U.S. patent application number 09/851324 was filed with the patent office on 2002-09-19 for spherical semiconductor device and method for fabricating the same.
This patent application is currently assigned to Nippon Steel Corporation. Invention is credited to Fukano, Atsuyuki, Hashino, Eiji, Shimokawa, Kenji, Takeda, Nobuo, Tatsumi, Kohei.
Application Number | 20020132462 09/851324 |
Document ID | / |
Family ID | 26518058 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020132462 |
Kind Code |
A1 |
Tatsumi, Kohei ; et
al. |
September 19, 2002 |
Spherical semiconductor device and method for fabricating the
same
Abstract
A spherical semiconductor device includes a spherical
semiconductor element having one or more electrodes on its surface.
Spherical conductive bumps are formed at the positions of the
electrodes. The electrodes are so arranged as to contact a common
plane. Spherical bumps constituting a group to be connected to the
outside protrude above the spherical semiconductor element such
that a predetermined gap is formed between a plane or a spherical
surface capable of contacting the spherical bumps and the surface
of the spherical semiconductor element. The spherical semiconductor
device is connected to various circuit boards or another
semiconductor device through the spherical bumps. This affords easy
and accurate electrical connections to the outside.
Inventors: |
Tatsumi, Kohei; (Chiba,
JP) ; Shimokawa, Kenji; (Chiba, JP) ; Hashino,
Eiji; (Chiba, JP) ; Takeda, Nobuo; (Chiba,
JP) ; Fukano, Atsuyuki; (Chiba, JP) |
Correspondence
Address: |
Connolly Bove Lodge & Hutz LLP
Suite 800
1990 M Street, N.W.
Washington
DC
20036-3425
US
|
Assignee: |
Nippon Steel Corporation
Tokyo
JP
|
Family ID: |
26518058 |
Appl. No.: |
09/851324 |
Filed: |
May 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09851324 |
May 9, 2001 |
|
|
|
09350125 |
Jul 9, 1999 |
|
|
|
Current U.S.
Class: |
438/613 ;
257/E23.021; 257/E25.01; 257/E29.022; 438/612; 438/666 |
Current CPC
Class: |
H01L 29/0657 20130101;
H01L 2924/181 20130101; H01L 2924/01074 20130101; H01L 24/13
20130101; H01L 2924/01024 20130101; H01L 2924/01049 20130101; H01L
2924/01015 20130101; H01L 2924/00014 20130101; H01L 2924/3025
20130101; H01L 2924/15311 20130101; H01L 2224/13099 20130101; H01L
2924/01006 20130101; H01L 2924/10155 20130101; H01L 2924/01047
20130101; H01L 2924/00014 20130101; H01L 2924/014 20130101; H01L
2924/3011 20130101; H01L 2924/14 20130101; H01L 2924/0103 20130101;
H01L 2924/181 20130101; H01L 2924/15787 20130101; H01L 2924/10253
20130101; H01L 2924/01079 20130101; H01L 25/065 20130101; H01L
24/81 20130101; H01L 2924/01082 20130101; H01L 2924/01022 20130101;
H01L 2924/01027 20130101; H01L 2924/01033 20130101; H01L 2924/01075
20130101; H01L 2224/16145 20130101; H01L 2924/01046 20130101; H01L
2924/01013 20130101; H01L 2924/01078 20130101; H01L 2924/15787
20130101; H01L 2224/48 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2924/00 20130101; H01L 2924/01029 20130101;
H01L 24/16 20130101; H01L 2924/1017 20130101; H01L 2924/10253
20130101 |
Class at
Publication: |
438/613 ;
438/612; 438/666 |
International
Class: |
H01L 021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 1998 |
JP |
10-210442 |
Jul 9, 1998 |
JP |
10-210443 |
Claims
15. (Amended) A method for fabricating a spherical semiconductor
device having spherical bumps on surface electrodes of a spherical
semiconductor element, comprising the steps of: temporarily
arranging conductive balls for forming said spherical bmps, on an
arrangement substrate at positions respectively corresponding to
said surface electrodes; and transferring said conductive balls
onto said surface electrodes to join the electrodes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor device and,
more particularly, to a spherical semiconductor device comprising a
spherical semiconductor element having one or more electrodes on
its surface. The present invention relates also to a method for
fabricating a semiconductor device and, more particularly, to a
method for fabricating a spherical semiconductor device comprising
a spherical semiconductor element having one or more electrodes on
its surface.
