Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Bump leads
Reexamination Certificate
2002-03-27
2003-09-09
Clark, Jasmine J B (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Bump leads
C257S777000, C257S780000
Reexamination Certificate
active
06617688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device in which a first semiconductor pellet is placed on a second semiconductor pellet to make an electric connection with each other.
2. Description of the Prior Art
Electronic components to be used in compact and lightweight portable electronic devices such as cellular phones have been miniaturized, or the packing density thereof have been increased without miniaturizing their bodies to substantially contribute the miniaturization of electronic devices. In addition, compact and lightweight high-functional semiconductor devices with large packing densities have been realized by integrating two or more semiconductor pellets that form integrated circuits having different functions therein, such as those of CPUs and memories.
An example of such conventional semiconductor devices will be now described with reference to FIG.
5
. In the figure, the reference numeral
1
denotes a first semiconductor pellet in which a plurality of flat electrodes
3
is formed on one side of a first semiconductor substrate that includes semiconductor elements (not shown) in its inside. In addition, electrodes (not shown) for external connection are formed on the periphery of that side of the first semiconductor pellet
1
or formed on the other side thereof. Furthermore, the reference numeral
4
denotes a second semiconductor pellet that comprises a second semiconductor substrate
5
with a diameter smaller than that of the first semiconductor substrate
2
. Also, there are protruded electrodes
6
mounted on one side of the second semiconductor substrate
5
such that the protruded electrodes
6
face to the flat electrodes
3
, respectively. Accordingly, the first and second semiconductor substrates
2
,
5
make up a semiconductor device
7
by facing their electrode-formed sides to each other such that each electrode of one substrate is placed over the corresponding electrode of the other substrate, followed by heating and pressurizing these superimposed portions to make an electrical connection between these substrates
2
,
5
.
A method for fabricating such a semiconductor device
7
will be described.
At first, as shown in
FIG. 6
, a first semiconductor pellet
1
is prepared. As shown in the figure, one side of a first semiconductor substrate
2
is covered with an insulating film
8
having a main part formed as an opening portion. Then, flat electrodes
3
are formed on the semiconductor substrate
2
. That is, an aluminum layer
3
a
is formed in the opening portion of the insulating film
8
and is electrically connected to an internal circuit (not shown) in the first semiconductor pellet
1
. In addition, a barrier metal(e.g., titanium or nickel) layer
3
b
is formed on the aluminum layer
3
a
. Furthermore, the surface of the titanium layer
3
b
is covered with a gold layer
3
c
to facilitate its external connection. In this manner, two or more flat electrodes
3
are provided in a ring form on the main surface of the semiconductor pellet
1
.
Next, as shown in
FIG. 7
, a second semiconductor pellet
4
is prepared. Just as with the first semiconductor substrate
2
, one side of a second semiconductor substrate
5
is covered with an insulating film
9
. The insulating film
9
has a main part formed as an opening portion where a protruded electrode
6
is formed on the semiconductor substrate
5
. That is, an aluminum layer
6
a
is formed in the opening portion of the insulating film
9
on which a stepped electrode
6
b
is provided. In this example, the electrode
6
b
is prepared by melting the tip of a gold wire to shape it like a ball and pressing the ball-shaped tip of the gold wire by the bottom end of a capillary followed by pulling out the gold wire around the pressed portion so as to form the stepped electrode
6
b
having a large-diameter base portion on the side of the semiconductor substrate
5
and a small-diameter tip portion extending from the base portion.
Subsequently, as shown in
FIG. 8
, the semiconductor pellet
1
of
FIG. 6
is exactly placed on a predetermined position on a stage
10
being heated. Thus, the flat electrode
3
is heated at a predetermined temperature (e.g., 200 degrees centigrade to 300 degrees centigrade). On the other hand, as shown in
FIG. 9
, the second semiconductor pellet
4
is held by a suction collet
11
and is then properly aligned with the first semiconductor
1
. Then, the collet
11
brings down the semiconductor pellet
4
to make each connection between the electrodes
3
,
6
. The collet
11
comprises a heating means (not shown) to heat the protruded electrode
6
at a predetermined temperature (e.g., 200 degrees centigrade to 300 degrees centigrade).
More concretely, the arrangement of the semiconductor pellet
4
in place can be performed as follows. At first, the suction collet
11
moves up and down by a pellet-supplying portion (not shown) to hold the semiconductor pellet under suction. Then, the position of the protruded electrode
6
is recognized by a visual monitoring system (not shown) at a middle position where the collet
11
can be laterally moved to correct the amount of deviation from alignment with the corresponding flat electrode
3
being arranged in place. Subsequently, the second semiconductor pellet
4
is brought down to the first semiconductor pellet
1
, while the collet
11
keeps its sucking state at a predetermined pressure. Consequently, the alignment between the semiconductor pellets
1
,
4
is completed. After the alignment, the suction collet
11
moves downward such that the second electrode
6
is brought into contact with the first electrode
3
. Subsequently, the suction collet
11
further moves downward to make a press-contact between the first and second electrodes
3
,
6
. At this time, the overall force to which the protruded electrode
6
is subjected in resisting the press-contact is concentrated onto the small-diameter tip portion (.e., an extremely small surface area) of the electrode
6
as such a portion is in the shape of a paraboloid of revolution. As a result, the small-diameter tip portion of the electrode
6
is crushed in its axial direction and is pressed into the flat electrode
3
while the periphery of the tip portion is extended outward. In other words, the electrodes
3
,
6
are pressed through the addition of heat and then extended outwardly at their contact surfaces to make an electrical contact between them, resulting in a semiconductor device
7
shown in FIG.
5
. After that, the suction collet
11
releases the second semiconductor pellet
4
and the application of heat is stopped. Then, the suction collet
11
moves upward to allow the removal of the semiconductor device
7
as a single-piece construction of the first and second semiconductor pellets
1
,
4
from the heating stage
10
. Alternatively, but not shown in the figure, the semiconductor device
7
may be prepared by sealing between the first and second semiconductor pellets
1
,
4
with a resin as needed. Such a construction protects any wiring layer (not shown) formed on the facing sides of these pellets
1
,
4
from outside air. As shown in the figure, the outer diameter of the first semiconductor pellet
1
is larger than that of the second semiconductor pellet
4
, so that the outer diameter of the semiconductor device
7
in a plane view can be determined by the outer diameter of the first one. On the other hand, the thickness of the semiconductor device
7
can be determined by the total thickness of two semiconductor pellets
1
,
4
including the electrodes
3
,
6
. Accordingly, the semiconductor device
7
can be miniaturized and thinned.
The semiconductor device
7
thus obtained can be solely surface-mounted on a printed circuit board as disclosed in publications such as Japanese Patent Application Laying-open Nos. 5-13663 (1993) and 11-135537 (1999). Alternatively, as disclosed in other publications such as Japanese Patent Application Laying-open Nos. 11-163256 (1999) an
Ikegami Gorou
Nagai Nobuaki
Clark Jasmine J B
NEC Electronics Corporation
Young & Thompson
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