Distributed Electron Cyclotron Resonance Reactor Research Articles

Plasma deposition of carbon layer: Correlations between plasma parameters, film structure and properties

The links between plasma parameters, discharge, film structure and properties are not really yet understood for amorphous hydrogenated carbon layers (a-C:H) plasma deposition. Here, a-C:H layers are deposited in a dual radio-frequency–multipolar microwave plasma excited by distributed electron cyclotron resonance reactor at low CH 4 pressure. This study deals with the plasma analysis, the film characterization and with plasma parameters effect on a-C:H films deposition, structure and properties. The discharge analysis shows that CH 4 is decomposed in CH y1 + H radicals and that C 2H 2 y2 are present in the discharge. As at low pressure, recombination can only take place on the surface, C 2 H 2 y2 desorbs from the surface. Moreover, C 2 species are observed attributed to C 2 H 2 y2 dissociation. The evolution of film composition with plasma power shows that the proportion of sp 2 CC decreases in contrast with those of CH bonds which increases. From these observations, a phenomenological model for a-C:H deposition can be proposed. Finally, properties are correlated with the film structure and the effect of MW plasma power can then be given.

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).

Control and monitoring of optical thin films deposition in a Matrix Distributed Electron Cyclotron Resonance reactor

A range of silicon-based optical thin films have been deposited in a matrix distributed electron cyclotron resonance (MDECR) reactor. Process parameters were optimized in order to obtain optical quality thin films at low substrate temperatures and high deposition rates without post-deposition treatment. Stoichiometric silica films have been deposited at the rates up to 70 nm/min at temperatures lower than 150 °C. Oxynitride films with a controllable refractive index ranging from 1.46 to 1.86 have been obtained from SiH 4 /O 2 /N 2 mixtures. Real time process control by multichannel ellipsometry has been implemented and successfully applied for the deposition of silica, silicon oxynitrides and amorphous silicon. Better than 0.3% in thickness accuracy was achieved in high rate deposition of silica layers of various predefined thickness. Refractive indices were determined in real-time with an absolute precision of 0.005-0.02. The control algorithm was used for fabrication of multilayer optical filters. The results show that the MDECR concept coupled with real-time process control by ellipsometry can be technology of choice for the deposition of interference coatings.

Investigation on the origin of dielectric constant evolution in films deposited from organosilicon molecules in microwave DECR plasma reactor

Low k dielectric thin films were elaborated in microwave distributed electron cyclotron resonance reactor by using organosilicon vapor and oxygen mixture as precursors. The dielectric constant evolution was studied as a function of the oxygen addition. Contribution of each permittivity component to the variation of the measured dielectric constant was carried out. Although the electronic and ionic polarizations have their influences on the value of the measured permittivity, they have not shown any effect on its evolution. A method to follow the dipolar polarization contribution to the dielectric constant is described. It suggests that both Si–O and Si–C polar groups present in the deposited films may have the predominant effect on the behavior of the dielectric constant.

The electrochemical reactivity of amorphous hydrogenated carbon nitrides for varying nitrogen contents: the role of the substrate

A series of hydrogenated carbon nitride films have been deposited on titanium and n-type highly doped (1 0 0) silicon substrates by the integrated distributed electron cyclotron resonance reactor from acetylene and nitrogen gas mixtures. It has been found that for nitrogen content between 5 and 25% the electrical conductivity and the electrochemical reactivity, for an outer sphere reaction such as that due to the ferri–ferrocyanide system, varies in opposite directions. In addition the overall kinetic behaviour of the same system, looking similar to that of a simple electron transfer with a partial mass transfer in solution, contains another contribution. This can be explained by the presence of a more resistive layer within the carbon film and close to the solution, where electronic transport would occur by hopping between a large number of localised states. Finally, in contrast to the silicon substrate which introduces a resistive layer resulting in an additional potential drop, titanium seems to be a more promising substrate because of the negligibility of the latter effect.

