HK1069674B - Method and device for producing a plasma - Google Patents

Description

Method and apparatus for generating plasma

Technical Field

The invention relates to a method for generating a plasma by means of an induction coil located in a vacuum chamber of a vacuum vessel, and to a device suitable for carrying out the method according to the invention. The invention also relates to the use of the method according to the invention for providing a substrate with a possible reactive coating or for performing a possible reactive etching on the substrate.

Background

When the substrates are subjected to an active treatment in vacuum, as is the case, for example, in the production of semiconductors, a plurality of treatment steps are generally carried out using a plasma generated in a vacuum chamber of a vacuum vessel, suitable examples being the possible active coating of the substrates or the possible active etching of the substrates.

In this regard, it is known that the plasma may be generated by inductive or capacitive means.

For example, EP0271341a1 describes an apparatus for dry etching semiconductor disks, which comprises an induction coil for generating a plasma and an electrode arrangement for extracting ionized particles from the plasma onto a substrate. Also in the apparatus described in US6068784, the energy for generating the plasma is inductively coupled into the vacuum chamber of the vacuum vessel by means of a coil-shaped antenna, in which case the vacuum chamber serves as a reactor. The substrate is mounted on an electrode serving as a substrate carrier, to which a so-called RF (radio frequency) bias or polarization potential is applied.

US5460707 describes a device for capacitively generating plasma, which can also be used for coating purposes. In this case, a magnetic field generated by an additional permanent magnet or electromagnet may be provided for controlling the density distribution of the plasma or generating a plasma having a large local density.

When vacuum treating a substrate, such as is the case when producing semiconductors, it is important to have a very uniform plasma density distribution over the entire surface of the substrate in order to ensure a suitably uniform substrate treatment. For this purpose, it is necessary to shield or compensate all external interference influences, in particular the influence of external fields.

Although shielding of the vacuum vessel, for example using a ferromagnetic housing, is theoretically possible, it is very disadvantageous from a practical point of view, since this housing would add significantly to the weight of the vacuum vessel. Furthermore, it is more difficult to gain access to the vacuum vessel when maintenance or repair work has to be performed.

EP0413283 teaches that planar plasmas can be obtained by means of electrically conductive planar pancake coils, the induction field being generated by connecting a high frequency voltage source to the pancake coils and coupling taking place in a dielectric shield.

US6022460 suggests that the electromagnetic field generated by a pair of helmholtz coils should be allowed to act on a plasma which is generated (or at least co-generated) inductively, for example by means of a flat coil or a coil having the form of a vacuum bell, to which a high-frequency alternating voltage is applied. Applied to the pair of helmholtz coils is a combination of direct and alternating current, thereby producing a weak magnetic field modulated by the alternating current component, which modulation is described as "vibration of the magnetic field". According to the patent, this is mainly used to obtain an increase in plasma density and an improvement in plasma uniformity.

One of the drawbacks of the apparatus for generating a plasma described in US6022460 consists of the addition of a pair of helmholtz coils, which makes it more difficult to achieve a compact design and increases the cost of the apparatus. Since the factors of high frequency technology require the decoupling of the induction coil from the pair of helmholtz coils, it is absolutely necessary that the induction coil be spatially separated from the helmholtz coils.

The invention thus makes it possible to obtain a method and a device for generating a high-density plasma which are able either to avoid the disadvantages associated with the prior art or to be affected only to a small extent by these disadvantages. Other tasks of the invention are described in detail below.

Disclosure of Invention

The invention relates to a method for generating a plasma which is co-generated at least in a vacuum chamber (1a) of a vacuum vessel (1) by means of at least one induction coil (2) supplied with an alternating current, wherein a gas for generating the plasma is introduced into the vacuum chamber (1) via at least one inlet (3), and the vacuum chamber (1a) is subjected to the suction action of at least one pumping device (4), and wherein a direct current which may be modulated and preferably is pulsed flows through the induction coil (2) for the purpose of influencing the plasma density.

The invention further relates to the use of the method according to the invention for the possible reactive coating and/or the possible reactive etching of a substrate.

The invention also relates to an apparatus suitable for plasma treatment, comprising at least one induction coil (2) for at least co-generating (co-generating) a plasma in a vacuum chamber (1a) of a vacuum vessel (1), wherein the vacuum chamber (1a) is provided with at least one inlet (3) for receiving a gas for generating the plasma, and with a pump device (4), wherein the induction coil (2) is connected to one or more generators for supplying the induction coil with alternating current and direct current, which may be pulsed in a unipolar or bipolar manner.

