CHARGE REMOVAL FROM ELECTRODES IN UNIPOLAR SPUTTERING SYSTEM

• US 20140231243A1
• Filed: 02/20/2014
• Published: 08/21/2014
• Est. Priority Date: 11/01/2012
• Status: Active Grant

• Current Assignee: AES Global Holdings Pte Ltd. (Advanced Energy Industries, Inc. (China))
• Original Assignee: Advanced Energy Industries Incorporated
• Inventors: Finley, Kenneth W.
• Granted Patent: US 9,287,098 B2
• Time in Patent Office: Days
• US Class Current: 204/192.12
• CPC Class Codes: C23C 14/3485 using pulsed power to the target
• CPC Class Codes: H01J 37/3444 Associated circuits
• CPC Class Codes: H01J 37/3467 Pulsed operation, e.g. HIPIMS
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence
• CPC Class Codes: H05H 2242/22 DC, AC or pulsed generators

Abstract

This disclosure describes a non-dissipative snubber circuit configured to boost a voltage applied to a load after the load'"'"'s impedance rises rapidly. The voltage boost can thereby cause more rapid current ramping after a decrease in power delivery to the load which results from the load impedance rise. In particular, the snubber can comprise a combination of a unidirectional switch, a voltage multiplier, and a current limiter. In some cases, these components can be a diode, voltage doubler, and an inductor, respectively.

Claims

1. A pulsed DC power supply system configured to provide pulsed DC voltage between an anode and a cathode of a plasma processing chamber, the pulsed DC voltage including a first power delivery period of positive voltage separated from a second power delivery period by a charge removal period comprising a charge removal voltage having a negative polarity for removing charge from the cathode, the pulsed DC power supply system comprising:

a DC power supply coupled to and providing power to a first and second rail;

a switching circuit coupled to the first and second rails and switched so as to convert the power on the first and second rails to the pulsed DC voltage, where positive voltage is referenced from the anode to the cathode;

a voltage-boosting circuit coupled between the first and second rails and comprising;

a first unidirectional switch coupled between the first rail and a first electrical node and only allowing current to pass from the first rail to the first electrical node;

a voltage multiplier coupled between the second rail and the first electrical node and including an output that provides access to a charge removal voltage within the voltage multiplier;

a switch coupled between the first electrical node and a second electrical node;

a first current limiter coupled between the second electrical node and the first rail; and

a charge removal bias circuit coupled to the output of the voltage multiplier and providing the charge removal voltage to the switching circuit.

2. The pulsed DC power supply of claim 1, wherein the switching circuit includes first, second, third, and fourth switches of the switching circuit arranged in an h-bridge topology such that when the first and fourth switches of the switching circuit are closed the positive voltage is applied from the anode to the cathode, and when the second and third switches of the switching circuit are closed the negative charge removal voltage is applied from the anode to the cathode.

3. The pulsed DC power supply of claim 2, wherein the charge removal circuit couples the output of the voltage multiplier to the third switch of the switching circuit, thereby providing the charge removal voltage to the third switch of the switching circuit.

4. The pulsed DC power supply of claim 3, wherein the voltage multiplier comprises at least two capacitive elements arranged in series relative to current passing from the first rail through the first unidirectional switch and arranged in parallel relative to current discharged from the at least two capacitive elements.

5. The pulsed DC power supply of claim 4, wherein the first of the at least two capacitive elements is coupled so as to discharge via the first electrical node, the switch of the voltage-boosting circuit, and the first current limiter to the first rail, and wherein the second of the at least two capacitive elements is coupled so as to discharge via the output of the voltage multiplier to the third switch of the switching circuit, the output of the voltage multiplier providing a voltage across the second of these at least two capacitive elements.

6. The pulsed DC power supply of claim 1, further comprising a second current limiter coupled between the first rail and the first unidirectional switch.

7. The pulsed DC power supply of claim 5, further comprising a second unidirectional switch coupled between the first current limiter and the first rail, wherein the second unidirectional switch only allows current to pass from the first current limiter to the first rail.

8. The pulsed DC power supply of claim 1, wherein the switching circuit delivers positive voltage from the anode to the cathode for longer periods of time than the switching circuit delivers a negative voltage from the anode to the cathode.

9. The pulsed DC power supply of claim 1, wherein a magnitude of the charge removal voltage applied during the charge removal period is less than a magnitude of the positive voltage applied during the power delivery period.

