METHOD OF DIFFUSION BONDING TARGETS TO BACKING PLATES

Abstract: The invention encompasses a method of bonding a first mass to a second mass. A first mass of first material and a second mass of second material are provided and joined in physical contact with one another. The first and second masses are then diffusion bonded to one another simultaneously with the development of grains of the second material in the second mass. The diffusion bonding comprises solid state diffusion between the first mass and the second mass. A predominate portion of the developed grains in the second material have a maximum dimension of less than 100 microns. The invention also encompasses methods of forming a physical vapor deposition target bonded to a backing plate.

Description: DESCRIPTION METHOD OF DIFUSION BONDING TARGETS TO BACKING PLATES Technical Field The invention pertains to methods of bonding first and second masses to one another, and in particular embodiments, pertains to methods of bonding two similar materi ils together, as well as to methods of bonding physical vapor deposition target materi lls to backing plate materials. Background Art There are numerous applications in which it is desired to bond a first mass to a second mass. One such application is in the bonding of physical vapor deposition targets (such is, for example, sputtering targets) to backing plates. The backing plates are configured to retain the targets in particular locations and orientations within pressure vapor deposition apparatuses. Modern developments in physical vapor deposition methodologies have created increasingly stringent requirements for robust bonding between targets and backing plates. A diagrammatic view of a portion of an exemplary sputter deposition apparatus 10 is siown in Fig. 1. Apparatus 10 comprises a backing plate 12 a sputtering target ] 4 bonded thereto. A semiconductive mateπal wafer 16 is within apparatus 10 and provided to be spaced from target 14. Sputtered material 18 is displaced from target 14 and uti ized to form a coating (not shown) over wafer 16. Among the modem improvements in sputter design is an increase in the distance between target 14 and semiconductive material substrate 16. Such increase in distance can enable more directional sputtering to be achieved over features of substrate 16 than can be achieved when target 14 is close to substrate 16 by allowing atoms that are not moving perpendicular to substrate 16 to land on the sidewall of the spu tenng chamber. Specifi .ally, substrate 16 will frequently have vertical holes or slots (kno wn as vias) with depths Five times their width or more (i.e., having relatively high critical dimensions). It is diffic ult to sputter materials into vias having high critical dimensions αnless there is a relatively long throw between a sputtering target and a substrate compπsi ng the vias. Although the longer throw creates advantages in coverage relative to shorter throw t-chniques, it also creates complications One of such complicaticms is caused by additional power utilized m long-throw technologies The additional power can cause sputtei ing targets to get hotl ;r than they had in older methods Such heat can disrupt a bond formed between backu g plate 12 and target 14 For instance, if target 14 is sαlder- bonde i to backing plate 12, the heat developed dunng long-throw sputienng techniques can be sufficient to melt the solder bond and actually break target 14 fiee from backing plate 2 Accoidmgly, solder-bondmg can be mappropnate for long- throw sputtenng technnjues A type of bonding which is generally able to withstand the high temperatures utilize 1 in long-throw sputtering techniques is diffusion bonding, which s a bond formed by solid state diffusion of components from target 14 to backing plate 12 and/or vice versa A difficulty in using diffusion bonding is that such typically compnses relatively high temperatures (300°C or more) to form the bond, and such temperatures can adversely affect target matenals Accordingly, it can be difficult to deve op diffusion bondir g processes for bonding physical vapor deposition targets to backing plates, and which further retain desirable properties of the physical vapor deposition targets It would be desirable to develop such diffusion bonding processes Disclo jure of the Invention In one aspect, the mvention encompasses a method of bondmg a first mass to a second mass A first mass of first material and a second mass of sec and material are provided and joined in physical contact with one another The first and second masses are then diffusion bonded to one another simultaneously with the development of grains of the .econd mateπal m the second mass The diffusion bonding com irises solid state diffusion between the first mass and the second mass A predominate portion of the developed grams in the second material have a maximum dimension of less than 100 microns In another aspect, the invention