Cooling device and cooling method for sputtering targets

Abstract

Cooling device for at least one sputtering target (1) comprising a material having a specific thermal conductivity of 1.4 W / mK or less at 20°C, comprising a target carrier (3) and a heat sink (2), at which a sputtering target (1) is held on the target carrier (3) and at least one heat pump (4) is arranged between the target carrier (3) and the heat sink (2), which heat pump comprises at least one Peltier element with ceramic discs, the outer surfaces of the ceramic discs being metallized and these outer metal surfaces being electrically insulated from the internal circuitry of the Peltier element, so that by means of the heat pump (4) the target carrier (3) and also the sputtering target (1), on the target underside (1-2) of which can be cooled to a temperature which is lower than the temperature of the heat sink (2).

Description

The invention relates to a cooling device and a cooling method for sputtering targets.During sputtering, which is frequently also referred to as cathode sputtering, atoms are released from a solid body referred to as target or sputtering target by bombardment with high-energy particles. As a rule, this process takes place in a vacuum container in order to carry out coating processes with these atoms or clusters of atoms dissolved out of the sputtering target.This method is based on the following mechanism, thus the sputtering mechanism: Bombarding particles directed onto the target, which usually comprise noble gas atoms or ions, transmit their impulse to atoms of the target which trigger further collisions within the target in a collision cascade. After multiple collisions, a portion of the target atoms have a pulse pointing out of the target and leave the target.The thickness of the target which is ablated per unit time during the sputtering is also referred to as the sputtering rate and depends, among other things, on the kinetic energy of the bombarding atoms. The kinetic energy of the bombarding atoms is typically in each case more than 300 eV and the kinetic energy of the atoms leaving the target and thus referred to as sputtered atoms is typically less than 10 eV, with the excess energy of the bombarding particles remaining in the target.Conductive and non-conductive target materials may be sputtered.In DC sputtering, a DC voltage of several hundred volts is present at the target relative to a reference anode. The bombarding atoms are charged ions and receive their energy substantially by acceleration in this electric field generated by the DC voltage. However, DC sputtering presupposes electrically conductive sputtering materials so that charges can flow away from the target.In RF sputtering, high-frequency alternating electric fields accelerate electrons in a plasma close to the target. These ionize atoms of a process gas. If electrons reach the electrically non-conductive target, the surface of the target is charged negatively, since the electrical charges cannot flow away. The positively charged noble gas ions are again accelerated in the direction of the target by the negative surface charge, as a result of which the above-described process of knocking out atoms from the solid composite of the target likewise takes place.RF, ion beam and atomic beam (neutral atom) sputtering are generally suitable for electrically non-conductive sputtering materials.Non-conductive coatings, which can comprise a large number of oxides or nitrides, for example, can also be produced by reactive sputtering. A target is thereby atomized, wherein the sputtering atoms then react with a separately supplied process gas.However, approximately 80-90% of the bombardment energy introduced into the target must be removed from the target again with an active cooling which is often expensive, in order to avoid its destruction or overheating.Efficient sputtering requires high flux densities of the bombarding particles: a sputtering rate of 1 μm / min, for example, requires an ion current density of the order of 0.005 A / cm 2. If an energy per ion is obtained of, for example. 400 eV is deposited in the target, then the target is applied with a surface heating density of the order of magnitude 2 W / cm 2 in this case. A target measuring 40 cm through, homogeneously irradiated would thus be heated at more than 2.5 kW, as a result of which it can melt.In addition to heating the target by bombarding ions, direct heating by the thermal radiation from the hot plasma can also play a considerable role. Therefore, as a rule, efficient measures for cooling the target are necessary or at least desirable.The heating power is often not a problem here, because even 5 kW can be discharged, for example, with water cooling at a heating up of about 50° C., with a throughput of about 25 cm 3 / s. On the other hand, transporting the heat from the target itself to the cooling medium may become difficult.JP S61-76 674A describes an apparatus for thin-film coating in which a thin layer is applied to a substrate by means of ion beam sputtering and the heat at the hot side of the substrate is dissipated by means of water