PVT process and equipment for the safe production of single crystals

Abstract

PVT processes and equipment for the safe production of single crystals In order to use hydrogen as a process gas in the PVT process, specific safety measures are established to ensure that the process can be performed safely. The apparatus for performing the PVT process comprises a highly heatable growth cell (1), which is placed in a process chamber (4), the walls of which consist of heat-resistant quartz 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 level of the growth cell (1) and heats the growth cell (1) to temperatures above 2,000°C and up to 2,400°C. However, the use of hydrogen poses the risk that, if the quartz glass of the process chamber (4) breaks, the hydrogen may mix with the oxygen in the surrounding air and generate an ignitable gas mixture which may quickly ignite in hot parts of the apparatus, although this cannot be completely excluded. The process chamber (4) is for this purpose surrounded by an enclosure (8), which is filled with an inert gas.

Description

Technical Field

[0001] The present invention relates to a PVT process for the process-safe production of single crystals in a device, the device having a highly heatable growth cell, a process chamber in which the growth cell is arranged, and a heating device surrounding the process chamber for heating the growth cell, wherein a source material and a seed are introduced into the growth cell, the process chamber is filled with a process gas, the growth cell is heated so that the source material sublimates, and on the seed crystallization and grown.

Background Art

[0002] In an industrial environment, the so-called physical vapor transport (PVT) process is considered a standard method for producing single-crystalline silicon carbide crystals (SiC crystals). The source material is usually a powder containing many different crystals. The use of bulk crystals is also possible. The high-temperature chemical vapor deposition (HT-CVD) process is known as an alternative process. In the PVT process, crystal growth typically occurs in a growth cell made of graphite, including sublimation of the SiC source and crystallization on a given SiC seed at temperatures above 2000 °C. The driving force for crystal growth is the temperature gradient applied to the growth cell by the heating device. A common method for heating a PVT device is to use a resistance heater or an induction heater. In induction heating, the growth cell (hot zone) of the vacuum-tight process chamber is surrounded by a non-conductive material, typically (quartz) glass, and contains process gases, among other things, that are used to affect crystal growth. The process chamber can be single- or double-walled and can be air-cooled or water-cooled, respectively. Commonly used process gases are argon, helium, nitrogen, hydrogen, and other possible gases for the intended doping. The process pressure ranges from vacuum conditions to atmospheric pressure. In a common process for the production of doped SiC single crystals, hydrogen-free or very little hydrogen is used.

[0003] Due to their large band gap and high thermal conductivity, SiC single crystals are used in a variety of applications in semiconductor technology.

[0004] The underlying processes for producing SiC single crystals have therefore been the subject of much literature. See, for example, US2011 / 0300323A1. According to this, an inert gas is used as the process gas, which does not pose a safety problem. Furthermore, EP 0 811 708A2, US2012 / 0086001A1, GB 772, 691, DE 60 2004 001 802 T2, and EP 3 760 765 A1 can be considered prior art.

[0005] In particular, enabling the intended effects of dopant addition or the processes carried out for the production of undoped SiC single crystals is a conceptual starting point and one of the issues addressed by the present invention. With regard to this starting point, the present invention develops the use of reactive gases, i.e., flammable and / or reactive (and potentially toxic) gases, such as hydrogen as a process gas at concentrations ranging from 5% to 100%, with better results and also more cost-effective than in the latest technology.

[0006] Reactive gas molecules, such as hydrogen atoms, adhere to the surface of the growing single crystal, but are immediately replaced by sublimated components of the source material. In this case, the reactive gas molecules, such as water atoms, only occupy space for a short time, allowing the crystal lattice to form with few or no defects. Reactive gas molecules can also react with other process gases, source materials, or hot zone materials, entering the process gas atmosphere and forming other gas species that can adhere to the crystal, at least temporarily. Possible reactive gases such as silane, methane, and propane provide elements such as silicon and carbon, among others, which are incorporated into the crystal. The addition of reactive gases can affect the overall defect density (whether desired and / or undesired). However, the exact effect depends on many parameters and their interactions. The addition of reactive gases is intended to influence crystal growth.

[0007] The object of the present invention is therefore to provide a device and method that enables improvement or modification of crystal growth.

[0008] In practical aspects or further improvements of the present invention, it can be recognized that one aspect of the problem is to provide a device and method for using a reactive gas to improve crystal growth.

[0009] In a further aspect or improvement of the present invention, the challenge would be to provide a device and method that can provide improved crystals at low cost, i.e., low expense.

[0010] However, the use of reactive gases, including hydrogen or other reactive elements, presents potential hazards when carrying out the process. Reactive gases are, for example, flammable or combustible and / or toxic. In the case of hydrogen, the oxyhydrogen reaction occurs with oxygen in the air, which is why hydrogen is referred to as a reactive gas herein. Other examples of reactive gases of concern here include, in addition to hydrogen, precursors containing carbon and silicon or hydrocarbons and their derivatives (e.g., silane or methane, propane, etc.).

