DE29823900U1 - Device for plasma-supported layer deposition - Google Patents

Description

by Ardenne Anlagentechnik GmbH 01324 Dresden

Device for plasma-assisted layer deposition

The invention relates to a magnetron sputtering device for large-area, reactive plasma-assisted deposition of mainly electrically insulating layers on substrates according to the preamble of claim 1.

The substrates to be coated can consist of a wide variety of base materials and have a wide variety of geometric shapes. In practice, however, the substrates that are considered are mainly metallic strips or flat glass panes.

Magnetron sputtering sources are used both for the deposition of dielectric layer systems, for example for the production of heat-reflecting glass panes for windows, and for the large-area coating of metallic strips with light-absorbing layers for the production of solar absorbers. This makes it possible to deposit layers that are homogeneous in terms of the properties and uniform in layer thickness, even on large surfaces, to the required extent.

In known processes for coating substrates using sputtering technology and materials that form insulating layers, there is the problem that in addition to the substrate, parts of the device itself are also coated with these electrically non-conductive or poorly conductive materials, which makes the process unstable and causes electrical arcing.

appear.

Furthermore, the increase in productivity of such coating systems, which is desirable from an economic point of view, is limited by the high coating speed required for each individual magnetron. The usual solution is to increase the number of magnetrons used to deposit a single layer or to increase the electrical power converted per magnetron. In practice, there are relatively strict limits to both measures.

The number of magnetrons is determined by geometric dimensions and the maximum applicable power per target surface unit is determined by material characteristics and the cooling options of the target. The desired increase in productivity of the system can therefore only be achieved if the specific properties of the individual layers, each of which is tied to a certain layer thickness, can be achieved even with lower layer thicknesses.

This is often possible if the layers are adjusted in their structure and density to the values of the respective compact material. One way to do this is to deposit the layers with the help of a dense plasma close to the substrate.

The positive effects of plasma, such as the increase in the refractive index from 2.35 to 2.55 in the TiO ₂ layers frequently used in optical coatings, have already been described (Zöllner: Plasma-assisted vapor deposition opens up new perspectives in spectacle and precision optics, Vacuum in Research and Practice 1997, No. 1, 19 - 24).

The reason for this is a change in the lattice structure from anatase to rutile even at low coating temperatures.
Analogously, it could be shown that the refractive index of SiO ₂ drops from 1.48 to 1.46 due to a denser structure (Szyzbowski, Bräuer, Teschner, Zmelty: Large Scale Antire-

(2006) 233-237.

It was also found that increasing the layer density leads to increased electrical conductivity, e.g. in silver coatings. Since the emissivity of metallic layers also increases with the layer resistance, it is possible to achieve the same reflection properties with thinner silver layers and at the same time improve the optical transmission.

Often, the magnetron discharge is not primarily used for sputtering target material, but serves as a plasma source. This is always the case when an almost complete coverage of the target with reaction products is required.

Usually, the sputtering rate of the reaction products is lower than that of the corresponding target material. As the proportion of reactive gas increases, the sputtering rate of the target material decreases and the power fed into the magnetron is increasingly converted into the plasma. In this case of magnetron-assisted plasma CVD, an important factor that determines the deposition rate is the plasma density in the immediate vicinity of the substrate. This is linked to the density of radicals and other high-energy species that are responsible for the layer deposition.

In both cases, both in the conventional reactive sputtering process and in magnetron-assisted plasma CVD, an increase in the plasma density in the immediate vicinity of the substrate leads to an increase in the coating productivity due to improved layer properties or a higher specific layer deposition rate.

There are a number of methods to increase the plasma density even at larger distances from the target to the substrate. One group of methods uses additional plasma sources in addition to the magnetron itself (hollow cathode assisted

Sputtering technology, hot cathode-assisted sputtering technology, additional microwave discharge). All of these methods have the fundamental disadvantage of high equipment costs and the associated low reliability of the setup and long-term stability of the processes.

Another method is to construct magnetrons operated with direct current in a magnetically unbalanced manner (Window, Surf.Coat. Technol. 71 81995) 93, DE 40 17 112).

This results in a significant increase in plasma density even at distances of a few tens of cm from the target, without requiring any significant additional equipment. The disadvantage here is, however, that in the reactive deposition of insulating layers, the electrodes (anode) required to maintain the discharge are also insulated during the deposition process, which makes the discharge unstable and eventually extinguishes. For this reason, this method has so far been used mainly for the deposition of metal layers or metallically conductive connecting layers (D.G. Teer, Surf. Coat. Technol. 39 (1989) 565; W. D. Münz, D. Schulze, F. J. M. Hauzer, Surf. Coat. Technol. 50 (1992) 169).

One way of avoiding the disadvantage of the unstable anode processes that occur during reactive sputtering with the DC-operated magnetron and of depositing dielectric oxide layers with long-term stability, without frequent electrical arcing and the resulting process disturbances, is described in both DD 252 205 and EP 0 502 242. This arrangement consists of two magnetrons lying parallel to one another and essentially on the same plane, the double magnetron or twin magnetron. The two individual magnetrons are connected to the output transformer of a power supply unit that supplies a voltage that changes sign at frequencies in the range between 20 ... 100 kHz.

This ensures that one magnetron acts as the anode of the second one during one voltage polarity; however, after reversal of polarity it sputters itself and thus a clean target surface is available as an anode after a further reversal of polarity.

