CN115176046B - Inlet mechanism for CVD reactor - Google Patents

Abstract

The present invention relates to a closing element for a CVD reactor. On its side facing the interior of the housing (1) closed by the closure plate, the closure element (2) carries an annular web (25) which encloses a cavity in which the air inlet means (3) is arranged. The end face of the annular web (25) extends flush with respect to the exhaust face (29) of the air intake. The plate (32) engages in a second cavity of the disk-shaped body (26) arranged in a first cavity (19) which is arranged on the side of the closing element (2) facing the interior of the housing (1).

Description

Inlet mechanism for CVD reactor

Technical Field

The invention relates to an air inlet mechanism, wherein a closing element has a cavity in which a gas distribution volume is arranged, which is in flow communication with a plurality of exhaust openings arranged on an exhaust face facing the interior of the housing.

The invention also relates to a CVD reactor designed with such an inlet mechanism.

Background

The patent document US 2004/0082251 A1 describes a CVD reactor with a pot-shaped housing in which a susceptor carrying a substrate is arranged, which substrate is treated in a process chamber. The top of the process chamber is formed by an exhaust plate having a plurality of exhaust openings from which process gas can flow into the process chamber. The exhaust plate is formed by an air intake mechanism that is an integral part of the cover of the housing. The cover has an outer edge forming a bearing surface by means of which the cover is supported on the end face of the housing wall of the housing. The gas inlet mechanism has a gas distribution chamber surrounded by heated walls and is located in the cavity of the lid.

DE 10136858 A1 describes an air inlet mechanism for a reactor for producing OLEDs. The air intake mechanism has a heating device by means of which the air intake mechanism can be heated to an elevated temperature. Vapor may be supplied into the gas distribution volume of the gas inlet mechanism and may be exhausted into the process chamber through the exhaust opening. The gas inlet means is located in a central cavity in a top plate forming a lid for closing the reactor.

A similar device is described in EP 1252363 B1. There, a shower-head-like air intake mechanism is inserted in the cavity of the top plate.

The inventive device for depositing layers on a substrate, in particular a MOCVD reactor, has a substantially disk-shaped exhaust surface with a plurality of exhaust openings arranged in a shower head shape, from which process gases can enter the process chamber. The distance between the exhaust face and the upper side of the susceptor carrying the substrate is between 9mm and 20 mm. It is technically desirable that the distance, i.e., the process chamber height, remain constant across the entire face of the susceptor. In particular, the height must remain constant even if the internal pressure in the process chamber changes. It is therefore necessary to avoid bending of the exhaust face in the event of a pressure decrease inside the housing.

The device of the same type or according to the invention also has a loading opening in the housing wall through which the substrate can be loaded for the susceptor. In the prior art it is necessary to raise the air intake mechanism or lower the susceptor so that the grippers passing through the loading opening can grip the substrate carried by the susceptor.

Disclosure of Invention

The object of the invention is to provide a means for stabilizing the position of a process chamber or of an exhaust surface in the event of pressure changes, which makes it possible to load the process chamber or the exhaust surface more easily.

This object is achieved by the invention as set forth in the claims. The dependent claims are not only advantageous developments of the parallel claims but also independent solutions to the technical problem.

