Patent Application
20240035200
The invention relates to a device for growing single crystals, in particular of silicon carbide (SiC), comprising a crucible, which crucible defines an outer lateral surface and moreover delimits an accommodation space with an axial extension between a bottom section and an opening section, wherein the accommodation space is designed for growing single crystals, wherein the device has at least one seed crystal layer.
Moreover, the invention relates to a method for producing a seed crystal layer, in particular of silicon carbide.
For many technical applications, single crystals are nowadays produced on an industrial scale. Based on the phase transitions leading to the crystal, a distinction can be made between the growth from the melt, from the solution and from the gas phase. In the case of growth from the gas phase, further distinctions can be made between the production methods of the sublimation and/or the physical vapor deposition and the method of the chemical vapor deposition. In the case of the physical vapor deposition, the substance to be grown is vaporized by means of heating, so that it transitions into the gas phase. Given suitable conditions, the gas can resublimate on a seed crystal, whereby a growth of the crystal takes place. The raw material (powder or granules) usually present in a polycrystalline form is thus recrystallized. The chemical vapor deposition works in a similar manner. In this process, the transition of the substance to be grown into the gas phase is only possible by means of an auxiliary substance, to which the substance chemically binds itself, since the vapor pressure would be too low otherwise. Thus, a higher transport rate towards the seed crystal is achieved in combination with the auxiliary substance.
A great interest is taken in silicon carbide single crystals, particularly because of their semi-conductor properties. Their production is carried out in furnaces with a crucible, in which the silicon carbide raw material is heated, and a seed crystal, on which the further crystal growth takes place by means of accumulation. Moreover, the interior of the process chamber is evacuated. The material used for the innermost process chamber with the crucible is graphite. Usually, the seed crystal is located directly on a cover of a crucible containing the raw material.
A problem, which occurs in known methods, is that the size of the area of the seed crystals is usually limited, which is why only ingots made of single crystals with a limited diameter can be produced.
Therefore, it is the object of the invention to overcome the disadvantages of the prior art and to make the production of ingots and, in further consequence, of wafers with a larger diameter possible.
This object is achieved according to the invention with a device of the initially mentioned type, by the seed crystal layer being assembled from multiple seed crystal plates in a tessellated manner.
The solution according to the invention makes the production of ingots and, in further consequence, of wafers made of silicon carbide with any desired diameter possible.
In order to obtain single crystals of very high quality, it is particularly advantageous of the crystal orientations of the seed crystal plates in the seed crystal layer are oriented uniformly.
An assembly of the seed crystal layer is significantly simplified by the seed crystal plates each having a polygonal, in particular hexagonal, circumferential contour.
According to an advantageous variant of the invention, it may be provided that the seed crystal plates are connected to a cover of the crucible, with or without intermediate layers arranged between the seed crystal plates and the cover.
However, the seed crystal plates may also be applied to a substrate separate from the cover.
It has proven particularly advantageous that the substrate is formed from graphite.
In order to obtain a good mechanical stability and a self-supporting seed crystal layer, it may be provided that the seed crystal layer has a thickness of between 350 and 2000 μm.
According to an advantageous advancement of the invention, it may be provided that the seed crystal layer has a mass per unit area of between 2.20 kg/m2 and 3.90 kg/m2.
Furthermore, it has proven advantageous that the seed crystal layer comprises at least one polished and/or sanded and/or dry-etched surface.
It has proven particularly favorable, regarding the quality of the grown single crystals, that the seed crystal layer has an area-related roughness value of between 10 nm and 0.01 nm.
Furthermore, the seed crystal layer may be doped with at least one material, in particular SiC or AlN.
The above-mentioned object can also be achieved according to the invention with a method of the initially mentioned type, by the seed crystal layer being assembled from multiple seed crystal plates in a tessellated manner.
It has proven particularly advantageous that the individual seed crystal plates are made from wafers.
The seed crystal plates may be applied to a substrate, with or without the arrangement of at least one intermediate layer between the substrate and the seed crystal plates.
Moreover, at least one epitaxy layer of a monocrystalline silicon carbide may be applied to the seed crystal plates, in particular by means of a CVD method. The seed crystal plates can be held together by the applied epitaxy layer.
It has also proven particularly advantageous that the individual seed crystal plates have an area-related roughness value of between 10 nm and 0.01 nm. By forming very smooth surfaces, the seed crystal plates may also adhere to a substrate, for example a cover of the crucible, without further intermediate layers, in particular adhesion agent layers.
