U.S. patent application number 12/213757 was filed with the patent office on 2008-11-27 for semiconductor package, method for fabricating the same, and semiconductor device.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Tetsuya Hirano, Hisaho Inao, Katsutoshi Shimizu.
Application Number | 20080293190 12/213757 |
Document ID | / |
Family ID | 35756609 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080293190 |
Kind Code |
A1 |
Inao; Hisaho ; et
al. |
November 27, 2008 |
Semiconductor package, method for fabricating the same, and
semiconductor device
Abstract
A semiconductor device includes a semiconductor chip, leads for
sending and receiving signals between the semiconductor chip and an
external device, fine metal wires, an encapsulant for sealing the
leads, and a lid member. On the surface of each of the leads, a
metal oxide film is formed by an oxidation treatment. The metal
oxide film has a thickness larger than a natural oxide film and no
more than 80 nm.
Inventors: |
Inao; Hisaho; (Niigata,
JP) ; Hirano; Tetsuya; (Niigata, JP) ;
Shimizu; Katsutoshi; (Kyoto, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
Osaka
JP
|
Family ID: |
35756609 |
Appl. No.: |
12/213757 |
Filed: |
June 24, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11196321 |
Aug 4, 2005 |
7402898 |
|
|
12213757 |
|
|
|
|
Current U.S.
Class: |
438/123 ;
257/E21.502; 257/E23.056; 257/E23.066; 257/E23.127;
257/E31.117 |
Current CPC
Class: |
H01L 24/45 20130101;
H01L 23/49861 20130101; H01L 2924/15153 20130101; H01L 2924/16195
20130101; H01L 23/3142 20130101; H01L 24/48 20130101; H01L
2924/01079 20130101; H01L 23/49586 20130101; H01L 2924/01078
20130101; H01L 2924/01025 20130101; H01L 2224/451 20130101; H01L
2924/15165 20130101; H01L 2224/48091 20130101; H01L 31/0203
20130101; H01L 2224/48247 20130101; H01L 2924/14 20130101; H01L
2224/48091 20130101; H01L 2924/00014 20130101; H01L 2224/451
20130101; H01L 2924/00014 20130101; H01L 2224/451 20130101; H01L
2924/00015 20130101; H01L 2924/14 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
438/123 ;
257/E21.502 |
International
Class: |
H01L 21/56 20060101
H01L021/56 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2004 |
JP |
2004-230718 |
Claims
1-4. (canceled)
5. A method for fabricating a semiconductor package, comprising the
steps of: (a) preparing a leadframe having a frame body and a
plurality of leads which are connected at the proximal ends to the
frame body and the distal ends of which are to face a region for
mounting a semiconductor chip; (b) forming a metal oxide film
having a thickness of no less than 1.7 nm and no more than 80 nm on
the surface of the leadframe by subjecting the leadframe to an
oxidation treatment; and (c) forming an encapsulant with a molding
material to seal parts of the plurality of leads.
6. The method of claim 5, wherein in the step (b), the leadframe is
held in an atmosphere having an oxygen concentration of 20%.+-.5%
at a temperature of 200 to 260.degree. C. for one hour.
7. The method of claim 5, wherein in the step (b), the metal oxide
film is formed to have a thickness of 10 nm or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Divisional of U.S. application
Ser. No. 11/196,321, filed Aug. 4, 2005, and claims priority under
35 USC 119(a) to Japanese Patent Application No. 2004-230718 filed
on Aug. 6, 2004, the entire contents of each of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a semiconductor package
which is equipped with an LSI chip, a solid-state imaging element,
a light receiving/emitting element or the like and is made of a
resin, a method for fabricating the same, and a semiconductor
device.
[0004] (b) Description of Related Art
[0005] Conventionally, a typical molding of a semiconductor package
has been carried out by sandwiching a leadframe having leads, dam
bars that couple the leads to each other and other components
between respective regions of upper and lower parts of a molding
die adjacent to its die cavity, pouring a resin in the die cavity,
and then curing the resin.
[0006] FIG. 9 shows a cross sectional view illustrating a
conventional optical device with a semiconductor package having an
overhang structure.
