WO2005094280A2

WO2005094280A2 - High-strength backing plates, target assemblies, and methods of forming high-strength backing plates and target assemblies

Info

Publication number: WO2005094280A2
Application number: PCT/US2005/010111
Authority: WO
Inventors: Stephane Ferrasse; Frank Alford
Original assignee: Honeywell International Inc.
Priority date: 2004-03-31
Filing date: 2005-03-24
Publication date: 2005-10-13
Also published as: TW200540956A; WO2005094280A3

Abstract

The invention includes backing plates having grain sizes of less than 10 microns and yield strengths of at least 30 ksi. The invention includes methods of producing backing plates by hot-forging, severe plastic deformation utilizing equal channel angular extrusion, and post-deformation processing utilizing at least one of rolling and forging. The backing plates have grain sizes of less than 10 microns and yield strengths of at least 30 ksi. The invention includes a target assembly including a target having a grain size of less than about 10 microns joined to a backing plate having a grain size of less than about 10 microns with a bond strength of at least 10 ksi. The invention includes methods of forming a target assembly by joining a target and a backing plate having an average grain size of less than about 10 microns and a yield strength of at least 30 ksi.

Description

HIGH-STRENGTH BACKING PLATES, TARGET ASSEMBLIES, AND METHODS OF FORMING HIGH-STRENGTH BACKING PLATES AND TARGET ASSEMBLIES

TECHNICAL FIELD [0001] The invention pertains to high-strength backing plates, target assemblies, methods of forming high-strength backing plates, and methods of forming target assemblies. BACKGROUND OF THE INVENTION [0002] Physical vapor deposition methodologies are used extensively for forming thin films of material over a variety of substrates. One area of extreme importance for such deposition technology is semiconductor fabrication. A diagrammatic view of a portion of an exemplary physical vapor deposition apparatus 10 is shown in Fig. 1. Apparatus 10 comprises a backing plate 12 having a sputtering target 14 bonded thereto. A semiconductive material wafer 16 is within apparatus 10 and provided to be spaced from target 14. A surface 15 of target 14 is a sputtering surface. In operation, sputtered material 18 is displaced from surface 15 of target 14 and utilized to form a coating (or thin film) 17 over wafer 16. [0003] Although monolithic targets are available for some sputtering applications

(where monolithic refers to a target formed from a single piece of material and utilized without a backing plate), most targets are joined to a backing plate as depicted in Fig. 1. It is to be understood that the target/backing plate assembly depicted in Fig. 1 is an exemplary configuration since both the target and the backing plate can be any of a number of sizes or shapes as will be understood by those skilled in the art. [0004] Various materials including, but not limited to, metals and alloys are deposited utilizing physical vapor deposition. Common target materials include, for example, aluminum, titanium, copper, tantalum, nickel, molybdenum, gold, silver, platinum and alloys thereof. Backing plates are commonly used for most applications involving these materials due to the convenience of mounting in sputtering systems and the ability to provide strength for supporting the target especially under pressures exerted by cooling systems. Target backing plate assemblies can also be less expensive than corresponding monolithic targets. [0005] Conventional backing plates are typically formed from copper, copper alloys (e.g. CuCr, CuZn) or aluminum alloys (e.g. AI6061 , AI2024). These materials are typically chosen due to their thermal electrical and/or magnetic properties. Aluminum alloys can have up to three times lower density than copper alloys but also can have a weaker Young's modulus. Fabrication of conventional aluminum or copper comprising backing plates can include alloy strengthening utilizing, for example, dispersion and precipitation of very fine second phase precipitates. However, these conventional backing plate materials typically have a fairly large grain size, consistently well over 10 microns. [0006] Advances in semiconductor wafer fabrication technology have led to a demand for increasingly large targets, especially for fabrication of 300 mm size wafers. Larger target sizes in turn require high strength backing plate materials to minimize or avoid target warping. Although many improvements have been made in backing plate materials, increasingly stronger materials are needed to provide sufficient strength for supporting larger target dimensions, especially under the increasingly high sputtering power being utilized to improved film quality and uniformity. [0007] Conventional backing plate materials are often of insufficient strength for large targets thereby limiting the size of high quality targets. Conventionally formed backing plates which are thick enough to support relatively large targets are very heavy. The weight of the backing plate can make target/backing plate assembly and mounting difficult. Finally, conventional backing plate materials often provide poor bond strength when the target is bonded to the backing plate. [0008] It is desirable to develop backing plates and backing plate materials having improved strength and bonding properties. SUMMARY OF THE INVENTION [0009] In one aspect the invention encompasses a high-strength backing plate which has an average grain size of less than 10 microns and has a yield strength of at least 30 ksi. [0010] In one aspect the invention encompasses a method of producing a target backing plate. The method includes performing preliminary processing which includes hot forging, and performing severe plastic deformation processing utilizing at least one of equal channel angular extrusion (ECAE), torsion, accumulative roll bonding (ARB), cyclic pressing or extrusion, friction stir welding, corrugative drawing, cryogenic rolling or pressing, and hammer forging. The method additionally includes performing post- deformation processing which utilizes at least one of rolling and forging. The target backing plate has an average grain size of less than 10 microns and has a yield strength of at least about 30 ksi. 2

