# Patent

## Title
Methods of manufacturing large-area sputtering targets using interlocking joints

## Abstract

In various embodiments, joined sputtering targets are formed at least in part by spray deposition of the sputtering material and/or welding.

## Background
RELATED APPLICATIONS
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/540,644, filed Sep. 29, 2011, and U.S. Provisional Patent Application No. 61/648,333, filed May 17, 2012, the entire disclosure of each of which is hereby incorporated herein by reference.


TECHNICAL FIELD
In various embodiments, the present invention relates to methods of forming large sputtering targets, in particular by joining smaller sputtering-target tiles.
BACKGROUND
Sputtering, a physical-vapor-deposition technique, is utilized in many industries to deposit thin films of various materials with highly controllable composition and uniformity on any of a variety of substrates. However, for many applications, the size of the desired substrate continues to increase, necessitating the use of larger and larger sputtering targets during the sputtering process. Unfortunately, sputtering targets formed via conventional fabrication methods tends to be too small for many such applications, particularly if the sputtering-target material is a composite (i.e., a substantially uniform mixture of two or more elemental or compound components), as such composite sputtering targets are difficult or impossible to form with a high degree of uniformity by other methods such as rolling. For example, alloys or mixtures of molybdenum and titanium (Mo/Ti) are typically formed into billets for sputtering targets via hot isostatic pressing (HIP) of a mixture of Mo and Ti powders. The largest such billets tend to be smaller than the sputtering-target size desired for, e.g., sputtering of Mo/Ti films on large glass substrates for flat panel displays (FPDs). In order to provide sputtering targets of the requisite dimensions, multiple smaller targets are often positioned in close proximity to each other (but not otherwise joined together) to form a larger target. For example, for use in a “generation 7” sputtering tool, 12 planar plates having dimensions 2700 mm×200 mm×18 mm may be used to form a larger segmented target of approximate dimensions 2700 mm×2400 mm×18 mm.
Such segmented targets present many disadvantages in terms of particle generation (which results in expensive yield loss for the manufacturer) and film nonuniformity. Particle generation may occur preferentially along the edges of the individual sub-targets, and film uniformity tends to decrease as the edges of the target are approached and/or as the edges of the sub-targets are exposed to the sputtering process. Particle generation is a particular problem for FPDs, as each particle generated during the thin-film deposition process can cause a pixel to fail, which in turn has a deleterious impact on image quality and sharpness in the finished FPD.
Similarly, tubular (or “rotary”) sputtering targets are frequently of a segmented design simply because some sputtering materials (e.g., tantalum (Ta) or composites such as Mo/Ti), generally cannot be formed in sufficiently long tubes. For example, in order to make a long rotary target, multiple short cylindrical tiles of the sputtering material are often simply slipped over and bonded to a tubular backing plate made from an easily formable material such as stainless steel or Ti. A single 2.7-meter tube may have six or more tiles, the edges (as many as 12) of which potentially generate contaminating particles. Particle generation is exacerbated in rotary sputtering machines, because such machines typically contain multiple tubular targets. For example, a “generation 8.5” sputtering tool typically contains 12 separate rotary targets, and thus 144 tile edges potentially generating particles.
Techniques such as electron-beam welding have been utilized in attempts to join sub-targets together to form a larger sputtering target, e.g., a composite target of a material such as Mo/Ti. However, electron-beam welding of Mo/Ti sputtering-target sections results in unacceptable porosity in the welded zone due to the relatively high gas (e.g., oxygen) content of the Mo and Ti in the plates. Furthermore, the electron-beam-welded zone tends to have a markedly different microstructure than that of the bulk of the target, which generally results in deleterious nonuniformity in films sputtered from such joined targets.
In view of the foregoing, there is a need for methods of joining smaller sputtering targets to form large joined targets with joints that are mechanically robust and that do not generate particles during sputtering of the joined target.
SUMMARY
In accordance with various embodiments of the present invention, large sputtering targets are formed by tiling together multiple smaller sputtering targets (or “tiles”) each having a desired composition and joining the tiles at least partially by spray deposition (e.g., cold spray) and/or welding techniques. The present embodiments are particularly applicable to sputtering targets including or consisting essentially of composite materials or alloys such as Mo/Ti, tungsten/titanium (W/Ti), or copper/tungsten (Cu/W), and are also applicable to targets of a single material such as Ti, niobium (Nb), Ta, etc. The tiles may be, at least initially, shaped as rectangular prisms or cylinders with substantially right-angled corners. However, the tiles are generally not merely placed in close proximity and spray-coated at the seams therebetween, as such joints may have insufficient strength to withstand subsequent handling and processing. Rather, a shaped joint area is formed in at least one of the tiles at each interface or seam between tiles, and this joint area is at least partially filled and/or coated via spray deposition to form the joint. Such joints may advantageously have superior strength, resistance to particle formation, and microstructures and densities substantially resembling those of the joined plates. The spray-deposited portion of the joint enables the elimination of internal exposed “edges” in the larger joined targets. Such joined targets may have areal dimensions of at least 2800 mm×2500 mm (if planar), or even larger. Rotary joined targets in accordance with embodiments of the invention have lengths of 2.7 meters or even longer. However, joined sputtering targets having smaller areal dimensions or shorter lengths may also be produced in accordance to the embodiments of the invention. Typically the sputtering targets include or consist essentially of only the desired material to be sputtered, and after joining, the joined target is bonded to a backing plate, although in some embodiments the joining of the targets is performed directly on a backing plate. As used herein, a “backing plate” may be substantially planar, tubular, or cylindrical, depending on the geometry of the final desired sputtering target, and may include or consist essentially of one or more materials having a melting point less than that of the target material and/or less than the temperature of the spray material during spray deposition. Herein, references to the joining of two sputtering-target tiles (thereby forming an interface therebetween) are understood to include cases where more than two tiles are joined together at the same interface or at multiple different interfaces (and thus are not limited to cases in which only two tiles are joined), as such cases include the joining of various combinations of two different tiles.
The tiles to be joined may be fabricated with any one or more of a variety of techniques, including HIP, cold isostatic pressing (CIP), spray deposition, molding, etc. As mentioned above, the tiles may, at least initially, have rectangular prismatic or cylindrical shapes with substantially right-angled corners, and then shaped joints (e.g., bevels or chamfers) may be machined or otherwise introduced into the tiles prior to joining them together. Alternatively, the tiles may be initially shaped already incorporating the bevel (or other suitable shape for joining) via a process such as molding in a shaped mold.
In an aspect, embodiments of the invention feature a method of forming a joined sputtering target that includes or consists essentially of a sputtering material. Two discrete sputtering-target tiles, which include or consist essentially of the sputtering material, are disposed proximate each other to form an interface between the tiles. The interface includes a gap between the tiles. At least a portion of the gap is filled with a gap-fill material. A spray material is spray-deposited on at least a portion of the gap-fill material (as well as, e.g., a portion of one or both tiles) to form a partial joint. After formation of the partial joint, at least a portion of the gap-fill material is removed from the interface. After such removal, additional spray material is spray-deposited on at least a portion of the partial joint to join the tiles and form the joined sputtering target.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. Filling the at least a portion of the gap with the gap-fill material may alter the microstructure of at least one of the tiles in a region proximate the interface. At least a portion of the altered-microstructure region may be removed prior to spray-depositing the spray material on at least a portion of the partial joint. The gap-fill material may include or consist essentially of a weld bead and/or a rod (which may be hollow) shaped to (and/or deformable to) fill at least a portion of the gap. The sputtering material may include or consist essentially of a mixture or alloy of at least two constituent materials. The gap-fill material may include or consist essentially of at least one (e.g., only one) of the constituent materials. The constituent materials may include or consist essentially of Mo and Ti. The spray material may include or consist essentially of at least one of (e.g., only one) of the constituent materials. The spray material may include or consist essentially of the sputtering material. The tiles may consist essentially of the sputtering material. The gap-fill material may include or consist essentially of the sputtering material. At least a portion of each of the two tiles may be substantially planar (and the joined target may be substantially planar). At least a portion of each of the two tiles may be substantially tubular (and the joined target may be substantially tubular).
The interface may include at least one recess defined by a beveled surface of at least one of the two tiles. The spray material may substantially fill the at least one recess to form a surface substantially coplanar with a surface of at least one of the tiles. The beveled surface may be reentrant. At least a portion of the beveled surface may be substantially planar and form an angle of greater than 45° with respect to the normal to the top surface of the joined sputtering target. The angle may be selected from the range of 45° to 60°. Spray material may be spray deposited on the gap-fill material or on the partial joint at an angle approximately perpendicular to the beveled surface. Spray material may be spray deposited on the gap-fill material or on the partial joint by (i) spray-depositing a first portion of the spray material at an angle approximately perpendicular to the beveled surface and (ii) thereafter, spray-depositing a second portion of the spray material at an angle approximately perpendicular to the top surface of the joined sputtering target. After its formation, the joined sputtering target may be annealed at a temperature selected from the range of approximately 480° C. to approximately 1425° C., or at a temperature selected from the range of approximately 1100° C. to approximately 1425° C. The joined sputtering target may be disposed on a backing plate after formation of the joined sputtering target. The joined sputtering target may be heat treated at least proximate the spray material. The spray material may be spray-deposited on the gap-fill material and/or on the partial joint by cold spray.
In another aspect, embodiments of the invention feature a method of forming a joined sputtering target that includes or consists essentially of a sputtering material. A mechanical joint is formed between two discrete sputtering-target tiles by overlapping and/or interlocking the tiles at an interface therebetween. The interface includes a recess over the mechanical joint. The tiles are joined by welding the mechanical joint. Thereafter, a spray material is spray-deposited over at least a portion of the welded mechanical joint to substantially fill at least a portion of the recess, thereby forming the joined sputtering target.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. Welding the mechanical joint may include or consist essentially of resistance seam welding. The sputtering material may include or consist essentially of a mixture or alloy of at least two constituent materials. Welding the mechanical joint may include or consist essentially of melting at least one constituent material while at least one other constituent material remains unmelted. The constituent materials may include or consist essentially of Mo and Ti. The spray material may include or consist essentially of at least one of (e.g., only one) of the constituent materials. The spray material may include or consist essentially of the sputtering material. The tiles may consist essentially of the sputtering material. The mechanical joint may include or consist essentially of an interlocking joint that includes or consists essentially of a tongue-in-groove joint, a dovetail joint, a rabbet joint, a finger joint, or a spline joint. At least a portion of each of the two tiles may be substantially planar (and the joined target may be substantially planar). At least a portion of each of the two tiles may be substantially tubular (and the joined target may be substantially tubular).
The recess may be defined by a beveled surface of at least one of the two tiles. The beveled surface may be reentrant. At least a portion of the beveled surface may be substantially planar and form an angle of greater than 45° with respect to the normal to the top surface of the joined sputtering target. The angle may be selected from the range of 45° to 60°. Spray material may be spray deposited at an angle approximately perpendicular to the beveled surface. Spray material may be spray deposited by (i) spray-depositing a first portion of the spray material at an angle approximately perpendicular to the beveled surface and (ii) thereafter, spray-depositing a second portion of the spray material at an angle approximately perpendicular to the top surface of the joined sputtering target. After its formation, the joined sputtering target may be annealed at a temperature selected from the range of approximately 480° C. to approximately 1425° C., or at a temperature selected from the range of approximately 1100° C. to approximately 1425° C. The joined sputtering target may be disposed on a backing plate after formation of the joined sputtering target. The joined sputtering target may be heat treated at least proximate the spray material. The spray material may be spray-deposited by cold spray.