[0007] As illustrated in FIG. 9, the optical device includes: an
optical chip 101 such as a solid-state imaging element, a light
receiving/emitting element or an LSI; leads 102 for sending and
receiving signals between the optical chip 101 and an external
device; fine metal wires 107 for connecting the optical chip 101
and the leads 102; a rectangular dished encapsulant 103 for sealing
the leads 102; and a lid member 105 such as a glass window or a
hologram which is attached to the top surface of the encapsulant
103. The encapsulant 103 is formed in one piece from a resin poured
during molding.
[0008] The lid member 105 is attached to the top of the encapsulant
103, and the optical chip 101 is mounted at the center of the
recess of the encapsulant 103. Therefore, the optical chip 101 is
placed in an internal space 106 surrounded with the encapsulant 103
and the glass window 105.
SUMMARY OF THE INVENTION
[0009] In the conventional semiconductor packages, it is known that
due to insufficient adhesive strength between leads and a resin,
the resin is peeled off from the leads and water or moisture enters
the inside of the semiconductor packages through bonded surfaces,
or breakage chips resulting from partial peeling-off of the resin
enter equipments or semiconductor devices during the fabrication,
leading to various disadvantages.
[0010] An object of the present invention is to provide a
semiconductor package with high reliability, a method for
fabricating the semiconductor package, and a semiconductor device
by taking measures to improve adhesivity of the leads of the
semiconductor package to the resin.
[0011] The semiconductor package of the present invention has leads
and an encapsulant for sealing part of each of the leads and is
provided with a metal oxide film having a thickness of no less than
1.7 nm and no more than 80 nm on the surface of each of the
leads.
[0012] With this configuration, adhesivity between a molding resin
forming the encapsulant and the leads is improved, which prevents
water or moisture from entering between the leads and the molding
resin and prevents peeling-off of the molding resin. As a result,
the reliability of the semiconductor package can be enhanced.
[0013] When the metal oxide film has a thickness of 10 nm or less,
the aforementioned effect can be achieved while the efficiency in a
plating process of the leadframe can be kept high.
[0014] The semiconductor device of the present invention is made by
containing a semiconductor chip in the semiconductor package.
[0015] The method for fabricating the semiconductor package of the
present invention comprises performing an oxidation treatment for a
leadframe to form a metal oxide film having a thickness of no less
than 1.7 nm and no more than 80 nm on the surface of the leadframe,
and then forming an encapsulant with a molding material to seal
parts of the leads.
[0016] According to the method, the semiconductor package having
the aforementioned configuration can be obtained.
[0017] In the oxidation, the leadframe is preferably held in an
atmosphere having an oxygen concentration of 20%.+-.5% at a
temperature in the range of 200 to 260.degree. C. for one hour.
Thus, a strong metal oxide film can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a cross sectional view of the configuration of a
semiconductor device according to an embodiment of the present
invention;
[0019] FIGS. 2A and 2B are a perspective view and a cross sectional
view, respectively, of the configuration of a semiconductor package
according to the embodiment at completion of a molding process
step;
[0020] FIG. 3 is a cross sectional view of the semiconductor
package according to the embodiment at completion of a lead bending
process step;
[0021] FIGS. 4A and 4B are a perspective view and a cross sectional
view, respectively, schematically illustrating the configuration of
a device for measuring adhesivity;
[0022] FIG. 5 is a graph illustrating the change of adhesivity
between leads and a resin (epoxy resin) with the thickness of a
metal oxide film;
[0023] FIG. 6 is a graph illustrating measurement results of
sharing adhesivity for a sample having a natural oxide film through
no treatment for improving adhesivity of the leads (POR), a sample
having a metal oxide film formed by an oxidation treatment
(annealing treatment), a sample having the leads with large surface
roughness formed by not the oxidation treatment but a blast
treatment, and a sample subjected to both the oxidation treatment
and the blast treatment;
[0024] FIGS. 7A and 7B are graphs for comparing the thickness of an
oxide film of the sample with no treatment (POR) with that of an
oxide film of the sample subjected to the annealing treatment among
the samples shown in FIG. 6;
[0025] FIGS. 8A and 8B are a diagram illustrating an adhesion
condition between a surface of a metal and resin molecules and a
diagram illustrating an adhesion condition between an oxide film
formed on a metal and resin molecules, respectively; and
[0026] FIG. 9 is a cross sectional view illustrating the
configuration of an optical device having a conventional
semiconductor package.
