Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-06-25
2001-06-05
Hall, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S285000, C451S288000, C451S289000, C451S291000, C451S292000, C451S401000
Reexamination Certificate
active
06241585
ABSTRACT:
BACKGROUND
The present invention relates generally to chemical mechanical polishing of substrates.
An integrated circuit is typically formed by the sequential deposition of conducting, semiconducting or insulating layers on a silicon wafer. One fabrication step involves depositing a filler layer over a patterned stop layer, and planarizing the filler layer until the stop layer is exposed. For example, trenches or holes in an insulating layer may be filled with a conductive layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulating layer form vias, plugs and lines that provide conductive paths between thin film circuits on the substrate.
Chemical mechanical polishing (CMP) is one accepted method of planarization. CMP typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, in other words, pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.
An effective CMP process provides not only a high polishing rate, but also a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad. The polishing rate sets the time needed to polish a layer, which in turn sets the maximum throughput of the CMP apparatus.
During CMP operations, the polishing pad needs to be replaced periodically. For a fixed-abrasive pad, the substrate wears away the containment media to expose the embedded abrasive particles. Thus, the fixed-abrasive pad is gradually consumed by the polishing process and, after a number of polishing runs (e.g., as few as about 40-50 and as many as several hundred), the fixed-abrasive pad needs to be replaced. For a standard pad, the substrate thermally and mechanically damages the polishing pad and causes the pad's surface to become smoother and less abrasive. Therefore, most standard pads must be periodically conditioned to restore a roughened texture to their surface. After a number of conditioning operations (e.g., as few as several hundred and as many as several thousand), the conditioning process consumes the pad or the pad is unable to be properly conditioned. The pad must then be replaced. An advantage of fixed-abrasive polishing pads is that they may not need to be conditioned.
One problem encountered in the CMP process is the difficulty in replacing the polishing pad. The polishing pad may be attached to the platen surface with an adhesive. Significant physical effort is often required to peel the polishing pad away from the platen surface. The adhesive then must be removed from the platen surface by scraping and washing with a solvent. A new polishing pad can then be adhesively attached to the clean surface of the platen. While this is happening, the platen is not available for the polishing of substrates, resulting in a decrease in polishing throughput. This problem is even more acute for fixed-abrasive pads, which need to be replaced more often than standard polishing pads. Thus, although the fixed-abrasive pads may not need to be conditioned, the use of fixed-abrasive pads in a CMP apparatus can result in a higher cost of operation.
Another problem that can arise when using a CMP process is difficulty in achieving a high throughput for the polishing process. Typically, substrates must be loaded and unloaded into the CMP apparatus. In addition to polishing the substrates using a fixed-abrasive pad, it is sometimes desirable to buff the substrates as well using a standard pas. The polishing, buffing, and loading/unloading steps are often performed sequentially using an architecture that performs only a single one of the steps at a time. It would, therefore, be desirable to modify the architecture of existing CMP apparatus to improve the overall throughput.
SUMMARY
In general, according to one aspect, a chemical mechanical polishing apparatus includes a rotatable carousel and multiple carrier head assemblies coupled to the carousel. Each carrier head assembly includes multiple carrier heads each of which can hold a substrate. Each carrier head assembly also includes a motor-driven system for causing the carrier head assembly to rotate about its center axis.
The CMP apparatus also can include multiple substrate processing stations. The processing stations can be separated from one another in substantially equal angular intervals, and the carrier head assemblies can be positioned in angular alignment with the stations. The carousel can be rotated to move each carrier head assembly from one station to another station.
According to another aspect, a polishing station of a CMP apparatus includes a substantially fixed polishing sheet and a fluid bearing surface that provides an upward pressure against the lower surface of the polishing sheet. In one implementation, the station includes a fixed abrasive polishing sheet and a rotatable plate disposed below an exposed portion of the polishing sheet. An upper surface of the plate is positioned near a lower surface of the polishing sheet. The rotatable plate includes a pattern of holes in its upper surface through which a fluid can flow to provide an upward pressure against the lower surface of the polishing sheet.
In some implementations, the polishing sheet includes a thin coated, micro-replicated, fixed-abrasive polishing pad having relatively high bulk compressibility and low bending stiffness.
In some implementations, the CMP apparatus also includes a source for providing fluid to the holes in the rotatable plate and a computer-controlled valve for controlling the flow of fluid from the source to the pattern of holes in the rotatable plate. The pattern of holes in the upper surface of the rotatable plate can include an area whose size corresponds to a substrate to be polished by the polishing sheet. In some cases, the pattern of holes in the upper surface of the rotatable plate includes multiple areas of vertical holes. Each area of holes can have a size that corresponds to a substrate to be polished by the polishing sheet. Furthermore, the flow of fluid to each of the areas of holes can be controlled independently. A motor can be coupled to the rotatable plate for causing the plate to rotate during polishing.
According to yet another aspect, a CMP apparatus includes a carrier head assembly with multiple carrier heads each of which can hold a substrate, a shaft about which the carrier head assembly can be rotated, and a motor-driven pulley system for causing the carrier head assembly to rotate about the shaft. The apparatus can further include a system of gears coupled to the carrier heads for causing each of the carrier heads to move in a circular path substantially without rotating with respect to a fixed point as the carrier head assembly is rotated about the shaft. In one implementation, the system of gears includes a central gear surrounding the shaft, idler gears coupled to the central gear, and outer gears. Each outer gear is coupled to one of the idler gears and a respective one of the carrier heads.
A rotatable fluid coupling can be positioned about the shaft. The apparatus can include multiple channels having one end coupled to the fluid coupling and a second end rotarily coupled to a respective one of the carrier heads. The flow of fluid can be used to provide a downward pressure on substrates held by the carrier heads. In some implementations, the pressure on a substrate held by each carrier h
Applied Materials Inc.
Fish & Richardson
Hall, III Joseph J.
McDonald Shantese
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