Abrading – Precision device or process - or with condition responsive... – Controlling temperature
Reexamination Certificate
1999-03-31
2001-11-13
Ostrager, Allen (Department: 3725)
Abrading
Precision device or process - or with condition responsive...
Controlling temperature
C451S005000, C451S053000, C451S287000
Reexamination Certificate
active
06315635
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and an apparatus for controlling slurry temperature that is used in a polishing process for a semiconductor substrate and more particularly, relates to a method and an apparatus for controlling slurry temperature used in a chemical mechanical polishing process by detecting temperatures of the dispensed slurry and the polishing pad and compensate the temperature difference by heating the slurry supply such that the polishing uniformity across the substrate can be improved.
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 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 semi-conductor wafer during the fabrication of semi-conductor 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 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. Nos. 4,141,180 to Gill, Jr., et al.; 5,205,082 to Shendon et al; and, 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 which differs from conventional CMP heads in two major respects is shown. 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.
In the polishing operation shown in the enlarged cross-sectional view of
FIG. 1B
, the slurry solution
24
must be forced into an interface between the wafer
10
and the polishing pad
12
in order for the chemical reaction and the mechanical removal process to operate efficiently. The slurry solution
24
(also shown in
FIG. 1A
) is dispensed from a dispensing nozzle (shown in
FIG. 2
) onto the polishing pad
12
. In most commercial CMP apparatus, the slurry solution
24
is stored in a reservoir and delivered to the dispensing nozzle through a conduit. The slurry solution stored in the reservoir and in the delivering conduit is not provided with a temperature control device. The slurry solution
24
is normally applied to the polishing pad
12
at the same temperature as the chamber temperature in the CMP apparatus, i.e., approximately at room temperature.
During the polishing process, a significant amount of frictional heat is generated between the top surface of the polishing pad and the surface of the substrate that is being polished. The interface formed between the wafer
10
and the polishing pad
12
(shown in
FIG. 1B
) and the slurry solution
24
trapped therein are therefore heated to a significant higher temperature, i.e., up to 50° C., or between about 40° C. and about 50° C., than the temperature of the slurry solution
24
on the edge of the wafer
10
. This creates a serious problem in achieving polishing uniformity across the surface of the wafer
10
. The room temperature slurry solution dispensed around the edge of the wafer
10
during the polishing process reduces the temperature of the wafer at the edge portion. This leads to a wafer edge polishing rate drop and a poor polishing uniformity.
It is therefore an object of the present invention to provide a method and apparatus for providing slurry temperature control in a polishing process that is not previously available in conventional polishing machines.
It is another object of the present invention to provide a method for slurry temperature control in a polishing process that can be readily adapted in a chemical mecha
Hong William
Ostrager Allen
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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