Institute of Experimental and Applied Physics XXII. Erfahrungsaustausch Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen Mühlleithen, 10.-12. 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 11.03.2015 1
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 11.03.2015 2
1. Motivation Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 3
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 11.03.2015 4
2. Theory Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 5
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 11.03.2015 6
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 11.03.2015 7
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 11.03.2015 8
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 11.03.2015 9
2. Theory conventional: transient: Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 10
2. Theory 2.3 Transient Method: Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 11
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 11.03.2015 12
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 11.03.2015 13
3. Experimental Setup Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 14
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 11.03.2015 15
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 11.03.2015 16
4. Experimental Results T e and n e Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 17
4.1 Electron temperature and plasma density Ti-Target P = 100 W Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 18
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 11.03.2015 19
4. Experimental Results Ionization probability Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 20
4.2 Ionization probability Ti-Target P = 100 W Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 21
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 11.03.2015 22
4. Experimental Results QCM and SRIM results Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 23
4.3 QCM and SRIM results 4.3.1 Quartz Crystal Microbalance (QCM): Ti-Target P = 100 W Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 24
4.3.2 SRIM simulations: 4.3 QCM and SRIM results simulation of 1.000.000 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) 1.3 17.2 12.1 22.7 2.5 16.6 11.7 22.1 4.0 16.6 11.7 21.1 Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 25
4. Experimental Results Energy influx contributions Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 26
4.4 Energy influx contributions Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 27
5. Summary Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 28
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 11.03.2015 29
Thank you for your attention! Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 30
Fabian Haase Increased ionization during magnetron sputtering 11.03.2015 31