WO2023274558A1

WO2023274558A1 - Cooling device and cooling method for sputter targets

Info

Publication number: WO2023274558A1
Application number: PCT/EP2021/068374
Authority: WO
Inventors: Kurt Nattermann; Thorsten Damm; Giho Lee; James Marro; Kazuyuki Inoguchi
Original assignee: Schott Ag; Schott Corporation; Schott Japan Corporation
Priority date: 2021-07-02
Filing date: 2021-07-02
Publication date: 2023-01-05

Abstract

The invention relates to a method for cooling at least one sputter target (1), wherein a sputter target (1) is retained on a target carrier (3), heat is removed from the target carrier (3) and the target by means of a heat sink (2), and the target carrier (3) and in particular also the sputter target (1) are cooled in particular by a heat pump (4) to a temperature that is lower than the temperature of the heat sink (2). The invention also relates to a device for carrying out said method.

Description

Cooling device and method for cooling sputter targets

description

The invention relates to a cooling device and a cooling method for sputtering targets.

During sputtering, which is often also referred to as cathode sputtering, atoms are detached from a solid body, referred to as a target or sputtering target, by bombarding it with high-energy particles. As a rule, this process takes place in a vacuum recipient in order to carry out coating processes with these atoms or clusters of atoms that have been detached from the sputtering target.

This method is based on the following mechanism, i.e. sputtering mechanism: Bombarding particles directed at the target, which usually include noble gas atoms or ions, transfer their momentum to atoms of the target, which trigger further collisions within the target in a collision cascade . After several collisions, some of the target atoms have an out-of-target momentum and leave the target.

The thickness of the target that is removed per unit of time during sputtering is also referred to as the sputtering rate and depends, among other things, on the kinetic energy of the bombarding ions. The kinetic energy of the bombarding ions is typically more than 300eV each and the kinetic energy of the atoms leaving the target and thus referred to as sputtered atoms is typically less than 10eV, with the excess energy of the bombarding particles remaining in the target.

Conductive and non-conductive target materials can be sputtered.

In DC sputtering, a DC voltage of a few hundred volts relative to a reference anode is applied to the target. The bombarding ions are positive charged ions and essentially get their energy through acceleration in an electrical field generated by the DC voltage. However, DC sputtering requires electrically conductive sputtering materials so that charges can flow off the target.

In HF 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 becomes negatively charged because the electrical charges cannot flow away. The negative surface charge in turn accelerates the positively charged noble gas ions in the direction of the target, as a result of which the previously described process of knocking out atoms from the solid-state compound of the target also 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 include a variety of oxides or nitrides, for example, can also be produced by reactive sputtering.

A target is sputtered, with the sputtering atoms then reacting with a separately supplied process gas.

However, around 80-90% of the bombardment energy introduced into the target has to be dissipated from the target again using active cooling, which is often complex, in order to prevent it from being destroyed or overheated.

Efficient sputtering requires high flux densities of the bombarding particles: a sputtering rate of 1 pm/min, for example, requires an ion current density of the order of 0.005 A/cm ² . If an energy of, for example, 400eV is deposited in the target per ion, then the target is subjected to a surface heating density of the order of magnitude of 2W/cm ² . A 40cm diameter, homogeneously irradiated target would be heated up with more than 2.5kW, which could cause it to melt.

In addition to the heating of the target by bombarding ions, direct heating by thermal radiation from the hot plasma can also occur play a significant role. Efficient measures for cooling the target are therefore generally necessary or at least desirable.

The heating output is often not a problem, because even 5kW can be dissipated with water cooling, for example, with a heating of approx. 50°C with a throughput of approx. 25cm ³ /s. On the other hand, transporting the heat from the target itself to the cooling medium can be difficult.

DE 3226717 A1 describes a movable target in the form of a strip or rod that moves in the bombarding particle beam in order to reduce local thermal stress.

In most cases, however, plate- or bowl-shaped targets are connected to heat sinks over a large area. DE 10056257 A1, DE 19916938 A1 and EP 0614997 A1 describe, by way of example, heat sinks with cooling channels for coolants.

