DUST FORMATION AND CHARGING IN AN AR SIH4 RADIOFREQUENCY DISCHARGE/

The formation and charging of submicrometer dust particles in a low pr essure argon/silane radio-frequency (rf) discharge was studied using l aser-induced photodetachment in combination with a microwave resonance technique. This method allows a measurement of the spatially averaged electron density, the spatially resolved negative ion density, and/or the charge on small clusters in the plasma as a function of time duri ng particle formation. The loss frequency of photodetached electrons y ields information about the recharging of small clusters. During the f irst second after plasma ignition dust particles are formed. Simultane ously, the electron density decreases from about 2 X 10(15) m(-3) to a bout 4 X 10(14) m(-3). In the first 10 ms after discharge ignition, ch arged particles are not present in the plasma and the photodetachment experiment gives a negative ion density of 4 X 10(15) m(-3). During th e first 50 ms after plasma ignition, nanocrystallites are formed, whic h is reflected by a strong increase of the loss frequency of photodeta ched electrons. After 50 ms the particles start to coalesce and acquir e a negative charge, which results in a strong increase of the photode tachment signal. After 1 s of plasma operation, the charge density on particles is about 8 X 10(16) m(-3). The photodetachment signal decrea ses with the gas flow rate, indicating that the clusters are expelled from the plasma by the gas flow. (C) 1996 American Vacuum Society.