Note: Descriptions are shown in the official language in which they were submitted.
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SPU I I tHlNG APPARATUS WITH ISOLATED COOLANT
~ AND SPIJ I I tHlNG TARGET THEREFOR
This invention relates to cathode sputtering and more particularly to the
configuring, utilizing and cooling of sputtering targets used in sputter deposition
processes and to the cooling of such targets in an assembly in a sputtering cathode
of a sputtering machine.
Backqround of the Invention:
In sputter deposition processes, substrates are placed adjacent to a
sputtering target in a processing chamber and the pressure in the chamber is
reduced to a high vacuum pressure level. A negative voltage is applied to the target
to produce a plasma discharge, which is often intensified and confined over the
target surface by the application of a magnetic field. The plasma production creates
large quantities of positive ions in the sparse gas within the chamber that bombard
the target and thereby dislodge atoms or small particles of target material from the
surface of the target.
The ionic bombardment of the target surface transfers energy to the target,
only a small percentage of which is imparted to the dislodged atoms or particles.
Generally, about ninety percent of the electrical power applied to the plasma isconverted to a heating of the target. With commonly used power densities in the
area of 30,000 watts per square foot of target surface area, aggressive cooling of
the target is required to prevent the melting or cracking of the target and to protect
the target supporting cathode assembly and adjacent structures from overheating.The cooling technique typically used in the prior art for removing heat from
the target employs a flow of water against the back face of the target or against the
backing plate to which the target is bonded in a thermally conductive manner. Insome cathode assembly designs, the target supporting structure of the cathode
assembly is water cooled, to indirectly cool the target, which is thermally attached
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in the cathode assembly, by conduction. In prior art cathode designs in which a
target having a concave cone shaped target surface is employed, a thick target
periphery or edge allows some degree of target cooling by heat flow at the
periphery of the target. One such target is disclosed in U.S. patent no. 4,855,033,
in which the primary cooling surface of the target is around the target periphery,
where cooperating surfaces of the target and supporting target nest intermesh for
enhanced heat conductivity. However, this deep cone shaped target, which erodes
in a narrow ring, is less ideally suited for the coating of step shaped three
dimensional surface features on objects like semiconductor wafers. Furthermore,
the cooling of other types of targets that relies on thermal conduction between the
target and the target nest is limited by mechanical gaps that develop between the
nest and target as mechanical distortions occur at high operating power. Such gaps
can result in a reduction in the heat transfer outward from the target, which results
in failures such as by the melting of the target.
More recenttarget designs, however, while providing improved performance
in many respects and added coating capabilities, use targets that are thinner inrelation to the sputtering surface dimensions, making the rear face of the target or
of the target backing plate the primary surface suitable for cooling.
In many cathode designs, magnet structures are located behind the target
rear face to shape and intensify the sputtering plasma. Often the magnet structure
includes rotating magnets and associated structure that occupy much of the area
of the rear target face. Examples of rotating magnet cathode assemblies are
disclosed in U.S. patents nos. 5,130,005,5,252,194 and 5,242,566. Such target
and cathode assemblies can be eroded in a controlled manner over the entire front
face of the target providing improved coating of micros~opic three dimensional
features on the substrate surface. In many cases, the provision of such magnet
assemblies results in design compromises between the magnet structure and the
cooling capabilities, which limit the performance or reliability of the cathode and
target as a unit.
In a rotating magnet apparatus, for example, cooling water has been made
to flow in an inlet into a cavity behind the target and across the rear face of the
target to an outlet. In such apparatus, the cooling of the target may be enhanced
by the motion of the cooling water imparted by the rotary motion of a magnet
carrier that rotates fully emersed in the cooling fluid in the cavity. However, the
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desired shape of target erosion is controlled by complexly shaped magnet structure
which is rotated in bearings driven by drive gears, an input shaft, a drive belt and
a motor. This immersion of components in cooling water can, over time, result incorrosion and degradation of the performance of the apparatus and a shortened life
Further, replacement of the depleted target can result in exposure of the cooling
water cavity, as the target or backing plate is detached from the assembly. Suchexposure can result in the introduction of small amounts of water, a primary
contaminant of sputtered films, into the sputtering chamber.
