Some more equations describing reactive magnetron sputtering.

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1 Some more equations describing reactive magnetron sputtering D. Depla, S. Mahieu, W. Leroy, K. Van Aeken, J. Haemers, R. De Gryse discharge voltage (V) S (Pumping speed) : 16 L/s PAr (argon pressure) :.4 Pa I (current) :.4 A Step : 2 minutes Target : Aluminium Reactive gas : oxygen total pressure (Pa) flow (sccm) increasing flow decreasing flow 1

2 3 : Why does the voltage change? V discharge W : effective ionisation energy W = ε ε me γ i ISEE ε i : ion collection efficiency (for magnetron : almost 1) (a first equation!) ε : fraction of maximum possible number of ions (for magnetron : almost 1) m : multiplication factor : accounts for ionisation in the sheath E : effective ionisation probability : influenced by electron recapture γ ISEE : ion induced secondary electron emission coefficient G. Buyle, Simplified model for the DC planar magnetron discharge (PhD, UGENT,25) D. Depla et al. J. Appl. Phys. 11 (27) 1331/1-1331/9 Depla D. et al. SCT 2 (26) : Why does the voltage change? Prior to the sputter cleaning : sputtering of the target in pure reactive gas discharge voltage (V) time (s) V C,Ar oxygen V C,Ar nitrogen V Ar 2

Mg Al Y Ce 5 Pb Zr Au Ag Cu Cr Ti In Pt Re Nb Ta Mo : Why does the voltage change? nitride oxide -1 1 2 (γ C -γ M )/γ M (%) γ C,nitride γ C,oxide.27.4.22.19.18.37.22.27.59.92.12.13.31.36.84.67.71.67.96.

3 Mg Al Y Ce 5 Pb Zr Au Ag Cu Cr Ti In Pt Re Nb Ta Mo : Why does the voltage change? nitride oxide (γ C -γ M )/γ M (%) γ C,nitride γ C,oxide Change related to the electronic properties of the formed compound. Wide band nitrides/oxides have a high SEEY. Conducting materials have a low SEEY. Some oxides become conductive due to preferential sputtering of oxygen. D. Depla et al. JAP 11 (27) 1331/1-1331/9 D. Depla et al. J.Phys D. : accepted for publication : Why does the pressure change? q q P q c Effective gas pressure q t target Prof. Berg in Ghent 6 q = q + q + q o p t c S. Berg et al., TSF 476 (25)

4 7 : some more equations The chemical reaction on the target and on the substrate is defined by chemisorption. θ t 1 θ t oxide F The effective reactive gas pressure defines the flux oxide θ c The coverage and substrate is given by θ + ( ) ( ) qt =αtf 1 θt At q =α F 1 θ A q = ps c c c c p metal metal 1 θ c Total reactive gas flow For more about the chemisorption mechanism : C. Li et al. J. Phys. D: Appl. Phys. 37 (24) F F= p 2πkTM 8 : But there happens more at the target! NRA measurements during magnetron sputtering 1.8 MeV D+ 14 N(d,α ) 12 C 14 N(d, α 1 ) 12 C* Nitrogen areal density (1 15 atoms cm -2 ) Nitrogen partial pressure (1-5 mbar) increasing N 2 flow decreasing N 2 flow Magnetron off increasing N 2 flow decreasing N 2 flow Nitrogen flow (sccm) Guttler D., Abendroth B., Grotzschel R., Moller W., Depla D, APL 85 (24)

5 Reactive ion implantation : More equations Start situation + t Start situation implantation depth D implantation depth D s b s b Target surface θ sr θ sm q θ bm θ br Target surface θ sr θ sm θ br q θ bm 9 x D D-s x D D-s In steady state : when the slab reaches the surface, the chemical reaction finishes and the oxidation degree at the target surface must be equal to θ sr nr nr = 2Ip x zknrnm vs t x nm nr = knrn m vs t x Or as an equation : ( ) D. Depla et al. J. Phys. : Appl. Phys. D, 4 (27) Reactive ion implantation : Knock on and chemisorption Chemical reaction between implanted reactive gas and target material With chemisorption and knock-on implantation 2Fαθ z sm ions neutrals s θ sm Target surface θ sr q θ bm θ sc θ br implantation depth D b Iβθsm z knock-on x D D-s Simplification : knock-on profile is identical to implantation profile 5

