Heating system and method for heating large-area substrates

Abstract

Heating system for heating large-area substrates, which features: a susceptor plate (1) with a top (1a) and a bottom (1b), wherein the susceptor plate (1) is opaque to infrared radiation; several spacers (2a; 2b; 2c) arranged above the susceptor plate (1) and resting directly on the top surface of the susceptor plate (1), wherein the spacers (2a; 2b; 2c) are made of a material with low thermal conductivity and protrude at least 1 mm from the top surface (1a) of the susceptor plate (1); and an infrared radiation source (3) which is arranged and configured to heat the underside (1b) of the susceptor plate (1) by means of infrared radiation.

Description

[0001] The present invention relates to a heating system and a method for heating large-area substrates.

[0002] For various processes, for example in thin-film photovoltaics, it is necessary to heat large-area substrates with dimensions of, for example, 1.5 mx 2 m to temperatures of, for example, 700 °C. The increased temperature can reduce the stability of the substrate; this occurs particularly when using glass if the glass softening point is exceeded. It is therefore necessary that the substrate is fully or partially supported by a carrier plate during the heating process. In the simplest case, the substrate is usually placed on a directly or indirectly heated heating plate. However, slight unevenness in the substrate can lead to locally varying contact between the substrate and the heating plate, for example, which influences the heating process and leads to considerable temperature inhomogeneities in the substrate.These local temperature differences can have a detrimental effect on the process or lead to substrate destruction due to thermal stresses. These problems occur particularly frequently when substrates with poor thermal conductivity (e.g., glass) are heated very quickly, for example, at rates of 5 K / s.

[0003] To address this problem, DE 199 36 081 A1 proposes heating through a so-called transparent body, which has a specific transmission and absorption for the relevant electromagnetic radiation. This heats the substrate partly directly by electromagnetic radiation passing through the transparent body, and partly indirectly by heat conduction through contact with the transparent body, which heats up through absorption. The transparent body can have a spacer against which the substrate rests. However, this type of heating is disadvantageous in that, among other things, it is difficult to precisely control. Complete temperature uniformity between the substrate to be heated and the transparent carrier body can only be achieved if tight tolerances are maintained.This equilibrium is disturbed by a change in the thickness ratios or the absorption capacity of the substrate. Such a change in absorption capacity occurs, for example, by applying reflective or highly absorbent layers to the substrate. Therefore, there is a need for heating systems for large-area substrates that also allow for larger temperature differences between the carrier and the substrate.

[0004] DE 11 2010 000 737 T5 discloses a method and apparatus for supporting, positioning, and rotating a semiconductor substrate during processing. US 2019 / 0043744 A1 describes a monitoring system for preventing substrate breakage.

[0005] It is therefore an object of the present invention to provide an improved heating system and an improved method for heating large-area substrates which overcome the disadvantages of the prior art.

[0006] This object is achieved with a heating system or with a method according to the independent claims.

[0007] Accordingly, according to a first aspect, the present invention provides a heating system for heating large-area substrates. The heating system comprises a susceptor plate having a top side and a bottom side, wherein the susceptor plate is opaque to infrared radiation. Furthermore, the heating system comprises a plurality of spacers above the susceptor plate, which spacers rest directly on the top side of the susceptor plate, are made of a material with low thermal conductivity, and protrude at least 1 mm from the top side of the susceptor plate. Finally, the heating system comprises an infrared radiation source arranged and configured to heat the bottom side of the susceptor plate using infrared radiation.

[0008] The invention is based, among other things, on the fact that the susceptor plate is heated indirectly by means of infrared radiation from the infrared radiation source and the absorbed energy is then transferred to the substrate to be heated by means of thermal radiation and / or thermal conduction. Due to the spacers, homogeneous heating can be achieved, since the problem described above cannot occur, namely that slight unevenness in the substrate leads to locally different contact between the substrate and the heating plate, which influences the heating process and leads to considerable temperature inhomogeneities in the substrate. Since the susceptor plate is opaque to infrared radiation, direct heating of the substrate by the infrared radiation source is not possible. The good thermal conductivity of the susceptor plate, particularly in the lateral direction, improves the homogeneity of the radiation emitted by the susceptor plate, so that, if necessary,Small inhomogeneities in the infrared radiation source can be compensated. The heating of the substrate by the heated susceptor plate via thermal radiation and / or thermal conduction can therefore be controlled very precisely.

[0009] In the context of the present invention, large-area substrates are substrates with an area of ​​at least 0.7 m 2 , preferably at least 1 m 2 , more preferably at least 2 m 2 and especially preferably at least 3 m 2 Possible substrates include, for example, coated or uncoated glass panes, coated or uncoated silicon wafers, with or without electronic components. In principle, however, the invention is suitable for any substrate.

[0010] According to a second aspect, the present invention is directed to a heating system for heating large-area substrates. The heating system comprises a susceptor plate with a top side and a bottom side, as well as a plurality of spacers above the susceptor plate, which rest directly on the top side of the susceptor plate and are made of a material with low thermal conductivity. Furthermore, the heating system comprises an infrared radiation source arranged and configured to heat the bottom side of the susceptor plate using infrared radiation.The susceptor plate should be made of such a material and dimensioned such that, during the heating test defined below using the reference substrate defined below, the susceptor plate is heated in such a way that the maximum heating rate of the susceptor plate during the first 20 s of heating is at least a factor of 4 greater than the maximum heating rate of the reference substrate during the first 20 s of heating. This large temperature gradient reflects a very rapid heating of the susceptor plate, which in turn heats the substrate with a time delay by means of thermal radiation and, if necessary, thermal conduction through the heat-conducting gas located between the susceptor plate and the substrate (preferably at atmospheric pressure).

[0011] If there is no vacuum between the top side of the susceptor plate and the substrate to be heated, heating of the substrate is generally based on a combination of thermal radiation, direct heat conduction at contact points between the susceptor plate and substrate, and heat conduction through the fluid located between the susceptor plate and substrate. The latter is relatively highly dependent on the distance at small distances, so that this component may again lead to inhomogeneities during heating. It is therefore preferable to select the distance between the susceptor plate and substrate so that heat conduction is very small and only very weakly dependent on the distance. It is therefore preferred that this distance is at least 1 mm and particularly preferably at least 2 mm, or that the spacers protrude at least 2 mm from the top side of the susceptor plate.More preferably, this distance is at least 2.5 mm and particularly preferably at least 3 mm.

[0012] Detailed simulations and experiments have shown that the influence of the gap between the susceptor plate and the substrate on the heating process is negligible above a minimum distance of approximately 2 mm. In other words, above a minimum distance of approximately 2 mm, gap variations caused by, for example, substrate unevenness no longer play a role, so that very homogeneous heating can be achieved with appropriately dimensioned spacers.

