Method for controlled deposition of oxide layer of target oxide on substrate in TLE system and TLE system

Abstract

The invention relates to a method for controlled deposition of an oxide layer (80) of a target oxide (82) on a substrate (70) in a thermal laser epitaxy (TLE) system (100), the target oxide (82) comprising defined stoichiometry and being formed from one or more vaporized and / or sublimated source materials and oxygen derived from a gaseous oxidant (54), the TLE system (100) further comprises a reaction chamber (10) and one or more laser sources (20) for providing a laser beam (22) within the reaction chamber (10). The invention further relates to a TLE system (100) designed to carry out the method.

Description

[0001] This invention relates to a method for controlled deposition of an oxide layer of a target oxide on a substrate in a thermal laser epitaxy (TLE) system. The target oxide comprises a defined stoichiometry and is formed from one or more evaporated and / or sublimated source materials and oxygen derived from a gaseous oxidant. The TLE system further includes a reaction chamber and one or more laser sources for providing a laser beam within the reaction chamber. Furthermore, this invention relates to a TLE system configured to perform the method.

[0002] Epitaxial oxide films can currently be produced by a variety of methods, such as pulsed laser deposition (PLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), sputtering, and molecular beam epitaxy (MBE). Although all of these methods allow for the deposition of oxide films with fairly good stoichiometry, the best stoichiometry to date has been achieved by growing epitaxial oxide films via MBE in an adsorption-controlled growth mode.

[0003] Adsorption-limited growth works best in ultra-high purity environments, which typically mean ultra-high vacuum or residual gas environments with extreme gas purity. This means that non-thermal flux generation (such as sputtering or ablation) will not be effective due to the release of impurities from the chamber walls or source material support, and due to alterations to the crystal surface during growth by charged and / or high-energy source material atoms or molecules. Therefore, thermal flux generation is required through evaporation (from molten material) or sublimation (from solid material).

[0004] Oxides are difficult to grow in adsorption-controlled growth modes because they generally require high substrate temperatures to achieve the desired oxidation state due to their high binding energies and the presence of oxygen or oxidants. In many cases, the strong oxidation conditions required for stoichiometric growth are incompatible with the Joule heater technology used in MBE, as conductors such as metals oxidize and fail in the presence of oxygen at high temperatures. Therefore, successful examples of oxide growth via MBE in adsorption-controlled growth modes are limited to low substrate temperatures (below approximately 1000 °C) and low oxygen or ozone pressures (below 10⁻⁵ hPa). The required high substrate temperatures also weaken the oxidation potential, meaning that, correspondingly, high-quality crystal growth requires even higher oxygen or oxidant pressures, a condition that is more difficult to meet for MBE.

[0005] In view of the above, one object of the present invention is to provide an improved method for controlled deposition of oxide layers and an improved thermal laser evaporation system that does not have the disadvantages of the prior art. In particular, one object of the present invention is to provide an improved method for controlled deposition of oxide layers and an improved thermal laser evaporation system that provides the possibility of depositing oxide layers composed of one or more elemental components and oxygen, wherein the stoichiometry of the deposited oxides and the actual deposition of the oxide layer can be actively controlled.

[0006] This objective is satisfied by the individual claims. In particular, this objective is satisfied by the method for controlled deposition of oxide layers according to independent claim 1 and the TLE system according to independent claim 31. The dependent claims describe preferred embodiments of the invention. Details and advantages described with respect to the method according to the first aspect of the invention also relate to the TLE system according to the second aspect of the invention, and vice versa, if technically significant.

[0007] According to a first aspect of the invention, this object is achieved by a method for controlled deposition of an oxide layer of a target oxide on a substrate in a thermal laser epitaxy (TLE) system, the target oxide comprising a defined stoichiometry and formed from one or more evaporated and / or sublimated source materials and oxygen derived from a gaseous oxidant, the TLE system further comprising a reaction chamber and one or more laser sources for providing a laser beam within the reaction chamber. The method according to the invention is characterized by the following steps:

[0008] a) A substrate and a first deposition source are provided in a reaction chamber, wherein the first deposition source contains an elemental material as a first source material;

[0009] b) The reaction chamber is filled with a reaction gas containing one or more oxidants provided by the gas system of the TLE system;

[0010] c) By irradiating the first source material with a laser beam from the TLE system at an intensity lower than the plasma generation threshold of the first source material, the first source material is evaporated and / or sublimated to provide a flux of the evaporated and / or sublimated first source material and / or the first binary oxide formed by the first source material and the oxidant, wherein the flux is directed toward the substrate.

[0011] d) The substrate is heated to the deposition temperature by the laser beam of the TLE system, wherein the deposition temperature of the substrate is equal to or higher than the desorption temperature, such that the first deposition source and / or the first binary oxide is at least partially desorbed from the substrate;

[0012] e) Forming a target oxide by combining one or more evaporated and / or sublimated source materials with oxygen derived from one or more oxidants, and depositing the target oxide onto a substrate as an oxide layer;

[0013] The formation of the target oxide and the deposition of the oxide layer on the substrate are controlled by controlling the filling of the reaction chamber with the reactive gas in step b) and / or by controlling the rate of evaporation and / or sublimation of the first source material at the substrate in step c) and / or by controlling the deposition temperature in step d).

[0014] The method according to the invention is intended to be performed in and using a thermal laser epitaxy (TLE) system. A TLE system is the optimal choice for providing controlled deposition of a target oxide comprising the desired and therefore defined stoichiometry.

[0015] The TLE system includes at least a reaction chamber for providing a sealable reaction space relative to the surrounding environment. Within the reaction chamber, one or more deposition sources and a substrate to be coated are arranged and held in place by a placement device.

[0016] In addition, the TLE system includes a gas system for providing an optional atmosphere within the reaction chamber. The gas system is at least capable of supplying a reactant gas into the reaction chamber, wherein the reactant gas contains one or more gaseous oxidants, such as molecular oxygen or ozone. However, the gas system can also be configured to supply other reactant gases, such as molecular nitrogen, and / or to evacuate the reaction chamber to certain pressures, particularly up to ultra-high vacuum, with pressures as low as 10... -12 hPa or even lower.

[0017] Furthermore, the TLE system includes one or more laser sources and corresponding coupling devices disposed on and / or at the reaction chamber for providing a laser beam within the reaction chamber. The laser beam is used for the evaporation and / or sublimation of one or more source materials and for heating the substrate. Therefore, no additional heating of the one or more deposition sources and the substrate via an electrically heated device, as used in MBE, is required. Limitations imposed by heating devices on the reaction gases used, such as those concerning the supplied oxidant and / or its pressure, can be avoided.

[0018] In summary, by using a TLE system to implement the method according to the invention, a high-purity environment for depositing oxide layers can be provided. Each element of the TLE system, particularly the evaporation and / or sublimation of one or more source materials, the heating of the substrate, and the gas system for providing the reaction gases, can be individually and actively controlled to ensure the deposition of the target oxide, which comprises the desired and therefore defined stoichiometry.

[0019] In the first step a) of the method according to the invention, the substrate and the first deposition source are arranged and thus provided in the reaction chamber. This can be done while the reaction chamber is still open relative to the surrounding environment, or it can be done by a correspondingly available airlock when the reaction chamber has been closed and sealed. Within the reaction chamber, there are arrangement means for arranging both the substrate and one or more deposition sources, respectively. The arrangement means can be provided for spatially fixing the substrate and / or one or more deposition sources only. Alternatively or additionally, these arrangement means can also be designed to provide movement of the substrate and / or one or more deposition sources, for example, moving the substrate into and out of the deposition position, and / or exchanging the deposition source to be used. In summary, after performing step a), the first deposition source and the substrate are arranged within the reaction chamber.

[0020] Specifically, the first deposition source contains elemental material as the source material. In other words, the source material is pure except for oxygen itself (meaning it consists largely of only one element from the periodic table) and provides the elemental material (therefore, this elemental material is chosen to form the non-oxygen component of the target oxide) without any precursor molecules. Nevertheless, the environmentally facing surface of the source material, especially after step b) of the method according to the invention, where the reaction gas contains one or more oxidants, may be oxidized, and thus the uppermost layer of the deposition source will be formed by oxides of the elemental material that forms the body of the deposition source.

[0021] In the next step b) of the method according to the invention, the gas system of the TLE system is used to prepare an atmosphere within the reaction chamber for depositing the oxide layer onto the substrate. Specifically, a reaction gas comprising one or more oxidants is filled into the reaction chamber. The oxidant in the context of the invention is a gaseous substance that can serve as a source of desired oxygen atoms during the formation of the target oxide. Preferably, the reaction gas consists of one or more oxidants.

