System and method for plasma control using boundary electrode
An ion source may include a chamber configured to house a plasma comprising ions to be directed to a substrate and an extraction power supply configured to apply an extraction terminal voltage to the plasma chamber with respect to a voltage of a substrate positioned downstream of the chamber. The system may further include a boundary electrode voltage supply configured to generate a boundary electrode voltage different than the extraction terminal voltage, and a boundary electrode disposed within the chamber and electrically coupled to the boundary electrode voltage supply, the boundary electrode configured to alter plasma potential of the plasma when the boundary electrode voltage is received.
1. An ion source, comprising:
a chamber configured to house a plasma comprising ions to be directed through an aperture to a substrate;
an extraction power supply configured to apply an extraction terminal voltage to the chamber with respect to a voltage of a substrate positioned downstream of the chamber;
a boundary electrode voltage supply configured to generate a boundary electrode voltage different than the extraction terminal voltage; and
a first boundary electrode disposed within the chamber adjacent a first distal portion of the aperture and electrically coupled to the boundary electrode voltage supply, the boundary electrode configured to alter plasma potential of the plasma when the boundary electrode voltage is received; and
a second boundary electrode disposed within the chamber adjacent a second distal portion of the aperture and configured to apply a second boundary electrode voltage different than the extraction terminal voltage.
2. The ion source of claim 1 , wherein the boundary electrode is configured to adjust local ion density in at least a portion of the plasma.
3. The ion source of claim 1 , further comprising one or more additional electrodes disposed at one or more respective additional locations within the chamber and configured to apply a respective boundary electrode voltage different than the extraction terminal voltage.
4. The ion source of claim 1 , wherein the boundary electrode and second boundary electrode are configured to move generally parallel to the long direction.
5. The ion source of claim 1 , further comprising an extraction aperture to extract the ions from the plasma, wherein the boundary electrode is disposed in a portion of the chamber opposite the extraction aperture.
6. The ion source of claim 1 , wherein the extraction power supply is configured to supply the extraction terminal voltage as a pulsed extraction terminal voltage signal, and the boundary electrode is configured to supply the boundary electrode voltage as a constant boundary electrode voltage or as a pulsed boundary electrode voltage signal that is synchronized to the pulsed extraction terminal voltage signal.
7. The ion source of claim 6 , wherein the pulsed extraction terminal voltage signal comprising an extraction terminal voltage period having an ON portion in which the extraction terminal voltage signal is positive respect to the substrate voltage and OFF portion in which the extraction terminal voltage signal is equal to the substrate voltage, wherein the boundary electrode voltage signal comprises a pulsed boundary electrode voltage signal having a boundary electrode period equal to the extraction terminal voltage period.
8. The ion source of claim 7 , wherein the boundary electrode voltage signal comprising a periodic positive voltage pulse that takes place within the ON portion of the extraction terminal voltage period and spans a duration less than that of the ON portion of the extraction terminal voltage period.
9. The ion source of claim 7 , wherein the boundary electrode voltage signal comprising an ON portion that includes a plurality of subportions in which boundary electrode voltage varies between subportions.
10. The ion source of claim 1 , wherein an absolute value of the difference between the boundary electrode voltage and extraction terminal voltage comprising five hundred volts or less.
11. The ion source of claim 1 , wherein a ratio of electrode surface area of the boundary electrode to area of internal chamber walls of the chamber is about 1% to about 30%.
12. The ion source of claim 1 , further comprising an extraction electrode configured to extract an ion beam from the plasma, wherein the boundary electrode is configured to adjust and uniformity of ions within the ion beam.
13. A method of processing a substrate, comprising:
generating a plasma in a chamber, the plasma comprising ions to be directed to the substrate;
applying an extraction terminal voltage between the chamber and substrate, the extraction terminal voltage effective to generate a first plasma potential in the plasma;
generating a first boundary electrode voltage at a first boundary electrode disposed within the chamber, the first boundary electrode voltage different than the extraction terminal voltage and generated at least partially during the applying the extraction terminal voltage, the first boundary electrode voltage effective to generate a second plasma potential for the plasma that is different from the first plasma potential; and
generating one or more additional boundary electrode voltages at a respective one or more additional boundary electrodes disposed at one or more respective additional locations within the chamber, wherein each respective boundary electrode voltage of the one or more additional boundary electrode voltages is different than the extraction terminal voltage.
14. The method of claim 13 , further comprising:
supplying the extraction terminal voltage as a pulsed extraction terminal voltage signal, and
supplying the boundary electrode voltage as a constant boundary electrode voltage or as a pulsed boundary electrode voltage signal that is synchronized to the pulsed extraction terminal voltage signal.
15. The method of claim 14 , the generating the plasma comprising sending a pulsed power signal to generate the plasma as a pulsed plasma, the method further comprising synchronizing the pulsed power signal to the pulsed extraction terminal voltage signal.
16. The method of claim 14 , further comprising:
generating the pulsed extraction terminal voltage signal as a periodic signal comprising an extraction terminal voltage period having an ON portion in which the extraction terminal voltage signal is positive with respect to the substrate voltage and OFF portion in which the extraction terminal voltage signal is equal to the substrate voltage; and
generating the boundary electrode voltage signal as a pulsed boundary electrode voltage signal having a boundary electrode period equal to the extraction terminal voltage period.
17. The method of claim 16 , further comprising generating a voltage pulse at the boundary electrode within the ON portion of the extraction terminal voltage period, wherein a duration of the voltage pulse is less than a duration of the ON portion.
18. The method of claim 16 , further comprising varying the boundary electrode voltage between two or more boundary electrode voltage levels within the ON portion of the extraction electrode period.
19. The method of claim 13 , wherein an absolute value of the difference between the boundary electrode voltage and extraction terminal voltage is less than 500 volts.
20. The method of claim 14 , further comprising
moving the substrate with respect to the chamber; and
adjusting the pulsed extraction terminal voltage signal to generate a patterned ion exposure of the substrate.
21. The method of claim 16 , further comprising
adjusting the boundary electrode voltage during at least an OFF portion of the pulsed extraction terminal voltage signal to reduce ion dose of ions that exit the plasma during the OFF portion.