Crucible for growing crystals

Abstract

The invention relates to a crucible (1) comprising a cover (2), a base (3), and a wall (4) which extends in a longitudinal central axis (L) of the crucible (1), said cover (2) and base (3) being used to delimit a growth chamber (5) within the crucible wall (4). Additionally, a crystal mounting (6) is provided in the upper region of the crucible (2) in order to receive at least one seed crystal (7). The crystal mounting (6) comprises a body (13) which is hollow-cylindrical with respect to the longitudinal central axis (L) and which has a receiving region (15) for the seed crystal (7) to be received at an end (14) facing away from the cover (2), wherein with respect to the central longitudinal axis (L), a first thickness (16) of the wall (4) is smaller in the region of the crystal mounting (6) than a second wall (4) thickness (17) formed in the direction of the base (3).

Description

[0001] Crucibles for growing crystals

[0002] The invention relates to a crucible for growing crystals, in particular SiC crystals; comprising a crucible lid and a crucible base, as well as a crucible wall extending along a longitudinal central axis of the crucible, wherein a growth chamber is defined within the crucible wall by means of the crucible lid and the crucible base. Furthermore, the crucible comprises a crystal holder arranged in an upper region of the crucible and designed to accommodate at least one seed crystal.

[0003] JP2007308355 A discloses a device comprising a crucible for growing SiC crystals. A crystal substrate is arranged on the crucible's top surface and a raw material for growing a crystal is accommodated in the bottom region. Furthermore, an upper section of the crucible wall is tapered with respect to its receiving space toward the crucible lid, which is placed on a lower section of the crucible in which the raw material is accommodated. Furthermore, the document discloses controlling the temperature gradient toward the lid, so that it is lower in the region of the crucible lid.

[0004] A disadvantage of such crucibles from the state of the art is that although they have an optimized temperature gradient from the crucible bottom towards the crucible lid, temperature fluctuations can still occur in the crystal area at the crucible lid, which can lead to stresses in the crystal and a reduction in crystal quality.

[0005] The object of the present invention was to overcome the disadvantages of the prior art and to provide a crucible by means of which a user is able to optimize the heat distribution in the crucible in order to improve the quality of the crystals to be produced.

[0006] This object is achieved by a crucible according to the claims.

[0007] The crucible according to the invention is characterized in that the crystal holder comprises a body which is hollow cylindrical with respect to the longitudinal central axis and in that a receiving area for the seed crystal to be received is formed at an end of the hollow cylindrical body facing away from the crucible lid and in that a first wall thickness of the crucible wall in the area of ​​the crystal holder is smaller with respect to the longitudinal central axis than a second wall thickness of the crucible wall formed below, in the direction of the crucible bottom.

[0008] Such a design makes it possible to optimize the temperature distribution in the region of the seed crystal (and above it). The varying or reduced wall thickness in this region allows for heating of the hollow cylindrical body or lateral heating of the crystal holder, thus achieving an improved, homogeneous temperature field in the horizontal direction across the crystal.

[0009] It is particularly advantageous if the first wall thickness of the crucible in the area of ​​the crystal holder is significantly smaller than the penetration depth of an electromagnetic field of an induction heater (depending on its frequency).

[0010] Within the hollow cylindrical body, or above the accommodated seed crystal, an uneven temperature distribution can thus be prevented in order to prevent stresses and further defects in the crystal.

[0011] A heating device mentioned above, in particular an induction heater, can, as is known from the prior art, be arranged outside the crucible along a predominant section of the crucible wall, or even along the entire crucible wall. In this regard, it is possible to control the heating achieved in the crucible by varying the wall thicknesses in the respective areas, e.g., with a uniformly arranged heating device (e.g., with a constant diameter of a heating coil and its heating power along the longitudinal center axis).

[0012] The opposite end of the hollow cylindrical body preferably comprises a radial shoulder in the direction of the longitudinal center axis, which is provided for receiving a seed crystal or a holding plate for the seed crystal.

[0013] In order to support the hollow cylindrical body in the crucible, it can also have a further radial shoulder in the direction of the crucible wall at its end facing the crucible lid, so that it can be inserted between the crucible wall and the crucible lid.

[0014] An inner diameter of the hollow cylindrical body is preferably dimensioned such that it at least corresponds to the seed crystal to be accommodated and is preferably larger. It can preferably be provided that the first wall thickness extends from the crucible lid to at least the opposite end of the hollow cylindrical body with respect to the longitudinal central axis.

