Abrading – Abrading process – With tool treating or forming
Reexamination Certificate
2000-06-08
2002-12-31
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
With tool treating or forming
C451S443000, C451S529000
Reexamination Certificate
active
06500054
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to semiconductor manufacturing and, more specifically, to the conditioning of polishing pads used for chemical-mechanical polishing (CMP).
BACKGROUND OF THE INVENTION
Chemical-Mechanical Polishing (CMP) is a key processing technology for fabricating semiconductor chips. Often, after the performance of a processing step, the resulting wafer surface is full of peaks and valleys. Peaks and valleys of subsequent processing steps can build upon one another, creating an uneven surface that may be undesirable for a number of reasons. CMP uses a polishing pad and a slurry of chemically active liquid and abrasive material to grind down the surface of a wafer, thus restoring the planar surface.
In particular, CMP is useful for planarizing intermetal dielectric layers of silicon dioxide or for removing portions of conductive layers within integrated circuit devices. Non-planar dielectric surfaces may interfere with the optical resolution of subsequent photolithography processing steps, making it extremely difficult to print high-resolution lines. The application of a second metal layer over an intermetal dielectric layer having large step heights can result in inadequate metal coverage, and ultimately in an open circuit.
FIG. 1
illustrates an exemplary linear CMP process. A semiconductor wafer
20
is typically held face down against a flat polishing pad
22
that has been coated with the slurry (not shown) and that moves relative to wafer
20
along arrow A. A rectangular conditioning pad
26
is used to condition polishing pad
22
continuously as wafer
20
is polished.
In an exemplary rotary CMP process, shown in
FIG. 2
, semiconductor wafer
20
is typically held face down and rotated along arrow C against a flat polishing pad
24
that has been coated with the slurry and that rotates along arrow B. Both wafer
20
and pad
24
are typically rotated relative to each other. Also shown in
FIG. 2
are a first reference location
32
on polishing pad
24
and a second reference location
30
on polishing pad
24
located radially inward of location
32
. As for the linear CMP process, rectangular conditioning pad
26
is used to condition polishing pad
24
continuously as wafer
20
is polished in the rotary CMP process. In both the linear and rotary CMP processes, the abrasive polishing process continues until the surface of wafer
20
contacting polishing pad
22
or
24
is substantially planar.
The motion of wafer
20
with respect to polishing pad
22
,
24
and the force applied to hold wafer
20
against the pad adds mechanical energy to the system that helps remove the wafer surface material. In addition, the process of supplying fresh chemical liquid and removing spent chemical liquid helps remove material from the wafer surface. Uniform removal of material from the surface of wafer
20
is pursued by adjusting a number of variables, such as the pad velocity with respect to the wafer surface, the force applied between the pad and the wafer, and the slurry composition and flow.
Over time, the initially rough surface of polishing pad
22
,
24
becomes worn and may glaze over due to a build-up of slurry and other deposits on the pad surface. To counteract the glazing and wear, polishing pad
22
,
24
is periodically mechanically scored or “conditioned.” Conditioning pad
26
removes the build-up on polishing pad
22
,
24
and roughens the surface of polishing pad
22
,
24
. Different approaches to conditioning may be required depending on the hardness of the pad surface and the particular slurry used for polishing. Further, conditioning may be performed by a conditioning apparatus in a discrete conditioning step or during wafer polishing depending on the specific conditioning process and apparatus used.
FIGS. 1 and 2
both show rectangular conditioning pad
26
that may be used to condition polishing pad
22
,
24
continuously as wafer
20
is polished.
The polishing pad-and-slurry combination may be envisioned as a piece of sandpaper in which the slurry acts as the sand and the polishing pad acts as the paper on which the sand is mounted. The slurry may have different particle sizes, with larger particles providing more grinding of the wafer surface than smaller particles, similar to the difference between larger and smaller grit sandpaper. The more slurry held against the wafer surface or greater particle size of the slurry, the more grinding that may occur. Grooves in polishing pad
22
,
24
drain the slurry away from the surface of the pad. Slurry in the grooves is thus ineffective or less effective at grinding than slurry on the surface of the pad.
The shape and volume of the grooves per unit area of polishing pad
22
,
24
therefore control to some degree the amount of polishing. For example, larger grooves not only take more slurry away from the surface, but also may completely or partially trap larger particles. Small grooves that are unable to trap large slurry particles leave the large particles in contact with wafer
20
, providing more grinding than parts of polishing pad
22
,
24
where the grooves are large enough to allow such particles to be trapped in the grooves. Intermediate size grooves may only partially trap the particles, leaving portions of the large particles protruding and providing less polishing than where only small grooves are present, but more so than where large grooves are present. The depth of the grooves may further control how much of the slurry is drained away, deeper grooves providing areas with less polishing capability than in shallower grooves.
Thus, the polishing rate and uniformity of the CMP process may be greatly affected by the characteristics of the polishing pad surface, which can make the slurry more or less effective. The ability to optimize the pad surface during conditioning is therefore highly desirable.
SUMMARY OF THE INVENTION
The present invention provides a chemical-mechanical polishing pad conditioner comprising a non-uniform conditioning surface having a plurality of conditioning elements and at least a first section and a second section. The first section has a first cutting volume per unit width that is greater than the second cutting volume per unit width of the second section. The first section may include at least one first conditioning element having a first projected width whereas the second section includes at least one second conditioning element having a second projected width that differs from the first projected width. The first section may also or instead have a first plurality of conditioning elements with a first density whereas the second section has a second plurality of conditioning elements with a second density that is different from the first density. The first section may also or instead have at least one conditioning element with a first cutting depth whereas the second section has at least one conditioning element with a second cutting depth different from the first depth.
The conditioner may be adapted for use in a linear or rotary CMP operation, and may be rectangular or may be a roller-type conditioner. In a rotary application, the non-uniform conditioning surface may be designed to compensate for a difference in relative velocity of the polishing pad at a radial-inward location as compared to a radial-outward location.
The conditioner may further comprise a third, transition section between the first section and the second section. The third section has a third cutting volume per unit width intermediate the first and second cutting volumes per unit width. The third section also has a gradual transition in cutting volume per unit width between the first and second cutting volumes per unit width.
The conditioner may be an element in a chemical-mechanical polishing tool comprising a polishing pad, the conditioner, and a mechanism for moving the polishing pad relative to the conditioner. The mechanism may further be adapted to move the polishing pad relative to the conditioner in a linear or rotary manner.
The conditioner may be u
Ma William H.
Ticknor Adam D.
Eley Timothy V.
International Business Machines - Corporation
Nguyen Dung Van
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