[0011] In addition, process chambers in conventional devices today are typically made of quartz glass, which is brittle and prone to breakage. However, the use of quartz glass is now preferred because it can withstand the high temperatures of the growth cells and does not shield against the electromagnetic field of the induction coil or the radiant heat of the resistance heater. Combinations of induction and resistance heaters are also provided. For example, an additional floor or ceiling heater can be designed as a resistance heater, while the main heater is designed as an induction heater. In principle, however, safety requirements also apply to other constituent materials for providing process chambers in a similar manner to, for example, quartz glass.

[0012] If the process chamber is damaged or leaks, for example if the quartz glass breaks, hydrogen will mix with oxygen in the environment to produce oxyhydrogen gas, which can be ignited by the heating device (on hot elements in the hot zone, typically the graphite portion within the process chamber), causing an explosion. When reactive gases are used, it is impossible to safely carry out the process with known devices.

[0013] The reactive gases described herein—such as hydrogen—are not equivalent to known doping gases. Typical known doping gases are not used at the concentrations desired herein and / or are not flammable or reactive in any other way in the sense used herein. The doping gas is flashed around the crystal, so the process takes place entirely within the process chamber. In this context, for example, the process chamber may also be purged with an inert gas such as argon to directly modify the PVT process. Typically, doping gases are intended to be introduced into the crystal or crystal structure—from which the term “doping gas” is derived—because they affect the physical and / or chemical properties of the crystal, such as electrical conductivity. In other words, molecules or components of the doping gas form parts that are later integrated into the crystal. Such molecules or components of the doping gas remain within the crystal, and their presence within the crystal is demonstrated retrospectively.

[0014] In contrast, reactive gases such as hydrogen can influence crystal growth and dopant introduction as reactive components of the gas atmosphere, but they are not intended to incorporate crystals in order to influence the physical and chemical properties of the crystals, as dopant gases do. Due to the hazards of reactive gases, such as the potential for ignition, combustion, deflagration, or toxicity, reactive gases have not been considered for use to improve crystal growth, or at least the safety aspects of handling reactive gases in this environment have not been adequately considered, as described above. Furthermore, the reactive gases used are not source materials in the correct sense of the term. In a typical PVT process, the source material is SiC powder. In a variation of the classic PVT process, such as HT-CVD, hydrogen can be used as a carrier gas to transport the actual source material, which is usually a gaseous C- or Si-containing precursor. The gas is provided as a carrier gas, or transport medium, for the precursor and dopant. Dopants are typically solid, liquid, or gaseous elements or compounds containing nitrogen, phosphorus, aluminum, boron, or vanadium.

[0015] Furthermore, as part of this development and improvement, a sealing vessel surrounding the process chamber was designed herein. In addition, protective atmospheres such as inert gases in the region between the process chamber and the vessel walls were explored. One specific purpose of the sealing vessel is to avoid or prevent explosive gas mixtures in damaging events such as process chamber rupture.

[0016] To ensure the safe execution of the process, the equipment for carrying out the process will be placed within a vacuum cell. However, such a cell must be absolutely vacuum-sealed and therefore relatively complex to manufacture, because a large number of feedthroughs are required to supply electricity, gas, and possibly cooling fluid to the equipment, and each of these must be vacuum-sealed.

[0017] On the other hand, it would be beneficial to propose a PVT process for the safe production of single crystals that can be carried out in easily manufactured and / or inexpensive equipment.

[0018] This problem is solved by the present invention as defined in the independent claim. The dependent claims provide further and preferred embodiments of the present invention.

[0019] To solve this problem, the present invention provides that the process gas consists of a partially or entirely reactive gas, and that the process chamber is placed in a safe container, where the intermediate space between the container wall of the safe container and the process chamber is filled with a protective atmosphere, such as an inert gas, to replace the air contained inside before the sublimation of the source material begins.

[0020] The containment vessel is filled last when sublimation of the source material occurs, as high temperatures may then be generated that could lead to ignition of the reactive gas. For safety reasons, however, the containment vessel should be filled before the reactive gas is introduced into the process chamber.

[0021] If the process chamber is damaged in this configuration—for example, if it is damaged—the reactive gases inside the process chamber will mix with the protective atmosphere inside the enclosure, such as an inert gas, to form a non-explosive gas mixture, so an explosion cannot occur even in a high-temperature environment.

[0022] This safety measure is especially important when the reactive gas is flammable, such as hydrogen, or deflagration-prone.

