Abrading – Work holder – Vacuum
Reexamination Certificate
2000-12-01
2002-12-31
Eley, Timothy V. (Department: 3723)
Abrading
Work holder
Vacuum
C451S289000, C451S397000, C451S398000
Reexamination Certificate
active
06500059
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for mounting a wafer in a polishing machine and more particularly, relates to an apparatus and a method for mounting a wafer to a wafer mounting plate in a polishing machine capable of preventing contamination to a vacuum line upon the occurrence of a wafer breakage.
BACKGROUND OF THE INVENTION
Apparatus for polishing thin, flat semi-conductor wafers is well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semiconductor 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 schematic of a typical CMP apparatus is shown in
FIGS. 1A and 1B
. The apparatus
10
for chemical mechanical polishing consists of a rotating wafer holder
14
that holds the wafer
10
, the appropriate slurry
24
, and a polishing pad
12
which is normally mounted to a rotating table
26
by adhesive means. The polishing pad
12
is applied to the wafer surface
22
at a specific to pressure. The chemical mechanical polishing method can be used to provide a planar surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. CMP polishing results from a combination of chemical and mechanical effects. 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 altered layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing a metal oxide may be formed and removed repeatedly.
A polishing pad is typically constructed in two layers overlying a platen with the resilient layer as the outer layer of the pad. The layers are typically made of polyurethane and may include a filler for controlling the dimensional stability of the layers. The polishing pad is usually several times the diameter of a wafer and the wafer is kept off-center on the pad to prevent polishing a non-planar surface onto the wafer. The wafer is also rotated to prevent polishing a taper into the wafer. Although the axis of rotation of the wafer and the axis of rotation of the pad are not collinear, the axes must be parallel. Polishing heads of the type described above used in the CMP process are shown in U.S. Pat. No. 4,141,180 to Gill, Jr., et al.; U.S. Pat. No. 5,205,082 to Shendon et al; and, U.S. Pat. No. 5,643,061 to Jackson, et al. It is known in the art that uniformity in wafer polishing is a function of pressure, velocity and the concentration of chemicals. Edge exclusion is caused, in part, by non-uniform pressure on a wafer. The problem is reduced somewhat through the use of a retaining ring which engages the polishing pad, as shown in the Shendon et al patent.
Referring now to
FIG. 1C
, wherein an improved CMP head, sometimes referred to as a Titan® head is shown. The Titan® head differs from conventional CMP heads in two major respects. First, the Titan® head employs a compliant wafer carrier and second, it utilizes a mechanical linkage (not shown) to constrain tilting of the head, thereby maintaining planarity relative to a polishing pad
12
, which in turn allows the head to achieve more uniform flatness of the wafer during polishing. The wafer
10
has one entire face thereof engaged by a flexible membrane
16
, which biases the opposite face of the wafer
10
into face-to-face engagement with the polishing pad
12
. The polishing head and/or pad
12
are moved relative to each other, in a motion to effect polishing of the wafer
10
. The polishing head includes an outer retaining ring
14
surrounding the membrane
16
, which also engages the polishing pad
12
and functions to hold the head in a steady, desired position during the polishing process. As shown in
FIG. 1C
, both the retaining ring
14
and the membrane
16
are urged downwardly toward the polishing pad
12
by a linear force indicated by the numeral
18
which is effected through a pneumatic system.
A more detailed cross-sectional view of the improved CMP
20
is shown in FIG.
1
D. The CMP head
20
further includes a wafer mounting plate
30
, a bumper ring
32
, an inner tube
34
for supplying the pneumatic force
18
(shown in
FIG. 1C
) and a base plate
36
. The bumper ring
32
is utilized between the wafer
10
and the mounting plate
30
for preventing edge defect by raising the edges of wafer
10
when pressed down onto a polishing pad (not shown). Without the use of the bumper ring
32
, the edge portion of the wafer
10
is not polished to the same degree as the center portion of the wafer
10
and therefore, the bumper ring
32
compensates for the poor polishing along the edges of wafer
10
by providing a support behind the wafer. Both the bumper ring
32
and the wafer mounting plate
30
are normally fabricated of a rigid material such as plastic or ceramic. The wafer mounting plate
30
is further provided with a plurality of through holes
40
, as shown in FIG.
2
A.
FIGS. 2A and 2B
illustrate a plane view and a side view, respectively of the wafer mounting plate
30
shown in FIG.
1
D. The plurality of through holes
40
, or apertures, are provided for fluid communication between an upper surface
38
and a lower surface
42
of the wafer mounting plate
30
which enables a vacuum to be exerted on the wafer
10
when positioned thereunder. It should be noted that the flexible membrane member
16
, shown in
FIG. 1D
, is not shown in
FIGS. 2A and 2B
for simplicity reasons. The flexible membrane member
16
may be fabricated of a breathable material, or a material that is perforated such that vacuum can be pulled on the membrane member for acting on the wafer surface. The flexible member
16
may be advantageously fabricated of an elastomeric material, such as a silicon rubber, a polyurethane rubber or any other high temperature and chemical resistant rubber that does not cause particle contamination.
In the configuration shown in
FIGS. 2A
,
2
B and
1
D, the wafer mounting plate
30
when used to mount wafer
10
frequently encounters wafer breakage problem since both the mounting plate
30
and the bumper ring
32
are fabricated of a rigid material which leads to a stress concentration on the wafer. Wafer breakage o
Chang Yi-Sen
Tsai Hsien-Shu
Eley Timothy V.
Grant Alvin J.
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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