Substrate heating method, substrate heater, and thermal laser deposition system

Abstract

The present invention relates to a method for heating a substrate 20, particularly a method for heating a substrate 20 in a thermal laser deposition (TLE) system 10. The present invention also relates to a substrate heater 30 for heating a substrate 20, particularly a substrate heater 30 for heating a substrate 20 in a TLE system 10. The substrate heater 30 includes a laser source 32 for providing a laser beam 34 and means for directing the laser beam 34 to the substrate 20. The present invention also relates to a TLE system 10 including a reaction chamber 12 that can be filled with a reaction atmosphere 14, a substrate 20 disposed within the reaction chamber 12, one or more sources 16 disposed within the reaction chamber 12, and a substrate heater 30 for providing a laser beam 34 that is irradiated onto the substrate 20, thereby heating the substrate 20.

Description

[Technical Field]

[0001] The present invention relates to a method for heating a substrate, in particular a method for heating a substrate in a thermal laser deposition (TLE) system. Furthermore, the present invention relates to a substrate heater for heating a substrate, in particular a substrate heater for heating a substrate in such a TLE system. The substrate heater comprises a laser source for providing a laser beam and means for directing the laser beam to the substrate. Furthermore, the present invention relates to a TLE system comprising a reaction chamber that can be filled with a reactive atmosphere, a substrate disposed in the reaction chamber, one or more sources disposed in the reaction chamber, and a substrate heater for providing a laser beam that is irradiated on the substrate and thereby heating the substrate. [Background technology]

[0002] In many modern applications, substrates are coated with materials evaporated or sublimated in a controlled environment, e.g., for electronic and / or optical components. These coatings are sometimes provided by TLE systems, but different evaporation and / or sublimation techniques are also possible, such as direct heating of the crucible containing the materials, electron beam heating, pulsed laser deposition (PLD), metal organic chemical vapor deposition (MOCVD), or molecular beam epitaxy (MBE).

[0003] In either case, it may be advantageous to additionally heat the substrate to be coated, which may improve the quality of the coating on said substrate, for example by increasing the mobility of the atoms and / or molecules deposited on the substrate surface.

[0004] One way to heat the substrate is to irradiate the material of the substrate with a laser beam produced by a laser source, which is at least partially absorbed by the material, such that the absorbed laser power heats the substrate.

[0005] However, it has been found that a particular laser beam suitable for heating a first substrate made of a first material is not automatically suitable for heating a second substrate made of a second, different material, and therefore simply providing any laser beam cannot guarantee that the substrate will be properly and sufficiently heated. Summary of the Invention [Problem to be solved by the invention]

[0006] In light of the above, it is an object of the present invention to provide an improved method for heating a substrate, an improved substrate heater, and an improved thermal laser deposition system that do not have the above-mentioned drawbacks of the prior art. In particular, it is an object of the present invention to provide an improved method for heating a substrate, an improved substrate heater, and an improved thermal laser deposition system that achieves simple and effective heating for a specific substrate, and that is particularly adapted to the material of each substrate.

[0007] The object of the present invention is achieved by the respective independent claims. In particular, the object of the present invention is achieved by a method for heating a substrate according to independent claim 1, a substrate heater according to independent claim 29, and a thermal laser deposition system according to independent claim 30. The dependent claims describe preferred embodiments of the invention. Details and advantages explained for the method according to the first aspect of the invention also apply, where technically meaningful, to the substrate heater according to the second aspect of the invention and the thermal laser deposition system according to the third aspect of the invention, and vice versa. [Means for solving the problem]

[0008] According to a first aspect of the invention, the object of the invention is a method for heating a substrate, in particular a method for heating a substrate in a thermal laser deposition (TLE) system, comprising: a) determining an absorption coefficient of electromagnetic waves in a base material of the substrate within a predetermined wavelength range; b) identifying an absorption band within the predetermined wavelength range, the absorption band including a wavelength range having a lower limit on the short wavelength side and an upper limit on the long wavelength side with respect to the wavelength of the electromagnetic wave to be absorbed; c) selecting a laser source that provides a laser beam, said laser beam having a laser wavelength that is within the absorption band identified in step b); d) driving the laser light source selected in step c) to heat the substrate; This is achieved by a heating method including:

[0009] The method according to the invention heats a substrate, particularly a substrate to be coated with a material to be evaporated and / or sublimated. Substrate in the context of the invention therefore particularly includes the base material, but also any material layers subsequently deposited during use in any evaporation and / or sublimation system.

[0010] In principle, the present method can be used to heat a substrate regardless of the coating method actually employed. However, TLE systems are the preferred apparatus for providing evaporated and / or sublimated materials due to the particularly wide range of usable raw materials and the high variability in flow densities of the evaporated and / or sublimated materials. At the same time, the TLE systems also allow the use of a variety of different reaction atmospheres, which also allows the deposition of reaction products between the evaporated and / or sublimated materials and elements of the reaction atmosphere.

[0011] To ensure high-quality deposition of different materials and / or reaction products, e.g., taking into account crystalline defects in the deposited layers, substrates made of suitable materials, often with complex surface treatments, are used, said materials differing in particular in their internal structure and / or composition.

[0012] On the other hand, laser beams are a well-established tool suitable for heating objects. In particular, in the TLE systems mentioned above, laser beams are used not only for heating but also for evaporation and / or sublimation of materials. However, a particular characteristic of laser beams is that they provide a narrow wavelength band, ideally only a single wavelength.

[0013] The narrow wavelength band of laser beams, combined with the wide variety of materials used for substrates to be coated, creates the problem that the substrate material may not be suitable for heating by a given laser beam. For example, the substrate material may be substantially transparent to the wavelength of a given laser beam, so that the laser beam passes through the substrate with little absorption. However, the method according to the first aspect of the present invention provides a process for solving this problem.

