PVT method and apparatus for process-safe production of single crystals

Abstract

The object of the present invention is to use hydrogen as a process gas in a PVT method. For this purpose, special protective measures are required to enable the method to be carried out safely in the process. The apparatus for carrying out the PVT method consists of a highly heatable growth cell (1) arranged in a process chamber (4) whose walls consist of heat-resistant silica glass. The process chamber (4) is filled with hydrogen via an inlet valve (5). The heating device (6) consists of an induction coil (7) which surrounds the process chamber (4) at the height of the growth cell (1) and heats the growth cell (1) to a temperature of more than 2000° C. to 2400° C. However, the use of hydrogen presents the following problem: in the event of an unavoidable breakage of the silica glass in the process chamber (4), the hydrogen mixes with the oxygen in the ambient air, thereby forming a flammable gas mixture which can immediately ignite in the hotter parts of the apparatus. Therefore, the process chamber (4) is surrounded by a safety container (8) filled with an inert gas.

Description

Technical Field

[0001] The present invention relates to a PVT method for safely producing single crystals in an apparatus comprising a highly heatable growth unit, a process chamber, and a heating device, wherein the growth unit is located in the process chamber and the heating device surrounds the process chamber for heating the growth unit, wherein source material and a seed crystal are introduced into the growth unit, the process chamber is filled with a process gas, and the growth unit is heated so that the source material sublimates and re-sublimes at the seed crystal.

[0002] Background and Summary of the Invention

[0003] In an industrial environment, the so-called physical vapor transport (PVT) method is considered the standard method for producing single-crystal silicon carbide (SiC) crystals. The source material is typically a powder containing a plurality of different crystallites. Bulk crystals can also be used. High-temperature chemical vapor deposition (HT-CVD) is known as an alternative method. In the PVT method, crystal growth is achieved by sublimation of SiC source material and crystallization at temperatures above 2000°C on a pre-set SiC seed crystal within a growth cell typically made of graphite. The driving force for crystal growth is a temperature gradient applied to the growth cell by a heating device. Conventional methods for heating PVT equipment use either resistive heaters or induction heaters. In the case of induction heating, the growth cell (hot zone) in a vacuum-sealed process chamber is made of a non-conductive material, typically surrounded by (silicon) glass, and contains the process gases required to influence crystal growth. The process chamber can be single-walled or double-walled and air- or water-cooled. Argon, helium, nitrogen, hydrogen, and possibly other gases for selective doping are commonly used as process gases. The process pressure can be extended from vacuum conditions to atmospheric pressure. In the conventional process of manufacturing doped SiC single crystals, no hydrogen is used or only a low concentration of hydrogen is used.

[0004] Since SiC single crystals have a large band gap and high thermal conductivity, they are required in many applications of semiconductor technology.

[0005] Therefore, the basic process for producing SiC single crystals has been the subject of numerous specifications. For example, see US 2011 / 0300323 A1. Therefore, using inert gas as a process gas presents no safety concerns. For prior art, see also EP 0811708 A2, US 2012 / 0086001 A1, GB 772,691, DE 602004001802 T2, and EP 3760765 A1.

[0006] One of the objectives of the present invention is to enable processes for selectively influencing the incorporation of dopants or for producing undoped SiC single crystals. Within this context, the present invention provides a development that ensures that, when using concentrations of reactive gases, i.e., flammable and / or reactive (possibly also toxic) gases (e.g., hydrogen as a process gas), exceeding 5% or even up to 100%, a process flow with improved results compared to the prior art and still at a lower cost.

[0007] Here, gas molecules of the reaction gas, in particular hydrogen atoms, adhere to the surface of the growing single crystal but are immediately expelled by subsequently sublimated components of the source material. In this case, the reaction gas molecules, such as hydrogen atoms, act as placeholders for a short period of time, allowing a low-defect (if not defect-free) crystal lattice to form. The reaction gas molecules can also react with other process gases, source materials, or even hot zone materials and form other gaseous species, which can enter the gaseous environment of the process gas and, at least during this period, adhere to the crystal. In addition, possible reaction gases such as silane, methane, propane, etc., also provide elemental silicon and carbon for incorporation into the crystal. The addition of reaction gases generally (desirably and / or undesirably) influences the defect density. However, the exact influence depends on several parameters and their interaction. Crystal growth should be influenced by the addition of reaction gases.

[0008] The present invention may therefore be seen as an object of providing an apparatus and a method for improving or modifying crystal growth.

[0009] In some aspects or further embodiments of the present invention, an apparatus and a method may be provided as one of the above aspects, wherein a reactive gas may be used to improve crystal growth.

[0010] In yet another aspect or further development of the present invention, an object may be to provide an apparatus and a method for providing an improved crystal with less effort or in a less costly manner.

