Device for evaporating material

Abstract

Device for evaporating materials, comprising at least one steam distributor, comprising at least three nozzles and at least one evaporator, characterized in that the steam distributor of the device is provided by a transport line with at least three nozzles arranged on the transport line and the evaporator is provided by the arrangement of at least one heater for the nozzles in the steam distributor and wherein a screw or belt conveyor is arranged in the transport line and the device comprises a supply line for materials which opens into the transport line.

Description

[0001] The present invention relates to a device for evaporating materials, such as such a device is used, for example, in the manufacture of solar cells for the deposition of layers by means of physical vapor deposition (PVD).

[0002] The PVD process according to the invention relates to vacuum-based thermal evaporation. In this context, a vacuum is defined as a pressure of 1 × 10⁻⁶. -1 up to 1·10 -9 mbar. The term thermal evaporation refers to the conversion of a material from a condensed form, i.e., solid (amorphous or crystalline) or liquid, into a vaporized form by the supply of heat, heating, or aeration, whereby the condensed form evaporates (from the liquid state) or sublimates (from the solid state) and is thus converted into a gaseous state, the vapor.

[0003] A device conforming to the invention, which is considered the closest prior art, is disclosed in DE 10 2010 046 389 A1. The device serves for the evaporation of materials, here referred to as the vaporization material, and their deposition onto substrates. The device comprises a heatable evaporator, here referred to as the primary evaporator, for evaporating the materials. This primary evaporator is arranged upstream of a vapor distributor within the device, so that the evaporated materials enter the vapor distributor as vapor. The device also includes at least one linear, heatable vapor distributor connected to the primary evaporator via a vapor-conducting line. The linear vapor distributor also serves as a line and has nozzles arranged linearly in a row, through which the vapor, i.e., the evaporated materials, is distributed.The vapor distributor, in which the nozzles are arranged, is rotatable around its longitudinal axis relative to the primary evaporator. Such a device includes a rate sensor, usually in the form of a quartz microbalance (QCM), which allows monitoring of the separation rate of the evaporated materials.

[0004] In PVD, the vaporized materials are deposited onto a substrate to form a layer, i.e., condensed or resublimated. The devices for carrying out the process are arranged in evacuable containers.

[0005] For the purposes of this invention, "material" refers to elements, compounds of elements, or mixtures thereof. With regard to the PVD process addressed by the invention, the term "compounds of elements" refers in particular to compounds of molecules, wherein a molecule is itself formed from two or more atoms of at least one element held together by chemical bonds. Although the device according to the invention offers a particular advantage in the vaporization of materials composed of molecules, it is nevertheless equally suitable for the vaporization of other materials. Atoms and complexes of several atoms connected by non-covalent interactions such as hydrogen or ionic bonds are not normally considered as individual molecules. The materials referred to in this invention can also be considered precursor materials for the layers to be deposited.The precursor materials are primarily aggregated, solid (i.e., crystalline or amorphous), or liquid forms of precursor molecules intended for vapor deposition. After deposition on a substrate, the vapor-containing precursor molecules form a layer of the material composed of these precursor molecules.

[0006] Certain materials, such as those used as precursor materials for the formation of perovskites, especially organic perovskites, are temperature-sensitive. This means that at temperatures approaching, and sometimes even below, the vaporization temperature, decomposition reactions of the materials' molecules (the precursor molecules) occur, which is undesirable and is discussed, for example, in article 1 by M. Roß et al. (Revealing the Role of Methylammonium Iodide Purity on the Vapor-Phase Deposition Process of Perovskites, Solar RRL, Vol. 6, 2020, 2200500 1-9). The decomposition of the precursor molecules can occur even before vaporization within the material, but it occurs to a particularly high degree after vaporization, since the vaporized molecules (precursor molecules) are less stable in the gas phase than when unvaporized.

[0007] The object of the present invention is to provide a device with which the decomposition of precursor molecules can be prevented more effectively compared to the prior art and a more homogeneous composition of the evaporated material is achieved.

[0008] The problem is solved by the device in claim 1. Advantageous embodiments are the subject of the dependent claims.

[0009] The inventive idea is based on the provision for the evaporation of materials immediately before the evaporated materials, in particular precursor molecules, exit the nozzles of the steam distributor for distribution. For this purpose, a transport mechanism for the materials is provided in the steam distributor, which transports the unevaporated materials to the distribution point, the nozzles, and evaporation in the nozzles is effected by heating them.

[0010] The steam distributor in the device according to the invention has in particular a linear design, which is advantageous for the steaming and the construction of the device as well as for its operation.

