Abrading – Machine – Rotary tool
Reexamination Certificate
2001-01-04
2002-06-18
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Rotary tool
C451S053000, C451S450000
Reexamination Certificate
active
06406362
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to apparatus for polishing or planarizing workpieces, such as silicon wafers, and, more particularly, to a seal used in conjunction with such apparatus.
BACKGROUND OF THE INVENTION
In the semiconductor manufacturing industry, silicon workpieces are used as substrates for the fabrication of integrated circuit components. The workpieces, known in the industry as “wafers”, typically are sliced from an elongated cylinder, or bole, of single crystal silicon, and they generally have a flat, circular, disk-like shape. During the fabrication process, the wafers usually undergo multiple masking, etching, and dielectric and conductor deposition processes to create microelectronic structures and integrated circuitry on the wafers. Since the character of the substrate surface may substantially impact the quality of the integrated circuitry formed upon that surface, careful preparation of the wafer surface is usually necessary throughout the various stages of the semiconductor fabrication process. Moreover, as rapid evolution in the industry provides a continual impetus for diminishing the size of integrated circuits while heightening the density of the microelectronic structures forming each circuit, the need for precise preparation of wafer surfaces becomes evermore critical in the fabrication of high-quality semiconductors.
The extremely precise surface configuration of the substrates used in the production of integrated circuit components generally can be obtained by appropriately planarizing or polishing the substrate surface. Chemical mechanical planarization or polishing (CMP) machines have been developed for this purpose and are used to ensure that the substrate is free from projections or other imperfections which might adversely affect the accuracy and performance of the microelectronic structures formed thereupon. Such CMP machines and processes are well known in the art and are commercially available. For a discussion of CMP processes and apparatus, see, for example, Arai, et al., U.S. Pat. No. 4,805,348, issued February, 1989; Arai, et al., U.S. Pat. No. 5,099,614, issued March, 1992; Karlsrud et al., U.S. Pat. No. 5,329,732, issued July, 1994; Karlsrud, U.S. Pat. No. 5,498,196, issued March, 1996; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March, 1996.
Conventionally, a CMP polishing apparatus includes a rotatable platen and a wafer carrier which each rotate about their respective vertical axes at individually selected speeds. As seen in
FIGS. 1 and 2
, a conventional abrasive polishing pad
126
is attached to the upper surface of a rotatable platen
128
which rotates by means of a rotary shaft (not shown). An upper portion of the rotary shaft is connected to the rotatable platen
128
and a lower portion of the rotary shaft is connected to a motor (not shown) which rotates the shaft as needed. A semiconductor wafer seated in the wafer carrier
124
is lowered into engagement with the polishing pad
126
and clamped between the carrier
124
and the rotatable platen
128
, typically through the exertion of downward force by the carrier
124
. The polishing pad
126
polishes the wafer surface by rotating when the wafer is brought into engagement with the polishing pad
126
by wafer carrier
124
. A liquid containing an abrasive, granular material, known as a slurry, is deposited onto and retained by the polishing pad
126
. During operation of the CMP apparatus, the wafer carrier
124
exerts pressure on the rotatable platen
128
, and the surface of the semiconductor wafer held against the polishing pad
126
is thereby planarized and/or polished by a combination of chemical planarization and/or polishing by the slurry and mechanical planarization and/or polishing by the pad
126
as the carrier
124
and the rotatable platen
128
are rotated, respectively.
The rotatable platen that supports the polishing pad typically is mounted to, supported upon, and rotated by a rotary shaft that is coupled to a motor. A conventional rotary shaft assembly is illustrated in FIG.
3
. The rotary shaft assembly
300
includes a rotary shaft
302
which passes through a hollow, non-rotatable housing
304
having a plurality of interior components, such as internal bearings
306
which support the shaft
302
and permit relative rotation between the shaft
302
and the housing
304
; spacers
308
; and seals (not shown). In order for the rotary shaft
302
to rotate about its vertical axis while supporting the platen
128
above the non-rotatable housing
304
, a void space or pocket
310
exists between a portion
301
of the rotary shaft
302
and an upper portion
305
of the assembly housing
304
. Typically, the void space
310
comprises a conventional step-tooth labyrinth seal
312
formed between portion
301
of the rotary shaft
302
and upper portion
305
of the assembly housing
304
. The particular configuration of labyrinth seal
312
is intended to prevent fluid, such as slurry, introduced onto the polishing pad
126
during the polishing process, from entering the assembly housing
304
.
During the polishing process, slurry frequently flows off the polishing pad
126
in the direction of arrow
314
and collects or pools at the opening of the labyrinth seal
312
. As the process continues, the heat generated by the rotation of the shaft
302
results in an increase in the temperature within the assembly housing
304
. This increased temperature frequently results in an eventual build-up of negative pressure within the assembly housing
304
as the components within the assembly housing
304
cool, which build-up of negative pressure effects a suction force on the slurry which has collected at the opening of the labyrinth seal
312
. Consequently, the slurry is drawn through the labyrinth seal
312
and into the housing
304
of the rotary shaft assembly
300
, where the slurry then gets trapped between the rotary shaft
302
and the internal bearings
306
, seals (not shown), and/or other stationary components of the assembly
300
. Any slurry which is interposed between or among the interior components of the rotary shaft assembly
300
, such as the bearings
306
for example, has a potentially corrosive and/or degenerative effect on the components which tends to cause premature and excessive wear as well as damage that compromises the functioning of the apparatus.
Presently known rotary shaft labyrinth seals are unsatisfactory in several regards. Specifically, prior art devices have proved to be ineffective at preventing abrasive or corrosive chemical slurry, slurry vapor, and other fluids from entering the shaft assembly and deteriorating or destroying the interior components of the assembly. For example, during the polishing process, the step-tooth design of current labyrinth seals permits slurry to collect in the valley created by the labyrinth opening. As the temperature naturally rises and falls within the housing of the rotary shaft assembly over the course of the polishing process, a negative pressure within the assembly housing is created, and the slurry which has collected in the opening of the labyrinth is drawn through the labyrinth and into the assembly housing. The slurry then gets trapped between the rotary shaft and the internal bearings, seals, and/or other stationary internal components of the assembly. Since typical CMP shaft assemblies do not permit post-manufacture application of additional grease to the internal bearings in the shaft assembly, deterioration and corrosion caused by slurry and/or slurry vapor entering the assembly effectively shortens the useful life of the bearings and therefore of the rotary shaft assembly. Moreover, the gradual deterioration and particle degeneration of various assembly components ultimately may contaminate the polishing process and compromise the overall quality of the wafer fabrication process. Consequently, deficiencies in prior art labyrinth seals likely contribute significantly to premature wear and damage of assembly components, increm
Rayer, II Phillip M.
Yednak, III Andrew
Hail III Joseph J.
Ojini Anthony
Snell & Wilmer L.L.P.
SpeedFam-IPEC Corporation
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