Method and device for depositing a chemically modified metal film

Abstract

The present invention pertains to a method comprising the steps of depositing a metal film on a surface of a substrate by sputtering from a metal target under a first atmosphere and at least partially chemically modifying the deposited metal film and a surface of the metal target under a second atmosphere. The invention further pertains to substrates having a surface coated with a chemically modified metal film and a device for performing the method of the invention.

Description

[0001] METHOD AND DEVICE FOR DEPOSITING A CHEMICALLY MODIFIED METAL FILM

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The current invention relates to the technical field of thin film deposition . In particular, the present invention pertains to a method comprising the steps of depositing a metal film on a surface of a substrate by sputtering from a metal target and at least partially chemically modi fying the deposited metal film and a surface of the metal target . The invention further pertains to substrates having a surface coated with a chemically modi fied metal film and a device for performing the method of the invention .

[0004] DESCRIPTION OF THE RELATED ART

[0005] Known methods and devices for depositing chemically modi fied metal films typically involve metal-organic chemical vapour deposition (MOCVD) or molecular beam epitaxy (MBE ) which are expensive and / or require high growth temperatures , which in turn can damage substrates or previously deposited layers . Also , high doping levels are generally di f ficult to achieve with these established processes . Alternative known methods include reactive sputtering which, however, has previously been found to deliver an inferior layer quality compared to MOCVD and

[0006] MBE . SUMMARY OF THE INVENTION

[0007] It is the obj ective of the present invention to provide an improved method and device for the deposition of a chemically modi fied metal film on a substrate , in particular a semiconductor film . A further obj ective is the provision of an improved substrate with a coated surface .

[0008] The obj ectives are achieved by a method with the features of claim 1 , a device with the features of claim 34 and a substrate with the features of claim 31 to 33 .

[0009] In a first aspect , the present invention is directed to a method for depositing a chemically modi fied metal film on a substrate , wherein the method comprises the steps :

[0010] ( a ) providing a substrate and a metal target in a vacuum chamber,

[0011] (b ) depositing a metal film on a surface of the substrate by sputtering the metal from the metal target under a first atmosphere , and

[0012] ( c ) at least partially chemically modi fying the deposited metal film and a surface of the metal target with a reactive gas under a second atmosphere , wherein the first atmosphere optionally is an atmosphere comprising at least 40 vol% of a noble gas , and wherein the second atmosphere is an atmosphere comprising the reactive gas .

[0013] The present method represents an improved method for the deposition of a chemically modi fied metal film on a substrate compared to MOCVD, MBE and standard sputtering methods. Compared to previous methods, the present method can, e.g., yield a higher layer quality (e.g. epitaxial layers) , allow for lower processing temperatures, yield high conductivities for doped metal films, as well as improve crystallinity and surface roughness of the sputtered metal film.

[0014] Suitable sputtering devices for carrying out the present method are known in the art and specific examples are described in greater detail below.

[0015] The substrate to be coated can be any substrate that is suitable for being coated by sputtering, e.g. sapphire or a Si-based substrate.

[0016] Step (b) can be carried out with means and parameters know to the skilled person in the art of sputtering and thin film deposition. The ions that cause sputtering can originate from known ion sources including plasma and particle accelerators (e.g. ion beam sputtering) .

[0017] Ionization in the plasma can be, e.g., further increased by the use of cold or hot cathodes, e.g. hot filament cathodes. The ions may be generated in the vacuum chamber in which the target and substrate are placed, or they may be generated in a separate chamber functionally connected to the vacuum chamber in which the metal target and substrate are placed. The ions for sputtering are ions of the gas component (s) of the first atmosphere.

[0018] The metal target can be any metal target that is suitable for sputtering and includes liquid and solid metal targets. It is noted that the terms liquid and solid do not refer to the physical state of the metal at room temperature but to the physical state during the current method (e.g. during the single steps of the method) , wherein the temperature of the metal target can be adjusted. One or multiple metal targets may be used in the present method, e.g. for cosputtering. The metal target may be liquified or solidified by adjusting its temperature, e.g. while performing the present method. A combination of liquid and solid metal targets may be used, e.g. for co-sputtering . It is within the purview of the present invention that the physical state of the metal target can be varied during the course of the instant method, e.g. that the physical state may differ from one method step to another and / or that the physical state may be adjusted, e.g. to solid, while positioning or re-positioning the metal target, e.g. dependent on the position of the metal target relative to gravity so as to avoid spillage or leakage of the metal target. If a liquid metal target is used, this target can for example be degassed before sputtering, e.g. to avoid the formation of gas bubbles, in particular those which result from the filling of the liquid target.

[0019] During step (b) , a metal film is deposited on the surface of the substrate by sputtering the metal (which forms the metal film on the surface of the substrate) from the metal target under a first atmosphere. The first atmosphere allows for sputtering but, together with other process parameters such as sputtering power, sputtering duration and / or temperature, does not or at least essentially does not cause a chemical modification of the metal target, the metal that is sputtered from the metal target and the metal that is deposited as a metal film on the substrate. In other words, metal accumulates on the substrate at a higher rate than a chemical modification of said metal can or could take place. The term "at least essentially does not cause a chemical modification " means that at most trace amounts of a metal are chemically reacted with a gas component of the first atmosphere during step (b) , for example at most 1 moll to 40 moll or at most 10 moll, 20 moll or 40 moll of the atoms of the metal which are deposited during step (b) . In an embodiment, these values only refer to the atoms being deposited during step (b) and not to any atoms that were deposited in a previously conducted step (b) or that were provided on the substrate before step (b) by any other means. Optionally the term "at least essentially does not cause a chemical modification " means that at most 1 moll to 40 moll or at most 10 moll, 20 moll or 40 moll of the surface atoms of the target of a metal are chemically reacted with a gas component of the first atmosphere during step (b) . Typically, this first atmosphere comprises a noble gas, and further (gas) components may optionally be comprised to the extent that essentially no chemical modification as detailed above occurs during method step (b) under the chosen process parameters (e.g. as detailed above and below) . For example, the first atmosphere can consist of a noble gas (e.g. Ar, Ne, Kr and / or Xe) . In an alternative example, the first atmosphere may comprise, in addition to a noble gas, one or more (potentially) reactive gas components (such as, e.g., N2, NH3, N2O, N2H4, methane, acetylene, propane, CO2 and / or H2S) . It is within the purview of the skilled person to adj ust the method parameters during step (b ) so that the optional and potentially reactive gas components of the first atmosphere essentially do not react with the metal target , the metal that is sputtered from the metal target and the metal that is deposited as a metal film on the substrate during step (b ) ( the term " essentially do not react" can include some degree of modi fication as noted above in the context of the chemical modi fication) . Also , for example , the reactive gas parts can be used to reduce the amount of metal overabundance which can exceed optimal conditions . For example , such process parameters include the volume ratio of the potentially reactive gas component relative to the noble gas in the atmosphere , the sputter power, the sputtering power type ( e . g . DC-sputtering including DC magnetron-sputtering, pulsed DC-sputtering, pulsed DC magnetron-sputtering, RF-sputtering or a combination of DC- and RF-sputtering) , the sputtering temperature and / or the duration of step (b ) .

[0020] During step (b ) a metal film of one or several atomic monolayers can be generated, depending on the duration and process conditions which can be routinely controlled by the skilled person . Step (b ) may, e . g . , be carried out up to and including metal droplet formation on the substrate .

