EP0359336A2 - Device for microwave transmission - Google Patents

Abstract

Microwave transmission between hollow conductor regions (a, b) of different internal gas pressure and/or different fill-gas composition, i.e. the coupling in or out of microwaves from one such hollow conductor region into another, is improved when at least one pump stage (6, 7, 8, 9) is arranged between the hollow conductor regions. The hollow conductor (1) is preferably connected to the pump stages via slots (2, 3, 4, 5) which virtually do not couple out the microwave power. <IMAGE>

Description

The invention relates to a device for microwave transmission between waveguide areas of different internal gas pressure and / or different filling gas composition, i.e. for coupling or decoupling microwaves from such a waveguide region into another.

DE-OS 36 22 614 discloses a method for producing electrically conductive shaped bodies by reactive deposition from a gas phase, which is activated by a microwave plasma. In such methods, high-power microwaves are coupled in via a gastightly insulating microwave window made of dielectric material into a microwave resonator serving as a reaction chamber, in which a plasma is formed and electrically conductive layers are deposited. The problem arises here that the microwave window arranged at the coupling-in point on its surface facing the reaction chamber, i.e. on the inside, is usually coated with an electrically conductive layer, whereby the coupling is prevented. According to DE-OS 36 22 614, this problem is solved either by flushing the inside of the microwave window with an inert gas or by choosing a dielectric material for the microwave window which is electrically conductive due to an etching reaction with one of the reactants Layer growth is kept free.

A related problem arises in the extraction of high power microwaves from gyrotrons during the transition from high vacuum to air. With microwave powers of the order of 0.1 to 1 MW, the thermal load on the known materials used for microwave windows becomes too great, as a result of which the output power is limited. With powers of at most 0.3 MW, one helps to widen the waveguide and to additionally cool the window, which consists, for example, of A1 ₂ 0 ₃ .

Pumping out a waveguide via non-radiating or non-coupling slots is known from GB-PS 644 749.

The invention has for its object to improve the microwave transmission between waveguide areas of different internal gas pressure and / or different filling gas composition.

This object is achieved in that at least one pump stage is arranged between the waveguide regions.

A pump stage is to be understood as a pump connection with a pump and pressure control, the pump always being outside the waveguide.

When operating the device according to the invention, gas is pumped out at least at one point between the waveguide regions.

The pump stages are preferably pressure-controllable, the flow resistances of the waveguide sections between the pump stages, the suction powers of the pumps and the pressure controls being dimensioned or adjustable in such a way that a predetermined pressure difference between the waveguide regions is generated and maintained - in other words: the suction power of the respective pump is in the target pressure range greater than or equal to the flow resistance of the waveguide section between the inlet or the pump stage with higher pressure and the pump-down point and the pressure control is set for the target pressure range at the pump-off point (at which there is also a pressure sensor or a pressure gauge).

The respective pump stage is preferably in the immediate vicinity of the low-pressure side.

In a preferred embodiment of the invention, the waveguide guiding a particular microwave mode is provided with a slot or with slots at successive locations, the slot or slots having a very weak or negligible coupling-out of the microwave mode and the waveguide via the slot with the pump stage or is connected via the slots to successive pump stages with adapted pumping power.

This embodiment is based on the basic idea of differential pumping. The waveguide is pumped out through the slots in successive pump stages, so that the microwave is either guided from a region of high internal gas pressure (e.g. air under atmospheric pressure) to a region of low internal gas pressure (e.g. 10 hpa) in the waveguide or in the opposite direction from a region low is led into an area of high internal gas pressure.

In this embodiment of the invention, the waveguide preferably has a rectangular cross section and is coiled several times.

The slots are preferably made in the waveguide side walls, namely in the narrow sides, and have the shape of vertical rectangles.

The distances between the slots are preferably integer multiples of half the waveguide wavelength.

It is also advantageous, especially for lower microwave frequencies, for example for frequencies below 40 GHz, that Reso in the waveguide are arranged.