Drawings

Fig. 1 shows a schematic view of an apparatus suitable for plasma processing according to the present invention.

FIG. 2 shows normalized etch depths along a diagonal of a wafer, where the plasma used for etching is co-generated at least by induction coils energized with direct current and alternating current (curve I) or alternating current only (curve II).

Detailed Description

The apparatus of the invention suitable for generating plasma comprises a vacuum vessel 1 with a vacuum chamber 1a which can be evacuated by one or more pumping devices 4.

In a preferred embodiment, the vacuum vessel 1 comprises an outer envelope 20 of a metal, such as stainless steel or aluminium, in order to ensure good tightness of the vacuum vessel and to shield it against stray external fields in particular. On the vacuum side, the metal outer shell 10 of the vacuum vessel 1 is preferably provided with a dielectric inner shell 7, which inner shell 7 can, for example, be self-supporting or attached as a shell to the inside of the outer shell 10. Dielectric materials are preferred which are not only as inert as possible with respect to the gases used for the reactive coating and etching processes, which may contain elements such as chlorine and fluorine, but which are also as transparent as possible to the coupling power supply. Preferred dielectric materials include polymeric materials, particularly ceramic materials, quartz and alumina. For example only the inner wall of the vacuum vessel 1 is either covered or coated in whole or in part with a dielectric material or is made of a dielectric material, while the upper and lower sides of the vacuum vessel 1 are provided with metal connections (couplings) as described in WO 00/19483. The vacuum vessel 1 described in EP0413283 is provided with a dielectric shield which is mounted for example in the upper wall of the vacuum vessel 1.

The above description of the vacuum vessel 1 should be understood as being merely an example, for the purpose of illustrating and not limiting the invention.

The vacuum chamber 1 comprisesOne or more gas inlets 3 for admitting a gas for generating the plasma. The gas, which may consist of a single gaseous mixture or of a mixture of several gaseous mixtures, is selected by appropriate consideration of the chemical composition and physical parameters of the substrate 9 to be treated and of the variations of the surface of the substrate to be obtained. If the surface of the substrate is to be cleaned (sputter etching), the gas can comprise, for example, argon or other inert gas, while the gas used for the reactive etching process can comprise, for example, chlorine (Cl)₂) Silicon tetrachloride (SiCl)₄) Boron trichloride (BCl)₃) Carbon tetrafluoride (CF)₄) Trifluoromethane (CHF)₃) Sulfur hexafluoride (SF)₆) And/or oxygen (O)₂). When the substrate must be coated with a thin film (for example, by chemical vapor deposition- -CVD or plasma-enhanced chemical vapor deposition- -PECVD), the organometallic compound methane (CH) is used₄) Silicon hydride (SiH)₄) Ammonia (NH)₃) Nitrogen (N)₂) Or hydrogen (H)₂) Is feasible. The aforementioned gaseous compounds and the method for treating the substrate 9 should also be understood as being merely an example, merely for the purpose of explanation and not limitation of the present invention.

The flow of the gas and the power supply of the pump device (4) are preferably such that the pressure in the vacuum chamber 1a of the vacuum container 1 is in particular in the range from 0.01 to 10Pa, preferably in the range from 0.05 to 0.2.

The apparatus of the invention comprises at least one induction coil 2 by means of which the plasma generated in the vacuum chamber 1a of the vacuum vessel 1 is at least co-generated. The induction coil 2 is preferably arranged in the vacuum vessel 1 and/or the vacuum chamber 1a so as not to be exposed to plasma, in order to avoid, for example, electrically conductive interference coatings or other coatings being deposited on the induction coil 2 or damage of the induction coil 2 caused by plasma. The induction coil 2 is preferably separated from at least part of the vacuum chamber 1a in which the plasma is generated by a dielectric shield, for example a dielectric inner envelope 7. The induction coil 2 is preferably also arranged outside the vacuum chamber 1 a.

The device of the invention comprises one or more induction coils 2, preferably one or two induction coils 2, in particular one induction coil 2.

