Semiconductor device

A semiconductor device has a semiconductor element, an output terminal coupled to the semiconductor element and a thin metal member or foil secured to an output terminal. A protective layer covers the semiconductor element including the periphery of the metal foil to define an opening located at the metal foil. By covering the periphery of the metal foil, the protective layer secures the metal foil to the semiconductor element. A lead element is affixed to the metal foil by soldering through the opening. The resulting structure increases the adhesion of the lead element. Furthermore, because the protective film covers and seals the periphery of the metal foil, the advance of moisture into the inside of the semiconductor device is retarded. Accordingly the moisture resistance of the semiconductor device is improved.

FIELD OF THE INVENTION 
The present invention relates generally to a semiconductor device and a 
method of manufacturing thereof, and more particularly to the structure of 
an output terminal region in the semiconductor device and a method of 
manufacturing such a structure. 
Background of the Invention 
Japanese Utility Model Laid-open No. SHO 64-13740 describes a semiconductor 
device in which each lead element is secured to a copper-containing pad in 
each output terminal region. The copper-containing pad enables the lead 
element to be strongly affixed to the pad by conventional soldering. The 
copper-containing pad is formed by screen-printing a copper paste which is 
then hardened by the application of heat. 
FIG. 1 shows a photovoltaic apparatus output terminal structures which 
include copper-containing pads. In each output terminal region, the output 
terminal structure comprises, in order, an insulating substrate 210, a 
conductive belt 220, a metal layer 230, an amorphous silicon layer 240, a 
transparent conductive layer 250, an output terminal 260, a 
copper-containing pad 270 and a lead element 280. 
The insulating substrate 210 is generally rectangular and is often made of 
polyimide and the like. The conductive belt 220 is disposed along one side 
edge of the insulating substrate 210, and is formed by screen-printing a 
metal paste onto the substrate and, then hardening the metal paste by 
heating. The output terminal 260 is of generally the same shape and the 
same material as the conductive belt 220 and is formed on the transparent 
conductive layer 250. The copper-containing pad 270 is generally 
rectangular, and is formed on and around one edge of the output terminal 
260. The lead element 280 is made of a metal strip and is soldered to the 
copper-containing pad 270. 
When the lead element 280 is pulled, the lead element 280 can inadvertently 
be readily removed as shown in FIG. 2. Because the adhesion between the 
insulating substrate 210 made of polyimide and the conductive belt 220 is 
generally weak, they will often separate easily. 
On the other hand, even if the metal layer 230 is directly formed on the 
insulating substrate 210 without the conductive belt 220, the adhesion 
between the insulating substrate 210 and the metal layer 230 is also 
generally weak. Therefore, when the lead element 280 is pulled, the lead 
element 280 can still be easily removed. 
U.S. Pat. No. 5,133,810 describes another output terminal structure of a 
photovoltaic apparatus having an output terminal. In the output terminal 
structure, a lead element is connected to the output terminal, and a 
protective film is formed on the photovoltaic apparatus including the 
output terminal. 
FIG. 3 shows another output terminal structure. It is noted that the same 
numerals represent corresponding elements shown in FIG. 1, and the 
explanation concerning these corresponding elements is omitted. In each 
such output terminal structure, a protective film 290 covers the output 
terminal region including a lead element 280. In such output terminal 
structures, because the protective film 290 covers the lead element 280, 
it is more difficult to inadvertently separate the lead element 280 from 
the terminal structure. However, spaces 300 are often formed at both sides 
along the lead element 280. As a result, moisture can advance into the 
interior of the photovoltaic apparatus through the spaces 300. 
Consequently, corrosion can occur, decreasing long term reliability. 
