Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2000-03-20
2003-02-18
Paladini, Albert W. (Department: 2827)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S734000, C257S737000
Reexamination Certificate
active
06522016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor devices, and, more particularly, to a semiconductor device provided with a durable metal film formed on an electrode pad. The present invention also relates to a method of producing such a semiconductor device.
2. Description of the Related Art
Conventionally, a semiconductor device has a metal film called a barrier metal layer formed on an electrode pad. Such a barrier metal layer may be formed by electroless metal plating. For instance,
FIG. 1A
is an enlarged schematic view of a part including a barrier metal layer of a conventional semiconductor device. A semiconductor device
100
has an electrode pad
103
on a chip
101
made mainly of silicon. A barrier metal layer
105
is disposed on the electrode pad
103
. A passivation film
106
serving as a protection film is further disposed in an area where the barrier metal layer
105
does not exist.
As shown in
FIG. 1A
, the peripheral end portion
105
A of the barrier metal layer
105
is in contact with the passivation film
106
. Here, the peripheral end portion
105
A has substantially the same thickness as the passivation film
106
. Also, the barrier metal layer
105
is entirely flat.
FIG. 1B
is an enlarged schematic view of a part including a barrier metal layer of another conventional semiconductor device
200
. In
FIG. 1B
, the same components as in
FIG. 1A
are denoted by the same reference numerals. The barrier metal layer of
FIG. 1B
is slightly thickener than the barrier metal layer of FIG.
1
A. Accordingly, the semiconductor device
200
differs from the semiconductor device
100
in having a slightly thicker barrier metal layer
115
and its peripheral end portion
115
A. In
FIG. 1B
, the peripheral end portion
115
A covers an end portion of the passivation film
106
. However, the rest of the barrier metal layer
115
has a uniform thickness and an entirely flat shape.
The semiconductor devices
100
and
200
both have a solder bump
107
on the respective barrier metal layers
105
and
115
to be attached to external electrodes.
As described above, the semiconductor devices
100
and
200
are connected to external electrodes via solder bumps. Conventional solder bumps are made mainly of lead. In recent years, however, solder bumps made mainly of tin are preferred in consideration of the environment.
However, when solder bumps made of tin as a main component and silver are used, the strength of the peripheral end portions
105
A and
115
A in contact with the solder bump
107
decreases, thereby causing incomplete bonding. Because of such incomplete bonding, there is a risk of the electrode pad
103
and the solder bump
107
being brought into contact with each other and nullifying the function of the barrier metal layer
105
. Also, there is another problem that the solder bump
107
and the barrier metal layer
105
might become separated from the electrode pad
103
.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide semiconductor devices in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a semiconductor device having a highly resistant metal film formed on an electrode pad, and a method of producing such a semiconductor device.
The reasons of the above problems are not known in detail. However, it is assumed that digestion and diffusion of a metallic element constituting a solder bump progresses preferentially at the peripheral end portion of a metal film. The inventors of the present invention have studied the above problems, and have discovered that the metal film should have a certain shape to reduce the occurrence of the problems.
The objects of the present invention are achieved by a semiconductor device comprising: an electrode pad; a metal film formed on the electrode pad; a protection film formed in an area where the metal film does not exist; and a bump disposed on the metal film. The metal film has a greater thickness at its peripheral end portion which is in contact with the protection film.
As the result of intensive studies made by the inventors, it was found that, even if the solder bump contains a component having digestion and diffusion properties, the thicker peripheral end portion of the metal film in contact with the protection film can improve the durability of the metal film. In the semiconductor device of the present invention, the peripheral end portion of the metal film is thicker than the flat portion of the metal film. When bonding the semiconductor to an external terminal via solder bumps, the peripheral end portion can presumably disperse the diffusive element, thereby improving the durability of the metal film.
The peripheral end portion of the metal film may be 1.3 to 2 times thicker than the flat portion of the metal film.
The metal film of the semiconductor device of the present invention may have a peripheral end portion covering the inner peripheral end portion of the protection film.
The objects of the present invention are also achieved by a semiconductor device production method including the steps of activating the surface of the electrode pad with a chelating solution containing glycine and a compound having a metallic element as nuclei, and forming a metal film by electroless metal plating.
By activating the surface of the electrode pad, the metallic element is precipitated on the surface of the electrode pad, which is a suitable condition for metal plating. Electroless metal plating is then performed on the surface of the electrode pad to form a metal film with the metallic element as nuclei. The peripheral end portion of the metal film in contact with the protection film is thicker than the central portion of the metal film.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5844320 (1998-12-01), Ono et al.
patent: 5877833 (1999-03-01), Schraivogel et al.
patent: 5889326 (1999-03-01), Tanaka
patent: 5936848 (1999-08-01), Mehr et al.
patent: 5998861 (1999-12-01), Hiruta
patent: 6084300 (2000-07-01), Oka
patent: 6-236887 (1994-08-01), None
Egami Toshiharu
Makino Yutaka
Watanabe Eiji
Armstrong Westerman & Hattori, LLP
Cruz Loudes
Fujitsu Limited
Paladini Albert W.
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