TWI881015B - CVD reactor with double front plate - Google Patents

Abstract

The present invention relates to a device, wherein a gas inlet component (5), a substrate base defining a process chamber (8) at the bottom, a heating device (6) for heating the substrate base (2), and a process chamber top (7) defining the process chamber (8) at the top are arranged in a reactor shell (1), wherein the substrate base (2) forms a substrate support area (S) for accommodating a substrate (4) to be coated, and a front zone plate (10) is arranged in the area of the substrate base (2) between the gas inlet component (5) and the substrate support area (S), so that a free space (12, 13) is left between the top side (2') of the substrate base (2) and the bottom side (10') of the front zone plate (10), and an additional plate (11) is arranged in the free space. The invention also relates to a method for depositing a III-V semiconductor layer. In order to keep the parameters affecting the wavelength of the device within a narrow tolerance range for optoelectronic devices, it is proposed to double the pre-zone plates (10, 11) so that the temperature of the pre-zone is 10 to 40°C lower than the substrate temperature.

Description

CVD reactor with double front plate

The present invention relates to an apparatus and a method for depositing a III-V group layer on a substrate, and more particularly to a MOCVD reactor and a MOCVD method.

The present invention particularly relates to a device, in which a gas inlet component is arranged in a reactor shell, a substrate seat defining a process chamber at the bottom, a heating device for heating the substrate seat, and a process chamber top defining the process chamber at the top, wherein the substrate seat forms a substrate support area for accommodating a substrate to be coated, and a front zone plate is arranged in the area of the substrate seat located between the gas inlet component and the substrate support area, so that a free space is left between the top side of the substrate seat and the bottom side of the front zone plate, and an additional plate is arranged in the free space.

The present invention particularly relates to a method for depositing a III-V semiconductor layer in an apparatus, wherein a gas inlet component is provided in a reactor housing, a substrate holder defining a process chamber at the bottom, a heating device for heating the substrate holder, and a process chamber top defining the process chamber at the top, wherein the substrate holder forms a substrate support area for accommodating a substrate to be coated, and a front zone plate is provided in the area of the substrate holder between the gas inlet component and the substrate support area, so that a free space is left between the top side of the substrate holder and the bottom side of the front zone plate, and an additional plate may be provided in the free space, and the following steps are provided: - The substrate holder is heated by the heating device, and a vertical temperature gradient is generated in the process chamber, so that the temperature of the top of the process chamber is lower than that of the substrate holder, the substrate support area has a temperature between 500°C and 800°C, and the pre-zone has a lower temperature; - The process gas is fed into the pre-zone through the gas inlet component, wherein the process gas includes at least one first reaction gas containing an element of the third group, at least one second reaction gas containing an element of the fifth group, and a carrier gas.

DE 10 2014 104 218 A1 discloses a similar method and a similar device. A substrate holder having a circular basic outline defines a process chamber at the bottom. A gas inlet member is provided at the center of the circular process chamber, through which hydrides of elements of the Vth main group and organometallic compounds of elements of the IIIth main group are fed into the process chamber together with a carrier gas. The substrate holder heated by the heating device is hotter than the top of the process chamber defining the process chamber at the top. Based on this temperature difference, a vertical temperature gradient is formed in the process chamber. Heat flows from the substrate holder to the top of the process chamber. The substrate holder is surrounded by a gas outlet member. In the area adjacent to the gas outlet member, the substrate holder forms a substrate support area. In this substrate support area, a plurality of substrates are arranged around the gas inlet member at a uniform distance from the gas inlet member. A pre-zone extends between the substrate support area and the gas inlet member. In the pre-zone, the pre-plate is located on the upward side of the substrate holder. In the free space between the bottom side of the pre-plate and the upward side of the substrate holder, an annular middle plate is provided. A temperature-adjusting gas is fed into the middle cavity between the pre-plate and the middle plate and between the middle plate and the substrate holder. By changing the composition of the gas, its thermal conductivity can be adjusted. By changing the thermal conductivity of the temperature-adjusting gas, the heat flow from the pre-zone to the top of the process chamber is changed, thereby changing the surface temperature of the pre-zone.

