Methods and apparatus for generating strongly-ionized plasmas with ionizational instabilities

• US 20060175197A1
• Filed: 03/15/2006
• Published: 08/10/2006
• Est. Priority Date: 02/22/2004
• Status: Active Grant

• Current Assignee: Roman Chistyakov
• Original Assignee: Roman Chistyakov
• Inventors: Chistyakov, Roman
• Granted Patent: US 7,345,429 B2
• Time in Patent Office: Days
• US Class Current: 204/298.200
• CPC Class Codes: C23C 14/35 by application of a magnetic field, e.g. magnetron sputtering C23C14/3457 takes precedence
• CPC Class Codes: H01J 37/3266 Magnetic control means
• CPC Class Codes: H01J 37/3408 Planar magnetron sputtering
• CPC Class Codes: H01J 37/3455 Movable magnets

Abstract

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.

Claims

1-47. -47. (canceled)

48. A pulsed power supply comprising:

a) a voltage source that generates a voltage at an output;

b) an energy storage device that is electrically connected to the voltage source, the voltage source charging the energy storage device to store an energy;

c) a switching device that is electrically connected to the energy storage device, the switching device releasing the energy stored in the energy storage device when activated;

d) a transformer comprising a primary coil that is electrically coupled to the switching device and a secondary coil, the primary coil receiving the energy stored in the energy storage device when the switch is activated and transforming the received energy to the secondary coil in order to generate multi-step voltage pulses; and

e) a driving circuit that is electrically connected to the transformer, the driving circuit forming at least one of a rise time, a fall time, a duration, and an amplitude of the multi-step voltage pulses to generate a strongly-ionized plasma.

49. The power supply of claim 48 wherein the switching device comprises a solid state switching device.

50. The power supply of claim 48 wherein the switching device comprises an insulated gate bipolar transistor device.

51. The power supply of claim 48 further comprising an arc suppression circuit that is coupled to the secondary coil, the arc suppression circuit dropping an amplitude of the multi-step voltage pulses for a certain period of time when a plasma discharge current reaches a certain level.

52. The power supply of claim 48 wherein at least some of the multi-step voltage pulses have predetermined shapes.

53. The power supply of claim 48 wherein at least some of the multi-step voltage pulses comprise a low-power stage and a high-power stage.

54. The power supply of claim 53 wherein the low power stage includes a first peak voltage having a magnitude and a rise time that is sufficient to generate and sustain a weakly-ionized plasma from a feed gas.

55. The power supply of claim 48 wherein at least some of the multi-step voltage pulses comprise a low-power stage, a transient stage, and a high-power stage.

56. The power supply of claim 55 wherein the transient stage includes a peak voltage having a magnitude and a rise time that is sufficient to shift an electron energy distribution in a 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.

57. The power supply of claim 48 wherein at least some of the multi-step voltage pulses include low frequency voltage oscillations.

58. The power supply of claim 57 wherein an amplitude of the low frequency voltage oscillations is greater than or equal to 50Volts.

59. The power supply of claim 48 wherein at least one of the switch and the transformer are configured to provide voltage pulses having a relatively fast rise time.

60. The power supply of claim 48 wherein the driving circuit is electrically connected to the secondary coil.

61. A pulsed power supply for generating a strongly ionized plasma, the pulsed power supply comprising:

a) a voltage source that generates a voltage at an output;

b) a bank of capacitors that is electrically connected to the voltage source, the voltage source charging the bank of capacitors to store an energy;

c) a parallel bank of high-power solid state switching device that is electrically connected to the bank of capacitors, the parallel bank of high-power solid state switching device releasing the energy stored in the bank of capacitors when activated;

d) a pulse transformer comprising a primary coil that is electrically connected to the switching device and a secondary coil, the primary coil receiving the energy stored in the bank of capacitors when the parallel bank of high-power solid state switching device is activated and transforming the received energy to multi-step voltage pulses; and

e) an array of driving circuits that is electrically connected to the pulse transformer, the array of driving circuits controlling at least one of a rise time, a fall time, a duration, and an amplitude of the multi-step voltage pulse to generate a strongly-ionized plasma.