[0003] 2. Description of the Related Art
[0004] Recently, instead of conventional semiconductor devices
fabricated by forming integrated circuits on silicon wafers, a
spherical semiconductor element fabricated by forming an electric
circuit on the surface of spherical silicon has been developed.
This spherical semiconductor element has one or more electrodes on
its surface. A semiconductor device having a variety of functions
can be realized by combining spherical semiconductor elements
having various functions.
[0005] Such a spherical semiconductor element cannot operate only
by itself. It requires input/output means for electrical connection
to the outside to exchange electrical signals with an external
circuit or the like. Although spherical semiconductor elements have
excellent functions, effective measures have not been found
particularly for packaging.
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to provide a
spherical semiconductor device having improved connectivity to the
outside.
[0007] It is another object of the present invention to provide a
method for fabricating a spherical semiconductor device having
improved connectivity to the outside.
[0008] According to the present invention, a spherical
semiconductor device comprises a spherical semiconductor element
comprising one or more electrodes on a surface of the element and
spherical conductive bumps formed at the positions of the
electrodes.
[0009] According to an aspect of the present invention, said
electrodes are arranged so as to contact a common plane.
[0010] According to another aspect of the present invention, the
spherical bumps constituting a group to be connected to the
outside, protrude above the spherical semiconductor element such
that there is formed no gap or a predetermined gap between a plane
or a spherical surface capable of contacting the group of spherical
bumps, and the surface of the spherical semiconductor element.
[0011] According to another aspect of the present invention, each
spherical bump is made of a refractory metal having a melting point
of not less than 550.degree. C..
[0012] According to another aspect of the present invention, each
electrode is made of a material selected from the group consisting
of aluminum, copper, and an alloy containing at least one of
aluminum and copper, and each spherical bump is made of a material
selected from the group consisting of gold, platinum, palladium,
silver, copper, aluminum, nickel, and an alloy containing at least
one of gold, platinum, palladium, silver, copper, aluminum, and
nickel.
[0013] According to another aspect of the present invention, each
spherical bump is made of a low-melting metal having a melting
point of not more then 450.degree. C.
[0014] According to another aspect of the present invention, each
electrode is made of a material selected from the group consisting
of aluminum, copper, and an alloy containing at least one of
aluminum and copper, and each spherical bump is made of a material
selected from the group consisting of lead, tin, indium, bismuth,
zinc, an alloy containing at least one of lead, tin, indium,
bismuth, and zinc, and an alloy mainly containing one of
gold-silicon alloy, gold-tin alloy, and silver-tin alloy.
[0015] According to another aspect of the present invention, at
least one metal layer selected from the group consisting of
titanium, tungsten, titanium-tungsten, nickel, chromium, gold,
palladium, copper, and platinum is formed on each electrode.
[0016] According to another aspect of the present invention, each
electrode is connected through the spherical bump formed thereon,
to an electrode of a ceramics substrate, a film carrier, a silicon
substrate, a printed circuit board, a lead frame, a semiconductor
chip, or a spherical semiconductor element.
[0017] According to another aspect of the present invention, each
spherical bump is made of a refractory metal and connected through
a low-melting metal to an electrode of a ceramics substrate, a film
carrier, a silicon substrate, a printed circuit board, a lead
frame, a semiconductor chip, or a spherical semiconductor element,
and the difference in melting point between the refractory metal
and the low-melting metal is not less than 50.degree. C.
[0018] According to another aspect of the present invention, each
spherical semiconductor element is encapsulated with an
encapsulating material.
[0019] According to another aspect of the present invention, each
electrode has a shape selected from the group of a trapezoid, a
polygon having at least five sides, and a circle.
[0020] According to another aspect of the present invention, each
electrode has an area equivalent to the area of a circle having a
diameter not less than 3% of a diameter of the spherical
semiconductor element.
[0021] According to another aspect of the present invention, each
spherical bump is made of a refractory metal coated with a
low-melting metal.
[0022] According to the present invention, since spherical
conductive bumps are formed at the positions of electrodes of a
spherical semiconductor element, electrical connections to the
outside can be easily and accurately made through the spherical
bumps.
[0023] In particular, a group of spherical bumps to be connected to
the outside are arranged to protrude above the spherical
semiconductor element such that a predetermined gap is formed
between a plane or a spherical surface capable of contacting the
group of spherical bumps and the surface of the spherical
semiconductor element. Since the spherical bumps thus protrude
above the spherical semiconductor element, extremely superior bump
joining properties can be obtained.
[0024] In case of melt joining, it can be performed by the wet
effect of each bump melted even if there is formed no gap.
