Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1998-09-29
2002-02-19
Ostrager, Allen (Department: 3725)
Abrading
Abrading process
Glass or stone abrading
C451S060000, C451S285000, C451S287000, C451S446000
Reexamination Certificate
active
06347979
ABSTRACT:
FIELD OF THE INVENTION
The field of the present invention pertains to semiconductor fabrication processing. More particularly, the present invention relates to a device for more efficiently utilizing slurry for polishing a semiconductor wafer in a chemical mechanical polishing machine.
BACKGROUND OF THE INVENTION
Most of the power and usefulness of today's digital IC devices can be attributed to the increasing levels of integration. More and more components (resistors, diodes, transistors, and the like) are continually being integrated into the underlying chip, or IC. The starting material for typical ICs is very high purity silicon. The material is grown as a single crystal. It takes the shape of a solid cylinder. This crystal is then sawed (like a loaf of bread) to produce wafers typically 10 to 30 cm in diameter and 250 microns thick.
The geometry of the features of the IC components are commonly defined photographically through a process known as photolithography. Very fine surface geometries can be reproduced accurately by this technique. The photolithography process is used to define component regions and build up components one layer on top of another. Complex ICs can often have many different built-up layers, each layer having components, each layer having differing interconnections, and each layer stacked on top of the previous layer. The resulting topography of these complex IC's often resemble familiar terrestrial “mountain ranges,” with many “hills” and “valleys” as the IC components are built up on the underlying surface of the silicon wafer.
In the photolithography process, a mask image, or pattern, defining the various components, is focused onto a photosensitive layer using ultraviolet light. The image is focused onto the surface using the optical means of the photolithography tool, and is imprinted into the photosensitive layer. To build ever smaller features, increasingly fine images must be focused onto the surface of the photosensitive layer, e.g. optical resolution must increase. As optical resolution increases, the depth of focus of the mask image correspondingly narrows. This is due to the narrow range in depth of focus imposed by the high numerical aperture lenses in the photolithography tool. This narrowing depth of focus is often the limiting factor in the degree of resolution obtainable, and thus, the smallest components obtainable using the photolithography tool. The extreme topography of complex ICs, the “hills” and “valleys,” exaggerate the effects of decreasing depth of focus. Thus, in order properly to focus the mask image defining sub-micron geometries onto the photosensitive layer, a precisely flat surface is desired. The precisely flat (e.g. fully planarized) surface will allow for extremely small depths of focus, and in turn, allow the definition and subsequent fabrication of extremely small components.
Chemical-mechanical polishing (CMP) is the preferred method of obtaining full planarization of a wafer. It involves removing a sacrificial layer of dielectric material using mechanical contact between the wafer and a moving polishing pad with chemical assistance from a polishing slurry. Polishing flattens out height differences, since high areas of topography (hills) are removed faster than areas of low topography (valleys). Polishing is the only technique with the capability of smoothing out topography over millimeter scale planarization distances leading to maximum angles of much less than one degree after polishing.
FIG. 1A
shows a down view of a CMP machine
100
and
FIG. 1B
shows a side cut away view of the CMP machine
100
taken through line AA. The CMP machine
100
is fed wafers to be polished. The CMP machine
100
picks up the wafers with an arm
101
and places them onto a rotating polishing pad
102
. The polishing pad
102
is made of a resilient material and is textured, often with a plurality of predetermined groves
103
, to aid the polishing process. The polishing pad
102
rotates on a platen
104
, or turn table located beneath the polishing pad
102
, at a predetermined speed. A wafer
105
is held in place on the polishing pad
102
and the arm
101
by a carrier ring
112
and a carrier
106
. The lower surface of the wafer
105
rests against the polishing pad
102
. The upper surface of the wafer
105
is against the lower surface of the carrier
106
of the arm
101
. As the polishing pad
102
rotates, the arm
101
rotates the wafer
105
at a predetermined rate. The arm
101
forces the wafer
105
into the polishing pad
102
with a predetermined amount of down force. The CMP machine
100
also includes a slurry dispense arm
107
extending across the radius of the polishing pad
102
. The slurry dispense arm
107
dispenses a flow of slurry onto the polishing pad
102
.
CMP machine
100
also includes a conditioner assembly
120
, which includes a conditioner arm
108
extending across the radius of the polishing pad
102
. An end effector
109
is connected to the conditioner arm
108
. The end effector
109
includes an abrasive conditioning disk
110
which is used to roughen the surface of the polishing pad
102
, thereby improving the transport of slurry to and from wafer
105
.
The slurry is a mixture of de ionized water and polishing agents designed to aid chemically the smooth and predictable planarization of the wafer. The rotating actions of both the polishing pad
102
and the wafer
105
, in conjunction with the polishing action of the slurry, combine to planarize, or polish, the wafer
105
at some nominal rate. This rate is referred to as the removal rate. A constant and predictable removal rate is important to the uniformity and performance of the wafer fabrication process. The removal rate should be expedient, yet yield precisely planarized wafers, free from surface topography. If the removal rate is too slow, the number of planarized wafers produced in a given period of time decreases, degrading wafer through-put of the fabrication process. If the removal rate is too fast, the CMP planarization process will not be uniform across the surface of the wafers, degrading the yield of the fabrication process.
Referring still to FIG.
1
A and
FIG. 1B
, the polishing action of the slurry largely determines the removal rate and removal rate uniformity, and, thus, the effectiveness of the CMP process. As slurry is “consumed” in the polishing process, the transport of fresh slurry to the surface of the wafer
105
and the removal of polishing by-products away from the surface of the wafer
105
become very important in maintaining the removal rate. Slurry transport is facilitated by the texture of the surface of the polishing pad
102
. This texture is comprised of both predefined pits and grooves
103
that are manufactured into the surface of the polishing pad
102
and the inherently rough surface of the material from which the polishing pad
102
is made.
Referring now to
FIG. 2A
,
FIG. 2B
, FIG.
2
C and
FIG. 2D
, the relationships between a wafer, a carrier ring, and a polishing pad are shown (for teaching purposes, the above elements are not necessarily drawn to scale). FIG.
2
A and
FIG. 2B
show a wafer
105
and a carrier ring
112
respectively. FIG.
2
C and
FIG. 2D
show a side view of the wafer
105
in the carrier ring
112
on a polishing pad
102
. As described above, the wafer
105
is held in place on the arm (not shown) by the carrier ring
112
as the polishing pad
102
rotates on the polishing platen. The carrier ring
112
accepts the wafer
105
within its inner radius surface
201
. The upper surface of the wafer
105
is against the carrier
106
(not shown) of the arm. The carrier
106
(not shown) presses the wafer into the polishing pad with a predetermined force. As the polishing pad
102
rotates, carrier
106
(not shown) rotates the wafer
105
.
Referring still to
FIG. 2D
, the wafer
105
typically protrudes slightly, relative to the lower surface of carrier ring
112
. This gives the polishing pad
102
and the slurry (not shown) on the polishing pad
Hong William
Ostrager Allen
VSLI Technology, Inc.
Wagner , Murabito & Hao LLP
LandOfFree
Slurry dispensing carrier ring does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Slurry dispensing carrier ring, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Slurry dispensing carrier ring will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2954938