By selecting the appropriate frequency, the formation of the insulating layer on the respective target occurs more slowly than the polarity reversal, thus providing a stable anode process.

In the frequency range up to approximately 1 MHz, the ions of the discharge plasma can still follow the changing electric field. This leads to a slight increase in the plasma density, or an expansion of the area of the dense plasma away from the target and to improved adhesion conditions of the layers on the substrates.

The decisive advantage of such devices is the long-term stability of the processes in reactive sputtering for the deposition of insulating layers. The required significant increase in plasma density at distant substrates, and thus the significant effect on the properties of the layer being formed, as well as the increase in density of radicals 5 and energetic species in the vicinity of the substrate in magnetron-assisted CVD processes, is only partially achieved.

The object of the invention is to provide a double magnetron sputtering device which generates a high plasma density in the vicinity of the substrate without high technical expenditure, in particular in reactive sputtering processes in which the resulting layer is itself insulating or poorly conductive, and which at the same time operates stably over long periods of time.

The task is solved in a double magnetron sputtering device of the type mentioned above, which is fed with medium frequency voltage, in that in each of the individual magnetrons forming the double magnetron, the respective magnetrons in the plane of the

Targets measured magnetic field strength of the inner magnetic pole is lower than that of the outer magnetic pole.

This makes it possible to achieve a high plasma density close to the substrate with little effort and with high long-term stability.

In a continuation of the invention, the different field strengths of the magnetic poles can be achieved by the outer magnetic pole being essentially made of hard magnetic material, the inner magnetic pole being essentially made of material with a high permeability and being composed in the same way as the back plate.

SmCo or NdFeB is preferably used as the hard magnetic material and St 3 7 is preferably used as the material with the high permeability, so that a particularly cost-effective implementation of the invention is possible.

To prevent parasitic discharges outside the outer magnetic poles, aluminum sheets are arranged next to them.

An embodiment of the invention is shown in the drawings and is described in more detail below.

The accompanying drawing shows a schematic cross-section through a device according to the invention. Two devices of the same design, each consisting of outer magnetic poles 2 and inner magnetic poles 3, mounted on back plates 6 and target plates 5, are mounted on insulating spacers 4 on a carrier plate made of stainless steel 1.

The target itself is made of chrome. The outer magnetic poles 2 are each made up of a layer of cuboid-shaped permanent magnets made of NdFeB with a cross-section of 10x10 mm ² and an overlying pole shoe made of St 37 with a cross-section of 10x5 mm ² .

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The inner magnetic poles 3, on the other hand, consist exclusively of a piece of cuboid-shaped steel St37 with a cross-section of 10x15 mm ² .

The outer magnetic poles 2 are arranged in such a way that a tunnel-shaped, closed magnetic field ring is generated around the inner magnetic pole 3. In the example, the north pole of the magnets of the outer magnetic poles 2 is arranged on the side facing the target 5 above.
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To prevent parasitic discharges outside the outer magnetic poles 2, aluminum sheets 7 with a thickness of approximately 3 mm are provided.

Another cuboid-shaped rod made of permeable material 8 is inserted between the two individual magnetrons to magnetically shield them from each other.

The two individual magnetrons are now connected to a medium frequency power supply (not shown). After creating the ambient conditions normally required for operating a magnetron sputter source, generating a low gas pressure in a closed chamber surrounding the source, and introducing a gas mixture typical for the process, the discharge is ignited and the sputtering process is thereby initiated.

At a typical gas pressure of approximately 5*10' ² mbar in an Ar/CH ₄ gas mixture, Me:CH layers are deposited by a magnetron-assisted plasma CVD process on a substrate 9, which is arranged at a distance of 100 mm from the target and is electrically at a negative DC potential of approximately -150 V. Even with a required low metal content in the layer of 15 at.% Cr, it is sufficient to conduct the process with long-term stability over several hours with constant stoichiometry of the layer, without disturbing changes in the target coverage and the associated instabilities and arc discharges at a high layer deposition rate.

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At the same time, an ion current density of 2 mA/cm ² can be set on the substrate, which leads to the formation of a hard and compact layer.

Claims (4)

1. Double magnetron sputtering device fed with medium frequency voltage, consisting of two individual magnetrons lying essentially parallel to one another in a plane with the same magnetic field direction, each comprising an inner magnetic pole 3 , an outer magnetic pole 2 with a polarity which is opposite to that of the inner magnetic pole 3 and which is arranged and designed such that it encloses the inner magnetic pole 3 , a target 5 which is arranged at least above the inner magnetic pole 3 and extends from there in the plane and in the direction of the outer magnetic pole 2 , both magnetic poles 2 , 3 fixed on a back plate 6 made of permeable material, characterized in that in each of the individual magnetrons forming the double magnetron, the magnetic field strength of the inner magnetic pole 3 , measured in the plane of the target, is lower than that of the outer magnetic pole 2 . 2. A medium frequency voltage powered double magnetron sputtering device according to claim 1, characterized in that the outer magnetic pole 2 is composed essentially of hard magnetic material, the inner magnetic pole 3 is composed essentially of material with a high permeability and in the same way as the back plate 6 . 3. A medium frequency voltage powered double magnetron sputtering device according to claim 1 and 2, characterized in that the hard magnetic material is SmCo or NdFeß and the material with the high permeability is St 37 . 4. Double magnetron sputtering device fed with medium frequency voltage according to one of claims 1 to 3, characterized in that outside the outer magnetic poles 2 , next to these, sheets 7 made of aluminum are arranged.