In addition, a MOCVD reactor is described in US 2004/0003779. DE 100 56 029 A1 describes a method for temperature control of the surface temperature of substrates, wherein the substrates are supported on substrate racks, which are located in the cavity of the substrate holder and supported there by air cushions. The surface temperature of the substrates can be balanced by the height of the air cushions, so that the surface temperature of all substrates has substantially the same value.

The invention has for its object to improve a device of the same type and a method of the same type, in particular in a manner which is advantageous for use, in order to more effectively regulate the surface temperature of a substrate individually. It is also an object of the invention to provide a device and a method by means of which layers for optoelectronic devices can be manufactured whose parameters influencing the wavelength are within narrow tolerance ranges.

The purpose is achieved through the invention given in the patent application scope, wherein the dependent items are not only improvements of the invention given in the parallel claims, but also original solutions to the purpose.

In the production of layers for optoelectronic devices by methods of the same type, only minimal differences in the layer properties of several layers produced simultaneously in a process chamber during one run are permitted. Narrow tolerances are required for the layer thickness and the layer composition of the ternary and quaternary III-V layers, so that the wavelengths of the optoelectronic devices, lasers or LEDs produced by the layer sequence differ only slightly. The growth temperature has a significant influence on the layer parameters that influence the wavelength. With the method described in DE 100 56 029 A1, it is intended to keep the surface temperature of the substrate at an average value by individual control of the height of the air cushion. Studies prior to the present application have shown that in order to ensure the effectiveness of this method, the temperature of the surface of the front zone must be lower than the temperature on the substrate. If the temperature of the pre-zone is the same as or even higher than the substrate support zone, the substrate temperature cannot be adjusted individually within the required range. The present invention proposes to reduce the pre-zone temperature to a temperature lower than the substrate temperature. Preferably, the temperature is reduced in the range of 10°C to 40°C or 20°C to 40°C. Preferably, the pre-zone temperature is about 25°C lower than the substrate temperature. The latter preferably falls in the range between 500°C and 800°C. The surface temperature of the substrate can be changed by individual energy flows. For example, the following solution can be adopted: the substrate holder is locally heated or cooled in the area where the substrate is provided. For example, local heating can be achieved by adding radiation heat, such as by a laser beam. However, it is also possible to modify the air cushion provided with a substrate rack that carries the substrate, thereby individually changing the surface temperature of the substrate. This can be achieved by varying the height of the gas cushion. However, the thermal conductivity of the gas constituting the gas cushion can also be varied as follows: for example, the gas cushion is produced from a mixture of two gases, one of which has a high thermal conductivity and the other has a low thermal conductivity. Based on the heat flow from the heating device through the substrate holder, through the gas cushion, through the substrate holder, through the substrate and through the process chamber to the top of the process chamber, the temperature of the substrate can be individually varied by varying the thermal resistance. In order to deposit a III-V group layer on the substrate in the substrate support area, a process gas is fed into the process chamber via the gas inlet component. The process gas has at least one first reaction gas, which contains an element of the III main group, such as gallium, indium or aluminum, and is in particular an organometallic compound. The process gas has at least one second reaction gas, which contains an element of the Vth main group, such as arsenic, phosphorus or nitrogen. The second reaction gas can be a hydride. The second reaction gas is transported together with a carrier gas such as hydrogen. A pre-decomposition takes place in the pre-zone, which is carried out according to the invention at a temperature lower than the surface temperature of the substrate. In addition, activation of the