Bias supply with resonant switching
Bias supplies and plasma processing systems are disclosed. One bias supply comprises an output node, a return node, and a power section coupled to the output node and the return node. A resonant switch section is coupled to the power section at a first node, a second node, and a third node wherein the resonant switch section is configured to connect and disconnect a current pathway between the first node and the second node to apply an asymmetric periodic voltage waveform at the output node relative to the return node. The asymmetric periodic voltage waveform includes a first portion that begins with a first negative voltage and changes to a positive peak voltage, a second portion that changes from the positive peak voltage level to a third voltage level and a fourth portion that includes a negative voltage ramp from the third voltage level to a fourth voltage level.
1. A bias supply to apply a periodic voltage comprising:
an output node;
a return node;
a resonant switch section comprising:
a first node, a second node, and a third node;
a first current pathway between the first node and the second node, the first current pathway comprising a series combination of a switch and a diode;
a second current pathway between the second node and the third node comprising a diode and an inductive element; and
a power section comprising:
a first voltage source coupled between the third node and the first node; and
a second voltage source coupled to the return node;
wherein closing the switch causes unidirectional current in the first and second current pathways to cause an application of the periodic voltage between the output node and the return node.
2. The bias supply of claim 1 ,
wherein the first current pathway is configured so the unidirectional current in the first pathway increases from zero current at a time t 0 when the switch is closed to a peak value and then decreases back to zero at a time t 1 when the switch is opened and a voltage between the output node and return node increases from a negative voltage at the time t 0 to a peak value at the time t 1 .
3. The bias supply of claim 1 , wherein the first current pathway comprises a series combination of the switch, inductive element, and the diode coupled between the first node and the second node.
4. The bias supply of claim 1 , wherein the first current pathway comprises two inductive elements that are coupled together at the second node.
5. The bias supply of claim 1 , wherein the power section comprises a series combination of the second voltage source and an inductive element coupled between the output node and the return node.
6. The bias supply of claim 1 , wherein the second voltage source is coupled between the second node and the return node.
7. The bias supply of claim 1 , wherein a negative terminal of the second voltage source is coupled to a negative terminal of the first voltage source.
8. The bias supply of claim 1 , comprising a third voltage source coupled between the third node and the return node.
9. A bias supply to apply a periodic voltage comprising:
an output node;
a return node;
a power section coupled to the output node and the return node;
a resonant switch section coupled to the power section at a first node, a second node, and a third node wherein the resonant switch section is configured to connect and disconnect a current pathway between the first node and the second node to cause an application of an asymmetric periodic voltage waveform at the output node relative to the return node, wherein each cycle of the asymmetric periodic voltage waveform includes a first portion that begins with a first negative voltage and changes to a positive peak voltage, a second portion that changes from the positive peak voltage level to a third voltage level and a fourth portion that includes a negative voltage ramp from the third voltage level to a fourth voltage level; and
an offset voltage source, wherein a second node of a secondary winding of the transformer is coupled to the return node via the offset voltage source;
wherein the power section comprises:
a transformer, a first node of a primary winding of the transformer coupled to a second node of the resonant switch section, a first node of the secondary winding of the transformer coupled to the output node, and a second node of the secondary winding of the transformer coupled to the return node; and
a voltage source coupled between a second node of the primary winding of the transformer and the return node.
10. The bias supply of claim 9 wherein connecting the current pathway causes the first portion of the asymmetric periodic voltage waveform that begins with a first negative voltage and changes to the positive peak voltage.
11. The bias supply of claim 10 , wherein disconnecting the current pathway causes the second portion of the asymmetric periodic voltage waveform that changes from the positive peak voltage level to the third voltage level.
12. The bias supply of claim 11 , wherein the power section comprises a voltage source in series with an inductive element coupled between the second node and the return node.