Method and device for protecting oxygen-sensitive target materials in a coating source

Abstract

The invention discloses a method and a device for protecting oxygen-sensitive target materials in a coating source. The problem of specifying a method and arrangement, by means of which reactive, in particular oxygen-sensitive target materials of a coating source can be protected against contaminations and undesired reactions, is solved by a method in which first of all the shutter sealingly closes the coating source, and a protective gas is fed via a gas inlet into a coating source chamber which is formed by the coating source and the shutter. Here, a positive pressure is set in the coating source chamber with respect to a vacuum chamber pressure within the process chamber. Subsequently, a further gas for reacting with, that is to say neutralizing coatings in the process chamber, is fed into the process chamber. The process chamber is then ventilated with air or nitrogen, without an undesired reaction taking place. The process chamber is subsequently opened towards atmosphere, that is to say the door of the process chamber to the surrounding area is opened, wherein a positive pressure with respect to atmosphere is then constantly maintained in the coating source chamber.

Description

[0001] Method and device for protecting oxygen-sensitive target materials in a coating source. The invention relates to a method and a device for protecting oxygen-sensitive target materials in a coating source. Sputtering is a coating technique from the group of PVD (physical vapor deposition) processes. Sputtering, also known as cathode sputtering, is a physical process in which atoms are released from a solid, the so-called target, by bombardment with high-energy (noble gas) ions and pass into the gas phase. Depending on the materials used as well as the intended layer properties and deposition rates, various sputtering technologies are used. In the field of coating technology, sputtering is used to atomize a material, which is then deposited on a substrate and forms a solid layer.In order to achieve a defined layer thickness when coating various materials onto a substrate, particularly during sputtering, shutter systems are used to control the material flow onto the substrates to be coated. Sputtering takes place in a coating system under vacuum conditions. Depending on the sputtering variant used (DC sputtering, RF sputtering, magnetron sputtering, ion beam sputtering, reactive sputtering, etc.), a voltage is applied between two electrodes and a working gas is admitted into the gas space. Impact ionization of the atoms of the working gas used, e.g. argon, creates a plasma in the gas space. The target usually forms the negative electrode and the substrate to be coated usually forms the positively charged electrode. In magnetron sputtering, an additional magnetic field is arranged behind the cathode. In reactive sputtering, one or more reactive gases are added to the inert working gas (argon).The gases react with the sputtered layer atoms on the target in the vacuum chamber or on the substrate to form new materials. In ion beam sputtering, a beam of noble gas sputter ions (argon, krypton, xenon) is directed from an ion source onto the target – sputtering occurs due to the impinging ion beam. To ensure a stable sputtering process, the coating system is switched on, i.e. the voltage is applied to the electrodes and the plasma is ignited. The desired operating power for a stable process is set and reached. Only then is the shutter opened to begin coating the substrates. Beforehand, the coating source is shielded by a shutter. To ensure that the plasma is ignited, a gap of a few millimeters must exist between the coating source and the shutter.Typically, a metal sheet is swung sideways in front of the coating source as a shutter to prevent any unwanted material from the coating source from reaching the substrates to be coated. Unwanted material flow, known as cross-contamination, onto the substrates and the area surrounding the coating source is most effectively prevented when the distance between the metal sheet and the coating source is as small as possible, thus optimally shielding the coating source from the substrates. Particularly when multiple coating sources are arranged within a coating or process chamber, cross-contamination can lead to mutual coating of the coating sources (targets) if the coating sources cannot be completely sealed off.As a result, it is often necessary to remove the contaminated targets by sputtering, also known as free sputtering, before the actual coating process on the substrates in order to maintain and guarantee the quality of the coating materials. This reduces the coating quality and material utilization as well as the productivity of the coating system. Until now, the shutter plates used have been pushed in front of the coating source at a distance of approximately 1 to 4 mm. However, this distance cannot guarantee completely enclosed shielding of the coating source. This distance is necessary for sputtering in a coating source. Smaller distances cannot be realized in practice because they usually lead to friction between the shutter plate and the coating source.These friction effects cause numerous unwanted particles, which can lead to additional contamination of the coated substrates, which can also cause the layers to detach from the substrate. The quality of the layers can be severely impaired by these effects. WO 2021 / 091890 A1 discloses