WO2012031722A1

WO2012031722A1 - Cvd reactor/gas converter and electrode unit therefore

Info

Publication number: WO2012031722A1
Application number: PCT/EP2011/004441
Authority: WO
Inventors: Frank Grundmann
Original assignee: Centrotherm Sitec Gmbh
Priority date: 2010-09-10
Filing date: 2011-09-02
Publication date: 2012-03-15
Also published as: TW201217573A; DE102010045041A1

Abstract

A CVD reactor/gas converter, a process for vapor deposition or gas conversion and an electrode unit are described. The CVD reactor/gas converter comprises a casing, which forms a process chamber inside and comprises one casing wall having at least two feedthroughs. At least one pair of first electrode units spaced with respect to each other, which comprise at least one contact part located in the process chamber and a connection part extending through a corresponding feedthrough in the casing wall, as well as at least one pair of spaced second electrode units completely located inside the casing are provided. An electrically conductive bridge element connects the pair of second electrode units inside the casing. In the method for vapor deposition or gas conversion, a plurality of rods and connection elements or of rod pairs connected to each other is positioned in a process chamber in such a way that two first electrode units are electrically serially connected via the rods and the connection elements or via the rod pairs and at least one pair of the second electrode units. A desired gas atmosphere is adjusted inside the process chamber, and a voltage is applied to the two first electrode units, so as to achieve a current flow through the rods and connection elements or through the rod pairs. The electrode unit is provided for use in a CVD reactor/gas converter having a casing, which forms a process chamber inside and comprises a casing wall having at least one feedthrough. The electrode unit comprises an electrically conductive contact part, an electrically conductive connection part connected to the contact part and an electrically conductive plate element having a diameter, which is larger than the diameter of the feedthroughs. The plate element is fixable to the casing wall comprising the feedthroughs from the outside in such a way, that the plate element seals a corresponding feedthrough and directly or indirectly supports the connection part of the electrode unit in an electrically conductive manner.

Description

CVD reactor/gas converter and electrode unit therefore The present invention relates to a CVD reactor/gas converter, further to a method for a vapor deposition or gas conversion in such a reactor as well as to an electrode unit for use in a CVD reactor/gas converter, particularly in a silicon deposition reactor or in a high temperature gas converter. It is known in the technical field of semiconductors and photovoltaic, to produce high purity silicon rods e.g. in the Siemens process in deposition reactors, which are also referred to as CVD reactors. In the Siemens process, first silicon thin rods are disposed in the reactors, and thereafter silicon is deposited during a depositing process. The silicon thin rods are disposed in clamping and contacting devices, which hold the silicon thin rods in a desired orientation on the one hand and which provide for electrical contacting on the other hand. Usually, each two of the silicon thin rods are connected via electrically conducting bridges and their respective free ends, in order to form an electrical circuit. During the deposition process, the silicon thin rods are heated to a predetermined temperature by a current flow at a predetermined voltage causing resistance heating, wherein deposition of silicon from a vapor or gas phase takes place on the silicon thin rods. The deposition temperature is usually 900-1350°C and particularly 1100-1200°C, but may also be another temperature.

The clamping and contacting devices may consist of a re-usable base element and a clamping unit, as is described e.g. in DE 202010002486.2, which also belongs to the same applicant and was not published before filing of this application, wherein the clamping unit provides for tide clamping and tide electrical contacting of the silicon thin rods. The base element and the clamping unit may consist e.g. of pure carbon or graphite. The base element may e.g. have a H-configuration in a cross-sectional view and may be in electrical contact with an electrode unit on the one hand and with the clamping unit on the other hand. It is also possible that the clamping unit directly contacts a part of the electrode unit located in the process chamber. Each of these electrode units comprise a contacting part located in the process chamber as well as a connection part extending through a wall of the process chamber to the outside.

Furthermore, also high temperature gas converters are known in the technical field of semiconductors, which are referred to as converters in the following, wherein these converters preprocess gases for e.g. CVD deposition processes as such as for the Siemens process described above. In one type of converter, graphite rods (or rods made from pure carbon) are disposed inside a processing chamber to form resistance heating elements, which are contacted via an electrode unit at their bottom side. Each of the electrode units used therefore comprise a contacting part located in the process chamber as well as a connection part extending through a wall of the process chamber to the outside. For high temperature gas conversion, the graphite rods are heated to the required temperature range, e.g. to 1400°C. Then, gases directed into the process chamber are converted at these high temperatures. As an example, a conversion of SiCL₄ (silicon tetrachloride) and H₂ (hydrogen) to SiHCL₃ (trichlorsilan) and HCL (hydrogen chloride) is mentioned. The trichlorsilan is usually used as a processing gas for silicon deposition.

In both reactor types, it is necessary to direct high currents through the rods (silicon thin rods/graphite rods) located in the process chamber. Thus, the electrode units must be constructed for correspondingly high currents as well as for the temperatures prevailing in the process chambers.

