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Fluid Modeling of Capacitive Plasma Tools. FLCC Presentation March 28, 2005 Berkeley, CA David B. Graves, Mark Nierode, and Yassine Kabouzi UC Berkeley. Motivation. Capacitively-coupled plasma etch tools commonly used, especially in dielectric etch
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Fluid Modeling of Capacitive Plasma Tools FLCC Presentation March 28, 2005 Berkeley, CA David B. Graves, Mark Nierode, and Yassine Kabouzi UC Berkeley FLCC - Plasma
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) FLCC - Plasma
Today’s Talk • Fluid model of 1-D dual frequency (27 MHz, 2 MHz) Ar discharge. • Fluid model of 2-D single frequency (13.5 MHz) Ar discharge. • Fluid model of non-isothermal, reacting neutral flow in typical industrial capacitive etch tool with split inlet flows. FLCC - Plasma
Plasma Model Equations Equations solved via FEMLAB FLCC - Plasma
27 MHz 2 MHz 0.02 m One Dimensional Dual Frequency Results Argon, p = 50 mtorr, 800 V rf @ 27 MHz, , 800 V rf @ 2 MHz applied at left electrode FLCC - Plasma
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 FLCC - Plasma
Dual Frequency Results: Plasma Density Argon, p = 50 mtorr, 800 V rf @ 27 MHz, , 800 V rf @ 2 MHz applied at left electrode FLCC - Plasma
Right Sheath Structure FLCC - Plasma
Left Sheath Structure FLCC - Plasma
Electron Density in Sheaths: 27 MHz Variation Electron loss at both sheaths Electron loss at right sheath only FLCC - Plasma
Electric Field and Plasma Potential: 2 MHz FLCC - Plasma
Potentials on Powered Electrode and in Plasma FLCC - Plasma
Currents at Powered Electrode FLCC - Plasma
Electron Temperature FLCC - Plasma
Two-Dimensional, Axisymmetric (r,z) Single Frequency Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode Powered electrode Grounded 0.025 m height 0.25 m radius Preliminary 2-D results obtained FLCC - Plasma
Period-Averaged Electron Density Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode FLCC - Plasma
Period-Averaged Electron Temperature Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode FLCC - Plasma
Period-Averaged Ion Density Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode FLCC - Plasma
Period-Averaged Plasma Potential FLCC - Plasma
Neutral Reacting Flow Model Equations solved via FEMLAB FLCC - Plasma
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-C4F8/O2 | 0-100 sccm O2 Neutral Flow Configuration Pressure ~ 30 mtorr FLCC - Plasma
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) FLCC - Plasma
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 FLCC - Plasma
Assumed Plasma Density Assume constant Te = 3 Assume radial plasma profile flat except when r > 0.2 FLCC - Plasma
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 O2 FLCC - Plasma
Total neutral density 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 FLCC - Plasma
Neutral Species Radial Profiles Qtune = 0 sccm FLCC - Plasma
Neutral Species Radial Profiles Qtune = 100 sccm • Note: scale different from previous slide FLCC - Plasma
Propose CF/F as model deposition/etch ratio index Varying the outer O2 flow (Qtune) the ratio of CF to F can be modified radially although the overall ratio of CF to F changes too Effects of Altering O2 ‘Tuning’ Gas Flow FLCC - Plasma
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) Concluding Remarks FLCC - Plasma