WO2011116990A1

WO2011116990A1 - Electrode arrangement

Info

Publication number: WO2011116990A1
Application number: PCT/EP2011/001552
Authority: WO
Inventors: Jürgen Haaga; Michael Leck
Original assignee: Centrotherm Sitec GmbH
Current assignee: Centrotherm Sitec GmbH
Priority date: 2010-03-26
Filing date: 2011-03-28
Publication date: 2011-09-29
Anticipated expiration: 2012-09-26
Also published as: DE102010013043A1; DE102010013043B4

Abstract

An electrode arrangement for use in a CVD-reactor/converter and CVD-reactors/converters are described. The electrode arrangement has a shaft portion of an electrically conducting material, a head portion of an electrically conducting material, which is connected to the shaft portion in an electrically conducting manner, which head portion has a seal surface axially facing towards the shaft portion and a biasing unit. The biasing unit has at least one elastic element and an adjustment unit which may be coupled to the shaft portion, wherein the adjustment unit comprises adjustment means which are capable of compressing the elastic element between two counter surfaces, such that a restoring force of the elastic element acts in an axial direction of the shaft portion, in order to bias the axially facing seal surface at the head portion against a counter seal surface. The CVD-reactor/converter has a process chamber defining a process space, the process chamber comprising at least one through opening in its floor in which an electrode arrangement is received, such that the head portion is at least partially received in the process space, and the shaft portion is at least partially received in the through opening and is arranged outside the process space. The electrode arrangement may be of the above described type or of the type having a shaft portion of a first, electrically conducting material and a head portion of a second, electrically conducting material, wherein the head portion is completely made from the second electrically conducting material, which differs from the first material and which does not negatively influence the process within the CVD-reactor/converter, and wherein the head portion is removably attached in an electrically conducting manner on a first end of the shaft portion.

Description

Electrode Arrangement

The present invention relates to an electrode arrangement for use in a CVD- reactor, in particular a silicon deposition reactor, or a high temperature gas converter.

In the semiconductor and photovoltaic industry, it is known to produce silicon rods having a high purity for example, in accordance with the Siemens method in deposition reactors, which are also known as CVD-reactors (CVD-chemical vapour deposition). In so doing, initially thin silicon rods are received in the reactor onto which rods, during a deposition process, silicon is deposited. The thin silicon rods are received in clamping and contacting devices, which on the one hand hold them in a desired orientation and on the other hand, provide electrical contacting thereof. At their respective free ends, usually two of the thin silicon rods are connected via an electrically conducting bridge in order to be able to form an electrical circuit. The thin silicon rods are heated to a predetermined temperature during the deposition process via resistance heating thereof caused by a flow of current at a predetermined voltage. The predetermined temperature is a temperature at which a deposition of silicon from a vapour or gas phase occurs on the thin silicon rods. The deposition temperature is typically in a range of 900 to 1350 degrees Celsius and in particular, between 1100 and 1200 degrees Celsius, but may also be in a different temperature range.

The clamping and contacting devices may, for example be of the type described in the not pre-published application DE 20 2010 002 486 of the applicant, which comprises a base element for multiple uses and a clamping unit. The clamping unit provides secure clamping and secure electrical contacting of the thin silicon rod. The base element and the clamping unit may for example be of pure carbon or graphite. The base element may for example comprise an H-configuration in cross section and may on the one hand be in electrically conducting contact with an electrode arrangement and on the other hand with the clamping unit. The base element typically is freely seated on the electrode arrangement, which has to be at least partially arranged within the process space of the CVD-reactor. The electrode arrangement also has a portion which extends through the bottom wall of the CVD-reactor to the outside.

Furthermore, in the semiconductor industry, also high temperature gas converters, which will be called converters in the following, are known, which prepare gases for example for CVD processes, such as the above mentioned Siemens method. In one type of converter, graphite rods (or also rods of pure carbon) are arranged as resistive heating elements within a process space. The rods are contacted at their lower surface via an electrode arrangement. For a high temperature gas conversion, the graphite rods are heated to the required temperature region, for example to 1400 degrees Celsius. Gases which are introduced into the process space are then converted at these high temperatures. One example for such a conversion, the conversion of SiCI₄ (silicon tetrachloride) and H₂ (hydrogen) to SiHCI₃ (Trichlorolsilane) and HCI (hydrogen chloride) is mentioned. The hydrogen chloride may subsequently be removed from the gas and the trichlorolsilane may for example be used for a CVD-method of the above type.