Cooling channels are arranged in the heat sink of DE 112010002010 T5 in such a way that the target is cooled in the area currently being irradiated.

EP 1826811 A1 describes cooling methods in which cooling media with a flow temperature well below room temperature down to -100° C. are guided through meandering cooling channels. Gases, water, alcohols, hydrocarbons, fluorocarbons and mixtures of these are proposed as the cooling medium. Water mixed with antifreeze or anti-boiling agents, e.g. based on propylene glycol, is preferably used.

As a rule, the flow temperature of the cooling medium is at room temperature, i.e. around 20°C, in order to avoid condensation and corrosion on the sputtering systems. In practice, it rarely happens that the inlet temperature of the coolant is significantly below room temperature or even below 0°C, because experience has shown that this leads to problems in the vacuum recipient.

The outlet temperature is rarely above 100°C.

It is technically easiest to cool with water-based coolants in the temperature range from room temperature to boiling point at normal pressure. The cooling devices, heat sinks, channels, lines, connection flanges should be permanently installed to reduce costs or at least be reusable for cost reasons.

Targets should be interchangeable in real operation, since the target materials are consumed as a matter of principle and a corresponding change of target materials is advantageous. For this purpose, detachable clamping devices for targets can be used on the cooling devices. Good heat transfer from targets to heat sinks is important. DE 3148354 A1, for example, describes screwing the target to the heat sink with additional, highly thermally conductive layers in the form of pastes, metal powders and metal foils between the target and the heat sink. However, the heat conduction in the sputtering target itself often poses a problem.

The object of the invention is to improve the cooling of targets, in particular of sputtering targets, which comprise poorly thermally conductive materials or consist of poorly thermally conductive materials.

The object on which the invention is based is achieved with the subject matter of independent claims 1 and 10, with 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 (3) and at least one heat pump (4), in which a sputtering target (1) is held on the target carrier (3) and the at least one heat pump (4) is at least one Peltier element includes.

The invention further relates to a cooling device for at least one sputtering target, comprising a target carrier, in which a sputtering target is held on the target carrier and at least one heat pump cools the target carrier and in particular the sputtering target to a temperature below 0°C, without using a cooling body with cooling channels . 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 by means of at least one heat pump (4) which comprises at least one Peltier element, the sputtering target (1) having a target underside (1-2). , and wherein the target underside (1-2) is preferably cooled to a temperature below 0°C before sputtering.

In order to better understand the invention, this situation is first outlined with reference to FIG. 2, which shows a vertical section through a target 1 and a heat sink 2 with cooling channels 2-3 at least partially integrated in the latter.

During sputtering, the heat is generated in a thin layer on the target surface 1-1 that is irradiated during sputtering or bombarded with the particles, which is also referred to as the upper side of the target for short, and is then generally distributed on the surface 1-2 that faces away from the beam, which is also known as the target surface Target underside is referred to, removed from the heat sink 2.

The heat must flow through the target 1 if you want to cool it down effectively, and this creates 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 than with the heat sink alone. In particular, it is possible here, for example before the start of the sputtering, to cool the target carrier and in particular also the sputtering target to a lower temperature.

The at least one heat pump advantageously includes or consists of a Peltier element. The outer surfaces of the Peltier elements are preferably metallized.

In a preferred embodiment, the cooling device comprises a monolithic target, which reduces the risk of particle formation.

According to alternative embodiments, the cooling device can also include segmented sputtering targets, which are preferably tiled or are held as tiles on the target carrier. Segmented sputtering targets can be helpful in keeping thermal stresses low when the temperature changes.

If the target carrier(s) comprise or consist of metals with good thermal conductivity, in particular aluminum, Al, or copper, Cu, this not only improves heat dissipation, but also the heat distribution within the sputtering target is more homogeneous and temperature-related stresses within the sputtering target are reduced.

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 in a defined manner individually or in groups.

