Ion beam sputtering of Ag: Properties of sputtered and scattered particles

Transkript

1 Ion beam sputtering of Ag: Properties of sputtered and scattered particles René Feder, Horst Neumann, Carsten Bundesmann 1

2 Outline Motivation Experimental setup Process simulation Scattered primary ions Sputtered target ions Sputtered neutrals Conclusions & Outlook 2

3 Motivation Ion beam and geometrical parameters Properties of secondary particles (scattered and sputtered) Thin film properties see talk by C. Bundesmann Systematic and comprehensive analysis of the correlation between the properties of the ion beam, the secondary particles and the deposited layers Simulations provide spatial and energetic distribution of sputtered and backscattered particles Comparison between experimental and simulated data to validate simulation code for ion beam sputtering 3

4 Experimental Setup: Chamber Rotary feedthrough Rotary table ESMS Target Ion source Sample holder Faraday cup Rotary table Linear tables 4

5 Process simulation Sputter process is simulated with TRIM.SP [1] Simulation provides spatial and energetic distribution of sputtered and scattered particles α = 0-90 [1] J.P. Biersack, W. Eckstein, Appl. Phys. A: Mater. Sci. Process. 34 (1984) 73 Visualizations done with the ray tracing program POV-Ray 5

6 Scattered primary particles: Experimental High-energetic peaks from direct scattering Shifting of the high-energetic peak with the emission angle Broadening for higher emission angles likely due to primary ion beam divergence and target surface roughness Problem: low energetic maxima Directly scattered primary particles 6

7 Scattered primary particles: Simulation Clear high-energetic maxima in the energy distributions of backscattered Ar Shifting of peak position with emission angle Information: maximum position, average particle energy, total energy 7

8 Comparison with Simulation Fitting by equation for direct scattered particles and inelastic energy loss Energy loss in TRIM.SP less than in experiment Stopping power in TRIM.SP too low? Depth of the direct collision? 8

9 Sputtered target ions: Experimental Average particle energy shifts to higher values with the emission angle Direct recoils change the shape of the curve (80 emission) Restriction: detectable particle energy limited to 500 ev 9

10 Sputtered target atoms: Simulation TRIM.SP simulations provide energy distribution of sputtered particles Average particle energy and total energy of sputtered particles changes with the emission angle Ag-distrib.: azim. forward (0-15 ) 28.8 Incident=30, 1keV Ar+ -> Ag Yield [counts] Energy [ev] 10

11 Sputtered target ions: Experimental Average particle energy increases with emission angle Higher incident angle leads to higher average particle energy aver. part. energ. [ev] eV; Ar; 0 in 1500eV; Ar; 0 in 1000eV; Ar; 30 in 1500eV; Ar; 30 in 1000eV; Ar; 60 in 1500eV; Ar; 60 in 1000eV; Xe; 0 in 1500eV; Xe; 0 in 1000eV; Xe; 30 in 1500eV; Xe; 30 in 1000eV; Xe; 60 in 1500eV; Xe; 60 in Emission [ ] 11

12 Sputtered target ions: Experimental Maximum in the total energy input shifts with incident angle Total energy input from sputtered particles is much higher for Xe than for Ar total energy [MeV] eV; Ar; 0 in 1500eV; Ar; 0 in 1000eV; Ar; 30 in 1500eV; Ar; 30 in 1000eV; Ar; 60 in 1500eV; Ar; 60 in 1000eV; Xe; 0 in 1500eV; Xe; 0 in 1000eV; Xe; 30 in 1500eV; Xe; 30 in 1000eV; Xe; 60 in 1500eV; Xe; 60 in Emission [ ] 12

13 Film forming particles: Simulation Average energy of scattered particles is 10 times higher than average energy of sputtered particles for Ar beam sputtering Average energy of scattered particles is 5 times higher than average energy of sputtered particles for Xe beam sputtering Ar->Ag Xe->Ag 1000 azimuthal: 0 +/- 15 polar: cos-interval sputtered particle scattered 1000 azimuthal: 0 +/- 15 polar: cos-interval sputtered particle scattered average energy [ev] 100 average energy [ev] angle [ ] angle [ ] 13

14 Film forming particles: Simulation Total energy input of sputtered and scattered particles is comparable for Ar beam sputtering For Xe beam sputtering, there is much less energy input from scattered particles Xe (131 amu) is heavier than Ag (108 amu) -> less backscattering Ar->Ag Xe->Ag azimuthal: 0 +/- 15 polar: cos-interval all sputtered part. all scattered part azimuthal: 0 +/- 15 polar: cos-interval all sputtered part. all scattered part total energy [ev] total energy [ev] angle [ ] angle [ ] 14

15 Sputtered target neutrals: Experimental Maximum in the energy distribution of sputtered neutrals is at the half of the valueof thesurfacebindingenergy(thompson) ESMS offers only a few ev scan range, restricted by ionization probability Energy distribution of residual gas components Surface binding energy: experiment: (2.72±0.6)eV sublimation: ev theor. : 3.33 [1] [1] Y. Kudriavtsev et al., Appl. Sur. Sci. 239 (2005)

16 Sputtered target neutrals: Experimental Ag target sputtered with Ar and Xe ions: additional maximum at "thermal energy" 16

17 Conclusions and Outlook Energy distributions of scattered Ar + and Xe + and sputtered Ag + change with the polar emission angle Average energy of film forming particles is higher for higher emission angles Total energy of film forming particles is much lower for Xe ion bombardment than for Ar ion bombardment Simulations confirm qualitatively the experimental findings, differences are most likely by energy losses, which seem to be underestimated in the simulation Energy distribution of neutral target atoms can be used to calculate the surface binding energy Find a correlation between the properties of the sputtered and scattered particles and the properties of the deposited films Changing the material system from metal to semiconductor: Replace the Ag target by a Ge target 17

18 Acknowledgement Prof. Dr. Dr. h. c. Bernd Rauschenbach Frank Scholze Ronny Woyciechowski IOM Workshop Marco Müller Petra Hertel Financial support: DFG (project BU2625/1-1) 18

19 Experimental Setup: ESMS Energy selective mass spectrometer (ESMS) for energy and mass distribution of primary and secondary particles Energy range ev 19

20 Energy distribution of sputtered neutrals Sputtering a Ge target with an Ar ion beam 20

21 Energy distribution of sputtered neutrals Sputtering a Ge target with an Ar ion beam 21