Projected plasma source
This disclosure describes systems, methods, and apparatuses for generating an ionizing electromagnetic field via a remote plasma source such that the field controllably extends through a field projection portion where the field attenuates, to a plasma processing portion where the field is attenuated but still strong enough to sustain a plasma. The plasma has a low voltage and RF energy and can be used for a variety of semiconductor and thin film processing operations including chamber cleaning via radical generation, etching, and deposition.
1. A plasma source comprising:
a field generation portion including:
a central electrode;
a perimeter electrode that at least partially surrounds the central electrode, the central and perimeter electrodes electrostatically generate a plasma by coupling energy into the plasma, and the central and perimeter electrodes generating an ionizing electromagnetic field that extends out of the field generation portion; and
a power input configured to receive a current to be passed between the central and perimeter electrode;
a field projection portion coupled to the field generation portion, wherein the field projection portion comprises a conductive tube having a dielectric inner layer, wherein the field projection portion attenuates the ionizing electromagnetic field to form an attenuated ionizing electromagnetic field configured to have sufficient energy to sustain a plasma within a plasma chamber configured for coupling to the field projection portion, wherein the field projection portion is configured to be at least partially external to the plasma chamber; and
a bias coupled to the field projection portion that capacitively applies one of the following to the field projection portion to attenuate the ionizing electromagnetic field: a controllable DC bias, and a combination of a controllable AC and a controllable DC bias;
wherein the field projection portion has a longitudinal axis that is longer than a widest inner diameter of the field projection portion, and where the field projection portion includes a dielectric that is parallel to the longitudinal axis of the field projection portion and thereby attenuates portions of the ionizing electromagnetic field that are transverse to a longitudinal axis of the field projection portion,
wherein electrodes of the field generation portion extend no further toward the plasma chamber than an end of the field generation portion.
2. The plasma source of claim 1 , wherein the field projection portion controllably attenuates the ionizing electromagnetic field.
3. The apparatus of claim 1 , wherein an interface between the field generation portion and the field projection portion is devoid of constrictions.
4. The apparatus of claim 1 , wherein an interface between the field projection portion and the plasma chamber is devoid of constrictions.
5. The apparatus of claim 1 , wherein the field projection portion includes a cylindrical dielectric wherein a thickness of the dielectric is less than an inner radius of the field projection portion, where the inner radius extends from a longitudinal axis of the field projection portion to an inner surface of the dielectric.
6. The apparatus of claim 1 , wherein the field generation portion includes a dielectric between electrodes of the field generation portion and an inside of the field generation portion.
7. The apparatus of claim 1 , wherein the bias is configured to be adjusted during operation of the plasma source.
8. The apparatus of claim 1 , wherein the controllable AC bias is phase shifted relative to an AC applied in the field generation portion.
9. The apparatus of claim 1 , further comprising one or more sensors within the plasma chamber that are coupled to the controllable AC bias and provide feedback for controlling the controllable AC bias and thereby for controlling attenuation of the ionizing electromagnetic field.
10. The apparatus of claim 9 , wherein the field projection portion is electrically isolated from the field generation portion via one or more devices having an impedance with a reactive component.
11. The apparatus of claim 10 , wherein the one or more devices have a variable impedance and a variable reactance and are controlled by control circuitry.
12. A plasma source comprising:
a field generation portion including:
a central electrode;
a perimeter electrode that at least partially surrounds the central electrode, the central and perimeter electrodes electrostatically generate a plasma by coupling energy into the plasma, and the central and perimeter electrodes generating an ionizing electromagnetic field that extends out of the field generation portion; and
a power input configured to receive a current to be passed between the central and perimeter electrode;
a field projection portion coupled to the field generation portion, wherein the field projection portion comprises a conductive tube having a dielectric inner layer, wherein the field projection portion attenuates the ionizing electromagnetic field to form an attenuated ionizing electromagnetic field, having a lower voltage than the ionizing electromagnetic field in the field generation portion, yet a voltage high enough to sustain a plasma within a plasma chamber configured for coupling to the field projection portion, wherein the field projection portion is configured to be at least partially external to the plasma chamber; and
a bias coupled to the field projection portion that applies one of the following to the field projection portion to attenuate the ionizing electromagnetic field, a level of the bias being such as to achieve a plasma voltage within the plasma chamber that is lower than the plasma voltage in the field generation portion and to achieve an ion energy in the plasma chamber that is independent from the current at the power input of the field generation portion:
a controllable AC bias;
a controllable DC bias; and
a combination of a controllable AC and a controllable DC bias;
wherein the bias coupled to the field projection portion is phase shifted from, and electrically isolated from, the central and perimeter electrodes of the field generation portion;
wherein the field projection portion has a longitudinal axis that is longer than a widest inner diameter of the field projection portion, and where the field projection portion includes a dielectric that is parallel to the longitudinal axis of the field projection portion.
13. The plasma source of claim 12 , wherein the bias coupled to the field projection portion is electrically isolated from the central and perimeter electrodes of the field generation portion by one or more reactive components.
14. The plasma source of claim 13 , wherein the one or more reactive components have a variable impedance and a variable reactance.
15. The plasma source of claim 12 , wherein the level of the bias is selected to achieve a 0.5 V-10 V plasma voltage within the plasma chamber.
16. The plasma source of claim 12 , wherein the level of the bias is selected to achieve a plasma voltage within the plasma chamber less than 1.0 V.
17. The plasma source of claim 12 , wherein the power input is configured to receive very high frequency current, while the plasma chamber is configured to receive low frequency current.
18. The plasma source of claim 17 , wherein the very high frequency is between 5 and 300 MHz.
19. The plasma source of claim 18 , wherein the very high frequency is between 30 and 150 MHz.
20. The plasma source of claim 18 , wherein the low frequency is below 5 MHz.
21. The plasma source of claim 12 , further comprising a power source coupled to a substrate through a substrate holder, wherein a bias on the substrate is dominated by the power source rather than a bias from the plasma.