Retaining ring for wafer polishing

Details Retaining ring for wafer polishing Retaining ring for wafer polishing

1998-07-15

2001-07-31

Rose, Robert A. (Department: 3723)

Abrading

Machine

Endless band tool

C451S398000

Reexamination Certificate

active

06267655

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to semiconductor wafer processing, and in particular to a retaining ring of a wafer holder for wafer polishing.
BACKGROUND OF THE INVENTION
In polishing applications such as chemical mechanical polishing, measures are taken to ensure that the surface being polished is subjected to uniform, isotropic polishing forces. The uniformity of the polishing force applied to the surface is a significant factor in determining the degree of surface uniformity that can be attained through polishing.
Thus, for example, in a chemical mechanical polishing machine with continuous belt polishing, the longitudinal motion of the belt is often supplemented by lateral and rotational motion of the wafer to ensure that every area of the wafer is subjected to uniform, isotropic polishing forces.
The force generated by friction between the wafer and the belt will, at any given instant, be exerted primarily in the direction of the belt movement across the surface of the wafer. Likewise, in other polishing configurations, a frictional force will be exerted by the polishing surface in the direction of movement of the polishing surface relative to the wafer. A retaining ring is generally used to counter this force and hold the wafer in position. The frictional force of the polishing surface impels the wafer against the retaining ring, which exerts a counterbalancing force to maintain the wafer in position.
The frictional force of the polishing surface and the reactive force exerted by the retaining ring on the wafer may be sufficient to cause the wafer to buckle. This buckling of the wafer may resemble a so-called Euler column familiar to those skilled in the art of material strain analysis. This buckling may result in uneven polishing of the wafer surface, particularly near the edge of the wafer. This problem has been observed in high-speed polishing, particularly for large-diameter, thin wafers.
SUMMARY OF THE INVENTION
Thus, a need has arisen for a wafer polishing machine that addresses the disadvantages and deficiencies of the prior art. In particular, a need has arisen for a wafer polishing machine with a retaining ring that prevents wafer buckling.
Accordingly, an improved wafer polishing machine is disclosed. In one embodiment, the wafer polishing machine has a movable polishing surface and a holder that holds an object, such as a semiconductor wafer, against the movable polishing surface. The holder includes a support structure that supports the object in contact with the polishing surface and an annular retaining ring that retains the object in alignment with the support structure. The retaining ring has a plurality of projections projecting inwardly from its inner circumference. The projections are evenly spaced around the inner circumference of the retaining ring. In one embodiment, the projections on the retaining ring define a circle with a diameter no less than the diameter of the object being polished.
In an alternative embodiment, the retaining ring has a circular inner circumference formed from a flexible material. The inner circumference distends to from a continuous arc of contact with the object during polishing.
A technical advantage of one embodiment of the present invention is that the projections on the retaining ring create multiple points of contact between retaining ring and the wafer, thereby distributing the pressure of the retaining ring on the wafer. Another technical advantage of the various embodiments of the present invention is that the multiple points of contact or continuous arc of contact between the retaining ring and the wafer reduce wafer buckling during polishing, thereby improving surface uniformity.


REFERENCES:
patent: 3860399 (1975-01-01), Noble et al.
patent: 5398459 (1995-03-01), Okumura et al.
patent: 5664988 (1997-09-01), Stroupe et al.
patent: 5722877 (1998-03-01), Meyer et al.
patent: 5967885 (1999-10-01), Crevasse et al.

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