DE2430432A1 - TUBE FURNACE WITH A GAS FLOWRED REACTION TUBE - Google Patents

Description

2430Λ32

Boeblingen, June 20, 1974 oe-fe

Applicant: International Business Machines

Corporation, Armonk, N.Y. 10504

Official file number: New application File number of the applicant: FI 9 72 125

■ Tube furnace with a reaction tube through which gas flows

The invention relates to a tube furnace with a gas flowing through it Reaction tube for treating flat platelets at specified temperatures.

Tube furnaces, also referred to simply as furnaces in the following, are used in many Branches of technology used. Particularly high requirements in terms of temperature constancy or stability and the guarantee a completely flat temperature profile in the reaction space are placed on tube furnaces that are used in semiconductor technology will. Tube furnaces, which are used in other branches of technology, are - because of the lower demands placed on them - are generally less expensive, but in principle they do not differ from the ovens used in semiconductor technology Find application. The following therefore only focuses on ovens that are also used in semiconductor technology However, it should be made clear that the use of these ovens is not limited to this area of technology.

When you first went to it. To manufacture semiconductor components the tube furnaces required for this from those already known at the time Furnace types according to the requirements of the new technology developed. As with the increasing trend towards ever smaller dimensions in semiconductor technology, the demands on the production facilities got higher and higher, it did not become that

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encountered that new tube furnaces developed but by adding the old ones have been improved. Such tube furnaces used in semiconductor technology are described, for example, in US Patents 2,661,385, 2,825,222, 3,264,148, 3,299,196, 3,296,354, and 3,343,518. The main requirements placed on these tube furnaces, which are mainly used for oxidizing, Diffusing and tempering are used, are an extreme temperature constancy over long times and a completely flat temperature profile in the region of the reaction tube in which the semiconductor wafers are processed, even if Gas flows through the reaction tube. Both demands must be within within a very small tolerance range. The known tube furnaces meet these requirements with the help of a heavy, stable construction and a very high term Mass, which, however, has the consequence that these ovens are thermally very sluggish when cooling and heating. The well-known tube furnaces in the semiconductor technology are used, are therefore kept at the same temperature and for each process temperature at least one tube furnace is required.

It is the object of the invention to provide a tube furnace for treatment of flat platelets in a gas stream that is able to rapidly absorb the introduced platelets from room temperature to heat the set temperature, which reacts quickly to changes in temperature, and quickly increases the platelets to be treated brings the new, desired temperature in which the platelets to be treated remain stable at a set, can be kept uniform temperature and supplied evenly over its entire surface with the process gases, the one has little wear and tear and is easy to maintain and operate.

This object is achieved with a tube furnace of the type mentioned in that the reaction tube at least in the area in which the treatment takes place, has a rectangular cross-section, consists of a material permeable to thermal radiation, and guide plates to create a clear transverse

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cut uniform gas flow that contains in the reaction tube a platelet boat with one parallel to the ceiling of the reaction tube upper surface is present that the ratio (B / A) of width (B) of the reaction tube to the distance between the on the upper surface of the boat and the Ceiling underside of the reaction tube is at least 1: 1 that below and above the top and bottom of the reaction tube and are arranged parallel to these heating plates that the heating energy controlling temperature regulators are available and that the Heizplattenr-und Volume containing reaction tube with an insulating jacket small heat mass and a thermal conductivity of at least 0.33 times 10 (cal / sec. cm «° C) is surrounded.

With the help of the guide plates and the correctly chosen ratio B / A generated even gas flow over the clear pipe cross-section, the platelets to be treated are over their entire area Surface evenly supplied with the process gases. The formation of the pipe cross-section, the location of the pipe to be treated Platelets in the reaction tube and the arrangement of the heating plates to the reaction tube causes the platelets to be treated to the evenly heated heating plates have the same distance everywhere, which is supported by the intrinsic thermal conductivity of the platelets to be treated leads to completely uniform heating of the platelets to be treated. The even supply with the process gases and the uniform heating ensure that the existing in the reaction chamber to be treated Platelets are exposed to exactly identical conditions and, as a result, the treatment is completely uniform. Because the ratio (B / A) has at least the value one, a strong heat radiation to the side is prevented. Through this the platelets and the platelet boat are sensitive to changes in the heating power, which can be seen in keeping it constant the temperature and also in the event of temperature changes (see below). The built-in temperature control ensures that the platelets to be treated reproducibly at the desired temperatures can be exposed. The accuracy with which this is possible

