TWI619839B - Heating device for the susceptor of the CVD reactor - Google Patents

Abstract

A heating device, in particular for a susceptor of a CVD reactor, having a first heating element (1.1) and a second heating element (1.2), wherein each heating element (1.1, 1.2) has a heating element consisting of a heating wire (2.1, 2.2), wherein the heating member (2.1, 2.2) located in a common plane or heating a plurality of parallel heating surface (H _1, H _2), and having a surface transverse to the heating (H _1, H ₂ ) the ends of the heating elements (2.1, 2.2) of the extended contact elements (3.1, 4.1, 3.2, _4.2 ) and the contact faces (K ₁ , respectively, located parallel to the heating faces (H ₁ , H ₂ ) The contact plates (5, 6) in K ₂ ) are connected, wherein the contact elements (3.1, 3.2, 4.1, 4.2) are arranged side by side in the contact surface (K ₁ , K ₂ ) such that the heating element 1.1, 1.2) Electrically parallel between the contact plates (5, 6). In order to increase the service life of the heating device, it is proposed here that the heating elements (2.1, 2.2) of the heating element (1.1, 1.2) are of equal length and have the same electrical resistance, the contact elements of the second heating element (1.2) (3.2, 4.2) having a spacing (A ₂ ) from each other, the spacing (A ₂ ) being smaller than the spacing (A ₁ ) of the contact elements (3.1, 4.1) of the first heating element (1.1), and the contact of the second heating element (1.2) The elements (3.2, 4.2) are shorter than the contact elements (3.1, 4.1) of the first heating element (1.1).

Description

Heating device for the susceptor of the CVD reactor

The invention relates to a heating device, in particular for a susceptor of a CVD (Chemical Vapor Deposition) reactor, having at least one first heating element and at least one second heating element, wherein each of the first and second heating elements Having a heating member consisting of one or more heating wires, wherein the heating member is located in one or more mutually parallel heating faces and has an end of the heating member transverse to the contact elements of the one or more heating faces a contact plate is situated in contact with one or more contact surfaces which are parallel to one another and parallel to the heating surface, wherein the contact elements are arranged side by side in the one or more contact surfaces such that the heating element is situated on the contact plate Electrically connected in parallel.

In a CVD reactor, the processing chamber is located in a reactor housing that is hermetically sealed relative to the surrounding environment, and the process gas is introduced into the processing chamber by the intake member. The susceptor is located within the processing chamber and is heated by the heating device. For example, a substrate to be coated made of tantalum or a Group III-V element material is located on the upper side of the base. On the upper surface of the substrate, a semiconductor layer, in particular a semiconductor layer composed of a group III-V element, is deposited. This is carried out at temperatures above 1000 °C. It is provided by the heating device in order to achieve the heat required to process the temperature. Because the intake member is actively cooled and the base is sealingly adjacent, a steep temperature gradient is formed between the base and the intake member. Due to this temperature gradient, a large heat flow is generated from the susceptor to the cooling means of the intake member. In order to be able to reach the required processing temperature, the heating device must heat the temperature to 2000 ° C and deliver sufficient thermal power.

A CVD with a heating device is described in DE 10 2009 043 960 A1, DE 103 29 107 A1, DE 10 2006 018 515 A1, DE 10 2007 009 145 A1, DE 10 2005 056 536 A1 or DE 10 2007 027 704 A1. reactor. The heating device described in DE 26 30 466 A1 or US Pat. No. 3,345,498 has a heating element which extends along a spiral in the heating surface. No. 7,573,004 describes a heating element extending along a circular arc in a heating surface.

In the heating device for the CVD reactor, at least two heating members extend side by side. The heating member is connected to the same contact plate by its connecting end. This is achieved by contact elements. Thereby, the heating elements are electrically connected in parallel. The heating elements extend so closely side by side that they may touch during heating due to thermal motion. If the heating element has a potential difference on the contact contact, this can lead to local overheating or arcing. This can cause damage to the heating element.

The technical problem to be solved by the present invention is to increase the service life of the heating device.

The above problems are solved by the specification of the present invention in the scope of the patent application.