[0023] Encapsulated containers are particularly easy to implement when they are constructed in a way that allows for very little gas loss to the outside, i.e., are approximately airtight. This makes the design of the enclosed container more cost-effective, as it eliminates the need to consider high airtightness and prevents unwanted reactions of reactive gases from occurring outside the process chamber. For example, the enclosed container can have an allowable leak rate greater than 0 l / min. For cost reasons, for example, due to design choices and construction, it will be effective and problem-free to allow a leak rate in the range of 0 ≤ leak rate ≤ 5 l / min or 0 ≤ leak rate ≤ 30 l / min. For example, the allowable leak rate can be greater than 2 ml / min, greater than 5 ml / min is less desirable, 10 ml / min is even more critically undesirable, and 50 ml / min or 100 ml / min are even more undesirable. On the other hand, for possible economic and workplace safety reasons, it is not expected that the enclosed container will allow an excessively high leak rate. For example, it is preferable to limit the leak rate to 30 l / min or less, preferably 10 l / min or less, more preferably 4 l / min or less, even more preferably 1 l / min, even more preferably 500 ml / min or less, and even more preferably 150 ml / min or less. The objective is to set the leak rate in the range of 2 ml / min to 50 ml / min, preferably 10 ml / min to 20 ml / min.

[0024] An inert gas may be added to maintain a protective atmosphere, for example, to compensate for gas loss and to form and / or maintain positive pressure within the sealed container. Positive pressure prevents ambient oxygen from entering the sealed container from the outside. For this reason, the relative positive pressure can be maintained within the sealed container by a pressure control system means to a range of, for example, 1 mBar or more above ambient pressure, more preferably 3 mBar or more, preferably 5 mBar or more, and 50 mBar or less above ambient pressure, preferably 30 mBar or lower. However, a completely gas-tight sealed container with a leak rate of 0 ml / min or a leak rate that is not measurable is also essentially included here, in which positive pressure can also be maintained within the sealed container.

[0025] To ensure the complete and possible replacement of air from the sealed container, this specification may further provide introducing an inert gas into the sealed container to initially fill it. Since the initial inert gas is heavier than air, it is introduced into the lower region of the sealed container, causing the air to move upward. For example, a closable outlet at the top of the sealed container may be left open until the air escapes.

[0026] Preferably, the protective atmosphere contains an inert gas such as argon. Because argon is dense, it collects at the bottom of the containment container and moves slowly through the air without mixing with it. Other examples of protective atmospheres currently available on the market include xenon, nitrogen, and carbon dioxide. In principle, the protective atmosphere can contain any fluid, either alone or in mixtures, which can provide a protective function by neutralizing the reactive gas in the event of excessive or unacceptable leakage of reactive gas from the process chamber and / or preventing negative effects such as deflagration. The protective atmosphere can also exist in a liquid or solid state under normal conditions of a standard atmosphere, for example.

[0027] Once the air is initially displaced by an inert gas, it can be replaced, for example, by another, less expensive inert gas. The present invention thus further provides that after the enclosure has been filled one or several times initially with an inert gas, it is replaced by a second inert gas such as nitrogen.

[0028] In order to ensure that no reactive gas is supplied into the device in the event of a rupture of the process chamber, it is intended that the enclosure has a gas sensor capable of detecting the presence of reactive gas within the enclosure. Further, it is provided that when the gas sensor detects reactive gas within the enclosure, the supply of process gas to the process chamber is stopped.

[0029] In further developments, the gas supply can also be stopped via a pressure sensor or a pressure switch, which monitors the pressure within the process chamber in the event of a damage situation such as the breakage of the quartz glass where a low pressure is detected. For example, a drop in the absolute pressure to p≦980 mbarAbs, preferably p≦950 mbarAbs, more preferably p≦920 mbarAbs is detected for detection purposes. The supply of reactive gas can thus also be stopped independently of the detection of reactive gas such as hydrogen between the process chamber and the cooling device surrounding it.

[0030] An opening in the process chamber, for example in the case where the quartz glass is damaged, can be detected or indicated, for example, by one of the following criteria. Reactive gas / hydrogen is detected by a gas sensor within the enclosure. Alternatively or additionally, a positive pressure within the enclosure can be detected and a process failure can be concluded when the positive pressure (e.g., p is about 2 mbar higher than atmospheric pressure) disappears.

[0031] Furthermore, the pressure within the process chamber can be measured alternatively or superimposedly. As long as this pressure remains below p ≤ 950 mbarAbs (or 920 or 980), no process failure will be detected, but exceeding the pressure threshold can indicate a process failure. Alternatively or superimposedly, a rapid pressure surge / pressure increase within 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 detected and can indicate a process failure, such as the breakage of the quartz glass. The criteria described above are effectively independent of each other and can be used individually or in combination to shut off the supply of process gas or hydrogen.

