Dual-magnetron open field sputtering system for sideways ...
DC and DC pulsed magnetron sputtering of dielectric materials€¦ · DC and DC pulsed magnetron...
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DC and DC pulsed magnetron sputtering of dielectric materials Georg Norbert Strauss, Stefan Schlichtherle PhysTech Coating Technology GmbH Knappenweg 34, A-6600 Pflach, Austria Markus Stolze, Joe Neff UMICORE MATERIALS AG Alte Landstr. 8, FL-9496 Balzers, Principality of Liechtenstein Results and discussion Nb oxide and Nb metal targets DC pulsed mode › increasing O 2 gas fraction → depopulation of high and low energy part of Ar + ion energy spectrum (Fig. 1). › increasing sputter power → shift of both peaks to higher energies (Fig. 2). › increasing pulse frequency from 50 to 100 kHz → shift of low and high-energy peaks to smaller or higher energies respectively (Fig. 3). › increasing O 2 gas fraction → simultaneous decrease of average energies of the Ar + ions and of refractive index for oxide and metal targets [1] → main com- paction contribution during film growth originating from Ar + ions (Fig. 4). › process windows (extinction coefficient k ≤ 2 x 10 -4 ) for suboxide targets at significantly smaller O 2 gas fraction than for metal targets → higher available refractive index and deposition rate for suboxide targets and absent post-oxidation [1]. DC mode › increasing O 2 fraction → decrease of deposition rate and refractive index for oxide and metal targets [1] (Fig. 5 and 6). › higher deposition rates and refractive indices for oxide targets in available process windows (k ≤ 2 x 10 -4 , stability). › similar dependencies as for DC pulsed mode → assumption of similar dependencies of film growth on plasma properties. Ta oxide targets DC and DC pulsed mode › increasing O 2 fraction → decrease of refractive index for both modes (Fig. 7). › process window for pulsed mode with high frequen- cy starts at smaller O 2 sputter gas fraction (Fig. 7). › increase of pulse frequency 0 – 350 kHz → increase of average Ar + ion energy (Fig. 8). › increase of pulse frequency 0 – 350 kHz → strong increase of total kinetic energy of the most relevant process ions influencing the film growth (Ar + ,O 2 + and Ta + ) in the frequency range up to 150 kHz (Fig. 9). Conclusions › The useful oxygen process window for suboxide tar- gets is located in a range of higher Ar + ion energies than for metal targets leading to higher deposition rates and refractive indices for the suboxide targets. › Increasing sputter power creates an increase in the amount of Ar + ions and in the Ar + ion energy distribution and thus results in higher deposition rates and refractive indices. › DC pulsed mode: The frequency plays an important role in shaping the energy spectra of the ions be- cause the frequency sets the timescale of the cycle. With an increasing frequency from DC to 350 kHz, less time is left per cycle for the charge to accumu- late, resulting in less change in the electric poten- tials. Furthermore, the increase in the frequency has also a significant impact on the ion energy distribution [2, 3, 4, 5]. › Duty factor: Is a critical factor in depositing high quality films at frequencies between 5 and 350 kHz → strong effect of the duty factor on the energy distribution of the process ions [3]. › DC pulsed sputter deposition gives additional de- grees of freedom to influence the film growth pro- cess by making the energy spectra getting bimodal and tuning the ion energies distribution of the high and low energy bands → enables the modification of film surfaces by bombardment of ions with higher kinetic energy than those observed in DC sputtering discharges [2, 6]. › Suboxide or metal targets each have their benefits and drawbacks in DC or DC pulsed sputter deposition with specific process conditions. › Suboxide targets → higher sputter rates and refrac- tive indices for lower oxygen gas fraction and hence absent control loop when no in- or ex-situ post- oxidation is available. › Metal targets → can be sputtered with higher power densities, are mostly less costly and provide more in-coater material stock which is contrasted by the necessity of reactive gas control loop and effective arc detection and suppression. References [1] M. Stolze, K. Leitner, Coating material innovation in conjunction with optimized deposition technologies, Accepted for publication in Thin Solid Films, Special Issue for ICCG 2008 [2] P.J. Kelly, P.S. Henderson, R.D. Arnell, G.A. Roche, D. Carter, J. Vac. Sci. Technol. A18 (2000), 2890-2896 [3] R.A. Scholl, Surf. Coat. Technol. 