cooling.DE 32 26 717 A1 describes a movable target in the form of a band or rod which moves in the bombarding particle beam in order to reduce the local thermal stress.However, plate-shaped or shell-shaped targets are usually connected flat to cooling bodies. DE 100 56 257 A1, DE 199 16 938 A1 and EP 0 614 997 A1 describe, by way of example, cooling bodies with cooling channels for cooling fluids. Cooling channels are arranged in the cooling body of DE 11 20 100 02010 T5 in such a way that the target is cooled in the currently irradiated region.EP 1 826 811 A1 describes cooling methods in which cooling media with a flow temperature are guided through meandering cooling channels well below room temperature to -100° C. As the cooling medium, gases, water, alcohols, hydrocarbons, fluorocarbons, and mixtures thereof are proposed. Preferably, water mixed with antifreeze agents or boiling protection agents, for example based on propylene glycol, is used.As a rule, the flow temperature of the cooling medium is room temperature, thus about 20° C., in order to avoid condensation and corrosion on the sputtering systems. It is hardly present in practice that the inlet temperature of the cooling liquid is significantly below room temperature or even below 0° C., because experience has shown that this leads to problems at the vacuum receiver.The run-off temperature is rarely above 100° C.It is technically simplest to cool with water-based cooling fluids in the temperature range from room temperature to the boiling temperature at normal pressure.The cooling devices, cooling bodies, cooling channels, cooling lines, connecting flanges, should be installed permanently for reducing the outlay or at least reusable for cost reasons.Targets should be exchangeable in real operation, since, due to the principle, consumption of the target materials is present and a corresponding exchange of target materials is advantageous. Releasable clamping devices for targets on the cooling devices can be used for this purpose. A good heat transfer from targets to cooling bodies is important in this case. DE 3148354 A1 describes, for example, a screw connection of the target to the cooling body with additional layers of good thermal conductivity in the form of pastes, metal powders and foils between the target and the cooling body. However, a problem in this case is frequently the thermal conduction in the sputtering target itself.The object of the invention is to improve the cooling of targets, in particular sputtering targets, which comprise materials of poor thermal conductivity or consist of materials of poor thermal conductivity.The object on which the invention is based is achieved by the subject matter of the independent claims 1 and 10, preferred and advantageous embodiments also being disclosed in the description and the drawings.The invention thus discloses a cooling device for at least one sputtering target, comprising a target carrier and a cooling body, in which a sputtering target is held on the target carrier and at least one heat pump is arranged between the target carrier and the cooling body, so that the target carrier and in particular also the sputtering target can be cooled by means of the heat pump to a temperature which is lower than the temperature of the cooling body.The invention further discloses a method for cooling at least one sputtering target, in which a sputtering target is held on a target carrier, and heat is extracted from the target carrier and the target by means of a heat sink, and in particular the target carrier and in particular also the sputtering target are cooled to a temperature which is lower than the temperature of the heat sink by means of a heat pump.In order to better understand the invention, this subject is initially outlined with reference to FIG. 2, which shows a vertical section through a target 1 and a cooling body 2 with cooling channels 2- 3 at least partially integrated therein.During sputtering, the heat arises in a thin layer on the target surface 1- 1 irradiated during sputtering or blasted with the particles, which is also referred to for short as the target top side, and is then usually discharged from the cooling body 2 on the surface 1- 2 facing away from the beam, which is also referred to as the target bottom side.The heat must flow through the target 1 if it is desired to cool it effectively, thereby creating a temperature gradient in the target 1 itself.With the heat pump mentioned above, it is now possible to cool the temperature of the target carrier even more strongly than with the cooling body alone. In particular, it is possible in this case, for example before the start of the sputtering, to cool the target carrier and in particular also the sputtering target to a temperature which is lower than the temperature of the heat sink.The at least one heat pump advantageously comprises or consists of a Peltier element. Preferably, the outer surfaces of the Peltier elements are metallized.In a preferred embodiment, the cooling device comprises segmented sputtering targets, which are preferably held on the target carrier in the manner of