Liquid Sputter Target

Abstract

A sputtering apparatus for sputtering a liquid target comprises a vessel for receiving the liquid target material, the apparatus comprising means for stirring or agitating the liquid target material, the means comprising means for degassing the liquid target material, dispersing solid particles or islands at the surface of the target, and dispersing such particles or islands to form an active surface area (S A ) to the inactive surface area (S P ) and / or vice versa, and the inactive surface area (S P ) is the active surface area (S A ) is exposed to at least 50% less sputtering than

Description

[Technical field]

[0001] The invention relates to a sputtering apparatus for sputtering a liquid target according to claim 1, to a vacuum system comprising such an apparatus according to claim 12, to a method for depositing a film by sputtering a liquid target according to claim 20 and to a method being part of the manufacture of a semiconductor device according to claim 35. [Background technology]

[0002] The concept of a vacuum coating system 10 comprising a sputtering device 1' as known from the prior art is shown in an exemplary manner in FIG. 1. The system comprises a side wall 12, a cover 11 and a bottom forming a vacuum chamber 38 of the system. The system is a face-down system, meaning that at least one substrate holder 15 is mounted on the cover 11 in order to position a substantially flat substrate 14 facing downwards in line of sight to the target surface 4 of the liquid target 3 to expose the substrate surface to the sputter plasma, the sputter plasma being confined and directed by a magnetic field 6 generated by an unbalanced magnetron magnet system 5 mounted on the underside of the target vessel 2 containing the liquid target 3. The liquid target material 3 can be gallium (Ga). The unbalanced magnetron magnets 5 promote a greater plasma density near the surface of the substrate 14. The vessel 2 is electrically connected via a vacuum-tight feed-through to the cathode (+) of the sputtering power supply 23 when a DC power supply is used, or to the pole (≈) of an RF power supply. Alternatively, a mixed power supply delivering DC and RF components may be used. The second pole of the power supply is grounded. To dissipate excess heat from the sputtering process, the chamber is fixed to the cooling surface of a cooling device 9 by fasteners 9', screws, or the like. The top surface, the outer side of each side wall of the chamber 2, the grounded anode 7, and the respective anode shield 37 covering are mounted electrically isolated from the chamber at a darkroom distance depending on the applied process pressure. A vacuum pump 19 is mounted on a pump port 20 that can be opened and closed by a pump valve 20'. Substrates can be transferred in and out of the system 10 by a substrate port 13, which can be a stand-alone system or a load lock for a multi-chamber system operated at different pressure levels between successive processes or between transfer chambers. Finally, a gas inlet 21 is provided for introducing argon as a sputtering gas and nitrogen as a reactive gas to deposit a GaN layer on the surface of the substrate 14. Summary of the Invention [Problem to be solved by the invention]

[0003] It is an object of the present invention to provide an alternative sputtering apparatus and vacuum system and method for depositing films by sputtering liquid targets that is particularly adapted for manufacturing semiconductor devices. [Means for solving the problem]

[0004] According to a first aspect, the present invention is directed to a sputtering apparatus for sputtering a liquid target comprising a vessel for receiving a liquid target material, the apparatus further comprising means for stirring or agitating the liquid target material, the means being adapted to degas the liquid target material, to disperse solid particles or islands at the surface of the target, to disperse such particles or islands into an active surface area S. A from the inactive surface area S P and / or move such particles or islands from the inactive surface area to the active surface area S. A is the surface area to which target atoms can be sputtered away when sputtering is performed, while the inactive surface area S P It is understood that in the active surface area S, sputtering does not proceed as strongly as in the active area or is completely avoided. A Based on this, the inactive surface area S P The surface sputtering of the active surface area S A The sputtering rate is reduced to at least 50%, at least 20%, or even 10% or less of the inactive surface area S. As mentioned, the particles or islands may be, for example, compound particles and may also include alloy compounds. In the case of slight alloys or individual islands caused by reactive sputtering processes involving surface compounding, they may also include alloying of the surface of the liquid target. Sputtering may occur on the inactive surface area S. PA transition surface region may occur during the downward movement of the target toward the target surface, or vice versa. The sputtering apparatus of the present invention may further comprise a magnet configured in an essentially planar magnetron system, or a magnet preferably recessed on the opposite side of the vessel or in the bottom of the vessel below the target liquid level. To generate the magnetic field, the magnetron system has a magnetic axis M A and is located in the central region of the target and has a magnetic axis M A The outer magnet includes an outer closed magnet loop surrounding an inner magnet of opposite polarity that is vertically oriented with a yaw angle M. The outer magnet has a slightly oblique magnetic axis M that is tilted toward or relative to the central vertical axis, e.g., between 5° and 15°, to further engineer the overall magnetic field. A It should be mentioned that the outer magnet may be arranged having a magnetic pole of 0.5 mm x 0.5 mm. The outer magnet may be, for example, an annular magnet or may be a smaller magnet arranged respectively. The inner magnet, if more than one magnet is used, may be arranged linearly or, for rectangular or other elongated targets, again as a closed loop, for example including linear and / or curved sections, or as a central pole for square or circular targets, in all varieties being aligned with the magnetic axis M of the outer magnet loop. A The magnetic field and active surface area S are essentially parallel to the surface but opposite to it. A Thus, so-called "race tracks" are formed between magnets of different polarity, meaning between the projections of the poles above each other on the target surface, while inactive surface areas S Pis located at the periphery of the magnetron system or in the central region of the magnetron system, outside the racetrack, e.g. where the magnetic field lines cross the target surface vertically or at least partially vertically. Permanent magnets have been used, e.g. NdFeB, CoSm, AlNiCo, and FeCoCr alloys, for large magnetic field strength, but electromagnets can be applied to modulate the entire field of the magnetron system. The location of the permanent magnet near the target surface, on the opposite side of the bath or even recessed into the liquid target, allows effective horizontal and vertical convection of the liquid target material during sputtering, as long as the liquid is provided at a sufficient depth in the bath, e.g. at least 6 mm or 8 mm. If the component of the magnetic field in the active region is predominantly horizontal, e.g. more than 50%, more than 60%, or more than 80%, the component of the magnetic field in the inactive region is predominantly vertical, e.g. more than 50%, more than 60%, or more than 80%. The respective regions of horizontal or vertical magnetic field both include regions of the respective field orientation within the target below the liquid surface and at least near above the surface, e.g., 3 mm, 5 mm, 10 mm below and above, or even greater. Also, for non-magnetron sputtering devices, the inactive surface region S Pmay be provided by a darkroom shield or by an anode formed as a darkroom shield, thereby protecting such a shielded surface against sputtering or other types of, for example, parasitic glow discharges. It must be mentioned that stirring and agitation, or stirring and agitation, are used below in the same usual sense of mixing or moving a liquid, for example by turning, the term stirring unit being used for a unit for mixing or moving a liquid by mechanical means, also including ultrasonic means, and the term stirring unit being used for a unit for mixing or moving a liquid by the use of the Lorentz force, which is a magnetoelectric phenomenon. The phenomenon of the Lorentz force causes, inter alia, the movement of electrically charged particles in a magnetic field perpendicular to the direction of the particle movement, which leads to a lateral turn of the respective particles according to the left-hand rule for positively charged particles or according to the right-hand rule for negatively charged particles.

