Samsung Electronics Co., Ltd. v. Demaray LLC
`Samsung Electronic's Exhibit 1052 Vol 2.
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`Ex. 1052, Page 386
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`Ex. 1052, Page 387
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`Ex. 1052, Page 387
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`: a
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`.
`
`International Bureau
`
`
`WORLD INTELLECTUALPROPERTY ORGANIZATION
`PCT
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`
`
`(11) International Publication Number:
`WO 96/23085
`
`(31) International Patent Classification 6;
`
`C23C 1434, H01J 37/34
`(43) International Publication Date:
`1 August 1996 (01.08.96)
`
`
`
`
`
`(21) International Application Number: PCT/US95/01089|(81) Designated States: AM, AT,
`
`
`
`CN, CZ, DE, DK, ES,Fl,
`
`5
`KR. KZ. LK. LT, LU, LV,
`MD, MG, MN, MW, MX,
`(22) International Filing Date:
`25 January 1995 (25.01.95)
`
`
`
`PT. RO,RU,SD, SE, SI, SK, T5,TT,
`
` (71) Applicant (for all designated States except US): APPLIED
`
`[JP/JP}; c/o Applied
`KOMATSU TECHNOLOGY, INC.
`Komatsu Technology America, Inc., 3050 Bowers Avenue,
`
`M/S 02634, Santa Clara, CA 95054 (US).
`
`
`
`
`(72) inventors; and
`With international search report.
`(75) Inventors/Applicants (for US only: DEMARAY, Richard,
`With amended claims and statement.
`
`
`-
`Emest [US/US]; 190 Fawn Lane, Portola Valley, CA 94028
`
`(US). HERRERA, Manvel
`[US/US];
`1583 Brandywine
`Road, San Mateo, CA 94402 (US).
`(74) Agent:
`STERN, Robert,
`J.; Legal/Patent Dept., Applied
`Materials, Inc., 3050 Bower Avenue, M/S 2634, Santa Clara,
`CA 95054 (US).
`
`
`
`
`
`
`
`
` (54) Title: AUTOCLAVE BONDING OF SPUTTERING TARGET ASSEMBLY
`
`
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`12, 114
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`
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`ESSMLDMISOMTAPPMFLfeelhw
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`ESSNLLLrygEEEITISTIDIIIINEES
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`Page hghagodphhilhagharehorhnees
`ge
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`(57) Abstract
`Fabrication techniques for an integrated sputtering target assembly include
`assisted bonding of soldered layers of material,
`
`
`in particulesoldering of the target material to its backing plate; pressure assisted curingofstructural adhesives sod foJos» Dites Sake
`plate (52)to abacking plate (50)which between them form passages for Buidcooling. andbondingan electrical insulating layerto theback
`surface of the backing plete. The pressure to assist in bondingis typically applied by an autoclave. The cooling ftuid passages disposed
`
`
`surface of the Doskire Enned backing plate can be sealed by using laser welding or electron beam welding rather than closing the cooling
`
`passages with structural adhesives.
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`::
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`:::8
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`it
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`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international
`
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`SSSSBRERREEPenssssasesgsss
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`WO 96/23085
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`PCT/US95/01089
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`AUTOCLAVE BONDING OF SPUTTERING
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`TARGET ASSEMBLY
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`
`
`Fieldofthe ] .
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`10
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`This invention relates to techniques used to fabricate internally cooled
`sputtering target assemblies generally used in planar magnetron sputtering, and in
`particular to fabrication techniques used to enhance and assure parallelism between
`the surface of a target material and the substrate being sputter deposited.
`
`15.
`
`BackgroundoftheInvention
`
`Sputtering describes a number of physical techniques commonly used in,
`for example, the semiconductor industry for the deposition of thin films of various
`metals such as aluminum, aluminum alloys,refractory metal silicides, gold,
`Copper, titanium-tungsten, tungsten, molybdenum, tantalum, indium-tin-oxide
`(ITO)and less commonly silicon dioxide and silicon on an item (a substrate), for
`example a wafer or glass plate being processed.