In a further preferred embodiment of the invention, which relates to the use in connection with a microwave plasma reactor e.g. according to DE-OS 36 22 614, a microwave window is arranged between the waveguide region connected to a microwave oscillator and the vacuum region generated by the (first) pump stage, the first pump stage being designed in such a way that it is able to generate such a low final pressure that no discharge is ignited.

It is preferred that a second pump stage is arranged between the first pump stage and a reaction chamber designed as a microwave resonator to relieve the first pump stage and to dispose of the gas from the reaction chamber.

It is also advantageous to arrange at least one resonance diaphragm between the first pump stage and the second pump stage.

In a modification of the previously described embodiment of the invention, the waveguide in the region of the first pump stage is filled with a gas with a high dielectric strength.

In a modification of the invention, the pump stage consists of a double-walled resonance diaphragm, which is designed as a nozzle for a flat liquid jet of high speed.

In a further modification of the invention, the waveguide is filled with a purge gas, an extinguishing gas or reactive gases. This is explained in more detail below.

In all of the above-mentioned microwave transmission devices according to the invention, it is expedient to also provide at least one EH tuner and / or a pin transformer in the waveguide in order to carry out a phase or length adjustment and to tune for optimal power transmission.

Furthermore, it is expedient that a plurality of directional couplers of low attenuation are placed between the waveguide regions, each of which is connected to a pump for setting a specific predetermined pressure, the directional coupler regions lying between the waveguide regions each having short-circuit slides at the ends and one EH tuner for the coordination of the transmission link I see. This is explained in more detail below.

• Fig. 1 eine Vorrichtung zur Mikrowellenübertragung mit mehrfach gewendeltem Hohlleiter,
• Fig. 2 eine Resonanzblende,
• Fig. 3 eine Vorrichtung zur Mikrowellenübertragung mit einem Mikrowellenfenster und Pumpansätzen und
• Fig. 4 ein Düsenstrahl-Mikrowellenfenster.

Some embodiments of the invention are shown in a drawing and are described in more detail below. In the drawing show in perspective

• 1 shows a device for microwave transmission with a multi-spiral waveguide,
• 2 shows a resonance diaphragm,
• Fig. 3 shows a device for microwave transmission with a microwave window and pump approaches and
• Fig. 4 shows a jet microwave window.

In Fig. 1, a waveguide area with high pressure (e.g. air, 1000 hpa) is designated with a and a waveguide area with low pressure with b.

, wobei also d_i = ρ_i/

2 (mit p; = 1,2 usw.) sind in den Hohlleiterseitenwänden, und zwar in den Schmalseiten, vertikale Rechteckschlitze 2, 3, 4, 5 angebracht, die sich durch eine sehr geringe Auskopplung des TElo-Modes auszeichnen, also nur eine relativ geringe Dämpfung dieses Wellentyps bewirken. Auf der Außenseite dieser Schlitze sind Pumpstutzen 6, 7, 8, 9 angebracht, über die mit verschiedenen Vakuumpumpen (nicht dargestellt) die Leitung in Richtung b sukzessive auf niedrigeren Druck evakuiert wird.Depending on the application, a TE ₁₀ microwave is guided either from a to b or from b to a in a multiply coiled curved rectangular waveguide line 1. At intervals d _i of integer multiples p; half the waveguide wavelength

, where d _i = ρ _i /

2 (with p; = 1.2, etc.) are in the waveguide side walls, namely in the narrow sides, vertical rectangular slots 2, 3, 4, 5, which are characterized by a very low coupling of the TElo mode, so only one cause relatively low damping of this type of wave. Pump nozzles 6, 7, 8, 9 are attached to the outside of these slots, via which the line in direction b is successively evacuated to lower pressure using various vacuum pumps (not shown).

The pressure difference Ap = p _a - p _{b to be set} between a and b is determined by the suction power and the final pressure of the pumps, the number of pump stages, the spacing of the slots and the cross section of the respective waveguide type. A large pressure difference, for example, is easier to achieve for the E-band (60 to 90 GHz) than for the X-band (8 to 12 GHz), due to the large cross-sectional area reduction of the E-band waveguide compared to the X-band - waveguide.