In yet another aspect, embodiments of the invention feature a method of forming a joined sputtering target that includes or consists essentially of a sputtering material. Two discrete sputtering-target tiles are disposed substantially in contact at an interface therebetween. A first welding electrode is disposed above the interface, and a second welding electrode is disposed below the interface. The first welding electrode is translated along at least portions of top surfaces of the tiles along the interface while, simultaneously, the second welding electrode is translated along at least portions of bottom surfaces of the tiles along the interface. The first welding electrode remains disposed substantially above the second welding electrode as the electrodes are translated. During at least part of the translation of the first and second welding electrodes, an electrical current is passed through the tiles between the first and second welding electrodes to weld the tiles together at the interface, thereby forming the joined sputtering target.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. A spray material may be spray-deposited on at least a portion of at least one of the tiles prior to disposing the tiles substantially in contact. The spray material may be disposed at the interface after the tiles are disposed substantially in contact. The spray material may include or consist essentially of the sputtering material. The sputtering material may include or consist essentially of a mixture or alloy of at least two constituent materials. The spray material may include or consist essentially of at least one of (e.g., only one) of the constituent materials. Spray-depositing the spray material may include or consist essentially of cold spray. Welding the tiles together may include or consist essentially of melting at least one constituent material while at least one other constituent material remains unmelted. The constituent materials may include or consist essentially of Mo and Ti. The tiles may consist essentially of the sputtering material. Mechanical force may be applied to the interface with the first and second welding electrodes. At least a portion of each of the two tiles may be substantially planar (and the joined target may be substantially planar). At least a portion of each of the two tiles may be substantially tubular (and the joined target may be substantially tubular). After its formation, the joined sputtering target may be annealed at a temperature selected from the range of approximately 480° C. to approximately 1425° C., or at a temperature selected from the range of approximately 1100° C. to approximately 1425° C. The joined sputtering target may be disposed on a backing plate after formation of the joined sputtering target. The joined sputtering target may be heat treated at least proximate the interface. The interface may define a plane that is not perpendicular to the top and/or bottom surfaces of the tiles.
In another aspect, embodiments of the invention feature a joined sputtering target comprising a sputtering material that comprises an alloy or mixture of first and second constituent materials. The joined sputtering target includes or consists essentially of first and second discrete sputtering-target tiles joined at an interface therebetween, the first and second tiles each including or consisting essentially of the sputtering material. Across the interface, (i) regions of the first tile consisting essentially of the first constituent material are bonded to regions of the second tile consisting essentially of the first constituent material, (ii) regions of the first tile consisting essentially of the first constituent material are bonded to regions of the second tile consisting essentially of the second constituent material, (iii) regions of the first tile consisting essentially of the second constituent material are bonded to regions of the second tile consisting essentially of the first constituent material, and (iv) regions of the first tile consisting essentially of the second constituent material are not bonded to regions of the second tile consisting essentially of the second constituent material.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The bonded regions may be partially melted and/or partially interdiffused. The first constituent material may include or consist essentially of Ti and the second constituent material may include or consist essentially of Mo. The first and second tiles may each consist essentially of the sputtering material.
In a further aspect, embodiments of the invention feature a method of forming a joined sputtering target including or consisting essentially of a sputtering material. Two discrete sputtering-target tiles, which include or consist essentially of the sputtering material, are disposed proximate each other, thereby forming an interface between the tiles. The interface includes or consists essentially of an interlocking joint therein and/or a recess in a top surface thereof. A spray material is spray-deposited over at least a portion of the interface, thereby joining the tiles to form the joined sputtering target.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. Disposing the two tiles proximate each other may include or consist essentially of disposing the two tiles substantially in contact with each other. At least a portion of each of the two tiles may be substantially planar (and the joined target may be substantially planar). At least a portion of each of the two tiles may be substantially tubular (and the joined target may be substantially tubular). The spray material may include or consist essentially of the sputtering material. The tiles may consist essentially of the sputtering material. The sputtering material may include or consist essentially of a mixture or alloy of at least two constituent materials. The constituent materials may include or consist essentially of Mo and Ti. The spray material may include or consist essentially of at least one of (e.g., only one) of the constituent materials. The interface may include a recess, and the spray deposition may fill at least a portion of the recess with the spray material. The interface may include a recess defined by a beveled surface (which may be reentrant) of at least one of the two tiles.
At least a portion of the beveled surface may be substantially planar and form an angle of greater than 45° with respect to the normal to the top surface of the joined sputtering target. The angle may be selected from the range of 45° to 60°. Spray material may be spray deposited at an angle approximately perpendicular to the beveled surface. Spray material may be spray deposited by (i) spray-depositing a first portion of the spray material at an angle approximately perpendicular to the beveled surface and (ii) thereafter, spray-depositing a second portion of the spray material at an angle approximately perpendicular to the top surface of the joined sputtering target. After its formation, the joined sputtering target may be annealed at a temperature selected from the range of approximately 480° C. to approximately 1425° C., or at a temperature selected from the range of approximately 1100° C. to approximately 1425° C. The interface may include an interlocking joint that includes or consists essentially of a tongue-in-groove joint, a dovetail joint, a rabbet joint, a finger joint, or a spline joint. An edge of at least one of the tiles may be beveled prior to disposing the tiles proximate each other, and the beveled edge(s) may form at least a portion of the recess. Spray-depositing the spray material may include or consist essentially of cold spray. The joined sputtering target may be sputtered, and the spray-deposited material may substantially prevent particle generation at the interface. The joined sputtering target may be disposed on a backing plate after spray deposition. The two tiles may be disposed proximate each other on a backing plate prior to spray deposition. The joined sputtering target may be heat treated at least proximate the spray material. The interface may define a plane that is not perpendicular to the top and/or bottom surfaces of the joined sputtering target.
In yet a further aspect, embodiments of the invention feature a joined sputtering target including or consisting essentially of a sputtering material. The joined sputtering target includes or consists essentially of two discrete sputtering-target tiles joined at an interface therebetween. The tiles include or consist essentially of the sputtering material. The interface includes a recess therealong at least partially filled with unmelted powder.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The two tiles may be joined at opposing edges, and the interface may include portions of the two opposing edges substantially in contact with each other and disposed beneath the at least partially filled recess. One of the two opposing edges may at least partially (or even completely) overlap the other opposing edge at the interface below the at least partially filled recess. The interface may define a plane that is not perpendicular to the top and/or bottom surfaces of the joined sputtering target. An interlocking joint that includes or consists essentially of portions of the two tiles may be present at the interface. The interlocking joint may include or consist essentially of a tongue-in-groove joint, a dovetail joint, a rabbet joint, a finger joint, or a spline joint. At least one of the tiles may include a beveled edge, and the beveled edge(s) may form at least a portion of the recess. The at least one beveled edge may have a reentrant surface. At least a portion of the at least one beveled edge may be substantially planar and form an angle of greater than 45° with respect to the normal to the top surface of the joined sputtering target. The angle may be selected from the range of 45° to 60°.
The unmelted powder may include or consist essentially of the sputtering material. The tiles may consist essentially of the sputtering material. The sputtering material may include or consist essentially of a mixture or an alloy of at least two constituent materials. The unmelted powder may include discrete regions each substantially free of at least one of the constituent materials. The joined sputtering target may include at least one region at the interface in which at least two of the constituent materials are interdiffused. The constituent materials may include or consist essentially of Mo and Ti. A backing plate may be attached to the tiles. The unmelted powder may be in contact with the backing plate. At least a portion of the joined sputtering target may be substantially planar. At least a portion of the joined sputtering target may be substantially tubular.
In another aspect, embodiments of the invention feature a joined sputtering target including or consisting essentially of a sputtering material. The joined sputtering target includes or consists essentially of two discrete sputtering-target tiles joined at an interface therebetween. The tiles include or consist essentially of the sputtering material. The interface includes a recess therealong at least partially filled with melted powder.
Embodiments of the invention may include one or more of the following in any of a variety of combinations. The two tiles may be joined at opposing edges, and the interface may include portions of the two opposing edges substantially in contact with each other and disposed beneath the at least partially filled recess. One of the two opposing edges may at least partially (or even completely) overlap the other opposing edge at the interface below the at least partially filled recess. The interface may define a plane that is not perpendicular to the top and/or bottom surfaces of the joined sputtering target. An interlocking joint that includes or consists essentially of portions of the two tiles may be present at the interface. The interlocking joint may include or consist essentially of a tongue-in-groove joint, a dovetail joint, a rabbet joint, a finger joint, or a spline joint. At least one of the tiles may include a beveled edge, and the beveled edge(s) may form at least a portion of the recess. The at least one beveled edge may have a reentrant surface. At least a portion of the at least one beveled edge may be substantially planar and form an angle of greater than 45° with respect to the normal to the top surface of the joined sputtering target. The angle may be selected from the range of 45° to 60°.
The melted powder may include or consist essentially of the sputtering material, and may have been deposited via thermal spray. The tiles may consist essentially of the sputtering material. The sputtering material may include or consist essentially of a mixture or an alloy of at least two constituent materials. The melted powder may include discrete regions each substantially free of at least one of the constituent materials. The joined sputtering target may include at least one region at the interface in which at least two of the constituent materials are interdiffused. The constituent materials may include or consist essentially of Mo and Ti. A backing plate may be attached to the tiles. The melted powder may be in contact with the backing plate. At least a portion of the joined sputtering target may be substantially planar. At least a portion of the joined sputtering target may be substantially tubular.
These and other objects, along with advantages and features of the present invention herein disclosed, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations. As used herein, the term “cold spray” refers to techniques in which one or more powders are spray-deposited without melting during spraying, e.g., cold spray, kinetic spray, and the like. The sprayed powders may be heated prior to and during deposition, but only to temperatures below their melting points. As used herein, the terms “approximately” and “substantially” mean±10%, and in some embodiments, ±5%. The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts.



BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
FIGS. 1A and 1B are schematic plan views of joined sputtering targets in accordance with various embodiments of the invention;
FIGS. 2A-2F are schematic cross-sections of two sputtering-target tiles being joined via utilization of a releasable rod and spray deposition in accordance with various embodiments of the invention;
FIGS. 3A-3F are schematic cross-sections of two sputtering-target tiles being joined via utilization of a gap-filling weld bead and spray deposition in accordance with various embodiments of the invention;
FIGS. 4A-4E are schematic cross-sections of two interlocking sputtering-target tiles being joined via welding and spray deposition in accordance with various embodiments of the invention;
FIGS. 5A-5E are schematic cross-sections of two overlapping sputtering-target tiles being joined via welding and spray deposition in accordance with various embodiments of the invention;
FIGS. 6A-6D are schematic cross-sections of two sputtering-target tiles being joined via welding in accordance with various embodiments of the invention;
FIGS. 6E and 6F are cross-sectional micrographs of sputtering target tiles joined in accordance with various embodiments of the invention;
FIGS. 7A-7C are schematic cross-sections of two abutting sputtering-target tiles being joined via spray deposition in accordance with various embodiments of the invention;
FIG. 7D is a schematic cross-section of a joined sputtering target formed of two interlocking sputtering-target tiles joined by the interlocking joint and by spray deposition in accordance with various embodiments of the invention;
FIG. 8A is a cross-sectional micrograph of the microstructure of a joined sputtering target at the sputtering-target tile/sprayed material interface prior to annealing in accordance with various embodiments of the invention;
FIG. 8B is a cross-sectional micrograph of the microstructure of a joined sputtering target at the sputtering-target tile/sprayed material interface after annealing in accordance with various embodiments of the invention;
FIG. 9A is a schematic cross-section of two beveled sputtering-target tiles prior to being joined in accordance with various embodiments of the invention;
FIG. 9B is a schematic cross-section of two beveled sputtering-target tiles after being joined by spray deposition in accordance with various embodiments of the invention; and
FIGS. 10A-10D are schematic cross-sections of sputtering-target tiles having different reentrant bevels in accordance with various embodiments of the invention.