In a first aspect of the invention, it is proposed that the air inlet means is an integral part of the closure element or is an integral part. The closing element is to some extent a cover by means of which the opening of the housing of the CVD reactor can be closed. According to the invention, a cavity is present on the side of the closure element facing the interior of the housing. The cavity may be surrounded by a tab extending over the edge of the closure element. However, the cavity may also be a recess, the inner wall of which is formed by an annular tab. However, the cavity may also be a central region of the closure element, where the material thickness of the closure element is smaller than at the edges or in the tab region. According to the invention, the wall of the cavity forms a wall of the gas distribution volume. The wall portion has an inner surface that forms an inner surface of the gas distribution volume. The cavity may also have an intermediate recess in which the material thickness of the wall of the closure element is further reduced. The recess may form a gas distribution volume. In this case, the volume of the recess is equal to the volume of the chamber of the inlet means forming the gas distribution volume. The recess may be closed by a plate. The plate preferably constitutes a partition by means of which the chamber forming the gas distribution volume is separated from the cooling chamber. The plate has a flat broad side facing the recess. The other broad side is preferably likewise flat. The broad-sided edge can rest against the bottom of the cavity. It refers in particular to the area of the bottom of the cavity surrounding the central recess. There, a sealing ring may be located in the groove, which sealing ring surrounds the recess and extends between the partition and the bottom of the cavity. Thus, the vertical height of the chamber forming the gas distribution volume is defined by the vertical depth of the recess extending in the horizontal plane. The recess preferably extends over the entire exhaust face, which is formed by an exhaust plate which extends at a vertical distance from the partition. A cooling chamber extends in the space between the exhaust plate and the partition plate, through which cooling chamber a coolant can flow. An assembly having substantially two parts may be disposed in the cavity. The assembly is formed of a first body forming an exhaust plate and a second body forming a partition. The partition plate may be supported with its edges on steps forming the outer edge section of the body of the exhaust plate. The outer wall of the annular or disc-shaped body may abut the inner wall of the tab surrounding the cavity. The end face of the tab facing the interior of the housing preferably merges flush into the exhaust face. The component is inserted in the cavity, i.e. preferably in the recess surrounded by the annular tab. The assembly does not form all of the components of the air intake mechanism. The assembly substantially only forms the boundary of the gas distribution volume of the gas inlet mechanism. The partition used for this purpose forms an inner surface of the gas distribution volume. The surface of the recess, i.e. the closure element or its base, forms the other inner surface of the gas distribution volume.

According to a second aspect of the invention, a stabilizing ring is provided, which is arranged on the side of the cover facing the interior of the housing and surrounds the air intake mechanism. The stabilizing ring is formed by a web which extends near the edge along the inner side of a preferably cylindrical housing wall of the housing of the CVD reactor. The webs can directly abut the support surface by means of which the closure element rests against the end face of the housing wall. The webs thus not only define a cavity in which the elements of the air intake mechanism are arranged, but also form stiffening elements by means of which bending of the exhaust face in the event of pressure changes in the housing can be prevented. It has proven to be advantageous if the webs extend as annular webs along the inner side of the housing wall without interruption. For this purpose, it has proven to be advantageous if the closing element has a first material thickness in the region of the bearing surface, which can be between 25mm and 35 mm. It is preferably 31mm. In the region of the tab, the closure element can have a second material thickness which is at least 1.5 times the first material thickness. The second material thickness may be between 40mm and 60 mm. It is preferably 51mm. The region of the inner side that is connected to the tab has a third material thickness that may be at least half of the first material thickness and at most equal to the first material thickness. This region forms the bottom of the cavity bounded by the tab and preferably having a material thickness of 25mm. A recess may be present in the cavity spaced from the tab. The hollow can also be understood as a first recess with a bottom, in which a second recess, spaced apart from the tab, extends. There, the closing element may have a material thickness in the range between 1/3 and 2/3 of the first material thickness and may preferably be 15mm. This region is preferably used as a gas distribution volume. The outer diameter of the closure element may be greater than 1000mm. The width of the bearing surface may be in the range between 50mm and 100mm and is preferably about 87mm. The tab width may be 25mm. The tab encloses a cup-shaped cavity in which the disc-shaped body is located. The body has an outer wall that is adjacently opposed to the inner wall of the tab. The outer wall can rest against the inner wall. The height of the body in the cavity is equal to the height of the tab in the region of the inner side such that the end face of the tab extends flush to the venting face formed by the body. The surface of the disk-shaped body facing the bottom of the cavity is supported on a sealing ring which extends in a groove in the bottom of the cavity extending along the tab. Numerical experiments were performed with different cover plates for covering the shell of the CVD reactor. The model calculations carried out show that the deflection of the cover plate can be reduced by the annular web when the interior of the housing is evacuated. The cover plate without annular tab has a maximum deflection of 0.81mm in the centre, but if the cover plate has the aforementioned annular tab, the maximum deflection is only 0.37mm. The annular web thus stabilizes the position of the air outlet surface which extends in a plane and has a plurality of air outlet openings which are regularly arranged, in particular, at the points of the grid.

