U.S. patent application number 14/744358 was filed with the patent office on 2015-12-31 for diode having a plate-shaped semiconductor element.
The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to Alfred GOERLACH.
Application Number | 20150380569 14/744358 |
Document ID | / |
Family ID | 54839755 |
Filed Date | 2015-12-31 |
United States Patent
Application |
20150380569 |
Kind Code |
A1 |
GOERLACH; Alfred |
December 31, 2015 |
DIODE HAVING A PLATE-SHAPED SEMICONDUCTOR ELEMENT
Abstract
A diode is provided having a plate-shaped semiconductor element
that includes a first side and a second side, the first side being
connected by a first connecting layer to a first metallic contact
and the second side being connected by a second connecting layer to
a second metallic contact, the first side having a diode element in
a middle area and having a further diode element in an edge area of
the first side, which has crystal defects as a result of a
separating process of the plate-shaped semiconductor element, the
first connecting layer only establishing an electrical contact to
the diode element and not to the further diode element and, on the
first side, the further diode element having an exposed contact,
which may be electrically contacted by the first connecting
layer.
Inventors: |
GOERLACH; Alfred;
(Kusterdingen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Family ID: |
54839755 |
Appl. No.: |
14/744358 |
Filed: |
June 19, 2015 |
Current U.S.
Class: |
257/379 ;
257/476; 257/617 |
Current CPC
Class: |
H01L 24/01 20130101;
H01L 27/0629 20130101; H01L 23/051 20130101; H01L 29/78 20130101;
H01L 27/0814 20130101; H01L 27/0727 20130101; H01L 29/8611
20130101 |
International
Class: |
H01L 29/861 20060101
H01L029/861; H01L 29/872 20060101 H01L029/872; H01L 27/06 20060101
H01L027/06; H01L 29/06 20060101 H01L029/06; H01L 29/417 20060101
H01L029/417; H01L 27/08 20060101 H01L027/08; H01L 29/78 20060101
H01L029/78; H01L 29/04 20060101 H01L029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2014 |
DE |
10 2014 212 455.7 |
Claims
1. A diode, comprising: a plate-shaped semiconductor element that
includes a first side and a second side; a first metallic contact;
a first connecting layer for connecting the first side to the first
metallic contact; a second metallic contact; and a second
connecting layer for connecting the second side the second metallic
contact, wherein: the first side includes a diode element in a
middle area and a further diode element in an edge area of the
first side, the further diode includes crystal defects as a result
of a separating process of the plate-shaped semiconductor element,
the first connecting layer only establishes an electrical contact
to the diode element and not to the further diode element, and on
the first side, the further diode element includes an exposed
contact that is electrically contactable by the first connecting
layer.
2. The diode as recited in claim 1, wherein, in the event of an
incorrect arrangement of the first connecting layer on the first
side one of during manufacturing and during an operation of the
diode, an electrical contact takes place to the exposed contact of
the further diode element.
3. The diode as recited in claim 1, wherein during the separating
process, the semiconductor element is separated from a larger plate
by a sawing that introduces the crystal defects into the edge
area.
4. The diode as recited in claim 1, wherein the first diode element
is one of a p-n diode, a Schottky diode, an MOS field effect
transistor, and an MOS field effect transistor having an
electrically connected gate, body region, and source region.
5. The diode as recited in claim 1, wherein the further diode is
implemented as a p-n diode.
6. The diode as recited in claim 1, wherein the first connecting
layer is one of a soldered layer and a sintered layer.
7. The diode as recited in claim 1, wherein the exposed contact
includes a further metal layer.
8. The diode as recited in claim 7, wherein the further metal layer
is implemented as circumferential metal strips.
9. The diode as recited in claim 1, wherein a lateral distance
between the diode and the further diode is greater than a width of
a space charge zone of the diode on an upper side of the
semiconductor element.
10. The diode as recited in claim 1, wherein a lateral extension of
the further diode is at least as large as a thickness of the first
connecting layer.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to a diode having a
plate-shaped semiconductor element.