DETAILED DESCRIPTION
FIGS. 1A and 1B are schematic plan views of joined sputtering targets 100 formed by the joining of smaller sputtering-target tiles 110 in accordance with embodiments of the invention. As shown, the tiles 110 are joined via regions 120 that, at least in part, include or consist essentially of one or more spray materials formed by spray deposition (e.g., cold spray, thermal spray, plasma spray, etc.). As shown, the tiles may be substantially rectilinear (FIG. 1A) or tubular (FIG. 1B) and may be joined on one or two sides. In other embodiments the tiles have other shapes (e.g., square) and/or are joined on more than two sides. The tiles may each be of substantially the same size and/or shape, or two or more of the tiles may have different sizes and/or shapes. In various embodiments, regions of the tiles are substantially planar or tubular (e.g., in portions between the regions 120), and the joined target 100 may be substantially planar or tubular. A joined target 100 may be disposed on a backing plate (not visible in FIG. 1A) or backing tube 130 (portions of which are visible in FIG. 1B) either before or after formation of the joining regions 120.
The backing plate or tube 130 may include or consist essentially of a metal such as Cu and/or Al, and may have a melting point below that of the material of tiles 110 and/or the material of regions 120, and may even have a melting point below the temperature that the sprayed material constituting regions 120 reaches during spray deposition (e.g., in cases where the backing plate or tube is attached to the joined target 100 after formation of regions 120). In some embodiments of the invention, particularly those in which the joined target is tubular, the backing plate or tube 130 may include or consist essentially of a metal such as stainless steel and/or Ti. The tiles 110 typically include or consist essentially of one or more metallic materials, e.g., Ti, Nb, Ta, W, Mo, other refractory metals, or composite materials (alloys or mixtures) such as Mo/Ti, W/Ti, Cu/W, etc. The regions 120 preferably include or consist essentially of at least one of the constituent materials of tiles 110. For example, the sprayed material in regions 120 may include or consist essentially of the same elemental metal as in tiles 110, one or more of the constituent metals of a composite tile 110 (e.g., a tile 110 may include or consist essentially of Mo/Ti, and the region 120 may include or consist essentially of Ti), or the same plurality of constituent metals of a composite tile 110, in the same concentration as in tile 110 or in a different mix of concentrations as in tile 110 (e.g., a tile 110 may include or consist essentially of 50% Mo and 50% Ti, and the region 120 may include or consist essentially of 40% Mo and 60% Ti). The tiles 110 and regions 120 preferably include or consist essentially of the same material(s) so that, when the joined target 100 is sputtered, the composition of the material sputtered from the target 100 is substantially constant across the dimensions of target 100 and as a function of sputtering time and/or lifetime (i.e., amount of utilization) of target 100.
FIGS. 2A-2F schematically depict, in cross-section, various steps of a process for forming a joined sputtering target in accordance with various embodiments of the present invention. FIGS. 2A-2F (and most subsequent figures) depict either substantially planar tiles 110 (i.e., utilized to fabricate a planar joined target 100) or to portions of substantially tubular tiles 110 (i.e., utilized to fabricate a tubular joined target 100), which appear planar in cross-section. (Specifically, the cross-section of a tubular tile 110 would include two substantially parallel regions, only one of which is shown for each tile 110 in FIGS. 2A-2F and many subsequent figures.) As shown in FIG. 2A, a bevel 200 is formed in at least one of the tiles 110, and the tiles 110 are positioned with a gap 210 at the interface between the tiles 110. The gap 210 may range from, e.g., approximately 2 mm to approximately 8 mm. As shown, bevels 200 are formed in both tiles 110, but in other embodiments a bevel (or chamfer) 200 is formed in only one of the tiles 110. While the bevels 200 in FIG. 2A are shown as having sloped and straight sidewalls, other embodiments of the invention feature bevels 200 having curved or even arbitrary sidewalls (and/or may be reentrant, as described in more detail below), and the bevels 200 may be asymmetric relative to the interface between the tiles 110 (i.e., any portion of the tiles 110 in close proximity or in contact). The bevels 200 may even be asymmetric relative to the horizontal axis (i.e., perpendicular to the interface between tiles 110) defined by the tiles 110 at approximately one-half of their thicknesses. Generally, the bevel(s) 200 may form any type of recess (i.e., a region depressed relative to the top surface and/or the bottom surface of at least one of the tiles 110 and at least partially defined by bevel(s) 200 of neighboring tiles 110) along an interface between tiles 110 that does not disturb close proximity or contact between at least a portion of the opposed faces of the tiles 110. As shown in FIG. 2A, the bevels 200 may define recesses relative to both the top and bottom surfaces of tiles 110. While FIG. 2A depicts the tiles 110 as being entirely separated by gap 210, portions of the tiles 110 may be in physical contact, and irregularities along the edge of at least one of the tiles 110 may at least partially define the gap 210. In various embodiments, substantially all of a sidewall of at least one of the tiles 110 may be beveled (i.e., cut at a non-right angle to the top and/or bottom surface of the tile), and the two tiles 110 may be placed in close proximity but not in contact prior to joining via spray deposition (as detailed below). In such embodiments the bevel(s) 200 increase the volume of the area to be at least partially filled by spray deposition and/or the surface area of contact between the sprayed material and the tiles 110.
As shown in FIG. 2B, the tiles 110 may be positioned on a support fixture 220, which may include or consist essentially of any suitably rigid material (e.g., metal, ceramic, or even wood) and that is preferably substantially planar. (For tubular tiles 110, the fixture 220 may be cylindrical or tubular and disposed within the annular space defined by the tiles 110.) Additionally, at least a portion of the gap 210 (e.g., along its length perpendicular to the plane of the page of FIGS. 2A-2F) is substantially filed with a gap-fill material such as a rod 230. The rod 230 may have a cross-section that is substantially circular or elliptical, as shown in FIG. 2B, or it may have any other cross-sectional shape suitable for filling at least a portion of the gap 210. Rod 230 may be substantially solid or hollow, and it preferably includes or consists essentially of the material of tiles 110 or material subsequently sprayed thereon (as detailed below), or at least one constituent material of tiles 110 or such sprayed material. Such compositional matching may reduce or substantially eliminate any contamination due to rod 230 from the final joined target, as the rod 230 is typically substantially or completely removed during the process detailed below. As shown in FIG. 2B, a recess 240 may be at least partially defined by the bevels in tiles 110 and a portion of the gap-fill material (here rod 230). The rod 230 may have a diameter or edge length ranging, e.g., from approximately 3 mm to approximately 9 mm. The diameter or edge length of the rod 230 may preferably be less than one-half of the thickness of the tiles 110 being joined. In some embodiments, the rod 230 is deformable to substantially “seal” the gap 210 and thereby substantially prevent the flow of powder particles during subsequent spray deposition (as detailed below).
After rod 230 has been positioned to fill at least a portion of the gap 210, a material 250 is spray-deposited thereover to partially or substantially fill the recess 240. The sprayed material 250 is preferably deposited by cold spray, and thus includes or consists essentially of substantially unmelted powder, but in particular instances may instead be deposited by other spray-deposition methods such as plasma spray or other thermal spray techniques (and thus sprayed material 250 may include or consist essentially of substantially melted powder). The volume of spray-deposited material 250 present within the recess 240 typically forms a partial joint joining the two tiles 110. The amount of material 250 at the partial joint, enabled by the recess 240 at least partially formed by the bevel(s) 200, contributes to the strength of the joint and thus of the entire joined sputtering target after completion. The material 250 preferably includes or consists essentially of the material of tiles 110, or at least one constituent material of tiles 110 (for tiles 110 that are composites of multiple constituent materials), as described above in relation to FIGS. 1A and 1B.
After spray-deposition of the material 250 to form the partial joint between the tiles 110, the rod 230 is removed from the tiles 110 and the material 250 by, e.g., mechanical force, grinding, and/or dissolution in an acidic agent. Preferably the entire rod 230 is removed, even if small portions of the material 250 and/or the tiles 110 are removed along with rod 230. As shown in FIG. 2D, the tiles 110 may then be flipped over and may be positioned on fixture 220 (not shown) or another suitable fixture for mechanical support. As shown in FIG. 2E, a recess 260 at least partially defined by the bevels 200 and the material 250 is subsequently filled (at least partially), preferably with the same material as material 250, to form the region (or “joint”) 120 joining the tiles 110. As shown, the sprayed material may be deposited to be substantially coplanar with the surfaces of the joined tiles 110, thus providing the joined target 100 with one or more surfaces that are substantially planar. As also shown, at least a portion of the joint 120 may consist essentially of the sprayed material through its entire thickness; as described in more detail below, such a configuration may result in a mechanically stronger joint 120. As shown in FIG. 2F, the tiles 110 (or effectively, the joined target 100) may be attached to a backing plate 130 either before or after the sprayed material is deposited within the recess 160 to complete the joint 120.