`In general, the techniques involve
`producing a gas plasma of ionized inert gas "particles" (atoms or molecules) by
`using an electrical field in an evacuated chamber. The ionized particles are then
`directed toward a "target" and collide with it. As a result of the collisions, free
`atoms are released from the surface of the target as atom sized projectiles,
`essentially converting the target material to its gas phase. Mostof the free atoms
`which escape the target surface condense (the atomicsized projectiles lodge on the
`surface of the substrate at impact) and form (deposit) a thin film on the surface of
`the object (e.g. wafer, substrate) being processed, whichis located a relatively
`
`20
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`1
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`SUBSTITUTE SHEET(RULE28)
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`short distance from the target.
`One common sputtering technique is magnetron sputtering. When
`processing wafers using magnetron sputtering, a magnetic field is used to
`concentrate sputtering action in the region of the magnetic field so that sputtering
`occurs at a higher rate and at a lower process pressure. The target itself is
`electrically biased with respect to the wafer and chamber, and functions as a
`cathode. The magnetic field’s influence on the ions is proportional to its distance
`from the front of the target. Optimally a target assembly (the target and its
`backingplate) is thin to allow the magnetic field to have the greatest influence.
`In generating the gas plasma and creating ion streams impacting on the
`cathode, considerable energy is used. This energy must be dissipated to avoid
`melting or nearly melting the structures and components involved. A technique
`used for cooling sputtering target assemblies is to pass water or other cooling
`liquid through fixed internal passages of the sputtering target assembly.
`An example is shown in the simplified perspective sketch of Figure lla
`sputtering system designed for large rectangular substrates, which includes a
`relatively thin sputtering target assembly with internal cooling passages.
`(Details
`of the chamber and its operation are described in earlier U.S. Patent Applications
`of the inventors: U.S. Serial No. 08/157,763 filed 11-24-93 and U-S. Serial No.
`08/236,715 filed 4-29-94, now hereby incorporated by reference herein.) The
`processing/sputtering chamber 30 encloses a dark space ring 31 surrounding a
`substrate 32 to be sputter deposited. The upper flange of the sputtering chamber
`30 supports a lower insulating ring 33 supporting a sputtering target assembly 40.
`Thetarget material on the sputtering target assembly is facing toward the substrate
`32 to be sputtered. The target assembly is negatively biased relative to the
`substrate to effect the sputtering.
`Inlet cooling lines 36 and outlet cooling lines 37
`connect to cooling passages in the sputtering target assembly 40 to cool the
`assembly during sputtering. The top of the sputtering target assembly 40 is
`enclosed by a top chamber 35 supported on the back of the sputtering target
`assembly by an upper insulating ring 34. Asfully discussed in the references
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`previously cited, the top chamber 35 can house a moveable magnetron in an
`evacuated top chamber. The top chamber can be evacuated so that its pressure
`approaches the pressure of the process chamber. The force exerted on the area of
`the target assembly due to differential pressure between the process chamber and
`the top chamberis then minimal and easily restrained by the thin Sputtering target
`assembly 40.
`
`A multi-layered sputtering target assembly 40, as shown in Figures 2 and
`3, is typically assembled according to the above mentioned patent applications
`using a two step process.
`In one step, a target material 48 is solder bonded to the
`backing plate 50.
`In another step, a finned (or grooved) cover plate 52 is bonded
`to the back of the backing plate 50 using a structural epoxy based adhesive. The
`structural epoxy based adhesive is cured by putting it in position and raising the
`temperature of the pieces to be joined while at the same time applying a pressure
`to keep the parts in intimate contact throughout the heating cycle. The order in
`which the two steps are done is dependent on the melting temperature of the solder
`and the curing temperature ofthe structural epoxy. The higher temperature
`bonding process is done first so that the integrity of the first formed bond is not
`affected by the subsequentprocess.
`The process and materials used in producing a structural epoxy bond
`generally create a good bond; however, the cooling fluid occasionally leaks due to
`imperfections in bonding thereby causing such sputtering target assemblies to be.
`rejected. The factors affecting the structural epoxy bond integrity are 1) surface
`treatment ofthe pieces to be joined, 2) epoxy selection and curing procedure, and
`3) mechanical fitting or mating of the surfaces being joined prior to adhesive cure.