According to the invention, the side-by-side extended heating elements are designed as equal length, mutually different, electrically parallel heating elements. Furthermore, the heating elements are also designed to be identical in terms of electrical or mechanical aspects. For example, the heating member may have one or more filaments extending in a spiral shape that have the same electrical resistance. The heating wire is placed in the heating surface. The contact elements of mutually different heating elements have mutually different spacings. Thereby, the mutual spacing of the contact elements of the second heating element is smaller than the mutual spacing of the contact elements of the first heating element. According to the invention it is further provided that the contact element ratio of the second heating element The contact elements of the first heating element are short. The heating wire has a resistance per unit length which is at least 10 times larger than the contact element, which is preferably designed as a thick-walled contact pin. The contact element has an extension direction that extends transverse to the heating or contact surface. One or more contact plates extend within the contact surface. The heating member consisting of one or more heating wires extends in one or more heating faces extending parallel to each other. In a preferred embodiment, the end of the heating member having a smaller spacing than the contact element of the first heating element extends at least in the gap between the heating surface and the contact surface. One or more third or fourth heating elements may be provided. The third and fourth heating elements likewise have a heating member consisting of one or more heating wires. The end of the heating member is connected by a contact element (preferably a contact pin) extending transversely to the one or more heating faces to one or more contact faces which are parallel to each other and which are parallel to the heating surface. The third and/or fourth heating element is electrically in parallel with the first and second heating elements. All of the heating members of the first to fourth heating elements are preferably of equal length and also have the same design. In particular they have the same resistance. On the heating member, the same voltage is applied across the same section. Thereby, the heating element is provided with a uniform potential at possible contact positions such that no reactive current is formed between the heating elements at the contact position. The third and fourth heating elements have contact elements that have a smaller spacing than the contact elements of the second heating element. The heating elements of the third heating element and the fourth heating element have end sections that protrude transversely to the respective heating surface in the direction of the contact surface, the end sections having a length that is greater than the first and second heating elements The length of the end section of the heating member. The end section of the heating element has a length which is substantially equal to the distance of the associated contact element from the adjacent contact elements belonging to the same heating element, the contact elements of which are also spaced apart from each other. The length of the contact element is substantially related to the length of the end section of the heating member and the position of the associated heating surface. In particular, it is provided that the end section extending substantially perpendicular to the heating surface and the extension of the associated contact element The end side of the contact element is connected flush to the ground. The opposite end sides of the contact elements are connected to the contact plates. The contact plates can be located on a uniform horizontal surface and in a uniform contact surface. However, it is also provided that the contact plates are arranged in parallel planes, that is to say spaced apart in a direction extending transversely to the plane.

Particularly preferably, all of the heating elements that are electrically connected in parallel between the contact plates have the same length and the same design of the heating element, wherein the heating element of the heating element projects through its end section into the respective heating element. In the gap between the heating surface and the contact surface assigned to the respective contact element, the contact elements of the heating element are spaced apart from each other by a smaller distance than the contact element of the first heating element, the contact being connected to the end section element. All heating members can extend within different heating surfaces. In particular, the heating member extends along a circular arc or a spiral arc in the heating surface. However, it is also possible for one or more heating elements of mutually different heating elements to extend within a common heating surface. In particular, it is provided that all heating elements extend in a common heating surface. However, it can optionally also be provided for all of the heating elements to extend in different heating surfaces. The length of the end section of the heating element which projects into the gap is preferably equal to the distance of the associated contact element to the contact element of the first heating element. In contrast, all other heating elements are spaced apart from the contact elements of the first heating element at the extreme distal end. The heating elements can be connected side by side and thus connected to the contact plate by their associated contact elements such that when a heating voltage is applied to the contact elements, the same potential is provided at the most likely contact position. The heating wire can be made of tungsten wire. The heating wire is set in a spiral shape. In particular, the elongate heating elements thus produced extend in an arc in the heating plane. The device has a substantially circular plan or base profile. The device can have a plurality of heating devices that are electrically separated from one another. Thereby, in particular a central heating device in the shape of a disk is provided, which is surrounded by a first annular heating device, which is again second ring The heating device surrounds.

