Sputtering target assemblies, backing plate for same, and processes for making

Abstract

A sputtering target assembly comprising a target plate comprising a refractory metal or a refractory metal alloy, an adjacent backing plate, and an iron-enriched interfacial zone. The backing plate comprises from 0.01 wt% to 0.5 wt% iron, 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper. The iron-enriched interfacial zone bonds the backing plate to the target plate and has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

Description

SPUTTERING TARGET ASSEMBLIES, BACKING PLATE FOR SAME, AND PROCESSES FOR MAKINGPRIORITY CLAIM

[0001] The present application claims priority to U.S. Provisional Application No. 63 / 610,738, filed on December 15, 2023, the entire contents and disclosure of which is hereby incorporated by reference.FIELD

[0002] The present disclosure relates to refractory metals and refractory metal alloys target plate assemblies including target plates, backing plates, and bonding thereof, for assemblies that are suitable for sputtering. In particular, the refractory metals and refractory metal alloys target plates are bonded to backing plates to form an iron-enriched interfacial zone.BACKGROUND

[0003] Sputtering processes are employed to deposit thin films from a target onto substrates, such as a silicon wafer, to manufacture any of a variety of devices. Sputtering processes typically involve bombarding a solid sputtering target body with energized particles to eject atoms from the target body. There are several parameters that affect sputtering, such as purity, interstitial content, crystal plane orientation, thickness uniformity, and / or grain size. By manipulating the target material one can control sputter deposition to obtain fine control over the growth and microstructure of the thin films.

[0004] Sputtering targets may be made by ingot metallurgy, pursuant to which an ingot is formed (e g., by electron beam melting of a metal), and thereafter therm omechanically processed for achieving a desired texture. Commercially available targets comprising tantalum are processed from an ingot obtained by subjecting a tantalum raw material to melting and casting, which may include thermomechanically processes such as forging, annealing, rolling, heat-treating, and other finishing processes.

[0005] Sputtering targets also may be made from powder metal starting materials, which are suitably consolidated to form a resulting target. When powder metals are used as starting materials it is typically desirable to employ high purity powders. For example, it is desired toemploy powders that have a low content of undesired metallic impurities, and / or a low content of oxygen.

[0006] Backing plates are bonded to target plates to provide support for the sputtering target and for mounting to the sputtering apparatus. Importantly, the backing plate also functions to provide heat dissipation during sputtering. Properties for the backing plate should include good electrical and thermal conductivity. The most common backing plate materials include copper and stainless steel. The backing plate selected should be compatible with the sputtering target material. Problems arise in assemblies where delamination or debonding of the sputtering target from the backing plate occur during sputtering, which severely limits the life of the assemblies.

[0007] Brass alloys have been considered for backing plates, e.g., see Japanese Pat. Pub. No. 1222047 A2. However, brass is known to suffer from dezincification, which can lead to delamination or debonding of the sputtering target from the backing plate.

[0008] U.S. Pub. No. 2008 / 0236738 describes methods for making sputtering target assemblies using powdered layers between the target and backing plate to assist in bonding. U.S. Pub. No. 2008 / 0197017 describes sputtering targets and backing plates that are bonded to one another through an interlayer, such as one or more of silver, copper, nickel, tin, titanium, and indium.

[0009] U.S. Pat. No. 6,164,519 describes a backing plate that is explosion bonded to a sputter target. Explosion bonding includes accelerating the sputter target and / or backing plate toward each other by one or more controlled detonations to form an atomic bond at the interface between the sputter target and backing plate, which requires machining of the non-bonded surfaces of the sputter target and backing plate to achieve the final assembly dimensions.

[0010] There is, therefore, a need in the art for sputtering target assemblies that do not require additional material, e.g., powders and / or interlayers, between the target and the backing plate yet have improved bonding. Further, there is a need for assemblies that avoid de-zincification of the backing plate. This disclosure addresses those needs.SUMMARY

[0011] In general, the disclosure relates to a sputtering target assembly comprising a target plate bonded to a backing plate. The target plate and backing plate are made of dissimilar materials. In one embodiment, the sputtering target assembly comprises a target plate that may be diffusion bonded to a backing plate. When bonded together an interfacial zone is formed. The inventorsunexpectedly found that the composition of the backing plate, and in particular iron, influences the microstructure to form an iron-enriched interfacial zone that bonds the backing plate to the sputtering target. The iron-enriched interfacial zone restricts the creation of deleterious intermetallic compounds in the interfacial zone and achieves a good metallurgical bonding. In one embodiment, the backing plate may comprise a copper-zinc-alloy containing iron suitable for bonding to target plates comprising refractory metal or refractory metal alloys, such as tantalum or tantalum alloy having a high purity. Using the sputtering target assembly can improve production of thin fdms during sputtering as well as extend life of the assembly.

[0012] In one aspect there is provided a sputtering target assembly comprising a target plate comprising a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate includes: from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding the backing plate to the target plate, the iron-enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0013] The target plate of the sputtering target assembly may include a center, a thickness, an edge, a target top planar surface, and a target bottom planar surface, where the top planar surface is opposite the bottom planar surface. The backing plate of the sputtering target assembly may include a center, a thickness, an edge, a backing top planar surface, and a backing bottom planar surface, where the backing top planar surface is opposite the backing bottom planar surface. The iron-enriched interfacial zone of the sputtering target assembly may be disposed between the target bottom planar surface and the backing top planar surface. The interfacial zone thickness may be less than or equal to 10 pm, e.g., less than 5 pm, or less than 3 pm, or less than 1 pm. The sputtering target assembly may include that the target bottom planar surface is coextensive with the backing top planar surface. The target bottom planar surface may be in contact with the backing top planar surface. The sputtering target assembly may have a bond strength, e.g., ultimate tensile strength, between the target plate and the backing plate that is preferably greater than or equal to 175 MPa, preferably greater than or equal to 200 MPa.

[0014] The iron-enriched interfacial zone preferably has an enriched concentration of iron. In one embodiment, the sputtering target assembly has a concentration of iron in the iron-enrichedinterfacial zone that may be at least 3 wt% greater than the concentration of iron in the backing plate.

[0015] In one embodiment, the backing plate may include from 0.01 wt% to 0.5 wt% iron, from 0.25 wt% to 2.0 wt% tin, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate. Within these ranges, the backing plate may have a ratio of Zn:Fe by weight from 70: 1 to 4000: 1.

[0016] In some embodiments, the backing plate may include from 0 to 0.1 wt% lead. Small limits of lead may be used and in one embodiment the backing plate includes less than 100 ppm lead.

[0017] The target plate of the sputtering target assembly may include a refractory metal or refractory metal alloy that includes tantalum, niobium, titanium, molybdenum, alloys thereof, or combinations thereof. Preferably, the target plate of the sputtering target assembly may include tantalum or niobium. The target plate may further include iron, cobalt, aluminum, copper, tungsten, or alloys or mixtures thereof. The target plate may include from 0 to 0.1 wt% iron, or less than 100 ppm iron.

[0018] High purity sputtering target assemblies are preferably used. In one embodiment, the target plate includes tantalum having a purity of 99.5% or greater, based on the total metals of the target plate, e.g., 99.95% or greater, 99.99% (4N) or greater, or more preferably a purity of 99.999% (5N) or greater. In another embodiment, the target plate includes one of niobium, titanium, or molybdenum having a purity of 99.5% or greater, based on the total metals of the target plate, e.g., 99.95% or greater, 99.99% (4N) or greater, or more preferably a purity of 99.999% (5N) or greater.