In a preferred embodiment, the sputtering target comprises a glass, in particular a glass containing SiO 2 with low thermal expansion. In a further embodiment, the sputtering target comprises a chalcogenide glass, in particular a chalcogenide glass IRG26 from Schott AG with the composition As4oSe6o or a chalcogenide glass of the same or similar composition. In a further embodiment, the sputtering targets can each include or consist of a different sputtering material.

In the method for cooling a sputtering target, the temperature of the sputtering target compared to the temperature of the target carrier can be reduced particularly advantageously before the start of sputtering, so that the temperature of the sputtering target then rises more slowly during the subsequent sputtering compared to a target carrier without a heat pump attached to it and as a result usually longer lasting sputtering processes are made possible.

Here, the lead time during which the sputtering target is cooled relative to the target carrier before sputtering begins can be up to 5 hours. In the case of the exemplary embodiments in FIGS. 7 and 10, no significant further cooling of the sputtering target occurs after a lead time of approximately three hours. Advantageously, however, heat can also continue to be withdrawn from the target by means of the heat pump during the sputtering.

In one embodiment disclosed herein, the target material comprises SiO 2 -containing glass. In another embodiment disclosed herein, the target material comprises chalcogenide glass.

In general, with the presently disclosed method and the presently disclosed device, coating processes can be carried out more effectively by means of sputtering than with devices and methods that do not have the heat pumps disclosed here.

In the methods disclosed herein, sputtering can be performed, for example, by means of DC, HF, magnetron, bias, or atomic beam sputtering.

The invention is described in more detail below on the basis of preferred embodiments and with reference to the accompanying drawings. Show it:

Figure 1 is a vertical section through a

Cooling device for a sputtering target with a target 1, which is held on a target holder 3, and a heat sink 2 with cooling channels 2-3 at least partially integrated in this, in which a heat pump 4 is arranged between the heat sink 2 and the target holder 4;

FIG. 2 shows a vertical section through a conventional cooling device for a sputtering target with a target 1 and a cooling body 2 with cooling channels 2-3 at least partially integrated therein;

Figures 3a to 3c electrical wiring of the sputtering system and the

Device for cooling a sputtering target and in each case the wiring of the heat pump comprising a Peltier element;

Figure 4 shows an embodiment of components of a

Cooling device for a sputtering target, shown in a partially sectioned three-dimensional view, in which a Circular sector has been shown cut out of both the target, the target carrier, the heat pump and the heat sink and the target comprises a low-expansion glass containing SiO 2 , in this example quartz glass; FIG. 5 shows the temperature development over time during sputtering in the sputtering target with an inactive heat pump, and thus inactive Peltier element or inactive Peltier cooler;

FIG. 6 shows the temperature development over time during sputtering in the sputtering target with an active heat pump, and thus an active Peltier element or active Peltier cooler;

FIG. 7 shows the temperature development over time in the sputtering target with an active heat pump, thus an active Peltier element or active Peltier cooler, which was activated with a time advance before the sputtering process; Figure 8 shows a further exemplary embodiment of components of a cooling device for a sputtering target, in a partially sectioned three-dimensional view, in which a sector of a circle has been cut out of both the target, the target carrier, the heat pump and the heat sink and the target is a chalcogenide glass in this Example includes the IRG26 chalcogenide glass from Schott AG;

FIG. 9 shows the temperature development over time without an active heat pump, thus without an active Peltier element or without an active Peltier cooler on the top and bottom of the sputtering target shown in FIG. 8 for a fleece density of 0.26 W/cm ² ;

FIG. 10 shows the temperature development over time with an active heat pump, thus with an active Peltier element or with an active Peltier cooler on the top and bottom of the sputtering target shown in FIG. 8 for a fleece density of 0.26 W/cm ² ; Figure 11 shows yet another exemplary embodiment of components of a cooling device for a sputtering target, in a three-dimensional, partially sectioned view, in which a sector of a circle has been cut out of both the target, the target carrier, the heat pump and the heat sink, and the target is a chalcogenide glass, in 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 designed in two stages; Figure 12 shows the temperature development over time with an active heat pump, i.e. with an active Peltier element or with an active Peltier cooler on the bottom and top of the sputtering target shown in Figure 11 for a heating density of 0.26W/cm ² , in the embodiment shown in Figure 11, in which the Heat pump and thus the Peltier element or the Peltier cooler are designed in two stages;

FIG. 13 shows a further exemplary embodiment 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 embodiments

In the following detailed description of preferred embodiments, not all components are drawn to scale for the sake of clarity. In the figures, however, the same reference symbols designate the same components or assemblies.