[0022] Before filling the reaction chamber with the reactive gas, it is preferable to vent the reaction chamber through a gas system. This provides or at least significantly improves the purity of the reaction atmosphere, which consists solely of reactive gases. After performing step b), the atmosphere within the reaction chamber is composed only of reactive gases containing one or more oxidants (preferably those oxidants) at concentrations on many orders of magnitude. If an airlock is used in step a) to arrange the substrate and / or the first deposition source in the reaction chamber, step b) can also be performed before and / or during step a).

[0023] After preparing the reaction chamber in steps a) and b), the actual evaporation and / or sublimation of the first source material (i.e., the elemental material) is performed in the next step c). Specifically, since the method according to the invention is carried out via a TLE system, laser beams provided by the various laser sources of the TLE system are used for evaporation and / or sublimation. The laser beams are coupled into the reaction chamber and guided onto the surface of the source material.

[0024] The intensity of the laser beam is selected to be below the plasma threshold of the first source material. Therefore, complete thermal evaporation and / or sublimation of the first source material is provided, particularly without the explosive ablation or plasma formation present in PLD and / or sputtering processes. This allows for the evaporation and / or sublimation of the first source material. If the surface of the deposition source is oxidized, as described above, evaporation and / or sublimation of the oxide of the source material is also possible. Furthermore, the evaporated and / or sublimated first source material can also react with one or more oxidizing agents in the reactive gas to form a first binary oxide of the first source material.

[0025] In this invention, a binary oxide is an oxide comprising two components: an elemental material and oxygen. The actual stoichiometry of the binary oxide is not fixed. For example, using titanium as the metal, oxides TiO, TiO2, and Ti2O3 are all binary oxides in this invention. This also applies accordingly to ternary or multi-element oxides, i.e., oxides having two, three, or more non-oxygenal elemental components.

[0026] In summary, in step c), a flux of the first source material and / or the first binary oxide is provided for evaporation and / or sublimation. For example, the flux is provided to the substrate to be coated by correspondingly arranging the first deposition source and the substrate within the reaction chamber in step a) of the method according to the invention.

[0027] In step d) of the method according to the invention, the substrate is prepared for depositing the target oxide to form the desired oxide layer. For this purpose, the substrate is heated by a laser beam provided by a corresponding laser source provided by the TLE system. Similarly, a laser beam for heating the substrate is also coupled into the reaction chamber and guided onto the substrate, for use with the laser beam used for evaporating and / or sublimating the first source material.

[0028] Specifically, heating of the substrate is provided to give the substrate a defined and selected deposition temperature. The deposition temperature is selected to be equal to or higher than the desorption temperature, such that the first deposition source and / or the first binary oxide is at least partially desorbed from the substrate. Therefore, the corresponding deposition temperature depends on the properties of the substrate itself, but also on the first source material used and / or the first binary oxide already formed.

[0029] Setting the deposition temperature to be equal to or higher than the corresponding desorption temperature has the effect of significantly reducing (preferably eliminating) the deposition rate of the target oxide and thus the dependence of the oxide layer growth rate on the flux density of the evaporating and / or sublimating first source material. On the other hand, the loss of this dependence allows the deposition rate to be controlled by other properties, namely, by selecting a suitable deposition temperature, particularly by the amount of oxygen available to form the target oxide. This is especially based on the finding that, in most cases, the first source material in its pure form, i.e., the elemental material, or its metastable oxide, is more volatile than the desired oxide of the corresponding material, and that the specific binary oxide of the first source material also provides a specific desorption temperature, which can be considered when selecting the deposition temperature (the temperature at which the substrate will be heated). In summary, the combination of these effects provides the possibility of also growing the binary oxide as the target oxide in an adsorption-controlled manner.

[0030] Finally, in step e) of the method according to the invention, a target oxide is formed and deposited on a substrate to form an oxide layer. The target oxide includes a first source material and oxygen as components. The stoichiometry of the target oxide is defined and selected. The formation of the target oxide can be directly provided on the substrate. However, if the target oxide is a first binary oxide that has been formed prior to deposition on the substrate, this is also considered to be included in the formation of the target oxide in step e) in the sense of the invention. According to the invention, the formation of the target oxide and the deposition of the oxide layer on the substrate are controlled separately.

[0031] Specifically, control over the formation of the target oxide and / or the deposition of the oxide layer can be provided by controlling the filling of the reaction chamber with a reactive gas. As described above, the deposition temperature of the substrate can be selected such that the first source material, in its pure or less stable oxide form, is desorbed from the substrate, and conversely, the target oxide is adsorbed onto the surface of the substrate. Therefore, by controlling the filling in step b), the amount of available oxygen can be controlled, and thus the formation rate of the less stable oxide or the target oxide can be actively adjusted. In other words, controlling the filling of the reaction chamber with a reactive gas provides a way to grow an oxide layer in an adsorption-controlled manner.

[0032] Additionally or alternatively, the rate of evaporation and / or sublimation of the first source material at the substrate in step c) can also be used to control the formation of the target oxide and / or the deposition of the oxide layer. Specifically, the rate of evaporation and / or sublimation of the first source material defines the maximum rate at which the target oxide can be formed, and thus the maximum growth rate of the oxide layer on the substrate. Reducing the rate of evaporation and / or sublimation of the first source material, for example by reducing the intensity of the laser beam used for evaporation and / or sublimation, also lowers the maximum value of the target oxide formation rate.

[0033] Similarly, additionally or alternatively, setting the deposition temperature of the substrate in step d) also affects the formation of the target oxide and the deposition of the oxide layer on the substrate. Specifically, as mentioned above, in most cases, different oxides of the first source material have different desorption temperatures. Therefore, by controlling and thus adjusting the deposition temperature accordingly, the selection of the target oxide can be actively altered. Furthermore, in most cases, the desorption portion (in other words, the portion of the impacted material on the substrate that is subsequently desorbed again) depends on the substrate temperature. This property can also be used to control the formation of the target oxide and the deposition of the oxide layer on the substrate. Finally, and most importantly, deposition will primarily occur only when the formed compound, i.e., the target oxide, has the desired suitable thermodynamic properties (primarily dependent on the substrate temperature). Thus, the deposited compound, i.e., the target oxide, can be actively selected, and therefore the quality of the deposited layer, particularly in terms of high purity and low defect density, can be maximized.

[0034] In summary, the method according to the invention provides the possibility of depositing an oxide layer composed of elemental material composition and oxygen at a controlled stoichiometry and an equally controlled growth rate. By implementing the method according to the invention, the deposition can be provided in an adsorption-controlled manner. This specifically utilizes the fact that deposition occurs only when the formed compound, i.e., the target oxide, possesses the desired appropriate thermodynamic properties (primarily dependent on the substrate temperature). Therefore, particularly controlling the substrate temperature allows for the production of oxide layers composed of the target oxide with extremely high quality, even when a binary oxide is chosen as the target oxide. This is due to the self-adjusting stoichiometry of the target oxide under adsorption-controlled conditions.

[0035] Preferably, at least steps c), d), and e) of the method according to the invention are performed simultaneously.

[0036] In a first embodiment, the method according to the invention is characterized in that, in step d), a deposition temperature is selected such that more than 40%, particularly more than 70%, preferably more than 99.99% of the inflow flux of the first source material is desorbed from the substrate, and in step e), the adsorbed portion of the first source material combines with oxygen derived from one or more oxidants and / or a first binary oxide to form a target oxide for depositing an oxide layer. In other words, the first source material not bound in a stable stoichiometric target oxide is desorbed from the substrate, preferably completely or at least substantially completely. Only the target oxide (and the first binary oxide if its stoichiometry matches the target oxide) is deposited on the substrate. Since the formation of the target oxide depends on oxygen availability, in step b) of the method according to the invention, oxygen availability is again controlled by filling the reaction chamber with a reactive gas, thus making it easier to provide an adsorption control mode for depositing binary oxides on the substrate, and therefore providing, in particular, the advantage of extremely high structural and stoichiometric quality of the oxide layer deposited in this manner.

[0037] According to an alternative embodiment, the method according to the invention may include: in step a), providing one or more second deposition sources in a reaction chamber, wherein each second deposition source contains an elemental material as a second source material; furthermore, step c) includes evaporating and / or sublimating one or more second source materials by irradiating one or more second source materials with a laser beam from a TLE system at an intensity lower than the plasma generation threshold of the various second source materials, for providing a flux of the evaporated and / or sublimated one or more second source materials and / or one or more second binary oxides formed by one or more second source materials with an oxidant directed to the substrate; wherein in step e), the first deposition source and / or the first binary oxide is combined with one or more second deposition sources and / or one or more second binary oxides, and, if necessary, with oxygen derived from one or more oxidants, to form a target oxide for depositing an oxide layer; and in step d), the deposition temperature of the substrate is equal to or higher than a certain temperature, such that the first deposition source and / or the first binary oxide is desorbed without being used to form the target oxide.