[0032] Enclosed containers can effectively provide a cooling function. The cooling function can be designed so that a cooling medium, such as water, circulates around or through the enclosed container. For example, an enclosed container may have cooling medium lines through which the cooling medium flows. Cooling medium lines can be attached to the container wall of the enclosed container or, in any case, connected in a manner that conducts heat with the assistance of a thermally conductive paste, if possible. For example, cooling medium lines can be soldered to the container wall. For example, cooling medium lines may include copper, which is easy to work with and / or particularly thermally conductive.

[0033] Ensulations can be equipped to provide temperature control of process conditions. For example, a constant temperature—or a similar temperature range—can be maintained at all times, regardless of the potentially highly variable ambient environment, by means of an enclosure designed in this manner. For example, the environment may include a daily temperature curve or seasonal temperature fluctuations, or may also be affected by any thermal processes occurring nearby, and an effectively designed enclosure can isolate these ambient conditions from the process. Alternatively or superimposed, the cooling function may also be affected in response to process parameters, i.e., the temperature within the process chamber, to achieve temperature control of the growth process. For example, the flow rate of the cooling medium through at least one cooling medium line can be varied in response to process parameters for changes in ambient conditions and / or heat removal. If the ambient and / or process temperature is hot, for example, more cooling medium can be circulated, and / or a colder cooling medium can be used, and / or an alternative cooling medium can be filled.

[0034] The cooling medium line can be positioned outside the container wall, preferably connected thermally and electrically to the container wall, or in any case, located close to the container wall. The cooling medium line then cools the container wall, ensuring that heat is not radiated directly to the device but is carried away by the temperature control device. The advantage of positioning the cooling medium line on the outside is that there is less feedthrough that needs to be sealed within a protective atmosphere or inside the protective container to prevent the cooling fluid from entering the interior.

[0035] For example, the container wall can have a double wall, i.e., an inner wall and an outer wall, so that a cooling medium line can be placed between the inner and outer walls of the container wall. The cooling medium line and its fixtures are then concealed and made invisible and protected from mechanical damage. Since the temperature control device can dissipate a significant proportion of the heat output from the process chamber, the outer wall of the container wall does not become hot and has no or few limitations in terms of material selection or contact prevention.

[0036] The present invention also relates to an apparatus for process-safe manufacturing of single crystals using a PVT process, which comprises a source material, a highly heatable growth cell for adapting a seed, a process chamber having a connection to a process gas source in which the growth cell is placed and filled with a process gas, and a heating device for heating the growth cell.

[0037] To ensure process-safe operation using a reactive gas as the process gas, the present invention provides an apparatus having a sealed container with a container wall, a process chamber positioned inside the sealed container, and a connection to an inert gas source to allow the intermediate space between the inner wall of the sealed container and the process chamber to be filled with an inert gas before the PVT process is carried out.

[0038] The containment body may be constructed in a manner that allows for gas loss to the outside. It may have a pressure sensor, thereby connecting the pressure sensor to a control device, which is designed such that a positive pressure (compared to ambient or atmospheric pressure) inside the containment body is set based on the pressure sensor signal.

[0039] A pressure sensor may also include a pressure switch or be formed from a pressure switch. For example, a pressure sensor may be formed by deactivation within a encapsulation and a differential pressure switch that measures the pressure difference between atmospheric pressure or the environment. If necessary, the pressure sensor may subsequently trigger a circuit, for example, a safety circuit or shutoff, if the pressure becomes excessive or drops below an adjustable pressure difference.

[0040] Considering the intended installation of the device, an inert gas connection is located in the lower region of the containment container, and a sealable outlet is located in the upper region. As a result, the air inside the containment is completely moved upward to the outlet by the inert gas flowing at the bottom, and there it leaves the containment.

[0041] The sealing container preferably has two inert gas connections for two inert gases. After the first inert gas has displaced air from the sealing container, the second inert gas connection can be used to fill with a less expensive fluid, such as nitrogen, which is a second fluid, and thus replace the first inert gas.

[0042] The encapsulated body preferably has a gas sensor that responds to a reactive gas. In this method, it is determined that a reactive gas (e.g., hydrogen) has entered the encapsulated body, for example, in the event of a process chamber failure.

[0043] As described above, the apparatus can be used, for example, to produce SiC single crystals using the PVT process. For this purpose, the growth cell is loaded with silicon carbide as the source material, and the process chamber is filled with hydrogen as a reactive gas in addition to other process gases (e.g., argon). [Brief explanation of the drawing]

[0044] [Figure 1] Figure 1 is a cross-sectional view of the apparatus of the present invention. [Figure 2] Figure 2 is a simplified perspective view of a partially assembled sealed container. [Figure 3] Figure 3 is a cross-sectional perspective view of an embodiment of the apparatus. [Figure 4] Figure 4 shows the details of the connection of the temperature control device for the sealed container. [Figure 5] Figure 5 shows a segment of the container wall of a sealed container that contains part of a temperature control device. [Figure 6] Figure 6 shows an exemplary segment design of a container wall with a temperature control device. [Figure 7] Figure 7 is a perspective view of an embodiment of the encapsulation body 8. [Modes for carrying out the invention]

[0045] The present invention will be described in more detail below with reference to the means and drawings of the embodiments, where identical and similar elements are sometimes given the same reference numerals, and the features of various embodiments can be combined with one another. Figure 1 shows a cross-sectional view of the apparatus of the present invention.