[0021] After the metal film is deposited during step (b ) , this metal film and a surface of the metal target is at least partially chemically modi fied during step ( c ) of the present method . As used herein, the term " chemically modi fying" refers to a chemical reaction of at least part of the deposited metal film ( referring to those metal atoms that were deposited during the previous step (b) , optionally more than one or all monolayers if more than one monolayer were deposited in the previous step (b) , optionally at least the surface of the metal film) and the surface of the metal target with a further reactive gas comprised in the second atmosphere. The skilled person knows conditions that are suitable for effecting the reaction of the deposited metal film and the surface of the metal target with a reactive gas comprised in the second atmosphere, e.g. by ionizing the reactive gas, e.g. with a plasma. Exemplary chemical reactions include nitridation, oxidation, carbidation and sulfidation. These chemical modifications are usually achieved in the art by reactive sputtering, i.e. a process, wherein the sputtered metal reacts with a reactive gas during the sputter / deposition process. In the present method, however, the process of sputtering / deposition is separated from the process of chemical modification. In other words, the current method comprises a two-step procedure, wherein the metal is sputtered and deposited in a first step (step (b) ) and subsequently chemically modified in a second step (step (c) ) . Furthermore, in step (c) of the present method, at least part of the surface of the metal target is chemically modified, essentially in analogy to the deposited metal film. The at least partial chemical modification of the surface of the metal target results in a reduction or even prevention of sputtering from the metal target during step (c) , further aiding in the separation of the sputter / deposition process from the chemical modification process . It is noted that, for all aspects and embodiments disclosed herein, the chemically modified metal film (e.g. obtained from step (c) of the present method) is termed "chemically modified metal film" for reasons of easier reading. Of course, if the chemical modification of the metal film leading to the chemically modified metal film entails a reaction that will render the metal "non-metallic" , e.g. modifying Ga to GaN, the resulting chemically modified metal film may no longer have metallic properties (e.g. GaN) but is still called chemically modified metal film herein. In other words, the term "chemically modified metal film" simply refers to a metal film was chemically modified and does not mean that the chemically modified metal film is still a pure metal film or has metallic properties. For example, in all aspects and embodiments described herein, the chemically modified metal film on the substrate can be a semiconductor film.

[0022] The term "at least partially chemically modifying deposited metal film " in the context of the present method means that the deposited metal film of step (b) is chemically modified to a desired degree which can be chosen by the skilled person, e.g. depending on the material properties that should be obtained. The skilled person is aware that also those atoms of the metal film deposited during previous step (b) that are not exposed to the reactive gas (i.e. the metal atoms inside the layers or inside droplets of the film) can be chemically modified if the metal film includes more than one atomic monolayer. Exemplary degrees of chemical modification include complete chemical modification of all metal atoms of the metal film deposited during the previous step (b) to achieve a desired stoichiometry, optionally at least 60 mol% thereof.

[0023] The term "at least partially chemically modifying a surface of the metal target" in the context of the present method means that a surface of the metal target is chemically modified with a reactive gas to the extent that sputtering from the target is significantly reduced by the chemically modified surface, e.g. in that at least the surface area of the metal target that would be sputter-active (or was sputter-active in step (b) ) is chemically modified. This modification can be considered a "poisoning" of the target. For example, "at least partially chemically modifying a surface of the metal target" and "significantly reducing sputtering from the target" means that at least the entire sputter-active surface of the target is chemically modified and / or that sputtering from the target is reduced by at least 50%, optionally at least 75% or 95% in step (c) compared to step (b) .

[0024] Step (c) can be carried out with means and parameters known to the skilled person in the art of sputtering and thin film deposition. The ions that cause the at least partial chemical modification of the deposited metal film and surface of the metal target can originate from known ion sources including plasma and particle accelerators (e.g. an ion beam) Ionization in the plasma can be, e.g., further increased by the use of cold or hot cathodes, e.g. hot filament cathodes. The ions may be generated in the vacuum chamber in which the target and substrate are placed, or they may be generated in a separate chamber functionally connected to the vacuum chamber in which the target and substrate are placed . The ion source ioni zes ions of the gas component ( s ) of the second atmosphere and optionally has no separate gas source .

[0025] For example , when a plasma is used in step ( c ) to generate ions of the second atmosphere , the partial chemical modi fication of the surface of the metal target can lead to electrical insulation which prevents a current flow and essentially no ions from the plasma are accelerated towards the metal target . Furthermore , due to the least partial chemical modi fication of the surface of the metal target no mechanical shutter is required in the present method to cover the metal target and / or the substrate in order to avoid or reduce sputtering during the chemical modi fication, e . g . until essentially all or at least the desired amount of metal atoms on the surface of the deposited metal film are chemically modi fied . Hence , in an example , the present method is one which does not involve the use of a mechanical shutter to cover the metal target and / or the substrate , and to avoid or reduce sputtering from the metal target and / or coating of the substrate . Alternatively, the present method may involve the use of a shutter which, however, is either not essential for avoiding or reducing sputtering from the metal target and / or coating of the substrate , or is not or not consistently ( e . g . only in one of two or more iterations of one of the method steps ) activated and / or positioned to cover the metal target and / or the substrate surface , and / or to avoid or reduce sputtering from the metal target and / or coating of the substrate during the step of chemically modifying the deposited metal film and / or during free sputtering .

[0026] In an example, step (c) involves the generation of a plasma of the second atmosphere including the reactive gas in effective proximity to the metal film and the metal target surface to achieve the chemical modification. For example, the power and means for sputtering used in step (b) can be used for plasma generation in step (c) , although the amounts and type of power (i.e. these process parameters) may vary between steps (b) and (c) .

[0027] The second atmosphere for use in the present invention comprises a reactive gas (such as, e.g., N2, NH3, N2O, N2H4, methane, acetylene, propane, CO2 and / or H2S) which allows for the at least partial chemical modification of the deposited metal film and surface of the metal target. The second atmosphere can, e.g., further comprise a noble gas as defined above in the context of the first atmosphere. The volume ratio between the reactive gas and the noble gas can be set by the skilled person, e.g. depending on the process parameters such as, e.g., the applied power, the power type (e.g. DC-power including DC magnetron-power, pulsed DC-power, pulsed DC magnetron-power or RF-power) used for plasma generation, the temperature and / or the duration of step (c) . Depending on these process parameters, the first and second atmosphere may be of the same chemical composition and process parameters noted above are used to either effect sputtering during step (b) or the chemical modification during step (c) . If the first atmosphere differs from the second atmosphere, the atmosphere can be changed after step (b) and before step (c) . The change in atmosphere can be achieved by purging or gradual exchange of the atmospheres, e.g. by adjusting the flow rates of the different gases. In an example, the change in atmosphere can occur seamless or while a plasma used for sputtering is extinguished while stabilizing the atmosphere followed by re-igniting the plasma for step (c) . For example, the atmospheres in steps (b) and (c) can be generated by defining flow rates of the desired gases, e.g. in the range of 0 standard cubic centimeter per minute (seem) to 150 seem for each of the gases. The difference in gas flow is considered to yield a corresponding volume ratio for the purpose of the present invention (i.e. a flow rate of gas A = 1 seem and gas B = 50 seem results in a volume ratio of gas A : gas B = 1:50) . Alternatively to defining flow rates of the desired gases, gas bursts, e.g. from a reservoir, can be introduced.

[0028] In an example, the first and second atmosphere during steps (b) and (c) , respectively, are essentially the same in proximity to the substrate and in proximity to the metal target. In other words, the difference in the atmosphere in this example is not achieved by localization of different atmospheres relative to the substrate and the metal target, but rather by exchanging the first and second atmosphere between steps (b) and (c) in proximity to both, the substrate and the metal target. Therefore, both, the substrate and the metal target are subjected to the same atmosphere in this example: the first atmosphere in step (b) and the second atmosphere in step (c) . In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the metal target is a liquid metal target, optionally a metal target that is in liquid form above about 30°C. As noted above, the metal target may be liquified or solidified by adjusting its temperature, e.g. while performing the present method. For example, a metal target can be solid during steps (a) , (b) and / or (c) , and then be liquified after step (c) in order to remove the at least partially chemically modified surface of the metal target by stirring or agitating (see below) .

