Method for preparing a shield to reduce particles in a physical vapor deposition chamber

In a method for preparing a shield and/or clamping ring prior to use in a physical vapor deposition process, the shield and/or clamping ring is first bead blasted using an abrasive powder, then is treated in an ultrasonic cleaning chamber to remove loose particles and then sputter etched or treated with a plasma. The sputtering or plasma treatment serves to loosen contamination which may form a diffusion barrier and prevent the deposits from bonding to the shield and also serves to roughen the surface of the shield and/or clamping ring, to reduce interface voids and improve adhesion of sputtered material onto the shield and/or clamping ring. The process of the invention results in improved cleaning of the shield and/or clamping ring and improved adhesion of sputtered material thereon, thereby increasing the time before the shield/clamping ring must be cleaned and reducing down-time of the physical vapor deposition chamber.

BACKGROUND OF THE INVENTION 
The present invention concerns the preparation of shields and/or clamping 
rings in a physical vapor deposition chamber in order to increase shield 
adhesion and thereby achieve particle reduction in the chamber. 
In physical vapor deposition (PVD) processes a target material, for example 
titanium tungsten, is bombarded by gaseous ions, for example argon ions. 
Material from the target is dislodged and sputters onto a workpiece. The 
workpiece is generally a semiconductor wafer, but may be, for example, a 
magnetic disk or a flat panel display. 
A PVD chamber generally includes shields in the area immediately around a 
workpiece. The shields reduce the deposit of excess material sputtered 
from the target from contaminating the remainder of the PVD chamber. In 
addition, a clamping ring for the workpiece may also be present. Excess 
sputtered material will also deposit on the clamping ring. 
For many types of sputtered materials, the build-up of excess material on 
the shields and/or clamping rings eventually results in flaking of the 
excess deposited material, producing particles in the chamber. At this 
point it is usually necessary to service the PVD chamber by replacing the 
shield and/or clamping ring. If shield or clamping ring replacement needs 
to be done at approximately the same time as target replacement, the 
servicing of the shield or clamping ring may be performed without loss of 
operation time. However, if the shield needs to be replaced much more 
often than the target, this can result in extra down time of the system 
which can seriously impair production throughput. It is desirable, 
therefore, to seek ways to reduce flaking and thereby lengthen the time 
between shield replacements. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a method is disclosed for preparing a 
shield and/or clamping ring prior to use in a physical vapor deposition 
chamber. The shield and/or clamping ring is bead blasted, treated with 
ultrasonic cleaning, and finally sputter etched or plasma cleaned. 
This process first treats the surface with bead blasting to create a 
specially roughened surface, then removes all embedded bead blast residue 
using the ultrasonic cleaning step, and then further treats the surfaces 
to remove oxide coatings that may form a diffusion barrier on the surface 
of the shield, thereby increasing adhesion of material deposited during 
processing of a workpiece in the PVD chamber.

DETAILED DESCRIPTION OF THE INVENTION 
The bead blasting step makes the surface of the shield and/or clamping ring 
irregular. This enhances interface crack propagation of deposited material 
on a submicroscopic scale and hinders the flaking of deposited material. 
The surface irregularities force a fracture propagating along a plane of 
weakness to change direction or pass through a stronger region. 
Secondly, the shield and/or clamping ring is subjected to an ultrasonic 
cleaning step to remove any loose particles on the surface after the bead 
blasting step. 
Lastly, the shield and/or clamping ring is subjected to a sputter etch or 
plasma processing to further aid in removal of surface oxides and further 
roughen the surface to increase the surface area and to improve adhesion 
of material deposited onto the shield during PVD processing. 
In FIG. 1, a PVD chamber 14 includes a movable workpiece table 24. During 
the course of processing a workpiece 36, such as a semiconductor wafer, is 
placed on the workpiece table 24. The workpiece table 24 is raised through 
a clamping ring 16 and a shield 17 to a processing location. An RF 
workpiece bias circuit 12 provides an RF bias voltage to the workpiece 36. 
