Impedance matching circuit, plasma process supply system and plasma process system

Abstract

The invention relates to an impedance matching circuit (1) for a plasma process supply system and a plasma process system designed for powers of ≥ 500 W and frequencies in the range from 2 MHz to 100 MHz, comprising: a) a matching unit (2, 2a-2f) having one or more reactances (C4a, L4a, C4b, C4b'; L4b, C5a, C5a', L5a, C5b, C5b', C5d, C5d', L5d, L5e, C5f', L5f), b) a resonator (3), c) wherein the impedance matching circuit (1) is designed for operation at a predefined HF power signal with a predefined basic frequency (f0) and AFT bandwidth (20), limited by a predefined upper AFT frequency (f2) and a predefined lower AFT frequency (f1), wherein the resonator (3) is designed to influence the HF power signal slightly, in particular to not influence same, at the basic frequency (f0), and to damp the HF power signal and / or influence it in the phase at least at one of the two AFT frequencies (f1, f2), in particular at both AFT frequencies (f1, f2).

Description

[0001] Impedance matching circuit, plasma process supply system and plasma process system

[0002] The invention relates to an impedance matching circuit for a plasma process supply system and a plasma process system designed for powers > 500 W, in particular > 2 kW and frequencies in the range from 2 MHz to 100 MHz, in particular in the range from 10 MHz to 50 MHz, a plasma process supply system and a plasma process system.

[0003] Such an impedance matching circuit can be used in systems in which a load is supplied with electrical power, particularly high-frequency power. "High frequency" is also abbreviated to "HF" below. Here, "HF" refers to frequencies in the range from 2 MHz to 100 MHz, particularly in the range from 10 MHz to 50 MHz.

[0004] In such a system, the load impedance should be matched to the impedance of the power supply, otherwise power reflection may occur. Power reflection has a direct impact on the efficiency of a system; it reduces its efficiency.

[0005] An example system in which an impedance matching circuit may be used may be a plasma processing system.

[0006] Such a plasma processing system may, for example, be a system in which a load, e.g. a plasma processing arrangement, is supplied with electrical power.

[0007] Such a plasma processing arrangement can, for example, be a plasma processing chamber that is used for industrial plasma processes such as the surface treatment of workpieces, semiconductor manufacturing with plasma or the processing of workpieces with gas lasers.

[0008] In such an application, the plasma process arrangement serves to generate plasma.

[0009] For this purpose, a plasma processing arrangement may comprise an electrode which is fed with a high-frequency power signal for generating the plasma, hereinafter referred to as the RF power signal.

[0010] Typically, a high-power and especially high-voltage power supply is required, for which the plasma processing arrangement can be connected to a high-frequency power supply, hereinafter referred to as RF power supply.

[0011] The plasma process occurring in the plasma processing system has the problem that the electrical load impedance of the plasma processing system, which occurs during the process, depends on the conditions within the plasma processing system and can vary greatly. In particular, the properties of the workpiece, electrode, and gas conditions are important.

[0012] For this reason, an impedance matching circuit is usually required to transform the load impedance to a nominal impedance of the RF power supply. Such an impedance matching circuit is typically placed between an RF power supply and the plasma processing device, usually in close proximity to the plasma processing device.

[0013] An impedance matching circuit is typically an arrangement that may contain inductances and / or capacitances.

[0014] For complex problems where it is important to be able to quickly change the impedance, semiconductor-switched impedance matching circuits are often used. These semiconductor switching elements can be used to switch inductors and / or capacitances in impedance matching circuits on and off. Control circuits can be used to control the switching on and off of the semiconductor switching elements. An example of such a semiconductor-switched impedance matching circuit is disclosed and described in DE 20 2020 102 084 U1.

[0015] Due to their principle, such semiconductor-switched impedance matching circuits have only a discrete set of possible output impedances at a given frequency.

[0016] By using an AFT (Auto-Frequency-Tuning) capable RF power supply, the range of possible output impedances can be increased because the RF power supply has a frequency band of possible frequencies available to it instead of a single frequency, which is called its bandwidth.