However, for the sake of better understanding, the temperature conditions prevailing in the sputtering target before and during sputtering should first be discussed. If, for the sake of brevity, only one target is spoken of instead of a sputtering target, this is intended to also reveal the term sputtering target in each case. Within the scope of the present disclosure, the terms sputtering target and target are used throughout for the same subject.

The temperature increase DTt of the temperature Tt,o of the target top 1-1 relative to the temperature TT.U of the target bottom 1-2 during sputtering due to a heating density jth on the target top 1-1 can be calculated using a thermal resistance d-r/kt, where dT is the thickness of the target and KT denotes the thermal conductivity of the target, can be estimated as follows:

(1)

where the thermal conductivity KT is assumed to be temperature-independent.

For a given heating density jth and a target thickness dT, the temperature rise or temperature rise DTt also depends on the thermal conductivity of the target material.

For a first example with jth = 2W/cm ² , dT = 1cm and metallic targets with KT > 20W/mK, DTt < 10°C follows, for example.

Metals usually withstand heating densities of more than 5W/cm ² without any problems.

For ceramic targets with KT < 2W/mK, with jth = 2W/cm ² , dT = 1cm, however, DTt > 100°C results, which is often unacceptable because it is too high, because thermal deformation of the target can then possibly damage the thermal contact with the Breaking the heat sink or thermo-mechanical stresses can cause brittle fractures in the target.

Alternatively, in order to avoid such disadvantages, a maximum temperature increase or thus a maximum temperature rise ATT.max is often specified and a maximum heat flow density is then calculated from this

(2) cent

An estimate for AT-r.max is based on allowable thermo-mechanical deformations and takes into account the thermal expansion coefficient at and the modulus of elasticity ET of the target material:

For low-expansion SiO2 glass with at < 1 · 10- ⁶ K-\

Et = 73GPa and

KT * 1.4W/mK (at 20°C)

If, for example, an ATT.max = 390°C is permissible and this results in the value jth < 6W/cm ² .

However, these values can be significantly different for other glass systems. For the chalcogenide glass IRG26, see for example its data sheet “Infrared Chalcogenide Glass IRG 26” from Schott AG in Mainz, for example a * 21 · 10 ⁶ K ¹ , Et * 18GPa and KT * 0.24W/mK (at 20°C), it follows

ATT.max = 300°C and the result is a significantly lower value of jth <

0.7W/ ^cm2 .

However, there are other limitations to be considered, especially for glasses, a maximum temperature, because at high temperatures glasses tend to evaporate, which can disturb the stoichiometry of the sputter particles, tend to form pimples and nodules on the surface or simply melt.

For the chalcogenide glass IRG26 with TG * 185°C, the surface temperature should also remain below 135°C for these reasons.

A better estimate of the permissible heat output for 1cm thick e.g. IRG26 targets is therefore as follows:

(3) Jt _h = ^(TT.o.max - * 0.0024 w/cm ² K (l 35°C - T _{T u} ) .aT For an underside of the target at room temperature, TT,U = 20°C, the permissible heating density on the upper side of the target is 0.35W/cm ² . The resulting low sputtering efficiency reduces profitability: Sputtering rates of more than 0.5pm/min can hardly be achieved.

Equation 3 given above also applies to other sputtering materials with the material data adapted in each case.

