We have proposed a novel method for synthesizing ultra low-k porous films (εr ≤2.0) as interlevel dielectrics in ULSI [1]. For the method, nano-particles are produced in reactive plasmas and are co-deposited on substrates together with radicals. The size of nano-particles as well as their transport from their generation region to substrates are important for controlling structure of such films. Up to now, we have succeeded in controlling their size using pulsed rf discharges [1,2]. To obtain information about their transport, we have applied amplitude modulation to the pulsed rf discharges and observed their transport in the discharges using a two-dimensional laser-light-scattering method. During the discharging period, nano-particles are mainly generated in the plasma/sheath boundary region near the powered electrode, and a large number of nano-particles reside in the plasma/sheath boundary region, due to a balance between ion drag force and electrostatic force exerted on nano-particles. After turning off unmodulated discharges, nano-particles move away at 10 cm/s from their generation region towards the upper grounded electrode due to thermophoretic force. Just after the modulation of amplitude modulated rf discharges, nano-particles are transported rapidly at more than 60 cm/s from their generation region towards the upper grounded electrode. Two key parameters for the rapid transport are the discharge voltage and the period of the modulation.
[1] S. Nunomura, et al., Jpn. J. Appl. Phys. 40(2005)L1509.
[2] S. Nunomura, et al., J. Appl. Phys. 99(2006)083302.
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