After formation of the joint 120, the joined target 100 (at least proximate the joint 120) may be heat treated for stress relief (e.g., to improve ductility) and/or to provide the joint 120 with a microstructure substantially equal to that of the joined tiles 110. For example, for tiles 110 including or consisting essentially of a mixture of multiple constituents, the microstructure of the tiles 110 may include interdiffused regions between regions corresponding to different constituents (as described in more detail below with reference to FIGS. 8A and 8B; for example, arising from a HIP process for forming the tiles 110). After a heat treatment, the joint 120 may feature such interdiffused regions, which may have approximately the same size of such regions in the tiles 110 prior to joining. In some embodiments of the invention, the heat treatment may be performed under vacuum, at a temperature between approximately 700° C. and approximately 900° C., and for a time between approximately 1 hour and approximately 16 hours.
In addition, the heat treatment may relieve residual stresses from the spray-deposition process. For example, in many cases, sprayed material melted during spraying tends to have tensile residual stress, while sprayed material that is not melted during spraying tends to have compressive residual stress. (For example, cold-sprayed Ta may have residual compressive stress of between 30 and 50,000 psi.) Such residual stresses may result in non-uniform sputtering rates from the target incorporating the sprayed material. In conventional (i.e., not incorporating sprayed material) targets, residual machining stresses frequently necessitate a costly burn-in period (i.e., sputtering away of the stressed surface layer) prior to sputtering with new targets. Embodiments of the present invention described herein facilitate the manufacture of joined sputtering targets and subsequent heat treatment prior to the target being joined to a backing plate. (The backing plate and the joining compound, e.g., In solder, typically have lower melting points and thus may not be able to withstand a heat treatment adequate to reduce or substantially eliminate residual stress from the target.) In this manner, the need for a burn-in period prior to sputtering from the joined target is reduced or substantially eliminated.
FIGS. 3A-3F depict another process for forming a joined sputtering target 100 utilizing a gap-fill material between sputtering-target tiles 110 in accordance with embodiments of the present invention. As described above in relation to FIG. 2A, the tiles 100 have one or more bevels 200 and are positioned with gap 210 at the interface between the tiles 110 (which may result, as discussed above, from portions of the tiles 110 being in contact or close proximity at the interface). As shown in FIG. 3B, in various embodiments of the invention, at least a portion of the gap 210 is subsequently filled with a gap-fill material that includes or consists essentially of a weld bead 300 disposed in a recess 310 at least partially defined by the bevels 200. The weld bead 300 may be formed by, e.g., tungsten inert gas (TIG) welding (utilizing an inert cover gas such as helium or argon), and may be formed with or without the use of a filler wire or rod (which preferably includes or consists essentially of the material of tiles 110 or at least one constituent material thereof). The weld bead 300 thus includes or consists essentially of portions of the tiles 110 and/or the filler material. The weld bead 300 may be a substantially continuous bead along the entire interface between the tiles 110 or may be a series of spot welds along the interface. In preferred embodiments in which material is subsequently deposited by cold spray (as detailed below), the weld bead 300 is a substantially continuous bead along the entire interface between the tiles 110 that substantially seals the gap 210. As shown in FIG. 3B, formation of the weld bead 300 may alter the microstructure of one or both tiles 110 near the weld bead 300 (due to, e.g., the elevated welding temperature), forming altered regions 320. Region 320 typically includes or consists essentially of a heat-affected zone (HAZ), which may be characterized by substantial grain growth compared to regions of the tiles 110 outside of the HAZ. The grain growth may result in the sweeping of impurities to the grain boundaries and significant embrittlement of the HAZ for materials such as Mo and its alloys. Additionally, for composite materials such as MoTi, the HAZ may feature increased porosity (compared to regions of the tiles 110 outside of the HAZ) due to gas evolution due to local melting of one or more of the constituent materials (e.g., melting of Ti but not of Mo).
After formation of the weld bead 300, the remainder of recess 310 is partially or substantially filled via spray-deposition of the material 250, as shown in FIG. 3C. Afterwards, because the weld bead 300 typically has a different microstructure that that of the bulk of the tiles 110, the weld bead 300 is removed from the tiles 110 and the material 250, as shown in FIG. 3D. The removal may be performed by, e.g., mechanical grinding and/or chemical (e.g., acid) treatment. As shown, regions 320 are preferably also removed along with the weld bead 300, forming a recess 330 (defined at least in part by bevels 200 and the surfaces of tiles 110 revealed during removal of weld bead 300 and/or regions 320) shown in FIG. 3D. Such removal may also remove portions of the original material 250 deposited in recess 310 and/or additional portions of the tiles 110. Additional material 250 is subsequently spray-deposited within the recess 330 to complete formation of the joint 120, as shown in FIG. 3E. As shown, the sprayed material may be deposited to be substantially coplanar with the surfaces of the joined tiles 110, thus providing the joined target 100 with one or more surfaces that are substantially planar. As also shown, at least a portion of the joint 120 may consist essentially of the sprayed material through its entire thickness; as described in more detail below, such a configuration may result in a mechanically stronger joint 120. As shown in FIG. 3F, the tiles 110 (or effectively, the joined target 100) may be attached to a backing plate 130 either before or after the sprayed material is deposited within the recess 330 to complete the joint 120. After formation of the joint 120, the joined target 100 (at least proximate the joint 120) may be heat treated, for example as described above with reference to FIGS. 2A-2F.
FIGS. 4A-4E depict a process for forming a joined sputtering target 100 utilizing sprayed material and an interlocking joint between sputtering-target tiles 110 in accordance with embodiments of the present invention. Specifically, the tiles 110 may be machined with complementary and/or interlocking features 400 that facilitate the joining of the tiles 110 and improve the strength of the joint 120 after spray deposition. As shown in FIG. 4B, the interlocking features 400 are joined to form a mechanical joint 410 (that may be, as detailed below, supplemented with spray-deposited material). While FIGS. 4A-4E depict a tongue-in-groove joint, other joints (including, e.g., dovetail joints, rabbet joints, finger joints, spline joints, etc.) may be utilized in conjunction with or instead of a tongue-in-groove joint. Furthermore, joined sputtering targets 100 may utilize different types of joints 410 to join different pairs of tiles 110. Generally, the interface between two tiles 110 may have one or more bevels 200, an interlocking feature (or “interlock”) 400, or both. The interlock 400 may have any geometry that varies the contact interface from a straight interface in order to increase the contact surface area and/or provide mechanical linkage between the tiles 110. Before the tiles 110 are physically joined (i.e., before they are placed in direct contact with each other) to form mechanical joint 410, one or more portions of the surfaces that will meet in the locking joint 410 may be coated with a spray-deposited coating. The coating may be sprayed on all or portions of such surfaces on only one of the tiles 110 or on both of them. Thus, in accordance with various embodiments, two discrete sputtering-target tiles 100 including or consisting essentially of the sputtering material are disposed proximate each other, thereby forming an interface between the tiles that contains an interlocking joint 410.
As shown in FIG. 4C, the mechanical joint 410 may preferably be strengthened and/or sealed together via use of welding, e.g., resistance seam welding. As shown, electrodes 420 are disposed on either side of mechanical joint 410 and, depending on the length of the joint 410 (i.e., out of the plane of the page), translated laterally along the joint 410. Mechanical force is generally applied to the mechanical joint 410 by the electrodes 420, and a large current is applied between the two electrodes 420. The heat resulting from the electrical resistance of the joint 410 welds the interlocks 400 together to strengthen the joint 410. Depending on the materials of tiles 110, a portion thereof within the joint 410 may even melt during the welding process. For example, for tiles 110 that include multiple constituent materials, one or more of the lower-melting-point constituents may melt during the welding to strengthen the joint 410 while one or more other constituents (i.e., having higher melting points) may remain substantially unmelted during the welding. In a specific example, for tiles 110 formed of Mo/Ti, the Ti may melt during the welding while the Mo phase remains unmelted. In preferred embodiments of the present invention, such melting is limited, and most of the bonding between the tiles 110 occurs due to solid-state diffusion between the tiles 110.
As shown in FIG. 4D, the mechanical joint 410 between the tiles 110 may be subsequently supplemented with a layer of spray-deposited material 250 to form joint 120 (which includes or consists essentially of the mechanical joint 410 and the layer of sprayed material 250). The tongue-in-groove joint (or alternative joint, as detailed above) may help prevent the propagation of defects through the subsequently sprayed layer of material 250. For example, a simple butt joint between the two tiles to be joined may result in a small gap or other discontinuity between the tiles at some point along the interface therebetween, and such a gap may propagate through the subsequently sprayed layer, weakening the sprayed joint and the final joined target. Accordingly, the tiles are desirably substantially in contact along the interface; by “substantially in contact” is meant that the interface is sufficiently free of gaps or discontinuities to avoid their perceptible or performance-affecting propagation through the sprayed layer of material 250. The welding described above with respect to FIG. 4C may be repeated after deposition of material 250, for example to enhance adhesion between the sprayed material 250 and the tiles 110. As shown in FIG. 4E, the tiles 110 (or effectively, the joined target 100) may be attached to a backing plate 130 either before or after the sprayed material 250 is deposited to complete the joint 120. After formation of the joint 120, the joined target 100 (at least proximate the joint 120) may be heat treated, for example as described above with reference to FIGS. 2A-2F.