[0011] The vaporization of the materials, immediately before they exit the nozzles of the steam distributor for distribution, is achieved by means of nozzle heating elements within the steam distributor. These heating elements can be a single unit for all nozzles or individual units for each nozzle. The materials are transported to the heated nozzles via a linear conveyor system, such as a screw conveyor or belt conveyor, within a linear transport line that forms part of the steam distributor. The term "immediately" refers to the fact that the materials remain unvaporized until they reach the immediate vicinity of the distribution point, which is the nozzles, and are only vaporized there, at the distribution point.The transport distance of the already vaporized materials, especially precursor molecules, is thus reduced to a minimum, which is particularly advantageous with regard to possible decomposition reactions of precursor molecules after vaporization. The minimized transport distance of the vaporized materials, especially precursor molecules, means a significant reduction in the time the precursor molecules are exposed to high temperatures, which in turn means that the decomposition of the vaporized precursor molecules is kinetically inhibited, thus providing the advantage.

[0012] The device according to the invention for evaporating materials comprises at least the following components: a vapor distributor with at least three nozzles and at least one evaporator. Advantageously, the number of nozzles is ≥ 13, with the number of nozzles being limited to 10,000 and, in particular, to a number in the range of 50 to 1,000. The number of nozzles depends on the design of the device, i.e., on the size of the substrates to be coated. The specified upper limits for the number of nozzles are not prerequisites for the regular operation of the device, but merely serve to inform those skilled in the art about possible dimensions. Advantageously, the device includes a rate sensor for optimizing and monitoring the evaporation parameters.The device according to the invention for evaporating materials comprises at least one supply line for chemical substances (materials), wherein the supply line for materials opens into a transport line of the steam distributor. The at least three nozzles are arranged on the transport line of the steam distributor. According to the invention, the at least one evaporator is provided by a heating element for the nozzles in the steam distributor. Furthermore, a temperature-controlled, in particular coolable, screw conveyor or belt conveyor is arranged in the transport line, so that the material from the supply line to the nozzles in the steam distributor can be transported and is already at a temperature just below the sublimation temperature.

[0013] In a second embodiment of the inventive device for evaporating materials, the transport line of the steam distributor is equipped with an outlet on the side opposite the material supply line. This outlet allows for the discharge of materials and any carrier media that have not evaporated after passing through the entire transport line of the steam distributor, thus simplifying the calculation of volume flows. Furthermore, it is possible to re-feed unevaporated materials and carrier media into the supply line, thereby increasing the material efficiency of the process.

[0014] The material is conveyed to the steam distributor via a feed line that empties into the steam distributor. Transport media, such as gases and liquids, can be used to assist this transport. The material can be moved through the feed line and the conveying line until it enters the steam distributor by gravity, for example, in the form of a bulk material. Transport from the storage container outside the vacuum system (at atmospheric pressure) to the storage container inside the vacuum system is achieved by pulsed vacuum conveying through a hose or pipe into a material transfer chamber located directly above the hopper. This chamber can be emptied separately. Once the differential pressure is sufficiently low, the chamber can be mechanically opened, and the material falls into the hopper of the material conveyor. This is necessary to guarantee a consistent material flow.In the steam distributor, transport takes place via at least one screw or belt conveyor, and this transport can be supported by transport media. In one embodiment, the device includes a screw conveyor. The transport speed of the precursor materials can be controlled by the design of the screw or belt conveyor. This is achieved in particular by interplay with the flow of a transport medium with regard to the parameters flow velocity and volume.

[0015] The screw conveyor can be optimized for the intended material and evaporation rates, for example, by adjusting the screw pitch and its design. This can be achieved as a shaftless screw conveyor (belt screw, shaftless screw) for sensitive materials or as a paddle screw conveyor, i.e., without a continuous thread (consisting of individual segments connected by a shaft). The screw speed allows for adjustment of the conveying volume. The screw conveyor is driven by an electric motor, which is connected to the steam distributor's transport line, for example, via a flange. The electric motor is positioned, for example, on the side of the transport line opposite the material supply line. If desired, the connection to the screw conveyor can thus coincide with an outlet of the transport line.