93 (1997), 7-13 [4] R.D. Arnell, P.J. Kelly, Surf. Coat. Technol. 112 (1999), 170-176 [5] H. Bartzsch, P. Frach, K. Goedicke, Surf. Coat. Technol. 132 (2000), 244-250 [6] G.N. Strauss, H.K. Pulker, Thin Solid Films 442 (2003), 66-73 Recent progress in DC and DC pulsed magnetron sputtering process technology has caused an increasing interest in using oxide target materials for the production of thin films in the application field of optical coatings, e.g. coatings for photovoltaic modules, architectural coatings, TFT displays, optical data storage and precision optics. In this work, the behavior of substoichiometric materials like Nb 2 O 5-X and Ta 2 O 5-X in DC continuous and DC pulsed sputter modus are discussed, partly in comparison with the results for metal targets obtained for absent additional in- or ex-situ post-oxidation. The influence of some process parameters like target power and frequency on the deposition process and the resulting optical film properties will be shown. Plasma characterization of the sputter process was done by means of a plasma monitoring system (PPM421 from Inficon) which consists of a quadrupol mass spectrometer with an additional energy analyser. The correlation between the nominal process parameters, the plasma properties (e.g. ion energy distribution), observed deposition rates and the resulting optical film properties (refractive index, process window with minimal absorption) will be presented. Conclusion will be drawn for the combination of target type and process mode. 1.E+03 1.E+04 1.E+05 1.E+06 0 20 40 60 80 100 120 Ion energy [eV] Intensity [a.u.] O2 = 0% vol. O2 = 10% vol. O2 = 20% vol. O2 = 30% vol. 7 sccm (Ar, O2) f = 150 kHz T = 2,9 μs P = 200 W DC pulsed mode Nb oxide Fig. 1: Ar + ion energy distribution for DC pulsed sputtering of Nb suboxide and varied O 2 gas fraction. 1.E+03 1.E+04 1.E+05 1.E+06 0 20 40 60 80 100 120 Ion energy [eV] Intensity [a.u.] P = 100 W P = 200 W 7 sccm (Ar, O2) O2 = 10% vol. f = 150 kHz DC pulsed mode Nb oxide Fig. 2: Ar + ion energy distribution for DC pulsed sputtering of Nb suboxide and varied peak power. 1.E+03 1.E+04 1.E+05 1.E+06 0 20 40 60 80 100 120 Ion energy [eV] Intensity [a.u.] 50 kHz 100 kHz 150 kHz 200 kHz 300 kHz DC pulsed mode Nb oxide 7 sccm (Ar, O2) O2 = 10% vol. P = 200 W Fig. 3: Ar + ion energy distribution for DC pulsed sputtering of Nb suboxide and varied pulse frequency. 2.20 2.25 2.30 2.35 2.40 0 5 10 15 20 25 30 35 40 45 O2 [% vol.] Refractive index n (550 nm) Average Ar + ion energy [a.u.] DC pulsed mode Nb oxide Nb metal Fig. 4: Left axis: Refractive index (at 500 nm) as a function of O 2 sputter gas fraction for Nb 2 O 5 films from DC pulsed sputtering of Nb suboxide and Nb metal. Process windows yielding non-absorbing films indicated as horizontal bars. Right axis: Average Ar + ion energies for the employed target types and process conditions. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0 10 20 30 40 50 60 O2 [% vol.] Deposition rate [nm/s] DC mode Nb oxide Nb metal Fig. 5: Deposition rates as a function of O 2 sputter gas fraction for Nb 2 O 5 films from DC sputtering of Nb suboxide and Nb metal. Process windows yielding non-absorbing films indicated as horizontal bars. 2.20 2.25 2.30 2.35 2.40 0 5 10 15 20 25 30 35 40 O2 [% vol.] Refractive index n (550 nm) DC mode Nb oxide Nb metal Fig. 6: Refractive index (at 500 nm) as a function of O 2 sputter gas fraction for Nb 2 O 5 films from DC sputtering of Nb suboxide and Nb metal. Process windows yielding non-absorbing films indicated as horizontal bars. 1.E+03 1.E+04 1.E+05 0 25 50 75 100 125 150 175 200 Ion energy [eV] Intensity [a.u.] O = 0% vol. Ar = 3 sccm P = 400 W 2 DC 150 kHz 350 kHz DC and DC pulsed mode Ta oxide Fig. 8: Ar + ion energy distribution for DC sputtering and DC pulsed sputtering of Ta suboxide with varied pulse frequency. 