DE29623199U1 - Device for generating powerful microwave plasmas - Google Patents

Description

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Description Device for generating powerful microwave plasmas

Microwave plasmas are used in technical areas such as the manufacture or processing of components, in microelectronics, in coating, in gas decomposition, in material synthesis or in material cleaning.

In the devices, the microwaves are fed into the plasma chamber with the recipient, i.e. usable space, possibly located therein, from a microwave generator, possibly via a feed line to a waveguide resonator around the plasma chamber by means of coupling points. Ring resonators are particularly common, i.e. ring-shaped waveguide resonators with a short length along their axis, compared to the relatively large diameter of the cross-section of the resonator ring. The axis of the ring resonator and the axis of the plasma chamber, which in this case is designed as a tube, for example, often have the same or a common z-axis.

According to DE 196 00 223.0 - 33, the resonator ring has a rectangular cross-section and the coupling points are, for example, slots in the short cross-section side. Such devices for generating microwave plasmas are very effective. However, there is a need for more homogeneous and more powerful plasma chambers and simpler devices.

The invention relates to a device for generating microwave plasmas, the resonator of which is designed as a coaxial resonator with an inner and outer conductor. As long as conductors form the inner and outer boundaries of the resonator in whole or in part, their shape and the shape of the conductors are arbitrary. Both conductors preferably have a similar, identical or identical axis direction or a common axis, e.g. A vacuum is surprisingly not absolutely necessary when operating the device.

The production is carried out from hollow profiles, preferably e.g. rolled profiles, of an elongated type, which are arranged as a coaxial conductor and can be closed or open at the ends. Two examples that are easy to design are

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Tubes or cylinders of any base area, including square ones, which are arranged inside one another. A wire or solid cylinder as an inner conductor is preferred if coupling is only carried out via the outer conductor.

The resonator can have essentially the same axis in the z-direction as the plasma chamber and the resonator and plasma chamber can be of equal or unequal length along the z-direction.

All components can also be included multiple times in the apparatus.

The invention is therefore based on the narrow resonator ring with a different cross-section, which surrounds the plasma chamber, which is designed as a resonator, for example, like a finger ring around the finger of a hand. Instead, the coaxial resonator is elongated according to the invention and can, for example, be designed as a sleeve like the space of a glove's finger sleeve around the finger over essentially the entire length in the direction of the z-axis. According to the invention, the plasma chamber and resonator are not tied to a specific shape of the hollow body. The inner and outer conductors of the coaxial resonator very preferably have essentially the same direction with their long or longest axis, called the z-axis. The same direction of the axes of the chamber and coaxial resonator is preferred, a common or parallel axis, but a small angle or tilt of up to 90° between the axes of both components is also possible.

Coaxial conductors made from flexible metal hoses, e.g. as spiral strips or interlocking rings are possible, with two hoses arranged one inside the other or one hose coiled around e.g. a tubular or egg-shaped chamber as one conductor forming the resonator. The wall of the plasma chamber can be one conductor, with the shape of the plasma chamber being arbitrary, but continuous formation as a tube, sphere or cylinder is preferred.

In all cases, the chamber and resonator can be of equal or unequal length, whereby one or more chambers, one or more coaxial resonators or divided chambers or coaxial resonators can be formed, e.g. perpendicular to the preferred direction.

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Coupling points such as antennas or preferably slots or recesses can be arranged on the walls of the coaxial resonator, i.e. on the walls common to the chamber, in any number, preferably in the number, geometry and arrangement required for the respective plasma mode selected.

Coupling points of small dimensions do not significantly disturb the resonance in the coaxial resonator. Such coupling points and a larger number of coupling points enable the often preferred homogeneous formation of the plasma in the plasma chamber and resonance in the chamber in the case of suitable dimensions.

The microwave source can be arranged directly, via a possibly regulated supply line or via another resonator at any point on the coaxial resonator, including on the inner boundary, and can be coupled into one or more plasma chambers. The plasma chamber as well as the coaxial resonator can contain a dielectric material such as ceramic, quartz glass or Teflon in whole or in part.

According to this invention, it is no longer necessary to arrange the chamber only inside the resonator. An inner chamber arranged entirely or partially in the inner conductor is possible, as is an outer chamber and possibly both one or more outer chambers and one or more inner chambers, each with a usable space or recipient with dielectric walls of any shape arranged therein.

The coaxial resonator of the invention thus allows for a variety of shapes and configurations. The plasma chamber can be an additional resonator or part of it. The plasma chamber is preferably designed as a cylindrical resonator and the associated formation of certain modes. Several feed lines for the microwaves to one or more coaxial resonators can be designed.

Certain apparatus and geometric designs of the device are particularly suitable for the modes of the respective type. The preferred coaxial modes TEM or TM _n1 are optimally formed in the coaxial resonator between two preferably cylindrical electrically conductive tubes of different diameters.

