Plasma diagnostics of pulsed sputtering discharge

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Plasma diagnostics of pulsed sputtering discharge Vitezslav Stranak Zdenek Hubicka, Martin Cada and Rainer Hippler University of Greifswald,

1 Plasma diagnostics of pulsed sputtering discharge Vitezslav Stranak Zdenek Hubicka, Martin Cada and Rainer Hippler University of Greifswald, Institute of Physics, Felix-Hausdorff-Str. 6, Greifswald, Germany Collaborative Research Center Transregio 24 Fundamentals of Complex Plasmas

2 Content of the contribution Introduction motivation, aims time resolved diagnostic of pulsed sputtering discharges dual magnetron sputtering an overview Experimental device, plasma diagnostic experimental device dual pulsed sputtering system for complex film deposition plasma diagnostic pulsed systems time-resolved diagnostic Langmuir probe measurements optical emission spectroscopy ion flux measurements energy influx to substrate controlling of film properties by input plasma parameters Conclusion, further plans summary of results

Motivation controlling of thin film properties by input experimental conditions deposition of required crystallography structures TiO 2 anatase, rutile, brookite deposition of thin bio-compatible

3 Motivation controlling of thin film properties by input experimental conditions deposition of required crystallography structures TiO 2 anatase, rutile, brookite deposition of thin bio-compatible coatings of complex properties (bio-, mechanical, physical) high biocompatibility Ti implants (Ti-C thin film on the top) good cellular adhesion of osteoblasts antimicrobial properties immersion of (Cu, Ag) agent onto surface input plasma parameters deposition of Ti-Cu films Magnetron sputtering deposition sputtering of target material by (usually buffer gas) ions supported by magnetic field comfinement the efficiency is influenced by the energy of ions and N N N mainly by sputtering yield of the material S

Pulsed magnetron sputtering (HiPIMS) dc sputtering: J. A. Thorton, J. Vac. Sci. Technol.

U ~ -4 V, I ~ 2 ma, P ~ 8 W pulsed sputtering: energy compressed into active part of

W, n e ~1 18 1 19 m -3 i avrg 1 = T T i () t dt peak current [A] 5 4 3 2 1 2 ON.15.

4 Pulsed magnetron sputtering (HiPIMS) dc sputtering: J. A. Thorton, J. Vac. Sci. Technol., Vol. 15, No.2, (1978). U ~ -4 V, I ~ 2 ma, P ~ 8 W pulsed sputtering: energy compressed into active part of the pulse U a ~ -85 V, I a ~ 5 A, P a ~ 48. W, n e ~ m -3 i avrg 1 = T T i () t dt peak current [A] ON OFF O 2 /Ar =.15 O 2 /Ar =.1 O 2 /Ar = 1 p = 1 Pa f = 25 Hz 4 cathode voltage [V] U C U C+R U cathode U cathode+resistor p = 1 Pa f = 25 Hz O 2 /Ar = time [μs]

5 Dual sputtering systems state of art Aijaz et al. the same cathode voltage on both magnetrons is applied, f = 1 Hz, duty 1% Musil et al. - mid-frequency dual pulsed system - f = 1 khz, duty 5 % usually the same target materials are employed 5

6 Deposition of thin Ti-Cu films of required properties problem: stoichiometry of multicomponent films different sputtering yield of materials influence of sputtering process by magnetic field energy transfer to growing film ion bombardment Cu sputtred by Ar + Ti sputtred by Ar + Y. Yamamura, H. Tawara, Atomic data and nuclear data tables 62, (1996),

7 Dual HiPIMS magnetron sputtering Principle of pulsing 7 U t a /T T D t a /T U 7

Dual HiPIMS system with closed magnetic field electric

vice versa Ti Cu ON ON magnetic confinement: reversed

electrodes Cu - ON U = -6 V cathode I a = 8-9 A, 8 P a = 5.

8 Dual HiPIMS system with closed magnetic field electric confinement: electrodes (targets) serve as cathode anode and vice versa Ti Cu ON ON magnetic confinement: reversed magnets configuration closed magnetic field between electrodes Cu - ON U = -6 V cathode I a = 8-9 A, 8 P a = 5.4 kw Cu-ON Ti - OFF t a /T = 1 μs, f = 1 Hz, T D > 5 μs Ti - OFF U = V - anode 8

9 Experimental device - quadruple magnetron sputtering quadruple magnetron 4 different targets : Ti, Cu, Ag, C other agents: buffer and reactive gases, liquids (precursors) rotational table time of deposition 1-6 minutes dc vs. pulsed (dual, HiPIMS, dual HiPIMS) magnetron sputtering 9

10 Aim: comparative study of dual pulsed sputtering systems dual pulsed magnetrons with closed magnetic field comparative study of dual and dual HiPIMS systems dual HiPIMS low frequency, small duty cycle, high power density f = 1 Hz, T active = 1 μs, pulse delay 15 μs labelled dual HiPIMS dual sputtering high frequency, duty cycle roughly 5 %, low power density comparable with dc f = 4.65 khz, T active = 1 μs, pulse delay 15 μs labelled dual MS 1 figures are NOT in ratio scale 1:1 1

