SEERS in Sampling Mode A Tool to Investigate Dynamics in Pulsed R.F.-Plasma Rolf-Dieter Schulze, Jörg F. Friedrich, Bundesanstalt für Materialforschung und -prüfung Berlin * Introduction - pulsed r.f.-plasma for polymerisation * Task - SEERS in sampling for time resolved investigations * Influence of external parameters on pulsed plasma * Influence of disturbances 2nd Workshop on Self Excited Electron Plasma Resonance Spectroscopy Dresden, Germany on 11th - 12th of December 2
Introduction A pulsed r.f.-plasma was used to produce polymer coatings by plasma polymerisation of different monomers. A continuous low-pressure plasma of glow discharge gerates fragments of monomer molecules, which are required to gerate a polymerisation on the sample surface. The mechanism can be characterised as an atomic polymerisation (H. Yasuda) or as polyrecombination of radicals. (VUV radiation and collision by high ergetic particles produce further destruction on the surface.) A dense twork of hydrocarbon with no or low similarity to the primarily used monomer structure is formed. Using delay times between short r.f.-pulses (pulsed plasma mode) non-destroyed monomer molecules can react with radicals, formed at the surface during the previous plasma pulse. Such pulsed plasma produced polymer films are more stable against exposure to air. They exhibit a structure similar to those of classic polymers. The retention of the monomer structure in the formed pulsed plasma polymer layer depends strongly on the used plasma parameters.
Influence of delay time on the formation of plasma polymerised film (J.G.Calderon and R.B.Timmons, Macromolecules, Vol.31, 1998, 1, 3216 ff.) Acryloyl chloride
Proposed mechanism of the pulsed plasma polymerisation of styre
Problem To solve the problems of more reproducibility, better structure and stability of plasma polymerised films and to optimise the plasma polymerisation process for various monomers there is interest to study the real behaviour of ionising molecules in the short plasma pulse, as possible resolved in time. Method In contrary to Langmuir probes and optical methods the SEERS method has the befit to be not influenced by continuously coating of the reactor walls. Calculated parameters of electron density n e and electron collusion rate ny e should correspond to geration of free radicals cessary for further chemical reactions. Data acquisition time of less than 1 µs for o measurement by the Hercules (ASI Berlin) allows to realise a sampling regime. With the modified apparatus we are able to investigate the real behaviour of the time resolved parameters within the r.f.-pulse.
Voltage [arb.units] 6 2-8 8.E-3 - Plasma development in a 25µsec r.f.-pulse N 2 5Pa 25W 1kHz U.Anode -5 5 1 15 2 25 3 t µs U.sensor -8.E-3 2.E-3-5 5 1 15 2 25 3 t [µsec] Sensor Sensor Sensor U.Anode U.A node U.Anode 2 2.E-3 2 2.E-3 2.E -3.E -3.E - 3.E -3.E -3.E - 3.E -3.5.1.15.E -3 3 3.5 3.1 3.15.E - 3.5.55.6.65 t µs t µs t µ s
8.E-3 U.sensor - -8.E-3-5 5 1 15 2 25 3 t [µsec] 6.E-3 Sensor 6 6.E-3 6 6.E-3 6 U.Anode 2.E-3 2 2.E-3 2 2.E-3 2.E - 3.E-3.E -3.E - 3 -.E -3.E - 3.E-3.E -3-8.E - 3-8 5.5 5.55 5.6 5.65 t µ s -8.E-3-8 8 8.5 8.1 8.15 t µs -8.E -3-8 12 12.5 12.1 12.15 t µs 6.E-3 8 6.E-3 6 6.E-3 6 6 2.E-3 2.E-3 2 2.E-3 2.E - 3 2.E -3.E -3.E - 3.E -3.E -3.E - 3.E -3.E -3-8.E - 3-8 -8.E -3-8 -8.E -3-8 19 19.5 19.1 19.15 2 2.5 2.1 2.15 21 21.5 21.1 21.15 t µs t µs t µs