[0019] In one embodiment, the backing plate includes an alloy phase comprising a copper- containing phase that is a-copper in solid solution with zinc. The backing plate may include a second copper-containing phase that is a 0-CuZn intermetallic. The second copper-containing phase may be present in an amount less than 5 vol%. The backing plate may include iron precipitates dispersed therein. The backing plate may further comprise tin and include tin precipitates dispersed therein.

[0020] A thin film may be formed using the sputtering target assembly described herein. In one embodiment, a deposition method is used to eject atoms from the target assembly onto a substrate to form a thin film. The thin film may be uniform.

[0021] Sputtering target assemblies disclosed in embodiments above include target / backing plate bonds that have a yield strength at 0.2% offset of greater than 150 MPa, e.g., greater than 155 MPa, greater than 160 MPa, greater than 165 MPa, greater than 170 MPa, or greater than 175 MPa. In one embodiment, the sputtering target assemblies target / backing plate bonds that may have an ultimate tensile strength of greater than 175 MPa, e.g., greater than 190 MPa, greater than 200 MPa, greater than 210 MPa, greater than 220 MPa, greater than 230 MPa, greater than 240 MPa, or greater than 245 MPa. Ultimate tensile strength is the bond strength.

[0022] In one aspect there is provided a process for making a sputtering target assembly including providing a target plate including a refractory metal or refractory metal alloy and a backing plate; and diffusion bonding a first planar surface of the backing plate to a second planar surface of the target plate in a vacuum, the second planar surface adjacent to the first planar surface, to form an iron-enriched interfacial zone to bond the backing plate to the target plate, where the backing plate includes: from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and wherein the iron-enriched interfacial zone has a thickness and a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The process may include wherein diffusion bonding is conducted at a temperature of 600°C to 850°C.

[0023] In one embodiment, a sputtering target assembly comprises a target plate including a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate consists of: from 0.01 wt% to 0.5 wt% iron, from 0.25 wt% to 2.0 wt% tin, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding the backing plate to the target plate, the iron-enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0024] These and other non-limiting characteristics are more particularly described below.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is further illustrated by the following drawings in which:

[0026] FIG. 1 is an illustration of a cross-sectional view of a backing plate for a sputtering target assembly in accordance with embodiments disclosed herein.

[0027] FIG. 2 is an illustration of a cross-sectional view of a target plate for a sputtering target assembly in accordance with embodiments disclosed herein.

[0028] FIG. 3 is an illustration of a cross-sectional view of a target plate / backing plate preassembly for a sputtering target assembly in accordance with embodiments disclosed herein.

[0029] FIG. 4 is a schematic illustration of thermomechanical processing to form a sputtering target assembly in accordance with embodiments disclosed herein.

[0030] FIG. 5 is an illustration of a cross-sectional view of a sputtering target assembly comprising a target plate, a backing plate adjacent to the target plate, and an iron-enriched interfacial zone bonding the backing plate to the target plate in accordance with embodiments disclosed herein.

[0031] FIG. 6 is an illustration of a binary phase diagram of Fe and Ta.

[0032] FIG. 7 is a micrograph of a conventional two phased brass where dezincification is evident.

[0033] FIG. 8 is an illustration of a binary phase diagram of Cu and Zn.

[0034] FIG. 9 is a graph illustrating the Fe+ signal over a 75x75 pm2analysis area at the target plate / backing plate interfacial zone of a sputtering target assembly in accordance with embodiments disclosed herein; the graph showing an increase in Fe content as a function of diffusion bonding temperature from 600°C to 850°C.

[0035] FIG. 10 is a graph illustrating overlaid line-scans across the target plate / backing plate interface of a sputtering target assembly in accordance with embodiments disclosed herein; the graph showing Cu descending as Ta increases and Fe increasing and decreasing at the interfacial zone.

[0036] FIG. 11 is an illustration of a cross section of the sputtering target assembly of Example 1C analyzed with ToF-SIMS over a 75x75 pm2analysis area showing an overlay showing an iron-enriched interfacial zone Fe disposed between the copper containing backing plate and a Ta containing target plate in accordance with embodiments disclosed herein.

[0037] FIG. 12 is an illustration of a cross section of the sputtering target assembly of Example ID analyzed with ToF-SIMS showing an overlay showing an iron-enriched interfacial zone Fedisposed between the copper containing backing plate and a Ta containing target plate in accordance with embodiments disclosed herein.

[0038] FIG. 13 is a graph illustrating the effect of bonding temperature, from 600°C to 850°C, showing stress strain curves in accordance with embodiments disclosed herein.

[0039] FIG. 14 is a graph comparing the Fe+ signal between Example 1C and Example 2B.

[0040] FIG. 15 is an illustration of a cross section of the sputtering target assembly of Comparative Example 2B analyzed with ToF-SIMS showing an overlay showing an iron- enriched interfacial zone Fe disposed between the copper containing backing plate and a Ta containing target plate in accordance with embodiments disclosed herein.

[0041] FIG. 16 is a micrograph of Comparative Example 2B.DETAILED DESCRIPTION

[0042] The present disclosure depicts sputtering target assemblies, thin fdms produced from such sputtering targets, and sputtering methods utilizing the sputtering targets. In one embodiment, the sputter deposition may be a physical vapor deposition method to form thin films. In forming the thin films, the material from the sputtering target may be exposed to energetic particles from a plasma or gas, such as argon, krypton, xenon, neon, nitrogen, or mixtures thereof. The exposure to the energetic particles from the of plasma or gas causes particles from the sputtering target to be ejected onto a substrate, such as a silicon wafer, to form a thin film. The sputtering target is positioned in a deposition chamber to sputter the target material towards the substrate.

[0043] As shown in FIG. 5, there is disclosed a sputtering target assembly 100 comprising a target plate 102 and a backing plate 104. In one embodiment, the backing plate 104 is bonded to the target plate 102 using a solid-state welding technique such as diffusion-bonding, brazing, welding, soldering, brazing, mechanical fastening, epoxy bonding, friction welding, or explosion bonding. In certain embodiments, the backing plate 104 is bonded to the target plate 102 using diffusion-bonding as discussed in detail below. In embodiments herein, the bond is achieved without an interlayer or similar additional material. Accordingly, there is an absence of any interlayer, intervening material, powder, foil, tile, or other added material. These intervening materials are specifically omitted for bonding the backing plate 104 and target plate 102. Such intervening materials are unnecessary because the composition of the backing plate disclosedherein influentially affects the formation of an iron-enriched interfacial zone during diffusion bonding of the backing plate to the target plate.

[0044] The backing plate 104, also shown in FIG. 1, may comprise an alloy of copper, zinc, and iron. In one embodiment, the backing plate 104 may comprise a copper-zinc alloy that contains iron. Preferably, the backing plate 104 and the target plate 102 are dissimilar compositions. The backing plate is configured to hold the target plate 102 in a position suitable for sputter deposition towards a substrate (not shown). In addition, the backing plate 104 may provide mechanical strength, electrical conductivity, and thermal conductivity to the sputtering target. Heat treatment may be used to provide the backing plate 104 with a higher mechanical strength than the target plate 102. A non-bonded backing plate may also be used in some embodiments.

[0045] The target plate 102, also shown in FIG. 2, comprises a center, a thickness (T), an edge, a target top planar surface 112, and a target bottom planar surface 113, where the top planar surface is opposite the bottom planar surface. The target bottom planar surface comprises an adjacent portion that may be bonded to a backing plate. The top planar surface comprises the sputtering portion that is exposed during the sputtering process. The backing plate 104 includes a center, a thickness (B), an edge, a backing top planar surface 114, and a backing bottom planar surface 115, where the backing top planar surface 112 is opposite the backing bottom planar surface 115.