`Surface treatment removes mechanically weak or non-adherent surface film
`on the metal. For example, surface treatment may simply consist of mechanically
`abrading the surface to be bonded in order to obtain a “clean” metal surface. Or,
`for superior results, the procedure may involve a) degreasing, followed by b) an
`acid etch to remove anyvisible oxide film or scale, c) rinsing to remove all traces
`of the acid, d) a surface-conditioning step to deliberately form a corrosion film of
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`controlled chemical composition and thickness which promotes primer adhesion, e€)
`drying, and f) priming within an hourto seal the surface from atmospheric oxygen —
`and moisture.
`:
`,
`
`type of carrier,
`Epoxy selection is based on several factors including:
`strength ofthe adhesive, adhesion to the primed surface, curing temperature and
`pressure procedure, and ability of the adhesive to flow to create a leak-free joint.
`Surface treatment, epoxy selection, andcuring procedures are factors
`controlled by manufacturing rigor. However, good mechanical fitting or mating of
`the surfaces being joined is also required to achieve leak-free joints. Distortion
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`10
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`and voids are introduced by the two-step soldering process presently used to join
`
`large areas (e.g. 643mm x 550mm target material dimension) of a) dissimilar
`metals and/or b) non-uniformly heated or cooled similar metals. The present
`process includes the solder wetting of the two surfaces to be bonded. The target
`
`material is then heated and a pool of solder is created at the soldering location.
`
`15
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`The backing plate, also heated, is then slid into the pool of solder to avoid
`trapping the solder oxide that normally floats over the molten solder, and the
`weight of the piece and a light pressure cause the solder in the pool to spread out
`over the surfaces to be soldered and bring the two materials generally in close
`
`contact. The pieces are held aligned one to the other until the solder cools below
`its melting temperature and the two pieces are bonded.
`For example, when solder bonding indium-tin-oxide (ITO) to a
`
`commercially pure titanium backing plate, during cooling from the soldering
`temperature (e.g., 156°C for pure indium solder) to ambient temperature, the
`differential thermal contraction of the soldered connection tends to cause bending
`
`of the pieces. The edges of the target material, being the first to cool, initially
`
`form a stronger bond thanthe higher temperature center of the target. As a result,
`
`the strong connection between pieces of the outer edge of the target material
`causes the center of the target material to buckle and lift from the backing plate at
`the center of the target, by as much as 0.125” (3.175 mm), as the target material
`and backing plate continue to contract at different rates.
`In the subsequent
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`Structural epoxy bond step (the finned cover 52 is bonded to this highly distorted
`target/backing plate assembly), mechanical fitting or mating of the surfaces being
`joined is difficult. Poor mating results in uneven bond thickness which can cause
`the cooling fluid to leak resulting in rejection of the sputtering target assembly.
`In addition, if such a sputtering target assembly is not flattened, the
`non-parallelism between the target material and the substrate being sputtered
`creates non-uniform films on the substrate. Raised areas at the center of the target
`material may create a void behind the raised area, or the target material may
`fracture. Such voids change the thermal conductivity between the target and
`backing plate and the temperature distribution across its face. Since the
`distribution of sputtered material and the rate of sputtering ofthe target are
`directly dependentrespectively on the target material distance from the substrate
`and on its temperature,variations in the gap (distance) between thetarget and
`Substrate and in the temperature ofthe target material will also change the
`uniformity of target material sputter deposited on the substrate.
`Since the object of large area sputtering chambers, as described above,
`includes uniform film thickness across the entire area ofthe substrate being sputter
`deposited, variations in film thickness due to variable properties in the target
`surface ofthe sputteringtarget assembly are a preat impediment to improving
`processing efficiency and sputter depositing a uniform film thickness over the
`whole surface.
`
`10
`
`15
`
`SummaryoftheInvention
`
`A method according to the present invention includes overcoming the
`distortion and imperfections introduced by the sputtering target assembly
`fabrication techniques described above to provide generally uniform target
`properties across the surface ofthe target. Specifically, the improved fabrication
`techniques include: pressure-assisted bonding when using solder and/or structural
`adhesives to bond the material layers making up a sputtering target assembly; and
`enclosing cooling passages in the target backing plate by laser welding or electron
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`beam welding one or more cover plates over the void in the backing plate forming
`the cooling passages. Variations of both techniques are discussed.