DETAILED DESCRIPTION OF THE INVENTION
[0027] FIG. 1 is a cross sectional view illustrating the
configuration of a semiconductor device 1 according to an
embodiment of the present invention. The left end of FIG. 1 shows a
cross section of a resin portion between leads, and the right end
of FIG. 1 shows a cross section of a lead. As shown in FIG. 1, the
semiconductor device 1 includes: a semiconductor chip 11 such as a
solid-state imaging element, a light receiving/emitting element or
an LSI; leads 12 for sending and receiving signals between the
semiconductor chip 11 and an external device; fine metal wires 17
as electrically connecting members for connecting the semiconductor
chip 11 to the leads 12; a rectangular dished encapsulant 13 for
sealing the leads 12; and a lid member 15 such as a glass window or
a hologram which is attached to the top surface of the encapsulant
13. The encapsulant 13 is formed in one piece from an epoxy resin
poured during molding.
[0028] Moreover, the lid member 15 is attached to the top surface
of the encapsulant 13, and the semiconductor chip 11 is mounted at
the center of the recess of the encapsulant 13. Therefore, the
semiconductor chip 11 is placed in an internal space 16 surrounded
with the encapsulant 13 and the lid member 15.
[0029] In the embodiment, the leads 12 and the encapsulant 13 form
a semiconductor package 2 and the semiconductor chip 11, the fine
metal wires 17 and the lid member 15 are integrated with the
semiconductor package 2 into a semiconductor device 1.
[0030] The feature of the semiconductor package of the embodiment
resides in that a metal oxide film 20 (an oxide film made of a
Fe--Ni alloy) is formed on the surface of each of the leads 12 by
an oxidation treatment. The oxide film has a thickness of no less
than 1.7 nm and no more than 80 nm.
[0031] The metal oxide film 20 of the embodiment is formed by
holding the leadframe in an atmosphere having an oxygen
concentration of 20%.+-.5% at a temperature in the range of 200 to
260.degree. C. for one hour.
[0032] In the embodiment, since the metal oxide film thicker than
the natural oxide film is formed on the surface of each of the
leads 12 by a heat treatment, adhesivity between the leads 12 and a
resin of the encapsulant 13 can be enhanced. Therefore, it is
possible to prevent water or moisture from entering between the
leads 12 and the encapsulant 13 and to prevent the leads 12 from
being peeled off from the encapsulant 13.
[0033] Next, there is described a fabrication process of the
semiconductor package according to the embodiment of the present
invention, using resin molding.
[0034] FIGS. 2A and 2B are a perspective view and a cross sectional
view, respectively, of the configuration of a semiconductor package
according to the embodiment at completion of a molding process step
in the fabrication process. The left end of FIG. 2B shows a cross
section of resin portion with no lead, and the right end of FIG. 2B
shows a cross section of a lead. Note that the scale of FIG. 2A is
not the same as that of FIG. 2B. As shown in FIGS. 2A and 2B, a
leadframe 30 is sealed by the encapsulant 13 made of a molding
resin. The encapsulant 13 is formed into one piece from the resin
poured during the molding process step.
[0035] Regarding the leadframe 30, the leads inward of dam bars 30c
are referred to as inner leads 30a and leads outward of the dam
bars 30c are referred to as outer leads 30b. The leadframe 30 is
provided with a large number of encapsulant formation regions. The
ends of the upper surfaces of the inner leads 30a are exposed at
the inside of the encapsulant 13. The exposed ends of the inner
leads 30a are sites to which wires will be bonded later.
[0036] Prior to the molding process step, the leadframe 30 is
subjected to an annealing treatment of keeping it in an atmosphere
having an oxygen concentration of 20%.+-.5% at a temperature in the
range of 200 to 260.degree. C. for one hour, so that the metal
oxide film 20 is formed on the surface of the leadframe 30.
[0037] Subsequently, the dam bars 30c and part of the encapsulant
13 are punched out of the structure illustrated in FIG. 2. Then,
after the wire bonding and/or the mounting of the lid member 15,
the ends of the outer leads are cut off from the leadframe body and
the leadframe is cut along the sides of the encapsulant at which no
lead is provided, thereby separating individual semiconductor
packages from the leadframe.