encompasses a method of forming a physical vapor deposition target bonded to a backing plate A target material and a backing plate material are joined in physical contact with one another. The target matenal and backing plate material both comprise aluminum The joined target and backing plate matenals are thermally treated under an atmosphere which is inert relative to foπning oxides on the tarj;et and backing plate materials The thermal treatment simultaneously diffusion bonds he target matenal to the backmg plate matenal while recrystalhzing grains in the target natenal The diffusion bonding comprises solid state diffusion between the backing plate material and the target mateπal to adhere the target maten.il to the backing plate material with a bond strength of at least 5,000 pounds/inch 2 . A predominate portion of the grains developed in the target material are less than 100 microns in maxiirum dimension after the thermal treatment of the target and backing plate materi ils. Brief Description of the Drawings Preferred embodiments of the invention are descnbed below with reference to the fol lowing accompanying drawings. Fig. 1 is a diagrammatic view of a portion of a prior art sputter deposition apparatus. Fig. 2 is a flow chart diagram of a method encompassed by the present invention. Fig. 3 is a diagrammatic illustration of a method of introducing work hardening into a larget material. Fig 4 is a diagrammatic illustration of the target matenal of Fig. 3 with a backing plate at a preliminary bonding step. Fig. 5 is a diagrammatic view of the target mateπal and backing plate of Fig. 4 at a bonding step subsequent to that of Fig. 4. Best Modes for Carrying Out the Invention The invention encompasses methods of bonding materials to on. another, and in particular embodiments encompasses methods of bonding a physical "apor deposition target material to a backing plate material. One aspect of the invention is a recognition that it would be advantageous to devekn methodologies for diffusion bonding an aluminum-containi g target to an aluminum-containing backing plate, while achieving relatively small grain sizes in the target material. A difficulty associated with diffusion bonding of aluminum-containing targets to aluminum-containing backing plates is that the diffusion-bonding temperatures can cause growth of crystalline grains (actually polycrystalhne grains) n the aluminum targets It is generally desired that alummum grains remain relatively small (i.e., less than 100 microns, and more preferably less than 50 microns) in targets compπsing high purity aluminum (e.g., elemental alummum), and aluminum alloys. The smaller grains can improve sputtering processes which aluminum is sputtered from the target material relative to sputtering occumng from a target material having larger grains. The invention encompasses methodology for controlling grain {jrowth associated with i he diffusion bonding of aluminum Such methodology can form a diffusion bonded aluminum sputtenng target in which a predominate portion of the grains in the target material have a maximum gram size of less than 100 microns A method encompassed by the present invention is described by a flow diagram in Fig 2 At an initial step (labeled 30 in Fig 2) work hardemng is done to the a target mateπal If, for example, the target mateπal comprises alummum, work hardening can be introduced by compressing the aluminum from an initial thickness to a second thicknsss Such compression is illustrated in Fig 3, wherein a target 50 is illustrated before and after compression, with an arrow 52 provided to indicate the step of comprsssion Target 50 comprises a first thickness "X" prior to the conpression 52 and a seco id thickness "Y" after the compression The compression can be .lccomplished by, for example, cold forging or cold rolling The final thickness of target 50 ("Y") can be, for example, less than 2% of the initial thickness of target 50 (l e , a 98% compression), and is typically less than or equal to about 40% of the initial thickness o ' target 50 (l e , a 60% compression) In particular embodiments, target 50 can be subiected to a 95% compression (i e , compressed so that final thickness "Y" is about 5% of initial thickness "X") Target 50 can, for example, comprise or consist essentially of lew to high purity aluminum An exemplary commercial (low-puπty) aluminum that can be utilized for target >0 is 1100 series aluminum alloy. The material of target 50 can t e cast as a billet having a diameter of from about 4 inches to about 9 inches, and t aving an initial thickn. ss of from about 5 inches to about 10 inches After the compress ion of target 50, the res ilting cold- worked blank can be cut to form a round blank of a deured diameter Referring again to the flow chart of Fig 2, the target is joined to a backing plate (Fig 2, step 32) Preferably, the target and backing plate are cleaned pπor to joining them to remove contaminants that may be present A method of joi ng a target to a backin \ plate is descnbed with reference to Figs 4 and 5 Refemng to Fig 4, the work- harden ;d target 50 of Fig 3 is shown elevated above a backing plate 6C Backing plate 60 of F ig 3 is shown having a continuous channel 62 machmed mto a surface in a spiral pattern Ultimately, target 50 will be pressed against plate 60 to force material from target ! 