[0013] In order to minimize the possible disturbance of the heating process by the spacers, their geometry should be kept as small as possible, so that on the other hand it is preferred that the spacers protrude at most 10 mm, more preferably at most 8 mm and particularly preferably at most 5 mm from the top side of the susceptor plate.

[0014] The spacers can be arranged directly on the top side of the susceptor plate or connected to it. Alternatively, the spacers can also be arranged above the susceptor plate, spaced from the top side. For example, the spacers can be held by corresponding support strips or a grid running above the susceptor plate.

[0015] Furthermore, for a rapid heating process of the substrate, it is preferred that the temperature of the susceptor plate during the heating process is significantly higher than that of the substrate. Accordingly, the susceptor plate is preferably formed from a material and dimensioned such that, during the heating test defined below using the reference substrate defined below, the susceptor plate is heated such that the maximum temperature difference between the susceptor plate and the reference substrate during the first 90 s of heating is at least 100 K, preferably at least 200 K, more preferably at least 300 K, even more preferably at least 400 K, and particularly preferably at least 500 K. These high initial temperature differences also reflect the very rapid heating of the susceptor plate and the associated high radiation power of the susceptor plate onto the substrate.

[0016] In the context of the present invention, infrared radiation is understood to mean the wavelength range between 0.5 µm and 10.0 µm. Accordingly, the susceptor plate preferably has a transmission of less than 10%, more preferably less than 5%, even more preferably less than 3%, and particularly preferably less than 1% for electromagnetic radiation in the entire wavelength range between 0.5 µm and 10.0 µm. It may be sufficient if these transmission values ​​are achieved as an average over the entire wavelength range between 0.5 µm and 10.0 µm, since ultimately only the cumulative heating power is important. However, it is preferred that these transmission values ​​are actually achieved for each individual wavelength over the entire wavelength range between 0.5 µm and 10.0 µm.If the infrared radiation source only emits infrared radiation of a specific wavelength band (or several bands), it is sufficient for the susceptor plate to have the specified transmission values ​​for infrared radiation within this wavelength band (or these bands), since an increased transmission for radiation that is not emitted is harmless.

[0017] The high absorption coefficient of the susceptor plate initially causes the susceptor plate to heat exclusively, followed by the substrate heating due to the rapidly rising temperature of the susceptor plate. The high absorption coefficient of the susceptor plate and the indirect heating of the substrate are defined by measuring the heating temperatures of the susceptor plate and the substrate. It is also advantageous that the susceptor plate has a small thickness and heat capacity to achieve a rapid heating process.

[0018] It is further preferred that the susceptor plate has an absorption coefficient of at least 45%, more preferably of at least 50%, and particularly preferably of at least 55% for electromagnetic radiation across the entire wavelength range between 0.5 µm and 10.0 µm. A corresponding average absorption may also be sufficient here. However, it is preferred that these absorption coefficients are achieved for all wavelengths. The absorption of the susceptor plate can be further increased by appropriate measures such as, for example, structuring the surface or increasing the surface roughness or by coating it with graphite, for example. Absorption coefficients of at least 65%, more preferably of at least 75%, and particularly preferably of at least 85% are then possible.

[0019] It is further preferred that the susceptor plate has an emissivity of at least 45%, more preferably of at least 50%, and particularly preferably of at least 55% for electromagnetic radiation across the entire wavelength range between 0.5 µm and 10.0 µm. A corresponding average emission may also be sufficient here. However, it is preferred that these emissivity levels be achieved for all wavelengths. The emission of the susceptor plate can be further increased by appropriate measures such as surface structuring or a greater surface roughness or by coating it with graphite, for example. Emissivity levels of at least 65%, more preferably of at least 75%, and particularly preferably of at least 85% are then possible.

[0020] The above values ​​for transmission, absorption, and emission can generally be applied to the susceptor plate. However, with regard to the functionality of the susceptor plate, it is particularly desirable that the absorption values ​​be realized for the underside and the emissivity for the top side of the susceptor plate. The transmission values ​​mentioned should apply, in particular, to a bottom-to-top transmission. (This applies analogously and vice versa for the optional susceptor plate above the substrate, see below.)

[0021] According to a third aspect, the present invention is directed to a heating system for heating large-area substrates, comprising a susceptor plate with a top side and a bottom side, a plurality of spacers above the susceptor plate, and a heat source arranged directly on or in the susceptor plate and configured to directly heat the susceptor plate. The plurality of spacers rest directly on the top side of the susceptor plate and are made of a material with low thermal conductivity, wherein the spacers protrude at least 1 mm, preferably at least 2 mm, and particularly preferably at least 3 mm from the top side of the susceptor plate.

[0022] Since, in this aspect of the invention, the susceptor plate is not heated using infrared radiation, it is not necessary for this aspect for the susceptor plate to be opaque to infrared radiation. However, it is preferable that no image of the heat source geometry be created in the temperature distribution of the substrate. The heat source can, for example, be a resistance heater integrated into the susceptor plate. The resistance heater is preferably designed such that the surface of the susceptor plate has a homogeneous temperature distribution, with heat conduction within the susceptor plate also improving the homogeneous temperature distribution.

[0023] The susceptor plate of this third aspect of the invention also preferably consists of a material that corresponds to the heating tests defined above for the other aspects of the invention.

[0024] The preferred features described below are relevant to all three aspects of the present invention described above.

[0025] The thermal conductivity of the spacers in the entire temperature range between 20 °C and 1,000 °C is preferably less than 6.0 W / m·K, more preferably less than 4.5 W / m·K and particularly preferably less than 3.0 W / m·K. Since the materials used for the spacers can also be anisotropic, it is particularly preferred that the thermal conductivity of the spacers in the direction perpendicular to the substrate plane in the entire temperature range between 20 °C and 1,000 °C is preferably less than 6.0 W / m·K, more preferably less than 4.5 W / m·K and particularly preferably less than 3.0 W / m·K. The thermal conductivity of the spacers can be determined using conventional methods such as the laser flash method, the transient hot bridge method or by means of a heat flow meter (e.g. using the λ-Meter EP500e from Lambda-Meßtechnik GmbH Dresden). A particularly preferred measurement method in the context of the present invention is the needle probe method according to ASTM D5334-08.

[0026] It is therefore preferred that the spacers be made of quartz, glass, or glass ceramic, for example. These spacers can be tubes, rods, pyramid-shaped structures, or the like. As will be explained in more detail below, tubes or rods can extend along the transverse and / or longitudinal direction of the substrate and form a support grid or lattice. Alternatively, isolated, local spacers can also be provided to further minimize the support surface, for example, spherical, pyramid-shaped, or conical structures that support the substrate in a grid.