[0046] At the center of the apparatus, erected on a stand, is a growth cell 1 consisting of a base and a hollow cylinder with lids that close off the two ends of the hollow cylinder. The growth cell 1 is made of porous graphite. The growth material 2 is layered on the base. The seed 3 is placed on the underside of the lid.

[0047] The growth cell 1 is located within the process chamber 4, which consists of a hollow cylinder closed at both ends by the floor or ceiling. The cylindrical walls of the process chamber 4 are made of heat-resistant quartz glass and are filled with process gas via a process gas connection having an inlet valve 5. Because the graphite of the growth cell 1 is porous, the process gas from the process chamber 4 also enters the growth cell 1.

[0048] The heating device 6 consists of an induction coil 7 that surrounds the process chamber 4 at the level of the growth cell. When current flows through it, it generates an electromagnetic field that induces current within the graphite of the growth cell 1, which heats the growth cell 1 to over 2,000°C, up to 2,400°C.

[0049] The required permeability for high temperatures and the electromagnetic field of the induction coil 7 necessitates that at least the cylindrical wall of the process chamber 4 be manufactured from a suitable heat-resistant material. Typically, the cylindrical wall of the process chamber 4 is made of quartz glass, which has proven to be particularly suitable and inexpensive to manufacture.

[0050] To produce a SiC single crystal, silicon carbide is placed in a growth cell 1, and the process chamber 4 is filled with a process gas consisting of up to 100% hydrogen. When the growth cell 1 is heated using an induction coil 7, the silicon carbide sublimes and deposits itself in layers onto a seed 3, thereby growing a SiC single crystal. Hydrogen ensures that no crystal defects occur within the crystal, or that impurity atoms are deposited at their respective growth sites. The addition of unwanted impurity atoms typically results in changes in conductivity, which can also occur locally and result in defects such as variability or degradation of quality. The composition of the process gas can also be affected by reactions with other process gases or hot zones (graphite components) through the use of reactive gases. The altered process gas composition can then affect crystallinity, structure, crystal defects, and doping of the SiC crystal.

[0051] For example, favorable effects have been achieved with hydrogen concentrations of 5% or more in the process gas, and it has been shown that low concentrations of hydrogen, such as less than 5% in the process gas, typically do not require any protective measures, such as protection against explosions. Particularly favorable results were obtained between 5% and approximately 40% hydrogen concentrations, thereby achieving improved crystal purity in the range of 15% hydrogen in the process gas (preferably around ±5%). In principle, however, the use of the sealed container of the present invention is also effective at low concentrations.

[0052] However, as mentioned above, the use of reactive gases such as hydrogen is problematic because, in the event of a possible wall failure of the process chamber 4, the reactive gas—without the sealed container of the present invention—may mix with the ambient air to form an ignitable gas that would immediately ignite, for example, in a hot part of the apparatus.

[0053] In the example of this embodiment shown herein, the process chamber 4 is therefore surrounded by a sealed container 8, which includes a cylindrical container wall 9 surrounding the cylindrical wall of the process chamber 4, which is erected on a base and closed at the top by a ceiling 11. The base 10 and ceiling 11 of the sealed container 8 are connected to the base and ceiling of the process chamber 4.

[0054] The sealed container 8 can also be part of the cooling concept of the apparatus. In other words, the sealed container 8 can be integrated with the cooling concept of the apparatus. For this purpose, the cylindrical container wall 9 can be provided with cooling channels connected to a cooling system. The cooling concept can therefore result in the apparatus providing a cooling function for the sealed container 8. For example, a cooling medium such as water can be circulated through the sealed container 8. On the other hand, a safe atmosphere (or protective atmosphere) within the sealed container 8 can provide a cooling function. For example, the safe atmosphere is circulated to dissipate heat. Overall, the sealed body can be configured in such a way that a constant temperature—or a similar temperature range—can be maintained at all times, regardless of ambient conditions that may fluctuate greatly, so that the sealed body with its cooling function can be used to control the temperature of process conditions. For example, the environment may include daily temperature curves or seasonal temperature fluctuations, or may also be affected by any thermal processes occurring nearby.