`These techniques according to the invention, reduce the number of steps in
`the fabrication process and reduce, if not eliminate, distortion due to differences in
`coefficients of thermal expansion of adjacent layers. They also virtually eliminate
`the possibility of cooling fluid leakage due to the failure of cured adhesive based
`structural bonds.
`In one method (or technique), the sputtering target assembly (comprised
`principally of backing plate, finned cover (plate), insulating sheet, and target
`material layers) is, as required, machined, ground, lapped, chem-cleaned, primed,
`and polished prior to assembly. The final step of bonding the layers together
`under pressure is performed inside a gas-tight fabric bag (preferably in an
`oxygen-depleted environment) inside an autoclave. The pressurized autoclave
`exerts a uniform force on the surface of the bag to keep the layers in tight contact
`throughout the thermal cycting of bond formation and/or curing. During the
`cooling cycle, the exerted pressure forces the solder layer to plastically flow or
`yield preventing the assembly from distorting. Spacers, disposed between the
`target material and backing plate and interspersed in the solder layer control the
`thickness, uniformity, and integrity of the joint created by the solder layer.
`In the bonding step, pressure (preferably provided in an autoclave) bonding
`the target to the backing plate using solder, and bonding the finned (grooved)
`cover plate to the backing plate using a structural adhesive are performed in one
`step. The electrical insulating layer can be bonded to the back surface of the
`target assembly using a structural adhesive during this same step. To perform this
`bonding step, the target assembly is partially double vacuum bagged to isolate the
`solder bonding process from the structural bonding process. One (the lower)
`vacuum bag configuration (system)is attached to the backing plate and encloses
`only the target material to be solder bonded to the backing plate. The second (the
`upper) vacuum bag configuration (system) generally encloses the lower bag
`system, the backing plate, the finned cover, and the electrical insulating sheet and
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`provides a pass through gas connection to the lower vacuum bag. An epoxy based
`structural adhesive laminate placed between the backing plate and finned cover
`plate and between the finned cover plate and the electrical insulation sheet bonds
`these layers together.
`
`The vacuum bags are first evacuated and the autoclave pressure is increased
`to approximately 15 psi above atmospheric. The vacuum bags are then backfilled
`with a-moisture-free inert or oxygen absorbing gas to approximately one
`atmosphere to eliminate the possibility (in the event of bag failure) that a vacuum
`system evacuating the bag will suddenly receive high pressure gas from the
`_ autoclave environment. The autoclave pressure is then increased to provide the
`desired pressure on the unbonded target assembly layers. The assembly is then
`heated and cooled according to a predefined procedure.
`A variation of this method is to solder bond the target to the backing plate
`first, then enclose the whole assembly in a vacuum bag system and cure the
`structural adhesive bonded pieces in an autoclave while, at the same time, stress
`relieving and flattening the target backing plate sub-assembly.
`In another variation of this method, the target is solder bonded in the
`autoclave first, then the cover to hold the cooling fluid is attached by means of
`fasteners sealed by gasket type (preferably O-ring) seals.
`
`A second method according to the invention, involves construction and
`closure ofthe void forming the cooling fluid passages in the backing plate and
`cover assembly. The backing plate includes a recess to receive. the cover
`configured to fit in the recess. The cover and backing plate are joined by laser
`welding around the edge between the recess and the cover and by spot or seam ©
`welding across the field of the cover at generally regularly spaced locations
`corresponding to the ends of fins (or walls between grooves) in the finned backing
`plate. A variation would be to use electron beam welding (a low input of heat to
`avoid material distortion due to welding is desired). The target material can then
`be solder bonded to the welded assembly by a) solder bonding thetarget to the
`welded backing plate using a single vacuum-bagged autoclave procedure, or b)
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`solder bonding the target to the welded backingplate first, then enclosing the
`whole assembly in a vacuum bag to stress relieve and. flatten the target assembly in
`
`the autoclave.