There are other disadvantages. For example, the above described output 
terminal structure is not readily adapted to fabrication processes in 
which a plurality of photovoltaic apparatuses are divided from one large 
substrate. More specifically, if each of the lead elements of the output 
terminals of a plurality of photovoltaic apparatuses were covered with one 
protective film formed over the entire surface of all the photovoltaic 
apparatuses of the substrate, while one end portion of the lead element of 
each of the output terminals could be connected to the appropriate output 
terminal, the opposite end portion of the lead element might be located 
undesirably over another photovoltaic apparatus under the protective film. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a semiconductor device 
having an improved output terminal region and a method of manufacturing 
the same in which both the adhesion of the lead element and the resistance 
to moisture are improved. 
These and other objects are achieved by a semiconductor device, in 
accordance with one embodiment of the present invention, having a 
semiconductor element, an output terminal coupled to the semiconductor 
element, a metal foil secured to the output terminal, and a protective 
layer which covers the semiconductor element including the periphery of 
the metal foil and defines an opening located at the metal foil. By 
covering the periphery of the metal foil, the protective layer allows the 
metal foil to be strongly affixed to the semiconductor element. Further, a 
lead element may be strongly secured to the metal foil through the opening 
in the protective layer. Furthermore, since the protective film covers and 
seals the periphery of the metal foil, moisture intrusion into the 
interior of the semiconductor device is substantially reduced or 
eliminated. As a result, moisture resistance is improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will be described with 
reference to FIGS. 4-8. As will be explained in greater detail below, the 
semiconductor device of the illustrated embodiment includes a protective 
film which covers a semiconductor element including the periphery of a 
metal foil secured on an output terminal. The protective film defines an 
opening located on the metal foil. By covering the periphery of the metal 
foil, the protective layer strongly secures the metal foil to the 
semiconductor element. In addition, a lead element may be secured to the 
metal foil through the opening. As a result, the lead element resists 
inadvertent separation. In addition, moisture resistance is also improved 
by the protective film which covers and seals the periphery of the metal 
foil. 
FIGS. 4-6 show a structure in accordance with a preferred embodiment of the 
present invention at an intermediate step of the fabrication process of 
the semiconductor device. In this embodiment, the semiconductor device is 
a photovoltaic apparatus and comprises a semiconductor element 10 and a 
substrate 30. The substrate 30 may comprise a flexible metal sheet made of 
a suitable material, such as, for example, stainless steel and aluminum, 
and an insulating resin made of polyimide or the like formed on the 
flexible metal sheet. The substrate 30 may also be made of a film made of 
polyimide or the like. 
In the semiconductor element 10, a plurality of photovoltaic regions 
50a-50c are formed on the substrate 30. As shown in FIG. 5, first 
electrodes 60a-60c are disposed in each of the photovoltaic regions 
50a-50c on the substrate 30, respectively. The first electrodes 60a-60c 
are preferably approximately 0.1-1.0 .mu.m thick and each comprise either 
a single layer or a stacked layer. The single layer may be made of a 
suitable material, such as, for example, aluminum, titanium, nickel or 
copper. The stacked layer may also be made of suitable materials such as, 
for example, aluminum/titanium layers disposed in this order on the 
substrate 30, or tungsten/aluminum/titanium layers disposed in this order 
on the substrate 30. 
The first electrodes 60a-60c are preferably formed in the following manner. 
A metal layer for the first electrodes 60a-60c is formed on the entire 
surface of the substrate 30. A laser beam is directed onto the metal layer 
to remove the metal at predetermined surface portions. In this manner, 
dividing grooves 71(preferably about 50 .mu.m in width) between the 
photovoltaic regions 50a-50c and on the right edge of the photovoltaic 
region 50c, and a peripheral groove 72 (again, preferably about 50 .mu.m 
in width) in the vicinity of the periphery of the substrate 30, are 
formed. 
