1. FLCC March 28, 2005 FLCC - Plasma 1 Fluid Modeling of Capacitive Plasma Tools FLCC Presentation March 28, 2005 Berkeley, CA David B. Graves, Mark Nierode, and Yassine Kabouzi UC Berkeley

2. FLCC March 28, 2005 FLCC - Plasma 2 Motivation Capacitively-coupled plasma etch tools commonly used, especially in dielectric etch Popular strategy: dual frequency operation to separate control of ion flux and plasma density (high frequency) from ion energy control (low frequency) Overall goal is to develop a 2-D, time-dependent fluid plasma model that can be used for tool design and process control studies Tool-scale model can be coupled to feature scale (e.g. Prof. Chang, UCLA) Fluid model can complement PIC/MC model (Prof. Lieberman, UCB)

3. FLCC March 28, 2005 FLCC - Plasma 3 1.Fluid model of 1-D dual frequency (27 MHz, 2 MHz) Ar discharge. 2.Fluid model of 2-D single frequency (13.5 MHz) Ar discharge. 3.Fluid model of non-isothermal, reacting neutral flow in typical industrial capacitive etch tool with split inlet flows. Today’s Talk

4. FLCC March 28, 2005 FLCC - Plasma 4 Plasma Model Equations Equations solved via FEMLAB

5. FLCC March 28, 2005 FLCC - Plasma 5 One Dimensional Dual Frequency Results Argon, p = 50 mtorr, 800 V rf @ 27 MHz,, 800 V rf @ 2 MHz applied at left electrode 2 MHz 27 MHz 0.02 m

6. FLCC March 28, 2005 FLCC - Plasma 6 Potential on Powered (Left) Electrode Argon, p = 50 mtorr, 800 V rf @ 27 MHz,, 800 V rf @ 2 MHz applied at left electrode 0.5

7. FLCC March 28, 2005 FLCC - Plasma 7 Dual Frequency Results: Plasma Density Argon, p = 50 mtorr, 800 V rf @ 27 MHz,, 800 V rf @ 2 MHz applied at left electrode

8. FLCC March 28, 2005 FLCC - Plasma 8 Right Sheath Structure

9. FLCC March 28, 2005 FLCC - Plasma 9 Left Sheath Structure

10. FLCC March 28, 2005 FLCC - Plasma 10 Electron Density in Sheaths: 27 MHz Variation Electron loss at both sheaths Electron loss at right sheath only

11. FLCC March 28, 2005 FLCC - Plasma 11 Electric Field and Plasma Potential: 2 MHz

12. FLCC March 28, 2005 FLCC - Plasma 12 Potentials on Powered Electrode and in Plasma

13. FLCC March 28, 2005 FLCC - Plasma 13 Currents at Powered Electrode

14. FLCC March 28, 2005 FLCC - Plasma 14 Electron Temperature

15. FLCC March 28, 2005 FLCC - Plasma 15 Two-Dimensional, Axisymmetric (r,z) Single Frequency Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode 0.25 m radius 0.025 m height Powered electrode Grounded Preliminary 2-D results obtained

16. FLCC March 28, 2005 FLCC - Plasma 16 Period-Averaged Electron Density Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode

17. FLCC March 28, 2005 FLCC - Plasma 17 Period-Averaged Electron Temperature Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode

18. FLCC March 28, 2005 FLCC - Plasma 18 Period-Averaged Ion Density Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode

19. FLCC March 28, 2005 FLCC - Plasma 19 Period-Averaged Plasma Potential

20. FLCC March 28, 2005 FLCC - Plasma 20 Neutral Reacting Flow Model Equations solved via FEMLAB

21. FLCC March 28, 2005 FLCC - Plasma 21 Neutral Flow Configuration –Commercial tools typically feature dual flow configurations to allow for greater process control (e.g. balance fluorocarbon deposition and etching) –Investigate the transport of the tuning gas and its effect on reactor chemistry 400/20/9 sccm Ar/c-C 4 F 8 /O 2 | 0-100 sccm O 2 Pressure ~ 30 mtorr

22. FLCC March 28, 2005 FLCC - Plasma 22 Mesh and Numerics 3363 elements, 115106 d.o.f. All variables use quadratic Lagrangian elements except pressure which is linear Steady state solution obtained 1-2 hours using iteration script (FEMALB feature; eqns solved iteratively and sequentially)

23. FLCC March 28, 2005 FLCC - Plasma 23 Chemistry Model 1. Simplistic model will assume CF as the ‘depositing’ species and F as the ‘etching’ species 2. Increased O2 flow in the outer annulus leads to increased O2 and O in the outer region 3. Increased O increases rxns 6 & 7 producing F on the same order as rxn 4

24. FLCC March 28, 2005 FLCC - Plasma 24 Assumed Plasma Density Assume constant T e = 3 Assume radial plasma profile flat except when r > 0.2

25. FLCC March 28, 2005 FLCC - Plasma 25 Neutral Temperature Neutral gas heating is proportional to the (assumed) plasma density ‘Jump’ temperature and ‘slip’ velocity boundary conditions Temperature profile not affected by outer tuning flow up to 100 sccm O 2

26. FLCC March 28, 2005 FLCC - Plasma 26 Pressure and Temperature Effects Radial pressure drop is significant ~30% leading to a similar neutral number density profile (n); recall n ~ p/T Axial pressure gradients are minimal Total neutral density

27. FLCC March 28, 2005 FLCC - Plasma 27 Neutral Species Radial Profiles Qtune = 0 sccm

28. FLCC March 28, 2005 FLCC - Plasma 28 Neutral Species Radial Profiles – Note: scale different from previous slide Qtune = 100 sccm

29. FLCC March 28, 2005 FLCC - Plasma 29 Effects of Altering O 2 ‘Tuning’ Gas Flow Propose CF/F as model deposition/etch ratio index Varying the outer O 2 flow (Qtune) the ratio of CF to F can be modified radially although the overall ratio of CF to F changes too

30. FLCC March 28, 2005 FLCC - Plasma 30 Concluding Remarks FEMLAB-based fluid modeling powerful tool to simulate complex, multi-dimensional, reacting plasma tools –Tool-scale design/analysis possible –Fully transient, coupled neutral-plasma versions can simulate process control Two major limitations to tool-scale fluid models: –No feature profile evolution –No plasma kinetic information (e.g. EEDF, IEDF, IADF) FLCC plasma project couples fluid modeling (DBG, UCB), feature evolution modeling (JC, UCLA) and PIC/MC modeling (MAL, UCB)