Increased ionization during magnetron sputtering and its influence on the energy balance at the substrate

Transcription

1 Institute of Experimental and Applied Physics XXII. Erfahrungsaustausch Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen Mühlleithen, März, 2015 Increased ionization during magnetron sputtering and its influence on the energy balance at the substrate F. Haase 1, D. Lundin 2, S. Bornholdt 1 and H. Kersten 1 1 Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität Kiel 2 Laboratoire de Physique des Gaz et des Plasmas, Université Paris-Sud Fabian Haase Increased ionization during magnetron sputtering

2 Outline 1. Motivation 2. Theory 3. Experimental Setup 4. Experimental Results 1. Electron temperature and plasma density 2. Ionization probability 3. QCM and SRIM results 4. Energy influx contributions 5. Summary Fabian Haase Increased ionization during magnetron sputtering

3 1. Motivation Fabian Haase Increased ionization during magnetron sputtering

4 1. Motivation high degree of ionization enables deposition of thin films with improved qualities low degree of ionization (<10%) during DC magnetron sputtering (DCMS) [1] finding the buttons to achieve a higher degree of ionization for DCMS as in improved sputtering techniques (e.g. HiPIMS) [1] J.A. Hopwood (Ed.), Thin Films: Ionized Physical Vapor Deposition (Academic Press, San Diego, CA, 2000 Fabian Haase Increased ionization during magnetron sputtering

5 2. Theory Fabian Haase Increased ionization during magnetron sputtering

6 2. Theory 2.1 Degree of ionization: degree of ionization can be described by mean free path for ionization λλ mmmmmm : λλ mmmmmm = vv ss 1 nn ee kk 0 exp EE 0 kk BB TT ee vv ss = velocity of the sputtered neutrals nn ee = electron density T e residing in exponential expression provides a more effective way for increasing the ionization probability (decreasing λλ mmmmmm ) as compared to linear nn ee term. Fabian Haase Increased ionization during magnetron sputtering

7 2. Theory 2.2 Langmuir characteristic: I-V-characteristics are used for the determination of: floating potential Φ fl plasma potential Φ pl electron temperature T e plasma densities n i,e ability to calculate contribution of charged particles to total energy influx Fabian Haase Increased ionization during magnetron sputtering

8 2. Theory 2.2 Langmuir characteristic: calculation of energy influx contributions by electrons: JJ ee = 2 jj ee ee 0 kk BB TT ee for Maxwellian EEDF ions: JJ ii = jj ii ee 0 Φ pppp VV pppppppppp for monoenergetic ions recombination: JJ rrrrrr = jj ii ee 0 Φ iiiiii Φ eeeeee Fabian Haase Increased ionization during magnetron sputtering

9 2. Theory 2.3 Calorimetric probe: heat flux is described by simple thermodynamics: QQ = PP = CC ss TT temperature T s at the cross section A s depends on the influx P in and the loss mechanisms P out : CC ss TT ss,h = PP iiii PP oooooo = PP iiii aa( TT ss TT eeee cccccccccccccccccccc ) Fabian Haase Increased ionization during magnetron sputtering

10 2. Theory conventional: transient: Fabian Haase Increased ionization during magnetron sputtering

11 2. Theory 2.3 Transient Method: Fabian Haase Increased ionization during magnetron sputtering

12 2. Theory 2.4 Quartz Crystal Microbalance (QCM): Quartz crystal with resonance frequency at 6 MHz change in frequency by addition of small mass due to film growth measurements at substrate position ( z = 120 mm) calculation of deposition rate R R used for calculating energy influx contribution of neutrals and film condensation Fabian Haase Increased ionization during magnetron sputtering

13 2. Theory with QCM and SRIM data: calculation of energy influx contributions by neutrals: JJ nn = ρρ TTTTRR mm TTTT EE kkkkkk film condensation: JJ cccccccc = ρρ TTTTRR mm TTTT ααee bbbbbbbb αα 1 Fabian Haase Increased ionization during magnetron sputtering

14 3. Experimental Setup Fabian Haase Increased ionization during magnetron sputtering

15 3. Experimental Setup 3.1 Discharge Chamber: used gases: Ar (E i =15.76 ev) Ne (E i =21.56 ev) Kr (E i =14.00 ev) Fabian Haase Increased ionization during magnetron sputtering

16 3.2 Probe: 3. Experimental Setup simultaneous measurement of current and temperature calorimetric probe with Ø = 10 mm sample rate = 20 Hz used as planar Langmuir probe Kersten et al, TSF 377, 585 (2000) voltage sweep from -50 V to 20 V Fabian Haase Increased ionization during magnetron sputtering

17 4. Experimental Results T e and n e Fabian Haase Increased ionization during magnetron sputtering

18 4.1 Electron temperature and plasma density Ti-Target P = 100 W Fabian Haase Increased ionization during magnetron sputtering

19 4.1 Electron temperature and plasma density λλ mmmmmm = vv ss 1 nn ee kk 0 exp EE 0 kk BB TT ee T e is a factor of ~3 higher for Ne compared to Ar for Ne: n e is a about 40% of the value for Ar Fabian Haase Increased ionization during magnetron sputtering

20 4. Experimental Results Ionization probability Fabian Haase Increased ionization during magnetron sputtering

21 4.2 Ionization probability Ti-Target P = 100 W Fabian Haase Increased ionization during magnetron sputtering

22 4.2 Ionization probability probability of ionizing the sputtered neutrals increases strongly (λλ mmmmmm decreases) in the Ne/Ti case Fabian Haase Increased ionization during magnetron sputtering

23 4. Experimental Results QCM and SRIM results Fabian Haase Increased ionization during magnetron sputtering

24 4.3 QCM and SRIM results Quartz Crystal Microbalance (QCM): Ti-Target P = 100 W Fabian Haase Increased ionization during magnetron sputtering

25 4.3.2 SRIM simulations: 4.3 QCM and SRIM results simulation of particles hitting the target SRIM delivers velocity vector and particle energy detection of sputtered particles hitting the probe determination of mean kinetic energy EE kkkkkk of particles hitting the probe Pressure (Pa) Ar EE kkkkkk (ev) Kr EE kkkkkk (ev) Ne EE kkkkkk (ev) Fabian Haase Increased ionization during magnetron sputtering

26 4. Experimental Results Energy influx contributions Fabian Haase Increased ionization during magnetron sputtering

27 4.4 Energy influx contributions Fabian Haase Increased ionization during magnetron sputtering

28 5. Summary Fabian Haase Increased ionization during magnetron sputtering

29 5. Summary strong increase of T e in case of Ne/Ti increase of T e stronger than decrease in n e higher probability of ionizing sputtered metal atoms in the Ne/Ti case visible in decreasing λλ mmmmmm no significant addition to thermal stress upon substrate due to higher T e Use of Neon as process gas could be a valuable alternative despite drawbacks (lower sputter yield, more expensive than Argon) Finding an ideal gas mixture depends on target material work submitted to JAP Fabian Haase Increased ionization during magnetron sputtering

30 Thank you for your attention! Fabian Haase Increased ionization during magnetron sputtering

31 Fabian Haase Increased ionization during magnetron sputtering