Insulating bars 81 are provided to fill in the dividing grooves 71. Each 
insulating bar 81 extends laterally at its top portion over the metal 
layers in both sides of each of the dividing grooves 71. An insulating bar 
82 is filled in the peripheral groove 72. The top portion of the 
insulating bar 82 extends laterally over the metal layers on both sides of 
the peripheral groove 72. The insulating bars 81, 82 adhere more strongly 
to the surface insulating resin, of the substrate 30 than do the first 
electrodes made of metal layers. As a result, the insulating bars 81, 82 
prevent the first electrodes from being inadvertently removed from the 
substrate 30. Insulating bars 83 are each formed on each of the first 
electrodes 60a-60c along the left edge of each of the first electrodes 
60a-60c. 
The insulating bars 81, 82 and 83 are formed by screen-printing an 
insulating paste, then hardening the insulating paste at a temperature of 
250.degree.-300.degree. C. For example, each of the insulating bars 81, 82 
and 83 is preferably 10-50 .mu.m in height and 0.4-0.6 mm in width. The 
insulating paste comprises a powder of insulating material and a 
paste-like binder. The powder of the insulating material is made of a 
suitable material, such as, for example, silicon dioxide (about 1.5-7.0 
.mu.m in particle dimension). The binder is made of a suitable material, 
such as, for example, polyimide or phenol. 
Semiconductor photovoltaic layers 90a-90c are disposed on the first 
electrodes 60a-60c, respectively. The semiconductor photovoltaic layers 
90a-90c have the thickness of about 0.3-1.0 .mu.m and comprise for example 
a PIN or PN junction which may be made of, for example, amorphous silicon, 
amorphous silicon carbide, amorphous silicon germanium. 
Second electrodes 100a-100c are disposed on the semiconductor photovoltaic 
layers 90a-90c, respectively. The second electrodes 100a-100c comprise a 
transparent conductive film which is preferably about 0.3-1.0 .mu.m thick 
and formed of a suitable material such as tin oxide, zinc oxide or indium 
tin oxide. 
The semiconductor photo-active layers 90a-90c and the second electrodes 
100a-100c are preferably formed in the following manner. A continuous 
semiconductor photo-active layer for the semiconductor photo-active layers 
90a-90c is formed on the entire surface of the substrate to cover the 
first electrodes 60a-60c. Thereafter a continuous transparent conductive 
oxide film for the second electrodes 100a-100c is formed over the 
continuous semiconductor photo-active layer. Then, a laser beam is 
directed to the insulating bars 82 and 83 so that portions of both 
semiconductor active layer and transparent conductive oxide film over the 
insulating bars 82 and 83 are removed to form dividing grooves 102 and 
103. The dividing grooves 102 and 103 define the semiconductor 
photo-active layers 90a-90c and the second electrodes 100a-100c, 
respectively. 
Conductive bars 110b, 110c are located between the first electrodes 60b, 
60c and the substrate 30, at the left edge of the first electrodes 60b, 
60c, respectively, in order to electrically connect the first electrode of 
one photovoltaic region to the second electrode in the adjacent 
photovoltaic region. Electric connection between the first electrodes and 
the second electrodes is accomplished in the following manner. A laser 
beam is directed over the conductive bars 110b, 110c, to melt portions of 
both the second electrodes 100a, 100b and the semiconductor photo-active 
layers 90a, 90b over the conductive bars 110b, 110c, so that second 
electrodes 100a, 100b contact the conducive bars 110b, 110c respectively. 
Therefore the photovoltaic regions 50a-50c are connected in series. 
The conductive bars 110b, 110c are preferably formed by screen-printing a 
metal paste, then hardening the metal paste at a temperature ranging 
between 250.degree.-300.degree. C. In one embodiment, the conductive bars 
110b, 110c are 10-50 .mu.m in height and 0.4-0.6 mm in width. The metal 
paste comprises a powder of metal material and a paste-like binder. The 
powder of metal material is made of a suitable material, such as, for 
example, silver, nickel or aluminum (preferably about 3-7 .mu.m in 
particle dimension). The binder is made of a suitable material, such as, 
for example, polyimide or phenol. 