[0015] An advantageous embodiment provides that a third wall thickness of the hollow cylindrical body and the first wall thickness together are less than or equal to the second wall thickness. This allows for optimal, uniform heating of the crystal area.

[0016] In a possible refinement, a reflective layer can be arranged on an inner surface of the hollow cylindrical body (facing the longitudinal central axis), wherein the reflective layer reflects thermal radiation. Such a configuration makes it possible to achieve a low emission coefficient, thus preventing absorption of thermal radiation. Preferably, the reflective layer can extend, with respect to the longitudinal central axis, from the receiving area to an end of the hollow cylindrical body facing the crucible lid.

[0017] In principle, various materials are conceivable as possible reflective layers. The reflective layer can be formed as a coating on the hollow cylindrical body or arranged as a separate component. Furthermore, the reflective layer can consist of a ceramic material. Materials that have a significantly higher melting or boiling point than SiC and, preferably, chemical resistance to the material to be evaporated are preferably used. Furthermore, a graphite foil can also be used as a reflective layer. Nitrides, e.g., BN, AlN, TiN, TaN, or others, are also conceivable as possible materials for the reflective layer.

[0018] The reflective layer can preferably have a surface modification to influence the thermal radiation, such as mirror surfaces or micromirrors, curvatures, etc. By means of a surface modification, an optimized temperature field can be set in the region above the growth crystal. One possible embodiment provides for a transition region of the crucible wall between the first wall thickness and the second wall thickness to be conically tapered with respect to the longitudinal center axis in the direction of the crucible base. This embodiment enables easier filling of the crucible and also facilitates the insertion of parts into the crucible. Furthermore, improved load distribution with regard to the forces acting on the crucible wall in the event of stresses in the crucible is enabled.

[0019] In one possible embodiment, it can be provided that the crucible wall has the second wall thickness with respect to the longitudinal center axis in an entire area of ​​the crucible which is intended to receive a starting material to be evaporated.

[0020] One embodiment further provides that the outer diameter of the crucible wall is constant relative to the longitudinal center axis between the crucible lid and the crucible bottom. This allows for a particularly simple arrangement of heating elements and the introduction of the heat energy generated thereby into the crucible.

[0021] A preferred embodiment provides that an entire wall thickness of the crucible wall is designed to decrease over the entire extent of the crucible wall, in a direction with respect to the longitudinal center axis, starting from the crucible bottom in the direction of the crucible lid.

[0022] It can be particularly advantageous if at least one thermally conductive element is arranged between the receiving area of ​​the crystal holder and the crucible lid, with at least one cavity being formed between the thermally conductive element and the seed crystal to be accommodated. This cavity can preferably be arranged at a distance from the crystal and the crucible lid.

[0023] By means of the arrangement of the thermally conductive element, according to one embodiment, two cavities can already be provided, which are arranged one above the other and are separated from each other, for example, by the thermally conductive element.

[0024] The at least one cavity serves to introduce thermal radiation between the thermally conductive element and the seed crystal to be accommodated (during a growth process or operating state of the crucible). Preferably, the cavity can be closed.

[0025] Such a design enables anisotropic thermal conductivity above the crystal to be housed (during the growth process or operating state). This is primarily influenced by the high thermal conductivity in the horizontal direction and the low thermal conductivity in the vertical direction. Geometrically, a cavity formed in this way extends in the horizontal (or radial) direction, preferably at least over the crystal, and has a low vertical height. The high thermal conductivity in the horizontal direction is achieved by the aforementioned thermal radiation in the at least one cavity between the thermally conductive element and the seed crystal (or a holding plate of the crystal), with the thermal radiation in the vertical direction (or in the direction of the longitudinal central axis) being impeded by the respective elements, thus realizing the function of a heat spreader.Preferably, two cavities can already be formed with a thermally conductive element, namely between the thermally conductive element and the crystal, and between the element and the crucible lid.

[0026] In order to generate a significant thermal radiation-driven anisotropy, it may prove advantageous if the at least one cavity has a ratio of a vertical height to a horizontal width of at least 1:10. The vertical height of the cavity may preferably correspond to 1%-10% of its horizontal width (or diameter), in particular 2%-6%.

[0027] Furthermore, the cavity formed can preferably be designed to be closed at least with respect to the growth chamber, or sealed with respect to it, so that no material in the gas phase influences the cavity.

[0028] The thermally conductive elements can preferably be formed from the material of the crucible, or from a similar material as the seed crystal, e.g. a lower quality crystal material.