Deposition of silicon alloys in an integrated distributed electron cyclotron resonance reactor: Oxide, nitride, oxinitrides, and multilayer structures

The films of SiOxNy were deposited in an integrated distributed electron cyclotron resonance reactor. Due to planar geometry, such deposition processes can be scaled-up for processing of large areas. Deposition kinetics and material properties were studied in order to find the common principles for obtaining faster growth rates and more uniform deposition of high quality films. Films were grown without bias at room temperature from mixtures of SiH4, O2, and N2 at high deposition rates (more than 4.5 nm/s for silica). Optical properties of the films were analyzed using ultraviolet (UV)-visible and infrared spectroscopic ellipsometry. The influence of gas flows, temperature, pressure, microwave power, and rf bias was investigated. A multilayer optical filter was grown on a polycarbonate substrate using a UV-visible ellipsometer to control the deposition process. The success of this test confirms the accuracy of the experimental results and shows high promise for the technology.

New trends in DECR plasma technology: applications to novel duplex treatments and process combinations with extreme plasma specifications

After a brief review of the plasma production and diffusion mechanisms above multipolar magnetic field structures, the possible means of sustaining magnetron discharges are listed. In particular, various designs of distributed electron cyclotron resonance (DECR) plasma reactors are described. At the industrial level, besides gas and pumping distribution, the control of plasma uniformity (up to square meters) is a necessary condition to obtain the desired uniformity of reactive species. Another process parameter, controlled via independent substrate biasing, is the energy distribution function of ions onto surfaces. Plasma-based ion implantation (PBII) in the 100-keV range requires large volumes (cubic meters) of very low-pressure plasma (below 10 −4 torr), whereas ion bombardment in the very low energy range (a few eV) can only be obtained with quiescent, magnetic field-free plasmas exhibiting a very low electron temperature. In contrast, increasing the electron temperature of the diffusion plasma can enhance ionization of metallic vapors present in the central volume of a DECR reactor. The control of plasma parameters in magnetron-like plasmas opens new possibilities for complex treatments associating successive processes with extreme plasma specifications. As examples, thermochemical processing at low ion bombardment energy can be performed in DECR plasmas. Results on plasma nitriding of stainless steel for industrial applications are reported. More generally, plasma-assisted deposition (PAD) or PBII and deposition (PBIID), using chemical (CVD) or physical vapor deposition (PVD), can be operated with magnetron-like discharges: PACVD and PBIICVD in DECR plasmas, PAPVD and PBIIPVD in hybrid DECR magnetron reactors.

Plasma enhanced chemical vapour deposition of SiO xN y in an integrated distributed electron cyclotron resonance reactor

The deposition of silicon alloy thin films at room temperature is of increasing interest for various applications, such as functional, protective and optical coatings on polymers. In this work an integrated distributed electron cyclotron resonance (IDECR) high density plasma reactor is used for the deposition of SiO x N y thin films with variable optical properties. The reactor has planar geometry and is scalable for large area applications. Properties of material are analyzed with in situ UV–Visible ellipsometry, ex situ infrared transmission, RBS and ERDA measurements. Without substrate heating, dense, non-absorbing and low hydrogen content stoichiometric films of SiO 2 and Si 3N 4 are grown from the mixture of SiH 4, O 2 and N 2. Deposition rates are between 0.5 and 5 nm/s for Si 3N 4 and SiO 2, respectively. By changing the nitrogen to oxygen gas flow ratio the refractive index (measured at 632.8 nm) can be smoothly and reproducibly tuned from 1.96 to 1.46. The correlation between material properties and plasma parameters indicates that the silane partial pressure influences the hydrogen incorporation into the silicon nitride films.

Chemical contribution of oxygen to silicon carbide plasma etching kinetics in a distributed electron cyclotron resonance (DECR) reactor

This paper deals with the influence of the oxygen additive on the fluorinated plasma etch rate of silicon carbide. The assumption according to which the oxygen has a direct contribution to silicon carbide etching, by chemical reaction with carbon atoms, is generally reported in the literature. Our etching experiments are performed in a distributed electron cyclotron resonance reactor, on both 3C- and 6H-SiC. An SF6/O2 gas mixture (avoiding the presence of C species in the plasma), fluorine saturation conditions and constant ion bombardment energy and flux are used, allowing the study of O2 contribution exclusively. In these conditions, our results demonstrate the neutrality of O2 on SiC etching mechanisms. These results will be discussed reinfored both by several other experimental observations.

