Device for cooling a sputtering target
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-25
- Publication Date
- 2026-03-25
AI Technical Summary
Existing devices for cooling sputtering targets with melting points below 100 °C are insufficient in providing stable and efficient cooling without risking liquefaction, as they rely on heat conduction and evaporation of coolants, which require complex shielding and contamination prevention.
A device utilizing a heat sink with a refrigerant flowing through a cooling channel, where the refrigerant changes state from liquid to gas, enhancing heat transfer and cooling capacity, and a closed circuit with a compressor and pressure stage to manage the refrigerant's state change, ensuring efficient cooling of sputtering targets with materials like gallium, indium, and mercury.
The device achieves superior cooling capacity and stability for sputtering targets with melting points below 100 °C, preventing liquefaction and maintaining a long-term stable sputtering process by effectively managing thermal energy through refrigerant state changes, improving heat transfer and reducing refrigerant heating.
Smart Images
Figure EP2024061351_21112024_PF_FP_ABST
Abstract
Description
[0001] Device for cooling a sputtering target
[0002] Description
[0003] The invention relates to a device for cooling a sputtering target, which can be, for example, a component of a magnetron sputtering device.
[0004] Sputtering processes are often used to deposit thin films. In these processes, material particles are atomized from the surface of a target body (hereinafter referred to as the sputtering target) by ion bombardment, thus transferring them into the vapor phase and then depositing them onto a substrate to be coated. However, continuous ion bombardment of a sputtering target leads to high thermal stress on the target body. To protect it from embrittlement and overheating, cooling of the sputtering target is necessary.
[0005] Magnetron sputtering devices are known in which a sputtering target is attached, for example by bonding, to a heat sink that is traversed by at least one cooling channel through which a coolant flows (DE 100 18 858 A1). The at least one cooling channel can also be open on one side towards the sputtering target, so that the coolant flowing through the cooling channel is in direct contact with the sputtering target, which leads to better heat dissipation. Water is typically used as the coolant. However, other liquid or gaseous coolants flowing through a cooling channel are also known, which can be cooled to a temperature below 0 °C.In such devices, the coolant is often integrated into a closed cooling circuit, with the coolant heated by the sputtering process in the heat sink being fed to a heat exchanger, where it releases its thermal energy so that the cooled coolant can be fed back into the heat sink. However, such a device often cannot adequately or reliably cool sputter target materials with a melting point below 100 °C.
[0006] US 2013 / 0015056 A1 describes devices in which a target is mechanically connected to a cooling plate. The cooling plate comprises several open-topped vessels in which a liquid coolant is stored. The process heat dissipated into the coolant by heat conduction heats the coolant until it evaporates from the vessels. Evaporation of the coolant dissipates heat in such a device.
[0007] Finally, US 5 569 361 A discloses devices in which a sputtering target is connected to a cooling plate, wherein a liquid coolant is sprayed onto the surface of the cooling plate not connected to the sputtering target. Due to the process heat, a portion of the liquid coolant is converted into the vaporous state. During the process of converting a portion of the liquid coolant into the vaporous state, heat is extracted from the environment, which leads to additional cooling performance. A disadvantage, however, is that in this case too, the area of a working chamber within which the coolant is sprayed onto the surface of the cooling plate must be laboriously shielded from the rest of the working chamber and pumped out to prevent the sprayed liquid or vaporized coolant from contaminating the process zone of the sputtering process.
[0008] The invention is therefore based on the technical problem of creating a device for cooling a sputtering target that overcomes the disadvantages of the prior art. In particular, the device according to the invention should make it possible to permanently and efficiently cool target materials with a melting temperature below 100 °C without liquefying the target.
[0009] The solution to the technical problem is achieved by objects having the features of patent claims 1. Further advantageous embodiments of the invention are set out in the dependent patent claims.
[0010] A device according to the invention for cooling a sputtering target comprises a heat sink which has a contact surface by means of which mechanical contact with the sputtering target is formed. The mechanical contact between the heat sink and the sputtering target is preferably established by bonding. According to the invention, at least one cooling channel runs through the heat sink, so that the heat sink has at least one cooling channel inlet and at least one cooling channel outlet, and a fluid flows through the cooling channel. In a device according to the invention, however, the cooling effect is not only based on the fact that thermal energy of the sputtering target is first dissipated by thermal conduction into the heat sink and there into the cold fluid flowing through the cooling channel, but in a device according to the invention, the fluid flowing through the cooling channel is designed as a coolant.