[0011] However, the use of reactive gases, such as hydrogen or other reactive elements, during the implementation of this method presents potential hazards. Reactive gases may be flammable, combustible, and / or toxic. For example, hydrogen can react with oxygen in air to form a hydrogen-oxygen reaction, and therefore, for the purposes of this specification, hydrogen is referred to as the reactive gas. In addition to hydrogen, other examples of reactive gases discussed herein include carbon- and silicon-containing precursors or hydrocarbons and their derivatives (e.g., silane, methane, propane, etc.).

[0012] Furthermore, in today's commonly used equipment, the process chamber is typically constructed of silica glass, which is naturally brittle and prone to cracking. However, silica glass is particularly preferred because it can withstand the high temperatures of the growth cell and does not shield the electromagnetic field of the induction coil or the radiant heat of the resistance heater. Combinations of induction and resistance heaters are also possible. For example, the bottom or top auxiliary heaters can be implemented as resistance heaters, while the main heater is implemented as an induction heater. However, similar safety requirements generally apply to other construction materials used to provide the process chamber, at least when silica glass is used.

[0013] However, if the process chamber is damaged or leaks occur, such as when the silica glass breaks, hydrogen gas mixes with the ambient oxygen and produces oxyhydrogen gas. This oxyhydrogen gas is ignited by the heating device (the hot element in the hot zone, typically a graphite component inside the process chamber) and explodes. Therefore, with respect to the use of reactive gases, this method cannot be reliably implemented using conventional equipment.

[0014] The reactive gases mentioned in this description—in particular hydrogen—are not equivalent to known dopant gases. Typical known dopant gases are not used in the concentrations desired here and / or are neither flammable nor otherwise reactive in the sense used in this description. The dopant gas is flushed around the crystal, i.e. the processes take place entirely within the process chamber. In this context, flushing with inert gases such as argon is also possible, for example, in order to modify the PVT process directly. In general, dopant gases are suitable for incorporation into the crystal or the crystal structure—hence the term "dopant gas"—in order to influence the physical and / or chemical properties of the crystal, such as its electrical conductivity. In other words, molecules or components of the dopant gas form the subsequent integral building block of the crystal. Such molecules or components of the dopant gas remain in the crystal and can subsequently be detected there.

[0015] In contrast, reactive gases (such as hydrogen) as reactive components of the gaseous environment can influence crystal growth and dopant incorporation, but should not be incorporated into the crystal as dopant gases, thereby affecting its physical and chemical properties. Due to the potential hazards of reactive gases, particularly the possibility of ignition, combustion, deflagration, or poisoning, their use for improving crystal growth has not been considered to date, or at least these safety considerations have not been adequately considered when handling reactive gases in such environments. Furthermore, the reactive gas to be used is not a true source material. In a typical PVT process, the source material is SiC powder. In variations of typical PVT methods, such as HT-CVD, hydrogen can be used as a carrier gas, transporting the actual source material (typically a gaseous carbon or silicon precursor). Thus, the gas serves as a carrier gas, acting as a transport medium for both the precursor and the dopant. Dopants can be solid, liquid, or gaseous elements or compounds, typically containing nitrogen, phosphorus, aluminum, boron, or vanadium.

[0016] Within the scope of further development and improvement, a safety container is designed to surround the process chamber in conjunction with this specification. Furthermore, it is also intended to provide a protective gas atmosphere, in particular an inert gas, in the area between the process chamber and the container wall. One of the objectives sought to be achieved with the safety container is to avoid or prevent the formation of explosive gas mixtures in the event of damage to the process chamber, in particular a rupture.

[0017] To reliably implement the method, the apparatus for carrying out the method can be arranged in a vacuum unit. However, such a unit must be absolutely vacuum-tight and is therefore relatively complex to manufacture, as multiple channels are required to supply the apparatus with electricity, gases, and possibly cooling fluids, all of which must be vacuum-tight.

[0018] PVT methods for the stable processing of single crystals are advantageous, which can be carried out in systems that can be produced with little effort and / or at low cost.

[0019] The solution for achieving the above-mentioned object of the present invention lies in the invention defined in the independent claim. The appended claims show further solutions and preferred technical solutions of the present invention.

[0020] To achieve the above-mentioned objectives, the present invention proposes that: the process gas is partially or completely composed of reactive gas, and the process chamber is arranged in a safety container, wherein the space between the container wall of the safety container and the process chamber is filled with a protective gas environment, such as an inert gas, so that the air contained in the space is discharged before the source material sublimates.

[0021] The containment vessel should be filled at the latest when the source material is sublimating, as high temperatures are present at this time that could ignite the reactive gases. However, for safety reasons, the containment vessel should be filled before the reactive gases are introduced into the process chamber.

[0022] With such a configuration, if the process chamber is damaged, in particular ruptured, the reaction gas in the process chamber is mixed with, for example, an inert gas to form a non-explosive gas mixture in a protective gas environment in a safety container, so that no explosion occurs even in a hot environment.

[0023] This safety measure is particularly important if the reaction gas is flammable or easily explosive, such as hydrogen.