[0014] In a first step a) of the method according to the invention, the absorption coefficient of the base material of the substrate to be heated is determined within a given wavelength range. The base material is the material of the part of the substrate that is irradiated when heated by the laser beam. The absorption coefficient is a material property that is particularly important for the heating ability of the irradiating laser beam, and a high absorption coefficient at a certain wavelength means that the material absorbs electromagnetic radiation at that particular wavelength and heats efficiently. On the other hand, a low absorption coefficient relates to the wavelength of the electromagnetic radiation that the material of the substrate transmits, or at least substantially transmits, through the material.

[0015] By predetermining the wavelength range to be investigated, the effort required for this determination is limited, since the narrower the predetermining range selected, the less effort is required. The size of the range is preferably selected based on the wavelengths that can be provided by available laser sources. The determination of the absorption coefficient in the present invention may, for example, be provided as an actual measurement of the absorption coefficient, but may also use already available absorption coefficient data.

[0016] In summary, after step a) is performed, it is clear how the absorption coefficient depends on the wavelength of the irradiating electromagnetic radiation in the predetermined wavelength range under investigation. This makes it possible to identify an absorption band within the predetermined wavelength range in the next step b) of the method according to the present invention. An absorption band is a subregion within the predetermined wavelength range. In this subregion, the absorption coefficient is high, in particular significantly higher than in adjacent regions within the wavelength range under investigation. In other words, the substrate base material exhibits a significantly higher absorption rate for electromagnetic radiation with wavelengths longer than the lower limit on the short wavelength side and shorter than the upper limit on the long wavelength side than for electromagnetic radiation outside the absorption band. Therefore, the substrate base material is substantially transparent to electromagnetic radiation with wavelengths outside the absorption band, especially when reflections at the surface of the material are not taken into account.

[0017] The absorption characteristics of the substrate are taken into account by selecting a laser source that provides a laser beam with a wavelength within the absorption band identified in step b). The laser source is specifically selected so that its laser beam is absorbed by the substrate, and this is ensured by the laser wavelength being within the absorption band. However, absorbing electromagnetic waves always means that electromagnetic energy is deposited in each of the substrate's layers. This allows for effective heating of the substrate's layers.

[0018] In the final step d) of the method according to the invention, the substrate base is actually heated. A laser light source is driven, which generates a laser beam having a laser wavelength within the absorption band. The substrate is heated by irradiating the substrate with the laser beam, i.e., by allowing the laser beam to irradiate the surface of the substrate base. For this irradiation, it is preferable to provide appropriately selected means, including optical elements such as lenses, apertures, mirrors, optical waveguides, etc.

[0019] In summary, by carrying out the method according to the first aspect of the present invention, a substrate, in particular a substrate to be coated, can be effectively heated by an irradiating laser beam with evaporated and / or sublimated material. In particular, the method according to the present invention includes the step of actively selecting a laser source according to the absorption characteristics of the base material of the substrate.

[0020] Furthermore, the method according to the present invention is characterized in that the predetermined wavelength range used in step a) is 0.1 μm to 100 μm, particularly 0.2 μm to 20 μm. The electromagnetic spectrum is virtually infinite. However, the absorption bands of materials commonly used as substrate base materials and the wavelengths of laser light sources that can be practically used in most cases are located in the ultraviolet (UV), visible light, and / or infrared (IR) regions of the electromagnetic spectrum. Therefore, when determining the absorption coefficient in step a) of the method according to the present invention, limiting the predetermined wavelength range to 0.1 μm to 100 μm, particularly 0.2 μm to 20 μm, can reduce the effort required for the determination without risking missing information.

[0021] Furthermore, the method of the present invention may be configured such that the absorption band identified in step b) is associated with lattice vibrations within the substrate's matrix. This particularly includes cases where the absorption band identified in step b) is substantially a lattice absorption band. Generally, the absorption of electromagnetic waves by a material can be caused by several mechanisms. For example, the collective electron system of a metal can absorb electromagnetic waves, or individual atoms of a material can also absorb electromagnetic waves. However, the lattice itself, which is made up of multiple atoms, can also absorb electromagnetic waves and thereby undergo vibrational motions, known as lattice vibrations or phonons. As mentioned above, such lattice vibrations are often induced by the absorption of electromagnetic waves in the infrared region, which is the wavelength range accessible by powerful laser light sources. Furthermore, lattice vibrations are not limited to a single atom but extend throughout the entire lattice, i.e., the entire substrate. This allows for particularly uniform heating of the substrate.

[0022] According to another embodiment of the method of the present invention, in step c), the laser light source is selected so that the laser wavelength is located within the upper 25% and preferably within the upper 10% of the upper limit of the long-wavelength side of the wavelength range. It has been found that the actual location of the wavelength range of an absorption band in the electromagnetic spectrum often shifts toward longer wavelengths depending on the temperature of the substrate. However, since the primary objective of the present invention is to heat the substrate, the temperature will increase, at least at the beginning of the method of the present invention. By selecting a laser light source so that the laser wavelength is located within the upper 25% and preferably within the upper 10% of the upper limit of the long-wavelength side of the wavelength range, the heating laser wavelength is kept within the absorption band, taking into account the shift in the wavelength range of the absorption band, thereby effectively heating the substrate regardless of the actual temperature of the substrate. Furthermore, this allows a continuous, wide range of the absorption band to remain available for temperature measurement.

[0023] The method according to the present invention is further characterized in that, when heating the substrate in step d), the temperature of the substrate is measured by a temperature sensor. As mentioned above, in some applications, particularly in deposition reactions of evaporated and / or sublimated materials on the substrate, the substrate needs to be at a constant temperature. Actively measuring the temperature of the substrate using a temperature sensor can provide appropriate feedback regarding the actual temperature of the substrate, thereby improving the accuracy of heating the substrate base material.