[0027] The spacers should preferably be shaped in such a way that the support surface or the contact surface between the substrate and the spacer is minimized. The total (sum of) contact surface between the substrate and all spacers is preferably a maximum of 5%, more preferably a maximum of 1%, particularly preferably a maximum of 0.1% of the substrate surface. The thicker the substrate, the better temperature inhomogeneities within the substrate can be compensated for by lateral heat conduction in the substrate. For particularly thin substrates, a particularly small support surface is therefore advantageous. It is therefore preferred that the width of the contact line of spacers extending continuously along the transverse and / or longitudinal direction of the substrate is less than 50%, preferably less than 20% and particularly preferably less than 10% of the substrate thickness. In the case of insulated spacers, it is preferred that the diameter orthe maximum dimension of the support surface of a spacer is less than 50%, preferably less than 20% and particularly preferably less than 10% of the substrate thickness.

[0028] Minimizing the contact area is also achieved, for example, by a high elastic modulus, i.e., low elastic deformation, and / or low surface roughness of the contact bodies. Thus, the elastic modulus of the spacer material is preferably at least 50 GPa, more preferably at least 60 GPa, and even more preferably at least 70 GPa. The surface roughness of the spacers is preferably a maximum of 0.05 µm, more preferably a maximum of 0.03 µm, and even more preferably a maximum of 0.02 µm. This further minimizes the introduction of heat through conduction and the resulting temperature gradients.

[0029] To minimize disruption of the energy transfer from the susceptor plate to the substrate by thermal radiation, it is advantageous if the spacers shade as little of the substrate surface as possible. Therefore, it is preferred that the total projection area of ​​all spacers (projected perpendicular to the substrate surface) be a maximum of 10%, preferably a maximum of 6%, particularly preferably a maximum of 3% of the substrate surface.

[0030] It is further preferred to provide a plurality of spacers in order to support the substrate as evenly as possible. This is particularly relevant for glass substrates and heating beyond the softening point. In order to prevent any resulting deflection of the heated substrate as far as possible, it is preferred that the maximum unsupported distance between two spacers is less than 10 cm, more preferably less than 5 cm, and particularly preferably less than 3 cm. Thus, corresponding simulations for parallel spacers have shown that when a glass plate with a thickness of 2 mm is supported on spacers at a distance of 5 cm for a period of 5 minutes, a maximum deflection of 0.2 mm results, which is considered tolerable. Analogous calculations were carried out for discrete support points in a regular square pattern. Here, a diagonal of the square pattern (i.e.again the unsupported distance) of a maximum of 5 cm leads to good results.

[0031] The thickness of the susceptor plate is preferably less than 5 mm, more preferably less than 3 mm, and most preferably less than 2 mm. For example, plates made of fiber-reinforced carbon (so-called CFC materials) can be used.

[0032] The upper side of the susceptor plate preferably has an area of ​​at least 0.7 m 2 , more preferably at least 1 m 2 , more preferably at least 2 m 2 and particularly preferably at least 3 m 2 on.

[0033] In addition to the infrared radiation source or the heating source, a (further) infrared radiation source can be provided, which is arranged and configured to heat the upper side of the susceptor plate or the substrate by means of infrared radiation. Particularly preferably, heating also takes place indirectly from this side by means of a susceptor plate. It is therefore further preferred that a further susceptor plate with a top side and a bottom side is provided, wherein the susceptor plate is opaque to infrared radiation. Furthermore, a (further) infrared radiation source is preferably provided, which is arranged and configured to heat the upper side of the further susceptor plate by means of infrared radiation. The properties described above with regard to the lower susceptor plate also preferably apply to the upper susceptor plate, in particular also with regard to the optical parameters and the heating behavior.

[0034] In order to ensure the most homogeneous heating of the substrate possible, it is preferred that the (upper and / or lower) susceptor plate has a lateral thermal conductivity within the susceptor plate plane of at least 10 W / mK, more preferably of at least 30 W / m•K and particularly preferably of at least 50 W / m•K over the entire temperature range between 20 °C and 1,000 °C.

[0035] The present invention further relates to a method for heating a large-area substrate using the heating system described above (all three aspects). The method comprises introducing a large-area substrate into the heating system such that the substrate is supported on the spacers. The method further comprises heating the susceptor plate, whereby the substrate supported on the spacers is then heated primarily by thermal radiation.

[0036] Furthermore, the present invention is directed to a method for heating a large-area substrate comprising the following steps: - Providing a heating system as described above; - introducing a large-area substrate into the heating system in such a way that the substrate is supported on the spacers; and - Heating the susceptor plate.

[0037] The susceptor plate is preferably heated using the infrared radiation source such that the maximum heating rate of the susceptor plate during the first 20 s of heating is at least a factor of 4, preferably at least a factor of 6, more preferably at least a factor of 10, greater than the maximum heating rate of the substrate during the first 20 s of heating. Preferably, the maximum temperature difference between the susceptor plate and the substrate during the first 90 s of heating is at least 100 K, preferably at least 200 K, more preferably at least 300 K, even more preferably at least 400 K, and particularly preferably at least 500 K.

[0038] The substrate preferably has an area of ​​at least 0.7 m 2 , more preferably at least 1 m 2 , even more preferably at least 2 m 2 and especially preferably at least 3 m 2 on.

[0039] The susceptor plate is preferably heated to a temperature of at least 600 °C, more preferably at least 800 °C and particularly preferably at least 1,000 °C.

[0040] The substrate is heated over its entire surface by the heated susceptor plate, primarily by means of thermal radiation, wherein the heating of the substrate occurs at a rate of at least 2 K / s, more preferably at least 3 K / s, and particularly preferably at least 4 K / s. Furthermore, the heating rate is preferably less than 18 K / s, more preferably less than 15 K / s, and particularly preferably less than 10 K / s. In particular, according to the invention, a high initial heating rate of the susceptor plate is advantageous in order to quickly ensure a high energy transfer from the susceptor plate to the substrate. It is therefore preferred that the susceptor plate is heated to a temperature of at least 300 °C, preferably at least 400 °C, and particularly preferably at least 500 °C during the first 20 s of heating.

[0041] Preferably, the substrate is heated to a temperature of at most 700°C, more preferably at most 650°C, and particularly preferably at most 600°C. Preferably, the substrate is heated to a temperature of at least 300°C, more preferably at least 400°C, and particularly preferably at least 500°C.

