DEVELOPMENT OF ION ENERGY ANGULAR DISTRIBUTION THROUGH THE PRE-SHEATH AND SHEATH IN DUAL-FREQUENCY CAPACITIVELY COUPLED PLASMAS* Yiting Zhang a , Nathaniel Moore b , Walter Gekelman b and Mark J. Kushner a (a) Department of Electrical and Computer Engineering, University of Michigan, Ann Arbor, 48109 ([email protected] , [email protected]) (b) Department of Physics, University of California, Los Angeles, 90095 ([email protected] , [email protected] ) September 2011 * Work supported by National Science Foundation and Semiconductor Research Corp.
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DEVELOPMENT OF ION ENERGY ANGULAR DISTRIBUTION THROUGH THE PRE-SHEATH AND SHEATH IN DUAL-FREQUENCY CAPACITIVELY COUPLED PLASMAS* Yiting Zhang a, Nathaniel.
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DEVELOPMENT OF ION ENERGY ANGULAR DISTRIBUTION THROUGH THE PRE-SHEATH
AND SHEATH IN DUAL-FREQUENCY CAPACITIVELY COUPLED PLASMAS*
Yiting Zhanga, Nathaniel Mooreb, Walter Gekelmanb and Mark J. Kushnera
(a) Department of Electrical and Computer Engineering,University of Michigan, Ann Arbor, 48109
* Work supported by National Science Foundation and Semiconductor Research Corp.
AGENDA
Introduction to dual frequency capacitively coupled plasma (CCP) sources and Ion Energy Angular Distributions (IEAD)
Description of the model
Plasma properties for 2 MHz / 30 MHz
Ar Plasma properties
Ar/O2 Plasma Properties
Uniformity and Edge Effect
Concluding Remarks
YZHANG_MIPSE2011_01
University of MichiganInstitute for Plasma Science & Engr.
DUAL FREQUENCY CCP SOURCES
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Capacitively coupled discharges (CCPs) are widely used for etching and deposition of microelectronic industry.
High driving frequency achieve higher electron densities at moderate sheath voltage and higher ion fluxes with moderate ion energies.
A low frequency contributes the quasi-independent control of the ion flux and energy.
However, the non-uniformity problems arise with increases of the driving frequency.
A. Perret, Appl. Phys.Lett 86 (2005)University of Michigan
Institute for Plasma Science & Engr.
ION ENERGY AND ANGULAR DISTRIBUTIONS (IEAD)
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• Control of the ion energy and angular distribution (IEAD) at the substrate provides the potential for improving plasma processes.
• A narrow angular IEAD at the substrate with the majority ion flux perpendicular to the substrate is desired for anisotropic processing.
• Edge effects produce slanted IEADs.
•S.-B. Wang and A.E. Wendt,• J. Appl. Phys., Vol 88, No.2•B. Jacobs, PhD Dissertation
University of MichiganInstitute for Plasma Science & Engr.
GOALS
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Results from a computational investigation of ion transport through RF sheaths will be discussed.
Investigate the motion of ion species in the RF pre-sheath and sheath region of CCPs using sub-meshing technique to provide finer resolution at different phase of RF source.
Comparison to experimental results from laser induced fluorescence (LIF) measurements by Low Temperature Plasma Physics Laboratory at UCLA.
Assessment of O2 addition to Ar plasmas.
University of MichiganInstitute for Plasma Science & Engr.
HYBRID PLASMA EQUIPMENT MODEL (HPEM)
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Monte Carlo Simulation f(ε) or Electron Energy Equation
Electron Energy Transport Module ( EETM): Electron Monte Carlo Simulation provides EEDs of bulk electrons. Separate MCS used for secondary, sheath accelerated electrons.
Fluid Kinetics Module (FKM): Heavy particle and electron continuity, momentum, energy and
Poisson equations.
Plasma Chemistry Monte Carlo Module (PCMCM): IEADs in bulk, pre-sheath, sheath, and wafers Recorded phase, submesh resolution
EETM
Continuity, Momentum, Energy, Poisson equation
FKM
Monte Carlo Module
PCMCMSe(r)
N(r)Es(r)
•M.Kushner, J. Phys.D: Appl. Phys. 42(2009) University of MichiganInstitute for Plasma Science & Engr.
REACTOR GEOMETRY
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University of MichiganInstitute for Plasma Science & Engr.
Inductively coupled with 2-freq CCP on substrate
2D, cylindrically symmetric.
Base conditions ICP Power: 400kHz,300 Watt High Freq RF: 10 MHz
Due to periodic acceleration in sheath, development of IEAD depends on phase.
During low acceleration phases, IEAD drifts in sheath.
During high acceleration phase, IEAD narrows as perpendicular component of velocity distribution increases.
University of MichiganInstitute for Plasma Science & Engr.
YZHANG_MIPSE2011_14
O2 ADDITION TO AR
MIN MAX Log scale
MIN MAX MIN MAX Log scale
Ar+ IEAD on wafer 20 mTorr, 300 SCCM. Freq=2 MHz, 300 W.
With increasing O2, negative ion ( O2-, O-) formation increases
the sheath potential for fixed power.
IEAD for Ar+ extends in energy and narrows in angle.
University of MichiganInstitute for Plasma Science & Engr.
CONCLUDING REMARKS
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In the pre-sheath, IEAD is thermal and broad in angle. When the ion flux is accelerated through the sheath, the distribution increases in energy and narrows in angle.
Edge Effect can be observed clearly by using the high resolution afforded by sub-meshing. Multiple peaks in IEADs come from IEADs alternately accelerated by rf field during the whole RF period.
Increasing O2 changes the sheath properties – a narrower IEAD achieved when percentage of O2 increase from 5% to 20%.
University of MichiganInstitute for Plasma Science & Engr.