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is borrowed, then only depends on the sensitivity of the temperature control away. Very sensitive devices for temperature control are available in stores. The favorable design of the invention Oven makes it - unlike the known tube ovens - not necessary to ensure the uniform and reproducible heating of the platelets to be treated to provide a large thermal mass of the tube furnace. The heat mass of the The furnace is essentially determined by the thermal mass of the insulating jacket. In the tubular furnace according to the invention, the thermal mass is of the insulating jacket deliberately kept small. As a result, the tube furnace according to the invention is outstandingly suitable for to quickly change the set temperature up or down. There - again different from most of the known ones Tube furnaces - there is no heat in the tube furnace according to the invention absorbent material is located between the heating plates and the reaction tube, i.e., direct heat transfer through If radiation takes place, the heating can react very sensitively to the temperature of the platelets to be treated, which on the one hand ensures that, with a specific temperature change, the platelets to be treated open practically just as quickly Set the new temperature like the heating plates and, on the other hand, the heating in the tube furnace to be treated Platelet is accelerated to the desired temperature. In addition, with this type of heat transfer, the temperature of the tiles and the slide boat are particularly sensitive. The tubular furnace according to the invention is very simply constructed, which makes its maintenance very easy. The slide boat on which the platelets to be treated lie flat, are easy to load and can easily be pushed into the oven. Then there is the mentioned rapid reaction of the furnace to reaction changes. For these reasons, the oven is very easy to use and he is excellent for factory use.

It is advantageous if the reaction tube is made of clear, translucent Quartz glass exists because this material is very permeable to thermal radiation.

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In an advantageous manner, a uniform supply of the platelets to be treated with the reaction gases is achieved when in Reaction space between the inlet of the reaction gases and the space where the treatment takes place, at least one each across the width of the reaction tube extending and standing on the floor or hanging from the ceiling and at a specified distance There are guide plates that end from the ceiling or from the floor.

The heat transfer from the heating plates to the ones to be treated Platelets can still be improved and intensified and the heat generated can be applied even better to the platelets to be treated be concentrated when the platelet boat from one the heat radiation absorbent material. The absorption of the thermal radiation by the platelet boat is carried out in an advantageous manner achieved when the platelet boat made of superficially roughened Quartz glass is made.

The heat transfer from the heating plates to the ones to be treated Platelets, or / the ratio between the irradiated on the platelets to be treated or the platelet boat and of that of This radiated heat energy is particularly favorable and the heating the platelets to be treated and their supply with the process gases is particularly uniform if the ratio B / A, where B equals the width of the reaction tube and A equals the distance the upper surface of the platelets to be treated from the underside the top of the reaction tube is between 7: 1 and 30: 1, a ratio of 18: 1 was found to be particularly advantageous Has. *

The temperature characteristics of the tube furnace is also advantageously influenced if the platelet boat is so high that the upper Surface of the platelets to be treated from the ceiling and the floor of the reaction tube have approximately the same distance.

It is advantageous if the heating plates consist of an electrically insulating material with a thermal conductivity between 1.24 and 16.5. 10 (cal / sec.cm. ⁰ C). This area

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the thermal conductivity ensures that the heating plates are at a uniform temperature and consequently over their surface radiate evenly temperature. It is beneficial when the hot soldering points of the thermocouples belonging to the temperature control between the heating plates and the reaction tube are positioned. A temperature measurement at this point allows in the case of operation at a stable temperature quick and sensitive reaction to small deviations from the target temperature of the platelets to be treated and causes im In the case of desired temperature changes or when loading the tube furnace with cold platelets to be treated, that the heating power is optimally matched to the difference between the target and actual temperature of the platelets to be treated.

