Simulation of Metal TRAnport. SIMTRA : a tool to predict and understand deposition. K. Van Aeken, S. Mahieu, D. Depla.

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1 Simulation of Metal TRAnport SIMTRA : a tool to predict and understand deposition K. Van Aeken, S. Mahieu, D. Depla 1) : Why do we calculate? ) Scientific background : How do we calculate? 3) : What can we calculate? 4) Some conclusions K. Van Aeken, S. Mahieu, D. Depla J. Phys. D: Appl. Phys (8) 1

The results of each deposition technique is a thin film with given properties A few relevant properties are thickness, crystallographic

energy, ) - the number of arriving particles The major players are of course the film forming particles So SIMTRA is developed to predict the

The code is optimized for magnetron sputter deposition (see further) Why developing a new simulation code?

2 The results of each deposition technique is a thin film with given properties A few relevant properties are thickness, crystallographic orientation, morphology, density, composition, 3 All depend on : - the type of arriving species - the properties of the particles (charge, energy, ) - the number of arriving particles The major players are of course the film forming particles So SIMTRA is developed to predict the number and the properties of the particles leaving the source and arriving at the substrate. The code is optimized for magnetron sputter deposition (see further) Why developing a new simulation code? -Most codes are research group specific. -Most codes are hard to access. -Most codes are not user-friendly. They miss a good interface to assist the user. 4 An easy to access program ( ) with a simple interface (three VB sheets) is the answer.

Scientific background : magnetron sputter deposition Magnetron sputter deposition is based on a magnetically assisted gas discharge Source materials is the cathode, or

In this way the gas discharge can be maintained at lower pressures.

3 Scientific background : magnetron sputter deposition Magnetron sputter deposition is based on a magnetically assisted gas discharge Source materials is the cathode, or target Discharge voltage : order 4 V Working pressure (argon gas) : 1x1-3 tot 1x1 - mbar Behind the cathode magnets are placed. In this way the gas discharge can be maintained at lower pressures. Reason : higher deposition rates Scientific background : magnetron types inch diameter cathode Cilindrical planar kathode Lab scale 6 4 1/3 Rectangular planar cathode Industrial scale 1 Intrinsic disadvantages : Formation of an erosion groove Advantages : simple target design Less stable in reactive mode 3

4 Scientific background : magnetron types Rotating cylindrical magnetron cm 18 cm : but can be extended 7 14 cm 4 cm Advantages : Stable in reactive mode No erosion groove (i.e. longer lifetime) Disadvantages : Complex target design Scientific background : Target erosion : starting points of the sputtered particles Cooperation with VITO 8 4

Scientific background : sputtering Magnetron sputter deposition is an PVD technique Physical Vapour Deposition The production of a vapour by a physical process. This process is sputtering.

5 Scientific background : sputtering Magnetron sputter deposition is an PVD technique Physical Vapour Deposition The production of a vapour by a physical process. This process is sputtering. Ions from the plasma hit the target, and target atoms are ejected. These move towards the substrate to form the film. 9 Scientific background : sputtering 1 1 sputter yield The number of atoms sputtered per ion depends on the material and the discharge voltage For metal :. to (Al to Cu) For oxides : much lower.7 (Al) ion energy (ev)

6 Scientific background : angular distribution of sputtered particles Nascent angular distribution : Heart-like emission Deviation from cosine 11 Propose differential yield : d Y ( θ) = d Ω c i i= 1 i cos θ Fit coefficients c i from the simulated deposition profiles of an angular base set Scientific background : energy distribution 1..8 Copper evaporated at 13 K Copper sputtered by 3 ev Ar + Thompson distribution SRIM energy distribution relative number density.6.4 U sb / average energy of sputtered particles energy copper atoms (ev) 6

7 Scientific background : sputter yield To calculate a deposition rate, the sputter yield of the material must be known. Sputter yields Cu exp Yam model What yield to use?. Tridyn srim Yield Vd of Ei We decided to measure them. Scientific background : reactive magnetron sputtering Magnetron sputer deposition allows to deposit compounds. Oxides, nitrides : generally no conductive target available Solution : the reactive gas is added to the discharge reactive gas : O 14 Reaction occurs mainly on the substate, but at sufficient high reactive gas flows also on the target. Consequences? N - + Target S Ar-ions N 7