S \H057\537\pctformat doc [0011] In one aspect the invention encompasses a target assembly which includes a target and a backing plate. The target includes a first material which has an average grain size of less than about 10 microns. The backing plate comprises a second material which also has an average grain size of less than about 10 microns. The target and backing plate are bonded to each other with a bond having a bond strength of at least 10 ksi. [0012] In one aspect the invention encompasses a method of forming a target assembly. The method includes providing a target and a high-strength backing plate, and joining the target to the backing plate. The target comprises a first material, and the backing plate comprises a second material which has an average grain size of less than about 10 microns and has a yield strength of at least 30 ksi. BRIEF DESCRIPTION OF THE DRAWINGS [0013] Preferred embodiments of the invention are described below with reference to the following accompanying drawings. [0014] Fig. 1 is a diagrammatic view of a portion of a prior art physical vapor deposition apparatus. [0015] Fig. 2 is a flowchart diagram illustrating methodology encompassed by one aspect of the present invention. [0016] Fig. 3 is a diagrammatic cross-sectional view of a material being treated with an equal channel angular extrusion apparatus. [0017] Fig. 4 shows the effects of processing including equal channel angular extrusion, peak aging and recovery annealing on the yield strength of aluminum alloy AI6061. [0018] Fig. 5 shows effects of recovery annealing upon electrical conductivity of peak aged AI6061 processed utilizing equal channel angular extrusion. [0019] Fig. 6 shows effects of recovery annealing upon the percent elongation of a peak aged, equal angular extruded aluminum alloy AI6061. [0020] Fig. 7 shows effects of equal channel angular extrusion and recovery annealing on yield strength of a heat treatable aluminum-lithium alloy after peak aging. [0021] Fig. 8 shows effects of equal channel angular extrusion and recovery annealing upon the yield strength of non heat treatable alloys AI3004 and AI5052. [0022] Fig. 9 shows a comparison of the yield strength of standard CuCr and various equal channel angular extruded copper and copper alloys at 250°C, 350°C and 450°C. 3

S \H057\537\pctformat doc [0023] Fig. 10 is a TEM at a magnification of x 10,000 which shows the microstructure of an equal channel angular extruded aluminum alloy having an average grain size of 0.5 micron. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0024] One aspect of the invention is production of high strength backing plate materials and backing plates having improved strength and bonding characteristics. Methods of producing high strength backing plate materials, high strength backing plates, and target/backing plate assemblies according to the invention are described. [0025] Although high strength monolithic targets have been developed which can be utilized in certain instances to eliminate problems linked with bonding and bond strength between targets and backing plates, the usefulness of monolithic targets can be limited due to relatively poor strength of high purity target materials used for modern electronic device fabrication. Additionally, monolithic targets can be relatively heavy and expensive as compared to targets which can be bonded to a lighter and/or stronger backing plate material. [0026] Although conventional backing plate materials can be satisfactory for some applications, where large targets are desired and/or where high sputtering power is to be utilized, high strength backing plate materials can be essential to avoid warping and to provide sufficient strength to support large target sizes. Further, high strength backing plate materials of the invention can allow higher target to backing plate bond strength (discussed below). [0027] In general, qualities desirable for modern backing plates for use in advance sputtering system applications include: high mechanical strength including Young's modulus and yield strength since these properties affect target assembly deformation and warping during sputtering; light weight to allow relatively easy handling and mounting; thermal expansion coefficient comparable or matched to a specific target material to minimize or avoid de-bonding during sputtering; high thermal conductivity for enhanced or optimization of cooling efficiency; composition and physical metallurgical properties that allow for high strength joining and bonding which can preferably produce bond strength of greater than 10 ksi; and electrical and magnetic properties similar to the specific target material to enhance or optimize magnetic and electrical fluxes during sputtering. [0028] Backing plate materials and backing plates in accordance with the invention can preferably comprise an aluminum alloy, copper or a copper alloy. These