In the following example, the device according to FIG. 1 is used for the microwave plasma-activated CVD of electrically conductive substances.

example 1

• Pa - P_b =Q/C = p_b.S_p/[C_o(p_a + p_b)] wobei C ₌ C_o-(p_a + p_b) (2)

In area a, an X-band waveguide 1 is filled with air under p _a ≤ normal pressure and connected to an X-band microwave transmitter with a CW power of 300 W. The slots 2 to 4 are not provided in this example and only a rotary vane pump with the suction power Sp = 580 m ³ / h is pumped shortly before a (slot 5), since the pressure drop is essentially due to the flow resistance (for air) of the Waveguide is determined. According to A. Roth "Vacuum technology" p. 75/76, the flow resistance 1 / C for air in a rectangular tube of length L and with the cross-sectional area AB (for laminar flow) is given by
^{C = 260} _. ^Y. (A ² B ² / L). ( ^p a ^{+ p} _b ) / 2 (1)
where Y = ₀ , 82 for A = 2 B (A and B see Fig. 2) and [C] = 1 / sec, [A] = [B] = [L] = cm, p _a = Torr = 1.33 hPa apply. The pressure difference ρ _a - p _b between the pipe start and pipe end can now be determined from the flow rate Q and the flow conductance C:

• Pa - P _b = Q / C = p _b .S _p / [C _o (p _a + p _b )] where C ₌ C _o - (p _a + p _b ) (2)

The resolution from (2) to p _b gives p _b = p ⁺ (Sp ^{/ 2} Co) ^{2 -} S _P 2 C _o (3) If (3) p _a = 760 Torr = 1013 hPa, Sp = 580 m ³ h. A = 2.29 cm, B = 1.02 cm and L = 2600 cm, you get p _a - p _b = 375 Torr = 500-hpa.

The doubling to p _a - p _b = 750 Torr = 1000 hPa is achieved by installing resonance diaphragms (see Fig. 2) in the rectangular waveguide at a distance n. Λ2, which transmit this frequency undamped at 10 GHz and at the same time the flow resistance as increase desired.

A resonance aperture at a distance of 28 Λ (Λ- = 3.97 cm for TE ₀₁ and ν o = 10 GHz) or about every 110 cm along the helix (i.e. once per turn with a center diameter of about 35 cm) is sufficient so 24 pieces. The spatial extent of this arrangement for the X-band is still quite compact with an outer diameter of approximately 37 cm and a height of approximately 30 cm.

The estimation of the attenuation for a rectangular waveguide with copper inner walls gives a value of 26 m at ν _o = 10 GHz and L = 26 m. 0.026 dB / m = 0.676 dB, is less than 20%.

2 shows such a resonance diaphragm 10 for 10 GHz in the X band. A '= 1.4 cm and B' = 0.28 cm apply. The flow conductance of such an orifice can be determined from the formulas for laminar flow given in A. Roth, p. 70.

Furthermore, in the arrangement used in example 1, it is expedient to use a throttle valve or a pressure control for setting p _b in front of the pump in order to be able to set p _b to the respective desired value. In addition, another pump can be used for gas disposal from the reaction chamber, which relieves the rotary vane pump at b. Finally, because of the square relationship in (3), it is also more favorable for the arrangement used in Example 1 to provide a second pumping stage at a distance of approximately 2 m L from the first pumping stage.

Example 2

A microwave coupling pressure lock according to FIG. 1 for the E band (60 to 90 GHz) looks much cheaper. With a microwave transmission direction from b to a, it is also excellently suitable for windowless coupling of microwaves of high power, for example 200 kW, from a 70 GHz gyrotron. Because of the already relatively small required waveguide transverse dimensions, no resonance diaphragms are required in such an arrangement. Up to the 1st pump stage (pump nozzle 6) with a rotary vane pump with suction power S _P ⁽¹⁾ = 580 m ³ h, with two pump slots 2 at a distance L = 20 m from the "entrance" a of the rectangular waveguide coil on both narrow sides, the E-band spiral waveguide slot-free. From (3) follows, with A = 0.31 cm = 28, then p, = 38 Torr = 50.5 hPa. Another rotary vane pump (pump nozzle 7) at a distance of 1.5 m from the pump slots 2 with the suction power S _P ⁽²⁾ = 76 m ³ ih then gives a pressure of approximately 10 Torr = 1.33 hPa at the outlet b. This second pump stage is necessary because of the quadratic dependence in (3) and results in a significantly shorter overall length L than only with one pump stage alone.