[0042] The heating process preferably takes place in the presence of a process gas. The gas can be an inert gas, e.g., nitrogen or argon, a reactive gas, or a mixture of an inert gas and a reactive gas. The gas pressure between the susceptor plate and the substrate is preferably at least 20 mbar, more preferably at least 100 mbar, even more preferably at least 200 mbar, and most preferably atmospheric pressure.

[0043] The distance between the top side of the susceptor plate and the bottom side of the substrate is preferably at least 1 mm, more preferably at least 2 mm, and particularly preferably at least 3 mm. Furthermore, the distance between the top side of the susceptor plate and the bottom side of the substrate is preferably at most 10 mm, more preferably at most 8 mm, and particularly preferably at most 5 mm.

[0044] The minimum distance of 2 mm, as already explained, leads to particularly homogeneous heating within the substrate. In this context, it is preferred that the substrate is heated so homogeneously throughout the entire heating process that the temperature difference occurring on the substrate surface in the region of a spacer is at most 75 K, preferably at most 50 K, and particularly preferably at most 25 K. This can be measured, for example, using an infrared camera. For example, an infrared camera can be used to evaluate an area of ​​50 mm x 50 mm that has at least one contact surface on at least one spacer, as symmetrically as possible. Of all the temperatures determined within this area, the maximum difference is determined at each measurement time. Preferably, this should be at most 75 K, more preferably at most 50 K, and particularly preferably at most 25 K, for all measurement times.Corresponding simulations have shown that discrete spacers with contact surfaces that are as point-like as possible offer a clear advantage in this regard. This is due, among other things, to the fact that the shadowing is only point-like, and a local inhomogeneity in the temperature distribution caused by a discrete spacer can be compensated from all sides by heat conduction within the substrate, whereas a linear disturbance can only be compensated by heat conduction perpendicular to the line.

[0045] Preferably, the total contact area between the substrate and all spacers is a maximum of 5%, preferably a maximum of 1%, particularly preferably a maximum of 0.1% of the substrate surface. As already explained above, it is preferred that the width of the contact line of spacers extending continuously along the transverse and / or longitudinal direction of the substrate is less than 50%, preferably less than 20%, and particularly preferably less than 10% of the substrate thickness. In the case of insulated spacers, it is preferred that the diameter or the maximum dimension of the support surface of a spacer is less than 50%, preferably less than 20%, and particularly preferably less than 10% of the substrate thickness.

[0046] Preferably, the total projection area of ​​all spacers is a maximum of 10%, preferably a maximum of 6%, particularly preferably a maximum of 3% of the substrate surface.

[0047] Preferably, the maximum unsupported distance between the support surfaces of two spacers is a maximum of 10 cm, preferably a maximum of 5 cm, particularly preferably a maximum of 3 cm.

[0048] Within the scope of the method according to the invention, the heating system can also further comprise a further susceptor plate with a top side and a bottom side, and a further infrared radiation source arranged and configured to heat the top side of the further susceptor plate using infrared radiation. The large-area substrate is introduced into the heating system such that the substrate is supported on the spacers between the two susceptor plates. The distance between the bottom side of the further susceptor plate and the top side of the substrate is also preferably at least 1 mm, more preferably at least 2 mm.

[0049] The present invention describes an advantageous heating system and an advantageous heating method for the case where a large-area substrate (e.g., a large-area glass pane) rests on a susceptor plate that is rapidly heated, for example, by IR radiators, whereby a homogeneous temperature distribution is achieved within the large-area substrate. Various features according to the invention interact synergistically here. For example, the spacers enable a uniform energy supply, particularly at a distance of at least 2 mm, since variations in the gap size above this minimum distance have no significant influence on the heat conduction through the process gas. In order to enable high heating rates of the substrate at these distances, very rapid heating of the susceptor plate is provided, which is reflected in correspondingly large initial temperature differences and heating rate ratios between the susceptor plate and the substrate.Storing the substrate on the spacers, in turn, can lead to the substrate (e.g., the glass pane) bending between the spacers when heated to the glass transition temperature and stored for an extended period. This can be effectively prevented by specifying a corresponding maximum distance between the spacers depending on the temperature (and the resulting viscosity) and the storage time.

[0050] Preferred embodiments of the present invention are described in more detail below with reference to the figures. They show: ▪ Fig. 1 is a schematic sectional view through a heating system according to a preferred embodiment of the present invention; ▪ Fig. 2 is a schematic sectional view through a heating system according to another preferred embodiment of the present invention; ▪ Fig. 3 is a schematic sectional view through a heating system according to another preferred embodiment of the present invention; ▪ Fig. 4A schematically shows the arrangement of spacers according to a first preferred embodiment; ▪ Fig. 4B schematically shows the arrangement of spacers according to a second preferred embodiment; ▪ Fig. 4C schematically shows the arrangement of spacers according to a third preferred embodiment; ▪ Fig. 5A schematically shows the arrangement of the spacers according to the Fig. 4A-C according to a first preferred embodiment; ▪ Fig. 5B schematically shows the arrangement of the spacers according to the Fig. 4A-C according to a second preferred embodiment; ▪ Fig. 5C schematically shows the arrangement of the spacers according to the Fig. 4A-C according to a third preferred embodiment; ▪ Fig. 6A is a schematic perspective view of a heating system according to a preferred embodiment of the present invention; ▪ Fig. 6B is a schematic perspective view of a heating system according to another preferred embodiment of the present invention; ▪ Fig. 6C is a schematic perspective view of a heating system according to another preferred embodiment of the present invention; ▪ Fig. 6D is a schematic perspective view of a heating system according to another preferred embodiment of the present invention; ▪ Fig. 6E is a schematic perspective view of a heating system according to another preferred embodiment of the present invention; ▪ Fig. 6F is a schematic perspective view of a heating system according to another preferred embodiment of the present invention; ▪ Fig. 7 schematically shows a measuring arrangement for the heating test; ▪ Fig. 8 schematically shows the placement of the thermocouple TC1 for the heating test; ▪ Fig. 9 schematically shows the placement of the thermocouple TC2 for the heating test; ▪ Fig. 10 shows the temporal temperature profile of a susceptor plate and a substrate in the method according to the invention; and ▪ Fig. 11 which is derived from the temperature curves according to Fig. 10 determined heating rates.

[0051] Fig. 1 shows a schematic sectional view through a heating system for heating large-area substrates according to a preferred embodiment of the present invention. The heating system comprises a susceptor plate 1 with a top side 1a and a bottom side 1b, wherein the susceptor plate 1 is preferably opaque to infrared radiation. Several spacers 2 are arranged on the top side 1a of the susceptor plate 1. A large-area substrate 4 is mounted on the spacers 2. The spacers 2 are preferably made of a material with low thermal conductivity in order to largely prevent direct heat conduction from the susceptor plate 1 to the substrate 4.