[0024] Safety containers are particularly easy to implement if their design allows for a particularly low degree of gas loss to the outside, i.e., is only approximately gas-tight. This makes the design of the safety container more cost-effective, as particularly high gas-tightness requirements do not need to be taken into account, and undesirable reactions of the reaction gases outside the process chamber are prevented. The permissible leakage rate of the safety container can, for example, be greater than 0 l / min. Therefore, for cost reasons, it is advantageous and unproblematic to allow a leakage rate within the range of 0 ≤ leakage rate ≤ 5 l / min or within the range of 0 ≤ leakage rate ≤ 30 l / min, particularly based on the choice of structure and geometry. This permissible leakage rate can, for example, be greater than 2 ml / min, less preferably greater than 5 ml / min, even less preferably greater than 10 ml / min, and even less preferably greater than 50 ml / min or 100 ml / min. On the other hand, for economic reasons and, where appropriate, for workplace safety reasons, an excessively high permissible leakage rate of the safety container is disadvantageous. Therefore, for example, it is desirable to limit the leakage rate to 30 l / min or less, preferably 10 l / min or less, further preferably 4 l / min or less, more preferably 1 l / min or less, further preferably 500 ml / min or less, and further preferably 150 ml / min or less. A leakage rate of 2 ml / min to 50 ml / min, preferably 10 ml / min to 20 ml / min, is expected to be achieved.

[0025] To maintain a protective gas atmosphere, for example, inert gas can be added to compensate for gas loss and to establish and / or maintain an overpressure in the safety container. This overpressure prevents oxygen from the air from entering the safety container from the outside. Therefore, a relative overpressure in the safety container can be maintained by a pressure regulating device, for example, within a range of 1 mbar or more above ambient pressure, preferably 3 mbar or more above ambient pressure, further preferably 5 mbar or more above ambient pressure, to 50 mbar or less above ambient pressure, preferably 30 mbar or less above ambient pressure. However, this also includes completely airtight safety containers with a leakage rate of 0 ml / min or a leakage rate so low that it cannot be measured, in which case the overpressure in such safety containers can also be maintained.

[0026] To ensure that air is exhausted from the safety container as completely as possible, the present disclosure may further provide that a first inert gas is introduced into the safety container to fill the container. This first inert gas may be heavier than air so that it can be introduced into the lower region of the safety container, where air is exhausted upward. To this end, a closable outlet at the upper end of the safety container may, for example, remain open until the air escapes.

[0027] Preferably, the protective gas environment comprises an inert gas, particularly argon. Due to its high density, argon accumulates at the bottom of the containment vessel and slowly vents the air upward without mixing with it. Other examples of economically reasonable protective gas environment configurations currently include xenon, nitrogen, or carbon dioxide. In principle, the protective gas environment can include any fluid, either alone or in a mixture, that can provide a protective function, namely, neutralize and / or prevent negative effects such as deflagration in the event of excessive or unacceptable escape of the reaction gas from the process chamber. The protective gas environment can also exist in a liquid or solid state at room temperature and pressure, for example, in a standard gas environment.

[0028] When the air is expelled by the first inert gas, it can be replaced by another, for example cheaper, inert gas. Therefore, the present invention further proposes that after filling the safety container with the first inert gas once or multiple times, the first inert gas is replaced by a second inert gas, in particular nitrogen.

[0029] To ensure that further reactive gas is not introduced into the equipment in the event of a rupture of the process chamber, the safety container includes a gas sensor capable of detecting the presence of reactive gas in the safety container. Furthermore, the process gas supply to the process chamber can be interrupted if the gas sensor detects reactive gas in the safety container.

[0030] In a further embodiment, a pressure sensor or pressure switch that monitors the pressure within the process chamber can interrupt the gas supply if a lower pressure is detected in the event of damage (e.g., cracking) to the silica glass. For example, monitoring can detect an absolute pressure below p ≤ 980 mbar Abs, preferably p ≤ 950 mbar Abs, and further preferably p ≤ 920 mbar Abs. Thus, interruption of the reactant gas supply can be independent of the detection of reactant gas (e.g., hydrogen) in the space between the process chamber and the cooling jacket.

[0031] For example, in the event of a break in silica glass, the opening of the process chamber can be detected or indicated by one of the following criteria: Reactive gas / hydrogen can be detected by a gas sensor in the containment vessel. Alternatively or additionally, the overpressure in the containment vessel can be determined, and if this overpressure disappears, a process fault can be inferred (e.g., p <= approximately 2 mbar relative to atmosphere).

[0032] Alternatively or additionally, the pressure in the process chamber can be measured. As long as the pressure remains ≤ 950 mbar Abs (or 920 or 980), no process fault is detected, while exceeding a pressure threshold indicates a process fault. Alternatively or additionally, sudden pressure fluctuations / surges in the process chamber (a pressure increase rate greater than the maximum possible pressure increase rate due to the gas to be introduced) can also be determined and indicate a process fault, such as a silica glass break. The aforementioned criteria are advantageously independent of one another and can be used individually or in combination to shut off the process gas or hydrogen supply.