For a better understanding, the following additional calculation is carried out:

(1 ) Approach using the example of aluminum with p ^ 2.7g/cm3, atomic weight 27, ie an atomic density of: n = - 6.023 -10 ²³ - A -tome/ - -mol 2.7g/ /cm 3 » _e 6 - , 10„22 atoms/ / cm 3 or » 6 - .10„22 cm -3

Also for silver, Ag, with p « 10.5g/cm3, atomic weight 108, n « 6-1022cm-3 (aluminium and silver have relatively small atomic radii). For SiO2 glass (3 atoms): p « 2.2g/cm3, average atomic weight (28+2-16)/3 = 20 is n «

6.6-1022cm-3; for IRG26 (As2Se3 = 5 atoms): p « 4.3g/cm3, mean atomic weight (2-75+3-79)/5 « 77.4 is n « 3.6-1022cm ³ .

For this reason, an atomic density in the sputtering target of n≦4−1022 atoms/cm ³ is initially assumed for the purposes of the estimates disclosed here.

(2) It is assumed that electrons do not contribute to sputtering. The ions are assumed to be singly charged and an average of hA/I sputter atoms should be emitted for each ion. In order to "sputter off" a layer with the thickness d, or to achieve the sputtering rate w, this requires the electric current density of: j _el = (l -6 -10 ^_19 As) · — tp n ' ^h A/i

(3) It is assumed that at least fίh = 300V is required. This results in the radiation power density: Pin — Fίh Jei — Fίh

(4) A portion of the impact energy introduced into the sputtering target during sputtering is lost as kinetic energy of the emitted atoms: cpout = hA/I-fbGP.

The resulting (thermal) impact on the target surface is therefore

P ⁼ (fίh - ^A/IFQGP ) Jel ⁼ (fίh

The following order of magnitude is estimated: w = 1 pm/min = 17-10-7cm/s, hA/I = 4, n = 4-1022cm-3 This results in an ion current density of 0.0027A/cm2.

cpin = 200V is assumed as the lower limit for the impact energy; Irradiance pin = 0.54W/cm2.

Assuming cpem = 7.5V, the following then follows for the heating density of the target surface: p = 0.46W/cm2.

For the present calculations, a heating density of the target surface of 0.5W/cm2 at a sputtering rate of 1 pm/min is assumed.

The “thin target” approach, thus using a target with a smaller thickness and consequently a smaller dT with lower thermal resistance, could be considered interesting based on the above considerations. However, this noticeably reduces the process efficiency because of the more frequent replacement cycles that are then required and is therefore not advantageous.

In order to achieve large sputter particle streams, the irradiated target area can be increased. In practice, however, this leads to space problems in the recipient, particularly when different targets are to be used for a predetermined layer sequence. Opening recipients for target exchanges is hardly an option for economic reasons, because of the increased process time, in particular due to the need to pump out the recipient again.

In contrast to these two above-described and rather disadvantageous approaches, however, a target carrier 3 and a heat pump 4 can advantageously be inserted between the sputtering target 1 (see, for example, FIG. 1 in this regard) and the heat sink 2 . The heat pump then cools the target carrier 3 and the underside of the target 1-2 below the temperature of the heat sink 2. This increases the longitudinal temperature gradient in the target, increases the heat flow in the target 2 and thus enables a higher heat input and stronger irradiation during sputtering on the upper side of the target 1-1 . Alternatively, the heat sink 2 can be replaced by the heat pump 4 .

For the sake of simplicity, FIG. 1 shows diagrammatically plate-shaped or shell-shaped structures, but the technical solution proposed here also applies analogously to more complicated structures. If, for the sake of linguistic simplicity, individual components are referred to in the present disclosure, it is considered to include that these can also be or include pluralities.

The target 1 and the heat pump 4 are located on opposite faces of the target support. In the simplest embodiment, the target carrier 3 is a single-connected shell with a homogeneous thickness that completely covers the target 1 laterally. The target carrier 3 should generally enable the target to be clamped with little effort in fixing and loosening and should be sufficiently soft to be able to nestle against the target 1 to reduce the thermal resistance. Corresponding methods and devices for clamping are known to a person skilled in the present technical field.