[0025] The surface of each spherical bump made of a refractory
metal is coated with a low-melting metal. By setting the difference
in melting point between the refractory and low-melting metals to
50.degree. C. or more, preferably, 100.degree. C. or more, the
surface portion can be melted while the core remains solid during
joining. So, a certain distance, i.e., a distance not less than the
diameter of the core metal can be kept between the junction
portions.
[0026] Each spherical bump may deform into a shape like a Rugby
ball, or unevenly deform at its part, e.g., its junction portion.
In order for the spherical bumps surely to protrude beyond an apex
of the spherical semiconductor element, two or more layers of bumps
may be used.
[0027] According to the present invention, since spherical
conductive bumps are formed at the positions of electrodes of a
spherical semiconductor element, electrical connections to the
outside can be easily and accurately made through the spherical
bumps. In this case, by arranging the spherical bumps to protrude
above the spherical semiconductor element, extremely superior bump
joining properties can be obtained. As a result, high reliability
can be obtained when a semiconductor device comprising such a
spherical semiconductor element is packaged or the like.
[0028] According to another aspect of the present invention, a
method for fabricating a spherical semiconductor device having
spherical bumps on surface electrodes of a spherical semiconductor
element, comprises the steps of temporarily arranging conductive
balls for forming the spherical bumps, on an arrangement substrate
at positions respectively corresponding to said surface electrodes,
and transferring the conductive balls onto the surface electrodes
to join.
[0029] According to another aspect of the present invention, the
conductive balls are transferred from the arrangement substrate to
the surface electrodes while the position of each of the conductive
balls on the arrangement substrate is regulated.
[0030] According to another aspect of the present invention, the
conductive balls are transferred from the arrangement substrate to
the surface electrodes such that a predetermined gap is formed
between a surface of the arrangement substrate and a surface of the
spherical semiconductor element.
[0031] According to another aspect of the present invention, the
conductive balls are transferred onto and joined to the surface
electrodes by thermo-compression bonding.
[0032] According to another aspect of the present invention, the
conductive balls are transferred onto and joined to the surface
electrodes by melting.
[0033] According to another aspect of the present invention, each
conductive ball is transferred onto and joined to the corresponding
surface electrode after one of the surface electrode and conductive
ball is coated with a flux.
[0034] According to another aspect of the present invention,
conductive balls are arranged on the arrangement substrate to
correspond to electrodes of spherical semiconductor elements, and
the conductive balls are transferred onto the spherical
semiconductor elements at once from the arrangement substrate to
form bumps.
[0035] The fabrication method according to the present invention
uses an arrangement substrate having arrangement holes
corresponding to surface electrodes of a spherical semiconductor
element. Conductive balls are temporarily arranged on the
arrangement substrate and then transferred onto the surface
electrodes of the spherical semiconductor element, and thereby the
conductive balls and the surface electrodes are brought into
contact with each other while they are aligned with each other.
[0036] In this case, since the surface of the semiconductor element
is spherical, the position of each conductive ball may deviate
during the transfer process if it is simply placed on the
arrangement substrate for temporary arrangement. In the present
invention, therefore, positional regulation is effected when each
conductive ball on the arrangement substrate is brought into
contact with a corresponding electrode. This affords a proper and
reliable transfer operation for the conductive balls.