[0024] Furthermore, the method according to the present invention can be improved by using a pyrometer as the temperature sensor. A pyrometer is a non-contact sensor that measures the temperature of the element to be measured by measuring the light emitted by it. This allows the pyrometer to be located outside the reaction chamber, particularly if the element to be measured is within the pyrometer's view. Therefore, a pyrometer is a preferred temperature sensor, since it avoids the influence of the temperature measurement on other reactions, particularly the deposition reaction.

[0025] For further refinement, the method according to the present invention may be configured such that the pyrometer is sensitive to a wavelength and / or wavelength range different from the laser wavelength, preferably further away. In a practical embodiment, the laser beam of the laser source for heating the base material of the substrate is directed onto the same surface of the substrate that the pyrometer investigates for temperature measurement. By selecting a pyrometer sensitive to a wavelength and / or wavelength range different from the laser wavelength, it is possible to prevent the pyrometer from accidentally measuring a reflected portion of the laser beam, which could adversely affect the temperature measurement. Increasing the distance between the sensitivity range of the pyrometer and the laser wavelength further enhances the above advantages.

[0026] The method of the present invention can be further improved by selecting a pyrometer sensitive to wavelengths and / or wavelength regions within the wavelength range of the wavelength band identified in step b), particularly covering at least 30%, preferably at least 60%, and more preferably at least 90% of the wavelength range of the absorption band. The ability of a material to emit electromagnetic radiation at a specific wavelength, particularly its temperature-related radiation measured by a pyrometer, is strongly related to its absorption coefficient at that wavelength. In particular, in wavelength regions where the material is substantially transparent, the intensity of the radiation is expected to be low or even vanishingly low. Meanwhile, at wavelengths within the absorption band, the radiation exhibits high or maximum intensity. Therefore, the accuracy of the temperature measurement can be improved by selecting a pyrometer sensitive to wavelengths and / or wavelength regions within the wavelength range of the wavelength band. Setting the sensitivity of the pyrometer to a portion of the absorption band that covers as much of the wavelength range of the absorption band as possible, excluding the boundary most susceptible to thermal wavelength shifts, can make the temperature measurement robust against the above-mentioned heating-induced shift of the absorption band. The wider the wavelength range used for temperature measurement, the higher the integrated intensity of thermal radiation that the temperature sensor, preferably a pyrometer, can measure. This results in a strong signal, resulting in a high signal-to-noise ratio and enabling precise temperature measurement and temperature control. The sensitivity range of the pyrometer is preferably different from the laser wavelength of the laser beam and covers as wide as possible the absorption bands that are not used by the laser beam for heating the substrate.

[0027] To combine the advantages described above, it is preferable to select a laser source whose laser wavelength is within the upper 25%, preferably within the upper 10%, of the upper limit of the long-wavelength side of the wavelength range, and further, to select a pyrometer whose sensitivity covers most, preferably all, of the continuous wavelength range of the absorption band limited at the long-wavelength end by the laser wavelength. This maximizes the sensitivity range of the pyrometer while avoiding interference between the laser beam and the temperature measurement by the pyrometer. For example, in the case of silicon, for which a CO2 laser with a laser wavelength of approximately 10 μm is suitable, it is preferable to select a pyrometer whose sensitivity is between 7 and 9 μm as the substrate, and in the case of diamond, for which a CO2 laser with a laser wavelength of approximately 5.5 μm is suitable, it is preferable to select a pyrometer whose sensitivity is between 3 and 5 μm as the substrate.

[0028] According to another improved embodiment of the method according to the invention, the temperature of the substrate measured in step d) is used to control the operation of the laser light source in step d), in particular as an input for a closed-loop control of the operation of the laser light source. In many, but not almost all, applications of heated substrates, the temperature of the substrate is essential for the quality of the product, and keeping the temperature constant or a temperature with a constant time dependency is possible and / or required. The temperature information provided by the temperature measurement can be used to provide the basis for appropriately controlling the laser light source accordingly. In particular, the temperature information can be used as an input for an automatic closed-loop control of the operation of the laser light source.

[0029] Furthermore, the method according to the present invention may be configured so that the laser beam provided by the light source selected in step c) has a maximum power of at least 250 W, in particular at least 10 kW, and preferably at least 1 MW. The total power of the laser source is the main limiting factor for the size of the substrate that can be heated by carrying out the method according to the present invention. For example, an output power of 250 W can be applied to a substrate of 5 x 5 mm. 2This is sufficient to heat a diamond substrate of 1000°C to approximately 2000°C. However, a circular silicon substrate with a diameter of 300 mm, which is one of the industrial standards in use, has an area that is approximately 2.827 times larger. Since the power required for heating is roughly proportional to the area of ​​the substrate, when large-area heating and / or high-temperature heating is required, laser powers on the order of 1 MW are required. Examples of substrate materials that can be heated to temperatures of 2000°C or higher without reaching their melting point include SiC and Al2O3, among others.

[0030] Furthermore, the method according to the invention is characterized in that in step d) the substrate is heated to a temperature of 250°C or more, in particular to a temperature of 2000°C or more. As mentioned above, efficient heating of the substrate is the main objective of the method according to the invention. Thus, in some applications, a temperature of 250°C is sufficient. However, it is preferable to provide heating that can heat each substrate to a higher temperature, in particular to at least 2000°C. This is because in this case heating to lower temperatures can be easily achieved by simply reducing the power of each laser source.

[0031] In this context, the greatest advantage of laser heating sources is that the laser beam can be focused and concentrated to any degree, which allows very high power densities to be applied and, consequently, extremely high temperatures to be achieved.

[0032] According to another embodiment of the method of the present invention, in step d), the substrate is heated so that the wavelength of the maximum of the blackbody radiation corresponding to the heating temperature is located outside the absorption band identified in step b), preferably away from the absorption band, in the wavelength range substantially transparent to the substrate. As described above, in the wavelength range substantially transparent to the substrate, the intensity of the radiation related to the temperature of the substrate is expected to be low or almost disappear. The radiation related to the temperature corresponds to the blackbody radiation when each substrate is in thermal equilibrium with the surroundings. Therefore, by appropriately selecting the target temperature of the substrate, it is possible to achieve very high heating efficiency by selecting a laser beam having a wavelength within the absorption band, while minimizing radiation loss due to blackbody radiation by selecting a temperature at each wavelength corresponding to the maximum of the blackbody radiation, at which the radiation is blocked by the transparency of the substrate.

