Energy-efficient vacuum lock with preheating function as part of a high-temperature process plant

Abstract

The present invention relates to a vacuum lock (2) for a high-temperature process plant (42), and to a high-temperature process plant in which a heating chamber (3) is connected downstream of the vacuum lock (2) for processing, wherein the vacuum lock (2) comprises: a heating device with a first heat transfer medium (5) in fluid form for heating the vacuum lock (2), a heat exchanger (20), and a first heat transfer medium circuit (8) for the first heat transfer medium (5) with a circulation of the heat transfer medium (5) from the heat exchanger (20) to the heating device of the vacuum lock (2) and back to the heat exchanger (20), wherein the heat exchanger (20) is configured to heat the first heat transfer medium (5) by means of a second heat transfer medium circuit (9) coupled to the heat exchanger (20).

Description

Field of invention The present invention relates to a vacuum lock with a preheating function, which can be used as part of a high-temperature process plant. In particular, the invention relates to a vacuum lock with a heating system that recycles energy from downstream hot devices. Furthermore, the present invention also relates to a method for recycling energy from hot devices in a high-temperature process plant to heat the vacuum lock. Background of the invention Large-area glass substrates (e.g., 1-3 m²), coated or uncoated, with or without a carrier, or several smaller substrates on a single carrier, are heated and processed uniformly at temperatures above 400°C in a high-temperature processing plant, often also referred to as a continuous flow or in-line plant. An in-line plant preferably comprises at least one vacuum lock-in and a subsequent heating chamber (also called the processing area). In particular, the vacuum lock preferably serves as: i) a separation function between the outside air with normal humidity (e.g., 40%–80%) and the water-free processing atmosphere or vacuum (≤ -40°C DP (Dew Point) or ≤ 128 ppm H₂O or ≤ 1.28 × 10⁻¹ mbar H₂O partial pressure); ii) a transfer function for substrates with absorbed water multilayers (chemisorption, physisorption, also with hydrocarbons from the air) or with residual water, e.g., after exposure to air or after water washing; and / oriii) as a separation function between the processing area, in which toxic materials with vapor pressures above 10-3mbar at temperatures above 400°C (e.g.: Se, Pbl2, PbCI2, PbBr2, Cd, CdI2, CdCI2, CdTe) are present, and the atmospheric environment of the plant. To ensure that the large-area substrates can be processed as cleanly as possible (e.g., without residual water) in the system, the vacuum lock should be able to pretreat these substrates as efficiently as possible, preferably within a short time interval (e.g., 3 min, 1 min, and preferably within 0.5 min), without negatively impacting the energy balance of the process system, with a residual water content <=1 ML (monolayer), and clean for the environment, and then transfer them into the process system. The processes involved in processing substrates in a large-scale plant for the mass production of layers / interlayers / boundary layers / surface layers in the nanometer range (e.g., semiconductor layers with thicknesses of 5-10 nm, 10-100 nm) or composition-sensitive layers (e.g., 1-10 µm thick with purity levels <100 ppm, <10 ppm, <1 ppm) should take place under a controlled atmosphere with a high degree of repeatability and precision. A disruptive factor is an undefined amount of residual water that arises from previous processes or absorption from the air and adheres to the surfaces. If this water is introduced directly into the process area on the substrate, it leads to undesirable reactions on / in the substrate surface and to contamination of the processing area.Depending on the extent of the disruptive effect of the resulting water content, the large-scale plant will be adapted accordingly in a technically complex manner. Document DE 199 13 802 C1 discloses the preheating of a substrate in a vacuum lock of a high-temperature process plant. Document DE 40 36 344 A1 discloses the use of a circulating thermostat with heat exchange. The currently available approaches are based on the following technical solutions: a) Vacuum locks are designed with a large chamber volume / substrate area ratio, equipped with high-vacuum or ultra-high-vacuum pumps (e.g., turbopumps), and utilize relatively long lock or pumping times from the system turnover side (e.g., 10, 30, or 60 minutes). b) The process chamber following the vacuum lock is equipped with separate, cooled, large surfaces (e.g., LN2 cryopumps, also with getter material) that freeze or incorporate the residual water. c) Vacuum locks are equipped with short-wave emitters that enable relatively rapid water desorption, e.g., removing water from the surface using light in the 190–200 nm range (UV light), for example, within <10 minutes (e.g., UVB-100 from rbd instruments).d) Substrates are dewatered early and transferred to the vacuum lock under dry air (DP < 40°C, < 60°C, < 80°C). e) In the vacuum lock, substrates are heated under vacuum to temperatures at which the water desorbs using heating devices (e.g., >100°C, >150°C, >200°C). However, these devices for heating the substrates and removing residual water from the substrates require additional energy. It is therefore an object of the present invention to provide a vacuum lock that simplifies and energy-efficiently pretreats substrates before they enter a subsequent process chamber. In particular, it is an object of the present invention to provide an energy-efficient vacuum lock for and within a process plant, with which any residual water on a substrate to be processed can be removed. Summary of the invention This problem is solved by the subject matter of the independent claims. Preferred features of the subject matter according to the invention are described in the dependent claims. Since the process plant heats the substrates for processing, the vacuum lock is equipped with a preheating function according to the invention. Preferably, the vacuum lock is designed such that substrates are preheated to higher temperatures as uniformly and efficiently as possible, at which the water is already largely desorbed and the substrate surface is not damaged. The vacuum lock or the chamber within the vacuum lock is preferably coated with materials that heat the substrates present therein by means of thermal radiation. Thus, the inside of the vacuum lock or vacuum chamber preferably has a material with an emissivity ε (epsilon) > 0.4, > 0.6, or > 0.8. For example, the inside or parts of the inside of the vacuum lock or vacuum chamber can be coated with such a material, where graphite, for instance, can be used as the coating material. For example, even a thin layer of graphite inside the vacuum chamber may be sufficient. Thus, the vacuum chamber preferably has the construction of an (ideal) blackbody, and the substrates present in this chamber are heated by radiation emanating from the chamber surface. Preferably, tolerances lie in the ranges of + / - 5°C, + / - 10°C, or + / - 20°C. The vacuum chamber is preferably surrounded uniformly from several sides, preferably all sides, by a fluid-like heat transfer medium, preferably a liquid heat transfer medium, so that the entire chamber can be heated to the desired temperature and preferably also kept substantially constant at the desired temperature. Preferably, the walls of the chamber include uniformly distributed channels, or channels are provided on the walls of the chamber, either inside or outside. The chamber can also be double-walled to accommodate the liquid heat transfer medium between the walls. A vacuum atmosphere preferably prevails inside the chamber, the atmosphere outside the chamber, and the heat transfer medium in between. A heat transfer oil, often also called thermal oil, is preferably used as the heat transfer medium. However, molten salts or liquid metals can also be used as heat transfer media. To heat the heat transfer fluid or thermal oil at a different location, it is preferred that at least one other chamber of the process plant be designed similarly to the vacuum chamber in that this chamber is also coupled with a liquid heat transfer fluid. This heat transfer fluid can be of the same or a different type. However, it is preferred that the heat transfer fluid coupled to the vacuum chamber (hereinafter also referred to as the first heat transfer fluid) does not mix with the heat transfer fluid (second heat transfer fluid) of the other chamber of the process plant. Preferably, the two heat transfer fluids are in separate circuits. The second heat transfer medium preferably absorbs energy in the form of heat from the other chamber of the process plant. For example, energy losses generated during heating in the process area downstream of the vacuum lock can be absorbed and, according to the invention, reused to heat the vacuum lock. According to the invention, heat from the other chamber can be transferred directly to the vacuum chamber, essentially as a single-circuit design. This has the advantage, for example, that only one circuit and one heat transfer medium are used. Alternatively, a dual-circuit design can also be implemented, in which