[0033] The safety container can advantageously provide a cooling function. This cooling function can, for example, be configured such that a cooling medium, such as water in particular, circulates around or through the safety container. A safety container used for this purpose can, for example, include at least a cooling medium line through which the cooling medium flows. The cooling medium line can be fixed to the container wall of the safety container or thermally connected to the container wall, optionally via thermally conductive paste. The cooling medium line can, for example, be welded to the container wall. The cooling medium line can, for example, comprise copper, which is easy to process and / or has high thermal conductivity.

[0034] The containment vessel can be configured to thermoregulate the process conditions. For example, a constant temperature or a similar temperature range can be maintained by a containment vessel designed in this manner, regardless of ambient conditions. The ambient conditions can include, for example, a daily temperature profile or seasonal temperature fluctuations, or can also be influenced by possible thermal processes occurring nearby, wherein a containment vessel designed in an advantageous manner is able to maintain the ambient conditions for the process. Alternatively or additionally, the cooling function can also be influenced in response to process parameters, i.e., in particular, the temperature in the process chamber, in order to thermoregulate the growth process. For example, the cooling medium flow rate can be varied via at least one cooling medium line in response to ambient conditions and / or process parameters in order to vary the heat transfer. In hotter ambient and / or process temperatures, for example, more cooling medium can be converted, and / or a cooler cooling medium can be used, and / or an alternative cooling medium can be added.

[0035] The cooling medium line can be arranged outside the container wall, preferably in thermally conductive connection with the container wall or at least adjacent to it. In this case, the cooling medium line cools the container wall and ensures that heat is not radiated into the immediate surroundings of the equipment, but rather is carried away by the temperature control device. The advantage of arranging the cooling medium line outside is that fewer sealed passages into the protective gas atmosphere or the interior of the protected container are required, as the cooling fluid cannot penetrate into the interior space. For example, the container wall can be double-walled, i.e., having an inner wall and an outer wall, with the cooling medium line arranged between the inner and outer walls. In this case, the cooling medium line, along with its fixings, is opaquely concealed and protected from mechanical damage. The temperature control device can dissipate the majority of the heat output from the process chamber, so the outer wall of the container faces few or no restrictions in terms of material selection or contact protection, as it does not heat up.

[0036] The present invention also relates to an apparatus for safely producing single crystals using a PVT method process, the apparatus comprising a highly heatable growth unit, a process chamber, and a heating device, the growth unit being used to receive source materials and crystal seeds, the growth unit being located in the process chamber, and the process chamber being filled with process gas and connected to a process gas source, the heating device being used to heat the growth unit.

[0037] In order to ensure the safe operation of the process using reactive gas as process gas, the present invention proposes that: the equipment has a safety container including a container wall, and the process chamber is arranged in the safety container, wherein the safety container is connected to an inert gas source so that the space between the container wall of the safety container and the process chamber is filled with inert gas before implementing the PVT method.

[0038] The safety container may be constructed to allow gas to be lost to the outside. The safety container may have a pressure sensor, wherein the pressure sensor is signal-connected to a control device and the control device is designed to regulate the overpressure in the safety container (relative to the environment or atmosphere) based on the pressure sensor signals.

[0039] The pressure sensor may also include or consist of a pressure switch.

[0040] The pressure sensor can, for example, be formed by a differential pressure switch that measures the pressure difference between the inert gas in the containment vessel and the atmosphere or surroundings. In this case, the pressure sensor can trigger a switch when an adjustable pressure difference is exceeded or fallen below as required, in particular as a safety circuit or shielding element.

[0041] For the intended installation of the device, an inert gas connection is provided in the lower region of the safety container, and a closable outlet is provided in its upper region. In this way, the inert gas flowing in from the lower region completely vents the air in the safety container upwards to the outlet, where it leaves the safety container.

[0042] The safety container preferably has two inert gas connections for two different inert gases. After the first inert gas has driven the air out of the safety container, the second inert gas connection can be used to fill the second fluid (such as nitrogen) with lower cost to replace the first inert gas.

[0043] The containment vessel preferably has a gas sensor responsive to the reactive gas, so that it can be determined that the reactive gas (eg, hydrogen) has penetrated into the containment vessel, for example, in the event of a process chamber rupture.

[0044] As described above, the apparatus can be used in particular to produce SiC single crystals using the PVT method. For this purpose, the growth unit is equipped with silicon carbide as the source material, and the process chamber is also filled with hydrogen as the reaction gas, in addition to other process gases (such as argon). BRIEF DESCRIPTION OF THE DRAWINGS

[0045] in:

[0046] Figure 1 is a cross-sectional view of an apparatus according to the present invention,

[0047] Figure 2 A perspective and simplified view of a partially assembled safety container.