[0052] Below the susceptor plate 1, an infrared radiation source 3 is schematically indicated. This source is designed to heat the underside 1b of the susceptor plate 1 using infrared radiation. The infrared radiation source 3 can be a single, extensive radiation source or an arrangement of several heating radiators, for example, several tubular IR radiators.

[0053] In this context, it should be emphasized that the sketch according to Fig. 1 is not to scale. In fact, the substrate 4 can have an area of ​​several square meters, whereas the cross-sectional area of ​​the individual spacers 2 is typically only a few square millimeters.

[0054] In Fig. 1, the spacers 2 are solid rods with a round cross-section. Alternatively, the spacers 2 can have the shape of a tube with an internal cavity, as shown in Fig. 2. Different variants of cross sections of spacers 2a, 2b and 2c according to the invention are shown in the Fig. 4A-C. Thus, instead of a tube 2a with an internal cavity (cf. Fig. 4A) bars with a triangular or rectangular cross-sectional profile can also be used (cf. Fig. 4B and C). These rods 2b, 2c can also be hollow (cf. Fig. 4B) or be solid (cf. Fig. 4C). Alternatively, the spacer 2c (cf. Fig. 4C) is also pyramid-shaped with a point-shaped contact surface and the spacer 2b (cf. Fig. 4B) can be cylindrical with, for example, a circular support surface.

[0055] In reality, one will usually choose one type of spacer and arrange a large number of such spacers in a regular pattern with essentially constant spacing. Example arrangements are shown in the Fig. 6A-C. For example, rod-shaped spacers 2 can be arranged parallel to each other (cf. Fig. 6A and Fig. 6B) or in a crossing pattern (cf. Fig. 6C), so that rectangular or square areas of the substrate 4 are supported on all four sides. The distance between adjacent spacers 2 can be variable (cf. Fig. 6A and Fig. 6B) and should be adapted to the deformability (e.g., deflection) of the substrate.

[0056] The applicant has conducted extensive experiments with different spacers, which revealed that several parameters are relevant for the geometry and arrangement of the spacers. As already explained above, the spacers should preferably be dimensioned such that the substrate is at least 1 mm, more preferably at least 2 mm, away from the susceptor plate in order to minimize the influence of the gap on energy transfer. This allows for homogeneous heating.

[0057] Furthermore, the distance between adjacent spacers plays a role, as already explained above. The higher the glass substrate is heated, the lower its viscosity becomes. In the range of the glass transition temperature, the substrate material slowly begins to flow. Depending on the maximum temperature achieved and the time the substrate is stored on the spacers at this temperature, it is possible to determine which maximum distance between adjacent spacers still leads to tolerable deformations of the substrate. The applicant's analyses have shown that for arrangements according to the Fig. 6A and Fig. 6B shows that for substrate materials, temperatures and storage times commonly used in practice, distances of a maximum of 10 cm, preferably a maximum of 5 cm and particularly preferably a maximum of 3 cm lead to good results. With a grid-like arrangement of the spacers, as in Fig. As indicated in Figure 6C, larger distances might also be tolerable.

[0058] In order to minimize direct heat conduction through the spacers, it is also advantageous to have the smallest possible contact area between the spacers and the substrate. Therefore, geometries such as those shown in Fig. 4A and Fig. 4C, is particularly advantageous because in the case of cylinders, tubes, or spacers with a triangular cross-section, the contact surface is more or less reduced to a contact line. In corresponding experiments, the tubular spacer according to Fig. 4A proved to be particularly advantageous.

[0059] The geometry of the spacers also influences the heating of the substrate by thermal radiation, as the spacers shade the substrate in this regard. It is therefore also desirable that the maximum cross-sectional area, or the projection of the spacers onto the substrate surface, be as small as possible. Indeed, in the applicant's experiments, as already mentioned above, the greatest temperature inhomogeneities during heating were determined in the area of ​​the spacers.

[0060] Furthermore, it is particularly preferred to use the Fig. 6A-C, which extend continuously along the transverse and / or longitudinal direction of the substrate and form a support grid or grid, to provide isolated or discrete spacers, as exemplified in the Fig. 6D-F, where conical or spherical spacers 2 are arranged in a regular square grid and form only point-like contact surfaces. Both with regard to the above-mentioned shading of the substrate and with regard to heat conduction through the spacers, such discretely arranged spacers generate the smallest disturbances, which – as already explained – are particularly well compensated for by heat conduction within the substrate. Of course, these discrete spacers do not have to be conical or spherical, as shown in the example, but can also be pyramidal or cylindrical, for example. The arrangement in a square grid is also not mandatory, although the most regular distribution of the spacers is preferable with regard to the smallest possible disturbance and the smallest possible unsupported distances.When using spherical spacers, it is advisable to place the balls in corresponding holes or recesses 8 so that they remain in their grid position (see . Fig. 6F).

[0061] The spacers 2 preferably ensure that the distance between the top side 1a of the susceptor plate 1 and the bottom side of the substrate 4 is at least 2 mm. This can be achieved, for example, by the spacers 2a, 2b, 2c, as shown in Fig. 5A, are arranged directly on the top side 1a of the susceptor plate 1 and protrude at least 2 mm from the top side 1a of the susceptor plate 1. In this case, the distance h between the top side 1a of the susceptor plate 1 and the underside of the substrate 4 is defined by the thickness or height of the spacers 2a, 2b, 2c.

[0062] However, the spacers 2a, 2b, 2c do not have to rest on the upper side 1a of the susceptor plate 1, but can be arranged at a distance above the susceptor plate 1 by other support mechanisms, for example, as shown schematically in Fig. 5B. Here, too, the spacers 2a, 2b, 2c preferably protrude at least 2 mm from the upper side 1a of the susceptor plate 1. However, here the distance h between the susceptor plate and the substrate is greater than the thickness or height of the spacers 2a, 2b, 2c.

[0063] In another alternative, as schematically Fig. 5C, the spacers 2a, 2b, 2c can also be stored in corresponding recesses 5a, 5b, 5c in the upper side 1a of the susceptor plate 1, which results in the distance h between the susceptor plate and the substrate being smaller than the thickness or height of the spacers 2a, 2b, 2c.

