Method for the controlled deposition of a nitride layer of a target nitride on a substrate in a tle system, and tle system

Abstract

The invention relates to a method for the controlled deposition of a nitride layer (80) of a target nitride (82) on a substrate (70) in a thermal laser epitaxy (TLE) system (100), the target nitride (82) comprising a defined stoichiometry and being formed from one or more evaporated and / or sublimated source materials and nitrogen originating from a gaseous nitridizing agent (54), the TLE system (100) further comprising a reaction chamber (10) and one or more laser sources (20) for providing laser beams (22) within the reaction chamber (10). Further, the invention relates to a TLE system (100) constructed for carrying out said method.

Description

[0001] Method for the controlled deposition of a nitride layer of a target nitride on a substrate in a TLE system, and TLE system

[0002] The invention relates to a method for the controlled deposition of a nitride layer of a target nitride on a substrate in a thermal laser epitaxy (TLE) system, the target nitride comprising a defined stoichiometry and being formed from one or more evaporated and / or sublimated source materials and nitrogen originating from a gaseous nitridizing agent, the TLE system further comprising a reaction chamber and one or more laser sources for providing laser beams within the reaction chamber. Further, the invention relates to a TLE system constructed for carrying out said method.

[0003] Epitaxial nitride films may currently be produced by a variety of methods such as atomic layer deposition (ALD), chemical vapor deposition (CVD), sputtering and molecular beam epitaxy (MBE). Whereas all of these methods allow the deposition of nitride films with rather good stoichiometry, by far the best stoichiometry is achieved by growing epitaxial nitride films by (MetalOrganical) Chemical Vapor Deposition ([MO]CVD) or by MBE in the adsorption-controlled growth mode.

[0004] Adsorption-limited growth works best in an ultrahigh purity environment, which usually means ultrahigh vacuum, or a residual gas atmosphere with extreme gas purity. This implies that non-thermal flux generation such as by sputtering or ablation, will not work well due to the liberation of impurities from the chamber walls or source material holders, and due to changes to the growing crystal surface by charged and / or highly energetic source material atoms or molecules. Thermal flux generation by evaporation (from a molten material) or sublimation (from a solid material) is therefore required or at least strongly preferred. Gaseous source material, and in particular the nitrogen required to grow nitrides, may not be reactive enough in its common form as N2 molecule. It therefore needs to be either made more reactive by physical activation, usually by the formation of a nitrogen plasma to form excited molecules or even dissociated atoms, or by providing it in a more reactive compound form, such as, e.g., as ammonia, NH3.

[0005] Even the binary nitrides (element plus nitrogen in various stoichiometries) already span a very wide range of vapor pressures. The temperatures corresponding to a vapor pressure of 10-5hPa range from instability at room temperature to well above 2000 K. Especially the high-temperatures ones are difficult to grow in the adsorption-controlled growth mode, for example via MBE, as they mostly require high substrate temperatures due to their high binding energies, and the presence of nitrogen or a nitridizing agent to achieve the desired nitridation state, often in addition to very high source temperatures. In many cases, the strong nitridizing conditions necessary for stoichiometric growth are incompatible with the Joule heater technology used in MBE, since conductors, such as for instance Ta wires, nitridize and fail in the presence of nitrogen at high temperatures. Successful examples of nitrides grown by MBE in the adsorption-controlled growth mode are therefore restricted to low (less than about 1000 °C) substrate temperatures and low (less than 10-5hPa) nitrogen pressures. The required high substrate temperature also weakens the nitridation potential, which means that correspondingly even higher nitrogen or nitridant pressures are required for high quality crystal growth, a condition which is even harder to meet with MBE.

[0006] In view of the above, it is an object of the present invention to provide an improved method for the controlled deposition of a nitride layer, and an improved thermal laser evaporation system which do not have the aforementioned drawbacks of the state of the art. In particular, it is an object of the present invention to provide an improved method for the controlled deposition of a nitride layer, and an improved thermal laser evaporation system which provide the possibility of a deposition of a nitride layer consisting of one or more elemental constituents and nitrogen, wherein both the stoichiometry of the deposited nitride and also the actual deposition of the nitride layer can actively be controlled.

[0007] This object is satisfied by the respective independent patent claims. In particular, this object is satisfied by a method for the controlled deposition of a nitride layer according to independent claim 1 , and by a 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 refer to a TLE system according to the second aspect of the invention, and vice versa, if of technical sense.

[0008] According to a first aspect of the invention the object is satisfied by a method for the controlled deposition of a nitride layer of a target nitride on a substrate in a thermal laser epitaxy (TLE) system, the target nitride comprising a defined stoichiometry and being formed from one or more evaporated and / or sublimated source materials and nitrogen originating from a gaseous nitridizing agent, the TLE system further comprising a reaction chamber and one or more laser sources for providing laser beams within the reaction chamber. The method according to the present invention is characterized by the steps of: a) providing the substrate and a first deposition source in the reaction chamber, wherein the first deposition source contains an elemental material as first source material, b) filling the reaction chamber with a reaction gas comprising one or more nitridizing agents provided by a gas system of the TLE system, c) evaporating and / or sublimating the first source material by impinging a laser beam of the TLE system on the first source material with an intensity below a plasma generation threshold of the first source material, for providing a flux of evaporated and / or sublimated first source material and / or of a first binary nitride formed from the first source material with the nitridizing agent, wherein the flux is directed towards the substrate, d) heating the substrate to a deposition temperature by a laser beam of the TLE system, wherein the deposition temperature of the substrate is equal or higher to a desorption temperature such that the first source material and / or the first binary nitride desorb at least partly from the substrate, e) forming the target nitride by combining the one or more evaporated and / or sublimated source materials and nitrogen originating from the one or more nitridizing agents and depositing the target nitride as nitride layer onto the substrate, wherein the formation of the target nitride and the deposition of the nitride layer on the substrate is controlled by controlling the filling of the reaction chamber with the reaction gas in step b) and / or by controlling the rate of the evaporated and / or sublimated first source material at the substrate in step c) and / or by controlling the deposition temperature in step d).

[0009] The method according to the present invention is intended to be carried out in and with a thermal laser epitaxy (TLE) system. TLE systems are the best choice for providing a controlled deposition of a target nitride comprising a desired and hence defined stoichiometry.

[0010] Said TLE system at least comprises a reaction chamber for providing a reaction volume sealable with respect to the ambient environment. In said reaction chamber, one or more deposition sources and a substrate to be coated are arranged, held in place by arrangement means.

[0011] Further, the TLE system comprises a gas system for providing a selectable atmosphere within the reaction chamber. The gas system is at least capable of providing a reaction gas into the reaction chamber, wherein the reaction gas contains one or more gaseous nitridizing agents such as for instance molecular nitrogen or ammonia. However, the gas system can also be constructed for providing other reaction gases, such as for instance a noble gas such as argon as inert reaction gas, a so-called dilution gas, and / or for evacuating the reaction chamber to pressures, in particular up to ultra-high vacuum with pressures as low as 10-12hPa or even lower.

[0012] In addition, the TLE system comprises one or more laser sources and coupling means accordingly provided on and / or at the reaction chamber for providing laser beams within the reaction chamber. The laser beams are used for evaporation and / or sublimation of the one or more source materials and for the heating of a substrate. Thereby any additional heating of the one or more deposition sources and of the substrate by electric heating means, such as for instance used in conventional MBE, are not needed. Limitations caused by said heating means for the used reaction gas, for instance concerning the provided nitridizing agent and / or its pressure, can be avoided.

[0013] In summary, by using a TLE system for carrying out the method according to the present invention, a high purity environment for the deposition of the nitride layer can be provided. Every element of the TLE system, in particular the evaporation and / or sublimation of the one or more source materials, the heating of the substrate, and also the gas system for providing the reaction gas, can be individually and actively controlled for ensuring the deposition of the target nitride comprising the desired and hence defined stoichiometry.

[0014] In the first step a) of the method according to the present invention, the substrate and a first deposition source are arranged and hence provided in the reaction chamber. This can be carried out when the reaction chamber is still open with respect to the ambient environment, but can also be made possible by means of correspondingly available airlocks when the reaction chamber is already closed and sealed. Within the reaction chamber, arrangement means are present for the respective arrangement of both the substrate and the one or more deposition source, respectively. Said arrangement means can be provided for spatially fixing the substrate and / or the one or more deposition source only. Alternatively, or additionally, these arrangement means can also be designed to provide movements of the substrate and / or of the one or more deposition source, for example to move the substrate in and out of a deposition position, and / or to exchange the deposition source to be used. In summary, after execution of step a), the first deposition source and the substrate are arranged within the reaction chamber.

[0015] In particular, the first deposition source contains an elemental material as source material. In other words, the source material is pure, which means it consists to a very large degree of one element from the periodic table of elements only, except nitrogen itself, and the elemental material, which is accordingly selected for forming the non-nitrogen constituent of the target nitride, is provided without any precursor molecules. Nevertheless, it is possible that the surface of the source material, which faces the environment and especially, after execution of step b) of the method according to the present invention, the reaction gas comprising one or more nitridizing agents, is nitridized and hence an uppermost layer of the deposition source is formed by a nitride of the elemental material forming the bulk of the deposition source.

[0016] It is to be noted that the aforementioned selection of the elemental material for forming the non-nitrogen constituent and the accompanied effects are not only applicable for binary nitrides, in which nitrogen bonds to a single type of non-nitrogen constituent, but also in an analogue way for ternary of even multernary nitrides, in which two or even more non-nitrogen constituents are bound to the one or more nitrogen atoms.

[0017] In the next step b) of the method according to the present invention, the gas system of the TLE system is used for accordingly preparing the atmosphere within the reaction chamber for the deposition of the nitride layer onto the substrate. In particular, the reaction gas comprising one or more nitridizing agents is filled into the reaction chamber. A nitridizing agent in the sense of the present invention is a gaseous substance which can be used as source for the required nitrogen atoms during the formation of the target nitride. Preferably, the reaction gas consists of the one or more nitridizing agents.