tiles or tiles.If the target carrier or carriers comprise or consist of metals with good thermal conductivity, in particular aluminum, Al, or copper, Cu, this not only results in better heat dissipation but also results in a more homogeneous heat distribution within the sputtering target and temperature-induced stresses within the sputtering target are mitigated.In a further embodiment, the cooling device comprises segmented heat pumps, in particular tile-shaped Peltier elements. In this case, the tile-shaped Peltier elements can be controlled individually or in groups in a defined manner.In a preferred embodiment, the sputtering target comprises a glass, in particular a glass containing SiO 2- and having a low thermal expansion. In a further embodiment, the sputtering target comprises a chalcogenide glass, in particular a chalcogenide glass IRG26 from Schott AG. In a further refinement, the sputtering targets can each comprise a different sputtering material or consist of this.In the method for cooling a sputtering target, the temperature of the sputtering target can be lowered compared to the temperature of the target carrier particularly advantageously even before the start of the sputtering, so that during the subsequent sputtering the temperature of the sputtering target then rises more slowly compared to a target carrier without a heat pump attached thereto and as a result generally sputtering processes lasting longer are also made possible.In this case, the lead time during which the sputtering target is cooled relative to the target carrier before the start of the sputtering can be up to 5 hours. In the exemplary embodiments of FIGS. 7 and 10, no significant further cooling of the sputtering target occurs starting from approximately three hours of lead time.Advantageously, however, heat can also be removed from the target by means of the heat pump during sputtering.In one embodiment disclosed herein, the target material comprises SiO 2- containing glass and heat is applied to the target top during sputtering. In another embodiment disclosed herein, the target material comprises chalcogenide glass and heat is applied to the target top during sputtering.In general, with the method disclosed herein and the device disclosed herein, coating processes can be carried out more effectively by means of sputtering than with devices and methods which do not have the heat pumps disclosed herein.In the methods disclosed herein, the sputtering can be carried out, for example, by means of DC, RF, magnetron, bias or atomic beam sputtering.The invention will be described in more detail below with reference to preferred embodiments and with reference to the accompanying drawings. The following are shown: FIG. 1 shows a vertical section through a cooling device according to the invention for a sputtering target, having a target 1, which is held on a target holder 3, and a cooling body 2 having cooling channels 2- 3 integrated therein at least partially, in which a heat pump 4 is arranged between the cooling body 2 and the target holder 4; FIG. 2 shows a vertical section through a conventional cooling device for a sputtering target having a target 1 and a cooling body 2 with cooling channels 2- 3 integrated therein at least partially; FIGS. 3 ato 3 c show electrical circuitry of the sputtering system and of the apparatus for cooling a sputtering target and in each case the circuitry of the heat pump comprising a Peltier element; FIG. 4 shows an exemplary embodiment of components of a cooling device for a sputtering target, in a three-dimensional view, shown partially in section, in which a circle sector has been shown in section from both the target, the target carrier, the heat pump and the cooling body and the target comprises a low-stretching SiO 2- containing glass, in this example quartz glass; FIG. 5 shows the development of temperature over time during sputtering in the sputtering target when the heat pump is inactive, thus inactive Peltier element or inactive Peltier cooler; FIG. 6 shows the development over time of temperature during sputtering in the sputtering target with an active heat pump, thus an active Peltier element or an active Peltier cooler; FIG. 7 shows the development over time of temperature in the sputtering target with an active heat pump, thus an active Peltier element or an active Peltier cooler, which was activated with a temporal lead before the sputtering process; FIG. 8 shows a further exemplary embodiment of components of a cooling device for a sputtering target, in a three-dimensional view, shown partially in section, in which a circle sector has been shown in section from both the target, the target carrier, the heat pump and the cooling body, and the target comprises a chalcogenide glass, in this example the chalcogenide glass IRG26 from Schott AG; FIG. 9 shows the development of temperature over time without an active heat pump, thus without an active Peltier element or without an active Peltier cooler on the bottom side and top side of the sputtering target shown in FIG. 8 for a heating density of 0.26 W / cm 2; FIG. 10 shows the development over