1‧‧‧ heating element

2‧‧‧heating components

3‧‧‧Contact elements

4‧‧‧Contact elements

5‧‧‧Contact plate

6‧‧‧Contact plate

7‧‧‧End section

8‧‧‧heat wire

9‧‧‧heat wire bracket

10‧‧‧ CVD reactor

11‧‧‧Intake components

12‧‧‧ Pedestal

13‧‧‧Processing room

14‧‧‧ heating device

15‧‧‧ heating device

16‧‧‧ heating device

1.1‧‧‧ heating element

1.2‧‧‧ heating element

1.3‧‧‧ heating elements

1.4‧‧‧ heating element

2.1‧‧‧ heating elements

2.2‧‧‧ heating components

2.3‧‧‧ heating elements

2.4‧‧‧ heating elements

3.1‧‧‧Contact elements

3.2‧‧‧Contact elements

3.3‧‧‧Contact elements

3.4‧‧‧Contact elements

4.1‧‧‧Contact elements

4.2‧‧‧Contact elements

4.3‧‧‧Contact elements

4.4‧‧‧Contact elements

7.1‧‧‧End section

7.2‧‧‧End section

7.3‧‧‧End section

7.4‧‧‧End section

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings: Figure 1 shows a schematic view of the structure of a CVD reactor; Figure 2 shows a top view of a heater consisting of three heating zones 14, 15, 16 which in particular have three heating means 14, 15, 16 Figure 3 shows a side view of the heater shown in Figure 2 as seen in the direction of arrow III; Figure 4 shows the radial outermost heating device 14 of Figure 2 as seen in the direction of arrow IV in Figure 2 Figure 5 shows a view of two contact areas of a heating element arrangement, wherein the heating elements 1.1, 1.2, 1.3, 1.4 are designed according to the invention and are provided with contact elements 3.1, 3.2, 3.3, 3.4 according to the invention. Figure 6 shows a first embodiment of the heating element 1 in which the contact element 3 is connected to the end section 7 of the single helical coil 2; and Figure 7 shows a second embodiment of the heating element 7, wherein the heating element 2 Designed as a double helix coil.

Figures 1 to 4 are first and basically used to display this type of device. In the drawings, the following claims of the present invention solve the technical problem.

Figure 1 shows schematically some of the basic components of a CVD reactor 10. The CVD reactor 10 has a housing that is hermetically sealed outward. An intake member 11 having an exhaust port disposed in the form of a shower head is located inside the housing, the exhaust port being oriented in the direction of the process chamber 13. One or more mutually different process gases may be passed through the intake member 11 The exhaust port is introduced into the processing chamber 13. The bottom plate of the processing chamber 13 is constituted by a susceptor 12 made of, for example, coated graphite, on the upper side of the susceptor 12 facing the processing chamber 13, one or more substrates, which should be coated with a single crystal Semiconductor layer. A heater composed of a plurality of heating devices 14, 15, 16 is located below the susceptor 12, which generates heat by being supplied with electric energy, and the susceptor 12 raises the processing temperature by the heat.

Fig. 2 shows a plan view of only the heater constituted by the heating means 14, 15, 16 in Fig. 1. A disc-shaped heating device 16 having a plurality of heating elements is centrally located, these heating elements being helically placed in a single heating plane.

The central heating device 16 is surrounded by an intermediate heating device 15, which likewise has a plurality of heating elements which extend over a helical curve in a common heating plane. The outermost heating element can only extend over a further heating surface.