[0029] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method is one, wherein after step (c) , the method further comprises step (d) of at least partially removing the chemically modified surface of the metal target, optionally under the first atmosphere. At least partial removal of the chemically modified surface of the metal target can be achieved by free sputtering of the metal target under suitable conditions (e.g. using the first atmosphere and suitable sputtering conditions) known to the skilled person. Exemplary conditions for free sputtering include applying a sputtering power density selected from 0.3 W / cm2to 2.4

[0030] W / cm2DC and / or 0.45 W / cm2to 3.1 W / cm2RF.

[0031] If the target is liquid or liquified (e.g. for the purpose of at least partial removal of the chemically modified surface) , stirring or agitating of the liquid metal target can be employed, e.g. alternative to or in addition to free sputtering, to partially remove the chemically modified surface of the metal target. "At least partially remove" in the context of the present method refers to a degree of removal of the chemically modified surface that allows for sputtering from the metal target after the removal step. For example, "at least partially remove" means that the same degree of sputtering can be reached after step (d) compared to the previously conducted step (b) before step (c) was carried out, and / or that at least 80% of the modified surface of the target is removed. If other methods are used for at least partially removing the chemically modified surface of the metal target, such as stirring or agitating, it is noted that these methods do not exclude that free sputtering occurs additionally.

[0032] For example, it is further noted that the method conditions in step (c) are chosen such that for the example of a liquid or liquified target, no stirring or agitating or only a degree of stirring or agitating takes place during step (c) which does not significantly remove (see above) the chemically modified surface of the metal target to the extent that sputtering from the target is still significantly reduced by the chemically modified surface during step (c) . For example, mechanical stirring or ultrasound agitation can be switched of f . Additionally or alternatively, the sputtering power can be set or reduced during step ( c ) to a power which does not ef fect signi ficant stirring of the liquid metal target so that the chemically modi fied surface remains intact to the extent that sputtering from the target is still signi ficantly reduced during step ( c ) . For example , the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method is one, wherein during step ( c ) stirring of a liquid target is reduced or stopped .

[0033] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method is one, wherein after step ( d) , the method further comprises repeating step (b ) to deposit a further metal film on the surface of the substrate by sputtering the metal from the metal target under a third atmosphere , optionally the first atmosphere .

[0034] Repeating step (b ) means that a further metal film is deposited on the metal film that was deposited in a previous step (b ) . Repetition of step (b ) does not necessarily mean that the exact same process conditions are used compared to a previous ( or further ) step (b ) . In other words , the repetition of step (b ) can be considered a " step (b ' ) " which entails di f ferent processing conditions but again leads to the deposition of a metal film on a previously deposited metal film on the substrate of the previous step (b) by sputtering from a metal target. Also, the metal target of step (b' ) can be the same as in step (b) or different from step (b) . The third atmosphere may be identical to the first atmosphere or different to the first atmosphere. However, the functional limitations explained above for the first atmosphere also apply to the third atmosphere. The third atmosphere may be altered compared to the first atmosphere, for example, if a different metal target is used in step (b' ) .

[0035] For example, the repetition of step (b) (e.g. step (b' ) ) can be conducted in the same vacuum chamber as the previous step (b) , or it can be conducted in a different vacuum chamber. Also, if step (d) is carried out as free sputtering, step (d) can be carried out together with the repetition of step (b) , i.e. step (d) is not performed previous to step (b) but concomitantly.

[0036] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method comprises repeating step (c) and optionally step (d) .

[0037] In the context of the present method, repeating step (c) means that the further metal film of further step (b) (or step (b' ) ) is chemically modified. Repetition of step (c) does not necessarily mean that the exact same process conditions are used compared to a previous (or further) step (c) . In other words, the repetition of step (c) can be considered a "step (c' )" which entails different processing conditions but again leads to the at least partial chemical modification of the previously deposited metal film on the substrate and the at least partial chemical modification of the surface of the metal target of the previous step (b) . The second atmosphere when repeating step (c) (or conducting step (o' ) ) may be identical to the second atmosphere or different to the second atmosphere. However, the functional limitations explained above for the second atmosphere also apply to the atmosphere for repeating step (c) (or conducting step (o' ) ) . The second atmosphere during repetition of step (c) (or when conducting step (o' ) ) may be altered compared to the previously used second atmosphere, for example, if a different metal target was used in step (b' ) and / or if a different chemical modification of the deposited layer compared to the previous step (c) is desired.

[0038] For example, the repetition of step (c) (e.g. step (o' ) ) can be conducted in the same vacuum chamber as the previous step (c) , or it can be conducted in a different vacuum chamber. If step (d) is also repeated after the repetition of step (c) (or if step (o' ) is conducted) , the definitions provided above for step (d) also apply to the repetition of step (d) but the at least partial removal does not necessarily have to be conducted in the same way compared to the previous step (d) (e.g. by stirring instead of agitating or by free sputtering instead of stirring, etc.) . In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method comprises repeating steps (b) , (c) and (d) in this order to deposit and at least partially chemically modify multiple metal films on the surface of the substrate, optionally wherein the steps are repeated 2 to 120 times, optionally wherein step (d) is not performed after the last repetition of steps (b) and (c) .

[0039] The explanations provided above for the repetition of steps

[0040] (b) , (c) and (d) apply to the repetition of the steps (b) ,

[0041] (c) and (d) in this order.

[0042] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the chemically modified metal film of step (c) has a thickness of about 0.1 nm to 20 nm, optionally about 0.3 nm to 15 nm, optionally about 10 nm.

[0043] The thickness indicated above refers to the thickness of the metal film after one iteration of step (b) and (c) . If steps (b) , (c) and optionally (d) are repeated, greater thicknesses can be achieved by multiple layers of the metal film, e.g. thicknesses of about 1 nm to about 1.5 pm. In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the at least partially chemically modi fied metal film is an epitaxial film . The at least partially chemically modi fied film is the film that is obtained from step ( c ) of the present method, or from a repetition of steps (b ) , ( c ) and optionally ( d) as outlined above .

[0044] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the sputtering in step (b ) is DC-sputtering, optionally DC magnetron-sputtering, pulsed DC-sputtering, or pulsed DC magnetron-sputtering; RF-sputtering; or a combination thereof . These conditions also optionally apply for step ( d) .

[0045] As used herein, the term "DC-sputtering (... ) RF-sputtering; or a combination thereof" means that either DC or RF- sputtering, or DC and RF-sputtering can be used .

[0046] For example , an essentially planar magnetron system may be used as described on pages 4 to 5 of WO 2020 / 083882 Al , incorporated by reference in its entirety . Also , it is within the scope of the present invention that an inductively coupled plasma ( ICR ) is ( e . g . additionally or alternatively) used in step (b ) . In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the sputtering power density is selected from 0.3 W / cm2to 2.4 W / cm2DC and / or 0.45 W / cm2to 3.1 W / cm2RF.

[0047] The sputtering power density refers to the power density used for sputtering in step (b) and the area in cm2refers to the area of the surface of the metal target from which the metal is sputtered. For example, by adjusting the sputtering power and the sputtering power type (e.g. DC, pulsed DC, optionally in combination with a magnetron, or RF) , the reaction conditions can be controlled in that also a first atmosphere comprising a reactive gas does not significantly lead to any chemical modification of the deposited metal film with the reactive gas.

[0048] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method is one, wherein in step (c) , a reactive gas-comprising plasma is generated between the target and the substrate, wherein the reactive gas-comprising plasma optionally is a DC-plasma, an RF-plasma or a mixture thereof.