6 11 The total model : let us play with the equations P Ar (argon pressure) :.4 Pa I (current) :.4 A Step : 2 minutes Target : Aluminium Reactive gas : oxygen RSD28 Download the program pressure difference ( Pa) voltage difference ( V) S =16 L /s S =32 L /s -4 S =65 L /s S =13 L /s flow (sccm) 4 5 A α c t k β α c 12 α t.17 (.34) α c.35 (.13) β.22 (.93) k 2.E-23 (4.9E-26) A c 38 (15) 387 combinations 6 results in a good fit 6

7 13 : Chemisorption : one smart guy Studying the reactive magnetron sputtering deposition of oxides, with mass spectrometry Wouter Leroy, S. Mahieu, Y. Aranda-Gonzalvo, D. Depla See poster PO357 on Wednesday Counts (a.u.) Plasma ON no O Plasma OFF 6 8 Time (s) Plasma ON intended O Plasma OFF 14 amu 16 amu 17 amu 27 amu 32 amu 36 net O 2 counts during sputtering The determination of the sticking coefficient of oxygen during aluminium sputtering 14 :substrate area: an experiment in a cylinder Depositions were performed in a closed cylinder to collect all particles on a well defined substrate Can we model this? critical point (sccm) Critical point shift to lower reactive gas flow with decreasing substrate area substrate area (cm 2 ) 4 5 7

8 :substrate area: an experiment in a cylinder critical point (sccm) ( ) q =α F 1 θ A c c c c substrate area (cm 2 ) So, we assume an uniform deposition profile. 2F IdθtYc A t α c + z As θ c = 2F Iθ d( θ d tyc A I 1 t t) Ym At α c + + z A A c c 16 :substrate area: another smart guy MC-simulation of the metallic flux during magnetron sputtering Koen Van Aeken, S. Mahieu, M. Horkel,Y. Aranda-Gonzalvo D. Depla, C. Eisenmenger-Sittner critical point (sccm) Download the program substrate area (cm 2 ) The average flux towards the substrate is NOT given by 1/A c because the interaction of the deposition profile is more complicated than we think. 8

and the future : + The plasma contains more then neutral reactive gas molecules + The target erosion is not uniform +

9 : Oxidized Metallic Magnetron position 17 : a first set of conclusions The implementation of reactive ion implantation is necessary to understand the details of magnetron sputtering. So more equations are needed. and the future : + The plasma contains more then neutral reactive gas molecules + The target erosion is not uniform + Other types of behave differently 18 Input of plasma composition measurements and e.g. PIC/MC models is needed See E. Bultinck et al. OR224 (Thursday) 9

10 : Target erosion θ sr depth (mm) position on the target (mm) oxygen pressure (Pa) flow (sccm) Implementing the erosion profile by segmenting the target based on the measured race track. The future is to measure the effective current density on the target Rotating cylindrical : what equations do we need discharge voltage (V) oxygen flow (sccm) RPM 1.1 RPM 2.4 RPM 5.8 RPM 8.9 RPM 19.5 RPM 26.5 RPM 4.1 RPM 64.1 RPM 1

11 21 critical point (sccm) Rotating cylindrical : experimental results critical point (sccm) Critical point on oxygen addition 15 rotation speed (RPM) rotation speed (RPM) Hardly any variation as a function of the rotation speed Rotating cylindrical : 22 What happens here? Further chemical reaction between implanted species and the target material nr nr = 2Ip( x) zknrnm vs t x Chemisorption of reactive gas 11

