Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1998-03-24
2001-06-19
Rose, Robert A. (Department: 3203)
Abrading
Abrading process
Glass or stone abrading
C451S006000
Reexamination Certificate
active
06248000
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to Coon et al.
Application Ser. No. 09/021,767 and Aiyer et al. Application Ser. No. 09/021,740, which are incorporated herein by reference in their entirety.
BACKGROUND
1. Field of the Invention
This invention relates generally to an apparatus and method for planarizing a substrate, and more specifically, to an apparatus and method for in-situ monitoring of chemical-mechanical planarization of semiconductor wafers.
2. Background
Planarization of the active or device surface of a substrate has become an important step in the fabrication of modern integrated circuits (ICs). Of the several methods of planarization that have been developed, Chemical Mechanical Polishing (CMP) is perhaps the most commonly used method. This popularity is due, in part, to its broad range of applicability with acceptably uniform results, relative ease of use, and low cost. However, the move to larger diameter wafers and device technologies that require constant improvement in process uniformity requires that an improved planarization system become available.
A typical CMP system uses a flat, rotating disk or platen with a pliable monolithic polishing pad mounted on its upper surface. As the disk is rotated, a slurry is deposited near the center of the polishing pad and spread outward using, at least in part, centrifugal force caused by the rotation. A wafer or substrate is then pressed against the polishing pad such that the rotating polishing pad moves the slurry over the wafer's surface. In this manner, surface high spots are removed and an essentially planar surface is achieved.
The planarization of an interlayer dielectric is one common use for CMP. As the topology of the underlying surface is not uniform, dielectric surface coating replicates or even magnifies those non-uniformities. Thus, as the surface is planarized, the high spots are removed and then the total thickness of the dielectric is reduced to a predetermined value. Thus, the planarized dielectric layer will be thinner over high points of the underlying surface than over low points of that surface. Typically, it is important to maintain a minimum dielectric thickness over each of the highest points of the underlying layer, both locally (with a die) and globally (across the wafer). Thus, uniform removal of the dielectric layer at all points of the wafer is required.
A problem with most existing CMP systems is their inability to perform in-situ thickness monitoring. As the surface of the wafer is pressed against the polishing pad during removal, typically, no measurements as to the progress of the polishing can be made. Thus, wafers are either polished for fixed times, and/or periodically removed for off-line measurement. Recently, Lustig et al., U.S. Pat. No. 5,433,651 (Lustig) proposed placement of at least one viewing window in the working surface through the thickness of the polishing pad to provide access for in-situ measurement. However, a window placed in a polishing pad creates a mechanical discontinuity in the working surface each time the window passes across the surface of the wafer. A more conventional approach is to use a monolithic polishing pad.
Thus there is a need for a CMP apparatus, and method thereof, that provides optical access to the wafer front surface for continuous in-situ process monitoring, without undue process complexity or expense.
SUMMARY
A CMP method and apparatus for enhanced optical access to the wafer surface in accordance with at least one embodiment of the invention is provided. In some embodiments, an essentially circular polishing pad is mounted on a rotating platen. A region of the polishing pad is thinned to provide enhanced optical transparency and homogeneity. In some embodiments, a portion of the platen underlying at least some of the thinned pad region is optically transparent. In this manner the thinned pad and the underlying transparent portion of the platen advantageously provide optical access to the surface of a substrate for in-situ process monitoring. Since enhanced access is provided for in-situ process monitoring, some embodiments of the invention enable dynamic process control.
In some embodiments, different polishing pads comprise different material compositions. Thus textures, thicknesses, hardnesses, and optical transparencies are varied between polishing pads. In some embodiments, the thinned region of the polishing pad has different shapes, locations, or comprises distributed multiple regions applied to single or multiple pads. In some embodiments, thinning is accomplished from either surface of the polishing pad. However, it is preferable to thin the polishing pad from the platen side, thereby leaving the working surface intact and minimizing any mechanical discontinuity in wafer contact. In some embodiments, the platen has a raised portion aligned and interlocked with the thinned region, thereby providing mechanical support to prevent deformation of the polishing pad. Thus embodiments of the invention provide a system and method for optically accessing a wafer surface to enable enhanced in-situ monitoring of a CMP process.
REFERENCES:
patent: 5394655 (1995-03-01), Allen et al.
patent: 5433651 (1995-07-01), Lustig et al.
patent: 5605760 (1997-02-01), Roberts
patent: 5609511 (1997-03-01), Moriyama et al.
patent: 5637185 (1997-06-01), Murarka et al.
patent: 5725420 (1998-03-01), Torii
patent: 5853317 (1998-12-01), Yamamoto
Klivans Norman R.
Nikon Research Corporation of America
Rose Robert A.
Skjerven Morrill & MacPherson LLP
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