[0029] Further preferably, the at least one cavity can have the previously described reflective layer and / or be surrounded by the reflective layer. In this regard, a radial boundary wall of the cavity can particularly preferably be formed by the hollow cylindrical body, wherein the hollow cylindrical body has the reflective layer.

[0030] A possible refinement provides that the crucible has at least two receiving areas spaced apart from one another along the longitudinal central axis, each spaced apart from the other for receiving a starting material, with the respective crucible wall thicknesses differing from one another with respect to the respective receiving areas. This makes it possible to provide different process conditions for the individual receiving areas or different starting materials (e.g., with regard to their composition and / or particle size) by varying the wall thickness.

[0031] For a better understanding of the invention, it is explained in more detail using the following figures.

[0032] They show in a highly simplified, schematic representation:

[0033] Fig. 1 A device for producing crystals with a crucible accommodated therein;

[0034] Fig. 2 shows an embodiment of a crucible according to the invention;

[0035] Fig. 3 shows another embodiment of a crucible.

[0036] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the position information chosen in the description, such as top, bottom, side, etc., refer to the directly described and illustrated figure, and these position information must be applied analogously to the new position in the event of a change in position.

[0037] Fig. 1 shows a device for producing single crystals by means of vapor deposition. The device 9 comprises an evacuable chamber 10, with a crucible 1 according to the preamble accommodated therein (whereby a crucible according to the invention can also be accommodated therein in this way). An underside of the crucible lid 2 can form a crystal holder 6 of the crucible 1 and is designed to attach (at least) one seed crystal 7. In a bottom region of the crucible 1, delimited by the crucible wall 4 and the crucible bottom 3, there is a starting material 8, which is intended for crystal growth on the seed crystal 7 and is used up during the growth or breeding process.

[0038] The transition of the starting material into the gas phase is achieved by heating it using at least one heater 11. According to this exemplary embodiment, the heating of the starting material 8 and the crucible 1 by the heater 11 occurs inductively. The crucible 1 arranged in the chamber 10 can also be enclosed by insulation 12 for thermal insulation. The insulation 12 simultaneously prevents heat loss from the crucible 1 and achieves a heat distribution in the interior of the crucible 1 that is favorable for the crystal growth process on the seed crystal 7.

[0039] The material for the chamber 10 is preferably a glass material, in particular quartz glass. The crucible 1 and the insulation 12 surrounding it are preferably made of graphite, with the insulation 12 being formed by a graphite felt or the like.

[0040] When the starting material 8 is heated, its atoms or molecules pass into the gas phase. They can diffuse into the interior of the crucible 1 via the gas phase and deposit on the seed crystal 7, thereby causing crystal growth. The aim is to form a single crystal that is as free of defects as possible. The quality of the crystal forming on the seed crystal 7 depends, among other things, on the temperature gradient between the starting material 8 and the seed crystal 7, and also, among other things, on the evaporation rate of the starting material 8. The evaporation rate of the starting material 8, in turn, depends on the form in which the starting material 8 is made available in the crucible 1. It can prove advantageous if the starting material 8 is formed from a mixture of a powdered raw material and a raw material in the form of lumps.Alternatively, this can also be in the form of particles (especially silicon carbide) with a very limited size distribution.

[0041] Fig. 2 shows a possible embodiment of a crucible 1 according to the invention, which is preferably used for growing SiC crystals.

[0042] This comprises a crucible lid 2, a crucible base 3, and a crucible wall 4, wherein the crucible wall 4 extends relative to a longitudinal central axis L of the crucible 1 and a growth chamber 5 is defined within the crucible wall 4 by means of the crucible lid 2 and the crucible base 3. A crystal holder 6 is arranged in an upper region of the crucible 1 and is intended to receive at least one seed crystal 7.

[0043] The crystal holder 6 comprises a hollow cylindrical

[0044] Body 13, wherein at one end 14 of the hollow cylindrical body facing away from the crucible lid 2

[0045] Body 13, a receiving area 15 is formed for the seed crystal 7 to be received and, with respect to the longitudinal center axis L, a first wall thickness 16 of the crucible wall 4 in the area of ​​the crystal holder 6 is less than a second wall thickness 17 of the crucible wall 4 formed in the direction of the crucible bottom 3. The second wall thickness 17 preferably extends from an area of ​​the crucible wall 4 in which the starting material 8 to be evaporated is arranged.