a shutter mechanism in which a shutter is connected to an actuator via a coupling system in such a way that the shutter can be moved in a compound movement from an open position to a closed position over a coating source. The actuator merely performs a linear movement along a translation axis, with a grooved cam converting a linear movement of the shutter into a tilting movement and back into a final linear movement until the shutter encloses the sputter source.The shutter first performs a linear movement along the actuator's translation axis, then a rotational movement, e.g., by 90°, relative to the actuator's translation axis, and finally a linear movement again along the actuator's translation axis. A disadvantage is that these movements cannot be controlled separately and independently of one another, as they are predetermined by the grooved cam, and fine adjustment of the shutter using the actuator is only possible to a very limited extent. Particularly when using a pneumatic actuator, maintaining the shutter in an intermediate position, e.g., for pre-sputtering or pre-sputtering processes, i.e., a few millimeters above the sputter source, is not possible without additional technical devices according to the solution described in WO 2021 / 091890 A1, and can only be reproduced with limited accuracy.Due to the fact that in the solution described in WO 2021 / 091890 A1, the shutter's rotation axis is not parallel to the longitudinal axis of the coating source, a disadvantageous curvature of the gas plasma can occur during the opening and closing of the shutter, as the angle between the target and shutter surfaces changes. This can also result in undesirable coating of the chamber interior or the coating source itself. Another disadvantage is that the actuator in WO 2021 / 091890 A1 is arranged with the grooved cam inside the vacuum chamber. The mechanical stress on the coupling system and the associated friction in the grooved cam can lead to abrasion, which is undesirable in a coating system with high purity requirements. Maintenance and / or repair of the shutter control is also significantly more complex, as this can only be carried out when the vacuum chamber is ventilated.The use of conventional shutter systems is also not possible for the use of oxygen-sensitive target materials in a coating source (sputter source). Especially for cleaning or maintenance work, it is often necessary to open the vacuum or process chambers in which the coating sources are located. If oxygen-sensitive materials, such as lithium, are used, contact with oxygen can lead to a chemical reaction with the target material, rendering the target material unusable and necessitating special safety measures. The gap between the shutter plate and the coating source promotes the penetration of oxygen and should therefore be avoided, even for maintenance purposes. It is therefore an object of the invention to provide both a method and an arrangement by means of which reactive, in particular oxygen-sensitive, target materials of a coating source can be protected from contamination.The object is achieved by a method according to independent method claim 1. In the method for protecting a coating source which comprises a reactive coating material, wherein the coating source with the coating material is shielded from a process chamber by a shutter, the shutter first seals off the coating source and a protective gas is admitted via a gas inlet into a coating source space formed by the coating source and the shutter. An overpressure is set in the coating source space compared to a vacuum chamber pressure inside the process chamber and later during ventilation of the process chamber compared to an atmospheric pressure outside the process chamber. Subsequently, a further gas is admitted into the process chamber to react, i.e. to neutralize coatings in the process chamber. The layers are passivated.The process chamber can now be ventilated with air or nitrogen without an unwanted reaction taking place. The process chamber is then opened to the atmosphere, i.e. the door of the process chamber to the environment is opened, whereby an overpressure is always maintained in the coating source chamber. This permanent overpressure in the coating source chamber prevents gases, in particular oxygen, from reaching the coating source, in particular the reactive target material, and reacting with it. It is important that the shutter seals the coating source chamber and is accordingly closed, i.e. pivoted over the coating source. Furthermore, the coating source should be switched off. In one embodiment of the method according to the invention, the reactive coating material is an oxygen-sensitive target material, for example lithium, magnesium, calcium and / or a similarly highly reactive material as those mentioned above.Lithium is very reactive and reacts with many elements and compounds. It must therefore be specially protected to avoid cross-contamination. This is ensured by the closed shutter, which is operated by a rotating and / or pivoting and / or folding / tilting movement and an additional lifting movement in the direction of the coating source, and by the set overpressure in the coating source chamber. In another embodiment of the method according to the invention, an inert gas, in particular nitrogen or argon, is used as a further protective measure. The constant overpressure in the coating source chamber closed by the shutter and the admitted protective gas has the advantage that no oxygen or