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 0 50 100 150 200 250 300 350 400 Pulse frequency [kHz] Total kinetic ion energy [a.u.] DC pulsed mode Ta oxide Fig. 9: Total kinetic energy of Ar + , Ta + , O 2 + ions in DC pulsed sputtering of Ta suboxide as a function of pulse frequency. 2.00 2.02 2.04 2.06 2.08 2.10 0 5 10 15 20 25 O2 [% vol.] Refractive index n (550 nm) 350 kHz DC DC and DC pulsed mode Ta oxide Fig. 7: Refractive index (at 500 nm) as a function of O 2 sputter gas fraction for Ta 2 O 5 films from DC and DC pulsed sputtering of Ta suboxide. Experimental Sputtertargets and coater setup › Nb metal and Nb suboxide (Nb 2 O 5-X , x < 0.3) targets (UMICORE) › diameter 3”, thickness 6 mm, Cu backing plate 3 mm › purity 4N › Nb suboxide: specific resistivity 30 – 100 mΩcm › coater Edwards 500 › unbalanced single magnetron in bottom-up orientation › gas inlet through ring gas shower › target-substrate distance ~ 65 mm Coating process conditions › substrate temperature < 80°C (no intentional heating) › residual gas pressure 1 x 10 -5 mbar › total operating pressure 2 – 3 x 10 -3 mbar › O 2 content in the sputter gas 0 – 50 %vol. › DC and DC pulsed operation › DC sputter power 100 – 400 W (~ 2-10 W/cm 2 ) › Peak power for DC pulsed mode 100 – 400 W › ratio plasma on/off (“duty cycle”) 50% › pulse frequency 0 – 350 kHz In-situ plasma analysis › plasma monitor system: Inficon PPM421 › process relevant ions (mostly Ar + ) › kinetic energies as function of total gas pressure, gas composition (O 2 /Ar), target power, pulse frequency Film deposition and characterization › thicknesses 280 – 400 nm › spectrophotometry (optical transmittance and reflectance) › determination of refractive index and absorption Principal sketch of sputter coater Edwards 500 with single unbalanced magnetron sputter source, sample holder and plasma monitor Inficon PPM421. Sputter targets, sputter source and schematic of the applied pulses for DC pulsed mode.
Transcript of DC and DC pulsed magnetron sputtering of dielectric materials€¦ · DC and DC pulsed magnetron...
DC and DC pulsed magnetron sputtering of dielectric materialsGeorg Norbert Strauss, Stefan Schlichtherle PhysTech Coating Technology GmbH Knappenweg 34, A-6600 Pflach, Austria
Markus Stolze, Joe Neff UMICORE MATERIALS AG Alte Landstr. 8, FL-9496 Balzers, Principality of Liechtenstein
Results and discussion
Nb oxide and Nb metal targets
DC pulsed mode
› increasingO2gasfraction→depopulationofhighandlowenergypartofAr+ionenergyspectrum(Fig. 1).
› increasingsputterpower→shiftofbothpeakstohigherenergies(Fig. 2).
› increasingpulsefrequencyfrom50to100kHz→shiftoflowandhigh-energypeakstosmallerorhigherenergiesrespectively(Fig. 3).
› increasingO2gasfraction→simultaneousdecreaseofaverageenergiesoftheAr+ionsandofrefractiveindexforoxideandmetaltargets[1]→maincom-pactioncontributionduringfilmgrowthoriginatingfromAr+ions(Fig. 4).
› processwindows(extinctioncoefficientk≤2x10-4)forsuboxidetargetsatsignificantlysmallerO2gasfractionthanformetaltargets→higheravailablerefractiveindexanddepositionrateforsuboxidetargetsandabsentpost-oxidation[1].
DC mode
› increasingO2fraction→decreaseofdepositionrateandrefractiveindexforoxideandmetaltargets[1](Fig. 5 and 6).
› higherdepositionratesandrefractiveindicesforoxidetargetsinavailableprocesswindows(k≤2x10-4,stability).
› similardependenciesasforDCpulsedmode→assumptionofsimilardependenciesoffilmgrowthonplasmaproperties.
Ta oxide targets
DC and DC pulsed mode
› increasingO2fraction→decreaseofrefractiveindexforbothmodes(Fig. 7).
› processwindowforpulsedmodewithhighfrequen-cystartsatsmallerO2sputtergasfraction(Fig. 7).
› increaseofpulsefrequency0–350kHz→increaseofaverageAr+ionenergy(Fig. 8).
› increaseofpulsefrequency0–350kHz→strongincreaseoftotalkineticenergyofthemostrelevantprocessionsinfluencingthefilmgrowth(Ar+,O2
+andTa+)inthefrequencyrangeupto150kHz(Fig. 9).
Conclusions
› Theusefuloxygenprocesswindowforsuboxidetar-getsislocatedinarangeofhigherAr+ionenergiesthanformetaltargetsleadingtohigherdepositionratesandrefractiveindicesforthesuboxidetargets.
