Energy fluxes in plasmas for fabrication of nanostructured materials IEAP, Universität Kiel 2nd Graduate Summer Institute "Complex Plasmas" August 5-13, 2010 in Greifswald (Germany) AG 1
Outline Motivation Contributions to the total energy influx The method of calorimetric probes Example 1: Deposition of c-bn Example 2: Generation of silver nano clusters Summary 1 AG 2
Motivation Contributions to the total energy influx The method of calorimetric probes Example 1: Deposition of c-bn Example 2: Generation of silver nano clusters Summary 2 AG 3
Motivation Deposition and modification of functional thin films and materials by plasmas Treatment of heat sensitive materials Chemical reactions induced by electrons Modification and fine tuning by ions... Film properties depend on [1]: substrate temperature pressure particle energies... [1] Thornton, J. Vac. Sci. Technol. 11, 4, 1974 3 4
Examples SiOx thin films: Protective layers Adhesion control Diffusion barriers... Picture taken from [2]. c-bn thin films: Protective coatings [3]: Chemical inert against oxidation Very hard Excellent thermal conductivity Noble metal nano clusters [4]: Anti-bacterial coatings Optical devices / filters Sensors... Photo: Peter Binder [2] Schäfer et al.: Plasma Process. Polym. 2009, 6, 519-524 [3] Sell et al.: Surf. and Coat. Technol. 2003, 174-175, 1121-1125 [4] Faupel et al: Contrib. Plasma Phys. 2007, 47, 7, 537-544 4 5
Motivation Contributions to the total energy influx The method of calorimetric probes Example 1: Deposition of c-bn Example 2: Generation of silver nano clusters Summary 5 6
Contributions to the total energy influx plasma electrons ions surface J e =n e J i=ne kbte e 0 pl S exp 2kBT e 2 me kbte k BT e exp 0.5 e 0 pl S mi neutrals J rec = j i E ion W radiation J e, sec = j e E kin W J cond =qc R= n j n E B surface: chem. reactions recombination film growth sec. electron emission J total = J x [5] Kersten et al.: Vacuum 2001, 63, 3, 385-431 7 6
Motivation Contributions to the total energy influx The method of calorimetric probes Example 1: Deposition of c-bn Example 2: Generation of silver nano clusters Summary 7 8
The method of calorimetric probes Substrate dummy : Material: Brass Radius: 0.5 cm Connections: thermo couple (type K) copper wire for probe bias Ceramic shielding: Material: Macor low heat conductivity high heat capacity keeps backside of the dummy at constant temperature 8 9
Change of enthalpy during heating: H h =C S T h=p in Pout Change of enthalpy during cooling: H c =C S T c =P out Total or integral energy influx: P in=c S [ T h T c ] 9 [5] Kersten et al.: Vacuum 2001, 63, 3, 385-431 10
Calibration of the calorimetric probe: Exposing the probe to a source of known power: Electrons are accelerated towards the positively biased probe [6]. [6] Stahl et al.: Rev. Sci. Instrum., 2010, 81, 023504 CS 11 10
Motivation Contributions to the total energy influx The method of calorimetric probes Example 1: Deposition of c-bn Example 2: Generation of silver nano clusters Summary 11 12
Excursion: Magnetron sputtering mv v B r L= q B r L, e r L, i ion sputtered atom E B target magnets collision cascades in the target material number of sputtered atoms Y S= number of impinging ions [7] Betz, Wien: Int. J. Mass. Spectrom. 140, 1994 [8] Hippler et al.: Low Temperature Plasmas, Wiley-VCH, 2007 12 13
Experimental conditions: -- 3'' hot pressed h-bn target -- 50-500 W @ 13.56 MHz -- pressures: 0.17 1.5 Pa Investigations on: -- power -- probe bias -- pressure -- nitrogen and oxygen addition 13 14
Plasma parameter measured with double probe: Conditions: 400 W 80 sccm argon flow 0.4 0.42 Pa Plasma parameters obtained from double probe measurements are used to calculate the different contributions of impinging electrons and ions and recombination at the surface. [9] Ulrich et al.: Surf. Coat. Techn. 2010 14 15
Determination of the energy influx by neutral sputtered atoms: SRIM [10,11] simulations: Projectile energy (Ar): Voltage at electrode (~200 ev) Incident angle: 90 Displacement energy: 15 ev Lattice binding energy: 3 ev Surface binding energy: 3 ev Density of h-bn target: 2.28 g/cm2 Results: YS ~ 0.1 Only 0.78% of the sputtered particles reach the probe Mean kinetic energy ~6.3 ev [10] www.srim.org [11] Chen: IEEE Trans. P. Sci, 1998, 26, 6 AG AG 15 16
Contributions by different plasma species and processes: Energy influx by neutral sputtered atoms is the dominating effect. Calculations are higher than the values from the measurement because: No SEE included No collisions of sputtered atoms All sputtered atoms are incorporated Estimations of Pi, Pe, Prec represent the upper limit 16 17
The influence of oxygen addition Oxygen addition reduces internal stress and c-bn content Increasing energy influx due to negatively charged oxygen ions. Hysteresis caused by target poisoning 17 [12] Ulrich et al.: Thin Solid Films, 2009, 518, 1443-1450 18
Motivation Contributions to the total energy influx The method of calorimetric probes Example 1: Deposition of c-bn Example 2: Generation of silver nano clusters Summary 18 19
Experimental conditions: 2 ' silver target 5-75 W @ DC pressures: 10 100 Pa POSTER 19 20
The influence of the total pressure Experimental conditions: 50 W Ar flow : He flow = 1:1 Biased probe, because of the low energy influx at floating or grounded operation. 20 21
The influence of helium addition Experimental conditions: 50 W p=10-40 Pa Helium neutral collisions open new paths for sputtered atoms to loose energy [13], thus enhances cluster formation. [13] Wagatsuma, Hirokawa, 1988, Anal. Chem., 60, 7 21 22
Summary: Introduction to calorimetric probe method Examples for different types of magnetron discharges: Model of total energy influx comparison to measurements 22 23
Thanks to: J. Ye, S. Ulrich T. Peter, T. Strunskus, V. Zaporojtchenko, F. Faupel M. Wolter, H. Kersten 1 24
Thank you for your attention! end 25