Due to the employed process atmospheres, it is necessary to use corresponding sealings in the region of the electrode feedthroughs, wherein these sealings reliable inhibit exhaust of gases also at high temperatures. In known electrode units, such as described in DE 10 2010 013 043.5, also belonging to the applicant of the present application, which was not published before filing of the present application, sealings, which are e.g. made of PTFE, are inserted at the chamber side between a collar of the connection part of the electrode unit and the bottom wall of the process chamber. Thereafter, the electrode units are clamped from the outside and are pulled against the sealings. In this arrangement, on the one hand the construction of the connection parts and the feedthroughs in the bottom wall of the process chamber is complicated, and on the other hand the assembling effort is comparatively high. Furthermore, a problem exists in that the seal material, such as PTFE, modifies over the lifetime of the seal, particularly regarding the temperatures in the process chambers. Particularly, the seal material becomes thinner due to plastic flow or deformation. Therefore, it may be necessary to tighten the electrode units at regular intervals. However, tightening is very time consuming, since CVD reactors/converters usually have many electrode units of the type described above. Furthermore, access to corresponding tightening screws below the bottom of the CVD reactor/converter is usually a quite constraint. Furthermore, the PTFE sealings need to be elaborately cooled, since the sealings cannot resist the high temperatures, wherein the cooling is carried out via internal water cooling of the connection parts of the electrode units in the electrode unit described above.

Furthermore, processes take place in the reactors, which may be affected by metals in the electrode, particularly by copper. Specifically, metal contamination from the electrode material may occur. In order to not negatively affect the corresponding process (silicon deposition process/gas conversion), the part of the electrode unit exposed to the process gas in the process chamber must be made from a material, which does not affect the processes. Even though, copper would be used as a conductor for the electrodes, copper would lead to undesired pollution inside the process chamber. Therefore, it is e.g. known to provide a silver coating on copper electrodes in order to avoid pollution inside the process chamber. However, a problem exists that these coatings may wear off, and, after a while, copper is exposed again inside the process chamber and leads to undesired pollutions. In an alternative solution, an electrode unit had been proposed, wherein the electrode completely consists of silver. Such an electrode overcomes the problem of pollutions caused by electrodes within the process chamber, however, this solution leads to very high costs, since the electrode has to have a certain length so as to extend through the bottom wall of the CVD reactor/converter, and furthermore, the electrode has to have a certain thickness in order to provide the required currents. Starting from the prior art described above, the problem to be solved by the present invention is to provide for an alternative CVD reactor/gas converter, an alternative process for vapor deposition or gas conversion in such a CVD reactor/gas converter and for an alternative electrode unit for use in such a CVD reactor/gas converter, which overcome at least one of the problems mentioned above.

According to the invention, a CVD reactor/gas converter according to claim 1 , a process for vapor deposition or gas conversion in such a CVD reactor/gas converter according to claim 8 and an electrode unit according to claim 1 1 is provided. The dependent claims are directed to further embodiments of the invention.

In particular, a CVD reactor/gas converter is provided, which comprises a casing forming a process chamber within and comprising a casing wall having at least two feedthroughs. At least one pair of first electrode units is provided, which are spaced and comprise at least one contact part located inside the process chamber and one connection part extending through a corresponding feedthrough in the casing wall. Furthermore, a pair of second electrode units is provided, which are spaced and located completely inside the casing, further an electrically conducting bridge element is provided, which electrically connects the pair of second electrode units inside the casing. Thus, at least two first electrode units are provided, wherein a current may be directed into the process chamber from the outside. Furthermore, at least two electrode units are provided, which are completely located inside the casing, and thus do not provide an electrical connection out of the casing. With such an arrangement, it is possible to serially connect the two first electrode units via the second electrode units via rods, such as silicon rods, located in the process chamber. Thus, it is possible to connect e.g. a first electrode unit via a silicon rod pair or a graphite rod pair with a corresponding bridge of silicon or graphite to a second electrode unit, while the other electrode unit of the second electrode units is connected via a corresponding silicon rod pair or a corresponding graphite rod pair having bridges of silicon or graphite, to the other unit of the first electrode units. The two second electrode units may be connected e.g. via a bridge element made of graphite or via an appropriate silicon nitride coated electrical conductor to each other so that the second electrode units have about the same electrical potential. Thus, a serial connection is created between the two first electrode units via the silicon rod pairs, the second electrode units and the bridge element.

Since the two electrode units are completely disposed inside the casing and are electrically conductive connected via the bridge element, feedthroughs in the region of these electrode units may be avoided, which substantially simplifies the construction of the CVD reactor/gas converter. Particularly, also maintenance is simplified, since the amount of electrode units possibly to be tightened, is reduced, whereas the space generally becomes more ample, since some of the feedthroughs are omitted. Depending on the construction of the power source, it is possible to provide several pairs of second electrode units, which may be serially connected or made up from one pair of first electrode units in the manner described above.

