MEMS_13-14 gw dry etch tech_01A

MEMS_13-14 gw dry etch tech_01A - Plasma discharge Common...

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Plasma discharge Common base in plasma Using high energy electric/magnetic field Dissociate a feed gas To form neutrals, energetic ions, photons, electrons and highly reactive radicals Surface contacting plasma is exposed to flux of these particles The corresponding bombardment stimulate production of outgoing fluxes of these particles Causing etching or surface modification
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Plasma discharge: physics of DC plasma Physics of DC plasma The simplest plasma reactor consist of Chamber filled with inert gas Opposed parallel plate electrodes Low Pressure (P) Electrical breakdown of inert gas, e.g. Argon when electrons, accelerated in the field, transfer an amount of kinetic energy (> argon ionization potential) to the argon neutrals -> 2 nd free electron and + ion -> avalanche -> Gas breakdown emitting a characteristic glow
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Plasma discharge: physics of DC plasma Physics of DC plasma
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Plasma discharge: physics of DC plasma Physics of DC plasma Avalanche -> sustain gas breakdown -> current flow -> voltage drop Build a discharge current -> equilibrium Glow region of plasma is a good conductor -> sustain a very low field -> its potential is almost a constant Two sheath fields Secondary electron emission (auger electrons) to sustain a plasma
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Plasma discharge: physics of DC plasma Physics of DC plasma Plasma characteristic: permanent +charge, because of loss of electron Due to random motion of electrons and ions ion 4000-100000 times heavier than electron Flux j of ions and electrons: equ. (2.1) j = nv/4 n: density v: velocity
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Plasma discharge: physics of DC plasma Physics of DC plasma Asymmetric voltage distribution: electrons are, due to low mass, accelerated fast Cathode-fall region is built in Bombardment energy of ions ~ potential difference between the plasma and the surface being struck by the ions Average electron energy Ve = kTe (e.g. 1-10 eV) Average ion energy Vi = kTi (e.g. 0.04 eV)
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Plasma discharge: physics of DC plasma DC plasma for dry etching Place the substrate to the cathode Plasma will produce sufficiently energetic ion To induce physically ion etching, or sputtering Atoms are billiard-ball-wise ejected from the bombarded substrate Low P -> long mean free path E concentrates in the cathode plasma sheath to accelerate the ions The ions loss much energy before hitting the substrate when transverse the sheath due to collisions
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physics of DC plasma DC plasma for dry etching Physical etching Choice of dry itching technique: efficiency Plasma’s average –e or ion energy kT e,i = E/P Bombarding ion flux: equ. (2.5) J = qnμE q: charge μ mobility Typical sputtering profile: Fig. 2.2A
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MEMS_13-14 gw dry etch tech_01A - Plasma discharge Common...

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