[0037] According to the present invention, in fabricating a
semiconductor device comprising such a spherical semiconductor
element, conductive balls are temporarily arranged on an
arrangement substrate and then transferred onto the surface
electrodes of the spherical semiconductor element, and thereby the
conductive balls and the surface electrodes are brought into
contact with each other while they are aligned with each other. It
is, therefore, possible to form spherical bumps of the conductive
balls and having excellent characteristics, and realize good
electrical connections to an external circuit or the like through
the spherical bumps.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a perspective view showing a semiconductor device
according to the first embodiment of the present invention;
[0039] FIG. 2 is a representation for illustrating arrangements of
spherical bumps in the semiconductor device according to the first
embodiment;
[0040] FIG. 3 is a sectional view showing a packaging example of
the semiconductor device according to the first embodiment;
[0041] FIGS. 4A and 4B are sectional views showing another
packaging example of the semiconductor device according to the
first embodiment;
[0042] FIG. 5 is a sectional view showing another packaging example
of the semiconductor device according to the first embodiment;
[0043] FIG. 6 is a sectional view showing another packaging example
of the semiconductor device according to the first embodiment;
[0044] FIGS. 7A to 7C are views showing another packaging example
of the semiconductor device according to the first embodiment;
[0045] FIGS. 8A to 8C are views showing another packaging example
of the semiconductor device according to the first embodiment;
[0046] FIG. 9 is a plan view showing an arrangement of electrodes
in the semiconductor device according to the first embodiment;
[0047] FIG. 10 is a perspective view showing a semiconductor device
according to the second embodiment;
[0048] FIG. 11 is a representation for illustrating arrangements of
spherical bumps in the semiconductor device according to the second
embodiment;
[0049] FIG. 12 is a plan view showing the state that metal balls
are temporarily arranged on an arrangement substrate in the
semiconductor device according to the second embodiment;
[0050] FIG. 13 is a sectional view showing a metal ball temporarily
arranged on the arrangement substrate according to the second
embodiment shown in FIG. 12;
[0051] FIG. 14 is a partially enlarged view of an arrangement hole
of the arrangement substrate in a fabrication method of the
semiconductor device according to the second embodiment;
[0052] FIG. 15 is a sectional view showing the state that metal
balls are transferred in the fabrication method of the
semiconductor device according to the second embodiment;
[0053] FIGS. 16A and 16B are sectional views showing a packaging
example of the semiconductor device according to the second
embodiment;
[0054] FIG. 17 is a sectional view showing another packaging
example of the semiconductor device according to the second
embodiment; and
[0055] FIGS. 18A and 18B are perspective views showing a
construction for transferring metal balls onto spherical
semiconductor elements at once in the fabrication method of the
semiconductor device according to the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] Preferred embodiments of the present invention will be
described below with reference to the accompanying drawings.
[0057] First Embodiment
[0058] FIG. 1 shows a semiconductor device according to an
embodiment of the present invention. In this embodiment, spherical
conductive bumps 10 are formed at the positions of electrodes of a
spherical semiconductor element 1.
[0059] The spherical semiconductor element 1 is fabricated by
forming a desired electric circuit on the surface of a spherical
silicon crystal material through fabrication steps. The fabrication
steps mainly includes steps of cleaning a crystal material, forming
oxide films, forming photoresist films, photolithographing by
spherical exposure, patterning by developing, etching, etc. For the
circuit formed through these steps, electrodes are formed for
electrical connection to the outside. More specifically, an
arrangement of electrodes is formed on the spherical surface of the
spherical semiconductor element 1.
[0060] Referring to FIG. 1, a group of spherical bumps for making
connection to the outside are formed on a circumference on the
surface of the spherical semiconductor element 1. These spherical
bumps 10 are made by the manner of transferring conductive metal
balls onto the electrode portions of the spherical semiconductor
element 1. These spherical bumps 10 have a common contact plane
(that may be spherical) S. These spherical bumps 10 protrude above
the spherical semiconductor element 1 such that a predetermined gap
is formed between the contact plane S and the surface of the
spherical semiconductor element 1.
[0061] FIG. 2 schematically shows examples of arrangement of
spherical bumps 10. Each of the spherical bumps 10 contacting the
contact plane S is joined to an electrode 2 formed on the surface
of the spherical semiconductor element 1. As shown in FIG. 2, a gap
G is formed between the contact surface S and the surface (having
an apex P) of the spherical semiconductor element 1. The spherical
bumps 10 are disposed to protrude above the spherical semiconductor
element 1 and form the gap G. This affords an effective margin for
pressure deformation of the spherical bumps 10 when the spherical
bumps 10 are pressed onto objects to join, and ensures proper bump
joining. Note that bump joining is possible even when no gap is
formed between the contact plane S and the surface of the spherical
semiconductor element 1, i.e., when G =0.
[0062] In another example shown in FIG. 2, no gap is formed between
a contact surface S' that includes the apex P, and the surface of
the spherical semiconductor element 1. In this state, however,
proper bump joining becomes difficult. So, it is preferable that
the level of arrangement of spherical bumps 10 meets the following
expression:
R-r.ltoreq.(r+R)cos .theta.(0.ltoreq..theta..ltoreq.2.pi.)
[0063] where R represents the radius of the spherical semiconductor
element, r does the radius of each spherical bump, and .theta. does
the angle between the line connecting the centers of the spherical
semiconductor element and spherical bump, and the diameter
extending through the apex P. The relation between the size r of
each spherical bump and the position 0 of the spherical bump is
designed in accordance with the size of each electrode on the
element surface and the necessary number of electrodes.