starting material fed into the process chamber via the gas inlet component also takes place in the pre-zone. The activation follows an exponential function, so it is sufficient to reduce the temperature in the pre-zone by, for example, 10 to 40° C. compared to the temperature in the substrate support zone as described above. By changing the height of the air cushion, or by local energy input, or by changing the composition of the gas constituting the air cushion, the surface temperature of the substrate can be changed, for example, by +/-3 or +/-5° C. The device of the present invention is characterized in that the additional plate and the front zone plate are overlapped congruently. Therefore, the present invention adopts a double front zone plate. The additional plate and the front zone plate preferably have the same basic contour. The front zone plate can be conductive. The front zone plate can be made of graphite, for example. The surface of the front zone plate can be coated. The additional plate can be electrically insulated. The additional plate can be made of quartz or ceramic material. In a preferred technical solution, the front zone plate and the additional plate each have a central opening. A gas inlet component centrally arranged in the process chamber can be inserted into the central opening, and the gas inlet component has a basic contour that is preferably oval. In this case, the central openings of the front zone plate and the additional plate are also circular. According to another preferred technical solution, the front zone plate and the additional plate are respectively one-piece components. Each of them is a flat body. The periphery of the additional plate and the front zone plate can be directly adjacent to the disc-shaped substrate frame. In this regard, the periphery of the additional plate and the front zone plate constitutes a plurality of side-by-side recesses, wherein each recess extends along a circular arc line. According to a preferred technical solution of the present invention, the additional plate is separated from the top side of the substrate holder facing the process chamber by a gap. The height of the gap can be about 0.8 mm +/-10%. The material thickness of the additional plate can be 3.2 mm +/-10%. The distance between the top side of the substrate holder and the top side of the front zone plate can be 9.6 mm +/-10%. Therefore, the following solution can be adopted: the heights of the two gaps are the same. The following scheme can also be adopted: the gap height falls within the range between one-fifth and one-third of the material thickness of the additional plate. The gap height of either of the two gaps is preferably <1 mm. The material thickness of the front zone plate may be greater than the material thickness of the additional plate. The material thickness may be at least five times the gap height. In order to adjust the free space between the top side of the substrate seat and the bottom side of the front zone plate, that is, the gap height, a spacer element may be used. A first spacer element may be provided, and the front zone plate is supported on the top side of the substrate seat by the first spacer elements. These first spacer elements may pass through the opening of the additional plate. The additional plate may have a second spacer element, which is supported on the top side of the substrate seat. The two gaps thus produced have the same vertical gap distance over the entire extent of their surface extending in the horizontal plane, so that all width sides of the additional plate and the front zone plate extend parallel to each other. The spacer elements can be fixed to the additional plate or the front zone plate. By configuring the substrate holder of the CVD reactor according to the technical solution of the invention, it is not necessary to feed gases such as temperature control gases into the free space or the gap. By using an additional plate with the same basic contour as the front zone plate, several gaps with smaller gap widths are formed. During the deposition process, the gas cannot flow through this gap. Due to the small gap width, only a small amount of the process gas diffuses into the free space below the front zone plate, resulting in an acceptable parasitic deposition there. The two parallel gaps together with the additional plate, which is made of quartz or ceramic material, form a heat insulating zone below the front zone plate. The front zone plate has a higher thermal conductivity than the additional plate, which acts as an insulating plate. In a top view, the front zone plate and the additional plate have a star-shaped appearance.