› IncreasingsputterpowercreatesanincreaseintheamountofAr+ionsandintheAr+ionenergydistributionandthusresultsinhigherdepositionratesandrefractiveindices.
› DCpulsedmode:Thefrequencyplaysanimportantroleinshapingtheenergyspectraoftheionsbe-causethefrequencysetsthetimescaleofthecycle.WithanincreasingfrequencyfromDCto350kHz,lesstimeisleftpercycleforthechargetoaccumu-late,resultinginlesschangeintheelectricpoten-tials.Furthermore,theincreaseinthefrequencyhasalsoasignificantimpactontheionenergydistribution[2,3,4,5].
› Dutyfactor:Isacriticalfactorindepositinghighqualityfilmsatfrequenciesbetween5and350kHz→strongeffectofthedutyfactorontheenergydistributionoftheprocessions[3].
› DCpulsedsputterdepositiongivesadditionalde-greesoffreedomtoinfluencethefilmgrowthpro-cessbymakingtheenergyspectragettingbimodalandtuningtheionenergiesdistributionofthehighandlowenergybands→enablesthemodificationoffilmsurfacesbybombardmentofionswithhigherkineticenergythanthoseobservedinDCsputteringdischarges[2,6].
› SuboxideormetaltargetseachhavetheirbenefitsanddrawbacksinDCorDCpulsedsputterdepositionwithspecificprocessconditions.
› Suboxidetargets→highersputterratesandrefrac-tiveindicesforloweroxygengasfractionandhenceabsentcontrolloopwhennoin-orex-situpost-oxidationisavailable.
› Metaltargets→canbesputteredwithhigherpowerdensities,aremostlylesscostlyandprovidemorein-coatermaterialstockwhichiscontrastedbythenecessityofreactivegascontrolloopandeffectivearcdetectionandsuppression.
References
[1] M.Stolze,K.Leitner,Coatingmaterialinnovationinconjunctionwithoptimizeddepositiontechnologies,AcceptedforpublicationinThinSolidFilms,SpecialIssueforICCG2008
[2] P.J.Kelly,P.S.Henderson,R.D.Arnell,G.A.Roche,D.Carter,J.Vac.Sci.Technol.A18(2000),2890-2896
[3] R.A.Scholl,Surf.Coat.Technol.93(1997),7-13
[4] R.D.Arnell,P.J.Kelly,Surf.Coat.Technol.112(1999),170-176
[5] H.Bartzsch,P.Frach,K.Goedicke,Surf.Coat.Technol.132(2000),244-250
[6] G.N.Strauss,H.K.Pulker,ThinSolidFilms442(2003),66-73
Recent progress in DC and DC pulsed magnetron sputtering process technology has caused an increasing interest in using oxide target materials for the production of thin films in the application field of optical coatings, e.g. coatings for photovoltaic modules, architectural coatings, TFT displays, optical data storage and precision optics.
In this work, the behavior of substoichiometric materials like Nb2O5-X and Ta2O5-X in DC continuous and DC pulsed sputter modus are discussed, partly in comparison with the results for metal targets obtained for absent additional in- or ex-situ post-oxidation. The influence of some process parameters like target power and frequency on the deposition process and the resulting optical film properties will be shown. Plasma characterization of the sputter process was done by means of a plasma monitoring system (PPM421 from Inficon) which consists of a quadrupol mass spectrometer with an additional energy analyser.
The correlation between the nominal process parameters, the plasma properties (e.g. ion energy distribution), observed deposition rates and the resulting optical film properties (refractive index, process window with minimal absorption) will be presented. Conclusion will be drawn for the combination of target type and process mode.
1.E+03
1.E+04
1.E+05
1.E+06
0 20 40 60 80 100 120Ion energy [eV]
Inte
nsit
y [a
.u.]
O2 = 0% vol.O2 = 10% vol.O2 = 20% vol.O2 = 30% vol.
7 sccm (Ar, O2)f = 150 kHzT = 2,9 µsP = 200 W
DC pulsed modeNb oxide
Fig. 1: Ar+ ion energy distribution for DC pulsed sputtering of Nb suboxide and varied O2 gas fraction.
1.E+03
1.E+04
1.E+05
1.E+06
0 20 40 60 80 100 120Ion energy [eV]
Inte
nsit
y [a
.u.]
P = 100 W
P = 200 W
7 sccm (Ar, O2)O2 = 10% vol.f = 150 kHz
DC pulsed modeNb oxide
Fig. 2: Ar+ ion energy distribution for DC pulsed sputtering of Nb suboxide and varied peak power.