[0064] The spherical bumps 10 can be formed on the electrodes 2 of
the spherical semiconductor element 1 by thermo-compression
bonding. In this case, each spherical bump 10 is made of a
refractory metal material having a melting point preferably of not
less than 550.degree. C., more preferably of not less than
600.degree. C. Particularly in case of each electrode 2 made of
aluminum or copper, or an alloy containing one or more of those
metals, each spherical bump 10 is made of gold, platinum,
palladium, silver, copper, aluminum or nickel, or an alloy
containing one or more of those metals.
[0065] Each spherical bump 10 may deform into a shape like a Rugby
ball, or unevenly deform at its part, e.g., its junction portion.
In order for the spherical bumps 10 surely to protrude beyond the
apex P of the spherical semiconductor element 1, two or more layers
of bumps may be used that are stacked like "dumplings" or
"rosary".
[0066] Alternatively, the spherical bumps 10 can be formed on the
electrodes 2 of the spherical semiconductor element 1 by melting.
In this case, each spherical bump 10 is made of a low-melting metal
material having a melting point preferably of not more than
450.degree. C., more preferably of not less than 400.degree. C.
Particularly in case of each electrode 2 made of aluminum or
copper, or an alloy containing one or more of those metals, each
spherical bump 10 is made of lead, tin, indium, bismuth or zinc, or
an alloy containing one or more of those metals, or an alloy mainly
containing gold-silicon alloy, gold-tin alloy, or silver-tin
alloy.
[0067] In the latter case, one or more metals selected from
titanium, tungsten, titanium tungsten, nickel, chromium, gold,
palladium, copper, and platinum are preferably formed on each
electrode 2 in layers. The electrodes 2 made of aluminum or its
alloy show bad wettability to a low-melting metal such as solder.
For this reason, such a metal layer or layers as described above
are provided on each electrode 2 as underlayer for giving good
wettability and preventing diffusion or oxidation.
[0068] When the semiconductor device of this embodiment is
packaged, its inner electric circuit is connected to an external
circuit or the like through the spherical bumps 10 formed as
described above. The electrodes 2 are then connected to electrodes
of, e.g., a ceramics substrate, a film carrier, a silicon
substrate, a printed circuit board, a lead frame, a semiconductor
chip, or another spherical semiconductor element. Note that two or
more spherical semiconductor elements may be connected to a
substrate or the like after being connected to each other.
[0069] FIG. 3 shows an example of a BGA (Ball Grid Arrangement)
package using a spherical semiconductor element 1 according to this
embodiment. Referring to FIG. 3, each electrode 2 of the spherical
semiconductor element 1 is connected to a printed circuit board 20
through the spherical bump 10 formed on the electrode 2. The
printed circuit board 20 connected to the spherical semiconductor
element 1 is further connected to various electronic devices to
exchange electrical signals with those devices. Note that two or
more spherical semiconductor elements 1 may be packaged in a single
BGA package.
[0070] When a semiconductor device according to this embodiment is
packaged, its spherical semiconductor element 1 is preferably
encapsulated with an encapsulating material 3 as shown in FIG. 3.
As the encapsulating material 3, it is preferable to use an
insulating material such as a resin or a mold compound containing a
resin and filler. With this encapsulation, it is possible to
protect the circuit surface of the spherical semiconductor element
1 or effectively to suppress thermal strain resulting from the
difference in thermal expansion coefficient between the spherical
semiconductor element 1 and the printed circuit board 20 or the
like.
[0071] Referring to FIG. 4A, spherical semiconductor elements 1
according to this embodiment are connected to each other through
some of spherical bumps 10 formed on their electrodes 2, and
mounted on a printed circuit board 20. In this case, such spherical
semiconductor elements 1 are preferably encapsulated as a whole
with an encapsulating resin 3, as shown in FIG. 4B.
[0072] FIG. 5 shows an example of a QFP (Quad Flat Package) using a
spherical semiconductor element 1 according to this embodiment.
Referring to FIG. 5, each electrode 2 of the spherical
semiconductor element 1 is connected to a lead frame 21 through the
spherical bump 10 formed on the electrode 2. This spherical
semiconductor element 1 is also preferably encapsulated with an
encapsulating material 3. Also in such a semiconductor device, two
or more spherical semiconductor elements 1 may be connected to such
a lead frame substrate.
[0073] FIG. 6 shows another example of packaging for a
semiconductor device according to this embodiment. Referring to
FIG. 6, each electrode 2 of a spherical semiconductor element 1 for
a memory device is connected to a semiconductor chip 22 through the
spherical bump 10 formed on the electrode 2.
[0074] As shown in FIG. 7A, two spherical semiconductor elements 1
according to this embodiment can be connected to each other through
spherical bumps 10 of one of them.