time of temperature with an active heat pump, thus with an active Peltier element or with an active Peltier cooler at the bottom and top side of the sputtering target shown in FIG. 8 for a heating density of 0.26 W / cm 2; FIG. 11 shows a still further exemplary embodiment of components of a cooling device for a sputtering target, in a three-dimensional view, which is shown partly in section, in which a circle sector has been shown cut out both from the target, the target carrier, the heat pump and the cooling body, and the target comprises a chalcogenide glass, in this example the chalcogenide glass IRG26 from Schott AG, and in which the heat pump and thus the Peltier element or the Peltier cooler are configured in two stages; FIG. 12 shows the development over time of temperature with an active heat pump, thus with an active Peltier element or with an active Peltier cooler at the bottom and top side of the sputtering target shown in FIG. 11 for a heating density of 0.26 W / cm 2, in the exemplary embodiment shown in FIG. 11, in which the heat pump and thus the Peltier element or the Peltier cooler are designed in two stages; FIGS. 13 and 14 show further exemplary embodiments of components of the cooling device for at least one sputtering target; FIG. 14 shows an embodiment in which a plurality of sputtering targets 1 are held on a target carrier 3.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTSIn the following detailed description of preferred embodiments, not all components are shown to scale for clarity. In the figures, however, like reference numerals designate like constituent parts or assemblies, respectively.However, first, for a better understanding, the temperature conditions prevailing in the sputtering target before and during the sputtering will be discussed.If, for the sake of brevity, reference is made below not to a sputtering target but only to a target, this is nevertheless intended to disclose the term sputtering target in each case. Thus, in the context of the present disclosure, the terms sputtering target and target are used throughout the same subject matter.The temperature increase ΔT T of the temperature T T,o of the target top side 1- 1 relative to the temperature T T.u of the target bottom side 1- 2 during sputtering by a heating density j th at the target top side 1- 1 can be estimated on the basis of a thermal resistance d T / κ T, wherein d T represents the thickness of the target and κ T denotes the thermal conductivity of the target, as follows: wherein the thermal conductivity κ T is assumed to be temperature-independent.For a given heating density j th and a target thickness d T the temperature increase or temperature swing ΔT T also depends on the thermal conductivity of the target material.For a first example with j th= 2 W / cm 2, d T= 1 cm and metallic targets with κ T >20 W / mK, for example, ΔT follows T< 10 ° C.Metals usually yield even heating densities of more than 5 W / cm 2. without problems.For ceramic targets with κ T< 2 W / mK, however, ΔT T>100° C. is obtained at j th= 2 W / cm 2, d T= 1 cm, which is often unacceptable since thermal deformations of the target can then possibly interrupt the thermal contact with the cooling body or thermo-mechanical stresses can trigger brittle fractures in the target.Alternatively, to avoid such disadvantages, a maximum temperature increase or thus a maximum temperature swing ΔT T,max is frequently preset and a maximum heat flux density is then calculated therefromAn estimate for ΔT T,max is based on permissible thermo-mechanical deformations and takes into account the thermal expansion coefficient α T and the elastic modulus E T of the target material:For low-stretching SiO 2- glass withIf, for example, a ΔT T,max= 390 ° C. is permissible and the value j th< 6 W / cm 2. results from this.However, for other glass systems, these values may look significantly different. For the chalcogenide glass IRG26, see for example its data sheet "Infrared Chalcogenide Glass IRG 26" from Schott AG in Mainz, for example, α≈21·10 -6 K -1, E T≈18GPa, and κ T≈0.24W / mK (at 20° C.) followsHowever, still further restrictions must be taken into account, in particular in the case of glasses, a maximum temperature, since glasses tend to vaporises at high temperature, which can disturb the stoichiometry of the sputter particles, tend to chip and nodulene formation on the surface or simply to melt.For chalcogenide glass IRG26 with T G ≈ 185° C., the surface temperature should also remain safely below 135° C. for these reasons.A better estimate of the permissible heating power for 1 cm thick e.g. IRG26 targets is therefore obtained as follows:For a target bottom at room temperature, T T,u= 20 °C, the allowable heating density at the target top is 0.35W / cm 2. The low sputtering efficiency resulting therefrom reduces the economic efficiency: sputtering rates of more than 0.5 μm / min can hardly be achieved.Equation 3 given above also applies to other sputtering materials with respectively adapted material data.For better understanding, the following secondary calculation is carried out: (1) Approach using