Slurry with chelating agent for chemical-mechanical...

Details Slurry with chelating agent for chemical-mechanical... Slurry with chelating agent for chemical-mechanical...

2000-06-27

2001-11-06

Koslow, C. Melissa (Department: 1755)

Abrasive tool making process, material, or composition

With inorganic material

C051S308000, C051S309000, C106S003000, C438S692000, C438S693000, C216S089000, C252S079100

Reexamination Certificate

active

06312486

ABSTRACT:

TECHNICAL FIELD
The present invention relates to slurry compositions and methods for using the slurry compositions in chemical-mechanical polishing of oxide or nitride layers from semiconductor wafers.
BACKGROUND OF THE INVENTION
Chemical-mechanical polishing (“CMP”) processes are widely used to remove material from the surface of semiconductor wafers, and they are particularly useful for planarizing wafers, and layers thereof, in the production of ultra-high density integrated circuits. In a typical CMP process, a wafer is pressed against a polishing pad in the presence of a slurry under controlled chemical, pressure, velocity, and temperature conditions. The slurry generally contains small, abrasive particles that abrade the surface of the wafer, and chemicals that etch and/or oxidize the newly formed surface of the wafer. The polishing pad is generally a planar pad made from a continuous phase matrix material such as polyurethane. Thus, when the pad and/or the wafer moves with respect to the other, material is removed from the surface of the wafer mechanically by the abrasive particles and chemically by the etchants and/or oxidants in the slurry.
FIG. 1
schematically illustrates a polishing machine
10
, often called a planarizer, used in a conventional CMP process. The polishing machine
10
has a platen
20
, a wafer carrier
30
, a polishing pad
40
, and a slurry
44
on the polishing pad. An under-pad
25
is typically attached to the upper surface
22
of platen
20
, and the polishing pad
40
is positioned on the under-pad
25
. In conventional CMP machines, a drive assembly
26
rotates the platen
20
as indicated by arrow A. In other existing CMP machines, the drive assembly
26
reciprocates the platen
20
back and forth as indicated by arrow B. The motion of the platen
20
is imparted to the pad
40
through the under-pad
25
because the polishing pad
40
frictionally engages the under-pad
25
. The wafer carrier
30
has a lower surface
32
to which a wafer
12
may be attached, or the wafer
12
may be attached to a resilient pad
34
positioned between the wafer
12
and the lower surface
32
. The wafer carrier
30
may be a weighted, free-floating wafer carrier, or an actuator assembly
36
may be attached to the wafer carrier
30
to impart axial and rotational motion, as indicated by arrows C and D, respectively.
In the operation of the conventional polishing machine
10
, the wafer
12
is positioned face-downward against the polishing pad
40
, and then the platen
20
and the wafer carrier
30
move relative to one another. As the face of the wafer
12
moves across the planarizing surface
42
of the polishing pad
40
, the polishing pad
40
and the slurry
44
remove material from the wafer
12
.
CMP processes must consistently and accurately produce a uniform, planar surface on the wafer because such a surface is needed in order to accurately focus optical or electromagnetic circuit patterns on the surface of the wafer. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the circuit-pattern to achieve a resolution of approximately 0.35-0.5 &mgr;m. Focusing the circuit-patterns to such small tolerances, however, is very difficult when the distance between the emission source and the surface of the wafer varies because the surface of the wafer is not uniformly planar. In fact, several devices may be defective on a wafer having a non-uniform planar surface. Thus, CMP processes must create a highly uniform, planar surface.
In the competitive semiconductor industry, it is also desirable to maximize the throughput of finished wafers. The throughput of wafers in a CMP process is a function of several factors, one of which is the rate at which the thickness of the wafer decreases as it is being planarized (the “polishing rate”). Because the polishing period per wafer (the time needed to achieve a desired wafer planarity and end-point) generally decreases with increasing polishing rate, it is desirable to maximize the polishing rate within controlled limits to increase the number of finished wafers that are produced in a given period of time.
The polishing rate of a wafer is often retarded by surface groups which form when freshly exposed surface comes into contact with the CMP slurry. The CMP processing of silicon oxide illustrates this problem. During CMP of a silicon oxide wafer, there is a continuous formation of surface Si—OH groups. These Si—OH groups can be very difficult to dislodge from the underlying bulk silicon oxide, and thus their presence retards the polishing rate of the CMP process. To increase the polishing rate of a silicon oxide wafer, conventional CMP processes use aggressive mechanical polishing techniques (e.g., high down-forces and high pad velocities) to physically remove the Si—OH groups and some of the underlying silicon oxide from the wafer.
Aggressive mechanical polishing techniques, however, tend to reduce the uniformity of the polished surface on the wafer. A high pad velocity, for example, exacerbates the center-to-edge gradient in the polishing rate so that the polishing rate at the edge of the wafer is greater than that at the center of the wafer. Similarly, high down-forces worsen dishing over large area features formed on the wafer and reduce the ability to control the planarization process. Therefore, in order to produce a desirably uniform planar surface on a wafer, the polishing rate is limited to a relatively low rate that is not overly aggressive.
Accordingly, there is a strongly-felt need in the art for improved chemical-mechanical polishing slurries that afford an increased polishing rate for semiconductor wafers and layers present thereon. The present invention fulfills this need, and provides other related advantages.
SUMMARY OF THE INVENTION
The invention provides for a slurry composition and a method for its preparation. The slurry enhances the removal of polish-resistant surface moieties from the surface of a wafer during chemical-mechanical polishing of a semiconductor wafer. The inventive slurry composition is formed by mixing together components including a solvent, a plurality of abrasive particles, and at least one chelating agent The abrasive particles are selected so that they preferably abrade the surface of the wafer to remove some of the surface moieties and the underlying bulk material. The chelating agent is preferably selected to react with the polish-resistant surface moieties on the surface of the wafer and to make the surface moieties easier to remove from the wafer with substantially non-aggressive chemical-mechanical polishing techniques. In operation, the surface moieties and the underlying bulk material are removed by a combination of the chemical effects of the chelating agent and the mechanical effects of the abrasive particles.
The invention also provides an improved method for chemical-mechanical polishing of a semiconductor wafer surface. At least one of the polishing pad and the wafer is moved with respect to the other so that the surface of the wafer passes over the polishing pad in the presence of the slurry to remove material from the wafer surface. The chelating agent may react with the polish-resistant surface moieties on the surface of the wafer to make the surface moieties easier to remove from the underlying material with substantially non-aggressive chemical-mechanical polishing techniques. These and other aspects of this invention will become evident upon reference to the attached drawings and following detailed description.


REFERENCES:
patent: 4910155 (1990-03-01), Cote et al.
patent: 4954142 (1990-09-01), Carr et al.
patent: 5300155 (1994-04-01), Sandhu et al.
patent: 5318927 (1994-06-01), Sandhu et al.
patent: 5354490 (1994-10-01), Yu et al.
patent: 5366542 (1994-11-01), Yamada et al.
patent: 5735963 (1998-04-01), Obeng
patent: 6099604 (2000-08-01), Sandhu et al.

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