Method for producing a sputtering target or bond target

Abstract

The present invention relates to a method for producing a sputtering target or bond target (1) in which an intermediate layer (4) is inserted between a target carrier (3) and a target layer (2), wherein the intermediate layer (4) is formed from a high-energy reactive material in the form of a layer system of at least two layers of different materials, and wherein these materials comprise Zr and Si or Ti and C. Subsequently, a pressure is applied to the system consisting of the target carrier (3), the intermediate layer (4), and the target layer (2), and a reaction of the intermediate layer (4) is initiated, such that the intermediate layer (4) reacts exothermically and the target layer (2), the intermediate layer (4), and the target carrier (3) are metallurgically bonded together.

Description

[0001] The present invention relates to a method for producing a sputtering target or a bond target.

[0002] Coating targets for PVD (physical vapor deposition) processes can be manufactured as either monolithic targets or bonded targets. In a bonded target, the target material to be sputtered is bonded to a target support (usually flat copper or molybdenum plates, or corresponding tubes for cylindrical targets). Bonding can be achieved in various ways and forms the bond zone. The advantage of bonded targets lies in the fact that brittle (e.g., Si, C), expensive (e.g., Au, Ag, Pt, Rh, Ir), or composite materials (e.g., ceramics) can be sputtered, thus making them available for thin-film processes and applications.

[0003] The challenge in bonding lies in the properties of the target material and the differing coefficients of thermal expansion between the target material and the substrate. If the target material consists of low-melting-point (e.g., Sn, In, Bi), highly reactive materials (e.g., La), or sintered materials (e.g., ceramics), the bonding process temperature must be kept low to prevent degradation or destruction of the target material. Another reason for keeping bonding temperatures low is the often differing coefficients of thermal expansion between the substrate and the target material being bonded. If there is a significant difference, the substrate and target material expand differently when heated during the bonding process, and mechanical stress develops between the two bonding partners upon cooling.Consequently, damage to brittle target materials (e.g., Si, C, ceramics) or deformation of the bond target can occur even during the cooling of the bonding process, potentially preventing its integration or rendering it insufficiently cooled. Therefore, a bonding process that exposes both the target support and the target material to the lowest possible temperatures is of fundamental importance.

[0004] Another crucial point is the high resilience of the bond during operation. In sputtering processes, power densities of tens of W / cm² can be achieved on the target. 2This can lead to temperatures of several hundred degrees Celsius on the target surface. To prevent the targets from melting and simultaneously protect the permanent magnets in the sputtering sources, efficient cooling is required. This is generally achieved by a high flow rate of cooling water through the sputtering source, which also cools the back or inner surface of the targets. During the sputtering process, this creates a high temperature gradient between the cooled target support and the sputtering material, while the sputtering process itself results in a high energy input onto the surface of the target material.

[0005] Mechanical stresses arise from two main causes: Firstly, the water cooling exerts mechanical pressure on the target carrier, which can lead to deformation of the bond target. If this pressure becomes too high, bending stress can occur in the bond zone, resulting in bond failure or damage to fracture-prone target materials (e.g., silicon, ceramics). However, a far greater challenge for the bond is a significant difference in the thermal expansion of the cooled target carrier combined with the simultaneous heating of the target material during the sputtering process. If the coefficients of thermal expansion of the target carrier and target material are similar, the temperature difference, and the associated differential expansion of the target carrier and target material, already generates shear stresses in the bond zone.If the target carrier and target material also have a large difference in their coefficients of thermal expansion, considerable shear stresses arise in the bonding zone, which the bonding must withstand so that the bond target is not destroyed during the process.