Further aspects of the invention relate to elongated openings in the closure element. A window extends in the opening. The direction of extension of the window is preferably radial with respect to the central axis of the disc-shaped closing element. In addition, the top plate may have a plurality of openings in which tubes forming the viewing openings are inserted, respectively, which tubes protrude through the gas distribution volume, the cooling chamber and the exhaust plate.

A CVD reactor designed according to the invention has a closing element as described above and a housing with a loading opening directly below the closing element. The loading opening is slightly below the end face of the tab. The loading opening is located at the level of a process chamber which is bounded on its side facing away from the gas inlet means by a base carrying the substrate. The heating device is located below the base, by means of which the base can be heated.

Drawings

Embodiments of the invention are described below with the aid of the figures. In the drawings:

FIG. 1 schematically shows a cross-sectional view of a first embodiment of a CVD reactor;

FIG. 1a shows an enlarged view of part Ia of FIG. 1;

Fig. 2 shows a perspective view of a closure element forming a lid of the housing 1 of the CVD reactor;

fig. 3 shows a second perspective view of the lid 2 from the rear side towards the venting face 29;

FIG. 4 shows a top view of the exhaust face;

Fig. 5 shows a top view of the outside of the lid 2;

FIG. 6 shows a section taken along line VI-VI in FIG. 5;

fig. 7 shows a section taken along line VII-VII in fig. 5;

Fig. 8 shows a section taken along line VIII-VIII in fig. 5.

Detailed Description

The figure shows an embodiment of a CVD reactor constituted by a housing 1 with an opening 24, which is closed by a cover 2. The lid 2 carries an air inlet means 4 by which process air can be supplied to a process chamber 23 bounded upwardly by the air inlet means 4 and downwardly by a base 5. The inlet means 4 forms an outlet plate 21 which, on its side facing away from the cover 2, forms an outlet surface 29 into which the outlet opening 17 opens, through which process gas supplied into the gas distribution volume 27 can be discharged from the inlet means 4. The exhaust face is the central face region of the closure element 2 facing the wide side of the housing 1 and is surrounded by the edge region R. In the case of the formation of the gap 15, the shielding plate 6 with the ventilation openings 16 open toward the process chamber 23 extends in front of the exhaust face 29, through which ventilation openings the process gas supplied into the gap 15 through the exhaust openings 17 can flow into the process chamber 23. The shielding plate 6 has, in its radially outer region, an annular circumferential projection 14 which seals the gap 15 to the edge.

The susceptor 5 is heated from below by a heating device 7. This may be done in the susceptor 5 by heat radiation, heat conduction or by inductive heat generation. The base 5 is carried by a carrying device having a lifting element 10. The heating means 7 may be carried by the stem 8. The process chamber 23 is surrounded by an air outlet 3, which can be adjusted in height by a lifting device 9. The base may be lowered by the lifting device 10. The air outlet mechanism 3 can be lowered by the lifting device 9. In the lowered position, the holder can pass through the loading opening 18 of the housing wall 13 of the housing 1. The loading opening 18 extends until it directly adjoins an annular tab 25 which is of the same material or uniform as the lid 2

Shaped so that the cover forms a plate extending over the entire opening 24.

Fig. 1 and 1a show an annular tab 25 formed from the underside of the lid, which is shaped in conformity with the metal cover plate material. The annular web 25 has a radially outwardly directed surface which rests against a surface of a wall of the housing 1. When the lid is closed, the annular tab 25 protrudes into the opening 24.