In a preferred embodiment of the induction coil 2, said coil comprises windings wound directly on the vacuum chamber 1a and/or preferably on a dielectric inner envelope 7 mounted inside the vacuum chamber. In the inventive device shown in fig. 1, the coil winding is wound, for example, on the side wall of the dielectric inner envelope 7. In this case, the uniformity of the induction field may be affected by, for example, the number and arrangement of windings of the induction coil 2 and the geometry of the dielectric inner shell 7.

In another embodiment, the induction coil 2 takes the form of a flat or planar coil comprising a plurality of spiral windings or a series of windings arranged in concentric rings, for example as described in EP 0413282. The flat coil has, for example, a preferably circular or oval shape. The term "flat" or "planar" means that the ratio of the thickness of the coil to the extent of the coil in two other directions at appropriate angles to the thickness direction is less than 0.3, preferably less than 0.2. EP0413282 discloses that the flat coil is preferably arranged close to a dielectric shield located in the housing 10 of the vacuum vessel, said shield acting as a dielectric window allowing coupling of the inductive field. Of course, it is also possible to arrange the flat coil close to the dielectric inner housing 7.

In another embodiment the induction coil 2 has the form of a vacuum clock as described in US 6022460.

It has been found that the density of the plasma at least co-generated by the induction coil 2 is affected and, in particular, the uniformity of the plasma is increased when both an alternating current and a direct current are applied to the induction coil 2.

An alternating current is applied to the induction coil 2 for coupling a high frequency power supply to the vacuum vessel for at least co-generating a plasma. For this purpose, the induction coil 2 is connected to a high-frequency generator 6, preferably via an adapter network 13. The adapter network 13 serves to adjust the initial resistance of the high-frequency generator 6 and the impedance of the induction coil 2 and the vacuum chamber 1a and/or the plasma generated in the vacuum chamber clock, so that an efficient coupling of the high-frequency power supply is possible.

In the present invention, the concept "high frequency" is used for electromagnetic vibrations or waves having a frequency in the range of 10KHz to 3 GHz. The high-frequency generator 6 operates in a wide high-frequency spectrum range, preferably 100KHz to 100MHz, more preferably 100KHz to 14MHz, and further preferably 400KHz to 2 MHz.

The choice of the preferred frequency also depends on the geometry of the induction coil 2. Thus, for a non-flat three-dimensional induction coil 2 to be obtained, for example, when winding a coil winding around the dielectric inner case 7, in which high-frequency energy is coupled into the vacuum chamber 1a through the volume of space within the winding, the selected frequency is preferably in the range of 100KHz to 2MHz, particularly in the range of 200KHz to 1 MHz. On the other hand, for a two-dimensional flat coil, in which high-frequency energy is coupled into the vacuum chamber 1a through the coil region, the selected frequency will be higher, preferably in the range of 2MHz to 14 MHz. The upper limit of the frequency range is determined because the standard frequency of the high frequency generator widely used in the industry is 13.56 MHz. International communications protocols agree to employ this frequency in industrial use.

It has been found that when a direct current is also applied to the induction coil 2, the density distribution of the plasma is affected and thereby the uniformity of the plasma, for example, at the surface of the substrate 9 is improved. For this purpose, the induction coil 2 is also connected to a dc generator 6', preferably via a low-pass filter 12. The low-pass filter 12, which may comprise, for example, a coil and a capacitor connected in parallel therewith, is preferably designed such that direct current can reach the induction coil 2 when high-frequency current is blocked, so that high-frequency current cannot find its way into the direct current supply.

The direct current may be uniform or modulatable, for example it may be pulsed in a unipolar or bipolar manner. Bearing in mind the number of windings of the induction coil 2, the direct current is regulated so that the average and absolute value of the product of the number of windings and the direct current is between 10 and 1000, preferably between 100 and 400 ampere windings. The number of windings of the induction coil 2 is preferably at least 7, more preferably a minimum value of 10, even more preferably a minimum value of 12, since the current required for a uniform density distribution of the generated plasma will increase when the number of windings is reduced, so that the requirements on the dc generator 6' and the low-pass filter 12 will increase.

The density distribution of the plasma can be measured, for example, using a langmuir detector. For sputter etch and reactive etch processes, and possibly for reactive coating processes, the uniformity of the plasma density distribution can also be measured by measuring the etch depth and/or coating thickness distribution, since the uniformity of the plasma density distribution over the area of the substrate affects the uniformity of the etch depth distribution and/or coating thickness distribution along the substrate cross-section.