62. A method of generating multi-step voltage pulses for creating a strongly ionized plasma, the method comprising:

a) generating a voltage;

b) charging an energy storage device to store an energy;

c) releasing the stored energy at predetermined times;

d) transforming the released energy into multi-step voltage pulses; and

e) controlling at least one of a rise time, a fall time, a duration, and an amplitude of at least some of the multi-step voltage pulses to generate a strongly-ionized plasma.

63. The method of claim 62 wherein the controlling the at least one of a rise time, a fall time, a duration, and an amplitude of at least some of the multi-step voltage pulses generates a weakly ionized plasma and then a strongly-ionized plasma.

64. The method of claim 63 wherein the controlling the at least one of the rise time, the fall time, the duration, and the amplitude of the multi-step voltage pulse shifts 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 the strongly-ionized plasma.

65. The method of claim 63 wherein the weakly-ionized plasma is in a steady state condition before the multi-step voltage pulses generate the strongly-ionized plasma.

66. The method of claim 63 wherein the weakly-ionized plasma is in a quasi-steady state condition before the multi-step voltage pulses generate the strongly-ionized plasma.

67. The method of claim 63 further comprising discharging energy from the energy storage device into the weakly-ionized plasma to enhance the rapid increase in electron density and the formation of the strongly-ionized plasma.

68. The method of claim 63 wherein a magnitude and a rise time of the multi-step voltage pulses are sufficient to generate and sustain plasma instabilities in the weakly-ionized plasma that enhance the ionization rate and result in a rapid increase in electron density and the formation of the strongly-ionized plasma.

69. The method of claim 68 wherein the ionizational instabilities comprise diocotron instabilities.

70. The method of claim 62 further comprising applying a magnetic field to the strongly ionized plasma.

71. The method of claim 70 further comprising generating an electron Hall current from an electric field generated by the multi-step voltage pulses and from the magnetic field, the electron Hall current raising a temperature of the electrons in the plasma to a temperature that enhances an increase in electron density and a formation of the strongly-ionized plasma.

72. The method of claim 62 wherein at least some of the multi-step voltage pulses further comprises a voltage step that sustains the strongly-ionized plasma.

73. The method of claim 72 wherein an average value of the voltage step that sustains the strongly-ionized is relatively constant.

74. The method of claim 62 further comprising generating low frequency voltage oscillations.

75. The method of claim 62 wherein a lifetime of the strongly-ionized plasma is greater than 200μ

sec.

76. The method of claim 62 further comprising reducing a probability of arcing in the plasma.

77. The method of claim 62 wherein a rise time of at least a portion of the multi-step voltage pulses is greater than about 0.5V/μ

sec.

78. The method of claim 62 wherein a peak magnitude of the multi-step voltage pulses is less than about 1,000V.

79. The method of claim 62 wherein the charging the energy storage device to store the energy comprises charging at least one capacitor.

80. The method of claim 62 wherein the multi-step voltage pulses have predetermined shapes.

81. The method of claim 62 wherein a peak voltage of the multi-step voltage pulses has a magnitude that is sufficient to generate ionizational instabilities that enhance the ionization rate resulting in the rapid increase in electron density and the formation of the strongly-ionized plasma.

82. The method of claim 62 wherein a rise time of the multi-step voltage pulses has a value that is sufficient to generate ionizational instabilities that enhance the ionization rate resulting in the rapid increase in electron density and the formation of the strongly-ionized plasma.

83. A pulsed power supply comprising:

a) a means for generating a voltage;

b) a means for storing an energy;

c) a means for releasing the stored energy at predetermined times;

d) a means for transforming the released energy into multi-step voltage pulses; and

e) a means for controlling at least one of a rise time and a fall time of at least some of the multi-step voltage pulses to generate a strongly-ionized plasma.