1 / 23

INVESTIGATIONS OF MAGNETICALLY ENHANCED RIE REACTORS WITH ROTATING (NON-UNIFORM) MAGNETIC FIELDS

INVESTIGATIONS OF MAGNETICALLY ENHANCED RIE REACTORS WITH ROTATING (NON-UNIFORM) MAGNETIC FIELDS. Natalia Yu. Babaeva and Mark J. Kushner University of Michigan Department of Electrical Engineering and Computer Science Ann Arbor, MI 48109 http://uigelz.eecs.umich.edu mjkush@umich.edu

zeheb
Download Presentation

INVESTIGATIONS OF MAGNETICALLY ENHANCED RIE REACTORS WITH ROTATING (NON-UNIFORM) MAGNETIC FIELDS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. INVESTIGATIONS OF MAGNETICALLY ENHANCED RIE REACTORS WITH ROTATING (NON-UNIFORM) MAGNETIC FIELDS Natalia Yu. Babaeva and Mark J. Kushner University of Michigan Department of Electrical Engineering and Computer Science Ann Arbor, MI 48109 http://uigelz.eecs.umich.edu mjkush@umich.edu 61st Annual Gaseous Electronics Conference Dallas, Texas October 13–17, 2008 GEC08_MERIE

  2. University of Michigan Institute for Plasma Science and Engineering AGENDA • Introduction to Magnetically Enhanced Reactive Ion Etching (MERIE) reactors. • Description of Model • Uniform and tilted magnetic field • Uniform and graded solenoids • Concluding Remarks • Acknowledgement: Semiconductor Research Corp., Applied Materials Inc., Tokyo Electron, Ltd. GEC08_MERIE

  3. University of Michigan Institute for Plasma Science and Engineering MERIE PLASMA SOURCES • Magnetically Enhanced Reactive Ion Etching plasma sources use transverse static magnetic fields in capacitively coupled discharges for confinement to increase plasma density. • The B-field is usually non-uniform across the wafer. Rotating the field averages out non-uniformities in plasma properties. • D. Cheng et al, US Patent 4,842,683 • M. Buie et al, JVST A 16, 1464 (1998) GEC08_MERIE

  4. University of Michigan Institute for Plasma Science and Engineering CONSEQUENCES OF NON-UNIFORM B-FIELD • What are the consequences on plasma properties (uniformity, ion energy and angular distributions) resulting from “side-to-side” variations in B-field? • This is a 3-d problem…Our computational investigation is performed with a 2-dimensional model in Cartesian coordinates. • Enables assessment of side-to-side variations. • Does not capture closed paths that might occur in 3-d cylindrical coordinates. • Restrict investigation to pure argon to isolate plasma effects. GEC08_MERIE

  5. University of Michigan Institute for Plasma Science and Engineering MODELING OF MERIE • 2-dimensional Hybrid Model • Electron energy equation for bulk electrons • Continuity, Momentum and Energy (temperature) equations for all neutral and ion species. • Poisson equation for electrostatic potential • Circuit model for bias • Tensor transport coefficients. • Monte Carlo Simulation • Secondary electrons from biased surfaces • Ion transport to surfaces to obtain IEADs GEC08_MERIE

  6. University of Michigan Institute for Plasma Science and Engineering ELECTRON ENERGY TRANSPORT S(Te) = Power deposition from electric fields L(Te) = Electron power loss due to collisions  = Electron flux (Te) = Electron thermal conductivity tensor SEB = Power source source from beam electrons • All transport coefficients are tensors in time domain: GEC08_MERIE

  7. University of Michigan Institute for Plasma Science and Engineering IMPROVEMENTS FOR LARGE MAGNETIC FIELDS • Poisson’s equation is solved using a semi-Implicit technique where charge densities are predicted at future times. • Predictor-corrector methods are used where fluxes at future times are approximated using past histories or Jacobian elements. GEC08_MERIE

  8. University of Michigan Institute for Plasma Science and Engineering REVIEW: MERIE REACTOR RADIALLY SYMMETRY • 2-D, Cylindrically Symmetric • Magnetic field is purely radial, an approximation validated by 2-D Cartesian comparisons. GEC08_MERIE

  9. University of Michigan Institute for Plasma Science and Engineering Ar+ DENSITY vs MAGNETIC FIELD • Increasing B-field shifts plasma towards center and increases density. • Decreasing Larmor radius localizes sheath heating closer to wafer. • Plasma is localized closer to wafer. • Large B-fields (> 100 G) decrease density due to diffusion losses of Ar* • Ar, 40 mTorr, 100W, 10 MHz GEC08_MERIE

  10. University of Michigan Institute for Plasma Science and Engineering SHEATH REVERSAL, THICKENING, IEDs • As the magnetic field increases, the electrons become less mobile than ions. • Electric field in the sheath reverses, sheath thickens, IEDs lower in energy and broaden. GEC08_MERIE

  11. University of Michigan Institute for Plasma Science and Engineering “SIDE-TO-SIDE” MERIE WITH SOLENOID COILS • Actual Aspect Ratio • 2-d Cartesian Geometry GEC08_MERIE

