Diagnostics of particle formation in an Ar-Silane RF capacitively coupled plasma.

1. Comparison between electrical and optical measurements Diagnostics of particle formation in an Ar-Silane RF capacitively coupled plasma. R. Ghidini1, C.H.J.M. Groothuis, M. Sorokine, W.W. Stoffels, G.M.W. Kroesen Department of Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 1Department of Electrical Engineering, University of Bologna, 40136 Bologna, Italy Plasma discharges are widely used in many specialized commercial production environments. One of these is the production of amorphous silicon solar cells. The key process in that production is the plasma enhanced silicon layers deposition. Currently these cells have efficiency of about 10% and it goes down in one to three years. Under certain production conditions, nanometer sized particles incorporate themselves into the amorphous silicon layers, which leads to a significant increase in quality of the solar cells. To find and control these conditions we monitor the plasma electric parameters – voltage, current and phase shift between the voltage and the current for the first five harmonics. At the same time we look at the optical emission from the plasma and at the intensity of a laser light scattered on the particles. We performed experiments for several different temperatures of the discharge chamber, ranging from 170C till 1800C . Theory of particle growth. f = 13.56 MHz Pf = 10 W Pr = 20% Pf Pb = 1•10-6mbar f = 10 sccm p = 0.133 mbar Ar/SiH4(95/5%) IV sensor For our electrical measurements we used the original Smart PIM hardware of Scientific Systems. Electrical results Optical results Dust particles expulsion Discharge is on – see particles streaming out of the chamber through the hole in the grid. Discharge is off – cloud of dust particles moves to the wall. Discharge is off – particle cloud takes shape of a sphere. Temperature dependence • Occurrence of dust particles in plasma changes the electrical parameters • Higher harmonics are much more sensitive to the formation of dust particles • Higher gas temperature delays all the formation phases • Probably at higher temperatures we have particles of a smaller size • We find a correspondence between the optical and the electrical measurements 5th Euregional WELT-PP Conference, November 28-29, 2002, Kerkrade, the Netherlands