11 Peak cathode voltages and discharge currents voltages measured on the cathode(s): U Ti = -46 V, U Cu = -51 V for dual-hipims U Ti = -31 V, U Cu = -3 V for dual-ms for both modes I m = 4 ma (Ti) and I m = 1 ma (Cu), kept constant as a parameter dual HiPIMS peak current 6 A (Ti) and 8 A (Cu) different currents vs. different sputtering yields schoichiometric thin films cathode voltage - Ti dual HIPIMS [V] dual HIPIMS - Ti dual MS - Ti I m (Ti) = 4 ma I m (Cu) = 1 ma Ti - ON delay time [μs] dual HIPIMS - Cu dual MS - Cu Cu - ON cathode voltage [V] peak discharge current - Ti dual HIPIMS [A] Ti - ON dual HIPIMS - Ti dual MS - Ti delay time [μs] Cu - ON I m (Ti) = 4 ma I m (Cu) = 1 ma dual HIPIMS - Cu dual MS - Cu peak discharge current [A]

12 Time-resolved optical emission spectroscopy plasma spectrograph Andor Shamrock SR5D iccd detector istar DH74I Andor Technology intelligate optical gate width ~ 1-3 ns propagation delay for measurements 3 ns Working range Resolution G1 6gr/mm G2 239gr/mm G3 12gr/mm.5 nm.1 nm.22nm 3 nm 7 nm 1 nm

13 Optical emission spectroscopy normalized relative intensity [a.u.] Ti + Ti + Cu Cu Cu Ti + Ti + Ti + Ti Ti Ti Ti dual HIPIMS f = 1 Hz, duty 1 % delay 15 μs Ar Cu Ar + Ar + Ti Ti Ti Ti wavelength [nm] dual MS f = 4.65 khz, duty 5 % delay 15 μs Cu + Cu + 13 time averaged measurements of pulsed discharges high intensities of Ar + and Ti + emission lines in dual HiPIMS above λ > 69 nm strong Ar emission lines (excluded from the figure) spectrograph Shamrok 5 (l = 5 mm), wavelength resolution.1 nm

14 Time-resolved optical emission spectroscopy normalized intensity [a.u.] Ti - ON delay Cu - ON pause Ti Ti + Cu Cu time [μs] f = 1 Hz normalized intensity Cu, Ti [a.u.] Ti Ti + Ti - ON delay Cu Cu + Cu - ON f = 4.9 khz time [μs] delay relative intensity Ti +, Cu + [a.u.] selected emission lines: dual vs. dual HiPIMS: 14 Ti (λ Ti = nm), Ti + (λ Ti+ = nm) Cu (λ Cu = nm), Cu + (λ Cu+ = 647. nm) broader first Ti peak in dual mode preionization effect diffusion of metal ions in Ar atmosphere: D Cu+(Ar) = cm 2 s -1 in Bogaerts et al, Spectrochemica Acta B 53, (1998) D Ti+(Ar) = cm 2 s -1 in Ohebsian et al, Optics Communications 32/1, (198) ion velocity caused by diffusion ~(.1.5) cm.μs -1

15 Technique of time-resolved Langmuir probe measurements discharge Langmuir probe magnetron cathode U c entrance ampllifier oscilloscope Tektronix TDS112 resistor R = 2.1 Ω U c+r trigger unit waveform generator Agilent 3312A power switch (capacitors) data acquisition + pc oscilloscope Tektronix TDS 52A AE MDX -62 V (cw) V V V + 1. V keying edge 126x data acquisition 1 ns time resolution acquisition step 1 ns 1 μs voltage span 5 V (+ external bias if needed) probe current [1-4 A] IV characteristic 2 nd derivative 1 Ar, 5 Pa, 1 A in peak, t = 5 μs voltage [V] (di/du)" (EEPF)

16 Langmuir probe measurements electron density time-resolved Langmuir probe measurement substrate position between sputtering sources calculated from integrated EEDF: n = f ( ε ) n e in dual-hipims higher about three orders of magnitude than in dual-ms e dε E m 1 = n e ε f ( ε ) dε electron density (dual HiPIMS) [1 18 m -3 ] Ti - ON dual HiPIMS, f = 1 Hz dual, f = 4.65 khz delay time [μs] Cu - ON electron density (dual MS) [1 15 m -3 ] mean electron energy [ev] Ti - ON delay time [μs] Cu - ON dual MS, f = 4.65 khz dual HiPIMS, f = 1 Hz