[0064] As can be seen from these variants, the spacers protruding from the top of the susceptor plate are intended to ensure a defined distance h between the susceptor plate and the substrate. If the spacers, as in Fig. 5B, do not rest on the upper side 1a of the susceptor plate 1, the spacers are preferably rod-shaped and rest at their ends on a corresponding support frame 6. This is shown schematically in the Fig. 6A-C, where the spacers 2 extend from one edge of the support frame 6 across a rectangular cutout to the opposite edge of the support frame 6. In the rectangular cutout, the spacers 2 extend freely suspended from the upper side 1a of the susceptor plate 1 (cf. Fig. 5B).

[0065] As explained above, according to a third aspect, the invention is directed to a heating system for heating large-area substrates, which comprises a susceptor plate with a top side and a bottom side, a plurality of spacers above the susceptor plate, and a heat source arranged directly on or in the susceptor plate and configured to heat the susceptor plate directly. A preferred embodiment of this aspect of the invention is schematically shown in Fig. 3. Here, a heating coil 3a runs within the susceptor plate 1. Otherwise, the preferred features discussed in the context of the other figures also apply to this embodiment.

[0066] The applicant carried out the method according to the invention with a heating device according to the invention (with components corresponding to those described below in the context of the heating test, wherein a CFC plate with dimensions of 200 mm x 200 mm x 1 mm was used as the susceptor plate) and determined the temporal temperature profiles of the susceptor plate of the heating device and a glass substrate. Fig. 10 shows the corresponding result. Fig. 11 shows the temperature curves according to Fig. 10 determined heating rates. As can be clearly seen, the susceptor plate is heated very rapidly by the heating device according to the invention, particularly during the first 20-30 seconds, with the corresponding heating rate reaching a maximum of greater than 25 K / s. The heating of the substrate occurs with a time delay and at significantly lower heating rates: the maximum substrate heating rate – reached much later – is below 5 K / s. Accordingly, very large temperature gradients form between the susceptor plate and the substrate, which ultimately ensure effective, homogeneous, and rapid heating of the substrate. Heating test

[0067] The following describes a heating test which can be used to check whether the maximum heating rate ratios according to the invention can be achieved with a susceptor plate or whether the susceptor plate has the properties according to the invention for electromagnetic waves, in particular IR radiation. For this purpose, the Fig. 7 schematically shown test setup was used.

[0068] The test setup contains four regularly arranged shortwave IR circular tube radiators (300 - 460 mm long), with one or two coils, each with a total power of 1.5 - 3 kW. The IR circular tube radiators are coated with a reflective layer of gold, aluminum oxide, or QRC™ (quartz reflective coating), with R ≥ 50%. The IR circular tube radiators are arranged in Fig. 7 is marked with the reference symbol 3. The distance between the IR circular tube radiators 3 should be 50-55 mm.

[0069] Above the four circular IR tube radiators 3, the susceptor plate 1 to be tested is mounted on two symmetrically positioned tubes 7 such that the distance between the susceptor plate 1 and the circular IR tube radiators 3 is also 50-55 mm. Ceramic tubes made of aluminum oxide 10x1 or quartz tubes 10x1 (300-500 mm long) can be used for this purpose. The tubes 7 run perpendicular to the circular IR tube radiators 3 and are spaced 90-100 mm apart. If the susceptor plate to be tested is larger than 200 mm x 200 mm (+20 / -5), the plate is cut to this size, and a 200 mm x 200 mm (+20 / -5) section of the plate is measured.

[0070] On the top side of the susceptor plate 1, a thermocouple TC1 is attached as centrally as possible using a high-temperature adhesive such as silver lacquer (cf. Fig. 8).

[0071] The reference substrate for the heating test is a glass substrate made of clear float glass with a softening temperature of 510-600 °C and an area of ​​100 (+10 / -5) mm x 100 (+10 / - 5) mm and a thickness of 2 (+ / -0.2) mm.

[0072] The reference substrate 4 is placed as centrally as possible with respect to the susceptor plate 1 on four spacers 2, which are placed at the four corners of the reference substrate 4 (cf. Fig. 7). The spacers 2 are made of ceramic and have a height of 2-3 mm and a diameter of 8-10 mm.

[0073] A thermocouple TC2 is attached to the top side of the reference substrate, preferably in the center, using a high-temperature adhesive such as silver lacquer (see Fig. Fig. 9). For thermocouples TC1 and TC2, for example, a sheathed thermocouple type K with sheath material 1.4541 or 2.4816 and a sheath diameter of 0.5 (+ / -0.2) mm can be used.

[0074] The heating test is conducted in a closed room under a nitrogen atmosphere at 1,000 (+ / -100) hPa, a maximum oxygen partial pressure of 10 ppm, and a maximum water dew point of -40 °C. The test begins at room temperature, i.e., 23 (+ / -3) °C.

[0075] At time t = 0 s, the four circular IR tube radiators are switched on simultaneously with a power of 1.5 kW each (corresponding to a total radiation power of 6 kW), and the susceptor plate is heated at a constant radiation power until a temperature of greater than or equal to 600 °C is measured on the reference substrate using the TC2 thermocouple. The circular IR tube radiators are then switched off.

[0076] During the heating process, a temperature of the susceptor plate is measured using thermocouple TC1 and a temperature of the reference substrate is measured using thermocouple TC2 for a total of 90 s every full second (i.e., for t = 1 s, t = 2 s, ..., t = 90 s). From these measured temperatures, a heating rate for the susceptor plate and the reference substrate is determined for each full second by determining the difference quotient (e.g., heating rate for the susceptor plate for t = 1 s: (T TC1 (t=1 s) - T TC1 (t=0 s)) / 1 s).

[0077] According to the invention, the maximum heating rate of the susceptor plate during the first 20 seconds of heating is understood to be the maximum of the 20 values ​​thus determined for the susceptor plate. According to the invention, the maximum heating rate of the reference substrate during the first 20 seconds of heating is understood to be the maximum of the 20 values ​​thus determined for the reference substrate.

[0078] According to the invention, the maximum temperature difference between the susceptor plate and the reference substrate during the first 90 s of heating is understood to be the maximum difference between the temperatures determined for the susceptor plate and the reference substrate at the 90 times.