[0055] Finally, the encapsulation body 8 can be constructed in a manner that is metallically conductive. A metallically conductive encapsulation body 8 provides shielding in a Faraday cage manner for processes occurring inside, so that, for example, an alternating electromagnetic field has a defined endpoint within the container wall 9 of the encapsulation body 8 and does not dissipate asymmetrically with infinite possibilities. This is effective when several devices are set up one after another, thereby potentially causing the corresponding alternating electric fields to influence each other and disrupt process conditions. In other words, a metallically conductive encapsulation body 8 can ensure uniform process conditions without interfering with each other's processes, even when several devices of different types are set up in close proximity to each other.

[0056] Overall, the containment vessel 8 can solve several problems in a synergistic manner. Not only does it enable the aforementioned protective atmosphere that allows the use of reactive gases within the process chamber, but it also enables the containment vessel 8 to shield the process chamber from ambient conditions such as temperature fluctuations or electric and / or magnetic field fluctuations, thus ensuring uniform process conditions for the process carried out within the process chamber.

[0057] At the base of the sealed container 8, there is an annular line having one or more connections to an annular intermediate space 12 between the container wall 9 of the sealed container 8 and the process chamber 4. This annular line connects to the argon source 14 and the nitrogen source via the shuttle valve 13. 15 It connects to the network.

[0058] A closable outlet valve 16 is located on the ceiling 11 of the sealed container 8. A gas sensor 17 (e.g., a hydrogen sensor) and a pressure sensor 18 are also provided therein.

[0059] A non-damaging plastic or sheet metal covering 20 can be placed to cover the entire device, and this is installed on the base of the sealing container 8.

[0060] Furthermore, a control device 19 is provided, which is signal-connected to both sensors 17 and 18, and controls the shuttle valve 13, the outlet valve 16, and the inlet valve 5 for hydrogen supply via a control line.

[0061] The control device 19 enables the following procedure to be performed: The safety container 8 is filled with an inert gas before the process chamber 4 is filled with hydrogen: (1) Open outlet valve 16. (2) Switch the shuttle valve 13 to slowly allow argon gas from the argon source 14 to flow from below into the intermediate chamber 12, filling the intermediate chamber 12 with argon gas from below, thereby moving any existing air through the open outlet valve 16 (or pressure relief valve, etc.). (3) Close the outlet valve 16 and the shuttle valve 13. (4) Take a pause in filling to allow any remaining air from the argon gas to migrate to the top. (5) Repeat steps (1) to (3) once or several times if necessary. (6) Open the exhaust valve 16. (7) Switch the shuttle valve 13 to allow nitrogen gas to flow slowly from below into the intermediate chamber 12, thereby filling the intermediate chamber 12 with nitrogen gas from the nitrogen source 15 from below, and allowing any existing argon gas to move through the open outlet valve 16. (8) Close the exhaust valve 16. (9) By controlling the opening of the shuttle valve 13, a positive pressure is set and maintained in the intermediate chamber 12 so that air does not flow into the intermediate chamber 12 due to leaks that exist in the sealed container and are permissible.

[0062] Sufficient positive pressure is an approximation; it is 2 mbar higher than the surrounding area.

[0063] In all cases, steps (1) through (3) and (9) must be carried out. Steps (4) and (6) through (8) are optional.

[0064] An oxygen sensor can also be provided to allow checking whether the intermediate space 12 is sufficiently oxygen-free.

[0065] Actions to take in the event that the glass wall breaks during operation: (1) Continuously monitor the gas sensor 17, (2) If the gas sensor 17 detects hydrogen in the intermediate space 12, the hydrogen supply is stopped.

[0066] Referring to Figure 2, a perspective view of a simplified embodiment of the partially assembled sealed container 8 is shown, and therefore the mounting portion and process chamber 4 are not shown for the sake of clarity. For the purpose of completeness, the embodiment shown in Figure 2 does not have details of the sealing of the internal area 12, and it should also be noted that the leak rate that can be achieved in this embodiment is relatively high. A sealed container 8 with an improved seal is presented in further drawings.

[0067] In Figure 2, a temperature control device 21 is located in at least part of the sealed container 8, thereby allowing the fluid to be supplied to the refrigerant line 22 through a connecting piece 23. The refrigerant line 22 is connected to the inner wall 44 of the sealed container 8, for example, by brazing, soldering, welding, or screwing. From the process chamber 4, thermal capacity is transferred to the inner wall 44 mainly as radiant heat, from which the thermal capacity can be effectively dissipated by means of the temperature control device 21. For example, liquid water can be used as the refrigerant. The amount of heat that can be dissipated by the temperature control device 21 can preferably be adjustable. For example, the amount of heat that can be dissipated may be influenced through the temperature specifications and / or flow rate or velocity of the refrigerant, i.e., temperature control can be provided. Subsequently, in response to sensor signals measuring the ambient temperature and / or process temperature, temperature control of the process chamber 4 is achievable by temperature control, so that an essentially constant temperature exists within the process chamber 4 during the process sequence.

