Methods and apparatus for generating strongly-ionized plasmas with ionizational instabilities
Methods and apparatus for generating strongly-ionized plasmas are disclosed. A strongly-ionized plasma generator according to one embodiment includes a chamber for confining a feed gas. An anode and a cathode assembly are positioned inside the chamber. A pulsed power supply is electrically connected between the anode and the cathode assembly. The pulsed power supply generates a multi-stage voltage pulse that includes a low-power stage with a first peak voltage having a magnitude and a rise time that is sufficient to generate a weakly-ionized plasma from the feed gas. The multi-stage voltage pulse also includes a transient stage with a second peak voltage having a magnitude and a rise time that is sufficient to shift an electron energy distribution in the weakly-ionized plasma to higher energies that increase an ionization rate which results in a rapid increase in electron density and a formation of a strongly-ionized plasma.
1. A strongly-ionized plasma generator comprising:
a) a chamber for confining a feed gas;
b) an anode that is positioned inside the chamber;
c) a cathode assembly that is positioned adjacent to the anode inside the chamber; and
d) a pulsed power supply having an output that is electrically connected between the anode and the cathode assembly, the pulsed power supply generating at the output a voltage pulse having at least one of a controlled amplitude and a controlled rise time that increases an ionization rate of sputtered material atoms so that a rapid increase in electron density and a formation of a strongly-ionized plasma occurs without forming an arc between the anode and the cathode assembly.
2. The plasma generator of claim 1 further comprising a magnet that generates a magnetic field proximate to the cathode assembly.
3. The plasma generator of claim 2 wherein the magnet is movable.
4. The plasma generator of claim 2 wherein the magnetic field generated by the magnet confines the strongly ionized plasmas proximate to the cathode assembly.
5. The plasma generator of claim 1 further comprising a substrate support that is biased with a negative voltage so as to attract positive ions to the sputtered film.
6. The plasma generator of claim 1 further comprising a substrate support comprising a temperature controller that controls a temperature of the substrate.
7. The plasma generator of claim 1 wherein the feed gas comprises at least one of noble and reactive atoms.
8. The plasma generator of claim 1 wherein the pulsed power supply provides enough energy to shift the electron energy distribution of the plasma to higher energies until the strongly ionized plasma is formed.
9. The plasma generator of claim 1 further comprising an energy storage device that is electrically coupled to the cathode assembly, the energy storage device discharging energy into the plasma to enhance the rapid increase in electron density and the formation of the strongly-ionized plasma.
10. The plasma generator of claim 1 wherein the voltage pulse forms ionizational instabilities.
11. The plasma generator of claim 1 wherein the voltage pulse includes at least one low frequency voltage oscillation.
12. The plasma generator of claim 11 wherein an amplitude of the at least one low frequency voltage oscillation is greater than or equal to 50 Volts.
13. The plasma generator of claim 1 wherein a discharge current density of the strongly-ionized plasma is greater than about 0.5 A/cm 2 .
14. The plasma generator of claim 1 wherein the power density of the strongly-ionized plasma is greater than 250 W/cm 2 .
15. The plasma generator of claim 1 wherein the voltage pulse sustains the strongly-ionized plasma.
16. The plasma generator of claim 1 wherein a lifetime of the strongly-ionized plasma is greater than about 200 μsec.
17. An apparatus for generating a strongly-ionized plasma, the apparatus comprising:
a) means for supplying feed gas proximate to an anode and a cathode assembly;
b) means for generating a voltage pulse that forms a plasma between the anode and the cathode; and
c) means for controlling an amplitude and a rise time of the voltage pulse to increase an ionization rate of sputtered material atoms so that a rapid increase in electron density and a formation of a strongly-ionized plasma occurs without forming an arc between the anode and the cathode assembly.
18. The apparatus of claim 17 further comprising shifting an electron energy distribution in the plasma to higher energies that increase the ionization rate of sputtered material atoms.
19. The apparatus of claim 17 further comprising a means for sustaining the strongly-ionized plasma for greater than 200 μsec.