Referring to FIG. 4, collecting electrodes 120 each comprise a plurality of 
branch portions 121 and a bar-shaped trunk portion 122. The branch 
portions 121 extend within each of the photovoltaic regions 50a-50c in the 
direction in which the photovoltaic regions 50a-50c are arranged. The 
branch portions 121 are connected to each trunk portion 122 at the right 
edges thereof. The trunk portions 122 are located over the conductive bars 
110b, 110c, respectively as best shown in FIG. 5. In the collecting 
electrode 120 at the right end, an output terminal 130c which will be 
explained below is used as a trunk portion. 
A feature of the invention in an improved output terminal region which will 
be explained in detail below. As shown in FIG. 5, the output terminal 
region may be located at the left edge on the substrate 30. The output 
terminal region of the illustrated embodiment comprises a conductive belt 
110at, a first electrode extending portion 60at, a semiconductor pad 90at, 
and a second electrode pad 100at. The extending portion 60at extends from 
the first electrode 60a. The conductive belt 110at is located between the 
extending portion 60at and the substrate 30, extending along the left side 
of the substrate 30. The conductive belt 110at is made of the similar 
materials as the conductive bar 110b, 110c, and is formed in a similar 
process as the conductor bars 110b, 110c. The semiconductor pad 90at is 
formed on the conductive belt 110at in the same process as the 
above-mentioned semiconductor photo-active layer, and is made of the same 
material as the above-mentioned semiconductor photo-active layer. The 
second electrode pad 100at is formed on the semiconductor pad 90at in a 
similar shape as the semiconductor pad 90at, and in the same process as 
the second electrode. The second electrode pad 100at is made of the same 
material as the second electrode. To electrically connect the conductive 
belt 110at and the second electrode pad 100at, a laser beam is directed 
thereon to melt the conductive belt 110at and the second electrode pad 
100at. As a result, the second electrode pad 100at contacts and is 
electrically connected to the conductive belt 110at. 
An output terminal 130a is formed by screen-printing a metal paste which is 
subsequently hardened by heating. The output terminal 130a extends along 
the left side of the substrate 30 on the second electrode pad 100at. A 
generally rectangular copper-containing pad 140a is located on one end of 
the output terminal 130a. The pad 140a may be formed by screen-printing a 
copper paste and, then hardening the copper paste. The copper paste 
comprises a powder of copper and a paste-like binder. The powder of copper 
is preferably about 5-7 .mu.m in particle dimension and about 90 wt %. The 
binder is made of a suitable material, such as, for example, phenol. The 
copper-containing pad 140a facilitates soldering a lead element thereon 
using ordinary soldering methods. 
A metal foil 150a having a rectangular sheet shape is secured to the 
copper-containing pad 140a. The metal foil 150a is made of copper and the 
entire surface thereof is covered with solder plating. The metal foil 150a 
is secured to the pad 140a in the following manner. Soldering flux is 
first spread over the copper-containing pad 140a. Then the metal foil 150a 
is placed on the copper-containing pad 140a. Heat is subsequently applied 
through the metal foil by means of, for example, soldering iron. As a 
result, the solder plating melts which secures the metal foil 150a to the 
copper-containing pad 140a. 
When the metal foil 150a (preferably about 50-3000 .mu.m, more preferably 
about 80 .mu.m in thickness) is covered with solder plating, the metal 
foil 150a may be secured to the pad with only this thin solder plating 
(preferably about 2 .mu.m in thickness) thereby eliminating the need for a 
solder layer (about 100-1000 .mu.m in thickness). As a result, the total 
thickness of the output terminal region can become substantially thin. On 
the other hand, when the metal foil 150a is not covered with solder 
plating, the metal foil 150a can be secured by a solder layer(about 
100-1000 .mu.m in thickness) between the metal foil 150a and the 
copper-containing pad 140a, resulting in an output terminal region which 
is somewhat more thick. In yet another alternative, to secure the foil and 
pad more strongly, the metal foil 150a covered with solder plating may be 
also secured by a solder layer between the metal foil 150a and the 
copper-containing pad 140a. 