S:\H057\537\pctformat.doc materials can be preferred in many instances due to their thermal and electrical conductivity, magnetic properties and coefficient of thermal expansion. The invention also encompasses alternative backing plate materials including but not limited to Ti, Ag, Fe, Co, Ni, Mo, Cr, Si, Ta, Sn, In, and alloy thereof. [0029] An appropriate backing plate material can be chosen based on the material of the sputtering target to which the backing plate will ultimately be joined. Typical sputtering targets for target/backing plate assemblies in accordance with the invention include targets comprising Al, Cu, Ti, Ni, Co, Ta, Mo, W, Cr, Si and alloys thereof. The backing plates of the invention can be joined to the targets utilizing any bonding technique including, but not limited to, soldering, brazing, solid state diffusion bonding, hipping, explosive bonding, hot rolling, and mechanical joining. [0030] In particular instances, it can be preferable that the backing plates of the present invention be utilized with high strength sputtering targets such as those formed utilizing equal channel angular extrusion (ECAE) or other severe plastic deformation techniques. Due the relatively small grain size in targets produced utilizing ECAE, the high strength backing plate materials of the invention in combination with ECAE targets can produce an increase in bond strength relative to alternative target materials and/or backing plate materials. [0031] Materials which can be utilized for backing plates in accordance with the invention include heat-treatable and non-heat-treatable materials, where heat-treatable materials are those that can be hardened by heat treatment, and non-heat-treatable materials are those which are not hardenable and/or can lose strength through thermal treatment. As will be described, the general methodology and processing in accordance with the invention can be modified and adapted based upon the heat treatability of the specific material to be utilized for the backing plate. [0032] General methodology for processing of heat-treatable and non-heat- treatable materials in accordance with the invention can typically include casting of an ingot of material, preliminary thermal processing, and extruding utilizing equal channel angular extrusion. The general processing can also, in some instances, utilize annealing at one or more stages of processing of the material. The described methodology can be utilized for forming high strength backing plates, high strength backing plate materials and backing plate/target assemblies in accordance with the invention.

S \H057\537\pctlormat doc [0033] Methodology of the invention is described generally with reference to

Figs. 2-3. An exemplary processing scheme 100 for treating aluminum alloys, copper, or copper alloys is shown in Fig. 2. The outlined process shown in Fig. 2 can be utilized for both heat-treatable and non heat-treatable alloys. Heat-treatable alloys can optionally undergo additional processing treatments (described below). [0034] An initial alloy material can be provided to an initial processing step 110.

The initial processing can comprise, for example, one or more of standard-casting, forging, solutionizing and homogenizing. As will be understood by those skilled in the art, appropriate temperatures for conducting solutionizing, homogenizing or hot-forging can depend upon the specific composition of the initial material. [0035] In particular aspects, the invention preferably comprises hot-forging during preliminary processing. Hot-forging can comprise a single heating or can comprise an initial heating and one or more subsequent reheating events. The height reduction produced during each forging event between the initial heating and each subsequent reheating can vary depending on factors such as the particular composition and forging temperature utilized. Any quenching that is conducted can preferably occur only after the final reheating. Where quenching is conducted, the quenching preferably immediately follows the hot-forging. Although alternative quenching techniques can be utilized it can be preferable to utilize water quenching. [0036] Where the backing plate material comprises aluminum, the hot-forging is preferably conducted at a temperature of above 200°C, and more preferably at about 300°C, with a total reduction of at least about 40%. Initial processing of aluminum materials preferably additionally comprises solutionizing at a temperature of above about 400°C for a time period of at least about 1 hour, followed by either water or oil quenching. In the absence of solutionizing, the preliminary processing of aluminum materials can preferably include an annealing step at a temperature of above about 200°C for at least 1 hour to allow static recrystallization of the initial material. [0037] Where the backing plate material comprises copper or a copper alloy, hot-forging is preferably conducted at a temperature of above 200°C, and more preferably at about 350°C, with a total reduction of at least about 40%. Initial processing of copper materials preferably additionally comprises solutionizing at a temperature of above about 500°C for a time period of at least about 1 hour, followed by either water or oil quenching. In the absence of solutionizing, the preliminary processing of copper and copper alloy materials can preferably include an annealing 6

S \H057\537\pclformat doc step at a temperature of above about 250°C for at least 1 hour to allow static recrystallization of the initial material. [0038] Where the preliminary treatment includes hot-forging and an additional heat treatment step, the additional heat treatment can precede or follow the hot-forging and can comprise solutionizing and/or homogenizing of the initial material. Heat treatment can be conducted at a temperature sufficient to induce solutionization and/or homogenization to occur in the particular composition being treated. The solutionizing/homogenizing temperature can preferably be maintained for time sufficient to maximize the solutionization and/or homogenization of the composition. [0039] It is to be noted that temperatures sufficient for solutionizing or homogenizing can result in grain growth producing a grain size above the desired ultimate grain size for the backing plate material. Accordingly, conventional methods which attempt to achieve smaller grain sizes tend to minimize solutionizing or homogenizing treatments. However, methodology according to the present invention allows post homogenization/solutionization reduction in grain size and can thereby achieve the benefits of both the solutionizing/homogenizing treatment and small grain size. It can be advantageous to solutionize and or homogenize during preliminary treatment step 110 to dissolve any precipitates and/or particles present in the initial material. Homogenizing can additionally decrease or eliminate chemical segregation within the material being processed. [0040] Preliminary treatment processes of the present invention are not limited to particular ordering of homogenizing, solutionizing and/or hot-forging treatments. In particular aspects, preliminary treatment 1 10 can comprise homogenizing of a cast material followed by hot-forging and subsequent solutionizing. In other instances, solutionizing can be conducted followed by hot-forging. [0041] Following the preliminary treatment, the hot-forged material can subsequently undergo severe plastic deformation processing 120, preferably utilizing equal channel angular extrusion (ECAE). Referring to Fig. 3, such illustrates an exemplary ECAE device 20. Device 20 comprises a mold assembly 22 that defines a pair of intersecting channels 24 and 26. Intersecting channels 24 and 26 are identical or at least substantially identical in cross-section, with the term "substantially identical" indicating the channels are identical within acceptable tolerances of an ECAE apparatus. In operation, a preliminary treated material (which can be the hot-forged material described above) is extruded through channels 24 and 26. Such extrusion 7