air can penetrate behind the shutter into the coating source chamber. In a further embodiment of the method according to the invention, an additional gas is used for reacting orTo neutralize coatings in the process chamber, carbon dioxide is introduced into the process chamber. This prevents further reactions in the process chamber and further minimizes contamination of the coating source. The object of the invention is also achieved by a sputtering system according to the invention according to independent claim 6. The sputtering system comprises a process chamber and at least one coating source space, which is formed from a coating source and a shutter and is arranged within the process chamber. This sputtering system or coating system is suitable for carrying out the method according to claims 1 to 5.It is particularly advantageous that the shutter can be positioned above the coating source by means of a rotating and / or pivoting and / or folding / tilting movement and the shutter is designed to carry out an additional relative movement to the coating source and / or the coating source is designed to carry out an additional relative movement to the shutter, wherein the shutter sealingly covers the coating source and a permanent overpressure can be created in the coating source chamber during a maintenance operation of the sputtering system. The relative movement is advantageously a lifting movement. This prevents unwanted particles, gas atoms, etc. from reaching the target, i.e. into the coating source chamber. The design proves to be particularly advantageous when the coating source chamber comprises a target made of an oxygen-sensitive material, for example lithium, magnesium and / or calcium.According to the invention, the shutter can be positioned above the coating source by means of a rotating and / or pivoting and / or folding / tilting movement, and the shutter is designed to perform an additional relative movement in the form of a lifting movement to the coating source, and / or the coating source is designed to perform an additional relative movement in the form of a lifting movement to the shutter, wherein the shutter seals the coating source. Sealing means the complete shielding of the coating source from the rest of the process chamber, thus preventing any cross-contamination of the coating source and unwanted coatings on the substrate to be coated. Oxygen cannot thus enter the coating source chamber and contaminate the target material and cause unwanted reactions.It is advantageous that the shutter of the sputtering system according to the invention is not only pivoted, rotated, or folded / tilted over the coating source according to a first degree of freedom, but the shutter or the coating source are moved sealingly relative to one another according to a second degree of freedom by a relative movement between the shutter and the coating source. Either the shutter performs a lifting movement toward the coating source, or the coating source performs a lifting movement toward the shutter, so that the shutter and the coating source are positioned one above the other in a sealing manner, i.e., completely closed. Both movements can be performed independently of one another, so that the shutter can be positioned in any required and desired position. The gas plasma is not deflected by the movements of the shutter.This eliminates the creation of particles due to friction between the shutter plate and the coating source, as occurs when the shutter is simply pivoted over the coating source. When the shutter is closed, there is no longer a gap through which contamination of the target material could occur due to the operation of other coating sources in the same arrangement or through the ingress of oxygen during maintenance work. The shutter can be positioned over the coating source, for example, by a rotational movement around an axis or by a pivoting movement by moving sideways towards the coating source or by a folding / tilting movement. Only then does the relative movement or lifting movement between the shutter and the coating source occur. The rotational / swivelling / folding / tilting and / or lifting movements are caused by shutter movement devices such as motors or lifting cylinders.The shutter system's control is located outside the vacuum chamber, so that wear caused by mechanical components within the vacuum chamber is reduced to a minimum. The proposed solution enables a significantly more compact arrangement of different coating sources in a parallel and / or co-coating arrangement (e.g., sputter arrangement), as cross-contamination of the coating sources is prevented. A large overhang of the shutter plates is no longer necessary. In one embodiment of the shutter system according to the invention, the relative movement between the shutter and coating source is achieved by means of bellows or ring seals and / or sliding bushings. This reduces mechanical wear within the vacuum chamber to a minimum. Contamination due to abrasion or mechanical friction does not occur.The relative movement between the shutter and the coating source is achieved by means of a lifting movement, which is carried out either by the shutter or by the coating source. A structurally simpler implementation involves moving the shutter while the coating source remains stationary. In another embodiment of the sputtering system according to the invention, the distance between the coating source and the shutter is adjustable. This has the advantage that, particularly during