[0046] Preferably, the first wall thickness 16 extends, relative to the longitudinal center axis L, from the crucible lid 2, at least to the remote end 14 of the hollow cylindrical body 13, as indicated by the height 29. Furthermore, as mentioned above, a third wall thickness 18 of the hollow cylindrical body 13 and the first wall thickness 16 together can be less than or equal to the second wall thickness 17. Preferably, the hollow cylindrical body 13 can have a uniform third wall thickness 18.

[0047] As indicated, the crucible lid 2 can have a recess in the region of the longitudinal central axis L, by means of which, for example, an opening for measuring the temperature inside the crucible 1 in the region of the seed crystal 7 is possible.

[0048] The crystal holder 6 or the hollow cylindrical body 13 can have a fastening section 30 with regard to the arrangement in the crucible 1, by means of which the crystal holder 6 can be inserted into the crucible 1. As shown in Figs. 2 and 3, the crystal holder 6 can be fastened or inserted between the crucible lid 2 and the crucible wall 4 by means of the fastening section. The fastening section can be formed in the form of a radial shoulder which extends from the longitudinal central axis L (at the end 21 facing the crucible lid) in the direction of the crucible wall. Preferably, the fastening section can extend radially up to the outer diameter 23 of the crucible 1 and thus be flush with the crucible wall 4 and / or the crucible lid 2.Alternatively, the fastening section can also be accommodated within the crucible wall 4 by means of a shoulder or the like, or such a receiving element can be provided on the crucible lid 2. Furthermore, Fig. 2 shows a possible arrangement of the starting material 8 in the crucible 1, which is delimited by a porous or permeable cone toward the longitudinal central axis L, thereby promoting gas circulation toward the center of the crucible or in this region. Furthermore, a cover element 28 can be arranged above the starting material.

[0049] Preferably, a reflection layer 20 is arranged on the inner surface 19 of the hollow cylindrical body 13, wherein the reflection layer 20 reflects thermal radiation which preferably extends, as shown, with respect to the longitudinal center axis L from the receiving area 15 to an end 21 of the hollow cylindrical body 13 facing the crucible lid 2.

[0050] As shown, the crystal holder 6 or the hollow cylindrical body can have a radial shoulder in the direction of the longitudinal central axis L at its end 14 facing away from the crucible lid for receiving the seed crystal 7. The seed crystal 7 or the holding plate can be mounted in the crystal holder 6 by means of the radial shoulder, which shoulder can form the receiving area 15 of the crystal holder 6. As also shown, the holding plate and the seed crystal 7 are preferably dimensioned such that they have play with regard to their degrees of freedom in the radial direction relative to the crystal holder 6, so that they can expand with regard to their thermal expansion in the direction of the crystal holder 6 and thus also avoid stresses that would be caused by a radial limitation.Alternatively, the crystal holder can also be designed to be closed at the opposite end 14, so that the seed crystal 7 is glued or the like to it.

[0051] The seed crystal 7 can preferably be secured to a holding plate with respect to its receptacle in the crucible 1, which corresponds to the properties of the seed crystal 7 in terms of thermal conductivity and thermal expansion coefficient, or has only minor differences compared to the crystal. The holding plate is preferably made of a similar material or a lower-quality material to the seed crystal 7, e.g., SiC, and can be connected to the seed crystal 7 by gluing, clamping, bonding, or the like. Furthermore, the holding plate can be equipped with a base with the same diameter as the seed crystal, so that the seed crystal is thus positioned lower in the assembly than the rest of the receptacle arrangement, or the hollow cylindrical body 13.

[0052] As can be seen from Fig. 2, it can be provided that the crucible wall 4 has the second wall thickness 17 with respect to the longitudinal center axis L in an entire region of the crucible 1 that is intended to receive a starting material 8 to be evaporated. As can also be seen, it can be provided that a transition region 22 of the crucible wall 4 between the first wall thickness 16 and the second wall thickness 17 is conically tapered with respect to the longitudinal center axis L in the direction of the crucible bottom 3.

[0053] The outer diameter 23 of the crucible wall 4 relative to the longitudinal center axis L is preferably constant, as can be seen from Figs. 2 and 3. In addition, a crucible according to the invention is preferably designed such that an overall wall thickness of the crucible wall 4 decreases over the entire extent of the crucible wall 4 in a direction relative to the longitudinal center axis L, starting from the crucible bottom 3 in the direction of the crucible lid 2.

[0054] As can further be seen from the figures, the hollow cylindrical body 13 can have an (outer) diameter which, compared to the inner diameter of the crucible wall 4 in this area, is dimensioned such that an (annular) free space is formed between the hollow cylindrical body 13 and the crucible wall.