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Any TE _nm or TM _nm field distribution is also possible. The length of both tubes is preferably a multiple of half the line wavelength of the microwave used. The tubes are then electrically conductively limited at both ends, e.g. by a wall, gas-permeable grid or a short-circuit slide.

The recipient(s), as usual made of dielectric material, can be large-volume according to the invention and can serve different purposes when divided. In the case of a large-scale recipient arranged on the outside, a metallic end wall is not absolutely necessary.

Permanent magnets or coil arrangements, e.g. according to Helmholz, around the outer tube or the metal outer wall enable the conditions for electron cyclotron resonance plasmas in the chamber. An arrangement of magnets in the inner conductor of the coaxial resonator is also possible.

Fig.1 shows in Fig.1a a section through a device along the z-axis, Fig.1b the corresponding top view. A device is shown with inner wall 2 and outer wall 3 of a tubular coaxial resonator with microwave source 4, which couples into the resonator between 2 and 3, and receiver 1. In Fig.1 two coupling slots 5 are designed as circumferential slots in the inner wall 2; these are thus perpendicular to the z-axis of the device. In this embodiment, the coaxial resonator and the inner plasma chamber, which is designed as a cylinder resonator, have the same length in the z-direction. 10 is an optional, e.g. metallic, grid that divides the plasma chamber into two chambers. Openings 6 for the supply and removal of, e.g. process gases are shown in the upper and lower ends of the plasma chamber.

Fig.2 shows a similar device to Fig.1, but here the coupling points 5 are arranged as longitudinal slots in the wall of the inner coaxial conductor and thus run parallel to the z-axis of the device. Furthermore, some tuning options for the coaxial resonator and plasma chamber are shown as examples in Fig.2. The end slide 7 is used to tune the coaxial resonator. The tuning pin or screw 8 serves the same purpose. The position and number

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such tuning elements can be varied as required. The tuning pin 9 shows a tuning option for the plasma chamber. A closing slide (not shown here) that changes the length of the plasma chamber has a similar function. The arrows in the figure indicate the direction of movement of the tuning elements.

Fig. 3 shows a section of a device with an external plasma chamber, not shown in full here. The microwave generator 4 is mounted inside the inner conductor 2 of the coaxial resonator. The coupling points 5 are designed as three azimuthal, partially circumferential coupling slots in the outer wall of the coaxial resonator.

Further embodiments of the device are outlined in Fig. 4, with Fig. 4a showing a section through a device with both an inner plasma chamber 11 and an outer chamber 12. If required, the plasma chambers 11, 12 can be equipped with recipients.

Fig. 4b shows a section through a device in which the microwave is directly coupled into a cylinder resonator 13 and this resonator is coupled to the coaxial resonator via a circumferential azimuthal slot. The coupling into the plasma chamber 11, which is designed as a further cylinder resonator, with recipient 1 takes place via further coupling slots.

Fig. 4c shows a section through a device in which a coaxial resonator, e.g. spirally wound, with an outer conductor 3 and a similarly wound inner conductor 2, e.g. designed as a wire, is located in a cylindrical chamber 12. A design in which the coaxial resonator in a spiral or wound form with the outer conductor completely or partially encloses a chamber, i.e. like a band or a cord wound around a chamber, is also possible.

Fig. 4d shows a section through a device with a conical plasma chamber 11. The antenna of the microwave generator 4 is directly connected to the inner conductor 2 of the coaxial resonator. The outer conductor 3 is tapered towards the microwave generator 4. The microwave power is coupled into the plasma chamber via an azimuthal coupling slot 5.

Claims (7)

A9602 y \": · l I #/. ..· Page 7 Claims 1. Device for generating microwave plasmas with microwave generator, supply resonator with coupling points, plasma chamber and, if necessary, recipient, consisting of a resonator, the outer and inner boundaries of which are designed as outer and inner conductors of a coaxial resonator with or without a preferred geometric direction. 2. Device according to claim 1, characterized in that the plasma chamber is completely or partially enclosed by the resonator. 3. Device according to claim 1, characterized in that the resonator is completely or partially enclosed by the plasma chamber. 4. Device according to claim 1, characterized in that one or more chambers are arranged inside and/or outside the resonator, or the plasma chamber is divided. 5. Device according to claim 1, characterized in that the coaxial resonator and the plasma chamber are designed to be of the same length or of different lengths in the same preferred direction. 6. Device according to one of the preceding claims, characterized in that the coupling points for coupling in or out the microwaves from the resonator are arranged in or on the walls of the coaxial resonator or in or on the common wall of the chamber and the resonator. 7. Device according to one of the preceding claims, characterized in that the coupling points are rod antennas and/or loops and/or slots and/or recesses.