S \H057\537\pctformat doc results in plastic deformation of the material by simple shear, layer after layer, in a thin zone located at the crossing plane of the channels. Although it can be preferable that channels 24 and 26 intersect at an angle of about 90°, it is to be understood that an alternative tool angle can be utilized (not shown). The tool angle (channel intersect angle) of about 90° can be preferable since an optimal deformation (true shear strain) can be attained. [0042] ECAE can introduce severe plastic deformation in the preliminary processed material while leaving the dimension of the block of material unchanged. ECAE can be a preferred method for inducing severe strain in a metallic material in that ECAE can be utilized at low loads and pressures to induce strictly uniform and homogenous strain. Additionally, ECAE can achieve a high deformation per pass (true strain ε=1.17); can achieve high accumulated strains with multiple passes through an ECAE device (at n=4 passes, ε=4.64); and can be utilized to create various textures/microstructures within materials by utilizing different deformation routes (i.e. by changing an orientation of the forged block between passes through an ECAE device). [0043] The material being processed by ECAE can be passed through the

ECAE apparatus several times and with numerous routes. A preferred route to utilize with multiple passes through ECAE apparatus 20 can be the "route D", which corresponds to a constant 90° rotation of the block of material before each successive pass. [0044] ECAE processing in accordance with the invention includes at least one pass, will typically include at least two passes and preferably between 4 and 6 passes in order to produce a sub-micron structure, where sub-micron structure refers to a structure having an average grain size of less than 1 micron. Where intermediate annealing between passes is utilized or where the die are heated during ECAE passes, the temperature utilized is preferably less than a temperature which would cause an increase in grain size over 1 micron for the particular material being processed. [0045] During ECAE processing, the extrusion can be conducted either at a cold or a hot processing temperature. For aluminum alloys, the ECAE is preferably conducted at temperatures between 125°C and 450°C where the processing temperature is achieved by heating of the ECAE dies. Alternatively to or in addition to heating of the dies during the ECAE passes, intermediate annealing between passes may be conducted. When utilized, intermediate annealing of aluminum alloy materials is preferably conducted at a temperature of from 125°C and 450°C. 8

S \H057\537\pctformat doc [0046] For copper or copper alloys, where heating is conducted during ECAE passes and/or during one or more intermediate anneal treatment, the heating preferable at a temperature of from about 125°C and 450°C. [0047] The ECAE processing, along with the described thermo-mechanical heat treatments, can be utilized to refine the microstructure of backing plate materials to produce an average grain size of less than or equal to about 10 microns and in particular instances can produce an average grain size of less than about 1 micron. These exceedingly small grain sizes can dramatically increase the yield strength of material relative to conventional backing plate materials which typically have a grain size of well over 10 microns. A typical increase in yield strength of material processed in accordance with the invention is at least 1.5 times the yield strength of the same material processed by conventional methods. In particular instances the increase in yield strength can be from about 2 to about 5 fold relative to the yield strength of conventional materials. The increase in strength of backing plates produced in accordance with methodology of the invention can also allow backing plates to be made thinner to support a given target relative to conventional backing plates. The high strength backing plate materials of the invention can inhibit or prevent target warping and can additionally assist solid state diffusion bonding between the backing plate and target (discussed below). [0048] In addition to strengthening backing plate materials, equal channel angular extrusion or alternative severe plastic deformation techniques can substantially increase the coefficient of diffusion along grain boundaries relative to conventionally processed materials. The enhanced diffusion properties equate to a greater efficiency for bonding at a given set of conditions (temperature, time and pressure) relative to conventionally processed materials. Accordingly, to produce a bond strength equivalent to conventional methods, the bonding temperature can be decreased relative to temperatures utilized for bonding conventional materials. This decreased bonding temperature can allow decreased grain growth in both the target and the backing plate during the bonding processing. Accordingly, the target and backing plate materials are better able to retain the strength imparted by the fine grain size of the materials, particularly in instances where both the backing plate material and target materials have grain sizes of less than 10 microns and in particular instances less than 1 micron producible by ECAE methodology.

