Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Reexamination Certificate
2001-09-19
2004-06-08
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
C205S101000, C205S123000, C205S148000, C205S170000, C205S182000
Reexamination Certificate
active
06746589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plating method and a plating apparatus, and more particularly to a plating method and a plating apparatus for filling a metal such as copper (Cu) or the like into fine interconnection patterns (trenches) on a semiconductor substrate.
2. Description of the Related Art
Aluminum or an aluminum alloy has generally been used as a material for forming interconnect circuits on semiconductor substrates. As integrated density has increased in recent years, there is a demand for usage of a material having a higher conductivity as an interconnect material. It has been proposed to plate a substrate having interconnect pattern trenches thereon to fill the trenches with copper or its alloy.
There are known various processes including CVD (chemical vapor deposition), sputtering, and the like to fill interconnect pattern trenches with copper or its alloy. However, the CVD process is costly for forming copper interconnections, and the sputtering process fails to embed copper or its alloy in interconnect pattern trenches when the interconnect pattern trenches have a high aspect ratio, i.e., a high ratio of depth to width. A plating process is most effective to deposit a metal layer of copper or its alloy on a substrate to form copper interconnections thereon.
Various processes are available for plating semiconductor substrates with copper. These include a process of immersing a substrate in a plating liquid held at all times in a plating tank, referred to as a cup-type or dipping-type process; a process of holding a plating liquid in a plating tank only when a substrate, to be plated, is supplied to the plating tank; an electric plating process for plating a substrate with a potential difference; and an electroless plating process for plating a substrate with no potential difference.
In carrying out filling of fine interconnect patterns with copper by electric copper-plating using a copper sulfate solution as a plating liquid, it is required to perform a plating process with high throwing power and high leveling properties. With a view to meeting this requirement, it is generally known to add to the plating liquid a compound called an additive.
Such an additive, generally in use, includes:
sulfur compounds called “carrier”, which grow crystal nuclei all over a plated surface, thereby promoting deposition of finer particles;
polymers which increase over-voltage of copper deposition, thereby enhancing throwing power; and
nitrogen compounds called “leveler”, which adhere to convex portions, where plating preferentially grows, to thereby increase over-voltage and retard copper deposition at the convex portions, thereby providing a flat plated layer.
However, when filling fine interconnect patterns with copper by electric copper-plating is conducted by using a plating liquid which, due to use of the above additives, has enhanced throwing power and leveling properties, there occurs a phenomena that a film thickness of an interconnection region of a substrate becomes thicker than a film thickness of a non-interconnection region. Unevenness in film thickness is not a problem in filling the interconnection region with copper; however, unevenness makes it difficult to obtain a flat surface by performing later CMP (chemical mechanical polishing) processing.
A plating treatment of a substrate for filling interconnect pattern trenches with a metal, such as copper or its alloy, may be carried out by using a plating apparatus as shown in FIG.
30
. As shown in
FIG. 30
, a substrate W and an anode
302
are disposed in parallel, facing each other, in a plating tank
301
accommodating a plating liquid
300
. Plating is conducted by flowing a plating current i between the substrate W and the anode
302
. A film thickness h of a plated film formed at a certain point on a surface of the substrate W is proportional to a product of a plating current value and energization time. The plating current value in
FIG. 30
is defined by the following formula (1):
i=E/
(
R
1+
R
2
+R
3
+R
4) (1)
In the above formula (1), E represents power source voltage, R
1
anodic polarization resistance, R
2
resistance of the plating liquid
300
, R
3
substrate (cathodic) polarization resistance, and R
4
sheet resistance of the substrate W at the certain point. The anodic polarization resistance R
1
and the substrate polarization resistance R
3
are interfacial resistances of the anode
302
and of the substrate W, respectively, and change with concentration of an additive or of the plating liquid. The resistance R
2
of the plating liquid
300
is proportional to a distance between the anode
302
and the substrate (cathode) W.
An electric supply to the substrate W is made via a cathode electrode
303
which is generally connected to a peripheral end of the substrate W. Accordingly, the sheet resistance R
4
at a point increases as a distance from the peripheral end of the substrate W increases, i.e., as the point comes near to center P of the substrate W. Therefore, the plating current value on an inner central side of the substrate W is smaller than that on an outer peripheral side (see the above formula (1)), whereby it is likely that film thickness becomes smaller on the inner central side as compared to the outer peripheral side. There has thus been a problem in conventional plating apparatuses that a plated film having a uniform film thickness over an entire substrate surface is difficult to form. Especially when an LSI interconnection is formed by plating, a small thickness, generally 50-200 nm, of a seed layer of the substrate (Si substrate) makes the sheet resistance R
4
considerably larger. Such a large sheet resistance R
4
has a larger influence on film thickness.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above drawbacks in the related art. It is therefore a first object of the present invention to provide a plating method and a plating apparatus which can attain embedding of copper into fine interconnect patterns with use of a plating liquid having high throwing power and leveling properties, and which can make film thickness of a plated film substantially equal between an interconnection region and a non-interconnection region, thereby facilitating later CMP processing.
It is a second object of the present invention to provide a plating apparatus and a plating method which can form a plated film having a more uniform film thickness over an entire surface of a substrate.
In order to achieve the first object, the present invention provides a plating method, comprising: filling a plating liquid containing metal ions and an additive into a plating space formed between a substrate and an anode disposed closely to the substrate so as to face the substrate; and changing concentration of an additive in the plating liquid filled into the plating space during a plating process.
In the course of plating of a substrate, concentration of an additive in a plating liquid filled into a plating space formed between the substrate and an anode gradually decreases with duration of the plating due to take-in of the additive within deposited metal film and oxidation degradation at the anode. The change of additive concentration is larger in cases where {circle around (1)} plating of a substrate is by a close-to-anode plating where an amount of plating liquid itself is small, {circle around (2)} introduction of a plating liquid into the plating space is conducted only before plating, and not conducted during plating (batch-wise introduction), and {circle around (3)} a plating liquid is introduced intermittently during plating. The concentration change of the plating liquid is larger when, during a plating process, an additional solution or a plating liquid containing a different concentration of additive is separately introduced into the plating space with a separate liquid introduction device.
By thus changing additive concentration of a plating liquid filled into a plating space dur
Inoue Hiroaki
Kaneko Hisashi
Kunisawa Junji
Makino Natsuki
Matsuda Tetsuo
Ebara Corporation
King Roy
Leader William T.
Wenderoth , Lind & Ponack, L.L.P.
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