Influence of gas flow Nitrogen, 5 Pa, 1kHz5µsec 2W 15 sccm 5 sccm.e+ 1.E-5 2.E-5 1 2 t [µs].e+ 1.E-5 1 2.E-5 2 t [µs]
Influence of chamber pressure Nitrogen, 5sccm, 1kHz5µsec 2W 5Pa 1Pa 16Pa 1 2 1.E-5 1 2.E-5 2 1 2 1.E-5 2.E-5 t [µs] 1.E-5 2.E-5
Influence of r.f.-power Nitrogen, 3 sccm, 5 Pa, 1kHz5µsec 5 W 2 W 6 W ny e [1/s] n e [1/cm³] [1/s], [ 1/cm³] 1 2.E+ 1.E-5 1 2.E-5 2.E+ 1.E-5 1 2.E-5 2.E+ 1.E-5 2.E-5 t [µs]
Influence of pulse time Nitrogen, 5 Pa, 3sccm, 2W 25 µsec 1kHz 2(28)W 1 µsec 5kHz 2(17)W ny e [1/s], n e [1/cm³], [1/s] t [µs].e+ 2.E-5 2.E-5 6.E-5 6 8.E-5 8 1.E 1 power: nominal (indicated in pulsed mode)
Influence of pulse time Ethyle, Pa, 3sccm, 2W 25 µsec 1kHz 2(28)W 1 µsec 1kHz 2(23)W ny e [1/s], n e [1/cm³] 2.E-5 2.E-5 6.E-5 6 8.E-5 8 t [µs] 1.E 1 power: nominal (indicated in pulsed mode)
Influence of gas flow disturbance ethyle, 5 Pa, 1kHz5µsec 2W [1/s], e n e [1/cm³] 1.E-5 1 t [µs] 2.E-5 2
Styre in pulsed plasma at pressure variation t [s] 1.E-5 2.E-5 5,5(1)Pa 2sccm, 15(2)W 1kHz 25µsec 2 6 real time t [min] 1.E-5 2.E-5 t [s] 2(5)Pa 2sccm, 15(25)W 1kHz 25µsec pressure: capacitance gage (Pirani gage) power: nominal (indicated in pulsed mode) 2 6 8 1 real time t [min]
Influence of chamber conditions and wall contamination without sampleholder 2.E-5.E-5 6.E-5 8.E-5 5 min styre 2.E-5.E-5 6.E-5 8.E-5 oxygen t [s] inserted substrate Aluminium 2.E-5.E-5 6.E-5 t [s] 8.E-5 2.E-5.E-5 6.E-5 8.E-5 t [s] pulsed plasma: 5 min oxygen 5Pa 3sccm 1µsec 1kHz a) oxygen without sample holder; 2(23)W b) inserted sample holder with Al substrate; 2(23)W changes during 5 minutes pulsed plasma: 5 min 1µsec 1kHz c) plasma polymerisation of styre 2sccm 2(11)W 2(5)Pa d) without sample holder as (a ); oxygen 5Pa 3sccm 2(28)W changes during 5 minutes
Oxygen pulsed plasma in styre contaminated chamber 1. E + 1 [1/s], [1/cm³] 1. E + 9 n y e n e 1. E + 8 1. E + 7 real time t [min] 2 6 8 1 1 2 1 1 6 1 8 Calculated parameters of graphic (d) in real time scale (not equidistant relation in pulse time)
Summary Using a sampled SEERS the parameters of pulsed r.f.-plasma have been investigated in time resolution. For nitrogen and oxygen we established an influence of - input power - chamber pressure - time of pulse length but - no influence of gas flow (at our conditions) - no notable differences between nitrogen and oxygen according to comparable atomic properties. At pulse time variation the amplitude behaviour seems to be more complex and eds further investigation Pulsed plasma polymerisation conditions show comparable behaviour, but are less stable (suggested chamber contamination). Using ethyle and styre we demonstrated the influence of pressure variation or gas flow disturbances. The method is extreme sensitive to changes in plasma conditions. The results suggest an essential influence of the chamber wall (and sample and holder surface) isolation on the plasma development in the r.f.- pulse. The SEERS method is extremely sensitive to changes in plasma conditions and an useful tool to compare plasma conditions.