S \H057\537\pctformat doc [0049] Production of target backing plates in accordance with the invention utilizing ECAE can be especially advantageous for non-heat-treatable alloys (those whose strength is not increased by thermal treatments such as aging). ECAE plastic deformation of non-heat-treatable alloys can strengthen such materials by grain refinement to produce a sufficiently high strength without the need for aging. Similarly, high purity materials can be utilized for backing plates when processed according to methods of the invention including ECAE since the described processing can impart sufficient strength for such materials to be utilized as a backing plate. Prior to the methodology described herein, high purity materials were typically not utilized for backing plate applications since an absence or low level of alloying element did not sufficiently provide dispersion or precipitation strengthening for backing plate applications. [0050] Although the severe plastic deformation step 120 is described as comprising equal channel angular extrusion, alternative plastic deformation techniques can be utilized individually or in addition to equal channel angular extrusion. Exemplary alternative plastic deformation techniques include torsion, accumulative roll bonding (ARB), cyclic pressing or extrusion, friction stir welding, corrugative drawing, cryogenic rolling or pressing, hammer forging and related techniques. [0051] After severe plastic deformation 120, a post-deformation processing 130 can be conducted. Post-plastic deformation processing can comprise one or both of rolling and forging. The forging and/or rolling is preferably conducted produce a total reduction of less than 90% to achieve a final backing plate thickness. Machining and or other shaping techniques can be utilized either independently or in combination with forging and/or rolling. [0052] Post-deformation processing step 130 can optionally comprise an annealing treatment such as, for example, recovery annealing. Where recovery annealing is included in the processing, the recovery annealing is preferably conducted at a temperature and for a time insufficient to induce grains to grow over 10 microns. In particular instances, it is preferable that the recovery annealing maintains a grain size of less than or equal to 1 micron. In other words, post plastic deformation annealing is preferably conducted under conditions insufficient to result in static recrystallization of the corresponding material. It can be advantageous to include recovery annealing after plastic deformation to reduce defects and free energy present at grain boundaries particularly in materials having submicron grain sizes. The recovery anneal can be 10

S \HOS7\S37\pctformat doc critical for release of internal stresses and optimization of properties such as ductility and/or conductivity. [0053] Recovery annealing of aluminum alloys in accordance with the invention is typically conducted at temperatures between 100°C and 450°C for at least 1 hour. For copper and copper alloy materials, recovery annealing can typically utilize temperatures of from 100°C and 550°C for at least 1 hour. [0054] Upon completion of post-deformation processing step 130, processing of the invention can proceed to preparation and bonding of the resulting backing plate to a sputtering target to produce a target/backing plate assembly. A bonding step 140 can include surface preparation such as cleaning, machining and/or electroplating. Where preliminary surface treatment includes machining, the machining can include, for example, machining grooves in the backing plate surface which will ultimately be bonded to the target. Such machine grooves can help diffusion processes during target-backing plate joining. Additionally, in particular instances preliminary surface treatment prior to bonding can include providing an insert to enhance bonding ability and/or bond strength. Insert materials can comprise, for example, Ag, Ni or Cu. [0055] Upon completion of any preliminary surface treatment, the resulting backing plate can be bonded to a target by utilizing any of a number of bonding techniques. Bonding can comprise low temperature or high temperature bonding depending upon the particular backing plate material and target material to which the backing plate is to be bonded. Exemplary bonding techniques which can be utilized for bonding the backing plate materials of the invention include, but are not limited to, soldering, brazing, solid phase bonding, roll cladding, friction stir welding, hot isostatic pressing, explosion bonding, and mechanical joining techniques. In particular instances, solid phase bonding can be utilized, where solid phase bonding refers to bonding between a target and a backing plate while both the target and backing plate materials are in their solid phase. Solid phase bonding can produce diffusion bonding to occur along bonding interface without affecting the microstructure and precipitates of the target and backing plate materials. The solid phase bonding can be performed utilizing insert material as described above. Alternatively, one or more of electroplating, ionization and surface machining can be utilized to enhance diffusion bonding processes and the strength of the resulting bond. [0056] Target/backing plate assemblies produced in accordance with the methodology of the invention can typically have a bond strength of at least about 10 ksi. 11 In particular instances, bonds between backing plates of the invention and sputtering targets can exceed 15 ksi, with the strongest bonds being formed where both the target and the backing plate have submicron grain sizes. [0057] Methodology of the present invention can also be utilized to produce backing plates from heat-treatable materials with increased strength and bonding properties relative to backing plates produced by conventional methods. Processing of heat-treatable materials in accordance with the invention can in general include all of the processing steps discussed above with reference to Fig. 2. It is noted that processing of heat-treatable aluminum alloys, copper and copper alloys in accordance with the invention typically includes solutionizing treatment in initial processing step 1 10. [0058] For heat-treatable aluminum alloys, solutionizing treatment can typically be conducted at a temperature of between 500°C and 600°C, for a time period of greater than 1 hour, followed by either water or oil quenching. Where the material is a heat-treatable copper or copper alloy, the solutionizing treatment typically comprises a temperature of about 500°C which is maintained for a period of over 1 hour and is also followed by water or oil quenching. [0059] In addition to the processing utilized for non-heat-treatable alloys, processing of heat-treatable alloys in accordance with the invention can additionally comprise one or more aging steps. The aging can be performed before ECAE, after ECAE and/or between ECAE passes. Where rolling and/or forging is utilized, the aging can be conducted either prior to or after such rolling/forging processes. [0060] Aging of heat-treatable materials in accordance with the invention can comprise either peak aging or over aging conditions, where peak aging refers to aging at a temperature for a length of time for maximum production of very small precipitates. Upon achieving peak aging, the materials of the invention are preferably cooled to prevent over aging since over aging can result in precipitate coalescence or enlargement thereby decreasing strength of the material. However, it is to be understood that peak aging is a preferred embodiment and over aging of materials is also contemplated by the invention. [0061] Aging can be utilized to produce uniformly dispersed fine precipitates and, where peak aging is formed, precipitates can preferably have a maximum diameter of less than 1 micron and more preferably less than 0.5 micron to achieve optimal strengthening. In heat-treatable materials, the combination of grain refinement by equal channel angular extrusion and formation of exceedingly fine precipitates by aging can 12

