The deposition was carried out in a microwave DECR (Distributed Electron Cyclotron Resonance) plasma reactor from a mixture of HMDSO/O2. During deposition, the PI substrate was located downstream, exposed to long‐lived reactive precursors and to VUV radiation (position I) or located again downstream but shielded from VUV radiation (position II). Deposition time was varied in order to observe different stages of the film growth. The surfaces of the deposited films were investigated by means of contact angle, atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS) measurements. According to contact angle measurements, the coated PI surface became hydrophilic already at a thickness of about 2.8 nm and stayed nearly at the same level still for thicker coating. The plasma deposition of the ultra‐thin SiOx layer increased significantly the polar component of the surface energy from 9 to 53 mJ · m−2 and consequently enhanced the wettability of the material. The treated surfaces were only moderately affected after eight weeks storage time in air, indicating stable surface treatments. AFM images revealed that during deposition, the PI surface topography remains relatively smooth when coated in position I. However, for PI coated in position II, the surface roughness becomes more pronounced as thickness is increased. XPS analysis showed that VUV irradiation of the PI surface leads to the formation of a high proportion of polar species which enhance the wettability of the surface. Curve fitting of the Si2p peak showed that, as the film thickness increases, the deposited film becomes more oxidized.Surface roughness of 6.6 nm thick SiOx film (Rav = 1.8 nm, Rrms = 2.3 nm).magnified imageSurface roughness of 6.6 nm thick SiOx film (Rav = 1.8 nm, Rrms = 2.3 nm).

Electron cyclotron resonance deposition, structure, and properties of oxygen incorporated hydrogenated diamondlike amorphous carbon films

Oxygen-incorporated hydrogenated amorphous carbon films were grown by the integrated distributed electron cyclotron resonance plasma technique from a mixture of acetylene and oxygen. It has been found that the increase of the oxygen to acetylene gas ratio results in more oxygen incorporation up to O∕(O+C)=0.2 with a decrease in the hydrogen concentration within the film as measured by the nuclear reaction analysis (NRA) and a combination of the elastic recoil detection analysis and Rutherford backscattering techniques. The spectroscopic ellipsometry in the range of 1.5–5eV showed a negligible decrease of the E04 optical band gap for increasing the oxygen content. At the same time, the decrease of the refractive index from 2.2 to 2.0 denotes the decrease of the films density, which was independently estimated by NRA. The visible (488nm) Raman spectroscopy showed that the increase of the oxygen content favors the clustering of the six-fold sp2C rings. The Fourier transform infrared spectroscopy gives evidence of both C–O and CO bonding configurations. No evidence of O–H bonds formation is found. Simultaneously, the chemisorption of CO2 seems to increased with increasing the oxygen to acetylene gas ratio, which is consistent with the lower film density. The previously trends denote the “softening” of the films, which is consistent with the significant decrease (of about 35%) of the compressive stress allowing the growth of thicker but still transparent films.

The combined study of the organosilicon films by RBS, ERDA and AFM analytical methods obtained from PECVD and PACVD

Organosilicon plasma deposited polymers are of interest for different kinds of applications like packaging, passivation and dielectric layers. A large set of plasma processes is possible, among which are low-pressure plasma enhanced chemical vapour deposition (PECVD) and plasma assisted chemical vapour deposition (PACVD) often used. In this work, we studied the composition and surface morphology of the hexamethyldisiloxane (HMDSO) and tetramethyldisiloxane (TMDSO) layers produced by PECVD and PACVD deposition using three plasma generation processes (plasma reactors): RF inductively coupled plasma (RFICP), microwave distributed electron cyclotron resonance plasma (DECR) and microwave induced remote nitrogen afterglow (MIRA). The layer composition was investigated by Rutherford backscattering spectrometry (RBS) and by elastic recoil detection analysis (ERDA) and the layer surface morphology was determined by atomic force microscopy (AFM). Composition, density and morphology (roughness, porosity) of the layers is discussed in connection with deposition techniques used.

Hypersonic shock waves and hybridization of a-C:H thin films

A distributed electron cyclotron resonance plasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit a-C:H films at room temperature on rf biased 〈100〉 Si substrates. Modifying substrate bias, substrate current density and composition of the precursor gas enabled the average deposited energy density to be varied. The physical properties of a-C:H were investigated using atomic force microscopy (AFM), x-ray photoelectron spectroscopy, and electron energy loss spectroscopy (EELS). The experimental results were correlated with the predictions of the binary collision theory. The influence of the deposited energy density on the nucleation and growth processes was investigated using both pure C2H2 and C2H2 mixed with Ar. The sp3 nucleation process is shown to be stimulated by high energy density cascades generated by (C2H2)+ and Ar+ ions. For the pure acetylene plasma, the AFM topography displays a random network of circular, crater-like objects close to 1 μm in diameter. These objects are associated with plastic flow of a-C:H and are attributed to the transversal hypersonic shock waves generated by overlapping binary collision cascades. EELS analysis shows that an increasing ion current density applied under constant substrate bias leads to an increased sp3 hybridized carbon fraction. The effect is attributed to interference between the shock waves triggered by individual ions and the corresponding high pressure transients. The probability Pi of a dynamic overlap of order i between shock waves is estimated under the assumption that in order to modify the quantum state and bonding type, the overlap must occur during the wave propagation time τ. The observed evolution of the sp3 hybridized fraction is consistent with theoretical predictions for i=2 and a propagation time τ≈1 ps, indicating that shock waves are generated during the cascade’s lifetime. Analysis of the AFM images shows that once the shock wave comes to rest, the subsequent nucleation of the sp3 hybridized component is controlled by the tensile stress-mediated nucleation process.

Impact of energy density and stress fields on the nucleation dynamics of plasma deposited a-C:H films

A distributed electron cyclotron resonance plasma reactor powered by a microwave generator operating at 2.45 GHz was used to deposit a-C:H films at room temperature on RF biased (1 0 0) silicon substrates. Modifying the substrate bias, the ion dose rate and the composition of the precursor gas enabled the average deposited energy density to be varied. For the pure acetylene plasma and under constant substrate bias an increasing ion dose-rate leads to an increased sp 3 hybridized C fraction. The effect is correlated to propagation and overlap of the hypersonic shock waves generated by high energy density collision cascades. The corresponding timescale is within the picosecond range. The shock wave related effects are enhanced when argon is added to the acetylene plasma. Once the collision cascades and shock wave comes to rest, the subsequent nucleation of the sp 3 hybridized component is enhanced by the tensile stress-mediated nucleation process.