Method for impedance matching, impedance matching arrangement and plasma system

1 . A method for impedance matching using an impedance matching network having an input for connection of an RF power generator and an output for connection to a load, the impedance matching network comprising at least a first matching stage and a second matching stage connected in series, each of the first matching stage and the second matching stage having a respective variable reactance, the method comprising:

a) measuring an input impedance at the input,

b) determining an intermediate impedance that occurs between the first matching stage and the second matching stage by:

determining an input admittance based on the measured input impedance,

determining a position of a mechanically alterable reactance or a circuit state of an electronically alterable reactance as a present state value of at least one of the first matching stage and the second matching stage,

c) determining an alteration target value for at least one of the variable reactances of the first matching stage and the second matching stage from the intermediate impedance and a model of the impedance matching network, the alteration target value being determined based on an intermediate impedance target value,

d) altering a state of at least one of the first matching stage and the second matching stage based on the alteration target value, and

e) repeating steps a) to d).

2 . The method according to claim 1 , wherein steps a) to d) are repeated until the input impedance exceeds or falls below a predefined value.

3 . The method according to claim 1 , wherein the intermediate impedance is determined based on an assignment of the input impedance to the intermediate impedance depending on the state.

4 . The method according to claim 1 , wherein the intermediate impedance target value is determined based on at least one predefined boundary condition.

5 . The method according to claim 1 , wherein the state of at least one of the first matching stage and the second matching stage is altered by the alteration target value or in a direction of the alteration target value.

6 . The method according to claim 1 , wherein the state of the first matching stage and the state of the second matching stage are altered simultaneously.

7 . The method according to claim 1 , wherein the model of the impedance matching network comprises a circuit model.

8 . The method according to claim 1 , wherein the model of the impedance matching network comprises a transmission parameter model, a scattering parameter model, or a parameter model derivable from the transmission parameter model or the scattering parameter model.

9 . The method according to claim 1 , wherein the impedance matching network has an L, T, inverse L or n configuration.

10 . The method according to claim 1 , wherein the alteration target value is determined for the respective reactance of each of the first matching stage and the second matching stage from the intermediate impedance and a model of each of the first matching stage and the second matching stage, and wherein both of the state of the first matching stage and the state of the second matching stage are altered based on the alteration target values.

11 . The method according to claim 10 , wherein the alteration target values are linearly independent.

12 . An impedance matching arrangement comprising:

a. an impedance matching network having an input for connection of an RF power generator and an output for connection to a load, the impedance matching network comprising at least two matching stages, each matching stage having a respective alterable reactance,

b. a model of the impedance matching network,

c. an impedance measuring device for measuring an input impedance,

d. at least one look-up table containing values that allow an intermediate impedance to be deduced from the input impedance, the intermediate impedance being an impedance that occurs between the two matching stages,

e. a determining device for determining the intermediate impedance by:

determining an input admittance based on the measured input impedance,

determining a position of a mechanically alterable reactance or a circuit state of an electronically alterable reactance as a present state value of at least one of the two matching stages,

determining an alteration target value for the respective reactance of at least one of the two matching stages from the intermediate impedance and the model of the impedance matching network, the alteration target value being determined based on an intermediate impedance target value, and

f. a setting device for altering a state of at least one of the two matching stages based on the determined alteration target value.

13 . A plasma system comprising an impedance matching arrangement according to claim 12 , and an RF-excited plasma process apparatus as the load connected to the output of the impedance matching network.

14 . The method according to claim 1 , wherein determining the position of the mechanically alterable reactance includes determining a motor position of at least one of a motor drive of the first matching stage and a motor drive of the second matching stage.

15 . The method according to claim 14 , wherein determining the intermediate impedance includes determining a reactance corresponding to the determined motor position and determining the intermediate impedance based on the determined input admittance and the determined reactance corresponding to the determined motor position.

16 . The method according to claim 15 , wherein determining the intermediate impedance based on the determined input admittance and the determined reactance corresponding to the determined motor position includes altering the input admittance such that the input admittance lies on an ellipse representing variation of an imaginary part of the intermediate impedance in the admittance plane.

17 . A non-transitory computer-readable medium having instructions stored thereon, the instructions, when executed by a computer processor, causing performance of a method for controlling an impedance matching network, the impedance matching network having an input for connection of an RF power generator and an output for connection to a load, the impedance matching network comprising at least a first matching stage and a second matching stage connected in series, each of the first matching stage and the second matching stage having a respective variable reactance, the method comprising:

a) determining an intermediate impedance that occurs between the first matching stage and the second matching stage by:

determining an input admittance based on the from a measured input impedance,

determining a position of a mechanically alterable reactance or a circuit state of an electronically alterable reactance as a present state value of at least one of the first matching stage and the second matching stage,

b) determining an alteration target value for the respective reactance of at least one of the first matching stage and the second matching stage from the intermediate impedance and a model of the impedance matching network, the alteration target value being determined based on an intermediate impedance target value,

c) outputting a signal for altering a state of at least one of the first matching stage and the second matching stage based on the alteration target value, and

d) repeating steps a) to c).