S \H057\537\pctformat doc have a cumulative strengthening effect. Additionally, aging can increase the thermal stability of the sub-micron grain structures due to pinning effect of the fine precipitates present at grain boundaries of the sub-micron grains. [0062] Aging of heat-treatable aluminum alloys can typically comprise one or more aging steps at a temperature of between 100°C and 300°C for greater than 30 minutes. Aging of copper or copper alloys of the invention can typically comprise one or more aging treatments at temperatures of between 100°C and 300°C for at least 30 minutes. [0063] The described methodology of the invention can be utilized for producing backing plates from any desired heat-treatable or non-heat-treatable backing plate material. In particular instances, backing plate materials can preferably be aluminum alloys, copper or copper alloy materials. These aluminum and copper materials can be particularly useful as backing plate materials due to their thermal and electrical conductivities and magnetic properties. Exemplary aluminum alloy backing plate materials which can be favorably processed to produce high strength backing plates in accordance with the invention include aluminum alloys comprising aluminum and from about 0.05% to about 15%, by mass, of one or more alloying elements selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Cu, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc, and Hf. In particular instances preferred alloying elements can be selected from Si, Mn, Mg, Fe, Li, Cu, Zr, Zn, V, Sc, Ti and Cr. In particular embodiments, the aluminum alloys of the invention can consist essentially of or consist of aluminum and one or more of these alloying elements. [0064] Activation energy values for grain boundary diffusion of conventional materials and aluminum, copper and copper alloy materials of the invention are set forth in Table 1. As shown in the table, copper materials and copper alloy materials subjected to ECAE treatment in accordance with the invention have activation energies decreased approximately 1.5 times relative to conventional materials. Aluminum alloys processed in accordance with the invention including ECAE show a decrease in activation energy of about 2-3 times relative to conventional alloys or pure aluminum. Results similar to those presented in the table were obtained for additional copper and aluminum alloys processed in accordance with the invention. The low activation energy corresponds to an increase in coefficient of diffusion by approximately 1.5-6 orders of magnitude. Such is indicative of a high atomic mobility of non-equilibrium grain boundaries of materials processed utilizing equal channel angular extrusion. 13

SΛH057\537\pctforma1 doc TABLE 1 : Activation Energies

[0065] Figs. 4-10 set forth various properties of backing plate materials processed in accordance with methodology described herein. Referring initially to Fig. 4, such shows the effect of aging on the yield strength of a conventional aluminum alloy AI6061. This alloy is widely used for conventional backing plates due to its heat treatability, light weight, low expense, as well as its welding and bonding properties. Typical time and temperature for soldering/brazing for solid phase bonding of conventional AI6061 backing plates to an aluminum or a copper target (or aluminum alloy or copper alloy targets) is from 225°C to 300°C for approximately 2-3 hours for aluminum and aluminum alloy targets, and approximately 1 hour for copper or copper alloy targets. However, at temperatures over 200°C, fine precipitates created by peak aging grow and coalesce thereby decreasing the yield strength as shown in Fig. 4. As a result the backing plate strength is non-optimal and after annealing at 225°C for one hour is less than 30 ksi. [0066] In comparison, curves 2 and 3 show the yield strength of materials in accordance with the invention that have been processed utilizing ECAE and aging. Curve 2 represents AI6061 after deformation utilizing four ECAE passes via route D, and subsequent peak aging at 100°C for 40 hours. Curve 3 represents yield strength for AI6061 which has been peak aged at 175°C for 8 hours and subjected to severe plastic deformation via four ECAE passes utilizing route C. Each of the materials represented in curve 2 and curve 3 have a structure with an average grain size less than 1 micron with such structure being maintained after annealing of two hours at 280°C. ECAE performed either before or after aging can increase strength by 20-50% for recovery annealing over a wide range of temperatures, and yield strengths of greater than 30 ksi can be maintained for annealing temperatures of up to 275°C. These results indicate that for the most common range of bonding temperatures (180°C-300°C for 14