The radially outermost heating device 14 is annular and has a heating element 1 extending over a circular curve. The heating elements 1 are electrically connected in parallel. A total of five heating elements are respectively provided, which each extend over a circular arc of approximately 1/3. The ends of the heating element 1 are connected to the mutually different contact plates 5, 6, respectively. On the contact plates 5, 6, the heating element 1 is energized. The contact plates 5 and 6 spaced from each other at the contact surfaces K _1, K ₂ extend. In Figures 3 and 4, the contact elements 3, 4 are shown as contact pins, each having a uniform length. The individual heating elements 1.1, 1.2, 1.3, 1.4, 1.5 are connected to the contact plates 5, 6 by respective contact elements 3, 4 of the same length. The heating elements 1.1, 1.2, 1.3, 1.4, 1.5 each have heating members 2.1, 2.2, 2.3, 2.4, 2.5, which are composed of helically curved tungsten wires which are not shown in detail. In FIGS. 1 to 4, the heating members 2.1 to 2.5 are not shown by a schematic view of a spiral-like structure, but are shown as a cylindrical structure. The spiral shaped tungsten wire extends in a cylindrical structure. The individual contact elements 3, 4 of mutually different heating elements 1.1 to 1.5 have different spacing from one another. Therefore, different voltages are released at different circumferential positions of the heating members 2.1 to 2.5. In the case where the respective heating wires of the mutually different heating members 2.1 to 2.5 are relatively thermally deformed upon heating, a local ineffective current may flow therethrough. Therefore, local overheating may occur at the touched portion. An arc may be formed at the touched portion.

In order to avoid such local temperature peaks, the first claim of the present invention suggests that the individual heating members 2.1 to 2.5 are designed to be identical. In particular, the heating members 2.1, 2.5 are spiral shaped heating wires of the same length. They have the same resistance over their length so that the same current flows through them in parallel. It is also provided that the contact elements 3, 4 arranged in the contact position have different lengths. The length of the contact element is related to the spacing of the contact elements 3 of the heating element 1. The further the distance between the contact elements 3, 4 of the heating element is, the longer the contact elements 3, 4 are. The contact element can be a cylindrical pin which extends transversely to the contact faces K ₁ , K ₂ or transverse to the heating faces H ₁ , H ₂ , H ₃ , H ₄ .

The present invention will be described in detail below based on FIG. Figure 5 shows two contact plates 5, 6 on which different potentials are placed. In FIG. 5, these contact plates are assigned to two mutually spaced contact faces K ₁ and K ₂ . But it is also possible that the contact plates 5 and 6 located in a common contact surface K _1. In any case, the currents on these contact plates 5, 6 are separated from each other.

Figure 5 shows a total of four heating elements 1.1, 1.2, 1.3, 1.4. These heating elements extend over the heating surfaces H ₁ , H ₂ , H ₃ , H ₄ , respectively. The heating surfaces H ₁ , H ₂ , H ₃ , H ₄ extend parallel to the two contact faces K ₁ , K ₂ . In the heating faces H ₁ , H ₂ , H ₃ , H ₄ , the heating members 2.1, 2.2, _2.3 , _2.4 of the heating elements 1.1 to 1.4 respectively extend on a circular arc line, as shown in Figs. According to the simplified diagram, the heating members 2.1 to 2.4 are only shown on the heating faces H ₁ , H ₂ , H ₃ , H ₄ which are different from each other. However, the heating members 2.1 to 2.4 of the heating elements 1.1 to 1.4 which are different from each other can also extend in the same heating surface.

The heating elements 2.1 to 2.4 have their contact sections 3.1, 3.2, 3.3, 3.4 or 4.1, 4.2, 4.3, 4.4 and the two contact plates 5, respectively, by their end sections 7.1, 7.2, 7.3, 7.4. 6 one electrical connection. The lengths of the heating members 2.1 to 2.4 are the same. This length consists respectively of the section of the respective heating elements 2.1 to 2.4 extending in the associated heating faces H ₁ , H ₂ , H ₃ , H ₄ and the length of the two end sections 7.1 to 7.4. The end sections 7.1 to 7.4 extend perpendicular to the associated heating faces H ₁ , H ₂ , H ₃ , H ₄ and in the direction of the contact faces K ₁ , K ₂ . The direction of extension of the end sections 7.1 to 7.4 is flush with the direction of extension of the contact pins 3.1 to 3.4 or 4.1 to 4.4.