`
`f the Drawi
`Brief Descripti
`Figure 1 is a perspective view of a simplified sputtering chamber system
`using a sputtering target assembly 40 fabricated according to the invention;
`
`Figure 2 is a plan view of a target side of a sputtering target assembly
`according to the invention;
`Figure 3 is a side cross-section view of Figure 2 taken at 3-3;
`Figure 4 is a side cross-sectional exploded view showing one embodiment
`of the layers of material involved in assembling a target assembly such as the one
`
`shown in Figure 3;
`
`Figure 5 is a side cross-sectional exploded view showing a second
`embodimentof layers of material used in assembling a target assembly such as the
`one shown in Figure 3;
`
`Figure 6 shows a close-up view of the assembled target assembly as
`
`pictured in Figure 3;
`Figure 7 shows a panel of target material consisting of three tiles used with
`the sputtering target assembly according to the invention;
`
`Figure 8 showsa tape a) wrapped aroundthetiles to cover the joints
`
`between the tiles of the target panel, and b) covering the target side of the tiles of
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`Figure 7;
`Figures 8A and 8B show a pre-assembly perspective view andafinal
`configuration cross sectional view of a joint between adjacent tiles as shown in
`
`Figs. 8, 9 and 10;
`Figure 9 shows the assembly of the target panel of Figure 8 on a base piate
`
`according to the invention;
`Figure 10 shows a perspective view of the assembled sputtering target
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`assembly of Figure 9;
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`Figure 11 showsa partial cutaway view of a bottom of a target backing
`plate utilizing two welded cover panels covering the cooling passage void in the
`backing plate;
`,
`:
`Figure 12 shows a cross-section of Figure 11 taken at 12-12;
`Figure 13 shows a target backing plate having the cooling passage void
`covered by a single cover plate;
`.
`Figure 14 showsa close-up cross-sectional view of typical weldsat the
`edge ofthe cover plate and along the tops ofthe fins for finned backing plate
`assemblies with welded cover plates as shown in Figures 11, 12, 13, and 15;
`Figure 15 shows another embodimentofa target backing plate with two
`Separate cover plates;
`Figure 16 shows an overall side cross-sectional view of the material layers
`used to envelope and create bags around the target assembly being processed in an
`autoclave;
`Figure 17 shows a simplified perspective view of the layers of Figure 16,
`but not showing gas connection fittings;
`Figure 18 shows a plan view of the polyamide tape layer on the backing
`plate surrounding the target material used when Processing the target assembly
`according to the invention;
`Figure 19 shows a side cross-sectional view of the items of Figure 16 in
`position for processing;
`Figure 20 shows a close-up view of the material layers of Figure 19
`surrounding the gas fitting 92;
`Figure 21 shows a close-up view of the edge seal of the outside bag shown
`in close proximity to the gas fitting 90;
`Figure 22 shows a configuration for providing thermocouple wiring into the
`vacuum bag enclosures to monitor the temperature of the target material and/or
`backing plate;
`Figure 23 is a side view of a typical gas fitting connection through a
`barrier film of a vacuum bag;
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`Figure 24 is a side cross-sectional exploded view of a single vacuum bag
`bonding system according to the invention;
`Figure 25 is a side cross-sectional view of the. material layers of Figure 24
`ready to be bonded according to the invention;
`Figure 26 is a plan view of the sputtering target assembly as pictured in
`Figure 9; it clearly shows one example of the possible locations for gas
`connections to the gas barrier layers of the vacuum bags, and
`Figure 27 is a perspective view showing a typical configuration of a gas
`connection through the outer (upper) bag barrier to the inner (lower)bag barrier of
`the dual bag configuration as pictured in Figures 16, 19, 20, and 26.
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`Detailed Descrinti
`Figure 1, as discussed above, shows a sputtering process system which uses
`a sputtering target assembly 40 fabricated according to the invention.
`A general configuration of an embodiment according to the invention is
`shown in Figure 2. The integrated sputtering target assembly 40 is shown in plan
`view with its target side up. The sputtering target material 48 is bonded to the
`backing plate 50. Bonds can be made by soldering, diffusion bonding, or other
`techniques which provide and maintain satisfactory bonds between dissimilar
`metals at process temperatures.