[0016] In particular, in the process belonging to the invention, the inventive form of transport enables the material to be transported in unvaporized form up to the nozzles. This allows a gas (e.g., ammonia) or another added chemical substance in the material feed line to shift the equilibrium in a decomposition reaction of the precursor molecules in favor of the undecomposed molecules, i.e., the precursor molecules. This is generally achieved by chemical substances, especially molecules in the gas phase, which, at the temperatures before and after evaporation, shift the equilibrium of the decomposition reaction in favor of the undecomposed precursor molecules due to the vapor pressure generated by the additives. Two exemplary known decomposition reactions of formamidinium iodide (FAI) are described in Article 2 by S. Thampy et al.(Bulk and interfacial decomposition of formamidinium iodide (HC(NH2)2I) in contact with metal oxide, Material Advances, Vol. 1, 2020, pp. 3349-3357), are . and

[0017] In both decomposition reactions, ammonia as a carrier gas would shift the chemical equilibrium towards the precursor molecule FAI.

[0018] The material supply line can advantageously be temperature-controlled, encompassing both cooling and heating. The transport line in the steam distributor is also advantageously temperature-controlled. By allowing temperature control of the transport line, decomposition reactions of precursor molecules in the materials and premature evaporation of the material can be influenced, or their condensation prevented.

[0019] The material supply line is adapted in its dimensions and arrangement at the steam distributor to the materials and the transport line. Typical dimensions for the transport line range from 1 to 10 cm in diameter and from 0.1 to 10 m in length within the steam distributor, which also significantly determines the overall dimensions of the device. The supply line can also be advantageously designed in the form of a funnel, which facilitates the feeding of materials by bulk material.

[0020] The material intended for evaporation must be in a form that allows transport by the screw or belt conveyor of the device. Advantageously, the materials are in powder form, as a powder (i.e., a powder with a very small particle size), as granular matter, as bulk material, or as a liquid.

[0021] The nozzles are arranged so that the path from the screw or belt conveyor to the outlet is as short as possible (0.5 - 5 cm). They have a funnel-shaped opening with an opening angle of 0 - 35° to widen the material jet.

[0022] The nozzles are heated by heating filaments embedded in ceramic, which surround the actual nozzle. A thermocouple is located in the immediate vicinity of at least one nozzle to monitor the current temperature.

[0023] The rate sensor is located at the edge of the linear source and can be retracted into the steam jet for rate control, or it can remain permanently at the edge of the linear source in the coating area. A quartz oscillator turret can be used to increase the rate measurement time.

[0024] In one embodiment of the device, a vacuum lock for introducing material is arranged on the supply line for materials, wherein the vacuum lock can be subjected to negative pressure for suction of material.

[0025] The device according to the invention for evaporating materials is designed for use in PVD. For carrying out PVD, the device is arranged in an evaporable container so that the evaporated material, in particular the precursor molecules, can be deposited onto a substrate when operating under vacuum.

[0026] The materials from which the components of the device for evaporating material are made correspond to the usual materials known from the prior art, such as stainless steel 316, aluminium, glass and ceramic components.

[0027] A method for evaporating materials belonging to the device according to the invention comprises the following steps. a. Provision of a device for evaporating materials according to one of the embodiments described above, b. Provision of at least one material under atmospheric pressure and transport into a vacuum, c. Supply of the material via the supply line into the steam distributor, d. Transport of the material in the transport line of the steam distributor to the heated nozzles of the steam distributor by means of a screw or belt conveyor, e. Evaporation of the material in the heated nozzles.

[0028] In an alternative embodiment of the process, in step b. at least one chemical substance is added to the material which shifts the equilibrium of a decomposition reaction of the precursor molecules in favor of the precursor molecules.

[0029] With the device according to the invention for vaporizing material and an associated method, the undesired decomposition of vaporized precursor molecules for vapor deposition can be suppressed more effectively and in a more controlled manner compared to the prior art. Furthermore, the device according to the invention achieves a more homogeneous vapor deposition compared to the prior art. This is because the invention prevents the decomposition of precursor molecules along the transport path, which increases with increasing distance and is therefore inhomogeneous along the vapor distributor path, and ensures that the same conditions for the vapor exist at all points where the vaporized material exits, i.e., from the nozzles, leading to improved homogeneity in the deposited layers. Example

[0030] The invention in an exemplary embodiment is described in more detail below by means of an embodiment of the device according to the invention for the evaporation of chemical substances and for the associated process and three figures.

[0031] The figures show: Fig. 1: Schematic representation of the device according to the invention for the evaporation of chemical substances in cross-section, in a side view, with a separately shown enlargement of a part of the device. Fig. 2: Schematic representation of the device according to the invention for the evaporation of chemical substances in a side view. Fig. 3: Schematic representation of the device according to the invention for the evaporation of chemical substances in cross-section, in a view from below (bottom = opposite the nozzles).