[0046] As shown in FIG. 3, a target plate / backing plate pre-assembly 90 is prepared by positioning the backing top planar surface 114 adjacent to and in contact with the target bottom planar surface 113. FIG. 4 represents thermomechanical processing 150 applied to the preassembly 90 to form the sputtering target assembly 100 of FIG. 5. The iron-enriched interfacial zone 106 forms between the target bottom planar surface 113 and the backing top planar surface 114 and has a thickness 108. The improvement joint is owing to the good metallurgical bonding and presence of an enriched concentration of iron at the iron-enriched interfacial zone 106.

[0047] The thickness of the target plate may be varied as desired according to application in use. In one embodiment, the thickness of the target plate may be from 0.2 mm to 100 mm, e.g., from 0.25 mm to 100 mm, from 0.3 mm to 80 mm, from 0.5 mm to 75 mm, from 1 mm to 60 mm, or from 1 mm to 50 mm. The thickness of the backing plate may also be varied as desired according to application in use. In one embodiment, the thickness of the backing plate may be from 0.2 mm to 200 mm, e.g., from 0.25 mm to 150 mm, from 0.3 mm to 125 mm, from 0.5 mm to 100 mm,from 1 mm to 60 mm, or from 1 mm to 60 mm. In one embodiment, the backing plate is thicker than the target plate.

[0048] The iron-enriched interfacial zone has a thickness. The thickness 108 of the iron-enriched interfacial zone 106 disposed between the target bottom planar surface and the backing top planar surface may be from 1 pm to 10 pm, e.g., from 2 pm to 8 pm or from 2 pm to 5 pm. In some embodiments, the thickness of the iron-enriched interfacial zone may be less than or equal to 10 pm, e.g., less than 5 pm, less than 3 pm, or less than 1 pm. The minimal thickness of the iron-enriched interfacial zone is sufficient to enhance the bond strength for the sputtering target assembly due to the presence of iron.

[0049] Although a rotary configuration is shown in FIG. 5, the sputtering target assembly may have another configuration without departing from the embodiments described herein. In some embodiments, the sputtering target and / or backing plate may have a square configuration, rectangle configuration, round configuration, tubular configuration, or rotary configuration. The sputtering targets and / or backing plates described herein may be used for large scale target assemblies and small scale target assemblies. By way of example, larger scale target assemblies may be sized such that they are capable of sputtering generally uniformly onto a wafer or other substrate having a diameter or largest dimension of at least about 200 mm, at least about 300 mm, or even at least about 450 mm. Examples of such target assemblies may be generally circular or rectangular plate structures having a diameter (or largest dimension) that exceeds about 0.2 meters, about 0.3 meters, or even about 0.4 meters.

[0050] In one embodiment, the configuration of the backing plate 104 may be similar to the target plate 102. It is also contemplated that the backing plate 104 may have a slightly larger dimension than the target plate 102. FIG. 5 illustrates a rotary configuration for the backing plate 104 that has a larger radius than the target plate 102 with a similar thickness. Other embodiments may include sputtering targets where the backing plate 104 and target plate 102 have different thicknesses.

[0051] The sputtering target assembly according to the descriptions herein may permit the bonding of multiple target plates to one backing plate, i.e., the target body optionally may include at least two consolidated preformed blocks that are joined together to define the resulting target plate. This may allow greater output of target materials. If a multiblock assembly is employed, two or more of the resulting consolidated masses may be joined together to form atarget body by hot isostatically pressing two or more blocks (e.g., while encapsulated in a suitable hot isostatic pressing container). The two or more blocks may be joined together in the presence or the absence of any powder, foil, tile, or other added material within the space between adjoining blocks of target material.

[0052] The backing plate is adjacent to the target plate, and the target bottom planar surface is in contact with the backing top planar surface in the pre-assembly (as in FIG. 3). The composition of the backing plate is critical to the formation of an iron-enriched interfacial zone upon thermomechanical processing, e.g., diffusion bonding. The backing plate comprises copper, zinc, and iron. In one embodiment, the backing plate disclosed herein has a composition that is different and distinct from commercial brass compositions, e.g., C46400 (Naval Brass), C26800 (Yellow Brass), and C46200 (Japanese Naval Brass).

[0053] Inventors found unexpectedly that an iron concentration in the backing plate from 0.01 wt% to 0.5 wt% influentially affects the microstructure of the iron-enriched interfacial zone. The iron is micro-alloyed with the copper and zinc when forming the backing plate. The iron in the backing plate, evidenced by ToF-SIMS analysis, migrates from the backing plate toward the target plate during diffusion bonding, thus forming the interfacial zone and providing strong bonding between the backing plate to the target plate. The iron enrichment may reduce the presence of brittle intermetallic phases such as a zinc-rich intermetallic P phase. In some embodiments herein, the target plate refractory metal or refractory metal alloy is tantalum or tantalum alloy. As shown in FIG. 6, the circled portion toward 100% tantalum shows the solubility of iron in tantalum. Without being bound by theory, it is believed that the iron tends to diffuse into tantalum forming solid solution, which strengthens the bonding to the tantalum target plate. Thus, at temperatures used for diffusion bonding, e.g., ranging from 600°C to 850°C, the iron is attracted to and migrates toward the target plate.

[0054] The backing plate as disclosed herein comprises from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper.

[0055] In one embodiment, the backing plate may comprise from 0.01 wt% to 0.5 wt% iron, e.g., from 0.01 wt% to 0.4 wt%, from 0.01 wt% to 0.3 wt%, from 0.011 wt% to 0.3 wt%, from 0.012 wt% to 0.3 wt%, from 0.015 wt% to 0.3 wt%, from 0.02 wt% to 0.2 wt%, or from 0.025 wt% to 0.1 wt%. In terms of upper limits, the backing plate may comprise less than or equal to 0.5 wt% iron, e g., less than 0.4 wt%, less than 0.3 wt%, less than 0.2 wt%, less than 0.1 wt%, less than0.05 wt%, less than 0.02 wt%, less than 0.015 wt% or less than 0.013 wt%. In terms of lower limits, the backing plate may comprise greater than or equal to 0.01 wt% iron, e.g., greater than 0.011 wt%, greater than 0.012 wt%, greater than 0.013 wt%, greater than 0.014 wt%, greater than 0.015 wt%, greater than from 0.02 wt%, or greater than 0.025 wt% iron. When the amounts of iron in the backing plate is less than 0.01 wt%, the rate of debonding increases which leads to poor performance of the sputtering assembly. In one embodiment, the backing plate may preferably comprise about 0.011 to 0.013 wt% iron based on the total weight of the backing plate.

[0056] The sputtering target assembly according to the descriptions herein may have a concentration of iron in the iron-enriched interfacial zone that is greater than the concentration of iron in the backing plate. In one embodiment, the concentration of iron in the iron-enriched interfacial zone may be at least 2 wt% greater than the concentration of iron in the backing plate, e.g., at least 3 wt% greater, at least 4 wt% greater, at least 5 wt% greater, at least 6 wt% greater, at least 7 wt% greater, at least 8 wt% greater, at least 9 wt% greater, at least 10 wt% greater, or more.

[0057] The backing plate composition disclosed herein also includes zinc. For example, in addition to the micro-alloyed iron content in the backing plate as disclosed above, the backing plate composition includes a lower zinc and higher copper concentration as compared with typical brass.