In addition, target carrier 3 should be arranged laterally offset in those cases in which target 1 and heat pump 4 or several Target tiles or heat pump tiles are used, as shown for example in Figure 15, bring about a lateral heat equalization. The heat should be able to flow off the respective target 1 or the respective target tile as homogeneously as possible.

A homogeneous temperature distribution in the target carrier 3 is favorable here, i.e. the highest possible thermal conductivity of the carrier 3. Copper with a thermal conductivity of approx. 400 W/mK) and aluminum with a thermal conductivity of approx. 200 W/mK) are well suited materials for this purpose.

For some embodiments, the target carriers 3 should also be electrically conductive. 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 event of thermal warping.

Despite the higher modulus of elasticity, target carriers 3 made of copper often prove to be slightly cheaper than those made of aluminum, with a modulus of elasticity of 110 instead of 70GPa, because thinner shells with lower flexural rigidity are possible due to the higher thermal conductivity.

Shells made of copper and aluminum are thus preferred for the target carrier 3, with a thickness of about 1mm for copper and a thickness of 2mm for Al being usually sufficient for thermal compensation in order to achieve a sufficiently high level of thermal conductivity and a usable rigidity. These aforementioned thicknesses and are considered “thin” for purposes of the present disclosure.

All components should be in good thermal contact. In one embodiment, the target 1 is therefore glued to the target carrier 3 with a thin layer of thermally conductive paste. Vacuum-capable, temperature-resistant and electrically conductive heat-conducting pastes are known to the person skilled in this technical field.

Negligible thermal resistances dP/kR < 10-3K/(W/cm2) are achieved for corresponding thermal paste connections.

The target carrier 3 is connected to the heat pump or heat pump unit 4 with good thermal contact. In one embodiment, the connection is permanent, i.e. the target carrier 1 is a permanent part of a target table installed in a sputtering system. Since both sputter systems and target tables are known to those skilled in the art, 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 jointly exchangeable unit with it. The sputtering target 1 can then also be permanently connected to the target carrier 3.

Many methods are known for this, e.g. soldering. The clamping of the (metallic) target carrier onto the heat pump unit is assumed to be known; a thermally conductive paste can also be used here to improve the thermal coupling.

Heat pumps can be implemented using Peltier coolers. The mode of operation of Peltier coolers or Peltier elements is known to the person skilled in the art responsible here and is therefore not explained in more detail. Inexpensive standard designs consist of parallel, mostly square, thin, thermally conductive, electrically insulating ceramic discs with an edge length of 2 to 10 cm and a distance of 3 to 6 mm between which fiber optic rods are soldered.

Typical semiconductors here are B Teß and PbO. The temperature rise can be more than 70K for single-stage Peltier coolers and more than 110K for multi-stage Peltier coolers or Peltier elements with thermal Pump powers of more than 1W/cm ² . Peltier coolers are operated with direct current with nominal voltages in the 10V range and operating currents in the 10A range. The ohmic losses in a Peltier cooler can be more than 100W and must be taken into account when designing the respective cooling.

The outer surfaces of the ceramic discs can be (galvanically) metallized to make soldering to other components easier, for example. These outer metal surfaces are electrically insulated from the internal wiring of the Peltier cooler. The creation of Peltier coolers is not part of the present disclosure; since commercially available designs can often already be sufficient for the purposes of the invention.

However, the further exemplary description of the invention is based on 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.

The problem with HC and DC sputtering is that the Peltier cooler introduces an incompatible electrical circuit into the "high-voltage circuit".

FIGS. 3a to 3c show corresponding electrical wiring of the sputtering system and the device for cooling a sputtering target and the wiring of the heat pump comprising a Peltier element,

In DC sputtering, for example, it is advantageous to also use the electrically insulating ceramic foils of the Peltier cooler to separate the circuits, which means that in this case the target carrier 1 can be connected to the high-voltage circuit. The heat sink 2 can be grounded, with the advantage of greater electrical safety, because the coolant circuit is then generally voltage-free.