FIG2 schematically shows the structure of the CVD reactor of the present invention. A disc-shaped substrate holder 2 made of graphite and especially coated graphite is arranged in an airtight housing 1. The substrate holder is heated by a heating device 6 through thermal radiation or by generating a high-frequency alternating electromagnetic field. The substrate holder 2 is supported by a rod 19, which can also constitute a rotating shaft, and the substrate holder 2 can be driven to rotate around its graphic axis by the rotating shaft. A generally cylindrical gas inlet component 5 is arranged above the center of the substrate holder 2, and the process gas can be fed into the process chamber 8 through the gas inlet component. The process chamber 8 extends radially outward from the gas inlet member 5 between the substrate holder 2 and the process chamber ceiling 7 to the gas outlet member 20. The gas outlet member 20 is connected to a vacuum pump via a gas pipeline (not shown) for evacuating the interior of the housing 1.

The process chamber 8 has two peripheral areas. The radially inner peripheral area adjacent to the gas inlet member 5 constitutes a front area V. The area adjacent to the front area V in the radially outer direction constitutes a substrate support area S. The substrate support area S is adjacent to the gas outlet member 20 that circularly surrounds the substrate holder 2.

In the substrate support area S, a plurality of (twelve in the present embodiment) substrate racks 3 are arranged in a uniform distribution around the center of the substrate rack 3. Each substrate rack 3 is formed of a disc-shaped flat body, for example, graphite. The bottom side of the substrate rack 3 may be flat or curved. The top side of the substrate rack 3 may have a recess for accommodating the substrate 4. In the middle cavity between the bottoms of the cavities of the substrate holder 2 in which the substrate racks 3 are provided, a flushing gas may be fed through a gas delivery pipeline (not shown), by which the substrate rack 3 is lifted and rotated around its graphic axis. The temperature Ts of the substrate 4 provided on the substrate rack 3 can be changed by the height of the air cushion 21 thus generated. For this purpose, the air cushions can be adjusted individually.

As shown in FIG. 4 , the front zone plate 10 extends in the front zone V. The front zone plate 10 is made of graphite, in particular coated graphite, and has a central opening 15 at its center, in which the gas inlet member 5 is inserted. The front zone plate 10 completely fills the area between the gas inlet member 5 and the substrate rack 3 extending along the arc line around the center of the substrate holder 2. The front zone plate has a plurality of recesses extending along the arc line. The recesses are adjacent to the substrate rack 3. The intermediate cavity between the recesses extends to a radial height at which the distance between two adjacent substrate racks 3 is the smallest. The recesses give the front zone plate 10 a star-shaped shape. A supplementary cover plate may be provided radially outside the front zone plate 10.

An additional plate 11 made of quartz or ceramic material is provided below the pre-zone plate 10. The additional plate 11 is an insulating plate and has the same basic profile as the pre-zone plate 10. The gas inlet member 5 is also inserted into the central opening 17 of the additional plate. The additional plate 11 has the same recess as the pre-zone plate 10 and is adjacent to the substrate holder 3 in the same manner through its recess.

The front zone plate 10 is supported on the top side 2' of the substrate base 2 by the spacer elements 14. The additional plate 11 has openings 16 through which the spacer elements 14 extend. The additional plate 11 also has spacer elements 18 by which the additional plate is supported on the top side 2' of the substrate base 2. The spacer elements 14, 18 are arranged around the center of the front zone plate 10 or the additional plate 11 at uniform angles.

The distance a between the top side 2' of the substrate holder 2 and the top side of the front zone plate 10 facing the process chamber 8 is about 10 mm, preferably about 9.6 mm. The distance b of the gap 12 between the front zone plate 10 and the additional plate 11 is preferably about 0.8 mm. The distance c of the gap 13 between the top side 2' of the substrate holder 2 and the bottom side of the additional plate 11 is preferably 0.8 mm. The distance between the bottom side 10' of the front zone plate 10 and the top side 2' of the substrate holder 2 is preferably about 4.8 mm.

Based on the layout of the front zone plate 10 and the additional plate 11 according to the present invention, a method can be implemented in which a III-V group layer is deposited on a substrate in order to manufacture an optoelectronic device thereby, wherein the wavelength of the energy band transition of the layer is approximately the same by individually changing the temperature Ts of the substrate 4. The reaction gas is transported to the gas inlet component 5 by suitable inlet pipelines and a gas mixing system not shown. The first reaction gas can be a hydride of arsenic, phosphorus or nitrogen. The second reaction gas can be an organometallic compound of gallium, indium or aluminum. Preferably, a total of three reaction gases or four reaction gases are fed into the process chamber 8 together with a carrier gas through the gas inlet component 5 at the same time, thereby depositing a ternary or quaternary layer on the substrate. The layer composition is related to the temperature Ts of the substrate holder and to the partial pressure of the reaction gas. For optical devices in which layers are deposited by this method, the wavelength is related to the layer composition. Therefore, it is necessary for each substrate holder or each substrate to have the same substrate temperature Ts during the deposition process. In the process of adjusting the substrate temperature Ts, this substrate temperature is slightly changed around an average temperature between 500°C and 800°C. Among them, it is better to change the temperature Ts by influencing the air cushion 21. For this purpose, it is important that by providing the front zone plate 10 and the additional plate 11, the temperature Tv on the side of the front zone plate 10 facing the process chamber 8 is 10 to 40°C lower than the temperature Ts of the substrate. Preferably, the temperature difference between the temperature Tv of the pre-zone V and the temperature Ts of the substrate 4 or the substrate support zone S is 25°C, in particular at least 25°C. Since the pre-zone temperature Tv is lower than the substrate temperature Ts, the temperature can be changed by changing the gap height. The gaps 12, 13 preferably not flushed by the flushing gas constitute an idle volume. However, due to the small gap height, a permissible parasitic growth occurs there.