The annular tab 25 surrounds the air intake mechanism 4. The annular webs 25 form a circular receiving space in which the air inlet means 4, which is fixed in contact on the underside of the cover 2, is located. The outer edge section 26 of the inlet means 4, which is preferably formed in a material-wise manner from the outlet plate 21, has a radially outwardly directed wall which rests against a radially inwardly directed wall of the annular web 25. The height of the annular web 25 is preferably equal to the height of the air intake means 4, so that the surface of the air intake means 4 pointing towards the process chamber 23 extends flush with the axially directed surface of the annular web 25.

The annular web 25 extends in the edge region R as well as the bearing surface 33 and the radially outer region of the exhaust plate 21.

Fig. 1a shows that the face of the shielding plate 6 facing the air intake 4 extends obliquely in the edge region, so that the material thickness of the shielding plate 6 decreases in a wedge shape at the edge. In this region, the projection 14 extends, which rests in contact against the inlet means 4 or against the exhaust plate 21 of the inlet means 4. In this embodiment, the circularly extending projection 14 rests on the outer edge section 26. The process gas which has entered the gap 15 through the exhaust opening 17 is prevented from being laterally discharged from the gap 15 by the bulge 14. The process gas thus passes only through the ventilation openings 16 of the shielding plate 6 and is distributed uniformly into the process chamber 23 arranged below.

The second embodiment of the closure element 2 shown in fig. 2 to 8 in the form of a plate-like cover with an outer wall extending in a plane forms a chamber with the inner cavity 19 or recess 30, which chamber serves as a gas distribution volume 27 for distributing the process gas supplied into the gas distribution volume 27 via the supply openings 37 to the plurality of ventilation tubes 28. The ventilation ducts 28 are distributed in a uniform arrangement over the whole face over which the recesses 30 extend. An intermediate plate 31 extends in the recess 30 and divides the gas distribution volume 27 into an upper region, into which process gas is supplied, and a lower region, from which the venting tubules 28 originate.

The recess 30 is surrounded by a section of the bottom of the cavity 19, which cavity 19 is surrounded by the annular tab 25. The seal ring 35 is located in a groove extending around the recess 30 having a circular planar profile. The partition 32 extending parallel to the bottom of the recess 30 rests with its edges on the section of the bottom of the cavity 19 and on the sealing ring 35.

The cavity 19 accommodates a disc-shaped body 26 having an outer edge section 26'. The outer edge section 26' has an outer wall 26″ which is opposite the inner wall 25″ of the web 25 with a small gap. The gap may also have a gap width of 0. The end face 25 '"of the annular web 25 merges flush into a vent surface 29 formed by the vent plate 21, which is connected in a uniform manner to the outer edge section 26'.

An intermediate space forming the cooling chamber 22 remains between the exhaust plate 21 and the partition plate 32. Liquid coolant may be supplied to the cooling chamber 22 through a coolant input line 36. The coolant may leave the cooling chamber 22 through a coolant discharge line 36'. The outer edge section 26' rests against a further sealing ring 34, which is located in a groove extending annularly around the recess 30 and the sealing ring 35.

The ventilation ducts 28 intersect the cooling chamber 22 and open into the exhaust openings 17 of the exhaust face 29.

The metal cover material of the closure element 2 forms the bearing surface 33, the webs 25, the walls of the cavity 19 and the walls of the recess 30 in a uniform manner. The inner surface of the recess 30 forms the inner surface of the gas distribution volume 27. The inner surface of the gas distribution volume 27 is thus largely formed by the surface of the cover plate of the closure element 2. In the edge region of the cover plate, bores are provided through which fastening elements, such as screws, pass, by means of which the cover 2 can be fastened to the housing 1.