[0038] In contrast to the above-described embodiments, in step a) of the method according to the invention, one or more additional second deposition sources are arranged in the reaction chamber. Subsequently, one or more second source materials of the one or more second deposition sources, which are also elemental non-oxygen materials, are evaporated and / or sublimated by a laser beam from a correspondingly provided TLE system. All the features and advantages described above regarding the first deposition source and the first source material also apply to each of the one or more second deposition sources and the corresponding one or more second source materials.

[0039] By providing one or more second source materials, and by providing fluxes of one or more source materials evaporated and / or sublimated and / or their respective binary oxides, a ternary oxide can be formed as the target oxide if a single second deposition source is present, or a multi-component oxide can be formed as the target oxide if two or more second deposition sources are present. Similarly, the target oxide comprises a first source material, one or more second source materials, and oxygen as components, wherein the stoichiometry of the target oxide is defined and selected in a self-adjusting manner based on the thermodynamic properties of the target oxide, the substrate temperature, and the flux densities of the source materials and oxidants.

[0040] Specifically, in this embodiment of the method according to the invention, the heating of the substrate in step d) is controlled such that the resulting deposition temperature of the substrate is sufficiently high to cause the first source material and the first binary oxide to desorb, respectively. Deposition of the reaction products at the substrate occurs only when the first source material and / or the first binary oxide (depending on which one is present on the substrate) combines with one or more second source materials and / or one or more second binary oxides to form a target oxide with a selective and defined stoichiometry; in other words, only when a corresponding ternary or multi-component oxide defined as the target oxide is formed.

[0041] In other words, the deposition of the target oxide is adsorption-controlled. Therefore, by implementing this embodiment of the method according to the invention, all the aforementioned advantages of adsorption-controlled deposition, particularly the extremely high structural and stoichiometric quality of the deposited oxide layer, can also be provided for oxide layers formed from ternary and multi-component oxides. Specifically, the first source material and / or the first binary oxide represents the volatile portion of the compound to be formed, i.e., the target oxide provided in excess. Furthermore, one or more second source materials and / or corresponding second binary oxides form the non-volatile portion of the compound at a rate-limited rate. Therefore, the flux of one or more evaporated and / or sublimated second source materials and / or one or more second binary oxides defines the formation rate of the target oxide, thereby defining the growth rate of the oxide layer. In summary, oxide layers can also be provided for ternary or multi-component oxides by depositing the target oxide with extremely high quality.

[0042] Furthermore, the method according to the invention can be enhanced by selecting a sufficiently high deposition temperature in step d) such that the amount of the first deposition source and / or the first binary oxide deposited on the substrate in any way is less than 1 / 10 of the elemental composition of the target oxide. 4 Especially less than 1 / 10 7 Preferably less than 10 10As described above, oxide layers can be produced with very high quality. Furthermore, the first source material and the first binary oxide desorb from the substrate at the deposition temperature provided with the substrate. However, since deposition is a chemical reaction, individual cases may still occur where the first source material and the first binary oxide are deposited on the substrate. On the other hand, the probability of the aforementioned undesirable deposition of the first source material and / or the first binary oxide decreases as the substrate temperature increases. Therefore, by appropriately selecting the deposition temperature, a probability of less than 1 / 10 can be achieved. 4 Especially less than 1 / 10 7 Preferably less than 10 10 The defect density is the ratio of the amount of the first source material and / or the first binary oxide to the amount of the target oxide.

[0043] This also applies to the opposite situation where the substrate temperature is too high, causing the first source material to be incorporated in a slightly insufficient amount, such that the target oxide contains fewer units of the first source material and / or the first binary oxide compared to the unit amount of the target oxide, less than 1 / 10. 4 Especially less than 1 / 10 7 Preferably less than 10 10 .

[0044] Furthermore, the method can be enhanced by: in step c), by correspondingly controlling the laser beam used for evaporating and / or sublimating one or more second source materials, providing one or more evaporating and / or sublimating second source materials and / or one or more second binary oxides at intermittent and / or constant and / or variable fluxes. As described above, in the adsorption-controlled manner, one or more second source materials and (if applicable) one or more second binary oxides are part of a compound that restricts the formation of the target oxide and thus restricts the growth of the oxide layer. Therefore, by changing the flux of these components, the formation rate of the target oxide and the corresponding growth rate of the oxide layer can also be actively changed and controlled.

[0045] In another enhanced embodiment of the method according to the invention, the target oxide formed in step e) comprises a perovskite structure and / or a perovskite-related structure and / or a Ruddlesden-Popper structure. Perovskites and perovskite-related compounds, especially Ruddlesden-Popper structures, are of great scientific and industrial interest as candidates for strongly correlated electronic systems, odd parity superconductivity, and highly efficient catalysts. For example, perovskite oxides and oxides with Ruddlesden-Popper layer stacks can possess interesting properties and / or applications, such as colossal magnetoresistance, superconductivity, ferroelectricity, catalytic activity, white light-emitting diodes, scintillators, fuel cells, and solar cells. All of these structures are ternary oxides. Therefore, by using the method according to the invention, oxide layers can be produced from target oxides comprising perovskite structures and / or perovskite-related structures and / or Ruddlesden-Popper structures with extremely high quality, thereby enhancing all the aforementioned properties and advantages of these structures.

[0046] Furthermore, the method according to the invention is characterized in that, in step d), a deposition temperature is selected such that the first source material and / or the first binary oxide and / or one or more second source materials and / or one or more second binary oxides can migrate along the surface of the substrate. In other words, the deposition temperature is selected such that all components of the target oxide can move to find energy-favorable positions on the substrate surface, and thus find their designated ideal positions within the periodic lattice. This can further reduce the lattice defect density of the target oxide and, correspondingly, the lattice defect density of the oxide layer.

[0047] Furthermore, the method according to the invention may include, in step d), providing a deposition temperature between 250°K and 4500°K. In the method according to the invention, a variety of elemental materials, particularly elemental metals, and more advantageously all metals available as solid deposition sources, can be used as the first source material. By providing a deposition temperature between 250°K and 4500°K, the substrate can be heated to a temperature suitable for all these possible first deposition sources.

[0048] The TLE system, particularly the corresponding laser source and the laser beam provided by said laser source, is preferably capable of heating the substrate to any temperature within this range, i.e., as low as 250°K and as high as 4500°K. Thus, the same TLE system can be used to produce an unprecedented variety of oxide layers with extremely high quality.

[0049] Furthermore, the method according to the invention is further characterized in that, in step d), the deposition temperature is selected relative to the first binary oxide. Compared to the first source material, the first binary oxide exhibits a different desorption temperature due to the alteration of its chemical properties by the presence of one or more oxygen atoms. Therefore, by selecting the deposition temperature relative to the first binary oxide, the selected deposition temperature is sufficiently high in all cases to ensure that the first deposition source also desorbs.

[0050] According to an enhanced embodiment, the method according to the invention may include selecting a deposition temperature relative to the first binary oxide as equal to or higher than the following temperatures:

[0051]

[0052] The temperature values ​​listed in the table above are the calculated desorption temperatures of the respective binary oxides in vacuum. It should be noted that if a reactant gas, and therefore one or more oxidants, are present in the reaction chamber, the actual deposition temperature may differ from the listed temperatures. For example, if molecular oxygen at a pressure of 0.001 hPa is present as the reactant gas in the reaction chamber, the suitable deposition temperature for Al₂O₃ as the first binary oxide decreases from 1650°K to 1070°K.

[0053] Furthermore, the method according to the invention may include, in step c), and particularly also in step d), using a continuous laser beam or laser beam with a pulse intensity below the plasma generation threshold. By using a continuous laser beam, the same continuous heating of the corresponding source material can be provided, and, if applicable, continuous heating of the substrate can also be provided. This also applies to pulsed lasers operating for TLE purposes, such that the plasma threshold for evaporating the source material is not reached. In particular, the corresponding pulse width and repetition rate of the laser beam can be preferably selected such that the heated entity does not undergo significant cooling during the pulse of the laser beam, and thus the laser heating is quasi-continuous. A suitable pulse length equal to or greater than 1 µs, particularly greater than 1 ms, preferably greater than 1 s, can be selected, wherein a suitable repetition rate can be selected in the range of 10-100 kHz.

