AVS 58th Annual International Symposium and Exhibition | |

Energy Frontiers Focus Topic |
Monday Sessions |

Session EN+PS-MoM |

RF-PECVD Processes Excited by Asymmetric Voltage Waveforms

Session: |
Plasmas for Photovoltaics & Energy Applications |

Presenter: |
Pierre-Alexandre Delattre, Laboratoire de Physique des Plasmas, France |

Authors: |
P.-A. Delattre, Laboratoire de Physique des Plasmas, FranceS. Pouliquen, Laboratoire de Physique des Plasmas, FranceE.V. Johnson, Laboratory of Physics of Interfaces and Thin Films, FranceJ.-P. Booth, Laboratoire de Physique des Plasmas, France |

Correspondent: |
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Voltage Waveform Tailoring (VWT) is a promising new technique for Radio-Frequency (RF) process plasma excitation. It is known that asymmetric waveforms resembling *peaks* (short positive and long negative voltage) or *valleys* (long positive, short negative voltage) can produce a voltage self-bias, even in a symmetrical reactor [1], known as the Electrical Asymmetry Effect (EAE). We have implemented a system to provide such voltage waveforms on the RF electrode of our Capacitively Coupled Plasma (CCP) reactor. For a peak to peak voltage (V_{PP}) of 300 V, we can control the self-bias from -190 V to 15 V, without changing any other process parameter. A new differential RF probe gives us the real-time current and voltage derivatives, and therefore, the instantaneous power. For a voltage waveform composed of a 15 MHz fundamental and three harmonics, instantaneous power changes from +1 kW to –1kW in 10 ns. Using a hairpin resonator probe in hydrogen at 13 Pa, we have measured an electron density of 2E8 cm^{-3} with a standard sine waveform, 2E9 cm^{-3} with a valleys waveform and 2E10 cm^{-3} with a peaks waveform (all with V_{PP}= 300V). With a view towards photovoltaic applications, using a gas mixture of 4 % of SiH_{4} in H_{2} at 65 Pa, we have achieved a deposition rate of high-quality amorphous silicon of 1 Å/s for sine, 2.7 Å/s for valleys, and 3.8 Å/s for peaks voltage waveforms.

^{1}Brian G Heil *et al* 2008 *J. Phys. D: Appl. Phys.* **41** 165202