8 Scientific background : reactive magnetron sputtering 1 target voltage (V) full symbols : addition open symbols : removal Reactive deposition of TiO.6.8 oxygen flow (sccm) / target voltage / deposition rate deposition rate (mass unit/s) Scientific background : SIMTRA Initialization Generate particles -planar : radial erosion profile -cylindrical : measured or simulated erosion profile Calculate free path length λ= λ lnx m 16 YES 1 High energy λ m = ngσ vs Near thermal energy λ m = ngσ vr 1 Thermal λ m = ms ngσ 1+ m Boundary Implements geometry Does particles trajectory intersects surface before collision? g NO 8

9 Scientific background : SIMTRA YES Boundary Implements geometry Does particles trajectory intersects surface before collision? NO 17 Deposition Generate new particle θ com Describe collision : Calculate scattering angle Calculate new velocity 1 (E com,p) =π p dr V(r) p R r 1 E com r Go back to free path calculation Scientific background : SIMTRA 18 θ com 1 (E com,p) =π p dr V(r) p R r 1 E com r 9

10 Scientific background : SIMTRA Interatomic potential (ev) Internuclear distance r (Å) Screened Coulomb potential : Only repulsive! 19 Quantum-mechanical potentials Attractive and repulsive (only Cu-Ar and Al-Ar) Interatomic potential (ev) Internuclear distance r (Å) : Verification of the code? The Metal Flux Monitor Pinhole Camera : A particle that passes the orifice (diameter 1mm) at a given angle x impinges the substrate a the position y Angular distribution of metal flux Thickness Profile C. Eisenmenger-Sittner M. Horkel 1

rotating magnetron Measure deposition rate with a quartz crystal microbalance for : Cu, Ti, Al target Ar pressure :.

11 : Verification of the code? Comparison Cu at variable pressures 1 Comparison Al at variable pressures : Deposition rate distribution for a rotating magnetron Measure deposition rate with a quartz crystal microbalance for : Cu, Ti, Al target Ar pressure :.3,.6 and 1 Pa as function of θ at : 3 radial distances : r 1,r,r 3 3 z-positions : z 1,z,z 3 Compare to simulation Example : Al,.3Pa Ar r = r, θ = -3, z = z V d = 37 V, I =.4 A Outward radial metal flux (r,θ,z) 11

12 : Deposition rate distribution for a rotating magnetron Spatial dependence Pressure dependence : P =.3 Pa r = r 1 r = r 1 z = z 3 : A simple thing to start We can expect that the deposition rate decreases as a function of the target-substrate distance. What is the relationship? We expect a 1/d relationship at sufficient high pressure. Well, let us test this idea with SiMTRA 4 A planar circular magnetron (inch) mounted in a cubic vacuum chamber (1x1x1 m). The substrate was a circular plate of 1x1 cm placed under the target centre at several distances. The target material was aluminum. Using an output file of SIMTRA and MatLab one can check the configuration 1

: A simple thing to start target-substrate distance d (cm) 1 1 1 8 6 6.

d - (cm - ) : Prediction of the composition for dual planar magnetrons

13 : A simple thing to start target-substrate distance d (cm) number of arriving particles Pa.3 Pa.6 Pa.9 Pa Seems to fit quite well. d - (cm - ) : Prediction of the composition for dual planar magnetrons Experimental set-up 6 Thanks to M. Saraiva 13

14 7 : Prediction of the composition for dual planar magnetrons Discharge current Mg, Cr =. A Source-sample distance Oxygen flow Mg-Cr-O target-sample distance (cm) composition 41 9 target position Mg target position Cr oxygen flow Mg concentration (%) Cr concentration (%) O concentration (%) Mg metal ratio (%) oxygen flow (sccm) : Prediction of the composition for dual planar magnetrons Mg(Al)O Mg(Cr)O Mg(Ti)O M/(M+Mg) % Mg(Y)O Mg(Zr)O (R'/(R'+1))x1 1 open symbols : experimental closed symbols : SiMTRA : fitted line through the experimental points 14

rotating magnetrons 3 Simulation : Separate calculation for both magnetrons Using correct