[0068] The containment body 8 has a viewing window 32 for bridging to the internal region 12, allowing viewing of the process chamber 4 for purposes such as monitoring the process. The viewing window 32 is relatively small to minimize direct thermal radiation. Figure 4 also shows details of the refrigerant line 22 having a line fixture 22A, a connecting piece 23, a switching piece 23B, and a connecting piece fixture 23A.

[0069] Figure 3 shows a cross-sectional view of an embodiment of the apparatus 100. The process chamber 4 is partially surrounded by an induction coil 7, which is powered by a heating device 6. The heating device 6 is partially located inside and outside the sealed container 8, so that, for example, power electronics can be located on the outside, thereby providing a sealed feedthrough 62 and reducing gas leakage. The induction coil 7, which has electronic components, is located inside 12, i.e., in a space occupied by a protective atmosphere.

[0070] The shielding gas can be supplied through a shielding gas supply 54 outside the interior 12 (several shielding gas supply lines 54 are available). An outlet valve 16 is located on the upper side 11, by means of allowing external air (containing oxygen) initially placed inside the sealed container 8 to be expelled from the sealed container 8 by introducing a protective gas heavier than air, for example. Subsequently, if a connecting line is connected to the outlet valve 16 (not shown), circulation of the shielding gas is also provided, for example, to remove heat from the sealed container 8 or to ensure a regular steel pipe of shielding gas.

[0071] In the configuration described herein, the refrigerant line 22 of the temperature control device 21 is located in the container wall 9, which is a double wall. In the cross-section of the sealed container 8 having the process chamber 4 shown in Figure 3, the interior 12 of the sealed container 8 extends from the chamber wall 41, for example, surrounding the process chamber 4 and to the container wall 9, to regulate the protective atmosphere, and the interior 12 is sealed against the container wall 9 to maintain a low gas leak rate from the interior 12 to the environment.

[0072] Furthermore, the embodiment shown in Figure 3 exhibits a unique feature in which the process chamber 4 is equipped with an adapter 46. In the shown embodiment, the adapter 46 has two alternative top covers 47, 48, and top cover 47 or top cover 48, which is positioned further inward, can be used depending on the desired process height. The covers 47, 48 can thus be used interchangeably with each other.

[0073] Referring to Figure 5, the first segment 91 of the container wall 9 of a segmented sealed container 8 having a temperature control device 21 is shown, where a refrigerant line 22 is located in an intermediate region 122 of the container wall 9. As shown herein, the container wall 9 includes an inner wall 98, frame portions 92, 94, and the refrigerant line 22 of the temperature control device 21, which is located in the intermediate region 122. The frame portions 92, 94 are fixed to the first segment 91 by fastening means 97. Further fastening means 96 (e.g., screw holes) are arranged at regular intervals on the frame portions 92, 94 so that the intermediate region 122 is surrounded by them.

[0074] Referring to Figure 6, an embodiment of the first segment 91 having a sandwich structure is further illustrated. The refrigerant lines 22 of the temperature control device 21 are located in the inner wall 98 and can be connected to the outside by connecting means 23. Frames 92, 94 surround, i.e. restrict, the segment 91 in the circumferential direction, so that the outer panel 99 can be screwed to the frames 92, 94. The outer cover 99 covers the refrigerant lines 22 and the fixing means 97, so that they are prevented from being accessed on the one hand and from being damaged on the other hand. The outer cover 99 is therefore a technical shield from direct view and access, and provides a favorable appearance to the device 100.

[0075] Finally, Figure 7 shows the apparatus 100 mounted on a base having a multi-part container wall 9, which includes wall sections 91 and 91A. The refrigerant lines 22 (see Figures 5 and 6) extend protected behind the outer panel 99 and are connected to each other by balancing bends 24 so that the refrigerant—e.g., water—can flow through the temperature control device 21. The process chamber 4 (see Figure 1 or 3) is surrounded on all sides by a protective atmosphere—or, depending on the embodiment, on all sides above the base by a protective atmosphere. If the process chamber 4 is destroyed or otherwise malfunctions and process gas leaks, the process gas mixes with the protective gas held inside 12 to form a non-hazardous mixed gas.