maintenance work in the process chamber, the distance between the shutter and the coating source can be set to zero, thus preventing contamination of the target.A further advantage is that at the start of the process for igniting the plasma during the sputtering process, the necessary gap between the coating source and the shutter can be adjusted. And during the actual coating process, especially when multiple coating sources are used, the respective coating source that is not currently in use can be optimally shielded and sealed. The control of the shutter system according to the invention allows the shutter to be held in any required and desired position. This is made possible by the separately controllable and independently executable movements of the shutter system. Shielding is further optimized if, in a further embodiment of the shutter system according to the invention, the shutter has a cranked edge. Due to the cranked edge, the shutter acts like a kind of hood over the coating source, so that cross-contamination can be completely prevented.Furthermore, the shutter and the coating source have a round, oval, rectangular, or polygonal shape. This allows the shutter to be adapted to the shape of the coating source to be covered in order to optimally seal it. Due to the independently executable movements (rotation and / or pivoting and / or folding or tilting movement as well as the additional relative movement) of the shutter, the shutter system of the sputtering system can also be easily adapted to any coating source. The inventive method for protecting a coating source, in particular a reactive, oxygen-sensitive target material, in a sputtering system and the inventive sputtering system for carrying out the inventive method can be used for any coating source with a directed particle stream.Effective prevention of cross-contamination of the coating source and prevention of reactions with a reactive target material is thus possible in a simple and compact manner. The invention will be explained in more detail below using exemplary embodiments. The accompanying drawings show: Fig. 1: A sputtering system according to the invention with a coating source (a sputter target) in a coating source chamber, which can be closed with a shutter with a cranked edge; Fig. 2: A schematic representation of the method steps a) to i) according to the invention. Figure 1 shows a schematic representation of the sputtering system 1 according to the invention, which comprises a process chamber 2 in which at least one coating source chamber 3 is arranged, which is formed from a coating source 4 and a shutter 5.The process chamber 2 further comprises an inlet valve 6 for a reacting gas, a vent valve 7 for the process chamber 2, a vacuum pump 8, and a glove box 9 for carrying out maintenance work or changing the substrate and / or target 11 without having to interrupt the vacuum in the process chamber 2. The coating source chamber 3 additionally comprises an inlet 10 for a protective gas, e.g., nitrogen and / or argon. The protective gas, which is pressurized into the coating source chamber 3 at an overpressure compared to a vacuum chamber pressure within the process chamber 2 and later, when the process chamber 2 is vented, to an atmospheric pressure outside the process chamber 2, prevents oxygen from penetrating the coating source chamber 3 through a residual gap. Figure 2 shows a schematic representation of the method steps according to the invention using the sputtering system according to the invention.In a normal coating process, the substrate 13 to be coated is located in the process or vacuum chamber 2 opposite the coating source 4. During the coating process, the coating source chamber 3 is open, i.e. the shutter 5 is pivoted / rotated / folded to the side so that material is removed / sputtered from the target 11 and deposits on the substrate surface 13. Once the coating process is finished, the shutter 5 is moved back in front of the coating source 4 such that no gap remains between the shutter 5 and the coating source 4. This is mechanically ensured by the additional relative movement between the shutter 5 and the coating source 4. The control of the shutter system 5 is located outside the vacuum chamber 2 so that abrasion caused by mechanical components within the vacuum chamber 2 is reduced to a minimum. The coating source 4 is now switched off. Subsequently, a protective gas, e.g.Nitrogen or argon is introduced into the coating source chamber 3 via a gas inlet 10. The process chamber 2 is then flooded with a reaction gas, e.g., CO2, so that components in the vacuum chamber 2 can react and the process chamber 2 is neutralized internally. At the same time, an overpressure is generated in the coating source chamber 3 to effectively prevent the penetration of particles and gases, e.g., oxygen. In a next step, the gas is pumped out of the process chamber 2, and the overpressure in the coating source chamber 3 is maintained. In a further process step, nitrogen or another ventilation gas is fed into the process chamber 2 via a ventilation valve 7, and a slight overpressure compared to atmospheric pressure outside the process chamber 2 is maintained in the coating source chamber 3. The process chamber 2 can then be opened, and any necessary maintenance work, etc., can be carried out.be carried out, whereby the constant low overpressure in the coating source chamber 3 completely prevents contamination of the reactive, in particular oxygen-sensitive, target materials 11.