[0048] Figure 3 is a sectional perspective view of an embodiment of the device,

[0049] Figure 4 Details of the connections for the temperature control devices of the safety containers,

[0050] Figure 5 a segment of a container wall of a safety container which is part of a temperature control device,

[0051] Figure 6 is an exemplary segmented structure of a container wall with a temperature control device,

[0052] Figure 7 A perspective view of an embodiment of a safety container. DETAILED DESCRIPTION

[0053] The present invention will be described in detail below in conjunction with embodiments and with reference to the accompanying drawings, wherein identical and similar elements are partially denoted by identical reference numerals and features of different embodiments may be combined with each other. Figure 1 is a cross-sectional view of an apparatus according to the present invention.

[0054] At the center of the apparatus is a hollow cylindrical growth unit 1, located on a pillar. The unit has a base and a top cover, which seal the ends of the hollow cylinder. The growth unit 1 is made of porous graphite. Source material 2 is deposited in layers on the base. A seed crystal 3 is located on the underside of the top cover.

[0055] The growth unit 1 is arranged in a process chamber 4, which is composed of a hollow cylinder closed at both ends by a bottom and a top. The cylindrical wall of the process chamber 4 is made of heat-resistant silica glass and can be opened via process gas inlet lines 51, 52 having an inlet valve 5 (see FIG. Figure 3 ) is used to fill the cylindrical wall with process gas. The graphite of the growth unit 1 is porous, so the process gas of the process chamber 4 also enters the growth unit 1.

[0056] The heating device 6 consists of an induction coil 7 surrounding the process chamber 4 at the height of the growth cell. When current flows through the induction coil, it generates an electromagnetic field that induces a current in the graphite of the growth cell 1, which heats the growth cell 1 to a temperature exceeding 2000°C to 2400°C.

[0057] Due to the high temperatures and the required permeability to the electromagnetic field of the induction coil 7, it is necessary to manufacture at least the cylindrical wall of the process chamber 4 from a heat-resistant material suitable for this purpose. The cylindrical wall of the process chamber 4 is usually made of silica glass, which has proven to be particularly suitable and inexpensive to manufacture.

[0058] To produce a SiC single crystal, silicon carbide is placed in a growth unit 1 and the process chamber 4 is filled with a process gas consisting of up to 100% hydrogen. If the growth unit 1 is heated by means of an induction coil 7, the silicon carbide sublimates and adheres layer by layer to the seed crystal 3, thereby growing a SiC single crystal. The hydrogen ensures that in this case no crystal defects are formed in the crystal or that impurity atoms are not embedded in the corresponding growth positions. The embedding of undesirable impurity atoms periodically causes changes in the electrical conductivity, which may also occur locally and may have an adverse effect as interference or quality degradation. By using reactive gases, the process gas composition can also be influenced by reactions with other process gases or hot zones (graphite components). The changed process gas composition in turn affects the crystallinity, structure, crystal defects and doping of the SiC crystal.

[0059] For example, it has been shown that advantageous effects can be achieved with a hydrogen content of 5% or more in the process gas. At relatively low hydrogen concentrations of less than 5% in the process gas, protective measures, such as for explosion protection, are generally unnecessary. Particularly advantageous results are achieved in the range from 5% to approximately 40% hydrogen content, with higher crystal purities being achieved with a hydrogen content in the process gas of 15% (particularly ±5%). In principle, however, the use of the safety container according to the invention is also advantageous at low concentrations.

[0060] However, as mentioned in the introduction, the use of a reaction gas such as hydrogen is problematic because, in the event of a possible rupture of the wall of the process chamber 4, the reaction gas would—without the use of a safety container according to the invention—mix with the ambient air and could, for example, form a flammable gas mixture which could immediately ignite at the hotter parts of the apparatus.

[0061] Thus, the process chamber 4 of the embodiment shown here is surrounded by a safety container 8, which comprises a cylindrical container wall 9 surrounding the cylindrical wall of the process chamber 4, which cylindrical container wall rests on a bottom 10 and is closed above by a top 11. The bottom 10 and the top 11 of the safety container 8 are connected to the bottom and the top of the process chamber 4.

[0062] Here, the safety container 8 can also be a component of the cooling concept of the system. In other words, the safety container 8 can be integrated into the cooling concept of the system. For this purpose, the cylindrical container wall 9 can be equipped with cooling channels connected to the cooling system. Therefore, the cooling concept can be set up so that the safety container 8 provides a cooling function for the system. A cooling medium, such as water in particular, can be circulated through the safety container 8, for example. On the other hand, it can be set up so that the safety gas environment in the safety container 8 provides a cooling function. For this purpose, for example, the safety gas environment can be circulated in order to dissipate the heat output. In general, the safety container can be equipped so that the safety container with its cooling function can be used to temperature-control the process conditions so that a constant temperature or a similar temperature range can always be maintained, regardless of potentially fluctuating ambient conditions. This environment can, for example, include a daily temperature profile or seasonal temperature fluctuations, or can be influenced by thermal processes occurring nearby.

