Device and method for preventing settlement of particles on a chemical-mechanical polishing pad

A device and method for preventing settlement of particles on a chemical-mechanical polishing pad is provided. Specifically, a device capable of preventing settlement of particles on the pad is located between the polishing pad and a platen of a chemical-mechanical polishing apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a device and method for preventing 
settlement of particles on a chemical-mechanical polishing pad, and more 
particularly, to a device placed between the polishing pad and a platen of 
a chemical-mechanical polishing apparatus used during the fabrication of 
semiconductor devices. 
2. Discussion of the Prior Art 
During fabrication of semiconductor devices, irregular top surfaces result 
due to many manufacturing processes, such as forming conductive lines and 
single or multiple layers. During various stages of semiconductor wafer 
production, irregular top surfaces of the wafers are planarized or 
flattened to provide smooth surfaces. Planarized surfaces improve 
performance and yield of integrated circuits formed on the wafer. 
Chemical-mechanical polishing (CMP) is one method to planarized wafer 
surfaces. In the CMP process, the wafer is rubbed with a polishing pad. 
The rubbing is accomplished by pressing the wafer or polishing pad toward 
each other, and rotating one or both of them relative to each other. A 
slurry is used to chemically/mechanically attack the wafer surface and 
facilitate removal thereof by the mechanical abrasion provided by the 
rotating polishing pad. 
Particles are generated from wafer abrasion (i.e., the mechanical abrasion 
of the wafer surface being polished), from slurry agglomeration (i.e., 
slurry particles that coalesce, which slurry particles are approximately 
0.05 microns in size), and from pad debris resulting from polishing pad 
disintegration. These particles embed or settle within the polishing pad 
fabric, and protrude during the polish process causing wafer scratching, 
defects and improper planarazation. 
Furthermore, the embedded particles change the surface structure of the 
polishing pad, resulting in process instability, and reduced repeatability 
and polish or removal rate. In extreme cases, the decline in the polish or 
removal rate results in an incomplete removal of material, leading to 
degradation in polishing uniformity. Polishing uniformity is further 
degraded due to particles being embedded on the pad in a non-uniform 
fashion. For example, a particular area of the pad may have more particles 
embedded therein than other areas. This non-uniformity is further 
accentuated when the wafer surface contains areas of different material, 
that are removed or polished at different rates. 
The embedded particles also reduce the pad useful life, thus requiring 
frequent changing of the polishing pads. In addition to the cost of the 
pads, replacing the pads interrupts the wafer manufacturing process and 
reduces efficiency and yield. Moreover, this necessitates conditioning the 
pads prior to use, e.g., by planarizing the pads prior to use. 
To prevent particles from being embedded in the polishing pad, an 
ultrasonic transducer has been placed in the slurry to vibrate or agitate 
the slurry. The ultrasonic transducer is either suspended in the slurry, 
or rests on the polishing pad. Alternatively, the ultrasonic transducer 
has been placed in contact with the wafer being polished, or placed under 
a platen disk onto which the polishing pad is attached, on a side of the 
platen that is opposite the pad polishing side. However, conventional 
devices using an ultrasonic transducer do not provide flexibility in 
providing directed vibration to specifically desired regions of the pad. 
This causes regional defects on the polished wafer surface and requires 
frequent changing of the polishing pad. 
In addition to the slurry vibration, a large portion of the CMP device is 
also vibrated, causing undue wear and noise that degrade performance of 
the CMP device. This results in slow polishing rates and defective wafer 
polishing. Accordingly, there is a need for a versatile CMP device that 
variably controls prevention of particles from being embedding in the 
polishing pad at specific desired locations, and reduces vibration of 
portions of the CMP device that are adversely affected by undesired 
vibration. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a device and method for 
preventing settlement of particles on a chemical-mechanical polishing pad 
used in chemical-mechanical polishing (CMP) that eliminate the problems of 
conventional CMP devices and methods. 
Another object of the present invention is to lengthen the useful life of a 
polishing pad used in CMP devices. 
Yet another object of the present invention is to reduce defects in the 
polished surface of the wafer. 
A further object of the present invention is to maintain a fast and uniform 
polish rate of wafer surfaces. 
A still further object of the present invention is to direct controlled 
vibration at desired locations of the polishing pad, while reducing 
vibration at other portions of the CMP device. 
These and other objects of the present invention are achieved by a device, 
located between a polishing pad and a platen of a chemical-mechanical 
polishing apparatus, for preventing settlement of particles on the 
polishing pad, comprising a first layer formed on the platen for 
interfacing therewith, also referred to as a platen interface layer; a 
second layer formed on the first layer having at least one vibration 
module embedded therein, also referred to as an active layer; and a third 
layer formed on the second layer facing the pad and having an energy 
transport medium, also referred to as an energy transport layer. 