The dimensions shown in fig. 6 have the following values:

A is about 30mm, B is about 50mm, C is about 25mm, D is about 15mm, E about 25mm, G about 15mm, H about 5mm, E about 25mm, about 90mm F, about 1100mm K, about H1000 mm, I about 900mm, J about 700mm. Dimensions I, J, H and K refer to diameters.

The gas inlet means 4 is arranged in the cavity 19 of the metal cover plate and forms a chamber of the gas distribution volume by means of the recess 30, so that the surface of the recess is at the same time the inner surface of the gas distribution volume, which realizes a closing element for closing a very narrow housing. The thickness is about 50mm. The loading opening 18 can thus be at a minimum distance from the end face 13' of the housing wall 13, on which end face the bearing surface 33 of the lid 2 is supported.

Advantageously, the air intake means 4 are located in a cavity 19, which is surrounded by an annular tab 25. The annular tab 25 provides a stiffening element which reduces the deflection of the central region of the lid 2 in the event of a pressure change within the housing 1. Model calculations indicate that the annular tab 25 results in a significant reduction in deflection compared to a cap of the same design but without such an annular tab 25.

The foregoing embodiments are intended to illustrate the application generally included in the present application, which extends to the prior art at least by the following feature combinations, also independently, wherein two, more or all of these feature combinations may also be combined with each other, namely:

an inlet mechanism 4 is characterized in that the wall of the gas distribution volume 27 is formed by the wall of the cavity 19.

An air intake mechanism 4 is characterized by a tab 25 projecting from the inside of the lid 2 directly abutting the bearing surface 33.

An inlet means 4 is characterized in that the wall of the cavity 1 and/or the wall of the recess 30 extending in the cavity 19 form the inner surface of a gas distribution volume 27 extending over the entire exhaust face 29.

The gas inlet means 4 is characterized in that the cavity 19 has a recess 30 forming a gas distribution volume 27, which is delimited by a partition 23, which rests in a gas-tight manner against the bottom of the cavity 19 surrounding the recess 30.

An air intake mechanism 4 is characterized in that the webs 25 extend uninterrupted along the inner side 13″ of the housing wall 13 as annular webs and/or the annular webs extend circularly and/or the closure element 2 has a first material thickness a in the region of the support surface 33 and a second material thickness B in the region of the webs 25, which is at least 1.5 times the first material thickness a and a third material thickness C in the inner region of the closure element 2 immediately adjoining the webs 25 enclosed by the webs 25, which lies in the range between 0.5 and 1 times the first material thickness a and/or the width E of the webs 25 lies in the range between 50 and 150% of the width F of the support surface 3 and/or the width E of the webs 25 is greater than the difference between the material thickness B of the closure element 2 in the region of the webs 25 and the material thickness a of the closure element 2 in the region of the support surface 33.

An air inlet mechanism is characterized in that a disk-shaped body 26 forming the air outlet plate 21 is arranged in a form-filling manner in a bowl-shaped or cup-shaped cavity 19 surrounded by a web 25, and/or that the disk-shaped body 26 has an outer wall 26″ which is arranged adjacently opposite an inner wall 25″ of the web 25, and/or that the disk-shaped body 26 has an outer edge section 26 'which has a height which is equal to the height of the web 25, such that an end face 25' "of the web facing away from the closure element 2 extends flush with an air outlet face 29 formed by the air outlet plate 21 of the body 26.

The air intake mechanism 4 is characterized in that the outer edge section 26' of the main body 26 arranged in the cavity 19 enclosed by the webs 25 encloses a cavity in which a partition 23 is arranged, which delimits the cooling chamber 22 towards the closing element 2, which delimits the cooling chamber away from the closing element 2 is the air outlet plate 21, and/or that the edge region of the partition 23 rests on the bottom of the cavity enclosed by the main body 26 and is supported on the step 44 of the outer edge section 26', and/or that the partition 23 has a broad side which extends flush with respect to the abutment surface of the outer edge section 26' resting on the bottom of the cavity 19 enclosed by the webs 25.