For thermally oxidized silicon wafers, for example, the etch depth can be measured using, for example, an ellipsometer, measuring the thickness of the silicon oxide layer prior to etching, on, for example, a grating covering the entire surface of the silicon wafer or along the diameter of the silicon wafer. The thickness of the remaining silicon oxide is then measured after the etching process is complete. The etching thickness can be obtained by the thickness difference of the silicon wafer before and after etching.

The method can be used to measure coating thickness in a similar manner.

The uniformity of the distribution, for example of the etching thickness, the plasma density or the coating thickness, for example along a cross section of the substrate 9 can be characterized by a so-called uniformity index, which is defined as follows:

uniformity index ═ (max-min)/(max + min)

Wherein the maximum and minimum values are the maximum and minimum values of the characteristic distribution over the entire surface area of the substrate 9 or along a cross section of the substrate, respectively. The uniformity index is usually expressed as a percentage.

It is preferable that the direct current applied to the induction coil 2 is such that the uniformity index of the plasma density distribution, the etching depth or the coating depth, for example, along an optional cross section of the substrate 9 or at a specific portion of the entire surface of the substrate 9 is not more than 10%, preferably not more than 7.5%, more preferably not more than 5%.

In a further preferred embodiment of the device according to the invention, the device comprises a pair of electrodes 5a and 5b spaced apart by a certain distance. In the special design of the vacuum processing chamber described in WO00/19483, the electrodes 5a and 5b can be formed, for example, by a metal connection between the upper and lower housing walls of the vacuum vessel 1, which are electrically separated by a side wall composed of a dielectric material. US6068784 describes an arrangement of three electrodes in which the base plate 8 serves as the cathode, the side wall of the vacuum vessel as the anode and the shell wall of the upper dome-shaped projection of the vacuum vessel as the third electrode.

In a particularly preferred embodiment, one electrode 5a of the electrode pair 5a and 5b is formed by a base plate 8, the base 9 is pressed against the base plate 8, and the base 9 is fixed to the base plate 8 by customary electrostatic or mechanical holding and/or centering means (sometimes referred to as a wafer chuck for wafer substrates). The substrate plate itself is typically electrically insulated from the enclosure 10 of the vacuum chamber. When an electrical connection is present, the counter electrode 5b is constituted by an electrical connection of, for example, the upper wall or end face of the vacuum chamber. In a particularly preferred variant, the possibly circular base plate 8, which is usually referred to as dark space shield, is surrounded by a ring serving as counter electrode. The vacuum environment in vacuum chamber 1a results in insulation between the base plate 8 on top of the dark space shield and the dark space shield. In its lower part, the dark space shield is fixed to the base plate 8-although electrically separated from the latter-so that the dark space shield is centered with respect to the annular ceramic insulator.

The electrode pair 5a, 5b may be connected to a direct current power supply, an alternating current power supply, or to both a direct current and an alternating current power supply, which may be pulsed in a unipolar or bipolar manner, for example. The plasma is capacitively excited by a voltage, which may also be referred to as a bias voltage, applied across the pair of electrodes 5a, 5 b.

Preferably, a direct or alternating voltage, in particular a high-frequency alternating voltage with a frequency of between 100KHz and 100MHz, is applied to the electrode pair 5a, 5 b. When choosing a suitable frequency of the alternating voltage, it is preferred to take into account the influence on the substrate 9 and/or the vacuum chamber 1a, as described in US6068784, column 4, lines 23 to 52, and this discussion is incorporated herein by reference. In a preferred embodiment of the invention, the base plate 8 serves as the electrode 5a, the dark space shield as the counter electrode 5b, the base plate 8 is connected to a high-frequency generator 11, preferably at a frequency of more than 3MHz, particularly preferably more than 10MHz, and the dark space shield is grounded.