For the reasons stated above, there is a need for a more effective and
efficient structure for cooling a sputtering target.
Summarv of the Invention:
It is a primary objective of the present invention to provide a sputtering
cathode assembly in which a target can be effectively cooled without interferingwith access to the target that is needed by magnet structure and other sputtering
performance affecting components of the assembly. It is a particular objective of
the present invention to provide cooling for a sputtering cathode assembly without
intruding on space required by rotating magnet components and while maintaining
the magnet components in isolation from cooling fluid. It is a more particular
objective of the present invention to provide such a sputtering cathode assemblyin which magnets, bearings and other motion drive components in particular are
isolated from the cooling fluid. It is a still further objective of the present invention
to provide a sputtering cathode assembly in which the cooling fluid is contained to
prevent contamination of the processing chamber, particularly during removal andreplacement of the sputtering target, and particularly while providing direct contact
between the target and the cooling fluid during operation of the sputtering
apparatus.
It is another objective of the present invention to provide a sputtering target
that can be maintained in direct contact with cooling fluid when mounted in a
sputtering cathode assembly while containing the cooling fluid so as to prevent
contamination of the processing chamber during removal and replacement of the
target. It is a still further objective of the present invention to provide a sputtering
target that can be maintained in direct contact with a cooling fluid but that isprotected against the contaminating or corrosive effects that the cooling fluid could
have on the target itself. It is yet another objective of the present invention to
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provide a sputtering target that can be mounted so as to maintain a seal of the
vacuum processing chamber and to maintain a seal of a cooling fluid cavity,
preferably without the need for bonding the target to a structural backing plate or
other such member, and without excessively increasing the non-productive amountsof sputtering grade material required in the fabrication of the target.
According to the principles of the present invention, there is provided a
sputtering target, particularly a target that is relatively thin in relation to the size of
its sputtering front face, that is provided with a rear face that is adapted for contact
by flowing cooling fluid maintained in a cavity behind the target, when the target
is mounted in a sputtering cathode assembly. The preferred embodiment of the
target is provided with an annular outwardly projecting target rim, which has a
forward facing front edge having a vacuum-sealing surface that is adapted to form
a vacuum tight seal with the sputtering chamber, and which has a rearward facingrear edge having a cooling fluid-sealing surface that is adapted to form a seal that
surrounds the cooling fluid cavity. Preferably, the target, which is preferably
circular, is formed of an integral'single piece of sputtering grade material, the rear
face of which is adapted to be maintained in direct contact with the cooling fluid.
Additionally, the surface that is in direct contact with the fluid is preferably coated
or otherwise sealed from contamination by the fluid, where the target is of a
material that may absorb or otherwise interact with the fluid in a disadvantageous
way.
Further, in one preferred embodiment, the target rim is preferably formed
integrally of the single piece of sputtering grade material with the front and rear
edges thereof adapted to support or form the seals. In addition, it is preferred that
the center of the rear face of the target be provided with structure by which the
center of the target can be supported, so that the target is supported at both the
center and the rim thereof to prevent distortion or deformation of the target during
use. Preferably also the supporting structure at the center of the target is a center
hub extension formed integrally of the single piece of target material.
Further in accordance with the principles of the present invention, a
sputtering cathode assembly is provided in which a sputtering target, either formed
of an integral piece of sputtering material, or formed of a sputtering material bonded
to a backing plate to provide the rear face thereof, is adapted to lie in contact with
cooling fluid in a cavity, which is formed by sealing the target at the rear edge of
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its rim to a rim of the cathode assembly target mounting structure. In the preferred
embodiment, the cathode assembly target mounting structure includes a cavity wall
segment in the form of a cooling jacket that is removably mountable onto the
cathode assembly and to which the target can be sealably secured, with the target
back face forming an opposing wall to the cavity. The cooling jacket structurally
connects the target to the cathode assembly and is removable as a target assembly
with the target when the target is removed from the chamber for replacement.