the example of aluminum with ρ≈2.7 g / cm3, atomic weight 27, i.e. an atomic density of: Also for silver, Ag, with ρ≈10.5 g / cm3, atomic weight 108, n≈6·1022cm-3(aluminum and silver have relatively small atomic radii). For SiO 2- glass (3 atoms): ρ≈2.2 g / cm3, average atomic weight (28+2·16) / 3=20, n≈6.6·1022cm-3; for IRG26 (As2Se3=5 atoms): ρ≈4.3 g / cm3, average atomic weight (2·75+3·79) / 5≈77.4 is n≈3.6·1022cm -3. For this reason, for the estimates disclosed here, an atomic density in the sputtering target of n≈4·1022atoms / cm 3 is initially assumed for the sake of simplification. (2) It is assumed that electrons do not contribute to sputtering. The ions are assumed to be singly charged and, for each ion, ηA / I sputter atoms are to be emitted on average. In order to "sputter off" a layer with the thickness d or to achieve the sputtering rate ω̅, this requires the electrical current density of: (3) It is assumed that at least φin=300V is required. The irradiation power density results from this in: (4) Of the impact energy introduced into the sputtering target during sputtering, a fraction flows as kinetic energy of the emitted atoms:The resulting (thermal) impingement of the target surface is thereforeThe following magnitude estimation is performed:ω̅=1μm / min=117·10-7cm / s, ηA / I=4, n=4·1022cm-3, resulting in an ion current density of 0.0027A / cm2.It is assumed that φin=1200 V is the lower limit for the impact energy; irradiation power density pin=0.54 W / cm2.With assumed φem=7.5V, the heating density of the target surface is then: p=0.46 W / cm2.For the present calculations, a heating density of the target surface of 0.5 W / cm2is thus assumed at a sputtering rate of 1 μm / min.The approach of "thin targets", thus the use of a target with a smaller thickness and consequently a smaller d T with lower thermal resistance, could be considered interesting based on the above considerations. However, this reduces the process efficiency markedly because of the replacement cycles which are then frequently necessary and is therefore not advantageous.In order to achieve large sputter particle currents, the irradiated target areas can be enlarged. In practice, however, this leads to space problems in the recipient, in particular when different targets are to be used for a predetermined layer sequence.For economic reasons, opening recipients for target changes is hardly possible because of the increased process time, in particular also because of the necessary pumping back of the recipient.In contrast to these two approaches described above and which are rather disadvantageous, however, a target carrier 3 of a heat pump 4 can advantageously be inserted between the sputtering target 1, see for example FIG. 1 in this respect, and the cooling body 2. The heat pump then cools the target carrier 3 and the target underside 1- 2 below the temperature of the cooling body 2.For the sake of simplicity, FIG. 1 schematically outlines plate-shaped or shell-shaped structures, but the technical solution proposed in the present case also applies analogously to more complicated structures. Where individual components are referred to for convenience in language in the present disclosure, it is contemplated that they may be or include multiples.The target 1 and the heat pump 4 are located on opposite surfaces of the target carrier. In the simplest embodiment, the target carrier 3 is a single-contiguous shell of homogeneous thickness, which completely covers the target 1 laterally. The target carriers 3 should generally allow the target to be tensioned with little effort in terms of fixing and detachment and be sufficiently soft to be able to conform to the target 1 in order to reduce the thermal resistance. Corresponding methods and devices for clamping are known to a person skilled in the art.Furthermore, in those cases in which target 1 and heat pump 4 are arranged laterally offset or a plurality of target tiles or heat pump tiles are used, as is illustrated for example in FIG. 15, target carriers 3 are intended to bring about a lateral heat compensation. The heat should be able to flow away from the respective target 1 or the respective target tile as homogeneously as possible.A homogeneous temperature distribution in the target carrier 3, i.e. the highest possible thermal conductivity of the carrier 3, is favorable here. copper with a thermal conductivity of approximately 400 W / mK) and aluminum with a thermal conductivity of approximately 200 W / mK) are well-suited materials for this purpose.The target carriers 3 should also be electrically conductive for some embodiments. It is generally advantageous if the target carrier 3 is thin in order to be able to adapt to the target 1 with low bending moments in the case of thermal warping.In this case, target carriers 3 made of copper often prove to be somewhat more favorable than made of aluminum, despite the higher modulus of elasticity, with a modulus of elasticity of 110 instead of 70 GPa, because thinner shells with lower bending stiffness are possible because of the higher thermal conductivity.Thus, for the target carriers 