12 Rotating cylindrical : model results 1 16 RPM Chemisorption is a surface process Substrate condition Target Surface condition Contribution of chemisorption to oxidation in the target Bulk condition 5 ms after start Rotating cylindrical : model results Reactive ion implantation takes over Substrate condition Target Surface condition Contribution of chemisorption to oxidation in the target Bulk condition 2 s after start 12

13 I Rotating cylindrical : model results Compound formed outside the race track influences the condition in the race track Substrate condition Target Surface condition Contribution of chemisorption to oxidation in the target Bulk condition 26 Rotating cylindrical : model results critical point (sccm) critical point (sccm) Critical point on oxygen addition rotation speed (RPM) Critical point on oxygen removal rotation speed (RPM) Help : it does not fit with the experiment! 13

14 Rotating cylindrical : Why doesn t it fit? What happens here? There is another process : deposition! race track position Thickness (nm) 45 9 Deposition of copper on a stationary target after 1 h deposition Nice to know : SiMTRA makes it possible to simulate this! 28 Rotating cylindrical : Deposition How strongly does this effect the hysteresis behaviour? 34 discharge voltage (V) sccm : in poisoning sccm : in metal mode time (s) 14

15 I Rotating cylindrical : Deposition in the model! critical point (sccm) 2.2 Critical point on oxygen addition rotation speed (RPM) 29 critical point (sccm) Critical point on oxygen removal rotation speed (RPM) : and diffusion α is the angle between the second race track leg and the beam 3.5 MeV He+ beam Rotation speed : 1 round per 8 seconds 3 The backscattered ions were recorded by a surface barrier detector, which was protected from the plasma by a 6 µm thick Al foil Target material : Ti Experimental conditions : discharge current :.85 A Gas composition and pressure : Xe (.4 Pa) or a mixture of Xe and 1% N 2 (.44 Pa) 15

16 31 : some experimental results Steady state Xe areal density in the race track (α=) In pure Xe In Xe/N 2 Metallic target Poisoned target 3.85x1 12 at/cm x1 12 at/cm 2 Assuming a homogenous distribution of Xe in the first 2 nm 3.4 ±.5% 9.8 ± 1% No influence of the rotation speed (varied from to 1 turn per 1 seconds) No influence of the discharge current (varied between.25 and.95 A) Conclusion : a significant amount of noble gas is incorporated into the target The presence of the noble gas atoms can influence the amount, and the angular and energy distribution of the sputtered and backscattered particles. Furthermore, they can take part in the collision cascade resulting in an additional mechanism besides diffusion for the Xe atoms to leave the target. TRIDYN (static mode) : partial Xe sputter yield of.7 for 39 ev Xe + on Ti partial Xe sputter yield of.176 for 5 ev Xe + on TiN : some experimental results Xe % Changingα Switching off the discharge time (sec) 1 1 So no diffusion and subsequent desorption S. Mahieu, W.P. Leroy, D. Depla, S. Schreiber, W. Möller APL 93 (28)

17 Final conclusions of reactive sputter deposition From 1986 until now : a long way has been gone. 33 From now until : still quite some research (and equations) are needed 34 17

18 35 -W. Leroy : Measuring of sticking coefficients -S. Mahieu : Xe experiments (and book editing) -X.Y. Li : rotating magnetron measurements (and the Chinese title!) -K. Van Aeken : SiMTRA -M. Saraiva : Bringing reactive sputter deposition into practice (see poster) -J. Haemers : magnetron design -R. De Gryse : a good old boss Financial support : IWT-Flanders (SBO project 63) Bekaert N.V. FWO-Flanders And of course YOU. Oh, no more equations, please 18

In search for the limits of

In search for the limits of rotating cylindrical magnetron sputtering W. P. Leroy, S. Mahieu, R. De Gryse, D. Depla DRAFT Dept. Solid State Sciences Ghent University Belgium www.draft.ugent.be Planar Magnetron