[0076] As those skilled in the art will see, the embodiments described above are illustrative and the invention is not limited thereto, and can be modified in many ways without departing the scope of the claims. Furthermore, it will be clear that the claims, drawings, or otherwise define essential elements of the invention, whether or not features are disclosed herein, even if they are not described in conjunction with other features. Since the same reference numerals in all drawings represent the same subject matter, any description of a subject matter that is described for only one, or not for at least all of the drawings, can also be directed to these drawings and embodiments if the subject matter is not explicitly described in the specification. [Explanation of Symbols]

[0077] 1 Growth Cell 2. Sauce ingredients 3rd seed 4 process chambers 5 Inlet Valves 6. Heating devices 7. Induction coil 8. Encapsulating container 9 Container wall 10 base 11 Ceiling 12 Intermediate Chamber 13 Shuttle Valve 14 Argon Sauce 15 Nitrogen Sources 16 Outlets (Valves) 17 Gas Sensor 18. Pressure Sensor 19 Control Unit 20 Covers 21 Cooling or temperature control devices 22 Refrigerant lines 22A Line Fixing Device 23 connecting pieces 23A Connection holder 23B Conversion piece 24 Compensation Bend 30 Environment 32 peepholes 41 Process chamber wall 44 Inner wall of the sealed container 46 adapters 47. Top cover of the process chamber 48. Top cover of the process chamber 51 Process Gas Supply 52 Process gas discharge 54 Protective Gas Supply 62 Seal Bushing 91 Part of the container wall 91A Further portion of the container wall 92 Frame section 94 Frame section 96 fixed elements 97 Fixed elements 98 Inner wall 99 Outer panel 100 devices 122 Intermediate area

Claims

1. A PVT process for process-safe manufacturing of single crystals in an apparatus, the apparatus comprising a highly heatable growth cell (1), a process chamber (4) in which the growth cell (1) is placed, and a heating device (6) surrounding the process chamber (4) for heating the growth cell (1), wherein a sublimable source material (2) and a seed (3) are introduced into the growth cell (1), the process chamber (4) is filled with a process gas, the growth cell (1) is heated, and the source material (2) sublimes and A PVT process characterized in that the seed (3) is crystallized, the process gas consists partially or entirely of a reactive gas, the process chamber (4) is placed inside a sealed container (8), an intermediate chamber (12) between the container wall (9) of the sealed container (8) and the process chamber (4) is filled with a protective atmosphere to replace the air present inside it before the sublimation of the source material (2) begins, and the sealed container (8) includes a cooling medium line through which a cooling medium flows.

2. The PVT process according to claim 1, characterized in that the reactive gas contains or consists of hydrogen, and / or the protective atmosphere contains or consists of an inert gas.

3. The PVT process according to claim 1, characterized in that the sealed container (8) allows for gas loss to the outside and an inert gas is supplied to compensate for the gas loss and to maintain positive pressure inside the sealed container (8).

4. The PVT process according to claim 3, characterized in that, in order to fill the sealed container (8), an inert gas heavier than air is first allowed to enter its lower region, the air is replaced by the air in the upper region, and for that purpose a closable outlet at the upper end of the sealed container (8) is kept open until the air escapes.

5. The PVT process according to claim 4, characterized in that the inert gas heavier than air is argon.

6. The PVT process according to claim 4, characterized in that the sealed container (8) is filled once or several times with an inert gas heavier than air, and then replaced with a second inert gas, such as nitrogen.

7. The PVT process according to claim 1, wherein the sealed container (8) has a gas sensor (17) capable of detecting the reactive gas, and the supply of the process gas to the process chamber (4) is stopped when the gas sensor (17) detects the reactive gas in the sealed container (8).

8. An apparatus for process-safe manufacturing of single crystals by a PVT process, comprising: a growth cell (1) that is highly heatable and contains a source material (2) and a seed (3); a process chamber (4) in which the growth cell (1) is located and which has a connection to a gas source for filling it with a process gas; and a heating device (6) for heating the growth cell (1), wherein the apparatus has a sealed container (8) having a container wall (9) in which the process chamber (4) is located, and the sealed container (8) has a connection to a protective gas source (14, 15) for filling an intermediate chamber (12) between the container wall (9) of the sealed container (8) and the process chamber (4) with a protective atmosphere before the PVT process is carried out, and the sealed container (8) includes a cooling medium line through which a cooling medium flows.

9. The apparatus according to claim 8, wherein the sealed container (8) is configured to allow gas loss to the outside, has a pressure sensor (18), the pressure sensor (18) is signal-connected to a control device (19), and the control device (19) is designed to set a positive pressure inside the sealed container (8) based on the signal from the pressure sensor.

10. The apparatus according to claim 8, characterized in that, in relation to the intended installation of the apparatus, an inert gas connection is located in the lower region of the sealed container (8) and a closable outlet is located in its upper region.

11. The apparatus according to claim 8, characterized in that the sealed container has two inert gas connections for two different inert gases.

12. The apparatus according to claim 8, characterized in that the sealed container (8) includes a gas sensor (17) that responds to a reactive gas.

13. The apparatus according to claim 8, characterized in that the growth cell (1) is equipped with silicon carbide as the source material (2), and the process chamber (4) is filled with hydrogen as a reactive gas.

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