Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Involving measuring – analyzing – or testing
Reexamination Certificate
2001-10-24
2004-04-06
Nelms, David (Department: 2818)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Involving measuring, analyzing, or testing
C204S232000
Reexamination Certificate
active
06716330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electroless plating apparatus and method which are preferably used for forming interconnects on a semiconductor substrate (including filling of a metal such as copper into an interconnection groove or the like, forming of a seed layer, and forming of a reinforcing seed layer on a seed layer for the purpose of reinforcing the seed layer), an interconnection-protective film, and a diffusion-preventive film.
2. Description of the Related Art
An electroless plating is such a method that a plated film is formed on a surface of a material to be plated by chemically reducing metal ions in a plating liquid without supplying any electric current from the outside, and electroless plating is widely used in nickel-phosphorus plating and nickel-boron plating for providing corrosion resistance and wear resistance, and copper plating for a printed-wiring substrate.
As an electroless plating apparatus, there has been generally known an apparatus comprising a plating bath for holding an electroless plating liquid while causing the electroless plating liquid to overflow, and a vertically movable holding portion disposed above the plating bath for holding a material, to be plated, such as a substrate so as to face laterally, whereby the material, to be plated, held by the holding portion is dipped into the plating liquid in the plating bath (the so-called dipping(dip)). Further, there has been also generally known an apparatus comprising a holding portion for holding a material, to be plated, such as a substrate so as to face upwardly (face up), and a plating liquid supply portion for supplying a plating liquid to an upper surface (surface to be plate) of the material, to be plated, held by the holding portion, whereby the plating liquid flows along the upper surface of the material, to be plated, held by the holding portion. As a face-up type plating apparatus, there is a coater face-up type plating apparatus in which a plating liquid flows along an upper surface of a material to be plated by supplying the plating liquid to the upper surface of the material to be plated from the plating liquid supply portion and rotating the material to be plated.
In recent years, as the processing speed and integration of a semiconductor chip becomes higher, there has been a growing tendency to replace aluminum or aluminum alloy with copper having a low electric conductivity and a high electromigration resistance as metallic materials for forming interconnection circuits on the semiconductor substrate. This kind of copper interconnect is generally formed by filling copper into fine recesses formed in the surface of the substrate. As a method for forming the copper interconnect, plating is generally used. In any case, after a copper film is deposited on the surface of the substrate, the surface of the substrate is polished to a flat finish by chemical mechanical polishing (CMP).
An electroless plating is applied to main filling materials (Cu) for the copper interconnect, the formation of the seed layer on the barrier metal, or the reinforcement of the seed (Cu), further the formation of the barrier metal itself, or the formation of cap material for the copper interconnect (in any case, Ni—P, Ni—B, Co—P, Ni—W—P, Ni—Co—P, Co—W—P), or the like. In any electroless plating process, uniformity of the film thickness over an entire surface of the substrate is required.
In this case, in the electroless plating, as soon as a material to be plated is brought into contact with a plating liquid, a plating metal begins to be deposited on the surface to be plated, and the deposition velocity of the plating metal varies with the temperature of the plating liquid. Thus, in order to form a plated film having a uniform thickness on the surface of the material to be plated, it is necessary that the temperature of the plating liquid should be uniform on the entire surface to be plated from the time when the plating liquid begins to be brought into contact with the material to be plated, and should be kept constant during all the plating process of this contact, and the velocity distribution (thickness of a diffusion layer or a boundary layer formed along the surface to be plated) of the plating liquid in a direction perpendicular to the surface to be plated during the plating process should be uniform over the entire surface to be plated.
However, in the conventional dip type and jig fixing type plating, it has been difficult to make a flow of the plating liquid on the substrate uniform. Further, in the coater face-up type plating, there has been problems of a control of flow and a uniformity of liquid temperature.
FIG. 11
is a schematic view showing a conventional dip type electroless plating apparatus. As shown in
FIG. 11
, this electroless plating apparatus comprises a plating bath
280
for storing a plating liquid
281
therein, and a substrate holding apparatus (substrate holding means)
290
for holding a semiconductor substrate W.
In the electroless plating, a good reaction cannot take place unless the temperature at the contacting portion between a surface W
1
, to be plated, of a semiconductor substrate W and a plating liquid is kept at a predetermined temperature (for example, 60° C.). Therefore, in order to heat the plating liquid
281
in the plating bath
280
and keep the plating liquid
281
at a predetermined constant temperature, a pipe
282
is connected to the plating bath
280
to withdraw the plating liquid in the plating bath
280
and to circulate the plating liquid by a pump P, and there is provided a heating apparatus (heating means)
283
, in the pipe
282
, such as a heater for heating the plating liquid to a predetermined temperature.
On the other hand, the substrate holding apparatus
290
is formed into such a shape that the substrate holding apparatus
290
covers the surface of the semiconductor substrate except for the surface W
1
, to be plated, of the semiconductor substrate W, and is adapted to dip the semiconductor substrate W into the plating bath
280
in such a state the surface W
1
to be plated is placed in a vertical direction. The reason for placing the surface W
1
, to be plated, of the semiconductor W in a vertical direction in the plating bath
280
is that gas is generated on the surface W
1
to be plated by a plating reaction, and if the generated gas remains on a certain area of the surface W
1
to be plated, the plating reaction is obstructed at such area, and hence such generated gas is required to be easily separated from the surface W
1
to be plated.
However, in the above conventional electroless plating apparatus, because the surface W
1
, to be plated, of the semiconductor substrate W must be placed vertically in the plating bath
280
, the plating bath
280
is required to have a large depth, and thus cannot be downsized. Further, because it is necessary to provide the heating apparatus
283
outside the plating bath
280
, an overall apparatus cannot be downsized also in this respect.
On the other hand, in the case where a copper plating is applied to the semiconductor substrate W, when the temperature of the plating liquid varies by 1° C. in a plating time of one minute at, for example, around 60° C., the difference of the film thickness amounts to approximately 1.8 nm, and hence an extremely precise temperature control of the plating liquid is required. However, as described above, the plating bath
280
cannot be downsized, and thus a large amount of the plating liquid is required to be contained. Consequently, the temperature of the plating liquid cannot be precisely controlled, and the amount of the plating liquid to be used increases to thus increase electric power consumption for heating the plating liquid and keeping the plating liquid warm.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above drawbacks. It is therefore a first object of the present invention to provide an electroless plating apparatus which can easily form a plated film having
Hongo Akihisa
Inoue Hiroaki
Karimata Tsutomu
Kimura Norio
Mishima Koji
Ebara Corporation
Nelms David
Vu David
Wenderoth , Lind & Ponack, L.L.P.
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