BACKGROUND INFORMATION
[0002] Diodes having a plate-shaped semiconductor element, which is
connected by a first and second connecting layer to a first and
second metallic contact, are already known from German Published
Patent Application No. 195 49 202.
SUMMARY
[0003] The diode according to the present invention has the
advantage in relation thereto that the diode element is contacted
by the first connecting layer, and a further diode element, which
is situated in an edge region which has crystal defects, is not
contacted. In the case of correct contacting, current therefore
exclusively flows via the diode element and not via the further
diode element. If contacting of the further diode element occurs as
a result of a flawed arrangement of the first connecting layer,
this is thus detectable by a simple electrical measurement at the
diode. It may therefore be established by a simple electrical
measurement at the diode whether the first connecting layer is
embodied correctly between the first metallic contact and the first
side of the semiconductor element. Because of the arrangement of
the further diode in a region having crystal defects, it may be
ascertained by a simple measurement of the blocking current whether
this further diode is also electrically connected by the first
connecting layer to the first metallic contact. The manufacturing
process may thus be monitored or thermally related travel of the
connecting layer may be detected. The quality of the diodes may
thus be improved.
[0004] The contacting of the further diode takes place particularly
simply in that, in the event of a flawed arrangement of the first
connecting layer, the exposed contact of the further diode element
is electrically contacted. Such a flawed arrangement may arise in a
faulty manufacturing process or also during operation of the diode
as a result of mechanical stress as a result of the different
coefficients of thermal expansion of the participating materials.
The semiconductor element is particularly simply cut out of a large
plate, which is spatially very much larger, by sawing in a
separating process. Crystal defects are automatically introduced
into an edge region of the semiconductor element by the sawing
process. A variety of different diodes, for example, p-n diode, a
Schottky diode, planar or trenched MOS field effect transistors, or
an MOS field effect transistor in which gate, body, and source
regions are short-circuited with one another, come into
consideration for the first diode element. The further diode is
particularly simply designed as a p-n diode. Both a solder, in
particular a lead-free solder, or also a sintered layer made of
metal particles may be used as the connecting layer. The exposed
contacts preferably have metal layers, since contacting of the
first connecting layer with the exposed contacts of the further
diode is thus simplified. These metal structures may be implemented
in particular as ring structures, whereby further thermal creep of
the connecting layer is prevented. To reliably ensure, by way of a
simple measurement, whether the first connecting layer is correctly
embodied between the first metallic contact and the first side of
the semiconductor element, the diode and the further diode are to
have a lateral distance from one another which is greater than the
width of the space charge zone, which propagates from the diode in
the blocking case, so that the space charge zone of the diode does
not extend up to the further diode element. The blocking case is
understood here as the extension of the space charge zone in the
event of the maximum applicable blocking voltage. The maximum
applicable blocking voltage is limited to a maximum value by a
breakthrough of the diode in the middle region of the semiconductor
element due to the avalanche effect. Also in this case (or up to a
somewhat higher voltage), the space charge zone is not to extend up
to the further diode in the edge region. Alternatively, a
circumferential highly doped semiconductor layer having inverted
polarity may be located between the two diodes at the semiconductor
surface, which delimits the extension of the space charge zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 shows a side view/sectional view of a diode according
to the related art.
[0006] FIG. 2 shows a first exemplary embodiment.
[0007] FIG. 3 shows a second exemplary embodiment.
[0008] FIG. 4 shows a third exemplary embodiment.
[0009] FIG. 5 shows a fourth exemplary embodiment of the diode
according to the present invention.