[0049] Alternatively, a remote plasma (e.g. in a different vacuum chamber) can be used to create ions of the reactive gas of the second atmosphere which then lead to the at least partial chemical modi fication of the deposited metal film in step ( c ) .

[0050] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method is one, wherein the power density for plasma generation in step ( c ) is selected from 0 . 24 W / cm2to 1 . 55 W / cm2DC and / or 0 . 3 W / cm2to 1 . 55 W / cm2RF .

[0051] The area in cm2refers to the area of the surface of the metal target from which the metal is sputtered .

[0052] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, step ( d) is performed under the conditions of step (b ) , optionally is performed as step (b ) , and wherein the chemically modi fied surface of the metal target is at least partially removed by sputtering .

[0053] The sputtering used to at least partially remove the chemically modi fied surface of the metal target is also referred to as free sputtering and may occur additionally to other means of partial removal of the chemically modi fied surface of the metal target . In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the chemically modi fied surface of the liquid metal target is at least partially removed in step ( d) by stirring and / or agitating the liquid metal target .

[0054] Stirring or agitating, as used herein, mean mixing the liquid metal target to the extent that the chemically modi fied surface of the liquid metal target is at least partially removed so that sputtering can occur from the liquid metal target .

[0055] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the stirring or agitating is performed by mechanical stirring, by ultrasound agitation, by application of a magnetic field, or by a combination thereof .

[0056] Means for stirring and / or agitating the metal target are disclosed in WO 2020 / 083882 Al , incorporated by reference in its entirety, speci fically on pages 6 to 11 and 13 to 15 , including magnetic field-based agitation (using a magnetron and / or additional agitation electrode ( s ) ) , ultrasound agitation and mechanical stirrer ( s ) .

[0057] The magnetic field used for stirring can be used together with a current flow through the liquid metal target , wherein the magnetic field is at least in part orthogonal to the current flow, resulting in a Lorentz force and stirring of the liquid metal target . The current flow can be superimposed to a sputter voltage , or can be directly induced in the liquid metal target by a sputter-voltage , or be generated as a combination thereof , whereby the magnetic field can be generated by a magnetron system ( e . g . also used for sputtering) or a magnetron system and further agitation magnets , e . g . side magnets . Furthermore , during the sputter process , the Lorentz forces induced by a ( e . g . plasma ) current and the magnetic field cause the liquid metal target material to move in a manner that prevents the formation of gas bubbles and thus avoids the ej ection of target material droplets toward the substrate .

[0058] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the magnetic field is applied with the aid of a magnetron system .

[0059] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, agitating is performed by application of a magnetic field and a DC- or RF-plasma between the target and the substrate , optionally under the first atmosphere .

[0060] Alternatively, an agitation unit comprising an inner and outer agitation-electrode as disclosed on pages 14 to 15 of WO 2020 / 083882 Al can be used . For Lorentz force stirring, the means and methods described in Figures 6 , 7 and 8 , as well as their description on pages 25 to 32 of WO 2020 / 083882 Al are specifically included for the purposes of the present invention.

[0061] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the first and / or third atmosphere comprises at least 60 vol% of a noble gas, and / or the second atmosphere comprises at least 5 vol% of a reactive gas.

[0062] As noted above, the gas vol% can be generated by defining flow rates of the respective gases. The difference in gas flow is considered to yield a corresponding volume ratio for the purpose of the present invention (i.e. a flow rate of gas A = 40 seem and gas B = 60 seem results in 60 volume-% of gas B) .

[0063] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the first and / or third atmosphere is a gas atmosphere free of a reactive gas or a gas mixture of noble gas and reactive gas with a volume ratio of about 1:0.6 or lower or 1:0.4 or lower, optionally from about 1:0.01 to about 1:0.6 or from about 1:0.01 to about 1:0.6, and / or the second atmosphere is a gas atmosphere consisting of a reactive gas or a gas mixture of noble gas and reactive gas with a volume ratio of about 1:0.6 or higher, optionally from about 1:0.6 to about 1:8, optionally from about 1:3 to about 1:4.

[0064] A gas mixture of noble gas an reactive gas with a volume ratio of about 1 : 0.6 refers to a ratio of noble gas to reactive gas of 1:0.6, wherein the ratio of the gases can be generated by defining flow rates of the respective gases. The difference in gas flow is considered to yield a corresponding volume ratio for the purpose of the present invention (i.e. a flow rate of noble gas = 10 seem and reactive gas = 6 seem results in a ratio of noble gas to reactive gas of 1:0.6) .

[0065] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the noble gas is selected from the group consisting of Ar, Ne, Kr and Xe, and / or the reactive gas is a nitrogen-comprising gas, optionally selected from the group consisting of N2, NH3, N2O and N2H4, or a gas selected from the group consisting of methane, acetylene, propane, O2, CO2 and H2S .

[0066] Mixtures of noble gases, nitrogen-comprising gases and methane, acetylene, propane, O2, CO2 and H2S are within the scope of the present invention. In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the chemical modi fication is a nitridation or oxidation .

[0067] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the chemical modi fication is a nitridation, and the reactive gas is a nitrogen-comprising gas , optionally selected from the group consisting of N2 , NH3 and N2H4 .

[0068] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the metal target is a liquid metal target , wherein the liquid metal target is a liquid metal or an alloy of at least two metals having a melting point of about 300 ° C or lower, optionally about 70 ° C or lower, optionally about 40 ° C or lower .

[0069] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the metal target is a liquid metal target selected from the group consisting of Ga, GaAs, Gain, GaAl, InAl, TiGa, Hg, HgAg, HgAu, HgCu, Hgln, HgSn and HgZn. Mixtures of these metals and alloys are included in the scope of the present invention.

[0070] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, step (b) is performed for about 1 second to about 60 seconds, optionally about 3 seconds to about 15 seconds, and / or step (c) is performed for about 2 seconds to about 80 seconds, optionally about 5 seconds to about 35 seconds.

[0071] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, steps (b) and (c) are separated by no pause or by a pause of about 0.1 seconds to about 10 seconds, and / or wherein the steps (c) and (b) , including step (d) , are separated by no pause or by a pause of about 0.1 seconds to about 20 seconds. The process parameters (including the atmosphere) can be changed during the pause or they can be changed seamlessly without a pause .

[0072] If a plasma is generated during step (b) , (c) and / or (d) , this plasma can be turned off during the optional pause between the steps. In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the substrate is heated in steps (b) and / or (c) to a temperature from about room temperature to about 900°C, optionally from about 500°C to about 900°C, optionally from about 650°C to about 850°C.

[0073] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the substrate is selected from the group consisting of sapphire, a substrate having a GaN-surface, a substrate having an AlN-surface, a substrate having an AlGaN-surf ace, a substrate having an AlScN-surf ace, a substrate having a Si-surface and a substrate having a SiC-surface.

[0074] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method further comprises doping the metal film on the surface of the substrate, in particular a metal film consisting of Ga and / or GaN, with a dopant selected from the group consisting of 0, O2, Zr, Ti, F, Ge, germane (GeH.4) , isobutyl germane ( (CH3) 2CHCH2GeH3) , Nb, S, Se, Mg, cyclopentadienyl magnesium (Cp2Mg) , Be, Ca, Zn, Mn, Cd, C and Fe .

[0075] Doping the metal film is, in the context of the present method, a different step from the step of at least partially chemically modifying the metal film. Methods for doping are known in the context of thin film deposition and sputtering and the skilled person can routinely apply suitable methods of introducing the dopants into the metal film. For example, doping can be performed during steps (b) and optionally (d) of the present method, e.g. by cosputtering from a suitable target. For other doping methods, such as the introduction of a dopant gas or by evaporation or sputtering a dopant from an independent source, doping can be performed during any of steps (b) , (c) , and / or (d) , or it can be performed in an additional step, e.g. after step (b) or (c) . If the dopant is a gas, it can be introduced as part of the first, second and / or third atmosphere.