FIG5 schematically shows the characteristic curves of the surface temperature of the front zone plate 10 and the substrate 4 along the radial direction R. The front zone temperature Tv is lower than the substrate temperature Ts. The front zone temperature Tv may be in a range between an upper limit temperature T1 and a lower limit temperature T2, wherein the upper limit temperature T1 is, for example, 10 or 20°C lower than the substrate temperature Ts, and the lower limit temperature T2 is, for example, 50°C lower than the substrate temperature Ts.

An air gap 22 as shown in Fig. 1 also extends between the front zone plate 10 or the intermediate plate 11 and the substrate holder 3. In this air gap 22, the front zone temperature Tv almost abruptly changes to the substrate temperature Ts.

The aforementioned embodiments are used to illustrate the inventions included in the present application as a whole, which at least independently constitute improvements over the prior art through the following feature combinations, wherein two, several or all of these feature combinations may also be combined with each other, namely:

A device is characterized in that the additional plate 11 and the front zone plate 10 are overlapped congruently.

A device is characterized in that the vertical height of the free spaces 12, 13 is selected so that the temperature of the front area V is 10 to 40°C or 20 to 40°C lower than the temperature of the substrate support area S.

A device or a method, characterized in that an additional plate 11 is arranged in the free space 12, 13, which has a basic contour consistent with the front zone plate 10, and/or the front zone plate 10 is electrically conductive and/or consists of graphite, and/or the additional plate 11 has a lower thermal conductivity than the front zone plate 10.

A device or a method is characterized in that the additional plate 11 is electrically insulating and/or consists of quartz and/or ceramic material.

A device or a method is characterized in that the pre-zone plate 10 and the additional plate 11 have a central opening 15, 17 respectively, in which the gas inlet member 5 is inserted, and/or the pre-zone plate and the additional plate are respectively an integral component.

A device or a method, characterized by a first spacer element 14 and a second spacer element 18, wherein the front zone plate 10 is held by the first spacer elements in a manner of being spaced a predetermined first distance d from the top side 2' of the substrate base 2, and the additional plate 11 is held by the second spacer elements in a manner of being spaced a predetermined second distance c from the top side of the substrate base 2, wherein the additional plate 11 has an opening 16 and the first spacer element 14 passes through the openings.

A device or a method, characterized in that: the front zone plate 10 and the additional plate 11 are flat pieces with flat wide sides, and the front zone plate 10 and the additional plate 11 extend in parallel to each other and parallel to the flat top side 2' of the substrate base 2.

A device or a method, characterized in that: the vertical distance between the additional plate 11 and the top side 2' extending in the horizontal plane of the substrate seat 2 is 0.8 mm +/-10%, and the vertical distance between the front zone plate 10 and the additional plate 11 is 0.8 mm +/-10%, and/or the vertical distance between the top side of the front zone plate 10 and the top side of the substrate seat 2 is 9.6 mm +/-10%, and/or the material thickness of the additional plate 11 is 3.2 mm +/-10%.