[0075] Alternatively, two spherical semiconductor elements 1
according to this embodiment can be connected to each other through
spherical bumps 10 of both of them, as shown in FIG. 7B. In this
case, the spherical bumps of each couple have been previously
joined to each other. Also in this case, each spherical bumps 10
may deform after being pressed, as shown in FIG. 7C.
[0076] As shown in FIG. 8A, a spherical semiconductor element 1
according to this embodiment can be connected to a junction surface
of, e.g., a printed circuit board 20 through spherical bumps 10a
and 10b of different sizes. In this case, the spherical bumps 10a
and 10b are concentrically arranged on the surface of the spherical
semiconductor element 1, as shown in FIG. 8B. As the outer
spherical bumps 10a, two or more layers of spherical bumps can be
used, as shown in FIG. 8C.
[0077] Several examples of semiconductor device of the present
invention have been explained together with several typical
packaging manners. As described above, a semiconductor device
according to the present invention is provided with spherical
conductive bumps 10 formed at the positions of the electrodes 2 of
each spherical semiconductor element 1. So, electrical connections
to the outside can be easily and accurately made through the
spherical conductive bumps 10.
[0078] In a spherical semiconductor element 1 according to the
present invention, each electrode 2 preferably has a trapezoidal
shape or a fan shape. The electrodes 2 constituting one connection
group are arranged around a center such that the longer side of
each electrode 2 is positioned outside, as shown in FIG. 9. With
such an arrangement, peeling resistance to external stress after
joining can be increased.
[0079] Alternatively, each electrode 2 can be a polygon having five
sides or more, or a circle (as plane figure). When the spherical
bump 10 on each electrode 2 is pressed onto an object to join, such
a shape of the electrode 2 makes it possible uniformly to disperse
the load produced between the electrode 2 ad spherical bump 10, and
so avoid stress concentration. So, the generation of strain or the
like during bump joining process can be eliminated, and proper bump
joining is ensured.
[0080] In a spherical semiconductor element 1 according to the
present invention, each electrode 2 preferably has an area
equivalent to that of a circle having a diameter which is 3% or
more of the diameter of the spherical semiconductor element 1. By
thus setting the area of each electrode 2, when the semiconductor
device is put into practical use by packaging or the like, it is
possible to obtain enough joining strength to resist the pressure
load during bump joining process. Proper and good bump joining is
ensured also in this respect.
[0081] In the above embodiment, a high-melting bump having a
melting point of 600.degree. C. or more may be formed on each
electrode 2 of a spherical semiconductor element 1 and connected to
an electrode of a ceramic substrate, a film carrier, a silicon
substrate, a printed circuit board, a lead frame, a semiconductor
chip, or another spherical semiconductor element through a
low-melting metal having a melting point of 400.degree. C. or less.
It may also be possible previously to form a refractory metal bump
also on the other electrode to connect, and then to join the
refractory metals on both electrodes through a low-melting
metal.
[0082] Second Embodiment
[0083] Next, a fabrication method for a semiconductor device
according to an embodiment of the present invention will be
described.
[0084] FIG. 10 shows a semiconductor device according to an
embodiment of the present invention. In this device, spherical
conductive bumps 110 are formed at the positions of electrodes of a
spherical semiconductor element 101.
[0085] The spherical semiconductor element 101 is fabricated by
forming a desired electric circuit on the surface of a spherical
silicon crystal material through fabrication steps. The fabrication
steps mainly includes steps of cleaning a crystal material, forming
oxide films, forming photoresist films, photolithographing by
spherical exposure, patterning by developing, etching, etc. For the
circuit formed through these steps, electrodes are formed for
electrical connection to the outside. More specifically, an
arrangement of electrodes is formed on the spherical surface of the
spherical semiconductor element 101.
[0086] Referring to FIG. 10, a group of spherical bumps 110 for
making connection to the outside are formed on a circumference on
the surface of the spherical semiconductor element 101. These
spherical bumps 110 are made by the manner of transferring
conductive metal balls onto the electrode portions of the spherical
semiconductor element 101. These spherical bumps 110 have a common
contact plane (that may be spherical) S. These spherical bumps 110
protrude above the spherical semiconductor element 101 such that a
predetermined gap is formed between the contact plane S and the
surface of the spherical semiconductor element 101.