[0018] Before said filling of the reaction chamber with the reaction gas, the reaction chamber preferably is evacuated by the gas system. By that the purity of a reaction atmosphere consisting only of the reaction gas can be provided or at least drastically improved. After execution of step b), by many orders of magnitude in concentration, only the reaction gas comprising, preferably consisting of, the one or more nitridizing agents is present as atmosphere within the reaction chamber. If air locks are used in step a) for arranging the substrate and / or the first deposition source in the reaction chamber, step b) can be carried out also before and / or during the execution of step a).

[0019] After preparing the reaction chamber in steps a), b), in the next step c) the actual evaporation and / or sublimation of the first source material, namely the elemental material, takes place. In particular, as the method according to the present invention is carried out by a TLE system, a laser beam provided by a respective laser source of the TLE system is used for the evaporation and / or sublimation. The laser beam is coupled into the reaction chamber and directed onto the surface of the source material.

[0020] The intensity of the laser beam is selected below a plasma threshold of the first source material. Hence, an exclusively thermal evaporation and / or sublimation of the first source material is provided, in particular without explosive ablation or the formation of a plasma as present in PLD and / or sputtering processes. Evaporated and / or sublimated first source material can thereby be provided. If the surface of the deposition source is nitridized, as described above, also evaporation and / or sublimation of said nitride of the source material is possible. In addition, the evaporated and / or sublimated first source material can also react with the one or more nitridizing agents of the reaction gas, forming a first binary nitride of the first source material. In most of the cases the nitride of the source material present at the surface of the deposition source is also said first binary nitride.

[0021] A binary nitride in the sense of the invention is a nitride comprising two types of constituents, namely an elemental material and nitrogen, the actual stoichiometry of said binary nitride is not fixed. For instance, with lithium as metal, the nitrides LiN, LiN2, LiaN, and LiNs are all binary nitrides in the sense of the present invention. The same applies accordingly to ternary or multernary nitrides, i.e. nitrides with two and three or more elemental non-nitrogen constituents.

[0022] In summary, in step c) a flux of the evaporated and / or sublimated first source material and / or of the first binary nitride is provided. Said flux is provided towards the substrate to be coated, for instance by accordingly arranging the first deposition source and the substrate within the reaction chamber in step a) of the method according to the present invention.

[0023] In step d) of the method according to the present invention, the substrate is prepared for the deposition of the target nitride for forming the intended nitride layer. For this, the substrate is heated by a laser beam provided by an accordingly provided laser source of the TLE system. Analogous, to the laser beam used for evaporating and / or sublimating the first source material, the laser beam for the heating of the substrate is also coupled into the reaction chamber and directed onto the substrate.

[0024] In particular, the heating of the substrate is provided such that the substrate comprises a defined and selected deposition temperature. Said deposition temperature is selected to be equal to or higher than a desorption temperature such that the first source material and / or the first binary nitride desorbs at least partially from the substrate. Thereby the respective deposition temperature depends on the properties of the substrate itself, but also on the used first source material and / or the already formed first binary nitride.

[0025] Setting the deposition temperature equal or higher than the respective desorption temperature provides the effect that a dependency of a deposition rate of the target nitride, and hence a growth rate of the nitride layer, from the flux density of the evaporated and / or sublimated first source material is drastically reduced, preferably eliminated. This is due to the fact that between the deposition rate and the desorption rate of the first source material and / or the first binary nitride, respectively, an equilibrium is established. In other words, the rate of first source material and / or the first binary nitride, respectively, deposited onto the substrate is equal or at least essentially equal to the rate of first source material and / or the first binary nitride desorbed from the substrate.

[0026] On the other hand, this loss of dependency allows controlling the deposition rate of the target nitride by other properties, namely by the selection of a suitable deposition temperature and especially by the amount of nitrogen available for the formation of the target nitride. This is especially based on the finding that the first source material in its pure form, namely the elemental material, or a metastable nitride of this material, in other words the first binary nitride, are in most of the cases more volatile than the desired target nitride of the respective material, and that a specific binary nitride of the first source material, the first binary nitride and if applicable also the target nitride, also provides a specific desorption temperature which can be considered when selecting the deposition temperature at which the substrate is to be heated. In summary, these effects combined provide the possibility to grow also a binary nitride as target nitride in an adsorption-controlled way.

[0027] Finally, in step e) of the method according to the present invention, the target nitride is formed and deposited onto the substrate for forming the nitride layer. The target nitride comprises as constituents the first source material and nitrogen. The stoichiometry of the target nitride is defined and selected. Said forming of the target nitride can be provided directly on the substrate. However, if the target nitride is a first binary nitride already formed in advance of the deposition on the substrate, this is also considered as enclosed in forming the target nitride in of step e) in the sense of the present invention. According to the present invention, both said formation of the target nitride, and the deposition of the nitride layer onto the substrate, respectively, are controlled.

[0028] In particular, controlling the formation of the target nitride and / or the deposition of the nitride layer can be provided by controlling the filling of the reaction chamber with the reaction gas. As mentioned above, the deposition temperature of the substrate can preferably be chosen such that the first source material in its pure form, or in the form of a less stable nitride, desorbs from the substrate, and in contrast to that the target nitride is adsorbed and forms at the surface of the substrate. Hence by controlling the filling in step b), the amount of available nitrogen can be controlled and hence the formation rate of the less stable or the target nitride can be actively adjusted. In other words, controlling the filling of the reaction chamber with reaction gas provides a way of growing the nitride layer in an adsorption-controlled way.

[0029] Additionally, or alternatively, also the rate of the evaporated and / or sublimated first source material at the substrate in step c) can be used for controlling the formation of the target nitride and / or the deposition of the nitride layer. In particular, the rate of evaporated and / or sublimated first source material defines the maximal rate at which the target nitride can be formed, and hence the maximum growth rate of the nitride layer on the substrate. Lowering the rate of the evaporated and / or sublimated first source material, for instance by lowering the intensity of the laser beam used for the evaporation and / or sublimation, also lowers the maximum value of the formation rate of the target nitride.

[0030] Again additionally, or alternatively, also the deposition temperature at which the substrate is set in step d) has an influence on the formation of the target nitride and the deposition of the nitride layer on the substrate. In particular, as mentioned above, different nitrides of the first source material in most of the cases comprise different desorption temperatures. Hence, by controlling, and thereby accordingly adjusting, the deposition temperature, the selection of the target nitride can be actively altered. Also, the fraction of desorption, in other words the fraction of impinging material on the substrate which again subsequently desorbs, depends in most of the cases on the temperature of the substrate. Also, this property can be used for controlling the formation of the target nitride and the deposition of the nitride layer on the substrate. Finally, and most important, a deposition predominantly only takes place, if the formed compound, namely the target nitride, possesses the required suitable thermodynamic properties, which dominantly depend on the substrate temperature. Thereby the deposited compound, namely the target nitride, can be actively selected and hence the quality of the deposited layer, in particular concerning high purity and low defect density, can be maximized.

[0031] In summary, the method according to the present invention provides the possibility of a deposition of a nitride layer consisting of an elemental material constituent and nitrogen with controlled stoichiometry and likewise controlled growth rate. By implementing the method according to the present invention, said deposition can be provided in an adsorption-controlled way. This exploits in particular, that the deposition only takes place if the formed compound, namely the target nitride, possess the required suitable thermodynamic properties, which dominantly depend on the substrate temperature. Hence, in particular controlling the substrate temperature allows producing said nitride layer consisting of the target nitride in exceedingly high quality, even if binary nitrides are chosen for target nitrides. This is due to the self-adjusting stoichiometry of the target nitride under adsorption-controlled conditions.

[0032] Preferably, at least steps c), d), and e) of the method according to the present invention are carried out simultaneously.

[0033] In a first embodiment, the method according to the present invention can be characterized in that in step d) the deposition temperature is selected such that more than 40%, in particular more than 70%, preferably more than 99.99%, of the incoming flux of the first source material desorbs from the substrate, and that in step e) the adsorbed part of the first source material combined with nitrogen originating from the one or more nitridizing agents and / or the first binary nitride form the target nitride for the deposition of the nitride layer. In other words, the first source material not bound in the stable stoichiometric target nitride desorbs from the substrate, preferably completely or at least essentially completely. Only the target nitride, and with it the first binary nitride if its stoichiometry complies to the target nitride, is deposited onto the substrate. As the formation of the target nitride depends on the availability of nitrogen, which again is controlled in step b) of the method according to the present invention by the filling of the reaction chamber with reaction gas, an adsorption-controlled way for depositing a binary nitride on a substrate, and hence in particular the advantage of the exceedingly high structural and stoichiometric quality of a nitride layer deposited in this way, can be provided more easily.

[0034] According to an alternative embodiment, the method according to the present invention can comprise that in step a) one or more second deposition sources are provided in the reaction chamber, wherein each second deposition source contains an elemental material as second source material, further that step c) includes evaporating and / or sublimating one or more second source materials by impinging a laser beam of the TLE system on the one or more second source materials with an intensity below a plasma generation threshold of the respective second source material, for providing a flux of evaporated and / or sublimated one or more second source materials and / or of one or more second binary nitrides formed from one of the one or more second source materials with the nitridizing agent directed towards the substrate, wherein in step e) the first source material and / or the first binary nitride combined with the one or more second sources materials and / or the one or more second binary nitrides, if necessary additionally combined with nitrogen originating from the one or more nitridizing agents, form the target nitride for the deposition of the nitride layer, and that in step d) the deposition temperature of the substrate is equal or higher to a temperature such that the first source material and / or the first binary nitride and / or the one or more second sources materials and / or the one or more second binary nitrides desorb if they are not used for forming the target nitride.