[0011] According to DIN EN 378-1, paragraph 3.7.1, a refrigerant is defined as a “fluid used for heat transfer in a refrigeration system, which absorbs heat at low temperature and low pressure and releases heat at higher temperature and higher pressure, usually involving changes in the state of the fluid”.
[0012] While a coolant within a cooling circuit known from the prior art can only transport cold in the form of a cold coolant or dissipate heat energy with the coolant, a refrigerant can extract heat energy from an environment during the change of state of the refrigerant from the liquid to the gaseous or vaporous state.
[0013] In a device according to the invention, a refrigerant used undergoes a change of state, at least partially, from the liquid state to the vapor or gaseous state, predominantly within the cooling channel in the heat sink, due to the thermal energy introduced into the target and the heat sink by a sputtering process. Thermal energy is extracted from the surroundings of the refrigerant due to the change in the refrigerant's state. The use of a refrigerant is also advantageous in that the turbulent flow of the liquid-vapor mixture of a refrigerant within the cooling channel contributes to improved heat transfer between the refrigerant and the heat sink compared to the laminar flow of a cooling liquid known from the prior art. Furthermore, in a device according to the invention, the heat input into a refrigerant leads, if at all, to only an insignificant heating of the refrigerant itself.Due to the above-mentioned circumstances, a device according to the invention can achieve a higher cooling performance compared to known devices in which only a fluid is conveyed through a cooling channel without a change in state of aggregation.
[0014] Suitable for use in a device according to the invention are refrigerants known from the prior art which have a boiling point of 0°C or less at a pressure of 1 bar and a boiling point of -10°C or less at a pressure of 0.7 bar. It is particularly advantageous if a refrigerant is used which has a boiling point of -40°C or less at a pressure of 1 bar and a boiling point of -50°C or less at a pressure of 0.7 bar. When using such a refrigerant, sputtering target materials which have a melting point in the range of -40°C to +200°C can also be efficiently cooled, for example sputtering targets which comprise at least one of the chemical elements gallium, indium and / or mercury.
[0015] A device according to the invention further comprises at least one compressor, by means of which the vaporous components of the refrigerant emerging from the cooling channel of the heat sink are compressed and finally converted back into the liquid state. The cooling channel outlet of the heat sink is therefore connected to the inlet of the compressor by means of a first pipe. The outlet of the compressor is connected to the inlet of a pressure stage by means of a second pipe, and a third pipe finally connects the outlet of the pressure stage to the cooling channel inlet. In the sense of the invention, a pressure stage is considered to be such devices by means of which a pressure change of a fluid flowing through the pressure stage can be effected from the inlet of the device to the outlet of the device. A nozzle or a controllable valve, for example, can be used as a pressure stage.
[0016] The pressure stage of a device according to the invention is dimensioned or configured such that a pressure reduction of at least 2 bar is brought about on average over time from the inlet of the pressure stage to the outlet of the pressure stage. In a preferred embodiment, a pressure reduction of at least 8 bar is brought about on average over time from the inlet of the pressure stage to the outlet of the pressure stage. Due to the pressure reduction, the first liquid components of the refrigerant are converted from the liquid to the vapor state immediately after flowing through the pressure stage. It is therefore advantageous if the pressure stage is arranged as close as possible to the cooling channel inlet within the cooling circuit or, alternatively, is formed within the heat sink so that the majority of the liquid components of the refrigerant undergo a change of state from the liquid to the vapor state within the cooling channel.
[0017] A device according to the invention thus comprises a closed cooling circuit through which a liquid-vapor mixture of a refrigerant flows. The refrigerant has the highest proportion of liquid components within the second pipeline after exiting the compressor, which then decreases within the third pipeline and within the cooling channel. Within the first pipeline immediately before the refrigerant enters the compressor, the refrigerant preferably no longer contains any liquid components, because liquid components flowing into a compressor can negatively impact its functionality.
[0018] After exiting the compressor, the refrigerant has a relatively high temperature, which must be lowered again before the refrigerant flows into the heat sink. In a device according to the invention, at least a first portion of the second pipe extends through a first heat exchanger, in which the heat of the refrigerant is transferred to a coolant, such as water.