0 into channel 62 In embodiments in which target 50 comprises high-puπty aluminum, backing plate 60 can also compnse aluminum, and can specifically comprise, fo - example, 2000 Series, 5000 Series, 6000 Series or 7000 Senes heat-treatable aluminum alloys In partici lar embodiments, backing plate 60 can comprise heat-treatable alummum alloy 6061 11 either a T4 or T6 precipitate hardened condition An initial step in bonding target 50 to backing plate 60 is typ cally to join the target d backing plate by physically contact target 50 with plate 60 jrows 54 of Fig 4 mdic ate such joining by showing that target 50 is lowered onto plate 00 Fig 5 shows an assi mbly 70 comprising target 50 joined to plate 60 In the shown as 1 embly 70, target 50 covers channel 62 (Fig 4) of backing plate 60 Although the shown embodiment has a channel formed in backing plate 60 to enhance coupling of target 50 to backing plate 60, it is to be understood that such channel can be eliminated in particular embodiments of the mvention, or can be provided m target 50, rather than in backing plate 60 In embodiments m which one of backing plate 60 and target 50 is harder than another of backing plate 60 and target 50, channel 62 will preferably be provided in the harder of the two, so that the softer of the two can be pressed into the chanm.l m subsequent proces sing Assembly 70 is can be formed in, or placed in, an atmospheie which is inert rclativ ; to oxide formation from materials of plate 60 and target 50 In embodiments in which plate 60 and target 50 compπse high-puπty alummum, or aluminum alloys, the inert amosphere can compnse a vacuum, or consist essentially of, for example, one or more c f nitrogen gas and argon gas The inert atmosphere preferably does not comprise oxidative components (like oxygen), as such could adversely cause sxidation of the mateπ ils of one or both of the blank 60 and target 50 Refernng again to the flow chart of Fig 2, the joined backing phite and target are thermally treated (step 34 of Fig 2) to simultaneously 1) diffusion bond the target to the backing plate, and 2) develop grains in the target If target 50 and backing plate 60 compr se high-purity aluminum, the theimal treatment can comprise, for example, heatinj; the joined target and backing plate to a temperature of between 280°C and 400°C (preferably between 300°C and 340°C), and maintaining such temperatire for a time of from i bout 15 minutes to about an hour Dunng the time that the temperature is maintained, target 50 and backing plate 60 can be compressed in a forge to pressure of from aaout 10,000 pounds per square inch (psi) to about 16,000 psi An exemplary thermal treatment procedure for treating a target and backing plate which compnse aluminum is as follows Initially, an assembly conipnsmg a target j oined against a backing plate is heated to a temperature of from about 280°C to about 400°C (preferably form about 300°C to about 350 α C, and more preferably from about 300°C to about 344°C) and maintained at such temperature for a time of from 15 to 30 minut.s. The assembly is then transfened to a forge which is also maintained at a temperature of from about 280°C to about 400°C. The forge is util zed to compress target 50 and backing plate 50 together to a temperature of from about 10,000 psi to about 16,000 psi After compressing the target and backing plate, the assembly is transfc.ned back to the furnace havmg a temperature of from about 280°C to about 400°C, and maintained at such temperature for an additional time of from about 10 minutes to about 30 minutes. The above-described exemplary method allows diffusion bonding (specifically, solid ; tate diffusion of aluminum between target 50 and backing plate 60), as well as develcpment of grains withm target 50. Such grains form due to cold work introduced m target 50 during the compression of Fig. 3. The grain development typically involves three distinct steps. First, recovery in which stresses are relieved from in the most severe 'y deformed regions. Second, the cold- worked grams recrystal ∑e foπning small, new, stress-free grains in target 50, and finally gram growth of the new grains occurs. Preferably, target 50 is not exposed to a temperature above about 280°C from the time it is work- hardened in the step of Fig 3, until it is exposed to the thsrmal treatment. Accordingly, substantially an entirety of the grain development of target 50 occurs during the thermal treatment of target 50 and backing plate 60. The phrase "substantial entirety" is utilized