The contact pins 3.1, 4.1 of the first heating element 1.1 are spaced farthest from one another. This spacing is labeled A ₁ . The associated contact pins 3.1, 4.1 are longer than the contact pins 3.2 to 3.4 or 4.2 to 4.4 of the remaining heating elements 1.2 to 1.4. The end section 7.1 of the first heating element 1.1 is shorter relative to the other end sections.

The contact elements 3.2 to 3.4 or 4.2 to 4.4 having a shorter spacing A ₂ to A ₄ have a shorter length than the contact elements 3.1, 4.1. The shortest contact elements 3.4, 4.4 belong to the heating element 2.4, the end section 7.4 of the heating element 2.4 extending transversely to the heating surface H ₄ is the longest, and the spacing A _{4 is} smaller than the remaining contact elements 3.1 to 3.3 or 4.1 to 4.3 The spacing A ₁ , A ₂ , A ₃ .

The end sections 7.2 to 7.4 of the heating spiral coils 2.2 to 2.4 of the heating elements 1.2 to 1.4 have a length which is equal to the associated contact elements 3.2, 3.3, 3.4, 4.2, 4.3, 4.4 and has the shortest end zone. The spacing of the respective contact elements 3.1, 4.1 of the heating element of section 7.1, the contact elements 3.2 to 3.4, 4.2 to 4.4 of the heating elements 1.2 to 1.4 have a smaller spacing A ₂ than the contact elements 3.1, 4.1 of the heating element 1.1, A ₃ , A ₄ , the heating spiral coil 2.1 of the heating element 1.1 has the shortest end section 7.1. The difference in the distance to the respective outermost contact elements 3.1, 4.1 determines the length of the length of the end sections 7.2 to 7.3, and the latter determines the contact elements 3.1 to 3.4 or 4.1 to 4.4 together with the height of the heating spiral coils 2.1 to 2.4. length.

The heating wire holder of the component symbol 9 is made of metal. The heating wire holder 9 supports all four heating elements at respective circumferential positions, in which the same voltage is applied to the heating members 2.1 to 2.4, respectively, so that no reactive current flows through the heating wire holder 9.

In Fig. 5, the heating members 2.1 to 2.4 are shown by two parallel extending lines in accordance with the simplified diagram. A first preferred design of the heating member 2 is shown in the form of a heating wire 8 extending in a spiral shape in FIG. Figure 6 shows a single, helically shaped heating wire 8. However, it is also provided that two or three heating wires 8 are arranged in a spiral shape as a whole. Figure 7 shows a particularly particularly preferred design with a double helix coil.

The electrical resistance per unit length of the heating member 2 or the heating wire 8 is at least 10 times greater than the electrical resistance per unit length of the contact elements 3, 4. The contact elements 3, 4 are preferably cylindrical pins having a sufficiently large diameter such that only a slight voltage is applied across the axial length of each of the contact pins 3, 4. Thus, although the axial lengths of the contact pins 3, 4 are different, the same potential is provided on the end faces of the contact pins 3, 4 to which the heating members 2.1 to 2.4 are fixed. A contact section of the contact pin 3 having a smaller diameter is inserted into the hollow spiral coil of the heating member 2.

The foregoing embodiments are intended to illustrate the invention obtained by the present application, which at least independently improve the prior art by at least the following combination of technical features, namely: a device characterized in that the heating members 2.1, 2.2 of the heating elements 1.1, 1.2 are The isometric and structurally identical design, the contact elements 3.2, 4.2 of the second heating element 1.2 have a smaller spacing A ₂ and are shorter than the contact elements 3.1, 4.1 of the first heating element 1.1.

