Abrading – Machine – Endless band tool
Reexamination Certificate
1999-04-06
2001-04-17
Banks, Derris H. (Department: 3723)
Abrading
Machine
Endless band tool
C451S300000
Reexamination Certificate
active
06217427
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the chemical-mechanical-polishing (CMP) of flat surfaces and, more particularly, to such polishing of silicon wafers to achieve global planarization in the manufacture of integrated circuits.
2. Description of the Related Art
As is well known and understood, the traditional technique for polishing silicon wafers flat across the entire surface is through the use of circular motion in which a polishing pad and the wafer below it rotate together. As is also known to those skilled in the art, whether the polishing is done purely mechanically, or combined with a liquid affording a chemical function, the typical pad life (because of wear and tear) extends from about 100 wafers to about 500 wafers. Independent of the manner by which the deterioration is measured or determined, there then follows a “down-time” for the changing of the pad, and for the conditioning of its replacement to bring it to the state at which the polish rate is constant. When considering the $40.00-$50.00 cost of each pad as used in polishing silicon wafers of some 8 inches in diameter—and the time spent in replacing and conditioning the pad—calculations have shown that these rotatable pads account for anywhere between 15 and 30 percent of the cost associated with the CMP tool. Because of the necessity to replace, and then condition these pads, a manner of extending the interval between their exchange would be highly desirable.
SUMMARY OF THE INVENTION
As will become clear from the following description, the present invention proceeds by the doing-away of the conventional circular platen, and replacing it, instead, with a linear pad to provide a CMP tool analogous to a belt sander. As will be understood, this follows from a recognition of the control that becomes afforded (in particular, with the linear implementation of the invention) when the speed of the belt left-and-right across the silicon wafer substrate is set so that the velocities and the velocity vectors stay constant. On the other hand, with the traditional circular, rotary motion between the substrate and the polishing pad, the wear which results tends to form a groove in the pad. This groove causes the relative velocities to vary, and the vectors on the surfaces to change, thereby producing a very complex dynamic process.
As will also become clear from the following description, the present invention goes beyond the mere substitution of a linear polishing of the silicon wafer substrate for the previously employed rotatable polishing—and, by the incorporation of a twist in the linear belt, to make it a Mobius strip utilizing both the front and back surfaces of the belt to increase its life. Such Mobius strips are generally defined as being a surface with only one side and one edge, made by placing a twist of 180 degrees in the strip whose ends are secured together. In accordance with the present invention, such an endless belt of continuous strength is employed, wrapped about a pair of oppositely positioned tensioning rollers, with the 180 degree twist substantially giving the belt the appearance of a helix of predetermined length and width. As will be understood, utilizing the belt in this manner as the polishing pad thus increases by a factor of 2×, the interval before the pad must be changed due to its deterioration. This increase in lifetime significantly decreases the cost associated with the CMP tool because of the reduced down time of the polishing pad.
As will additionally become clear from the description that follows, a linear polishing tool constructed in this manner, and in further accordance with the invention, also can be provided with an adhesive surface on the tensioning rollers for the capture of particles that are removed from the substrate during the polishing process. Alternative to this, and similarly in accordance with the invention, a vacuum system arrangement can be included for the capturing of these removed particles, or a brush-cleaner configuration can be employed for their capture.
Further embodying the invention to be described is the applicability of the linear tool to be used either with slurry, or slurryless systems for providing both the abrasive and chemical components which typify traditional rotatable CMP tools —with the slurryless system, however, being the preferable one due to the resulting absence of any slurry build up on the tensioning rollers, and without the loss of any slurry as the linear belt makes its way through the linear polishing tool.
Particularly useful in the chemical-mechanical polishing of silicon wafer substrates, moreover, the invention will be understood to find usefulness in any type of linear polishing operation, and not strictly to silicon wafer polishing. In such configuration, the linear polishing tool could be operative with apparatus for measuring the removal rate from a substrate during the polishing process, as an aid to indicate the time at which even the linear polishing pad should be replaced and conditioned. Operative with either the abrasive alone, or in a chemical or any other type of liquid solution, the advantages which follow from the invention will readily become apparent.
REFERENCES:
patent: 5361546 (1994-11-01), Jonsson
patent: 5716264 (1998-02-01), Kimura et al.
patent: 5722877 (1998-03-01), Meyer
patent: 5727989 (1998-03-01), Ohno et al.
patent: 5755614 (1998-05-01), Adams et al.
patent: 5762536 (1998-06-01), Pant et al.
patent: 5775980 (1998-07-01), Sasaki et al.
patent: 5791969 (1998-08-01), Lund
patent: 5928068 (1999-07-01), Matsuda et al.
patent: 7230973 (1995-07-01), None
Case Carlye B.
Case Christopher J.
Agere Systems Inc.
Banks Derris H.
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