The power attenuation of the E-band wave with ν _o = 70 GHz is thus 0.027 dB / m. 21.5 m = 0.58 dB or about 13%.

The arrangement shown in FIG. 3 relates to use with a microwave plasma reactor. Here, the microwave transmission takes place through a waveguide 1, which is sealed airtight at one point with a microwave window 11 made of dielectric material, for example glass, quartz, PTFE, against the vacuum side 12. The negative pressure side is more than two slots 2 and 3 in the narrow sides of the waveguide to such a low discharge pressure, for example ₁ 0- ⁴ Torr = 10- ² hPa, evacuated (pump port 13), that even with high microwave power densities no microwave gas discharge is ignited and the window always free. In the further course of the waveguide, there is again an increase in pressure up to a working pressure of, for example, 10 hPa in the reaction chamber designed as a microwave resonator. Another rotary vane pump (pump connection 14) pumps at two further opposite slots 4 and 5 at a distance L between the pump connection 13 and the coupling point into the reaction chamber (arrow 15) and serves both to relieve the pump at 13 and for gas disposal, ie for removal of the gaseous PCVD end products. For better decoupling of the two pumping areas, one or more resonance diaphragms 10 can be used in the (eg X-band) waveguide.

A modification of this embodiment is obtained in that the vacuum region in the waveguide between the window 11 and the pump connections 13 and 14 is filled with a gas with a high dielectric strength, ie with an extinguishing gas, for example SF ₆ , and a pressure of about 10 Torr = 13.3 hPa at the window and in the reaction chamber is also produced via the pump connections 13 and 14, whereby again a series of resonance diaphragms between the pump connections 13 and 14 ensure that no mixing of the reactive gases with the higher gas Dielectric strength takes place in the reaction chamber. Such a gas prevents a plasma from forming in the waveguide in spite of the low gas pressure and thus almost no microwave power reaching the reaction chamber.

In the case of multi-component PCVD deposition of metallic layers, for example tungsten also being deposited from WFs + H ₂ , there is an even more elegant solution: instead of SFs, WF _{6 is} introduced into the reaction chamber through the microwave feed, since WF ₆ also has a high dielectric strength.

Only in the reaction chamber are hydrogen and argon and possibly other gaseous components mixed in, whereby argon ensures that the breakdown voltage is reduced and a microwave plasma does not build up in the waveguide if the microwave power is not too high, but in the reaction chamber, i.e. in the cavity resonator.

Depending on the wave type, the microwaves are coupled into the reaction chamber via a coupling hole or via an antenna pin through a coupling hole. 16 denotes the coupling from the microwave oscillator (e.g. klystron, RWO = reverse wave oscillator = carcinotron, gyrotron).

In the case of this modification, the pump connection 13 is omitted and, for example, WFs or SF _{6 is} introduced at this point. When SFs are supplied, pumping continues through the pump connection 14, and there are further resonance diaphragms in the rectangular waveguide after the slots 4 and 5 in the direction of the arrow 15. When WF ₆ , which serves for the tungsten deposition in the reaction chamber, is introduced, the pump connection 14 and the slots 4 and 5 are also omitted, and the gas is removed at an outlet opening from the reaction chamber.

A further possibility is the use of one or more low-damping directional couplers with rectangular waveguides arranged in parallel, which are pumped or gas-purged separately and in which the coupling holes represent an additional flow resistance ("orifice plate"). However, such an arrangement is only effective when the pressure differences are not too great.