`In other instances (e.g., aluminum or titanium)
`the target 48 and backing plate 50 may be a monolith of a single material
`requiring no bonding.
`In general,it is preferable to machine, grind, lap and
`polish the target side of the backing plate to formahighly polished vacuum
`sealing surface 77 (preferably polished to a surface finish of 8pin (0.20nm) Ra, a
`mirror finish), on the backing plate border 78, circumscribing the target area prior
`to bonding the target material 48. This surface 77 provides an exceptional
`leak-tight seal when an O-ringis placed against it. The backing plate 50 includes
`inlet water fitting ports 67 and 68, outlet water fitting ports 69 and 71, and a
`rough vacuum port 75 which are preferably machined into the backing plate 50
`prior to bonding according to the invention.
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`Figure 3 is a cross-sectional view of Figure 2 taken at 3-3 showing target
`material 48 attached to backing plate 50 which,in tum,is attached to a finned
`cover plate 52 which is covered on its outside surface by an electrical insulating
`sheet 54.
`Figure 4 is an exploded view of an embodimentofthe configuration as
`typically shown by Figure 3 showingafirst structural adhesive laminate 60
`disposed between the electrical insulating sheet 54 and finned cover plate 52. The
`first adhesive laminate 60 is trimmed to match the outline of the finned cover plate
`52 to bond the insulating sheet 54 to the coverplate 52. A second layer of
`structural adhesive laminate 58 is disposed between the top of the finned cover
`Plate 52 and the back of the backing plate 50. The second laminate layer 58 has
`been trimmed (typically suspended from a carrying screen or mesh not shown)to
`match the surface pattern ofthe top of the fins 59 of the cooling passages so that
`only the surfaces intended to be in contact with each other are bonded (i.¢., the
`top of the fins 59 and the border of the finned side of the cover plate 52). A
`solder layer 56 consisting of solder-material strips 0.010”-0.020” (0.25
`mm-0.51mm) thick is disposed between the tanget material 48 and front of the
`backing plate 50. The solder layer 56 mayalso be formed by pre-wetting the
`target material 48 and front of the backing plate 50 using other means such as a) a
`hot plate to dip the surfaces to be bonded in a pool ofsolder, b) brushing on the
`solder over the surfaces to be bonded, or c) sputter coating the surfaces to be
`' bonded with a solder layer.
`Figure 5 is an exploded view of another configuration as typically shown
`by Figure 3 showing another embodiment according to the invention.
`In some
`instances, to improve surface adhesion or wetting prior to attempting to make a
`solder bond, the surfaces to be solder bonded can be cleaned by sputter etching
`(bombarded with ions), and one or more layers of sputter coating material 65 can
`be sputter coated (deposited) onto the bonded side of the target material 48 and the
`backing plate 50 to pre-wet or tin their surfaces in preparation ‘for soldering.
`Another less reliable procedure involves conventionally pre-wetting the surfaces to
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`be solder bonded and scuffing the wetted solder prior to bonding to remove
`surface oxides. Once the surfaces to be bonded are tinned (pre-wetted), solder
`material strips 56, e.g. pure indium, and spacers 63 (e.g., pre-wetted
`0.001”-0.010” (0.025mm-0.25mm) diameter copper wires) are positioned between
`the target material 48 and the backing plate 50 in preparation for solder bonding.