[0002] Method and device for protecting oxygen-sensitive target materials in a coating source List of reference symbols 1 Sputtering system 2 Process / vacuum chamber 3 Coating source chamber 4 Coating source 5 Shutter 6 Inlet valve for gas for the reaction process 7 Ventilation valve 8 Vacuum pump 9 Glove box 10 Shielding gas inlet 11 Target 12 Process chamber door 13 Substrate to be coated 14 Shutter movement means

Claims

Method and apparatus for protecting oxygen-sensitive target materials in a coating source Claims 1. Method for protecting a coating source (4) comprising a reactive coating material (11), wherein the coating source (4) with the coating material (11) is shielded from a process chamber (2) by a shutter (5), characterized in that - the shutter (5) seals the coating source (4) and a protective gas is admitted via a gas inlet (10) into a coating source chamber (3) formed by the coating source (4) and the shutter (5), and an overpressure is set in the coating source chamber (3) relative to a vacuum chamber pressure inside the process chamber (2) and subsequently to atmospheric pressure outside the process chamber (2).- another gas is introduced into the process chamber (2) for the reaction of coatings in the process chamber (2), - the additional gas is pumped out of the process chamber (2), - the process chamber (2) is vented (7) by introducing nitrogen or another gas, - the process chamber (2) is opened to the atmosphere, whereby - an overpressure is always maintained in the coating source chamber (3).

2. The method of claim 1, characterized in that the reactive coating material (11) is an oxygen-sensitive target material.

3. The method of claim 2, characterized in that the target material (11) is formed from lithium, magnesium, calcium and / or a similarly highly reactive material.

4. The method of claim 1, characterized in that the protective gas is an inert gas, in particular nitrogen or argon.

5. The method of claim 1, characterized in that carbon dioxide, in particular, is introduced as a further gas for reaction. 6.Sputtering system (1) comprising a process chamber (2) and at least one coating source chamber (3), which is formed from a coating source (4) and a shutter (5) and is arranged within the process chamber (2) and is designed and suitable for carrying out the method according to claims 1 to 5, wherein the shutter (5) can be positioned above the coating source (4) by means of a rotary and / or pivoting and / or folding / tilting movement and the shutter (5) is designed to perform an additional relative movement to the coating source (4) and / or the coating source (4) is designed to perform an additional relative movement to the shutter (5), wherein the shutter (5) covers the coating source (4) in a sealing manner and a permanent overpressure is maintained in the coating source chamber (3) during a maintenance operation of the sputtering system (1).

7. Sputtering system (1) according to claim 6, characterized in that the relative movement between shutter (5) and coating source (4) is formed by means of bellows or ring seals and / or sliding feedthroughs.

8. Sputtering system according to claim 6 or 7, characterized in that a distance between coating source (4) and shutter (5) is adjustable.

9. Sputtering system according to claim 6, characterized in that the shutter (5) has a cranked edge.

10. Sputtering system according to claim 6, characterized in that the shutter (5) and the coating source (4) have a round, oval, rectangular, or polygonal shape.

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