[0035] In contrast to the embodiment described above, one or more additional second deposition sources are arranged in the reaction chamber in step a) of the method according to the present invention. Subsequently, the one or more second source materials of said one or more second deposition sources, again elemental non-ni- trogen materials, are evaporated and / or sublimated by accordingly provided laser beams of the TLE system. All features and advantages described above concerning the first deposition source and the first source material also apply for each of the one or more second deposition sources and the respective one or more second source materials.

[0036] By providing one or more second source materials, respectively by providing the fluxes of the evaporated and / or sublimated one or more second source materials and / or their respective second binary nitrides, the formation of a ternary, if a single second deposition source is present, or of a multernary nitride, if two or more second deposition sources are present, can be provided as target nitride. Again, the target nitride comprises as constituents the first source material, the one or more second source materials, and nitrogen, wherein the stoichiometry of the target nitride is defined and selected in a self-adjusting way by the thermodynamic properties of the target nitride, the substrate temperature and the flux densities of the source materials and the nitridizing agents. Examples for ternary nitrides are for instance AIGaN, LiZnN, U3AIN2, MgSnN2, or Cae / WNs, where M= Ga, Mn, or Fe. A known multernary nitride is for example GalnNAs.

[0037] In particular, in the present embodiment of the method according to the present invention, the heating of the substrate in step d) is controlled such that the resulting deposition temperature of the substrate is high enough that both the first source material and the first binary nitride, respectively, desorb. Only if the first source material and / or the first binary nitride, depending on which of them is present at the substrate, combines with an element of the one or more second source materials and / or the one or more second binary nitrides to form the target nitride with the selected and defined stoichiometry, in other words only if the respective ternary or multernary nitride defined as target nitride is formed, a deposition of the reaction product at the substrate takes place.

[0038] In other words, the deposition of the target nitride is adsorption-controlled. Hence, by implementing this embodiment of the method according to the present invention, all advantages described above concerning a deposition of a binary nitride in an adsorption-controlled way, in particular the exceedingly high structural and stoichiometric quality of the deposited nitride layer, can also be provided for nitride layers formed from ternary and multernary nitrides.

[0039] In a first alternative approach, the first source material and / or the first binary nitride represents the volatile part of the compound to be formed, namely the target nitride, which is provided in excess. Further, the one or more second source materials and / or the respective second binary nitrides form the rate limiting, nonvolatile part of the compound. Hence, the flux of the one or more evaporated and / or sublimated second source materials and / or one or more second binary nitrides define the forming rate of the target nitride and thereby the growth rate of the nitride layer.

[0040] According to second alternative approach, both the first source material and / or the first binary nitride, and also the one or more second source materials and / or the respective second binary nitrides form volatile parts of the compound to be formed, namely the target nitride, which are provided in excess. In this alternative, the amount of available nitridizing agent forms the rate limiting, non-volatile part of the compound and hence defines the forming rate of the target nitride and thereby the growth rate of the nitride layer.

[0041] In summary, in both alternatives, providing the nitride layer by depositing the target nitride in exceedingly high quality can also be provided also for ternary or multer- nary nitrides.

[0042] Further, the method according to the present invention can be enhanced by that the deposition temperature in step d) is selected high enough that the amount of the first source material and / or the first binary nitride and / or the one or more second source material and / or the one or more second binary nitrides nevertheless deposited onto the substrate is less than 1 in 104, in particular less than 1 in 107, preferably less than 1 O10, compared to elements of the target nitride. As described above, the nitride layer formed of the ternary or multernary nitride as target nitride can be produced in exceedingly high quality. Further, the first source material and / or the first binary nitride and / or the one or more second source material and / or the one or more second binary nitrides desorb from the substrate at the deposition temperature at which the substrate is provided. However, as a deposition is a chemical reaction, there can still be isolated cases of deposition of the first source material and / or the first binary nitride and / or the one or more second source material and / or the one or more second binary nitrides on the substrate. On the other hand, the probability of said undesired depositions of the first source material and / or the first binary nitride and / or the one or more second source material and / or the one or more second binary nitrides gets lower with rising temperature of the substrate. Hence, by accordingly selecting the deposition temperature a defect density, namely the number of units of the first source material and / or the first binary nitride and / or the one or more second source material and / or the one or more second binary nitrides and / or any impurity from the residual chamber background pressure compared to the number of units of the target nitride, of less than 1 in 104, in particular less than 1 in 107, preferably less than 1 O10, can be achieved.

[0043] The same applies to the opposite case of a too high substrate temperature, such that the first source material and / or the one or more second source materials are incorporated in slight deficiency, such that the nitride actually deposited onto the substrate contains fewer units of the first source material and / or the one or more second source materials compared to the amount of units of the target nitride, of less than 1 in 104, in particular less than 1 in 107, preferably less than 1 O10. Hence, the deposition temperature can be preferably selected low enough to avoid this effect.

[0044] In addition, the method can also be enhanced by that in step c) the one or more evaporated and / or sublimated second source materials and / or the one or more second binary nitride is provided with an intermittent and / or constant and / or variable flux by accordingly controlling the laser beam used for evaporating and / or sublimating the one or more second source materials. As mentioned above, in one of the alternative embodiments of the adsorption-controlled deposition the one or more second source materials and, if applicable, the one or more second binary nitrides can be used as the part of the compound limiting the formation of the target nitride and hence the growth of the nitride layer. Hence, in this alternative embodiment by altering the flux of these components, also the formation rate of the target nitride and accordingly the growth rate of the nitride layer can be actively altered and thereby directly controlled. However, also in the embodiment in which the amount of nitridizing agent controls the formation rate of the target nitride, altering the flux of the one or more second source materials and / or their respective one or more second binary nitrides can be used for altering the growth rate of the target nitride as nitride layer on the substrate.

[0045] In addition, the method according to the present invention can be characterized in that in step d) the deposition temperature is selected such that the first source material and / or the first binary nitride and / or the one or more second source materials and / or the one or more second binary nitrides are enabled to migrate along a surface of the substrate. In other words, the deposition temperature is selected such that all constituents of the target nitride can move to find an energetically favorable location at the surface of the substrate, and hence to find their designated, ideal place within the periodic crystal lattice. A lattice defect density of the target nitride and accordingly of the nitride layer can thereby be lowered even further.

[0046] Further, the method according to the present invention can comprise that in step d) the deposition temperature is provided between 150 °K and 4500 °K. In the method according to the present invention, a wide variety of elemental materials, in particular elemental metals, more favorably all metals providable as a solid or liquid deposition source, can be used as first source materials. By providing the deposition temperature between 150 °K and 4500 °K, the substrate can be heated to a temperature suitable for all of these possible first deposition sources.

[0047] The TLE system, especially the respective laser source and the laser beam provided by said laser source, is preferably capable to heat the substrate to any temperature in this range, namely to a temperature as low as 150 °K, if an adequately cooled inner chamber surface is provided, for instance by a liquid nitrogen cooling shroud, and likewise to a temperature as high as 4500 °K. However, if needed, the substrate can also be heated to temperatures beyond 4500 °C by the laser beam of the TLE system. Thereby the same TLE system can be used for producing an unprecedentedly wide variety of nitride layers with exceedingly high quality.

[0048] In addition, the method according to the present invention can also be characterized in that in step d) the deposition temperature is selected with respect to the first binary nitride. In comparison to the first source material, the first binary nitride comprises a different desorption temperature due to its chemical properties changed by the presence of the one or more nitrogen atoms. Hence, by selecting the deposition temperature with respect to the first binary nitride, the selected deposition temperature is in all cases high enough to ensure a desorption also of the first source material.

[0049] According to an enhanced embodiment, the method according to the present invention can comprise that the deposition temperature is selected with respect to the first binary nitride equal or higher as listed below:

[0050] The temperature values listed in the table above are the calculated desorption temperatures of the respective binary nitrides in at a vapor pressure of 10-5hPa. It should be noted that with reaction gas, and hence with one or more nitridizing agents, present in the reaction chamber at pressures different to 10-5hPa, the actual deposition temperature can differ from the listed temperature.

[0051] In the context of adsorption-controlled growth, taking advantage of the property of TLE that there are practically no limits on the substrate temperature, the binary nitrides with the highest temperature values in the table presented above are most interesting for technological applications, as they are very stable at room temperature and therefore suitable for devices, in particular high-power devices.

[0052] Further, the method according to the present invention can comprise that in step c), in particular also in step d), a continuous laser beam, or a laser beam with a pulsed intensity, respectively, below the plasma generation threshold, is used. As already described, using a laser with an intensity below the plasma generation threshold guaranties a pure thermal evaporation and / or sublimation of the respective source materials and, if applicable, the first and / or second binary nitrides.

[0053] By using a continuous laser beam, a likewise continuous heating of the respective source material, if applicable also of the substrate, can be provided. This also applies to pulsed lasers when operated for TLE purposes such that the plasma threshold for vaporizing the source material is not reached. In particular, the respective pulse width and repetition rates of the laser beam can be preferably selected such that no significant cooling of the heated entity occurs during the pulses of the laser beam, and therefore the laser heating is quasi-continuous. Suitable pulse length can be selected equal to or larger than 1 ps, in particular larger than 1 ms, preferably larger than 1 s, wherein suitable repetition rates can be selected in the range of 0.1 - 100 kHz.

[0054] In both cases, the laser beam is continuously or at least substantially continuously incident on the respective source material, if applicable also on the substrate. The respective laser beam is thus particularly not operated in a pulsed manner, that is with high laser energies and / or lengths of the laser pulses in the nanosecond range. A particularly constant and controllable or adjustable energy transfer of the laser beam into the respective source material, if applicable also into the substrate, can be provided in this way. A constant and / or controllable and adjustable temperature of the respective source material and thus a resulting evaporation rate and / or sublimation rate can be made possible in this way. If applicable, also a constant and / or controllable and adjustable temperature of the substrate can thereby be provided.