Claims

[1] Heating system for heating large-area substrates, which comprises: a susceptor plate (1) having a top side (1a) and a bottom side (1b), the susceptor plate (1) being opaque to infrared radiation; a plurality of spacers (2a; 2b; 2c) arranged above the susceptor plate (1) and resting directly on the upper side of the susceptor plate (1), wherein the spacers (2a; 2b; 2c) are made of a material with low thermal conductivity and protrude at least 1 mm from the upper side (1a) of the susceptor plate (1); and an infrared radiation source (3) arranged and configured to heat the underside (1b) of the susceptor plate (1) by means of infrared radiation. [2] Heating system for heating large-area substrates, which comprises: a susceptor plate (1) with a top side (1a) and a bottom side (1b); a plurality of spacers (2a; 2b; 2c) arranged above the susceptor plate (1) and resting directly on the upper side of the susceptor plate (1), wherein the spacers (2a; 2b; 2c) are made of a material with low thermal conductivity; and an infrared radiation source (3) arranged and configured to heat the underside (1b) of the susceptor plate (1) by means of infrared radiation; wherein the susceptor plate (1) is formed from a material and dimensioned such that the susceptor plate (1) is heated in the heating test defined below using the reference substrate defined below such that the maximum heating rate of the susceptor plate during the first 20 s of heating is at least a factor of 4 greater than the maximum heating rate of the reference substrate during the first 20 s of heating, wherein the heating test is defined as follows: Providing a test setup containing four regularly arranged shortwave infrared circular tube radiators with a length of 300 - 460 mm, each with a total power of 1.5 - 3 kW, wherein the infrared circular tube radiators are provided with a reflective coating of gold, aluminum oxide or QRC™ (quartz reflective coating), where R ≥ 50%, and where the distance between the infrared circular tube radiators is 50-55 mm; Arranging and supporting the susceptor plate to be tested above the four infrared circular tube radiators on two symmetrically placed tubes in such a way that the distance between the susceptor plate and the infrared circular tube radiators is also 50-55 mm; Centrally attaching a first thermocouple to the top of the susceptor plate using a high-temperature adhesive; Placing a reference substrate, centrally with respect to the susceptor plate, on four spacers which are placed at the four corners of the reference substrate, wherein the spacers are made of ceramic and have a height of 2-3 mm and a diameter of 8-10 mm, wherein the reference substrate is a glass substrate made of clear float glass with a softening temperature of 510-600 °C and an area of ​​100 (+10 / -5) mm × 100 (+10 / -5) mm and a thickness of 2 (+ / -0.2) mm; Centrally attaching a second thermocouple to the top of the reference substrate using a high-temperature adhesive; Carrying out the heating test in a closed room under a nitrogen atmosphere at 1,000 (+ / -100) hPa, an oxygen partial pressure of not more than 10 ppm and a water dew point of not more than -40 °C, starting the test at 23 (+ / -3) °C; Switching on the four infrared circular tube radiators with a power of 1.5 kW each at time t = 0 s and heating the susceptor plate with constant radiation power until a temperature of greater than or equal to 600 °C is measured on the reference substrate by means of the first thermocouple; and Subsequent switching off of the infrared circular tube radiators; wherein during the heating process, for a total of 90 s, a temperature on the susceptor plate is measured every full second by means of the first thermocouple and a temperature on the reference substrate is measured by means of the second thermocouple, wherein a heating rate for the susceptor plate and the reference substrate is determined from these measured temperatures for every full second by determining the difference quotient, and wherein the maximum heating rate of the susceptor plate during the first 20 s of heating is understood to be the maximum of the 20 values ​​thus determined for the susceptor plate and the maximum heating rate of the reference substrate during the first 20 s of heating is understood to be the maximum of the 20 values ​​thus determined for the reference substrate. [3] Heating system according to claim 2, wherein the maximum heating rate of the susceptor plate during the first 20 s of heating is at least a factor of 6, preferably at least a factor of 10, greater than the maximum heating rate of the reference substrate during the first 20 s of heating. [4] Heating system according to claim 2 or 3, wherein the susceptor plate (1) is formed from such a material and dimensioned such that the susceptor plate (1) is heated in the heating test defined below using the reference substrate defined below such that the maximum temperature difference between the susceptor plate and the reference substrate during the first 90 s of heating is at least 100 K, preferably at least 200 K, more preferably at least 300 K, even more preferably at least 400 K and particularly preferably at least 500 K, wherein the heating test is defined as follows: Providing a test setup containing four regularly arranged shortwave infrared circular tube radiators with a length of 300 - 460 mm, each with a total power of 1.5 - 3 kW, wherein the infrared circular tube radiators are provided with a reflective coating of gold, aluminum oxide or QRC™ (quartz reflective coating), where R ≥ 50%, and where the distance between the infrared circular tube radiators is 50-55 mm; Arranging and supporting the susceptor plate to be tested above the four infrared circular tube radiators on two symmetrically placed tubes in such a way that the distance between the susceptor plate and the infrared circular tube radiators is also 50-55 mm; Centrally attaching a first thermocouple to the top of the susceptor plate using a high-temperature adhesive; Placing a reference substrate, centrally with respect to the susceptor plate, on four spacers which are placed at the four corners of the reference substrate, wherein the spacers are made of ceramic and have a height of 2-3 mm and a diameter of 8-10 mm, wherein the reference substrate is a glass substrate made of clear float glass with a softening temperature of 510-600 °C and an area of ​​100 (+10 / -5) mm x 100 (+10 / -5) mm and a thickness of 2 (+ / -0.2) mm; Centrally attaching a second thermocouple to the top of the reference substrate using a high-temperature adhesive; Carrying out the heating test in a closed room under a nitrogen atmosphere at 1,000 (+ / -100) hPa, an oxygen partial pressure of not more than 10 ppm and a water dew point of not more than -40 °C, starting the test at 23 (+ / -3) °C; Switching on the four infrared circular tube radiators with a power of 1.5 kW each at time t = 0 s and heating the susceptor plate with constant radiation power until a temperature of greater than or equal to 600 °C is measured on the reference substrate by means of the first thermocouple; and Subsequent switching off of the infrared circular tube radiators; wherein during the heating process, for a total of 90 s, a temperature on the susceptor plate is measured every full second by means of the first thermocouple and a temperature on the reference substrate is measured by means of the second thermocouple, wherein a heating rate for the susceptor plate and the reference substrate is determined from these measured temperatures for every full second by determining the difference quotient, and wherein the maximum temperature difference between the susceptor plate and the reference substrate during the first 90 s of heating is understood to mean the maximum difference between the differences determined at the 90 times between the temperatures determined for the susceptor plate and the reference substrate. [5] Heating system according to one of the preceding claims, wherein