In situ infrared ellipsometry study of plasma processing of metallic surfaces

Aluminium and stainless-steel surfaces were processed using H 2 plasma in an Integrated Distributed Electron Cyclotron Resonance reactor. H 2 plasma treatment was monitored by in situ infrared (IR) ellipsometry in the range 2800–3050 cm −1 and correlated with ex situ AES depth profiling measurements. The removal of hydrocarbon surface contamination was first demonstrated. Real-time monitoring was also performed during treatment. The evolution of the ellipsometrical angle Δ at fixed wavelength, out of any vibration range, reveals a reduction of the native oxide layer. On Al, Δ shifts are attributed to the reduction of the external hydroxylated and porous oxide phase, the dense Al 2O 3 passivating layer remaining unchanged. In contrast, stainless-steel oxide is found less stable than Al 2O 3 and its reduction is almost complete (thickness estimated to be 1.1 ± 0.2 nm) using the same plasma conditions. As a consequence, the adhesion of SiO 2 thin films to stainless-steel substrate is found to be enhanced after H 2 plasma treatment. The enhancement is attributed to an increase in the substrate surface energy due simultaneously to cleaning and to native oxide reduction, which leads to stronger interactions with SiO 2. In conclusion, IR ellipsometry appears a very promising in situ technique to probe plasma processing of surfaces.

Plasma enhanced chemical vapour deposition of silica thin films in an integrated distributed electron cyclotron resonance reactor

The deposition of amorphous SiO 2 at low temperature in an integrated distributed electron cyclotron resonance (IDECR) reactor is studied. Due to planar geometry such deposition process can be scaled-up for processing of large surfaces. Stoichiometric and dense silica films are deposited without bias at room temperature from a SiH 4+O 2 mixture at high deposition rates (>2 nm/s). Optical properties of the films are analyzed by UV-visible spectroellipsometry. The influence of gas flows, pressure and microwave power is investigated. The gas phase is found to determine the film stoichiometry, the SiH 4 flow being the growth rate limiting factor. Optical properties match those of thermal silica. Electrical properties appear promising even for electronic applications.

Angle etch control for silicon carbide power devices

Silicon carbide plasma etching results are reported. Etching experiments are performed in a distributed electron cyclotron resonance reactor, using a SF6/O2 gas mixture, on both 3C- and 6H-SiC. A special interest has been given to the slope of the etched sidewalls. Slopes between 30° and 80° have been achieved by varying selectivities between SiC and the SiO2 masking layer. Two parameters have been investigated to modulate selectivity: bias voltage and O2 additive flow. A wide range of selectivities (from 1 to 6.5) has been obtained for suitable etch rate (100 to 270 nm/min) with very smooth surfaces.

Comparison of Dry Development Techniques using O2 and SO2/O2 Low-Pressure Plasmas

A parametric study of the pattern transfer step in a trilevel resist system using oxygen-based plasmas has been performed using a distributed electron cyclotron resonance reactor with independent rf biasing. In pure oxygen plasmas, critical dimension loss is always present. The mechanisms most likely to be responsible for these defects during the pattern transfer process are presented and discussed. A novel plasma etching process based on sidewall passivation by sulfur is proposed using SO2/O2 mixtures. Perfect anisotropy with negligiable critical dimension loss is obtained at room temperature.

Dry development and trilevel resist etching in a DECR reactor

Ion currents to the substrate holder in a Distributed Electron Cyclotron Resonance (DECR) etcher are maximum at a pressure of 0.15 Pa in oxygen plasmas. The ion current is strongly enhanced by changing the magnet configuration. In the pressure region of maximum ion current the etching characteristics of oxygen plasmas for dry development of the desire process are measured. The etch selectivity between silylated and unsilylated resist and the lithographic contrast increase with decreasing ion-bombardment energy. From trilevel etching it is found that wafer cooling is important for profile control. Characteristics of 0.5 μm Desire patterns made with i-line 0.42 NA exposure are shown.