Further in accordance with the preferred embodiment of the invention, the
cooling fluid cavity is removable with the assembled target and cooling jacket,
leaving the inlet and outlet port structure of the cathode assembly remaining with
the cathode unit when a target is removed or replaced. Upon removal of the target
and cooling jacket, seals between the cooling fluid ports in the cathode unit and
cooling ducts in the removed cooling jacket automatically disconnect from each
other and, preferably, seal against leakage of cooling fluid therefrom. More
importantly, the magnet assembly, and particularly the drive linkage by which anassembly of rotating or otherwise moveable magnets, may be used in complete
isolation from the cooling fluid, which has potentially corrosive effects.
Additionally in accordance with the preferred embodiment of the invention,
distortion and deformation of the target is prevented by a structural support at the
center of the target that cooperates with the mounting of the target around the
target rim to hold the target firmly in a plane. The center support is preferably
threaded into the target material or threaded into a central hub that is rigidlysecured to the rear of the target material at the center of the target. The central
support, which may also serve as a central axis about which a rotating magnet
assembly may rotate, is further mounted at the back end thereof to structure that
is rigid relative to the frame of the sputtering apparatus and to the chamber opening
rim against which the target rim is sealed. This rigid attachment of the centralsupport resists deformation of the target into the cavity due in part to the pressure
gradient from the cooling fluid toward the vacuum of the processing chamber and
~ 30 in part to thermal distortion of the target due to expansion of the hot sputtering
surface of the target relative to the cooled rear face of the target.
The present invention provides the advantages of effectively cooling a
sputtering target, particularly where such cooling must be carried out across the
rear face of the target. The cooling allows access to the rear face of the target for
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such magnet assemblies as are desired to shape and intensify the plasma on the
front side of the target.
The present invention further provides the advantages of allowing effective
rear face target cooling with cooling fluid while allowing for the use of magnetassemblies, particularly rotating or other moving magnet assemblies, that may
remain isolated from the cooling fluid.
Further with the present invention, there is provided a target that can be
operated with its rear face in direct contact with cooling fluid, while the surface of
the target material that is in contact with the fluid is protected from a
disadvantageous interaction with or contamination by the fluid. A separate backing
plate may be eliminated in some embodiments of the invention by the provision ofa target rim that utilizes only a small amount of sputtering grade material but seals
directly against the sputtering chamber wall and the cooling fluid cavity.
Further, the invention provides the advantage of allowing removal of a
sputtering target for replacement, where the target is cooled by direct contact with
the cooling fluid, without allowing leakage of the fluid that can cause contamination
of the sputtering chamber.
The present invention provides the further advantages of rigidly supporting
a relatively thin target against pressure gradient and thermal deformation, which is
particularly advantageous with the trend to targets of larger and larger diameter.
These and other objectives of the present invention will be more readily
apparent from the following detailed description of the preferred embodiment of the
invention in which:
Brief Descri,.lion of the Drawinqs:
Fig. 1 is a cross-sectional view of a portion of a sputtering apparatus
illustrating particularly a sputtering target and cathode assembly according to a
preferred embodiment of the present invention.
Fig. 2 is an enlarged cross-sectional view illustrating a sputtering target and
cooling fluid cavity of the cathode assembly of Fig. 1.
Fig. 3 is an enlarged partial cross-sectional view of a portion of Fig. 2
illustrating fluid ducts or ports to the fluid cavity and protective insulator shield.
Fig. 3A is a view similar to Fig. 3 illustrating a shield in the form of the prior
art.
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Fig. 4 is a view similar to Fig. 3 of an alternative embodiment in which the
projecting target unit rim also performs the function of a clamping ring.
Detailed Descr;,.lio~ of the r~erer.ed Embodi.nel,L.
Referring to Fig. 1, a portion of a sputtering apparatus 10 is illustrated
'I 5 showing an apparatus frame 11 having fixed thereto structure that forms part of the
wall 12 of a vacuum processing chamber 13 of the apparatus 10. A target access
door or other removable panel 14 is hinged or by hinge 14a otherwise removably
connected to the frame 11 at an opening 15 to the chamber 13. The door 14,
when closed, forms a vacuum tight seal to the frame 11 through a seal 16.