[0076] In an embodiment of the method according to the present invention, which may be combined with any of the embodiments of the method preaddressed or still to be addressed unless in contradiction, the method further comprises doping the metal film on the surface with Si by introducing a silane gas, a SiH-compound, a S1H2C12- compund, a SiHCla-compound, a SiHaCl-compound a S1C14- compound or a combination thereof, optionally during step (b) , (c) , and / or (d) , by thermal evaporation of Si , optionally during step (b ) , ( c ) , and / or ( d) , and / or by sputtering from a Si-comprising target , optionally during step (b ) , ( c ) , and / or ( d) , optionally by positioning a solid silicon component above the liquid metal target .

[0077] In the context of the present method, doping, in particular doping with Si , can be performed during one of the method steps (b ) , ( c ) , and / or ( d) , or during an independent step between any of the aforementioned steps of the instant method . The skilled person can routinely determine the suitable time point or method step for doping, e . g . depending on the type of dopant and method of doping ( gaseous dopant , doping by evaporation or ( co- ) sputtering) .

[0078] In another aspect which may be combined with any of the embodiments or aspects preaddressed or still to be addressed unless in contradiction, the present invention is directed to a substrate having a surface coated with a chemically modi fied metal film obtained or obtainable by the method disclosed herein, optionally with a metal nitride film, optionally wherein the film has a thickness of about 1 nm to about 1 . 5 pm .

[0079] As explained in the context of the present method, the chemically modi fied metal film on the surface of the substrate may comprise one or several layers (which may vary in thickness , metal type and type of chemical modi fication) of the chemically modi fied metal film, wherein the layers are the result of the repetition of the method steps as detailed above. For example, the chemically modified metal film is a semiconductor film.

[0080] In another aspect which may be combined with any of the embodiments or aspects preaddressed or still to be addressed unless in contradiction, the present invention is directed to a substrate having a surface coated with a chemically modified metal film obtained or obtainable by the method disclosed herein, optionally with a metal nitride film, wherein the film has a resistivity of at least 1000 Qcm. The film with a resistivity of at least 1000 Qcm is a non-doped chemically modified metal film, optionally a chemically modified metal film comprising essentially no Si, obtained by the method according to the present invention, i.e. a film obtained or obtainable by the method according to the present invention excluding the steps of doping the (chemically modified) metal film. As outlined above, the chemically modified metal film (e.g. obtained from step (c) of the present method) is termed "chemically modified metal film" for reasons of easier reading. Specifically in the case of a substrate coated with a chemically modified metal film having a resistivity of at least 1000 Qcm the chemical modification of the metal film rendered the metal "non-metallic" , e.g. Ga modified to GaN, and the resulting chemically modified metal film no longer has metallic properties (e.g. GaN) but is still called chemically modified metal film herein. For example, the chemically modified metal film on the substrate having a resistivity of at least 1000 Qcm can be a semiconductor film .

[0081] In another aspect which may be combined with any of the embodiments or aspects preaddressed or still to be addressed unless in contradiction, the present invention is directed to a substrate having a surface coated with a chemically modi fied metal film obtained or obtainable by the method disclosed herein, optionally with a metal nitride film, wherein the film has a resistivity of about 10000 pQcm or less , optionally about 5000 pQcm or less , optionally about 1000 pQcm or less , optionally about 650 pQcm or less , optionally about 600 pQcm or less , optionally about 580 pQcm or less . The film with a resistivity of less than about 10000 pQcm is a doped metal film, optionally a metal film comprising Si , obtained by the method according to the present invention, i . e . a film obtained or obtainable by the method according to the present invention including the step of doping the metal film .

[0082] In another aspect which may be combined with any of the embodiments or aspects preaddressed or still to be addressed unless in contradiction, the present invention is directed to a device configured to perform the method disclosed herein, wherein the device comprises a vacuum sputtering chamber comprising : a substrate holder, a receptacle for receiving a metal target , optionally a liquid metal target , wherein the receptacle is connected or connectable to a power supply, a vacuum port , and a gas inlet , wherein the device further comprises a control unit configured to control and execute the steps according to the method described herein .

[0083] The device of the present invention can, e . g . , be any known coating device suitable for thin film coating by sputtering which can be used to sputter from a solid or liquid target in the context of the present method . In addition, the device of the present invention comprises a control unit that is configured, e . g . programmed by a computer program, to execute the method steps of the present method .

[0084] In an embodiment of the device according to the present invention, which may be combined with any of the embodiments of the device preaddressed or still to be addressed unless in contradiction, the receptacle is connected or connectable to the cathode of a DC power supply, the cathode of a pulsed DC power supply, to a RF power supply or to a power supply providing a combination of DC, pulsed DC and / or RF power .

[0085] The device of the present invention can be a device disclosed in WO 2020 / 083882 Al , incorporated by reference in its entirety . The skilled person finds no di f ficulties to adapt the device disclosed therein to also ( or alternatively) suit solid metal targets . However, and for example only, the device of the present invention and / or for use in the present method does not comprise a shutter to cover the metal target and / or the substrate surface , and / or to avoid or reduce sputtering from the metal target and / or coating of the substrate during the step of chemically modi fying the deposited metal film and / or during free sputtering . Alternatively, the device of the present invention and / or for use in the present method may comprise a shutter which, however, is not activated and / or positioned to cover the metal target and / or the substrate surface , and / or to avoid or reduce sputtering from the metal target and / or coating of the substrate during the step of chemically modi fying the deposited metal film and / or during free sputtering, wherein, e . g . , the control unit controls the non-activation and / or positioning of the shutter .

[0086] The receptacle for receiving a metal target , optionally a liquid metal target , is shaped according to the nature of the metal target . For example , i f a liquid target is used, the receptacle can be a trough formed at least partially concave in a peripheral region to compensate for the high surface tension of liquid metals , center the liquid material and create a large flat target area . Alternatively, the bottom of the trough can be formed at least partially convex at least in a peripheral region to provide more material in a sputter-active area . Furthermore , the device may comprise means to heat and / or to cool the metal target , e . g . to change its physical state from liquid to solid and vice versa . Such means may comprise a cooling and / or heating circulation within the receptacle ( e . g . trough) or a heating / cooling plate to which the receptacle ( e . g . trough) is thermally connected . Alternatively, heating can be provided by a radiation lamp or other radiation devices ( e . g . carbon heater ) , by a plasma, or by electron bombardment of the surface of the metal target .

[0087] In an embodiment of the device according to the present invention, which may be combined with any of the embodiments of the device preaddressed or still to be addressed unless in contradiction, the substrate holder is connected or connectable to ground or a power supply, optionally a floating power supply .

[0088] The power supply connected or connectable to the substrate holder can be a DC or RF power supply .

[0089] In an embodiment of the device according to the present invention, which may be combined with any of the embodiments of the device preaddressed or still to be addressed unless in contradiction, the device further comprises an anode electrically isolated from the receptacle , wherein the anode is optionally positioned circumferential around the receptacle and / or in a central region of the receptacle . In an embodiment of the device according to the present invention, which may be combined with any of the embodiments of the device preaddressed or still to be addressed unless in contradiction, the device comprises means to stir and / or agitate a liquid metal target in the receptacle .

[0090] The means for stirring or agitating can be those disclosed in WO 2020 / 083882 Al , incorporated by reference in its entirety, e . g . on pages 7 to 11 .

[0091] In an embodiment of the device according to the present invention, which may be combined with any of the embodiments of the device preaddressed or still to be addressed unless in contradiction, the device comprises a magnetron system being positioned on the side of the receptacle that is opposite to the side that can receive a metal target , optionally a liquid metal target .