[0087] FIG. 11 schematically shows examples of arrangement of
spherical bumps 110. Each of the spherical bumps 110 contacting the
contact plane S is joined to an electrode 102 formed on the surface
of the spherical semiconductor element 101. As shown in FIG. 11, a
gap G is formed between the contact surface S and the surface
(having an apex P) of the spherical semiconductor element 101. The
spherical bumps 110 are disposed to protrude above the spherical
semiconductor element 101 and form the gap G. This affords an
effective margin for pressure deformation of the spherical bumps
110 when the spherical bumps 110 are pressed onto objects to join,
and ensures proper bump joining.
[0088] In another example shown in FIG. 11, no gap is formed
between a contact surface S' that includes the apex P, and the
surface of the spherical semiconductor element 101. In this state,
however, proper bump joining becomes difficult. So, it is
preferable that the level of arrangement of spherical bumps 110
meets the following expression:
R-r.ltoreq.(r+R) cos .theta.(0.ltoreq..theta.2.pi.)
[0089] where R represents the radius of the spherical semiconductor
element, r does the radius of each spherical bump, and .theta. does
the angle between the line connecting the centers of the spherical
semiconductor element and spherical bump, and the diameter
extending through the apex P.
[0090] For fabricating the spherical semiconductor device as
described above that has the spherical bumps 110 formed on the
electrodes 102 on the spherical semiconductor element 101, an
arrangement substrate is used which has holes in the arrangement
corresponding to the electrodes 102 on the spherical semiconductor
element 101. Conductive metal balls for forming the spherical bumps
110 are temporarily arranged on this arrangement substrate, and
then transferred onto the surfaces of the electrodes 102 of the
spherical semiconductor element 101 to join.
[0091] FIG. 12 shows the state that the conductive metal balls 111
for forming the spherical bumps 110 are temporarily arranged on the
arrangement substrate 120. For forming the spherical bumps 110
arranged on a circumference on the surface of the spherical
semiconductor element 101 as shown in FIG. 10, the metal balls 111
are temporarily arranged in the form of a circle as shown in FIG.
12.
[0092] Referring to FIG. 13, each metal ball 111 is positioned and
held by an arrangement hole 121 of the arrangement substrate 120.
In this example, each arrangement hole 121 is formed at the
position along a circumference corresponding to each electrode 102
on the spherical semiconductor element 101. The arrangement
substrate 120 may be a flat plate. An opening portion 121a of each
arrangement hole 121 is tapered. This taper makes the metal ball
111 stable, so the metal ball 111 can be accurately positioned and
held.
[0093] Referring to FIG. 14, the taper angle .alpha. at the opening
portion 121a of each arrangement hole 121 is designed to be within
the range of preferably 10.degree.<.alpha.<60.degree., more
preferably,
30.degree..theta.<.alpha.<60.degree.-.theta.(.theta.<20.degree.)
[0094] An appropriate vacuum source (not shown) may be connected to
the arrangement holes 121 of the arrangement substrate 120. With
the vacuum source, the metal ball 111 temporarily arranged on each
arrangement hole 121 can be drawn by negative pressure, as
indicated by the dotted line in FIG. 13, and held on the
arrangement hole 121 by the sucking force.
[0095] The metal balls 111 can be transferred onto and joined to
the surfaces of the electrodes 102 of the spherical semiconductor
element 101 by thermo-compression bonding. In FIG. 15, the metal
balls 111 ate temporarily arranged in the form of a circle on the
arrangement substrate 120, as shown in FIG. 12. The spherical
semiconductor element 101 is moved down toward the metal balls 111.
The metal balls 111 and the electrodes 102 of the spherical
semiconductor element 101 are brought into contact with each other
while being aligned. The metal balls 111 can be transferred onto
and joined to the electrodes 102 by pressing the metal balls 111
against the electrodes 102 with appropriately heating. The
spherical bump 110 is thus formed on each electrode 102 of the
spherical semiconductor element 101.
[0096] In this example, each metal ball 111 is accurately
positioned and held by the tapered opening 121a of the
corresponding arrangement hole 121 of the arrangement substrate
120, as shown in FIG. 13. Each metal ball 111 can be properly and
reliably transferred onto the corresponding electrode 102 by
regulating the position of the metal ball 111 so as to be
stable.
[0097] The metal balls 111 are transferred such that a gap G is
formed between the surface 120a of the arrangement substrate 120
and the lowermost point (the apex P shown in FIG. 11) of the
spherical semiconductor element 101. The gap G is determined by
geometrical relations such as the arrangement position of the
electrodes 102 and the size of the metal balls 111.