[0055] Regardless of the embodiment, at least one thermally conductive element 24 can be provided along the longitudinal center axis between the receiving area 15 of the crystal holder 6 and the crucible lid 2, wherein at least one cavity H is formed between the thermally conductive element 24 and the seed crystal 7 to be received, which cavity serves to optimize the horizontal temperature gradient Th in the area of ​​the crucible lid 2, so that an improved temperature distribution in the radial direction is enabled, or the temperature distribution above the seed crystal 7 can be further optimized.

[0056] The thermally conductive element 24 can be plate-shaped, but can also have other geometric shapes suitable for forming a cavity H. Furthermore, it can be formed integrally with the hollow cylindrical body 13, or the latter can enclose the thermally conductive element 24. The formed cavity H preferably has a low height, so that, with respect to its cross-section, the cavity can have a height-to-width ratio of approximately 1:10 to 1:100. With respect to its width (or diameter), the cavity preferably extends at least over the crystal or the receiving area 15.

[0057] Furthermore, the shape of the cavity can preferably also be cylindrical, wherein, facing the seed crystal, it preferably has a concavely curved ceiling surface with respect to the components bounding the cavity, so that heat radiation within the cavity is directed toward a cavity center. For example, a previously mentioned plate-shaped, thermally conductive element 24 can be concave on its underside (facing the crystal). The cavity itself can thus be convex, at least on its side facing the crucible lid, or else have a convex outer contour throughout its entire configuration.

[0058] Depending on the design of the cavities, a previously mentioned reflection layer 20 may also be provided within the cavity H, at least on the radial walls of the cavity.

[0059] When forming the thermally conductive elements 24 in the form of plates or the like, it can further be provided that they are spaced apart by means of rings to form a cavity H, wherein the rings preferably have the same outer diameter as the thermally conductive elements. Furthermore, the thermally conductive elements 24 can also be formed integrally with such rings, so that they are provided as an axial extension (e.g., to form a cavity).

[0060] These heat-conductive elements 24 can further preferably be inserted from above, so that they are already fixed by gravity.

[0061] As can be seen from Fig. 3, the crucible wall can have additional wall thicknesses 25 in the direction of the crucible bottom 3, which wall thicknesses increase in the same direction. Different inner diameters 27 of the crucible 1 can be formed by means of the second wall thickness 17 and the additional wall thicknesses 25, and furthermore, stepped shoulders can be formed in the radial direction by means of the different inner diameters 27 or wall thicknesses.

[0062] It should be clarified that a second wall thickness 17 in the sense of the patent description means a wall thickness below the first wall thickness 16, which is preferably formed in the region of the starting material 8 to be received, and with regard to a formation or arrangement of further wall thicknesses 25 is preferably the smallest (or thinnest) in this region.

[0063] As indicated by dashed lines in Fig. 3, in the area of ​​the hollow cylindrical body 13, the crucible wall 4 can explicitly have a smaller first wall thickness 16 with respect to its height.

[0064] Furthermore, it can be provided that, in order to form individual receiving areas for the starting material 8, which are arranged one above the other along the longitudinal central axis L, are provided, which are separated from one another by means of annular receiving elements 26, wherein at least one of the receiving areas is formed on a receiving element 26.

[0065] In an advantageous embodiment, the receiving elements 26 for receiving the starting material 8 can be mounted on the radial shoulders, as shown, or also a cover element 28 which is provided for directing a gas flow in the direction of the crucible center.

[0066] By means of such receiving elements 26, for example, differently formed layers of the starting material 8 can be stored in the crucible, as shown.

[0067] Furthermore, the crucible base 3 can also be mounted on such a shoulder. The receiving elements 26 can preferably rest circumferentially against the crucible wall 4 and have an opening in the center of the crucible, as also shown, to promote gas flow toward the center of the crucible. Furthermore, the receiving elements 26 preferably extend from the wall in the direction of the longitudinal center axis L and can also have boundary walls for the starting material, which extend from the receiving element toward the crucible lid, as shown.

[0068] Preferably, a separate wall thickness 25 is provided for each receiving area, so that a separate process condition with regard to the sublimation of the starting material 8 located in this area can be specifically controlled via the respective wall thickness.

[0069] The embodiments show possible embodiments, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments with each other are also possible and this possibility of variation lies within the skill of the person skilled in the art in this technical field due to the teaching of technical action by means of the objective invention.