[0033] The method according to the present invention can be further improved by ensuring that the wavelength of the blackbody radiation maximum is lower than, and preferably far from, the lower short-wave limit of the absorption band identified in step b). As mentioned above, an increase in the temperature of the substrate often shifts the absorption band towards higher wavelengths. Conversely, an increase in the temperature of each substrate shifts the wavelength of the blackbody radiation maximum towards lower wavelengths. Therefore, by selecting the temperature of the heated substrate such that the wavelength of the corresponding blackbody radiation maximum is lower than, and preferably far from, the lower short-wave limit of the absorption band, the relative positions of the radiation wavelength and the absorption wavelength range can be maintained even after the wavelength shift due to heating of the substrate.

[0034] Furthermore, the method of the present invention may be configured so that the base material of the substrate heated by the laser serves as a backing for a different second material of the substrate. Not all materials to be coated can be used as the base material in the present invention; for example, a suitable laser source may not be available for the absorption band of each material. However, by providing a substrate including both the material to be coated as the second material and a suitable base material as a backing that can be heated by carrying out the method of the present invention, these second materials can also be effectively heated by carrying out the method of the present invention. An appropriately selected laser beam is irradiated onto the backing made of the base material, and the backing is effectively heated. The heating of the backing is transferred to the second material by contact heating due to thermal conduction.

[0035] In the following, exemplary embodiments of the method according to the invention are described for the explicit combination of substrates and laser sources for heating them. In this respect, a substrate "comprising" a particular material means that it may also comprise other materials, for example, the substrate may be doped with other materials and / or form part of an alloy.

[0036] According to a first exemplary embodiment of the method according to the invention, the base material of the substrate is based on diamond and / or diamond-like carbon, and the laser light source selected in step c) is a CO laser providing a laser beam with a laser wavelength of approximately 5.5 μm. Diamond and diamond-like carbon have a wide absorption band from approximately 2.5 μm to 6 μm. Therefore, a CO laser providing a laser beam with a laser wavelength of approximately 5.5 μm is particularly suitable for heating such a diamond substrate according to the invention.

[0037] The method according to the invention can be further improved in that the base material of the substrate consists of diamond and / or diamond-like carbon, which makes it possible to provide a substrate of particularly high purity.

[0038] According to a second exemplary embodiment of the method according to the invention, the base material of the substrate is based on SiC, and the laser light source selected in step c) is a CO laser providing a laser beam with a laser wavelength of approximately 9.3 μm. SiC has a wide absorption band, the upper limit of which is approximately 10 μm on the long wavelength side. Therefore, a CO laser providing a laser beam with a laser wavelength of approximately 9.3 μm is particularly suitable for heating such SiC substrates according to the invention. This is because the laser wavelength is close to the upper limit of the long wavelength side of the absorption band wavelength range, and therefore, a shift in the absorption band wavelength range due to heating of the respective substrate does not affect the heating.

[0039] According to a third exemplary embodiment of the method of the present invention, the base material of the substrate is based on SiC, and the laser light source selected in step c) is a CO laser providing a laser beam with a laser wavelength of approximately 5.5 μm. As described above, SiC has a wide absorption band, the upper limit of which is approximately 10 μm on the long-wavelength side. Therefore, a CO laser providing a laser beam with a laser wavelength of approximately 5.5 μm is particularly suitable for heating the SiC substrate of the present invention. Furthermore, when SiC is heated to a high temperature, Si evaporates and is deposited in the reaction chamber, for example, on the entrance window of the laser beam that heats the substrate. Because a pure Si layer is almost transparent to electromagnetic waves with a wavelength of approximately 5 μm, when a substrate is heated using a CO laser providing a laser beam with a laser wavelength of approximately 5.5 μm, the deposition has no or only a negligible effect on the heating of the substrate.

[0040] The method according to the invention can be further improved in that the base material of the substrate consists of SiC, which makes it possible to provide a particularly pure substrate.

[0041] According to a fourth exemplary embodiment of the method according to the invention, the base material of the substrate is based on oxide and / or Si, and the laser light source selected in step c) is a CO laser providing a laser beam with a laser wavelength of about 9.3 μm and / or 10.2 μm and / or 10.6 μm. Many, if not most, oxides and Si used as substrates for deposition have a wide absorption band around 10 μm. Therefore, a CO laser providing a laser beam with a laser wavelength of about 9.3 μm and / or 10.2 μm and / or 10.6 μm is particularly suitable for heating such oxide and / or Si substrates according to the invention.

[0042] The method according to the invention can be further improved in that the base material of the substrate consists of the oxide or Si, thereby providing a substrate of particularly high purity.

[0043] Furthermore, according to another improved embodiment, the method according to the invention is characterized in that the oxide is Al2O3, SrTiO3, LaAlO3, NdGaO3, DyScO3, MgO, GdScO3, Gd3Ga5O 12 , LiAlO3, LiAlO2, LiGaO2, LiNbO3, LiTaO3, TbScO3, MgAl2O4, SrLaAlO4, SrLaGaO4, YAlO3, YSC, LSAT, ZnO, SiO2, or Ga2O3. This list is not exhaustive and can be expanded with further examples of oxides used as the base material of the substrate.

[0044] According to a fifth exemplary embodiment of the method according to the invention, the base material of the substrate is nitride-based, and the laser light source selected in step c) is a CO laser providing a laser beam with a laser wavelength of about 9.3 μm and / or 10.2 μm and / or 10.6 μm. Furthermore, many, if not most, nitrides used as substrates for deposition have a wide absorption band around 10 μm. Therefore, CO lasers providing a laser beam with a laser wavelength of about 9.3 μm and / or 10.2 μm and / or 10.6 μm are particularly suitable for heating such nitride substrates according to the invention.