[0005] Degassing in this specification also means, apart from the general meaning of the word, avoiding the formation of gas bubbles in the liquid target material, for example by including process gas, or at least preventing the bursting of gas bubbles during the sputtering process.

[0006] Convection is used herein in the general sense of externally forced fluid movement, for example in the context of the effect of Lorentz forces or mechanical agitation.

[0007] A metal or alloy is a material consisting of one or at least two metallic elements, but in the sense of the present invention, metals or alloys containing one or more dopants up to a concentration of about 1 at% or at least 0.5 at% are also referred to as metals. Such dopants can be Al, Ag, Au, Cu, Hg, In, Sn, Zn or C, as examples for metallic gallium (Ga).

[0008] The target may be electrically connected to the cathode of a DC power supply, the cathode of a pulsed DC power supply, one pole of an RF power supply, or one or several power supplies providing DC / RF mixed, DC / pulsed DC mixed, or DC / RF / pulsed DC mixed, respectively.

[0009] The sputtering apparatus may comprise an anode electrically isolated from the liquid target, the anode usually being positioned peripherally around the target and / or in special cases in the central region of the target.

[0010] Inactive surface area (S P At least a portion of the ion beam may be projected and electrically isolated from the target by a darkroom shield, e.g., a grounded or anode shield mounted within the sheath width. Thereby, the darkroom distance between the projecting shield / anode and the target surface is selected to be within the sheath width of the sputter darkroom, i.e., about 1×10 -5 mbar to 1×10 -2 For normal sputtering processes with a process pressure of mbar it is 0.5-12 mm or 0.5-6 mm.

[0011] The bottom of the vessel may be formed at least in part concave in at least the peripheral region to counteract the large surface tension of the liquid metal, to center the liquid material, and to create a large flat target area. Alternatively, the bottom of the vessel may be formed at least in part convex in at least the peripheral region to provide more material for the active area or racetrack.

[0012] The means for stirring may comprise a stirring unit comprising a stirrer positioned in the liquid target material and a drive mounted on or near the opposite side of the vessel, for example in the central region of the horizontal projection of the liquid target. The stirrer should be completely covered by the liquid target material if alloying or doping of the coating with the material of the stirrer is to be avoided. The stirrer can be one of the following: a rod, a disk, a paddle or an impeller, and can be connected to the drive by a transmission shaft. The transmission shaft comprises a seal against leakage of the liquid target material and a vacuum seal if the drive is positioned in the atmosphere.

[0013] Alternatively, the drive may comprise a magnetic unit configured to create a rotating electric field and the stirrer comprises or is a magnetic stirrer bar.

[0014] In an alternative embodiment, the agitation unit may comprise an ultrasonic source.

[0015] As an alternative to mechanical stirring means for stirring the liquid target, the apparatus may comprise a stirring unit with an inner stirring electrode and an outer stirring electrode, and a magnet system, which may be a magnetron system or a magnetron system in combination with other magnets, where at least the inner stirring electrode is below the liquid level of the target material and is connected to a DC or low-frequency AC current source. A DC current may be applied between the stirring electrodes to generate a circular movement of the target liquid at least between the stirring electrodes by Lorentz forces as explained above. Alternatively, the magnetic field of the magnetron magnet may be set in such a way that the current flowing through the plasma to or at the target results in a sufficient Lorentz force, e.g. the magnetic field is a partially closed loop between the inner and outer poles (below or in the target) and the plasma current is perpendicular to the target surface. Alternatively, a standing wave may be generated by applying a low-frequency (1-100 Hz) AC current, which may be useful for example for degassing.

[0016] When at least one stirring electrode is electrically isolated from the sputtering electrodes (e.g. the anode and cathode of the target), an additional DC current source or a low-frequency AC current source as mentioned must be used, with at least the inner stirring electrode, both stirring electrodes or in special cases only the outer stirring electrode being at least partially below the liquid level of the target material. If alloying or doping of the coating with the material of the separated stirring electrodes is to be avoided, the stirring electrodes may be fully immersed in the target liquid in order to avoid that the electrode material is sputtered together with the target material. However, by exposing a part of the stirring electrode containing or made of a dopant material to the sputter plasma, such an electrode can be used as a material source for doping the coating made of the liquid target.

[0017] Regarding the shape of the stirring electrodes, the outer electrodes are positioned over the active area S of the liquid target material. Aor the outer periphery can be near the outer inactive surface area S of the target. P , and the inner electrode can be a linear or point electrode in the central region of the liquid target, or the active region S of the liquid target material. A The inactive surface area S at the center P Alternatively, the electrodes may be confined to the inner and / or outer inactive surface regions S along the outer and / or inner side of the magnetron racetrack below the surface of the liquid target material. P With such an arrangement of electrically isolated stirring and sputtering electrodes, for example, sputtering can be performed by RF sputtering, while stirring of the liquid material can be performed by DC current provided by the stirring electrodes. The outer and inner stirring electrodes are set to different potentials and can be formed as continuous electrodes, e.g. in the form of a closed loop or linear electrodes, or alternatively can be provided as inner and / or outer electrode arrays, each arranged consisting of several single electrodes of the same or different shapes.

[0018] However, in a simpler arrangement, it has surprisingly been demonstrated that only one stirring electrode is sufficient when a DC stirring current is superimposed on an HF sputtering voltage, e.g. an RF sputtering voltage or a pulsed DC sputtering voltage, applied to the liquid target. In this case, the sputtering anode also serves as an outer counter electrode to the central stirring electrode. Even more surprisingly, such an effect can also be produced by driving the sputtering electrodes only by a DC power supply.

[0019] Such an effect can also be achieved with a sputtering electrode comprising a pot-shaped target electrode (tank) containing the liquid target material and connected to the cathode of a sputtering power supply, and a grounded counter electrode which is a sputtering anode electrically isolated from the target and the respective target electrode and which covers at least the peripheral area of ​​the pot-shaped target electrode as well as a darkroom shield at a distance of 0.5-20 mm from the target. Thereby, when the target is DC-driven or RF-driven and DC-superimposed, the anode is simultaneously the outer stirring electrode and the cathode (here the pot-shaped target electrode forming the tank) is simultaneously the inner stirring electrode. In case of DC-superimposed operation, the anode and cathode can be reversed and the flow direction can also be reversed.

[0020] The liquid target material may be at least one of the following materials: Ga, GaAs, GaIn, GaAl, InAl, TiGa, Hg, or an amalgam such as HgAg, HgAu, HgCu, HgIn, HgSn, HgZn, or an alloy of one of them.

[0021] Additionally, the apparatus may comprise means for heating, cooling, or heating and cooling the target. Such means may include liquid cooling and / or heating circulation in the pot-shaped target electrode itself, or in a heating / cooling plate to which the target electrode is firmly and thermally attached, for example by screws, fasteners, or the like. Thereby, certain target materials may be heated to above their melting temperature, or may be more efficiently degassed before or during the initial phase of the sputtering process, and then cooled during sputtering, if the heating and cooling circulation is provided by a device that can be switched depending on the needs of the process. Alternatively, heating may be provided by radiant lamps, other radiant devices (e.g., carbon heaters), the plasma itself, or by electron bombardment of the surface of the target material.