[0058] Generally, brass containing less than 15 wt% zinc resists dezincification, while brass with more than 15 wt% zinc is susceptible to dezincification. As known, duplex (two phased) brass (a+P) is more prone to dezincification than alpha brass. In two phased brasses, the beta phase is attacked preferentially leaving discrete plugs of dealloyed metal. Brass having a conventional two phased structure is shown in FIG. 7.

[0059] This is important because the backing plate composition herein disclosed, even at higher zinc content, e.g., 34.0 wt% to 40 wt% zinc, also prevents dezincification of the backing plate. The zinc content herein influences the backing plate to form a single copper-containing phase that is a-copper in solid solution with zinc. This zinc content avoids the formation of a second beta copper-containing phase that is P-CuZn intermetallic, as shown in the binary phase diagram for Cu-Zn as in FIG. 8. Importantly, the -CuZn intermetallic phase is largely prevented, which can be detrimental and lead to dezincification. Dezincification can cause the backing plate to failby cracking or delamination within the backing plate and / or delaminating from the attached target plate. By synergistically combining the zinc content to prevent dezincification in the backing plate and the micro-alloyed iron to promote bonding of the backing plate with the target plate, the resultant sputtering target assembly exhibits a superior bond and long life.

[0060] In one embodiment, the backing plate may comprise from 34.0 wt% to 40.0 wt% zinc, e.g., from 34.0 wt% to 39.0 wt%, from 35.0 wt% to 38.0 wt%, from 35.0 wt% to 37.0 wt%, or from 35.5 wt% to 36.5 wt%. In terms of lower limits, the backing plate may comprise greater than or equal to 34.0 wt% zinc, e g., greater than 35.0 wt% zinc or greater than 35.5 wt% zinc. In terms of upper limits, the backing plate may comprise less than or equal to 40.0 wt% zinc, e.g., less than 39.0 wt%, less than 38.0 wt%, less than 37.0 wt%, or less than 36.5 wt%. The backing plate may preferably comprise about 36.0 wt% zinc based on the total weight of the backing plate.

[0061] In one embodiment, the backing plate may comprise from 60.0 wt% to 66.0 wt% copper, e.g., from 61.0 wt% to 66.0 wt%, from 62.0 wt% to 66.0 wt%, from 63.0 wt% to 66.0 wt%, or from 63.5 wt% to 66.0 wt%. In terms of lower limits, the backing plate may comprise greater than or equal to 60.0 wt% copper, e.g., greater than 61.0 wt%, greater than from 62.0 wt%, greater than 63.0 wt%, or greater than 63.5 wt%. In terms of upper limits, the backing plate may comprise less than or equal to 66.0 wt% copper, e.g., less than 65.0 wt. The backing plate may preferably comprise from about 63.5 wt% to about 66.0 wt% copper based on the total weight of the backing plate.

[0062] In some embodiments, the backing plate may further comprise additional metals. These additional metals do not affect the migration of the iron to the interfacial zone. In one embodiment, the backing plate may comprise from 0.25 wt% to 2.0 wt% tin, e.g., from 0.45 wt% to 1.0 wt%, from 0.65 wt% to 0.85 wt%, or from 0.70 wt% to 0.80 wt%. In terms of lower limits, the backing plate may comprise greater than or equal to 0.25 wt% tin, e.g., greater than 0.45 wt%, greater than 0.65 wt%, or greater than 0.70 wt%. In terms of upper limits, the backing plate may comprise less than or equal to 2.0 wt% tin, e g., less than 1.0 wt%, less than 0.85 wt%, or less than 0.80 wt%. The backing plate may preferably comprise about 0.75 wt% tin based on the total weight of the backing plate. The tin forms precipitates that may enhance mechanical properties of the backing plate.

[0063] The backing plate according to embodiments herein has an absence of lead, which is detrimental to the environment. The backing plate herein may comprise from 0 to 1000 ppm lead, 0 to 500 ppm lead, 0 to 200 ppm lead, or 0 to 100 ppm lead. The backing plate for the sputtering target assemblies herein may be preferably devoid of lead, e.g., less than 500 ppm, less than 200 ppm, or less than 100 ppm lead.

[0064] The synergistic combination of zinc and iron in the copper-zinc-iron alloys in the backing plate for the sputtering target assemblies herein can be characterized by a ratio of Zn:Fe by weight in the backing plate from 70: 1 to 4000: 1. In one embodiment, the backing plate may comprise a ratio of Zn:Fe from 70: 1 to 4000: 1, e.g., from 100: 1 to 3500: 1, or from 1500: 1 to 2500:1. In certain embodiments, the backing plate comprises a ratio of Zn:Fe of 1440:1.

[0065] In specific embodiments, the sputtering target assembly comprises a target plate comprising a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate consists of: from 0.01 wt% to 0.5 wt% iron, from 0.25 wt% to 2.0 wt% tin, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding the backing plate to the target plate, the iron-enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0066] As disclosed above, the backing plate is synergistically paired with a target plate to which iron has a preference to migrate from the backing plate to the target plate for bonding the backing plate to the target plate. As shown in FIG. 6 and discussed above, tantalum and / or tantalum alloys are suitable as target plates for sputtering target assemblies as described herein because the iron is attracted to and / or migrates from the backing plate toward the target plate to form an iron-enriched interfacial zone. Target plates suitable for the assemblies herein may comprise tantalum, niobium, titanium, molybdenum, alloys thereof, or combinations thereof.

[0067] The sputtering target assembly herein comprises a target plate comprising a refractory metal and in particular tantalum or tantalum alloy. In one embodiment, the tantalum or tantalum alloy has a purity of 99.5% or greater, based on the total metals of the target plate, e.g., 99.95% or greater, 99.99% (4N) or greater, or more preferably a purity of 99.999% (5N) or greater. In some embodiments, the tantalum alloy may comprise niobium, iron, cobalt, aluminum, copper,molybdenum, tungsten, titanium or alloys or mixtures thereof. For purposes of the present disclosure, the purity of the tantalum or tantalum alloy is determined based on the total metals, not including any interstitial impurities (C, O, N, H). In certain embodiments, the target plate comprises tantalum having a purity of 99.99% (4N), or a purity of 99.999% (5N) or greater.

[0068] In one embodiment, the target plate contains high purity tantalum that permits the target plate to have a density in the range from 15.4 g / cm3to 16.7 g / cm3, e.g., from 15.9 g / cm3to 16.7 g / cm3, or from 16.4 g / cm3to 16.7 g / cm3. Although the backing plate may provide structural integrity, the target plate may also be sufficiently strong so that it withstands, without fracture, routine stresses encountered during subsequent assembly operations (e.g., a three point straightening assembly operation, a creep flattening operation, or some other operation during which the target body is subjected to application of a stress).

[0069] The target plate may comprise one of niobium, titanium, or molybdenum having a purity of 99.5% or greater, based on the total metals of the target plate, e.g., 99.95% or greater, 99.99% (4N) or greater, or more preferably a purity of 99.999% (5N) or greater. In certain embodiments, the target plate comprises one of niobium, titanium, or molybdenum having a purity of 99.99% (4N) or greater, or a purity of 99.999% (5N) or greater.