[0019] Because the power input into a sputtering target during a sputtering process is not always constant, and thus, in phases of low sputtering power or no sputtering power at all, there may not be enough process heat available to convert all liquid components of the refrigerant into the vapor state, it is advantageous if the cooling circuit in the area of the first pipe still has a thermal base load, which ensures that all components of the refrigerant are converted into the vapor state before entering the compressor. Such a thermal base load can be provided, for example, by means of a heating device that heats at least a portion of the first pipe and the refrigerant contained therein.
[0020] Alternatively, the thermal base load can also be provided by means of a second heat exchanger. As the liquid components of the refrigerant decrease from the second pipe, via the third pipe, the cooling channel, to the first pipe, the temperature of the refrigerant also decreases. This means that the refrigerant has the highest temperature within the second pipe and the lowest temperature within the first pipe. When using a second heat exchanger for the thermal base load within the first pipe, a second section of the second pipe can exchange heat with a section of the first pipe. It is advantageous to set the cross-section of the cooling channel and the cross-section of the first pipe with an area of 2 cm 2 or larger in order to keep the temperature and pressure of the refrigerant as low as possible.
[0021] To ensure the best possible heat exchange between the heat sink and the coolant, it is advantageous if the contact area of the coolant with the heat sink is as large as possible. In a device according to the invention, the contact area of the coolant with the heat sink corresponds to the cooling channel surface area. The total size of the cooling channel surface area can be adjusted, for example, via the length of the cooling channel and / or the number of cooling channels. In a further embodiment of the invention, the cooling channel surface area is at least three times as large as the surface of the sputtering target used for sputtering.
[0022] The invention is explained in more detail below using exemplary embodiments. The figures show:
[0023] Fig. 1 is a schematic representation of a device according to the invention;
[0024] Fig. 2 is a schematic representation of a first alternative inventive
[0025] Device comprising a heating device;
[0026] Fig. 3 is a schematic representation of a second alternative device according to the invention, which comprises a heat exchanger;
[0027] Fig. 4 is a schematic representation of a third alternative device according to the invention, in which a compressor is designed as a two-stage compressor.
[0028] Fig. 1 schematically illustrates a device 100 according to the invention for cooling a sputtering target 101. The device 100 comprises a heat sink 102 having a contact surface 103, wherein the contact surface 103 forms a mechanical contact with the sputtering target 101. The mechanical contact between the contact surface 103 and the sputtering target is preferably established by bonding. The heat sink 102 is traversed by a cooling channel 104, so that the heat sink 102 has a cooling channel inlet 105 and a cooling channel outlet 106. The cooling channel 104 is preferably configured with a cross-section of 2 cm 2 or larger and is flowed through by a fluid for cooling the heat sink, wherein the fluid is designed according to the invention as a coolant.
[0029] By means of a first pipe 107, which preferably has a cross section of 2 cm 2or larger, the cooling channel outlet 106 is connected to an inlet 108 of a compressor 109 (hereinafter also referred to as compressor inlet 108). A second pipe 110 connects an outlet 111 of the compressor 109 (hereinafter also referred to as compressor outlet 109) to an inlet 112 of a pressure stage 113 (hereinafter also referred to as pressure stage inlet 112). And by means of a third pipe 114, an outlet 115 of the pressure stage 113 (hereinafter also referred to as pressure stage outlet 115) is connected to the cooling channel inlet 105, thereby forming a closed cooling circuit through which the refrigerant flows. An arrow within the first pipe indicates the flow direction of the refrigerant within the cooling circuit.
[0030] The sputtering target 101 and the heat sink 102 are typically arranged within a working chamber, which can be configured, for example, as a vacuum chamber. Within the working chamber, material particles are typically dusted from the sputtering target 101 during a sputtering process and deposited on at least one substrate. For reasons of clarity, the working chamber and a substrate to be coated are not shown in Fig. 1.
[0031] According to the invention, the refrigerant flowing through the cooling channel 104 is a fluid that has a boiling point of 0°C or lower at a pressure of 1 bar and a boiling point of -10°C or lower at a pressure of 0.7 bar. Such refrigerants are known from the prior art, such as the refrigerant R449A.
[0032] Within the second pipe 110, after exiting the compressor 109, the refrigerant within the cooling circuit has the highest temperature and the highest proportion of liquid components.
[0033] To cool the refrigerant after it exits the compressor, a first portion of the second pipe 110 extends through a first heat exchanger 130, within which thermal energy of the refrigerant is transferred to a cooling fluid flowing through a cooling line 131. Water, for example, can be used as the cooling fluid.