Welded to the side of the door 14 opposite the chamber 13 is a door frame member17 which encloses a door frame cooling passage 18 between the door 14 and the
door frame member 17. An additional seal 19 is provided on the opposite side of
the door frame member 18 to form a vacuum tight seal between the door frame
member 18 and an annular cathode assembly adapter flange 20, which is bolted to
the door frame member 18 by bolts 18a.
Removably mounted to the adapter flange 20 is a sputtering cathode
assembly 21, which includes a cathode unit and target support 22 and a target
assembly 23, which contains a replaceable expendable sputtering target 25. The
cathode assembly 21 is held to the flange 20 by a set of electrically insulated
clamping members 26 spaced around the opening 15 and secured to the frame 11.
The clamping members 26 urge the assembly 21 against the flange 20. Between
the flange 20 and the cathode assembly 21 is an electrically insulating ring 27
formed of a non-electrically conductive material such as TeflonTM. Between the
insulating ring 27 and the flange 20, and between the insulating ring 27 and thecathode assembly 21, are a pair of 0-ring seals 28 and 29 that maintain a vacuumtight seal with the intervening insulator 27 between the flange 20 and the cathode
assembly 21. Removal of the cathode assembly 21 from the adapter flange 20 is
carried out by releasing the clamps 26 and separating the cathode assembly 21
from the flange 20 at the insulator 27.
The portion of the cathode assembly 21 that mounts against the flange 20
is the target assembly 23, which is illustrated in solid lines in Fig. 2. The target
assembly includes the target 25 which, for materials that are reasonably machinable
such as titanium and aluminum alloys, is preferably formed of a single integral piece
of sputtering material that has a generally circular periphery 31, a sputtering surface
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or target face 32, a coolant fluid impermeable and preferably corrosion resisting rear
face 33, an annular lip or rim 34 extending outwardly from the periphery 31 and
spaced rearwardly from the target face 32 proximate the rear face 33 of the target
25, and a central rearwardly projecting hub 35, all preferably formed integrally from
the same piece of sputtering material. The rim 34 has a forward facing face or
surface 34a, recessed rearwardly from the target face 32, which is polished, coated
or otherwise processed in a manner that will effectively support a vacuum seal.
Similarly, the rim 34 has a rearwardly facing rear face or surface 34b that is
polished, coated or otherwise processed in a manner that will effectively support
a fl~iid tight seal.
For targets 25 of some types of sputtering materials such as silicon or
certain magnetic materials, the sputtering material itself does not have the physical
properties to provide sufficient structural strength to support the assembly 21 or to
enable its formation, by machining for example, into the desired configuration. With
such materials, a target 25 is preferably formed of a disc 25a of sputtering material
bonded by soldering or some other conventional technique to a backing plate 25b
at a bonding surface 25c, as illustrated as the straight phantom line to the left in
Fig. 2. With such a bonded target, the rim 34 is formed on the backing plate
portion 25b. With a target 25 formed of sputtering material without the backing
plate 25b, where the material permits, greater target utilization is possible, as is
apparent from the erosion profile 36 illustrated by the curved broken line in Fig. 2,
which shows an erosion groove 37 that may exceed the depth of the bonding
surface 25c, were one present. With either a bonded or an integral target 25, the
central hub 35 may be formed of a separate piece of material and fastened to therear face 33 of the target 25, but is preferably integral with the target material or
backing plate of the target 25. The central hub 35 of the target 25 should be
formed of a material that will support threads 38 in a central bore 39 therein, or
that will support a threaded insert.