Preferably, at least one thermal and/or one electrical isolation is provided between the first and second electrode units and the casing. In a preferred embodiment, at least those parts of the first electrode units, of the second electrode units and/or of the bridge elements exposed to the process space are made of a material, in particular graphite, which does not form any pollution for a process in the CVD reactor/gas converter. Thus, it is ensured that the process is not affected. Specifically graphite is appropriate, since graphite also holds its shape at high temperatures. In particular, in case a thermal isolation is provided between the electrode units and the usually cooled casing wall, the corresponding components are not cooled and are exposed to the process temperatures.

In order to avoid unnecessary heat dissipation via the casing, at least the casing wall comprising the feedthroughs is covered at least partially with a thermal isolating medium, such as graphite felt, wherein the thermally isolating medium is not permeable in the region between the first electrode units and the second electrode units, and wherein an electrically isolating material, such as quartz glass is provided at least in this area. Thermal isolation and, thus, unnecessary heat dissipation in the region of the casing wall is avoided or at least decreased by the graphite felt. Furthermore, corresponding cooling of the casing wall may either be totally omitted, or the amount of cooling may be substantially reduced in comparison to a system without graphite felt. The electrically isolating material between the first and second electrode units is provided to avoid a short circuit between the two electrode units.

According to a particularly preferred embodiment of the invention, each of the first electrode units comprises a plate element having a diameter, which is larger than the diameter of the feedthroughs, wherein the plate element is fixed from the outside to the casing wall comprising the feedthroughs in such a way that the plate element seals a corresponding feedthrough, and wherein the plate element preferably directly or indirectly carries the connection part of the electrode unit in electrically conductive manner. By providing a plate element located outside, which seals the feedthroughs from the outer side, the sealing area is further away from the process chamber, and thus is not exposed to the high temperatures, which may provide a better sealing. Furthermore, such a plate element may be simply fixed to the casing wall. Preferably, at least one electrically isolating seal element is provided between the plate element and one outer surface of the casing wall. By this means, the plate element is electrically isolated from the casing wall, since the plate element itself is electrically conductive connected to the connection part of the electrode unit and, thus, may have the same electrical bias.

In one embodiment of the invention, a cooling unit connected to the plate element is provided , so as to avoid excessive heating of the plate element and , thus, excessive heating of the sealing area between the plate element and the casing wall. Such excessive heating might also be caused by heat dissipation from the process chamber through the contact part located in the process chamber and through the connection part extending through the feedthrough in the casing wall. Such cooling of the plate element is particularly advantageous in case the components are thermally isolated with respect to the usually cooled casing wall having feedthroughs.

In the method for vapor deposition or gas conversion in a CVD reactor/gas converter of the type mentioned above, a plurality of rods and connection elements are rod pairs connected to each other is disposed in the process chamber such that two first electrode units are electrically serially connected via the rods and the connection elements or the rod pairs and at least one pair of the second electrode units. Thereafter, a desired gas atmosphere is adjusted inside the process chamber, and a voltage is applied to the two first electrode units, in order to cause a current flow through the rods and the connection elements or the rod pairs so as to heat these elements by the current flow. In this manner, corresponding treatment inside the process chamber may be carried out in a simple and cost effective manner. Preferably, the rods and the connection elements or the rod pairs are made of silicon, and the gas atmosphere contains silicon, particularly trichlorsilan, in order to cause deposition of silicon on the rods and the connection elements or on the rod pairs. The electrode unit for use in a CVD reactor/gas converter in a casing, forming a process chamber inside and comprising a casing wall having at least one feedthrough, comprises particularly an electrically conductive contact part, an electrically conductive connection part connected to the contact part, wherein the length of the connection part is larger than the feedthrough in the casing wall, and an electrically conductive plate element having a diameter, which is larger than the diameter of the feedthroughs, wherein the plate element is fixable from the outside to the casing wall comprising the feedthroughs in such a way that the plate element seals a corresponding feedthrough, and wherein the plate element preferably directly or indirectly carries the connection part of the electrode unit in an electrically conductive condition. Such an electrode unit has the benefits mentioned above. Preferably, at least one electrically isolating seal element is provided to be disposed between the plate element and the casing wall. At least the exposed parts of the contact part and/or of the connection part of the electrode unit are made of an material, such as in particular graphite, which does not form pollutions for a process inside the CVD reactor/gas converter in order to avoid to affect the process inside the CVD reactor/gas converter. Preferably, the plate element comprises feedthroughs for conducting a cooling fluid in order to provide for cooling of the plate element so as to avoid that the plate element becomes too warm, and particularly affects a sealing between the plate element and the casing wall. Preferably, a CVD reactor/gas converter having a casing forming a process chamber inside and having a casing wall having at least one feedthrough, comprises at least one electrode unit of the type described above, wherein the plate element seals the corresponding feedthrough. The invention will be explained in more detail in the following referring to the figures. In the drawings, Figs. 1 shows a schematic sectional view through a central region of a

CVD reactor/gas converter;

Fig. 2 shows an enlarged detail of a partial area in Fig. 1 ;

Fig. 3 shows an enlarged detailed view of a partial area of Fig. 1 , showing the region of the first electrode unit;

Fig. 4 shows an enlarged partial view of an electrode unit, similar to Fig.