It is advantageous if the material from which the insulating jacket

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exists, one between about 0.33. IO and about 0.45. IO (cal / sec. Cm. ⁰ C) lying thermal conductivity and a mass lying between about 6.8 and about 15.5 s. With smaller thermal conductivities and larger masses, the furnace reacts too slowly to temperature changes. With higher thermal conductivities and smaller masses, an unnecessarily high heating output is required to maintain the temperature in the furnace and the furnace is too sensitive to external temperature influences.

It is advantageous if the tree enclosed by the insulating jacket has a gas inlet and a gas outlet opening. This design allows the cooling process in cases in which a particularly rapid cooling of the tube furnace is desired accelerate by introducing cold gas.

The tube furnace according to the invention is particularly advantageous when to carry out several successive high-temperature process steps which take place at different temperatures are. While using the known ovens in which the Setting to a new temperature takes a long time and the

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therefore are usually set to a fixed temperature and as a result are only available for one method step, the utilization is often poor, can with the invention Tube furnace changes the temperature and equilibrates to the new temperature very quickly are made, and it is therefore possible to use the tube furnace according to the invention in several process steps. It can therefore be better utilized and more versatile, whereby tube furnaces can be saved.

The invention is based on exemplary embodiments illustrated by drawings described. Show it:

Fig. 1 is a perspective, partially cut away

View of an embodiment of the invention Tube furnace,

Fig.IA is a drawing to show details of that shown in FIG Tube furnace to show

Fig. 2 is a partially cut-away side view

an embodiment of the inventive Tube furnace belonging to the reaction tube,

3 shows a profile edge of a static temperature distribution in the reaction tube, as can be achieved with the tube furnace according to the invention and

4 plotted against time in a diagram

dynamic temperature profile of an embodiment of the tube furnace according to the invention.

As the drawings show, the furnace described here exists in its basic configuration from a housing 1 / through which a reaction tube 2 transparent to radiant heat extends, that e.g. made of quartz glass with a wall thickness of approx

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3.2 ram and in which there is an area 3 tin performing High temperature processes. As shown, the reaction tube has a rectangular cross-section with an internal width equal to is between 33 mm and 50.8 cm and an inner height that is in the Range is between 4.8 and 25.4 mm. In a typical training the reaction tube has an inner width of 18.1 cm, a height Iran 12.7 mm and a total length of 58.5 cm. The one end 4 of the reaction tube 2 is open, while the other end 5 tapers and merges into a gas inlet 6, which is connected by means of suitable tubes to the sources of the required reaction gases is. Within the reaction tube 2 and adjacent to its tapered end 5 there is a downwardly directed guide plate 7, the lower end of which has a distance from the inner surface 8 of the bottom 9 of the reaction tube which is between approximately 0.76 and approximately 6.35 mm. A second guide plate 10 stands on the floor 9 and its upper end has from the inner surface of the ceiling 11 of the reaction tube a distance which is between about 0.76 and about 6.35 mm. In general, the ceiling 11 and the run Bottom 9 of the reaction tube 2 parallel to each other at a certain distance, the guide plates 10 and 7 extending over the whole Width of the reaction tube 2 extend. In a special application, described below, they have on the opposite Pipe wall facing ends of the guide plates 7 and 10 each a defined distance from the opposite pipe wall of about 1.4 mm.

The upwardly directed guide plate 10 can, if so desired, - as a stop for a platelet pad or a platelet boat 12 are used, which or which has been pushed into the interior of the reaction tube 2. It is possible in this way Platelets 13, which are between about 0.4 and 0.45 mm thick, in the reaction tube when carrying out the desired reaction to bring into a fixed position. In the application of the furnace described here, it is generally advantageous if the platelet substrate 12 is impermeable to radiant heat and absorbs them. The radiant heat comes from several

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Heat radiating heating plates 14, usually four Heat radiating heating plates on the reaction tube 2 and four heat radiating heating plates 14 under the reaction tube 2 / are arranged side by side. .The location of four heating plates each to one another can be seen from FIG. 3. In general, the wafer pads or wafer boats 12 are designed so that that the plate 13 is parallel to the bottom 9 of the reaction tube 9 and about the same from the ceiling and from the floor Have a distance. A typical platelet boat 12 can consist of quartz, which by roughening the surface for radiant heat and has been made permeable, and that one thickness which is between about 1.6 and about 6.4 mm. At a special When the furnace was designed, the platelet boat 12 had a thickness of about 3.2 mm.