In a similar manner, the output terminal region located at the right edge 
on the substrate 30 comprises a conductive belt 110ct, a first electrode 
pad 60ct, a semiconductor pad 90ct, and a second electrode extending 
portion 100ct. The first electrode pad 60ct is disposed next to the right 
side of the photovoltaic region 50c on the substrate 30. The first 
electrode pad 60ct may be formed in the same process as the first 
electrode, and be made of the same material as the first electrode. The 
conductive belt 110ct is located between the first electrode pad 60ct and 
the substrate 30, and extends along the right side of the substrate 30. 
The conductive belt 110ct is made of a similar material as the conductive 
bar 110b, 110c, and may be formed in a similar process as the conductor 
bars 110b, 110c. The semiconductor pad 90ct extends from the semiconductor 
photo-active layer 90c, and is formed on the first electrode pad 60ct. The 
extending portion 100ct extends from the second electrode 100c, and is 
formed on the semiconductor pad 90ct. To reduce electrical resistance so 
as to more effectively collect electricity, a laser beam is directed to 
the conductive belt 110ct and the extending portion 100ct, to melt the 
conductive belt 110ct and the extending portion 100ct. The extending 
portion 100ct contacts and is electrically connected to the conductive 
belt 110ct. 
The output terminal 130c is formed by screen-printing a metal paste, then 
hardening the metal paste by heating. The output terminal 130c extends 
along the right side of the substrate 30 on the extending portion 100ct. 
The copper-containing pad 140c having generally rectangular shape is 
located on one end of the output terminal 130a. The copper-containing pad 
140c is formed by screen-printing a copper paste, then hardening the 
copper paste. Materials of the copper paste may be the same as the 
above-mentioned copper-containing pad 140a. 
A metal foil 150c in a rectangular sheet shape is secured to the 
copper-containing pad 140c. The metal foil 150c is made of copper, and the 
entire surface thereof is covered with solder plating. The metal foil 150c 
is secured in the output terminal region at the right edge in a similar 
manner as the above-mentioned output terminal region at the left edge. 
When the semiconductor element 10 shown in FIGS. 4-6 is completed, the 
semiconductor device of the first embodiment appears as shown in FIGS. 
7-8. As shown therein, a protective film 20 coated with an adhesive layer 
(not shown) (which is preferably made of an thermoplastic resin) covers 
the semiconductor element 10. The protective film 20 is preferably about 
100-1000 .mu.m in thickness, and is made of a transparent thermoplastic 
resin, such as, for example, polyethylene terephthalate, or fluorocarbon 
polymers. The protective film 20 preferably has a higher melting 
temperature than that of the adhesive layer. When the protective film 20 
is laminated on the semiconductor element by a heat roller(not shown), 
only the adhesive layer melts and secures the protective film 20 to the 
semiconductor element 10. 
The protective film 20 defines openings 21a, 21b over the metal foils 150a, 
150c respectively. The openings 21a, 21b are formed in the following 
manner. A tip of a soldering iron which provides a means for heating is 
placed on the protective film 20 over the metal foils 150a, 150c, while 
solder is being melt. Openings 21a, 21b are consequently formed by this 
heat, and a solder layer (not shown) is formed. Then, lead elements 160a, 
160b are soldered onto the metal foils 150a, 150b by the above-mentioned 
solder layer. Each of the lead elements 160a, 160b are preferably made of 
copper in the form of a foil, and the entire surface thereof is preferably 
covered with solder plating. 
Tests have been carried out to examine the adhesions of the lead element, 
in the first embodiment as compared to the lead element in the prior art 
shown in FIG. 1, in the following manner. The lead element was pulled in a 
direction normal to the surface of the semiconductor device, and the 
adhesion strength at which the lead element was removed from the surface 
was measured. 