The water impermeable and corrosion resisting rear face 33 is easily
provided for targets 25 that incorporate a backing plate 25b by selection of thematerial and service finish of the rear face of the backing plate. With targets 25
that are formed of an integral piece of sputtering material on which the rear face is
formed, certain materials such as titanium and some alloys of aluminum have
sufficient intrinsic water impermeability and non-corrosive properties to form the
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cooling surface on the rear face to directly contact cooling fluid. The corrosive
effects of water on sorne target materials can be prevented by chemical treatment
of the rear surface of the target, by treatment such as anodizing on aluminum
targets, or by the application of coating films or layers of, for example, organic
materials on porous targets, such as those of sintered titanium-tungsten. With
sputtering materials such as silicon, however, even though the material itself may
have sufficient intrinsic water impermeability, the use of a protective backing plate
will prevent water contamination of a more serious nature, such as a total flooding
of the processing chamber that could be caused if a brittle silicon target, without
a backing plate, were to structurally fail.
The target assembly 23 further includes a cooling jacket 40, which is
preferably a non-expendable reusable part of the target, assembly 23 that is
removable from the target 25 for connection to a replacement target. In the
alternative, the cooling jacket 40 may be expendable along with the target 25 and
replaced as part of the new replacement target. The cooling jacket 40 has formedthereon a central lip 41 and a peripheral lip 42 that seat against the back face 33
of the target 25, each lip 41,42 having an 0-ring seal 44 and 43 respectively
seated therein. When so connected, the jacket 40 encloses a space between it andthe back face 33 of the target 25 that defines a cooling channel 45. The coolingchannel 45 may have the shape of an annular disc as illustrated, or some other
configuration such as a pattern of grooves in the jacket 40, or a plurality of vanes
spaced by upstanding ribs in the cooling jacket 40. The cooling channel 45 is
configured so as to cooperate with the differential pressure of cooling fluid to and
from the channel 45 to cause a high velocity of cooling fluid through the channel
45 along the back face 33 of the target 25, thereby enhancing the flow of heat
from the target 25 to the fluid. To further enhance this thermal conductivity, the
cooling jacket 40 may also be provided with ducts that include impingement jets
directed toward the target back face 33, or such other conductivity enhancing
features as are more particularly disclosed in the copending commonly assigned
U.S. patent application serial no. 08/398,743, filed February 15, 1995, and
expressly incorporated herein by reference.
The target assembly 23 also includes, in one embodiment, an annular clamp
ring 47 that surrounds the outer periphery 31 of the target 25 and overlies the outer
lip or rim 34 of the target 25 opposite the jacket outer lip 42, to which it is held by
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a plurality of approximately twelve screws 48 spaced around the cooling jacket
outer rim 42. The screws 48 are accessible from the back of the jacket 40 and
thread into threads in the clamp ring 47. The clamp ring 47 has an 0-ring seal 49
seated in an annular groove in the back thereof to seal to the outer rim 34 of the
target 25. The clamp ring 47 also carries the seal 29 in an annular groove in the
front thereof.
The cooling jacket 40 contains a pair of ducts, or arrays of ducts, 50 for
communicating cooling fluid between the channel 45 and inlet and outlet ports 51and 52, respectively, in a cathode body 53 (Fig.1) of the cathode unit and target
support 22 of the cathode and target assembly 21. Preferably, the ports 51 and
52 and ducts 50 are formed in a stainless steel or other non-corrosive attachment
(not separately shown) to the cathode body 53. The cathode body 53 is the main
structural frame of the cathode unit 22 against which the clamps 26 bear to urgethe cathode assembly 21 against the insulator 27. The target assembly 23 is
secured to the cathode body 53 by a set of screws 55, approximately four in
number, which also serve in place of some of the screws 48 in clamping the clampring 47 to the cooling jacket 40. The screws 55 are accessible when the cathode
assembly 21 is unclamped from the adapter bracket 20 of the door 14.
When the target assembly 23 is removed from the cathode unit 22, the
ducts 50 automatically disconnect. By "automatically" is meant that the
disconnection of the ducts 50 does not require additional operator action, such as
the separate disconnection of tubing leading to the ports 51,52, or other step to
disconnect the cooperating parts of structure surrounding the ducts 50. When thetarget assembly 23 is reconnected to unit 22, the ducts 50 automatically reconnect.
