Slurry residence time enhancement system

Description

FIELD OF THE INVENTION

The present invention relates to chemical mechanical polishers used for polishing semiconductor wafers in the semiconductor fabrication industry. More particularly, the present invention relates to a slurry conservation system for reducing waste of polishing slurry by increasing the slurry utilization rate in a chemical mechanical polishing (CMP) apparatus.

BACKGROUND OF THE INVENTION

Apparatus for polishing thin, flat semiconductor wafers are 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 deionized water.

In current CMP apparatuses, about 90% of the polishing slurry is not utilized to polish wafers, and therefore, is wasted. Accordingly, a slurry residence time enhancement system is needed for reducing waste of polishing slurry by increasing the slurry utilization rate in a chemical mechanical polishing (CMP) apparatus.

SUMMARY OF THE INVENTION

The present invention is generally directed to a slurry residence time enhancement system for a chemical mechanical polishing apparatus having a base, a platen on the base, a polishing pad on the platen and a polishing head over the polishing pad. The system includes at least one slurry distribution unit having a slurry distribution member for positioning on the polishing pad. In operation of the CMP apparatus, the slurry distribution member redirects polishing slurry on the polishing pad to the polishing head. The system may alternatively or additionally include a rim for upward extension from the base and a seal for insertion between the platen and the polishing pad adjacent to the rim.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an illustrative embodiment of the slurry residence time enhancement system according to the present invention;

FIG. 2 is a perspective view of a slurry distributor of the slurry residence time enhancement system;

FIGS. 3A-3D are schematic views of a chemical mechanical polishing (CMP) apparatus, in implementation of the slurry residence time enhancement system according to the present invention; and

FIG. 4 is a perspective sectional view of a CMP apparatus, illustrating a seal between the polishing pad and rim of the apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, an illustrative embodiment of the slurry residence time enhancement system, hereinafter system, according to the present invention is generally indicated by reference numeral 10. The system 10 is shown in conjunction with a rotary-type chemical mechanical polishing (CMP) apparatus 12, which may be conventional. The CMP apparatus 12 includes a circular base 14. A platen 17 is mounted for rotation on the base 14, and a motor (not shown) which is typically provided in the base 14 engages and rotates the platen 17 in operation of the CMP apparatus 10. A polishing pad 18 is supported by the platen 17. A polishing head 24 is supported over the polishing pad 18 for holding and pressing a wafer (not shown) against the polishing pad 18 as the polishing pad 18 is rotated by the platen 17. A slurry delivery arm 26 (FIGS. 3A-3D), having a pair of nozzles 26a, is extendible over the polishing pad 18 to dispense a polishing slurry 28 onto the polishing pad 18 during polishing of a wafer (not shown) mounted on the bottom of the polishing head 24.

As shown in FIG. 1, the slurry residence time enhancement system 10 includes at least one, and preferably, a pair of slurry distribution units 30 which are provided in conjunction with the CMP apparatus 12. As shown in FIG. 2, each slurry distribution unit 30 typically includes a base 32 from which extends a support conduit 34. An arm tee 36 includes a vertical segment 38 which is inserted and secured in the support conduit 34 typically using multiple fasteners and a horizontal segment 40 which extends generally perpendicularly from the vertical segment 38. A support arm 42 extends generally horizontally from the horizontal segment 40.

A slurry distribution member 48 is mounted on the support arm 42. Accordingly, a sleeve 44 is provided on the extending end of the support arm 42, and an insert 46, to which is mounted the slurry distribution member 48, extends into the sleeve 44. The insert 46 is mounted in the sleeve 44 typically using multiple fasteners (not shown) or other suitable technique. The slurry distribution member 48 typically includes a generally elongated, arcuate or semicircular upper segment 52, from which the insert 46 extends, and a generally elongated, arcuate or semicircular lower segment 50 which is secured to the upper segment 52 typically using multiple fasteners 54 or alternative technique. A tapered end portion 51 terminates each end of the lower segment 51. Each slurry distribution member 48 includes a concave side 49a and a convex side 49b and typically has a curvature equal to that of a circle having a diameter of about 12 inches.

As shown in FIG. 1, the slurry residence time enhancement system 10 includes at least one, and preferably, a pair of the slurry distribution units 30, each of which is positioned adjacent to the base 14 of the CMP apparatus 12. The support arm 42 extends over the rim 16 and the polishing pad 18 of the CMP apparatus 12. The slurry distribution member 48, suspended from the support arm 42, contacts the polishing pad 18. As shown in FIG. 3A, the concave side 49a of each slurry distribution member 48 is oriented against the direction of rotation, and the convex side 49b of each slurry distribution member 48 is oriented with the direction of rotation, of the polishing pad 18 during polishing of a wafer on the polishing polishing head 24. As shown in FIG. 4, the slurry residence time enhancement system 10 may further include a rim 16 which extends upwardly from the base 14, around the circumference of the base 14, and a liquid-tight seal 20 which is provided between the platen 17 and the polishing pad 18, adjacent to the rim 16. Preferably, the rim 16 has a height of at least about 6 mm and the seal 20 has a width of at least about 0.5 mm and may be offset with respect to the base 14, as further shown in FIG. 4.

Referring next to FIGS. 3A-3D, in typical use of the slurry residence time enhancement system 10, the CMP apparatus 12 is operated typically in the conventional fashion. Accordingly, a wafer (not shown) is mounted on the bottom surface of the polishing head 24. As the polishing slurry 28 is dispensed from the nozzles 26a of the slurry dispensing arm 26, onto the polishing pad 18, as shown in FIG. 3A, the polishing pad 18 and the polishing head 24 are rotated typically in the counterclockwise direction, as indicated by the arrows.

As it rotates, the polishing head 24 presses the wafer against the polishing pad 18. Simultaneously, as shown in FIG. 3B, the polishing slurry 28 on the polishing pad 18 contacts the wafer on the polishing head 24 and facilitates polishing of the wafer. The polishing slurry 28 may be continually dispensed from the slurry delivery arm 26 to ensure adequate contact of the polishing slurry with the rotating wafer throughout the chemical mechanical polishing operation. Consequently, were it not for the presence of the slurry distribution members 48, the polishing slurry 28 would have a tendency to gradually accumulate at the edge of the polishing pad 18, as shown in FIG. 3C, due to centrifugal force. However, the polishing pad 18 rotates the polishing slurry 28 into contact with the concave surface 49a of each slurry distribution member 48, causing the polishing slurry 28 to accumulate in the concave surface 49a of the slurry distribution member 48, as shown in FIG. 3D. Furthermore, the slurry distribution members 48 redistribute or redirect the accumulated polishing slurry 28 to the polishing head 24 and ensure continued polishing of the wafer without requiring the dispensing of additional polishing slurry 28 from the slurry dispensing arm 26 and onto the polishing pad 18. This increases the utilization rate of the polishing slurry 28 by increasing the residence time of the polishing slurry 28 on the polishing pad 18, thereby preventing wasting of the polishing slurry 28 throughout the chemical mechanical polishing operation. Also, the seal 20 prevents the polishing slurry 28 from rotating off of the platen 17 due to the centrifugal force acting on the polishing slurry 28 as it is rotated on the polishing pad 18.

While the preferred embodiments of the invention have been described, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.