[0017] This results in a trajectory of possible output impedances across frequency for each discrete output impedance. The length of this trajectory is considered a quality characteristic of an impedance matching circuit. The longer the trajectory, the more possible output impedances can be set. However, the bandwidth of the AFT-capable RF power supply continues to limit the set of possible output impedances.

[0018] The present invention is therefore based on the object of providing an impedance matching circuit which increases the length of the trajectory of possible output impedances over frequency and thus increases the set of possible output impedances.

[0019] This object is achieved by an impedance matching circuit according to independent claim 1. Advantageous developments of the invention emerge from the subclaims and / or the description.

[0020] According to the present invention, an impedance matching circuit for lines > 500 W and frequencies in the range from 2 MHz to 100 MHz is disclosed, in particular for a plasma process supply system and plasma process system, comprising: a) a matching unit comprising one or more reactances, e.g. coils and / or capacitors, b) a resonator, c) wherein the impedance matching circuit is designed for operation at a predetermined RF power signal with a predetermined fundamental frequency and AFT bandwidth, limited by a predetermined upper AFT frequency and a predetermined lower AFT frequency, d) wherein the resonator is designed to slightly influence the RF power signal at the fundamental frequency, in particular not at all, and to attenuate and / or influence the phase at least at one of the two AFT frequencies, in particular at both AFT frequencies.This makes it possible to increase the number of possible output impedances of the impedance matching circuit for frequencies within the bandwidth of the AFT-capable RF power supply, resulting in an impedance matching circuit that improves the length of the trajectory of possible output impedances over frequency. This also allows for a reduction in the number of components, such as reactances such as coils and / or capacitors, thus achieving a more compact design.

[0021] It is particularly advantageous if the resonator is designed to slightly, in particular not, influence the RF power signal at the fundamental frequency and to both damp and influence the phase at least at one of the two AFT frequencies, in particular at both AFT frequencies.

[0022] A "minor influence" means an influence that is very small within the scope of what is technically reasonably feasible and in any case smaller, in particular by a factor of 10, preferably by a factor of 100 smaller than that at the upper or lower AFT frequency.

[0023] The impedance matching circuit can be implemented either with fixed reactances or with discrete reactances that can be switched on and off using semiconductors. The output impedance of an impedance matching circuit with fixed reactances can be varied over frequency. In a semiconductor-switched impedance matching circuit, the output impedance can also be varied by switching reactances on and off. Semiconductor switches, such as PIN diodes or metal-oxide-semiconductor field-effect transistors (MOSFETs), can be used for this switching, which can be controlled via a drive circuit.

[0024] Impedance matching circuits with fixed reactances offer the advantage of being simple and inexpensive to implement and do not require expensive components such as semiconductor switching elements. Semiconductor-switched impedance matching circuits offer significantly greater variability in their output impedance and can also change the output impedance very quickly. Both of these factors lead to a significantly broader range of possible applications for semiconductor-switched impedance matching circuits.

[0025] The resonator of the impedance matching circuit can be designed as a bandpass filter. This allows for a particularly simple, component-saving design.

[0026] The resonator of the impedance matching circuit can comprise a series and / or parallel resonator. This allows the design of the impedance matching circuit to be variable and adapted to different circumstances. For the precise implementation of the resonator, one or more discrete capacitors and / or one or more discrete inductors can be used. The capacitors and / or inductors can be replaced individually or in combination by line arrangements. A resonator can, for example, be implemented as a 4-wire line that is open-ended or terminated with a short circuit. is the wavelength associated with the resonant frequency.

[0027] In one aspect, the resonator is placed downstream of the matching unit. This can improve the trajectory properties.

[0028] In one aspect, the resonator and the matching unit are constructed independently of each other. This means that the resonator and matching unit do not share any components. This allows the properties of the resonator to be tuned particularly well.

[0029] For implementation with discrete reactances, a planar inductor on a circuit board and / or a vacuum or ceramic capacitor and / or a capacitor formed by exposed conductive surfaces on a circuit board can be used. The components can be connected in series or parallel. Implementing the resonator with a line arrangement can enable the additional input of a second frequency at the end of the impedance matching circuit. Even with implementation with a line arrangement, a resonator can be provided that effectively acts either as a parallel or a series resonator.