A method, characterized in that: the temperature difference between the temperature Tv of the front zone V and the temperature Ts of the substrate 4 is greater than 25°C, and/or, the temperature-regulating gas is not fed into the free spaces 12, 13, and/or, the substrate temperatures of several substrates 4 arranged in the substrate support area S are individually adjusted, and/or, the substrate temperature of each substrate 4 is changed by changing the energy flow or by changing the height or composition of the air cushion supporting the substrate rack 3, and/or, the element of the Vth main group is arsenic or phosphorus.

All disclosed features (as individual features or in combination of features) are essential to the invention. Therefore, the disclosure of this application also includes all the contents disclosed in the relevant/attached priority files (copies of prior applications), and the features described in such files are also included in the scope of the patent application of this application. The dependent items describe the features of the invention as an improvement over the prior art by their features (even if they do not contain the features of the relevant claim items), and their main purpose is to make divisional applications based on such claim items. The invention given in each claim item may further have one or more of the features given in the preceding description, especially those indicated by symbols and/or given in the symbol description. The present invention also relates to the following design forms: individual features described in the above description are not realized, especially features that are not necessary for a specific use or can be replaced by other components with the same technical effect.

1: Shell 2: Substrate holder 2': Top 3: Substrate rack 4: Substrate 5: Gas inlet assembly 6: Heating device 7: Process chamber top 8: Process chamber 9: Gas outlet opening 10: Front zone plate 10': Bottom 11: Additional plate 12: Gap, free space 13: Gap, free space 14: Spacer element 15: Central opening 16: Opening 17: Central opening 18: Spacer element 19: Rod 20: Gas outlet assembly 21: Air cushion 22: Air gap a: Distance b: Distance c: Distance d: Distance R: Radial S: Substrate support area T1: Upper limit temperature T2: Lower limit temperature Ts: Substrate temperature Tv: Pre-zone temperature V: Pre-zone

An embodiment of the present invention is described in detail below with reference to the attached figures. Among them: FIG. 1 is a top view of the substrate holder 2 of the CVD reactor, for example, according to the section line Ⅰ-Ⅰ in FIG. 2, FIG. 2 is a schematic cross-sectional view of the CVD reactor along the section line Ⅱ-Ⅱ in FIG. 1, FIG. 3 is an enlarged view of the local Ⅲ in FIG. 2, FIG. 4 is a perspective view of the front zone plate 10 of the present invention and the additional plate 11 of the present invention, FIG. 5 is a schematic diagram similar to FIG. 2 or FIG. 3, and additionally shows the temperature characteristic curve of the surface of the front zone plate 10 and the substrate 4 in the process chamber along the radial direction R.

2: Base plate

3: Substrate rack

4: Substrate

5: Gas inlet component

7: Top of the process room

8: Processing room

9: Exhaust opening

10: Front area board

11: Additional board

14: Spacer element

18: Spacer element

21: Air cushion

22: Air gap

R: Radial

S: Substrate support area

T1: Upper limit temperature

T2: Lower limit temperature

Ts: substrate temperature

Tv: front zone temperature

V: Pre-area

Claims (16)

