M Chesaux’s research while affiliated with Swiss Federal Institute of Technology in Lausanne and other places

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Publications (4)


Schematic of the two-part grounded chamber. The upper chamber is a parallel plate capacitively coupled rf plasma reactor with rf electrode area Arf = 88 × 88 mm², ground area Ag = 110 × 110 mm² with a 7 mm electrode gap. The lower chamber is a grounded enclosure, separated from the upper chamber by the thin grounded grid.
Schematic of the four grids, the potentials and charged particle trajectories inside the RFEA.
Schematic of the time-averaged and PROES setup. The different steps for generating a delayed trigger signal are the following: reduction of the rf signal amplitude; generating a trigger synchronized to the rf signal; adding the desired delay to the camera trigger.
Time-averaged image of the plasma intensity (a) with the rf glow discharge only in the chamber above the grid, and (b) when a plasmoid is ignited in the grid orifice. Note the change in the logarithmic color scale range.
The measured ratio of self-bias voltage to rf voltage amplitude, , as a function of . A → B: plasma only above the grid, no plasmoid. BC: plasmoid ignites, accompanied by a faint plasma below the grid and a strong drop in self-bias voltage. C → D: plasmoid sustains plasma below the grid. DA′: plasmoid extinguished. Each point corresponds to a measurement under steady-state conditions, whereas arrows BC and DA′ are spontaneous transitions. The blue diamonds and red squares represent two measurement series separated by hours of plasma.

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Funnelling of rf current via a plasmoid through a grid hole in an rf capacitive plasma reactor
  • Article
  • Publisher preview available

August 2013

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98 Reads

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7 Citations

M Chesaux

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The boundaries of capacitively coupled radio-frequency (rf) plasma reactors generally include at least one grounded metal grid or perforated plate for purposes of gas flow or diagnostic access. When increasing the rf power, an intense localized plasma (a plasmoid) can spontaneously ignite in a hole of a grounded surface. Experiments described here show that the plasmoid funnels rf current through the hole to the other side of the grounded plate, thereby increasing the effective grounded area in contact with the plasma. Hence, plasmoid ignition is always accompanied by a drop in the dc self-bias voltage of the rf electrode. The small area of the plasmoid aperture means that the rf current density passing through the plasmoid is very high, causing intense optical emission and strong local heating. Plasmoid ignition can therefore cause a loss of process reproducibility and potentially lead to melting and eventual destruction of reactor components.

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Low ion energy RF reactor using an array of plasmas through a grounded grid

March 2013

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124 Reads

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8 Citations

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films

Michael Chesaux

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Ulrich Kroll

A reactor using localized remote plasma in a grid electrode is presented in this study. The aim is to reduce the ion bombardment energy inherent in RF capacitively coupled parallel plate reactors used to deposit large area thin film silicon solar cells. High ion bombardment energy could cause defects in silicon layers and deteriorate electrical interfaces, therefore, by reducing the ion bombardment energy, lower defect density might be obtained. In this study, the low ion bombardment energy results from the reactor design. By inserting a grounded grid close to the RF electrode of a parallel plate reactor, the electrode area asymmetry is increased while retaining the lateral uniformity required for large area deposition. This asymmetry causes a strong negative self-bias voltage, which reduces the time-averaged plasma potential and thus lowers the ion bombardment energy. In addition to the self-bias, the time evolution of plasma light emission and plasma potential RF waveform are also affected by the grid, thereby further reducing the time-averaged plasma potential and ion bombardment energy. Finally, a good correlation between the measured time-averaged plasma potential and measured low ion bombardment energy is found in a broad range of RF voltages.



Plasma deposition in an ideal showerhead reactor: A two-dimensional analytical solution

February 2012

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737 Reads

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22 Citations

The interplay of gas flow and depletion by plasma dissociation determines the spatial distribution of species and the deposition uniformity in a plasma source. Many plasma reactors use a gas showerhead and the design of the flow dynamics is a critical aspect of the reactor performance. In this paper, plasma deposition is considered as chemically reacting gas flow in an ideal showerhead reactor. The gas fluid flow is described by finite-gap stagnation-point creeping flow. The distribution of neutral species across the electrode gap is determined by diffusion equations, whereas their lateral transport is purely convective. Parameters relevant to large-area radio-frequency plasma deposition are particularly suitable for a complete analytical solution of the multi-component transport. A representative reaction scheme for hydrogen/silane plasma deposition is used for an analytical example from first principles which shows good agreement with numerical simulation. For a laterally uniform plasma, apart from edge effects, the deposition uniformity is limited only by the lateral uniformity of the pressure: if the electrode gap is very small in a large-area reactor, the pressure and deposition rate will be non-uniform even for a uniform showerhead. The deposition mass flux is self-consistently accounted for by the Stefan velocity for arbitrary levels of gas concentration and depletion, and its influence on streamlines and fluid velocity is shown.

Citations (4)


... This high-quality a-Si:H absorber layer is one of the key achievements of AIST enabling world-record solar cells mentioned in Section 2. The deposition rate, being typically one order of magnitude below that of a diode reactor, is the main drawback of this reactor type. The grid reactor design as presented in [126] is related to the triode reactor design. The third reactor concept (Fig. 3(c)) uses a plasma box as in Kai reactors built by Oerlikon Solar/Tokyo Electron, or IRFE electrodes as in Octopus systems built by INDEOtec, and is related to the reactor concept presented in [127]. ...

Reference:

Review: Progress in solar cells from hydrogenated amorphous silicon
A Grid Reactor with Low Ion Bombardment Energy for Large Area PECVD of Thin Film Silicon Solar Cells
  • Citing Article
  • January 2013

... Under typical operating conditions (inter-electrode distances of a few cm and gas pressures of a few Torr) such slits would provide a hollow cathode enhancement to the plasma [4,5], making the plasma denser but maintaining a uniform distribution. However, by approaching the powered electrode to within a very short distance of the substrate surface, plasma ignition is inhibited in all zones outside of the slits, as depicted in Fig. 1 (b). ...

Low ion energy RF reactor using an array of plasmas through a grounded grid
  • Citing Article
  • March 2013

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films

... Plasmoids can sometimes be observed near the powered electrodes of plasma discharges, especially in the case of structured, grid-shaped electrodes. An interesting work on this subject was published by Chesaux and coworkers in 2013, ref. [29] in which the authors measured, by means of PROES, the time-resolved Hα emission (656 nm) from plasma near a grid positioned in the middle of a CCP reactor, parallel to the grounded electrode, during an RF (13.56 MHz) discharge in H 2 at 100 Pa, working in normal conditions, and during the formation of a plasmoid. Figure 32a shows the emission intensity as a function of time and the distance from the grid, which is shown as a blue bar, while Figure 32b shows the corresponding time evolution of the RF bias applied at the powered electrode. ...

Funnelling of rf current via a plasmoid through a grid hole in an rf capacitive plasma reactor

... Since the ionization and excitation rates are proportional to both electron and neutral densities, a gas shower head is installed to make the neutral density profile uniform. [41][42][43][44] In this study, the neutral gas is injected from shower-patterned holes on the back wall to enhance the ionization process at the peripheral region, where the high electron temperature is often observed. The effect of the showered pattern gas injection is discussed with the electron temperature and plasma density measured by the rf-compensated Langmuir probe (CLP) and the power transfer efficiency. ...

Plasma deposition in an ideal showerhead reactor: A two-dimensional analytical solution
  • Citing Article
  • February 2012