[0022] The vessel material may be, for example, stainless steel such as 316 British Standard or 2343 Swedish Standard, molybdenum (Mo), a molybdenum alloy, or graphite.

[0023] According to a second aspect, the present invention is directed to a vacuum coating system comprising a sputtering device as previously described, the system further comprising at least a sputter gas inlet for an inert gas and a vacuum pump. Also, an inlet for a reactive gas may be provided, which may comprise a different inlet, for example closer to the surface to be coated, while the sputter gas inlet is adjacent to the target surface.

[0024] According to a third aspect, the present invention is directed to a method for depositing a film on a substrate, in which at least one first liquid component is sputtered by a sputtering apparatus as described above. The sputtering apparatus comprises a liquid metal target material arranged in a target bath and sputtered from the target onto a surface of a substrate to be coated. The substrate is disposed such that the surface to be coated is within the active surface area S of the target. A The target is mounted above and opposite the sputtering apparatus with a line of sight to the sputter ions, and the target has at least an active surface area S exposed to the sputter ions. A and the active surface area S A Inactive surface area S exposed to sputtering at least 50% less than P The method further comprises: dispersing the solid particles or islands in order to degas the liquid target material and / or dispersing the solid particles or islands in the active surface area S. A from the inactive surface area S P This includes agitating the liquid target to move it towards or away from the target.

[0025] The method may further include the formation of a film, which is a film of a metal, alloy, or compound, where at least one first component is sputtered from a liquid target onto the surface of the substrate to be coated, and in the case of a compound, at least one second component of the compound is introduced as a reactive gas to form the compound in the gas phase and / or on the surface of the substrate, whereby the compound or alloy may have a higher melting point than the liquid component and tend to form solid particles or islands on the surface of the target.

[0026] In order to avoid any failure or interruption of the sputtering process, the inactive surface area S P should be provided around and / or in the central area of ​​the liquid target surface. P At least a part of the region S P To shield the target from sputtering or other glow discharge phenomena, the target may be projected and electrically isolated from the target by a darkroom shield.

[0027] Thereby, the shield can form a counter electrode, for example the anode of the target, which can be formed by grounding the shield.

[0028] The sputtering device may be a magnetron comprising a magnetron magnet system and a DC power supply and / or an RF power supply.

[0029] The stirring of the liquid target can be performed by mechanical stirring, by stirring caused by an electric current and a magnetic field at least partially perpendicular to the electric current, and / or by applying ultrasound to the liquid target, which can be generated, for example, by one or several ultrasonic sources integrated or attached to the bottom or side wall of the vessel, or a combination of stirring and applying ultrasound. When the stirring is generated by an electric current and a partially perpendicular magnetic field as described above, the electric current can be generated either superimposed on the sputtering voltage, or induced directly in the target by the sputtering voltage, or a combination thereof, and the magnetic field can be generated by a magnetron system or by a magnetron system and further magnets, for example side magnets.

[0030] When stirring is performed by a stirring unit, the unit may comprise a stirrer and a drive mounted on or near the opposite side of the vessel, whereby the power transmission between the drive and the stirrer may be performed mechanically, for example by a transmission shaft connecting the drive and the stirrer, or magnetically, for example by a rotating magnetic unit, both capable of creating a rotating electric field, or a controllable electromagnet in the drive and a magnetic stirrer comprising at least one magnetic bar or being a magnetic stirrer bar, respectively.

[0031] Furthermore, stirring or agitation can alternatively be performed by a stirring unit comprising an inner stirring electrode and an outer stirring electrode both connected to a DC current source, a DC current being applied between the stirring electrodes to generate a circular movement of the target liquid at least between the stirring electrodes by Lorentz forces resulting from the orthogonality of the current and the magnetic field, which DC current can be applied externally, for example by magnetron magnets or / and other magnets, or / and induced by the DC component of the plasma current. In a particular structurally simple embodiment of the invention, an unbalanced magnetron system in combination with a sputter power supply can be used to generate a current in the liquid target that provides a magnetic field high enough to allow sufficient stirring of the liquid target in order to permanently degas during the sputtering process and to avoid splashing due to bursting bubbles. In other embodiments, the inner stirring electrode, the outer stirring electrode, or both can be positioned in the target liquid, for example below the liquid target level to avoid doping with the electrode material, or partly above the target level if doping with the electrode material is desired.

[0032] The target material may be a liquid metal or an alloy of at least two metals having a melting point Tm≦300° C., Tm≦70° C., or Tm≦40° C. Specifically, the target material may be one of Ga, GaAs, GaIn, GaAl, InAl, TiGa, Hg, HgAg, HgAu, HgCu, HgIn, HgSn, HgZn.

[0033] The layer deposited on the substrate can be, for example, a metal layer having essentially the same composition as the target material (meaning within ±10% or ±5% of the composition of the target), or a compound layer, for example a nitride, carbonitride, carbide, oxide, boride, or alloy, respectively, with the liquid target material or a mixture thereof. Again, the proportion of the metal elements will be essentially the same as in the target material. Specifically, the compound can be a nitride of one of Ga, GaAs, GaIn, GaAl, InAl, TiGa.

[0034] Alternatively or additionally, a further target from a different material, for example a solid target, may be used to deposit the compound on the substrate surface by co-sputtering.

[0035] The following description describes general principles for liquid targets and is therefore also applicable to state-of-the-art methods and systems for sputtering liquid target materials. However, this principle, which was surprisingly found by comparing the current-voltage characteristics of the sputter discharge at different liquid levels, can also be advantageously used in further embodiments of the invention, for example by including a method for indicating the liquid level LL of the liquid target, a method for refilling the liquid target, and a liquid sputtering apparatus or a system comprising a liquid sputtering apparatus having a liquid level indicating and / or liquid refilling system for the respective liquid target.

[0036] Thus, a method is disclosed that uses the dependence of one of the electrical values ​​of the sputter voltage, sputter current or sputter power from the liquid target liquid level to generate a liquid level signal SLL by measuring a value V1 and comparing it with a benchmark value V2 corresponding to a defined liquid level, and the value signals S1 and S2 can correspond to the respective measured value V1 or V2 or to the respective converted value. The conversion can include, for example, conversion to a smaller voltage, current, power or other value of the same electrical quality, such as conversion to a digital value for a system that processes normal data. The liquid level signal SLL can be used for liquid level indication and / or signal for an automatic liquid refill system that can be activated automatically or by the operating staff, for example between deposition processes when the sputter power is off.

[0037] Further disclosed is a liquid sputtering device or system comprising a measuring device for measuring the sputter value and an electronic device with a comparator, wherein one input I Vis connected to the output signal or the converted output signal of the measurement device and to a comparator, the other input of which is connected to an output from an electronic benchmark database for comparing signals S1 and S2 to generate a liquid level signal SLL at an output O of the electronic device. In further embodiments of such a sputtering device or system, the output of the electronic device may be connected to a liquid level indication device and / or a refill device of the system.