[0030] Furthermore, the impedance matching circuit can be used in a plasma process supply system or a plasma processing system. Such a plasma process supply system can comprise, in addition to the impedance matching circuit, an AFT-capable RF power supply for providing the RF power signal. The impedance matching circuit can be electrically connected to the AFT-capable RF power supply and can be designed to be connected to a plasma processing arrangement.

[0031] In a plasma processing system, such a plasma processing arrangement may be present and connected to the plasma processing supply system. The plasma processing arrangement may be supplied with power from the RF power signal via the plasma processing supply system.

[0032] Preferred embodiments of the invention are illustrated schematically in the drawings and are explained in more detail below with reference to the figures of the drawing.

[0033] They show:

[0034] Fig. 1 is a schematic view of a first embodiment of a plasma process system with an impedance matching circuit according to the invention;

[0035] Fig. 2a,b,c,d various circuit diagrams of resonators;

[0036] Fig. 3a shows an AFT-capable RF power supply and its output power in a diagram;

[0037] Fig. 3b shows a resonator as a bandpass filter and its transfer function; Fig. 4a, b shows various circuit diagrams of matching units without a semiconductor switching element;

[0038] Fig. 5a to f various circuit diagrams of matching units with semiconductor switching element.

[0039] Fig. 1 shows an embodiment of an exemplary plasma process system 9. The plasma process system 9 has a plasma process supply system 6 and a plasma process arrangement 8. The plasma process supply system 6 comprises an impedance matching circuit 1 according to the invention and an AFT-capable RF power supply 7. The impedance matching circuit 1 has a matching unit 2 and a resonator 3. The matching unit 2 has one or more reactances. The reactances can be coils and / or capacitors. Examples of such matching units 2 are shown by way of example in Figures 4a to 4b. In addition, the impedance matching circuit 1 can have semiconductor switching elements 4 and a drive circuit 5, which can switch reactances on and off in order to change the output impedance. Examples of such matching units 2 are shown in Figures 5a to 5f.

[0040] Resonator 3 can be implemented in different ways. Several possibilities for resonator 3 are shown in Figs. 2a to 2d.

[0041] Fig. 2a to 2d show a selection of possibilities for the resonator 3 of the impedance matching circuit 1 according to the invention. The resonators 3 each have two connection options 12a, 12b, via which a resonator 3 can be integrated into the impedance matching circuit 1.

[0042] Fig. 2a shows a series resonator as resonator 3, which has an inductance L3a and a capacitance C3a connected in series. This series resonator is connected between the two connection points 12a, 12b. With appropriate design of the inductance L3a and the capacitance C3a, it can have a transfer function as shown in Fig. 3b.

[0043] Fig. 2b shows a parallel resonator comprising an inductance L3b and a capacitance C3b connected in parallel. This parallel resonator is connected between the two connection points 12a, 12b and ground. With appropriate design of the inductance L3b and the capacitance C3b, it can exhibit a transfer function as shown in Fig. 3b.

[0044] Fig. 2c shows a parallel resonator implemented by a line arrangement 10c. The line arrangement 10c can comprise a coaxial or microstrip line. It can be tuned to the characteristic impedance at that point, for example, 50 Ω. Its length can preferably be λ / 4, with the wavelength of the fundamental frequency being fO (shown in Fig. 3). The line arrangement 10c has an outer conductor 13c connected to ground. The line arrangement 10c has a signal conductor 14c, which is also connected to ground at one end and to the two connection options 12a, 12b at the other end. This creates a parallel resonant circuit which, at the fundamental frequency fO, does not influence the signal flowing between the two connection options 12a, 12b, but causes attenuation and / or phase shift at adjacent frequencies.