[0045] The method according to the invention can be further improved in that the base material of the substrate consists of the nitride, which makes it possible to provide a particularly pure substrate.

[0046] Furthermore, according to another refinement, the method according to the invention may be configured so that said nitride is GaN or AlN, this list is not exhaustive and can be extended with further examples of nitrides used as the base material of the substrate.

[0047] According to a sixth exemplary embodiment of the method according to the present invention, the base material of the substrate is based on a halide, and the laser light source selected in step c) is a CO laser providing a laser beam with a laser wavelength of about 9.3 μm and / or 10.2 μm and / or 10.6 μm. Furthermore, many, if not most, halides used as base materials have a wide absorption band around 10 μm. Therefore, a CO laser providing a laser beam with a laser wavelength of about 9.3 μm and / or 10.2 μm and / or 10.6 μm is particularly suitable for heating such halide substrates according to the present invention.

[0048] The method according to the invention can be further improved in that the substrate base material consists of a halide, which makes it possible to provide a substrate of particularly high purity.

[0049] Furthermore, according to another improved embodiment, the method according to the invention may be configured in such a way that the halide is BaF2, CaF2, KBr, KCl, NaCl or Mg2F2, this list is not exhaustive and can be extended with further examples of halides used as the basis for the substrate.

[0050] According to a second aspect of the present invention, the objects of the present invention are achieved by a substrate heater for heating a substrate, in particular a substrate heater for heating a substrate in a thermal laser deposition (TLE) system, comprising a laser source for providing a laser beam and means for directing said laser beam to said substrate, wherein the laser source of said substrate heater is selected in accordance with steps a) to c) of the method according to the first aspect of the present invention, and wherein the substrate heater is configured to perform step d) of the method according to the first aspect of the present invention.

[0051] In particular, the substrate heater can effectively heat each substrate by selecting the laser light source to be used depending on the base material of the substrate to be heated. This is achieved by carrying out the method according to the first aspect of the present invention when preparing and using the substrate heater according to the second aspect of the present invention. As a result, the substrate heater according to the second aspect of the present invention has all of the advantages already described for the method according to the first aspect of the present invention.

[0052] According to a third aspect of the present invention, the objects of the present invention are achieved by a thermal laser deposition (TLE) system comprising a reaction chamber fillable with a reaction atmosphere, a substrate disposed in the reaction chamber, one or more sources disposed in the reaction chamber, and a substrate heater for providing a laser beam that is irradiated onto the substrate and thereby heating the substrate, the substrate heater being configured according to the second aspect of the present invention. The substrate heater according to the second aspect of the present invention implements the method according to the first aspect of the present invention. In summary, the TLE system according to the third aspect of the present invention has all the advantages already described for the method according to the first aspect of the present invention and the substrate heater according to the second aspect of the present invention.

[0053] In the TLE system according to the present invention, a laser beam is used to evaporate or sublimate the raw material and heat the substrate material, respectively. Such TLE systems are generally known. The raw material evaporated and / or sublimated by the irradiated source laser beam is deposited on a substrate provided as a target. A substrate heater according to the second aspect of the present invention, which is used to carry out the method according to the first aspect of the present invention, is used to heat the base material of the substrate.

[0054] The raw materials are provided as source elements arranged in a source within the reaction chamber, where one or more sources can be arranged, and which can provide the same and / or different raw materials. A source laser beam is directed onto a surface (most often the top surface) of the source element, causing the evaporated or sublimated raw materials to flow.

[0055] The source and substrate are placed in a reaction chamber that can be sealed against the surrounding atmosphere and filled with a reaction atmosphere. The reaction atmosphere can be under vacuum conditions (particularly 10 -12 hPa or less), or may contain a reactive gas under a pressure appropriate for the material to be deposited, for example, oxygen to deposit the oxide of the sublimated raw material. In tests at a working distance of 60 mm, the maximum value observed to date is 10 -2 hPa. 10 -2 Since deposition was performed without problems at 1000 kPa, it is believed that higher values ​​are also achievable.

[0056] The present invention will be described in detail below based on embodiments and with reference to the drawings. In particular, the drawings are as follows: [Brief explanation of the drawings]

[0057] [Figure 1] 1 is a schematic diagram of a TLE system according to the present invention; [Figure 2] 1 is a schematic diagram of a method according to the present invention; [Figure 3]1 shows the transmission spectrum of diamond. [Figure 4] The reflectance spectrum of SiC is shown. [Figure 5] The transmission spectra of two types of Si are shown. [Figure 6] 1 shows the absorption spectra of diamond at different temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0058] 1 shows a schematic diagram of a TLE system 10 according to the present invention, including its most basic elements. Within a reaction chamber 12 filled with a reaction atmosphere 14, a source 16 provides one or more raw materials to be evaporated and / or sublimated. A source laser beam 18 is directed at the source 16 to evaporate and / or sublimate each material in the source 16. Materials evaporated and / or sublimated from the source 16 are indicated by arrows originating from the source 16.

[0059] Additionally, a substrate 20 to be coated is placed in the reaction chamber 14. In the illustrated embodiment of the TLE system 10, the substrate 20 includes a second material 26 for the actual deposition disposed on a support 24 made of a base material 22, and can be heated particularly effectively by a dedicated substrate heater 30 according to the present invention.

[0060] The substrate heater 30 comprises a laser source 32 which is selected by implementing a method according to the invention, which is shown schematically in Figure 2 and described below.

[0061] In a first step a)A of the method, the absorption coefficient of the base material 22 of the substrate 20 to be heated is determined. To reduce the effort, the absorption coefficient is determined in a predetermined wavelength range, for example from 0.1 μm to 100 μm, in particular from 0.2 μm to 20 μm. This indicates how the base material 22 reacts to irradiating electromagnetic radiation of different wavelengths, i.e., whether or how effectively it absorbs said radiation, or whether the base material 22 is more transparent or opaque to said radiation, so that it passes through the base material 22 substantially unaffected.