S \H057\537\pctforrnat doc soldering/brazing, and 200°C-300°C for solid state bonding) equal channel angular extrusion can greatly improve the strength of AI6061 backing plates. [0067] Recovery annealing additionally affects the electrical conductivity and elongation properties of backing plate materials of the invention. Referring to Fig. 5, such shows the effect on electrical conductivity of annealing for one hour as a function of temperature. As shown, electrical conductivity increases with anneal temperature. Similarly, elongation properties are also improved upon annealing at higher temperatures as shown in Fig. 6. Accordingly, when utilizing equal channel angular extruded AI6061 backing plate materials, annealing can preferably be conducted at a temperature of 175°C to 275°C to allow improved electrical conductivity and elongation while maintaining high strength and average grain size of less than 1 micron. [0068] Referring to Fig. 7, such shows the effect of equal channel angular extrusion and recovery annealing on yield strength of a peak aged AI7075 alloy relative to non-aged (lower curve) Al-Li alloy. Each of the two alloys depicted in Fig. 7 are inherently stronger than AI6061 and have a grain size achieved by ECAE of less than 1 micron after treatment of at least 300°C for one hour. The yield strength of each of these alloys is over 40 ksi after such treatment. Accordingly, either of these two alloys would be particularly advantageous for high temperature bonding applications. Additionally, the Al-Li alloy can be processed by treating at a temperature up to 450°C for one hour while maintaining a yield strength of over 30 ksi and additionally maintaining a submicron average grain size. [0069] The Al-Li alloys are of particular interest for backing plate applications due to the extreme low density of Li. For each 1 % of Li within an alloy, the density is reduced by about 5% with a corresponding increase in Young's modulus. Small amounts of Li additionally allow for precipitation strengthening by thermal aging after solution heat treatment. However, as indicated in Fig. 7, equal channel angular extrusion processing and treatment of these alloys in accordance with the invention allows high yield strength to be achieved in an absence of peak aging. This aspect can be of great benefit since typical peak aging can involve costly heat treating, and extensive time periods. [0070] The effect of equal channel angular extrusion and recovery annealing on yield strength of non-heat treatable aluminum alloys AI3004 and AI5052 are shown in Fig. 8. For each of the two alloys the average grain size achieved by equal channel angular extrusion is less than 1 micron. Each has resulting yield strength of over 30 ksi 15

S \H057\537\pctformat doc when treated at temperatures of up to about 280°C for 1 hour. Relative to conventional AI5052 and AI3004 alloys (lower curves) the yield strengths obtained by processing in accordance with the invention is 2.5-5 times higher. Accordingly, ECAE allows utilization of non-heat treatable alloys for producing high-strength backing plates. Additionally, processing of the non-heat treatable alloys in accordance with the invention can produce high-strength backing plate materials utilizing relatively simple processing since such high-strength materials can be achieved in an absence of solutionizing and aging treatments. Accordingly, processing in accordance with the invention increases the choice of possible backing plate materials and allows utilization of lower cost materials and/or materials having more desirable welding/bonding properties. [0071] Referring to Fig. 9, such shows the yield strengths of various copper and copper alloy backing plates produced by processing in accordance with the invention. Temperatures are reported for each ECAE processed alloy where such temperatures maintain a submicron average grain size in the material. As indicated yield strength of greater than 50 ksi can be achieved in each of the materials. The strength is improved from 30%-200% relative to that of standard commercial grade CuCr (which has an average grain size of over 10 microns). A typical submicron structure of a copper alloy processed utilizing methodology in accordance with the invention including equal channel angular extrusion is shown in Fig. 10. [0072] These results demonstrate the advantage of equal channel angular extrusion copper and copper alloyed backing plates. For example, higher purity materials can be utilized relative to conventional CuCr to thereby optimize other important properties such as, for example, thermal and electrical conductivity. Additionally, high purity ECAE backing plates can be produced having few or limited amount of foreign second phase particles thereby minimizing or eliminating formation of oxides and/or brittle intermetallic elements at the bonding interface allowing superior and stronger bonding to occur. Further, due to enhanced diffusion properties, high purity copper and copper alloy backing plates produced by methodology of the invention can be successfully bonded to aluminum and/or copper targets with a bond strength of over 15 ksi. [0073] Aluminum backing plates having the described aluminum alloy compositions and processed in accordance with methodology of the invention can have an average grain size of less than 10 microns, preferably less than 1 micron, and in particular instances less than 0.5 microns. The aluminum alloy backing plates can have 16

S \H057\537\pc«ormat doc a yield strength of greater than 30 ksi and in particular instances greater than 35 ksi. The activation energy of grain boundary diffusion in aluminum alloy backing plate materials of the invention can be less than 80 kJ/mole and in particular instances less than 50 kJ/mole. Aluminum backing plates of the invention can have a grain size uniformity characterized by a standard deviation of less than 15% (1 sigma), and in particular instances less than 10% (1 sigma). [0074] Copper alloy backing plates of the invention can typically comprise copper alloyed with from about 0.001 % to about 10%, by mass, of one or more alloying elements selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Al, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc and Hf. In particular instances the copper alloy materials of the invention can consist essentially of or consist of copper and one or more of the listed alloying elements. For particular applications, preferable elements which can be alloyed with copper include Ag, Mg, Ti, Al, Be, Cr, Zr, Zn, Fe, Sn and In. [0075] High purity copper and copper alloy backing plates of the invention can have an average grain size of less than about 10 microns and typically less than 1 micron. In particular instances the copper and copper alloy backing plates of the invention can have an average grain size of less than about 0.5 microns. Copper comprising backing plates of the invention can typically have a yield strength of greater than 45 ksi, and in particular instances greater than 55 ksi. The activation energy of grain boundary diffusion for copper and copper alloyed backing plates of the invention can be less than 95 kJ/mole, and in particular instances less than 85 kJ/mole. Grain size uniformity of copper comprising backing plates of the invention is typically characterized by a standard deviation of less than 15% (1 sigma), and in particular instances less than 10% (1 sigma).