A third embodiment of the invention is the jet microwave window. Fig. 4 shows such an arrangement. Here, the microwaves (arrow 16) are radiated through a double-walled resonance diaphragm 17, which is designed as a nozzle 18 for a large-area liquid jet (arrows 19 and 20), again from an inner waveguide area of approximately atmospheric pressure into a low-pressure area.

The advantage of such a nozzle jet microwave window is, among other things, that no additional window cooling is required and that there is no longer any limitation at high microwave powers. In addition, the pumping effect of the nozzle jet can also be exploited here, such as that e.g. is used in water jet pumps or in diffusion pumps. There is a microwave transmission through a pump. In a further stage in the transition to high vacuum, a steam jet nozzle can then be used instead of a liquid jet nozzle.

Claims (16)

1. Device for microwave transmission between waveguide areas of different internal gas pressure and / or different filling gas composition,
characterized in that at least one pump stage (6, 7, 8, 9) is arranged between the waveguide regions (a, b). 2. Device according to claim 1,
characterized in that the pump stages (6, 7, 8, 9) are pressure-controllable, the flow resistances of the waveguide sections between the pump stages, the suction powers of the pumps and the pressure controls being dimensioned or adjustable such that a predetermined pressure difference between the waveguide regions (a , b) is generated and maintained. 3. Device according to claim 1 or 2,
characterized in that the respective pump stage (6, 7, 8, 9) is in the immediate vicinity of the low-pressure side. 4. Apparatus according to claim 1, 2 or 3,
characterized in that the waveguide (1) carrying a specific microwave mode is provided with a slot or at successive locations with slots (2, 3, 4, 5), the slot or slots having a very weak or negligible coupling-out of the microwave mode and wherein the waveguide is connected via the slot to the pump stage or via the slots to successive pump stages (6, 7, 8, 9) with adapted pumping power. 5. The device according to claim 4,
characterized in that the waveguide (1) has a rectangular cross section and is coiled several times. 6. The device according to claim 4 or 5.
characterized in that the slots (2, 3. 4, 5) are made in the waveguide side walls, namely in the narrow sides, and have the shape of vertical rectangles. 7. The device according to claim 4, 5 or 6,
characterized in that the distances between the slots (2, 3, 4, 5) are integer multiples of half the waveguide wavelength. 8. The device according to claim 4, 5, 6 or 7,
characterized in that resonance diaphragms (10) are arranged in the waveguide (i). 9. The device according to claim 1 or 2,
characterized in that a microwave window (11) is arranged between the waveguide region (16) connected to a microwave oscillator and the vacuum region (12) generated by the (first) pump stage (13), the first pump stage being designed such that it is capable of to produce a final pressure so low that no discharge is ignited. 10. The device according to claim 9,
characterized in that between the first pump stage (13) and a reaction chamber designed as a microwave resonator, a second pump stage (14) is arranged to relieve the first pump stage and to remove gas from the reaction chamber. 11. The device according to claim 10,
characterized in that at least one resonance diaphragm (10) is arranged between the first pump stage (13) and the second pump stage (14). 12. modification of the device according to claim 9, 10 or 11,
characterized in that the waveguide (1) is filled with a gas with a high dielectric strength in the region of the first pump stage (13). 13. The apparatus of claim 1,
characterized in that the pump stage consists of a double-walled resonance diaphragm (17) which is designed as a nozzle for a flat liquid jet (19, 20) of high speed. 14. The apparatus of claim 1, 2, 3 and / or 10,
characterized in that the waveguide (1) is filled with a purge gas, an extinguishing gas or reactive gases. 15. The apparatus according to claim 1, 2 or 8, characterized in that in the waveguide (1) at least one EH tuner and / or a pin transformer are provided. 16. The apparatus of claim 1 or 2,
characterized in that between the waveguide areas (a, b) a plurality of directional couplers of low damping are arranged, which are each connected to a pump for setting a certain predetermined pressure, the directional coupler areas lying between the waveguide areas (a, b) each having short-circuit slides the ends and an EH tuner for tuning the transmission link.

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