[0045] Fig. 2d shows the same parallel resonator as Fig. 2c, except that here there is the option of feeding in a second additional frequency via a second frequency feed 11. For this purpose, the resonator 3 has a, in particular discrete, capacitance C3d, which is connected in series with the line arrangement 10d and is dimensioned large enough that the resonator 3 acts like a short circuit for the fundamental frequency f0. If this effect as a short circuit is not sufficient, this can be compensated for by adjusting the length of the line arrangement 10d. Thus, this resonator 3 cannot influence the signal flowing between the two connection options 12a, 12b at the fundamental frequency f0, but can cause attenuation and / or phase shift at adjacent frequencies. The line arrangement 10d has an outer conductor 13d and a signal conductor 14d.

[0046] It is also possible to realize the series resonant circuit from Fig. 2a with a / 4 line (not shown).

[0047] Fig. 3a shows an AFT-capable RF power supply 7 and its output power P in a diagram that represents the power versus frequency f. The possible output power of the AFT-capable RF power supply 7 is constant across the entire AFT bandwidth 20. This means that the RF power supply 7 can deliver an output signal with a power spanned within the rectangle of f1, f2 from the lower AFT frequency f1 to the upper AFT frequency f2.

[0048] Fig. 3b shows two possible embodiments of the resonator 3 from Fig. 2a, 2b. Since this acts as a bandpass filter, a transfer function can be represented for it. Function 22 shows the attenuation curve in dB. At the fundamental frequency f0 the attenuation is close to or equal to zero, i.e. there is comparatively little or no attenuation. At the lower AFT frequency f1 and at the upper AFT frequency f2 the attenuation increases. At the same time the phase is influenced, which is shown in the dashed line 23. At the fundamental frequency f0 the phase influence is zero or close to zero. Towards the upper AFT frequency f2 the phase shift increases. Towards the lower AFT frequency f1 the phase shift decreases.Accordingly, resonator 3 is designed to slightly, in particular not at all, influence the RF power signal at the fundamental frequency f0 and to damp and / or influence the phase at least at one of the two AFT frequencies f1, f2, in particular at both AFT frequencies f1, f2. The range between the two AFT frequencies f1, f2 represents the AFT bandwidth 20.

[0049] In Fig. 4a and Fig. 4b two different circuit diagrams of adaptation units 2 are shown, which in these embodiments do not have a semiconductor switching element 4.

[0050] Fig. 4a shows a typical L-shaped matching unit 2 comprising an inductor L4a and a capacitor C4a. The inductor L4a is connected from input 15 to ground. The capacitor C4a is connected between input 15 and output 16. This matching unit 2 is designed to convert the impedance ZI to the impedance Z0.

[0051] Fig. 4b shows a typical n-type matching unit comprising an inductor L4b and two capacitors C4b, C4b'. The inductor L4b is connected from input 15 to ground. The capacitor C4b is connected between input 15 and output 16. The capacitor C4b' is connected from output 16 to ground.

[0052] This matching unit 2 is designed to convert the impedance ZI into the impedance ZO.

[0053] In Fig. 5a to f are various circuit diagrams of adaptation units 2a-2f, which in these embodiments are designed with one or more semiconductor switching elements 4a-4f and one or more control circuits 5a-5f.

[0054] Fig. 5a shows a typical L-shaped matching unit comprising an inductor L5a and two capacitors C5a, C5a'. The inductor L5a is connected between input 15 and output 16. The capacitors C5a, C5a' are connected in series, and this series circuit is connected from input 15 to ground. The capacitor C5a' is connected directly to ground. A semiconductor switching element 4a is connected in parallel with the capacitor C5a'. This semiconductor switching element 4a is connected to a control circuit 5a, which is configured to switch the semiconductor switching element 4a on and off. When the semiconductor switching element 4a is switched on, the capacitor C5a' is short-circuited, and the resulting capacitance of the series circuit is equal to the capacitance of the capacitor C5a.When the semiconductor switching element 4a is turned off, the capacitor C5a' is not short-circuited and the resulting capacitance value of the series circuit is equal to that of a series circuit of the two capacitors C5a, C5a'.

[0055] This adaptation unit 2a is designed to convert the impedance ZI into the impedance Z0 and can be changed by the control circuit 5a.