case preferably two heat transfer media are used in separate circuits and the energy transfer from one heat transfer medium to the other takes place via a heat exchanger. For example, when using oil in both circuits, an oil-to-oil heat exchanger can be used to transfer the energy from one oil to the other. The substrates are preferably heated in the vacuum lock such that the water is largely desorbed from the substrate surface under vacuum (e.g., 0.1 mbar, 1 mbar, 10 mbar) within a short time (e.g., 60 s, 30 s, 10 s). The temperatures are preferably >100°C, >150°C. Since the entire lock chamber is preferably located at the same or slightly higher temperatures as the substrate temperature, the desorbed water will not remain in the vacuum lock and can preferably be pumped away using forevacuum pumps. This allows the chamber volume / substrate area ratio to be significantly reduced and thus optimized for fast pump-out times. It is also preferred that the water does not remain in the chamber. For example, a cryopump, as in case b) above, is dewatered by heating cycles during which processing is not possible. Since, according to the invention, water desorption preferably takes place in the vacuum lock, water desorption in upstream processes, including anhydrous transfer as in case d) above, is preferably no longer necessary. The uniform radiation from the inner surface of the vacuum chamber heats the substrates evenly, eliminating the need for a complex and bulky construction of heating devices within the chamber, including control of the heating cycles. Due to the design of the vacuum lock according to the invention, it does not become a cold trap or condensation trap. While the substrates are being introduced into the process area (with the connection between the process area and the lock chamber open), the vacuum lock remains clean or only minimally contaminated with the materials from the process area, whereby contamination is particularly critical with the aforementioned toxic materials. Uniform preheating facilitates the control of subsequent heating process steps, as the initial state of the process heating ramps remains clearly defined and is already at temperatures above 100°C, compared to, for example, a final process temperature of 550°C. The typical heat loss generated during the heating processes is typically in the range of 30-50% of the energy required for heating. Utilizing this wasted energy leads to more efficient energy use. Depending on the temperature range, energy savings can reach 2 to 5%, and even up to 10%. Although this may not seem like much at first glance, even these small values ​​can save thousands of kilowatts of electrical energy per year when energy consumption is in the megawatt range. Furthermore, the process control (including the heating phases of the entire system) and the temperature control using the inert heat transfer fluid are precise and easily monitored. The present invention relates to a vacuum lock for a high-temperature process plant, in which a heating chamber is connected downstream of the vacuum lock for processing. The vacuum lock preferably comprises: a heating device with a first heat transfer fluid for heating the vacuum lock, a heat exchanger, and a first heat transfer fluid circuit for the first heat transfer fluid, with the heat transfer fluid circulating from the heat exchanger to the heating device of the vacuum lock and back to the heat exchanger. Preferably, the heat exchanger is configured to heat the first heat transfer fluid by means of a second heat transfer fluid circuit coupled to the heat exchanger. Preferably, the heat exchanger is arranged outside the vacuum lock. The first heat transfer medium and / or a second heat transfer medium of the second heat transfer medium cycle can be a thermal oil or a molten salt, without being limited to that. Preferably, the heat exchanger has a heat source coupled to the first heat transfer fluid circuit and a heat sink coupled to the second heat transfer fluid circuit. It is also preferred that a membrane is present between the heat source and the heat sink, allowing heat to be transferred from the heat sink to the heat source, but preferably preventing fluid transfer between the two heat transfer fluid circuits. At least one pump can also be present in the first and / or second heat transfer fluid circuit to keep the fluid-like heat transfer fluid in circulation. Preferably, the vacuum lock has an inner surface with an epsilon > 0.4, so that a substrate located in the vacuum lock is heated by thermal radiation radiated from the inner surface. According to further preferred embodiments, the epsilon can be > 0.6, preferably > 0.7, preferably > 0.8, wherein the inner surface of the vacuum lock is preferably formed by a graphite layer. The heating device of the vacuum lock can be configured to heat the temperature in the vacuum lock to temperatures > 100°C, preferably > 150°C, so that water is desorbed from the surface of a substrate to be processed. At least one vacuum pump can also be in fluid connection with the vacuum lock to generate a pressure of less than 10 mbar, preferably less than 1 mbar and preferably less than 0.1 mbar in the vacuum lock. Preferably, the walls of the vacuum lock have distributed channels in which the first heat transfer medium can circulate to heat the vacuum lock, wherein the channels are preferably evenly distributed on, around and / or within the walls to heat the vacuum lock evenly. The present invention also relates to a high-temperature process plant with at least one vacuum lock according to the invention and at least one heating chamber connected to the vacuum lock and adjoining it in the process direction. The heating chamber may have a heating device or heat source for heating the heating chamber and for directing excess heat from the heating chamber to the heat exchanger. The temperature in the vacuum lock is preferably greater than 100°C to effectively desorb water on a substrate, and the temperature in the heating chamber is preferably greater than 300°C, preferably greater than 400°C. The present invention also relates to a method for heating a vacuum lock according to the invention, wherein waste heat from the heating chamber is preferably transferred to the first heat carrier by means of the second heat carrier and the heat exchanger and is transferred to the vacuum lock by means of the first heat carrier circuit. Furthermore, it is preferred that the vacuum lock is heated to temperatures > 100°C, preferably > 150°C, by means of the first heat transfer medium so that water is desorbed from the surface of a substrate to be processed. The heating chamber is heated to temperatures greater than 300°C, preferably greater than 400°C, by means of the second heat transfer medium in order to process the substrate, preferably to coat it. Brief description of the drawing A preferred embodiment of the present invention is described in more detail below with reference to the figure. Figure 1 shows a schematic representation of a process plant with a vacuum lock heated according to the invention. Detailed description of preferred embodiments Fig. 1 schematically shows an embodiment of a process plant 42 according to the invention, in which a substrate 1 is processed, e.g., coated. For this purpose, the substrate 1 passes through a vacuum lock 2 according to the invention, a subsequent heating chamber 3 in which the substrate is, for example, coated, and can then be further processed in a subsequent heating chamber 4. Since the subsequent heating chamber 4 is only optional, it is shown only with dashed lines. The illustrated process plant 42 is preferably part of a more complex process plant, i.e., any number of upstream or downstream processes can be carried out. In the illustrated embodiment, the vacuum lock 2 is heated using thermal oil as a heat transfer medium. The substrate 1 (or multiple substrates on a carrier or without a carrier) is first transferred into the vacuum lock 2 in step 15. After pump cycles or pump-purge cycles, the substrate 1 is transferred from the vacuum lock to the heating chamber 3 in step 16. Details of the pump-purge cycles are not explicitly shown. However, a person skilled in the art understands that, for example, a vacuum can be generated in the vacuum lock 2 by means of a backing pump and that the vacuum chamber in the vacuum lock can be filled, for example, with clean nitrogen with a DP < -60°C. In heating chamber 3, the substrate 1 is heated under a defined anhydrous atmosphere with / without process gas and with / without a coating process. Heating chamber 3 can, for example, be heated by means of a heating device 7 attached in / to the heating chamber 3. According to the invention, any type of heating device can be used, since, according to the invention, only the waste heat is reused and is therefore independent of the heating device. After heating in heating chamber 3, substrate 1 is transferred, for example, in step 17 to another chamber 4. This further chamber 4 can be, for example, another process chamber or an airlock chamber for other process steps within / outside the system. According to the invention, the vacuum lock 2 is surrounded by a first heat transfer medium 5, for example thermal oil, to transfer heat to the substrate 1. For example, the first heat transfer medium 5, in the form of