[0038] For such comparative measurements, benchmark values ​​V2 and respective output signals S2 for different liquid levels need to be determined in a previous step under constant current, voltage or power conditions for every tank configuration, e.g., shape, which are stored electronically as a look-up table and / or a computer implemented algorithm in order to assign the output signal S1 to the respective benchmark signal S2 and to output the accurate liquid level signal SLL.

[0039] An electronic comparator may be used to compare the signals of the respective values ​​in a control device, computer or other electronic device containing look-up tables and / or algorithms, for example after digital conversion, to compare the benchmark and the sputter voltage. As an example for measuring electrical values ​​related to sputtering, a measuring device may be electrically connected between the cathode bath and the ground potential to measure the sputter voltage, while the sputter current or at least the equivalent of the sputter current may be measured in the circuit of the sputter power supply, the sputter power being an electrical quantity that may usually be set constant in the power supply. For practical reasons, the liquid level detection is usually performed at constant power, and one of the voltage or current values ​​is changed and the other is measured and / or calculated depending thereon.

[0040] The invention will now be further illustrated with the aid of the figures. [Brief description of the drawings]

[0041] [Figure 1]FIG. 1 is a diagram of a vacuum system including a sputtering device according to the prior art. [Diagram 2] FIG. 1 is a conceptual diagram of a sputtering apparatus according to the present invention. [Diagram 3] FIG. 2 is a diagram of a sputtering apparatus of the present invention with a magnetic stirrer. [Figure 4] FIG. 2 is a diagram of a sputtering apparatus of the present invention with Lorentz force stirring. [Diagram 5] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 6a] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 6b] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 6c] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 7a] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 7b] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 7c] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 8] FIG. 13 is a diagram of a further inventive sputtering apparatus with Lorentz force stirring. [Figure 9] FIG. 1 is a diagram of an apparatus and system of the present invention including a liquid refill system. [Figure 10] FIG. 1 is a diagram of voltage / current characteristics. [Figure 11] A diagram of the voltage / liquid level relationship. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] FIG. 2 shows a schematic diagram of a sputtering device according to the invention, with a mechanical agitator 25 driven by a drive 28 via a shaft 26. The shaft 26 is guided by a liquid-tight and also by a vacuum-tight feedthrough 27 at the bottom of the target vessel 2, if the bottom of the vessel forms part of the bottom of the vacuum chamber. If this is not the case, a respective vacuum-tight feedthrough must be provided at the bottom of the vacuum chamber of the system, as will be clear to a person skilled in the art. By setting the agitator to work, the liquid material of the target is agitated, and the static surface 4 of the liquid becomes a dynamic surface 4', symbolized by its corrugation. However, the actual dynamic surface 4' will be formed more like a vortex, at least in the embodiment as drafted in FIGS. 2 and 3. The bottom of the vessel 24 may be concave as shown in the figure, or convex, at least in the border region of the vessel bottom, as previously described and symbolized by dotted line 24', or completely concave, as symbolized by dotted line 24", or completely convex, to counteract the large surface tension of the liquid metal that may otherwise result in non-wettable surface areas at and near the vessel's periphery inner edge, thereby forming blowholes below the liquid surface and resulting in gas breakthrough during the sputtering process. For better heat dissipation, a liquid circuit 36 ​​may be implemented directly to the vessel bottom, e.g., a closed cycle cooling system. Alternatively, a combined heating and cooling system may be used to moderate the target material during and / or before the sputtering process, with the advantage that target materials with a higher melting point, e.g. above room temperature, can be liquefied before sputtering, thereby avoiding local critical phase transitions during the sputtering process, e.g. at the surface of the target. The heating and cooling system may be switched from heating to cooling before or at the start of the sputtering process depending on, e.g., the sputtering power or depending on the temperature output of a temperature measuring device, not shown, which may be arranged on the side wall of the bath.The anode 7 protrudes above a boundary area, for example the boundary area around the liquid target 3, thereby obscuring the inactive surface area S. P A swivel mounted shutter 45 facilitates protecting the substrate surface against unintentional coating, for example during initial sputtering to clean or degas a liquid target. Such a shutter may be realized as an aperture wheel or a sliding shutter.

[0043] The mentioned features such as the shutter, the concave or convex trough bottom 24', 24", the liquid circuit 36, the provision of heating and cooling systems, etc., may be useful for any embodiment of the invention even if not explicitly mentioned.

[0044] The same can be said for certain additional features that can be applied to the vacuum coating system 1 to make the deposition process with the sputtering device of the invention even more efficient. Such features, superimposed on the vacuum system in Fig. 1 for ease of use, are a separate reactive gas inlet 22 in the cover 11 of the vacuum chamber, means 17, 18 for biasing the substrate holder, as well as means 16 for cooling and / or heating the substrate holder, respectively the substrate. It must be mentioned that such features, together with their combination with liquid sputtering, have not been found to be disclosed by the prior art documents.

[0045] By using a separate reactive gas inlet 22 near the surface of the substrate 14, the partial pressure of the reactive gas can be reduced, and the gas inlet 21, used only as an inert gas inlet, can be placed at the height of the target surface 4, 4', allowing better flushing of the surface 4, 4' or better protection of the surface 4, 4' from the reactive gas. Both measures reduce the active surface S of the target surface 4, 4'. AIn this way, target poisoning and the formation of solid particles or islands can be further reduced. Gas showers may also be used along the periphery of the substrate holder 15 for the reactive gas inlets 22 and / or along the periphery of the target for the sputter gas inlets 21.

[0046] The means for applying a bias to the substrate holder may comprise a bias power supply 17, which may again be DC (-), but usually, at least for non-conductive substrate materials, be radio frequency (HF), e.g. a radio frequency (RF) power supply, connected to the substrate holder 15 through power lines 18 and feedthroughs. On the other hand, the holder 15 may comprise a holding circuit for cooling or a holding circuit for cooling and heating, respectively with means for cooling or means for cooling and heating. By use of an electrostatic chuck (ESC) clamping, shadowing of certain areas of the surface of the substrate 14 can be avoided.

[0047] The essential features of the prior art sputtering apparatus 1' as magnet system 5, power supply 23, power lines 8, etc. shown and described in FIG. 1 should also be considered to be present in FIGS. 2-5 even if not explicitly shown or mentioned in order to maintain clarity of the drawings.

[0048] Figure 3 shows a further type of mechanical stirring showing two magnetic bars 29 positioned on the liquid target 3 driven by a magnetic stirrer 30 on an axis 31. Such a stirrer 30 can be replaced in a known manner by a stirrer using a rotating electric field instead of a further rotating magnet. Such magnetic stirring means 30, 31 can be arranged, for example, in the racetrack of the magnetron target. Further auxiliary or independent stirring of the liquid target material may be provided by an ultrasonic source 32 mounted on the sidewall and / or bottom of the vessel 2 (see Figure 4).