[0054] In both cases, the laser beam is continuously or at least substantially continuously incident on the various source materials, and, if applicable, on the substrate. Therefore, the corresponding laser beam is specifically not operated in a pulsed manner, i.e., it has high laser energy and / or laser pulse lengths in the nanosecond range. This allows for a particularly constant and controllable or adjustable energy transfer of the laser beam into the various source materials (and, if applicable, the substrate). In this way, constant and / or controllable and adjustable temperatures can be achieved in the various source materials, thereby achieving constant and / or controllable and adjustable evaporation and / or sublimation rates. If applicable, this also provides a constant and / or controllable and adjustable temperature for the substrate.

[0055] According to another embodiment of the method of the invention, in step b), the pressure and / or composition of the reactant gases are changed by correspondingly controlling the gas system of the TLE system to actively change the stoichiometry of the target oxide formed without altering its composition. By changing the properties of the reactant gases, such as their pressure and / or the relative or absolute composition of their oxidants, the abundance of available oxygen atoms for forming the target oxide can be actively altered. Therefore, which of several possible stoichiometry for forming the target oxide can be actively selected, or at least supported, can be chosen. For example, in the case of Sr as the first source material and Ru as the second source material, the pressure at the substrate surface is 10... -4 and 10 -3 At a pressure between hPa, molecular oxygen (O2) as a reactant gas favors the formation of Sr2RuO4 as the target oxide, while for the same reactant gas, 5 × 10 -3 and 2×10 -2 The pressure between hPa is favorable for using SrRuO3 as the stoichiometric target oxide.

[0056] Alternatively or additionally, the method according to the invention may further include: in step c), by correspondingly controlling the laser beam of the TLE system used in step c), changing the flux of the first source material and / or the first binary oxide provided for evaporation and / or sublimation, to actively change the stoichiometry of the target oxide formed without changing the composition. As mentioned above, in most cases, the first source material and / or the first binary oxide is present in excess at the substrate. However, by controlling the abundance of the first source material and / or the first binary oxide, the influence on the target oxide to be formed can also be provided.

[0057] Similarly, or additionally, the method according to the invention can be enhanced by: in step d), changing the deposition temperature of the substrate by correspondingly controlling the laser beam of the TLE system, thereby actively altering the stoichiometry of the target oxide formed without changing the composition. As mentioned above, the temperature of the substrate determines which elements or compounds desorb from the surface of the substrate. Therefore, by correspondingly selecting the deposition temperature, the selection of the target oxide to be deposited on the substrate can be automatically provided.

[0058] In the above examples of Sr and Ru with changes in the reactant gases, setting the desorption temperature in the range of 730°K to 1030°K can help select Sr2RuO4 as the target oxide, while the deposition temperature between 330°K and 730°K is favorable for selecting SrRuO3 as the stoichiometric target oxide.

[0059] According to another enhanced embodiment, the method according to the invention may include: providing changes in the reactant gas and / or the flux of the first source material and / or the first binary oxide provided for evaporation and / or sublimation and / or deposition temperature before and / or during and / or after repeating step c). In step c), the first source material and, if present, one or more second source materials are evaporated and / or sublimated. Thus, by providing corresponding changes before and / or after repeating step c), different target oxides can be selected for the repetition of step c). This allows for a sharp transition from one target oxide to another in the oxide layer. On the other hand, by providing corresponding changes during the execution of step c), a smoother transition from one target oxide to the next can be provided.

[0060] Another advantage of the method according to the invention arises regarding the aforementioned abrupt transitions in the oxide layer. Since the provision of each source material is based on the evaporation and / or sublimation of each source material, continuous heating of each source material is required to continuously provide the respective evaporating and / or sublimating source material. Without such heating, the source material cools immediately due to radiative cooling, and evaporation and / or sublimation cease. Therefore, by starting and stopping each laser beam, for example by installing shutters in the beamlines of each laser beam, a defined deposition interval can be defined, thereby enabling control over the thickness of the deposited oxide layer and allowing abrupt transitions between different oxide layers.

[0061] Furthermore, the method can be enhanced by the following: the oxide layer deposited in step e) comprises two or more subsequent sublayers formed from target oxides having the same composition but different stoichiometry, preferably different perovskite structures and / or perovskite-associated structures and / or Ruddlesden-Popper structures. This can be provided, in particular, by variations in the flux of the aforementioned reactant gas and / or the first source material and / or the flux of the first binary oxide and / or the deposition temperature. This can thus provide oxide layers with a variety of different properties. For example, the aforementioned examples of target oxides having Sr, Ru, and O as components actually include Ruddlesden-Popper structures. In addition to the already mentioned examples of Sr2RuO4 and SrRuO3, Sr2RuO4, Sr3Ru2O7, and Sr4Ru3O4 are also possible. 10 It is also a possible target oxide for different sublayers of the oxide layer.

[0062] In another embodiment of the method according to the invention, the first source material and / or one or more second source materials are elemental metals. Metals are an extremely diverse group of elements, where metal oxides provide extremely different properties, for example, in terms of electrical or thermal conductivity, or in physical properties such as hardness and toughness. By performing the method according to the invention, a variety of binary, ternary, or even multi-component oxides based on metals as non-oxygen components can be provided as possible target oxides for the resulting oxide layer.

[0063] Furthermore, the method according to the invention may also be characterized in that the first source material and / or one or more second source materials are selected from the group consisting of materials including: Li, Na, K, Ca, Sr, Y, Ag, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, Bi, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Mo, Ru, Rh, Pd, In, Sn, Sb, Be, B, Mg, Si, Cu, Zn, Ge, Se, Cd, Te, Cs, Re, Pt, Au, Hg, Tl, Th, U, Np, Pu, Am, Tc, Os, Rb, As. Thus, a variety of binary oxides, ternary oxides, and even multi-component oxides can be provided as possible target oxides for the oxide layer produced by implementing the method of the invention.

[0064] The method according to the invention may further include: continuously performing step b) during the execution of steps c) and / or d) and / or e). In step b), the reaction chamber is filled with a reaction gas containing one or more oxidants, preferably composed of one or more oxidants. The continuous performance of step b) during the execution of steps c) and / or d) and / or e) allows the reaction chamber to be filled with the reaction gas simultaneously during the evaporation and / or sublimation of the first source material and, if applicable, one or more second source materials, and / or during the heating of the substrate, and / or during the formation of the target oxide and the deposition of the oxide layer. Therefore, during the execution of the method according to the invention, preferably throughout the deposition process in steps c), d), and e), a consistently high-purity atmosphere can be provided within the reaction chamber.

[0065] Furthermore, the method according to the invention is characterized in that, in step b), filling the reaction chamber includes providing a directional flow of reactive gas to the substrate. The target oxide is deposited onto the substrate, thereby forming an oxide layer at the substrate. By providing a directional flow of reactive gas, and thus a directional flow of one or more oxidants, the increased oxygen flux density required to form the target oxide at the substrate can be ensured. In particular, oxygen deficiency can be avoided during adsorption-controlled deposition processes.

[0066] The directional flow of the reactant gas simultaneously reduces the non-directional background pressure of the reactant gas. This reduces scattering of the source material along its path from the source to the substrate, allowing for a relatively increased reactant gas flux density at the substrate surface with reduced scattering. Consequently, this allows for a higher growth rate or stronger oxidation of the target oxide compared to a uniform distribution of the background gas.

[0067] Furthermore, the method according to the invention can be enhanced by using a single oxidizing agent as the reaction gas. In other words, after step b), the entire reaction chamber is filled with only this single oxidizing agent. This provides the purity of the reaction atmosphere present in the reaction chamber, which helps to further improve the extremely high quality of the provided oxide layer.

[0068] According to another embodiment of the method of the present invention, one or more oxidants are selected from molecular oxygen (O2), ozone (O3), plasma-activated oxygen (O2). ), ionized oxygen (O) - The list includes atomic oxygen (O) and combinations thereof. This list is not closed; other oxidizing agents can be used to provide the oxygen required to form the target oxide. In particular, the oxidizing agents listed above consist of oxygen atoms. This avoids contamination from other elements caused by the oxidizing agent.

[0069] Furthermore, a feature of the method according to the invention is that, in step b), the reactant gas is supplied at 10-9 hPa to 10 5 The pressure selected within the hPa range is preferably 10. -5 hPa to 10 5 The pressure is selected within the hPa range. In the method according to the invention, a variety of elemental materials, particularly all metals available as solid source materials, can be used as a first source material, and, if applicable, as one or more second source materials. This results in a variety of selectable target oxides, each of which has a reaction gas pressure and / or reaction gas pressure range most suitable for depositing that particular target oxide as an oxide layer. By providing the reaction gas with a pressure within 10 hPa... -9 hPa to 10 5 The pressure selected within the hPa range is preferably 10. -5 hPa to 10 5 The pressure selected within the hPa range allows for the selection of the most suitable pressure and / or pressure range for the reactant gases for most (if not all) target oxides.

