Fyzikální ústav Akademie věd ČR

Seminar Wednesday, 08/04/2015 15:00 - 17:00

Speakers: Holger Kersten (Institute for Experimental and Applied Physics, University of Kiel, Germany)
Place: Lecture Hall of the Institute of Physics CAS, Pod vodárenskou věží 1, Prague
Presented in English
Organisers: Institute of Physics

For an optimization of plasma-based thin film deposition suitable diagnostics are required. In addition to well-established plasma diagnostic methods (e.g. emission spectroscopy, mass spectrometry, Langmuir probes, …) we perform examples of “non-conventional” low-cost diagnostics which are applicable in technological plasma processes. Examples are i. the determination of energy fluxes by calorimetric probes, ii. the measurement of momentum transfer due to sputtered particles by SPIN, and iii. the experimental determination of electric field in front of surfaces by microscopic test particles.

1. The total energy influx from a plasma to substrates can be measured by special calorimetric sensors (thermal probes). One method is based on the determination of the temporal slope of the substrate surface temperature in the course of the plasma process. The heating curve as well as the cooling curve (after switching-off) are fitted by suitable functions and the time derivatives at same environmental temperature are calculated. By knowing the calibrated heat capacity of the sensor the difference of the time derivatives yields the integral energy influx to the surface. Simultaneously, the electrical current to the substrate can be obtained and by variation of the sensors bias voltage the energetic contribution of charge carriers can be determined. By comparison with model assumptions on the involved plasma-surface mechanisms the different energetic contributions to the total energy influx can be separated.
2. For thin film deposition by sputtering it is essential to determine the sputtering yield as well as the angular distribution of sputtered atoms. Therefore, in addition to model calculations (TRIM, TRIDYN etc.) an experimental determination of the related quantities is highly demanded. For this purpose we propose a novel and rather simple method – the so-called sputtering-propelled instrument (SPIN). In principal, the SPIN is a kind of wind wheel where the rotor blades are plane targets of the sputtering material. The wheel, which is stack nearly without friction and exposed to a vertical ion beam, starts to rotate due to momentum transfer by the released particles, i.e. sputtered target atoms and recoiled ions. By knowing the moment of inertia and by measuring the accelerated rotation, the propelling force can be determined experimentally. In the present study measurements by SPIN and simulation by TRIM are compared for different experimental conditions.
3. The idea to use microscopic test particles as electrostatic probes in complex process plasmas has been developed during the last years. Due to the force balance of the particles, however, it is very difficult to change their position in the plasma sheath without changing the external and internal plasma parameters. Recently, experiments have been performed where the confined particles are affected by additional centrifugal force or by laser radiation. By vertical motion of the electrode the fixed probe particle could be shifted to a certain extent through the sheath in front of the electrode. By this non-invasive method it is possible to perform flexible investigations without changing or disturbance of the plasma conditions. The evaluation of the affected force balance yields information about the potential and electric field at arbitrary positions in the sheath.

Prof. Dr. Holger Kersten is the professor of experimental and applied physics and the leader of the working group for plasma physics and plasma technology at the University of Kiel in Germany.