Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
1999-09-13
2001-12-04
Rachuba, M. (Department: 3724)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S006000, C451S011000, C451S041000, C451S288000, C451S380000
Reexamination Certificate
active
06325696
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to chemical-mechanical polishing of semiconductor wafers and, more particularly, to an apparatus and method for controlled actuation of a wafer backing film.
BACKGROUND OF THE INVENTION
Chemical-mechanical polishing (CMP) is performed in the processing of semiconductor wafers and/or chips on commercially available polishers. The CMP polisher can have a circular rotating polish pad and rotating carrier for holding the wafer or, as with the newest tools entering the market, may be designed with an orbital or linear motion of the pad and carrier. In general practice, a slurry is supplied to the polish pad to initiate the polishing action. However, here again, newest tooling may make use of what is referred to as Fixed Abrasive pads, whereby the abrasive is embedded within the polish pad and is activated by DI water or some other chemical as may be desired for the specific polish process.
Ideally, a CMP polisher delivers a globally uniform, as well as locally planarized wafer. However, global uniformity on a wafer-to-wafer basis is difficult to achieve. Hard pads are used on a polishing table or platen for their ability to provide optimum planarity. However, these pads require a softer pad under layer to generate an acceptable level of uniformity. The application of wafer backside air is also a standard practice in an attempt to provide a localized area of force to the backside of the wafer in those radii where the polish may be lower due to wafer bow, collapse of the backing film, degradation or collapse of the polish pads, or poor slurry distribution.
Recently, a phenomenon known as “edge bead” has detracted from acceptable yields. The edge bead is a ring of thicker oxide at a radius of 96 mm with a 100 mm wafer. A secondary thickness variation at 80-90 mm has also been observed. The location of these thickness variations may also shift across the wafer unexpectedly for reasons not fully understood. This results in nonusable chips at the wafer perimeter or a variation in chip performance regionally across the wafer. Also, the wafer film to be polished may have a varying consistency from doping, thickness or the like, across the surface of the wafer. This creates varying, uncontrollable polish rates across the wafer. Neither of the problems described above can be compensated for with the tooling currently available.
Various mechanical methods have been attempted to alter the final thickness profile of a polished wafer. One method uses fixed curvatures or shapings of the carrier face. These are directed to control only a centered edge thickness variation by bowing the carrier face at the center to supply a greater force at the wafer center. This provides an increased rate of polish center to edge.
Another known method applies shims to the carrier face behind the wafer backing film. This enables a wider range of diameters and widths to be rotated on and off a flat carrier as needed. However, the milling of a carrier face to a shape requires a number of carriers to provide a range of results. This requires substantial time to change from one shaped carrier to another as the need arises.
The present invention is directed to overcoming one or more of the problems discussed above, in a novel and simple manner.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided an active control mechanism by which concentric, non-uniformity on a wafer-to-wafer basis is tailored to meet desired results.
It is one object of the invention to provide a means by which regional, non-concentric non-uniformity can be overcome.
It is another object of the invention to provide the capability to use non-uniform controls to within die levels, thereby overcoming film polish rate variations due to chip design.
In one aspect of the invention there is disclosed a chemical-mechanical polishing (CMP) apparatus for polishing a semiconductor wafer, in which the CMP apparatus has a carrier for the wafer. The carrier includes a carrier base and a wafer retaining ring mounted to the base for retaining the wafer for polishing. A plurality of dual function piezoelectric actuators are mounted to the base within a perimeter of the retaining ring. The actuators sense pressure variations across the wafer and are individually controllable to provide a controlled pressure distribution across the wafer.
It is a feature of the invention that the actuators comprise thin film dual function piezoelectric actuators.
It is another feature of the invention to provide a backing film mounted to the base between the actuators and the wafer.
It is a further feature of the invention that the actuators are embedded in the backing film.
In accordance with another aspect of the invention there is disclosed a CMP control system for controlling distribution of pressure across the backside of a semiconductor wafer being polished. The system includes a CMP apparatus having a carrier for supporting the wafer. The carrier includes a plurality of dual function piezoelectric actuators. The actuators sense pressure variations across the wafer and are individually controllable. A control is connected to the actuators for monitoring sensed pressure variations and controlling the actuators to provide a controlled pressure distribution across the wafer.
It is a feature of the invention that the control comprises a programmed control that controls pressure distribution according to a die layout of the wafer.
It is another feature of the invention that the control includes a notch location program for determining orientation of the wafer in the carrier and the control varies the pressure distribution responsive to the die layout and determined orientation.
In accordance with a further aspect of the invention there is disclosed a method of polishing a semiconductor wafer in a CMP system. The method comprises the steps of providing a CMP apparatus having a carrier for supporting the wafer, the carrier including a plurality of dual function piezoelectric actuators, the actuators sensing pressure variations across the semiconductor wafer and being individually controllable; monitoring sensed pressure variations; and controlling the actuators to provide a controlled pressure distribution across the semiconductor wafer.
In accordance with an additional aspect of the invention, there is disclosed a computer-readable storage medium having stored therein instructions for performing a method of polishing a semiconductor wafer in a chemical-mechanical polishing (CMP) system. The CMP system has a carrier for supporting the wafer, and the carrier includes a plurality of dual function piezoelectric actuators; the actuators sense pressure variations across the wafer and are individually controllable. The method comprises the steps of monitoring sensed pressure variations, and controlling the actuators to provide a controlled pressure distribution across the wafer. The actuators may comprise thin film dual function piezoelectric actuators. Furthermore, the computer-readable storage medium may have stored therein information regarding a die layout of the wafer; the controlling step may further comprise the step of controlling the actuators to provide a controlled pressure distribution according to the die layout of the wafer. In addition, the wafer may have a notch for determining orientation of the wafer, and the medium may have stored therein an algorithm for determining the orientation of the wafer in accordance with location of the notch; the controlling step may further comprise the steps of implementing a program using the algorithm to determine the orientation of the wafer in the carrier, and controlling the actuators to vary the pressure distribution responsive to the die layout and the determined orientation.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.
REFERENCES:
patent: 4272924 (1981-06-01), Masuko et al.
patent: 4450652 (1984-05-01), Walsh
patent: 4602459 (1986-07-01), Drits et al.
patent: 5036015 (1991-07-01), Sandhu et
Boggs Karl E.
Davis Kenneth M.
Fiege Ronald D.
Landers William F.
Lofaro Michael F.
International Business Machines - Corporation
Rachuba M.
Wood, Phillips, VanSaten, Clark & Mortimer
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