Presentation is loading. Please wait.

Presentation is loading. Please wait.

ION ENERGY DISTRIBUTIONS IN INDUCTIVELY COUPLED PLASMAS HAVING A BIASED BOUNDARY ELECTRODE* Michael D. Logue and Mark J. Kushner Dept. of Electrical Engineering.

Similar presentations


Presentation on theme: "ION ENERGY DISTRIBUTIONS IN INDUCTIVELY COUPLED PLASMAS HAVING A BIASED BOUNDARY ELECTRODE* Michael D. Logue and Mark J. Kushner Dept. of Electrical Engineering."— Presentation transcript:

1 ION ENERGY DISTRIBUTIONS IN INDUCTIVELY COUPLED PLASMAS HAVING A BIASED BOUNDARY ELECTRODE* Michael D. Logue and Mark J. Kushner Dept. of Electrical Engineering and Computer Science University of Michigan, Ann Arbor, MI 48109, USA Hyungjoo Shin, Weiye Zhu, Lin Xu, Vincent M. Donnelly, and Demetre J. Economou University of Houston, Department of Chemical & Biomolecular Engineering, Houston, TX November 2011 GECNov2011 * Work supported by SRC and US Dept. of Energy Office of Fusion Energy Sciences

2 AGENDA University of Michigan Institute for Plasma Science & Engr. GECNov2011  Control Of Ion Distribution Functions  Description of the Model and Geometry  Ion Energy Distributions (IEDs) and Plasma Parameters for Pulsed ICP  Pulsed ICP With Constant DC Boundary Electrode (BE) Bias  Pulsed ICP With Pulsed DC Boundary Electrode (BE) Bias  Concluding Remarks

3 CONTROL OF ION DISTRIBUTION FUNCTIONS University of Michigan Institute for Plasma Science & Engr. GECNov2011  In plasma materials processing there is a need to control the ion energy distributions (IEDs) to surfaces with increasing precision.  A recent development controlling of IEDs in inductively coupled plasmas (ICPs) is use of a boundary electrode.  A dc or pulsed dc bias to the boundary electrode shifts the quasi-dc plasma potential and in turn the peak in the IED incident onto grounded surfaces.  Using results from a computational investigation, the effect of pressure and BE bias (both dc and pulsed dc) on plasma parameters and IEDs will be discussed.  Example: Simulated IEDs and etch profiles for Ar/Cl 2 =80/20, 10 mTorr, 300 W peak ICP power, 100 W peak bias power, and 5 kHz pulse frequency, Duty Cycle=50%  Agarwal, J. Vac. Sci. Technol. A, Vol 29 (2011)

4 DESCRIPTION OF HPEM  Modular simulator that combines fluid and kinetic approaches.  Resolves cycle-dependent phenomena while using time-slicing techniques to advance to the steady state. GECNov2011 University of Michigan Institute for Plasma Science & Engr.

5 HPEM-EQUATIONS SOLVED -  Maxwell’s Equations – Frequency Domain Wave Equation GECNov2011  Azimuthal antenna currents – retain only E , B rz  Plasma currents  Collisional ion currents  Kinetically derived non-local electron currents capture nonlocal effects. University of Michigan Institute for Plasma Science & Engr.

6  Electron Energy Distributions – Electron Monte Carlo Simulation GECNov2011  Cycle dependent electrostatic fields  Phase dependent electromagnetic fields  Electron-electron collisions using particle-mesh algorithm  Phase resolved electron currents computed for wave equation solution.  Captures long-mean-free path and anomalous behavior. University of Michigan Institute for Plasma Science & Engr. HPEM-EQUATIONS SOLVED -

7 GECNov2011 University of Michigan Institute for Plasma Science & Engr. HPEM-EQUATIONS SOLVED -

8 GECNov2011 University of Michigan Institute for Plasma Science & Engr. PLASMA CHEMISTRY MONTE CARLO MODULE  Pseudo-Particles are launched at random times during the rf cycle based on ion source functions vs position.  Trajectories are integrated based on stored electric fields interpolated as a function of time during pulse period.  Null collision techniques are used to account for elastic and inelastic collisions.  Since transit time of ions may exceed pulse period, the stored electric fields during pulse are treated as being periodic. For species K For (r,z) mesh cell I,J Get Source Function for Species K Determine # of particles To launch Launch particle at random time during rf cycle Follow particles until a surface Is hit. Include acceleration from Fields and particle collisions Collect statistics on particles That hit specified surface For particle 1:Total Particles Go to top of particle loop Go to top of mesh cell loop Go to top of species loop

9 BOUNDARY ELECTRODE ICP (BE-ICP): EXPERIMENT  BE-ICP is a cylindrical plasma driven by a solenoidal coil.  The biased electrode is at the top boundary consisting of annular rings.  Ion energies measured by retarding field energy analyzer (RFEA).  Electron, ion densities, temperatures: Langmuir probe  Argon, 10s mTorr, 40 sccm University of Michigan Institute for Plasma Science & Engr. GECNov2011