In both processes, high currents may be required to flow through the rods (thin silicon rod/graphite rod) which are arranged in the process space. Such high currents may be conducted into the process space via respective electrode arrangements. Furthermore, in each case processes occur, which may be impaired by some metallic materials of the electrode, in particular copper. Undesired metal contaminations may occur due to the electrode material. In order not to impair the respective process (silicon deposition process/gas conversion), at least the portion of the electrode arrangement which is exposed to the process gas in the process space has to be of a material which does not impair the process. Despite the fact that typically copper is used as the electrical conductor for electrode arrangements, such copper would lead to undesired contaminations within the process space. Therefore, it is for example known to provide copper electrodes with a silver coating, in order to avoid contaminations within the process space. In so doing, the problem occurs that the coating may be worn down and that after a certain time, copper may again be exposed within the process space, which may lead to undesired contaminations.

In an alternative solution, an electrode arrangement was suggested in which the electrode was made completely of silver. Such an electrode solves the problem with respect to the possibility of contaminations within the process space but leads to high costs with respect to the electrode arrangement since the electrode arrangement has to have a certain length in order to extend through the bottom wall of the CVD-reactor/converter and it also has to have a certain size in order to be able to carry the required currents.

To avoid process gases from escaping from the CVD reactor/converter, it is known to provide a seal between an axially facing surface of the electrode arrangement and the bottom wall of the CVD-reactor/converter. For example, PTFE seals are used here. In order to provide a good sealing effect, it is known to pull the electrode arrangement for example via a screw firmly against the seal. In so doing, the problem occurs that the sealing material, such as PTFE changes over the lifetime of the seal, in particular it may become thinner due to flowage. Therefore, it is required to retighten the screw, which pulls the electrode arrangement against the seal in regular intervals. This, however, is very time consuming due to the fact that the CVD-reactor/converter typically has many electrode arrangements of the above type. Furthermore, access to the respective tightening screw below the bottom of the CVD reactors/converters is typically difficult. In view of the previously described art, it is an object to the present invention to provide an alternative electrode arrangement which overcomes at least one of the previously mentioned problems.

In accordance with the present invention, an electrode arrangement according to claim 1 and a CVD-reactor/converter as set forth in claims 112 and 15, respectively, is provided. Further embodiments of the invention may be derived from the dependent claims. In accordance with a first embodiment, an electrode arrangement for use in a CVD-reactor/converter is provided wherein the electrode arrangement comprises a shaft portion of a first, electrically conducting material and a head portion of a second, electrically conducting material. The head portion is completely made from the second electrically conducting material, which differs from the first material, and which does not negatively influence the process within the CVD- reactor/converter. The head portion is removably attached in an electrically conducting manner on a first end of the shaft portion. Such an electrode arrangement enables the shaft portion to be made of a less expensive material, which should not be used directly within the CVD-reactor/converter, such as copper, while the head portion may be made of a more expensive material which does not impair the process, such as silver. In contrast to a silver coating on a copper base body, the head portion is completely made from the second material, such as silver and thus, there is no danger that, due to wear for example by cleaning processes or damages, copper parts are exposed within the CVD- reactor/converter. Furthermore, the head portion is removably attached to a first end of the shaft portion in an electrically conducting manner such that it may be exchanged if required. The term, removably attached, may be understood such that the separation of the two parts is possible in a manner that a new head portion may be attached to the shaft portion, i.e. the shaft portion may be used several times. The removal process should therefore leave the shaft portion in a substantially undamaged condition, even if the head portion may be damaged or even destroyed. A typical removable attachment is a threaded connection. The present invention, however, as an example also takes a solder connection into consideration, which may for example be separated by heating the parts of the electrode, or a bonding of the parts. For separation purposes, it may also be required that the head portion is cut off or sawed off or that the copper shaft has to be reworked marginally. The above mentioned configuration of the electrode arrangement enables placing the head portion within the process space in which it is exposed to process gases while the shaft portion may be arranged outside the process space and thus, there is no danger that the material of the shaft portion negatively influences processes within the CVD-reactor/converter. In an alternative embodiment, an electrode arrangement for use in a CVD reactor/converter is provided which comprises a shaft portion of an electrically conducting material, a head portion of an electrically conducting material, which is connected to the shaft portion in an electrically conducting manner, which head portion has a seal surface axially facing towards the shaft portion and a biasing unit. The biasing unit has at least one elastic element and an adjustment unit which may be coupled to the shaft portion, wherein the adjustment unit comprises adjustment means which are capable of compressing the elastic element between two counter surfaces, such that a restoring force of the elastic element acts in an axial direction of the shaft portion, in order to bias the axially facing seal surface at the head portion against a counter seal surface.