FIGS. 5A-5E depict a process for forming a joined sputtering target 100 similar to that depicted in FIGS. 4A-4E but utilizing overlapping sputtering-target tiles 110 in accordance with embodiments of the present invention. Specifically, the bevels 200 of tiles 110 may be machined such that a portion of one tile 110 overlaps a portion of the other tile 110 when the tiles are brought into proximity or substantial contact. This overlap feature, similar to mechanical joint 410 described above, facilitates the joining of the tiles 110 and improves the strength of the joint 120 after spray deposition. As shown in FIG. 5B, the tiles 110 are brought into close proximity or substantial contact, forming an overlapping region 500 (that may be, as detailed below, supplemented with spray-deposited material). Joined sputtering targets 100 may utilize different types of overlapping regions 500 between different pairs of tiles 110. Before the tiles 110 are placed in direct contact with each other to form overlapping region 500, one or more portions of the surfaces that will meet in the overlapping region 500 may be coated with a spray-deposited coating. The coating may be sprayed on all or portions of such surfaces on only one of the tiles 110 or on both of them.
As shown in FIG. 5C, the overlapping region 500 may preferably be strengthened and/or sealed together via use of welding, e.g., resistance seam welding. As shown, electrodes 420 are disposed on either side of overlapping region 500 and, depending on the length of the overlapping region 500 (i.e., out of the plane of the page), translated laterally along the overlapping region 500. Mechanical force is generally applied to the overlapping region 500 by the electrodes 420, and a large current is applied between the two electrodes 420. The heat resulting from the electrical resistance of the overlapping region 500 welds tiles 110 together to strengthen the overlapping region 500. Depending on the materials of tiles 110, a portion thereof within the overlapping region 500 may even melt during the welding process. For example, for tiles 110 that include multiple constituent materials, one or more of the lower-melting-point constituents may melt during the welding to strengthen the overlapping region 500 while one or more other constituents (i.e., having higher melting points) may remain substantially unmelted during the welding. In a specific example, for tiles 110 formed of Mo/Ti, the Ti may melt during the welding while the Mo phase remains unmelted.
As shown in FIG. 5D, the overlapping region 500 between the tiles 110 may be subsequently supplemented with a layer of spray-deposited material 250 to form joint 120 (which includes or consists essentially of the overlapping region 500 and the layer of sprayed material 250). The overlapping region 500 (where the tiles 110 are substantially in contact) may help prevent the propagation of defects through the subsequently sprayed layer of material 250, as it may eliminate small gaps or discontinuities between the tiles 110 that may propagate through the subsequently sprayed layer, weakening the sprayed joint and the final joined target 100. As shown in FIG. 5E, the tiles 110 (or effectively, the joined target 100) may be attached to a backing plate 130 either before or after the sprayed material 250 is deposited to complete the joint 120. After formation of the joint 120, the joined target 100 (at least proximate the joint 120) may be heat treated, for example as described above with reference to FIGS. 2A-2F.
In some embodiments of the present invention, particularly those utilizing thinner sputtering-target tiles 110, the tiles 110 may be joined to form a joined target 100 utilizing welding (e.g., resistance seam welding) without material spray-deposited over the resulting welded joint. As shown in FIG. 6A, the tiles 110 may be provided with complementary bevels 200 such that, as shown in FIG. 6B, the tiles 110 may be fit together substantially gaplessly (and preferably without recesses on the top and bottom surfaces on the resulting joined tile). Before the tiles 110 are placed in direct contact with each other, one or more portions of the bevels 200 may be coated with a spray-deposited coating (e.g., including or consisting essentially of one or more, or even all, of the constituent materials of tiles 110, or even of the same material as that of tiles 110). The coating may be sprayed on all or portions of bevels 200 on only one of the tiles 110 or on both of them.
As shown in FIG. 6C, the interface between the tiles 110 is then strengthened and/or sealed together via use of welding, e.g., resistance seam welding. As shown, electrodes 420 are disposed on either side of the interface and, depending on the length of the interface (i.e., out of the plane of the page), translated laterally along the interface. Mechanical force is generally applied to the interface by the electrodes 420, and a large current is applied between the two electrodes 420. The heat resulting from the electrical resistance of the tiles 110 welds tiles 110 together to strengthen the bond between the tiles 110. Depending on the materials of tiles 110, a portion thereof may even melt during the welding process. For example, for tiles 110 that include multiple constituent materials, one or more of the lower-melting-point constituents may melt during the welding to strengthen the joint while one or more other constituents (i.e., having higher melting points) may remain substantially unmelted during the welding. In a specific example, for tiles 110 formed of Mo/Ti, the Ti may melt during the welding while the Mo phase remains unmelted. As shown in FIG. 6D, the tiles 110 (or effectively, the joined target 100) may be attached to a backing plate 130 after the welding process that forms joint 600. After formation of the joint 600, the joined target 100 (at least proximate the joint 600) may be heat treated, for example as described above with reference to FIGS. 2A-2F.
In some embodiments of the present invention, the above-described welding technique joins composite tiles 110 together via preferential bonding (via, e.g., at least partial melting and/or solid-state diffusion) of only one of (or less than all of) the constituents of the tiles, e.g., the constituent(s) having lower individual melting point(s). FIG. 6E is a micrograph of two Mo/Ti composite tiles joined in such a manner, in which preferential bonding was achieved via adjustment of the power density utilized in the welding process. As shown, Ti regions in the two tiles 110 are preferentially bonded to other Ti regions and to Mo regions across a bonding interface 610, but Mo regions of the two tiles 110 that abut at interface 610 have not bonded (at least not completely). The tiles 110 shown in FIG. 6E were approximately 9 mm thick, and the resulting bonding was successful across the full thickness. Closure pressure of the welding electrodes was approximately 55 MPa and the weld current density was 50 kA/m2. Tiles 110 having larger thicknesses (e.g., up to 20 mm, or even thicker) may be joined with the techniques described herein by, e.g., increasing the weld pressure and/or the weld power density. The welding may be performed at speeds of, e.g., 10-16 cm/min, or even faster.
As shown in FIG. 6E, the two tiles 110 have been bonded together while retaining the microstructure of the tiles 110 in the vicinity of the bonding interface 610 without formation of a HAZ and without the above-described concomitant properties of a HAZ. Moreover, tiles 110 joined via this technique have sufficient bonding strength at interface 610 such that the interface 610 is not a failure point when stress is applied to the joined target. FIG. 6F depicts a joined sputtering target fabricated via seam welding of two tiles 110 after tensile stress testing to fracture. As shown, the fracture 620 does not correspond to or follow the bonding interface 610 (shown schematically by the dashed line). In addition, as in FIG. 6E, the microstructure along the interface 610 is substantially identical to that of the two tiles 110 away from interface 610, demonstrating that the joining process does not disrupt the microstructure of the tiles 110.
FIGS. 7A-7D illustrate another embodiment of the present invention in which sputtering-target tiles 110 are brought into substantial contact and a joint 120 between the tiles 110 is formed via spray deposition. As shown, one or both of the tiles 110 has a bevel 200 that, when the tiles 110 are brought into substantial contact, defines a recess 700 above the interface 710 between the tiles 110. As shown in FIG. 7D, the interface 710 may include or consist essentially of a mechanical joint 410 (as described above) rather than a butt joint between the tiles 110. The interface 710 is preferably substantially free of gaps, as such gaps may result in cracks or other points of weakness propagating through material spray-deposited above the interface 710. As shown in FIGS. 7C and 7D, after the tiles 110 are brought together and are substantially in contact, material 250 is spray-deposited within recess 700 to form joint 120. The material 250 is preferably sprayed to form a top surface substantially coplanar with the top surfaces of the tiles 110, such that the joined tile 100 has a substantially planar top surface. As also shown in FIGS. 7C and 7D, the tiles 110 (or effectively, the joined target 100) may be attached to a backing plate 130 either before or after the sprayed material 250 is deposited to complete the joint 120. After formation of the joint 120, the joined target 100 (at least proximate the joint 120) may be heat treated, for example as described above with reference to FIGS. 2A-2F.
Various embodiments of the present invention incorporate annealing steps to strengthen any or all of (i) the original material matrix of the tiles 110, (ii) the spray-deposited joint 120, and (iii) the bonding region between the original tile matrix and the sprayed layer (i.e., the tensile strength across the interface between the original tile and the sprayed layer). The table below shows the increase in tensile strength in all three regions for two different anneal conditions, a 16-hour anneal at 700° C. and a one-hour anneal at 900° C. In these joined targets, which are formed of MoTi, the original tile matrix was formed by HIP and the sprayed layer was formed by cold spray.