[0049] Figures 4 and 5 show different principles for stirring or agitating the liquid target, using the Lorentz force phenomenon as explained in the overview of the invention. Thereby, Figure 4 shows a simple setup with a central two-dimensional electrode 33, e.g. circular or linear, or with a three-dimensional electrode 33' (dotted line), e.g. rod or wall-like, depending on the shape of the target, which may be circular, square, rectangular or other elongated shape. The electrode is powered by a separate electrode current supply 34, which is an electrically isolated feed-through from the bath. The current can be a DC current or a pulsed DC current. With this arrangement, the anode can have the function of an outer stirring electrode, with the stirring current flowing from the inner stirring electrode through the liquid target and the conductive plasma to the anode. The DC potential of the electrode can be set between the potential of the anode, which is usually ground, and the potential of the cathode of the sputter target, which may be at least between -100 kV and about -4 kV. Thus, the DC potential of the stirring electrode can be set from -10 kV to about -3.9 kV for normal sputtering processes. In addition to the magnetron magnets 5, 5', 5" further magnets 44 may be provided, for example as side magnets at the periphery of the vessel, to enhance the vertical magnetic field component within the liquid target material. Such magnets may be solid permanent magnets or electromagnets whose magnetic force can be controlled by an applied current. Such magnets may be arranged as a ring (or as a given array of magnets).

[0050] A further embodiment of the invention is shown in FIG. 5, in which an inner, here horizontally linear, stirring electrode 33″ and an outer stirring electrode 35 are in the form of a closed loop, as shown here by the dotted superimposed vertical sections. The inner electrode 33″ and the outer electrode 35 are connected to different poles of an electrode current supply 34, similar to the connection described in FIG. 4. Such stirring electrodes may be positioned parallel to the target racetrack to provide a circular or rotational movement along the racetrack as symbolized by the dotted arrow 40. It should be mentioned that the direction of rotation may be reversed if the polarity of the outer magnetron magnets and the inner magnetron magnets are reversed. The stirring electrodes 33, 33', 33" and 35 can be designed as one-piece electrodes or as split electrodes comprising several electrode sections or partial electrodes. In other embodiments, such electrodes can be designed to be swivel-mounted or movably mounted and to be submerged in the target liquid (not shown). Such embodiments and mechanical stirring can be used, for example, if stirring should be performed before the sputtering process starts or if the stirring caused by the sputtering electrodes is not sufficient.

[0051] 6-7 refer to a sputtering apparatus of the invention operable with Lorentz force stirring using a magnetron magnetic field 6 and a DC or pulsed DC target current 42 to stir the liquid target 3. Therefore, separate stirring electrodes 33, 35 are not required. Nevertheless, it may be useful to add one or more separate stirring electrodes, for example as in the previous examples. As in FIGS. 3-5, only features essential for the understanding of the illustrated embodiment or process are shown, and reference is made to FIG. 1 and the respective description for other features necessary for carrying out the sputtering operation, similar power lines and supplies, substrate holders, pumping systems, etc.

[0052] In Fig. 6a-7c, a simplified description of the electric current caused by the vertical convection is symbolized by the circular arrows 39. It should be mentioned that such vertical convection requires a certain minimum depth of the liquid in the bath, which should be at least 6 mm, but better still be deeper than 8 mm or 10 mm. Fig. 6a shows the sputtering apparatus 1 of the present invention in operation with a bath 2 dimensioned to allow vertical convection 39 and horizontal convection overlapping with a circular movement 40 in a race track as shown in Fig. 5. Both types of convection are only symbolic of the vertical and horizontal components of the overall convection, and therefore both have their origin in the electric current and the magnetic field applied to the liquid target 2. It should be mentioned that some of the information in the following description is not based on proven theory, but is only inferred as a first guess from experimental results and general physics knowledge, and may require further refinement. As symbolized by the arrow 41, the plasma current of the pulsed or static DC-driven sputter magnetron discharge enters the target approximately perpendicular to the surface under the magnetic tunnel of the magnetic field 6. The arrow 41 symbolizes the location of the highest current density, which corresponds approximately to the middle of the so-called racetrack formed on the target surface. Under the assumption that both the liquid target 3 and the bath 2 provide in each case a uniformly distributed electrical conductivity of, for example, at least 0.1 MS / m for metallic materials or carbon materials such as graphite, currents as symbolized by the arrow 42 will result, as seen in FIG. 7a. The internal currents of the liquid target 3, together with the magnetic field 41 from the magnet system 5 of the sputtering device 1, will create current-induced vertical convection currents 39. It should be mentioned that the magnetic field 41 provided by the magnet system 5 is of course also present in the liquid target 3, but is not shown in order to avoid overloading the drawing.

[0053] It should further be noted that when the induced currents are small, or at least at the beginning of the sputtering process, such a predominantly vertical convection 39 can be achieved, resulting in an essentially linear, horizontal movement at the liquid surface. However, such a vertical movement will continue even at larger currents and will be superimposed on the horizontal movement in order to provide an effective stirring of the liquid, as long as the liquid is provided at a sufficient depth in the bath. Thereby, the liquid at the surface, together with possible contaminants or surface islands, e.g. compounds such as GaN that form at the surface during the reactive sputtering process, is forced to move essentially vertically from both sides towards the racetrack. Such stirring allows the target to be cleaned under a closed shutter 45 in the first sputtering step, which at low sputtering powers results in a small sputtering current at the liquid target, so that the deposition process can be started only after the cleaning is completed by opening the shutter 45, see FIG. 2. Furthermore, when a reactive sputtering process is to be applied, which is the usual mode when sputtering a liquid target to coat a substrate, the coating parameters such as the sputtering power and the partial pressure of the reactive gas, for example nitrogen, oxygen or a carbon-containing gas such as methane, can be modified so that the target surface or at least the racetrack is free of solid compounds of a critical size distribution suspended in the liquid target, which can lead to process irregularities resulting in troublesome particles on the surface of the substrate to be coated.

[0054] For example, a higher sputter power, together with a higher flow of reactive gas, can be applied just before opening the shutter for deposition. With the higher sputter power and resulting current, the horizontal component of the Lorentz force is strong enough to also impose a rotational movement of the target liquid, at least in the region of the racetrack. Such superimposed horizontal and vertical movements in the target liquid cause the subcritical small solid compound particles to move towards the most active surface area S. Acan be used to provide a racetrack of 0.1 μm to the surface of the substrate, which will be sputtered without forming harmful particles on the substrate surface, thereby effectively avoiding the formation of particles or solid islands of a critical size, at least within the active surface area.

[0055] In Fig. 6b and Fig. 6c, a further embodiment of the sputtering device 1 of the invention is shown with its magnet system 5' mounted in a respective recess in the upper side of the bath bottom 24. Such an embodiment allows better access to the magnet system for servicing. Thereby, another magnet system can be more easily implemented for other sputtering processes, for example for sputtering another type of liquid target material, without having to remove the entire bath from the coating system 10. Furthermore, such an embodiment allows a higher liquid level due to a higher position of the magnets, which allows to shorten the service time for material supply. As an alternative to extend such service intervals, a supply of liquid target material may be foreseen, for example by feeding a wire of the respective material (Ga, In or respectively adapted alloy) into the liquid target, or via a feed tube from a material supply positioned inside or outside the vacuum coating system, the feed inlet being below the surface at the target level. In the case of the variants shown in Figs. 6a-6c, 7a and 8 below, essentially the entire vessel inner surface electrically connected to the cathode of the sputter feed is also in electrical contact with the liquid target and is thereby used as the inner stirring electrode. This also applies to the magnet 5' at the bottom of the vessel, since it is conductive and therefore also acts as an electrode surface. Flow facilities 46 as shown in Fig. 6c can be provided to help develop the flow pattern from the stirring electrode to be faster or to help change the flow pattern. Such facilities can be placed as shown or formed on the bottom or side walls of the inner vessel. These facilities 46 can also be conductive like the vessel surface, as explained below in Figs. 7b and 7c, or can be made of or coated with an insulating material that provides additional parameters to influence the flow pattern. Side magnets 44 as shown in Fig. 6c provide additional parameters to influence the flow pattern of the magnetic field and the liquid movement.

