Plasma processing with phase-locked waveforms
A plasma processing method includes applying AC waveforms to a bottom electrode in a plasma chamber to generate a plasma. The method further includes applying a first pulse train including a first plurality of DC pulses to a top electrode in the plasma chamber, where each DC pulse of the first plurality of DC pulses includes a first on-state and a first off-state. And the method further includes applying a second pulse train including a second plurality of DC pulses to the bottom electrode in the plasma chamber, and where each DC pulse of the second plurality of DC pulses includes a second on-state and a second off-state, the first pulse train being offset in phase relative to the second pulse train so that each first off-state overlaps with each second on-state.
1 . A plasma processing method comprising:
continuously applying AC waveforms to a bottom electrode in a plasma chamber to generate a plasma;
while continuously applying the AC waveforms to the bottom electrode, applying a first pulse train comprising a first plurality of DC pulses to a top electrode in the plasma chamber, wherein each DC pulse of the first plurality of DC pulses comprises a first on-state and a first off-state, the first on-state accelerating ions of the plasma towards the top electrode to form secondary electrons, the first off-state repelling ions of the plasma from the top electrode; and
while continuously applying the AC waveforms to the bottom electrode, applying a second pulse train comprising a second plurality of DC pulses to the bottom electrode in the plasma chamber, wherein each DC pulse of the second plurality of DC pulses comprises a second on-state and a second off-state, the second on-state accelerating ions of the plasma towards a substrate disposed on the bottom electrode to process the substrate, the second off-state enabling the secondary electrons to neutralize charge build up on the substrate, the first pulse train being offset in phase relative to the second pulse train so that each first off-state overlaps with each second on-state.
2 . The plasma processing method of claim 1 , wherein the first plurality of DC pulses each comprise a first frequency, a first amplitude, and a first duty cycle.
3 . The plasma processing method of claim 2 , wherein the second plurality of DC pulses each comprise a second frequency, a second amplitude, and a second duty cycle.
4 . The plasma processing method of claim 3 , wherein the AC waveforms are sine waves comprising a third frequency, and a third amplitude.
5 . The plasma processing method of claim 4 , wherein the first frequency is equal to the second frequency, and the third frequency is at least an order of magnitude larger than the first frequency and the second frequency.
6 . The plasma processing method of claim 4 , wherein an absolute value of the first amplitude is smaller in magnitude than the absolute value of the second amplitude, and the first amplitude and the second amplitude are a same polarity.
7 . The plasma processing method of claim 4 , wherein the first amplitude and the second amplitude are negative voltages.
8 . The plasma processing method of claim 4 , wherein the third amplitude is smaller in magnitude than the second amplitude, and the third amplitude is a peak-to-peak voltage.
9 . The plasma processing method of claim 1 , wherein the second on-state of each of the second plurality of DC pulses is contained within the first off-state of each of the first plurality of DC pulses.
10 . The plasma processing method of claim 1 , wherein more than 80% of a duration of each instance of the first off-state overlaps with each instance of the second on-state.
11 . A plasma processing method comprising:
providing a first pulse train comprising a first plurality of DC pulses to a top electrode in a plasma chamber; and
providing AC waveforms and a second pulse train comprising a second plurality of DC pulses to a bottom electrode in the plasma chamber, the AC waveforms continuously generating a plasma in the plasma chamber, the second pulse train controlling the plasma to process a substrate disposed on the bottom electrode, wherein a second time duration that is a length of time of each on-state of the second plurality of DC pulses is contained within an off time duration that is the length of time of each off-state of the first plurality of DC pulses such that each off-state of the first pulse train aligns with each on-state of the second pulse train.
12 . The plasma processing method of claim 11 , wherein the first pulse train comprises a first frequency, a first amplitude, and a first duty cycle.
13 . The plasma processing method of claim 12 , wherein the second pulse train comprises a second frequency, a second amplitude, and a second duty cycle.
14 . The plasma processing method of claim 13 , wherein the AC waveforms are sine waves comprising a third frequency, and a third amplitude.
15 . The plasma processing method of claim 14 , wherein the first frequency is equal to the second frequency, and the third frequency is an order of magnitude larger than the first frequency and the second frequency.
16 . The plasma processing method of claim 14 , wherein an absolute value of the first amplitude is smaller in magnitude than the absolute value of the second amplitude, and the first amplitude and the second amplitude are a same polarity.
17 . The plasma processing method of claim 14 , wherein the first amplitude and the second amplitude are negative voltages.
18 . The plasma processing method of claim 14 , wherein the third amplitude is smaller in magnitude than the second amplitude, and the third amplitude is a peak-to-peak voltage.
19 . A plasma processing system comprising:
a plasma chamber;
a top electrode and a bottom electrode;
a first DC pulse generator coupled to the top electrode and configured to generate a first pulse train;
a second DC pulse generator coupled to the bottom electrode and configured to generate a second pulse train to control a plasma to process a substrate disposed on the bottom electrode;
a function generator coupled to the bottom electrode and configured to generate an AC waveform to generate the plasma independent of the first pulse train and the second pulse train; and
a controller coupled to and configured to control outputs of the first DC pulse generator, the second DC pulse generator, and the function generator, the controller being configured to phase lock the first pulse train with the second pulse train.
20 . The plasma processing system of claim 19 , further comprising a reference clock coupled between the first DC pulse generator and the second DC pulse generator, wherein the reference clock is configured to provide a signal to synchronize the outputs of the first DC pulse generator and the second DC pulse generator.