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Claims

CLAIMS The invention claimed is:

1. A high-strength backing plate having an average grain size of less than 10 microns and a yield strength of at least 30 ksi.

2. The backing plate of claim 1 comprising at least one of aluminum and copper.

3. The backing plate of claim 2 wherein the backing plate comprises aluminum, and additionally comprises one or more alloying elements selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Cu, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc, and Hf.

4. The backing plate of claim 3 wherein the backing plate comprises from about 0.05% to about 15%, by mass, of each of the one or more alloying elements.

5. The backing plate of claim 3 having a yield strength of greater than 35 ksi.

6. The backing plate of claim 2 wherein the backing plate comprises copper and additionally comprises one or more alloying elements selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Al, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc and Hf.

7. The backing plate of claim 6 comprising from about 0.001 % to about 10%, by mass, of each of the one or more alloying elements.

8. The backing plate of claim 6 having a yield strength of greater than 45 ksi.

9. The backing plate of claim 1 comprising a non-heat treatable material.

10. The backing plate of claim 1 comprising a heat treatable material.

1 1. The backing plate of claim 1 having an average grain size of less than 1 micron.

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12. The backing plate of claim 1 having an average grain size of less than 0.5 micron.

13. A method of producing a target backing plate comprising: performing preliminary processing comprising hot-forging; performing severe plastic deformation processing comprising at least one of equal channel angular extrusion (ECAE), torsion, accumulative roll bonding (ARB), cyclic pressing or extrusion, friction stir welding, corrugative drawing, cryogenic rolling or pressing, and hammer forging; and performing post-deformation processing comprising at least one of rolling and forging, the target backing plate having an average grain size of less than 10 microns and having a yield strength of at least about 30 ksi.

14. The method of claim 13 wherein the plastic deformation processing comprises at least one pass of ECAE.

15. The method of claim 14 further comprising performing intermediate annealing between at least some of the ECAE passes.

16. The method of claim 13 wherein the preliminary processing further comprises at least one of solutionizing and homogenizing.

17. The method of claim 13 wherein the post-deformation processing comprises annealing.

18. A target assembly comprising: a target comprising a first material having an average grain size of less than about 10 microns; a backing plate comprising a second material having an average grain size of less than about 10 microns; and a bond between the backing plate and the target having a bond strength of at least 10 ksi.

19. The target assembly of claim 18 wherein the second material comprises at least one of aluminum and copper.

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20. The target assembly of claim 19 wherein the second material comprises aluminum and additionally comprises one or more alloying elements selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Cu, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc, and Hf.

21. The target assembly of claim 19 wherein the second material comprises copper and additionally comprises one or more alloying elements selected from the group consisting of Cd, Ca, Au, Ag, Be, Li, Mg, Al, Pd, Hg, Ni, In, Zn, B, Ga, Mn, Sn, Ge, W, Cr, O, Sb, Ir, P, As, Co, Te, Fe, S, Ti, Zr, Sc and Hf.

22. The target assembly of claim 18 wherein the second material is non-heat treatable material.

23. The target assembly of claim 18 wherein the second material is heat treatable material.

24. The target assembly of claim 18 wherein the first and second materials each have sub-micron average grain size.

25. The target assembly of claim 18 wherein the second material has an average grain size of less than 0.5 microns.

26. A method of forming a target assembly comprising: providing a target comprising a first material; providing a high-strength backing plate comprising a second material having an average grain size of less than about 10 microns and a yield strength of at least 30 ksi; and joining the target to the backing plate.

27. The method of claim 26 wherein the joining comprises at least one of soldering, brazing, solid phase bonding, roll cladding, friction stir welding, hot isostatic pressing, explosion bonding, and mechanical joining techniques.

28. The method of claim 26 wherein the joining comprises proving an insert comprising at least one of Ag, Ni and Cu to enhance bonding ability of the backing plate.

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29. The method of claim 26 further comprising performing a surface preparation process prior to the joining, the surface preparation process comprising treating a backing place surface utilizing at least one of machining grooves into the surface and electroplating.

30. The method of claim 26 wherein the joining produces a bond strength of at least about 10 ksi.

31. The method of claim 26 wherein the first material has an average grain size of less than 10 microns.

32. The method of claim 26 wherein the first and second materials each have a sub-micron average grain size.

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