[0055] According to a further embodiment of the method according to the present invention, in step b) a pressure and / or a composition of the reaction gas is varied by accordingly controlling the gas system of the TLE system for actively changing the stoichiometry of the formed target nitride without changing the constituents. By changing the properties of the reaction gas, for instance its pressure and / or its relative or absolute composition of nitridizing agents, the abundance of available nitrogen atoms for forming the target nitride can be actively changed. Hence, it can be actively selected, which of several possible stoichiometries of the target nitride is formed, or at least said selection can be supported.

[0056] Alternatively, or additionally, the method according to the present invention can also comprise that in step c) the provided flux of evaporated and / or sublimated first source material and / or of a first binary nitride and / or of the evaporated and / or sublimated one or more second source materials and / or of the one or more second binary nitrides is varied by accordingly controlling the laser beam of the TLE system used in step c) for actively changing the stoichiometry of the formed target nitride without changing the constituents. As mentioned above, in most of the cases at least one, preferably all, of the first source material and / or the first binary nitride and / or of the evaporated and / or sublimated one or more second source materials and / or of the one or more second binary nitrides is present in excess at the substrate. However, by controlling the extent of the abundance, in particular of the rate-limiting elements of the respective component or components, also an influence on the target nitride to be formed can be provided.

[0057] Again alternatively, or additionally, the method according to the present invention can be enhanced by that in step d) the deposition temperature of the substrate is varied by accordingly controlling the laser beam of the TLE system for actively changing the stoichiometry of the formed target nitride without changing the constituents. As mentioned above, the temperature of the substrate defines which elements or compounds are desorbed from the surface of the substrate. Hence, by accordingly selecting the deposition temperature, automatically a selection of the target nitride to be deposited onto the substrate can be provided.

[0058] According to another enhanced embodiment, the method according to the present invention can comprise that the variation of the reaction gas and / or the variation of the provided flux of the evaporated and / or sublimated first source material and / or of the first binary nitride and / or of the evaporated and / or sublimated one or more second source material and / or of the one or more second binary nitride and / or the variation of the deposition temperature are provided before and / or during and / or after an iteration of step c). In step c) the first source material, and if present also the one or more second source materials, are evaporated and / or sublimated.

[0059] Hence, by providing the respective variation before and / or after an iteration of step c), for the upcoming iteration of step c), a different target nitride can be selected. A sharp transition in the nitride layer from one target nitride to the other can thereby be provided. On the other hand, by providing the respective variations during the execution of step c), the transition from one target nitride to the next target nitride can be provided more smoothly and in a controlled way, for instance by providing a predetermined composition profile in the growth direction.

[0060] For the above-mentioned sharp transition in the nitride layer, another advantage of the method according to the present invention emerges. As providing the respective source material is based on the evaporation and / or sublimation of the respective source material(s), a continuous heating of the respective source material(s) is required for continuously providing the respective evaporated and / or sublimated source material(s). Without said heating, the deposition source providing the respective source material immediately cools down due to radiative cooling, and the evaporation and / or sublimation stops. Hence, by starting and stopping the respective laser beam, for instance by modulating or switching a pump source of the respective laser beam, a defined deposition interval can be defined, which in turn enables the provision of controlling a thickness of the deposited nitride layer of the respective target nitride, and additionally allows sharp transitions between nitride layers of different target nitrides.

[0061] Further, the method can be enhanced by that the nitride layer deposited in step e) comprises two or more subsequent sub-layers formed by target nitrides with the same constituents but different stoichiometry. This can be provided in particular by the variations of the reaction gas and / or the flux of the first source material and / or of the flux of the first binary nitride and / or of the deposition temperature mentioned above. Nitride layers with a vast variety of properties can thereby be provided.

[0062] According to another embodiment of the method according to the present invention, the first source material and / or the one or more second source material is an elemental metal. Metals are an extreme diverse group of elements, wherein in particular nitrides of metals provide extremely different properties, for instance with respect to electrical or thermal conductivity, or physical properties like hardness and toughness. By executing the method according to the present invention, a wide variety of binary nitrides, ternary nitrides or even multernary nitrides based on metals as non-nitrogen constituents can thereby be provided as possible target nitrides for the produced nitride layer.

[0063] In addition, the method according to the present invention can also be characterized in that the first source material and / or the one or more second source material is selected from a group of materials comprising the members of: 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, TI, Th, U, Np, Pu, Am, Tc, Os, Rb, As, Hf, Nb, Ta, W, Ir, Al. A wide variety of binary nitrides, ternary nitrides or even multernary nitrides can thereby be provided as possible target nitrides for the nitride layer produced by executing the method according to the present invention.

[0064] The most widely used nitride material family is that of the semiconducting group III nitrides, which may be doped and grown as heterostructures, as well as alloyed to produce band gap engineering functionalities. There are many other binary nitrides, however, that show interesting properties. For instance, binary nitrides with Ti, V, Zr, Nb, Mo, Hf, Ta, W, La, Ce, or Pr as second component are good electrical conductors, all of them have at least one superconducting phase. SiN on the other hand is insulating and a suitable barrier material for devices. ScN is piezoelectric and thermoelectric, CrN and MnN are magnetic. YN is water soluble. EuN is a ferromagnetic semiconductor, SmN even a ferromagnetic superconductor. From theoretical considerations, all rare earth nitrides are ferromagnetic (semiconductors, however, the ferromagnetism is sometimes suppressed, such as for PrN and CeN.

[0065] The method according to the present invention can also comprise that step b) is carried out continuously during the execution of step c) and / or step d) and / or step e). In step b), the reaction chamber is filled with the reaction gas, the reaction gas comprising, preferably consisting of, one or more nitridizing agents. Carrying out step b) continuously during the execution of step c) and / or step d) and / or step e) provides that also during evaporation and / or sublimation of the first source material and, if applicable, of the one or more second source materials, and / or during heating the substrate, and / or during formation of the target nitride and deposition of the nitride layer, simultaneously the reaction chamber is filled with reaction gas. A consistently high purity of the atmosphere inside the reaction chamber during the execution of the method according to the present invention, preferably during the whole deposition process in steps c), d), and e), can thereby be provided.

[0066] Further, the method according to the present invention can be characterized in that in step b) the filling of the reaction chamber includes providing a directed flow of reaction gas towards the substrate. The target nitride is deposited onto the substrate and thereby forms the nitride layer at the substrate. By providing a directed flow of reaction gas, and hence a directed flow of the one or more nitridizing agents, an increased flux density of nitrogen needed for forming the target nitride at the substrate can be ensured. In particular in an adsorption-controlled deposition process, a lack of nitrogen can be avoided in this way.

[0067] The directed flow of reaction gas at the same time reduces the non-directional background pressure of reaction gas. This reduces the scattering of source materials on their way from the source to the substrate, allowing a relative increase of reaction gas flux density at the substrate surface with reduced scattering, thereby allowing higher growth rates or stronger nitridation of the target nitride than what is possible with a homogeneous distribution of background gas.

[0068] In addition, the method according to the present invention can be enhanced by that the reaction gas consists of a single nitridizing agent. In other words, after step b) the whole reaction chamber is filled with this single nitridizing agent only. A purity of the reaction atmosphere present in the reaction chamber can thereby be provided, which contributes to enhancing the exceedingly high quality of the provided nitride layer even further.

[0069] According to another embodiment of the method according to the present invention, the one or more nitridizing agents are selected from the group of members consisting of molecular nitrogen (N2), plasma-activated nitrogen (N2*), ionized nitrogen (N j, atomic nitrogen (N), ammonia (NH3), and combinations of the foregoing. This list is not closed, and also other nitridizing agents providing the nitrogen needed for forming the target nitride can be used.

[0070] In particular, some of the nitridizing agents listed above consist of nitrogen atoms, in particular molecular nitrogen (N2), plasma-activated nitrogen (N2*), ionized nitrogen (N ), and atomic nitrogen (N), respectively. Said nitridizing agents allow physical vapor deposition (PVD) processes, in which only the atom and molecule species intended to be incorporated in the target nitride as growing epitaxial nitride layer are supplied as fluxes. A contamination with other elements caused by the nitridizing agent ca thereby be avoided.

[0071] On the other hand, as an alternative to said PVD processes, also chemical vapor deposition (CVD) processes can be established, in which molecules are supplied as nitridizing agents, which contain additional atoms, such as for instance hydrogen (H) in ammonia (NH3). CVD, and in particular metalorganic MOCVD, uses molecules that have ligands attached to the cargo atom, in the present invention nitrogen (N), which is supposed to be incorporated in the target nitride. The molecules with these ligands are designed to disintegrate upon contact with the growing surface on the hot substrate, and release the cargo atom, while the ligands are volatile enough to not incorporate and be pumped away. This approach allows a convenient handling of the source materials, which are usually supplied as vapors in an inert carrier gas, and a good reactivity, which allows high growth rates within a targeted, rather narrow substrate temperature range.

[0072] In addition, the method according to the present invention can be characterized in that in step b) the reaction gas is provided with a pressure selected in the range of 10-9hPa to 105hPa, preferably selected in the range of 10-5hPa to 105hPa. In the method according to the present invention, a wide variety of elemental materials, in particular all metals providable as a solid source material, can be used as first source materials and if applicable as one of the one or more second source material. This leads to a vast variety of selectable target nitrides, wherein each of the target nitrides has a reaction gas pressure and / or a reaction gas pressure range most suitable for the deposition of that specific target nitride as nitride layer. By providing the reaction gas with a pressure selected in the range of 10-9hPa to 105hPa, preferably selected in the range from 10-5hPa to 105hPa, for most, if not all target nitrides the respective most suitable pressure and / or pressure range can be selected for the reaction gas.

[0073] The TLE system, especially the gas system of the TLE system, is preferably capable to provide the reaction gas with any pressure in this range, namely with a pressure as low as 10-9hPa, preferably 10-5hPa, and likewise with a pressure as high as 105hPa. Thereby the same TLE system can be used for producing an unprecedentedly wide variety of nitride layers with exceedingly high quality of the deposited target nitride.

[0074] According to another embodiment, the method according to the present invention can comprise that before step c), a step of preparing a surface of the substrate intended for the deposition of the nitride layer is carried out. The surface condition of the substrate influences the deposition of the nitride layer. For instance, for a crystalline substrate, defects in a crystal lattice of the substrate and / or steps due to a misalignment of the surface cut to a crystal plane of the substrate and / or impurities at the surface can continue as defects in the deposited layer. By introducing a step of preparing the surface of the substrate, said surface condition of the substrate can be improved for the subsequent deposition of the target nitride as nitride layer. Providing the exceedingly high quality of the nitride layer reachable during the execution of the method according to the present invention can thereby be supported.

[0075] The method according to the present invention can be enhanced further by that the step of preparing the surface includes tempering the surface by heating the substrate with a laser beam of the TLE system, preferably by the laser beam used in step d). Heating the substrate enables the desorption of impurity atoms, the healing of defects in the bulk, and enables especially the atoms forming the surface of the substrate to migrate and to find an energetically favorable location at the surface of the substrate, and hence to find their ideal places on the surface of the substrate, in particular for a crystalline substrate within the periodic crystal lattice of the substrate. In other words, heating the substrate triggers annealing effects, especially at the surface of the substrate. A surface of the substrate more suitable for the subsequent deposition of the target nitride as nitride layer can thereby be provided.

[0076] Additionally, or alternatively, the method according to the present invention can also comprise that the step of preparing the surface includes coating the surface with one or more buffer layers. Said one or more buffer layers can help to smoothen steps on the surface of the substrate. In addition, especially for a crystalline substrate the target nitride to be deposited as nitride layer may have a different lattice structure and / or lattice constant than the substrate. Hence, at least the first atomic layer of the target nitride on the substrate has to compensate these differences. However, a buffer layer can be suitably selected such that it comprises similar, if not even identical crystal properties compared to the target nitride within the nitride layer. Hence, by adding such a suitably selected buffer layer between the substrate and the nitride layer, the compensations of the differences of the respective crystal lattices are provided within the buffer layer, and the nitride layer can be provided with its ideal crystal structure starting from the first atomic layer of the target nitride.

[0077] Generally, in most of the applications the one or more buffer layer is very thin, namely 1 to 10, preferably 1 to 3, monolayers. Further, said buffer layers normally comprises an internal structure different to both, the structure of the substrate and the structure of the target nitride.

[0078] According to a first enhanced embodiment, the method according to the present invention can be enhanced by that the buffer layer comprises, preferably consists of, the first source material and / or a nitride of the first source material, in particular the first binary nitride.

[0079] According to an additional, or alternative, second enhanced embodiment, the method according to the present invention can be enhanced by that the buffer layer comprises, preferably consists of, one of the one or more second source materials and / or a nitride of one of the one or more second source materials, in particular one of the one or more second binary nitrides.

[0080] According to an again additional, or alternative, third enhanced embodiment, the method according to the present invention can be enhanced by that the buffer layer comprises, preferably consists of, the material of the substrate.

[0081] In the latter embodiment, the method according to the present invention can be enhanced further by that the buffer layer comprises, preferably consists of, a nitride of the material of the substrate.

[0082] In the first two alternative embodiments, the buffer layer is formed by evaporation and / or sublimation of a source material already present in the reaction chamber for the subsequent deposition of the target nitride as nitride layer. The need for providing additional deposition sources with additional source materials can be avoided in both alternative enhanced embodiments. Depending on the lattice structure of the target nitride, the most suitable composition of the buffer layer can be chosen based on the components already present in the TLE system: the first source material or a nitride of the first source material, or, if applicable, one of the one or more second source materials or a nitride of the one or more second source materials.

[0083] For the third alternative embodiment, providing respective deposition sources providing said constituents of the material of the substrate, preferably as elemental material, might be necessary. Providing a buffer layer comprising, preferably consisting of, the substrate material provides the advantage that said buffer layer can thereby be deposited with high quality. Defects on the surface of the substrate itself can thereby be smoothen. Also, a buffer layer comprising two or more sublayers of these materials can be implemented if suitable for the subsequent deposition of the target nitride forming the nitride layer. However, also providing the buffer layer by incorporating atoms of the substrate itself is possible.

[0084] Said buffer layer comprising the substrate material can for instance also comprise a mixture of the first source material or a nitride of the first source material, or, if applicable, one of the one or more second source materials or a nitride of the one or more second source materials.

[0085] The buffer layer may also comprise, preferably consist of, atoms from the substrate material plus nitrogen, meaning that it is formed by exposing the substrate surface only to the nitridizing flux to form the buffer layer. This nitridizing flux then reacts with substrate atoms to form a nitride layer and / or a substrate material I nitride alloy. A typical example in the context of the present invention is the preparation of AIN on sapphire (AI2O3), either by nitridation of the sapphire, or by growing a buffer layer that shares the Al with the underlying substrate. Such a layer is more stable than layers of compounds having no shared elements with the substrate.

[0086] Further, the method according to the present invention can be characterized in that before step c) a step of preparing the evaporation and / or sublimation is carried out, wherein the first source material and / or the one or more second source materials are heated by a laser beam, preferably the laser beam used in step c), for cleaning the first source material and / or the one or more second source material, respectively, without deposition of material onto the substrate. In step c) of the method according to the present invention, the first source material, and if applicable also the one or more second source materials, are evaporated and / or sublimated by the respective laser beams. In other words, the laser beams impinge onto the surface of the respective deposition source, and the respective source material evaporates and / or sublimates. However, especially at the beginning of the evaporation and / or sublimation process, said surface of the respective deposition source might be contaminated by impurities. By a preceding heating of the respective source material, said impurities can be eliminated, again by evaporation and / or sublimation. For avoiding a deposition of the evaporated and / or sublimated impurities onto the substrate, the substrate can be shielded and / or moved aside. Also, a removal of the substrate from the reaction chamber is possible for this preparation step, preferably via airlocks. In summary, by said preparation step, an evaporation and / or sublimation of the respective source materials with high purity can be provided from the beginning of the execution of step c) of the method according to the present invention.

[0087] According to a second aspect of the invention, the object is satisfied by a TLE system constructed for carrying out the method according to the first aspect of the present invention. The TLE system according to the second aspect of the present invention comprises:

[0088] - The reaction chamber,

[0089] - The One or more laser sources for providing laser beams for heating the substrate and for evaporating and / or sublimating the one or more source materials,

[0090] - A Coupling means for coupling the one or more laser beams into the reaction chamber,

[0091] - An Arrangement means for arranging the substrate and the one or more deposition sources providing the one or more source materials in the reaction chamber, and

[0092] - The gas system for providing the reaction gas within the reaction chamber.

[0093] The TLE system according to the second aspect of the present invention is constructed for carrying out the method according to the first aspect of the present invention. Hence, all features and advantages described in detail with respect to the method according to the first aspect of the present invention can also be provided by the TLE system according to the second aspect of the present invention.

[0094] As already mentioned, the TLE system, especially the respective laser source and the laser beam provided by said laser source, is preferably capable to heat the substrate to any temperature in this range, namely to a temperature as low as 250 °K and likewise to a temperature as high as 4500 °K. Thereby the same TLE system can be used for producing an unprecedentedly wide variety of nitride layers with exceedingly high quality. It is to be noted that, depending on the one or more laser source of the TLE system according to the present invention, the providable upper limit of the temperature of the substrate can even be higher than 4500 °C. Additionally, or alternatively, and as also already mentioned, the TLE system, especially the gas system of the TLE system, is preferably capable to provide the reaction gas with any pressure in this range, namely with a pressure as low as 10-9hPa, preferably 10-5hPa and likewise with a pressure as high as 105hPa. Thereby the same TLE system can be used for producing an unprecedentedly wide variety of nitride layers with exceedingly high quality of the deposited target nitride.

[0095] A single laser source can be used for evaporating and / or sublimating the respective source materials, wherein for each of the source materials a separate laser beam is provided. Alternatively, also separate laser sources, each providing a laser beam specifically selected for a respective source material, can be implemented.

[0096] The reaction chamber can be equipped with airlocks for an access into the reaction chamber without losing and / or contaminating the present atmosphere within the reaction chamber. Said airlocks can be used for instance for installing and / or removing the substrate and / or one or more of the used deposition sources.

[0097] In summary, TLE enables the deposition and synthesis of target nitrides at substrates heated up to deposition temperatures, where the desorption of material from the growing surface may be controlled to amount to a significant fraction of the deposited flux. This implies that the so-called sticking coefficient, the fraction of the number of atoms per time unit arriving at the surface and not desorbing from the surface, is smaller than unity. This is called adsorption-controlled growth. This growth mode is characterized by the stoichiometry of the grown film being self-determined by the physico-chemical reaction of the elements on the film surface being in dynamical equilibrium with the incoming and leaving fluxes. This equilibrium is controlled mostly by the substrate temperature and the offered fluxes of different elemental or compound fluxes. In addition, the reactivity of fluxes of chemical compounds affects this dynamical equilibrium. In the present case of target nitrides, in particular nitrogen may be supplied as normal gaseous N2 molecules, as N2 plasma typically containing up to 60% of dissociated nitrogen molecules produced in a corresponding plasma source, usually close to the substrate inside the process chamber, or in the form of chemical compounds such as, e.g., NH3 supplied via gas nozzles. These latter, physically or chemically activated forms possess a much higher reactivity and therefore often allow practically useful reaction rates at low enough substrate temperatures where a stable reaction may occur while the substrate crystal does not yet deteriorate.

[0098] As already described with respect to the method according to the present invention, both physical vapor deposition (PVD) processes and chemical vapor deposition (CVD) processes, respectively, can be established in the TLE system according to the present invention carrying out the method according to the present invention.

[0099] PVD is the typical MBE growth process, which is also the standard, default, mode in TLE. The reactivity of nitrogen as the important example here may be increased in this mode by sending it through a plasma source which transforms the rather inert N2 molecules into either excited molecules, or even dissociated atoms. Both have a reactivity that is orders of magnitude higher than nitrogen under standard conditions.

[0100] CVD, and in particular metalorganic (MO)CVD, uses molecules such as ammonia (NH3) that have ligands (H) attached to the cargo atom (N), which is supposed to be incorporated in the film. The molecules with these ligands are designed to disintegrate upon contact with the growing surface on the hot substrate, and release the cargo atom, while the ligands are volatile enough to not incorporate and be pumped away. In the present invention, this approach allows a convenient handling of the nitridizing agents supplied as vapors, sometimes in an inert carrier gas, and a good reactivity, which allows high growth rates within a targeted, rather narrow substrate temperature range. With a substrate at deposition temperatures which are lower than the ideal window, the precursor molecules will not crack efficiently, growth rates drop and ligands get incorporated into the growing crystal. At too high deposition temperatures, the precursors may crack in the gas phase, before reaching the substrate surface, and form crystallites which may produce defects when being incorporated as such into the growing surface. (MO)CVD therefore works well for established, fine-tuned processes in production environments. It is less suited for exploratory research, since variations in the substrate temperature require different precursors, which then also need to be matched to possible further precursors for other elements.

[0101] TLE offers the advantage of a very wide process parameter range which encompasses the ranges of all other PVD and (MO)CVD methods. In particular, it allows the simultaneous use of both approaches, e.g. by combining a CVD precursor for one element, here NH3 for nitrogen, with direct thermal evaporation of other elements that do not have process window limitations and therefore can span very wide ranges in substrate temperature and nitrogen activity. It is therefore ideally suited for exploratory research, where large volumes of parameter space need to be covered. At the same time, however, such combined TLE processes may also be seamlessly scaled to production volumes, such that a switch to an (MO)CVD- only process is not required.

[0102] The self-limiting dynamic equilibrium characteristic of adsorption-controlled growth usually produces layers of the target nitride with a superior crystal quality and purity, since non-stoichiometric amounts of atoms arriving at the surface will re-evap- orate as they do not find the lowest energy positions within the forming crystal lattice. The same applies to possible impurity atoms, their incorporation would also require higher energies. This higher energy expels them from the lattice and makes them evaporate at high enough substrate temperatures where their lower energetic distance to the vacuum level leads to their desorption. Finally, the principle also applies to the formation of structural defects such as dislocations or point defects (e.g. individual misplaced atoms such as interstitials and antisites) from atoms contained in the desired compound, as these also have higher energies.

[0103] The invention will be explained in detail in the following by means of embodiments and with reference to the drawings. In particular, in the figures are shown:

[0104] Fig. 1 A phase diagram for an MBE process of the synthesis of GaAs,

[0105] Fig. 2 A schematic view of a TLE system according to the present invention,

[0106] Fig. 3 A schematic view of a method according to the present invention,

[0107] Fig. 4 Growth rates for absorption-limited synthesized BN,

[0108] Fig. 5 Raman measurement of a BN layer grown with plasma-activated nitrogen (N2*), and

[0109] Fig. 6 Raman measurement of a BN layer grown with ammonia (NH3).

[0110] In Fig. 1 a calculated phase diagram is depicted for GaAs, whose adsorption-limited synthesis in an MBE process is well known in the state of the art. In the diagram, the pressure, and hence the flux, of As is shown versus possible deposition temperatures 72 of a substrate 70, on which GaAs should be deposited as an epitaxial layer.

[0111] The upper line denotes, depending on the pressure of the provided As, the boundary temperature, beyond which, to the right and below this line, the As will desorb from the surface of the substrate. Said temperature is hence denoted as desorption temperature 36. The second, lower line denotes the boundary temperature beyond which, to the right and below this line, the substrate and / or the GaAs layer disintegrates by the desorption of bound As and the formation of Ga droplets on the surface. In between these lines, in the area denoted by “growth window”, an adsorption-controlled growth of GaAs is possible, as the provided As desorbs, preferably completely desorbs, and hence the flux density or local pressure of Ga as the second component of GaAs limits and hence defines the growth rate of GaAs layer on the substrate.

[0112] As depicted, the pressures reachable by fluxes of As in MBE processes according to the present invention, and likewise the providable substrate temperatures are located well in said “growth window”. Hence, a deposition of GaAs in the adsorption-limited growth mode is possible in classical MBE systems according to the present invention. However, MBE processes comprise some limitations. First of all, only a very limited selection of elements can be provided as molecular beams as necessary for MBE via effusion sources. Further, also the possible range of temperatures for the substrates is limited, excluding materials that require a substrate temperature above 800 °C.

[0113] However, the method and the TLE system according to the present invention extend the possibilities of the adsorption-limited growth mode well beyond the limits of MBE processes. Thermal laser epitaxy is a deposition process, which not only intrinsically does not comprise the limitations concerning possible deposition temperatures 72 of the substrate 70 present in MBE, but can also simultaneously provide fluxes of almost arbitrary source materials at purities significantly higher than PLD. In fact, the purity of the provided fluxes of source materials are at least similar, mostly even better than achievable in MBE processes.

[0114] Hence, according to the present invention an accordingly constructed TLE system

[0115] 100, depicted in Fig. 2, is used for execution of a method according to the present invention as depicted in Fig. 3, for providing a controlled deposition of a nitride layer 80 of a target nitride 82 on a substrate 70. In the following, the TLE system 100 and the method according to the present invention, respectively, are described together.

[0116] As already mentioned, the method according to the present invention is carried out in an accordingly constructed TLE system 100. The main part of said TLE system 100 is a reaction chamber 10, in which the deposition of the nitride layer 80 on the substrate 70 takes place. Further parts of the TLE system 100 are one or more, as exemplarily depicted three, laser sources 20 for providing laser beams 22, and a gas system 50, fluidly connected to the interior of the reaction chamber 10.

[0117] The laser beams 22 are used for both, evaporating and / or sublimating source materials 32, 42, and for heating the substrate 70, respectively. For guiding said laser beams 22 to their respective destination within the reaction chamber 10, suitable coupling means 12 are provided. Preferably, the laser beams 22 are continuous in time, but also pulsed laser beams 22 can be used. It is however essential, that in both cases the continuous laser beams 22 or the individual pulses of the laser beams 22 comprise an intensity below the plasma generation threshold. In the latter case, the pulse length preferably can be selected equal to or larger than 1 ps, in particular larger than 1 ms, preferably larger than 1 s.

[0118] The gas system 50 is at least capable of filling the reaction chamber 10 with a reaction gas 52 comprising, preferably consisting of, one or more nitridizing agents 54 such as for instance molecular nitrogen (N2), plasma-activated nitrogen (N2*), ionized nitrogen (N j, atomic nitrogen (N), ammonia (NH3), or combinations of the foregoing. The reaction gas 52 can be provided as directed flow towards the substrate 70. Preferably, the reaction gas 52 consists of a single nitridizing agent 54. The one or more nitridizing agents 54 are the sources of the nitrogen atoms needed for the formation of the target nitride 82, as will be described in the following. The gas system 50 can provide the reaction gas 52 with a wide variety of pressures, preferably pressures selected in the range of 10-5hPa to 105hPa. In most of the embodiments, the gas system 50 not only provides the reaction gas 52, but is also capable of evacuating the reaction chamber 10.

[0119] Further in the reaction chamber 10, the substrate 70 to be coated with a nitride layer 80 is provided and held in place by arrangement means 60. The nitride layer 80 is formed by depositing a target nitride 82, which comprises a defined stoichiometry and is formed from one or more evaporated and / or sublimated source materials 32, 42 and by nitrogen originating from the gaseous nitridizing agent 54. As it will be described in the following, one of the laser beams 22 is used for heating the substrate 70 to a deposition temperature 72 suitably selected for the intended deposition of the nitride layer 80.

[0120] The one or more components of the target nitride 82 different to nitrogen are provided by evaporating and / or sublimating one or more source materials 32, 42. In the depicted embodiment of the TLE system 100, a first deposition source 30 containing an elemental material, preferably an elemental metal, as first source material 32 and a second deposition source 40 containing an elemental material, preferably an elemental metal, as second source material 42 are provided, in particular held in place within the reaction chamber 10 by accordingly constructed and provided arrangement means 60. Each of the source materials 32, 42 is evaporated and / or sublimated by a respective laser beam 22. As the source materials 32, 42 are provided as elemental materials, the evaporated and / or sublimated source materials 32,42 can be extremely pure. Only reactions with the one or more nitridizing agents 54 of the reaction gas 52 can lead to a formation of a first binary nitride 34 and a second binary nitride 44, respectively.

[0121] The source materials 32, 42 usable in the TLE system 100 according to the present invention and for the method according to the present invention are variable. In particular, all elemental materials can be used as source material 32, 42, in particular 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, TI, Th, U, Np, Pu, Am, Tc, Os, Rb, As, Hf, Nb, Ta, W, Ir, and AL

[0122] In the following, the method according to the present invention is described in detail. Please note that step a) A is already finished in the TLE system 100 depicted in Fig. 2. Further please note that steps b) B, c) C, d) D, and e) E can be carried out simultaneously.

[0123] In a first step a) A, the substrate 70 and all used deposition sources 30, 40 are arranged in the reaction chamber 10. Afterwards, the reaction chamber 10 is closed and sealed with respect to the ambient environment, and preferably evacuated by the gas system 50.

[0124] This allows in the next step b) B to fill the reaction chamber 10 with the reaction gas 50. Please note that said filling in step b) B can be preferably carried out continuously additionally also throughout all following steps c) C, d) D, and e) E of the method according to the present invention.

[0125] To ensure continued purity of the reaction gas 52, filling of the reaction gas 52, preferably from one side of the TLE system 100, even more preferably by a nozzle directed to the front of the substrate 70, and pumping of the reaction gas 52 from the other side of the TLE system 100, may be performed simultaneously by different parts of the gas system 50 (not depicted).

[0126] As further preparation of the subsequent deposition of the nitride layer 80 on the substrate 70, the surface of the substrate 70 can be prepared, for instance by heating the substrate to perform annealing processes. Alternatively, or additionally, as depicted in Fig. 2 also a buffer layer 74 can be deposited onto the surface of the substrate 70, for instance consisting of elements already present in the reaction chamber 10 such as the first source material 32, the first binary nitride 34, the second source material 42 and / or the second binary nitride 44. However, also the material of the substrate 70 can be used for said buffer layer 74, either provided by the substrate 70 itself, of by an additional source element, of both. In this case, the buffer layer can be provided consisting of the material of the substrate 70, or comprising a mixture of the material of the substrate 70 and the first source material 32, the first binary nitride 34, the second source material 42 and / or the second binary nitride 44. Also providing a nitride of the material of the substrate 70 as buffer layer 74 is possible.

[0127] In most of the cases, the target nitride 82 has a different lattice structure and / or lattice constant than the substrate 70. Hence, when directly depositing the target nitride 82 as nitride layer 80 onto the surface of the substrate 70, at least the first atomic layer of the target nitride 82 on the substrate 70 has to compensate these differences. However, a buffer layer 74 can be suitably selected such that it comprises similar, if not even identical crystal properties compared to the target nitride 82. Hence, by adding such a suitably selected buffer layer 74 between the substrate 70 and the nitride layer 80, the compensations of the differences of the respective crystal lattices are provided within the buffer layer 74, and the nitride layer 80 can be provided with its ideal crystal structure starting from the first atomic layer of the target nitride 82.

[0128] Generally, in most of the applications the one or more buffer layer 74 is very thin, namely 1 to 10, preferably 1 to 5, monolayers. Further, said buffer layers 74 normally comprises an internal structure different to both, the structure of the substrate 70 and the structure of the target nitride 82. Further preparation steps may include pre-heating the source materials 32, 42 for cleaning purposes, wherein a deposition of already evaporated and / or sublimated material on the substrate is avoided.

[0129] In the following step c) C of the method according to the present invention, the actual evaporation and / or sublimation of the source materials 32, 42 is provided. For this, the intensity of the respective laser beams 22 are selected such that they are below a plasma threshold of the respective source material 32, 42. Thereby, a strictly thermal evaporation and / or sublimation can be provided. The flux of evaporated and / or sublimated source material 32, 42, or existing of an accordingly formed binary nitride 34, 44, is directed towards the substrate 70 for the subsequent coating of the substrate 70.

[0130] In the following step d) D, the substrate 70 is heated by an accordingly provided laser beam 22. In this crucial step, the substrate 70 is in particular heated to a deposition temperature 72, which is equal or higher to a desorption temperature 36 (see Fig. 5) of the first source material 32 and / or the first binary nitride 34 and / or of the second source material 42 and / or the second binary nitride 44, respectively. Depending on the respective first and / or second source materials 32, 42, and especially of the respective first and / or second binary nitride 34, 44, the deposition temperature 72 can be preferably selected between 150 °K and 4500 °K.

[0131] Thereby the respective first source material 32 and / or the first binary nitride 34 and / or the second source material 42 and / or the second binary nitride 44, respectively, desorbs from the substrate 70. The deposition temperature 72 can be preferably selected such that more than 40%, in particular more than 70%, preferably more than 99.9%, of the incoming flux of said components desorb from the substrate 70. This ensures that the deposition of the target nitride 82 solely depends on the component or components additionally needed to form the target nitride 82. In the case of a binary nitride as target nitride 82, this is the available amount of nitrogen at the substrate, in the case of a ternary or multernary nitride as target nitride 82, this can be one of the one or more additional second source materials 42, or the respective second binary nitrides 44 of said second source material 42, and / or also again the available amount of nitrogen at the substrate.

[0132] In summary, said heating of the substrate 70 in step d) allows an adsorption-con- trolled deposition of the target nitride 82 and hence of the nitride layer 80 in step e) of the method according to the present invention. In other words, the number of compounds needed in addition to the first source material 32 and / or the first binary nitride 34, namely the one or more second source material 42 and / or the one or more second binary nitride 44, additionally or alternatively also the amount of available nitrogen provided by the one or more nitridizing agents 54, solely defines and hence controls the formation rate of the target nitride 82 and thereby the growth rate of the nitride layer 80. For said control, if applicable the one or more second source material 42 and / or the respective one or more second binary nitride 44 can be provided with an intermittent and / or constant and / or variable flux, for accordingly altering the growth rate of the nitride layer 80.

[0133] In particular, due to the desorption of at least some of the compounds of the target nitride 82, namely the first source material 32 and / or the first binary nitride 34 and / or the second source material 42 and / or the second binary nitride 44, from the substrate 70, the formation of the target nitride 82 and the deposition of the nitride layer 80 on the substrate 70 can be provided with an exceedingly high quality. This is due to the physical effect that a deposition of the target nitride 82 predominantly only takes place, if the formed compound, namely the target nitride 82, possess the required suitable thermodynamic properties, which dominantly depend on the substrate temperature, namely the deposition temperature 72. Thereby the deposited compound, namely the target nitride 82, can be actively selected and hence the quality of the deposited nitride layer 80, in particular concerning high purity and low defect density, can be maximized. Defect densities concerning nevertheless deposited elements of the first source material 32 and / or the first binary nitride 34 as low as 1 in 104, in particular less than 1 in 107, preferably less than 1 in 1 O10, can be achieved.

[0134] In Fig. 4, growth rates of boron nitride (BN) deposited on a (0001 ) sapphire substrate 70 (see Fig. 2) are depicted, as a function of the deposition temperature 72, to which the substrate 70 was heated. The depicted growth rates were achieved in the TLE system 100 (see Fig. 2) according to the present invention during carrying out the method according to the present invention. Additionally, growth rates of elemental boron without reactive gas background on said sapphire substrate 70 are also depicted, again as a function of the deposition temperature 72. The boron flux is approximately the same for the different deposition temperatures 72, namely 400, 800, 1200, 1400 and 1600 °C.

[0135] The squares in Fig. 4 denote the growth rates of elemental boron, the first source material 32, without reaction gas 52 (see Fig. 2) background. At deposition temperatures 72 above 1200 °C, the growth rate drops to zero, at 1600 °C, it is even negative, i.e. the boron etches the sapphire substrate 70. This proves the desorption of elemental boron at these high temperatures, and hence the principal availability of an adsorption-limited growth process for BN as target nitride 82.

[0136] With the addition of a reactive nitrogen flux as nitridizing agent 54, however, finite growth rates of BN as denoted by the circle and triangle data points are obtained. The growth rates are a lot smaller than for the elemental boron alone, nevertheless a stable fraction of the supplied boron gets incorporated into the film of BN, namely the target nitride 82. This is typical for adsorption-limited growth, in which the reaction kinetics at the growing surface determine the growth rate instead of the fractions of the supplied fluxes. The circle dot in Fig. 4 denotes BN grown with a nitrogen plasma source providing plasma activated nitrogen (N2*) as nitridizing agent 54, the triangle dots denote BN grown with NHs as nitridizing agent 54. The lower tringle at 1600 °C is measured for a NH3 pressure of 1 x10-3hPa, the upper one for a NH3 pressure of 5x10-3hPa. In general, this confirms that the mechanism of adsorption-limited growth does not rely on the nitrogen species and the used nitridizing agent 54 as such, and that the same process can be achieved under both physical and chemical vapor deposition conditions.

[0137] However, the quality of the two nitride layers 80, the first (circle) synthesized with a nitrogen plasma source as nitridizing agent 54, the second (triangle) synthesized NHs as nitridizing agent 54, is different. This is depicted in Fig. 5, 6, in which Raman measurements of said BN nitride layer 80 grown with plasma activated nitrogen (N2*) (Fig. 5, deposition temperature 72 1400 °C, film thickness 20 nm) and NH3 gas (Fig. 6, deposition temperature 72 1600 °C, film thickness 81 nm) are shown.

[0138] As is clearly visible, a significantly smaller width (full width at half max, FWHM), and hence a better quality of the deposited nitride layer 80 of the target nitride 82 BN, could be achieved for the ammonia-grown sample shown in Fig. 6. This may be due to the chemical reaction with hydrogen of the ammonia being involved in the process. From the general understanding of the adsorption-limited process, however, it is more likely that the possibility to assemble the crystal on the growing surface at higher temperatures leads to a better discrimination between the stoi- chiometrically correct atoms being incorporated at the ideal positions vs. impurity atoms being incorporated or ‘correct’ atoms being incorporated at the wrong positions in the crystal, since the higher temperature increases the chance of these atoms desorbing during growth. A comparison between the two triangles in Fig. 4 demonstrates how the adsorption-limited equilibrium between the fluxes determines the growth rate of the layer. A higher NH3 pressure leads to a higher growth rate of the nitride layer 80 (see Fig. 2) by decreasing the rate of boron desorption and the formation rate of boron nitride as target nitride 82.

[0139] List of references

[0140] 10 Reaction chamber

[0141] 12 Coupling means

[0142] 20 Laser source

[0143] 22 Laser beam

[0144] 30 First deposition source

[0145] 32 First source material

[0146] 34 First binary nitride

[0147] 36 Desorption temperature

[0148] 40 Second deposition source

[0149] 42 Second source material

[0150] 44 Second binary nitride

[0151] 50 Gas system

[0152] 52 Reaction gas

[0153] 54 Nitridizing agent

[0154] 60 Arrangement means

[0155] 70 Substrate

[0156] 72 Deposition temperature

[0157] 74 Buffer layer

[0158] 80 Nitride layer

[0159] 82 Target nitride 100 TLE system

[0160] A step a)

[0161] B step b) C step c)

[0162] D step d)

[0163] E Step e)

Claims

Claims1 . Method for the controlled deposition of a nitride layer (80) of a target nitride (82) on a substrate (70) in a thermal laser epitaxy (TLE) system (100), the target nitride (82) comprising a defined stoichiometry and being formed from one or more evaporated and / or sublimated source materials and nitrogen originating from a gaseous nitridizing agent (54), the TLE system (100) further comprising a reaction chamber (10) and one or more laser sources (20) for providing laser beams (22) within the reaction chamber (10), characterized by the steps of: a) providing the substrate (70) and a first deposition source (30) in the reaction chamber (10), wherein the first deposition source (30) contains an elemental material as first source material (32), b) filling the reaction chamber (10) with a reaction gas (52) comprising one or more nitridizing agents (54) provided by a gas system (50) of the TLE system (100), c) evaporating and / or sublimating the first source material (32) by impinging a laser beam (22) of the TLE system (100) on the first source material (32) with an intensity below a plasma generation threshold of the first source material (32), for providing a flux of evaporated and / or sublimated first source material (32) and / or of a first binary nitride (34) formed from the first source material (32) with the nitridizing agent (54), wherein the flux is directed towards the substrate (70), d) heating the substrate (70) 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 or higher to a desorptiontemperature (36) such that the first source material (32) and / or the first binary nitride (34) desorb at least partly from the substrate (70), e) forming the target nitride (82) by combining the one or more evaporated and / or sublimated source materials and nitrogen originating from the one or more nitridizing agents (54) and depositing the target nitride (82) as nitride layer (80) onto the substrate (70), wherein the formation of the target nitride (82) and the deposition of the nitride layer (80) on the substrate (70) is 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 the evaporated and / or sublimated first source material (32) at the substrate (70) in step c) and / or by controlling the deposition temperature (72) in step d).

2. Method according to claim 1 , characterized in that in step d) the deposition temperature (72) is selected such that more than 40%, in particular more than 70%, preferably more than 99.9%, of the incoming flux of the first source material (32) desorbs from the substrate (70), and that in step e) the adsorbed part of the first source material (32) combined with nitrogen originating from the one or more nitridizing agents (54) and / or the first binary nitride (34) form the target nitride (82) for the deposition of the nitride layer (80).

3. Method according to 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 second source material (42), further that step c) includes evaporating and / or sublimating one or more second source materials (42) by impinging a laser beam (22) of the TLEsystem (100) on the one or more second source materials (42) with an intensity below a plasma generation threshold of the respective second source material (42), for providing a flux of evaporated and / or sublimated one or more second source materials (42) and / or of one or more second binary nitrides (44) formed from one of the one or more second source materials (42) with the nitridizing agent (54) directed towards the substrate (70), wherein in step e) the first source material (32) and / or the first binary nitride (34) combined with the one or more second sources materials (42) and / or the one or more second binary nitrides (44), if necessary additionally combined with nitrogen originating from the one or more nitridizing agents (54), form the target nitride (82) for the deposition of the nitride layer (80), and that in step d) the deposition temperature (72) of the substrate (70) is equal or higher to a temperature such that the first source material (32) and / or the first binary nitride (34) and / or the one or more second sources materials (42) and / or the one or more second binary nitrides (44) desorb if they are not used for forming the target nitride (82).

4. Method according to claim 3, characterized in that the deposition temperature (72) in step d) is selected high enough that the amount of the first source material (32) and / or the first binary nitride (34) and / or the one or more second source material (42) and / or the one or more second binary nitrides (44) nevertheless deposited onto the substrate (70) is less than 1 in 104, in particular less than 1 in 107, preferably less than 1010, compared to elements of the target nitride (82).

5. Method according to one of the preceding claims 3 or 4, characterized in that in step c) the one or more evaporated and / or sublimated second source materials (42) and / or the one or more second binary nitride (44) is providedwith an intermittent and / or constant and / or variable flux by accordingly controlling the laser beam (22) used for evaporating and / or sublimating the one or more second source materials (42).

6. Method according to one of the preceding claims 1 to 5, characterized in that in step d) the deposition temperature (72) is selected such that the first source material (32) and / or the first binary nitride (34) and / or the one or more second source materials (42) and / or the one or more second binary nitrides (44) are enabled to migrate along a surface of the substrate (70).

7. Method according to one of the preceding claims 1 to 6, characterized in that in step d) the deposition temperature (72) is provided between 150 °K and 4500 °K.

8. Method according to one of the preceding claims 1 to 7, characterized in that in step d) the deposition temperature (72) is selected with respect to the first binary nitride (34).

9. Method according to claim 8, characterized in that the deposition temperature (72) is selected with respect to the first binary nitride (34) equal or higher as listed below:

10. Method according to one of the preceding claims 1 to 9, characterized in that in step c), in particular also in step d), a continuous laser beam (22) or a pulsed laser beam (22), respectively, with an intensity below the plasma generation threshold, is used.11 . Method according to one of the preceding claims 1 to 10, characterized in that in step b) a pressure and / or a composition of the reaction gas (52) is varied by accordingly controlling the gas system (50) of the TLE system (100) for actively changing the stoichiometry of the formed target nitride (82) without changing the constituents.

12. Method according to one of the preceding claims 1 to 11 , characterized in that in step c) the provided flux of the evaporated and / or sublimated first source material (32) and / or of the first binary nitride (34) and / or of the evaporated and / or sublimated one or more second source materials (42) and / or of the one or more second binary nitrides (44) is varied by accordingly controlling the laser beam (22) of the TLE system (100) used in step c) for actively changing the stoichiometry of the formed target nitride (82) without changing the constituents.

13. Method according to one of the preceding claims 1 to 12, characterized in that in step d) the deposition temperature (72) of the substrate (70) is varied by accordingly controlling the laser beam (22) of the TLE system (100) for actively changing the stoichiometry of the formed target nitride (82) without changing the constituents.

14. Method according to one of the preceding claims 11 to 13, characterized in that the variation of the reaction gas (52) and / or the variation of the provided flux of the evaporated and / or sublimated first source material (32) and / or of the first binary nitride (34) and / or of the evaporated and / or sublimated one or more second source material (42) and / or of the one or more second binary nitride (44) and / or the variation of the deposition temperature (72) are provided before and / or during and / or after an iteration of step c).

15. Method according to one of the preceding claims 11 to 14, characterized in that the nitride layer (80) deposited in step e) comprises two or more subsequent sub-layers formed by target nitrides (82) with the same constituents but different stoichiometry.

16. Method according to one of the preceding claims 1 to 15 characterized in that the first source material (32) and / or the one or more second source material (42) is an elemental metal.

17. Method according to one of the preceding claims 1 to 16 characterized in thatthe first source material (32) and / or the one or more second source material (42) is selected from a group of materials comprising the members of: 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, TI, Th, U, Np, Pu, Am, Tc, Os, Rb, As, Hf, Nb, Ta, W, Ir, AL18. Method according to one of the preceding claims 1 to 17, characterized in that step b) is carried out continuously during the execution of step c) and / or step d) and / or step e).

19. Method according to one of the preceding claims 1 to 18, characterized in that in step b) the filling of the reaction chamber (10) includes providing a directed flow of reaction gas (52) towards the substrate (70).

20. Method according to one of the preceding claims 1 to 19, characterized in that the reaction gas (52) consists of a single nitridizing agent (54).21 . Method according to one of the preceding claims 1 to 20, characterized in that the one or more nitridizing agents (54) are selected from the group of members consisting of molecular nitrogen (N2), plasma-activated nitrogen (N2*), ionized nitrogen (N j, atomic nitrogen (N), ammonia (NH3), and combinations of the foregoing.

22. Method according to one of the preceding claims 1 to 21 , characterized in thatin step b) the reaction gas (52) is provided with a pressure selected in the range of 10-9hPa to 105hPa, preferably selected in the range of 10-5hPa to 105hPa.

23. Method according to one of the preceding claims 1 to 22, characterized in that before step c) a step of preparing a surface of the substrate (70) intended for the deposition of the nitride layer (80) is carried out.

24. Method according to claim 23, characterized in that the step of preparing the surface includes tempering the surface by heating the substrate (70) with a laser beam (22) of the TLE system (100), preferably by the laser beam (22) used in step d).

25. Method according to claim 23 or 24, characterized in that the step of preparing the surface includes coating the surface with one or more buffer layers (74).

26. Method according to claim 25, characterized in that the buffer layer (74) comprises, preferably consists of, the first source material (32) and / or a nitride of the first source material (32), in particular the first binary nitride (34).

27. Method according to claim 25 or 26, characterized in that the buffer layer (74) comprises, preferably consists of, one of the one or more second source materials (42) and / or a nitride of one of the one ormore second source materials (42), in particular one of the one or more second binary nitrides (44).

28. Method according to one of the preceding claims 25 to 27, characterized in that the buffer layer (74) comprises, preferably consists of, the material of the substrate (70).

29. Method according to claim 28, characterized in that the buffer layer (74) comprises, preferably consists of, a nitride of the material of the substrate (70).

30. Method according to one of the preceding claims 1 to 29, characterized in that before step c) a step of preparing the evaporation and / or sublimation is carried out, wherein the first source material (32) and / or the one or more second source materials (42) are heated by a laser beam (22), preferably the laser beam (22) used in step c), for cleaning the first source material (32) and / or the one or more second source material (42), respectively, without deposition of material onto the substrate (70).31 . TLE system (100) constructed for carrying out the method according to one of the preceding claims, comprising- The reaction chamber (10),- The 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 means (12) for coupling the one or more laser beams (22) into the reaction chamber (10),- An Arrangement means (60) for arranging 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- The gas system (50) for providing the reaction gas (52) within the reaction chamber (10).

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