[0070] TLE systems, especially gas systems of TLE systems, are preferably capable of providing the reactant gas with any pressure within this range, i.e., down to 10. -9 hPa, preferably 10 -5 The pressure is hPa, and it is also as high as 10. 5 The pressure is hPa. Therefore, the same TLE system can be used to produce an unprecedented variety of oxide layers with extremely high quality of the deposited target oxide.

[0071] According to another embodiment, the method according to the invention may include a step prior to step c) of preparing the surface of a substrate intended for depositing an oxide layer. The surface conditions of the substrate affect the deposition of the oxide layer. For example, for a crystalline substrate, defects in the substrate lattice and / or steps and / or surface impurities resulting from misalignment of surface cuts with the substrate's crystal planes can persist as defects in the deposited layer. By introducing the step of preparing the substrate surface, the surface conditions of the substrate can be improved so that the target oxide can be subsequently deposited as an oxide layer. Therefore, it is possible to support the delivery of an achievable, extremely high-quality oxide layer during the execution of the method according to the invention.

[0072] The method according to the invention can be further enhanced by the following step: the surface preparation step includes tempering the surface by heating the substrate with a laser beam from a TLE system (preferably the laser beam used in step d). Heating the substrate allows impurity atoms to desorb, defects in the bulk to heal, and, in particular, allows atoms forming the substrate surface to migrate and find energy-favorable positions on the substrate surface, thereby finding their ideal positions on the substrate surface, especially for crystalline substrates, ideal positions within the periodic lattice of the substrate. In other words, heating the substrate induces an annealing effect, especially at the substrate surface. Therefore, a substrate surface more suitable for subsequent deposition of the target oxide as an oxide layer can be provided.

[0073] Additionally or alternatively, the method according to the invention may further include: the step of preparing the surface includes coating the surface with one or more buffer layers. The one or more buffer layers can help smooth steps on the substrate surface. Furthermore, particularly for crystalline substrates, the target oxide to be deposited as an oxide layer may have a different lattice structure and / or lattice constant than the substrate. Therefore, at least the first atomic layer of the target oxide on the substrate must compensate for these differences. However, the buffer layer can be suitably selected such that it has similar or even identical crystal properties to the target oxide within the oxide layer. Thus, by adding such a suitably selected buffer layer between the substrate and the oxide layer, compensation for the differences in the respective lattices is provided within the buffer layer, and the oxide layer can be provided with its desired crystal structure starting from the first atomic layer of the target oxide.

[0074] According to the first enhanced embodiment, the method according to the invention can be enhanced by the following manner: the buffer layer comprises a first source material and / or an oxide of the first source material (especially a first binary oxide), preferably composed thereof.

[0075] According to an additional or alternative second reinforcing embodiment, the method according to the invention can be enhanced by the following: the buffer layer comprises an oxide of one or more second source materials and / or an oxide of one or more second source materials (particularly one or more second binary oxides), preferably composed thereof.

[0076] According to yet another additional or alternative third reinforcing embodiment, the method according to the invention can be enhanced by the following: the buffer layer comprises, preferably is composed of, the material of the substrate.

[0077] In the first two alternative embodiments, the buffer layer is formed by evaporating and / or sublimating the source material already present in the reaction chamber for subsequent deposition of the target oxide as an oxide layer. Both of these enhanced alternative embodiments avoid the need to provide additional deposition sources with additional source material. Depending on the crystal structure of the target oxide, the most suitable composition of the buffer layer can be selected based on the components already present in the TLE system: a first source material or an oxide of the first source material, or, if applicable, one or more second source materials or oxides of one or more second source materials. For the third alternative embodiment, it may be necessary to provide individual deposition sources to provide the aforementioned composition of the substrate material, preferably in the form of elemental materials. Providing a buffer layer comprising the substrate material (preferably composed of the substrate material) offers the advantage of being able to deposit the buffer layer with high quality. Therefore, defects on the surface of the substrate itself can be smoothed. Furthermore, if suitable for the subsequent deposition of the target oxide to form an oxide layer, a buffer layer comprising two or more sublayers of these materials can be implemented.

[0078] Furthermore, the method according to the invention is characterized by a preparatory evaporation and / or sublimation step prior to step c), wherein a first source material and / or one or more second source materials are heated by a laser beam (preferably the laser beam used in step c) to clean the first source material and / or one or more second source materials respectively, without depositing the material onto the substrate. In step c) of the method according to the invention, the first source material is evaporated and / or sublimated by each laser beam, and, if applicable, one or more second source materials are also evaporated and / or sublimated. In other words, the laser beam is incident on the surface of each deposition source, and the source material evaporates and / or sublimates. However, particularly at the start of the evaporation and / or sublimation process, the surfaces of the respective deposition sources may be contaminated with impurities. By the prior heating of the source materials, these impurities can be removed again by evaporation and / or sublimation. To avoid the deposition of evaporated and / or sublimated impurities onto the substrate, the substrate can be shielded and / or moved aside. Furthermore, for this preparatory step, it is possible to remove the substrate from the reaction chamber, preferably by means of an airlock. In summary, through the aforementioned preparation steps, starting from step c) of performing the method according to the invention, evaporation and / or sublimation of various source materials with high purity can be provided.

[0079] According to a second aspect of the invention, this objective is achieved by a TLE system configured to perform the method according to the first aspect of the invention.

[0080] - Reaction chamber,

[0081] - One or more laser sources for providing laser beams for heating a substrate and for evaporating and / or sublimating one or more source materials.

[0082] - A coupling device for coupling one or more laser beams into the reaction cavity.

[0083] - A placement apparatus for placing a substrate in a reaction chamber and one or more deposition sources providing one or more source materials, and

[0084] - Gas system, used to supply reaction gases within the reaction chamber.

[0085] The TLE system according to the second aspect of the invention is configured to implement the method according to the first aspect of the invention. Therefore, all the features and advantages described in detail with respect to the method according to the first aspect of the invention can also be provided by the TLE system according to the second aspect of the invention.

[0086] As previously mentioned, the TLE system, particularly the laser sources and the laser beams provided by those sources, is preferably capable of heating the substrate to any temperature within this range, from as low as 250°K to as high as 4500°K. Therefore, the same TLE system can be used to produce an unprecedented variety of oxide layers with extremely high quality.

[0087] Additionally or alternatively, and also as already mentioned, the TLE system, particularly the gas system of the TLE system, is preferably capable of providing a reaction gas with any pressure within that range, i.e., with pressures as low as 10. -9 hPa, preferably 10 -5 The pressure is hPa, and it is also as high as 10. 5 The pressure is hPa. Therefore, the same TLE system can be used to produce an unprecedented variety of oxide layers, and the quality of the deposited target oxides is extremely high.

[0088] A single laser source can be used to evaporate and / or sublimate various source materials, with a separate laser beam provided for each source material. Alternatively, separate laser sources can be implemented, each providing a laser beam specifically selected for each source material.

[0089] The reaction chamber can be equipped with an airlock for entry into the reaction chamber without loss and / or contamination of the existing atmosphere within the reaction chamber. The airlock can be used, for example, to install and / or remove the substrate and / or one or more deposition sources used.

[0090] The invention will now be explained in detail with reference to the accompanying drawings and embodiments. In particular, the drawings show:

[0091] Figure 1 The phase diagram of SrTiO3 is shown below.

[0092] Figure 2 This is a schematic diagram of the TLE system according to the present invention.

[0093] Figure 3 This is a schematic diagram of the method according to the present invention.

[0094] Figure 4 Phase diagram of Sr-Ru-O Ruddlesden Popper material,

[0095] Figure 5 The relationship between the growth rate and deposition temperature of Al2O3, and

[0096] Figure 6 This represents the relationship between the growth rate of Al2O3 and the pressure of the reacting gas.

[0097] exist Figure 1 The figure depicts a calculated phase diagram of a known possible target oxide 82 (i.e., SrTiO3). The figure shows the relationship between the pressure and therefore the flux of SrO, which serves as the first source material 32 (not explicitly depicted), and the possible deposition temperature 72 of the substrate 70. Ideally, the target oxide 82 should be deposited on the substrate 70 as an oxide layer 80 (see Figure 1). Figure 2 ).