A CVD reactor, wherein a gas inlet component (5), a substrate holder defining a process chamber (8) below, a heating device (6) for heating the substrate holder (2), and a process chamber top (7) defining a process chamber (8) above are provided in a reactor housing (1), wherein the substrate holder (2) forms a substrate support area (S) for accommodating a substrate (4) to be coated, and a substrate support area (S) is formed between the substrate holder (2) and the substrate support area (S). A front zone plate (10) is arranged in the area between the gas inlet component (5) and the substrate support area (S), so that a free space (12, 13) is left between the top side (2') of the substrate seat (2) and the bottom side (10') of the front zone plate (10), and an additional plate (11) is arranged in the free space, which is characterized in that the additional plate (11) and the front zone plate (10) are overlapped congruently. A CVD reactor as claimed in claim 1, wherein the additional plate (11) has a basic contour consistent with the front zone plate (10), and/or the front zone plate (10) is electrically conductive and/or is made of graphite, and/or the additional plate (11) has a lower thermal conductivity than the front zone plate (10). A CVD reactor as claimed in claim 1, wherein the additional plate (11) is electrically insulating and/or made of quartz and/or ceramic material. A CVD reactor as claimed in claim 1, wherein the front zone plate (10) and the additional plate (11) respectively have a central opening (15, 17), and the gas inlet member (5) is inserted into the central opening. A CVD reactor as claimed in claim 1, wherein the front zone plate (10) and the additional plate (11) are respectively integrated components. A CVD reactor as claimed in claim 1, wherein the front zone plate (10) is maintained at a predetermined first distance (d) from the top side (2') of the substrate holder (2) by the first spacer elements and the front zone plate (10) is maintained at a predetermined second distance (c) from the top side (2') of the substrate holder (2) by the second spacer elements. An additional plate (11), wherein the additional plate (11) has an opening (16), the first spacing elements (14) pass through the openings, wherein the predetermined first distance (d) is the distance between the upper surface of the substrate base (2) and the lower surface of the front zone plate (10), and the predetermined second distance (c) is the distance between the upper surface of the substrate base (2) and the lower surface of the additional plate (11). A CVD reactor as claimed in claim 1, wherein the front zone plate (10) and the additional plate (11) are respectively flat pieces with flat wide sides, and the front zone plate (10) and the additional plate (11) extend in parallel with each other and in parallel with the flat top side (2') of the substrate holder (2). A CVD reactor as claimed in claim 1, wherein the vertical distance between the additional plate (11) and the top side (2') of the substrate holder (2) extending in a horizontal plane is 0.8 mm +/- 10%, and the vertical distance between the front zone plate (10) and the additional plate (11) is 0.8 mm +/- 10%. A CVD reactor as claimed in claim 1, wherein the vertical distance between the top side of the front zone plate (10) and the top side of the substrate holder (2) is 9.6 mm +/- 10%. A CVD reactor as claimed in claim 1, wherein the material thickness of the additional plate (11) is 3.2 mm +/- 10%. A method for depositing a III-V group layer in a device, wherein a gas inlet component (5), a substrate holder defining a process chamber (8) below, a heating device (6) for heating the substrate holder (2), and a process chamber top (7) defining a process chamber (8) above are provided in a reactor shell (1), wherein the substrate holder (2) forms a substrate support area (S) for accommodating a substrate (4) to be coated, and a front zone plate (10) is provided in an area of the substrate holder (2) between the gas inlet component (5) and the substrate support area (S), so that free space (12, 13) is left between the top side (2') of the substrate holder (2) and the bottom side (10') of the front zone plate (10), comprising the following steps: The substrate holder (2) is heated by the heating device (6) and a vertical temperature gradient is generated in the process chamber (8), so that the temperature of the process chamber or the top of the process chamber (7) is lower than that of the substrate holder (2), the substrate support area (S) has a temperature (Ts) between 500°C and 800°C, and the front area (V) has a lower temperature (Tv); The process gas is fed into the front area (V) through the gas inlet component (5), wherein the process gas comprises at least one first reaction gas containing an element of the third group, at least one second reaction gas containing an element of the fifth group, and a carrier gas; Its characteristic is that the vertical height of the free space (12, 13) is selected so that the temperature of the front area (V) is 10 to 40°C lower than the temperature of the substrate support area (S). A method as claimed in claim 11, wherein the vertical height of the free space (12, 13) is selected so that the temperature of the front zone (V) is 20 to 40°C lower than the temperature of the substrate support zone (S). A method as claimed in claim 11, wherein the temperature difference between the temperature (Tv) of the pre-zone (V) and the temperature (Ts) of the substrate (4) is greater than 25°C. A method as claimed in claim 11, wherein temperature-controlled gas is not fed into the free space (12, 13). A method as claimed in claim 11, wherein the substrate temperatures of several substrates (4) arranged in the substrate support area (S) are individually adjusted, and/or the substrate temperature of each substrate (4) is changed by changing the energy flow or by changing the height or composition of the air cushion supporting the substrate rack (3). The method of claim 11, wherein the element of Group V is arsenic or phosphorus.