[0062] The information provided in step a)A makes it possible to identify, in the subsequent step b)B, an absorption band 50, i.e., a wavelength range in which the absorption coefficient increases, starting from a lower limit 52 on the short wavelength side and extending continuously to an upper limit 54 on the long wavelength side. Such an absorption band 50 is therefore a wavelength range particularly suitable for heating by appropriately applied electromagnetic waves. If the absorption band 50 is associated with lattice vibrations in the substrate 22, efficient heating of the substrate 20 can be achieved.

[0063] Therefore, in the next step c)C of the method according to the present invention, the laser source 32 of the substrate heater 30 is selected based on the information provided in the previous steps a)A and b)B. That is, the laser source 32 is selected so that the laser wavelength 36 of the laser beam 34 provided by the laser source 32 is within the specified absorption band 50, in particular within the upper 25%, preferably within the upper 10%, of the upper limit 54 on the long wavelength side of the wavelength range of the absorption band 50. This improves, preferably maximizes, the absorption of the laser beam 34 by the substrate 22 of the substrate 20, enabling effective heating of the substrate 20.

[0064] In the final step d)D of the method according to the invention, the actual heating of the substrate 20, in particular the actual heating of the substrate 22 of the substrate 20, takes place. The laser source 30 is activated and a laser beam 34 is directed at the substrate 22, which is thereby heated. The laser source 32 preferably provides the laser beam 34 with a maximum power of at least 250 W, in particular at least 10 kW, and preferably at least 1 MW. In the embodiment shown in Figure 1, the substrate 22 forms the support material 24, and therefore the second material 26 of the substrate 20, which is actually used for the evaporation of the source 16 and / or the deposition of the sublimated material, is indirectly heated by physical contact with the substrate 22.

[0065] In step d)D, the substrate 20 may be heated to 250° C., preferably to 2000° C. or higher. Additionally or alternatively, the substrate 20 may be heated to a temperature at which the wavelength of the blackbody radiation maximum corresponding to the heating temperature is outside the absorption band 50, in particular away from the absorption band 50, and / or lower, i.e., shorter than the absorption band 50. In particular, the blackbody radiation maximum is preferably in a wavelength range that is substantially transparent to the base material 22 of the substrate 20 to suppress radiative cooling of the substrate.

[0066] 1 also shows a pyrometer 40 for measuring the temperature of the substrate 20, in particular the substrate 22. The pyrometer 40 may be provided as part of the substrate heater 30 or as an additional element of the TLE system 10. Basically, the pyrometer 40 is already a preferred embodiment, but any suitable sensor for measuring said temperature may be implemented. In a further preferred embodiment, the pyrometer is positioned on the optical axis of the heating laser via a beam splitter and collects the intensity from the entire back surface of the substrate irradiated by the heating laser.

[0067] To prevent the laser beam 34 from directly impinging on the pyrometer 40, the pyrometer can be selected to be sensitive to a different wavelength and / or wavelength range than the laser wavelength 36, preferably to a wavelength range further away. Additionally or alternatively, the pyrometer 40 can be selected to be sensitive to a wavelength and / or wavelength range covering at least 30%, preferably at least 60%, and more preferably at least 90% of the wavelength range of the absorption band 50, since the substrate 22 emits thermal radiation in this wavelength range.

[0068] Additionally, the measured temperature can be used as an input to control the operation of the laser source 32. In particular, closed-loop control over the operation of the laser source 32 can be provided.

[0069] Figures 3 and 5 show transmission spectra, and Figure 4 shows reflection spectra for candidate substrates 22: diamond (Figure 3), SiC (Figure 4), and Si (Figure 5). In the case of Si, spectra are shown corresponding to p-type Si (solid line) and n-type Si (dashed line), respectively. The low values ​​of transmission coefficient and similarly low values ​​of reflection coefficient shown correspond to an increased absorption coefficient, and therefore these spectra can also be interpreted as a representation of the absorption coefficient.

[0070] FIG. 3 shows the transmission spectrum of diamond. Diamond is a candidate substrate 22 for the substrate 20 in the TLE system 10. The absorption band 50 of diamond identified in the practice of the method of the present invention extends from a lower limit 52 on the short wavelength side near 3.5 μm to an upper limit 54 on the long wavelength side near 7.5 μm. Furthermore, the laser wavelength 36 of a CO laser is approximately 5.5 μm, clearly located within the absorption band 50. Therefore, a CO laser is a laser light source 32 that can be selected when the method of the present invention is practiced on a substrate 20 whose substrate 22 is made of diamond or a substrate 20 made of diamond. In particular, the laser wavelength 36 of the CO laser is located within the upper 25% of the upper limit 54 on the long wavelength side of the wavelength range of the absorption band 50. Considering the characteristic that the absorption band 50 shifts to the long wavelength side as the temperature of the heated substrate 22 increases (see FIGS. 1 and 6), this is particularly preferable.

[0071] FIG. 4 shows a cutaway view of the reflectance spectrum of SiC. SiC is also a candidate substrate 22, particularly for the substrate 20 in the TLE system 10. As can be seen, the reflectance of this substrate 22 is very high, particularly in the range from about 10 μm to 13 μm, where it exhibits near-perfect reflectance. Adjacent to this wavelength range of high reflectance are two absorption bands 50, one of which terminates at a long-wavelength upper limit 54 near 10 μm and the other of which begins at a short-wavelength lower limit 52 near 13 μm.

[0072] 4, the laser wavelength 36 of the laser beam 34 of the laser source 32 that can be selected in the method of the present invention is shown, and it is clearly located within the absorption band 50. However, in the example shown in FIG. 4, a CO laser has a laser wavelength of about 9.3 μm. Therefore, a CO laser is a laser source 32 that can be selected when the base material 22 is made of SiC or when the method of the present invention is performed on a substrate 20 made of SiC.

