Compositions – Preservative agents – Anti-corrosion
Reexamination Certificate
2000-03-15
2002-05-07
Anthony, Joseph D. (Department: 1714)
Compositions
Preservative agents
Anti-corrosion
C252S389220, C252S389240, C252S389230, C252S400210, C252S400220, C252S400230, C510S175000, C510S178000, C422S015000, C422S016000
Reexamination Certificate
active
06383414
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to inhibiting corrosion of metal plugs in an integrated circuit, which corrosion may occur during and after a chemical-mechanical polishing (CMP) process of the integrated circuit. More particularly, the present invention relates to using a corrosion inhibiting compound, such as a thiazole compound, during chemical-mechanical polishing (CMP) and/or after CMP to effectively inhibit metal plug corrosion.
Chemical mechanical polishing (sometimes referred to as “CMP”) typically involves mounting a wafer face down on a holder and rotating the wafer face against a polishing pad mounted on a platen, which in turn is rotating or is in an orbital state. A slurry containing a chemical that chemically interacts with the facing wafer layer and an abrasive that physically removes that layer is flowed between the wafer and the polishing pad or on the pad near the wafer. In semiconductor wafer fabrication, this technique is commonly applied to planarize various wafer layers such as dielectric layers, metallization layers, etc.
A metal plug, typically a tungsten plug, is formed in a dielectric layer to provide a conductive pathway between a metallization layer and an underlying integrated circuit (IC) substrate layer and/or between two successive metallization layers disposed above the integrated circuit (IC) substrate.
FIG. 1A
shows a partially fabricated IC
10
that includes a tungsten layer
16
, which is subjected to CMP to form tungsten plugs
26
as shown in FIG.
1
B. CMP typically involves mounting a substrate face down on a holder and rotating the substrate face against a polishing pad mounted on a pallet, which in turn is rotating or is in orbital state. A slurry containing a chemical, e.g. an oxidizing agent such as ferric nitrate (Fe(NO
3
)
3
), that chemically interacts with the tungsten layer and an abrasive, e.g. alumina (Al
2
O
3
), that physically removes the tungsten layer, is flowed between the wafer and the polishing pad or on the pad near the substrate.
Referring to
FIG. 1A
, which shows partially fabricated IC
10
before the substrate surface undergoes CMP. A dielectric layer
12
disposed above a substrate surface
18
and having contact holes
14
. A tungsten layer
16
is also disposed atop dielectric layer
12
and fills contact holes
14
. Some significant steps involved in forming the partially fabricated IC of
FIG. 1A
include blanket depositing dielectric layer
12
, such as SiO
2
, on substrate surface
18
. After dielectric layer
12
is planarized, a masking layer (not shown), which typically includes photoresist, is blanket deposited over dielectric layer
12
and patterned by conventional photolithography. Next, the unmasked portions of dielectric layer
12
are etched to form contact holes
14
that provide an opening to the underlying substrate layer. After the masking layer is removed, tungsten layer
16
is blanket deposited over the substrate surface, filling contact holes
14
with tungsten. During metal deposition, a vertical “seam” structure
30
forms in the middle region of the contact hole that is filled with tungsten. Those skilled in the art will recognize that before the contact holes are filled with tungsten, they may be filled with a conductive titanium layer (not shown to simplify illustration) and a titanium nitride barrier layer (not shown to simplify illustration). Those skilled in the art will also recognize that vias may be similarly etched to provide an opening in a dielectric layer that is disposed between two metallization layers and that metal plugs may similarly be formed in such vias.
Next, tungsten layer
16
of partially fabricated IC
10
undergoes CMP, as described above, to form tungsten plugs by removing the tungsten layer deposited above the dielectric layer. Now referring to
FIG. 1B
, which shows a partially fabricated IC
20
after undergoing CMP. Partially fabricated IC has tungsten plugs
26
formed in a dielectric layer
12
disposed atop a substrate
18
. During tungsten CMP, ferric nitrate (Fe(NO
3
)
3
) oxidizes the tungsten to form tungsten oxide that is abraded by the alumina (Al
2
O
3
) particles in the slurry. In this manner, the tungsten layer above the dielectric layer is removed to form tungsten plug
26
shown in FIG.
1
B.
Unfortunately, during CMP, the slurry undesirably chemically attacks and opens up seam
30
(shown in
FIG. 1A
) of the tungsten plug, forming a “V-shaped” crack
30
′ in the middle region of the plug, as shown in FIG.
1
B. This opening in the seam provides a pathway for the slurry, slurry residue and corrosive processing chemicals used in the post CMP cleaning steps to migrate or seep into the tungsten plug. After the crack side-walls have been exposed to these compounds for over a period of time, the tungsten plug corrodes, making the IC susceptible to catastrophic device failure.
What is therefore needed is an improved process, which effectively inhibits metal plug corrosion during the CMP process as well as after CMP, such as during post CMP cleaning steps.
SUMMARY OF THE INVENTION
To achieve the foregoing, the present invention provides a process of inhibiting a corrosion of metal plugs formed in integrated circuits. The corrosion inhibiting process includes providing a partially fabricated integrated circuit surface including the metal plugs on a polishing pad to carry out chemical-mechanical polishing, introducing slurry including a corrosion inhibiting compound on the polishing pad in sufficient concentration to inhibit corrosion of the metal plugs of the partially fabricated integrated circuit surface, and polishing the partially fabricated integrated circuit surface.
The metal plug may include a contact plug or a via plug. The corrosion inhibiting compound may include at least one of sulfur containing compounds, phosphorous containing compounds and azoles. The azoles may include at least one of a thiazole compound and a triazole compound. The concentration of the corrosion inhibiting compound may range from between about 0.0001% (in volume) to a value that is limited by the solubility of the corrosion inhibiting compound in the slurry. In one embodiment, before the step of providing the partially fabricated integrated circuit on the polishing pad, the process of the present invention further includes applying the corrosion inhibiting compound on the partially fabricated integrated circuit surface that is being polished.
In another aspect, the present invention provides another process of inhibiting corrosion of metal plugs formed in integrated circuits. This process of inhibiting corrosion includes providing a partially fabricated integrated circuit surface including the metal plugs, introducing a fining solution including a corrosion inhibiting compound on a polishing pad in sufficient concentration to inhibit corrosion of the metal plugs of the partially fabricated integrated circuit, and fine polishing a surface of the partially fabricated integrated circuit.
The fining solution may include between about 1% and about 3% (in volume) ammonium hydroxide in deionized water. The corrosion inhibiting compound may include at least one of sulfur containing compounds, phosphorous containing compounds and azoles. The concentration of the corrosion inhibiting compound may range from between about 0.0001% (in volume) to a value that is limited by the solubility of the corrosion inhibiting compound in the fining solution.
In yet another aspect, the present invention provides a yet another process of inhibiting corrosion of metal plugs formed in integrated circuits. This process includes providing a partially fabricated integrated circuit surface including the metal plugs and soaking the partially fabricated integrated circuit surface in a rinsing solution including a corrosion inhibiting compound in sufficient concentration to inhibit corrosion of the metal plugs of the partially fabricated integrated circuit surface.
The rinsing solution may include a wet storage solution, in which the partially fabricated integrate
Anthony Joseph D.
Beyer Weaver & Thomas LLP
LSI Logic Corporation
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