thermal oil 5, is transported in a circuit from a heat source 12 to the vacuum lock 2 and then back again via an oil line 8 and a pump 10. The heat source 12 according to the invention is preferably part of an oil-to-oil heat exchanger 20, which, for example, comprises a heat source 12, a membrane 13, and a heat exchanger discharge point (heat sink) 14. The heating chamber 3, which is heated by the heating device 7, is preferably also surrounded by a second heat transfer medium. For example, thermal oil 6 can also be used for this second heat transfer medium. The waste heat generated during the heating process can be absorbed by this second heat transfer medium and transported to the oil-to-oil heat exchanger 20. For this purpose, the thermal oil 6 is circulated, for example, through an oil line 9 in a circuit 19 from the heating chamber 3 by means of a pump 11 to a heat exchanger discharge point 14 and then back to the heating chamber 3. The heat exchanger discharge point 14 is in turn part of the oil-to-oil heat exchanger 20. The two oil circuits 18 and 19 are separated from each other in the oil-to-oil heat exchanger 20 by a thermally conductive membrane 13, wherein the membrane 13 is thermally conductive but prevents the two oils from the two oil circuits from mixing.In particular, it is preferred that the two oil circuits 18 and 19 are controlled separately. For example, the pumps 10 and 11 in the first and second circuits can be controlled individually. If necessary, for example, if too much energy is lost or transferred from the heating chamber 3 to the second thermal oil of the oil circuit 19, i.e., if more energy is available than is required at the heat source 12, additional oil coolers can be provided in the oil circuit 19, for example in the form of oil-water coolers, to transfer energy to a cooling water of the oil-water cooler (not shown in Fig. 1). If too little waste heat is generated by the heating chamber 3, additional heaters can also be installed in the oil circuit 19 to ensure the energy required to heat the vacuum lock 2. The following are some examples of temperature values ​​and energies to show that the energy balance leads to the desired results in typical applications. However, a person skilled in the art understands that these values ​​are purely exemplary and that the present invention is not limited to these values. In the heating chamber 3, at a temperature of 400°C and an ε of 0.6, a power density of up to 11.6 kW / m² can be achieved. With losses of 40%, up to 4.65 kW / m² can be dissipated with the thermal oil 6. The power density of 4.65 kW / m² can be sufficient to heat the vacuum lock 2 with an ε of 0.6 up to 262°C. Thus, with a chamber area of ​​12 m² and a substrate area of ​​3 m², up to 55.8 kW would be available in the processing plant for heating the vacuum lock 2 with the substrates. At the preferred temperature of the lock of 150°C, for example 1.8 kW / m2 is required and thus the energy saving is 1.8 / 11.6 = 15.5%.• With a second 400°C heating chamber 4 (not shown in Fig. 1) in the process balance, the proportion of energy savings would be reduced accordingly and would amount to 7.75%. • The waste heat can also be utilized by the other process chamber(s). This can be achieved either by increasing the temperature of the vacuum lock 2, which is limited by the flash point of the heat transfer fluid thermal oil (e.g., 210°C for Perfecto HT5), or by using a second vacuum lock. This also enhances the effect of the separation functions (see i), ii), iii) in the introduction). In this description, the terms warming and heating are used synonymously; that is, heating should not be interpreted as referring to temperatures higher than warming. Furthermore, the terms vacuum lock and vacuum chamber are used almost synonymously, with the term vacuum lock being preferred when the lock function is paramount and the term vacuum chamber being preferred when the heating function or heat radiation emission is paramount. Reference symbol list: 1 Substrate 2 Vacuum lock or vacuum chamber 3 Heating chamber or process chamber, machining chamber 4 (Further) chamber / process chamber or lock chamber 5 First heat transfer medium (thermal oil) 6 Second heat transfer medium (thermal oil) 7 Heating device, e.g., heat source (crucible heat source for larger crucible) 8 First oil line 9 Second oil line 10 First feed pump 11 Second feed pump 12 Heat source 13 Membrane 14 Heat transfer, heat sink 15 Transfer to vacuum lock 16 Transfer to heating chamber 17 Transfer to (further) chamber 18 First heat transfer medium circuit 19 Second heat transfer medium circuit 20 Oil-to-oil heat exchanger 42 Process or processing plant

Claims