the spacers (2a; 2b; 2c) protrude at least 1 mm, preferably at least 2 mm, from the upper side (1a) of the susceptor plate (1). [6] Heating system for heating large-area substrates, which comprises: a susceptor plate (1) with a top side (1a) and a bottom side (1b); a plurality of spacers (2a; 2b; 2c) arranged above the susceptor plate (1) and resting directly on the upper side of the susceptor plate (1), wherein the spacers (2a; 2b; 2c) are made of a material with low thermal conductivity, wherein the spacers (2a; 2b; 2c) protrude at least 1 mm from the upper side (1a) of the susceptor plate (1); and a heat source arranged directly on or in the susceptor plate (1) and adapted to heat the susceptor plate (1) directly. [7] Heating system according to claim 6, wherein the spacers (2a; 2b; 2c) protrude at least 2 mm from the top side (1a) of the susceptor plate (1). [8] Heating system according to one of the preceding claims, wherein the thermal conductivity of the spacers (2a; 2b; 2c) in the direction perpendicular to the plane defined by the susceptor plate is less than 6.0 W / m•K, preferably less than 4.5 W / m•K, particularly preferably less than 3.0 W / m•K, in the entire temperature range between 20 °C and 1,000 °C. [9] Heating system according to one of the preceding claims, wherein the spacers (2a; 2b; 2c) protrude at most 10 mm, preferably at most 8 mm and particularly preferably at most 5 mm from the upper side (1a) of the susceptor plate (1). [10] Heating system according to one of the preceding claims, wherein the thickness of the susceptor plate (1) is less than 5 mm, preferably less than 3 mm, particularly preferably less than 2 mm. [11] Heating system according to one of the preceding claims, wherein the upper side (1a) of the susceptor plate (1) has an area of ​​at least 0.7 m 2 , preferably at least 1 m 2 , more preferably at least 2 m 2 and especially preferably at least 3 m 2 has. [12] Heating system according to one of the preceding claims, wherein the susceptor plate (1) has a transmission of less than 10%, preferably less than 5%, more preferably less than 3% and particularly preferably less than 1% for infrared radiation in the entire wavelength range between 0.5 µm and 10.0 µm. [13] Heating system according to one of the preceding claims, wherein the susceptor plate (1) has an absorption factor of at least 45%, preferably at least 50% and more preferably at least 55% for infrared radiation in the entire wavelength range between 0.5 µm and 10.0 µm. [14] Heating system according to one of the preceding claims, wherein the susceptor plate (1) has a lateral thermal conductivity within the susceptor plate plane of at least 10 W / m·K, preferably at least 30 W / m·K, particularly preferably at least 50 W / m·K, over the entire temperature range between 20°C and 1,000°C. [15] Heating system according to one of the preceding claims, wherein the total contact area between the substrate and all spacers is a maximum of 5%, preferably a maximum of 1%, particularly preferably a maximum of 0.1% of the substrate surface. [16] Heating system according to one of the preceding claims, wherein the total projection area of ​​all spacers is a maximum of 15%, preferably a maximum of 12%, particularly preferably a maximum of 9% of the substrate surface. [17] Heating system according to one of the preceding claims, wherein the maximum unsupported distance between the support surfaces of two spacers is a maximum of 10 cm, preferably a maximum of 5 cm, particularly preferably a maximum of 3 cm. [18] Method for heating a large-area substrate comprising the following steps: Providing a heating system according to any one of the preceding claims; Introducing a large-area substrate (4) into the heating system such that the substrate (4) is supported on the spacers (2a; 2b; 2c); and heating the susceptor plate (1). [19] Method according to claim 18, wherein the susceptor plate (1) is heated using the infrared radiation source (3) such that the maximum heating rate of the susceptor plate during the first 20 s of heating is at least a factor of 4, preferably at least a factor of 6, more preferably at least a factor of 10, greater than the maximum heating rate of the substrate (4) during the first 20 s of heating. [20] A method according to any one of claims 18 to 19, wherein the maximum temperature difference between the susceptor plate and the substrate during the first 90 s of heating is at least 100 K, preferably at least 200 K, more preferably at least 300 K, even more preferably at least 400 K and most preferably at least 500 K. [21] Method according to one of claims 18 to 20, wherein the substrate (4) has an area of ​​at least 0.7 m 2 , preferably at least 1 m 2, more preferably at least 2 m 2 and especially preferably at least 3 m 2 has. [22] Method according to one of claims 18 to 21, wherein the susceptor plate (1) is heated during the first 20 s of heating to a temperature of at least 300 °C, preferably of at least 350 °C and particularly preferably of at least 400 °C. [23] Method according to one of claims 18 to 22, wherein the substrate (4) is heated over its entire surface by the heated susceptor plate (1) by means of thermal radiation, wherein the heating of the substrate (4) takes place at a rate of at least 2 K / s, preferably of at least 3 K / s and particularly preferably of at least 4 K / s and / or of at most 18 K / s, preferably of at most 15 K / s and particularly preferably of at most 10 K / s. [24] Method according to claim 23, wherein the substrate (4) is heated to a temperature of at most 700 °C, preferably at most 650 °C and particularly preferably at most 600 °C. [25] Method according to claim 23 or 24, wherein the substrate (4) is heated to a temperature of at least 300 °C, preferably at least 400 °C and particularly preferably at least 500 °C. [26] Method according to claim 23, 24 or 25, wherein the substrate (4) is heated homogeneously during the entire heating process such that the temperature difference occurring in the substrate surface in the region of the spacers is at most 75 K, preferably at most 50 K and particularly preferably at most 25 K. [27] Method according to one of claims 18 to 26, wherein a gas pressure of at least 20 mbar, preferably of at least 100 mbar and particularly preferably atmospheric pressure prevails between the susceptor plate (1) and the substrate (4). [28] Method according to one of claims 18 to 27, wherein the distance between the upper side (1a) of the susceptor plate (1) and the underside of the substrate (4) is at least 1 mm, preferably at least 2 mm. [29] Method according to one of claims 18 to 28, wherein the distance between the upper side (1a) of the susceptor plate (1) and the underside of the substrate (4) is at most 10 mm, preferably at most 8 mm and particularly preferably at most 5 mm. [30] Method according to one of claims 18 to 29, wherein the total contact area between the substrate and all spacers is a maximum of 5%, preferably a maximum of 1%, particularly preferably a maximum of 0.1% of the substrate surface. [31] Method according to one of claims 18 to 30, wherein the width of the contact line of spacers extending continuously along the transverse and / or longitudinal direction of the substrate is less than 50%, preferably less than 20% and particularly preferably less than 10% of the substrate thickness or wherein the diameter or the maximum dimension of the support surface of a spacer is less than 50%, preferably less than 20% and particularly preferably less than 10% of the substrate thickness. [32] Method according to one of claims 18 to 31, wherein the total projection area of ​​all spacers is a maximum of 10%, preferably a maximum of 6%, particularly preferably a maximum of 3% of the substrate surface. [33] Method according to one of claims 18 to 32, wherein the maximum unsupported distance between the support surfaces of two spacers is a maximum of 10 cm, preferably a maximum of 5 cm, particularly preferably a maximum of 3 cm.

Images