The platelet boat 12 has a notch 40 at one end into which a claw 41 of the front part 42 of a boat slide 43, which is used to push the platelet boat into the reaction tube 2 and pull it out of it, engages. The front part 42 is connected by means of a rod 45 to the rear part 44, designed as a plug, which is inserted in the open tube end and has the purpose of restricting the escape of process gases from the reaction tube. The handling of the boat slide 63 is facilitated by a handle 46, which is located on the outwardly facing side of the rear part 44. In general, the rear part 44 is dimensioned such that between it and the inner surface of the reaction tube 2, a passage with a clearance of between about O _f 75 and 1.5 mm is left. All parts of the boat slide 43 can be made of quartz. .

Essential for the use of the device described here is the distance (A) between the inner surface of the ceiling 11 and the upper surface of the platelets 13. This distance is determined by the shape of the platelet boat 12 on which the platelets 13 lie. The ratio of this distance to the

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inner width (B) of the reaction tube defines a critical ratio A / B, which together with the guide plates 7 and 10 ensures a uniformly distributed gas flow in the process space of the reaction tube 2 and over the surface of the plate 13, without there being areas where the gas does not flow. Generally the distance between the inner surface of the ceiling 11 and the upper surface of the platelets are between about 3.2 and about 19 mm. It is necessary that this distance (A) matches the inner width (B) of the reaction tube 2 so that a favorable ratio B / A is obtained. Generally this will The ratio B / A is in the range between about 7 and about 30 and is optimally about 18. Located inside the reaction tube 2 there is also a throttle plate 16, which is directed from the ceiling 11 downwards xmd serves to divert the gas flows in the direction of the To stow outlet pipes 17. Through these outlet pipes 17 are the Gases removed, which is assisted by a back pressure created by the injection of an inert gas released from the Inlet pipe 2O via branch 19 and inlets 18 into the Reaction tube 2 flows in.

The heat radiating heating plates 14 consist of an electrically insulating material, dad by a relatively high thermal conductivity, which is in the range of about 1.24. 10 ~ and about 16.5 · IQ (cal / sec. Cm. ⁰ C) moved, is excellent. Typical materials of this type are, for example, aluminum oxide (Al ₃ O ₃ ) of relatively high purity and mulite, the Al ₂ O content of which is between approximately 25 and 96 percent by weight. The back of the heat radiating heating plates have grooves 25 between which a spiral-shaped resistance element 26 is threaded, which generates the heat to be radiated. The heat generation is controlled with the aid of conventional thermocouples, which are pushed into the furnace and whose hot soldering points are arranged at the points shown in FIG .

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The heating elements and the reaction tube 2 are any suitable Surrounding insulating jacket 28, which has a mass between about 6.8 and 15.5 kg and its thermal conductivity in

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Range between about 0.33. 10 and about 0.45. 10 (cal / sec. Cm. ⁰ G). The insulating jacket is enclosed in the housing 29 which is used for packing the furnace. A particularly advantageous insulating material is fibrous aluminum silicate, which z. As can be purchased from the Eagle-Picker Company of Cincinnati, Ohio, and which is readily, dimensionally stable, very effective, and about half the thermal conductivity of refractory brick at 1000 ⁰ C. Another advantage of this ceramic fibrous material is that it is available in blocks which can be conveniently molded to conform to the furnace parts to be enclosed.

Fig. 2 illustrates another embodiment of that described here Furnace in which a modified reaction tube 2A is used, which can be used for process gases, which tolerated with air, i.e. with oxygen. In the modified Reaction tube, the outlet tubes 17 as well as the inlet tube 20 and the inlets 18 are omitted. In use the gas flows from the reaction tube 2A through the open end, i.e. through the End through which the reaction tube is loaded into the atmosphere, In all other respects, the reaction tube 2A is like the reaction tube 2 designed.