[0070] The scope of protection is determined by the claims. However, the description and drawings must be used to interpret the claims. Individual features or combinations of features from the various embodiments shown and described may represent independent inventive solutions. The problem underlying these independent inventive solutions can be derived from the description.

[0071] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0072] For the sake of clarity, it should be noted that some elements have been shown not to scale and / or enlarged and / or reduced in size to improve understanding of the structure.

[0073] Crucible Th Temperature gradient horizontal

[0074] Crucible lid L Longitudinal center axis Crucible bottom H Cavity Crucible wall

[0075] Breeding chamber crystal holder seed crystal

[0076] Starting material Device Chamber

[0077] Heating

[0078] Insulation hollow cylindrical body opposite end receiving area first wall thickness second wall thickness third wall thickness inner surface

[0079] Reflection layer facing end Transition area Outer diameter Thermally conductive element Additional wall thickness Receptacle inner diameter

[0080] Cover element height

[0081] Fastening section

Claims

Patent claims 1. Crucible (1) for growing crystals comprising; - a crucible lid (2) and a crucible bottom (3), and - a crucible wall (4), wherein the crucible wall (4) extends with respect to a longitudinal central axis (L) of the crucible (1) and a growth chamber (5) is delimited within the crucible wall (4) by means of the crucible lid (2) and the crucible bottom (3); - a crystal holder (6), wherein the crystal holder (6) is arranged in an upper region of the crucible (2) and is provided for receiving at least one seed crystal (7); characterized in that the crystal holder (6) comprises a body (13) which is hollow cylindrical with respect to the longitudinal central axis (L), and in that a receiving region (15) for the seed crystal (7) to be received is formed on an end (14) of the hollow cylindrical body (13) facing away from the crucible lid (2), and in that, with respect to the longitudinal central axis (L), a first wall thickness (16) of the crucible wall (4) in the region of the crystal holder (6) is less than a second wall thickness (17) of the crucible wall (4) formed in the direction of the crucible bottom (3).

2. Crucible (1) according to claim 1, characterized in that the first wall thickness (16) is formed with respect to the longitudinal central axis (L), starting from the crucible lid (2) at least up to the remote end (14) of the hollow cylindrical body (13).

3. Crucible (1) according to claim 1 or 2, characterized in that a third wall thickness (18) of the hollow cylindrical body (13) and the first wall thickness (16) together are less than or equal to the second wall thickness (17).

4. Crucible (1) according to one of claims 1 to 3, characterized in that a reflection layer (20) is arranged on an inner surface (19) of the hollow cylindrical body (13), wherein the reflection layer (20) reflects thermal radiation.

5. Crucible (1) according to claim 4, characterized in that the reflection layer (20) extends with respect to the longitudinal central axis (L) from the receiving area (15) to an end (21) of the hollow cylindrical body (13) facing the crucible lid (2).

6. Crucible (1) according to one of claims 1 to 5, characterized in that a transition region (22) of the crucible wall (4) between the first wall thickness (16) and the second wall thickness (17) is conically tapered with respect to the longitudinal center axis (L) in the direction of the crucible bottom (3).

7. Crucible (1) according to one of claims 1 to 6, characterized in that the crucible wall (4) has the second wall thickness (17) with respect to the longitudinal center axis (L) in an entire region of the crucible (1) which is intended to receive a starting material (8) to be evaporated.

8. Crucible (1) according to one of claims 1 to 7, characterized in that an outer diameter (23) of the crucible wall (4) is constant to the longitudinal center axis (L) between the crucible lid (2) and the crucible bottom (3).

9. Crucible (1) according to one of claims 1 to 8, characterized in that an overall wall thickness of the crucible wall (4) is designed to decrease over the entire extent of the crucible wall (4), in a direction with respect to the longitudinal center axis (L), starting from the crucible bottom (3) in the direction of the crucible lid (2).

10. Crucible (1) according to one of claims 1 to 9, characterized in that at least one thermally conductive element (24) is arranged between the receiving area (15) of the crystal holder (6) and the crucible lid (2), wherein at least one cavity (H) is formed between the thermally conductive element (24) and the seed crystal (7) to be received.

11. Crucible (1) according to one of claims 1 to 10, characterized in that the crucible (1) has at least two receiving areas spaced apart from one another along the longitudinal central axis (L) for a respective receiving area spaced apart from one another for a starting material (8), wherein a respective crucible wall thickness is different from one another with respect to the respective receiving areas.

Images