[0006] The high energy input into the target surface during the sputtering process also places high demands on the thermal conductivity and thermal stability of the bonding. The bonding must be able to withstand the high heat input generated during a PVD process (e.g., evaporation, sputtering) and reliably dissipate the heat from the target material to the cooled target substrate. High thermal conductivity of the bonding allows for better heat dissipation and results in lower target temperatures. This reduces damage to the target material (e.g., melting) as well as the thermal stress on the bond. Area bonds are advantageous in this respect, as they allow for effective heat dissipation over a large surface area.Furthermore, the bonding agent must exhibit high thermal resistance to enable high process temperatures and thus ensure the economic efficiency of the sputtering process. High energy input during the sputtering process leads to high temperatures in the bonding zone. If the melting temperature of the bonding agent is reached, the bond target will spontaneously destroy, resulting in the failure of the coating process.

[0007] Several planar bonding methods for target bonding are already known from the prior art, namely gluing, soft soldering with indium solders, soft soldering with tin solders, and the use of so-called nanofoils. However, gluing achieves only low thermal and electrical conductivity, which limits its application in the sputtering process.

[0008] Soft soldering with indium solders achieves only low mechanical strength, so that, for example, high temperature differences can quickly lead to bond failure and destruction of the bond target. Tin solders, on the other hand, must be heated to temperatures of 230 °C to 250 °C during bonding, which means that heat-sensitive components cannot be bonded using this method.

[0009] The so-called nanofoils are based on a reactive multilayer system (RMS) and feature Ni / Al layers. However, the low energy density of these nanofoils limits their use to soft solder joints. In general, though, joining with RMS is already an established process and is described, for example, in US 5,381,944 A.

[0010] The present invention therefore aims to propose a method for producing a bond target or sputtering target that avoids the aforementioned disadvantages, thus achieving sufficient mechanical strength as well as high thermal and ideally also electrical conductivity of the resulting connection.

[0011] This problem is solved according to the invention by a method according to claim 1. Advantageous embodiments and further developments are described in the dependent claims.

[0012] In a process for manufacturing a sputtering target or bond target, an intermediate layer is inserted between a target carrier and a target layer. The intermediate layer is made of a high-energy reactive material in the form of a layered system consisting of at least two layers of different materials, where these materials are Zr and Si or Ti and C. Subsequently, a pressure is applied to the system comprising the target carrier, the intermediate layer, and the target layer, and a reaction is initiated in the intermediate layer, causing it to react exothermically and resulting in a metallurgical bond between the target layer, the intermediate layer, and the target carrier.

[0013] By replacing the nickel and aluminum materials previously used for reactive multilayer systems with higher-energy material systems such as zirconium / silicon or titanium / carbon, reliable metallurgical bonds can be formed even at room temperature. This enables the production of planar, thermally and electrically highly conductive target bonds with significantly improved mechanical and thermal properties. Furthermore, it allows for new material combinations between the target substrate and the target layer or target material, and the efficiency of current sputtering processes can be significantly increased through higher process temperatures. After the process is complete, the clamping force can be released and the resulting component can be used.The bonding process thus fulfills the main requirements for a sputtering target, namely sufficient mechanical strength combined with high thermal conductivity and thermal resilience.

[0014] It may be provided that a hard solder based on aluminum, silver, copper, or titanium is applied to the target support and / or the target layer prior to initiating the reaction, the hard solder preferably having a melting point above 450 °C. The reactive multilayer system is typically defined by the use of a binary or ternary reactive material combination of zirconium and silicon. Alternatively, a binary or ternary reactive material combination of titanium and carbon may be used. In both cases, aluminum or copper may also be present in the multilayer system. The bond enthalpy released during the reaction is generally greater than 45 kJ / mol (and can be verified by differential scanning calorimetry).By using solders based on aluminium, silver, copper or titanium, which have a significantly higher melting temperature and strength compared to soft solders, hard solder joints can be created at room temperature.

[0015] Typically, the reaction is initiated by an electric spark, an electric current, a flame, a laser pulse, a mechanical action, preferably scratching or hammering, and / or an ultrasound input, so that the reaction is started in a controlled and targeted manner.

[0016] The interlayer can have a total thickness between 5 µm and 60 µm. Preferably, the period thickness is between 10 nm and 200 nm, with a single-layer thickness of a layer in the system being between 2 nm and 150 nm. The interlayer, or reactive multilayer system, is generally a periodically structured, alternating layer system consisting of individual layers of materials such as Zr and Si or Ti and C, or their alloys (for example, ZrHf and ZrSi).