To more positively isolate the fluid in the parts 51, 52 and cavity 45, each of the
ducts 50 may be provided with a spring biased or other type of valve element 57,58, in the cooling jacket 40 and cathode body 53 to close off the ducts 50 when
the target assembly 23 is removed from the cathode unit 22 by removal of the
screws 55, as illustrated in Fig. 3.
The cathode body 53 is structurally rigid. Fixed to the back thereof is a
spindle housing 60 which is also structurally rigid. The spindle housing 60 has a
bore 61 therethrough in which are carried two sets of bearings 62 and 63 on which
is rotatably supported a spindle shaft 65. At the back end of the shaft 65 is a drive
pulley 66 around which extends a drive belt 67 that connects the pulley 66 to the
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output shaft 68 of a magnet drive motor 69. At the front end of the shaft 65 is
fixed a magnet assembly 70 that rotates with the shaft 65 under the power of themotor 69. The magnet assembly 70 includes a magnet pack 71, preferably formed
of a specially configured loop of permanent magnets that is designed to produce
desired erosion profile 37 on the target 25. Details of the preferred configuration
of the magnet assembly 70 are set forth in U.S. patent no. 5,130,005, expressly
incorporated herein by reference. When the magnet assembly 70 rotates, the
magnets 71 are maintained out of contact with the body 53 and the back of the
cooling jacket 40. Because the coolant, however, is maintained in channel 45 outof communication with the magnet assembly 70, the corrosive effect of the cooling
fluid, which is usually water, on the magnet assembly 70 and the magnet rotatingcomponents is avoided, thus easing the corrosion resistance requirements on their
design.
Additional support at the center hub 35 of the target 25 is provided by a
central support rod 75 that has threads 76 at its front end that directly thread into
the threads 38 in the central bore 39 in the hub 35 of the target 25. The rod 75is secured at its back end by a threaded nut 77 which draws snugly against a capplate 78 that is bolted to the back end of the spindle 60. The shaft 75 so installed
provides a tension force that resists the deformation of the target center into the
processing chamber 13 due to forces caused by the pressure of the cooling fluid in
the cavity 45 and by the thermal stresses in the target 25 during sputtering.
Precise registration of the position of the center of the target 25 is achieved by
provision of a shoulder 81 on the forward end of a cylindrical spacer 82 that abuts
with the rearward surface 83 of inner rim 41 of the cooling jacket 40. The shoulder
81 is drawn against the surface 83 of the jacket 40 by the tension on the shaft 75
(Fig. 2). This tension also causes the inner rim 41 on the jacket 40 to seat tightly
against the rear face 33 of the target 25 and to compress the seal 44 that isolates
the cooling fluid in the channel 45 at the center of the target 25. This supportstructure facilitates the direct mechanical drive between the motor 69 and the shaft
75, without the need for offset drive gears.
Referring again to Fig. 3, at the inner end of the cathode adapter 20 is
mounted a shield 85, which secured to the adapter 20 by screws 86 spaced around
the shield 85. The shield 85 is provided with a rearwardly projecting lip 87, shaped
and positioned so as to face the outer periphery 31 of the target 25 in close
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proximity thereto, spaced only by a gap 88 that is wide enough to avoid arcing
between the target 25 and the shield 85. The inner lip 87 of the shield 85 protects
the electrical insulator 27 against material sputtered from the target 25 passing
through the gap 88 and lighting upon, and thus providing a possibly conductive
path across, the insulator 27, which would cause arcing across the path. With
shields 85a of the prior art, as illustrated in Fig. 3A, a small portion of the material
sputtered from the target 25 will bounce from sputtered gas molecules, such as
indicated at 89, and enter the gap 88a, contributing to the eventual buildup of
deposits on the insulator 27. The shield 85 with the lip 87 interrupts the path of
such particles 89 and protects the insulator 27 from such buildup.
