Physical vapor deposition (PVD) target manufacturing method

Abstract

A method for constructing and / or completing a PVD target, the method including a process step in which target material is added using an addition method.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing targets for use in PVD coating equipment.

[0002] PVD targets are used in a variety of physical vapor deposition processes to deposit thin films on substrates, most notably arc evaporation and sputtering. In both processes, the target is used as a cathode. In both cases, the target is placed in a coating chamber that is evacuated during the deposition process.

[0003] In arc evaporation, electrons are generated at an arc spot on the cathode (target) and drawn to the anode. The arc spot moves more or less randomly across the target surface, heating the target surface in the spot's area and causing the target material to evaporate almost explosively. In the coating process, the substrate to be coated is positioned opposite the target surface in such a way that the evaporated particles are deposited on the surface of the substrate to be coated. Because the majority of the evaporated particles are ionized, applying a negative bias to the substrate (relative to the target) accelerates the particles further toward the substrate, resulting in a denser coating layer, which constitutes one of the advantages of this coating method. However, in many cases, not only do the particles / ions evaporate from the target surface, but the high-temperature impact melts the surface material, forming droplets that are then ejected and deposited on the surface of the substrate to be coated. In some applications, this can be a disadvantage, as these droplets form discontinuities on the substrate surface that can sometimes break off, creating holes in the coating layer.

[0004] There are various efficient ways to avoid the droplet problem, such as filtering and / or pulsing, but this impacts the economics of the coating process, for example by reducing the deposition rate.

[0005] In sputtering, positive ions are generated from a working gas (e.g., argon) in front of the target surface. When a high negative voltage is applied to the target, the ions are accelerated toward the target surface, colliding with it and vaporizing / knocking off material from the target surface upon impact. However, this vaporization process with the ionized working gas results in the formation of only a small amount of ionized metal vapor in standard sputtering (as opposed to cathodic arc evaporation). In the coating process, the substrate to be coated is positioned opposite the sputter target surface in such a way that the vaporized target material is deposited on the surface of the substrate to be coated.

[0006] One advantage of the sputtering process is that, if performed properly and arcing is avoided, droplets do not form and the resulting coating layer is homogeneous and smooth. However, a drawback is that, when using conventional sputtering power, most of the vaporized particles are not ionized. Therefore, biasing the substrate with a negative potential only increases the energy of the working gas ions, without changing or increasing the number of atoms of the vaporized target material. Increasing the energy of the working gas (e.g., argon) can help increase the density of the coating, but it can also cause sputtering of the substrate surface and the coating synthesized on the substrate surface.

[0007] It is known that very high sputtering powers can be used to achieve a high percentage of ionized particles in sputtering. Unfortunately, this process also inputs a very large amount of energy into the target, causing the target's temperature to rise rapidly, which can destroy the target in a short period of time. To avoid this, the power is pulsed, interrupting the energy input and allowing time for the target to cool down again. However, this also has a negative impact on the economics of the coating, e.g., deposition rate.

[0008] Therefore, the key to all these methods is to have good contact between the plate provided to carry the target material and the "plate" of the holder on which the target is "mounted." Contact in this context means mechanical contact and / or thermal contact and / or electrical contact. Good mechanical contact in this context means that there is no gap between the plate carrying the target material and the surface of the target holder on which the target is mounted for operation, and that the holder is configured to prevent bending of the target.

[0009] Good thermal contact in this context means that only a negligible temperature difference can be measured between the plate provided for carrying the target material and the plate of the holder on which the target is mounted and cooled in the contact area between these two surfaces. [RJ(L1] Additional external pressure may be applied to increase the contact pressure between the target plate and holder, improving thermal contact.

[0010] In this context, good electrical contact means that the electrical resistance I between the plate provided for carrying the target material and the holder on which the target is mounted is less than 1 ohm, more preferably less than 0.1 ohm, and even more preferably less than 0.05 ohm. [RJ(L2] The mechanical contact must be good to prevent deformation of the target surface when temperature gradients act on it due to local energy impingement, for example during arc discharge. The thermal contact must be good to ensure fast and efficient cooling of the target which is heated by the extreme energy bombardment, for example in high power pulsed magnetron sputtering. In order to use the target as a cathode surface during the deposition process, good electrical contact must be achieved in all cases.

[0011] Various techniques are used to manufacture PVD targets. Known methods can be basically divided into powder metallurgy methods and methods based on metal fusion. There are many different powder metallurgy methods, which must be used and selected depending on the desired target composition, taking into account the properties of the elements to be incorporated. Examples are pressing (e.g., hot isostatic pressing) or sintering, welding, rolling, hot pressing, and spark plasma sintering, or a combination thereof.

[0012] One problem with all these PVD target manufacturing methods is that the target material itself is manufactured separately from the base plate, which requires mounting it and ensuring good mechanical, thermal, and electrical contact, among other things. This mounting requires an elaborate second step, which makes the overall process complex and expensive, and in some cases (especially when brittle target materials are involved) significantly reduces yield.

[0013] Another problem, at least when targets are used for magnetron sputtering, is that material is extracted from the target primarily along a so-called racetrack. After a while, grooves form along this track, and if they become too deep, the target becomes unusable, despite the fact that, as mentioned, there is still a lot of material outside the groove. Since target materials are very expensive, the yield of target material usage plays a major role.

[0014] Therefore, there is a need for a target manufacturing method that at least partially overcomes the deficiencies of the prior art, as just described.

[0015] It is therefore an object of the present invention to at least partially overcome these problems.

[0016] According to the invention, the manufacturing method includes a process step in which target material is added using an additive method.