Tile Matrix
Sprayed Layer
Bonding Region



(psi)
(psi)
(psi)



















No anneal
64,958
28,600
1,297


700° C., 16 hours
108,667
74,273
7,881


900° C., 1 hour
94,793
57,364
6,445









As shown in the table, both annealing conditions significantly increase the tensile strength of the joined target in all three regions. FIGS. 8A and 8B depict one contributor to the increased strength in the annealed targets. FIG. 8A is a cross-sectional micrograph of a spray joined MoTi tile in accordance with various embodiments of the invention before annealing, in which the original tile 110 matrix was formed by HIP and the sprayed layer 250 was formed by cold spray. As shown in FIG. 8A and as the above table indicates, the matrix of the original tile 110 has a higher initial tensile strength at least in part because the matrix includes not only discrete Mo and Ti phases (the light and dark areas), but also an interdiffused region 800 (indicated in gray) therebetween. In contrast, the sprayed layer 250 consists essentially of the pure Mo and Ti phases without any interdiffusion (likely due to the reduced temperature of the cold-spray process).
FIG. 8B is a cross-sectional micrograph of the same sample after annealing, where the original material matrix of the tile 110, the layer of spray-deposited material 250, and the bonding region between the original tile 110 matrix and the sprayed layer 250 all exhibit higher tensile strength (as shown in the above table). As shown in FIG. 8B, the annealing step has increased the size of the interdiffused area 800 in the original tile matrix and resulted in formation of interdiffused areas 810 in the spray-deposited layer 250. Furthermore, interdiffused material is evident at the bonding interface between the two regions, demonstrating that the anneal has resulted in diffusion bonding between the original tile 110 matrix and the sprayed layer 250, thus resulting in enhanced mechanical strength of the joined target 100. The interdiffused areas 800, 810 include or consist essentially of two or more (or even all) of the constituent materials of the tiles 110, while other areas of the tiles 100 and/or the sprayed material 250, at the microscale, include or consist only fewer (or even only one) of the constituents, as shown in FIGS. 8A and 8B. Various embodiments of the present invention incorporate a high-temperature annealing step after spray-deposition of the joining layer(s) 120 between the tiles 110. The annealing step is preferably of sufficient temperature and time to result in diffusion bonding between the tile(s) 110 and the material 250 of the sprayed joint 120. For example, the annealing step may be performed for a time between approximately 1⁄2 hour and approximately 20 hours and at a temperature between approximately 480° C. and approximately 1425° C., or at a temperature between approximately 1100° C. and approximately 1425° C. (i.e., higher than the melting point of conventional backing plates and soldering materials utilized to join sputtering targets to backing plates, e.g., In solder). In embodiments in which the tiles 110 are composites of multiple constituent materials, a thin layer of one or more (but not all) of the constituent materials (e.g., Ti for a Mo/Ti tile 110) may be spray-deposited prior to the spraying of the remaining material 250 (which may include or consist essentially of the material of the tiles 110, e.g., Mo/Ti). This thin layer may further improve bonding and interdiffusion across the joint 120. For example, for Mo/Ti tiles 110, a thin layer of Ti may substantially prevent Mo-to-Mo contact across the interface between the tile 110 and the sprayed material 250, where Mo self-contact may have little or no adhesive strength. The thickness of the thin layer may be, e.g., approximately 50 μm to approximately 100 μm, and/or the thickness may be approximately the same or slightly (e.g., 5-20%) larger than the average diameter of particles of one or more of the constituents in the layer. (For example, for a thin layer of Ti for a Mo/Ti tile 110, the thickness of the thin layer may be approximately the same or slightly larger than the average diameter of the Mo particles to substantially prevent self-contact thereof.)
As mentioned above, the bevels 200 formed in tiles 110 to be joined may have any of a variety of shapes and make a variety of different angles with respect to the substantially planar top and/or bottom surfaces. (For tubular targets, the top and bottom surfaces are generally planar when viewed in cross-section, even though the surfaces themselves have curvature, as discussed above.) FIG. 9A depicts two tiles 110 to be joined in accordance with embodiments of the present invention each having a bevel 200 that is substantially planar and forms a bevel angle A with respect to the normal to the top and bottom surfaces. Tensile strength measurements were performed on three samples each having different angles A, where at each joint 120 each tile 110 had a bevel of angle A, and thus the entire included angle at the joint was 2A, as shown in FIG. 9B. The samples were tested utilizing the ASTM three-point bending test where loading was applied to the center of the joint 120. The table below presents the fracture stress for each sample, as well as the location of the crack formation at failure (in the matrix of the original tile 110, within the sprayed layer of material 250, and/or at the bonding interface therebetween).
