In Fig. 3 is a static profile map of the termic characteristic * of the tube furnace described here and shown in FIG. 1. When the static profile map was recorded, gas flowed through the reaction tube 2 in the same quantities as it continued below in an application example, in the case of the silicon semiconductor wafer treated, of the furnace are specified. The hot soldering points of the used thermal lines were directly above the Plättehenböot 12 arranged at a »distance of about 1.6 mm. There was at least two minutes between readings

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waited for the temperature to stabilize. In the the-Fig. 3 temperatures specified relate only to the immediate Surrounding the measuring points and not in large areas, the temperature of which is usually measured by means of thermocouples, which are in a nitrogen environment. The values given in Fig. 3 must be preceded by a nine, In other words, the measured value 55 actually stands for 9.55, the measured values mean thermal voltages, measured in Millivolts, whereby the temperature values corresponding to the millivolts can be found in the table.

TABEL
mV ⁰ C

9.30 = 976

9.40 = 984

9.50 β 993

9.56 = 998

9.57 = 999
9,585 = 1000 9,596 = 1001

Fig. 4 shows in a diagram a dynamic temperature profile, in which a temperature increase of the furnace described here from 840 to 1050 ° C and the subsequent cooling down 840 ° c is shown as a function of time. This temperature cycle can be completed in less than 66 minutes.

Curves 1 and 2 illustrate the temperature profile measured by two thermocouples installed in the heating elements in were embedded in one of the zones indicated in the drawing. It would also have been possible to place the two thermocouples between the Position the heat-emitting heating plates and the reaction tube. Curves 3 and 4 show the temperatures used by each one of the thermocouples, which, as when recording the static profile described above, is directly above the centers of

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two platelet positions were positioned on the platelet boat, were displayed. Curve 3 was recorded in zone 1 and the curve in zone 2. As can be seen from Fig. 4, the temperatures follow, on the one hand, in the area of the heating elements and, on the other hand, directly above the platelet position in both Zones essentially have an identical curve shape.

The following describes the use of the ovens described here at the formation of the gate oxide of field effect transistors in which Source and drain regions have been formed in previous operations. Two ovens are used for this oxidation as described here. The first furnace includes a reaction tube 2A, which the Ficr. 2 shows and the second furnace contains a reaction tube 2, as shown in FIG. 1.

The silicon substrates 13 used for the oxidation have gate openings in an oxide layer, these openings having been etched into the oxide layer by means of a photolithographic process. The silicon substrates 13 are placed on the wafer boat 12 and this is then ^{pushed into the first furnace, which is heated to 1000 °} C. and oxygen flows through its reaction tube 2A at a rate of 1300 cc / min, and left there for 72 minutes. In this process step, a dry gate oxide made of silicon dioxide is grown on the chip 13. The platelet boat 12 is then immediately transferred to the second furnace, which is at a temperature of 840 ° C. and through whose reaction tube 2 1182 cc of nitrogen and 118 cc of oxygen flow per minute. The gases pass through the inlet tube 6 into the reaction tube 2. At the same time, 945 cc nitrogen / min flow through the inlets 18 into the reaction tube 2. Under these conditions, the platelets 13 are stabilized for 2 to 5 minutes.

After stabilization is through the inlet pipe 6 in addition A doping gas into the reaction tube 2 for 5 to 7 minutes injected. The doping gas stream consisted of 15 cc stick-fi 972 125 409883/127 8

substance / min, which contained 440 ppm POCl-. The doping gas causes a phosphorus silicate glass (PSG) to be deposited on the substrate. This process step also took place at 840 ⁰ C. After the end of the PSG precipitate the oxygen and POCl ₃ were switched off -doped nitrogen flow and the furnace temperature was increased to 1050 ⁰ C during a 15 minutes lasting annealing. The purpose of the annealing is to stabilize the surface charges and to distribute the phosphorus impurities in the silicon oxide covering of the substrate. After the end of the annealing, the furnace was cooled to 840 ° C. In the meantime, the platelet was pulled out to allow the platelets to cool at room temperature. The total thickness of the SiO and PSG layers formed was 675 8, the PSG layer thickness being 110 S.