[0017] According to one aspect of the invention, the target material is added by a thermal spray process.

[0018] According to a second aspect of the invention, the target material is added by conventional laser cladding.

[0019] According to a third aspect of the invention, the target material is added by extreme high speed laser cladding (EHLA Extremes Hochgeschwindigkeits Laser Auftragsschweissen). This is very efficient when disk-shaped targets need to be made, as they have rotational symmetry.

[0020] According to a fourth aspect of the present invention, target material is added via 3D printing. This is particularly effective when the target material needs to have internal structures, such as microgaps. These gaps can be used to further enhance the target's heat resistance. The principle itself is described in WO20151971696. However, whereas WO20151971696 uses randomly distributed microgaps, additive methods, particularly 3D printing, allow for predefined microgaps in the target. Another advantage is that 3D printing the target material itself allows for the creation of cooling channels for water or air cooling, which allows for a highly efficient cooling approach.

[0021] Another aspect of the present invention is target repair and / or target replenishment. In addition to building the material completely by additive methods, the material can be added partially by one or more of these methods. It is also possible to combine one or more of these additive methods with traditional target manufacturing methods such as sintering and / or hot isostatic pressing.

[0022] For example, additive methods can locally refill the grooves of the racetrack, allowing used targets to be reconditioned and used again. There is no need to start with an entirely new target and build it from the base up. Nor is there any need to strip it from the base plate to recover the remaining target material. In this context, conventional laser cladding, thermal spraying, or 3D printing are particularly effective.

[0023] In the case of arc targets, some process defects can cause holes in the target plate, and the doping process of the present invention can repair such targets.

[0024] Another aspect of the present invention is that it is possible to use combinations of materials that have previously been difficult or impossible to combine. If the additive method is based on powder materials, a powder mixture can be used to perform the additive steps to build or complete the target plate.

[0025] The invention will now be explained in more detail on the basis of non-limiting examples and with reference to the figures shown. [Brief explanation of the drawings]

[0026] [Figure 1] Shows the target before the process. [Figure 2] The target after the process is shown. [Figure 3] The surface of the coated layer is shown. [Figure 4] Another photograph of the surface of the coated layer is shown at a higher magnification. [Figure 5] EDX is shown, showing the chemical composition of the surface coated layer. [Figure 6] 1 shows an SEM at high magnification of a fracture cross section of a layer coated with a target according to the invention. [Figure 7]7 shows another SEM of a layer coated with a target according to the present invention at a lower magnification than FIG. 6. [Figure 8] 1 shows the so-called carrote criter profile obtained by carrote grinding of the coated layer. [Figure 9-1] 1 shows an EDX line scan along a cross section of the coated layer. [Figure 9-2] 1 shows an EDX line scan along a cross section of the coated layer. DETAILED DESCRIPTION OF THE INVENTION

[0027] In the following example, the target base plate was coated using a laser cladding process. The cladding material consisted of 21.5% Ni, 8.5% Cr, 3.5% Mo, 3% Nb, and the remainder Fe. It was a standard size powder. Oerlikon Metco sells this powder under the trade name MetcoClad 625F.

[0028] MetcoClad 625F was applied to the surface of the base plate, suitable for fastening to a bayonet fixture. The method for applying the material to the surface is laser cladding.

[0029] Figure 1 shows the resulting unused target. The target was slightly bent after fabrication. However, it could be easily mechanically flattened in a way that made it suitable for insertion into an arc deposition coating apparatus. This already indicates excellent adhesion of the laser-clad coating to the metal base plate. The target was inserted into the coating apparatus, and a coating layer of approximately 10 μm could be deposited without any problems. To test the reliability of operation in non-reactive and reactive arc deposition, the target was first operated without oxygen, and then oxygen flow was gradually added to the arc deposition to form successive oxidized layers as they grew toward the layer surface.

[0030] Figure 2 shows the target after it was used for deposition, and no problems were observed on the surface of the target.

[0031] The inventors then analyzed the coated layer. Figures 3 and 4 show the surface of the coated layer. As can be seen, the coating process resulted in a rough surface containing a significant amount of droplets. However, this is not necessarily a disadvantage.

[0032] EDX was performed to measure the chemical composition of the coated layer surface, as shown in Figure 5. The EDX shows the oxidized layer surface. The chemical composition of the metal elements contained in the oxidized layer closely matches that of the MetcoClad 625F powder used for laser cladding. As previously mentioned, layers were fabricated with increasing amounts of oxygen to test the process stability in non-reactive (no oxygen) and reactive (different oxygen flow) atmospheres. In Figure 8, the calorie count profile shows a change in morphology after 7.2 μm due to a color change toward the surface near the layer region (3.5 μm), a result of increased oxygen during deposition.

[0033] To show the morphology of the deposited coating, SEM photographs of two cross sections of the deposited layer were taken, which are shown in Figures 6 and 7. The change in morphology can also be seen in this cross-sectional micrograph (Figure 6, after about 7 μm).

[0034] FIG. 9 shows an EDX line scan across the coating layer, clearly showing oxygen enrichment within the layer.

Claims

1. 1. A method for manufacturing a PVD target, comprising: the PVD target includes a target base plate and a target material; The method includes a process step in which the target material is placed directly on the target base plate using an additive method, the additive method being a laser cladding method.

2. The method of claim 1 , wherein the target material is a powder material.

3. 3. The method according to claim 1, wherein the method is a method for repairing and / or replenishing the PVD target.

4. The method according to any one of claims 1 to 3, characterized in that after the target material has been added, the PVD target is planarized.

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