15 : Prediction of the composition for dual rotating magnetrons Setup: 9 Cu - target Al - target discharge shield in order to minimize re-deposition : Prediction of the composition for dual rotating magnetrons 3 Simulation : Separate calculation for both magnetrons Using correct sputter yields for Al and Cu Calculate the composition Experiment : Measuring Cu/Al using EPMA and EDX 1

16 : Prediction of the composition for dual rotating magnetrons Deposition of Cu-Al: SiMTRA vs. experiments discharge current Cu =.3 A, Al = A source-sample distance = 9. cm SiMTRA can be used to predict composition in a dual magnetron setup relative # of atoms arriving at substrate distance from chamber wall (cm) 4 Al exp Al SiMTRA Cu exp Cu SiMTRA 31 Thanks to F. Boydens at. % Cu distance from chamber wall (cm).3 A exp.3 A SiMTRA.6 A exp.6 A SiMTRA.9 A exp.9 A SiMTRA : Reactive magnetron sputtering : condition of the substrate θ t 1 θ t F 1 F 3 F 4 F F 3 θc 1 θc The composition at the substrate is defined by the deposition rate on the substrate, and the reactive gas pressure Homogeneous deposition and steady state conditions: J A J A = αcf1 θ e A e A t t ( θc) + YNθt ( 1 θc) YM( 1 θt) c c c 16

$f θ e e c c,i N t t, i c,i M t t d,i c, i 33 The fraction f d,i of sputtered atoms arriving at each cell i can be calculated with SiMTRA.$

17 : Reactive magnetron sputtering : condition of the substrate Subdivide the substrate in several cells and the condition of cell i can be calculated by J J = α F( 1 θ ) + Y θ A fd ( 1 θ ) Y ( 1 θ ) A f θ e e c c,i N t t, i c,i M t t d,i c, i 33 The fraction f d,i of sputtered atoms arriving at each cell i can be calculated with SiMTRA. So, we included the output of SiMTRA in another simulation tool (also available at ) RSD9. : Reactive magnetron sputtering : condition of the substrate Total pressure (Pa) Oxygen flow (sccm) 3. Blue : metal Red : oxide Thanks to Wouter Leroy 17

18 : Negative oxygen emission Measurement of negative oxygen emission during reactive magnetron sputtering Y or Al P(Ar).4 Pa P(O ).4 Pa 3 M + O - 8 cm Masspec Cps (a.u.) : Negative oxygen emission AlO - => AlO + O - exp O SiMTRA O SiMTRA AlO SiMTRA AlO SiMTRA AlO - => Al + O - O - => O + O E (ev) exp O SiMTRA O SiMTRA YO SiMTRA YO SiMTRA O - O - M( O) Vdx = 9V M( O) M( O) Vdx = 14V M( O) M( O) Vdx = 18V M( AlO) M( O) Vdx = 78V M( AlO) 36 Cps (a.u.) YO => 1 - YO + O - O => YO - => O + O - Y + O Simulation of the energy distribution E (ev) M( O) Vdx = 18V M( O) M( O) Vdx = M( O) M( O) Vdx = M( YO) 9.V 8V M( O) Vdx = 4.V M( YO) 18

19 : Negative oxygen emission 37 Masspec Masspec Masspec Masspec Masspec Masspec Direction of the negative ions. Masspec : Negative oxygen emission Al Y 'O exp' 'O SiMTRA' 'O/Al SiMTRA (a.u.)' Thanks to Stijn Mahieu 'magnetron' 1 'O exp' 'O SiMTRA' 'O/Y SiMTRA (a.u.)' 'magnetron' 19