3, according to another embodiment;

Fig. 5 shows an enlarged sectional view of a pair of second electrode units according to one embodiment of the invention;

Fig. 6 shows an enlarged detailed view of a second electrode unit according to another embodiment of the invention;

Fig. 7 shows a schematic sectional view of a pair of second electrode units according to another embodiment of the invention. Terms such as above, below, right, left etc. used in the following description, relate to the illustration in the figures and are not to be seen as limiting, even though these terms may refer to a preferred embodiment.

Fig. 1 shows a schematic sectional view through a CVD reactor, which is formed as a silicon deposition reactor in the shown construction.

In the view according to Fig. 1 , a bottom wall 3 of a casing (not shown in detail) of the CVD reactor 1 is shown. Thus, a process chamber of the CVD reactor is formed above the bottom wall 3, wherein the process chamber is sealed to the environment by casing walls not shown in detail.

Furthermore, first and second electrode units 5 and 6 are shown in Fig. 1 , wherein these electrode units are shown in more detail also in Figs. 2 and 3. An isolating unit 8 as well as an arrangement of silicon rods 10 is shown adjacent to the bottom wall 3. The bottom wall 3 may be of a generally known type, which comprises internal cooling passages for actively cooling the bottom wall 3. Furthermore, feedthroughs 14 for feeding through the first electrode units are formed in the bottom wall 3, as will be explained in more detail in the following. In the region between the two electrode units 6, the bottom wall 3 comprises corresponding recesses 16. The first electrode units 5, wherein one thereof is enlarged shown in Fig. 3, comprise a contact part 18 located in the process chamber of the CVD reactor, a connection part 19 as well a plate element 20.

The contact part 18 of the first electrode unit 5 consists of an electrically conductive material and is in electrically conductive contact to the connection part 19, which also consists of electrically conductive material. In the shown preferred embodiment, the contact part 18 as well as the connection part 19 consist of graphite, since graphite does not affect a silicon deposition process inside the process chamber. Alternatively, these parts may also be made of another appropriate electrically conductive material. However, graphite is particularly appropriate, since graphite is able to resist the temperatures in the process chamber.

The contact part 18 may be detachably supported at the connection part 19 and forms a fixture for a silicon rod 11 of the silicon rod arrangement 10. This fixture is of any appropriate type, which provides for electrically contacting the silicon rod 11 and furthermore provides for sufficient form fit, so as to hold the silicon rod 11 in the position shown in Fig. 1 during a silicon deposition process.

The connection part 19 has a T-shape in the shown embodiment having a horizontal section 22 and a stem section 23. The horizontal section 22 has a recess (not shown in detail) at its upper surface for receiving the contact part 18. The horizontal section 22 forms an abutment surface at its bottom side, wherein the connection part 19 may at least partially abut at this abutment surface on the isolating unit 8, as will be explained in more detail in the following, so as to hold the connection part 19 in the shown orientation. Alternatively, it is also possible to omit the horizontal section 22. The length of the stem section 23 of the connection part 19 is larger than the length of the feedthrough opening 14 in the bottom wall 3. Furthermore, the diameter of the stem section is smaller than the diameter of the feedthrough opening 14 in the bottom wall 3. The stem section 23 has a recess 25 at its lower end for receiving a contact bolt 27 of the plate element 20, as will be explained in more detail below.

The plate element 20 consists of a plate body 26, the contact bolt 27 mentioned above as well as of a contact bolt 28. The plate body 26 as well as the contact bolts 27, 28 are made of an electrically conductive material each. Whereas the plate body 26 preferably consists of steel, the contact balls may be made e.g. from copper. However, it is also possible to use different materials for these elements.

The diameter of the plate body 26 is larger than the diameter of the feedthrough opening 14 in the bottom wall 3. The plate body 26 comprises at least one internal passage, through which a cooling fluid may be directed, as is shown by the cooling fluid inlet and outlet passages 30. The plate body 26 further comprises feedthroughs 32 for extending fixing elements 33 therethrough. The feedthroughs 32 are formed in a region of the plate body 26, which is outside a projected area of the feedthroughs 14 of the bottom wall 3, in order to allow for fixing the plate body 26 at the bottom wall 3 by the fixing elements 33, as is best shown in Fig. 3. In the region of the feedthroughs 32, electrically isolating bushings, such as PTFE bushings, are provided, so as to electrically isolate the fixing element 33 with respect to the plate body 26. Furthermore, also at the bottom side of the plate body 26, an electrically isolating element is provided, so as to provide also electrical isolation with respect to the fixing element 33 in this region.

Furthermore, an electrically isolating seal 35 is provided between the plate body 26 and the bottom side of the bottom wall 3. This seal 35 consists e.g. of PTFE and provides also a sealing function besides an electrical isolation between the plate body 26 and the bottom wall 3 in order to seal the process chamber of the CVD reactor to the environment.