Figure 1 shows a schematic cross-sectional view of a preferred embodiment of the device of the present invention. The vacuum vessel 1 comprises a tank 10, the tank 10 being made of, for example, stainless steel, capable of being evacuated, which encloses a vacuum chamber 1a and comprises a dielectric inner envelope 7 composed of, for example, quartz or alumina. The induction coil 2 is wound around the dielectric inner housing and is connected to the alternator 6 through an adapter network 13 and to the dc generator 6' through a low pass filter 12, ending the circuit configuration by grounding. The substrate plate 8, on which the substrate 9 is supported, serves as the electrode 5a, surrounded by a circular dark space shield arranged in a central position, serving as the counter electrode 5 b. The vacuum chamber 1a is subjected to the suction action of the pump device 4. The upper shell wall of the vacuum vessel 1 is provided with a gas inlet 3 in its centre.

In the embodiment of the arrangement shown in fig. 1, which is designed for processing wafers having a diameter of 200mm, the diameter of the dielectric inner shell is up to 275 mm. The distance between the base plate 8 and the upper housing wall of the vacuum vessel is 180 mm. The induction coil 2 wound around the dielectric inner envelope 7 has a diameter of 304mm and comprises 15 windings. Argon for sputter etching is introduced into the vacuum chamber via a gas inlet 3 to an operating pressure of 10^-3. When the dark space shield serving as the counter electrode is grounded, the bias voltage applied to the base plate 8 serving as the electrode 5a has a frequency of 13.56 MHz. The induction coil 2 is connected to an alternator 6 operating at 400KHz through an adapter network 13 consisting of two capacitors. The magnetic field generated by the structure located within the induction coil 2 amounts to 5 gauss. The induction coil 2 is also connected to the dc generator via a low-pass filter 12 comprising a capacitor and a coil connected in parallel therewith. The direct current is selected such that the sputter etch depth distribution along the diameter of the wafer used as substrate 9 has a uniformity index of less than ± 3%, the required direct current reaches about 10A, and a magnetic field of about 12 gauss is generated.

FIG. 2 shows a normalized sputter etch depth profile along the diameter of a circular wafer having a diameter of 300mm, which has been subjected to a thermal oxidation treatment. The measurements were made in the operating conditions described in figure 1 and a similar apparatus with the geometry required to accommodate a 300mm wafer. Curve I in fig. 2 is obtained with the method according to the invention, wherein an alternating current and an additional alternating current of about 10A are applied to the induction coil 2. For comparison, curve II is the sputter etch depth profile obtained when only alternating current is applied to the induction coil. As can be seen from curve 2, the closer to the edge of the wafer substrate 9, the smaller the sputter etch depth when only an alternating current is applied to the induction coil; moreover, the sputter etching depth distribution is not uniform. Curve I shows that the uniformity of the sputter etch depth profile is significantly improved when an additional direct current is applied to the induction coil 2. The sputter etch depth profile is no longer associated with a lack of symmetry for all purposes to be achieved. In particular, the reduction in sputter etch depth toward the wafer edge observed in curve II is now compensated for. The homogenization of the plasma density distribution obtained by the additional applied magnetic field generated by the direct current is reflected in a uniformity index of not more than ± 3%. If so desired, the amperage of the direct current can also be selected to obtain overcompensation for curve II, thereby resulting in a greater etch depth at the edge of the wafer than at its center; at this time, the uncompensated curve II having a convex curvature is "inverted" in a specific sense with respect to the compensation state of the curve I, thereby generating an overcompensated curve having a concave curvature.

In a preferred embodiment of the invention, the apparatus of the invention can be a so-called group of elements as one processing station. The term "group" is to be understood here as a combination of several often different treatment stations, which are assisted by a common transport device, such as a handling robot. A PVD (physical vapor deposition) plant may be referred to herein as another processing station. The individual treatment stations are preferably separated from the transport space by suitable gates.

In this group, the transport device will be used to introduce the substrate 9 into the device of the invention through a transport gate (not shown in fig. 1). The transport device places the substrate 9 on the substrate plate 8, is centered (if necessary) on the substrate plate 8 and held in place. After the gate is closed in a vacuum closed manner, the vacuum chamber is pumped out by a pump device 4; simultaneously with or immediately after evacuation, the substrate 9 is brought to the desired treatment temperature, possibly by means of a temperature-regulating device incorporated in the substrate plate 8. The gas required for generating the plasma is then filled into the vacuum chamber via the gas inlet 3. Then, the plasma is ignited by applying a high-frequency voltage to the induction coil 2 and a high-frequency bias to the base plate 8. While a direct current is applied to the induction coil 2. After completion of the desired treatment, the substrate 9 is taken out of the vacuum vessel 1 via the shutter.