Vacuum lock (2) for a high-temperature process plant (42), in which a heating chamber (3) is connected downstream of the vacuum lock (2) for processing, wherein the vacuum lock (2) comprises: a heating device (7) with a first heat transfer medium (5) in fluid form for heating the vacuum lock (2), a heat exchanger (20), and a first heat transfer medium circuit (18) for the first heat transfer medium (5) with a circulation of the heat transfer medium (5) from the heat exchanger (20) to the heating device (7) of the vacuum lock (2) and back to the heat exchanger (20), wherein the heat exchanger (20) is configured to heat the first heat transfer medium (5) by means of a second heat transfer medium circuit (19) coupled to the heat exchanger (20). Vacuum lock according to claim 1, wherein the heat exchanger (20) is arranged outside the vacuum lock (2). Vacuum lock according to claim 1 or 2, wherein the first heat transfer medium (5) and / or a second heat transfer medium (6) of the second heat transfer medium circuit (19) is a thermal oil or a molten salt. Vacuum lock according to one of the preceding claims, wherein the heat exchanger (20) a. has a heat source (12) coupled to the first heat transfer circuit (18) and b. has a heat sink (14) coupled to the second heat transfer circuit (19), and c. preferably has a membrane (13) between the heat source (12) and the heat sink (14) such that heat can be transferred from the heat sink (14) to the heat source (12), but no fluid transfer takes place between the two heat transfer circuits (18, 19). Vacuum lock according to one of the preceding claims, wherein at least one first and / or one second feed pump (10, 11) is provided in the first and / or second heat transfer fluid circuit (18, 19) to keep the fluid-shaped heat transfer fluid (5, 6) in circulation. Vacuum lock according to one of the preceding claims, wherein the vacuum lock (2) has an inner surface with an epsilon > 0.4, such that a substrate (1) located in the vacuum lock (2) is heated by means of heat radiation emitted from the inner surface. Vacuum lock according to claim 6, wherein the epsilon is > 0.6, preferably > 0.8 and the inner surface of the vacuum lock (2) is preferably formed by a graphite layer. Vacuum lock according to one of the preceding claims, wherein the heating device (7) of the vacuum lock (2) is configured to heat the temperature in the vacuum lock (2) to temperatures > 100°C, preferably > 150°C, so that water is desorbed from the surface of a substrate (1) to be processed. Vacuum lock according to one of the preceding claims, wherein at least one vacuum pump is in fluid connection with the vacuum lock (2) to generate a pressure of less than 10 mbar, preferably less than 1 mbar and preferably less than 0.1 mbar in the vacuum lock (2). Vacuum lock according to one of the preceding claims, wherein walls of the vacuum lock (2) have distributed channels in which the first heat carrier (5) can circulate to heat the vacuum lock (2), wherein the channels are preferably distributed uniformly on, around and / or in the walls to heat the vacuum lock (2) uniformly. High-temperature process plant (42) with at least one vacuum lock (2) according to one of the preceding claims and at least one heating chamber (3) connected to the vacuum lock (2) in the process direction. High-temperature process plant according to claim 11, wherein the heating chamber (3) has a heating device (7) for heating the heating chamber (3) and excess heat is directed from the heating chamber (3) to the heat exchanger (20). High-temperature process plant according to claim 11 or 12, wherein the temperature in the vacuum lock (2) is greater than 100°C to desorb water on a substrate (1) and the temperature in the heating chamber (3) is preferably greater than 300°C, preferably greater than 400°C. Method for heating a vacuum lock (2) according to one of claims 1 to 10, wherein waste heat from the heating chamber (3) is transferred to the first heat carrier (5) by means of the second heat carrier (6) and the heat exchanger (20) and is transferred to the vacuum lock (2) by means of the first heat carrier circuit (18). Method according to claim 14, wherein the vacuum lock (2) is heated to temperatures > 100°C, preferably > 150°C, by means of the first heat transfer medium (5) so that water is desorbed from the surface of a substrate (1) to be processed. Method according to claim 14 or 15, wherein the heating chamber (3) is heated to temperatures greater than 300°C, preferably greater than 400°C, by means of the second heat transfer medium (6) in order to process the substrate (1), preferably to coat it.

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