[0070] In one embodiment, the target plate may have an interstitial content of less than or equal to 500 ppm, based on the total weight of the target plate. More preferably, the interstitial content of the target plate may be less than 400 ppm, less than 300 ppm or less than 200 ppm. In terms of ranges, the interstitial content may be from greater than 0 to 500 ppm, e.g., from 10 to 500 ppm, or from 100 to 400 ppm. For embodiments where the target plate is made from a powder process, the target plate may have an interstitial content of less than or equal to 1000 ppm, based on the total weight of the target plate, e.g., less than 950 ppm, less than 750 ppm, less than 700 ppm, less than 500 ppm, less than 400 ppm, less than 350 ppm. In terms of ranges, the interstitial content of target plates made from a powder process may be from greater than 0 to 1000 ppm, e.g., from 10 to 1000 ppm, from 50 to 950 ppm, or from 100 to 600 ppm or from 100 to 500 ppm. A scavenger metal such as magnesium may be used to reduce the oxygen when processing powders.

[0071] The target plate may further comprise iron, cobalt, aluminum, copper, tungsten, or alloys or mixtures thereof. These are contemplated as minor alloying components and / or as unavoidable impurities, e.g., present in an amount less than 0.1 wt%.

[0072] The target plate according to embodiments herein has an absence of iron. The target plate herein may comprise from 0 to 1000 ppm iron, e.g., 0 to 500 ppm iron, 0 to 200 ppm iron, or 0 to 100 ppm iron. The target plate for the sputtering target assemblies herein may be preferably devoid of iron, e.g., less than 500 ppm, less than 200 ppm, less than 100 ppm iron, or less than 1 ppm iron.

[0073] As in the backing plate, the target plate according to embodiments herein has an absence of lead. The target plate herein may comprise from 0 to 1000 ppm lead, e.g., 0 to 500 ppm lead, 0 to 200 ppm lead, or 0 to 100 ppm lead. The target plate for the sputtering target assemblies herein may be preferably devoid of lead, e.g., less than 500 ppm, less than 200 ppm, less than 100 ppm lead, or less than 1 ppm lead.

[0074] As discussed above, the backing plate composition disclosed herein promotes strong bonding with a target plate for forming the sputtering target assembly while also preventing dezincification within the backing plate. This is done by controlling the iron content and the zinc content, respectively. The microstructure of the backing plate should, desirably, include a (single) copper-containing phase that is a-copper in solid solution with zinc. Ideally, there is an absence of any second copper-containing phase that is P-CuZn intermetallic phase. In one embodiment, the backing plate comprises an alloy phase comprising a solid solution of zinc and alpha copper phase. The backing plate may comprise a second alloy phase comprising a solid solution of zinc and beta copper phase, however, the second alloy phase comprising a solid solution of zinc and beta copper phase is present in an amount less than or equal to 10 vol%, e g., less than 5 vol%, less than 2 vol%, or less than 1 vol% as measured by image analysis using ImageJ software or other known image analysis techniques.

[0075] The microstructure of the backing plate may further include precipitates dispersed therein. Precipitates (formed from minor components) in the backing plate may include iron precipitates. Additionally or alternatively, backing plates further comprising tin may include tin precipitates dispersed therein.

[0076] The sputtering target assembly comprises a backing plate having a reduced grain size. The microstructure of the backing plate includes where an average grain size of the backing plate ranges from 10 to 120 pm. In one embodiment, the backing plate may have an average grain size ranging from 10 to 120 pm, e.g., from 15 to 120 pm, from 20 to 120 pm, from 30 to 120 pm,from 40 to 120 pm, or from 50 to 120 pm. Grain size measurements are made according to ASTM El 12-12.

[0077] The sputtering target assembly comprises a target plate having a reduced grain size. The microstructure of the target plate includes where an average grain size of the target plate ranges from 10 to 120 pm. In one embodiment, the target plate may have an average grain size ranging from 10 to 120 pm, e.g., from 15 to 120 pm, from 20 to 120 pm, from 30 to 120 pm, from 40 to 120 pm, or from 50 to 120 pm.

[0078] The sputtering target assembly comprises an iron-enriched interfacial zone having a fine grain size. The microstructure of the iron-enriched interfacial zone includes where an average grain size of the interfacial zone ranges from 0.1 to 10 pm. In one embodiment, the iron-enriched interfacial zone may have an average grain size ranging from 0.1 to 10 pm, e.g., from 0.1 to 7 pm, or from 0.1 to 5 pm, from 0.1 to 4 pm, from 0.1 to 3 pm, from 0.1 to 2 pm, or from 0.1 to 1 pm. Grain size measurements are made according to ASTM El 12-12.

[0079] The sputtering target assembly disclosed in embodiments above is used to sputter a thin film according to embodiments herein. Uniformity of film thickness is of importance. In integrated circuits, several hundred of which are created simultaneously on a silicon wafer, for example, poor deposition of the sputtering target results in deleterious performance such as in adequate diffusion barrier or restricted vias or trenches. Non-uniformity of the film deposited results in a device that may not be fit for service, and the total cost of manufacture up to the point of test is lost, since no repair or rework is normally possible.

[0080] The thin film for semiconductor application is created by using the method according to the previous embodiments, where variation in film thickness uniformity (percent non-uniformity) is 3% or less, and variation in sheet resistance, within wafers, and between wafers is 3% or less.

[0081] Particle generation and / or other adverse conditions that could prematurely shorten the life of a sputtering target may also be avoided by using the sputtering target assembly described herein.

[0082] The sputtering target assembly disclosed in embodiments above demonstrates a bond strength, i.e. ultimate tensile strength, between the target plate and the backing plate that is greater than or equal to 175 MPa. Bond strength measurements were collected for samples diffusion bonded at varying temperatures, e.g., from 600°C to 850°C. In one embodiment, the sputtering target assembly may have a bond strength greater than or equal to 175 MPa, e.g.,greater than or equal to 180 MPa, greater than or equal to 185 MPa, greater than or equal to 190 MPa, greater than or equal to 200 MPa, greater than or equal to 210 MPa, greater than or equal to 220 MPa, greater than or equal to 240 MPa, greater than or equal to 260 MPa, or greater than or equal to 280 MPa. Further, sputtering target assemblies disclosed in embodiments above include backing plates having an ultimate tensile strength from 175 MPa to 1300 MPa, e.g., from 175 MPa to 1200 MPa, from 180 MPa to 1100 MPa, from 180 MPa to 400 MPa, from 180 MPa to 300 MPa, from 185 MPa to 275 MPa or more preferably from 190 MPa to 250 MPa. Bond strength measurements are made according to according to an Arcan tensile testing.

[0083] In addition to the bond strength, the sputtering target assemblies disclosed in embodiments above include target / backing plate bonds that may have a yield strength at 0.2% offset of greater than or equal to 150 MPa, e.g., greater than or equal to 155 MPa, greater than or equal to 160 MPa, greater than or equal to 165 MPa, greater than or equal to 170 MPa, or greater than or equal to 175 MPa. Yield strength at 0.2% offset measurements are made according to according to an Arcan tensile testing.

[0084] In one embodiment, the processes for making a sputtering target assembly as described in the embodiments above comprise providing a target plate and a backing plate followed by a bonding process, such as a diffusion bonding process. The target plate comprises a refractory metal or refractory metal alloy. The backing plate comprises from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate. The target plate and backing plate are disposed adjacent one another. The process includes diffusion bonding a first planar surface of the backing plate to a second planar surface of the target plate in a vacuum, the second planar surface adjacent to the first planar surface. Diffusion bonding may be conducted at temperatures ranging from 600°C to 850°C forms an iron-enriched interfacial zone to bond the backing plate to the target plate. The iron-enriched interfacial zone has a thickness and a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0085] The target plate provided includes target material that may be produced using a powder or billet using thermomechanical processing steps. In one embodiment, a tantalum (or other refractory metal) powder billet may be cold isostatically pressed, then hot isostatically pressed, and then subjected to thermomechanical processing (i.e., a series of cross-rolls). Following thestep of hot isostatic pressing, there may be one or more steps of machining and / or surface finishing of the target plate. For example, surface material may be removed by grinding and / or polishing. One or more structural features may be machined as well (e.g., one or more features for fixturing, for receiving an O-ring in a backing plate for high vacuum applications, or otherwise). To produce the sputtering target assembly as above, the teachings herein also attach a backing plate to the target plate.