In principle, the same procedure can be used for HF sputtering. Here, however, it can be beneficial to prevent the alternating field from being disturbed by DC couplings prevent, e.g. by a series capacitor C1, and to prevent disturbance of the DC supply circuit for the Peltier cooler, e.g. by a capacitor C2 in parallel with the Peltier cooler. It is also possible to introduce the AC voltage into the heat sink 2 itself during HF sputtering if the DC Peltier circuit is short-circuited with a capacitor C2 for AC voltages.

However, maximum performance should not be assumed when designing Peltier coolers.

A thermal pumping power of 1 W/cm ² at a temperature difference of 60K has proven advantageous for single-stage Peltier coolers. Multi-stage Peltier coolers should be used if higher pump capacities or larger temperature differences are desired. A thermal pump power of 2W/cm ² at a temperature difference of 90K 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 400mm diameter and 10mm thick round 5 made of silica glass with a thermal conductivity of 1.4W/mK is joined as a sputtering target 1 to a 2mm thick target carrier 3 made of aluminum. Instead of the silica glass, the body 5 in the form of a circular disc can also comprise a chalcogenide glass with a thermal conductivity of 1.6 W/nK or less and/or a glass transition temperature of less than 400°C.

To protect the edges of the glass, the target carrier 3 is overdesigned. The target carrier 3 is clamped on a cold surface 7 of a ring-shaped 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 directly on a ring-shaped heat sink 2 made of copper or aluminum with an inner radius of 10 mm, an outer radius of 190 mm and a thickness of 12 mm. In the heat sink 2 are 6mm diameter cooling channels 7, of which for the sake of clarity only one cooling channel with a reference number is provided. In some embodiments, the Peltier cooler 6 is used without a heat sink 2 or cooling channels 7 . Through the 20mm diameter inner hole of the target carrier 3, sensors, for example for. Thickness and / or temperature measurement for monitoring the sputtering target 1 are performed.

As a reference, FIG. 5 first shows the temperature development when the Peltier cooler 6 is switched off on the bottom 1-2 and on the top 1-1 of the sputtering target 1 designed as a glass disk 5 for a heating density on the top 1-1 of the sputtering target of 2.5 W/cm 2 . The logarithmically divided time axis has the time unit minutes. The starting temperature is 20°C. The process is set to a constant sputtering rate of 3pm/min; the temperature of the sputtering target 1 should remain below 210° C. during sputtering. The temperature on the upper side of the target 1-1 reaches 206°C after approx. 15 minutes and then drops again because the thermal resistance of the target 1 decreases due to material removal. Despite intensive cooling, the underside of the target 1-2 heats up to approx. 27°C due to the thermal resistance of the heat sink 2 and Peltier cooler 6.

FIG. 6 shows the temperature development with the Peltier cooler 6 switched on on the underside 1-2 and the upper side 1-1 of the sputtering target 1 designed as a glass disk 5 for a heating density on the upper side 1-1 of 3.5 W/cm 2 . The process is set to a constant sputtering rate of 4.5pm/min.

The temperature on the top of the target 1-1 reaches 205°C after approx. 15 minutes and then drops more quickly because of the greater material removal.

The underside 1-2 of the sputtering target 1 sinks to about -38° C. in the quasi-stationary range. The cooling by means of the Peltier elements 6 allows the sputtering rate to be increased by approximately 50%.

At the start of irradiation with the sputtering target 1 at room temperature, an additional temperature rise often occurs on the upper side of the target 1-1, which disappears when a quasi-stationary range is reached. The irradiation of the sputtering process therefore preferably only begins 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/cm 2 .

FIG. 8 shows a further exemplary embodiment. A 400 mm diameter and 10 mm thick blank 5 made of the aforementioned IRG26 chalcogenide glass with a thermal conductivity at room temperature of 0.26 W/mK forms the sputtering target 1 and is joined to a 2 mm thick copper target carrier 3 . On a single-stage Peltier cooler 6, a 4mm thick copper mounting plate 8 is joined, the target carrier 3 is clamped onto the mounting plate 8. Target carrier 3 and mounting plate 8 are preferably made of "similar base metals" to prevent electrocorrosion - however, Cu/Al pairings should be avoided. The Peltier cooler 6 is soldered onto an annular heat sink 2 made of copper.