[0034] As the coolant subsequently flows through pressure stage 113, the pressure is reduced. According to the invention, the pressure stage is dimensioned such that pressure stage 113, from pressure stage inlet 112 to pressure stage outlet 115, results in a pressure reduction of at least 2 bar on average over time. Pressure stage 113 can, for example, be designed as a controllable valve, in which the flow rate is regulated depending on the pressure and / or the temperature within the piping system.
[0035] A pressure reduction can, however, also be brought about or supported by making the pipe cross-section of the third pipe 114 larger than the pipe cross-section of the second pipe 110. Due to the pressure reduction, the first liquid components of the refrigerant are converted from the liquid to the vaporous state after flowing through the pressure stage 113. It is therefore advantageous if the third pipe 114 is dimensioned to be as short as possible. The heat introduced into the sputtering target 101 by the sputtering process passes through the contact surface 103 into the cooling body 102 by thermal conduction and ultimately also heats the refrigerant flowing through the cooling channel 104. Due to the thermal energy introduced into the refrigerant within the cooling channel 104 by thermal conduction, further components of the refrigerant within the cooling channel 104 change their state from the liquid state to the vaporous orgaseous state. Due to this change in the state of the coolant within the cooling channel 104, heat is extracted from the environment, which contributes to the cooling of the heat sink 102 and ultimately also to the cooling of the sputtering target 101.
[0036] By means of such a device 100 according to the invention, sputter targets can be cooled more effectively than with prior art cooling devices, in which the thermal energy of a sputtering process is introduced into a cooling fluid merely by heat conduction without a change in state of matter. If a coolant known from the prior art is selected which has a boiling point of -40°C or lower at a pressure of 1 bar and a boiling point of -60°C or lower at a pressure of 0.7 bar, a sputtering target 101 comprising the materials gallium, indium, and / or mercury can also be cooled with a device 100 according to the invention, thereby enabling a long-term stable sputtering process for these materials without liquefying the target.
[0037] The following are merely examples of temperature values that are or can be set within a device according to the invention in a previously described structure:
[0038] Refrigerant in cooling channel 104: -50 °C,
[0039] Refrigerant within the first pipe 107: -60 °C,
[0040] Refrigerant after leaving compressor 109: 40 °C,
[0041] Refrigerant after passing through the first heat exchanger 130: 25 °C, Refrigerant after pressure stage 1 13: -40 °C,
[0042] Target 101 at its surface: 20 °C,
[0043] Target 101 at the interface 103 to the heat sink 102: 0 °C, heat sink 102: -5 °C.
[0044] Before entering the compressor 109, all components of the refrigerant are preferably converted into the vapor or gaseous state. Within the compressor 109, the vapor or gaseous components of the refrigerant are compressed and converted into the liquid state, so that after the liquefied refrigerant exits the compressor 109, the cooling cycle can begin again.
[0045] Fig. 2 schematically illustrates a first alternative device 200 for cooling the sputter target 101. The device 200 initially comprises all the components and functionalities described for the device 100 in Fig. 1. In addition, the device 200 has a heating device 216, by means of which at least a partial region of the first pipe 107 and thus also the coolant flowing through this partial region can be heated. The heating device 216 can be designed, for example, as a radiant heater, as a current-carrying heating coil wound around the first pipe 107, or as a heating coil wound around the first pipe through which a warm fluid flows.Since performance fluctuations or process pauses can occur during the sputtering process, which leads to irregularities in the process-related heat input into the heat sink, the heating device 216 as a thermal base load ensures that at all times during the sputtering process all components of the refrigerant are converted into the vaporous or gaseous state before entering the compressor 109, so that the compressor 109 is not damaged by liquid refrigerant components.
[0046] A second alternative device 300 for cooling the sputtering target 101 is shown schematically in Fig. 3. The device 300 initially comprises all the components and functionalities as described for the device 100 in Fig. 1. In addition, the device 300 comprises a second heat exchanger 317, through which a partial region of the first pipeline 107 and a second partial region of the second pipeline 110 extend. As already explained above, the refrigerant within the second pipeline 110 has a higher temperature than the refrigerant within the first pipeline 107. In the embodiment according to the device 300, thermal energy of the refrigerant from the second pipeline 110 is therefore used to heat the refrigerant within the first pipeline 107, in order to ensure that all components of the refrigerant are converted into the vapor or solid state before entering the compressor 109.are converted into a gaseous state. Device 300 of Fig. 3 is more energy-efficient than device 200 of Fig. 2, since in device 300, no additional energy needs to be supplied to heat the refrigerant within the first pipe 107. Alternatively, however, in addition to the second heat exchanger 317, a heating device according to the heating device 216 of Fig. 2 can also be installed in the cooling circuit.