[0086] Tantalum (and / or other refractory metal powders including niobium, titanium, molybdenum, or combinations thereof) powder may also be used for the target material. A sputtering target body in accordance with the present teachings may be prepared by consolidating the powders of the present teachings. Consolidating may be by one or any combination of sintering, hot isostatic pressing, hot extruding, or otherwise. A mass of powders can be cold isostatically pressed by applying a suitable pressure (e.g., to an initial state at a pressure of about 220 MPa) to achieve a density ranging from about 82 to about 88% of theoretical density. The cold isostatic pressed powders, while within a container, may be hot isostatically pressed under suitable temperature and pressure conditions and for suitable time (e.g., at a temperature of about 1250°C, a pressure of about 207 MPa for a period of time such as about 6 hours) to achieve a density near theoretical density (e.g., at least 98% of theoretical density). The resulting hot isostatically pressed body is removed from the container and can be processed (e.g., by cutting and / or machining to final dimensions).

[0087] In one embodiment, the method for making a target plate includes providing a powder of tantalum, or other refractory metal, having a purity of at least 99.95 wt%, e.g., at least 99.99 wt%, or still more preferably at least 99.995 wt%, and having an oxygen content below 75 ppm, e.g., below 60 ppm or below 50 ppm, and / or having a maximum magnesium content below 10 ppm (or even 5 ppm). The powder may have a particle size that is below 1000 pm, e.g., below 850 pm, below 650 pm, below 500 pm, below 350 pm or even below 250 pm. For instance, about 95 percent, about 85 percent, about 75 percent by weight of the total particles may have a particle size that is at least 10 pm, e.g., at least 40 pm, at least 65 pm or at least 90 pm. About 95 percent of the total particles may have a particle size that is below 1000 pm, e.g., below 850 pm, below 650 pm, below 500 pm, below 350 pm or below 250 pm. In one embodiment, no particles in the powder exceed 1000 pm.

[0088] In one embodiment, 25 to 65 percent by weight of the particles, e.g., 29 to 56 percent or even 35 to 47 percent, in the powder may have a particle size that is larger than 65 pm, e.g., larger than 150 pm, larger than 250 pm, larger than 500 pm, larger than 650 pm or larger than 850 pm, but below about 1000 pm. In accordance, the embodiments described herein may use powders having 25 to 65 percent by weight of the particles, e.g., 29 to 56 percent or even 35 to 47 percent, with a particle size that is less than 1000 pm, e.g., less than 850 pm, less than 650 pm, less than 500 pm, less than 350 pm, or less than 250 pm, but above about 10 pm. To effectively consolidate the target plate, the process may use a powder that contains at least 10 percent by weight of particles having a particle size greater than 150 pm, which results in an effectively consolidated mass (e.g., as a result of hot isostatic pressing). Preferably, the process may use a powder that contains at least 20 percent by weight of particles having a particle size greater than 150 pm results, e.g., at least 30 percent, at least 40 percent, or at least 50 percent.

[0089] Unless otherwise stated, powder particle sizes are determined by screen analysis in accordance with ASTM B214-07(2011). Further, unless otherwise stated, particle sizes refer to pre-consolidation sizes.

[0090] The powder may be isostatically pressed to define a target body at a temperature that is at most 1400°C, e.g., at most 1325°C, at most 1250°C, at most 1100°C, at most 1080°C, or at most 1000°C. Pressing may be in the range from 100 MPa to 300 MPa, e.g., about 170 MPa to about 250 MPa.

[0091] By way of example, without limitation, the material may be pressed to form a diskshaped body that will be subject to bombardment during the sputtering process.

[0092] In one embodiment, the rolling process may contribute plane orientation of the target material. The amount and distribution of strain that is introduced from the rolling process may be controlled by several factors including, asymmetric rolling, the diameter of the rolling mill roll, rolling speed, and rolling reduction. In one embodiment, the process is not necessarily limited provided that the desired plane orientation may be achieved.

[0093] The sputtering targets comprising tantalum or tantalum alloy are particular suited for forming thin films for optical fibers, semiconductor wafers, and integrated circuits. It also is contemplated that thin films result that are used in any of a number of electronic components or devices (e.g., as a layer, such as a barrier layer, an electrode layer, as part of a semiconductor, as part of an integrated circuit, or otherwise), such as one or more of a television, a video display, asmartphone, a tablet computer, a personal digital assistant, a navigation device, a sensor, a portable entertainment device (e.g., video players, music players, etc.), or even a photovoltaic device. Alternatively, or in addition to tantalum as target material in the processes described above, the following may be used: niobium, titanium, molybdenum, alloys thereof, or combinations thereof. The target plate may further comprise iron, cobalt, aluminum, copper, tungsten, or alloys or mixtures thereof.

[0094] Importantly, as discussed above, the backing plate includes copper, zinc, tin, and iron in specific, controlled amounts to form an iron-enriched interfacial zone with the target plate described above via diffusion bonding.

[0095] The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.

[0096] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0097] The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0098] As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of’ and “consisting essentially of’. The terms “comprise(s)”, “include(s)”, “having”, “has”, “can”, “contain(s)”, and variants thereof, as used herein, are intended to be open-ended transitional phrases that require the presence of the named ingredients / steps and permit the presence of other ingredients / steps. However, such description should be construed as also describing compositions or methods as “consisting of’ and “consisting essentially of’ the enumerated ingredients / steps, which allows the presence of onlythe named ingredients / steps, along with any impurities that might result therefrom, and excludes other ingredients / steps.

[0099] Numerical values in the specification and claims of this application, as they relate to sputtering target assemblies or assembly component compositions, e.g., backing plate composition, target plate composition, and the like, reflect average values for a composition. The numerical values disclosed herein should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0100] All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 1 pm to 40 pm” is inclusive of the endpoints, 1 pm and 40 pm, and all the intermediate values). The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and / or values.

[0101] As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 10” also discloses the range “from 2 to 10”. The term “about” may refer to plus or minus 10% of the indicated number. For example, “about 10%” may indicate a range of 9% to 11%, and “about 1” may mean from 0.9-1.1.

[0102] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0103] As used herein, “greater than” and “less than” limits may also include the number associated therewith. Stated another way, “greater than” and “less than” may be interpreted as “greater than or equal to” and “less than or equal to.” It is contemplated that this language may be subsequently modified in the claims to include “or equal to.” For example, “greater than 4.0” may be interpreted as, and subsequently modified in the claims as “greater than or equal to 4.0.”

[0104] Some of the components and steps disclosed herein may be considered optional. In some cases, the disclosed compositions, processes, etc. may expressly exclude one or more of the aforementioned components or steps in this description, e.g., via claim language. This is contemplated herein by the inventors. For example, claim language may be modified to recite that the disclosed compositions, processes, streams, etc., do not utilize or comprise one or more of the aforementioned components or steps, e.g., tin (or any other of the aforementioned additives). Such negative limitations are contemplated, and this text serves as support for negative limitations for components, steps, and / or features.EXAMPLES

[0105] Examples 1A-1D. Sputtering target assemblies were made and tested for bond strength.