[0038] Then, portions of the leads (outer leads) extending outside
from the encapsulant 13 are bent down, so that the semiconductor
package 2 is made in a configuration mountable on a mother board
(lead bending process step).
[0039] FIG. 3 is a cross sectional view of the semiconductor
package at completion of the lead bending process step. The left
end of FIG. 3 shows a cross section of a resin portion with no
lead, and the right end of FIG. 3 shows a cross section of a
lead.
[0040] In the fabrication process of the semiconductor package
according to the embodiment, prior to the molding process step, the
annealing treatment is performed for oxidization to form the metal
oxide film 20 on the surface of the leadframe 30. Therefore, after
the molding, the molding resin can be strongly adhered to the leads
12 and thus the high-reliability semiconductor package and the
high-reliability semiconductor device can be obtained.
[0041] Note that the lead bending process step may be performed
before the mounting of the semiconductor chip 11 on the encapsulant
13 so as to form the semiconductor package shown in FIG. 3.
Alternatively, the lead bending process step may be performed after
the attachment of the lid member 15.
--Test for Confirming Enhancement of Adhesivity Due to the Metal
Oxide Film--
[0042] FIGS. 4A and 4B are a perspective view and a cross sectional
view, respectively, schematically illustrating the configuration of
a device for measuring adhesivity. As shown in FIG. 4A, a
tower-like molded article was formed on an adherend made by forming
a metal oxide film on a surface of a metal plate making up a
leadframe. For the test, a plurality of adherends were used which
have metal oxide films of various thicknesses. As shown in FIG. 4B,
the adherend with the molded article was placed on a hot plate, a
bending load was applied to the molded article by a bending member
with the left end of the adherend brought into abutment on a fixed
member, and adhesivity was measured on the basis of the load
required to bend the molded article.
[0043] FIG. 5 is a graph illustrating the change of adhesivity
between leads and a resin (epoxy resin) with the thickness of a
metal oxide film. As shown in FIG. 5, a great adhesivity can be
obtained when the thickness of the oxide film is within the range
of 1.7 nm to 80 nm both inclusive.
[0044] FIG. 6 is a graph illustrating measurement results of
sharing adhesivity for a sample having a natural oxide film without
performing any treatment for improving adhesivity of the leads
(POR), a sample having a metal oxide film formed by the oxidation
treatment (annealing treatment), a sample having the leads with
large surface roughness formed by not the oxidation treatment but a
blast treatment, and a sample subjected to both the oxidation
treatment and the blast treatment.
[0045] As shown in FIG. 6, all of the maximum value, the minimum
value and the average value of the sample subjected to the
annealing treatment are larger than those of the sample through no
treatment. Turning to the sample subjected to the blast treatment
and the sample subjected to both the oxidation treatment and the
blast treatment, they have higher maximum values of the shearing
adhesivity but lower minimum values thereof than the sample
subjected to the annealing treatment, and thus the difference is
widened. Hence, the result shown in FIG. 6 indicates that the
sample having the oxide film formed by the oxidation treatment is
most effective in improving the adhesivity.
[0046] FIGS. 7A and 7B are graphs for comparing the thickness of an
oxide film of the sample with no treatment (POR) to that of an
oxide film of the sample subjected to only the annealing treatment
among the samples shown in FIG. 6. The measurement conditions are
as follows: an analysis region of .times.3000; a stage angle of
30.degree., an electron beam acceleration voltage of 10 keV; an
electron beam current of 10 nA; an ion beam energy of 1 keV; a
sputtering rate of about 1.82 nm/min; and an etching interval of 1
(min). In FIGS. 7A and 7B, the abscissa axes denote sputtering
time, and the ordinate axes denote detecting intensity of elements,
wherein the solid lines L-1 denote detecting intensity of oxygen,
the broken lines L-2 denote detecting intensity of nickel, and the
dotted lines L-3 denote detecting intensity of iron. The time
between the sputtering time at the peak value of the solid line L-1
and the sputtering time at the intersect point of the solid line
L-1 and the broken line L-2 is obtained. Since the sputtering rate
is about 1.82 nm/min, the thickness of the oxide film of the sample
through no treatment (natural oxide film) can be obtained as
follows: 1.82 nm.times.0.5 min (sputtering time)=0.91 nm. Likewise,
the thickness of the metal oxide film of the sample subjected to
only the annealing treatment can be obtained as follows: 1.82
nm.times.0.92 min=1.7 nm. Based upon the foregoing, the lead on
which the metal oxide film having a thickness of 1.7 nm or more
exhibits greater adhesive strength than the lead on which only the
natural oxide film is formed.