Claims (28)

1. A method for generating plasma, which is at least co-generated in a vacuum chamber (1a) of a vacuum vessel (1) of an apparatus suitable for plasma treatment, which apparatus has at least one induction coil (2) to which an alternating current is passed, wherein gas for generating the plasma is charged into the vacuum chamber (1a) via at least one inlet (3), the vacuum chamber (1a) being subjected to the pumping action of at least one pumping device (4), and a direct current being also applied to the induction coil (2) in order to influence the density of the plasma, characterized in that the direct current is modulated.

2. The method of claim 1, wherein the direct current is pulsed in a unipolar or bipolar manner.

3. A method as claimed in claim 1, wherein the alternating current is generated by a high-frequency generator (6).

4. A method according to claim 3, wherein the high frequency generator (6) operates in the range of 100 to 14000 KHz.

5. The method of claim 1, wherein the direct current and the number of windings of the induction coil are selected such that the average and absolute value of the product of the number of windings and the direct current reaches 10-1000 ampere windings.

6. The method of claim 5, wherein the direct current and the number of windings of the induction coil are selected such that the average and absolute value of the product of the number of windings of the induction coil and the direct current reaches 100 to 400 ampere windings.

7. A method as claimed in claim 1, wherein the direct current is applied to the induction coil (2) via a low-pass filter (12).

8. The method according to claim 1, wherein the pressure in the vacuum chamber (1a) is 0.01 to 10 Pa.

9. A method as claimed in claim 1, wherein the plasma is co-generated or co-excited by a voltage applied to at least one pair of electrodes comprising an electrode (5a) and a counter electrode (5b) spaced apart.

10. The method of claim 9, wherein the voltage is an alternating voltage or a direct voltage.

11. The method of claim 10, wherein the direct current is pulsed in a unipolar or bipolar manner.

12. The method of claim 10, wherein the ac voltage is a high frequency ac voltage having a frequency of at least 1 MHz.

13. A method according to claim 1, wherein the vacuum chamber (1a) comprises a substrate plate (8) for the substrate (9).

14. The method of claim 13, wherein the substrate plate (8) is formed by an electrode (5 a).

15. A method as claimed in claim 14, wherein a dark space shield is used as the counter electrode (5 b).

16. The method of claim 14, wherein the alternating current and the direct current are selected such that the index of uniformity of the plasma density in the plane of the substrate (9) and/or in a plane parallel thereto is not more than 10%.

17. The method of claim 1, wherein the induction coil (2) is separated from at least a part of the vacuum vessel (1) generating the plasma by means of a dielectric inner envelope (7) or a dielectric window.

18. Use of a method according to any one of claims 1 to 17 for the reactive coating of at least one substrate (9).

19. Use of a method according to any of claims 1-17 for reactive etching of at least one substrate (9).

20. An apparatus suitable for performing plasma treatments, comprising at least one induction coil (2) for at least co-generating a plasma in a vacuum chamber (1a) of a vacuum vessel (1), wherein the vacuum chamber (1a) is provided with at least one inlet (3) for admitting a gas for generating the plasma, and the induction coil (2) is connected to one or more generators, which apply an alternating current or a direct current to the induction coil, characterized in that the direct current is modulated.

21. The apparatus of claim 20, wherein the direct current is pulsed in a unipolar or bipolar manner.

22. The apparatus of claim 20, wherein the induction coil (2) is connected to the alternator (6) via an adapter filter (12) and to the dc generator (6') via a low pass filter (13).

23. The device of claim 20, comprising at least one pair of spaced apart electrodes, said pair of electrodes comprising an electrode (5a) and a counter electrode (5 b).

24. The apparatus of claim 20, wherein the vacuum chamber (1a) is provided with a substrate plate (8) for the substrate (9).

25. A device as claimed in claim 24, wherein the substrate plate (8) is formed by the electrodes (5 a).

26. A device as claimed in claim 23, wherein the dark space shield serves as a counter electrode (5 b).

27. The apparatus according to any of claims 20 to 26, wherein the induction coil (2) is separated from at least a part of the vacuum vessel (1) generating the plasma by means of a dielectric inner envelope (7) or a dielectric window.

28. Group of several treatment stations connected by transport gates to a common transport means, wherein at least one treatment station is a device according to claims 20-27.