1.E+03
1.E+04
1.E+05
1.E+06
0 20 40 60 80 100 120Ion energy [eV]
Inte
nsit
y [a
.u.]
50 kHz
100 kHz
150 kHz
200 kHz
300 kHz
DC pulsed modeNb oxide
7 sccm (Ar, O2)O2 = 10% vol.P = 200 W
Fig. 3: Ar+ ion energy distribution for DC pulsed sputtering of Nb suboxide and varied pulse frequency.
2.20
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2.30
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0 5 10 15 20 25 30 35 40 45
O2 [% vol.]
Refr
acti
ve in
dex
n (5
50 n
m)
Ave
rage
Ar+ io
n en
ergy
[a
.u.]
DC pulsed mode
Nb oxide Nb metal
Fig. 4: Left axis: Refractive index (at 500 nm) as a function of O2 sputter gas fraction for Nb2O5 films from DC pulsed sputtering of Nb suboxide and Nb metal. Process windows yielding non-absorbing films indicated as horizontal bars. Right axis: Average Ar+ ion energies for the employed target types and process conditions.
0.00
0.20
0.40
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0.80
1.00
1.20
0 10 20 30 40 50 60
O2 [% vol.]
Dep
osit
ion
rate
[nm
/s]
DC modeNb oxide Nb metal
Fig. 5: Deposition rates as a function of O2 sputter gas fraction for Nb2O5 films from DC sputtering of Nb suboxide and Nb metal. Process windows yielding non-absorbing films indicated as horizontal bars.
2.20
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0 5 10 15 20 25 30 35 40
O2 [% vol.]
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n (5
50 n
m) DC mode
Nb oxide Nb metal
Fig. 6: Refractive index (at 500 nm) as a function of O2 sputter gas fraction for Nb2O5 films from DC sputtering of Nb suboxide and Nb metal. Process windows yielding non-absorbing films indicated as horizontal bars.
1.E+03
1.E+04
1.E+05
0 25 50 75 100 125 150 175 200
Ion energy [eV]
Inte
nsit
y [a
.u.]
O = 0% vol.Ar = 3 sccmP = 400 W
2
DC 150 kHz 350 kHz
DC and DC pulsed modeTa oxide
Fig. 8: Ar+ ion energy distribution for DC sputtering and DC pulsed sputtering of Ta suboxide with varied pulse frequency.
1.E+05
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1.E+09
0 50 100 150 200 250 300 350 400
Pulse frequency [kHz]
Tota
l kin
etic
ion
ener
gy [
a.u.
]
DC pulsed modeTa oxide
Fig. 9: Total kinetic energy of Ar+, Ta+, O2+ ions in DC pulsed
sputtering of Ta suboxide as a function of pulse frequency.
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0 5 10 15 20 25
O2 [% vol.]
Refr
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50 n
m)
350 kHz
DC
DC and DC pulsed modeTa oxide
Fig. 7: Refractive index (at 500 nm) as a function of O2 sputter gas fraction for Ta2O5 films from DC and DC pulsed sputtering of Ta suboxide.
Experimental
Sputtertargets and coater setup› NbmetalandNbsuboxide(Nb2O5-X,x<0.3)targets(UMICORE)
› diameter3”,thickness6mm,Cubackingplate3mm› purity4N› Nbsuboxide:specificresistivity30–100mΩcm› coaterEdwards500› unbalancedsinglemagnetroninbottom-uporientation
› gasinletthroughringgasshower› target-substratedistance~65mm
Coating process conditions› substratetemperature<80°C(nointentionalheating)› residualgaspressure1x10-5mbar› totaloperatingpressure2–3x10-3mbar› O2contentinthesputtergas0–50%vol.› DCandDCpulsedoperation› DCsputterpower100–400W(~2-10W/cm2)› PeakpowerforDCpulsedmode100–400W› ratioplasmaon/off(“dutycycle”)50%› pulsefrequency0–350kHz
In-situ plasma analysis› plasmamonitorsystem:InficonPPM421› processrelevantions(mostlyAr+)› kineticenergiesasfunctionoftotalgaspressure,gascomposition(O2/Ar),targetpower,pulsefrequency
Film deposition and characterization› thicknesses280–400nm› spectrophotometry(opticaltransmittanceandreflectance)
› determinationofrefractiveindexandabsorption
Principal sketch of sputter coater Edwards 500 with single unbalanced magnetron sputter source, sample holder and plasma monitor Inficon PPM421.
Sputter targets, sputter source and schematic of the applied pulses for DC pulsed mode.
