System for providing variable capacitance
In one embodiment, a radio frequency (RF) impedance matching network includes electronically variable capacitors (EVCs), each EVC including discrete capacitors operably coupled in parallel. The discrete capacitors include fine capacitors each having a capacitance value substantially similar to a fine capacitance value, and coarse capacitors each having a capacitance value substantially similar to a coarse capacitance value. The increase of the variable total capacitance of each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.
1. A radio frequency (RF) impedance matching network comprising:
an RF input configured to operably couple to an RF source;
an RF output configured to operably couple to a plasma chamber having a variable impedance;
electronically variable capacitors (EVCs) each comprising discrete capacitors operably coupled in parallel, the discrete capacitors comprising:
fine capacitors each having a capacitance value substantially similar to a fine capacitance value; and
coarse capacitors each having a capacitance value substantially similar to a coarse capacitance value, the coarse capacitance value being greater than the fine capacitance value;
wherein each EVC has a variable total capacitance that is increased when the discrete capacitors are switched in and decreased when the discrete capacitors are switched out; and
a control circuit operably coupled to the EVCs, the control circuit configured to determine the variable impedance of the plasma chamber;
the control circuit further configured to:
determine, based on the determined variable impedance, a total number of coarse capacitors of the coarse capacitors to have switched in;
determine, based on the determined variable impedance, a total number of fine capacitors of the fine capacitors to have switched in; and
cause an impedance match by causing the total number of coarse capacitors and the total number of fine capacitors to be switched in;
wherein the increase of the variable total capacitance of each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.
2. The matching network of claim 1 further comprising a driver circuit operatively coupled between the control circuit and the EVCs, the driver circuit being configured to alter the variable total capacitance of each EVC based upon a control signal received from the control circuit.
3. The matching network of claim 2 further comprising an RF filter operatively coupled between the driver circuit and the EVCs.
4. The matching network of claim 2 wherein the driver circuit is configured to switch a high voltage source on or off in less than 15 μsec, the high voltage source controlling electronic switches of each of the EVCs for purposes of altering the variable capacitance.
5. The matching network of claim 1 wherein when the variable total capacitance is increased and the control circuit does not switch in more of the coarse capacitors than are already switched in, then the control circuit switches in more fine capacitors than are already switched in without switching out a fine capacitor that is already switched in.
6. The matching network of claim 1 wherein any increase of the variable total capacitance of each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.
7. The matching network of claim 1 wherein the coarse capacitance value and the fine capacitance value have a ratio substantially similar to 10:1.
8. The matching network of claim 1 wherein the fine capacitance value is:
less than or equal to one-half (½) of the coarse capacitance value;
less than or equal to one-third (⅓) of the coarse capacitance value; or
less than or equal to one-fourth (¼) of the coarse capacitance value.
9. The matching network of claim 1 wherein the EVCs comprise three EVCs.
10. The matching network of claim 1 wherein each discrete capacitor of each EVC is switched out by applying a high voltage to an electronic switch and switched in by applying a low voltage to the electronic switch, the low voltage being opposite in polarity to the high voltage, and both the high voltage and the low voltage being applied from a common output of a driver circuit.
11. A method of controlling an impedance matching network, the method comprising:
providing an RF impedance matching network comprising:
an RF input configured to operably couple to an RF source;
an RF output configured to operably couple to a plasma chamber having a variable impedance;
electronically variable capacitors (EVCs) each comprising discrete capacitors operably coupled in parallel, the discrete capacitors comprising:
fine capacitors each having a capacitance value substantially similar to a fine capacitance value; and
coarse capacitors each having a capacitance value substantially similar to a coarse capacitance value, the coarse capacitance value being greater than the fine capacitance value;
wherein each EVC has a variable total capacitance that is increased when the discrete capacitors are switched in and decreased when the discrete capacitors are switched out;
a control circuit operably coupled to the EVCs;
by the control circuit, determining the variable impedance of the plasma chamber;
by the control circuit, determining, based on the determined variable impedance, a total number of coarse capacitors of the coarse capacitors to have switched in;
by the control circuit, determining, based on the determined variable impedance, a total number of fine capacitors of the fine capacitors to have switched in; and
by the control circuit, causing an impedance match by causing the total number of coarse capacitors and the total number of fine capacitors to be switched in;
wherein the increase of the variable total capacitance of the each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.