[0098] The upper line, marked as desorption temperature 36, represents a boundary temperature based on the pressure of the first binary oxide 34. Above this boundary temperature, to the right and below this line, the first binary oxide 34 will desorb from the surface of the substrate 70. The second unmarked line represents a boundary temperature above which, to the right and below this line, the target oxide 82 on the substrate 70 and / or the oxide layer 80 on the substrate 70 is no longer sufficiently stable for effective growth, and the phases will separate into more stable TiO2 and gaseous SrO. Between these lines, in the region marked as the "growth window," adsorption-controlled growth of the target oxide 82 SrTiO3 is possible because the first binary oxide 34 SrO desorbs, preferably completely, and therefore the flux density or local pressure of the second binary oxide 44 TiO limits and thus restricts the growth rate of the target oxide 82 SrTiO3.

[0099] However, Figure 1The region in the figure space is also depicted, which can be achieved by existing MBE and PLD processes. It is clear that depositing SrTiO3 as the target oxide 82 in an adsorption-limited growth mode using the deposition processes known in the prior art is impossible because the accessible temperature range of the substrate 70 (550-900°C, up to 1200°C in special cases) and the SrO pressure range (10) are limited for a technically useful growth rate of 0.01 to 1 formula unit layer per second. -7 Up to 10 -5 The intersection of hPa is not within the growth window.

[0100] However, thermolaser epitaxy is a deposition process that, by its very nature, does not include limitations on the possible deposition temperature 72 of the substrate 70 present in the MBE, but can simultaneously provide a flux of virtually any source material with a purity significantly higher than that of PLD. In fact, the purity of the source material flux provided is at least similar to, and in most cases even better than, the purity achievable in the MBE process.

[0101] Therefore, according to the present invention, using such Figure 2 The corresponding TLE system 100 shown is used to perform, as described above. Figure 3 The method shown according to the invention is for the controlled deposition of an oxide layer 80 of a target oxide 82 on a substrate 70. Hereinafter, the TLE system 100 and the method according to the invention are described together.

[0102] As previously described, the method according to the invention is carried out in a correspondingly constructed TLE system 100. The main part of the TLE system 100 is a reaction chamber 10 in which an oxide layer 80 is deposited on a substrate 70. Other parts of the TLE system 100 are one or more (such as three exemplarily depicted) laser sources 20 for providing a laser beam 22, and a gas system 50 fluidly connected to the interior of the reaction chamber 10.

[0103] Laser beams 22 are used for both evaporating and / or sublimating source materials 32 and 42, and for heating the substrate 70. Suitable coupling devices 12 are provided to guide the laser beams 22 to their respective destinations within the reaction chamber 10. Preferably, the laser beams 22 are continuous or at least comprise pulse intensities below the plasma generation threshold. In the latter case, the pulse length is preferably selected to be equal to or greater than 1 µs, particularly greater than 1 ms, and preferably greater than 1 s.

[0104] The gas system 50 is capable of filling the reaction chamber 10 with at least a reaction gas 52, which contains one or more oxidants 54 (preferably composed of one or more oxidants 54), such as molecular oxygen (O2), ozone (O3), plasma-activated oxygen (O2). ), ionized oxygen (O) - The reaction gas 52 may be supplied in the form of a directional flow toward the substrate 70, or a combination thereof, containing atomic oxygen (O). Preferably, the reaction gas 52 consists of a single oxidant 54. This one or more oxidants 54 are the source of oxygen atoms required to form the target oxide 82, as will be described below. The gas system 50 can provide the reaction gas 52 with a variety of pressures, preferably at 10... -5 hPa to 10 5 The pressure is selected within the range of hPa. In most embodiments, the gas system 50 not only supplies the reaction gas 52, but is also capable of venting the reaction chamber 10.

[0105] Furthermore, in the reaction chamber 10, a substrate 70 to be coated with an oxide layer 80 is provided, which is held in place by a placement device 60. The oxide layer 80 is formed by depositing a target oxide 82 comprising a defined stoichiometry and formed from one or more evaporated and / or sublimated source materials 32, 42 and oxygen derived from a gaseous oxidant 54. As will be described below, one of the laser beams 22 is used to heat the substrate 70 to a deposition temperature 72, which is appropriately selected for the intended deposition of the oxide layer 80.

[0106] One or more components different from oxygen in the target oxide 82 are provided by evaporation and / or sublimation of one or more source materials 32, 42. In the described embodiment of the TLE system 100, a first deposition source 30 containing an elemental material (preferably an elemental metal) as the first source material 32 and a second deposition source 40 containing an elemental material (preferably an elemental metal) as the second source material 42 are provided, and are held in appropriate positions within the reaction chamber 10, in particular by a suitably constructed and provided arrangement device 60. Each of the source materials 32, 42 is evaporated and / or sublimated by its respective laser beam 22. Since the source materials 32, 42 are provided as elemental materials, the evaporated and / or sublimated source materials 32, 42 can be very pure. Only reactions with one or more oxidants 54 of the reaction gas 52 can lead to the formation of the first binary oxide 34 and the second binary oxide 44, respectively.

[0107] The source materials 32 and 42 used in the TLE system 100 according to the invention and in the method according to the invention are variable. In particular, all elemental materials can be used as source materials 32 and 42, especially Li, Na, K, Ca, Sr, Y, Ag, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, Bi, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Mo, Ru, Rh, Pd, In, Sn, Sb, Be, B, Mg, Si, Cu, Zn, Ge, Se, Cd, Te, Cs, Re, Pt, Au, Hg, Tl, Th, U, Np, Pu, Am, Tc, Os, Rb, and As.

[0108] The method according to the invention is described in detail below. Note that step a) A has already been... Figure 2 This is completed in the TLE system 100 shown. Furthermore, note that steps b) B, c) C, d) D, and e) E can be performed simultaneously.

[0109] In the first step a) A, the substrate 70 and all the deposition sources 30, 40 used are arranged in the reaction chamber 10. Then, the reaction chamber 10 is closed and sealed relative to the surrounding environment, and preferably evaporated by the gas system 50.

[0110] This allows the reaction chamber 10 to be filled with the reactive gas 50 in the next step b) B. Note that the filling in step b) B can preferably also be carried out subsequently in all subsequent steps c) C, d) D and e) E of the method according to the invention.

[0111] To ensure the continuous purity of the reactive gas 52, the reactive gas 52 can be filled simultaneously through different parts of the gas system 50 (not shown), preferably from one side of the TLE system 100, or even more preferably through a nozzle pointing to the front of the substrate 70, and the reactive gas 52 can be pumped from the other side of the TLE system 100.

[0112] As a further preparation for the subsequent deposition of the oxide layer 80 on the substrate 70, the surface of the substrate 70 can be prepared, for example, by heating the substrate to perform an annealing process. Alternatively or additionally, such as Figure 2 As shown, the buffer layer 74 can also be deposited on the surface of the substrate 70, for example, composed of elements already present in the reaction chamber 10, such as the first source material 32, the first binary oxide 34, the second source material 42 and / or the second binary oxide 44.

[0113] Further preparation steps may include preheating the source materials 32, 42 for cleaning purposes, wherein material that has evaporated and / or sublimated is deposited on the substrate.

[0114] In a subsequent step c) C of the method according to the invention, actual evaporation and / or sublimation of the source materials 32, 42 are provided. For this purpose, the intensities of the respective laser beams 22 are selected such that they are below the plasma threshold of the respective source materials 32, 42. Thus, precise thermal evaporation and / or sublimation can be provided. The flux of the evaporated and / or sublimated source materials 32, 42, or the flux of the correspondingly formed binary oxides 34, 44, is directed toward the substrate 70 for subsequent coating of the substrate 70.

[0115] In subsequent step d) D, the substrate 70 is heated by the correspondingly provided laser beam 22. In this crucial step, the substrate 70 is specifically heated to a deposition temperature 72, which is equal to or higher than the desorption temperature 36 of the first source material 32 or the first binary oxide 34 (see [reference]). Figure 5 Depending on the various first source materials 32, especially the various first binary oxides 34, the deposition temperature 72 can preferably be selected between 250°K and 4500°K.

[0116] Thus, the first source material 32 or the first binary oxide 34 is desorbed from the substrate 70. The deposition temperature 72 can be preferably selected such that more than 40%, particularly more than 70%, preferably more than 99.9% of the inflow flux of the first source material 32 and (if present) the first binary oxide 34 are desorbed from the substrate 70. This ensures that the deposition of the target oxide 82 depends only on one or more additional components required to form the target oxide 82. In the case of a binary oxide as the target oxide 82, this is the amount of oxygen available at the substrate (see...). Figure 6 In the case of a ternary or multi-component oxide as the target oxide 82, this is one of one or more additional second source materials 42, or various second binary oxides 44 of the second source material 42.