[0056] Figures 7b and 7c show a sputtering apparatus with different current guidance in the liquid target material 3 compared to Figure 7a. In Figures 7b and 7c only a part of the inner surface of the vessel which is in contact with the liquid target is used as the inner stirring electrode. Therefore, an electrically insulating material 43', 43", e.g. Teflon, which is inert to the liquid target material, can be arranged as a cover or coating on certain surface areas of the bath. Thereby, the current is changed in the target material as symbolized by the arrows 42' and 42", providing also different flow patterns of liquid movement 39', 39" between the liquid and the surface of the target 3. This allows the stirring and flow design within the target to be easily adapted and optimized according to the actual process needs. An alternative, but less flexible and more expensive embodiment would be to incorporate an electrically insulating bath body and provide the respective contacts or contact areas on its inner surface. Such use of an electrically insulating material 43', 43" may additionally be combined with other embodiments, as shown for example in Figures 1, 4, 5, 6b, 6c and 8.

[0057] Sputtering tests for sputtering gallium under inert and reactive sputtering conditions have been carried out in water cooled around a stainless steel (AISI 1.4301) bath with an inner diameter of 200 mm and a depth of 15 mm. Within the inner circumference of 10 mm, a concave border area with a maximum height of 5 mm from the bottom is provided at the bottom in order to counteract the large surface tension of gallium on the stainless steel and thereby flatten the Ga surface in this area. The bath was filled with 1.5-3 kg of Ga to a height of about 8-14 mm. The magnet system 5″ used was an unbalanced magnetron system mounted in respective recesses on the lower (opposite) side of the bath bottom 24, with the magnetic axis M of the inner and outer magnets being oriented in the direction of the magnetron axis. AThe magnets are vertically but oppositely oriented, as shown in FIG. 8, allowing the magnets, their respective poles, to be placed close to the liquid surface area, i.e., at a distance of up to 17-35 mm, providing high magnetic flux and field parallelism to the unstirred target surface. The magnetic flux density was measured in a racetrack region at a radius of 75 mm from the vessel center, approximately 5 mm above the Ga surface, and had a horizontal component B x is about 0.038 T and the vertical component is about 0.013 T, giving a total magnetic flux |B| of about 0.05 T. So, at this location, about 75% of the magnetic field is due to the horizontal and essentially parallel to the surface component B x and only about 25% is contributed by each vertical component B y Within the region of each racetrack projection that is above the stationary liquid surface within a distance of at least 5-10 mm, at least 60% of the racetrack, or even better, 70% or more of the horizontal component B x It can be shown that a magnetic field having a field characteristic of can help to stir the liquid more efficiently. A similar strong, surface-parallel magnetic field can be provided, for example, in the configurations shown in Figures 6b and 6c, where the magnets are close to the liquid surface because of their position in the vessel. It should be mentioned that side magnets 44 can help to provide such field characteristics, but are not a prerequisite.

[0058] A further modification that can be used to improve the parallelism of the magnetic field in the liquid gallium target, at least immediately above its surface, could be to provide a central yoke 5''' made of a magnetizable material having a Curie temperature above 500° C. in the center of the target, as shown by the dotted line in FIG. 8. Such a yoke could cooperate with the magnet 5'' to design the magnetic field lines more parallel to the surface.

[0059] It should be mentioned that magnetic systems 5, 5', 5" (5''') with inner or central magnets and outer magnets with respect to the center of the target will usually result in a highly unbalanced magnetic field due to the larger number of peripheral magnets, especially for circular target designs, or due to larger peripheral magnets if annular magnets are used. Nevertheless, within the liquid target and close to its surface, an almost symmetrical parallel magnetic field can be applied by each design of the magnetic system as shown.

[0060] The process was divided into two process steps, the first at a closed shutter at low sputter power under inert gas to condition the liquid target by essentially linear horizontal movement as described above, followed by a second step at higher sputter power under a mixture of inert and reactive gases, the shutter being opened after a few seconds to deposit a compound layer on the polished wafer substrate. The following parameters were applied to produce an intact compound (GaN) layer on the wafer surface:

[0061] First step - Linear surface movement for target conditioning: Ar flow: 20sccm Flow rate N2: 0sccm Total pressure: 0.29Pa Sputtering power (DC): 50W Sputter current: 0.19A Sputter voltage: 268V

[0062] Second step - Rotational surface transfer for coating Ar flow: 20sccm Flow N2: 10sccm Total pressure: 0.37Pa Sputtering power (DC): 600W Sputter current: 1.71A Sputter voltage: 350V

[0063] Alternatively, the following steps were applied:

[0064] The first step - conditioning of the target is carried out with high sputter power providing high maneuverability and heat, both of which result in very effective outgassing of the liquid gallium, as compared to, for example, linear surface movement. A dummy wafer was used in this conditioning step. Ar flow: 30sccm Flow N2: 60sccm Total pressure: 0.33Pa Sputtering power (DC): 1700W Sputter current: 3.7A Sputter voltage: 460V

[0065] Second step - Rotational surface transfer for coating Ar flow: 14sccm Flow N2: 72sccm Total pressure: 0.36Pa Sputtering power (DC): 500W Sputter current: 1.33A Sputter voltage: 376V

[0066] Below typical ranges that are applicable, and that have provided very good results for GaN coating, are provided for each coating process parameter. Ar flow: 5~70sccm, 8~14sccm Flow N2: 0~100sccm, 5~80sccm Total pressure: 0.1~0.8Pa, 0.2~0.6Pa Sputtering power (DC): 10~600W, 20~500W Sputter current: 0.05~10A, 0.08~8.38A Sputtering voltage: 200V~800V, 261V~538V

[0067] It should be mentioned that the critical minimum dimensions for stirring the liquid target vessel 2 with Lorentz forces in a good and reproducible way seem to be, for example, an inner diameter of the round or inner smaller side of a rectangular vessel of at least 55 mm or 60 mm, with a protruding edge of at least 8 mm or 10 mm to avoid spillage of the target liquid during stirring or filling, and a depth allowing a liquid level of at least 4 mm or 6 mm. For the critical maximum dimensions, a size of 2000 mm seems still manageable with a reasonable attempt. For larger material containers, a liquid level of up to 20 mm or 30 mm seems manageable with the respective magnet system, for example at or in the upper side of the vessel bottom to ensure a manageable distance from the liquid surface.

[0068] Due to the symmetrical setup and movement of the respective fluids, a round target has been found to be a good solution, especially for vessel inner diameters of 100 mm to 1000 mm, such as 200 mm to 800 mm.