[0073] In particular, laser wavelength 36 of the CO laser is located within the upper 25% of upper limit 54 on the long-wavelength side of the wavelength range of absorption band 50, and is particularly preferable considering the characteristic that absorption band 50 shifts to the long-wavelength side as the temperature of heated substrate 22 increases (see FIGS. 1 and 6). Furthermore, the CO laser described above can also be selected as an appropriate laser light source 32, and absorption band 50 ends at approximately 7 μm, extending sufficiently below laser wavelength 36 (5.5 μm) of the CO laser.

[0074] FIG. 5 shows the transmission spectra of two substrates 20 containing Si as the substrate 22 (see FIG. 1 ): p-type Si (solid line) and n-type Si (dashed line). The slight differences in the transmission spectra due to differences in the intrinsic Si doping are clearly visible. However, the general features remain the same, including, for example, the short-wavelength lower limit 52 of the absorption spectrum 50 corresponding to the illustrated transmission spectrum. Furthermore, Si, whether intrinsic or doped, is a particular candidate substrate 22 for the substrate 20 in the TLE system 10. The absorption band 50 of Si identified by the method of the present invention begins at the short-wavelength lower limit 52 near 6.5 μm and extends beyond the range of the illustrated transmission spectrum. Furthermore, the laser wavelengths 36 of the CO laser (approximately 9.3 μm, 10.2 μm, and 10.6 μm) are shown, clearly falling within the absorption band 50, with the highest absorption at 10.6 μm. Therefore, a CO laser is the laser source 32 of choice when the substrate 22 is made of Si or when the method of the present invention is performed on a substrate 20 made of Si. Currently, there are no economical high-power lasers that exhibit the highest absorption in the 16 μm to 16.5 μm range or near the upper long-wavelength end of the spectrum. Therefore, a CO laser with a wavelength of 10.6 μm currently provides the best results for the method of the present invention on Si.

[0075] 5 also applies to a substrate 20 including, for example, an oxide such as Al2O3, SrTiO3, LaAlO3, NdGaO3, DyScO3, MgO, or GdScO3, a nitride such as GaN or AlN, or a halide such as BaF2, CaF2, KBr, KCl, NaCl, or Mg2F2 as the base material 22. In particular, oxides, nitrides, and halides can form a broad absorption band 50 in which the lower limit 52 on the short wavelength side is significantly below 10 μm and the upper limit 54 on the long wavelength side is significantly above 10 μm. Therefore, even for these substrates, when the method according to the present invention is performed on a substrate 20 including an oxide, nitride, or halide as the base material 22, or on a substrate 20 including an oxide, nitride, or halide, the CO2 lasers described above with laser wavelengths of approximately 9.3 μm, 10.2 μm, and 10.6 μm can be selected as the laser light source 32.

[0076] 6 shows several absorption spectra of substrate 20 containing diamond in the base material 22, which vary substantially depending on the temperature of substrate 20 at which the absorption coefficient is determined. Measurements are shown at 25°C, 100°C, 250°C, 400°C, and 500°C. Additionally, the approximate locations of the short wavelength lower limit 52 and long wavelength upper limit 54 of the absorption band 50 are shown.

[0077] It can be clearly seen that as the temperature of substrate 20 increases, the actual long-wavelength upper limit 54 of absorption band 50 shifts slightly toward higher wavelengths. Therefore, by selecting laser source 32 (see FIG. 1) so that its laser wavelength 36 is within the upper 25% of absorption band 50, it is possible to avoid laser wavelength 36 moving outside absorption band 50 due to the temperature shift. [Explanation of symbols]

[0078] 10...TLE system 12...Reaction chamber 14...Reaction atmosphere 16...Sauce 18...Source laser beam 20...Substrate 22...Base material 24...Supporting material 26...Second ingredient 30...Substrate heater 32...Laser light source 34...Laser beam 36...Laser wavelength 40...pyrometer 50...Absorption band 52...Lower limit of short wavelength 54...Upper limit of long wavelength A... Step a) of the method according to the invention B... Step b) of the method according to the invention C... Step c) of the method according to the invention D... Step d) of the method according to the invention

Claims

1. A method for heating a substrate (20), particularly a substrate (20) in a thermal laser deposition (TLE) system (10), comprising: a) determining the absorption coefficient of electromagnetic waves in the base material (22) of the substrate (20) within a predetermined wavelength range; b) a step (B) of identifying an absorption band (50) within the predetermined wavelength range, the absorption band (50) comprising a wavelength range having a lower limit (52) on the short wavelength side and an upper limit (54) on the long wavelength side with respect to the wavelength of the electromagnetic wave to be absorbed; c) selecting a laser source (32) that provides a laser beam (34), the laser beam (34) having a laser wavelength (36) that is within the absorption band (50) identified in step b)(B); d) a step (D) of driving the laser light source (32) selected in the step c) (C) to heat the substrate (20); A heating method comprising:

2. The heating method according to claim 1, The predetermined wavelength range used in step a) (A) is from 0.1 μm to 100 μm, in particular from 0.2 μm to 20 μm. Heating method.

3. The heating method according to claim 1 or 2, The absorption band (50) identified in step b)(B) is associated with lattice vibrations in the base material (22) of the substrate (20), and in particular, the absorption band (50) identified in step b)(B) is substantially a lattice absorption band (50). Heating method.

4. The heating method according to any one of claims 1 to 3, In step c) (C), the laser light source (32) is selected so that the laser wavelength (36) is located within the upper 25%, preferably within the upper 10%, of the upper limit (54) on the long wavelength side of the wavelength range. Heating method.

5. The heating method according to any one of claims 1 to 4, When the substrate (20) is heated in the step d) (D), the temperature of the substrate (20) is measured by a temperature sensor. Heating method.

