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Raunvísindaþing í Reykjavík 2006:

The high power impulsemagnetron sputtering dis harge:A brief reviewJ. T. Gudmundsson

S ien e Institute andDepartment of Ele tri al and Computer Engineering,University of I elandtumi�hi.is3.-4. Mar h 20061

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Introdu tion

• Magnetron sputtering dis harges are widely used in thin �lmpro essing

• Appli ations in lude� thin �lms in integrated ir uits� magneti material� hard, prote tive, and wear resistant oatings� opti al oatings� de orative oatings� low fri tion �lms2

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Introdu tion

• The demand for new materials and layer stru tures has lead todevelopment of more advan ed sputtering systems

• One su h sputtering system is the high power pulsedmagnetron sputtering dis harge (HPPMS) or high powerimpulse magnetron sputtering dis harge (HiPIMS)

• It gives high ele tron density and highly ionized �ux of thesputtered material3

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Introdu tion

• Introdu tion to magnetron sputtering

• Introdu tion to Ionized Physi al Vapor Deposition (IPVD)

• High power impulse magnetron sputtering dis harge (HiPIMS)� Power supply� Ele tron density� Plasma dynami s� Ionization fra tion� Deposition rate� Appli ations4

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Introdu tion• This work is a result of ollaboration with� Kristinn B. Gylfason (University of I eland)� Dr. Jones Alami (Linkoping University, Sweden)� Johan Bohlmark (Linkoping University, Sweden)� Dr. Arutiun Ehiasarian (She�eld Hallam University, UK)� Prof. Ulf Helmersson (Linkoping University, Sweden)� Dr. Martina Latteman (Linkoping University, Sweden)

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Planar Magnetron Sputtering Dis harge

magnetsgas in

substrate

gas out

target − cathode���������������������������������������������

���������������������������������������������

���������������������������������������������

���������������������������������������������

soft iron

N

N

N

S

S

S

annularmagnetcylindrical

magnet

• A typi al d planar magnetron dis harge operates at a pressureof 1 � 10 mTorr with a magneti �eld strength of 0.01 � 0.05 Tand at athode potentials 300 � 700 V

• Ele tron density in the substrate vi inity is in the range

1015− 1016 m−3

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Planar Magnetron Sputtering Dis harge• Conventional magnetron sputtering pro esses su�er fromfundamental problems su h as� low target utilisation� target poisoning� poor deposition rates for diele tri and ferromagneti materials� target thermal load limits the available urrent� ele tri al instabilities or ar s ause pro ess instability� low fra tion of the sputtered material is ionized

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Ionized Physi al Vapour Deposition(IPVD)

• When the �ux of ions is higher than the �ux of neutrals or

Γ+ > Γm the pro ess is referred to as ionized physi al vapourdeposition (IPVD)

• This is a hieved by� in reased power to the athode (high power pulse)� a se ondary dis harge between the target and the substrate(rf oil or mi rowaves)� reshaping the geometry of the athode to get more fo usedplasma (hollow athodes)• Common to all highly ionized te hniques is very high densityplasma 8

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Ionized Physi al Vapour Deposition(IPVD)• The development of ionized physi al vapour deposition (IPVD)devi es was mainly driven by the need to deposit metal layersand di�usion barriers into tren hes or vias of high aspe t ratios

• Ionizing the sputtered vapour has several advantages:� improvement of the �lm quality� ontrol of the rea tivity� deposition on substrates with omplex shapes and highaspe t ratio9

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rf Indu tive Coil in a Magnetron

permanentmagnets

gas in

target

substrateinductive coil

gas out

• In order to generate highly ionized dis harge a radio-frequen ydis harge an be added in the region between the athode andthe anode

• The metal ions an then be a elerated to the substrate bymeans of a low voltage d bias10

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HiPIMS

• In a onventional d magnetron dis harge the power density islimited by the thermal load on the target

• Most of the ion bombarding energy is transformed into heat atthe target

• In unipolar pulsing the power supply is at low (or zero) powerand then a high power pulse is supplied for a short period

• The high power pulsed magnetron sputtering dis harge usesthe same sputtering apparatus ex ept the power supply

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HiPIMS - Power supply

DischargeChargingcircuit Cs

L

• The high power pulsed dis harge operates with a� Cathode voltage in the range of 500-2000 V� Current densities of 3-4 A/ m2� Power densities in the range of 1-3 kW/ m2� Frequen y in the range of 50 � 500 Hz� Duty y le in the range of 0.5 � 5 %12

