Method and system for slurry usage reduction in chemical...

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Reexamination Certificate

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C451S036000, C451S041000, C451S285000, C451S446000

Reexamination Certificate

active

06769959

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to semiconductor fabrication methods and systems. The present invention also generally relates to chemical mechanical polishing devices and techniques thereof. The present invention additionally relates to slurry delivery methods and systems. The present invention also relates to methods and systems for reducing slurry usage during chemical mechanical polishing operations.
BACKGROUND OF THE INVENTION
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively more non-planar. This occurs because the distance between the outer surface and the underlying substrate is greatest in regions of the substrate where the least etching has occurred, and least in regions where the greatest etching has occurred. With a single patterned underlying layer, this non-planar surface comprises a series of peaks and valleys wherein the distance between the highest peak and the lowest valley may be the order of 7000 to 10,000 Angstroms. With multiple patterned underlying layers, the height difference between the peaks and valleys becomes even more severe, and can reach several microns.
This non-planar outer surface presents a problem for the integrated circuit manufacturer. If the outer surface is non-planar, then photo lithographic techniques used to pattern photoresist layers might not be suitable, as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize this substrate surface to provide a planar layer surface. Planarization, in effect, polishes away a non-planar, outer surface, whether conductive, semiconductive, or insulative, to form a relatively flat, smooth surface. Following planarization, additional layers may be deposited on the outer surface to form interconnect lines between features, or the outer surface may be etched to form vias to lower features.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. In addition, the carrier head may rotate to provide additional motion between the substrate and polishing surface. Further, a polishing slurry, including an abrasive and at least one chemically-reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
Important factors in the chemical mechanical polishing process are: the finish (roughness) and flatness (lack of large scale topography) of the substrate surface, and the polishing rate. Inadequate flatness and finish can produce substrate defects. The polishing rate sets the time needed to polish a layer. Thus, it sets the maximum throughput of the polishing apparatus.
Each polishing pad provides a surface, which, in combination with the specific slurry mixture, can provide specific polishing characteristics. Thus, for any material being polished, the pad and slurry combination is theoretically capable of providing a specified finish and flatness on the polished surface. The pad and slurry combination can provide this finish and flatness in a specified polishing time. Additional factors, such as the relative speed between the substrate and pad, and the force pressing the substrate against the pad, affect the polishing rate, finish and flatness.
In some chemical mechanical polishing systems, the slurry flows continuously onto a flat polish table. As the table rotates, slurry is flung off the edge and carried away by a drain. This is wasteful of slurry material, leads to nonuniformity of the slurry at different locations, and splatters the abrasive slurry into surrounding machinery. Some prior art chemical mechanical polishing devices or systems includes a raised wall of rectangular cross-section surrounds the table's edge. Such a wall or containment device must form a liquid-tight seal around the entire periphery of the polish table. Yet, at the same time, the wall must be easily removable in order to clean the polish table periodically, and must be quickly reinstallable on the table for setting up the next run with a new batch of slurry.
FIG. 1
depicts a prior art diagram
10
illustrating the manner in which particle size increases the number of particles contacting a surface during chemical mechanical polishing operations. As depicted in
FIG. 1
, at high particle concentrations, when the particle fill factor is near unity, decreasing particle size increases the number of particles contacting the surface.
FIG. 2
, on the other hand, illustrates a prior art diagram
20
illustrating the manner in which decreasing particle size does not increase the number of particles contacting a surface during chemical mechanical polishing operations. As illustrated in diagram
20
of
FIG. 2
, at low abrasive concentrations, when the particle fill factor is much lass than unity, decreasing particle size does not increase the number of particles contacting the surface.
FIG. 3
depicts a block diagram
30
of a prior art wafer, slurry, and pad configuration utilized in chemical mechanical polishing operations. Diagram
30
illustrates a wafer
32
, a slurry
34
, and a polishing pad
36
. Thus, based on
FIGS. 1
to
3
, it can be appreciated that in prior art slurry delivery systems, a low continuous slurry flow rate affects the total removal rate. Additionally, a low continuous slurry flow rate induces high noise and can damage parts.
FIG. 4
illustrates a prior dam and polishing arrangement
40
. The configuration illustrated in
FIG. 4
is a type of device utilized to implement the apparatus disclosed in U.S. Pat. No. 5,299,393 to Chandler, et al, “Slurry Containment Device for Polishing Semiconductor Wafers.” Chandler et al generally claims a containment device for the chemical-mechanical polishing of semiconductor wafers and similar workpieces. The device attempts to prevent the leakage of liquid slurry from a polish table. The device can be removed for cleaning and then reinstalled. The device contains a circular continuous band shaped to fit a polish table having a substantially circular periphery. Another circular continuous band of less stiff flexible material, capable of conforming closely to the table periphery, has a continuous, impermeable bond to the first band. A flexible clamp completely encircles the second band so as to force all of said inside surface of said second band tightly against the periphery of the table. The clamp has a release or latch for loosening said second band sufficiently to allow removal of the entire containment device from the table periphery. The device of Chandler et al, however, suffers from several disadvantages, including an unstable slurry concentration and removal rate, in addition to being unable to meet current and expected requirements for the reprocessing of slurry.
Traditional chemical mechanical polishing operations and devices and systems thereof, thus utilize continuous slurry delivery processes. The present inventors have concluded that such continuous slurry delivery techniques are costly and result in a high number of scratch defects. In addition, the present inventors have concluded that such slurry delivery techniques also suffer from low slurry removal rates and high polishing noise. Because the continuous slurry flow rate is proportional to the slurry removal rate, low removal rates are a significant factor affecting costs. Based on the foregoing, the present inventors have concluded that a need exists for a slurry delivery method and system which would avoid the aforemen

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