The contact bolt 27 is appropriately fixed to a plate body 26 in a fixed spacial relationship or is integrally formed with the plate body. The contact bolt 27 is matched to the dimensions of the recess 25 in the stem section 23 of the connection part 19, so as to provide a tightly fitting fixture. By tis means, on the one hand a good electrical contact and on the other hand mechanical stability for holding the connection part 19 in a predetermined orientation shall be provided. In particular, the contact bolt and the recess 25 may be formed in such a way that a bolt or screw connection or a bayonet connection is possible. The contact bolt 28 is electrically conductive connected to a plate body 26 in opposing relation to the contact bolt 27. The contact bolt 28 is provided for externally electrically contacting the first electrode unit 5. Alternatively it will be obvious to the person skilled in the art, that a corresponding electrical contact may also be achieved in another way via a plate body 26.

Also the second electrode 6 is provided for fixing a corresponding silicon rod 1 1 of the silicon rod arrangement 10. For this purpose, the second electrode unit 6, which is shown in more detail in Fig. 2, includes a contact part 38 as well as a stabilizing part 39. The contact part 38 may be constructed in the same way as the contact part 18 of the first electrode unit 5. In particular, the contact part 38 has a corresponding fixture for a silicon rod 1 1 , the fixture being sized such that a good electrical contact to the silicon rod 1 1 as well as a corresponding mechanical support is provided.

Also the stabilizing part 39 may be constructed generally similar to the connection part 19 of the first electrode unit 5. However, the stabilizing part 39 must be formed shorter, since the stabilizing part shall not extend through the bottom wall 3 and does not need a recess for receiving a contact bolt at its lower end. The stabilizing part 39 may comprise a corresponding fixture for the contact part 38 in order to provide for electrical contact between the two elements and in order to mechanically hold the contact part 39.

Furthermore, the stabilizing part 39 comprises a fixture (not shown in detail) for an electrically conductive connection bridge 40. This connection bridge 40 may be best seen in Fig. 1 . The connection bridge 40 extends between and electrically connects a pair of the second electrode units 6, as will be explained in more detail in the following. The isolating unit 8 consists of thermal isolating elements 41 , 42 and 43 as well as of electrically isolating elements 45, 46, and 47.

The thermal isolating elements 41 -43 may e.g. consist of a graphite felt or of another appropriate material, which may resist the high temperatures within the CVD reactor on the one hand and does not introduce any pollutions into the CVD process on the other hand.

The thermal isolating element 41 has the form of a bushing having an outer diameter, which is smaller than the inner diameter of the feedthroughs 14 in the bottom wall 3, and has a length, which is slightly larger than the length of the feedthroughs 14. Furthermore, each of the thermal isolating elements 41 have an inner diameter sized for receiving the stem section 23 of a connection part 19 of the first electrode units 5. Each of the thermal isolating elements 42 have an appropriate shape for being received in the recesses 16 of the bottom wall 3, wherein the circumference of the thermal isolating elements 42 is smaller than an inner circumference of the recesses 16, as can be seen in Figs. 1 and 2. Furthermore, each of the thermal isolating elements 42 have a fixture for at least partially receiving the stabilizing part 39. The fixture is matched to a corresponding part of the stabilizing part 39 in order to receive the stabilizing part 39 as tightly as possible so as to provide for a mechanical support by this means. The thermal isolating elements 43 are formed as mats or plates and are adjacently arranged to the bottom plate 2. Plates are the preferred form, since these provide more mechanical strength and have a more stable form compared to mats. The thermal isolating elements are cut in such a way that the isolating elements may be received between the electrode units 5 and 6. The isolating elements are not continuous between the first and second electrode units, as will be explained in more detail in the following. Between two second electrode units, a corresponding isolating element may be continuous, however, as can be seen in Fig. 1.

Each of the electrically isolating elements 45 have a bushing part, which may be positioned between an inner circumference of a corresponding feedthrough 14 and an outer circumference of the thermal isolating element 41 received therein. Furthermore, the thermal isolating element may comprise a part extending perpendicular to the feedthrough, the part being parallel to the bottom wall 3 and being located between the thermal isolating elements 43 and the bottom wall 3.