[0092] In an embodiment of the device according to the present invention, which may be combined with any of the embodiments of the device preaddressed or still to be addressed unless in contradiction, the magnetron system is configured to induce a magnetic field with axisymmetric or non-axisymmetric geometry relative to an axis that is perpendicular to the surface of a metal target in the receptacle . BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Embodiments of the current invention are described in more detail in the following with reference to the figures.

[0094] These are for illustrative purposes only and are not to be construed as limiting.

[0095] Figs. 1 to 3 show flowcharts for exemplary methods according to the present invention; and

[0096] Figs. 4 to 6 show exemplary devices according to the present invention.

[0097] DETAILED DESCRIPTION OF THE DRAWINGS

[0098] Figure 1 shows a flowchart for an exemplary method according to the present invention with one iteration of steps (b) and (c) , and optionally (d) . After a substrate and a metal target are provided in step (a) , step (b) is carried out (arrow I) , followed by step (c) (arrow II) . After at least partially chemically modifying the deposited metal film and a surface of the metal target with a reactive gas under a second atmosphere in step (c) , the method can be ended (arrow Illa) and the coated substrate can be removed from the vacuum chamber. Further processing (e.g. plasma etching or doping the metal film) of the coated substrate after step (c) is also possible, either in the same or in a different vacuum chamber. Alternatively, after step (c) , step (d) can be carried out (arrow Illb) and the method can be ended thereafter (arrow IV) leading essentially to the same product (coated substrate) as described for arrow Illa, including the possibility for further processing as described above.

[0099] Figure 2 shows a flowchart for an exemplary method according to the present invention with at least one repetition of steps (b) and (c) and including step (d) as a separate step. Steps (a) , (b) , (c) and (d) are carried out in this order (arrows I, II and III) . After step (d) , step

[0100] (b) is repeated either under the same conditions as the previous step (b) or under different conditions (i.e. as step (b' ) as disclosed above) , e.g. including a third atmosphere being different to the first atmosphere, a different metal target and / or different sputtering powers and power types. Hence, the same or a different metal film can be deposited on the previously deposited and chemically modified metal film. After the repetition of step (b) , the method can be ended (arrow Va) without further chemical modification (a previously deposited layer in the first step (b) was chemically modified) , or step (c) can be repeated (arrow Vb) under the same or different conditions as the first iteration of step (c) . The repetition of step

[0101] (c) can be considered a "step (c' )" which entails different processing conditions but again leads to the at least partial chemical modification of the previously deposited metal film on the substrate and the at least partial chemical modification of the surface of the metal target of the previous step (b) . The second atmosphere when repeating step (c) (or conducting step (o' ) ) may be identical to the second atmosphere or different to the second atmosphere.

[0102] However, the functional limitations explained above for the second atmosphere also apply to the atmosphere for repeating step (c) (or conducting step (o' ) ) . The second atmosphere during repetition of step (c) (or when conducting step (o' ) ) may be altered compared to the previously used second atmosphere, for example, if a different metal target was used in step (b' ) and / or if a different chemical modification of the deposited layer compared to the previous step (c) is desired. After the repetition of step (c) , the method can be ended (arrow Via) . Alternatively, step (d) is repeated (arrow VIb) , optionally followed by further steps (b) and / or (c) . The explanations given above for the first repetition of steps (b) and (c) apply to the second and further repetitions of these steps. By repeating steps (b) and / or (c) (and optionally (d) ) , further layers of a (chemically modified) metal target are added to the layers obtained from previous steps (b) and / or (c) . Essentially, the steps can be repeated as many times as desired, e.g. until a certain film thickness or layer number is achieved.

[0103] Figure 3 shows a flowchart for an exemplary method according to the present invention with at least one repetition of steps (b) and (c) , wherein step (d) is part of step (b) . For example, the at least partial removal of the chemically modified surface of the metal target can be achieved during step (b) by free sputtering of the metal target under suitable conditions, while sputter deposition occurs essentially at the same time as soon as at least part of the chemically modified surface of the metal target is available for sputtering. Exemplary conditions are provided above and the explanations given for figure 2 apply mutatis mutandis for figure 3. Figure 4 shows an exemplary device according to the present invention for conducting the method of the present invention. The device (1) comprises a vacuum sputtering chamber (2) and, within the vacuum sputtering chamber, a substrate holder (3) (which may optionally comprise means for heating and / or cooling (16) ) and a receptacle for receiving a metal target in liquid or solid form. The receptacle may also comprise or be connected to heating and / or cooling means (not shown) . The substrate holder (3) is configured to hold a substrate on the surface facing the receptacle (4) and the receptacle is configured to receive a metal target such that the metal target faces the substrate holder (3) . The vacuum sputtering chamber (2) further comprises a vacuum port (6) and a gas inlet (7) which (each or only one of these) may optionally comprise regulating valves (10) for regulating gas flow and vacuum, respectively. The gas inlet is used for installing the first, second and optionally third atmosphere in the vacuum chamber. The receptacle is connected or connectable to a sputter power supply (5) . The power supply can be a cathode of a DC power supply, the cathode of a pulsed DC power supply, a RF power supply or a power supply providing a combination of DC, pulsed DC and / or RF power. A plasma (9) can be generated between a metal target on the receptacle (4) and a substrate on the substrate holder (3) . A magnetron system (17) is typically used which - for all embodiments and figures disclosed herein - may be positioned outside of the vacuum chamber and includes symmetric or asymmetric magnetron systems. Typically, the magnetron system is static and the receptacle is configured to rotate . Alternatively, the magnetron system may rotate and / or the receptacle can be static . The device further comprises a control unit ( 8 ) which executes the method of the present invention . The control unit may be positioned outside and detachably from the device and vacuum sputtering chamber and it is , at least during the operation of the method, connected to the relevant components of the device which determine the method parameters and steps , such as the gas inlet valve or any other suitable gas control means , the sputter power supply and optionally to means for heating and cooling the substrate and / or receptacle . The vacuum chamber further comprises a substrate port (not shown) which can be a load lock for stand-alone systems or multi-chamber-systems operated with di f ferent pressure levels between successive process or trans fer chambers . An exemplary device of the present invention does not comprise a mechanical shutter to cover the metal target and / or the target , and to avoid or reduce sputtering from the metal target / coating of the substrate . Alternatively, the device of the present invention and / or for use in the present method may comprise a shutter which, however, is not activated and / or positioned to cover the metal target and / or the substrate surface , and / or to avoid or reduce sputtering from the metal target and / or coating of the substrate during the step of chemically modi fying the deposited metal film and / or during free sputtering, wherein, e . g . , the control unit controls the non-activation and / or positioning of the shutter . Figure 5 shows an exemplary device according to figure 4 further comprising the following. A power supply (11) is connected or connectable to the substrate holder which is in conductive contact with a substrate to be inserted during the method (the substrate holder may optionally comprise means for heating and / or cooling) . Power supply (11) can alternatively be ground, a DC or RF power supply or a floating power supply. An optional grounded anode (13) may be comprised which is electrically isolated from the receptacle (4) (and its power supply (5) ) and which may optionally be positioned circumferentially around the receptacle. The circumferential position of the anode can render this anode an outer electrode for agitation of a liquid metal target, while the receptacle can act as an inner electrode. An optional anode shield (14) can be mounted electrically isolated from the receptacle in a dark room distance according to the process pressure applied. The vacuum sputtering chamber further comprise magnets (12) configured in an essentially planar magnetron system on or, for example, recessed in the reverse side of the receptacle (4) or at or in the bottom of the receptacle (4) , e.g. below a liquid level of a liquid metal target. To generate a magnetic field the magnetron system comprises an outer closed magnet loop which is essentially perpendicular to the target surface with its magnetic axis MA, and encloses the inner magnet (s) of inverse polarity being arranged in a central region of the target and vertically oriented with it's magnetic axis M . Note that the pole orientation shown can be inversed. It should be mentioned that outer magnet (s) can be also arranged having a slightly oblique magnetic axis MA tilted towards or against a central vertical axis, e.g. between 5° and 15°, to further design the overall magnetic field. The outer magnet can be, e.g. a ring-magnet or respectively arranged smaller magnets. The inner magnets, if more than one magnet is used, may be arranged linearly, or again as a closed loop, e.g. including linear and / or curved sections, for rectangular or other elongated targets, or as a central pole for square or circular targets, with all types essentially parallel but inverse to the magnetic axis M of the outer magnet loop. The magnetic field of the magnetron together with a current flow through a liquid metal target results in a Lorentz force and stirring of the liquid metal target. Alternative means for stirring are not shown but can be included, e.g. as disclosed in WO 2020 / 083882 Al, incorporated by reference in its entirety. The control unit (8) in this example is, at least during the operation of the method, further connected to power supply (11) .