[0056] Fig. 5b shows a typical matching unit 2b comprising two capacitors C5b, C5b'. The capacitor C5b is connected in series with a semiconductor switching element 4b. This series circuit comprising capacitor C5b and semiconductor switching element 4b is connected between input 15 and output 16. The capacitor C5b' is connected in parallel with the semiconductor switching element 4b. The semiconductor switching element 4b is connected to a control circuit 5b configured to switch the semiconductor switching element 4b on and off. When the semiconductor switching element 4b is switched on, the capacitor C5b' is short-circuited, and the resulting capacitance value of the matching unit 2b is equal to that of the capacitor C5b. When the semiconductor switching element 4b is switched off, the capacitor C5b' is not short-circuited, and the resulting capacitance value of the matching unit 2b is equal to that of a series circuit of the two capacitors C5b, C5b'.

[0057] This adaptation unit 2b is designed to convert the impedance ZI into the impedance Z0 and can be changed by the control circuit 5b.

[0058] Fig. 5c shows a typical matching unit 2c, which comprises a series connection of the two matching units 2a, 2b from Fig. 5a and Fig. 5b. This series connection is connected between input 15 and output 16. The function of the matching unit 2c, i.e., the series connection of the matching units 2a, 2b, results from the functionalities of the individual matching units 2a, 2b described in the descriptions of Fig. 5a and Fig. 5b, only combined as a series connection. This matching unit 2c is designed to convert the impedance ZI into the impedance Z0 and can be modified by the control circuit 5a, 5b.

[0059] Fig. 5d shows a typical L-shaped matching unit 2d comprising an inductor L5d, a capacitor C5d, three further capacitors C5d', and three semiconductor switching elements 4d. The inductor L5d is connected between input 15 and output 16. The capacitor C5d is connected in series with a parallel circuit comprising the three further capacitors C5d' and the three semiconductor switching elements 4d. This parallel circuit comprises three parallel series circuits comprising a capacitor C5d' and a semiconductor switching element 4d. Each semiconductor switching element 4d is connected to a control circuit 5d configured to switch the semiconductor switching elements 4d on and off. When one of the three semiconductor switching elements 4d is switched on, the capacitor C5d is connected in series with one of the three capacitors C5d'. This series circuit is connected from input 15 to ground.If one or both of the additional semiconductor switching elements 4d are also switched on, the capacitor C5d is connected in series with a parallel circuit of two or three of the capacitors C5d'. This parallel circuit can be expanded by additional parallel series circuits, but can also consist of only two parallel series circuits. If all semiconductor switching elements 4d are switched off, the capacitors C5d and C5d' have no influence on the impedance of the matching unit 2d. In this case, the impedance results solely from the inductance L5d.

[0060] This matching unit 2d is designed to convert the impedance ZI into the impedance ZO and can be changed by the control circuit 5d.

[0061] Fig. 5e shows a typical L-shaped matching unit 2e, which includes the matching unit 2d from Fig. 5d. In addition to the matching unit 2d described in the description of Fig. 5d, this matching unit 2e here includes an additional inductance L5e and an additional semiconductor switching element 4e. The inductance L5e is connected in series with the semiconductor switching element 4e. The series circuit is connected in parallel with the inductance L5d. The semiconductor switching element 4e is connected to a control circuit 5e, which is configured to switch the semiconductor switching element 4e on and off. When the semiconductor switching element 4e is switched on, the two inductances L5e, L5d are connected in parallel. When the semiconductor switching element 4e is switched off, the inductance L5e has no influence on the impedance of the matching unit 2e, and the matching unit 2e corresponds to the matching unit 2d from Fig. 5d.

[0062] This matching unit 2e is designed to convert the impedance ZI into the impedance Z0 and can be changed by the control circuits 5d, 5e.