Such an electrode arrangement is capable of providing a certain bias of the seal surface of the electrode arrangement against a counterseal surface, which may also be maintained if an intermediate sealing material, such as a PTFE seal, becomes thinner. In contrast to a simple screw, the elastic element may accommodate a certain movement, in particular, a thinning of the sealing material and at the same time, ensure air tightness in the sealing area. The electrode arrangement having the biasing unit may also comprise a head portion which is made from a different material to the material of the shaft portion, as well as a preferably removable attachment for the head portion at a first end of the shaft portion. In accordance with an embodiment of the invention, the electrode arrangement may comprise an axially facing sealing surface at the head portion and/or the shaft portion, in order to provide a reliable sealing of a process space of a CVD- reactor/converter. Preferably, the head portion has a mounting section adjacent to the first end of the shaft portion and a plate section, which is spaced from the mounting section, which plate section has a diameter which is larger than the diameter of the mounting section, in order to form a sealing surface which faces in an axial direction towards the shaft portion. The plate section is preferably larger than a corresponding through opening for the electrode arrangement within the floor of a CVD-reactor/converter. In so doing, it is ensured that exclusively the head portion of the electrode arrangement is within the process space and a sealing of the process space with respect to the shaft portion is possible. A sealing unit having at least an annular or ring portion to be arranged between the axially facing sealing surface at the head portion and/or the shaft portion of the electrode arrangement and a wall portion of the CVD-reactor/converter is advantageously provided, in order to provide a respective sealing of the process space of the CVD- reactor/converter. In one embodiment of the invention, the sealing unit also comprises a tube portion, which is sized to radially encompass at least a section of the shaft portion and/or the head portion of the electrode arrangement, wherein the tube portion and the annular portion are integrally formed. This may form a sealing sleeve, which may in substance completely encompass the electrode arrangement and provide a good sealing of the shaft portion with respect to the process space and also with respect to the bottom wall of the CVD-reactor/con- verter, in order to prohibit diffusion effects of undesired contaminants. Such a sealing unit may substantially completely surround the electrode arrangement with the exception of the upper end of the head portion and a lower end of the shaft portion. In the biasing unit, the at least one elastic element is preferably a plate spring surrounding the shaft portion or an annular arrangement of compression springs, which are arranged around the shaft portion. A plate spring is particularly capable of providing a homogeneous distribution of force onto the shaft portion over its travel in order to achieve a homogeneous sealing effect. The adjustment unit preferably comprises an adjustment ring having an interior thread, which may be threaded onto an exterior thread of the shaft portion, which enables adjustment of the biasing force or a pre-adjustment thereof in a simple manner. In an alternative embodiment of the invention, at least three adjustment screws extending in an axial direction through the adjustment ring are provided. Such adjustment screws which extend in an axial direction through the adjustment ring may enable compression of the elastic element between the two counter surfaces, if access to the adjustment ring is difficult. In such a case, the adjustment ring may provide a prepositioning of the elastic element while the adjustment screws may provide compression of the elastic element.

In another embodiment of the invention, the biasing unit comprises at least one of the counter surfaces, wherein at least said one counter surface comprises a spacer facing the other counter surface in order to limit movement of the counter surfaces towards each other. In so doing, a consistent biasing force for elastic elements may be provided in a simple manner. In a preferred embodiment of the invention, the head portion and the shaft portion are attached to each other via a threaded connection which on the one hand, provides a secure hold for the elastic elements and on the other hand, provides good electrical contact between the two parts via the threaded connection.