The electrically isolating elements 46 are formed for being positioned in the area of the recesses 16 of the bottom wall 3 and are sized in such a way that the electrically isolating elements may be received between the thermal isolating elements 42 and the walls of the recesses 16. The electrically isolating elements 46 may also comprise a part extending generally between the thermal isolating elements 43 and the bottom wall 3. Alternatively, separate isolating elements may be provided for this region. The electrically isolating elements 45 and 46 consist e.g. of corresponding PTFE elements, however, the electrically isolating elements may also be formed of another appropriate electrically isolating material. Since the electrically isolating elements 45, 46 are thermally isolated from the process chamber of the CVD reactor by means of the thermal isolating elements 41-43, the electrically isolating elements 45, 46 are confronted generally only with the temperature of the bottom wall 3 and not to the high temperatures inside the process chamber of the CVD reactor. The electrically isolating elements 47 extend between adjacent thermal isolating elements 43 in a region between the first and second electrode units 5, 6, as may be seen in Figs. 1 and 2. By these means, an electrical short circuit between first and second electrode units extending across that thermal isolating element 43 may be avoided. The electrical isolating elements 47 may consist e.g. of quartz glass. Quartz glass provides for good electrical isolation on the one hand, is sufficiently thermally stable, and does not introduce impurities into the process in the CVD reactor on the other hand.

The silicon rod arrangement 10 consists of two silicon rods 11 and one electrical connection bridge 12. Thus, silicon rod pairs being electrically connected are formed. One silicon rod 11 of such a pair is received in a corresponding first electrode unit 5, while the other silicon rod 11 of the pair is received in a second electrode unit 6. Thus, a connection between the first and second electrode units 5, 6 is formed via the silicon rods 11 and the bridge 12. Thus, a serial circuit between the two first electrode units is formed via the connection bridge 40 between two adjacent second electrode units 6, the serial circuit extending over the silicon rods 11 , the bridges 12, the two electrode units 6 and the connection bridge 40. It should be noted that the serial circuit may be extended by additional pairs of second electrode units 6 and corresponding silicon rod arrangements 10. Therefore, each two of the second electrode units are electrically connected in pairs via a corresponding connection bridge 40, and the second electrode units are electrically isolated with respect to another first or also second electrode unit in a corresponding manner. The connection bridge 40 may also consist of an electrically conductive material such as graphite or of an appropriate electrically conductive material coated with silicon nitride. Graphite does not introduce inadmissible pollutions into the reactor. In this way, e.g. eight silicon rod arrangements 10 may be serially connected between one pair of first electrode units 5. During operation of the CVD reactor, the silicon rod arrangements 10 are positioned in the process chamber of the CVD reactor, as is shown in Fig. 1 , wherein a plurality of arrangements shown in Fig. 1 may be positioned in a process chamber. As an example, 12, 18, 24, 30 or 36 rod pairs 10 may be positioned inside a process chamber. Of course, also more or less silicon rod arrangements 10 may be provided, which form, as is described above, a serial circuit between two first electrode units 5 via the second electrode units. Thereafter, a desired gas atmosphere is adjusted in the process chamber, and a voltage is applied to the first electrode units in order to initialize a current flow through the silicon rods 1 1 , the bridges 12, the second electrode units and the connection bridge 40. The rods 11 and the bridges 12 may be heated by means of the connection bridge 40 via resistance heating in order to allow for deposition of silicon thereon, as is known in the art. Fig. 5 shows an alternative embodiment of the invention in the region of a first electrode unit 5. In this embodiment, the same reference signs as above are used, as far as the same or similar elements are described.

The first electrode unit 5 according to Fig. 4 has no separate contact part 18, as in the first embodiment, but only has a connection part 19 as well as a plate element 20. The plate element 20 is constructed in the same manner as described above. The connection part 19 is formed as a straight stem section

50, which comprises a recess 52 corresponding the recess 25 at its lower end.

In its upper end, the stem section 50 comprises a corresponding fixture for a silicon rod 11 , which is not shown in detail. Alternatively, it is also possible to provide a second contact part for holding a silicon rod 11 , which may be placed e.g. on the stem section 50.

In the embodiment according to Fig. 4, an isolating unit 8 is provided. However, in this embodiment, the isolating unit 8 is punctually provided in a region of the first electrode unit 5 and does not extend over the whole region of the bottom wall 3. Particularly, the isolating unit 8 comprises a thermal isolating element 45 and an electrically isolating element 55. The thermal isolating element has a bushing section, which is adapted to be received in a feedthrough 14 in a bottom wall 3 of the CVD reactor 1 . An internal opening of the bushing part is formed for receiving the stem section 50 of the connection part 19. Furthermore, the thermal isolating element 54 has an enlarged part having a larger diameter than the feedthrough 14 in the bottom wall 3. Particularly, this region is sized in such a way that the region generally covers the electrically isolating element 55 towards the process chamber, as is shown in Fig. 4. The electrically isolating part 55 has a bushing section, which may be placed between the thermal isolating element 54 and the feedthrough 14, as well as a section extending perpendicularly thereto, which extends parallel to a surface of the bottom wall 3.

Fig. 5 shows an alternative embodiment of a CVD reactor in the region of a pair of second electrode units 6. Also in this embodiment, the same reference signs are used as were used before, as far as the same or similar elements are described. The second electrode units 6 according to Fig. 5 generally consist of a stem section 58 having lateral fixtures for a connection bridge 40. Each of the stem sections 58 may comprise fixtures for holding a corresponding silicon rod 1 1 at their upper end. Alternatively, it is also possible to provide a separate contact part, which may be e.g. placed on the stem section 58.