[0063] Finally, the containment vessel 8 can be constructed to have metallic conductivity. The metallically conductive containment vessel 8 can shield the processes occurring within it, similar to a Faraday cage, so that, for example, the alternating electromagnetic field in the containment vessel wall 9 of the containment vessel 8 has a defined endpoint and does not decay asymptotically, potentially to infinity. Advantageously, multiple devices can be positioned adjacent to one another, where the corresponding alternating fields influence each other and can affect each other's process conditions. In other words, even when multiple, possibly different, devices are placed in close proximity, the metallically conductive containment vessel 8 ensures balanced process conditions without processes interfering with each other.

[0064] In general, the containment vessel 8 can achieve multiple purposes in a coordinated manner. It not only provides the aforementioned protective gas environment for the application of reactive gases within the process chamber, but also protects the process chamber from varying environmental conditions, such as temperature fluctuations or variations in electric and / or magnetic fields, thereby ensuring balanced process conditions for the processes performed within the process chamber.

[0065] A ring-shaped pipeline with one or more joints is provided in the bottom of the safety container 8, in the space 12 between the container wall 9 of the safety container 8 and the cylindrical wall of the process chamber 4 made of silica glass. The ring-shaped pipeline is connected to an argon source 14 and a nitrogen source 15 via a switching valve 13.

[0066] A closable outlet valve 16 is provided in the top 11 of the safety container 8. Furthermore, a gas sensor 17 (in particular as a hydrogen sensor) and a pressure sensor 18 are provided there.

[0067] A cover 20 made of non-fragile plastic or plate can be set on the entire device and installed on the bottom of the safety container 8.

[0068] Furthermore, a control device 19 is provided, which is signal-connected to the gas sensor 17 and the pressure sensor 18 and controls the switching valve 13 , the outlet valve 16 and the inlet valve 5 for supplying hydrogen via control lines.

[0069] The control device 19 allows the following methods to be implemented:

[0070] Before filling the process chamber 4 with hydrogen, fill the safety container 8 with inert gas:

[0071] (1) Open the outlet valve 16.

[0072] (2) The switching valve 13 is switched so that argon from the argon source 14 slowly flows into the space 12 from below, so that the space 12 is filled with argon from below, and the existing air is discharged through the opened outlet valve 16 (or overpressure valve or similar valve).

[0073] (3) Close the outlet valve 16 and the switching valve 13.

[0074] (4) Keep the filling interrupted so that any remaining residual air can settle upwards from the argon.

[0075] (5) Repeat steps (1) to (3) once or multiple times as needed.

[0076] (6) Open the outlet valve 16.

[0077] (7) Switch the switching valve 13 so that nitrogen slowly flows into the compartment 12 from below, wherein the compartment 12 is filled with nitrogen from the nitrogen source 15 from below, and the existing argon is discharged through the opened outlet valve 16.

[0078] (8) Close the outlet valve 16.

[0079] (9) The overpressure in the compartment 12 is adjusted and maintained by the controlled opening of the switching valve 13, whereby air cannot flow into the compartment 12 despite a normal leakage of the safety container.

[0080] A sufficient overpressure is approximately 2 mbar above ambient.

[0081] In any case, steps (1) to (3) and (9) must be performed. Steps (4) or (6) to (8) are optional.

[0082] In order to be able to check whether the intermediate space 12 is sufficiently oxygen-free, an oxygen sensor can additionally be provided.

[0083] Behavior of glass walls when broken during operation:

[0084] (1) Continuously monitor the gas sensor 17 and

[0085] (2) When the gas sensor 17 detects hydrogen in the compartment 12, the hydrogen supply is shut off.

[0086] Reference Figure 2 A perspective view of a simplified embodiment of a partially assembled safety container 8 is shown, wherein some components and the process chamber 4 are not shown for clarity. In addition, for a complete understanding, it should be noted that Figure 2 The embodiment shown has no details for sealing the inner area 12, so the leakage rate achievable with this embodiment is relatively high. Safety containers 8 with improved sealing are presented by the embodiments shown in the other figures.

[0087] exist Figure 2In the embodiment, the temperature control device 21 is at least partially arranged in the safety container 8, wherein a fluid can be fed into the coolant line 22 via a connector 23. The coolant line 22 can be connected to the inner wall 44 of the safety container 8, for example by gluing, welding, fusion welding or screwing. The heat output is mainly transferred from the process chamber 4 to the inner wall 44 as radiant heat, from which it can be effectively dissipated by the temperature control device 21. For example, liquid water can be used as a coolant. The amount of heat that can be dissipated by the temperature control device 21 is preferably adjustable. For example, the dissipable heat can be influenced by a preset temperature value and / or a flow rate or flow velocity of the coolant, that is, temperature control can be provided. The temperature of the process chamber 4 can then be controlled by temperature control in response to sensor signals measuring the ambient temperature and / or process temperature, so that a substantially constant temperature prevails in the process chamber 4 during the processing flow.

[0088] The safety container 8 has sight glasses 32 which span the interior area 12 and allow observation of the process chamber 4, for example for the purpose of process monitoring. In order to keep direct heat radiation to a minimum, the sight glasses 32 are designed to be relatively small. Figure 4 Details of the coolant line 22 are shown, which has a line fixture 22A, a connector 23 , a transition piece 23B and a connector fixture 23A.

