Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-04-22
2001-04-03
Scherbel, David A. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S285000, C451S288000, C451S289000, C451S390000, C451S398000, C451S460000
Reexamination Certificate
active
06210255
ABSTRACT:
BACKGROUND
The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for chemical mechanical polishing a substrate.
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, it 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 increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method 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” or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., 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.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. 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.
One problem encountered in CMP is that a central portion of the substrate is often underpolished. This problem, which may be termed the “center slow effect”, may occur even if pressure is uniformly applied to the backside of the substrate.
Another problem is the difficulty in removing the substrate from the polishing pad surface once polishing has been completed. As mentioned, a layer of slurry is supplied to the surface of the polishing pad. When the substrate is placed in contact with the polishing pad, the surface tension of the slurry generates an adhesive force which binds the substrate to the polishing pad. The adhesive force may make it difficult to remove the substrate from the pad.
Typically, the substrate is vacuum-chucked to the underside of the carrier head, and the carrier head is used to remove the substrate from the polishing pad. When the carrier head is retracted from the polishing pad, the substrate is lifted off the pad. However, if the surface tension holding the substrate on the polishing pad is greater than the vacuum-chucking force holding the substrate on the carrier head, then the substrate will remain on the polishing pad when the carrier head retracts. This may cause the substrate to fracture or chip. In addition, failure to remove the substrate can cause a machine fault requiring manual intervention. This requires shutting down the polishing apparatus, decreasing throughput. To achieve reliable operation from the polishing apparatus, the substrate removal process should be essentially flawless.
Several techniques have been employed to reduce the surface tension between the substrate and the polishing pad. Once such technique is to slide the substrate horizontally off the polishing pad to break the surface tension before vertically retracting the carrier head. This technique may, however, scratch or otherwise damage the substrate as it slides off the edge of the polishing pad. The mechanical configuration of the CMP apparatus may also prohibit use of this technique.
Another technique is to treat the surface of the polishing pad to reduce the surface tension. However, this technique is not always successful, and such treatment of the pad surface may adversely affect the finish and flatness of the substrate and reduce the polishing rate.
Another technique is to apply a downward pressure to the edge of the substrate to create a seal that prevents ambient atmosphere from interfering with the vacuum-chucking process. However, this technique may require complex pneumatic controls for the carrier head. In addition, the structure of the carrier head may prevent the application of pressure to the edge of the substrate.
SUMMARY
In one aspect, the invention is directed to a carrier head for chemical mechanical polishing of a substrate. The carrier head has a base and a flexible membrane extending beneath the base to define a pressurizable chamber. A lower surface of the flexible membrane provides a mounting surface for a substrate. The flexible membrane includes an inner portion and an outer expandable lip portion. The lip portion is configured to inflate or collapse and arranged to break or form a seal with a substrate positioned against the mounting surface, according to pressure changes in the chamber.
Implementations of the invention may include one or more of the following. A portion of the flexible membrane may be folded to define the lip portion. The lip portion may include a pocket in fluid communication with the chamber. The lip portion may include an upper part, a lower part, and a pocket located between the upper and lower parts. The flexible memberane further may include an edge portion joined to the upper part. The flexible memberane may further include an annular wing portion having a first end joined to the edge portion and a second end secured to a retainer ring. A spacer may surround an edge portion of the lip portion to maintain the structural integrity of the lip portion. The lip portion may form the seal with the substrate when the chamber is evacuated. The lip portion may break the seal with the substrate when the chamber is pressurized.
In another aspect, the invention is directed to a method of chemical mechanical polishing. A substrate is positioned against a mounting surface of a flexible membrane of a carrier head, the flexible membrane defining a pressurizable chamber within the carrier head and including an expandable lip portion in fluid communication with the chamber. The chamber is evacuated to collapse the expandable lip portion and form a seal with the substrate. The substrate is transfered from a first location to a second location.
Advantages of the invention may include the following. The substrate can be reliably loaded to and removed from the polishing pad. A uniform load is applied to the substrate during polishing by allowing removal of air trapped between the substrate and the flexible membrane.
REFERENCES:
patent: 4669915 (1987-06-01), Shatto, Jr.
patent: 4918869 (1990-04-01), Kitta
patent: 5193316 (1993-03-01), Olmstead
patent: 5205082 (1993-04-01), Shendon et al.
patent: 5423716 (1995-06-01), Strasbaugh
patent: 5449316 (1995-09-01), Strasbaugh
patent: 5584751 (1996-12-01), Kobayashi et al.
patent: 5624299 (1997-04-01), Shendon
patent: 5643053 (1997-07-01), Shendon
patent: 5643061 (1997-07-01), Jackson et al.
patent: 5759918 (1998-06-01), Hoshizaki et al.
patent: 5803799 (1998-09-01), Volodarsky et al.
patent: 5851140 (1998-12-01), Barns et al.
patent: 5879220 (1999-03-01), Hasegawa et al.
patent: 5957751 (1999-09-01), Govzman et al.
patent: 5964653 (1999-10-01), Perlov et al.
patent: 5993302 (1999-11-01), Chen et al.
patent: 6056632 (2000-05-01), Mitchel et al.
patent: 3313707 A1 (1984-10-01), None
patent: 0 841 123 A1 (1998-05-01), None
patent: 2243263 (1990-09-01), None
patent: WO 99/07516 (1999-02-01), None
U.S. Patent Application Serial No. 09/149,806, filed September 8, 1998
Chen Hung Chih
Zuniga Steven M.
Applied Materials Inc.
Fish & Richardson
Nguyen George
Scherbel David A.
LandOfFree
Carrier head for chemical mechanical polishing a substrate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Carrier head for chemical mechanical polishing a substrate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carrier head for chemical mechanical polishing a substrate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2481297