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HiPIMS - Power supply0 50 100 150 200

0

50

100

150

200

t [ µs]

Id [

A]

(b)

0 50 100 150 200−1200

−1000

−800

−600

−400

−200

0

200

t [ µs]

Vd [

V]

(a)

0.5 mTorr (solid line), 2 mTorr (dashed line) and 20 mTorr (dot dashed line)(After Gudmundsson et al. (2002))

• The exa t pulse shape is determined by the load� the dis harge formed� it depends on the gas type and gas pressure

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HiPIMS - Ele tron density(From Bohlmark et al. (2005b))

• Temporal and spatial variation of the ele tron density

• Argon dis harge at 20 mTorr with a titanium target14

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HiPIMS - Ele tron density

0 200 400 600 800 1000

5 mTorr10 mTorr20 mTorr

PSfrag repla ements

1016

1017

1018

1019

1020

ne[m−3 ]

t [µs℄ (From Gudmundsson et al. (2002))

• The ele tron density versus time from the initiation of thepulse 9 m below the target

• The pulse is 100 µs long and the average power 300 W15

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HiPIMS - Plasma dynami s

−50 0 50 100 150 200 250 300

4 cm6 cm8 cm10 cm12 cm

PSfrag repla ementsI s

at[arbitra

ryunits℄

t [µs℄ (From Gylfason et al. (2005))

• The ele tron saturation urrent as a fun tion of time frompulse initiation• The argon pressure was 5 mTorr, the target was made oftitanium, and the pulse energy 6 J16

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HiPIMS - Plasma dynami s0 50 100 150 200

0

2

4

6

8

10

12

14

16

p = 1 mtorrp = 5 mtorrp = 20 mtorr

PSfrag repla ements z[ m℄

t [µs℄ (From Gylfason et al. (2005))

• Ea h peak travels with a �xed velo ity through the hamber

• The peaks travel with a velo ity of 5.3 × 103 m/s at 1 mTorr,

1.7 × 103 m/s at 5 mTorr, and 9.8 × 102 m/s at 20 mTorr

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HiPIMS - Ionization fra tion

• There have been on�i ting reports on the ionized �ux fra tion� 70 % for Cu (Kouznetsov et al., 1999)� 40 % for Ti0.5Al0.5 (Ma ák et al., 2000)� 9.5 % for Al (DeKoven et al., 2003)� 4.5 % for C (DeKoven et al., 2003)

• The degree of ionization� 90 % for Ti (Bohlmark et al., 2005a)18

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HiPIMS - Deposition rate

• Several groups report on a signi� antly lower deposition ratefor HIPIMS as ompared to d MS� a fa tor of 2 lower deposition rate for Cu and Ti thin �lms(Bugaev et al., 1996)� a fa tor of 4 � 7 lower deposition rate for rea tive sputteringof TiO2 from a Ti target (Davis et al., 2004)� a fa tor of 3 - 4 lower deposition rate for rea tive sputteringof AlOx from an Al target (Sproul et al., 2004)� the redu tion in deposition rate de reases with de reasedmagneti on�nement (weaker magneti �eld) (Bugaevet al., 1996)19

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HiPIMS - Deposition rate

• One explanation is that the sputtered material is ionized loseto the target and many of the metalli ions will be attra tedba k to the target surfa e by the athode potential

• A redu tion in the deposition rate would o ur mainly formetals with a low self-sputtering yield

• Maybe this an be redu ed by optimised magneti on�nement

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Appli ation - Tren h �lling

1 cm

2 cm

• Ta thin �lms grown on Si substrates pla ed along a wall of a 2 m deep and 1 m wide tren h� onventional d magnetron sputtering (d MS)� high power impulse magnetron sputtering (HiPIMS)

• Average power is the same 440 W• They were ompared by s anning ele tron mi ros ope (SEM),transmission ele tron mi ros ope (TEM), and Atomi For eMi ros ope (AFM)

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Appli ation - Tren h �lling(From Alami et al. (2005))

• d MS grown �lms exhibit rough surfa e, pores between grainsand in lined olumnar stru ture, leaning toward the aperture

• Ta �lms grown by HiPIMS have smooth surfa e, and dense rystalline stru ture with grains perpendi ular to the substrate22

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Other appli ations

• The advantage of high power pulsed magnetron dis harge for�lm growth has been demonstrated by several groups� ultra-thin arbon �lms grown by HIPIMS have signi� antlyhigher densities (2.7 g/ m3), than �lms grown by a onventional d MS dis harge (< 2.0 g/ m3) Furthermore,the surfa e roughness is lower (DeKoven et al., 2003)� TiO2 thin �lms grown by rea tive sputtering by HIPIMShave higher index of refra tion than grown by d MSdis harge - maybe due to higher density (Davis et al., 2004)