10. The pulsed DC power supply of claim 1, wherein the pulsed DC voltage includes, at different times, a boosted voltage, a process voltage, and a charge removal voltage having an opposite polarity to the boosted voltage and the process voltage, where the boosted voltage is the process voltage plus a boost voltage.

11. The pulsed DC power supply of claim 1, wherein the switching circuit comprises one or more h-bridge cells coupled in parallel.

12. The pulsed DC power supply of claim 1, wherein the cathode is both an electrode and a sputtering target, and the anode is not a sputtering target.

13. A pulsed DC power supply system configured to provide unipolar DC power to a sputtering cathode within a plasma processing chamber, the pulsed DC power supply comprising:

a first rail;

a second rail;

a DC power supply coupled to the first and second rails and providing a first voltage waveform to the first and second rails, the first voltage waveform having at least a magnitude of a process voltage;

a charge removal bias circuit coupled to at least the second rail and providing a second voltage waveform having a magnitude of a charge removal voltage; and

a switching circuit coupled to the charge removal bias circuit and the first and second rails, the switching circuit comprising;

a first switch and a second switch coupled in series between the first and second rails and having a first output tapped from between the first and second switches;

a third switch and a fourth switch coupled in series between the charge removal bias circuit and the second rail and having a second output tapped from between the third and fourth switches,

the first and second outputs configured for providing pulsed DC power between an anode and a sputtering cathode of a plasma processing chamber,

a switching pattern of the switching circuit including a plurality of power delivery periods alternating with a plurality of charge removal periods, wherein the first and fourth switches are closed during the power delivery period, and the second and third switches are closed during the charge removal period, wherein the first voltage waveform across the first and second rails is provided across the first and second outputs during the power delivery period and the second voltage waveform is provided across the first and second outputs during the charge removal period.

14. The pulsed DC power supply system of claim 13 further comprising a voltage-boosting circuit coupled between the first and second rails, the voltage-boosting circuit including at least one capacitive element and a fifth switch coupled to the at least one capacitive element, the at least one capacitive element arranged so as to be charged by current absorbed from the first rail, wherein charging of the at least one capacitive element raises a voltage across the first and second rails by a boost voltage for a first portion of each power delivery period, and wherein a magnitude of the boost voltage is controlled via a switching pattern of the fifth switch.

15. The pulsed DC power supply system of claim 14, wherein the first voltage waveform has a magnitude equal to the process voltage for a remainder of each power delivery period.

16. The pulsed DC power supply of claim 14, wherein the charge removal bias circuit includes a third capacitive element coupled between the third switch of the switching circuit and the second rail, wherein a voltage across the third capacitive element ramps to the charge removal voltage as a result of current passing into the third capacitive element from a plasma in the plasma processing chamber.

17. The pulsed DC power supply of claim 14, wherein the charge removal bias circuit includes at least one fifth switch that is periodically switched and at least one inductive element, the at least one fifth switch being coupled to the one of the at least two capacitive elements of the voltage-boosting circuit such that the periodic switching of the at least one fifth switch controls a magnitude of the charge removal voltage.

18. The pulsed DC power supply of claim 13, wherein the charge removal bias circuit downconverts a voltage across the first and second rails to the charge removal voltage and provides the charge removal voltage to the third switch of the switching circuit.

19. A method for unipolar sputtering of a sputtering cathode in a plasma processing chamber, the method comprising:

providing a DC power supply supplying DC power to first and second rails, the DC power having a magnitude of a process voltage or a boosted voltage greater than the process voltage;

providing a charge removal bias circuit that provides DC power having a charge removal voltage;

providing a switching circuit receiving the modified DC power and the charge removal voltage and performing a switching pattern the produces a pulsed DC voltage including power delivery periods alternating with charge removal periods, wherein the power delivery period provides a negative voltage waveform and the charge removal period provides a positive voltage waveform, wherein the positive voltage waveform is asymmetric to the negative voltage waveform, the pulsed DC voltage configured for application to a plasma load in the plasma processing chamber via a unipolar electrode configuration; and

providing a voltage-boosting circuit coupled between the first and second rails that boosts the process voltage between the first and second rails to a boosted voltage during a first portion of each of the power delivery periods, wherein a voltage across the voltage-boosting circuit and hence across the first and second rails returns to the process voltage for a remainder of each power delivery period,

wherein each power delivery period is longer than each charge removal period.