In accordance with the invention, a CVD-reactor/converter is provided having a process chamber defining a process space. The process chamber comprises at least one through opening in its floor in which an electrode arrangement of the above described type is received, such that the head portion is at least partially received in the process space, the shaft portion is at least partially received in the through opening and is arranged outside the process space. A CVD-reactor/con- verier having such an electrode arrangement exhibits the above mentioned advantages. The through opening may have a stepped configuration such that directly adjacent to the process space, a first section is defined which has a larger diameter than a directly adjacent second section, wherein the head portion is at least partially arranged in the first section of the through opening. In so doing, it is possible to provide different diameters of the head and shaft portion for the electrode arrangement and to provide an additional separation of the shaft portion with respect to the process space. In so doing, an axially facing shoulder is formed between the first and second sections to which the head or shaft portion may abut in a sealing manner.

The invention will be described in more detail herein below with reference to the drawings. In the drawings: Fig. 1 is a schematic explosive view of an electrode arrangement for use in a CVD-reactor;

Fig. 2 is a schematic sectional view of an alternative electrode arrangement as it is mounted in the floor of a CVD-reactor; and

Fig. 3 is a schematic sectional view of an alternative electrode arrangement as it is mounted in the floor of a converter.

In the following description, terms such as above, below, right and left refer to the representation in the drawings and should not be seen in a limiting sense even though they may refer to a preferred orientation.

Fig. 1 shows a schematic explosive side view of an electrode arrangement 1 in accordance with a first embodiment, while Fig. 2 shows a schematic sectional view of an electrode arrangement according to an alternative embodiment. Since the main elements of both embodiments are similar, in the following, both embodiments will be simultaneously described, using the same reference signs for the same or similar elements. During the description, the differences between the two embodiments will be explained. The electrode arrangement 1 consists in substance of a process chamber unit 4, a passage unit 6, a seal unit 8 and a biasing unit 10.

The process chamber unit 4 has a contact and clamping unit 12, a base element 14, a cover disk 16 made of quartz and a cover ring 18 made of quartz. The contact and clamping unit 12 has, as is known for example from the above referenced DE 20 2010 002 486 a plurality of contact elements which are movable relative to each other, and which form a receiving space for a thin silicon rod 20 (see Fig. 2). The contact and clamping unit 12 may be received in a corresponding receiving space of the base element 14, whereby during an insertion into the base element 14, the receiving space for the thin silicon rod 20 is narrowed, thereby ensuring that the thin silicon rod 20 is securely clamped and electrically contacted. The base element 14 also comprises a lower receptacle for receiving a contact tip of the passage unit 6 as will be explained in more detail herein below.

The cover disk 16 made of quartz has a central opening for passing the contact tip of the passage unit 6 therethrough as will be explained in more detail herein below.

The cover ring 18 made of quartz is sized such that it will at least partially radially encompass a portion of the passage unit which is arranged within a process chamber of a CVD-reactor.

The passage unit 6 has a cylindrical shaft portion 24 and a head portion 26.

The shaft portion 24 has an upper end having an outer thread to which the head portion 26 may be threadably connected as is shown in Fig. 2. In the embodiment of Fig. 2, the shaft portion comprises a radially projecting flange 30 adjacent to the upper end having the outer thread 28, while the shaft portion in the embodiment of Fig. 1 does not have such a flange 30. This is also the main difference between the two embodiments of Figs. 1 and 2. The flange 30 forms a sealing shoulder which axially faces downwards, as well as a head abutment surface 34, which axially faces upwards.

In the embodiment according to Fig. 1 , a head abutment surface which axially faces upwards would be formed adjacent to the outer thread (not shown) of the shaft portion 24. This embodiment, however, does not have a sealing shoulder axially facing downwards.

The shaft portion 24 has an interior space for receiving a cooling device (not shown) as well as ports 36 at its lower end for attachment to a cooling fluid supply and a cooling fluid discharge. The port 36 could also be provided at the side at a lower section of the shaft portion or one could be provided below and one at the side. The cooling device may be limited to the interior space of the shaft portion, which is shown but may also extend into the head portion, in which case a seal may be required between the head portion and the shaft portion.

In Fig. 2, the port 36 and details with respect to the interior cooling device are not shown in order to simplify the representation.

The shaft portion 24 has a further outer thread section 38, which is spaced from the upper end thereof, which operates together with the biasing unit, as will be explained in more detail herein below. The outer thread section 38 may be recognized in Figs. 1 and 2 by the shaft portion 24 having a reduced diameter in this area. Adjacent to the outer thread section 38, the shaft portion 24 has a lower end, which has a further reduced outer circumference with respect to the outer thread section 38. The head portion 26 has a mounting section 40, a plate section 42, as well as a support tip 44. The mounting section 40 is cylindrically shaped and has an interior space having an inner thread 44 which is shaped such that it fits onto the outer thread 28 at the upper end of the shaft portion 24. The mounting section 40 has an outer diameter corresponding to the adjacent part of the shaft portion such that they substantially form a continuous outer contour. In the embodiment of Fig. 1 , this corresponds to the main diameter of the shaft portion 24 and in the embodiment of Fig. 2, this corresponds to the outer diameter of the flange portion 32 of the shaft portion 24.

Alternatively, it is also possible in the embodiment of Fig. 1 that the mounting section 40 of the head portion 36 has a larger diameter than the adjacent section of the shaft portion 24. In this case, a corresponding step having an axially facing shoulder at the head portion would be formed between the mounting section 40 of the head portion 26 and the adjacent portion of the shaft portion 24.

The plate section 42 of the head portion 26 has a substantially larger diameter than the mounting section 40 and radially extends beyond the same, as is shown in the figures. In so doing, an axially downwardly facing, i.e. facing towards the shaft portion, abutment shoulder 48 is formed. The support tip 44 extends above the plate section 42 and forms a centered, conically tapering truncated cone. The base element 14 of the process chamber unit 4 may be placed thereon in a fitting manner, as is shown in Fig. 2.

In the currently preferred embodiment of the invention, the shaft portion 24 is made of copper while the head portion 26 is made of silver. However, other appropriate materials, which have a sufficient electrical conductivity, may be used within the electrode arrangement. The material for the head portion should be chosen such that the process within the process chamber of a CVD-reactor is not impaired.

The sealing unit 8 is made of a integral sealing sleeve, which in accordance with the embodiment of Fig. 1 comprises a cylindrical tube section 50 and an adjacent annular or ring portion 52. The tube portion 50 is sized such that it may receive the shaft portion 24 and the mounting section 40 of the head portion 26 in a tight fitting manner. The annular or ring portion 52 has a circumference corresponding to the circumference of the plate section 42 of the head portion 26. The annular or ring portion 52 is operable to provide a sealing effect between the lower surface of the plate section 42 and a bottom wall or floor of the CVD-reactor. The sealing sleeve may also be made of multiple parts, wherein the tube section also acts as an insulator. The sealing unit 8 of the embodiment of Fig. 2 has a similar configuration, wherein the tube section 50 comprises a step corresponding to the flange 30 of the shaft portion 24. Again, the tube section is sized such that it may receive the shaft portion 24 and the mounting section 40 of the head portion 26 in a tight fighting manner. The ring portion 52 again extends radially to the upper end of the tube section 50 and acts as an axial sealing surface between a lower surface of the plate section 42 of the head portion 26 and a floor of a CVD-reactor, as shown in Fig. 2. An axially extending tube section 54, which radially encompasses the plate section 42 of the head portion 26 is connected to the ring portion 52. The biasing unit 10 comprises an insulating ring 60, a first spring counter element 62, a plate spring 64, a second spring counter element 66 and an adjustment screw 68 as well as adjustment screws 70. The insulating ring 60 is sized such that it may receive an end portion of the tube section 50 of the sealing unit 8 as well a part of the shaft portion 24 which is received therein. The insulating ring 60 provides electrical insulation against accidental ground. The first spring counter element 62 has a round plate shape and has an interior opening, which is sized such that the first spring counter element 62 may be received around the shaft portion 24.

The plate spring 64 also has a round configuration and has a centered opening, which is sized such that the plate spring 64 may be received around the shaft portion 24.

The second spring counter element 66 again has a round plate shape having an interior opening that is sized such that it may be received around the shaft portion 24 in a tight fitting manner. The second spring counter element 66 may be a flat disk, as is shown in Fig. 1 or it may have an axially extending circumferential flange 72, as is shown in Fig. 2. The flange 72 acts as a spacer with respect to the first spring counter element 62 as will be explained in more detail herein below.

The adjustment ring 68 has an interior thread which matches the outer thread section 38 of the shaft portion 24 to be threadably connected thereto. The adjust- ment ring 68 also has a plurality of axially extending threaded bores for receiving the adjustment screws 70. Fig. 2 shows two of the adjustment screws 70 being received in corresponding axially extending threaded bores in the adjustment ring 68. Preferably, altogether at least three of the axially extending threaded bores are provided for receiving a respective adjustment screw 70 in the adjustment ring 68. In the following, mounting of the electrode arrangement 1 within a CVD-reactor will be explained with reference to Fig. 2. In Fig. 2, a partial section of a bottom wall or floor 80 of a CVD-reactor is schematically shown in section. Above the bottom wall 80, the process space of the CVD-reactor is located, which is not further shown, which process space will be sealed with respect to the environment. The bottom wall 80 of the CVD-reactor has a through opening 82, which has a stepped configuration corresponding to the outer dimensions of the shaft portion 24 and the mounting section 40 of the head portion 26 of the passage unit 6. The through opening 82 is sized such that it may receive, in a tight fitting manner, the tube portion 50 of the sealing unit 8 having the shaft portion 24 received therein and the mounting section 40 of the head portion 26. In the embodiment of Fig. 1 , the through opening 82 may not have such a stepped configuration. In order to mount the electrode arrangement in a CVD-reactor, first the head portion 26 will be threadably connected to the shaft portion 24 in a secure manner in order to form the passage unit 6. Thereafter, the passage unit 6 will be received in the sealing unit 8. In so doing, the shaft portion 24 and the mounting section 40 of the head portion 26 will be inserted into the tube portion 50 of the sealing unit 8. Thereafter, these assembled elements will be inserted from above i.e. from the process space into a corresponding through opening 82 in the bottom wall 80 of the CVD-reactor. Subsequently, the distance ring 60 will be guided over the shaft portion 24 and the lower part of the tube section 50 of the sealing unit 8 and will be pressed against the lower surface of the bottom wall 80. Thereafter, in the below order, the first spring counter element, the plate spring 64 and the second spring counter element will be guided onto the lower projecting part of the shaft portion 24. Finally, the adjustment ring 68 will be threaded onto the outer threaded section 38 of the shaft portion 24 until it abuts against the second spring counter element. In so doing, the adjustment ring 68 may be manually tightened or with the aid of a respective wrench, in order to pull the shaft portion 24 downwards and possibly to bias the plate spring 64 slightly between the two spring counter elements 62 and 66. Finally, the adjustment screws 70 are threaded through the adjustment ring 68 in order to push the second spring counter element towards the first counter element and to further bias the plate spring 64. In so doing, the adjustment screws 70 are threaded into the adjustment ring 68 until the flange 72 of the second spring counter element abuts against a lower surface of the first spring counter element. In so doing, the plate spring 64 is biased in a predetermined manner. Due to this biasing force, the abutment shoulder 48 of the plate section 42 is pulled in a defined manner against the ring portion 52 of the sealing unit 8, which at this point in time, abuts against an upper surface of the bottom wall 80 of the CVD-reactor. In so doing, the interior space of the CVD-reactor is sealed in a reliable manner with respect to the environment. Even if the ring portion 52 becomes thinner due to the flow characteristics of the sealing unit, the biasing force may be maintained over a certain region of travel of the plate spring 64. The electrode arrangement may provide a secure sealing for the process space in the area of the through opening 82 for an extended period of time. In the embodiment of Fig. 1 , only one axial sealing is provided between the abutment shoulder 48 of the plate section 42 and a bottom wall 80 of the CVD- reactor. In the embodiment of Fig. 2, an additional axial sealing is provided at the area of the sealing shoulder 42 and the step within the through opening 82 in the bottom wall 80 as the skilled person will recognize in Fig. 2.

Finally, the cover ring 18 and the cover disk 16, both made of quartz, may be placed over the plate section 42 in the process space of the CVD-reactor. Subsequently, the base element 14 may be placed onto the support tip 44 of the head portion 26 and in a last step, the contact and clamping unit having a thin silicon rod received therein may be inserted into the base element 14. In so doing, the thin silicon rod 20 will be firmly clamped and electrically contacted as described in DE 20 2010 002 486.2.

The invention was described herein above with reference to embodiments of an electrode arrangement 1 without being limited to the specific configuration thereof. In particular, the process chamber unit 4 may be completely dispensed with and can also have a different configuration. Also, the biasing unit may have a different configuration, as an example, in a simple embodiment it could only comprise an elastic element and the adjustment ring 68 which may be threaded onto the shaft portion 24. The lower surface of the bottom wall 80 of the CVD-reactor and the adjustment ring 68 could act in such a case as spring counter elements. Also in this case, the elastic element could be a plate spring or for example an annular arrangement of compression springs, which are arranged in an annular manner around the shaft portion 24.

Fig. 3 shows a schematic sectional view of an alternative electrode arrangement, as it is mounted in the bottom wall of a converter. The electrode arrangement in Fig. 3 corresponds in substance to the one in Fig. 2 and therefore, only the differences with respect to Fig. 2 will be described. A main difference lies in the process chamber (not shown in detail) which, as mentioned above, is configured as a converter. Instead of the thin silicon rod, a graphite rod 90 is provided, which may be directly seated onto the support tip 44 of the head portion 26 as shown in Fig. 3. Furthermore, the quartz cover ring 18 has a thicker configuration and a primary functionality of providing insulation against accidental ground. Other than that, the configuration of the electrode arrangement is similar to the one shown in Fig. 2. Obviously, also the electrode arrangement 1 according to Fig. 1 could be used in a corresponding manner in a converter. The electrode arrangement 1 may be used with great advantage both in a CVD-reactor and in a converter.

The skilled person will realize many alternative embodiments and modifications, in particular, with respect to certain details, which fall within the spirit and scope of the following claims. The head portion was described as a homogeneous solid part made of silver, but may also be made of a different well-conducting material which does not impair the processes within the CVD-reactor/converter. Also, the head portion does not necessarily have to be a solid homogeneous body made from the other material, as different material combinations are possible for the head portion. It is important that those portions of the head portion that are exposed to the process chamber of the CVD-reactor/converter permanently do not impair processes within the process chamber. In particular, combinations made of an electrical conductor and an insulator such as for example a PTFE plated head portion made of silver could be envisaged.

Claims

1. An electrode arrangement for use in a CVD-reactor/converter, comprising: a shaft portion of an electrically conducting material;

a head portion of an electrically conducting material, which is connected to the shaft portion in an electrically conducting manner, which head portion has a seal surface axially facing towards the shaft portion;

and a biasing unit, said biasing unit having at least one elastic element and an adjustment unit which may be coupled to the shaft portion, wherein the adjustment unit comprises adjustment means which are capable of

compressing the elastic element between two counter surfaces, such that a restoring force of the elastic element acts in an axial direction of the shaft portion, in order to bias the axially facing seal surface at the head portion against a counter seal surface.

2. The electrode arrangement of claim 1 , wherein the shaft portion is made of a first, electrically conducting material and the head portion is made of a second, electrically conducting material, wherein the head portion is completely or at least partially made from the second electrically conducting material, which differs from the first material and does not negatively influence the process within the CVD-reactor/converter, and wherein the head portion is removably attached in an electrically conducting manner on a first end of the shaft portion.

3. The electrode arrangement of claim 1 or 2, wherein the head portion and the shaft portion each comprise an axially facing sealing surface.

4. The electrode arrangement of any one of the preceding claims, wherein the head portion has a mounting section adjacent to the first end of the shaft portion and a plate section, which is spaced from the mounting section, the plate section having a diameter which is larger than the diameter of the mounting section to form a sealing surface which faces in an axial direction towards the shaft portion.

5. The electrode arrangement of any one of the preceding claims, further comprising a sealing unit having at least an annular portion to be arranged between the axially facing sealing surface at the head portion and/or the shaft portion of the electrode arrangement and a wall portion of the CVD- reactor/converter.

6. The electrode arrangement of claim 5, wherein the sealing unit further

comprises a tube portion, which is sized to radially encompass at least a section of the shaft portion and/or the head portion of the electrode

arrangement, wherein the tube portion and the annular portion are integrally formed.

7. The electrode arrangement of any one of the preceding claims, wherein the at least one elastic element is a plate spring surrounding the shaft portion or an annular arrangement of compression springs, which are arranged around the shaft portion.

8. The electrode arrangement of any one of the preceding claims, wherein the adjustment unit comprises an adjustment ring having an interior thread, which may be threaded onto an exterior thread of the shaft portion.

9. The electrode arrangement of claim 8, further comprising at least three

adjustment screws extending in an axial direction through the adjustment ring.

10. The electrode arrangement of any one of the preceding claims, wherein the biasing unit comprises at least one of the counter surfaces, wherein at least said one counter surface comprises a spacer facing the other counter surface for limiting movement of the counter surfaces towards each other.

11. The electrode arrangement of any one of the preceding claims, wherein the head portion and the shaft portion are attached to each other via a threaded connection.

12. A CVD-reactor/converter having a process chamber defining a process space, the process chamber comprising at least one through opening in its floor in which an electrode arrangement of any one of the preceding claims is received, such that the head portion is at least partially received in the process space, and the shaft portion is at least partially received in the through opening and is arranged outside the process space.

13. The CVD-reactor/converter of claim 12, wherein the through opening has a stepped configuration such that directly adjacent to the process space, a first section is defined which has a larger diameter than a directly adjacent second section, and wherein the head portion is at least partially arranged in the first section of the through opening.

14. The CVD-reactor/converter of claim 13, wherein an axially facing shoulder is formed between the first and second sections to which the head or shaft portion abuts in a sealing manner.

15. A CVD-reactor/converter having a process chamber defining a process

space, the process chamber comprising at least one through opening in its floor in which an electrode arrangement is received, the electrode

arrangement comprising a shaft portion of a first, electrically conducting material and a head portion of a second, electrically conducting material, wherein the head portion is completely made from the second electrically conducting material, which differs from the first material and which does not negatively influence the process within the CVD-reactor/converter, wherein the head portion is removably attached in an electrically conducting manner on a first end of the shaft portion, wherein the head portion is at least partially received in the process space, and wherein the shaft portion is at least partially received in the through opening and is arranged outside the process space.

16. The CVD-reactor/converter of claim 15, wherein the head portion and/or the shaft portion comprises an axially facing sealing surface, which is biased against an axially facing sealing surface at or in the floor of the process chamber.

17. The CVD-reactor/converter of claim 15 or 16, wherein the head portion has a mounting section adjacent to the first end of the shaft portion and a plate section, which is spaced from the mounting section, the plate section having a diameter which is larger than the diameter of the mounting section to form a sealing surface which faces in an axial direction towards the shaft portion..

18. The CVD-reactor/converter of claim any one of claims 15 to 17, further

comprising a sealing unit having at least an annular portion which is arranged between the axially facing sealing surface at the head portion and/or the shaft portion of the electrode arrangement and the axially facing sealing surface at or in the floor of the CVD-reactor/converter.

19. The CVD-reactor/converter of claim 18, wherein the sealing unit further

20. The CVD-reactor/converter of claim any on of claims 15 to 19, wherein the through opening has a stepped configuration such that directly adjacent to the process space, a first section is defined which has a larger diameter than a directly adjacent second section, and wherein the head portion is at least partially arranged in the first section of the through opening.

21. The CVD-reactor/converter of claim 20, wherein an axially facing shoulder is formed between the first and second sections to which the head or shaft portion abuts in a sealing manner.