• This illustrates how the bombarding ions transfer momentumto the surfa e allowing the mi rostru ture to be modi�ed

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Summary

• We reviewed the physi s of the high power impulse magnetronsputtering dis harge (HIPIMS)� Power supply� Ele tron density� Plasma dynami s� Ionization fra tion� Deposition rate• We demonstrated the use of a high power pulsed magnetronsputtering dis harge� for tren h �lling• A brief review has been submitted by Helmersson et al.(2005a,b) 24

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Referen esAlami, J., Petersson, P. O. A., Musi , D., Gudmundsson, J. T., Bohlmark, J., and Helmersson, U.(2005). Ion-assisted physi al vapor deposition for enhan ed �lm deposition on non-�atsurfa es. Journal of Va uum S ien e and Te hnology A, 23:278�280.Bohlmark, J., Alami, J., Christou, C., Ehiasarian, A. P., and Helmersson, U. (2005a). Ionizationof sputtered metals in high power pulsed magnetron sputtering. Journal of Va uum S ien eand Te hnology A, 23(1):18�22.Bohlmark, J., Gudmundsson, J. T., Alami, J., Latteman, M., and Helmersson, U. (2005b). Spatialele tron density distribution in a high-power pulsed magnetron dis harge. IEEE Transa tionson Plasma S ien e, 33(2):346�347.Bugaev, S. P., Koval, N. N., So hugov, N. S., and Zakharov, A. N. (1996). Investigation of ahigh- urrent pulsed magnetron dis harge initiated in the low-pressure di�use ar plasma. InXVIIth International Symposium on Dis harges and Ele tri al Insulation in Va uum, 1996,pages 1074�1076, Berkeley, CA USA. IEEE.Davis, J. A., Sproul, W. D., Christie, D. J., and Geisler, M. (2004). High power pulse rea tivesputtering of TiO2. In 47th Annual Te hni al Conferene e Pro eedings, pages 215�218, Dallas,TX, USA. So iety of Va uum Coaters.DeKoven, B. M., Ward, P. R., Weiss, R. E., Christie, D. J., S holl, R. A., Sproul, W. D., Tomasel,F., and Anders, A. (2003). Carbon thin �lm deposition using high power pulsed magnetronsputtering. In 46th Annual Te hni al Conferene e Pro eedings, pages 158�165, San Fran is o,CA, USA. So iety of Va uum Coaters.Gudmundsson, J. T., Alami, J., and Helmersson, U. (2002). Spatial and temporal behavior of theplasma parameters in a pulsed magnetron dis harge. Surfa e and Coatings Te hnology,161(2-3):249�256. 25

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Gylfason, K. B., Alami, J., Helmersson, U., and Gudmundsson, J. T. (2005). Ion-a ousti solitarywaves in a pulsed magnetron sputtering dis harge. Journal of Physi s D: Applied Physi s,38(18):3417�3421.Helmersson, U., Lattemann, M., Alami, J., Bohlmark, J., Ehiasarian, A. P., and Gudmundsson,J. T. (2005a). High power impulse magnetron sputtering dis harges and thin �lm growth: Abrief review. In 48th Annual Te hni al Conferene e Pro eedings, pages 458 � 464, Denver, CO,USA. So iety of Va uum Coaters.Helmersson, U., Lattemann, M., Bohlmark, J., Ehiasarian, A. P., and Gudmundsson, J. T.(submitted for publi ation 2005b). Ionized physi al vapor deposition (IPVD): A review ofte hnology and appli ations. Thin Solid Films.Kouznetsov, V., Ma ák, K., S hneider, J. M., Helmersson, U., and Petrov, I. (1999). A novelpulsed magnetron sputter te hnique utilizing very high target power densities. Surfa e andCoatings Te hnology, 122(2-3):290�293.Ma ák, K., Kouznetzov, V., S hneider, J. M., Helmersson, U., and Petrov, I. (2000). Ionizedsputter deposition using an extremely high plasma density pulsed magnetron dis harge.Journal of Va uum S ien e and Te hnology A, 18(4):1533�1537.Sproul, W. D., Christie, D. J., Carter, D. C., Tomasel, F., and Linz, T. (2004). Pulsed plasmas forsputtering appli ations. Surfa e Engineering, 20:174�176.26