Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1997-09-26
2001-07-03
Hail, III, Joseph J. (Department: 3203)
Abrading
Abrading process
Glass or stone abrading
C451S527000, C451S530000, C451S537000, C451S921000, C451S526000, C451S528000
Reexamination Certificate
active
06254456
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to polishing pads used for chemical-mechanical polishing of substrates. More particularly, the present invention relates to modified contact areas on a polishing pad surface to produce a more uniformly polished substrate surface.
Chemical mechanical polishing (sometimes referred to as “CMP”) typically involves mounting a substrate faced down on a holder and rotating the substrate face against a polishing pad mounted on a platen, which in turn is rotating or is in orbital state. A slurry containing a chemical component that chemically interacts with the facing substrate layer and an abrasive component that physically removes that layer is flowed between the substrate and the polishing pad or on the pad near the substrate. In semiconductor wafer fabrication, this technique is commonly applied to planarize various wafer layers such as dielectric layers, metallization layers, etc.
FIG. 1
shows a wafer
12
undergoing CMP on a surface of a rotating polishing pad
10
used in a conventional CMP system, such as an Avanti
472
, commercially available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Ariz.. In such conventional CMP systems, polishing pad
10
typically rotates during CMP about an axis that is perpendicular to and passes through a center point of the polishing pad surface and although it is not necessary, wafer
12
may rotate in the same direction. A rotating wafer
12
carves out on polishing pad
10
a wafer track area, which is defined by an inner boundary
16
and an outer boundary
14
. Those skilled in the art will recognize that the width of the wafer track area might be larger than the diameter of the wafer because during CMP, the rotating wafer also oscillates from side to side in a radial direction of the polishing pad.
FIG. 1
shows a wafer
12
in its displaced, oscillating position
12
′. Thus, in the conventional CMP systems, the wafer is polished on the wafer track area of the polishing pad.
FIG. 2A
shows a front view of a polishing pad
20
, e.g.,
1
C 1000 available from Rodel of Newark, Del., that is employed in modem CMP systems, such as the AvantGaard 676 also available from Integrated Processing Equipment Corporation (IPEC). A surface of polishing pad
20
includes a plurality of macrogrooves
22
, microgrooves
24
and slurry injection holes
26
. Macrogrooves
22
are shown in an X-Y configuration, i.e. vertical and horizontal macrogrooves intersect at various points to form a “grid”, microgrooves
24
are oriented substantially diagonally relative to macrogrooves
22
and slurry injection holes
26
are positioned at various intersections of the vertical and horizontal macrogrooves
22
. Those skilled in the art will recognize that the macrogrooves formed on the polishing pad surface are not limited to any particular configuration and may be obtained by a polishing pad manufacturer in other configurations, such as a spiral configuration.
FIG. 2B
shows a cross-sectional view of a macrogroove
22
of
FIG. 2A
, which macrogroove is shaped like a square channel with sharp comers having a width (labeled “w”) and a depth (labeled “d”). Macrogrooves
22
of
FIG. 2A
have a substantially uniform width and depth (of about 1 mm) throughout the substrate surface. The term “macrogroove spacing,” as used herein refers to a space on the polishing pad surface separating two parallel and adjacent macrogrooves. For macrogrooves in an X-Y configurations as shown in
FIG. 2A
, macrogrooves spacings
22
are typically between about 5 and about 6 mm and substantially uniform throughout the polishing pad surface.
During a typical CMP process, polishing pad
20
does not rotate, but orbits around an axis that is perpendicular to the polishing pad surface.
FIG. 2C
shows a polishing pad
20
(macrogrooves
22
, microgrooves
24
and slurry injection holes
26
are not shown to simplify illustration) of
FIG. 2A
in its orbital state and for exemplary purposes, reference number
20
′ denotes one position of polishing pad
20
as it orbits around an axis that is perpendicular to the polishing pad surface. In other words, during the orbital motion of the polishing pad, a center point
28
of polishing pad
20
moves in a circular path, as shown in FIG.
2
C. Wafer
12
subjected to CMP on orbiting polishing pad
20
is positioned off-center, i.e. the center-point of wafer
12
does not coincide with the center point of polishing pad
20
, but is near to the center-point of polishing pad
20
. In the modern CMP systems, therefore, a wafer surface mostly contacts the center area of the polishing pad during CMP.
After polishing a significant number of wafers on the same polishing pad, e.g., the polishing pad of
FIGS. 1
or
2
A, the part of the polishing pad that contacts a center region of the wafer deteriorates to a greater extent than other regions of the polishing pad. By way of example, in
FIG. 1
, a center region of the wafer track deteriorates to a greater extent than other areas of the polishing pad. As a further example, a center region of the polishing pad of
FIG. 2A
deteriorates similarly to a greater extent. This deterioration is attributed primarily to a constant down force applied by the wafer during CMP.
Unfortunately, well before the end of a production lot draws near, the degraded polishing pad surface causes the wafers subjected to CMP to experience a slower film removal rate at the center region of the wafer relative to the edge or peripheral regions of the wafer surface, which phenomenon is known in the art as “center slow polishing.” “Production lot” refers to a collection of wafers that are fabricated as a group under substantially similar conditions and may ultimately be sold. Center slow polishing is undesirable because it leads to a non-uniformly polished wafer surface, i.e. the center region of the wafer surface is not polished to the same extent as the peripheral region of the wafer. This prematurely ends the life of the polishing pad. In a typical wafer fabrication facility, where several CMP apparatus are employed, the replacement cost of polishing pads can be significant.
What is therefore needed is an improved polishing pad design for producing a uniformly polished substrate surface.
SUMMARY OF THE INVENTION
To achieve the foregoing, the present invention provides a polishing pad surface having a surface designed for chemical mechanical polishing of a substrate surface. The polishing pad surface includes a first area on the surface exposed to and capable of contacting a first amount of the substrate surface during chemical-mechanical polishing and a second area on the surface exposed to and capable of contacting a second amount of the substrate surface during chemical-mechanical polishing, wherein the second amount is larger than the first amount of the substrate surface to produce a more uniformly polished substrate surface.
By way of example, in polishing pads used in conventional CMP systems, macrogrooves are present on the first area, but not on the second area. The macrogrooves may have a width that is between about 1 mm. The macrogrooves may extend radially or may be arranged in a circular configuration at an inner and outer boundary of a wafer track on the polishing pad.
In one embodiment, in a modified polishing pad of the present invention employed in the modem CMP system, the first area has a first set of macrogrooves and the second area has a second set of macrogrooves, wherein the first set of macrogrooves have a larger width than the second set of macrogrooves. The first set of macrogrooves may have a width that is between about 1 and about 2 mm and the second set of macrogrooves may have a width that is between about 0.5 and about 1 mm.
In another embodiment, in the modified polishing pad of the present invention, the first area has a first set of macrogrooves and the second area has a second set of macrogrooves, wherein spacings between the first set of macrogrooves that are adjacent and parallel are narrower than spacings betwee
Kalpathy-Cramer Jayashree
Kirchner Eric J.
Beyer Weaver & Thomas
Hail III Joseph J.
LSI Logic Corporation
Nguyen George
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