Also the isolating unit 8 differs in this region from the isolating unit described above. Particularly, in Fig. 5 a thermal isolating element 60, a thermal isolating element 61 as well as electrically isolating elements 62 and 63 are shown. The thermal isolating element 60 has a lower section, which is sized for being received in a recess 16 of the bottom wall 3, as well as an upper section, which is sized in such a way that it covers the corresponding recess 16. The upper section of the thermal isolating element includes a surface conically tapered toward the center. The thermal isolating element 60 further comprises a fixture sized for receiving the stem section 58 of the second electrode unit 6 in order to stabilize it. The thermal isolating element is formed either as a mat or, preferably, as a plate, which extends between the second electrode units 6, particularly in the region of the connection bridge 40. The reason therefore is that the connection bridge 40 is substantially heated by the current flowing therethrough, so that a special thermal shielding to the bottom wall 3 should be provided.

The electrically isolating element 62 is sized in such a way that it may be received between the thermal isolating element 60 and the bottom wall 3 in the region of the recess 16. Furthermore, the electrically isolating element 63 has the form of a mat or a plate, which may be placed between the thermal isolating element 61 and the bottom wall 3.

Even though, the thermal isolating elements 60 and 61 and the electrically isolating elements 62 and 63 are shown as separate elements, these isolating elements may also be formed as one part.

Fig. 6 shows another embodiment of the invention in the region of an alternative second electrode unit 6. In this embodiment, the electrode unit 6 generally consists of a support element 67 and an electrically conductive contact element 68 received therein. The support element 67 needs to be made of a material, which has a sufficient mechanical and thermal stability and does not introduce pollutions into the process chamber. The support element 67 may be e.g. formed of graphite or silicon carbide, or may comprise or consist of e.g. a quartz glass body or a ceramic body. The support element 67 has a receiving space for the contact element 68 so as to be able to hold the contact element 68 mechanically stable. Furthermore, the support element 67 comprises a lateral feedthrough so as to be able to receive an end portion of a connection bridge 40 to allow an electrical connection between the contact element 68 and the connection bridge 40. Of course, it would be also possible to provide the connection bridge 40 in a region outside the support element 67. Further, the connection bridge 40 may be surrounded by a thermal isolation 70. The thermal isolation 70 may also be formed in such a way that the thermal isolation shields the connection bridge 40 from the process gas atmosphere. Thus, the thermal isolation 70 may perform the function to avoid contamination, which may be introduced by the connection bridge into the process chamber, or may perform the function of protecting the connection bridge 40 against corrosion by the process gases. The isolation may consist e.g. of silicon carbide or silicon nitride.

The contact element 68 has a fixture (not shown in detail) for receiving and holding a silicon rod 11. Alternatively, it would also be possible to provide an additionally detachable holding element for a silicon rod 11 , which may be placed e.g. on the contact element 68.

In the illustration according to Fig. 6, the connection bridge 40 is surrounded by a thermal isolating element 70. Furthermore, an electrically isolating element 71 and another thermal isolating element 72 are shown. The electrically isolating element 71 is sized for being positioned between the support element 67 and the bottom wall 3, particularly in the region of the recess 16. The thermal isolating element 72 is sized for covering the electrically isolating element.

Fig. 7 shows another embodiment of the invention in the region of a pair of second electrode units 6.

The second electrode units 6 generally consist of a stem section 73, which may comprise a corresponding recess for receiving a silicon rod 11 at the upper surface. Alternatively, it is also possible to include an additional contact element, which may be positioned on the stem section 73.

In the embodiment shown in Fig. 7, the connection bridge 40 is formed as a plate element, which comprises openings for receiving the stem sections 73. Thus, the stem sections 73 may be stabilized via the connection bridge 40.

Furthermore, Fig. 7 shows a thermal isolating element 75 in form of a plate element, which also comprises feedthroughs for the stem sections 73 of the second electrode units. Furthermore, also thermal isolating elements 76 are provided, which may be at least partially positioned in the recesses 16 in the bottom wall 3 of the CVD reactor 1. Furthermore, electrically isolating elements 77 and 78 are shown, which are sized to be positioned between the thermal isolating elements 76 and the bottom wall 3 or between the thermal isolating element 75 and the bottom wall 3, respectively.

Even though, recesses 16 are shown in the region of the second electrode units 6 also in this embodiment, it should be noted that particularly in this embodiment, the corresponding recesses may be omitted, in case the connection bridge 40 provides for sufficient mechanical stability for the stem sections 73. Of course, this is also true for the other embodiments, in which the recess 16 is provided so as to provide for improved mechanical stability for the two electrode units 6. Of course, also the electrode unit according to Fig. 1 , consisting of first electrode units 5 and second electrode units 6, may be used for a converter in the same manner. The electrode unit according to Fig. 1 may be used for CVE reactors as well as for converters, thus, providing a great benefit. Many alternative embodiments will be obvious for the person skilled in the art, wherein these embodiments shall be covered by the following claims. The head portion was described a homogeneous solid material made of silver, however, the head portion may also consist of another material having a good conductivity, provided that the material does not affect the processes inside the CVD reactor/converter. Furthermore, the head portion does not necessarily consist of the alternative material, which is homogeneous and fully formed, since also combinations of materials would be conceivable for the head portion. It is important that the region of the head portion, which is exposed to the process chamber of the CVD reactor/converter, permanently does not affect processes inside the process chamber. Particularly, combinations of an electrical conductor and an isolator are conceivable, such as a head portion made of silver and coated with PTFE.