17 Electron Energy Probability Function EEPF dual MS bi-maxwellian EEPF observed for T a > 35 μs dual HiPIMS deviation from Maxwellian distribution was observed EEPF [ev -3/2 ].1 dual HIPIMS - Ti, T a = 2 μs dual HIPIMS - Cu, T a = 135 μs delay (dual MS), T a = 11 μs dual MS - Ti, T a = 2 μs dual MS - Cu, T a = 135 μs EEPF [ev -3/2 ] 1.1 dual HiPIMS - delay t d = 5 μs f = 1 Hz, t a = 1 μs Ti discharge ignated at t a = μs 6 μs 1 μs 12 μs 25 μs 5 μs energy [ev] energy [ev] time evolution of EEPF for dual-hipims with pulse delay 5 μs cooling time roughly 75 μs - electrons lose half of kinetic energy preionization effect for electrons

Measurement of ion-flux to substrate during deposition the positive ions flux to the substrate is induced by a negative substrate biasing of dc-pulse modulated (5 khz) signal applied on dielectric

18 Measurement of ion-flux to substrate during deposition the positive ions flux to the substrate is induced by a negative substrate biasing of dc-pulse modulated (5 khz) signal applied on dielectric substrate current formula based on: U = U R 2 1 Ii for U 1 sufficiently negative. basic setup for the ion flux measurements with pulsed DC bias of substrate. an example of current and voltage waveforms on the substrate; U DC,S = -5 V. M.A. Sobolewski, Appl. Phys. Lett. 72, 1146 (1998) N.S.J. Braithwaite, J.P. Booth, and G. Cunge, Plasma Sources Sci. T. 5, 677 (1996)

19 Ion-flux to biased substrate: effect of probe position demostrated on discharge dual HiPIMS: f = 1 Hz, t a = 1 ms, delay t D = 5 μs ion flux [ma/cm 2 ] Ti - ON probe position: below Ti target below Cu target between targets U B = -5 V f = 1 Hz, t a = 1 μs I m-cu = 1 ma I m-ti = 4 ma Cu - ON ion flux [ma/cm 2 ] bellow Ti (1) U B = -5 V f = 1 Hz t a = 1 ms I m-cu = 1 ma I m-ti = 4 ma time [μs] time [μs] ion flux to biased (U B = -5 V) substrate ~ 1 ma/cm 2, peak current density i P ~ 2.5 ma/cm 2 no strong dependence on U B was observed, floating substrate U f = 7.3 V 19 estimated ion velocity caused by diffusion:.1.5 cm μs -1 comparable with pulse width and geometry of the experimental arrangement 19

20 Ion-flux to biased substrate ion flux - dual MS [ma/cm 2 ] 3. Ti - ON Cu - ON pause dual HiPIMS dual MS dual HiPIMS Ti - ON Cu - ON Ti - ON Cu - ON dual MS ion flux - dual HiPIMS [ma/cm 2 ] dual HiPIMS 1 periode dual MS 2 periods time [μs] f = 1 Hz, delay t D = 1 μs one maxima of i F-Ti and i F-Cu i F-Cu 6 ma/cm 2 i F-Ti 8 ma/cm 2 f = 4.83 khz, delay t D = 5 μs of i F-Ti i F-Cu i F.75 ma/cm 2 2 pre-ionization increases the ion-flux of second discharge HiPIMS incerases ion-flux about 2 orders of magnitude 2

21 Ion and energy flux to substrate dual HiPIMS ion flux proportional to probe bias for U b > - 3 V ion flux [ma.cm -2 ] dual MS probe bias [V] measured floating potential of the substrate U f = 7.3 V expected ion fluxes to floating substrate total power density flux measured by calorimetric probe at floating potential dual HIPIMS mode: i + ~ 9 ma/cm 2 dual mode of sputtering: i + ~.1 ma/cm 2 abbreviation P total [mw/cm 2 ] P ions /P total P electrons /P total P neutral /P total dual HiPIMS >.1 dual MS ~ ion contribution dominates in power density flux 21 H. Kersten H. Deutsch, H. Steffen, G.M.W. Kroesen, R. Hippler, Vacuum 63, 385 (21) M. Cada, J.W. Bradley, G.C.B. Clarke, P.J. Kelly, J. Appl. Phys. 12/6, 6331 (27) 21

22 Conclusion Dual HiPIMS system for complex thin film deposition dual HiPIMS magnetron sputtering system wide range of experimental parameters from dual MS to dual HiPIMS independent circuits stoichiometric deposition of materials with different sputering yields Time-resolved plasma diagnostics intensitve ionization of metallic atoms in dual HiPIMS electron density and ion flux higher about three/two orders of magnitude in dual HiPIMS ion contribution dominates in total power density flux effect of preionization and diffusion in discharge volume delay between pulses can influence the plasma parameters during the deposition process Future plan multistructural thin films deposition of Ti-Cu by dual magnetron sputtering in required stoichiometry crystallographic structure and copper release from Ti-Cu thin films effect of released Cu on living organisms

23 Thank you for your attention!!! V. Stranak, M. Cada, Z. Hubicka, M.. Tichy, R. Hippler, TIME-RESOLVED INVESTIGATION OF DUAL HIGH POWER IMPULSE MAGNETRON SPUTTERING WITH, J. Appl. Phys. (in print)

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