20 : momentum flux Torsion wire 39 Opening area A Torsion plate reflector Front view Back view Measure steady state rotation angle => know momentum flux Hardness (GPa) : momentum flux Measured M tot (kgm/s) 4x1-1 4 Contribution of backscatter ions, sputtered neutrals to the total momentum flux can be calculated using SIMTRA

21 : Biaxial aligned thin films Only preferred out-of-plane orientation : uniaxial alignment Out-ofplane Grain boundary Inplane Out-ofplane grain boundary Inplane Preferred in-plane and out-ofplane orientation: biaxial alignment 41 XRD polefigures FWHM : Biaxial aligned thin films Zone T growth: as seen in plan view - growth rate anisotropy due to anisotropy in capture cross-section of incoming adatoms Capture length (111) (111) 4 (111) (111) Sketch of plan view Direction of incoming material 1

22 : Biaxal aligned thin films 43 Conclusion 44 The code can give an answer to quite some questions related to Deposition rate Composition Energy of deposited sputtered particles And probably you can invent a few more In that case, or if you wish to cooperate on this project we are ready to assist you Contact : Koen.VanAeken@ugent.be Cost of SiMTRA : A scientific return in joint papers is a good alternative for money.

23 : vacuum chamber The influence of a shutter on the deposition profile. Set-up 6 cm 4 cm Cylindrical vacuum chamber : diameter : 6 cm length : cm : gas element, pressure, temperature 46 3

24 : the source Lab magnetron 47 : the source : position 6 cm cm 48 The centre of the axis is in the middle of the magnetron So, in the middle of the vacuum chamber lid and z=.3 m 4

25 : let s make a cylindrical substrate 1 cm cm This object consists of 3 surfaces! 1) Plane piece : outer boundary circle ) Cylindrical piece 3) Plane piece : outer boundary circle 49 This tells to SIMTRA where the surfaces are located in the reference system of the object (see manual, and next slide) : the position vectors for the substrate x Reference system of the object cm z y c b a

26 : the position vectors for the substrate x Reference system of the object cm z 1 y a b.1 c.1... : the position vectors for the substrate x Reference system of the object cm z y

27 : position the substrate 1 cm 6 cm cm 3 X : Y : Z :.17 m Magnetron length : 7 cm Centre of the substrate :. cm Anode-substrate top surface : 1 cm : check the output : Matlab file : plotdepositie 4 This looks just great! 7

28 Let us calculate : the deposition profile on the top surface R8.. R R R19 R16 R13 R Yellow is zero. What is the effect of the pressure? R7 R4 R1 Repeat the simulations at different pressures 4x number of arriving atoms argon pressure (Pa) 6 8 8

29 Including a shutter The shutter is built from a rod and a circular disk. 6 cm 7 cm The rod is 38 cm long and has a diameter of 1 cm. Make it. The position of the rod is cm off centre, and connected to the back of the chamber Including a shutter () The shutter is built from a rod and a circular disk. 6 cm 8 cm The disk is 1 cm in diameter and 1 mm thick. Make it Its centre is at 7 cm in X and cm in Y, and connected to the rod. 9

30 : check the output : Matlab file : plotdepositie 9 This looks just great! Repeat the simulations at different pressures 4x1 3 4 no shutter with shutter 3 6 number of arriving atoms But there is more The introduction of the shutter lowers the deposition rate as the shutter collects atoms which can not reach the substrate anymore. 4 argon pressure (Pa) 6 8 3

31 Let us look at the distributions Pa 1. Pa 1 1 Pa 1 Pa Pa 4 Pa Distorted deposition profile 1 Pa 1 8 Pa Let us look at the distributions with shutter without shutter 1 off centre position (a.u.) Error pressure (Pa) Weighted centre position

32 And what about the energy? without shutter with shutter 63 average energy (ev) Thermal energy pressure (Pa) 3

Some more equations describing reactive magnetron sputtering.

Some more equations describing reactive magnetron sputtering D. Depla, S. Mahieu, W. Leroy, K. Van Aeken, J. Haemers, R. De Gryse www.draft.ugent.be discharge voltage (V) 44 4 36 32 28..5 1. 1.5 S (Pumping