3, shells of copper and aluminum are preferred, wherein in the case of copper a thickness of about 1 mm and in the case of Al a thickness of 2 mm is usually already sufficient for the thermal compensation in order to achieve a sufficiently high thermal conductivity and a usable stiffness. These aforementioned thicknesses and are considered "thin" in the sense of the present disclosure.All components should be in good thermal contact. The target 1 is therefore bonded to the target carrier 3 with a thin layer of heat-conducting paste in one embodiment.Vacuum-suitable, temperature-resistant and electrically conductive heat-conducting pastes are known to the person skilled in the art in this technical field.For corresponding heat-conducting paste compounds, negligible heat resistances dP / κP<10-3K / (W / cm2) are achieved.The target carrier 3 is connected with good thermal contact with the heat pump or heat pump unit 4. In one embodiment, it is a permanent connection, i.e. the target carrier 1 is a permanent component of a target table installed in a sputtering installation. Since both sputtering systems and target tables are known to the skilled person, these are not shown again in the figures. In this case, the target carrier can be permanently electrically contacted.In another embodiment, the target carrier 3 is permanently connected to the sputtering target 1 and forms a commonly replaceable unit therewith. The sputtering target 1 can then also be non-detachably connected to the target carrier 3.Many methods are known for this purpose, for example soldering. The clamping of the (metallic) target carrier onto the heat pump unit is assumed to be known; a heat-conducting paste can likewise be used here to improve the thermal coupling.Heat pumps can be realized by Peltier coolers. The mode of operation of Peltier coolers or Peltier elements is known to the person skilled in the art responsible in the present case and is therefore not explained in more detail. Inexpensive standard designs consist of parallel, usually square, thin, highly thermally conductive, electrically insulating ceramic disks having an edge length of 2 to 10 cm at a distance of 3 to 6 mm, between which semiconductor rods are soldered.Typical semiconductors here are Bi 2 Te 3 and PbO. The temperature stroke can be more than 70 K in the case of single-stage Peltier coolers and more than 110 K in the case of multistage Peltier coolers or Peltier elements, with thermal pump powers of more than 1 W / cm 2. Peltier coolers are operated with direct current with rated voltages in the 10V range and operating currents in the 10A range. The ohmic losses in a Peltier cooler can be more than 100 W and must be taken into account accordingly in the design of the respective cooling system.The outer surfaces of the ceramic disks can be metallized (galvanically) in order to facilitate soldering to other components, for example. These outer metal surfaces are electrically insulated from the inner circuitry of the Peltier coolers. The provision of Peltier coolers is not the subject matter of the present disclosure; since often commercially available designs may already be sufficient for the purposes of the invention.The further exemplary description of the invention, however, proceeds from disk-shaped Peltier coolers with electrically insulating ceramic disks. However, it is clear to the person skilled in the art how other embodiments can also be used-these are therefore considered to be included in the present disclosure.In the case of HC and DC sputtering, the problem arises that an incompatible electrical circuit is introduced into the "high-voltage circuit" with the Peltier cooler.FIGS. 3 ato 3 c show corresponding electrical circuits of the sputtering system and of the device for cooling a sputtering target and in each case the circuit of the heat pump comprising a Peltier element,In the case of DC sputtering, it is advantageous, for example, to also use the electrically insulating ceramic films of the Peltier coolers for separating the circuits; this means that in this case the target carrier 1 can be connected to the high-voltage circuit. The cooling body 2 can be grounded with the advantage of a higher electrical safety, because the cooling liquid circuit is then generally free of stress.In principle, the method can be the same for RF sputtering. Here, however, it can be advantageous to prevent interference of the alternating field by DC couplings, for example by a series capacitor C 1, and to prevent interference of the DC supply circuit for the Peltier cooler, for example by a capacitor C 2 parallel to the Peltier cooler. It is also possible to introduce the AC voltage into the heat sink 2 itself during RF sputtering if the DC Peltier circuit is short-circuited with a capacitor C 2 for AC voltages.However, maximum powers should not be assumed in the design of Peltier coolers.A thermal pump line of 1 W / cm 2 at a temperature difference of 60 K has proven to be advantageous for single-stage Peltier coolers. If higher pump powers or greater temperature differences are sought, multistage Peltier coolers should be used. A