in referring to the recrystallization and grain growth Dccurnng dunng the thermal treatment, rather than stating an "entirety" of the recrystallization and grain growtl: to indicate that there may be a small and effectively inconsequ:ntial amount of recrystallization and grain growth occurring at temperatures below 280°C during proces ;ιng and cleaning of target 50 prior to the thermal treatment. A particular process for accomplishing the above-discussed thermal treatment method is to place the assembly of the target and backing plate in a can (for instance, a can made of thin- walled aluminum), and to retain the assembly in the can during the heating and forging (i.e., pressing) associated with the diffusion bor dmg. The can preferably comprises two parts, and a wide flange which allows for subsequent welding to seal the target and backing plate assembly in the can. Also, the can preferably has a small c lameter tube which allows for vacuum checking of a weld seal on the can, as well as for providing a vacuum or inert atmosphere inside the can. Once the target and backin.i plate assembly is provided in the can, the can is welded shut. An inert gas or vacuum can be utilized during the welding to alleviate oxidation of the target and backing plate assembly. Weld mtegnty can be determined by conducting a leak test using tie small diameter tube. A final weld can be done on the small diameter tube to allow a vacuum or inert gas atmosphere to be maintained in the can During the time that the target and backing plate assembly is subjected to diffusion bonding, a temperature of the assembly can be monitored indirectly by monitoπnj; the temperature of a s .-called dummy part having the same dimensions as the target and backing plate assemDly, and heated in either the same furnace as the assembly, or in an identical furnace After the thermal treatment of the target and backing plate assembly, such assemDly is cooled The cooling can be accomplished by exposmg the assembly to either a liquid or a gas, with an exemplary liquid being water, and an exemplary gas being air The methods discussed above can form a target and backing plate assembly 70 comprising a strong diffusion bond between target 50 and backing plate 60, with a tensile streng h of such bond being at least 5,000 psi, and typically being between about 8,000 psi and 10,000 psi The yield strength of fully recrystalhzed high purity alummum is 3,000 DSi, which is about equivalent to 20 mcgapascals (MPa) and th. ultimate tensile streng h is 12 ksi (81 MPa). The yield strength of 6061 T4 is 21 ksi (145 MPa), and the ultimate tensile strength of 6061 T4 is approximately 35 ksi (241 MPa) The diffusion bond can have a strength close to that of the ultimate tensile strengi h of high purity aluminum, with the bond frequently havmg a strength of from about ό8 5% to about 83% of the tensile strength of the high punty aluminum utilized in the taiget (typically from about 8230 psi to about 9948 psi at room temperature) In contrast, solder bonds typically have strength ranges from about 1470 psi to about 6740 psi I.onds formed by methods of the present invention can therefore be significantly strong :r than solder bonds, and accordingly, better suited for the long-throw target applications of modern sputtenng applications that were discussed in the "Background" sectior of this disclosure The backing plate preferably remains strong after the above-di; cussed diffusion bondir g In a particular embodiment, a 6061 backing plate was found to retain a minimum strength equal to 6061-T4 when subjected to diffusion bonding at a tempei ature of about 300°C In addition to the strong bond formed between target 50 and backing plate 60 of assembly 70, a gram size of target 50 is preferably below 100 microns, more preferably from about 30 to less than 100 microns, and more preferably below a out 50 microns after the diffusion bonding Specifically, a predommate (l e., more than 50%) of the grains in target 50 will preferably have a maximum dimension of less than 100 microns, more preferably from about 30 microns to less than 100 microns, and more preferably less than about 50 microns. In particular embodiments, an entirety of the grains in target 50 have a maximum dimension of less than 100 microns, more preferably from about 30 microns to less than 100 microns, and more preferably lens than about 50 micro is. The above-discussed small grain size can be accomplished by starting with a target which been cold- orked, but which does not have grains formed. Accordingly, a recrystallization process will occur in the target material prior to growh of grains. For aluminum, such recrystallization process typically takes from about 20 to 30 minutes at a temperature of between 288°C and about 316°C. Thus, a target will spend a significant amount of time that it is at a diffusion bonding temperature in a stage where grains are recrystallizing, rather than growing. Such