A DC workpiece bias circuit 13 provides a DC bias to the workpiece 36 
through a line 18. 
Gas control circuitry 26 controls gas flow in and out of chamber 14. A 
vacuum pump 25 is used to create a vacuum in the PVD chamber 14 during 
processing of workpieces 36. 
A source 20 has a sputter target 22 mounted thereon, which for example can 
be comprised of titanium-tungsten alloy. The source 20 is electrically 
isolated from the shield 17 and the clamping ring 16 and the rest of the 
PVD chamber 14 by an insulator ring 10. A DC power supply 21 establishes a 
voltage potential between the shield 17 and the source 20. When workpieces 
are being processed, the negative terminal of the DC power supply 21 is 
connected to the target 22. The positive terminal is grounded to the PVD 
chamber 14. This operating mode is used because gaseous ions from the 
plasma will be accelerated toward whatever surface is connected to the 
negative terminal of the power supply 21. Thus ions in the deposition 
plasma strike the target 22 and cause sputtering of the titanium-tungsten 
or other alloy onto the workpiece 36 on the workpiece table 24. 
FIG. 2 shows a PVD chamber 14, a shield 17 and a clamping ring 16. The 
chamber 14 is shown to include ports 27, 28, 29, 30, 31, 32 and 33. The 
port 30 may be used, for example, by the vacuum pump 25 or a roughing pump 
for initial pumping to create a vacuum in the chamber 14. The port 27 may 
be used, for example, by a residual gas analyzer. The port 28 may be used, 
for example, to allow a power line into the PVD chamber 14, to power a 
lamp used in the PVD process. The port 33 may be used, for example, for 
venting the chamber. The port 29 may be used, for example, as a window. 
The port 32 may be used, for example for supplying argon gas and any 
reactive gas into the chamber 14. Workpieces are placed in the PVD chamber 
14 through an opening 31 by automated machinery (not shown). 
During sputter deposition onto a workpiece, excess target material is 
deposited on the shield 17 and the clamping ring 16. This material builds 
up and eventually begins to flake. The flaking results in unwanted 
particles contaminating the PVD chamber 14. The present invention pertains 
to preparing the surface of the shield 17 and clamping ring 16 to increase 
adhesion of such excess material to these surfaces. 
The adhesion strength of the target material on the shield and clamping 
ring depends on both the bonding strength between the target material and 
the material of which the shield and clamping ring are made, and it 
depends on the microstructure of the interface region between the target 
material and the shield 17 and/or the clamping ring 16. 
For increased adhesion, before the sputter-etch cleaning of the shield 17 
and the clamping ring 16, the shield may be bead blasted. The bead 
blasting is done by bombarding the shield 17 and the clamping ring 16 with 
aluminum oxide abrasive powder. The bead blasting may be done in a 
commercially available sand blasting chamber. 
The bead blasting makes the surface of the shield 17 and the clamping ring 
16 irregular. The irregular surface, on a microscopic scale, will enhance 
interface crack propagation of material such as TiW which is later 
deposited on the shield 17 and the clamping ring 16. Thus the surface 
irregularities will result in the breaking up of the deposited films into 
sections that are small with respect to flake sizes. This significantly 
hinders flaking. 
Prior art treatments after a bead blasting step have been found to be 
completely inadequate. According to one method, the bead blasted part is 
dipped into dilute hydrofluoric acid (HF). This solution is capable of 
dissolving bead-blasted media composed of glass shot for example, but 
cannot dissolve aluminum oxide during the typical processing time, i.e., 
up to a few minutes. In addition, this process attacks the surface of the 
shield/clamping ring parts being processed, and, depending on the material 
of the part, may even reduce surface roughness. 
According to a second method, the bead blasted part is sprayed with 
high-pressure water to physically dislodge the bead blast medium. This 
process will remove various grades of aluminum oxide in addition to glass 
shot and other materials, but the full pressures required cannot be used 
for shield parts which are fabricated of sheet metal to very close 
tolerances. Full pressures can deform the precision machined parts, and 
lower pressures are inadequate to dislodge the bead blasting medium from 
their surfaces. 
In accordance with the process of the present invention, the shield 17 and 
clamping ring 16 are next cleaned by ultrasonic cleaning to remove all 
loose particles from the surface, whether they are due to particles 
remaining after the bead blasting, loose oxide, dust and the like. The 
shield 17/clamping ring 16 are rinsed with deionized water and immersed in 
an ultrasonic cleaner filled with deionized water. Suitable ultrasonic 
cleaners are commercially available and are generally set to run at power 
densities of from about 35-70 Watts/gal using a chamber containing about 
10 gallons of deionized water for several minutes. As soon as the 
ultrasonic generator is turned on, a cloud of formerly embedded solid 
residue is seen to form over bead blasted surfaces from which it 
originated. This cloud quickly dissipates and the solid material removed 
either remains in water suspension or settles out. Thus, most of the 
activity of ultrasonic processing occurs during the initial few seconds of 
treatment. Treatment is usually continued for several minutes however in 
order to assure thorough removal of all loose solid material. 
The parts are then rinsed with deionized water and dried with filtered 
inert gas such as nitrogen. 
To increase bonding strength, the shield 17 and/or clamping ring 16 is then 
treated in a vacuum chamber, and can be sputter etch cleaned, or cleaned 
in a reactive or non-reactive plasma. Preferably the shield and clamping 
ring parts are sputter etch cleaned before use. The sputter etch cleaning 
serves to loosen contamination which may form a diffusion barrier, such as 
oxides, and thereby prevent the target material from strongly bonding or 
adhering to the shield 17 and the clamping ring 16. Also, the sputter etch 
cleaning creates a high density of micro surface roughness. These defects 
allow for an increase in nucleation sites which minimize the formation of 
interface voids. 
In the preferred embodiment of the present invention, sputter etch cleaning 
of the shield and clamping ring is done in a chamber from which source 20 
is removed. As seen in FIG. 3, the source 20 is replaced with a flat cover 
plate 46 fabricated of aluminum alloy, stainless steel or some other 
vacuum compatible metallic material. In the center of the cover plate 46 
is mounted an arrangement of permanent magnets 34 which does not exceed 
half of the chamber lid size in diameter. During the etch process, the 
cover plate 46 is biased positive to a value between +300 volts and +1000 
volts. The cover plate 46 thus becomes the anode of a glow discharge in 
the vacuum chamber. Power in the range of 40 Watts to 500 Watts is applied 
to the cover plate 46. The negative terminal of the power supply 21 is 
grounded to the PVD chamber 14, the shield 17 and the clamping ring 16. 
The preferred operating ambient is three to twelve millitorr (0.5-2 Pa) of 
argon. 
The magnet assembly 34 is used to maintain plasma operation at the low 
operating pressures where the process is most efficient at etching the 
grounded shield 17 and the clamping ring 16. Alternate means of striking 
the shield etch plasma include momentary application of high pressure in 
the range of 50 millitorr to 500 millitorr (7-70 Pa) and include the 
momentary application of a high voltage AC or DC. Two types of power 
supplied may be used to maintain the plasma. The first is a constant power 
supply with a rating of 1000 volts and 1 kilowatt. The second is a 1000 
volt constant-voltage power supply used in conjunction with a high power 
ballast resistor 35. 
At discharge powers of 250 Watts, the shield 17 may typically be cleaned to 
a satisfactory degree after several minutes of the etch process. 
Making the surface of the shield 17 and clamping ring 16 rough, both 
through bead blasting and plasma treatment, increases adhesion due to 
purely mechanical effects. The rough surface provides a greater surface 
area, and distributes stress, that is, when one side of a ridge is in 
tensile stress, the other side of the ridge is in compression stress. 
The choice of material for the shield 17 and the clamping ring 16 is also 
important to maximize adhesion. Shields made of titanium, stainless steel 
covered with a film of aluminum, tungsten or molybdenum have proved to 
provide satisfactory adhesion. 
Further, designing the shield 17 and the clamping ring 16 to maximize the 
surface on which excess TiW material, for example, is deposited, reduces 
the thickness of the deposits in a given amount of sputtering time as 
well. 
Although the discussion of the preferred embodiment has focussed on 
increasing the adhesion of TiW to the shield 17, the invention is 
applicable to increasing adhesion of other materials used in PVD chambers. 
For instance, the inventive process may be used to increase adhesion from 
depositions of pure tungsten, or a reactive deposition of titanium 
nitride. 
As an alternative to an in situ sputter etch cleaning in argon, described 
above, the shield 17 and clamping ring 16 can be cleaned outside of the 
PVD processing chamber 14 in a stand-alone chamber 67. This is illustrated 
in FIG. 4 where a shield 17 and a clamping ring 16 are shown resting on an 
insulating fixture 68 in a stand-alone chamber 67. In the sputter cleaning 
process, the shield 17 and clamping ring 16 are made the cathode of a 
sputter etch plasma. This can be done, for example, by connecting the 
negative terminal of the power supply 21 to the shield 17 and the clamping 
ring 16, and grounding the positive terminal of the power supply 21 to the 
stand-alone chamber 67. The power applied may be, for example, in the 
range of 50-500 Watts. The operating pressure may be for example in the 
range of 2-8 millitorr. In order to etch only the side of the shield 17 
and the clamping ring 16 that receive sputter deposits during processing 
in the PVD chamber 14, portions of the shield 17 and the clamping ring 16 
which will not receive sputter deposits are held against the insulating 
fixture 68. 
FIG. 5 shows the system of FIG. 4 modified so that an RF power signal is 
applied to the shield 17 and the clamping ring 16 by RF power supply 66. 
The frequency of the RF signal may be, for example, 13.56 Megahertz (MHz) 
or some other industrial, scientific or medical (ISM) frequency, for 
example 27.12 or 40.68 MHz. When the operating pressure is in the range of 
2-8 millitorr, and the operating power is in the range of 50 to 500 Watts, 
adequate etching can be achieved in a few minutes. 
As an alternative to sputter etch cleaning, the shield 17 and the clamping 
ring 16 can be cleaned by gentle bombardment of a plasma (i.e., plasma 
cleaning) below the threshold and under process conditions where no shield 
etch material is physically removed. For example, the surface of the 
shield 17 and clamping ring 16 can be reacted in an oxygen plasma to 
intentionally produce an oxide scale to which certain sputtered materials 
might readily adhere. Alternately, oxide scale on the shield 17 and 
clamping ring 16 can be removed without the evolution of sputtered metal 
atoms through the action of a hydrogen plasma. Such reactive processes 
could be performed in situ in PVD chamber 14, or can be performed off line 
in the stand-alone chamber 67. 
In FIG. 6 the PVD chamber 14 is shown modified to facilitate plasma 
cleaning. An RF power signal at an ISM frequency (e.g., 13.56 MHz) is 
applied to the cover plate 46 of the PVD chamber 14 by RF power supply 66. 
Typically for plasma cleaning, the pressure inside the PVD chamber 14 is 
from 20 millitorr to about 2 torr, and the RF power signal generates power 
of about 50-200 Watts. At such an elevated pressure, collisions would 
retard sputter evolution of metal from the shield 17 and the clamping ring 
16. 
When plasma cleaning is done in a stand-alone chamber 67 as shown in FIG. 
5, the pressure inside the stand-alone chamber 67 could be about 20 
millitorr to about 2 Torr, and an RF power signal could generate power of 
50 to about 200 Watts. 
The clamping ring 16 and the shield 17 can also be cleaned using a 
non-reactive desorption cleaning process. For example the shield 17 and 
clamping ring 16 can be bombarded with argon at energies below the energy 
threshold at which sputtering will take place. Such a non-reactive 
desorption cleaning is useful to dislodge adsorbed water and residual 
liquid or solid contamination which might remain after wet cleaning the 
shield 17 and the clamping ring 16. 
Non-reactive desorption cleaning may be performed in situ in the PVD 
chamber 14 when the PVD chamber is arranged as shown in FIG. 6. An RF 
power signal at an ISM frequency is applied to the cover plate 46 of the 
PVD chamber 14 by RF power supply 66. Inside the PVD chamber 14 is an 
inert gas ambient, such as argon. Other inert gases such as helium, neon 
or krypton can be substituted for argon. When the pressure inside the PVD 
chamber 14 is about 20 millitorr to 2 Torr, sufficient collisions would 
slow down plasma ions so that a high density could be built up with less 
than 10 electron-Volts of energy. The impact of the plasma ions on the 
shield 17 and the clamping ring 16 would desorb physisorbed species. 
The non-reactive desorption cleaning may also be performed off line in the 
stand-alone chamber 67. An RF power signal at an ISM frequency is applied 
to the shield 17 and the clamping ring 16 by RF power supply 66. Inside 
the stand-alone chamber 67 is an inert gas ambient such as argon. When the 
pressure inside the stand-alone chamber 67 is about 20 millitorr to 2 
Torr, and the RF power signal generates power of 50 to 500 Watts, 
sufficient collisions would slow down plasma ions such that a high density 
could be built up with less than 10 electron-Volts of energy. The impact 
of the plasma ions on the shield 17 and the clamping ring 16 would desorb 
physisorbed species. The use of insulating fixture 68 is optional as no 
metal is sputtered from the shield 17 or the clamping ring 16. 
Plasma used in a reactive plasma process may be generated in a separate 
upstream plasma preparation chamber. One advantage of such a method is 
that an upstream plasma preparation chamber may be considerably smaller 
than the parts that are processed. Upstream activation of reactive plasma 
may be done whether the plasma etching is done in situ in a PVD chamber, 
or in a stand-alone chamber. 
FIG. 7 shows a shield 17 and a clamping ring 16 placed in a chamber 71. 
Plasma is activated in an upstream plasma preparation chamber 70 before 
being pumped through a port 69 to chamber 71. A power supply 51 supplies 
either a DC power signal or an RF power signal to the upstream plasma 
preparation chamber 70. Effluent, for example atomic hydrogen, atomic 
oxygen or atomic fluorine, or other fragments of gaseous precursors 
therefor, pass to the shield 17 and the clamping ring 16 in the chamber 71 
through a connection 69. When the pressure within the upstream plasma 
preparation chamber 70 is in the range of about 10 millitorr to 1 Torr, 
and the power supply 51 supplies power in the range of about 50 to 500 
Watts. the upstream plasma preparation chamber 70 is generally able to 
produce copious amounts of reactive atomic species. 
About twice as many workpieces can be processed in a PVD chamber after 
treating the shield and/or clamping ring in accordance with the present 
process before having to service or substitute new ones as when the 
ultrasonic cleaning is omitted. 
It will be apparent that various changes can be made to the above process 
without departing from the above teachings. For example, the shield 17 and 
the clamping ring 16 can be precleaned using a cleaning solution used to 
brighten titanium before the bead blasting step. In that case, chemical 
cleaning is followed by a deionized water rinse and drying of the parts. A 
filtered air stream can be used to remove loosely adhered particles from 
the surfaces or parts to be cleaned, or rinses with deionized water 
followed by a drying step can also be used or substituted between any of 
the above process steps, as will be known to one skilled in the art. The 
invention is only meant to be limited by the appended claims.