An inlet mechanism 4 is characterized in that a window 40 is arranged in an elongated opening 41 forming the top plate of the closing element 2 and/or at least one tube 45 forming the viewing opening 39 passes through the top plate forming the closing element 2, the gas distribution volume 27, the cooling chamber 22 and the exhaust plate 21 and/or the outer surface of the closing element 2 is planar.

CVD reactor with gas inlet means 4, wherein the gas outlet surface 29 is directed towards the process chamber 23, the bottom of which is formed by a susceptor 5 which can be heated by heating means 7 and is surrounded by gas outlet means 3, and/or the housing wall 13 has a loading opening 18, wherein the loading opening 18 extends until it directly adjoins the tab 25.

A CVD reactor is characterized in that the outer wall 25' of the tab 25, which extends over the cylinder circumference, is spaced at most 1mm from the inner side 13 "of the housing wall 13 and/or that a shielding plate 6 with ventilation openings 16 is arranged between the process chamber 23 and the exhaust face 29.

All features disclosed are essential to the application (either as individual features or as combinations of features). Accordingly, the disclosure of the present application also includes the disclosure of the related/attached priority file (copy of the prior application), and for this reason, the features of the priority file are also incorporated into the claims of the present application. The dependent claims characterise the unique inventive developments of the prior art with their features even when they do not have the technical features of the cited claims, in particular for the divisional application based on this technical feature. The application as set forth in each claim may additionally have one or more of the features set forth in the preceding description, particularly with reference numerals and/or in the list of reference numerals. The application also relates to various designs in which some of the features mentioned in the description above are not implemented, in particular when they are considered to be inconsequential for the respective purpose of use or can be replaced by other technically equivalent means.

List of reference numerals

1. Shell body

2. Closure element, cap

2' Edge

3. Air outlet mechanism

4. Air inlet mechanism

5. Base seat

6. Shielding plate

7. Heating device

8. Rod part

9. Lifting device

10. Lifting device

11. Lifting element

12. Support plate

13. Housing wall

13' End face

13' Inside

14. Raised portion

15. Gap of

16. Ventilation opening

17. Exhaust opening

18. Loading opening

19. Cavity cavity

20. Fixing element

21. Exhaust plate

22. Cooling chamber

23. Process chamber

24. An opening

25. Annular tab

25' Outer wall

25' Inner wall

26. Disc-shaped body

26' Outer edge section

26' Outer wall

27. Gas distribution volume

28. Small pipe

29. Exhaust surface

30. Concave part

31. Intermediate plate

32. Partition board

33. Bearing surface

34. Sealing ring

35. Sealing ring

36. Coolant inlet line

36. Coolant discharge line

37. Feed opening

38. Elongated opening

39. Viewing opening

40. Window

41. Elongated opening

42. Holding plate

43. Fixing element

44. Step part

45. Pipe and pipe

46. Viewing opening

R edge region

Claims (15)

1. A CVD reactor having a housing (1) with an upwardly directed opening, which is closed by a closing element (2), wherein the closing element (2) has a cover plate with a first cavity in which a gas distribution volume (27) is arranged, wherein a first inner surface of the gas distribution volume (27) is formed by a surface of a recess (30) in the first cavity formed by the cover plate in a material-consistent manner, and a second inner surface of the gas distribution volume (27) is formed by a plate arranged in the first cavity, wherein the closing element (2) has a bearing surface (33) which is supported on an end face (13 ') of a housing wall (13) of the housing (1), wherein the plate is located in a second cavity of a disk-shaped body (26) which is arranged in the first cavity, wherein an edge region of the plate is supported on a side of the closing element (2) facing the interior of the housing (1), wherein an outer edge region (26') of the plate rests on a floor (44) of the body (26) and the exhaust plate (21 ') is formed in contact with the interior of the housing (21), wherein the exhaust plate (21') is formed between the exhaust-gas-side wall region and the exhaust-side of the housing (21), and wherein a plurality of exhaust openings (17) arranged on the exhaust face (29) are in flow connection with the gas distribution volume (27) via ventilation ducts (28) intersecting the cooling chamber (22).