An apparatus, characterized in that at least a third and / or fourth heating member having a heating element 1.3, 1.4 of one or more heating wires constituted 2.3, 2.4, or having a plurality of transverse heating surface H _1, H ₂ , the ends of the heating elements 2.3, 2.4 of the contact elements 3.3, 3.4, 4.3, 4.4 of the H ₃ , H ₄ extension are located between one or more of the mutual and relative to the heating surfaces H ₁ , H ₂ , H ₃ , H parallel to the contact surface ₄ K _1, K ₂ are connected to the contact plates 5 and 6, wherein the third and / or fourth heating elements 1.3, 1.4 and 1.1, 1.2, the first and second heating element at the contact plate 5, 6 in parallel in parallel, wherein the heating elements 2.3, 2.4 of the third and/or fourth heating elements 1.3, 1.4 are of equal length and are designed with the heating elements 2.1, 2.2 of the first and second heating elements 1.1, 1.2 Likewise, wherein the contact elements 3.3, 3.4, 4.3, 4.4 of the third and/or fourth heating elements 1.3, 1.4 have a smaller spacing A ₃ , A ₄ than the contact elements 3.2 of the second heating element 1.2, 4.2 is shorter.

A device, characterized in that all heating elements 2.1, 2.2, 2.3, 2.4 electrically connected in parallel between the contact plates 5, 6 are of equal length and have the same design, wherein the heating elements 2.2, 1.3, 1.4 of the heating elements 2.2 The front faces 7.2, 7.3, 7.4 extend into the heating surfaces H ₁ , H ₂ , H ₃ , H ₄ assigned to the respective heating element and the contact surfaces K ₁ , K assigned to the respective contact elements. _In the gap between ₂ , the contact elements 3.2, 3.3, 3.4, 4.2, 4.3, 4.4 of the heating elements 1.2, 1.3, 1.4 are spaced apart from each other by a smaller distance than the contact elements 3.1, 4.1 of the first heating element 1.1, The contact elements 3.2, 3.3, 3.4, 4.2, 4.3, 4.4 are connected to the end sections 7.2, 7.3, 7.4.

A device, characterized in that the length of the end sections 7.2, 7.3, 7.4 of the heating elements 2.2, 2.3, 2.4 extending into the gap is equal to the associated contact elements 3.2, 3.3, 3.4, 4.2, 4.3, 4.4 to the first The distance of the contact elements 3.1, 4.1 of the heating element 1.1.

A device, characterized in that the heating elements 2.1, 2.2, 2.3, 2.4 extend side by side and are thus connected to the contact plates 5, 6 by means of their associated contact elements 3.1, 3.2, 3.3, 3.4, 4.1, 4.2, 4.3, 4.4 The connection is such that when a heating voltage is applied to the contact elements, the heating members 2.1, 2.2, 2.3, 2.4 arranged side by side are at the same potential at the contact positions that are in contact with each other due to thermal deformation.

A device characterized in that the heating wire 8 consists of a tungsten wire arranged in the shape of a helix, wherein in particular two or three tungsten wires extend parallel to each other.

An apparatus, characterized in that the heating member along an arc extending H ₄ 2.1,2.2,2.3,2.4 _a heating surface corresponding to H.

A device characterized in that it has a substantially circular plan or basic contour.

All of the disclosed features (as such and in combination with each other) have inventive or inventive value. In the publication of the present application, the disclosure of the attached/affiliated priority document (prior application document) is also fully included, and the features in the priority document are also included in the patent application scope of the present application. . The features of the patent application scope are all improved designs with independent invention significance or value for the prior art, and in particular, the divisional application can be filed on the basis of the subsidiary items of the patent application scope.

Claims (9)