[0047] Note that in forming the samples shown in FIGS. 5, 6, 7A and
7B, the leadframes were heated in an atmosphere having an oxygen
concentration of 20% at a temperature of 200.degree. C. for one
hour. The results of experiments with different oxygen
concentrations and heating temperatures showed that a strong metal
oxide capable of effectively preventing the peeling-off between the
leads and the molding resin can be formed by heating the leadframe
in an atmosphere having an oxygen concentration of 20%.+-.5% at a
temperature in the range of 200 to 260.degree. C. for one hour.
[0048] Summing up the data shown in FIGS. 5, 6, 7A and 7B, it can
be understood that the metal oxide film having a thickness of no
less than 1.7 nm and no more than 80 nm can improve the adhesive
strength between the leads and the molding resin.
[0049] When the leadframe has a thick oxide film, there is a
possibility that a stable film cannot be obtained without
performing a plating treatment on the surfaces of the leads for a
long time after a premolding process step. In particular, when the
metal oxide film has a thickness of more than 10 nm, the time
required for the plating pretreatment becomes longer, causing
decrease in the treatment capacity.
[0050] Therefore, taking the efficiency of fabrication into
consideration, the metal oxide film formed on the surface of each
lead most preferably has a thickness of no less than 1.7 nm and no
more than 10 nm.
--Mechanism for Reinforcing Adhesivity Between Leads and Molding
Resin--
[0051] Next, the mechanism for reinforcing the adhesivity between
leads and a molding resin in the present invention will be
described.
[0052] When a medium A is a molding resin and a medium B is a lead,
adhesion between the medium A and the medium B is either mechanical
adhesion or chemical adhesion, but not physical adhesion with a
solvent. In coupling flat members to each other without performing
the blast treatment, the mechanical adhesion is not so high, and
thus chemical adhesion is preferably used. When a molding resin
such as an epoxy resin is used as a material for the medium A, OH
groups on the side chain have been regarded as a reaction group in
the adhesion. This is because the OH groups on the side chain have
a higher degree of freedom than the terminal OH groups (OH groups
formed in an epoxy curing reaction).
[0053] FIGS. 8A and 8B are a diagram illustrating an adhesion
condition between the surface of a metal and resin molecules and a
diagram illustrating an adhesion condition between an oxide film
formed on a metal and resin molecules, respectively.
[0054] As shown in FIG. 8A, even when the molding resin has OH
groups, strong adhesion cannot be obtained unless the lead has
reaction groups bonded to the OH groups. In contrast, as shown in
FIG. 8B, when an oxide film is formed on the surface of the lead,
strong adhesivity can be obtained due to primary bonding between C
and O with an ether group interposed therebetween and secondary
bonding (hydrogen bonding) between O and H with a hydroxyl group
interposed therebetween.
[0055] According to the inventors' experiments, the obtained
adhesivity is not so strong in the case of a metal that is unlikely
to be oxidized. This is because that there are few hydroxyl groups
bonding the molding resin to the metal. However, it was found that
even in the case of a metal on which an oxide film is unlikely to
be formed, a strong adhesivity can be obtained by contriving the
metal to have an oxide film thereto.
[0056] Note that for example when the lead is made of a copper
alloy, the obtained oxide film is too thick and has a double
structure, causing, by contrast, the adhesivity between the lead
and the molding resin to decrease. Therefore, there is an upper
limit to the appropriate range of thicknesses of the oxide
film.
[0057] The embodiment has described on the semiconductor package of
which the encapsulant is dish-shaped and has an internal space, but
the semiconductor device of the present invention is also
applicable to semiconductor packages with no internal space and
with the surroundings of the semiconductor chip and the fine metal
wires being filled with a molding resin.
[0058] The aforementioned semiconductor package of the present
invention, the method for fabricating the same, and the
semiconductor device can be used for a semiconductor device on
which a solid-state imaging element, a light receiving/emitting
element, and an LSI such as a memory and a logic, or a method for
fabricating the same.
* * * * *