can prevent the grains from over-growing during the diffusion bonding to sizes that are, for example, in excess of 100 microns. Experiments have been performed to determine if increases in processing tempe ratures or times improve bonding of targets to backing plates. It is found that if a target is treated with higher temperatures or longer times, dramatic increases in grain size can occur, but only minor increases in bond strength are found. It is to be understood that although several of the particular .spects described above pertain to first and second masses comprising aluminum, the invention can be utilize! with masses other than those comprising aluminum. It is prefened that the masse:! comprise a component in common to enable diffusion bonding between the masse:;. Specifically, if the masses comprise a component in common, then the compc nent can diffuse as a solid from one of the masses to another of the masses. The first and second masses can also comprise no common componems, but diffusion between materials having the same component (known as self-diffusion) is typically faster than diffusion between materials comprising only dissimilar components. In particilar embodiments, the masses will comprise an element in common, such as, for example, elemental aluminum.

Claims: CLAIMS 1. A method of bonding a first mass to a second mass, comprising; providing a first mass of first material and a second mass of second material; joining the first mass and the second mass in physical contact with one another, and simultaneously diffusion bonding the first mass to the second mass and develcping grains of the second matenal in the second mass, the diffusion bonding comptismg solid state diffusion between the first mass and the second mass, a predominate portion of the developed grains having a maximum dimersion of less than 100 microns. □ 2. The method of claim 1 wherein all of the developed grains have the maximum dimension of the less than 100 microns. D 3. The method of claim 1 wherein the maximum dimension of the predominate portion of the developed grains is less than or equal to abo t 50 microns D 4. The method of claim 3 wherein all of the developed grains have the maxi um dimension of the less than or equal to about 50 microns. D 5. The method of claim 1 wherein the maximum dimension of the predoinmate portion of the developed grams is from about 30 microns to less than 100 microns. D 6 The method of claim 5 wherein all of the developed grains have the maximum dimension of from about 30 microns to less than 100 microns C 7. The method of claim 1 wherein the first material comprises a same predominate component as the second material. C 8. The method of claim 1 wherein the first material comprises a same predominate element as the second material. D 9. The method of claim 1 wherein the bonded first and second masses correspond to a backing plate and a physical vapor deposition target, respectively. D 10. A method o bonding a physical vapor deposition taiget material to a backing plate material, comprising: joining the target material and backing plate material in physical contact with one another; and thermally treating the joined target and backing plate materials ιo simultaneously diffus.on bond the target material to the backing plate material and devϊlop grains in the target material, the diffusion bonding comprising solid state diffusion between the backing plate and target materials, a predominate portion of the developed grains having a maximum dimension of less than 100 microns. D 11. The method of claim 10 wherein all of the developec. grains have the maximum dimension of the less than 100 microns. D 12. The method of claim 10 wherein the maximum dimension of the predominate portion of the developed grains is less than or equal to about 50 microns. D 13. The method of claim 12 wherein all of the developec grains have the maximum dimension of the less than or equal to about 50 microns. D 14. The method of claim 10 wherein the maximum dimension of the predominate portion of the developed grains is from about 30 microns to less than 100 microns. □ 15. The method of claim 14 wherein all of the developed grains have the maximum dimension of from about 30 microns to less than 100 microns D 16. The method of claim 10 wherein the backing plate material comprises a same predominate component as the target material. D 17. The method of claim 10 wherein the backing plate material comprises a same predominate element as the target material. C 18 The method of claim 10 whercm the backing plate matenal and target material both predominately comprise aluminum D 19 The method of claim 10 wherein the gram develo pment compnses recrystallization of grains within the target mateπal 3 20. The method of claim 10 wherein the gram development comprises growti of grains within the target material D 21 The method of claim 10 further comprising, before the joining, work- hardening the target