Plasma behaviors predicted by current measurements during asymmetric bias waveform application
A bias supply configured for predicting behavior of one or more aspects of a plasma load by measuring a current waveform is disclosed. The bias supply applies an asymmetric periodic voltage waveform and a corresponding current waveform. The asymmetric periodic voltage waveform includes a first section comprising a positive pulse peak and a second section comprising a negative voltage ramp. The bias supply receives data about the current waveform during the first section, and based upon the received data, provides information about a plasma load.
1 . A biasing system comprising:
an output node;
a bias supply configured to apply an asymmetric periodic voltage waveform and provide a corresponding current waveform at the output node wherein the asymmetric periodic voltage waveform comprises:
a first section that begins with a first negative voltage and changes to a peak voltage before changing to a second negative voltage; and
a second section that begins with the second negative voltage and comprises a voltage ramp between the second negative voltage and a third negative voltage; and
a metrology module comprising at least hardware, the metrology module configured to receive data about the current waveform during the first section and provide, based upon the current waveform during the first section, information about a plasma load during the second section when the bias supply is coupled to the plasma load.
2 . The biasing system of claim 1 , wherein the metrology module is configured to determine a total charge corresponding to a chuck capacitance based, at least in part, on integrating the data about the current waveform, and wherein the total charge corresponds to a measure of an ion current flowing from the plasma load to a workpiece surface during the second section of the asymmetric periodic voltage waveform.
3 . The biasing system of claim 2 , wherein the metrology module is configured to calculate a time-averaged value of the ion current of the plasma load based, at least in part, on the determined total charge.
4 . The biasing system of claim 1 , wherein the metrology module is configured to determine a resonant frequency of an alternating current (AC) portion of the current waveform, wherein the resonant frequency of the AC portion of the current waveform corresponds to a measure of a sheath capacitance.
5 . The biasing system of claim 4 , wherein the metrology module is further configured to:
monitor the resonant frequency as a function of time.
6 . The biasing system of claim 5 , wherein the metrology module is further configured to monitor the resonant frequency over a plurality of cycles of the asymmetric periodic voltage waveform.
7 . The biasing system of claim 1 , wherein the bias supply comprises a switch network and at least one power supply.
8 . The biasing system of claim 7 , wherein the bias supply comprises:
at least two switches wherein, when closed, a first of the at least two switches causes the bias supply to apply the peak voltage, and when closed, another of the at least two switches causes the bias supply to apply the second negative voltage.
9 . The biasing system of claim 7 , wherein the switch network comprises:
a single-switched current path, wherein the bias supply is configured to periodically close and open the single-switched current path to apply the asymmetric periodic voltage waveform and provide the corresponding current waveform at the output node.
10 . The biasing system of claim 7 , wherein the bias supply comprises at least two switches and at least two power supplies.
11 . A method for predicting plasma behavior, comprising:
applying an asymmetric periodic voltage waveform to a plasma processing chamber, the asymmetric periodic voltage waveform comprising:
a first section that begins with a first negative voltage and changes to a second, peak voltage before changing to a second negative voltage; and
a second section that begins with the second negative voltage and comprises a voltage ramp between the second negative voltage and a third negative voltage; and
providing a current waveform that corresponds to the asymmetric periodic voltage waveform;
measuring the current waveform while the first section of the asymmetric periodic voltage waveform is applied; and
providing, using the measurements of the current during the first section, information about a plasma load during the second section.
12 . The method of claim 11 , further comprising:
determining a total charge corresponding to a chuck capacitance based, at least in part, on integrating data about the current waveform, and wherein the total charge corresponds to a measure of an ion current flowing from the plasma load to a workpiece surface during the second section of the asymmetric periodic voltage waveform.
13 . The method of claim 12 , further comprising:
calculating a time-averaged value of the ion current based, at least in part, on the determined total charge; and
determining a resonant frequency of an alternating current (AC) portion of the current waveform, wherein the resonant frequency of the AC portion of the current waveform corresponds to a measure of a sheath capacitance.
14 . The method of claim 11 , comprising:
monitoring a resonant frequency of an alternating current (AC) portion of the current waveform.
15 . The method of claim 14 , further comprising:
monitoring the resonant frequency over a plurality of cycles of the asymmetric periodic voltage waveform.
16 . A non-transient computer-readable storage medium having instructions embodied thereon, the instructions are executable by a processor and/or capable of programming a field programmable gate array, the instructions comprising instructions for:
applying an asymmetric periodic voltage waveform at an output node of a bias supply, the asymmetric periodic voltage waveform comprising:
a first section that begins with a first negative voltage and changes to a second, peak voltage before changing to a second negative voltage;
a second section that begins with the second negative voltage and comprises a voltage ramp between the second negative voltage and a third negative voltage; and
providing a current waveform that corresponds to the asymmetric periodic voltage waveform;
measuring the current waveform while the first section of the asymmetric periodic voltage waveform is applied; and
providing, using the measurements of the current during the first section, information about a plasma load during the second section.
17 . The non-transient computer-readable storage medium of claim 16 , wherein the instructions comprise instructions for determining a total charge corresponding to a chuck capacitance based, at least in part, on integrating data about the current waveform, and wherein the total charge corresponds to a measure of an ion current flowing from the plasma load to a workpiece during the second section of the asymmetric periodic voltage waveform.
18 . The non-transient computer-readable storage medium of claim 17 , wherein the instructions comprise instructions for:
calculating a time-averaged value of the ion current based, at least in part, on the determined total charge; and
determining a resonant frequency of an alternating current (AC) portion of the current waveform, wherein the resonant frequency of the AC portion of the current waveform corresponds to a measure of a sheath capacitance.
19 . The non-transient computer-readable storage medium of claim 16 , wherein the instructions comprise instructions for:
monitoring a resonant frequency of an alternating current (AC) portion of the current waveform; and
monitoring the resonant frequency over a plurality of cycles of the asymmetric periodic voltage waveform.