[0098] When the metal balls 111 are transferred onto and joined to
the electrodes 102 of the spherical semiconductor element 101 to
form the spherical bumps 110, the metal balls 111 can be drawn onto
the arrangement holes 121 by vacuum. In this case, the metal balls
111 can be held on the lower side of the arrangement substrate 111,
so the above process can be performed in the reverse vertically
positional relation.
[0099] The metal balls 111 can be transferred onto and joined to
the electrodes 102 of the spherical semiconductor element 101 also
by melting. In this case, each electrode 102 of the spherical
semiconductor element 101 or each metal ball 111 is preferably
coated with a flux. It is because an electrode made of an alloy of,
e.g., aluminum shows bad wettability in general to a low-melting
metal such as solder. Such flux coating as described above affords
good joining properties. Such flux coating is useful also for
removing solder oxide films and fixing the metal balls.
[0100] When the semiconductor device fabricated as described above
is packaged, its inner electric circuit is connected to an external
circuit or the like through the spherical bumps 110 formed as
described above. The electrodes 102 of the spherical semiconductor
element 101 are then connected to electrodes of, e.g., a ceramics
substrate, a film carrier, a silicon substrate, a printed circuit
board, a lead frame, a semiconductor chip, or another spherical
semiconductor element.
[0101] FIG. 16A shows an example of a BGA package using a spherical
semiconductor element 101. Referring to FIG. 16A, each electrode
102 of the spherical semiconductor element 101 is connected to a
printed circuit board 130 through the spherical bump 110 formed on
the electrode 102. The printed circuit board 130 connected to the
spherical semiconductor element 101 is further connected to various
electronic devices to exchange electrical signals with those
devices.
[0102] When the semiconductor device fabricated as described above
is packaged, its spherical semiconductor element 101 is preferably
encapsulated with an encapsulating material 103 as shown in FIG.
16A. As the encapsulating material 103, it is preferable to use an
insulating material such as a resin or a mold compound containing a
resin and filler. With this encapsulation, it is possible to
protect the circuit surface of the spherical semiconductor element
101 or effectively to suppress thermal strain resulting from the
difference in thermal expansion coefficient between the spherical
semiconductor element 101 and the printed circuit board 130 or the
like.
[0103] Referring to FIG. 16B, spherical semiconductor elements 101
are connected to each other through some of spherical bumps 110
formed on their electrodes 102, and mounted on a printed circuit
board 120. In this case, such spherical semiconductor elements 101
are preferably encapsulated as a whole with an encapsulating resin
103.
[0104] FIG. 17 shows an example of a QFP using a spherical
semiconductor element 101. Referring to FIG. 17, each electrode 102
of the spherical semiconductor element 101 is connected to a lead
frame 131 through the spherical bump 110 formed on the electrode
102. This spherical semiconductor element 101 is also preferably
encapsulated with an encapsulating material 103.
[0105] FIGS. 18A and 18B show an example in which spherical bumps
110 are formed onto spherical semiconductor elements 101 at once.
In this example, metal balls are arranged on an arrangement
substrate so as to correspond to the arrangements of the electrodes
of the spherical semiconductor elements, and then the metal balls
are transferred onto the electrodes at once. In this manner, groups
of metal balls can be transferred at once from one arrangement
substrate.
[0106] More specifically, spherical semiconductor elements 101 are
arranged on a holding substrate 200 such that the electrodes 102 of
each spherical semiconductor element 101 face down, as shown in
FIG. 18A. Groups of metal balls 111 are temporarily arranged on an
arrangement substrate 300 so as to correspond to the spherical
semiconductor elements 101. The metal balls 111 are accurately
positioned by dimples or recesses 301 (see FIG. 18B) formed on the
arrangement substrate 300. While the electrodes 102 and the metal
balls 111 are aligned with each other, the holding substrate 200 is
overlaid on the arrangement substrate 300.
[0107] An appropriate pressure is applied to the layers of the
holding substrate 200 and arrangement substrate 300 to transfer the
metal balls 111 onto the electrodes 102 and join the former to the
latter. After this, the holding substrate 200 is pulled up, as
shown in FIG. 18B. A spherical bump 110 is then formed on each
electrode 102 of each spherical semiconductor element 101. By
forming the bumps on the spherical semiconductor elements 101 at
once in this manner, the efficiency of fabricating spherical
semiconductor devices can be greatly improved.
[0108] In the example described above, the arrangement of the
spherical bumps 110 to be formed at the positions of the electrodes
102 of each spherical semiconductor element 101 is not limited to a
circle as shown in FIG. 10, but other various arrangements can be
employed. In any case, electrical connections to the outside can be
easily and accurately made through spherical bumps 110 formed.
* * * * *