Two phase chemical/mechanical polishing process for tungsten...

Details Two phase chemical/mechanical polishing process for tungsten... Two phase chemical/mechanical polishing process for tungsten...

2000-08-04

2002-08-20

Kunemund, Robert (Department: 1765)

Semiconductor device manufacturing: process

Chemical etching

Combined with the removal of material by nonchemical means

C438S692000, C438S693000

Reexamination Certificate

active

06436829

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to manufacturing a semiconductor wafer and, more specifically, to a method of chemical/mechanical polishing of tungsten layers comprising two phases for reducing tungsten-seam defects in via plugs of integrated circuits.
BACKGROUND OF THE INVENTION
Referring initially to
FIGS. 1A
,
1
B and
1
C, illustrated are sectional views of a contact opening
110
, or Via, conventionally formed in a dielectric
101
of semiconductor wafer
100
at progressive stages of tungsten plug
130
formation.
FIG. 1A
shows a conventional tungsten plug
130
formed in the contact opening
110
. The contact opening
110
is typically cylindrical in shape, formed within the dielectric
101
, and comprises a bottom
111
and a wall
113
. A surface
103
of the dielectric
101
will surround the contact opening or via
110
. Underlying the bottom ill of the contact opening
110
is an active component
120
with a contact surface
122
. The active component
120
may be the source or drain, or gate region of a conventional semiconductor device, and in the situation where the contact opening
110
is a Via, the active component may be an aluminum trace.
After forming the contact opening
110
in the dielectric
101
, titanium (Ti) and titanium nitride (TiN) layers
114
,
115
, respectively, are deposited on the dielectric surface
103
, contact bottom
111
and wall
113
. The titanium/titanium nitride layers
114
,
115
, form adhesion/barrier layers for further deposition. Following the TiN layer, a blanket chemical vapor deposition of tungsten fills the remaining void of the contact opening
110
with tungsten forming a tungsten plug
130
. Sufficient tungsten is deposited to “overfill” the contact opening
110
, forming the tungsten plug
130
and a tungsten layer
136
over the TiN layer
115
. After filling the via
110
with the W plug
130
, some voids
133
a
or “tungsten seams” (W-seams) are usually observed in the surface
134
of the W plug
130
, especially when the etched profiles are straight.
Chemical/mechanical polishing (CMP) is commonly used to planarize both dielectric and metal layers. For example, CMP is used to remove part of the tungsten (W), Ti and TiN layers to finish the via plug formation down to the dielectric
101
. While planarizing the metal layer, a CMP process must avoid or cause only minimal metal dishing and oxide erosion while avoiding removal of the underlying oxide or other dielectric. The process must also avoid introducing non-uniformity to the dielectric thickness.
In CMP, a semiconductor wafer is rotated face-down against a polishing pad in the presence of an abrasive slurry comprising a suspension of small abrasive particles, usually an inorganic oxide, in a chemically acidic or basic aqueous solution. The acidic or basic solution is chosen based upon the primary material, in this instance a metal (tungsten), that is being planarized so as to induce a chemical reaction with the material. The chemical reaction changes the metal to a chemical compound that may be more readily removed by mechanical abrasion. For example, the surface of the tungsten layer
134
may be oxidized with a slurry comprising hydrogen peroxide (H
2
O
2
). The resulting tungsten oxide is then more readily removed with an abrasive comprising silicon dioxide (SiO
2
) and/or aluminum oxide (Al
2
O
3
), than metallic tungsten would be.
However, conventional tungsten CMP slurries with an Al
2
O
3
abrasive tend to cause wafer surface scratching because the primary tungsten removal mechanism is mechanical. In this case, polish (removal) rate is a function of the down-force on the wafer as well as the rotation speeds of the platen and wafer carrier; of course, other factors may also enter into the polish rate. Since a relatively high down-force on the wafer is needed with this slurry, metal dishing is a common undesirable effect. To correct for the dishing effect, an additional step, i.e., an “oxide buff,” is required. Tungsten removal rate with these slurries typically range from about 200 nm per minute to about 500 nm per minute. Of course, it should be understood that the slurry type can readily affect both the removal rate and the wafer uniformity. Slurries that contain aggressive chemistries may provide higher removal rates, but they tend to cause more dishing or erosion.
However, a W-polishing slurry using a silicon dioxide (SiO
2
) abrasive does not exhibit the scratching problem of the Al
2
O
3
slurry, and therefore does not require the additional oxide buff. The H
2
O
2
component of the slurry oxidizes the W surface, and the oxide is subsequently removed with the mechanical SiO
2
abrasive. Removal rate of the tungsten with this slurry ranges from about 250 nm per minute to about 600 nm per minute depending upon, among other factors, the H
2
O
2
concentration, apparatus down force and platen rotational speed. Metal (W, Ti, TiN) removal is continued until the Ti barrier layer
115
and the TiN adhesion layer
114
are planarized down to the dielectric
101
.
Referring now to
FIG. 1B
, illustrated is a sectional view of the conventional tungsten plug of
FIG. 1A
after removal of exposed tungsten by conventional chemical/mechanical planarization. It is known that the H
2
O
2
will attack W-seams
133
a
and may even widen them as shown in FIG.
1
B.
Referring now to
FIG. 1C
, illustrated is a sectional view of the conventional tungsten plug of
FIG. 1B
after removal of the titanium nitride and titanium barrier layers by conventional chemical/mechanical planarization. As can be seen in
FIGURE 1C
, the W-seam
133
a
defect may persist even into the finished tungsten plug
130
. Such W-seam
133
a
defects remaining in a finished integrated circuit have proven to cause some electrical device degradation, especially causing leakage current in MOM (metal-oxide-metal) capacitor structures.
Accordingly, what is needed in the art is a method of chemical/mechanical polishing for tungsten layers on semiconductor wafers that reduces the probability of W-seam defects.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides, in one embodiment, a method for polishing a semiconductor substrate comprising: (a) polishing a metal layer located on a semiconductor wafer with a first slurry at a first polishing rate wherein the first slurry has a predetermined concentration of an oxidizing agent therein; (b) forming a second slurry having less than the predetermined concentration of an oxidizing agent therein; and (c) polishing the metal layer at a second polishing rate less than the first polishing rate and in the presence of the second slurry.
In another embodiment, polishing a metal layer at a first polishing rate includes polishing a metal layer at a first polishing rate wherein the predetermined concentration of the oxidizing agent ranges from about 2 to about 6 weight percent by volume. Polishing a metal layer with a first slurry at a first polishing rate, in an alternative embodiment may include polishing a metal layer wherein the first slurry comprises silicon dioxide. Another embodiment provides a method where the step of polishing a metal layer with a first slurry at a first polishing rate includes polishing a metal layer at a first polishing rate wherein the oxidizing agent comprises hydrogen peroxide.
Forming a second slurry may include forming a second slurry having an oxidizer concentration less than about 2.0 percent by volume. In a particular aspect of this embodiment, forming a second slurry includes forming a second slurry having an oxidizer concentration not greater than about 1.7 weight percent by volume. Forming a second slurry, in a related embodiment, includes forming a second slurry by diluting the first slurry with deionized water. The second slurry may be formed by diluting the first slurry with a diluent-to-slurry ratio ranging from about 3:1 to about 6:1.
In another embodiment, polishing at a first polishing rate includes polish

Affiliated with

Also associated with

Rating

Two phase chemical/mechanical polishing process for tungsten... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Two phase chemical/mechanical polishing process for tungsten..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two phase chemical/mechanical polishing process for tungsten... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2925498