Abrading – Accessory – Guard or housing
Reexamination Certificate
2001-03-22
2001-11-13
Banks, Derris H. (Department: 3723)
Abrading
Accessory
Guard or housing
C451S443000
Reexamination Certificate
active
06315651
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a polishing pad assembly for a chemical mechanical polishing apparatus and more particularly, relates to a cover for a polishing pad condition arm in a chemical mechanical polishing apparatus that can be mounted and dismounted expeditiously without screw attachments.
BACKGROUND OF THE INVENTION
Apparatus for polishing thin, flat semi-conductor wafers is well not in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is “planarized” or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A perspective view of a typical CMP apparatus is shown in FIG.
1
A. The CMP apparatus
10
consists of a controlled mini-environment
12
and a control panel section
14
. In the controlled mini-environment
12
, typically four spindles
16
,
18
,
20
, and
22
are provided (the fourth spindle
22
is not shown in
FIG. 1
a
) which are mounted on a cross-head
24
. On the bottom of each spindle, for instance, under the spindle
16
, a polishing head
26
is mounted and rotated by a motor (not shown). A substrate such as a wafer is mounted on the polishing head
26
with the surface to be polished mounted in a face-down position (not shown). During a polishing operation, the polishing head
26
is moved longitudinally along the spindle
16
in a linear motion across the surface of a polishing pad
28
. As shown in
FIG. 1A
, the polishing pad
28
is mounted on a polishing disc
30
rotated by a motor (not shown) in a direction opposite to the rotational direction of the polishing head
26
.
Also shown in
FIG. 1
a
is a conditioner arm
32
which is equipped with a rotating conditioner disc
34
. The conditioner arm
332
pivots on its base
36
for conditioning the polishing pad
38
for the in-situ conditioning of the pad during polishing. While three stations each equipped with a polishing pad
28
,
38
and
40
are shown, the fourth station is a head clean load/unload (HCLU) station utilized for the loading and unloading of wafers into and out of the polishing head. After a wafer is mounted into a polishing head in the fourth head cleaning load/unload station, the cross head
24
rotates 90° clockwise to move the wafer just loaded into a polishing position, i.e., over the polishing pad
28
. Simultaneously, a polished wafer mounted on spindle
20
is moved into the head clean load/unload station for unloading.
A cross-sectional view of a polishing station
42
is shown in
FIGS. 1B and 1C
. As shown in
FIG. 1B
, a rotating polishing head
26
which holds a wafer
44
is pressed onto an oppositely rotating polishing pad
28
mounted on a polishing disc
30
by adhesive means. The polishing pad
28
is pressed against the wafer surface
46
at a predetermined pressure. During polishing, a slurry
48
is dispensed in droplets onto the surface of the polishing pad
28
to effectuate the chemical mechanical removal of materials from the wafer surface
46
.
An enlarged cross-sectional representation of the polishing action which results form a combination of chemical and mechanical effects is shown in FIG.
1
C. The CMP method can be used to provide a planner surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.
During a CMP process, a large volume of a slurry composition is dispensed. The slurry composition and the pressure applied between the wafer surface and the polishing pad determine the rate of polishing or material removal from the wafer surface. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that hag a pH of 11 than with a slurry that has a pH of 7. The hardness of the polishing particles contained in the slurry composition should be about the same as the hardness of the film to be removed to avoid damaging the film. A slurry composition typically consists of an abrasive component, i.e, hard particles and components that chemically react with the surface of the substrate. For instance, a typical oxide polishing slurry composition consists of a colloidal suspension of oxide particles with an average size of 30 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 120 nm/min can he achieved by using this slurry composition. Other abrasive components such as ceria suspensions may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e, larger than 500 nm/min. While ceria particles in the slurry composition remove silicon oxide at a higher rate than do silica, silica is still preferred because smoother surfaces can be produced. Other abrasive components, such as alumina (Al
3
O
2
)may also be used in the slurry composition.
The polishing pad
28
is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after about 12 hours of usage. Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard and stiffer pads are generally used to achieve planarity. Softer pads are generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.
A problem frequently encountered in the use of polishing pads in oxide planarization is the rapid deterioration in oxide polishing rates with successive wafers. The cause for the deterioration is known as “pad glazing” wherein the surface of a polishing pad becomes smooth such that the pad no longer holds slurry in-between the fibers. This is a physical phenomenon on the pad surface not caused by any chemical reacti
Banks Derris H.
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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