RF impedance matching network

• US 9,196,459 B2
• Filed: 03/26/2015
• Issued: 11/24/2015
• Est. Priority Date: 01/10/2014
• Status: Active Grant

• Current Assignee: ASM America Incorporated (ASM International NV)
• Original Assignee: Reno Technologies Inc.
• Inventors: Bhutta, Imran Ahmed
• Primary Examiner(s): Le, Dinh
• Application Number:
  US14/669,568
• Publication Number:
  US 20150200079A1
• Time in Patent Office: 243 Days
• Field of Search: 455/115.1, 455120-126, 31511121-1119, 315/344, 372/44
• US Class Current: 1/1
• CPC Class Codes: H01J 37/241 High voltage power supply or regulation circuits components H01J37/248
• CPC Class Codes: H01J 37/244 Detectors; Associated components or circuits therefor
• CPC Class Codes: H01J 37/248 Components associated with high voltage supply means for measuring the high voltage per se G01R15/00
• CPC Class Codes: H01J 37/32183 Matching circuits
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring
• CPC Class Codes: H03H 11/30 Automatic matching of source impedance to load impedance
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance

Abstract

An RF impedance matching network includes an RF input; an RF output configured to operably couple to a plasma chamber; a series electronically variable capacitor (“series EVC”), the series EVC electrically coupled in series between the RF input and the RF output; and a shunt electronically variable capacitor (“shunt EVC”), the shunt EVC electrically coupled in parallel between a ground and one of the RF input and the RF output; a control circuit to control the series variable capacitance and the shunt variable capacitance, wherein the control circuit is configured to determine the variable plasma impedance of the plasma chamber, determine a series capacitance value and a shunt capacitance value, and generate a control signal to alter at least one of the series variable capacitance and the shunt variable capacitance; wherein the alteration is caused by at least one of a plurality of switching circuits.

Claims

1. An RF impedance matching network comprising:

an RF input configured to operably couple to an RF source, the RF source having a fixed RF source impedance;

an RF output configured to operably couple to a plasma chamber, the plasma chamber having a variable plasma impedance;

a series electronically variable capacitor (“

series EVC”

) having a series variable capacitance and comprising a first plurality of capacitors, the series EVC electrically coupled in series between the RF input and the RF output;

a shunt electronically variable capacitor (“

shunt EVC”

) having a shunt variable capacitance and comprising a second plurality of capacitors, the shunt EVC electrically coupled in parallel between a ground and one of the RF input and the RF output;

an inductor electrically coupled in series between the RF input and the RF output; and

a control circuit operatively coupled to the series EVC and to the shunt EVC to control the series variable capacitance and the shunt variable capacitance, wherein the control circuit is configured to;

determine the variable plasma impedance of the plasma chamber;

determine a series capacitance value for the series variable capacitance and a shunt capacitance value for the shunt variable capacitance; and

generate a control signal to alter at least one of the series variable capacitance and the shunt variable capacitance to the series capacitance value and the shunt capacitance value, respectively, the control signal comprising a common input signal;

wherein the alteration of the at least one of the series variable capacitance and the shunt variable capacitance is caused by at least one of a plurality of switching circuits, wherein each of the plurality of switching circuits is configured to switch one capacitor of the first plurality of capacitors and the second plurality of capacitors such that each of the first plurality of capacitors and the second plurality of capacitors is configured to be switched, each switching circuit comprising;

an electronic switch electrically coupled to the one capacitor; and

a driver circuit having a common output electrically coupled to the electronic switch, the driver circuit comprising;

a first power switch receiving the common input signal and a first voltage and configured to switchably provide the first voltage to the common output in response to the common input signal, the first power switch comprising a plurality of optocoupler phototransistors connected in series; and

a second power switch receiving the common input signal and a second voltage and configured to switchably provide the second voltage to the common output in response to the common input signal, wherein;

the second voltage is opposite in polarity to the first voltage;

the first power switch and the second power switch are configured to asynchronously provide the first voltage and the second voltage, respectively, to the common output in response to the common input signal, the electronic switch being switched according to the first voltage or the second voltage being provided to the common output; and

when the plurality of optocoupler phototransistors of the first power switch are switched off, a voltage drop from the first voltage to the second voltage occurs across the plurality of optocoupler phototransistors.

2. The impedance matching network of claim 1, wherein an elapsed time between determining the plasma variable impedance to when RF power reflected back to the RF source decreases is less than about 150 μ

sec.

3. The RF impedance matching network of claim 2, wherein the control circuit is configured to repeat the steps of determining the variable plasma impedance, determining the series and shunt capacitance values, and generating the control signal to create an impedance match at the RF input.

4. The RF impedance matching network of claim 3, wherein the impedance match is created in about 500 μ

sec or less.

5. The RF impedance matching network of claim 4, wherein the control circuit determines the variable impedance before creating the impedance match.

6. The RF impedance matching network of claim 5, wherein the impedance match results in about 10% or less RF power reflected back to the RF source.

7. The RF impedance matching network of claim 1, wherein the one capacitor is deactivated by applying a high voltage to the electronic switch and activated by applying a low voltage to the electronic switch, both the high voltage and the low voltage being applied from the common output of the driver circuit.

8. The impedance matching network of claim 1, wherein the series EVC and the shunt EVC are configured to switch to the series capacitance value and the shunt capacitance value, respectively, in less than 15 μ

sec.