Fig. 4 illustrates an alternative embodiment of the target assembly 23 and
cathode assembly 22 in which the clamping ring 47 is formed integrally with the
outer rim 34 of the target 25, illustrated as rim 34c in Fig. 4. In this embodiment,
the threads of the bolts 48 are threaded directly into the back of the target 25, and
the seal 29 is set in a groove in the front face 34a of the rim 34. The seal 49 of
Fig. 3 is unnecessary. In Fig. 4, the rim 34c is illustrated a peripheral extension of
backing plate portion 25b of the target 25. Where no backing plate 25b is
employed with the target material portion 25a bonded thereto at the surface 25c,and the target 25 is formed of an integral piece of sputtering material, the rim 34c
is formed entirely integrally of such sputtering material. Such arrangement is
acceptable where the target 25 is formed of a structurally sound material such as
aluminum or certain metallic alloys. The embodiment of Fig. 4 allows the sputtering
face 32 of the target 25 to be maintained closer to the magnets 71, which is
particularly helpful where the sputtering material of the target is a magnetically soft
or high permeability material.
With the present invention, the effective cooling of the target 25 is provided
while allowing removal and replacement of the target 25 without the release of
cooling fluid into the chamber 13 or otherwise onto the machine 10 or the vicinity
of the machine 10. Removal of a spent target 25 is achieved by loosening of the
clamps 26 and releasing of the entire cathode assembly 21 into a space behind the
chamber 13. With many types of cathode assembly structures, particularly large
ones, the loosened assembly 21 remains supported on hinged brackets or on slides(not shown) mounted on the frame 11 of the machine 10. Otherwise, the target
25 may be placed on a support surface. With such removal of the cathode
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assembly 21, the electrical connections that consist of wires to the motor 69 and
power leads (not shown) to the target assembly 23, need not be disconnected.
Similarly, cooling fluid tubes that connect to the inlet and outlet ports 51,52
respectively to a cooling water supply and drain (not shown) may remain connected
also. It is desirable, nonetheless, to purge cooling fluid from the ducts 50 and the
channel 45 by flowing air through the inlet port 51 to the outlet port 52.
When the cathode assembly 21 has been removed from the door 14 by the
loosening of the clamps 26, the target assembly 23 is disconnected from the
cathode unit 22 by removal of the screws 55 that hold the clamp ring 47 and
cooling jacket 40 to the cathode body 53, and by loosening the nut 77 that holdsthe shaft 75 in the spindle 60. Due to the screws 48, which remain in place on the
target assembly 25, the target assembly 25 remains intact. The shaft 75 generally
remains with the target assembly 23, but it might loosen from the target at the
threads 76 at its threaded forward end rather than at the nut 77, in which case it
must be later removed from the threads 38 at the bore 39 at the target central hub
35. With the channel 45 and ducts 50 purged of cooling fluid, leakage of fluid from
the ducts 50 will be minimal as the target assembly 23 is removed from the
cathode body 53 and disassembled. Where valves 58 are provided in the ducts 50,
likelihood of even small leakage of cooling fluid is further reduced, as the valves
move under the force of their springs to block off the ducts 50 as the jacket 40 is
separated from the cathode body 53.
When the target assembly 25 has been removed from the cathode unit 22,
the target assembly may be moved to a remote location where the target 25 may
be disconnected from the cooling jacket 40 and replaced with another target 25.
This replacement process is carried out by removal of the screws 48 from the target
assembly 23 to release the clamp ring 47 and to permit removal of the target 25.With a new target 25 in place of the old expended target 25, the screws 48 are
replaced and the clamp ring 47 is resecured, and the assembled target assembly 23
is then reconnected to the cathode unit 22 by replacement of the screws 55. As
~ 30 the jacket 40 is brought against the cathode body 53, the valves 58, which will be
extended beyond the surfaces of the jacket 40 and body 53 by their springs, willbe forced by the engagement with the surfaces of the opposite one of the body 53and jacket 40, to cause the ducts 50 to reopen to the free passage of cooling fluid
therethrough. The shaft 75 is then replaced and the nut 77 tightened, completing
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the reassembiy of the cathode assembly 21, which can then be resecured to the
door 14 by tightening of the clamps 26.
From the above, it will be apparent to those of ordinary skill in the art that
changes and additions can be made to the embodiments described and above and
illustrated in the drawings without departing from the principles of the presentinvention. Therefore, what is claimed is as follows:
