Non-continuous bonding of sputtering target to backing material
TECHNICAL FIELD AND BACKGROUND
This invention relates to sputtering targets for thin film products. Such targets can be
planar or cylindrical, and have a backing body in the form of a plate or tube - the socalled
support - to which the ceramic or metallic target material is bonded.
During sputtering, targets are exposed to ion bombardment and by consequence high
thermal loads, and the backing body is therefore water-cooled. Large sputtering targets
generally consist of a backing tube or backing plate on which one or more target
segments are bonded, i.e. they are attached to the backing body by a bonding material
which can be a metal - or metal alloy - having a low melting temperature, also called a
metallic solder, or any other kind of electrically and thermally conductive adhesive, such
as a filled elastomer.
The function of the support is t o provide for electrical power transfer, mechanical
strength, and heat transfer to the cooling water, and it allows the target to be mounted
in the sputtering source. As the target segments - in the form of plates or cylinders - are
often bonded on the support by soldering, there is in most cases a mismatch in
coefficients of thermal expansion between the target material and the support
materials, which results in thermal stresses on the solder layer and on the interfaces
between target segment and solder as well as between solder and backing body,
especially during cooling down after bonding or soldering of the target, but also during
usage of the target in the sputtering process. In addition there can be a volume
contraction of the solder when it solidifies, which also leads to interface contraction
stress.
The cumulative thermal and contraction stress often leads to strong and uncontrolled
delamination of the solder layer from either the backing body or the target segment
material or from both. Where delamination over larger surface areas occurs, heat
dissipation from the target segment to the support is minimal, which leads to local
overheating, provoking more uneven thermal stress and eventually cracking of the target
segments during sputtering.
In an attempt to overcome the problem cited before, in US2009/01 52108 the adhesive
bonding of target t o backing body is replaced by a plastically deformable compensation
means that compensate for the deformation of both target and backing material. In one
embodiment, the compensation means are formed by locally limited solder bridges
partially connecting the target and the carrier member to one another. In the carrier
member, cut-outs are provided in the manner of a spiral or ring grooves, where the
solder resides before the bonding takes place. Upon heating and liquifying of the solder,
the target and carrier member are rotated such that the liquid solder moves out of the
cut-outs by centrifugal forces t o fill the gaps between target and carrier member and
form solder bridges, but not at the height of the cut-outs. The solution given to the
stress problem in this patent application is still rather complex.
In view of the above cited delamination problem, there is need for a more simple and
reliable bonding system.
SUMMARY
Viewed from a first aspect, the present invention can provide a target assembly
comprising a backing or support body having a carrying surface, and a sputtering target
having a back surface or attaching surface, said carrying surface facing said back surface,
thereby defining an intermediate space carrying a bonding material binding said back
surface to said carrying surface, characterized in that distinct areas of either one or both
of said back surface and said carrying surface are selectively, superficially treated so as
to enhance the bonding strength of said bonding material in said distinct areas.
In another aspect of the invention, a target assembly comprises a support body having a
carrying surface; a sputtering target having an attaching surface, said carrying surface
and said attaching surface being arranged in opposing facing relation to one another,
thereby defining an intermediate space between said carrying surface and said attaching
surface; and a bonding material disposed in the intermediate space for binding said
attaching surface to said carrying surface, wherein distinct areas of one or both of said
attaching surface and said carrying su rface are selectively, superficially treated to
enhance the bonding strength of said bonding material in said distinct areas.
In an embodiment of this aspect, said bonding material is introduced into said
intermediate space in liquid form. In another embodiment, treating the distinct areas
comprises enhancing the wetting characteristics of said distinct areas such that the
bonding material adheres strongly thereto. In an additional embodiment, the support
body and the sputtering target are cylindrical in shape and are concentrically arranged
with respect to one another.
In a further embodiment, the support body has an external diameter D1 and the
sputtering target has an internal diameter D2 such that the intermediate space has a
thickness D = (D2- D1 )/2 (evidently D>0). The bonding material may comprise a low
melting point solder. The low melting point solder may be indium.
In an additional embodiment, treatment of the distinct areas comprises atmospheric or
low pressure vacuum plasma treatment, Corona treatment, grinding, sand -blasting, or
C02 ice-blasting. In another embodiment, treatment of the distinct areas comprises
applying a metal layer by plasma spraying, sputtering through a mask or high energy
assisted soldering. In a particular embodiment, said metal layer comprises said low
melting point solder described above. High energy assisted soldering may comprise
ultrasonic soldering. In another embodiment, treatment of the distinct areas comprises
exerting mechanical friction such as brushing or rubbing.
In a further embodiment, the distinct areas comprise between 33 and 95 %of the total
surface of either one or both of said attaching surface and said carrying surface.
In another embodiment, the distinct areas are present on both said attaching surface and
said carrying su rface. In this embodiment, at least a portion of said distinct areas on
said attaching surface and said distinct areas on said carrying surface are not aligned
with one another. In embodiments, the support body may have a higher coefficient of
thermal expansion (CTE) than said sputtering target.
In another aspect of the invention, a method for controlling delamination of a bonding
material in a target assembly, the target assembly comprising a support body having a
carrying surface, a sputtering target having an attaching surface, said carrying surface
and said attaching surface arranged in opposing facing relation to one another, thereby
defining an intermediate space between said carrying surface and said attaching surface,
the bonding material for binding said attaching surface to said carrying surface being
disposed in the intermediate space, the method comprises selectively, superficially
treating distinct areas of one or both of said attaching surface and said carrying surface
to enhance the bonding strength of the bonding material in said distinct areas thereby
controlling delamination of the bonding material during solidification of the bonding
material and /or sputtering of the target.
In an embodiment, treating the distinct areas comprises enhancing the wetting
characteristics of said distinct areas such that the bonding material adheres strongly
thereto. In another embodiment, treating the distinct areas comprises atmospheric or
low pressure vacuum plasma treatment, Corona treatment, grinding, brushing, rubbing,
sand-blasting, or C02 ice-blasting. In an additional embodiment, treating the distinct
areas comprises applying a metal layer by plasma spraying, sputtering through a mask, or
high energy assisted soldering. High energy assisted soldering may comprise ultrasonic
soldering.
In another aspect of the invention, a method for controlling thermal stresses in a target
assembly, the target assembly comprising a support body having a carrying surface, a
sputtering target having an attaching surface, said carrying surface and said attaching
surface arranged in opposing facing relation to one another, thereby defining an
intermediate space between said carrying surface and said attaching surface, the
bonding material for binding said attaching surface to said carrying surface being
disposed in the intermediate space, the method comprises selectively, superficially
treating distinct areas of one or both of said attaching surface and said carrying surface
to enhance the bonding strength of the bonding material in said distinct areas thereby
controlling thermal stresses in the interfaces between the sputtering target and the
bonding material and the support body and the bonding material.
BRIEF INTRODUCTION TO THE DRAWINGS
- Figure 1a is a schematic representation illustrating the principle of bonding of cylinders
(front view);
- Figure 1b is a schematic representation illustrating the principle of bonding of cylinders
(top view);
- Figure 2 is a top view schematic representation of a prior art target assembly showing a
prior art delamination scheme;
- Figure 3a, b and c are schematic representations illustrating exemplary target
assemblies in use during sputtering; and
- Figure 4 is a front view schematic representation illustrating an exemplary arrangement
of backing tube with wetting layer pattern.
DETAILED DESCRIPTION
The target assembly prevents delamination of the bonding material over large areas by
controlling the stresses described above and by building in well chosen voids in the
bonding layer during the final cooling down and the resulting bonding of the
target/bonding layer/backing body assembly, using selective treatment of either the
carrying surface of the support and/or the backside material of the target (segments).
The selective treatment comprises a wetting or energizing process used t o make the
solder or bonding materials stick t o the support materials and/or the target materials by
changing the surface energy of one or both of those materials. One of ordinary skilled in
the art will recognize that there are several ways t o change the surface energy of the
surface materials. Examples include, but are not limited to, atmospheric or low pressure
vacuum plasma treatment (using an inert gas or a reactive gas), Corona treatment,
mechanical pre-treatment of the surface by grinding, brushing, rubbing, sand-blasting or
C0 2 ice-blasting, electrochemical deposition of a thin metal layer, depositing a thin
metal layer by plasma spraying, sputtering through a mask, or a high energy assisted
soldering technique, e.g. ultrasonic soldering. By selectively controlling the wetting
process, distinct areas of good (strong) solder adherence can be defined, and
consequently, also areas of bad (weak) solder adherence can be defined. The distinct
areas may comprise between 33 and 95 %of the total surface of either one or both of the
back surface and the carrying surface.
In an example embodiment, the target assembly comprises a support body having a
carrying surface and a sputtering target having an attaching surface. The carrying
surface and the attaching surface are arranged in opposing facing relation to one
another, thereby defining an intermediate space between the two surfaces. A bonding
or solder material is introduced into the intermediate space for binding the attaching
surface to the carrying surface. Before this however, distinct areas of one or both of the
attaching surface and the carrying surface are selectively, superficially treated to
enhance the bonding strength of the bonding material in the distinct areas. It is believed
that the wetting characteristic of the bonding material is enhanced in the distinct areas.
In an embodiment, the distinct areas of the attaching surface may not be facing or
aligned with (i.e., may be offset from) the distinct areas of the carrying surface. Where
the distinct areas are provided only on one of the attaching surface and the carrying
surface, the other surface can be treated in the same way over its complete surface (non
selective), so as to yield a full (continuous) wetting layer and an overall good wetting of
the bonding material on that surface.
The bonding material may be introduced in the intermediate space in liquid form. The
bonding material may be a low melting point solder, for example, indium.
The backing body or support may be cylindrical having an external diameter D1 , and the
external sputtering target may also be cylindrical having an internal diameter D2. The
backing tube and target can be concentrically arranged thus defining the intermediate
space as having a thickness D=(D2-D1 )/2 (D evidently being >0).
The bonding strength of the solder or bonding material is enhanced in the areas that are
wetted or energized. The selective wetting process results in a controlled delamination
of the bonding material from the non-wetted surfaces during bonding, thus reducing and
potentially alleviating thermal stresses created during the bonding process in a
controlled manner. Controlled delamination during bonding reduces and potentially
avoids uncontrolled delamination in the future. By controlling delamination, voids are
purposely, selectively created in the bonding layer. Thus, alternate areas of good and
bad adhesion are formed, resulting in an even distribution of heat transfer over the
whole area of the target segment by means of thermally conductive solders or other
bonding materials. As such, detrimental, local hot spots, which can result in excessively
high stress and eventually cracking of the sputter target during the sputtering process,
are avoided. By using the method of controlled wetting or delamination, one is able t o
bond the target segment material and the support material with minimal built-in stress,
resulting in a bonded sputtering target that can withstand higher thermal loads
compared t o a sputtering target with an inhomogeneous and uncontrolled distribution of
delaminated zones.
The target assembly described above is for example useful with rotary targets consisting
of a backing tube and one or more cylindrical target segments, and for example for
situations wherein the backing tube has a higher coefficient of thermal expansion (CTE)
than the target segment. Such difference in CTE (or delta CTE) between the backing
tube and the target segment may cause enough thermal stress in the system when
cooling down from the temperature at which bonding is performed that uncontrolled
delamination at any interface in the bonding system can arise.
Examples of target/backing tube assemblies are: Al:ZnO (Aluminum doped Zincoxide) on
stainless steel, Silicon on stainless steel, Si:Si02 on stainless steel, ITO (Indium Tin Oxide)
on stainless steel, AZO on aluminum, etc.
There are other ways t o reduce the delta CTE. As an example, backing tubes with lower
CTE are available, e.g. consisting of metals such as Ti and Mo. Tubes with lower CTE are
much more expensive than the usual backing tube materials (e.g., stainless steel AISI304,
stainless steel AISI31 6(L), A16060, Cu). Choosing a backing tube manufactured of much
more expensive materials would create a competitive disadvantage for the product.
An additional effect of the proposed method is that the required solder alloy volume per
target can be reduced. Because the bonding metal (alloy) is an expensive material, a
reduction in volume per target is advantageous. The proposed method results in a
sputtering target having a cost advantage.
For rotary targets, the areal appearance of the non-continuous wetting zones can have
various patterns such as dots, long or short strips, spirals in any directions (horizontal or
perpendicular or diagonal).
The ratio of surface area of the non-wetted zone to the wetted zone depends on the
coefficients of thermal expansion of the target and the supporting materials and the type
of solders, and also on the temperature of target segments and supporting material at
which the solder material is introduced and starts to cool. The temperature of both
parts, target segments and supporting material, can be different depending on the
selected heating and/or cooling techniques.
As described above, the structured, controlled wetting or metallisation results in
controlled local bonding errors or voids (e.g. small delamination of solder from the
backing tube or the target segments). Each local void will have a relatively small area
in comparison with the equivalent area of the wetted or distinct areas without defects so
that sufficient heat dissipation during sputtering is possible. Practically this can mean
between 1/20 and 2/1 of void/wetted areas without defects, or expressed in mm it could
be between 1mm:20mm to 10mm:5mm of void length or untreated area length: treated
or wetted area length. In embodiments, voids may appear in a more or less regular
pattern, alternated with well bonded, voidless areas with one local void having a certain
distance to the next one. The voids form automatically during the cooling process after
bonding (below the melting point of the solder) by the working of cohesion of solder and
adhesion and shear forces at the interfaces.
The cooling of the assembly after bonding can be done either actively or naturally (both
natural and controlled cooling can be applied), and when active either from the inside or
from the outside or from both sides.
The target assembly will be described with reference t o the Figures provided. It should
be understood that the Figures are illustrative only and are in no way limiting to the
scope of the invention.
Figure 1a & b illustrate the known principle of bonding a rotary target. A target segment
(TS) is inserted over the backing tube (BT), whereafter solder or bonding material (BM)
(molten indium or another low melting temperature alloy) is poured in the intermediate
space between both tubes that are heated to (and possibly above) the bonding material's
melting point. Thereafter, the target assembly is cooled down to room temperature.
Figure 2 illustrates the principle of delamination of solder in the prior art. In the prior art
example the coefficient of thermal expansion (CTE) of the supporting tube having the
carrying surface is larger than that of the target segment having the back surface. An
example target material to be sputtered is A doped or Al20 doped ZnO (AZO) with a
certain composition variation. A target segment has an outer diameter of 163 mm and an
inner diameter of 135 mm. The outer target surface is mechanically ground to these
dimension. The inner diameter can be achieved by mechanical grinding or in any other
suitable manner such as chemical etching. The example Al:ZnO (AZO) target material has
a CTE of ca. 5.5*10 / K in a temperature range of 20 °C to 200 °C. An example backing
tube having a carrying surface is made of stainless steel. The backing tube has an outer
diameter of 133 mm and an inner diameter of 125 mm. The outer surface can be
mechanically lathed or ground. The example backing tube (e.g. stainless steel AISI304)
has a CTE of ca. 15*1 0 / K in a temperature range of 20 °C to 200 °C. When a rotary
Al:ZnO(AZO) target is produced, the target/backing tube combination is heated to
approx. 180°C (in case that the solder material is indium), and solder or bonding
material is poured in the annular intermediate space or bonding gap between the target
and the Stainless Steel backing tube (SST). The annular space has a thickness of 0.3 - 1.5
mm (e.g. 0.7 mm) (see bottom left). However, whilst cooling down to room temperature
(RT), the annular space or gap widens to 1 mm, because of the difference in CTE. This
widening is illustrated at the top. The consequences are shown at the bottom right.
During cooling, the volume shrinkage of the solder combined with the volume extension
of the bond gap causes the weakest link (such as oxides or voids) t o be broken in favour
of the stronger bonding area.
In an example target assembly, contrary to the prior art, in order to obtain a guaranteed
bonding strength between carrying surface and solder material as well as between back
surface and solder material, both surfaces of the example in Figure 2 can be treated
beforehand by suitable energizing techniques.
In this example, the inner wall of the AZO target segments - in other words the back
surface - is provided with a thin metal layer, which afterwards allows a good wetting of
the binding material onto AZO ceramic surfaces. In one embodiment, the thin metal
layer, further referred to as the "wetting material" is the same material as the solder
material.
The wetting material can also be any other metallic alloy which has a good wetting
property for solder material such as In or In alloys, Sn or Sn alloys, Ag or Ag alloys. Such
alloys may include a certain amount of other metallic elements to improve the wetting
property and bonding strength or to reduce the melting point or as a contamination. Ti,
Zn, Cu, Ni, Ga, Ce, Bi, Sb, Si can be such elements. The wetting layer can be directly
applied on the AZO back surface without any intermediate layer, or the wetting layer can
be applied indirectly by using one or more intermediate layers which allow a stronger
adhesion of the wetting layer to the AZO back surface. The intermediate layer can be
any other metallic alloy which has good wetting properties for solder materials such as In
or In alloys, Sn or Sn alloys, Ag or Ag alloys, Au or Au alloys. Such alloys may include a
certain amount of other metallic elements t o improve the wetting property and bonding
strength or to reduce the melting point or as contamination. Ti, Zn, Cu, Ni, Ga, Ce, Bi,
Sb, Si can be such elements.
The intermediate and/or the wetting layer on the back surface of the target segment can
be applied by electrochemical deposition or ultrasonic treatment based on cavitation
principle or sputter coating technique or mechanical brushing or heat treatment. The
ultrasonic cavitation phenomenon is used to remove the oxidised layers on the surface to
be wetted by the impact of an intense ultrasonic source generating micro-vibrations that
cause a brushing effect. The back surface can be wetted either over its full surface area
or only partially.
A direct patterning of the wetting layer on the back surface can be achieved via a
selective wetting by using a mask for electrochemical deposition, heat treatment,
sputter coating or mechanical brushing or ultrasonic treatment.
For selective ultrasonic wetting, the patterning can be achieved by discontinuous
treatment of the ultrasonic equipment such as repetition of switch on and off, or
different movement with variable feed rate of ultrasonic sonotrode. To achieve this, a
well cleaned target segment is fixed in a horizontal position and rotated along its axis in
a heating furnace. The furnace temperature is set to a temperature above the melting
temperature of the wetting material. If the surface temperature is high enough to handle
the liquid material, it is applied onto the rotating back surface. The liquid material is
spread out by the use of mechanical means such as brushing. The material is kept liquid
and the sonotrode is introduced into the inner space of the cylindrical target segment.
During the rotation of the target segment in the furnace, the ultrasonic sonotrode is so
positioned on the targets back surface that there is a slight contact between said back
surface and the tip of the ultrasonic sonotrode. Hereby at least a few mm of the
sonotrode tip is dipped in the liquid wetting material. The sonotrode tip moves forward
from the front (the top or bottom of the target segment) towards the other end of the
target segment or backward from the backside to the front with a certain progress rate
such as by repetition of stop and go move, so that a ring type of wetting layers are
formed by ultrasonic soldering. At certain selected positions the ultrasonic sonotrode
treats the back surface without moving forward or backward whereby at least one
circumferential ring shaped target surface area is wetted by wetting material. The
sonotrode then moves further over a certain distance and the treatment mentioned
above is repeated. The sonotrode can also move continuously with a defined progress
rate so as to obtain a spiral type of pattern instead of a ring shaped pattern.
An alternative way to make a non-continuous wetting layer on the back surface of the
target segment is to apply a pre-patterned intermediate layer, so that the sufficient
adhesion of the wetting layer is guaranteed only for the pre-patterned area. The
patterning of the intermediate layer can be realized by using a mask for electrochemical
deposition or heat treatment or sputter coating. After pre-patterning of the intermediate
layer, the target segment is rotated in a heating furnace. The furnace temperature is set
to a temperature above the melting temperature of the wetting material. If the surface
temperature is high enough to treat the wetting material, the wetting material is put
onto the rotating back surface. The wetting material is spread out by means of
mechanical tools such as brushing. The wetting layer including intermediate layer has
typically a thickness of smaller than 0.1 mm.
In another example, in order to make a ring or spiral type of pattern of wetting layer on
the carrying surface, being the outer surface of the backing tube, a well-cleaned backing
tube which is machined to final dimensions is heated up to the temperature at which the
wetting material is melted, and the temperature must be high enough to keep the
wetting material in a liquid state during the surface treatment. Once the temperature
mentioned above is reached, the backing tube starts to rotate and the ultrasonic
sonotrode is applied to the wetting material. The ultrasonic wetting is concentrated on
one position so as to form at least one (circumferential) ring-shaped adhesion layer on
the carrying surface of the rotating backing tube. After the treatment of one ring-shaped
wetting layer, the tip of the ultrasonic sonotrode moves to a next position whereby a
certain distance between two ring-shaped wetting layers is kept over the whole length of
the bonding area. Hereby non-continuous wetting layers, in other words, selective
wetting layers are obtained by alternation of treatment and non -treatment of the
carrying surface over the length of the bond area as shown in Fig. 4.
Figure 4 shows the front view of part of the backing tube having a carrying surface,
where it can be clearly seen that selective wetting layers (bright colour) are obtained on
the outer surface of the backing tube in a ring shape manner by alternating ultrasonic
treatment of the surface.
The selective wetting can also be applied in a spiral shape. In that case, the ultrasonic
sonotrode moves continuously with a defined progress rate over the rotating backing
tube, so that the non-fully wetted carrying surface is obtained. The selective wetting can
also be prepared by electrochemical deposition or sputter coating or thermal spraying or
sand blasting whereby a mask is used to create the non continuous pattern of wetting
layer.
After the selective wetting is finished, and as illustrated in Fig. 1a6tb, the target segment
having a back surface with either a full (continuous) or partial (non-continuous) wetting
layer is positioned concentrically outside the surface of the backing tube having a
carrying surface with either full (continuous) or partial (non-continuous) wetting layer.
The bottom part of the bonding gap is sealed by high temperature sealing material. Both
parts - target segment and backing tube - are heated above the melting point of the
solder material such as In or In alloys, Sn or Sn alloys, Ag or Ag alloys. Such alloys may
include a certain amount of other metallic elements to improve wetting property and
bonding strength or to reduce the melting point or as contamination. Ti, Zn, Cu, Ni, Ga,
Ce, Bi, Sb, Si can be such elements.
When the surface temperature of the target segment reaches a sufficiently high
temperature, typically 20-30° C above the melting temperature of the solder material,
the liquid solder is introduced into the bonding gap. Once the bonding gap is completely
filled up with the molten solder, the heating is ceased and the target segment and
backing tube and solder start to cool. Whilst cooling, the solder solidifies below its
melting temperature and the bonding gap increases as illustrated above. As the solidified
solder material cannot compensate for the increased bonding gap, the weakest link in
the interface will break. This weakest binding spot in the interface between back surface
and solder and/or carrying surface and solder, is located - as illustrated above - where
the selective non-continuous wetting layer is absent. The predictable delamination or
void formation can be localized in this narrow range, which leads to a minimal size of
bonding error. This allows for a sufficient heat dissipation during the subsequent
sputtering process.
Figure 3a illustrates a cross section of part of an example arrangement of a rotary target
assembly in use (in front view). During sputtering, the cooling of the backing tube is
performed by water W flowing in it (left arrow), whilst the plasma P heats up the
target(at the right). Heat, illustrated by the small black arrows, is dissipated during
sputtering through the AZO layer and the indium solder bonding layer to the backing
tube. In this example the contact areas of the backing tube-solder and AZO-solder are
offset or not located at corresponding heights. By the presence of finely-distributed
small voids instead of large delaminated areas caused by the pre-defined wetting errors
on both contact areas, a sufficient and controlled heat dissipation is obtained.
Figure 3b illustrates an example arrangement where only the back surface of the target
segment is treated so as to create the non-discontinuous wetting layer with sufficient
adhesion (patterning of wetting layer). Figure 3c illustrates an example arrangement
where only the carrying surface of the backing tube is treated so as t o create the nondiscontinuous
wetting layer with sufficient adhesion.
The intermediate spaces between either back surface of target segment and bonding
layer, bonding layer and carrying surface of backing tube, or both of them in Figures 3a
t o c illustrate either a void space or a partially delaminated space, or a weaker binding
between solder and back surface or carrying surface.
An example of the use of an AZO target assembly treated as described above is
illustrated hereafter. Such targets may be used in the thin film photovoltaic industry t o
deposit Al:ZnO front window contact layers in case of CIGS or thin film Si solar cells. For
any ceramic target material, the market wants t o maximize deposition rate in order t o
reduce manufacturing costs (i.e. coating costs) and increase productivity. This is only
possible when high power loads on the targets can be used. Presently, allowable power
loads on AZO rotary have been limited by bonding technology.
Typical DC power loads of 18 - 20 kW/m are obtained for standard AZO rotary
dimensions, i.e. consisting of a stainless steel backing tube with an inner diameter of
125 mm and an AZO rotary cylinder having a diameter of 135 mm and a 14 mm wall
thickness. Only one-piece, sprayed rotary AZO targets have been reported t o sustain
power loads above 25 kW/m, and up t o even 32 kW/m. The latter targets have a limited
Al:ZnO wall thickness (typically 9 mm only), and have a density of only approx. 90 . As
such, they suffer from other disadvantages.
In one embodiment, corresponding t o the illustration in Fig. 3c, the back surface of the
AZO target is fully wetted with indium by applying the ultrasonic treatment as described
before. The carrying surface of the backing tube is partially wetted so as t o obtain a
pattern as illustrated in Fig. 4 (with ring shaped selective wetting layers), where
between 60 and 80% of the carrying surface is selectively wetted with an indium layer
using the sonotrode method. The width of each wetting ring is between 6 and 20 mm,
the width of each non-treated surface ring is between 2 and 6 mm. A DC power load of
27,27 kW/m is successfully handled on an AZO target after this selective wetting is
applied, which is much higher than for bonded rotary AZO targets as produced with the
state of the art technology.
The invention can also be described by the following clauses:
1. A target assembly comprising a backing body having a carrying surface, and a
sputtering target having a back surface, said carrying surface facing said back surface,
thereby defining an intermediate space carrying a bonding material binding said back
surface to said carrying surface, characterized in that distinct areas of either one or both
of said back surface and said carrying surface are superficially treated so as to enhance
the bonding strength of said bonding material in said distinct areas.
2. A target assembly according to clause 1, characterized in that said bonding material is
introduced in said intermediate space in liquid form, and that in said superficially
treated areas the wetting characteristics of said bonding material are enhanced.
3. A target assembly according to clauses 1 or 2, characterized in that said target
assembly comprises an internal cylindrical backing body having an external diameter D1 ,
and an external sputtering target having an internal diameter D2, said backing tube and
said target being concentric and defining said intermediate space having a thickness
D=(D2-D1 )/2.
4. A target assembly according to anyone of clauses 1 to 3, characterized in that said
bonding material is a low melting point solder such as indium.
5. A target assembly according to anyone of clauses 1 to 4, characterized in that said
superficially treated areas are obtained by either one of atmospheric or low pressure
vacuum plasma treatment, Corona treatment, grinding, sand-blasting and C0 2 iceblasting.
6. A target assembly according to anyone of clauses 1 to 5, characterized in that said
superficially treated areas are obtained by applying a metal layer by either plasma
spraying, sputtering through a mask or mechanical friction such as brushing or rubbing or
high energy assisted soldering, such as ultrasonic soldering.
7. A target assembly according to anyone of clauses 1 to 6, characterized in that said
distinct areas of each of said back surface and said carrying surface comprise between 33
and 95 %of the total surface of either one or both of said back surface and said carrying
surface.
8. A target assembly according to anyone of clauses 6 or 7, characterized in that said
back surface is superficially treated by applying a metal layer by ultrasonic soldering
whereby the distinct areas comprise between 90 and 100% of the total surface of said
back surface, and in that said carrying surface is superficially treated by applying a metal
layer by ultrasonic soldering whereby the distinct areas comprise between 60 and 80% of
the total surface of said carrying surface.
9. A target assembly according to anyone of clauses 1 to 7, characterized in that both
said back surface and said carrying surface are superficially treated, and that treated
areas of both of said back surface and said carrying surface are not facing each other.
10. A target assembly according to anyone of clauses 1 to 9, characterized in that said
backing body has a higher coefficient of thermal expansion (CTE) than said sputtering
target.
11. A target assembly comprising:
a support body comprising a carrying surface;
a sputtering target comprising an attaching surface;
an intermediate space between the carrying surface and an attaching surface, wherein
the intermediate space comprises a bonding material; and
selected and distinct areas of enhanced bonding strength on the carrying surface and/or
the attaching surface.
12. The target assembly of claim 11, wherein the bonding material is introduced into
the intermediate space in liquid form.
13. The target assembly of any one of claims 11-1 , wherein the selected and distinct
areas have
enhanced the wetting characteristics such that the bonding material adheres to the
selected and distinct areas.
1 . The target assembly of claim 11, wherein the surface energy of the selected and
distinct areas has been changed such that the bonding material adheres to the selected
and distinct areas.
15. The target assembly of claim 11, wherein the support body and the sputtering
target are cylindrical in shape and are concentrically arranged with respect to
one another.
16. The target assembly of claim 15, wherein the support body has an external diameter
D1 and the sputtering target has an internal diameter D2 such that the intermediate
space has a thickness D= (D2-D1 )/2.
17. The target assembly of claim 11, wherein the bonding material comprises a low
melting point solder.
18. The target assembly of claim 17, wherein the low melting point solder is indium.
19. The target assembly of claim 11, wherein the selected and distinct areas have been
treated by a method selected from the group consisting of atmospheric or low pressure
vacuum plasma treatment, Corona treatment, grinding, brushing, rubbing, sand-blasting,
and C02 ice-blasting.
20. The target assembly of claim 17, wherein a metal layer has been applied to the
selected and distinct areas by a method selected from the group consisting of plasma
spraying, sputtering through a mask, and high energy assisted soldering, wherein the
metal layer comprises the low melting point solder.
2 1. The target assembly of claim 20, wherein high energy assisted soldering comprises
ultrasonic soldering.
22. The target assembly of claim 11, wherein the selected and distinct areas comprise
either
between about 33 and about 95 %of the total surface of the attaching surface, or
between
about 33 and about 95 %of the total surface of the carrying surface.
23. The target assembly of claim 11, wherein the selected and distinct areas are present
on both
the attaching surface and the carrying surface, and wherein the distinct areas comprise
between about 33 and about 95 %of the total surface of the attaching surface and
between
about 33 and about 95 %of the total surface of the carrying surface.
24. The target assembly of claim 23, wherein at least a portion of the selected and
distinct areas on the attaching surface and the selected and distinct areas on the
carrying surface are not aligned with one another.
25. The target assembly of claim 11, wherein the support body has a higher
coefficient of thermal expansion (CTE) than the sputtering target.
26. Amethod for controlling delamination of a bonding material in a target assembly,
the method comprising:
forming an intermediate space between a carrying surface of a support body and an
attachment surface of a sputtering target;
selectively treating distinct areas on the carrying surface, the attachment surface,
and/or both, wherein the selective treatment enhances the bonding strength of a
bonding material at the distinct areas;
introducing a bonding material into the intermediate space thereby binding the carrying
surface and the attachment surface, wherein delamination of the bonding material on
the carrying surface and the attachment surface is controlled by the selective treatment
of the distinct areas.
27. The method of claim 26, wherein the bonding material is introduced into the
intermediate space in liquid form.
28. The method of claim 26, wherein treating the distinct areas comprises enhancing
the wetting characteristics of the distinct areas such that the bonding material
adheres strongly to the distinct areas.
29. The method of claim 26, wherein the support body and the sputtering target are
cylindrical in shape and are concentrically arranged with respect to one another.
30. The method of claim 29, wherein the support body has an external diameter D1
and the sputtering target has an internal diameter D2 such that the intermediate
space has a thickness D= (D2-D1 )/2.
3 1 . The method of claim 26, wherein the bonding material comprises a low melting
point solder.
32. The method of claim 3 1 , wherein the low melting point solder is indium.
33. The method of claim 26, wherein treating the distinct areas comprises treating the
sistinct areas by atmospheric or low pressure vacuum plasma treatment, Corona
treatment,
grinding, brushing, rubbing, sand-blasting, or C02 ice-blasting.
34. The method of claim 3 1 , wherein treating the distinct areas comprises applying
metal layer by plasma spraying, sputtering through a mask, or high energy
assisted soldering, and wherein said metal layer comprises the low
melting point solder.
35. The method of claim 34, wherein high energy assisted soldering comprises
ultrasonic soldering.
36. The method of claim 26, wherein the distinct areas comprise between about 33 and
about 95% of the total surface of either one or both of the attaching surface and the
carrying surface.
37. The method of claim 26, wherein the distinct areas are present on both the
attaching surface and the carrying surface.
38. The method of claim 37, wherein at least a portion of said distinct areas on the
attaching surface and the distinct areas on the carrying surface are not aligned
with one another.
39. The method of claim 26, wherein the support body has a higher coefficient of
thermal expansion (CTE) than the sputtering target.
40. A method for controlling thermal stresses in a target assembly of claim 1, the method
comprising:
Selectively and superficially treating distinct areas of one or both of the attaching
surface and
the carrying surface to enhance the bonding strength of the bonding material at
the distinct areas thereby controlling thermal stresses at the interfaces between
the sputtering target and the bonding material and the support body and the
bonding material.
4 1. The target assembly of claim 11, wherein the carrying surface and the attaching
surface are facing each other.
42. The target assembly of claim 26, wherein the carrying surface and the attachment
surface are facing each other.
43. Atarget that has been produced by the method according to claim 26, wherein the
target only contains areas of delamination at the distinct areas.
44. Atarget assembly comprising:
a support body comprising a carrying surface;
a sputtering target comprising an attaching surface;
an intermediate space between the carrying surface and an attaching surface, wherein
the intermediate space comprises a bonding material; and
a means of enhancing bonding strength at the distinct areas of the carrying surface
and/or the attaching surface.
While specific embodiments and/or details of the invention have been shown and
described above to illustrate the application of the principles of the invention, it is
understood that this invention may be embodied as more fully described in the claims, or
as otherwise known by those skilled in the art (including any and all equivalents),
without departing from such principles.
CLAIMS
A target assembly comprising
- a support body having a carrying surface;
- a sputtering target having an attaching surface, said carrying surface and said
attaching surface being arranged in opposing facing relation to one another,
thereby defining an intermediate space between said carrying surface and
said attaching surface; and
- a bonding material disposed in the intermediate space for binding said
attaching surface to said carrying surface,
- wherein distinct areas of one or both of said attaching surface and said
carrying surface are selectively, superficially treated t o enhance the bonding
strength of said bonding material in said distinct areas.
The target assembly of claim 1, wherein said bonding material is introduced into
said intermediate space in liquid form.
The target assembly of claim 1, wherein treating the distinct areas comprises
enhancing the wetting characteristics of said distinct areas such that the bonding
material adheres thereto.
The target assembly of claim 1, wherein treating the distinct areas comprises
changing the surface energy of the distinct areas such that the bonding material
adheres thereto.
The target assembly of claim 1, wherein the support body and the sputtering
target are cylindrical in shape and are concentrically arranged with respect to
one another.
The target assembly of claim 5, wherein the support body has an external
diameter D1 and the sputtering target has an internal diameter D2 such that the
intermediate space has a thickness D = (D2-D1 )/2.
7. The target assembly of claim 1, wherein said bonding material comprises a low
melting point solder.
8. The target assembly of claim 7, wherein the low melting point solder is indium.
9. The target assembly of claim 1, wherein treatment of the distinct areas comprises
atmospheric or low pressure vacuum plasma treatment, Corona treatment,
grinding, brushing, rubbing, sand-blasting, or C0 2 ice-blasting.
10. The target assembly of claim 7, wherein treatment of the distinct areas comprises
applying a metal layer by plasma spraying, sputtering through a mask, or high
energy assisted soldering, wherein said metal layer preferably comprises said low
melting point solder.
11. The target assembly of claim 10, wherein high energy assisted soldering comprises
ultrasonic soldering.
The target assembly of claim 1, wherein said distinct areas comprise either
between 33 and 95 %of the total surface of said attaching surface, or between
33 and 95 %of the total surface of said carrying surface.
The target assembly of claim 1, wherein said distinct areas are present on both
said attaching surface and said carrying surface, and said distinct areas comprise
between 33 and 95 %of the total surface of said attaching surface and between
33 and 95 %of the total surface of said carrying surface.
14. The target assembly of claim 13, wherein at least a portion of said distinct areas
on said attaching surface and said distinct areas on said carrying surface are not
aligned with one another.
15. The target assembly of claim 1, wherein said support body has a higher
coefficient of thermal expansion (CTE) than said sputtering target.
A method for controlling delamination of a bonding material in a target assembly,
the target assembly comprising:
- a support body having a carrying surface,
- a sputtering target having an attaching surface, said carrying surface and said
attaching surface arranged in opposing facing relation to one another, thereby
defining an intermediate space between said carrying surface and said
attaching surface, and
- the bonding material for binding said attaching surface to said carrying
surface being disposed in the intermediate space,
the method comprising selectively, superficially treating distinct areas of one or
both of said attaching surface and said carrying surface to enhance the bonding
strength of the bonding material in said distinct areas thereby controlling
delamination of the bonding material.
The method of claim 16, wherein said bonding material is introduced into said
intermediate space in liquid form.
The method of claim 16, wherein treating said distinct areas comprises enhancing
the wetting characteristics of said distinct areas such that the bonding material
adheres strongly thereto.
The method of claim 16, wherein the support body and the sputtering target are
cylindrical in shape and are concentrically arranged with respect to one another.
The method of claim 19, wherein the support body has an external diameter D1
and the sputtering target has an internal diameter D2 such that the intermediate
space has a thickness D= (D2-D1 )/2.
The method of claim 16, wherein said bonding material comprises a low melting
point solder.
22. The method of claim 2 1, wherein the low melting point solder is indium.
23. The method of claim 16, wherein treating said distinct areas comprises
atmospheric or low pressure vacuum plasma treatment, Corona treatment,
grinding, brushing, rubbing, sand-blasting, or C0 2 ice-blasting.
24. The method of claim 2 1, wherein treating said distinct areas comprises applying a
metal layer by plasma spraying, sputtering through a mask, or high energy
assisted soldering, and wherein said metal layer preferably comprises said low
melting point solder.
25. The method of claim 24, wherein high energy assisted soldering comprises
ultrasonic soldering.
26. The method of claim 16, wherein said distinct areas comprise between 33 and 95
%of the total surface of either one or both of said attaching surface and said
carrying surface.
27. The method of claim 16, wherein said distinct areas are present on both said
attaching surface and said carrying surface.
28. The method of claim 27, wherein at least a portion of said distinct areas on said
attaching surface and said distinct areas on said carrying surface are not aligned
with one another.
29. The method of claim 16, wherein said support body has a higher coefficient of
thermal expansion (CTE) than said sputtering target.
30. A method for controlling thermal stresses in a target assembly, the target
assembly comprising a support body having a carrying surface, a sputtering target
having an attaching surface, said carrying surface and said attaching surface
arranged in opposing facing relation to one another, thereby defining an
intermediate space between said carrying surface and said attaching surface, the
bonding material for binding said attaching surface to said carrying surface being
disposed in the intermediate space; the method comprising selectively,
superficially treating distinct areas of one or both of said attaching surface and
said carrying surface to enhance the bonding strength of the bonding material in
said distinct areas thereby controlling thermal stresses in the interfaces between
the sputtering target and the bonding material and the support body and the
bonding material.