[0089] Figure 3 1 is a cross-sectional view of one embodiment of apparatus 100. Process chamber 4 is partially surrounded by an induction coil 7, which is supplied with electrical power by a heating device 6. The heating device 6 is partially located inside and outside a safety container 8, with the power electronics being located outside, for example, to allow for a sealed sleeve 62 to minimize gas leakage. The induction coil 7, along with the electronics, is located within an interior space 12, i.e., within a space where a safe gas environment can reside.

[0090] The shielding gas can be fed via a shielding gas inlet line 54 (possibly a plurality of shielding gas inlet lines 54) located at the bottom side of the interior space 12. An outlet valve 16 is arranged at the top side 11 for, for example, discharging external air (containing oxygen) initially arranged in the protected safety container 8 from the protected safety container 8, for example by feeding a shielding gas heavier than air. In the case of a connecting line connected to the outlet valve 16 (not shown), a circulation of the shielding gas can also be provided, for example, in order to remove heat from the protected safety container 8 or to ensure periodic replacement of the shielding gas.

[0091] In the case shown here, the coolant line 22 of the temperature control device 21 is arranged in the container wall 9, which is designed in a double-walled manner. Figure 3In the cross section shown, the interior space 12 of the safety container 8 for accommodating a protective gas environment extends from the chamber wall 41 and, for example, around the process chamber 4 to the container wall 9, wherein the interior space 12 is implemented in a sealed manner relative to the container wall 9 so as to keep the gas leakage rate from the interior space 12 to the environment 30 at a low level.

[0092] also, Figure 3 The illustrated embodiment features the following features: the process chamber 4 is equipped with an adapter 46. In the illustrated embodiment, the adapter 46 has two alternative upper covers 47 and 48, so that depending on the desired processing height, either the upper cover 47 or the further built-in upper cover 48 can be used. Thus, the upper covers 47 and 48 can be used interchangeably as needed.

[0093] Reference Figure 5 , shows a first segment 91 of a container wall 9 of a segmented safety container 8 having a temperature control device 21, wherein the coolant line 22 is arranged in a central region 122 of the container wall 9. In the case shown here, the container wall 9 comprises an inner wall 98, frame parts 92, 94, and the coolant line 22 of the temperature control device 21, which is arranged in the central region 122. The frame parts 92, 94 are fastened to the first segment 91 with fastening means 97. Additional fastening means 96, such as screw holes, are arranged at regular intervals on the frame parts 92, 94 so that the central region 122 is surrounded by them.

[0094] Reference Figure 6 , further illustrating another embodiment of a first segment 91 having a sandwich structure. The coolant line 22 of the temperature control device 21 is arranged on the inner wall 98 and can be connected to the outside via connectors 23. Frame parts 92 and 94 surround or circumferentially define the first segment 91, with an outer plate 99 being screwed onto the frame parts 92 and 94. The coolant line 22 and the fixing element 97 are covered by the outer plate 99, thereby preventing contact and undue damage. Thus, the outer plate 99 conceals the technical equipment from direct view and access, giving the device 100 an attractive appearance.

[0095] at last, Figure 7 The apparatus 100 is shown with a multi-part container wall 9 mounted on a bottom 10, comprising a first section 91 and a wall section 91A. The coolant line 22 (see for example Figure 5 or Figure 6 ) extends protected behind the outer plate 99 and is connected to each other by means of a compensation elbow 24 so that a coolant (eg water) can flow through the temperature control device 21. The process chamber 4 (eg see Figure 1 or Figure 3) is surrounded by a safe gas environment on all sides—or, depending on the specific embodiment, is surrounded by a safe gas environment on all sides at least above the bottom 10. If the process chamber 4 ruptures or otherwise fails and the process gas escapes, the process gas mixes with the protective gas stored in the interior space 12 to form a harmless mixed gas.

[0096] It will be apparent to those skilled in the art that the above-described embodiments are to be understood as examples and that the present invention is not limited thereto but may be modified in various ways without departing from the scope of protection of the claims. Furthermore, it will be apparent that features disclosed in the specification, claims, and drawings, or otherwise disclosed, even when described together with other features, individually define essential components of the present invention. The same symbols denote the same objects in all figures, and thus, the description of objects that may be described only in a particular figure, or at least not in all figures, may also be transferred to those figures and embodiments, where the objects are not described in detail in the description.