[0104] Figure 6 shows an exemplary device according to figure 5 wherein the receptacle (4) comprises a liquid metal target (15) .

[0105] REFERENCE SIGNS LIST

[0106] 1 Device 10 Regulating valve

[0107] 2 Vacuum sputtering 11 Power supply chamber 12 Magnets for magnetron

[0108] 3 Substrate holder system

[0109] 4 Receptacle 13 Anode

[0110] 5 Sputter power supply 14 Shield

[0111] 6 Vacuum port 15 Liquid metal target

[0112] 7 Gas inlet 16 Cooling / heating means

[0113] 8 Control unit 17 Magnetron System

[0114] 9 Plasma

[0115] EXAMPLES OF THE INVENTION

[0116] Embodiments of the current method are described in more detail in the following examples , none of which are to be interpreted as limiting the scope of the present invention . For the following examples , a coating device as described above , speci fically a commercially available coating device from Evatec AG such as a CLN200 can be used . In this device , the cathode consists of a receptacle filled with liquid Ga . It can be supplied with DC and RE ( 13 . 56MHz ) voltages supplied by two separate generators . The anode can be arranged as needed, e . g . as a grounded shield which acts as anode . The magnetron is circular and slightly unbalanced such that the plasma extends more toward the substrate . Example 1 - General Procedure 1

[0117] In step ( a ) , a substrate is provided, e . g . in a device according to the present invention or in a commercial device, e.g. the above-referenced device from Evatec AG, wherein the substrate is, e.g., a sapphire or a silicon wafer. Exemplary substrate dimensions include 2 to 12 inch substrates. The metal target is, for example, a liquid metal target or a Ga-comprising target. Exemplary target sizes include 200 mm to 340 mm diameter, and 300 cm3to 10000 cm3volume for liquid targets. For step (b) , 0.3 W / cm2(area of the target) to 2.4 W / cm2DC and / or 0.24 W / cm2to 1.55 W / cm2RE power are applied to generate a plasma of a first atmosphere between the target and the substrate at a substrate temperature of about 500° to 900°C. The first atmosphere comprises a noble gas, e.g., about 40 vol% or more or 60 vol% or more of the noble gas. A metal film is deposited on the substrate by sputtering, e.g. during about 1 s to 50 s depending on the desired layer thickness. With or without interruption, the power is set for step (c) to no DC power or 0.24 W / cm2to 1.55 W / cm2DC, and / or no RE power or 0.3 W / cm2to 1.55 W / cm2RE (area of the target) , and the atmosphere is changed to the second atmosphere to generate a reactive gas plasma of the second atmosphere between the target and the substrate. If the process is interrupted (e.g. for about 1 s to 15 s) between steps (b) and (c) , the plasma can be turned off during that time. Without an interruption, the atmosphere can be changed gradually. The second atmosphere optionally comprises at least 5 vol% of a reactive gas, optionally selected from N2, NH3, N2O and N2H4, and may, optionally, correspond to the first atmosphere. The substrate temperature during step (c) is about 500° to 900°C and step (c) can be carried out for, e.g., about 1 s to 50 s depending on the speed and desired degree of chemical modification. After step (c) , an interruption or no interruption as described above can occur and optional step (d) can be carried out. If step (d) is exclusively performed as free sputtering of the surface of the metal target, step (d) can be carried out by performing step (b) , either as a separate step before repeating step (b) or not as a separate step but during the repetition of step (b) following step (c) , wherein the conditions are chosen such that they are sufficient for free sputtering of at least the active surface area of the metal target used for sputtering. Additionally or alternatively, step (d) can be carried out separately, e.g. by stirring and / or agitating the liquid metal target. Thereafter, the sequence of steps (b) and (c) and optionally (d) are repeated until a desired thickness (i.e. layer number) of the deposited metal film is achieved.

[0118] Example 2 - General Procedure 2

[0119] In step (a) , a substrate is provided, e.g. in a device according to the present invention or in a commercial device, e.g. the above-referenced device from Evatec AG, wherein the substrate is, e.g., a sapphire or a silicon wafer. Exemplary substrate dimensions include 2 to 6 inch. The metal target is a liquid metal target, optionally a liquid Ga target. Exemplary target sizes include 310 cm2area, and 1 cm to 3 cm depth. For step (b) , 0.3 W / cm2(area of the target) to 2.4 W / cm2DC and 0.24 W / cm2to 1.55 W / cm2RE power are applied to generate a plasma of a first atmosphere between the target and the substrate at a substrate temperature of about 500° to 900°C. The first atmosphere comprises about 40 vol% or more of the noble gas. For example, a gas flow of 25 seem to 35 seem of a noble gas and 8 seem to 15 seem of a reactive gas can be used to generate the first atmosphere. A metal film is deposited on the substrate by sputtering, e.g. during about 1 s to 30 s depending on the desired layer thickness. With or without interruption, the power is set for step (c) , to (I) no DC power and 0.3 W / cm2to 1.55 W / cm2RF, or to (II) 0.24 W / cm2to 1.55 W / cm2DC and no RF power (area of the target) . The first atmosphere is changed to the second atmosphere to generate a reactive gas plasma of the second atmosphere between the target and the substrate. If the process is interrupted (e.g. for about 1 to 15 s) between steps (b) and (c) , the plasma can be turned off during that time. Without an interruption, the atmosphere can be changed gradually. The second atmosphere optionally comprises at least 5 vol% of a reactive gas, optionally selected from N2 and NH3, and may, optionally correspond to the first atmosphere. For example, a gas flow of 0 seem to 26 seem of a noble gas and 14 seem to 45 seem of a reactive gas can be used to generate the first atmosphere. The substrate temperature during step (c) is about 500° to 900°C and step (c) can be carried out, e.g., for about 1 s to 40 s depending on the speed and desired degree of chemical modification. After step (c) , an interruption or no interruption as described above can occur and optional step (d) can be carried out. If step (d) is exclusively performed as free sputtering of the surface of the metal target, step (d) can be carried out by performing step (b) , either as a separate step before repeating step (b) or not as a separate step but during the repetition of step (b) following step (c) , wherein the conditions are chosen such that they are sufficient for free sputtering of at least the active surface area of the metal target used for sputtering. Additionally or alternatively, step (d) can be carried out separately, e.g. by stirring and / or agitating the liquid metal target. Thereafter, the sequence of steps (b) and (c) and optionally (d) are repeated until a desired thickness (i.e. layer number) of the deposited metal film is achieved.