2. CVD reactor according to claim 1, characterized in that a tab (25) rests against the housing wall (13).

3. CVD reactor according to claim 1, characterized in that the plate constitutes a partition between the cooling chamber (22) and the gas distribution volume (27).

4. CVD reactor according to claim 1, characterized in that a tab (25) protrudes from the inside of the closing element (2) into the interior of the housing (1), which tab is adjoined by the housing wall (13), wherein the tab (25) encloses the first cavity.

5. CVD reactor according to claim 4, characterized in that the tab (25) extends as an annular tab (25) uninterrupted along the inner side (13 ") of the housing wall (13) and that the exhaust plate (21) forming the exhaust face (29) is formed by the disk-shaped body (26) which is arranged in a form-filling manner in a bowl-shaped or cup-shaped first cavity surrounded by the tab (25), wherein the plate forms a partition between the cooling chamber (22) and the gas distribution volume (27), wherein the gas distribution volume (27) is in flow communication with the exhaust opening (17) arranged in the exhaust plate (21) via a venting tube (28) intersecting the cooling chamber (22).

6. CVD reactor according to claim 1, characterized in that the tab (25) has an end face (25' ") towards the interior of the housing (1) which extends flush with the venting face (29) formed by the disc-shaped body (26) and/or the outer wall (26") of the disc-shaped body (26) filling the first cavity surrounded by the tab (25) rests against the inner wall (25 "), the disc-shaped body forming the venting face (29).

7. CVD reactor according to claim 1, characterized in that the sealing ring (35) is located in a groove extending around the recess (30).

8. CVD reactor according to claim 4, characterized in that the tab (25) extends circularly, wherein the closing element (2) has a first material thickness (a) in the region of the support surface (33), a second material thickness (B) in the region of the tab (25), which is at least 1.5 times the first material thickness (a), and a third material thickness (C) in the inner region of the closing element (2) directly adjoining the tab (25), surrounded by the tab (25), which third material thickness lies in the range between 0.5 and 1 times the first material thickness (a), wherein the width (E) of the tab (25) lies in the range between 50 and 150% of the width (F) of the support surface (33), and/or the width (E) of the tab (25) is greater than the difference between the material thickness (B) of the closing element (2) in the region of the tab (25) and the material thickness (a) of the closing element (2) in the region of the support surface (33).

9. CVD reactor according to claim 1, characterized in that the disc-shaped body (26) has an outer edge section (26') with a height equal to the height of the tab (25).

10. CVD reactor according to claim 1, characterized in that the plate has a broad side which extends flush with respect to an abutment surface of the outer edge section (26') against the bottom of the first cavity surrounded by the tab (25).

11. CVD reactor according to claim 1, characterized in that a window (40) is arranged in an elongated opening (41) forming the ceiling of the closing element (2), wherein at least one tube (45) forming the viewing opening (39) passes through the ceiling forming the closing element (2), the gas distribution volume (27), the cooling chamber (22) and the exhaust plate (21), wherein the outer surface of the closing element (2) is planar.

12. CVD reactor according to claim 1, wherein the exhaust face (29) faces a process chamber (23), the bottom of which is formed by a susceptor (5) which can be heated by a heating device (7) and which is surrounded by an exhaust mechanism (3).

13. CVD reactor according to claim 12, characterized in that the housing wall (13) has a loading opening (18), wherein the loading opening (18) extends until directly adjoining the tab (25).

14. CVD reactor according to claim 12, characterized in that the outer wall (25') of the tab (25) extending over the circumference of the cylinder is spaced at most 1mm from the inner side (13 ") of the housing wall (13).

15. CVD reactor according to claim 12, characterized in that a shielding plate (6) with a ventilation opening (16) is arranged between the process chamber (23) and the exhaust face (29).