thermal pump line of 2 W / cm 2 at a temperature difference of 90 K is realistic for two-stage Peltier coolers.Further exemplary embodiments are described below.FIG. 4 shows an exemplary embodiment in which a round-disk-shaped body with a cut-out sector is shown in a perspective view. A round blank 5 of silica glass measuring 400 mm and 10 mm thick and having a thermal conductivity of 1.4 W / mK is joined as sputtering target 1 to a target carrier 3 of aluminum 2 mm thick.For protecting the glass edges, the target carrier 3 is each oversized. The target carrier 3 is clamped on a cold surface 7 of an annular Peltier cooler 6 with an inner radius of 20 mm, an outer radius of 180 mm and a thickness of 6 mm. The Peltier cooler 6 is mounted with the hot surface directly on an annular cooling body 2 with an inner radius of 10 mm, an outer radius of 190 mm and a thickness of 12 mm made of copper or aluminum. In the cooling body 2 are cooling channels 7 which extend through 6 mm, of which only one cooling channel is provided with a reference sign for the sake of clarity. The 20 mm through hole in the target carrier 3 allows sensors, for example to be provided. The thickness and / or temperature measurement can be carried out to monitor the sputtering target 1.FIG. 5 first shows, as a reference, the temperature development with the Peltier cooler 6 switched off on the underside 1- 2 and on the upper side 1- 1 of the sputtering target 1 embodied as a glass blank 5 for a heating density at the upper side 1- 1 of the sputtering target of 2.5 W / cm2. The logarithmically divided time axis has the time unit of minutes. The starting temperature is 20° C. The process is set to a constant sputtering rate of 3 μm / min; the temperature of the sputtering target 1 should remain below 210° C. during sputtering. The temperature at the target top 1-1 reaches 206° C. after approximately 15 min and then falls down again because the thermal resistance of the target 1 decreases again as a result of material removal. The target underside 1- 2 heats up to approximately 27° C. despite intensive cooling because of the thermal resistance of the cooling body 2 and Peltier cooler 6.FIG. 6 shows the temperature development with the Peltier cooler 6 on the underside 1- 2 and the upper side 1- 1 of the sputtering target 1 configured as a glass blank 5 for a heating density at the upper side 1- 1 of 3.5 W / cm2. The process is set here to a constant sputtering rate of 4.5 μm / min.The temperature at the target top 1-1 reaches 205° C. after about 15 min and then falls off more quickly because of the greater material removal.The underside 1-2 of the sputtering target 1 falls in the quasi-stationary region to approximately -38° C. By cooling by means of the Peltier elements 6, the sputtering rate can be increased by approximately 50%.When the sputtering target 1 starts to irradiate room temperature, an additional temperature swing often arises at the target top side 1- 1, which disappears when a quasi-stationary region is reached. Preferably, therefore, the irradiation of the sputtering process only starts when the target 1 has already been cooled.FIG. 7 shows an advantageous temperature development on the target underside 1- 2 and on the target upper side 1- 1 for a heating density on the upper side 1- 1 of 3.5 W / cm2.FIG. 8 shows a further exemplary embodiment. A round blank 5 measuring 400 mm and 10 mm thick and made of the chalcogenide glass IRG26 already mentioned above and having a thermal conductivity at room temperature of 0.26 W / mK forms the sputtering target 1 and is joined to a target carrier 3 made of copper and having a thickness of 2 mm. A mounting plate 8 made of copper and having a thickness of 4 mm is joined onto a single-stage Peltier cooler 6, and the target carrier 3 is clamped onto the mounting plate 8. Target carrier 3 and mounting plate 8 preferably consist of "similar base metals" in order to prevent electrocorrosion-Cu / Al pairings should be avoided in this case, however. The Peltier cooler 6 is soldered onto an annular cooling body 2 made of copper.FIG. 9 shows the development of temperature over time without Peltier cooling on the underside 1- 2 and on the upper side 1- 1 for a heating density of 0.26 W / cm2.The sputtering process is set to a constant sputtering rate of 0.3 μm / min; the temperature of the target should remain below 135° C. during the entire sputtering process.The temperature at the target top 1-1 reaches 133° C. and falls again by material removal during the sputtering process.FIG. 10 shows the development of temperature over time with Peltier cooling for a heating density of 0.42 W / cm2or a sputtering rate of 0.5 gm / min: the sputtering rate can already be increased by more than 50% by a single-stage Peltier cooling.FIG. 11 shows a yet further exemplary embodiment in which a round plate 5 of chalcogenide glass IRG26, which extends through 400 mm and extends through the sputtering target 1 and is 10 mm thick, is mounted on a target carrier 3 consisting of copper and having a thickness of 2 mm. The target carrier 3 is clamped to a mounting plate 8 which is 4 