[0063] Fig. 5f shows a typical L-shaped matching unit 2f, which has an inductance L5f, three additional capacitors C5f, and three semiconductor switching elements 4f. The three semiconductor switching elements 4f are designed as PIN diodes. The inductance L5f is connected between input 15 and output 16. The semiconductor switching elements 4f are each connected in series with a capacitor C5f. These three series circuits are connected in parallel. This parallel circuit can be expanded by additional series circuits connected in parallel, but can also have only two series circuits connected in parallel. Each semiconductor switching element 4f is connected to a control circuit 5f, which is configured to switch the semiconductor switching elements 4f on and off. When one of the three semiconductor switching elements 4f is switched on, one of the three capacitors C5f is connected from input 15 to ground.If one or the other two semiconductor switching elements 4f are also switched on, a parallel circuit of two or three capacitors C5f is connected from the input to ground. If all semiconductor switching elements 4f are switched off, the capacitors C5f have no influence on the impedance of the matching unit 2f. In this case, the impedance is determined solely by the inductance L5f.

[0064] This matching unit 2f is designed to convert the impedance ZI into the impedance ZO and can be changed by the control circuits 5f.

[0065] The previously described matching units 2, 2a-2f can be varied; for example, inductors can be used instead of capacitors, depending on the desired matching, or capacitors can be used instead of inductors, depending on the desired matching. The previously described matching units 2, 2a-2f can be used individually or in combination with two or more.

[0066] With the features described above, the number of components, such as semiconductor switching elements or reactances, such as coils and / or capacitors as well as capacitances and / or inductances, can be kept lower, thus achieving a more compact design.

Claims

Claims 1. Impedance matching circuit (1), in particular for a plasma process supply system (6) and a plasma process system (9), designed for powers > 500 W and frequencies in the range from 2 MHz to 100 MHz, comprising: a) a matching unit (2, 2a-2f) having one or more reactances (C4a, L4a, C4b, C4b'; L4b, C5a, C5a', L5a, C5b, C5b', C5d, C5d', L5d, L5e, C5f, L5f), b) a resonator (3), c) wherein the impedance matching circuit (1) is designed for operation with a predetermined RF power signal with a predetermined fundamental frequency (f0) and AFT bandwidth (20), limited by a predetermined upper AFT frequency (f2) and a predetermined lower AFT frequency (f1), d) wherein the resonator (3) is designed to slightly, in particular not, influence the RF power signal at the fundamental frequency (fO) and to damp and / or influence the phase at least at one of the two AFT frequencies (fl, f2), in particular at both AFT frequencies (fl, f2).

2. Impedance matching circuit (1) according to the preceding claim 1, wherein the impedance matching circuit (1) is implemented as an impedance matching circuit (1) with fixed reactances.

3. Impedance matching circuit (1) according to one of the preceding claims, wherein the impedance matching circuit (1) is implemented as a semiconductor-switched impedance matching circuit and has semiconductor switching elements (4a-4f) and a drive circuit (5a-5f) designed to switch reactances (C5a', C5b', C5d', C5f, L5e') on and off.

4. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) is designed as a bandpass filter.

5. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) comprises a series resonator.

6. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) comprises a parallel resonator.

7. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) has a discrete capacitance and a discrete inductance.

8. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) is realized by a line arrangement (10) which effectively acts as a parallel or series resonator.

9. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) is connected downstream of the matching unit (2, 2a-2f).

10. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) and the matching unit (2, 2a-2f) are constructed independently of one another.

11. Impedance matching circuit (1) according to one of the preceding claims, wherein the resonator (3) is designed to slightly, in particular not, influence the RF power signal at the fundamental frequency (fO) and to attenuate and influence the phase at least at one of the two AFT frequencies (f1, f2), in particular at both AFT frequencies (f1, f2).

12. Plasma process supply system (6) comprising an AFT-capable RF power supply (7) for providing the RF power signal and an impedance matching circuit (1) according to one of the preceding claims, wherein the impedance matching circuit (1) is electrically connected to the AFT-capable RF power supply (7) and is designed to be connected to a plasma process arrangement (8).

13. Plasma process system (9) comprising a plasma process supply system (6) according to the preceding claim 12 and a plasma processing arrangement (8), wherein the plasma processing arrangement (8) is provided with the Plasma process supply system (6) is connected and the plasma process supply system (6) is arranged to supply the plasma process arrangement (8) with power of the RF power signal.

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