  12. University of Michigan Institute for Plasma Science and Engineering Ar+ vs UNIFORM B-FIELD ANGLE • Uniform but tilted B-field. • Low cross field mobility increases plasma density and plasma stretches along field lines. • Tilt of B-field increases maximum density while plasma aligns with field. • Ar, 40 mTorr, 100 W, 10 MHz GEC08_MERIE

  13. University of Michigan Institute for Plasma Science and Engineering Te vs UNIFORM B-FIELD ANGLE • With B=0, E-field enhancement at edges produces local maximum in Te. • With B > 0, sheath heating is constrained to layer near substrate. • Tilt reduces Te above wafer where plasma density is maximum and sheath thickness shrinks. • Ar, 40 mTorr, 100 W, 10 MHz GEC08_MERIE

  14. University of Michigan Institute for Plasma Science and Engineering BULK IONIZATION vs B-FIELD ANGLE • With B=0, edge enhancement in Te translates to local maximum in bulk ionization. • With B > 0, confining of sheath heated electrons and low transverse mobility elongates ionization. • Tilt localizes ionization on one side of the wafer. • Ar, 40 mTorr, 100 W, 10 MHz GEC08_MERIE

  15. University of Michigan Institute for Plasma Science and Engineering BEAM IONIZATION vs B-FIELD ANGLE • With B=0, mean free paths of secondary electrons exceed gap spacing. • With B > 0, secondary electrons are confined near electrodes. • Tilt in B-field shifts secondary sources in opposite directions top-and-bottom. • Ar, 40 mTorr, 100 W, 10 MHz GEC08_MERIE

  16. University of Michigan Institute for Plasma Science and Engineering PLASMA POTENTIAL • Plasma potential reflects tilt in B-field with local perturbations due to positive charging of dielectrics by more mobile ions. • Uniform (0o) • Slanted (4o) • Graded Solenoid Animation Slide • Ar, 40 mTorr, 100 W, 10 MHz, 100 G GEC08_MERIE

  17. University of Michigan Institute for Plasma Science and Engineering IEAD (CENTER) vs UNIFORM B-FIELD ANGLE • IEDs broaden and move to lower energy with increase in B-field due to sheath reversal. • Tilt in B-field broadens angular distribution and produces angular asymmetries. • With a large tilt, plasma potential has time average tilt leading to angular assymetries. • Ar, 40 mTorr, 100 W, 10 MHz, 100 G GEC08_MERIE

  18. University of Michigan Institute for Plasma Science and Engineering IEADs ACROSS WAFER vs B-FIELD ANGLE • With tilts of  5o significant side-to-side variation in IEAD across wafer. • Broadening in energy of IEAD results from thinner sheath and less of sheath reversal. • Angular asymmetry most severe at low energies. • Ar, 40 mTorr, 100 W, • 100 G, 10 MHz, GEC08_MERIE

  19. University of Michigan Institute for Plasma Science and Engineering Ar+: UNIFORM AND GRADED SOLENOIDS • Side-to-side plasma density is highly sensitive to small axial gradients in B-field. • With graded solenoid, plasma density peaks in divergent, lower B-field. • For a fixed power, a larger fractional power is deposited in the less resistive region. • Ar, 40 mTorr, 200 W, 10 MHz • 100 G: 0.5 cm above left position GEC08_MERIE

  20. University of Michigan Institute for Plasma Science and Engineering Te, IONIZATION SOURCES: GRADED SOLENOIDS • Beam ionization also penetrates further on the weak field side. • Total ionization is larger inspite of lower electron temperature. • Ar, 40 mTorr, 200 W, 10 MHz • 100 G: 0.5 cm above left position GEC08_MERIE

  21. University of Michigan Institute for Plasma Science and Engineering PLASMA POTENTIAL • Plasma potential reflects tilt in B-field with local perturbations due to positive charging of dielectrics by more mobile ions. • Uniform (0o) • Slanted (4o) • Graded Solenoid Animation Slide • Ar, 40 mTorr, 100 W, 10 MHz, 100 G GEC08_MERIE

  22. University of Michigan Institute for Plasma Science and Engineering IEADs: UNIFORM AND GRADED SOLENOID • Graded solenoid produces side-to-side variation in IEAD. • Higher plasma density, thinner sheath and weaker B-field (reduced field reversal) broaden energy. • Ar, 40 mTorr, 200 W, 10 MHz • 100 G: 0.5 cm above left position GEC08_MERIE

  23. University of Michigan Institute for Plasma Science and Engineering CONCLUDING REMARKS • “Side-to-side” plasma uniformity and IEADs were computationally investigated MERIEs to provide insights to rotating magnetic field systems. • Tilt of 100 G magnetic fields of 5-10o are sufficient to skew plasma density and produce position dependent IEADs. • Solenoids with only a few percent variation in B-field also produce side-to-side variations. • Plasma density peaks in divergent, low B-field regions due to being less resistive to axial current. GEC08_MERIE

More Related