It should be noted that although cooling the furnace alone By controlling the heating energy and the heat radiation of the furnace, it is also quite possible to cool down to assist by sending a cooling stream of gas through the furnace is blown through this gas stream between the reaction tube and the heat radiating heating plates.

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Claims (15)

- 15 - ANSP kitchen Tube furnace with a reaction tube through which gas flows for treating flat platelets at specified temperatures, characterized in that the reaction tube (2) at least in the area in which the treatment takes place, has a rectangular cross-section, consists of a material permeable to thermal radiation, and guide plates (7, 10) for generating a gas flow uniform over the clear cross section contains that in the reaction tube (2) a platelet boat (12) with one facing the ceiling (11) of the reaction tube (2) parallel upper surface is present that the ratio (B / A) of width (B) of the reaction tube (2) to the distance between the on the upper platelet boat surface lying plates (13) and the ceiling (11) of the reaction tube (2) is at least one that below and above the ceiling (11) and floor (9) of the reaction tube and parallel to these heating plates (14) are arranged that the Temperature regulators controlling heating energy are present and that the heating plates (14) and reaction tube (2) containing volume with an insulating jacket (28) of small thermal mass and a thermal conductivity of at least 0.33. 10 ~ ³ (cal / sec. Cm. ⁰ C) is surrounded. 2. Tube furnace according to claim 1, characterized in that the Reaction tube (2) consists of clear, transparent quartz glass. 3. Tube furnace according to claim 1 or 2, characterized in that the reaction gases in the reaction space between the inlet (6) and the room where the treatment takes place, at least one each extending over the width of the tube the floor (9) standing or from the ceiling (11) hanging and at a fixed distance from the ceiling (11) or from Bottom (9) ending guide plate (7, 10) are present. Fi 972 125 409883/1278 4. Tube furnace according to one or more of claims 1 to 3, characterized in that the platelet boat (12) is the reaction tube (2) is adapted in its width and displaceable in it. 5. Tube furnace according to one or more of claims 1 to 4, characterized in that the platelet boat (12) consists of one the thermal radiation absorbing material consists. 6. Tube furnace according to claim 5, characterized in that the platelet boat (12) made of superficially roughened quartz glass consists. 7. Tube furnace according to one or more of claims 1 to 6, characterized in that the ratio (B / A) is in the range between 7: 1 and 30: 1. 8. Tube furnace according to claim 7, characterized in that the ratio (B / A) is 18: 1. 9. Tube furnace according to one or more of claims 1 to 8, characterized in that the platelet boat (12) is so high is that the upper surface of the plate to be treated (13) from the ceiling (11) and the bottom (9) of the reaction tube (2) have approximately the same distance. 10. Tube furnace according to one or more of claims 1 to 9, characterized in that the heating plates (14) consist of an electrically insulating material whose thermal conductivity is between 1.24. 10 ~ ³ and 16.5. io "" ³ (cal / sec cm. ° c) and on its side facing away from the reaction tube with a resistance wire electrically heated heating coil (26) are equipped. 11. Tube furnace according to one or more of claims 1 to 10, characterized in that the hot soldering points to the ^{FI 9} 72 125 409883/1278 Temperature control belonging thermocouples between the Heating plates (14) and the reaction tube (2) are positioned. 12 .. Tube furnace according to one or more of claims 1 to 11 / characterized in that the material from which the insulating jacket is made is between approximately 0.33. 10 and about 0.45. 10 (cal / sec. Cm. ⁰ C) lying thermal conductivity and a mass lying between about 6.8 and about 15.5 kg. 13. Tube furnace according to claim 12, characterized in that the The insulating jacket (28) consists of fibrous aluminum silicate. 14. Tube furnace according to one or more of claims 1 to 13, characterized in that the insulating jacket (28) from Reaction tube (2) and space delimited by two end faces has a gas inlet and a gas outlet opening. 15. Tube furnace according to one or more of claims 1 to 14, characterized by its use in several consecutive High-temperature process steps that take place at different temperatures. Fi. 9 72 125. .409883 / 1278 Blank page