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Berlin Aah

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plasma reyactor

Text of Berlin Aah

  • Plasma modelling & reactor designAlan Howling, Ben Strahm, Christoph Hollenstein

    Ecole Polytechnique Fdrale de Lausanne (EPFL), SwitzerlandCenter for Research in Plasma Physics (CRPP)

    1) The "plasma dimension" for plasma deposition of c-Si:H

    2) Direct pumping of a plasma reactor

    ... and one non-intrusive plasma diagnostic for each.

    IWTFSSC-2 Berlin April 2009

  • 1) Plasma-Enhanced Chemical Vapour Deposition of c-Si:H

    black boxPECVD

    sila

    nehy

    drog

    en

    SiH4

    H2

  • 1) PECVD reactor setup

    Plasma Box,Oerlikonprinciple:

    Jacques Schmitt

    sila

    nehy

    drog

    en

    p

    butterflyvalve

    processpumps

    vacuum chamber

    SiH4

    H2

    PRF[W]f [MHz]

    heating glass substrate

    RF connection

    grounded box

    showerhead RF electrode

    gas flowplasma boxside view

  • 1) Hydrogen dilution for plasma deposition of c-Si:H

    sila

    nehy

    drog

    en

    SiH4

    H2

    0

    0.05

    1c

    4SiH

    totalsilane concentration 5%

    is commonly used

    low c

    = 100 s ! time to steady-state < 1 s !

    Silane back-diffusion from any intermediatedead volume increases the equilibration time.

    t=0-100 s

    2) Compare open and closed reactors (numerical)

  • But the door is normally closed, the amorphous incubation layer is then thinner than 10 nm. substrate

    2) Practical consequence of the pumping configuration

    409 nm96 nm

    Amorphousincubation layers with open door

  • Two Conclusions1. Plasma composition and deposition depend on the silane concentration in the plasma,

    cpl=c(1-D) , and not only on the silane concentration in the input flow, c.

    Strong hydrogen dilution in the plasma, and c-Si:H deposition, can be obtained with high input concentration of silane.

    - monitored non-intrusively by FTIR in the pumping line.

    2. Rapid equilibration of plasma chemistry requires a closed, directly-pumped showerhead

    reactor with a uniform plasma - avoid gas circulation between the plasma and any dead volumes.

    - monitored non-intrusively by OES in the pumping line.

    Refs. B. Strahm et al, Plasma Sources, Sci. Technol. 16 80 (2007).

    A. A. Howling et al, Plasma Sources, Sci. Technol. 16 679 (2007).

    Acknowledgements: Swiss Federal Research Grant CTI 6947.1; and

    Dr. U. Kroll and colleagues, Oerlikon-Solar Lab SA, Neuchtel, Switzerland.

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