DC plasma control for electron enhanced material processing
Systems and methods for material processing using wafer scale waves of precisely controlled electrons in a DC plasma is presented. The anode and cathode of a DC plasma chamber are respectively connected to an adjustable DC voltage source and a DC current source. The anode potential is adjusted to shift a surface floating potential of a stage in a positive column of the DC plasma to a reference ground potential of the DC voltage/current sources. A conductive plate in a same region of the positive column opposite the stage is used to measure the surface floating potential of the stage. A control loop can be activated throughout various processing steps to maintain the surface floating potential of the stage to the reference ground potential. A signal generator referenced to the ground potential is capacitively coupled to the stage to control a surface potential at the stage for provision of kinetic energy to free electrons in the DC plasma.
1. A method for processing a surface of a substrate, the method comprising:
processing the substrate via a direct-current (DC) plasma system, wherein the DC plasma system comprises:
a DC plasma reaction chamber configured to contain a DC plasma that is generated between an anode and a cathode of the DC plasma reaction chamber;
an adjustable DC voltage source having an output that is electrically coupled to the anode;
a DC current source that is electrically coupled to the cathode; and
a substrate support stage arranged in a region of the DC plasma reaction chamber that contains a positive column of the DC plasma,
wherein
the adjustable DC voltage source and the DC current source are electrically coupled to a reference ground, and
the DC current source is configured to set, during the processing of the substrate, a constant DC current that flows between the anode and the cathode, and the adjustable DC voltage source is configured to adjust, during the processing of the substrate and independently from the constant DC current, an electrical potential at the anode to set a substrate floating potential at a surface of the substrate support stage to a potential of the reference ground.
2. The method according to claim 1 , wherein:
the constant DC current is configured to generate the DC plasma.
3. The method according to claim 2 , wherein:
an electrical potential at the cathode settles to a potential that is based on the electrical potential at the anode and the constant DC current, and
a positive or negative step change of the electrical potential at the anode causes a same positive or negative step change of the electrical potential at the cathode.
4. The method according to claim 1 , wherein the DC plasma system further comprises:
control electronics configured to generate an error signal based on a difference between the substrate floating potential and the potential of the reference ground.
5. The method according to claim 4 , wherein:
the control electronics is electrically coupled to a reference plate made of a conductive material arranged in the region of the DC plasma reaction chamber that contains the positive column so that a surface potential of the reference plate is equal to the substrate floating potential.
6. The method according to claim 4 , wherein:
the adjustable DC voltage source is configured to receive the error signal and adjust the electrical potential at the anode based on a value of the error signal.
7. The method according to claim 5 , wherein:
the adjustable DC voltage source, the reference plate and the control electronics are configured to provide a closed loop control system to maintain the substrate floating potential to the potential of the reference ground.
8. The method according to claim 1 , wherein the DC plasma system further comprises:
a biasing signal generator that is capacitively coupled to the substrate support stage, wherein
the biasing signal generator is configured to generate a biasing signal having a voltage level that is referenced to the potential of the reference ground, the biasing signal capacitively coupled to the substrate support stage, and
the biasing signal is configured to control a surface potential of the substrate support stage.
9. The method according to claim 8 , wherein:
the biasing signal generator is configured to control waveform characteristics of the biasing signal, the waveform characteristics comprising the voltage level, a frequency, a duty cycle, a rising edge, or a falling edge.
10. The method according to claim 8 , wherein:
when the voltage level of the biasing signal is zero volts, the surface potential of the substrate support stage is at zero volts, the energy level of free electrons in the DC plasma is at zero volts, and the energy level of nuclei of atoms at a surface of the substrate is at zero volts.
11. The method according to claim 10 , wherein:
when the voltage level of the biasing signal is increased by a positive voltage step, the surface potential of the substrate support stage is increased by the same positive voltage step, and the energy level of the free electrons is increased in proportion to the positive voltage step.
12. A method for processing a surface of a substrate, the method comprising:
placing a substrate support stage in a region of a DC plasma reaction chamber configured to produce a positive column of DC plasma;
generating the DC plasma by coupling an adjustable DC voltage source and a DC current source respectively to an anode and a cathode of the DC plasma reaction chamber;
based on the generating, producing a substrate floating potential at a surface of the substrate support stage;
establishing a constant DC current between the anode and the cathode via the DC current source;
adjusting, independently from the constant DC current, a potential at the anode via the adjustable DC voltage source; and
based on the adjusting, setting the substrate floating potential to a specific potential relative to a potential of a reference ground of the adjustable DC voltage source.
13. The method according to claim 12 , wherein:
the specific potential is at the potential of the reference ground.
14. The method according to claim 12 , wherein:
a potential at the cathode settles to a potential that is based on the establishing and the adjusting, and
the adjusting produces a positive or negative step change of the potential at the anode that is equal to a positive or negative step change of the potential at the cathode.
15. The method according to claim 12 , further comprising:
measuring the substrate floating potential; and
based on the measuring, generating an error signal based on a difference between the substrate floating potential and the potential of the reference ground.
16. The method according to claim 15 , further comprising:
arranging a reference plate made of a conductive material in a region of the positive column;
based on the arranging, obtaining a surface potential of the reference plate that is equal to the substrate floating potential; and
measuring the substrate floating potential by measuring the surface potential of the reference plate.
17. The method according to claim 16 , further comprising:
generating an error signal based on a difference between the surface potential of the reference plate and the potential of the reference ground.
18. The method according to claim 12 , further comprising:
generating an error signal based on a difference between the substrate floating potential and the potential of the reference ground.
19. The method according to claim 18 , further comprising:
further adjusting, via the adjustable DC voltage source, the potential at the anode based on a value of the error signal while maintaining the constant DC current source via a same setting of the DC current source.
20. The method according to claim 12 , further comprising:
placing a substrate on the substrate support stage;
capacitively coupling a biasing signal to the substrate support stage, thereby energizing free electrons in the DC plasma;
based on the energizing, accelerating the free electrons onto a surface of the substrate; and
based on the accelerating, colliding the free electrons with atoms at the surface of the substrate, thereby breaking energy bonds between electrons and nuclei of the atoms,
wherein a voltage level of the biasing signal is selected to target a specific energy level of the electrons of the atoms, the atoms making up a specific material.