10 PULSED BE-ICP  In the BE-ICP system both the ICP power and the DC bias on the boundary electrode can be independently pulsed.  This can allow for greater tunability of the plasma parameters as well as the IED  Investigate effects of using pulsed ICP power with and without pulsed dc bias on the boundary electrode University of Michigan Institute for Plasma Science & Engr. GECNov2011 Time  = 1/  Duty Cycle Power(t) P max P min ICP Power Envelope Boundary Electrode DC Bias(t) Δt Bias

11 BOUNDARY ELECTRODE ICP (BE-ICP): MODEL  Model representation of ICP system.  RFEA is modeled as a flat, grounded metal. Gridded structure is not be resolved at this scale.  Cylindrically symmetric model resolves pump as annular port.  Integration in time to a pulse-periodic steady state. University of Michigan Institute for Plasma Science & Engr. GECNov2011

12 T e, Φ, n e DURING PULSE, Δt Bias = 42-60μs  Electron density peaks to cm -3. Plasma potential controls the IED. University of Michigan Institute for Plasma Science & Engr. Animation Slide TeTe  Plasma Potential nene GECNov2011

13 T e, PLASMA POTENTIAL DURING PULSE PERIOD University of Michigan Institute for Plasma Science & Engr. GECNov2011  Experiment  T e and  both have “overshoot” at beginning of pulse period to re-establish plasma.  Modulation of  affords opportunity to shape IED.  Applying pulsed BE bias will further modulate , and so IED.  Duty cycle = 20%, PRF = 10 kHz, P(pulse average) = 120 W.  Model

14 University of Michigan Institute for Plasma Science & Engr. GECNov2011 IEDs – PULSED ICP WITH DC BOUNDARY  Experiment A B  IEDs consist of 2 peaks: High energy peak corresponding to large  during plasma on period.  Low energy peak due to smaller (and falling)  during plasma off period.  Vast majority of ionization occurs during plasma on part of cycle (20  s)  Ions “launched” during plasma on period require tens of  s to reach substrate.  High energy peak is broadened as ions sample dynamics of  during transport to substrate. Model A B Time Power(t) Boundary Electrode DC Bias (t) A B

15 University of Michigan Institute for Plasma Science & Engr. GECNov2011 IEDs – PULSED ICP WITH PULSED DC BOUNDARY  Experiment  Energy of peak is independent of pressure as  is determined by BE voltage.  Magnitude of peak decreases at high pressure due to collisionality, and populates intermediate energies.  Lower energy peak decreases as pressure increases due to increased collision frequency  Model predicts larger low energy component (very sensitive to acceptance angle of RFEA vs energy.) Model A A B B B Time Power(t) Boundary Electrode DC Bias (t) A B Δt Bias

16 University of Michigan Institute for Plasma Science & Engr. GECNov2011 IEDs – PULSED ICP, PULSED DC BOUNDARY IN EARLY AFTERGLOW  Experiment  The positions of the peaks in the IEADs are determined by the plasma potential  during the plasma on period, and the voltage of the BE.  The magnitude of the peak is determined by the length of time the BE is on.  Slight peak around 1.5 V in model due to non-zero minimum plasma potential. A B Time Power(t) Boundary Electrode DC Bias (t) Δt Bias Model B B B A A

17 University of Michigan Institute for Plasma Science & Engr. GECNov2011 IEDs – PULSED ICP WITH PULSED DC BOUNDARY IN LATE AFTERGLOW  Experiment  By moving pulse of BE to the late afterglow, the low and high energy peaks are more distinctively separate.  The magnitude of the high energy peak is controlled by the length of the BE pulse. A B Time Power(t) Boundary Electrode DC Bias (t) Model Δt Bias A A B B B

18 CONCLUDING REMARKS University of Michigan Institute for Plasma Science & Engr. GECNov2011  The use of a dc biased boundary electrode in ICP allows for control of the IED due to the shifting of the plasma potential by the dc bias.  Positive biases result in the increase of the IED peak energy by nearly the applied bias while negative biases resulted in a small, capped decrease in the IED peak energy.  Pulsing the dc bias on the boundary electrode in the ICP afterglow creates a narrower peak in the IED centered at approximately the applied bias potential. The height of the peak is determined by the length of the BE pulse.  This allows tuning of the energy and height of the peak energy of the IED.


Download ppt "ION ENERGY DISTRIBUTIONS IN INDUCTIVELY COUPLED PLASMAS HAVING A BIASED BOUNDARY ELECTRODE* Michael D. Logue and Mark J. Kushner Dept. of Electrical Engineering."

Similar presentations


Ads by Google