Claims

1. A CVD reactor/gas converter, which comprises:

a casing forming a process chamber inside and comprising a casing wall having at least two feedthroughs;

at least one pair of first electrode units spaced from each other and at least one corresponding contact part disposed in the process chamber, and comprising a connection part extending through a corresponding feedthrough in the casing wall;

at least one pair of second electrode units spaced from each other and positioned completely inside the casing; and

an electrically conductive bridge element, electrically connecting the pair of second electrode units inside the casing.

2. The CVD reactor/gas converter according to claim 1 , which comprises at least one thermal and/or one electrical isolation between the first and second electrode units and the casing.

3. The CVD reactor/gas converter according to claim 1 or 2, wherein at least the parts of the first electrode units, of the second electrode units and/or of the bridge element, which are exposed to the process chamber, are made of a material, particularly of graphite, which does not form pollutions for a process in the CVD reactor/gas converter.

4. The CVD reactor/gas converter according to one of the preceding claims, wherein at least the casing wall comprising the feedthroughs is covered at least partially with a thermally isolating medium, such as graphite felt, wherein the thermally isolating medium is not permeable in the region between the first electrode units and the second electrode units, and wherein at least an electrically isolating material, such as quartz glass, is provided in these regions.

5. The CVD reactor/gas converter according to one of the preceding claims, wherein each of the first electrode units comprises a plate element having a diameter, which is larger than the diameter of the feedthroughs, wherein each plate element is fixed from the outside to the casing wall comprising the feedthroughs in such a way that the plate element seals the corresponding feedthrough, and

wherein the plate element directly or indirectly supports the connection part of the electrode unit in electrically conductive manner.

6. The CVD reactor/gas converter according to claim 3, wherein at least one electrically isolating seal element is provided between the plate element and an outer surface of the casing wall.

7. The CVD reactor/gas converter according to claim 3 or 4, which further comprises a cooling unit in connection with the plate element.

8. A method for vapor deposition or gas conversion in a CVD reactor/gas converter according to one of the preceding claims, wherein the method comprises the following steps:

placing a plurality of rods and connection elements or rod pairs connected to each other in the process chamber in such a way that two first electrode units are electrically serially connected via the rods and the connection elements or via the rod pairs and at least one pair of the second electrode units;

adjusting a desired gas atmosphere inside the process chamber; and applying a voltage between the two first electrode units so as to achieve a current flow through the rods and the connection elements or through the rod pairs, so as to heat these rods or rod pairs respectively.

9. The method according to claim 8, wherein the rods and the connection elements or the rod pairs consist of silicon, and wherein the gas atmosphere contains silicon, particularly trichlorsilan, so as to cause deposition of silicon on the rods and the connection elements or the rod pairs.

10. The method according to claim 8, wherein the rods and the connection elements or the rod pairs consist of graphite, and wherein the gas atmosphere contains silicon, particularly silicon tetrachloride, so as to cause a conversion of silicon tetrachloride to trichlorsilan.

1 1 . An electrode unit for use in a CVD reactor/gas converter having a casing, which forms a process chamber inside and comprises a casing wall having at least one feedthrough, wherein the electrode unit comprises: an electrically conductive contact part;

an electrically conductive connection part, connected to the contact part, wherein the length of the connection part is larger than the length of the feedthrough in the casing wall; and

an electrically conductive plate element having a larger diameter than the diameter of the feedthroughs, wherein each plate element is fixable to the casing wall comprising the feedthroughs from the outside in such a way that the plate element seals a corresponding feedthrough, and wherein the plate element directly or indirectly supports the connection part of the electrode unit in an electrically conductive manner.

12. The electrode unit according to claim 1 1 , which comprises at least one electrically isolating seal element provided for being positioned between the plate element and the casing wall.

13. The electrode unit according to claim 1 1 or 12, wherein at least the exposed parts of the contact part and/or of the connection part of the electrode unit consist of a material, particularly of graphite, which does not form pollutions for a process in the CVD reactor/gas converter.

14. The electrode unit according to one of claims 1 1 to 13, wherein the plate element comprises feedthroughs for conducting a cooling fluid. A CVD reactor/gas converter having a casing, which forms a process chamber inside and comprises a casing wall having at least one feedthrough and at least one electrode unit according to one of claims 11 to 14, which are attached to the casing wall in such a way that the plate element seals a corresponding feedthrough.