12. The method of claim 11 wherein the RF impedance matching network further comprises a driver circuit operatively coupled between the control circuit and the EVCs, the driver circuit being configured to alter the variable total capacitance of each EVC based upon a control signal received from the control circuit.
13. The method of claim 12 wherein the RF impedance matching network further comprises an RF filter operatively coupled between the driver circuit and the EVCs.
14. The method of claim 12 further comprising switching a high voltage source on or off in less than 15 μsec, the high voltage source controlling electronic switches of each of the EVCs for purposes of altering the variable capacitance.
15. The method of claim 11 wherein when the variable total capacitance is increased and the control circuit does not switch in more of the coarse capacitors than are already switched in, then the control circuit switches in more fine capacitors than are already switched in without switching out a fine capacitor that is already switched in.
16. The method of claim 11 wherein any increase of the variable total capacitance of each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.
17. The method of claim 11 wherein the coarse capacitance value and the fine capacitance value have a ratio substantially similar to 10:1.
18. The method of claim 11 wherein the fine capacitance value is:
less than or equal to one-half (½) of the coarse capacitance value;
less than or equal to one-third (⅓) of the coarse capacitance value; or
less than or equal to one-fourth (¼) of the coarse capacitance value.
19. The method of claim 11 wherein the EVCs comprise three EVCs.
20. A method of fabricating a semiconductor, the method 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:
providing an RF matching network between the plasma chamber and the RF source, the RF matching network comprising:
an RF input configured to operably couple to an RF source;
an RF output configured to operably couple to a plasma chamber having a variable impedance;
electronically variable capacitors (EVCs) each comprising discrete capacitors operably coupled in parallel, the discrete capacitors comprising:
fine capacitors each having a capacitance value substantially similar to a fine capacitance value; and
coarse capacitors each having a capacitance value substantially similar to a coarse capacitance value, the coarse capacitance value being greater than the fine capacitance value;
wherein each EVC has a variable total capacitance that is increased when the discrete capacitors are switched in and decreased when the discrete capacitors are switched out;
a control circuit operably coupled to the EVCs;
by the control circuit, determining the variable impedance of the plasma chamber;
by the control circuit, determining, based on the determined variable impedance, a total number of coarse capacitors of the coarse capacitors to have switched in;
by the control circuit, determining, based on the determined variable impedance, a total number of fine capacitors of the fine capacitors to have switched in; and
by the control circuit, causing an impedance match by causing the total number of coarse capacitors and the total number of fine capacitors to be switched in;
wherein the increase of the variable total capacitance of the each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.
21. A semiconductor processing tool comprising:
a plasma chamber configured to deposit a material onto a substrate or etch a material from the substrate; and
an impedance matching circuit operably coupled to the plasma chamber, matching circuit comprising:
an RF input configured to be operably coupled to an RF source;
an RF output operably coupled to the plasma chamber, the plasma chamber having a variable impedance;
electronically variable capacitors (EVCs) each comprising discrete capacitors operably coupled in parallel, the discrete capacitors comprising:
fine capacitors each having a capacitance value substantially similar to a fine capacitance value; and
coarse capacitors each having a capacitance value substantially similar to a coarse capacitance value, the coarse capacitance value being greater than the fine capacitance value;
wherein each EVC has a variable total capacitance that is increased when the discrete capacitors are switched in and decreased when the discrete capacitors are switched out; and
a control circuit operably coupled to the EVCs, the control circuit configured to determine the variable impedance of the plasma chamber;
the control circuit further configured to:
determine, based on the determined variable impedance, a total number of coarse capacitors of the coarse capacitors to have switched in;
determine, based on the determined variable impedance, a total number of fine capacitors of the fine capacitors to have switched in; and
cause an impedance match by causing the total number of coarse capacitors and the total number of fine capacitors to be switched in;
wherein the increase of the variable total capacitance of each EVC is achieved by switching in more of the coarse capacitors or more of the fine capacitors than are already switched in without switching out a coarse capacitor that is already switched in.