[0069] FIG. 10 shows two typical current-voltage characteristics for a target with a liquid level as depicted in FIG. 8. The optional central yoke 5''' is not used. The lower curve is taken at a low liquid Ga level in the vessel 2, which corresponds to a height of about 8 mm above the bottom of the vessel. The upper curve is taken after refilling the vessel with a high liquid Ga level, which corresponds to a height of about 13 mm above the bottom of the vessel. Surprisingly, the deviation in sputter voltage between the two characteristic curves is shown to have a characteristic constant deviation of about 68.70 V, and sputtering at a higher liquid level results in a higher sputter voltage and power, as long as the sputter current is kept constant. Instead, when the sputter power is kept constant, for example when a power control is used to control the target power supply 23, the target current is smaller in a newly refilled target with a high liquid level than in a target with a low liquid level.

[0070] Although no proof can be provided to date, this effect is believed to be due to a more pronounced "dynamo effect" of the larger rotating target mass causing a greater electrical resistance to the sputter current. Such findings may be used by the inventors to extrapolate methods and apparatus to continuously monitor the liquid level in the target bath and indicate to an operator the need for refilling, and / or to initiate automatic refilling of low level targets between deposition processes.

[0071] In FIG. 11 and the following example of a lookup table, a simple linear scheme is extrapolated from a low (“before fill”) target voltage value at 1 amp from FIG. 10 to a high (“after fill”) target voltage value.

[0072] [Table 1]

[0073] Such a scheme, performed for several different target currents and therefore different target power levels, can be used with an electronic look-up table serving as a database to indicate the height of the liquid gallium level and output a control signal SLL to control the level refill device. The fill started with about 1.5 kg of gallium left in the target bath, to which 1 kg of liquid gallium was added, for a total of 2.5 kg of target liquid.

[0074] The logical scheme for operating the level refill device 53 and monitoring the liquid level in the target tank 2 is shown in Fig. 9. Here, a measuring device 47 for monitoring the target to ground voltage is electrically connected between the cathode tank and ground potential and transmits a voltage signal S1, which is usually a digitally converted voltage signal, to one input I of an electronic device 48 which is connected to one input of a comparator 49. VThe electronic device 48 may be a refill device 53 or a separate controller or computer for operating a control circuit in the system control of the coating system. A second signal S2 is applied to the other input of the comparator 49. The second signal S2 is measured in the circuit of the target power supply 23 and is sent to the input I of the electronic device 48 in order to select the respective look-up table 50 for the current. C / P The signal S2.n is generated by an electronic look-up table 50, which is selected depending on the height or range of the respective target current provided as a current signal SC to the level meter 23. Alternatively, the look-up table may be predicted for a constant power height or range of the supply 23. In this case, the power signal SP, again usually a digitally converted signal, may be used to select the respective look-up table. The look-up table 50 contains several values ​​S2.1, S2.2, ... S2.n depending on the required accuracy of the level detection. Such values ​​may be provided in series to one comparator, with S1 unchanged, or in parallel to a respective series of comparators as shown. For each signal S2.n, the respective level value SLL.n is provided to a logic element 51, which sends the respective value SLL to the indication device 52 and to the refilling device 53 only when the output signal of the comparator 49 refers to S1=S2. The indication of the level by the level meter 52 and the operation of the refilling system 53 may thereby be controlled. The refill system 53 comprises a refill passage 54 for filling the target liquid below the liquid surface 4, e.g. laterally through the bath, or at the periphery, e.g. in the inactive surface area. It should be mentioned that instead of a look-up table, an algorithm or a combination of a look-up table and an algorithm can be used to calculate the respective SLL signal essentially from the measured or converted voltage signal S1 and current signal SC or power signal SP.

[0075] As mentioned in the common parts of the above description, any of the electrical values ​​such as sputter voltage, sputter current or sputter power can be used to generate or estimate the signal S1, one of the remaining values ​​being kept constant and the last value being varied to generate a comparative benchmark signal S2 for different liquid levels, to generate a respective look-up table or to find an algorithm that fits the respective target shape and plasma area.

[0076] In the foregoing description, the present invention has been shown with respect to various embodiments, and any feature disclosed in one embodiment is presumed to be disclosed with any other embodiment, unless such feature is clearly inconsistent or inconsistent with other features of the respective embodiments to one of ordinary skill in the art. [Explanation of symbols]

[0077] 1, 1' Sputtering equipment 2. Target chamber 3 Liquid Target 4. Static Surfaces 4' Dynamic Surface 5,5' magnet system 6. Magnetic Field 7 Anode 8 Power Line Target Supply 9 Cooling device 9' Fastening 10 Vacuum Coating System 11 Cover 12 Side wall 13 Board Port 14 Substrates, wafers 15 Substrate holder 16 Cooling and / or heating means 17 Bias power supply 18 Power Line Bias Supply 19 Vacuum Pump 20 Pump Port 20' Pump Valve 22 Gas inlet 23 Sputter power supply 24 Bottom of the tank 24' Tank with partially concave bottom 24” fully concave bottom of basin 25 Mechanical Stirring Body 26 Axis 27 Feedthrough 28 Drive unit 29 Magnetic Rod 30 Stirring Body 31 Stirring Body Axis 32 Ultrasonic source 33 Center stirring electrode 34 Separate electrode current supply unit 35 Outside stirring electrode 36 Liquid circuit 37 Shield 38 Vacuum chamber 39 Liquid movement caused by vertical electric current 40 Liquid movement caused by horizontal currents 41 Current in sputtering plasma 42, 42', 42” Current in Liquid Target 43', 43" Insulating cover or sheath 44 Side Magnet 45 Shutter 46 Flow Equipment 47 Measuring Equipment 48 Electronic equipment 49 Comparator 50 Lookup Tables 51 Logical Elements 52 Liquid level indicator 53 Liquid level refilling device

Claims

1. A sputtering apparatus for sputtering a liquid target, comprising a vessel for receiving a liquid target material, the apparatus comprising: agitating and stirring the liquid target material; degassing the liquid target material; dispersing solid particles or islands on a surface of the target; and dispersing such particles or islands into an active surface area (S Ａ ) to the inactive surface area (S Ｐ ) or vice versa, and Ｐ ) is the active surface area (S Ａ 1. A sputtering apparatus comprising: a liquid target material that is exposed to at least 50% less sputtering than ...

2. 10. The apparatus of claim 1, wherein the target can be electrically connected to a cathode of a DC power supply, a cathode of a pulsed DC power supply, or one or several power supplies providing one of DC / RF mixed, DC / pulsed DC mixed, RF / pulsed DC mixed, or DC / RF / pulsed DC mixed, respectively.

3. 3. Apparatus according to claim 1 or 2, characterized in that the anode is arranged around the target and / or in a central region of the target.

4. The inactive surface area (S Ｐ 4. The apparatus according to claim 1, wherein at least a part of the light source 14 is projected by a darkroom shield and electrically isolated from the target.

5. 5. Apparatus according to claim 1, characterized in that the bottom of the vessel is formed concavely or convexly, at least in the peripheral area.

6. 6. The apparatus according to claim 1, wherein the means for stirring comprises a stirring unit comprising a stirring body positioned in the liquid target material and a drive mounted on or near the opposite side of the vessel.