9. A method of matching an impedance, the method comprising:

determining a variable plasma impedance of a plasma chamber, with an impedance matching network electrically coupled between the plasma chamber and an RF source, wherein the RF source has a fixed RF source impedance, and the impedance matching network includes;

a series electronically variable capacitor (“

series EVC”

) having a series variable capacitance and comprising a first plurality of capacitors, the series EVC coupled in series between the plasma chamber and the RF source;

a shunt electronically variable capacitor (“

shunt EVC”

) having a shunt variable capacitance and comprising a second plurality of capacitors, the shunt EVC coupled in parallel between a ground and one of the plasma chamber and the RF source; and

an inductor electrically coupled in series between the RF input and the RF output;

determining a series capacitance value for the series variable capacitance and a shunt capacitance value for the shunt variable capacitance for creating an impedance match at an RF input of the impedance matching network; and

generating a control signal to alter at least one of the series variable capacitance and the shunt variable capacitance to the series capacitance value and the shunt capacitance value, respectively, the control signal comprising a common input signal;

wherein the alteration of the at least one of the series variable capacitance and the shunt variable capacitance is caused by at least one of a plurality of switching circuits, wherein each of the plurality of switching circuits is configured to switch one capacitor of the first plurality of capacitors and the second plurality of capacitors such that each of the first plurality of capacitors and the second plurality of capacitors is configured to be switched, each switching circuit comprising;

an electronic switch electrically coupled to the one capacitor; and

a driver circuit having a common output electrically coupled to the electronic switch, the driver circuit comprising;

a first power switch receiving the common input signal and a first voltage and configured to switchably provide the first voltage to the common output in response to the common input signal, the first power switch comprising a plurality of optocoupler phototransistors connected in series; and

a second power switch receiving the common input signal and a second voltage and configured to switchably provide the second voltage to the common output in response to the common input signal, wherein;

the second voltage is opposite in polarity to the first voltage;

the first power switch and the second power switch are configured to asynchronously provide the first voltage and the second voltage, respectively, to the common output in response to the common input signal, the electronic switch being switched according to the first voltage or the second voltage being provided to the common output; and

when the plurality of optocoupler phototransistors of the first power switch are switched off, a voltage drop from the first voltage to the second voltage occurs across the plurality of optocoupler phototransistors.

10. The method of claim 9, wherein an elapsed time between determining the plasma variable impedance to when RF power reflected back to the RF source decreases is less than about 150 μ

sec.

11. The method of claim 10, wherein the control circuit is configured to repeat the steps of determining the variable plasma impedance, determining the series and shunt capacitance values, and generating the control signal to create the impedance match at the RF input.

12. The method of claim 11, wherein the impedance match is created in about 500 μ

sec or less.

13. The method of claim 12, wherein the control circuit determines the variable impedance before creating the impedance match.

14. The method of claim 13, wherein the impedance match results in about 10% or less RF power reflected back to the RF source.

15. The method of claim 9, wherein the one capacitor is deactivated by applying a high voltage to the electronic switch and activated by applying a low voltage to the electronic switch, both the high voltage and the low voltage being applied from the common output of the driver circuit.

16. The method of claim 9, wherein the series EVC and the shunt EVC are configured to switch to the series capacitance value and the shunt capacitance value, respectively, in less than 15 μ

sec.

17. A method of manufacturing a semiconductor comprising:

placing a substrate in a plasma chamber configured to deposit a material layer onto the substrate or etch a material layer from the substrate; and

energizing plasma within the plasma chamber by coupling RF power from an RF source into the plasma chamber to perform a deposition or etching, and while energizing the plasma;

determining a variable plasma impedance of the plasma chamber, with an impedance matching network electrically coupled between the plasma chamber and the RF source, wherein the RF source has a fixed RF source impedance, and the impedance matching network includes;

a series electronically variable capacitor (“

series EVC”

) having a series variable capacitance and comprising a first plurality of capacitors, the series EVC coupled in series between the plasma chamber and the RF source;

a shunt electronically variable capacitor (“

shunt EVC”

) having a shunt variable capacitance and comprising a second plurality of capacitors, the shunt EVC coupled in parallel between a ground and one of the plasma chamber and the RF source; and

an inductor electrically coupled in series between the RF input and the RF output;

determining a series capacitance value for the series variable capacitance and a shunt capacitance value for the shunt variable capacitance for creating an impedance match at an RF input of the impedance matching network; and

generating a control signal to alter at least one of the series variable capacitance and the shunt variable capacitance to the series capacitance value and the shunt capacitance value, respectively, the control signal comprising a common input signal;

wherein the alteration of the at least one of the series variable capacitance and the shunt variable capacitance is caused by at least one of a plurality of switching circuits, wherein each of the plurality of switching circuits is configured to switch one capacitor of the first plurality of capacitors and the second plurality of capacitors such that each of the first plurality of capacitors and the second plurality of capacitors is configured to be switched, each switching circuit comprising;

an electronic switch electrically coupled to the one capacitor; and

a driver circuit having a common output electrically coupled to the electronic switch, the driver circuit comprising;

a first power switch receiving the common input signal and a first voltage and configured to switchably provide the first voltage to the common output in response to the common input signal, the first power switch comprising a plurality of optocoupler phototransistors connected in series; and

a second power switch receiving the common input signal and a second voltage and configured to switchably provide the second voltage to the common output in response to the common input signal, wherein;

the second voltage is opposite in polarity to the first voltage;

the first power switch and the second power switch are configured to asynchronously provide the first voltage and the second voltage, respectively, to the common output in response to the common input signal, the electronic switch being switched according to the first voltage or the second voltage being provided to the common output; and

when the plurality of optocoupler phototransistors of the first power switch are switched off, a voltage drop from the first voltage to the second voltage occurs across the plurality of optocoupler phototransistors.

18. The method of claim 17, wherein an elapsed time between determining the plasma variable impedance to when RF power reflected back to the RF source decreases is less than about 150 μ

sec.