Influence of Tungsten/Carbon Interactions On Carbon Erosion Behavior In D 2 Plasma

1. Influence of Tungsten/Carbon Interactions On Carbon Erosion Behavior In D2 Plasma Nick Lyon, Florian Weilnboeck, and Gottlieb S. Oehrlein Department of Material Science and Engineering and Institute for Research in Electronics and Applied Physics University of Maryland, College Park, Maryland, 20742 Russ P. Doerner Center for Energy Research, University of California – San Diego July 2009 1

2. Outline 2 Experimental apparatus and diagnostics Erosion of hard a-C:H in deuterium plasma Influence of W near-monolayer coverage on a-C:H erosion Conclusions

3. University of Maryland Cluster System for Plasma Processing of Materials Multi-Technique Surface Analysis ICP Reactor Chamber (XPS, AES, ...) Numerous Plasma and Surface Diagnostic Techniques Shared Between All Systems Load Lock II Load Lock I Inductively Coupled Plasma Reactor Evaporator Evaporator Capacitively Coupled Plasma (CCP) Reactor 3

4. Experimental Setup Planar Coil ICP • Inductive Power • 600W to 800W • (13.56 MHz) • Operating Pressure • 10 mTorr Erosion • RF Bias • -100 V, 3.7 MHz • CH4, D2, Ar • Total gas flow = 40 • sccm • In situ ellipsometry •  real time monitoring of processes • XPS: surface characterization 4

5. ICP Device Measurements used as basis of computer simulations and model validation by several major plasma modeling groups – Sandia National Labs, M. J. Kushner In turn has helped us refine the measurements Geometry and B-Field Measurements Xi Li, Li Ling, X. Hua and G. S. Oehrlein, Y. Wang, A. V. Vasenkov and M. J. Kushner, J. Vac. Sci. Technol. A 22, 500 (2004). V. Vasenkov, Xi Li, G. S. Oehrlein, and M. J. Kushner, J. Vac. Sci. Technol. A 22, 511 (2004). 5

6. Process Sequences to be Discussed 6 • D2 erosion of • a-C:H films • a-C:H + in-situ deposited W (below and above 1 monolayer) • a-C:H + in-situ deposited W above 1 monolayer and air-exposed for oxidation

7. Ellipsometry Interpretation a-C:H Deuteration/Roughening 5 nm steps erosion deposition W coverage 1 mL (0.3nm) steps WOx on W 2nm Steps

8. Erosion of a-C:H Film in D2 Plasma Erosion Erosion Deposition Deposition D2 Plasma 8

9. Simulation of a-C:H:W Materials in ReactorExperimental Ar C, H a-C:H W D2 C, H, W a-C:H-W W • W sputter onto a-C:H film • Ar 10 mTorr 30 sccm • 600 W Source Power • -100V bias • D2 erosion of a-C:H/W films • D2 10 mTorr 30 sccm • 600 W Source Power • -100 V bias 9

10. Erosion of W/a-C:H Film in D2 Plasma Erosion stop 240s 120s Erosion start

11. Impact of W Monolayer Coverage On a-C:H Erosion ~8x lower 11

12. XPS Time Sequence:After W Deposition, 2min D2, 4min D2, Erosion Stop

13. W deposition RMS=2.4 nm 2min D2 RMS=3.4 nm 4min D2 RMS=17.38 nm Etch stop D2 RMS=9.24 nm

14. Roughness Formation Dominates Surface Modification Plasma Start

15. Real-Time Roughness Measurements 15

16. Fate of Oxidized W During a-C:H Erosion 120 s D2 0 s Roughness 40 nm 120 s D2 0 s 1.2nm W WOx  W

17. Oxygen removal after grounded deposition during D2 erosion

18. Optical Emission Spectroscopy • Although W emission is not detected for D2 plasma, exposure of test coupons show that W transport during D2 plasma exposure of W takes place for conditions employed

19. Conclusions • W monolayer coverage of a-C:H has profound influence on erosion behavior, including • Initial retardation of erosion • Lower steady-state erosion rate • Slow removal of W • Microscopic blocking of sites and surface roughening • The complex surface processes taking place can be efficiently studied by a combination of • Real-time • Post-plasma surface diagnostics

20. Acknowledgements 20 We gratefully acknowledge financial support of this work by the Department of Energy