The active layer selectively vibrates regions of the energy transport 
layer, and the energy transport layer selectively transfers the vibration 
to the pad located over the energy transport layer. 
The vibration module provides accentuated vibration to a side facing the 
energy transport layer, and attenuated vibration to remaining sides 
thereof. This is achieved, for example, by surrounding the vibration 
module by a damping material on all sides except a side contacting the 
energy transport layer. Illustratively, the vibration module is a 
piezoelectric or a mechanical actuator. Alternatively, the vibration 
module is a megasonic or an ultrasonic transducer. Power and signal lines 
are embedded in the platen interface layer and are connected to the 
vibration module. 
The energy transport medium is configured to provide selective energy 
transfer from the active layer to the polishing pad. To provide a 
selective energy transfer, the energy transfer characteristic of the 
energy transport medium varies over different regions thereof. For 
example, the density or thickness of the energy transport medium varies 
over different regions thereof. Illustratively, the energy transport 
medium is a mesh, such as a metal wire mesh, which may be embedded in bulk 
material. 
The energy transfer characteristic of the energy transport medium may also 
be selectively varied over different regions thereof by varying the weave 
of the embedded mesh, and the thickness or density of the wire. 
In one embodiment, the three layers are removably formed over each other. 
In another embodiment, the platen interface layer is affixed to the 
platen, for example, by an adhesive. The three layers are formed of the 
same bulk material, which may be a polymer, for example. The bulk material 
may be the same as that of the polishing pad. The bulk material of the 
active layer has a hole formed therein for receiving the vibration module. 
Another embodiment includes a method for preventing settlement of particles 
on a polishing pad of a chemical-mechanical polishing apparatus comprising 
the steps: of selectively vibrating at least one vibration module embedded 
in an active layer; and selectively transferring the vibration through an 
energy transport layer formed on the active layer to the polishing pad 
located over the energy transport layer. 
A further embodiment is a method for forming a device for preventing 
settlement of particles on a polishing pad of a chemical-mechanical 
polishing apparatus comprising the steps of: forming a platen interface 
layer for interfacing with a platen of the chemical-mechanical polishing 
apparatus; forming an active layer on the platen interface layer; and 
forming an energy transport layer on the active layer facing the pad. The 
active layer forming step forms the active layer to selectively vibrate 
regions of the energy transport layer, and the energy transport layer 
forming step forms the energy transport layer to selectively transfer the 
vibration to the polishing pad located over the energy transport layer. 
For example, the energy transport layer forming step forms the energy 
transport layer with an energy transfer characteristic that varies over 
different regions of the energy transport layer. The active layer forming 
step includes the steps of forming a bulk material; forming a hole in the 
bulk material; forming a vibration damping material in the hole; and 
placing a vibration module in the vibration damping material so that a top 
surface of the vibration module directs vibration energy to the energy 
transport layer, and sides and bottom of the vibration module direct 
vibration energy to the vibration damping material. 
The inventive device and method, where selected regions of the polishing 
pad are vibrated by a individually controlled vibration modules, prevent 
settlement of particle on the polishing pad, lengthen the useful life 
thereof, and reduce the need and frequency to condition the polishing pad, 
e.g., prior to use. Furthermore, the inventive device and method reduce 
defects in the polished surface of the wafer. In addition, the inventive 
device and method allow uniform polishing of the wafer at a high rate, 
thus improving yield. 
Moreover, the inventive device and method reduce CMP device wear by 
reducing undesired vibration of portions thereof, while directing 
controlled and selective vibration to the polishing pad and slurry.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a top view of a device 10 according to the present invention, 
where bulk material that contains the various elements of the device 10 is 
omitted. FIG. 1 shows a mesh 15, such as a wire frame mesh, formed over 
vibration modules 20. Illustratively, the wire mesh 15 and vibration 
modules 20 are embedded in bulk material 155, 160, respectively, shown in 
FIG. 3. Eight vibration modules 20 are shown in FIG. 1. However, any 
number of modules 20 including only one module may be used, depending on 
the amount and location of the desired vibration to be delivered to a 
polishing pad 70 (FIG. 2) placed over the device 10. In addition, each 
vibration module 20 may be controlled separately to selectively provide a 
desired level of vibration, or no vibration, to particle regions of the 
device 10. 
Each vibration modules 20 is surrounded by a vibration damping material 25 
on all sides except a top side facing the wire mesh 15, as is more clearly 
shown in FIGS. 2 and 3. This accentuates and directs vibration toward the 
wire mesh 15, and dampens vibration coming from the side and bottom 
portions of each vibration modules 20. 
FIG. 2 shows a cross section of the device 10 along the line 2-2' of FIG. 
1, where the device 10 is mounted on a chemical-mechanical polishing (CMP) 
apparatus 50, between a platen 55 and a polishing pad 70 of the CMP 
apparatus 50. The device 10 is mounted on the platen 55, which is 
rotatable and has a shaft 60 that is connected to a motor (not shown). The 
polishing pad 70 is mounted on the device 10. As the shaft 60 is rotated, 
as indicated by arrow 75, the platen 55, device 10 and pad 70 also rotate. 
A slurry 80 is introduced over the pad 70. The slurry 80 is contained 
within a raised rim 85 of the platen 55, for example. A wafer 90, attached 
to a carrier 95, is pressed against the rotating polishing pad 70 for 
planarizing a wafer surface 100 facing the pad 70. The wafer 90 may also 
be rotated by a motor (not shown) connected to the carrier 95. 
Power and signal lines 105 connect the vibration modules 20 to a controller 
110 for individually, collectively or selectively controlling and 
vibrating the vibration modules 20. Illustratively, the lines 105 have 
contact leads 115 embedded in an interface layer 120 of the device 10 for 
interfacing with the vibration modules 20. In addition, the lines 105 also 
have shaft contact leads 125, that are located on the shaft 60, for 
interfacing with the controller 110. 
In operation, the device 10 is attached to the platen 55 and is rotated by 
rotating the shaft 60 of the platen 55 with a motor (not shown). The 
controller 110 sends appropriate signals to the vibration modules 20 to 
selectively vibrate individual modules at desired frequencies and 
intensities. The frequency and/or intensity of each module 20 may be 
controlled collectively or individually. In the case where each module 20 
is individually controlled, different amount of vibration is provided over 
different regions. For example, one or many modules 20 may be vibrated at 
a different intensities or frequencies than other modules. 
Depending on the energy transfer characteristics of the wire mesh, which 
may also be varied over different regions of the device 10, a desired 
vibration is transferred to particular regions of the polishing pad 70. 
The vibrating pad 70 also vibrates the slurry 80, keeps particles 
suspended in the slurry, and prevents settlement thereof on the pad 70, or 
within pores of the pad 70. This results in fast and proper polishing of 
the wafer surface 100 which is pressed against the polishing pad 70. 
FIG. 3 shows a portion of the cross section of the device 10 in greater 
detail. In addition to the first layer 120, the device 10 also comprises 
second and third layers 130, 140. The first layer 120, also referred to as 
a platen interface layer, interfaces with the platen 55 (FIG. 2), and is 
formed of a bulk material 145, such as a polymer or other suitable casting 
material. The power and signal lines 105 are embedded in the polymer of 
the interface layer 120 and electrically connect the vibration modules 20 
to the contact leads 115 that are also embedded in the interface layer 
120. The contact leads 115 interface with the lines in the platen 55. 
The second layer 130, also referred to as an active layer, is formed on the 
interface layer 120 and contains embedded therein at least one vibration 
module 20. Illustratively, the vibration modules 20 are piezoelectric or 
mechanical actuators, such as those that are commercially available from 
Active Control eXperts, Inc., (ACX) of Cambridge, Mass. Alternatively the 
vibration modules 20 are conventional megasonic, ultrasonic or other 
suitable frequency transducers, such as those that are commonly used in 
the semiconductor industry for wafer cleaning devices. Different 
frequencies are used depending on process conditions. 
As previously described in connection with FIG. 1, each vibration module 20 
is enveloped within a cell having the vibration damping material 25 that 
surround the vibration module 20 on all sides except the top side 150 that 
faces the third layer 140. This top side 150 of the vibration module 20 
may contact the wire mesh 15 embedded in the third layer 140. 
The vibration damping material 25 ensures that no vibrations are 
transmitted to the platen 55 (FIG. 2), and thereby, to the physical 
components of the tooling or the CMP apparatus 50 (FIG. 2). Without the 
vibration damping material 25, undue vibration of the tooling causes 
accelerated wear and run-out of the tooling component operating 
specification. Furthermore, the undue vibration causes additional and 
unacceptable noise levels. 
Each vibration module 20 is embedded in a bulk material 155, which may be 
the same bulk material 160 that contains the wire mesh 15. Illustratively, 
all three bulk materials 145, 155, 160 of the first to third layers 120, 
130, 140, are of the same type, which may be the same type as the bulk 
material of the polishing pad 70 (FIG. 2). 
The third layer 140, also referred to as an energy transport layer, is 
formed on the active layer 130 and has an energy transport medium embedded 
therein. Illustratively, the energy transport medium is the wire mesh 15. 
The wire mesh 15 may be made from a wide variety of material that transfer 
or conduct vibration energy. A high density metal is preferable for its 
high workability and durability. 
The physical attributes of the wire mesh 15, such as wire thickness, 
density and the weave of the wire mesh, may be tailored to provide various 
effects as desired, depending on polishing pad type and thickness, for 
example. Illustratively, a thicker wire having a greater cross sectional 
area may be used for hard polishing pads than wire used for soft polishing 
pads. In addition, the density of the wire material affects the rate at 
which the vibration energy is distributed throughout the wire and 
transferred to the polishing pad 70 (FIG. 2). These and other physical 
attributes of the wire mesh are tailored for optimum performance to 
individual circumstances. 
One or more of the physical attributes or characteristics of the wire mesh 
15 or the energy transport layer 140 may be varied over different regions 
thereof, to provide selective energy transfer from the active layer 130 of 
the device 10 to the polishing pad 70 (FIG. 2). For example, if buildup of 
slurry particles, agglomerates or residuals is found to be greatest at the 
perimeter of the polishing pad 70, then the weave of the wire mesh 15 at 
regions near the periphery of device 10 is tighter than the weave at 
regions of the mesh that are away from the device periphery. 
Alternatively, or in addition to, the density or thickness of the wire 
near the device periphery is made different from the wire 
density/thickness located away from the device periphery to produce a 
correspondingly greater amount of vibration near the device periphery. 
The three layers 120, 130, 140 may be an integral unit. Alternatively, each 
of the three layers 120, 130, 140 are separate components that are placed 
over each other. This is desirable as it allows flexibility in exchanging 
the layers, in particular, exchanging the active and energy transport 
layers 130, 140, with similar layers having different desired 
characteristics. For example, different active layers 130 may be used in 
different condition, where the particular active layer 130 used has a 
desired number of vibration modules at desired locations. Similarly, the 
energy transport layer 140 may be exchanged with another energy transport 
layer having a desired thickness, density and weave of the wire mesh 15. 
Illustratively, the interface layer 120 is affixed to the platen 55 on a 
semi-permanent basis, e.g., with an adhesive. This prevents the interface 
layer 120 from slipping or moving during polishing, when the platen 55 is 
rotated. The top two layers, i.e., the active and energy transport layers 
130, 140 are removably affixed to each other, and the active layer 130 is 
removably affixed to the interface layer. This allows replacing thereof 
with other active and energy transport layers having desired 
characteristics, as described. In addition, the active layer 130 is 
removed for servicing or replacing the actuators or transducers of the 
vibration modules 20. 
The energy interface layer 140 may be formed by placing the wire mesh 15 in 
a mold or form, and the polymer poured to fill the form. The active layer 
130 is also formed in a similar fashion. Alternatively, the active layer 
130 is formed by first pouring the polymer in a form. After the poured 
polymer has cured, one or as many holes as desired are cut out, e.g., 
drilled, at desired locations. Next, the damping material 25, the 
vibration modules 20 and necessary wiring are placed in the holes. The 
size of the holes may be varied depending on the size of the damping 
material 25 and the vibration modules 20. 
Referring to FIGS. 2 and 3, another embodiment includes a method for 
preventing settlement of particles on the polishing pad 70 of the 
chemical-mechanical polishing apparatus 50. This method comprises the 
steps of selectively vibrating at least one vibration module embedded in 
the active layer 130; and selectively transferring the vibration, through 
the energy transport layer 140 formed on the active layer 130, to the 
polishing pad 70 located over the energy transport layer 140. 
A further embodiment is a method for forming the device 10 that prevents 
settlement of particles on the polishing pad 70. This method comprises the 
steps of forming a platen interface layer 120 for interfacing with the 
platen 55 of the chemical-mechanical polishing apparatus 50; forming the 
active layer 130 on the platen interface layer 120; and forming the energy 
transport layer 140 on the active layer facing the pad 70. The active 
layer forming step forms the active layer 130 to selectively vibrate 
regions of the energy transport layer 130, and the energy transport layer 
forming step forms the energy transport layer 140 to selectively transfer 
the vibration to the polishing pad 70 located over the energy transport 
layer 130. 
For example, the energy transport layer forming step forms the energy 
transport layer 140 with an energy transfer characteristic that varies 
over different regions thereof. The active layer forming step includes the 
steps of forming a bulk material; forming a hole in the bulk material; 
forming a vibration damping material 25 in the hole; and placing a 
vibration module 20 in the vibration damping material 25 so that a top 
surface 150 of the vibration module 20 directs vibration energy to the 
energy transport layer 140, and sides and bottom of the vibration module 
20 direct vibration energy to the vibration damping material 25. 
While the invention has been particularly shown and described with respect 
to illustrative and preformed embodiments thereof, it will be understood 
by those skilled in the art that the foregoing and other changes in form 
and details may be made therein without departing from the spirit and 
scope of the invention which should be linked only by the scope of the 
appended claims.