A heating device for a susceptor of a CVD reactor, having at least one first heating element (1.1) and at least one second heating element (1.2), wherein each heating element (1.1, 1.2) has one or more Article heating wire (8) heating means (2.1, 2.2) consisting of, wherein such heating means (2.1, 2.2) lie in a common heating system or a plurality of mutually parallel surfaces of the heating surface (H _1, H ₂₎ of , and having an end portion to the contact line transverse member (3.1,4.1,3.2,4.2) to (H _1, H ₂₎ extend such heating surface of such a heating element (2.1, 2.2) are located parallel to the the like heating surface (H _1, H ₂₎ of the contact surface (K _1, K ₂₎ of the contact plates (5, 6) as a conductive connection, and wherein such a contact element (3.1,3.2,4.1,4.2) -based The side faces are arranged side by side in the contact surface (K ₁ , K ₂ ) such that the heating elements (1.1, 1.2) are electrically connected in parallel between the contact plates (5, 6), characterized in that the heating elements (1.1) , 1.2) heating means (2.1, 2.2) are of equal length and have the same resistance, the contact member (3.2,4.2) of the second heating element (1.2) are at a spacing (a ₂₎ Pitch of the contact member (3.1,4.1) of the spacing (A ₂₎ less than the first heating element (1.1) (A _1), and the second heating element (1.2) of the contact member (3.2,4.2) than the first The contact elements (3.1, 4.1) of a heating element (1.1) are shorter. The heating device of claim 1, wherein the at least one third and/or fourth heating element (1.3, 1.4) has a heating member (2.3, 2.4) composed of one or more heating wires, and has a lateral direction The end portions of the heating members (2.3, 2.4) of the contact elements (3.3, 3.4, 4.3, 4.4) extending on the heating surfaces (H ₁ , H ₂ , H ₃ , H ₄ ) are respectively associated with the contact plates (5, 6) in an electrically conductive connection, wherein the third and / or fourth heating element (1.3, 1.4) and the first and second heating elements (1.1, 1.2) are electrically connected between the contact plates (5, 6) Parallel, wherein the heating members (2.3, 2.4) of the third and/or fourth heating elements (1.3, 1.4) are of equal length and are designed to be heated by the first and second heating elements (1.1, 1.2) The components (2.1, 2.2) are identical and have the same electrical resistance, wherein the contact elements (3.3, 3.4, 4.3, 4.4) of the third and/or fourth heating element (1.3, 1.4) have a smaller spacing from each other ( A ₃ , A ₄ ), and the contact elements (3.3, 3.4, 4.3, 4.4) of the third and/or fourth heating element (1.3, 1.4) are more than the contact elements of the second heating element (1.2) (3.2 , 4.2) Short. A heating device according to claim 1 wherein all of the heating members (2.1, 2.2, 2.3, 2.4) electrically connected in parallel between the contact plates (5, 6) have the same length and electrical design of the same heating. Components (2.1, 2.2, 2.3, 2.4), wherein the heating elements (2.2, 2.3, 2.4) of the heating elements (2.2, 1.3, 1.4) are by their end sections (7.2, 7.3, 7.4) Extending into a gap between the heating surfaces (H ₁ , H ₂ , H ₃ , H ₄ ) assigned to the respective heating element and the contact surfaces (K ₁ , K ₂ ) assigned to the respective contact elements, and the heating elements The contact elements (3.2, 3.3, 3.4, 4.2, 4.3, 4.4) of (1.2, 1.3, 1.4) are spaced apart from each other by a smaller distance than the contact elements (3.1, 4.1) of the first heating element (1.1), The contact elements (3.2, 3.3, 3.4, 4.2, 4.3, 4.4) are connected to the end sections (7.2, 7.3, 7.4). The heating device of claim 3, wherein the length of the end sections (7.2, 7.3, 7.4) of the heating elements (2.2, 2.3, 2.4) extending into the gap is equal to the associated contact element The distance from (3.2, 3.3, 3.4, 4.2, 4.3, 4.4) to the contact elements (3.1, 4.1) of the first heating element (1.1). The heating device of claim 1, wherein the heating members (2.1, 2.2, 2.3, 2.4) are extended side by side and by means of contact elements (3.1, 3.2, 3.3, 3.4) associated with the heating members. , 4.1, 4.2, 4.3, 4.4) are connected to the contact plates (5, 6) such that when a heating voltage is applied to the contact elements, the heating members are arranged side by side (2.1, 2.2, 2.3, 2.4) Touch positions that may touch each other due to thermal deformation Place the same potential. A heating device according to claim 1, wherein the heating wire (8) is composed of at least one tungsten wire provided in a spiral shape. The heating device of claim 6, wherein the two or three tungsten wires extend parallel to each other. The patent application range of the heating means, Paragraph 1, wherein such heating means (2.1,2.2,2.3,2.4) extending in an arc (H ₁ to H ₄₎ in a respective heating surface. A heating device according to claim 1, wherein the device has a substantially circular plan view or a basic profile.