mateπal. D 22 The method of claim 10 further comprising, before the joining, work- hardemng the target material by compressmg the target material from an initial thickness to a final thickness, the final thickness bemg less than or equal to about 10% of the initial thickness. D 23 The method of claim 10 further compπsing, before tf e joining, work- hardening the target mateπal by compressing the target matenal from an initial thickness to a fnal thickness, the final thickness bemg from about 40% to about 2% of the initial thicknsss □ 24 The method of claim 10 further compnsmg, before tbe joining, work- hardering the target matenal, and wherein the grain develop ment comprises recrys alhzation of grains from the work-hardened matenal. D 25 The method of claim 10 further comprising, before the joining, work- harder ing the target material, and wherein the grain development compr ses recrystallization of grains from the work-hardened material; and growth of the recrystallized grains D 26. A method of forming a physical vapor deposition target bonded to a backir g plate, comprising: joining a physical vapor deposition target material and backing plate material in physical contact with one another, the physical vapor deposition target .nd backing plate materials both comprising aluminum; and thermally treating the joined physical vapor deposition target and backing plate materials under an atmosphere which is inert relative to reaction with the physical vapor deposition target and backing plate materials, the thermally treating simultaneously diffusion bonding the physical vapor deposition target material to the backing plate material and developing grains in the physical vapor deposition tar.jet material, the diffusion bonding comprising solid state diffusion between the backing plate material and the physical vapor deposition target material to adhere the physical vapor deposition target material to the backing plate material with a bond strength of at least about 5000 pounds/inch 2 , and a predominate portion of the grains developed in ti e target material being less than 100 microns in maximum dimension after the thermal. y treating of the target and backing plate materials. D 27. The method of claim 26 wherein the backing plate material and physical vapor deposition target material both predominately comprise aluminum. D 28. The method of claim 26 wherein the grain development comprises recrystallization of grains within the physical vapor deposition target material. D 29. The method of claim 26 wherein the thermally treating comprises maintaining the joined physical vapor deposition target material and backing plate materi al at a temperature of from about 280°C to about 400° for a time of from about 20 minut:s to about 60 minutes and pressing the joined physical vapor depasition target and backing plate materials to a pressure of at least 12,500 pounds/in 2 during at least part of the tine that the temperature is maintained. D 30. The method of claim 29 further comprising cooling the joined physical vapor deposition target and backing plate materials with a liquid afte:- the temperature treatir ent. 3 31. The method of claim 29 further comprising cooling the joined physical vapor deposition target and backing plate materials with a gas after the temperature treatir ent. D 32. The method of claim 26 wherein the grain development comprises growt of grains within the physical vapor deposition target material. D 33. The method of claim 26 further comprising, before the joining, work- hardening the physical vapor deposition target material. D 34. The method of claim 26 further comprising, before the joining, work- hardening the physical vapor deposition target material by compressing the physical vapor deposition target material from an initial thickness to a final thickness, the final thickness being less than or equal to about 40% of the initial thickness. D 35. The method of claim 26 further comprising, before the joining, work- hardening the physical vapor deposition target material by compressing the physical vapor deposition target material from an initial thickness to a final thickness, the final thickness being from about 40% to about 2% of the initial thickness. D 36. The method of claim 26 further comprising, before the joining, work- hardening the physical vapor deposition target material, and wherein the grain development comprises recrystallization of grains from the work-hardened material. D 37. The method of claim 26 further comprising, before the joining, work- hardening the physical vapor deposition target material, and wherein the grain development comprises: recrystallization of grains from the work-hardened material; and growth of the recrystallized grains.

Inventors: BEIER TONY, PARFENIUK CHRIS, BEIER, TONY, PARFENIUK, CHRIS
Applicants: HONEYWELL INT INC, HONEYWELL INTERNATIONAL INC.
Application year: 2001
Main classification: C23C14
IPC codes: B23K20, C23C14