[0047] Fig. 4 schematically illustrates a third alternative device 400 for cooling the sputter target 101. The device 400 initially comprises all the components and functionalities described for the device 100 in Fig. 1. In the device 400, the compressor 109 is designed as a two-stage compressor such that it comprises a compressor 418 as the first component and a condenser 419 as the second component. By means of the compressor 418, the vaporous or gaseous components of the refrigerant flowing into the compressor 109 are initially only compressed, which is already accompanied by an increase in the temperature of the refrigerant. The compressed vaporous or gaseous components of the refrigerant are then converted into the liquid state by means of the condenser 419.In the device 400, a fourth pipe 420 connects the outlet of the compressor 418 to the first pipe 107, so that within the compressor 109, a portion of the compressed, but still vaporous or gaseous refrigerant is tapped by means of the fourth pipe 420 after passing through the compressor 418 and introduced into the first pipe 107. The supply of the compressed and heated.
[0048] Refrigerant into the pipe 107 also results in all components of the
[0049] The refrigerant is converted into the vaporous or gaseous state within the first pipe before entering the compressor 109. It is advantageous if the size of the portion of the coolant removed after passing the compressor 418
[0050] refrigerant is controlled depending on the amount of process heat introduced into the refrigerant within the heat sink.
[0051] For the sake of completeness, it should be noted that the assemblies or components known from Figs. 2 to 4, which go beyond the assemblies and components known from Fig. 1, can be combined with one another as desired in further embodiments.
Claims
Patent claims 1. A device for cooling a sputtering target (101), comprising a heat sink (102) having a contact surface (103) by means of which mechanical contact with the sputtering target (101) is formed, wherein the heat sink (102) is traversed by at least one cooling channel (104), so that the heat sink (102) has at least one cooling channel inlet (105) and at least one cooling channel outlet (106), and wherein a fluid flows through the cooling channel (104), characterized in that a) the cooling channel outlet (106) is connected to the inlet of a compressor (109) by means of a first pipe (107); b) the outlet of the compressor (109) is connected to the inlet of a pressure stage (113) by means of a second pipe (110); c) a first portion of the second pipe (110) extends through a first heat exchanger (130);d) the outlet of the pressure stage (113) is connected to the cooling channel inlet (105) by means of a third pipe (114); e) the fluid is designed as a refrigerant; wherein the refrigerant has a boiling point of 0°C or less at a pressure of 1 bar and a boiling point of -10°C or less at a pressure of 0.7 bar; and f) the pressure stage (113) is configured such that it effects a pressure reduction of at least 2 bar on average over time from the pressure stage inlet (112) to the pressure stage outlet (115); 2. Device according to claim 1, characterized in that the refrigerant has a boiling point of -40 °C or less at a pressure of 1 bar and a boiling point of -50 °C or less at a pressure of 0.7 bar.
3. Device according to claim 1 or 2, characterized by a heating device (216) by means of which at least a partial area of the first pipeline (107) can be heated.
4. Device according to claim 3, characterized in that the heating device (216) is designed as a heat radiator or as a current-carrying heating coil.
5. Device according to one of the preceding claims, characterized by a second heat exchanger (317) through which a partial region of the first pipeline (107) and a second partial region of the second pipeline (110) extend.
6. Device according to one of the preceding claims, characterized in that the pressure stage (1 13) is designed as a nozzle or as a controllable valve.
7. Device according to one of the preceding claims, characterized in that the first pipe (107) with a cross section of 2 cm 2 or larger.
8. Device according to one of the preceding claims, characterized in that the sputtering target (101) comprises at least one of the elements gallium, indium and / or mercury.
9. Device according to one of the preceding claims, characterized in that the sputtering target (101) is bonded to the heat sink (102).
10. Device according to one of the preceding claims, characterized in that the cooling channel surface is at least three times as large as the surface of the sputtering target (101) used for sputtering. 1 1. Device according to claim 10, characterized in that the cooling channel (104) with a cross section of 2 cm 2 or larger.
12. Device according to one of the preceding claims, characterized in that the compressor (109) is designed as a two-stage compressor such that it comprises a compressor (418) as a first assembly and a condenser (419) as a second assembly, wherein a fourth pipeline (420) connects the outlet of the compressor (418) to the first pipeline (107).