Bevel

Fracture
Std.
Crack
Crack in
Crack in


Angle A

Stress
Dev.
in Tile
Sprayed
Interfacial


(degrees)
Anneal
(psi)
(psi)
Matrix
Layer
Region





















45
None
1900
1550


X


45
700° C.
11,250
15,700


X



16



hours


45
900° C.
14,440
13,360


X



1 hour


52.5
None
3580
1382


X


52.5
700° C.
4480
2743


X



16



hours


52.5
900° C.
1710
1205


X



1 hour


60
None
13,010
4670

X


60
700° C.
28,440
1920

X
X



16



hours


60
900° C.
32,860
4210

X
X



1 hour









As shown in the above table, generally the fracture strength of the joined target 100 increases with increasing bevel angle A. Moreover, failure was more likely to occur within the stronger sprayed joint 120 than only within the interfacial region as the bevel angle A increases. In these samples, the spray-deposited joint 120 was sprayed normal to the top surface of the target 100 (rather than to the surface of the bevel 200 itself); thus, fracture strength of the joint 120 increases as the spray direction approaches perpendicular to the surface of the bevel 200. Therefore, in various embodiments of the invention, at least a portion (and preferably an initial portion) of the spray-deposited layer joining the tiles is sprayed substantially perpendicular to the surface (or at least a portion thereof) of the bevel 200 formed in the tile 110. For example, a first portion of the sprayed layer 120 may be deposited in a direction substantially perpendicular to the surface of the bevel 200, and a second portion may substantially fill the remaining recess and be sprayed substantially perpendicular to the top surfaces of the tiles 110 being joined. The first portion may have a thickness of, e.g., between 1 μm and 10 μm, or even between 10 μm and 100 μm, or even thicker than 100 μm. In various embodiments of the invention, the first and second portions of the sprayed layer 120 may be distinguished via examination of the microstructure of the sprayed powder. For example, when powder is deposited via cold spray, the powder particles tend to flatten on impact (having slowed from supersonic velocity) with the substrate, and the particles are flattened along the spraying direction. (That is, an initially spherical particle will be flattened such that its surfaces approximately parallel to the spraying direction are closer together than its other surfaces.
In another embodiment, the bevel 200 formed in a tile 110 to be joined may even have a slight concavity and may thus be more parallel to the top and/or bottom surfaces of the tile 110 in the proximity of the joining edge of the tile 110. In such embodiments typical spray deposition angles approximately perpendicular to the tile 110 top surface will be more perpendicular to the surface of the bevel 200 in the center of the joint 120 (i.e., the region of the joint 120 that tends to have the least mechanical strength), thereby strengthening the joint 120.
Various embodiments of the present invention utilize bevels 200 having reentrant surfaces to facilitate formation of stronger spray-deposited joints 120. FIGS. 10A-10D depict exemplary reentrant bevels in accordance with embodiments of the present invention. As utilized herein a “reentrant surface” is one through which a straight line (illustrated in FIGS. 10A-10D as dashed lines) may be drawn such that it enters, exits and re-enters the surface at least once, or even twice or more. In general, the number of exit and re-entry points is one of the parameters that may be varied to optimize the reentrant surface of the bevel(s) 200 for strength of the joint 120. Reentrant surfaces may be composed of two or more generally straight segments and may feature one or more inflection points indicating changes in slope. Three-point fracture strength measurements were performed on two different samples each having the reentrant bevel surface illustrated in FIG. 10A, but employing different radii R1, R2 on the curved sections. Specimen 1 had a 4 mm radius R2 of the concave-down surface and a 1 mm radius R1 of the concave-up surface. In specimen 2, both radii were 2.5 mm. The samples were tested utilizing the ASTM three-point bending test where loading was applied to the center of a spray-deposited joint 120 between the tiles 110 (as shown, e.g., in FIG. 9B for tiles 110 without reentrant bevels 200). The table below presents the fracture stress for each sample, as well as the location of the crack at failure (in the matrix of the tile 100, within the sprayed layer 120, and/or at the bonding interface therebetween).


















Fracture
Std.
Crack
Crack in
Crack in


Sample

Stress
Dev.
in Tile
Sprayed
Bonding


No.
Anneal
(psi)
(psi)
Matrix
Layer
Region





















1
None
11,800
771

X



1
700° C.
38,910
3875
X
X



16 hours


1
900° C.
38,860
13,113

X



1 hour


2
None
13,230
4547

X


2
700° C.
48,170
9545

X



16 hours


2
900° C.
51,080
2006

X



1 hour









As shown, the use of reentrant bevel surfaces not only results in generally stronger joints, but also shifts the failure location from the weaker interfacial bonding region to within the bulk of the sprayed layer 120 itself and sometimes even into the matrix of one of the tiles 110. Thus, the reentrant surface 200, at least in some embodiments, shifts the region of peak stress of the joined tile 100 away from the weakest part of the joint to a region of more mechanical strength.
Tiled sputtering targets 100 with spray-deposited joints 120, as described herein, do not only meet the larger size requirements of many sputtering applications, but also facilitate greater material utilization during sputtering. In magnetron sputtering with a set of individual tiles, the magnetron generally needs to provide a fixed electric field for each tile. Because of the shape of the field, the erosion pattern takes on the form of a race track in the plate, where the edges and the center of the tile are sputtered little if at all, resulting in the utilization of only about 30% of the target mass. On the other hand, a large tiled sputtering target, as provided by various embodiments of the present invention, facilitates use of a sweeping magnetron that causes a more uniform, larger erosion pattern (akin to the shape of an empty bath tub), as a result of which up to about 60% of the target may be sputtered.
The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.

## Claims

1. A method of forming a joined sputtering target comprising a sputtering material, the method comprising:
forming a mechanical joint between two discrete sputtering-target tiles by (i) overlapping or (ii) overlapping and interlocking the tiles at an interface therebetween, the interface comprising a recess over the mechanical joint, and each of the tiles consisting essentially of the sputtering material;
after (i) overlapping or (ii) overlapping and interlocking the tiles at the interface therebetween, joining the tiles by welding the mechanical joint; and
thereafter, spray-depositing a spray material over at least a portion of the welded mechanical joint to substantially fill at least a portion of the recess, thereby forming the joined sputtering target.

2. The method of claim 1, wherein welding the mechanical joint comprises resistance seam welding, the resistance seam welding comprising (i) contacting a top surface of the mechanical joint with a first electrode disposed at least partially within the recess, (ii) contacting a bottom surface of the mechanical joint with a second electrode, the bottom surface being opposite the top surface, (iii) applying a mechanical force to the mechanical joint with at least one of the first or second electrodes, and (iv) passing an electrical current between the first and second electrodes.

3. The method of claim 1, wherein the sputtering material comprises a mixture or alloy of at least two constituent materials.

4. The method of claim 3, wherein welding the mechanical joint comprises melting at least one constituent material, at least one other constituent material remaining unmelted thereduring.

5. The method of claim 3, wherein the at least two constituent materials comprise Mo and Ti.

6. The method of claim 3, wherein the spray material comprises at least one of the constituent materials.

7. The method of claim 1, wherein the spray material comprises the sputtering material.

8. The method of claim 7, wherein the spray material consists essentially of the sputtering material.

9. The method of claim 1, wherein the mechanical joint comprises an interlocking joint, the interlocking joint comprising a tongue-in-groove joint, a dovetail joint, a rabbet joint, a finger joint, or a spline joint.

10. The method of claim 1, wherein at least a portion of each of the two tiles is substantially planar.

11. The method of claim 1, wherein at least a portion of each of the two tiles is substantially tubular.

12. The method of claim 1, wherein the recess is defined by a beveled surface of at least one of the two tiles.

13. The method of claim 12, wherein the beveled surface is reentrant.

14. The method of claim 12, wherein at least a portion of the beveled surface is substantially planar and forms an angle of greater than 45° with respect to a normal to a top surface of the joined sputtering target.

15. The method of claim 14, wherein the angle is selected from the range of 45° to 60°.

16. The method of claim 12, wherein spray-depositing the spray material comprises spray-depositing at an angle approximately perpendicular to the beveled surface.

17. The method of claim 16, wherein spray-depositing the spray material comprises:
spray-depositing a first portion of the spray material at an angle approximately perpendicular to the beveled surface; and
thereafter, spray-depositing a second portion of the spray material at an angle approximately perpendicular to a top surface of the joined sputtering target.

18. The method of claim 1, further comprising, after forming the joined sputtering target, annealing the joined sputtering target at a temperature selected from the range of approximately 480° C. to approximately 1425° C.

19. The method of claim 1, further comprising, after forming the joined sputtering target, disposing the joined sputtering target on a backing plate.

20. The method of claim 1, wherein spray-depositing the spray material comprises cold spray.

21. The method of claim 1, further comprising, after forming the joined sputtering target, heat treating the joined sputtering target at least proximate the spray material.

22. The method of claim 1, wherein the mechanical joint is formed by overlapping the tiles at the interface therebetween.

23. The method of claim 1, wherein the mechanical joint is formed by overlapping and interlocking the tiles at the interface therebetween.