`Figure 6 shows a close-up of a cross-section of Figure 3 near its edge
`consisting of the layers as shown in the embodimentofthe invention shown in
`Figure 5. The backing plate 50 is a rectangular monolith, as generally described
`above, having a top target surface and a back surface. The top target surface,
`after having been sputter coated with an adhesion layer, can be wetted by
`sputtering pure indium on the backing plate 50 made of, for example, titanium. A
`target material 48 madeof, for example, indium-tin-oxide (ITO)is also coated
`with an adhesion layer and can be wetted with a coating (e.g., pure indium) on its
`back surface. A series of alternating strips of solder 56(¢.g., strips
`0.010°-0.020" (0.25 mm-0.51mm)thick of pure indium) and spacer 63 (e.g,
`pre-wetted 0.005"-0.010" (0.13mm-0.25mm) diameter copper wires) are
`positioned between the target material 48 and the backing plate 50. While a series
`of alternating spacers 63 and solder regions 56 with a high concentration are
`shown in Figure 6, such a high frequency of spacers 63 is not required. The
`spacers 63 provide a vertical spacing (preferably approximately 0.010" (0.25 mm))
`so that after bonding of the target plate 48 to the backing plate 50, a spacer
`thickness solder joint is maintained. This extra thickness of the solder joint allows
`the solder material to readily plastically yield when subjected to a clamping
`pressure during the solder cooling cycle. The solder yielding avoids excessive
`distortion of the surface of the target material 48 due to a differential thermal
`expansion. Without spacers 63, thesolder joint would have a much reduced
`thickness, e.g., less than 0.005” (0.13 mm), and thickness uniformity could not be
`controlled. Also, the excess solder from the thicker solder strips permits the
`surface oxide, which floats over the molten solder, to be forced out of the joint
`resulting in excellent solder bond coverage.
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`The finned cover plate 52 is covered with a layer of structural adhesive
`laminate 58 which has been trimmed with, for example, a razor blade to match the
`top of the exposed surfaces which will contact the back side of the backing plate
`50. When the structural adhesive laminate 58 is cured, a good bond will create a
`tight seal between the cooling passages of the finned cover plate 52 and the
`backing plate 50. Thorough bonding of the ends ofthe fins of the cover plate 52
`to the backingplate 50 will prevent ballooning of the cooling passages when
`cooling liquids under pressure are introduced into the cooling passages. An
`electrical insulating sheet 54 is bonded to the backside of the finned cover plate 52
`by a structural adhesive laminate 60 similar to the structural adhesive laminate 58
`used for the bond between the finned cover plate 52 and the backing plate 50.
`Figures 7, 8, 9, and 10 provide easy visualization of the steps taken to
`position a multi-tiled target material (e.g., ITO) to be bonded to a backing plate 50
`made of a material (e.g., titanium) with qualities compatible with the sputtering
`target material. As shown in Figure 7, because indium-tin-oxide is difficult to
`produce in large plates, when large plates of ITO are needed for sputtering,
`several tiles 49a, 49b, 49c are positioned adjacent to one another to provide full
`coverage for sputtering. The tiles are held adjacent to one another by an assembly
`frame (not shown).
`In Figure 8 the edges of the tiles and the target side of the
`tiles are covered with a high temperature polyamide flash breaker tape 43 to
`prevent the solder from wetting these surfaces. Also, the flash breaking tape 43
`facilitates removal of solder material from the spaces between the panels thereby
`avoiding solder contamination when sputtering the finished target assembly 40.
`Fig. 8A showseach tile’s perimeter edge wrapped with polyimide tape 43a,
`43b having a width equal to the thickness of the tile. The tiles (e.g. 49a, 49b) are
`placed adjacent to one another with a shim 45 maintaining the space between tiles.
`A joint forming flash breaker tape 43z is laid across two adjacenttiles 49a, 49b
`whose edges have been taped with polyamide tape 43a, 43b.
`Fig. 8B shows thetiles 49a and 49b positioned in a plane ready to be
`mounted on the backing plate 50. A joint shim 47 positioned between tiles 49a,
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`49b maintains uniform spacing between tiles as the joint formingflash breaker
`tape 43z is bent around the joint shim 47 to a position where thetiles are adjacent
`to one another in a plane. Typically the thickness of the tape 43a, 43b, and 43zis
`0.003" (0.076mm). Four layers of this tape, as seen in Figure 8B, provide a
`built-up thickness of 0.012" (0.30mm). Since it is desired that the final space
`between tiles be 0.015"-0.020" (0.38-0.51mm) when all tape and shims are
`removed, the thickness of the shim 47 should be between 0.003" and 0.008"
`(0.076" and 0.20mm). The shim 47 can be held in place until soldering is
`complete to assure uniform spacing between tiles. The height of the shi