[0017] Typically, the layer system comprises at least two layers of different materials, separated by an aluminum barrier layer. This results in a clear separation of the layers, which differ in their composition. Due to its elastic properties, the aluminum barrier layer also serves to reduce residual stresses, particularly in the zirconium-silicon layer system, and simultaneously, by separating the reactive materials, to raise the ignition threshold of the reactive multilayer system sufficiently to make the fabrication of such a system possible in the first place. The aluminum barrier layer can be located either at each junction of zirconium to silicon or silicon to zirconium, or at a single junction of zirconium to silicon or silicon to zirconium. The thickness of each individual aluminum layer is preferably between 2 nm and 30 nm.When using titanium and carbon, one or more barrier layers can optionally be employed to increase the ignition threshold and thus improve the manufacturability of the reactive multilayer system. In particular, 2 nm to 30 nm thick layers of saturated chemical compounds such as boron carbide (B4C) or tetragonal aramidic carbon (ta-C) can be used to separate the reactive materials Ti and C. The use of these barrier layers effectively prevents the interdiffusion of the two reactive materials (Ti and C). Furthermore, with the Ti / C system, the ignition threshold, manufacturability, and compliance with occupational safety risks during the handling process can be precisely controlled by adjusting the individual layer thicknesses, using a multi-stage deposition process for each layer, and varying the overall layer thickness.

[0018] Before initiating the reaction, the intermediate layer can already be applied to the target support and / or the target layer. Alternatively, the intermediate layer can be introduced as a separate component or, as a further alternative, applied to the target support and / or the target layer by a process, preferably sputtering or evaporation. If the intermediate layer is applied as a separate component, i.e., as a film, it can be applied without, or with at least one functional layer applied to its outer surface, such as a solder, a wetting layer, a corrosion inhibitor, or a flux. In particular, the functional layer can be selected from a solder or solder mixture with a melting point > 450 °C, such as Al, AlSi, Cu, CuP, Ag, AgCuln, Ti, or TiCu. Ni, Cu, Ag, Au, Ti, Cr, WTi, or a mixture thereof can be used as the flux or wetting layer.It is also possible to apply the intermediate layer to one or more carrier films with thicknesses between 5 µm and 200 µm. These carrier films offer a way to deposit the reactive material system in a "free-standing" manner. Unlike established Ni / Al RMS systems, corresponding Zr / Si and Ti / C material systems cannot be produced as purely free-standing films. The residual stresses are generally too high or the ignition threshold too low, making manual detachment of the reactive material system from a substrate disproportionately hazardous. An alternative is therefore to deposit Zr / Si and Ti / C reactive material systems onto very thin films. These thin carrier films allow for the production of a universally applicable energy carrier.This eliminates the need to coat each individual target or target carrier with the reactive material system; instead, a semi-finished product can be provided that can be manufactured on a large scale. A carrier film consists of solder, solder mixture, flux, or wetting layer material, or at least any combination of these components. When applied directly by sputtering or evaporation, the aforementioned functional layers can also be used or omitted. In both cases, the layer thickness is between 5 µm and 60 µm.

[0019] The target layer can also comprise a sputterable material, preferably a metal, a metal alloy, a semimetal, a solder, a ceramic, an oxide, or a mixture of at least two of the aforementioned materials. Alternatively or additionally, the target support can be a plate made of copper, molybdenum, optionally with added alloying elements, or pre-coated with the reactive multilayer system or material system. The target support can be round, oval, or rectangular, and is typically flat or with chamfers or steps. The target layer and / or the target support can be provided with an adhesive layer and / or a wetting layer, which typically comprises or consists of Ni, Cu, Ag, Au, Ti, Cr, WTi, or mixtures thereof.Alternatively or additionally, a solder or solder mixture with a melting temperature of more than 450 °C such as Al, AlSi, Cu, CuP, Ag, AgCuln, Ti or TiCu can be applied.