7. 7. The apparatus of claim 6, wherein the agitator is one of a rod, a disk, a paddle, or an impeller.

8. 8. Apparatus according to claim 6 or 7, characterized in that the drive and the agitator are connected by a transmission shaft.

9. 8. The apparatus according to claim 6 or 7, characterized in that the drive comprises a magnetic unit configured to create a rotating electric field, and the stirrer comprises or is a magnetic bar.

10. 6. The apparatus according to claim 1, wherein the means for stirring the liquid target comprises a stirring unit having an inner stirring electrode and an outer stirring electrode, and a magnet system, wherein at least the inner stirring electrode is at least partially below the liquid level of the target material, and wherein at least the inner stirring electrode is connected to a DC current source, a pulsed DC current source or a low frequency AC current source.

11. 11. The apparatus of claim 10, wherein the outer stirring electrode is at least partially below the surface of the target material.

12. The inactive surface area (S Ｐ ) is projected by a darkroom shield and electrically isolated from the target; the means for stirring the liquid target comprises a stirring unit having an inner stirring electrode and an outer stirring electrode, and a magnet system, at least the inner stirring electrode being at least partially below a liquid level of the target material, and at least the inner stirring electrode being connected to a DC current source, a pulsed DC current source, or a low frequency AC current source; 2. The apparatus of claim 1, wherein said outer stirring electrode is said anode.

13. 13. The apparatus of claim 12, wherein the inner stirring electrode is at least a portion of the interior surface of the vessel in contact with the liquid target.

14. 14. The apparatus of claim 13, wherein the inner stirring electrode is the interior surface of the vessel in contact with the liquid target.

15. 15. Apparatus according to any one of the preceding claims, characterized in that the liquid target material is at least one of the following materials: Ga, GaAs, GaIn, GaAl, InAl, TiGa, Hg, HgAg, HgAu, HgCu, HgIn, HgSn, HgZn, or an alloy of one of them.

16. 16. Apparatus according to any one of the preceding claims, characterized in that it comprises means for heating, cooling or both heating and cooling the target.

17. 17. Apparatus according to any one of claims 1 to 16, characterized in that the material of the vessel is stainless steel, molybdenum, a molybdenum alloy or graphite.

18. A vacuum coating system comprising a sputtering device according to any one of claims 1 to 17, characterized in that it comprises a sputter gas inlet and a vacuum pump.

19. 20. The system of claim 18, further comprising an inlet for a reactant gas.

20. 20. The system of claim 19, wherein the sputter gas inlet and the inlet for reactive gas comprise different inlets, the sputter gas inlet being proximate to the target surface and the inlet for reactive gas being near the surface to be coated.

21. The system (10) comprises a measuring device (47) for measuring the sputter voltage and an electronic device (48) comprising a comparator (49), one input I Ｖ is connected to the output signal or the converted output signal S1 of the measuring device (47) and to one input of the comparator (49), the other input of which is connected to an output from an electronic benchmark database (50) for comparing the signal S1 with a signal S2 from the electronic benchmark database (50) to generate a liquid level signal SLL at the output O of the electronic device (48).

22. 22. The system of claim 21, wherein the output O is connected to a level indicator (52) and / or a refilling device (53) of the system.

23. A method for depositing a film on a substrate, comprising: a sputtering device in which at least one first component is sputtered by a sputtering apparatus comprising a liquid metal target material disposed in a target bath and sputtered from the target onto a surface of the substrate to be coated, the target having an active surface area (S Ａ ), and the active surface area (S Ａ ) is exposed to sputtering at least 50% less than the inactive surface area (S Ｐ ) The method further comprises the steps of: degassing the liquid metal target material, dissipating solid particles or islands, and / or adsorbing solid particles or islands onto the active surface area (S Ａ ) to the inactive surface area (S Ｐ agitating the liquid metal target material to move the liquid metal target material toward the target surface or vice versa, the agitation forcing horizontal and vertical convection currents in the liquid metal target material during sputtering; The agitation of the liquid metal target material comprises: or - implemented by a stirring unit comprising an inner stirring electrode and an outer stirring electrode both connected to a DC current source, a DC current being applied between said stirring electrodes to generate a circulatory movement of liquid of said liquid metal target material at least between said stirring electrodes; The agitation of the liquid metal target material comprises: A method, characterized in that the stirring is performed by mechanical stirring, by applying ultrasound to the liquid metal target material, or by a combination of stirring and applying ultrasound, and the stirring is performed by a stirring unit comprising a stirring body and a drive mounted on or near the opposite side of the vessel.

24. 24. The method according to claim 23, characterized in that the film is a metal, alloy or compound film, at least one first metal component being sputtered from the target onto the surface of the substrate to be coated and, in the case of a compound film, at least one second component of the compound is introduced as a reactive gas in order to form the compound in the gas phase and / or on the surface of the substrate and / or on the surface of the film.

25. The inactive surface area (S Ｐ 25. The method according to claim 23 or 24, characterized in that the liquid metal target material is provided with a peripheral and / or central region of a surface thereof.

26. The inactive surface area (S Ｐ At least a part of the region (S Ｐ 26. The method according to claim 23, characterized in that the target is projected by a darkroom shield and electrically isolated from the target in order to shield it from sputtering or other glow discharge phenomena.

27. 27. The method of claim 26, wherein the darkroom shield forms a counter electrode for the target.

28. 28. The method according to any one of claims 23 to 27, characterized in that the sputtering device comprises a magnetron magnet system and a DC power supply or a pulsed DC power supply.

29. 24. The method according to claim 23, characterized in that the power transmission between the drive and the agitator is performed mechanically or magnetically.

30. 30. The method according to any one of claims 23 to 29, characterized in that the liquid metal target material is a liquid metal or an alloy of at least two metals having a melting point T≦300°C, T≦70°C, or T≦40°C.

31. 31. The method of claim 30, wherein the liquid metal target material is one of Ga, GaAs, GaIn, GaAl, InAl, TiGa, Hg, HgAg, HgAu, HgCu, HgIn, HgSn, HgZn.

32. The method of claim 23, wherein the film is a compound layer, the compound being a nitride, a carbonitride, a carbide, an oxide, a boride, an alloy of a liquid metal target material, or a mixture thereof.

33. 33. The method of claim 32, wherein the compound is a nitride of one of Ga, GaAs, GaIn, GaAl, InAl, TiGa.

34. 34. The method according to any one of claims 23 to 33, characterized in that further targets from different materials are used for depositing compounds at the surface of the substrate.

35. 35. The method according to any one of claims 23 to 34, characterized in that the dependence of an electrical value of the liquid metal target material from the level is used to generate a level signal SLL by measuring a value V1 or a transformed value signal S1 and comparing it with a benchmark value V2 or a respectively transformed value signal S2 corresponding to a defined level, said electrical value being a sputter voltage, a sputter current or a sputter power.

36. 36. A method according to claim 35, characterized in that the liquid level signal is used to drive a liquid level indicator device and / or to control a target liquid refill device.

37. Method for manufacturing a semiconductor device, characterized in that a method according to any one of claims 23 to 34 is used.

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