6. The heating method according to claim 5, The temperature sensor is a pyrometer (40). Heating method.

7. The heating method according to claim 6, The pyrometer (40) is sensitive to a wavelength and / or wavelength range different from, and preferably further apart from, the laser wavelength (36). Heating method.

8. The heating method according to claim 6 or 7, The pyrometer (40) is sensitive to wavelengths and / or wavelength regions within the wavelength range of the wavelength band identified in step b)(B), in particular covering at least 30%, preferably at least 60%, more preferably at least 90% of the wavelength range of the absorption band (50). Heating method.

9. The heating method according to any one of claims 5 to 8, The temperature of the substrate (20) measured in step d)(D) is used to control the operation of the laser light source (32) in step d)(D), and in particular is used as an input for closed-loop control of the operation of the laser light source (32). Heating method.

10. The heating method according to any one of claims 1 to 9, The laser beam (34) provided by the laser light source (32) selected in step c) (C) has a maximum power of at least 250 W, in particular at least 10 kW, preferably at least 1 MW. Heating method.

11. The heating method according to any one of claims 1 to 10, In step d) (D), the substrate (20) is heated to a temperature of 250° C. or higher, in particular to a temperature of 2000° C. or higher. Heating method.

12. 12. The heating method according to claim 1, In step d) (D), the substrate (20) is heated so that the wavelength of the maximum value of the blackbody radiation corresponding to the heating temperature is located outside, preferably away from, the absorption band (50) identified in step b) (B) in the wavelength region substantially transparent to the base material (22) of the substrate (20). Heating method.

13. The heating method according to claim 12, The wavelength of the maximum of the blackbody radiation is lower than, and preferably far from, the lower limit (52) of the short wavelength side of the absorption band (50) specified in step b)(B). Heating method.

14. 14. The heating method according to any one of claims 1 to 13, The substrate (20) has a base (22) that is heated by the laser and is a support (24) for a second, different material (26) of the substrate (20). Heating method.

15. 15. The heating method according to any one of claims 1 to 14, The substrate (20) has a base material (22) based on diamond and / or diamond-like carbon, and the laser light source (32) selected in step c) (C) is a CO laser providing a laser beam (34) with a laser wavelength (36) of about 5.5 μm. Heating method.

16. 16. The heating method according to claim 15, The substrate (22) of the substrate (20) is made of diamond and / or diamond-like carbon. Heating method.

17. 15. The heating method according to any one of claims 1 to 14, The substrate (20) has a base material (22) based on SiC, and the laser light source (32) selected in step c)(C) is a CO 2 laser beam (34) having a laser wavelength (36) of about 9.3 μm. 2 It is a laser Heating method.

18. 15. The heating method according to any one of claims 1 to 14, The substrate (20) has a base material (22) based on SiC, and the laser light source (32) selected in step c)(C) is a CO laser providing a laser beam (34) with a laser wavelength (36) of about 5.5 μm. Heating method.

19. 19. The heating method according to claim 17 or 18, The base material (22) of the substrate (20) is made of SiC. Heating method.

20. 15. The heating method according to any one of claims 1 to 14, The base material (22) of the substrate (20) is oxide and / or Si-based, and the laser light source (32) selected in step c) (C) is a CO laser beam (34) having a laser wavelength (36) of about 9.3 μm and / or 10.2 μm and / or 10.6 μm. 2 It is a laser Heating method.

21. 21. The heating method according to claim 20, The base material (22) of the substrate (20) is made of the oxide or Si. Heating method.

22. 22. The heating method according to claim 20 or 21, The oxide is Al 2 O 3 , SrTiO 3 , LaAlO 3 , NdGaO 3 , DyScO 3 , MgO, GdScO 3 , Gd 3 Ga 5 O 12 , LiAlO 3 , LiAlO 2 , LiGaO 2 , LiNbO 3 , LiTaO<00​​​​​​​​​​​​​​​​​​​ Heating method.

23. 15. The heating method according to any one of claims 1 to 14, The substrate (20) has a base material (22) based on nitride, and the laser light source (32) selected in step c)(C) is a CO laser source (34) providing a laser beam (34) having a laser wavelength (36) of about 9.3 μm and / or 10.2 μm and / or 10.6 μm. 2 It is a laser Heating method.

24. 24. The heating method according to claim 23, The base material (22) of the substrate (20) is made of the nitride. Heating method.

25. 25. The heating method according to claim 23 or 24, The nitride is GaN or AlN. Heating method.

26. 15. The heating method according to any one of claims 1 to 14, The substrate (20) has a base material (22) based on a halide, and the laser light source (32) selected in c)(C) is a CO laser source that provides a laser beam (34) having a laser wavelength (36) of about 9.3 μm and / or 10.2 μm and / or 10.6 μm. 2 It's a laser. Heating method.

27. 27. The heating method according to claim 26, The base material (22) of the substrate (20) is made of the halide. Heating method.

28. 28. The heating method according to claim 26 or 27, The halide is BaF 2 , CaF 2 , KBr, KCl, NaCl, or Mg 2 F 2 is Heating method.

29. A substrate heater (30) for heating a substrate (20), particularly a substrate heater (30) for heating a substrate (20) in a thermal laser deposition (TLE) system (10), comprising: a laser source (32) for providing a laser beam (34) and means for directing said laser beam (34) to said substrate (20); The laser light source (32) of the substrate heater (30) is selected according to steps a)(A) to c)(C) of the heating method according to any one of claims 1 to 28, The substrate heater (30) is configured to perform step d)(D) of the heating method of any one of claims 1 to 28. A substrate heater (30).

30. The apparatus comprises a reaction chamber (12) that can be filled with a reaction atmosphere (14), a substrate (20) disposed within the reaction chamber (12), one or more sources (16) disposed within the reaction chamber (12), and a substrate heater (30) that provides a laser beam (34) that is irradiated onto the substrate (20), thereby heating the substrate (20); The substrate heater (30) is constructed according to claim 29. A thermal laser deposition (TLE) system (10).

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