[0020] A sputtering target or a bond target has a target carrier and a target layer, wherein an intermediate layer made of a high-energy reactive material in the form of a layer system of at least two layers of different materials is arranged and metallurgically bonded between the target carrier and the target layer.

[0021] An embodiment of the invention is described in Fig. 1 is shown and explained using this drawing. Fig. Figure 1 shows a schematic side view of a sputtering target 1 (which in other embodiments can also be a bond target) composed of several layers. These layers consist of a target layer 2 as the top layer and a target carrier 3 as the bottom layer. An intermediate layer 4 is arranged between the target layer 2 and the target carrier 3.

[0022] The intermediate layer 4 is formed from a high-energy reactive material and exists as a layered system comprising at least two layers of different materials. These materials include zirconium and silicon, or, in an alternative embodiment, at least titanium and carbon. In particular, it can be provided that the materials do not include nickel and / or aluminum, meaning that the intermediate layer 4 is free of these two materials or contains them only in small amounts that are unavoidable in the production process. The individual layers are separated from each other, if necessary, by an aluminum barrier layer. The reactive material, which is also referred to as a reactive material system, is a reactive material system.This can be described as a reactive multilayer system, thus comprising a binary or ternary reactive material combination of the aforementioned materials, which may also contain aluminum and copper. The bond enthalpy released during a reaction is greater than 45 kJ / mol.

[0023] To produce the in Fig.In the sputtering target 1 shown, an intermediate layer 4 is inserted between the target carrier 3 and the target layer 2. The intermediate layer 4 can have the same dimensions and shape as the target layer 2, except for its thickness, so that they lie flush on top of each other. A pressure is applied to this arrangement to fix the individual layers and initiate a reaction, causing the intermediate layer 4 to react exothermically and form a metallurgical bond between the target layer 2, the intermediate layer 4, and the target carrier 3. Finally, the pressure is released, and the sputtering target 1 can be used.

[0024] The intermediate layer 4 can be structured as a periodically arranged, alternating layer system or system of layers consisting of individual layers or individual materials or their alloys (e.g., ZrHf, ZrSi), whereby Zr and Si or Ti and C must be present at least partially in their elemental form. Individual layer thicknesses are typically in the range of 2 nm to 150 nm, and the period thickness of the alternating layer system is between 10 nm and 200 nm.

[0025] The intermediate layer 4 can, for example, be provided as a separate component, such as a film. The outer surfaces can be free of any functional layers such as solders, wetting agents, corrosion protection layers, or fluxes; however, these functional layers can, of course, also be applied. In this case, the intermediate layer 4 can also be applied to one or more carrier films with a thickness between 5 µm and 200 µm. These carrier films can be made of metallic foils, in particular metallic foils of solder and solder mixtures with a melting point greater than 450 °C, such as Al, AlSi, Cu, CuP, Ag, AgCuln, Ti, or TiCu. The carrier films can also contain or be coated with fluxes.

[0026] The intermediate layer 4 can also be applied directly to the target carrier 3 and / or the target layer 2 by sputtering or evaporation. In both cases, the total thickness of the intermediate layer 4 is in the range of 5 µm to 60 µm.

[0027] The sputtering target system thus produced comprises the target layer 2 and the target carrier 3, which are connected to the reactive material system and, if necessary, to additional solder by the intermediate layer 4, a process also known as bonding. The target carrier 3 is typically plate-shaped with a round or rectangular base, and can be flat or have chamfers or steps made of copper, molybdenum, and, if necessary, other alloying elements. It is also possible that it is pre-coated with the intermediate layer 4 before the process begins. The target layer 2 can be made of any sputterable material, in particular a metal or metal alloy, a semimetal, a solder, a ceramic, an oxide, or mixtures thereof. The target layer 2 and / or...The target carrier 3 can be coated with solder or a solder mixture with a melting point greater than 450 °C prior to the actual manufacturing process of the sputtering target 1. Typical materials suitable for this include Al, AlSi, Cu, CuP, Ag, AgCuln, Ti, or TiCu. Furthermore, the target layer 2 and the target carrier 3 can be coated with flux.