FIG. 9 shows the temperature development over time without Peltier cooling on the bottom 1-2 and on the top 1-1 for a heating density of 0.26W/cm2.

The sputtering process is set to a constant sputtering rate of 0.3pm/min; the temperature of the target should remain below 135°C during the entire sputtering process.

The temperature on the top of the target 1-1 reaches 133°C and drops again due to material removal during the sputtering process.

FIG. 10 shows the temperature development over time with Peltier cooling for a heating density of 0.42W/cm2 or a sputtering rate of 0.5pm/min: The sputtering rate can already be increased by more than 50% with a single-stage Peltier cooling.

FIG. 11 shows yet another exemplary embodiment, in which a circular blank 5 made of IRG26 chalcogenide glass and forming the sputtering target 1 and measuring 400 mm in diameter and 10 mm thick is attached to a 2 mm thick target carrier 3 made of copper. The target carrier 3 is on a 4mm thick, also made of copper mounting plate 8 and with this on a two-stage Peltier cooler 6 tensioned. In this case, the Peltier cooler 6 is soldered onto the heat sink 2 .

For this further embodiment, FIG. 12 shows the temperature development 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/cm 2 and a sputtering rate

0.62pm/min: The sputtering rate can be increased by more than 65% thanks to the two-stage Peltier cooling available here.

FIGS. 13 and 14 show further exemplary embodiments of components of the cooling device for at least one sputtering target 1, with a ring-shaped clamping device 9 being visible, 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 several sputtering targets 1 are held on a target carrier 3 .

reference list

1 sputter target, also referred to as target for short,

1-1 upper target surface, which is also referred to as the target top

1-2 target surface facing away from the beam, which is also referred to as the underside of the target

2 heatsinks

2-3 cooling channels

3 target carriers

4 heat pump

5 rounds

6 Peltier element or Peltier cooler

7 cooling channel

8 mounting plate

9 Ring clamping device

Claims

patent claims

1. Cooling device for at least one sputtering target (1), comprising a target carrier (3) and at least one heat pump (4), in which a sputtering target (1) is held on the target carrier (3) and the at least one heat pump (4) has at least one Peltier element (6) includes.

2. Cooling device according to one of the preceding claims, wherein the at least one sputtering target (1) comprises a chalcogenide glass material with a thermal conductivity of at least 1.6 W/mK or less.

3. Cooling device according to one of the preceding claims, wherein the at least one sputtering target (1) comprises a chalcogenide glass material with a glass transition temperature of less than 400°C.

4. Cooling device according to one of the preceding claims, further comprising a heat sink, wherein the at least one heat pump (4) is arranged between the target carrier (3) and the heat sink.

5. Cooling device according to one of the preceding claims, wherein the Peltier element has outer metal surfaces which are electrically insulated from the internal wiring of the Peltier element.

6. 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 .

7. Cooling device according to one of the preceding claims 1 to 6, in which the sputtering target (1) comprises a chalcogenide glass, in particular a chalcogenide glass IRG26.

8. A method for cooling at least one sputtering target (1), in which a sputtering target (1) is held on a target carrier (3), and by means of at least one heat pump (4) which comprises at least one Peltier element (6), the sputtering target ( 1) has a target underside (1-2), and wherein the target underside (1-2) preferably before

sputtering is cooled to a temperature below 0°C.

9. The method according to claim 8, wherein the target material comprises glass containing SiO2.

10. The method as claimed in claim 8, in which the target material comprises a chalcogenide glass, in particular IRG26.

11. The method according to any one of claims 8 to 10, in which coating processes are carried out by means of sputtering.

12. The method according to any one of claims 8 to 11, in which the sputtering is carried out by means of DC, HF, magnetron, bias or atomic beam sputtering.