[0120] Example 3 - Deposition example 1

[0121] In step (a) , a single side polished sapphire substrate was provided in the above-referenced device from Evatec AG. The substrate dimensions were 2 inch. The metal target was a liquid Ga target with a 314 cm2area, and 1.5 cm depth. In step (b) , 300 W DC and 500 W RE power were applied to generate a plasma of a first atmosphere between the target and the substrate at a substrate temperature of about 800°C. The first atmosphere was obtained from a gas flow of 30 seem of Ar and 10 seem of N2. Sputtering was performed for 5 s to obtain a metal film of about 10 nm thickness. After step (b) , and without pause (plasma on) , the first atmosphere was changed to the second atmosphere by changing the gas flow to 5 seem of Ar and 35 seem of N2. The power was changed to 0 W DC and 500 W RE to sustain the plasma of the second atmosphere between the target and the substrate at a substrate temperature of about 800°C. Step (c) was carried out for 12 s to obtain more than 95% chemical modification. Subsequently, the plasma was turned off for 3 s, the atmosphere was changed to the first atmosphere as described above, and step (b) was repeated as indicated above, followed by step (c) . The cycle of steps (b) and (c) was repeated for a total of 97 times to yield a thickness of 1000 nm and a conductivity of 618 pQcm.

[0122] Example 4 - Deposition example 2

[0123] In step (a) , a single side polished sapphire was provided in the above-referenced device from Evatec AG. The substrate dimensions were 2 inch. The metal target was a liquid Ga target with a 314 cm2area, and 1.5 cm depth. In step (b) , 300 W DC and 300 W RE power were applied to generate a plasma of a first atmosphere between the target and the substrate at a substrate temperature of about 700 °C. The first atmosphere was obtained from a gas flow of 32 seem of Ar and 8 seem of N2. Sputtering was performed for 5 s to obtain a metal film of about 15 nm. After step (b) , a pause of 5 s was made (plasma off) during which time the first atmosphere was changed to the second atmosphere by changing the gas flow first to 5 seem of Ar and 35 seem of N2 and then to 0 seem of Ar and 40 seem of N2. The power was set to 300 W DC and 0 W RE to obtain a plasma of the second atmosphere between the target and the substrate at a substrate temperature of about 700 °C. Step (c) was carried out for 10 s to obtain of more than 95% chemical modification. Subsequently, the plasma was turned off for 5 s, the atmosphere was changed to the first atmosphere as described above, and step (b) was repeated as indicated above, followed by step (c) . The cycle of steps (b) and (c) was repeated for a total of 64 times to yield a thickness of 990 nm .

[0124] Example 5 - Deposition example 3

[0125] In step (a) , a AI2O3 substrate was provided in the abovereferenced device from Evatec AG. The substrate dimensions were 2 inch. The metal target was a liquid Ga target with a 314 cm2area, and 1.5 cm depth. In step (b) , 500 W DC and 500 W RE power were applied to generate a plasma of a first atmosphere between the target and the substrate at a substrate temperature of about 700 °C. The first atmosphere was obtained from a gas flow of 25.5 seem of Ar and 14.5 seem of N2. Sputtering was performed for 10 s to obtain a metal film of about 18 nm. After step (b) , no pause (plasma on) was made and the first atmosphere corresponded to the second atmosphere (gas flow was maintained at 25.5 seem of Ar and 14.5 seem of N2) . The power was changed to 0 W DC and 500 W RE to sustain the plasma of the second atmosphere between the target and the substrate at a substrate temperature of about 700 °C. Step (c) was carried out for 10 s to obtain more than 90% chemical modification.

[0126] Subsequently, no pause (plasma on) was made and step (b) was repeated as indicated above, followed by step (c) , all under the same gas flow conditions. The cycle of steps (b) and (c) was repeated for a total of 40 times to yield a thickness of 750 nm and an improved surface roughness (Rq about 7 nm) compared to prior art methods (Rq about 30 nm) .

Claims

CLAIMS1. A method for depositing a chemically modified metal film on a substrate, wherein the method comprises the steps :(a) providing a substrate and a metal target in a vacuum chamber,(b) depositing a metal film on a surface of the substrate by sputtering the metal from the metal target under a first atmosphere, and(c) at least partially chemically modifying the deposited metal film and a surface of the metal target with a reactive gas under a second atmosphere, wherein the first atmosphere optionally is an atmosphere comprising at least 40 vol% of a noble gas, and wherein the second atmosphere is an atmosphere comprising the reactive gas.

2. The method according to claim 1, wherein the metal target is a liquid metal target, optionally a metal target that is in liquid form above about 30°C.

3. The method according to claim 1 or 2, wherein after step (c) , the method further comprises step (d) of at least partially removing the chemically modifiedsurface of the metal target, optionally under the first atmosphere .

4. The method according to claim 3, wherein after step(d) , the method further comprises repeating step (b) to deposit a further metal film on the surface of the substrate by sputtering the metal from the metal target under a third atmosphere, optionally the first atmosphere .

5. The method according to claim 4, wherein the method comprises repeating step (c) and optionally step (d) .

6. The method according to claim 5, wherein the method comprises repeating steps (b) , (c) and (d) in this order to deposit and at least partially chemically modify multiple metal films on the surface of the substrate, optionally wherein the steps are repeated 2 to 120 times, optionally wherein step (d) is not performed after the last repetition of steps (b) and (c) .

7. The method according to any of claims 3 to 6, wherein step (d) is performed under the conditions of step (b) , optionally is performed as step (b) , and wherein the chemically modified surface of the metal target is at least partially removed by sputtering.

8. The method according to any of claims 3 to 6, wherein the chemically modified surface of the liquid metal target is at least partially removed in step (d) by stirring and / or agitating the liquid metal target.

9. The method according to any of claims 1 to 8, wherein the chemical modification is a nitridation or oxidation .

10. The method according to any of claims 1 to 9, wherein the method further comprises doping the metal film on the surface of the substrate with a dopant selected from the group consisting of 0, O2, Zr, Ti, F, Ge, germane (GeH4) , isobutyl germane ( (CH3) 2CHCH2GeH3) , Nb, S, Se, Mg, cyclopentadienyl magnesium (Cp2Mg) , Be, Ca, Zn, Mn, Cd, C and Fe .

11. The method according to any of claims 1 to 10, wherein the method further comprises doping the metal film on the surface with Si by introducing a silane gas, a SiH-compound, a S1H2C12- compund, a SiHCla-compound, a SiHaCl-compound a S1CL4- compound or a combination thereof, by thermal evaporation of Si, and / orby sputtering from a Si-comprising target, optionally by positioning a solid silicon component above the liquid metal target.

12. A substrate having a surface coated with a chemically modified metal film obtained or obtainable by a method according to any of claims 1 to 11, optionally with a metal nitride film, optionally wherein the film has a thickness of about 1 nm to about 1.5 pm.

13. A substrate having a surface coated with a chemically modified metal film obtained or obtainable by a method according to any of claims 1 to 9, optionally with a metal nitride film, wherein the film has a resistivity of at least 1000 Qcm.

14. A substrate having a surface coated with a chemically modified metal film obtained or obtainable by a method according to claim 10 or 11, optionally with a metal nitride film, wherein the film has a resistivity of about 10000 pQcm or less, optionally about 5000 pQcm or less, optionally about 1000 pQcm or less, optionally about 650 pQcm or less, optionally about 600 pQcm or less, optionally about 580 pQcm or less.

15. A device (1) configured to perform the method according to any of claims 1 to 11, wherein the device comprises a vacuum sputtering chamber (2) comprising:a substrate holder (3) , a receptacle (4) for receiving a metal target, optionally a liquid metal target, wherein the receptacle (4) is connected or connectable to a power supply (5) , a vacuum port (6) , and a gas inlet ( 7 ) , wherein the device further comprises a control unit (8) configured to control and execute the steps according to any of claims 1 to 11.

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