[0097] Reference Signs List

[0098] 1: Growth unit

[0099] 2: Source Material

[0100] 3: Seed crystal

[0101] 4: Processing Room

[0102] 5: Inlet valve

[0103] 6: Heating device

[0104] 7: Induction coil

[0105] 8: Secure Container

[0106] 9:Container wall

[0107] 10: Bottom

[0108] 11: Top

[0109] 12: Intermediate space / internal area / inner space

[0110] 13:Conversion valve

[0111] 14: Argon source

[0112] 15: Nitrogen source

[0113] 16: Outlet valve

[0114] 17: Gas sensor

[0115] 18: Pressure sensor

[0116] 19: Control device

[0117] 20: Cover

[0118] 21: Temperature control device

[0119] 22: Coolant line

[0120] 22A: Pipeline fixings

[0121] 23: Connectors

[0122] 23A: Connecting fixtures

[0123] 23B: elbow

[0124] 24: Compensating elbow

[0125] 30: Environment

[0126] 32: sight glass

[0127] 41: Process chamber wall

[0128] 44: Inner wall

[0129] 46:Adapter

[0130] 47: Upper cover

[0131] 48: Upper cover

[0132] 51: Process gas inlet

[0133] 52: Process gas outlet

[0134] 54: Shielding gas inlet

[0135] 62: Sealing sleeve

[0136] 91: First Segment

[0137] 91A: Wall segment

[0138] 92:Frame components

[0139] 94:Frame components

[0140] 96:Fixing element

[0141] 97:Fixing element

[0142] 98: Inner wall

[0143] 99: Outer panel

[0144] 100: Equipment

[0145] 122: Middle area

Claims

1. A PVT method for safely producing single crystals in an apparatus comprising a highly heatable growth unit (1), a process chamber (4), and a heating device (6), wherein the growth unit (1) is located in the process chamber, and the heating device surrounds the process chamber (4) for heating the growth unit (1), wherein a source material (2) and a seed crystal (3) are introduced into the growth unit (1), the process chamber (4) is filled with a process gas, and the growth unit (1) is heated so that the source material (2) sublimates and re-sublimates at the seed crystal (3), characterized in that The process gas is partially or completely composed of a reaction gas, which includes hydrogen or consists of hydrogen, and the process chamber (4) is arranged in a safety container (8), and the interval (12) between the container wall (9) of the safety container (8) and the process chamber (4) is filled with a protective gas environment so that the air contained in the interval is discharged before the source material (2) sublimates; the safety container (8) includes a cooling medium pipeline for the cooling medium to flow through.

2. The PVT method according to claim 1, wherein: The protective gas environment includes an inert gas or consists of an inert gas.

3. The PVT method according to claim 1, wherein: The safety container (8) is constructed so as to allow gas to be lost to the outside and to supplement inert gas in order to compensate for the gas loss and maintain overpressure in the safety container (8).

4. The PVT method according to claim 3, wherein: To fill the safety container (8), a first inert gas is introduced into the lower region of the safety container, the first inert gas being heavier than air, the air being exhausted upwards, for which purpose a closable outlet at the upper end of the safety container (8) remains open until the air escapes.

5. The PVT method according to claim 4, characterized in that: The first inert gas is argon.

6. The PVT method according to claim 4, characterized in that: After the safety container (8) is filled with the first inert gas once or multiple times, the first inert gas is replaced by a second inert gas.

7. The PVT method according to claim 6, characterized in that: The second inert gas is nitrogen.

8. The PVT method according to claim 1, wherein: The safety container (8) has a gas sensor (17) capable of detecting the reaction gas, and when the gas sensor (17) detects the reaction gas in the safety container (8), the supply of the process gas to the process chamber (4) is interrupted.

9. An apparatus for safely producing single crystals using a PVT process, the apparatus comprising a highly heatable growth unit (1), a process chamber (4), and a heating device (6), wherein the growth unit is used to receive a source material (2) and a seed crystal (3), the growth unit (1) is located in the process chamber, and the process chamber is filled with a process gas and connected to a process gas source, the heating device is used to heat the growth unit (1), and is characterized in that: The process gas is partially or completely composed of a reaction gas, and the reaction gas includes hydrogen or consists of hydrogen. The device has a safety container (8) including a container wall (9), and the process chamber (4) is arranged in the safety container. The safety container (8) is connected to an inert gas source (14, 15) so that before the PVT process is carried out, the space (12) between the container wall (9) of the safety container (8) and the process chamber (4) is filled with a protective gas environment; the safety container (8) includes a cooling medium pipeline for the cooling medium to flow through.

10. The device according to claim 9, characterized in that The safety container (8) is constructed so as to allow gas to be lost to the outside. The safety container has a pressure sensor (18), and the pressure sensor (18) is connected to a control device (19) by signal. The control device (19) is designed to set the overpressure in the safety container (8) based on the signal of the pressure sensor.

11. The device according to claim 9, characterized in that In the case of the intended installation of the device, the inert gas connection is located in the lower region of the safety container (8) and the closable outlet is located in the upper region of the safety container.

12. The device according to claim 9, characterized in that The safety container (8) has two inert gas connections for two different inert gases.

13. The device according to claim 9, characterized in that The safety container (8) includes a gas sensor (17) responsive to the reactive gas.

14. The device according to claim 9, characterized in that The growth unit (1) is provided with silicon carbide as the source material (2), and the process chamber (4) is filled with hydrogen as the reaction gas.

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