Furthermore, the seed crystal layer may be dry-etched, sanded and/or polished.
In order to eliminate any potential defects, the assembled seed crystal layer may be subjected to a heat treatment.
Furthermore, it may be provided that the seed crystal layer is provided with at least one material, in particular SiC or AlN, in a sublimation atmosphere.
For the purpose of better understanding of the invention, it will be elucidated in more detail by means of the figures below.
These show in a respectively very simplified schematic representation:
First of all, it is to be noted that in the different embodiments described, equal parts are provided with equal reference numbers and/or equal component designations, where the disclosures contained in the entire description may be analogously transferred to equal parts with equal reference numbers and/or equal component designations. Moreover, the specifications of location, such as at the top, at the bottom, at the side, chosen in the description refer to the directly described and depicted figure and in case of a change of position, these specifications of location are to be analogously transferred to the new position.
The transition of the base material 407 into the gas phase is achieved by heating with the aid of a heater 408. According to this exemplary embodiment, the heating of the base material 407 and the crucible 403 by means of the heater 408 is carried out inductively. The crucible 403 arranged in the chamber 402 is moreover enveloped by an insulation 409 for thermal insulation. By means of the insulation 409, thermal losses from the crucible 403 are simultaneously prevented, and a heat distribution favorable for the growth process of the crystal on the seed crystal 405 is achieved in the interior of the crucible 403.
The material for the chamber 402 is preferably a glass material, in particular a quartz glass. The crucible 403 and the insulation 409 surrounding it preferably consist of graphite, wherein the insulation 409 is formed by a graphite felt.
Because atoms and/or molecules of the base material 407 transition into the gas phase due to heating of the base material 407, the atoms and/or molecules can diffuse to the seed crystal 405 in the interior of the crucible 403 and accumulate thereon, whereby the crystal growth takes place.
According to
At least one epitaxy layer of monocrystalline silicon carbide may be applied to the seed crystal plates 507a, 507b, 507c, in particular by means of a CVD method. The application of the epitaxy layer, in addition to the arrangement and connection of the individual seed crystal plates 507a, 507b, 507c on a substrate, constitutes a possibility to connect the individual seed crystal plates 507a, 507b, 507c to one another. The assembled seed crystal layer 507 may be subjected to a heat treatment to eliminate any possible defects. This way, the seed crystal layer 507 may be heated, for example, to a temperature of more than 1200° C., and this temperature may be maintained between 10 min and 3 h. Afterwards, a cooling and thermal annealing of defects may take place at a temperature of less than 800° C. The heat treatment may take place in an inert gas atmosphere, for example.
Furthermore, the seed crystal layer 507 may be provided with a material, in particular SiC or AlN, in a sublimation atmosphere. The seed crystal layer may, in particular, be doped with the material.
As can further be seen in
The seed crystal plates 507a, 507b, 507c may be connected to the cover 404 of the crucible 403 with or without intermediate layers arranged between the seed crystal plates and the cover, as is shown for example in
The seed crystal layer 507 has a preferred thickness of 350-2000 μm and a preferred mass per unit area of between 2.20 kg/m2 and 3.90 kg/m2.
Moreover, the seed crystal layer 507 may have one or two polished and/or lapped surfaces. It has proven particularly favorable that the seed crystal layer has an area-related roughness value of between 10 nm and 0.01 nm. The area-related roughness value is defined, for example, in the EN ISO 25178 standard.
For producing the seed crystal layer 507, the seed crystal plates 507a, 507b, 507c are assembled in a tessellated manner.
According to
Contrary to the embodiment according to
As can further be seen in
The holding section 509 may be designed to extend circumferentially around an opening 510 of the opening section 506.
According to
According to the embodiment shown in
According to
The weighting mass 508 may be arranged between the seed crystal layer 507 and a cover 515 of the crucible 502, wherein the weighting mass 508 and the cover 515 are formed separately from one another. The weighting mass 508 is preferably arranged loosely between the cover 515 and the seed crystal layer 507.
The seed crystal layer 507 may be designed as a mechanically self-supporting layer or also be applied to a carrier substrate 516, as it is shown in
The weighting mass 508 and/or the mount 510 may be made of metal, ceramics, mineral or plastics. Fireproof materials, carbides, oxides, or nitrides have proven particularly suitable.
Finally, as a matter of form, it should be noted that for ease of understanding of the structure, elements are partially not depicted to scale and/or are enlarged and/or are reduced in size.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 50822/2020 | Sep 2020 | AT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AT2021/060344 | 9/23/2021 | WO |
