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Title: Direct ion flux measurements at high-pressure-depletion conditions for microcrystalline silicon deposition

The contribution of ions to the growth of microcrystalline silicon thin films has been investigated in the well-known high-pressure-depletion (HPD) regime by coupling thin-film analysis with plasma studies. The ion flux, measured by means of a capacitive probe, has been studied in two regimes, i.e., the amorphous-to-microcrystalline transition regime and a low-to-high power regime; the latter regime had been investigated to evaluate the impact of the plasma power on the ion flux in collisional plasmas. The ion flux was found not to change considerably under the conditions where the deposited material undergoes a transition from the amorphous to the microcrystalline silicon phase; for solar-grade material, an ion-to-Si deposition flux of ∼0.30 has been determined. As an upper-estimation of the ion energy, a mean ion energy of ∼19 eV has been measured under low-pressure conditions (<1 mbar) by means of a retarding field energy analyzer. Combining this upper-estimate with an ion per deposited Si atom ratio of ∼0.30, it is concluded that less than 6 eV is available per deposited Si atom. The addition of a small amount of SiH{sub 4} to an H{sub 2} plasma resulted in an increase of the ion flux by about 30% for higher power values,more » whereas the electron density, deduced from optical emission spectroscopy analysis, decreased. The electron temperature, also deduced from optical emission spectroscopy analysis, reveals a slight decrease with power. Although the dominant ion in the HPD regime is SiH{sub 3}{sup +}, i.e., a change from H{sub 3}{sup +} in pure hydrogen HPD conditions, the measured larger ion loss can be explained by assuming steeper electron density profiles. These results, therefore, confirm the results reported so far: the ion-to-Si deposition flux is relatively large but has neither influence on the microcrystalline silicon film properties nor on the phase transition. Possible explanations are the reported high atomic hydrogen to deposition flux ratio, mitigating the detrimental effects of an excessive ion flux.« less
Authors:
; ; ; ;  [1] ;  [1] ;  [2] ;  [1] ;  [3]
  1. Applied Physics Department, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven (Netherlands)
  2. (Netherlands)
  3. (DIFFER), P.O. Box 1207, 3430BE Nieuwegein (Netherlands)
Publication Date:
OSTI Identifier:
22218234
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 114; Journal Issue: 6; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COLLISIONAL PLASMA; CRYSTALLIZATION; DEPOSITION; ELECTRON DENSITY; ELECTRON TEMPERATURE; EMISSION SPECTROSCOPY; HYDROGEN; HYDROGEN IONS 3 PLUS; SEMICONDUCTOR MATERIALS; SILICON; THIN FILMS