[0028] In the process itself, the target layer 2 and the target carrier 3 are positioned to produce the sputtering target 1. A solder or an additional material that liquefies during the reaction of the intermediate layer 4 can be applied to one or both components. After everything has been positioned and a contact pressure applied, the reaction of the intermediate layer 4 is initiated by an electric spark, an electric current, a laser pulse, a mechanical action such as scratching or hammering, or ultrasonic stimulation. The intermediate layer 4, or rather the reactive material system contained within it, subsequently reacts exothermically, releasing heat, melting itself and / or the solder, a functional layer (if present), or the base materials of the target layer 2 or the target carrier 3, thus bonding the target layer 2 and the target carrier 3 together. At the end of the process, the contact pressure is released.Compared to established target bonding methods such as soft soldering and elastomer bonding, the mechanical strength, thermal conductivity, thermal stability, and fatigue strength of the bond can be significantly increased by using hard solders. This opens up the possibility of new target materials, new coating processes, and higher coating rates, leading to a significant increase in the cost-effectiveness of sputtering processes. The described method is primarily used for target bonding in sputtering and coating processes, but it can also be used more generally for joining with hard solders in toolmaking, power electronics, and battery technology—in other words, in all areas where a large-area, strong, thermally (and potentially electrically) highly conductive, and temperature-resistant connection is required. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 5 381 944 A

[0009]

Claims

[1] Method for producing a sputtering target or bond target (1) wherein An intermediate layer (4) is introduced between a target carrier (3) and a target layer (2), wherein the intermediate layer (4) is formed from a high-energy reactive material in the form of a layer system consisting of at least two layers of different materials, where these materials contain Zr and Si or Ti and C, and subsequently a pressure force is applied to the system consisting of the target carrier (3), the intermediate layer (4) and the target layer (2), and furthermore a reaction of the intermediate layer (4) is initiated, so that the intermediate layer (4) reacts exothermically and the target layer (2), the intermediate layer (4) and the target carrier (3) are chemically bonded together. [2] Method according to claim 1, characterized by, that a hard solder based on Al, Ag, Cu or Ti is applied to the target carrier (3) and / or to the target layer (2) before initiating the reaction, wherein the hard solder preferably has a melting temperature of more than 450 °C. [3] Method according to claim 1 or claim 2, characterized by that the reaction is initiated by an electric spark, an electric current, a flame, a laser pulse, a mechanical action, preferably scratching or hammering, and / or an ultrasound input. [4] Method according to any one of the preceding claims, characterized by , that the intermediate layer (4) has a total thickness between 5 µm and 60 µm, preferably with a period thickness between 10 nm and 200 nm, wherein a single layer thickness of a layer of the layer system is between 2 nm and 150 nm. [5] Method according to any one of the preceding claims, characterized bythat the layer system has at least two layers made of different materials and that these two layers are separated from each other by an Al barrier layer. [6] Method according to any one of the preceding claims, characterized by that the intermediate layer (4) is already applied to the target carrier (3) and / or to the target layer (2) or is introduced as a separate component or is applied to the target carrier and / or to the target layer by a process, preferably sputtering or evaporation. [7] Method according to any one of the preceding claims, characterized by that the target carrier (3) and / or the target layer (2) has an adhesive layer which preferably comprises Ni, Cu, Ag, Au, Ti, Cr, or WTi. [8] Method according to any one of the preceding claims, characterized by, that the target layer (2) comprises a sputterable material, preferably a metal, a metal alloy, a semi-metal, a solder, a ceramic, an oxide or a mixture of at least two of the aforementioned materials. [9] Sputter target or bond target (1) with a target support (3) and a target layer (2), wherein an intermediate layer (4) made of a high-energy reactive material in the form of a layer system of at least two layers of different materials is arranged and metallurgically bonded between the target support (3) and the target layer (2).

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