[0032] The Fig. 1, Fig. 2 to Fig. Figure 3 shows features of an embodiment of the invention in different views. For the sake of clarity, not all features are shown in all figures; this does not mean that they are not present, but merely that they are not shown in the respective figure, which is also due to the different views.

[0033] In the exemplary embodiment, as in the Fig. As can be seen from Figure 1, the steam distributor is designed as a linear source, with at least three nozzles (2) on a linear transport line (1, Fig. 1 and Fig. 3) of the steam distributor. For the sake of clarity, only one of the nozzles (2) is designated with the reference numeral “2”. In the transport line (1) ( Fig. 1 and Fig. 3) In the exemplary embodiment, a screw conveyor (11) is arranged. A belt conveyor (not shown separately) would also be possible according to the invention. A supply line for materials (10, Fig. 1 and Fig. 2), in this example designed in a funnel shape, opens into the transport line (1). The supply line (10) is temperature-controlled (not shown) and is connected to a vacuum in the receiver, which contains the device (not shown). Part of the outer wall of the receiver (13) is in the Fig. 1, Fig. 2 to Fig. Figure 3 shows that the outer wall of the receiver separates the inner area of ​​the receiver, which is evacuable and, by virtue of the vacuum prevailing during operation of the device, from the atmospheric pressure of the surroundings. The linear source (1) is supplied with material via a material feed (5) which includes a vacuum lock. The vacuum lock of the material feed (5) seals against the vacuum side via a lower gate valve (7), which can also be referred to as a shut-off valve. Above the feed line (10) is a temperature-controlled material reservoir (9), which is limited at the top by the upper gate valve (6) and at the bottom by the lower gate valve (7). With the upper gate valve (6) open and the lower gate valve (7) closed, fresh material can be drawn into the reservoir via the material feed (5) by means of a vacuum applied to a flange (8), which is created by the vacuum reservoir.The material can be automatically replenished via an external line at atmospheric pressure (not shown) through the material feed (5). When the upper gate valve (6) is closed and the lower gate valve (7) is opened, the material falls into the funnel-shaped feed line (10) and is thus available in the transport line (1). The material is then transported to the nozzles (2) via the screw conveyor (11), with a QCM (not shown) for rate measurement located directly above only one of the nozzles (2). In this embodiment, the nozzles (2) are heated by means of tungsten coils (3) as a heating element, although the transport line (1) has a lower temperature during operation of the device. For clarity, only one of the tungsten coils (3) is labeled with the reference numeral "3". Fig.Figure 1 shows the arrangement of the tungsten coils (3) on the nozzles (2), also in a magnified view. The tungsten coils (3) act as heaters in the device, vaporizing the material transported to them, particularly via, for example, a screw conveyor. Through a further closable opening (12) in the funnel-shaped feed line (10), the transport line (1) can be supplied with a transport gas (e.g., ammonia) at a constant flow rate, adjustable, for example, via a mass flow controller (not shown). Unused material exits the vaporizer via the outlet (4) as a material discharge and can be collected there for reuse or processing and thus reintroduced via the material feed (5).

[0034] The homogeneity of a vapor deposition process carried out with the device according to the invention is ensured by an optimized arrangement and number of nozzles. Simulations with a phyton-based computational model showed that, with the use of a device according to the invention for the vaporization of chemical substances, a homogeneity of better than 1% in the deposited layer can be achieved with a nozzle count of 13 or more, provided the substrate to be coated is transported perpendicular to its linear extent above the linearly designed evaporator (the linear source). This compares to 8% homogeneity of the same deposited material in currently commercially available systems using point sources and a rotating substrate. This is an advantage of this invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2010 046 389 A1

[0003]

Claims

[1] Device for evaporating materials, comprising at least one vapor distributor, comprising at least three nozzles and at least one evaporator, characterized by , that the steam distributor of the device is provided by a transport line with at least three nozzles arranged on the transport line and the evaporator is provided by the arrangement of at least one heater for the nozzles in the steam distributor and wherein a screw or belt conveyor is arranged in the transport line and the device includes a supply line for materials which leads into the transport line. [2] Device according to claim 1, characterized by that the transport line in the steam distributor is equipped with an outlet at the end opposite the supply line. [3] Device according to claim 1 or 2, characterized by that the number of nozzles is ≥ 13. [4] Device according to any one of the preceding claims, characterized bythat a screw conveyor is arranged in the transport line. [5] Device according to any one of the preceding claims, characterized by , that a vacuum lock for the introduction of material is arranged on the supply line for materials, wherein the vacuum lock can be subjected to negative pressure for the suction of material.

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