[0106] Example 1 backing plate composition: 38.66 wt% zinc; 0.4% tin; 0.012 wt% iron; 0.13 wt% lead; and remainder copper. The remainder 0.3 wt% or less accounted for interstitial and / or unavoidable impurities.

[0107] The backing plate and the target plate were brought into contact along coextensive, adjacent, prepared surfaces to form a pre-assembly. The surfaces were prepared and cleaned and the pre-assembly was then diffusion bonded in a hot press in an argon atmosphere at a various temperatures.

[0108] Examples 1A, IB, 1C, and ID were prepared and diffusion bonded at temperatures of 600°C, 700°C, 800°C, and 850°C, respectively.

[0109] Examples 1A, IB, 1C, and ID were then tested for mechanical and electrical properties.

[0110] Results, as in FIGs. 9-12, confirmed the presence of an iron-enriched interfacial zone. FIG. 9 demonstrated an increase in Fe content in the interfacial zone as a function of diffusion bonding temperature, where the Fe intensity increased with temperatures increasing from 600°C to 850°C. The Fe+ signal was collected over a 75x75 pm2analysis area at the target plate / backing plate interfacial zone.[0U1] FIG. 10 demonstrated the thickness of the iron-enriched interfacial zone by showing overlaid line-scans across the target plate / backing plate interface of a sputtering target assembly according to Example ID diffusion bonded at a temperature of 850°C. The graph showed Cu descending, Fe increasing and descending, and Ta increasing as measured across the interfacefrom the backing plate to the target plate. This data showed that the iron-enriched interfacial zone was about 1.4 pm in thickness.

[0112] The iron-enriched interfacial zone of Example 1C diffusion bonded at a temperature of 800°C was further shown as in FIG. 11 for a cross section of a sputtering target assembly analyzed with ToF-SIMS. The overlay of the main image (overlaying the three inset images labeled Fe, Ta, and Cu) showed an iron-enriched interfacial zone, the Fe being disposed between the copper containing backing plate and a Ta containing target plate for Example 1C.

[0113] The iron-enriched interfacial zone of Example ID diffusion bonded at a temperature of 850°C was further shown as in FIG. 12 for a cross section of a sputtering target assembly analyzed with ToF-SIMS. The overlay of the main image (overlaying the three inset images labeled Fe, Ta, and Cu) showed an iron-enriched interfacial zone, the Fe being disposed between the copper containing backing plate and a Ta containing target plate for Example ID.

[0114] There was no evidence of zinc depletion at the interface in the Examples analyzed. A narrow zone of zinc enrichment at the interface was observed that increased with increasing bonding temperature.

[0115] Stress-strain curves are shown in FIG. 13 for Examples 1A, IB, 1C, and ID showed the bonding temperature effect with numerical values for 0.2% offset yield strength and ultimate tensile strength (UTS) are listed in Table 1 below. UTS represents the bond strength. The 0.2% offset yield strength and UTS were obtained using an Arcan Tensile method. A bow-tie sample is obtained from the sputtering target assemblies and placed on a lOkN Arcan fixture designed by Grip Engineering. The fixture was placed in an Instron tensile test machine. The test fixture allows the samples to be run in pure tension or in shear.

[0116] As shown in Table 1, the yield strength at 0.2% offset was highest at 182.7 MPa for Example IB bonded at 700°C and the ultimate tensile strength was highest at 248.2 MPa for Example ID bonded at 850°C.

[0117] Examples 2A-2B: Comparative Example.

[0118] The comparative examples used the same conditions as Example 1, 800°C diffusion bonded, to produce a composition of 36.8 wt% zinc; 0.74 wt% tin; 0.009 wt% lead; 0.008 wt%; and remainder copper. The named elements comprised 99.8 wt%. The remainder 0.2 wt% or less accounted for interstitial and / or unavoidable impurities.

[0119] FIG. 14 is a comparison of the Fe content in the interfacial zone at 800°C diffusion bonding temperature between Example 1C and Comparative Example 2B. The Fe+ signal for Comparative Example 2B was collected over a 100x100 pm2analysis area at the target plate / backing plate interfacial zone.

[0120] The iron-enriched interfacial zone of Comparative Example 2B diffusion bonded at a temperature of 800°C is further shown as in FIG. 15 for a cross section of a sputtering target assembly analyzed with ToF-SIMS. The overlay of the main image (overlaying the three inset images labeled Fe, Ta, and Cu) showed an iron-enriched interfacial zone, the Fe being disposed between the copper containing backing plate and a Ta containing target plate for Comparative Example 2B.

[0121] The 0.2% offset yield and ultimate tensile strengths are obtained using an Arcan Tensile method and are listed in Table 2 below.

[0122] As shown in Table 2, a sputtering target assembly prepared with the same composition and under the same conditions demonstrated a large variability between Comparative Examples 2A and 2B. Thus, variability undermines performance of the sputtering target assembly and is expected to result in debonding of the target plate from the backing plate. In addition, the ultimate tensile strengths reported for the comparative examples are lower than the values in Table 1.

[0123] FIG. 16 is a micrograph of Comparative Example 2B. As compared with the conventional sputtering assembly in FIG. 7, the micrograph of FIG. 16 shows less phase at the interface.Embodiments

[0124] The following embodiments, among others, are disclosed.

[0125] Embodiment 1. A sputtering target assembly comprising: a target plate comprising a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate comprises: from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding the backing plate to the target plate, the iron-enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0126] Embodiment 2. The sputtering target assembly of embodiment 1, wherein the target plate includes a center, a thickness, an edge, a target top planar surface, and a target bottom planar surface, where the top planar surface is opposite the bottom planar surface.

[0127] Embodiment 3. The sputtering target assembly of embodiment 2, wherein the backing plate includes a center, a thickness, an edge, a backing top planar surface, and a backing bottom planar surface, where the backing top planar surface is opposite the backing bottom planar surface.

[0128] Embodiment 4. The sputtering target assembly of any of embodiments 1-3, wherein the iron-enriched interfacial zone is disposed between the target bottom planar surface and the backing top planar surface.

[0129] Embodiment 5. The sputtering target assembly of any of embodiments 1-4, wherein the interfacial zone thickness is less than 10 pm, or less than 5 pm, or less than 3 pm, or less than 1 pm.

[0130] Embodiment 6. The sputtering target assembly of any of embodiments 1-5, wherein the target bottom planar surface is coextensive with the backing top planar surface.

[0131] Embodiment 7. The sputtering target assembly of any of embodiments 1-6, wherein the target bottom planar surface is in contact with the backing top planar surface.

[0132] Embodiment 8. The sputtering target assembly of any of embodiments 1-7, having a bond strength between the target plate and the backing plate that is greater than or equal to 175, preferably greater than or equal to 200 MPa.

[0133] Embodiment 9. The sputtering target assembly of any of embodiments 1-8, wherein the concentration of iron in the iron-enriched interfacial zone is at least 3 wt% greater than the concentration of iron in the backing plate.

[0134] Embodiment 10. The sputtering target assembly of any of embodiments 1-9, wherein the backing plate further comprises from 0.25 wt% to 2.0 wt% tin.

[0135] Embodiment 11. The sputtering target assembly of any of embodiments 1-10, wherein the backing plate comprises from 0 to 0.1 wt% (1000 ppm) lead.

[0136] Embodiment 12. The sputtering target assembly of any of embodiments 1-11, wherein the backing plate comprises less than 100 ppm lead.

[0137] Embodiment 13. The sputtering target assembly of any of embodiments 1-12, wherein the backing plate has a ratio of Zn:Fe by weight from 70: 1 to 4000: 1.

