Pulsed voltage plasma processing apparatus and method
Embodiments provided herein generally include apparatus, plasma processing systems and methods for generation of a waveform for plasma processing of a substrate in a processing chamber that configured to adjust the timing and characteristics of the asymmetric voltage waveforms that are each provided to one or more electrodes or coils in a plasma processing chamber in an effort to improve the control of various characteristics of the generated plasma and control an ion energy distribution (IED) for the plasma generated ions that interact with a surface of a substrate during plasma processing. The methods and apparatus disclosed herein are configured to control and sustain a plasma formed in a processing region of the plasma processing chamber without the need for the delivery of a radio frequency (RF) waveform during processing. The ability to synchronize and control waveform characteristics, such as frequency, slope of the portions of the voltage waveform, waveform shape and applied voltage on-time during a pulse period, of the voltage pulses provided in each of the pulsed voltage waveforms applied to different electrodes and/or coils allows for an improved control of the generated plasma.
1 . A plasma processing system, comprising:
a plurality of pulsed voltage waveform generators;
a plurality of electrodes or coils that are each positioned and configured to alter a characteristic of a plasma formed in a processing volume of a plasma processing chamber of the plasma processing system when an asymmetric voltage waveform is provided to the electrode or coil from a pulsed voltage waveform generator of the plurality of pulsed voltage waveform generators, wherein each electrode or coil is coupled to a different pulsed voltage waveform generator of the plurality of pulsed voltage waveform generators; and
a system controller that is configured to cause the plasma processing system to perform operations comprising:
delivering a first asymmetric voltage waveform from a first pulsed voltage waveform generator of the plurality of pulsed voltage waveform generators to a first electrode or a first coil of the plurality of electrodes or coils, wherein:
the first asymmetric voltage waveform is configured to alter a characteristic of the plasma formed in the processing volume of the plasma processing chamber,
the first asymmetric voltage waveform comprises a first voltage pulse that comprises a first stage, a second stage, and a third stage,
the second stage of the first voltage pulse is disposed between the first stage and the third stage, and
a voltage of the first voltage pulse within the first stage and the third stage varies with time;
delivering a second asymmetric voltage waveform from a second pulsed voltage waveform generator of the plurality of pulsed voltage waveform generators to a second electrode or a second coil of the plurality of electrodes or coils, wherein the second asymmetric voltage waveform is configured to alter a characteristic of the plasma formed in the processing volume of the plasma processing chamber; and
synchronizing the delivery of the first asymmetric voltage waveform to the first electrode or the first coil from the first pulsed voltage waveform generator and the second asymmetric voltage waveform to the second electrode or the second coil from the second pulsed voltage waveform generator.
2 . The plasma processing system of claim 1 , wherein:
the first coil is coupled to the first pulsed voltage waveform generator, and
the first asymmetric voltage waveform varies between a first voltage level and a second voltage level.
3 . The plasma processing system of claim 2 , wherein the first voltage level is a positive voltage level and the second voltage level is a negative voltage level.
4 . The plasma processing system of claim 2 , wherein:
the second coil is coupled to the second pulsed voltage waveform generator, and
the second asymmetric voltage waveform comprises a plurality of stages that vary between a third voltage level and a fourth voltage level.
5 . The plasma processing system of claim 2 , wherein:
the second electrode is coupled to the second pulsed voltage waveform generator, and
the second asymmetric voltage waveform comprises a plurality of stages that vary between a third voltage level and a fourth voltage level.
6 . The plasma processing system of claim 5 , wherein the third voltage level is a positive voltage level and the fourth voltage level is a negative voltage level.
7 . The plasma processing system of claim 5 , wherein when the second asymmetric voltage waveform reaches the fourth voltage level, and wherein the fourth voltage level is configured to generate a plasma sheath after the third voltage level is reached during each asymmetric voltage pulse.
8 . A method of controlling a plasma formed in a plasma processing system, comprising:
delivering a first asymmetric voltage waveform from a first pulsed voltage waveform generator to a first electrode or a first coil, wherein:
the first asymmetric voltage waveform is configured to alter a characteristic of a plasma formed in a processing volume of a plasma processing chamber of the plasma processing system,
the first asymmetric voltage waveform comprises a first voltage pulse that comprises a first stage, a second stage, and a third stage,
the second stage of the first voltage pulse is disposed between the first stage and the third stage, and
a voltage of the first voltage pulse within the first stage and the third stage varies with time;
delivering a second asymmetric voltage waveform from a second pulsed voltage waveform generator to a second electrode or a second coil, wherein the second asymmetric voltage waveform is configured to alter a characteristic of the plasma formed in the processing volume of the plasma processing chamber; and
synchronizing the delivery of the first asymmetric voltage waveform and the second asymmetric voltage waveform.
9 . The method of claim 8 , wherein:
the first asymmetric voltage waveform is delivered to the first coil,
the second asymmetric voltage waveform is delivered to the second electrode, and
the first and second asymmetric voltage waveforms each comprises a plurality of stages.
10 . The method of claim 9 , wherein the first asymmetric voltage waveform varies between a first voltage level that is positive and a second voltage level that is negative.
11 . The method of claim 10 , wherein the second asymmetric voltage waveform comprises a plurality of stages that vary between a third voltage level and a fourth voltage level.
12 . The method of claim 8 , wherein:
the first asymmetric voltage waveform is delivered to the first coil,
the second asymmetric voltage waveform is delivered to the second coil, and the first and second asymmetric voltage waveforms each comprises a plurality of stages.
13 . The method of claim 8 , wherein:
the second asymmetric voltage waveform comprises a second voltage pulse that comprises a first stage, a second stage, and a third stage,
the second stage of the second voltage pulse is disposed between the first stage and the third stage of the second voltage pulse, and
respective voltages of the first and second voltage pulses within the first stage and the third stage vary linearly with time.
14 . The method of claim 8 , wherein:
the second asymmetric voltage waveform comprises a second voltage pulse that comprises a first stage, a second stage, and a third stage,
the second stage of the second voltage pulse is disposed between the first stage and the third stage of the second voltage pulse, and
respective voltages of the first and second voltage pulses within the first stage and the third stage vary non-linearly with time.
15 . The method of claim 8 , wherein:
the first asymmetric voltage waveform comprises a plurality of voltage pulses that extend between a first voltage level and a second voltage level,
the second asymmetric voltage waveform comprises a plurality of voltage pulses that extend between a third voltage level and a fourth voltage level, and
at least one of the first voltage level, the second voltage level, the third voltage level, or the fourth voltage level is different.
16 . The method of claim 8 , wherein:
the first asymmetric voltage waveform comprises:
a plurality of voltage pulses that each comprises a first pulse period and at least one sloped region that has first slope (dV 1 /dt),
wherein the first slope (dV 1 /dt) is equal to a slope (dV s /dt) of a sinusoidal waveform when measured at a phase angle at which the sinusoidal waveform crosses zero, and the sinusoidal waveform has a frequency between 1 MHz and 100 MHz, and a peak voltage between 500 volts and 5000 volts.
17 . The method of claim 8 , wherein delivering the first asymmetric voltage waveform and delivering the second asymmetric voltage waveform is performed without another source of electrical energy to sustain the plasma.
18 . The method of claim 8 , wherein a sinusoidal waveform is not present within the processing volume during the delivery of the first asymmetric voltage waveform and the delivering the second asymmetric voltage waveform.
19 . The method of claim 8 , wherein the plasma is not sustained in the processing volume by use of a sinusoidal waveform.