mm thick and likewise made of copper and with the latter to a two-stage Peltier cooler 6. The Peltier cooler 6 is soldered onto the cooling body 2.FIG. 12 shows, for this yet further embodiment, the development of temperature over time without Peltier cooling on the underside 1- 2 and on the upper side 1- 1 for a heating density of 0.53 W / cm2and a sputtering rate of 0.62 μm / min: the sputtering rate can be increased by more than 65% by means of the two-stage Peltier cooling present here.FIGS. 13 and 14 show further exemplary embodiments of components of the cooling device for at least one sputtering target 1, wherein an annular clamping device 9 can be seen, by means of which the target carrier 3 and the target 1 fastened to it are held on the cooling body 2.Fig. 14 shows an embodiment in which a plurality of sputtering targets 1 are held on a target carrier 3.List of reference characters1 Sputtering target, also referred to as target for short, 1-1 upper target surface, which is also referred to as target upper side 1-2 target surface facing away from the beam, which is also referred to as target lower side 2 cooling body 2-3 cooling channels 3 target carrier 4 heat pump 5 round bottom 6 Peltier element or Peltier cooler 7 cooling channel 8 mounting plate 9 annular clamping device

Claims

Cooling device for at least one sputtering target (1) which has a material which has a specific thermal conductivity of 1.4 W / mK or less at 20°C, comprising a target carrier (3) and a cooling body (2), in which a sputtering target (1) is held on the target carrier (3) and at least one heat pump (4) is arranged between the target carrier (3) and the cooling body (2), said heat pump comprising at least one Peltier element with ceramic disks, wherein the outer surfaces of the ceramic disks are metallized and these outer metal surfaces are electrically insulated from the inner wiring of the Peltier element, such that the target carrier (3) and also the sputtering target (1), at the target underside (1-2) thereof, can be cooled to a temperature which is lower than the temperature of the cooling body (2) by means of the heat pump (4).Cooling device according to claim 1 comprising segmented sputtering targets (1) which are preferably held on the target carrier (3) in the manner of tiles or tiles.Cooling device according to claim 1 or 2, wherein the target carrier or carriers (3) comprise or consist of metals with good thermal conductivity, in particular aluminum, Al, or copper, Cu.A cooling device according to claim 2 or 3, wherein the outer surfaces of the Peltier elements (6) are metallized.Cooling device according to one of the preceding claims from 1 to 4, comprising segmented heat pumps (4), in particular tile-shaped Peltier elements (6).Cooling device according to Claim 5, in which the tile-shaped Peltier elements (6) can be controlled individually or in groups in a defined manner.Cooling device according to one of the preceding claims, in which the sputtering target (1) comprises a glass, in particular a glass containing SiO 2- .Cooling device according to one of the preceding claims 1 to 6, wherein the sputtering target (1) comprises a chalcogenide glass, in particular a chalcogenide glass IRG26.Cooling device according to one of the preceding claims 3 to 8, wherein the sputtering targets (1) each comprise or consist of a different sputtering material.Method for cooling at least one sputtering target (1) which has a material which has a specific thermal conductivity of 1.4 W / mK or less at 20°C, in which a sputtering target (1) is held on a target carrier (3) and heat is extracted from the target carrier (3) and the target by means of a heat sink (2), and the target carrier (3) and also the sputtering target (1) are cooled at its target underside (1-2) to a temperature which is lower than the temperature of the heat sink (2) by means of a heat pump (4), and in which the temperature of the sputtering target (1) is lowered compared with the temperature of the heat sink (2) before the start of the sputtering.Method according to claim 10, wherein the heat pump (4) comprises or consists of a Peltier element (6).Method according to Claim 10 or 11, in which the lead time during which the sputtering target (1) is cooled relative to the cooling body (2) before the start of the sputtering is at least three hours.Method according to one of claims 10 to 12, in which heat is extracted from the target by means of the heat pump (4) during sputtering.The method of any one of claims 10 to 13, wherein the target material comprises SiO 2- containing glass.Method according to any one of claims 10 to 14, wherein the target material comprises a chalcogenide glass, in particular IRG26.Method according to claim 14 or 15, in which heat is supplied to the target top side (1-1) during the sputtering.Method according to one of Claims 10 to 16, in which coating processes are carried out by means of the sputtering.The method according to any one of claims 10 to 17, wherein the sputtering is performed by DC, RF, magnetron, bias or atomic beam sputtering.

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