[0138] Embodiment 14. The sputtering target assembly of any of embodiments 1-13, wherein the refractory metal or refractory metal alloy of the target plate comprises tantalum, niobium, titanium, molybdenum, alloys thereof, or combinations thereof.

[0139] Embodiment 15. The sputtering target assembly of any of embodiments 1-14, wherein the target plate further comprises iron, cobalt, aluminum, copper, tungsten, or alloys or mixtures thereof.

[0140] Embodiment 16. The sputtering target assembly of any of embodiments 1-15, wherein the target plate comprises from 0 to 0.1 wt% (1000 ppm) iron.

[0141] Embodiment 17. The sputtering target assembly of any of embodiments 1-16, wherein the target plate comprises less than 100 ppm iron.

[0142] Embodiment 18. The sputtering target assembly of any of embodiments 1-17, wherein the target plate comprises tantalum having a purity of 99.99% (4N) or greater.

[0143] Embodiment 19. The sputtering target assembly of any of embodiments 1-18, wherein the tantalum has a purity of 99.999% (5N) or greater.

[0144] Embodiment 20. The sputtering target assembly of any of embodiments 1-19, wherein the target plate comprises one of niobium, titanium, or molybdenum having a purity of 99.99% (4N) or greater.

[0145] Embodiment 21. The sputtering target assembly of any of embodiments 1-20, wherein the one of niobium, titanium, or molybdenum has a purity of 99.999% (5N) or greater.

[0146] Embodiment 22. The sputtering target assembly of any of embodiments 1-21, wherein the backing plate comprises an alloy phase comprising a copper-containing phase that is a-copper in solid solution with zinc.

[0147] Embodiment 23. The sputtering target assembly of any of embodiments 1-22, wherein the backing plate comprises a second copper-containing phase that is a P-CuZn intermetallic, the second copper-containing phase present in an amount less than 5 vol%.

[0148] Embodiment 24. The sputtering target assembly of any of embodiments 1-23, wherein the backing plate further includes iron precipitates dispersed therein.

[0149] Embodiment 25. The sputtering target assembly of any of embodiments 1-24, wherein the backing plate further comprises tin and includes tin precipitates dispersed therein.

[0150] Embodiment 26. A thin film formed using the sputtering target assembly of any of embodiments 1-25.

[0151] Embodiment 27. The sputtering target assembly of any of embodiments 1-26, wherein the backing plate has an ultimate tensile strength from 175 MPa to 1300 MPa.

[0152] Embodiment 28. A process for making a sputtering target assembly comprising: providing a target plate comprising a refractory metal or refractory metal alloy and a backing plate; and diffusion bonding a first planar surface of the backing plate to a second planar surface of the target plate in a vacuum, the second planar surface adjacent to the first planar surface, to form an iron-enriched interfacial zone to bond the backing plate to the target plate, where the backing plate comprises: from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and wherein the iron-enriched interfacial zone has a thickness and a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0153] Embodiment 29. The process of embodiment 28, wherein diffusion bonding is conducted at a temperature of 600°C to 850°C.

[0154] Embodiment 30. A sputtering target assembly comprising: a target plate comprising a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate consists of: from 0.01 wt% to 0.5 wt% iron, from 0.25 wt% to 2.0 wt% tin, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding thebacking plate to the target plate, the iron-enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

[0155] While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited below and / or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to limit.

Claims

We Claim:

1. A sputtering target assembly comprising: a target plate comprising a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate comprises: from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding the backing plate to the target plate, the iron- enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

2. The sputtering target assembly of claim 1, wherein the target plate includes a center, a thickness, an edge, a target top planar surface, and a target bottom planar surface, where the top planar surface is opposite the bottom planar surface and wherein the backing plate includes a center, a thickness, an edge, a backing top planar surface, and a backing bottom planar surface, where the backing top planar surface is opposite the backing bottom planar surface3. The sputtering target assembly of any one of claims 1 or 2, wherein the iron-enriched interfacial zone is disposed between the target bottom planar surface and the backing top planar surface, wherein the interfacial zone thickness is less than 10 pm, preferably less than 5 pm, preferably less than 3 pm, or more preferably less than 1 pm.

4. The sputtering target assembly of claim 3, wherein the target bottom planar surface is coextensive with the backing top planar surface.

5. The sputtering target assembly of any one of claims 3 or 4, wherein the target bottom planar surface is in contact with the backing top planar surface.

6. The sputtering target assembly of any one of claims 1 -5, having a bond strength between the target plate and the backing plate that is greater than or equal to 175, preferably greater than or equal to 200 MPa.

7. The sputtering target assembly of any one of claims 1-6, wherein the concentration of iron in the iron-enriched interfacial zone is at least 3 wt% greater than the concentration of iron in the backing plate.

8. The sputtering target assembly of any one of claims 1-7, wherein the backing plate further comprises from 0.25 wt% to 2.0 wt% tin.

9. The sputtering target assembly of any one of claims 1-8, wherein the backing plate comprises from 0 to 0.1 wt% (1000 ppm) lead, preferably the backing plate comprises less than 100 ppm lead.

10. The sputtering target assembly of any one of claims 1-9, wherein the refractory metal or refractory metal alloy of the target plate comprises tantalum, niobium, titanium, molybdenum, alloys thereof, or combinations thereof.

11. The sputtering target assembly of any one of claims 1-10, wherein the target plate comprises iron, cobalt, aluminum, copper, tungsten, or alloys or mixtures thereof, provided that the target plate comprises from 0 to 0.1 wt% (1000 ppm) iron.

12. The sputtering target assembly of any one of claims 1-11, wherein the target plate comprises tantalum having a purity of 99.99% (4N) or greater, preferably having a purity of 99.999% (5N) or greater.

13. The sputtering target assembly of any one of claims 1-12, wherein the backing plate comprises an alloy phase comprising a copper-containing phase that is a-copper in solid solution with zinc.

14. The sputtering target assembly of any one of claims 1 -13, wherein the backing plate comprises a second copper-containing phase that is a P-CuZn intermetallic, the second copper- containing phase present in an amount less than 5 vol%.

15. The sputtering target assembly of any one of claims 1-14, wherein the backing plate further includes iron precipitates dispersed therein.

16. A thin film formed using the sputtering target assembly of any one of claims 1-15.

17. A process for making a sputtering target assembly comprising: providing a target plate comprising a refractory metal or refractory metal alloy and a backing plate; and diffusion bonding a first planar surface of the backing plate to a second planar surface of the target plate in a vacuum, the second planar surface adjacent to the first planar surface, to form an iron-enriched interfacial zone to bond the backing plate to the target plate, where the backing plate comprises: from 0.01 wt% to 0.5 wt% iron, from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and wherein the iron-enriched interfacial zone has a thickness and a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

18. The process of claim 17, wherein diffusion bonding is conducted at a temperature of 600°C to 850°C.

19. A sputtering target assembly comprising: a target plate comprising a refractory metal or a refractory metal alloy; a backing plate adjacent to the target plate, wherein the backing plate consists of: from 0.01 wt% to 0.5 wt% iron, from 0.25 wt% to 2.0 wt% tin,from 34.0 wt% to 40.0 wt% zinc, and from 60.0 wt% to 66.0 wt% copper; wherein the wt% are based on the total weight of the backing plate; and an iron-enriched interfacial zone bonding the backing plate to the target plate, the iron- enriched interfacial zone having a thickness, wherein the iron-enriched interfacial zone has a concentration of iron that is greater than a concentration of iron in the backing plate as determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS).

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