As a result, in the prior art device, the adhesion was measured at 
0.98-2.94N. In the first embodiment of FIGS. 7-8, the adhesion was 
measured at 14.7-19.6N. This test indicated that a semiconductor device in 
accordance with the present invention can have a lead element with 
significantly improved adhesion to the surface. 
As mentioned above, the protective film 20 has the openings 21a, 21c at the 
center of the metal foils 150a, 150b respectively, and covers the 
semiconductor element 10 including the periphery of the metal foils 150a 
and 150c. By covering the periphery of the metal foils 150a and 150c, the 
protective film 20 strongly secures the metals foil 150a and 150c to the 
semiconductor element 10. Such a structure of the output terminal regions 
significantly increases the adhesion of the lead element. Furthermore, 
since the protective film 20 covers and seals the periphery of the metal 
foil 150a, 150c, moisture advance into the interior of the semiconductor 
device is significantly retarded. As a result, the moisture resistance of 
the semiconductor device is substantially improved. 
As noted above, the openings 21a, 21c are preferably made by heat, through 
a process in which the tip of the soldering iron is placed on the 
protective film 20 over the metal foils 150a, 150c respectively, while the 
solder is being melted. Such a process is easier than the prior art 
processes which use a protective film having preformed openings in which 
the preformed openings generally must be precisely aligned with respect to 
the output terminals. Another advantage of the openings by heat is that a 
solder layer is formed on the metal foil at the same time. 
In an alternative construction in which the metal foils 150a, 150c are 
directly secured to the output terminals 130a, 130c respectively, the 
copper-containing pad can be omitted. 
It is appreciated that copper has a high adhesion strength to solder. 
Therefore when the metal foils 150a, 150c, and the lead elements 160a, 
160c are made of copper, contacting areas between the metal foils 150a, 
150c and the lead elements 160a, 160c respectively, can be made smaller. 
This can also reduce the width of the lead elements 160a, 160c. 
In the first embodiment, though the contacting area between the metal foil 
and the lead element is relatively small, the contacting area between the 
output terminal and the metal foil is preferably larger. This large 
contact area enables the metal foil to be strongly secured to the output 
terminal. In addition, by covering the periphery of the metal foil, the 
protective film permits the metal foil to be strongly affixed to the 
semiconductor element. In turn, the lead element is strongly secured to 
the metal foil by soldering through the opening. Consequently, this 
structure of the output terminal region increases the adhesion of the lead 
element. 
In the prior art shown in FIG. 3, a plurality of the photovoltaic 
apparatuses could not readily be formed by dividing from one large 
substrate. However, in accordance with one feature of the present 
invention, one large substrate can be readily divided into a plurality of 
substrates for plural photovoltaic apparatuses, after openings 21a, 21c 
are made by heat from a soldering iron. 
In the first embodiment, after the protective film 10 is formed on the 
semiconductor element 10, openings 21a, 21c are made by heat from a 
soldering iron. However, in a second embodiment shown in FIGS. 9-10, a 
protective film 23 has rectangular-shaped openings 22a, 22c formed in 
advance. Therefore the openings 22a, 22c of the protective film 23 are 
aligned with the output terminals. 
In both embodiments, the second electrodes and the protective film are 
transparent so that light passes through them. However, the first 
electrode and the substrate may also be transparent so that light can 
enter through them. 
In both embodiments, a protective film is used. However, in stead of the 
protective film, a protective layer made of a substrate material such as a 
thermoplastic resin, formed by screen-printing or other suitable method 
can also be used. 
It will, of course, be understood that modifications of the present 
invention, in its various aspects will be apparent to those skilled in the 
art, some being apparent only after study and others being matters of 
routine semiconductor fabrication techniques. As such, the scope of the 
invention should not be limited by the particular embodiment herein 
described but should be defined only by the appended claims and 
equivalents thereof.