[0117] In summary, the heating of the substrate 70 in step d) allows for adsorption-controlled deposition of the target oxide 82 in step e) of the method according to the invention, and thus adsorption-controlled deposition of the oxide layer 80. In other words, the amount of the desired compound (i.e., primarily one or more second source materials 42 and / or one or more second binary oxides 44, sometimes also including available oxygen provided by one or more oxidants 54) in addition to the first source material 32 and / or the first binary oxide 34 only defines and thus controls the formation rate of the target oxide 82, and thus controls the growth rate of the oxide layer 80. For this control, intermittent and / or constant and / or variable fluxes can be provided to one or more second source materials 42 and / or corresponding one or more second binary oxides 44 to correspondingly change the growth rate of the oxide layer 80.

[0118] Specifically, since the first source material 32 and / or (if present) the first binary oxide 34 desorbed from the substrate, the formation of the target oxide 82 and the deposition of the oxide layer 80 on the substrate 70 can be provided with very high quality. This is because the physical effect of primarily depositing the target oxide 82 only occurs when the formed compound (i.e., the target oxide 82) has the required appropriate thermodynamic properties (which depend primarily on the substrate temperature, i.e., the deposition temperature 72). Thus, the compound to be deposited, i.e., the target oxide 82, can be actively selected, and therefore the quality of the deposited oxide layer 80 can be maximized, particularly in terms of high purity and low defect density. The defect density of the elements deposited, regardless of the method, with respect to the first source material 32 and / or the first binary oxide 34 is as low as 1 / 10. 4 Especially less than 1 / 10 7 Preferably less than 1 / 10 10 .

[0119] exist Figure 4 This demonstrates another advantage of the method according to the invention. By correspondingly controlling the variables of the deposition process, the actual target oxide 82 can be specifically selected. As shown, even target oxides 82 with different stoichiometry of the same composition can be provided. In particular, the selection can be provided very rapidly in less than 5 seconds. Thus, oxide layers 80 comprising different sublayers with the same composition but different structures can be provided.

[0120] Figure 4 Thermodynamic phase diagrams of different Sr-Ru-O Ruddlesden-Popper materials were actually depicted. By implementing the method according to the invention, such Ruddlesden-Popper materials and oxides having perovskite or perovskite-related structures can be deposited with extremely high quality.

[0121] This phase diagram shows the relationship between the deposition temperature 72, which is most suitable for selecting each structure as the target oxide 82, and the oxygen pressure provided by the reactive gas 52. It can be clearly seen that by correspondingly controlling the pressure and the heating of the substrate 70, a specific selection of the target oxide 82 for depositing the oxide layer 80 can be made.

[0122] Experiments have shown that the deposition temperature and pressure between 1000℃ and 1300℃ are optimal for 10... -4 Up to 10 -2 hPa ( Oxygen (Tor) is used as an oxidant 54, resulting in the deposition of a high-quality epitaxial crystalline film of Sr2RuO4 as the target oxide 82 of the oxide layer 80.

[0123] Similarly, it was found that the deposition temperature and pressure between 600°C and 1000°C were 5 × 10⁻⁶. -3 Up to 2×10 -2 Oxygen at hPa acts as an oxidant 54, resulting in the deposition of a high-quality epitaxial crystalline film of SrRuO3 as the target oxide 82 of the oxide layer 80.

[0124] In both cases, the flux of Ru provided as the first source material 32 is (5 × 10⁻⁶). 12 and 3×10 14 atoms / s cm 2 ) and the flux of Sr provided as the second source material 42 (1×10) 13 and 1×10 15 atoms / s cm 2 ) are the same.

[0125] exist Figure 5 , Figure 6 The document describes the verification of the principle of performing this method on a binary oxide, namely Al₂O₃, as the target oxide 82. In the following sections, [the document discusses...]. Figure 5 and Figure 6 Together, they are described. In summary, the ability of TLE to grow adsorption-controlled binary materials is demonstrated through the described adsorption-controlled growth of c-plane sapphire (Al2O3). Note that Al2O3 is expected to have one of the highest deposition temperatures of 72 (1650°K in vacuum) for adsorption-controlled growth. Furthermore, it has high scientific and industrial relevance due to its high band gap (9 eV), high dielectric constant (9), high thermal conductivity (46 W / Km), and high thermal stability. For example, it is used as a high-k gate oxide in many optical applications and is being investigated for use in high-power electronic devices.

[0126] High thermal stability is accompanied by the high deposition temperature of 72°C required to induce volatility. Figure 5 The relationship between growth rate and substrate temperature under constant element flux is shown. A sharp decrease in growth rate was observed at 900 °C, which was at the pressure of the supplied reactive gas 52 (see [reference]). Figure 2 The desorption temperature of Al2O3 at 0.001 hPa is 36°C. At this temperature of 900°C, the actual desorbed substances are Al2O3 and pure Al (which is the primary source material 32). Figure 2 Suboxides of ))

[0127] By heating the substrate 70 to a temperature much higher than Figure 5 The desorption temperature 36 shown is used to select the growth rate under adsorption control. Therefore, the supply flux of reactant gas 52 or oxidant 54 determines the growth rate, which allows for oxidation to the less volatile Al2O3. This is as follows: Figure 6 As shown, Figure 6 The relationship between the growth rate and the pressure of the reactive gas 52 (in this case, O2) is shown when the first source material 32 (pure Al) is at a fixed flux and the substrate 70 is heated to a deposition temperature 72 of 1600°C.

[0128] It can be clearly seen that the growth rate increases with increasing supply of oxidant 54 (in this case, molecular oxygen) until the mean free path limits the growth rate under high pressure. This demonstrates the ability to grow Al2O3 in an adsorption-controlled manner—a binary substance that has not been previously shown to be grown in an adsorption-controlled manner. Furthermore, it shows that the formation rate of the target oxide 82, and therefore the growth rate of the oxide layer 80, can also be controlled by actively filling the reaction chamber 10 with the reactive gas 52.

[0129] List of reference numerals

[0130] 10: Reaction Chamber

[0131] 12: Coupling device

[0132] 20: Laser source

[0133] 22: Laser beam

[0134] 30: First sedimentary source

[0135] 32: First Source Material

[0136] 34: First binary oxide

[0137] 36: Desorption temperature

[0138] 40: Second sedimentary source

[0139] 42: Second source material

[0140] 44: Second binary oxide

[0141] 50: Gas System

[0142] 52: Reaction gas

[0143] 54: Oxidizing agent

[0144] 60: Arrangement device

[0145] 70: Substrate

[0146] 72: Deposition temperature

[0147] 74: Buffer layer

[0148] 80: Oxide layer

[0149] 82: Target oxide

[0150] 100: TLE system

[0151] A: Step a)

[0152] B: Step b)

[0153] C: Step c)

[0154] D: Step d)

[0155] E: Step e)

Claims

1. A method for controlled deposition of an oxide layer (80) of a target oxide (82) on a substrate (70) in a thermal laser epitaxy (TLE) system (100), the target oxide (82) comprising a defined stoichiometry and formed from one or more evaporated and / or sublimated source materials and oxygen derived from a gaseous oxidant (54), the TLE system (100) further comprising a reaction chamber (10) and one or more laser sources (20) for providing a laser beam (22) within the reaction chamber (10); characterized in that The following steps: a) The substrate (70) and a first deposition source (30) are provided in the reaction chamber (10), wherein the first deposition source (30) contains an elemental material as a first source material (32). b) The reaction chamber (10) is filled with a reaction gas (52) containing one or more oxidants (54) supplied by the gas system (50) of the TLE system (100). c) By irradiating the first source material (32) with a laser beam (22) of the TLE system (100) at an intensity lower than the plasma generation threshold of the first source material (32), the first source material (32) is evaporated and / or sublimated to provide a flux of the evaporated and / or sublimated first source material (32) and / or the first binary oxide (34) formed by the first source material (32) and the oxidant (54), wherein the flux is directed toward the substrate (70). d) The substrate (70) is heated to a deposition temperature (72) by a laser beam (22) of the TLE system (100), wherein the deposition temperature (72) of the substrate (70) is equal to or higher than the desorption temperature (36), such that the first deposition source (30) and / or the first binary oxide (34) are at least partially desorbed from the substrate (70); e) The target oxide (82) is formed by combining one or more evaporated and / or sublimated source materials with oxygen derived from one or more oxidants (54), and the target oxide (82) is deposited on the substrate (70) as an oxide layer (80). The formation of the target oxide (82) and the deposition of the oxide layer (80) on the substrate (70) are controlled by controlling the filling of the reaction chamber (10) with the reaction gas (52) in step b) and / or by controlling the rate of evaporation and / or sublimation of the first source material (32) at the substrate (70) in step c) and / or by controlling the deposition temperature (72) in step d).

2. The method as described in claim 1, characterized in that, In step d), the deposition temperature (72) is selected such that more than 40%, particularly more than 70%, preferably more than 99.9% of the inflow flux of the first source material (32) is desorbed from the substrate (70), and in step e), the adsorbed portion of the first source material (32) combines with oxygen derived from the one or more oxidants (54) and / or the first binary oxide (34) forms the target oxide (82) for depositing the oxide layer (80).

3. The method as described in claim 1, characterized in that, In step a), one or more second deposition sources (40) are provided in the reaction chamber (10), wherein each second deposition source (40) contains an elemental material as a second source material (42); Furthermore, step c) includes evaporating and / or sublimating the one or more second source materials (42) by irradiating the laser beam (22) of the TLE system (100) onto the one or more second source materials (42) at an intensity lower than the plasma generation threshold of the various second source materials (42), for providing a flux of the evaporated and / or sublimated one or more second source materials (42) and / or one or more second binary oxides (44) formed by one of the one or more second source materials (42) with the oxidant (54) directed toward the substrate (70); In step e), the first deposition source (30) and / or the first binary oxide (34) are combined with one or more second deposition sources (40) and / or one or more second binary oxides (44), and if necessary, with oxygen derived from one or more oxidants (54) to form the target oxide (82) for depositing the oxide layer (80). And in step d), the deposition temperature (72) of the substrate (70) is equal to or higher than a certain temperature, such that the first deposition source (30) and / or the first binary oxide (34) are desorbed without being used to form the target oxide (82).

4. The method as described in claim 3, characterized in that, The deposition temperature (72) in step d) is selected to be high enough that the amount of the first deposition source (30) and / or the first binary oxide (34) deposited onto the substrate (70) in any way is less than 1 / 10 of the elemental composition of the target oxide (82). 4 Especially less than 1 / 10 7 Preferably less than 10 10 .

5. The method as described in any one of claims 3 or 4, characterized in that, In step c), the laser beam (22) used for evaporating and / or sublimating the one or more second source materials (42) is controlled accordingly to pass through the one or more evaporated and / or sublimated second source materials (42) and / or the one or more second binary oxides (44) at intermittent and / or constant and / or variable flux.

6. The method as described in any one of claims 3 to 5, characterized in that, The target oxide (82) formed in step e) includes a perovskite structure and / or a perovskite-related structure and / or a Ruddlesden-Popper structure.

7. The method as described in any one of claims 1 to 6, characterized in that, In step d), the deposition temperature (72) is selected such that the first source material (32) and / or the first binary oxide (34) and / or one or more second source materials (42) and / or one or more second binary oxides (44) can migrate along the surface of the substrate (70).

8. The method as described in any one of claims 1 to 7, characterized in that, In step d), the deposition temperature (72) is provided between 250°K and 4500°K.

9. The method as described in any one of claims 1 to 8, characterized in that, In step d), the deposition temperature (72) is selected relative to the first binary oxide (34).

10. The method as described in claim 9, characterized in that, The deposition temperature (72) is selected relative to the first binary oxide (34) to be equal to or higher than the following temperatures: 。 11. The method as described in any one of claims 1 to 10, characterized in that, In step c), and especially in step d), a continuous laser beam (22) or a laser beam (22) with an intensity lower than the plasma generation threshold is used.

12. The method as described in any one of claims 1 to 11, characterized in that, In step b), the pressure and / or composition of the reaction gas (52) are changed by correspondingly controlling the gas system (50) of the TLE system (100) to actively change the stoichiometry of the target oxide (82) formed without changing the composition.

13. The method as described in any one of claims 1 to 12, characterized in that, In step c), by correspondingly controlling the laser beam (22) of the TLE system (100) used in step c), the flux of the first source material (32) and / or the first binary oxide (34) provided for evaporation and / or sublimation is changed to actively change the stoichiometry of the target oxide (82) formed without changing the composition.

14. The method as described in any one of claims 1 to 13, characterized in that, In step d), the deposition temperature (72) of the substrate (70) is changed by correspondingly controlling the laser beam (22) of the TLE system (100) to actively change the stoichiometry of the formed target oxide (82) without changing the composition.

15. The method as described in any one of claims 12 to 14, characterized in that, Before and / or during and / or after repeating step c), the changes in the reaction gas (52) and / or the changes in the flux of the first source material (32) and / or the first binary oxide (34) provided for evaporation and / or sublimation and / or the changes in the deposition temperature (72) are provided.

16. The method as described in any one of claims 12 to 15, characterized in that, The oxide layer (80) deposited in step e) comprises two or more subsequent sublayers formed from target oxides (82) having the same composition but different stoichiometry, preferably different perovskite structures and / or perovskite-associated structures and / or Ruddlesden-Popper structures.

17. The method as described in any one of claims 1 to 16, characterized in that, The first source material (32) and / or one or more second source materials (42) are elemental metals.

18. The method as described in any one of claims 1 to 17, characterized in that, The first source material (32) and / or one or more second source materials (42) are selected from the group consisting of materials including the following members: Li, Na, K, Ca, Sr, Y, Ag, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, Bi, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Mo, Ru, Rh, Pd, In, Sn, Sb, Be, B, Mg, Si, Cu, Zn, Ge, Se, Cd, Te, Cs, Re, Pt, Au, Hg, Tl, Th, U, Np, Pu, Am, Tc, Os, Rb, As.

19. The method as described in any one of claims 1 to 18, characterized in that, Step b) is performed consecutively during the execution of step c) and / or step d) and / or step e).

20. The method according to any one of claims 1 to 19, characterized in that, In step b), filling the reaction chamber (10) includes providing a directional flow of reaction gas (52) to the substrate (70).

21. The method as described in any one of claims 1 to 20, characterized in that, The reaction gas (52) consists of a single oxidant (54).

22. The method as described in any one of claims 1 to 21, characterized in that, The one or more oxidants (54) are selected from molecular oxygen (O2), ozone (O3), plasma-activated oxygen (O2). ), ionized oxygen (O-), atomic oxygen (O) and combinations thereof.

23. The method as described in any one of claims 1 to 22, characterized in that, In step b), the reactant gas (52) is supplied at 10 -9 hPa to 10 5 Within the hPa range, preferably at 10 hPa. -5 hPa to 10 5 The pressure to be selected within the hPa range.

24. The method as described in any one of claims 1 to 23, characterized in that, Prior to step c), a step is performed to prepare the surface of the substrate (70) for deposition of the oxide layer (80).

25. The method as described in claim 24, characterized in that, The steps of preparing the surface include tempering the surface by heating the substrate (70) with the laser beam (22) of the TLE system (100), preferably by the laser beam (22) used in step d).

26. The method as described in claim 24 or 25, characterized in that, The steps of preparing the surface include coating the surface with one or more buffer layers (74).

27. The method as described in claim 26, characterized in that, The buffer layer (74) comprises the first source material (32) and / or an oxide of the first source material (32), particularly the first binary oxide (34), preferably composed thereof.

28. The method as described in claim 26 or 27, characterized in that, The buffer layer (74) comprises one of the one or more second source materials (42) and / or an oxide of one of the one or more second source materials (42), particularly one of the one or more second binary oxides (44), preferably composed thereof.

29. The method as described in any one of claims 26 to 28, characterized in that, The buffer layer (74) comprises the material of the substrate (70), preferably composed of it.

30. The method as described in any one of claims 1 to 29, characterized in that, Prior to step c), a preparation step for evaporation and / or sublimation is performed, wherein the first source material (32) and / or one or more second source materials (42) are heated by a laser beam (22), preferably the laser beam (22) used in step c), to remove the first source material (32) and / or one or more second source materials (42) respectively, without depositing the material onto the substrate (70).

31. A TLE system (100) configured to perform the method as described in any one of the preceding claims, comprising: - Reaction chamber (10), - One or more laser sources (20) for providing laser beams (22) for heating the substrate (70) and for evaporating and / or sublimating the one or more source materials (32, 42), - A coupling device (12) for coupling the one or more laser beams (22) into the reaction cavity (10). - A placement device (60) for placing the substrate (70) and the one or more deposition sources (30, 40) providing the one or more source materials (32, 42) in the reaction chamber (10), and - Gas system (50) for supplying the reaction gas (52) within the reaction chamber (10).

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