DETAILED DESCRIPTION
[0010] In FIG. 1, a cross section is shown on the left side of axis
100 and an external view is shown on the right side of axis 100 of
a diode for a generator, in particular for a generator in a motor
vehicle. This diode has a press-in base 1, which is provided on its
outer side with so-called knurling, i.e., score marks. Press-in
base 1 is pressed into a corresponding opening of a metallic
rectifier arrangement using this knurling. A particularly close
formfitting connection of press-in base 1 to the rectifier
arrangement takes place due to the score marks of the knurling,
whereby very good electrical contacting and very good dissipation
of heat are ensured. As may be seen in the cross section, press-in
base 1 also has a mounting base 2, on which actual semiconductor
element 3 is mounted. This metallic base 2 therefore represents a
metallic contact 2 for semiconductor element 3. Semiconductor
element 3 is connected to metallic contact 2 by an electrically
conductive connecting layer 4. Semiconductor element 3 is also
connected by an electrically conductive connecting layer 5 to
metallic contact 6. For the further discussion, metallic contact 6
is referred to as the first metallic contact, connecting layer 5 is
referred to as the first connecting layer, connecting layer 4 is
referred to as the second connecting layer, and metallic contact 2
is referred to as the second contact. Furthermore, semiconductor
element 3 may also have thin superficial contacting layers, which
are situated between semiconductor element 3 and first connecting
layer 5 and second connecting layer 4. For example, a layer
sequence made of Cr, NiV.sub.7, and Ag may be used for the
connection of semiconductor element 3 to first connecting layer 5
and second connecting layer 4. Furthermore, the entirety of first
metallic contact 6, semiconductor component 3, and second metallic
contact 2 is completely enveloped by a potting compound 7. Potting
compound 7 is an insulating plastic compound, which has the task of
absorbing a part of the mechanical forces which act on first
contact 6, first connecting layer 5 of semiconductor element 3,
second connecting layer 4, and second metallic contact 2. As an aid
for the potting, a plastic ring 8 is also provided, which is used
during the mounting as a potting sleeve for plastic compound 7. An
epoxy filled with quartz grains or another
high-temperature-resistant plastic may be used as plastic compound
7, for example. A material having good electrical conductivity and
a material having good heat conductivity, for example, copper, is
preferably used as the material for first contact 6 and/or second
contact 2 and/or press-in base 1. To ensure a good surface quality,
these copper materials may be provided with a thin superficial
nickel layer. Such a diode element, as shown in FIG. 1, is already
known, for example, from DE 195 49 202.
[0011] Either a solder or a sintering material may be used for
first connecting layer 5 and second connecting layer 4. For the
manufacturing, a solder is typically placed as a small solder plate
between semiconductor element 3 and the first and second electrical
contacts and then melted by a temperature treatment. The molten
solder then wets (possibly with the aid of a flux) the surface of
semiconductor element 3 and electrical contacts 2, 6 and produces
an electrical and mechanical connection between semiconductor
element 3 and metallic contacts 2, 6 after the solidification of
the solder. For a sintering material as connecting layer 4, 5,
initially a pasty material made of a plastic having metal particles
is applied to semiconductor element 3 and/or the metallic contacts.
Printing or inlaying appropriate films is suitable for this
purpose. The plastic is then converted into a gaseous state by a
temperature treatment and the metal particles are bonded to one
another and to the surfaces of semiconductor element 3 and metallic
contacts 2, 6 by a sintering process. An electrical and mechanical
connection is thus provided between semiconductor element 3 and
metallic contacts 2, 6. Misalignment may occur during this
manufacturing method, i.e., the arrangement of the small solder
plate or the molten solder or the sintering material may not
correspond to the intended position. In particular, the connecting
layer may not only reach into an intended middle region of
semiconductor element 3, but rather also into an unintended edge
region due to such misalignment.
[0012] During operation of the diodes in the forward direction, a
forward voltage UF drops thereon, which results, at room
temperature and current densities of 500 A/cm.sup.2, in the case of
p-n diodes in a value of approximately 1 V, and in the case of
high-efficiency diodes in approximately 0.6 V-0.8 V. The power drop
linked thereto is converted into heat and is essentially dissipated
via the press-in base and the rectifier arrangement of the
generator. As a result, barrier layer temperature Tj of the diodes
increases. Thus, in the case of high generator currents and, in
addition, high ambient temperatures, barrier layer temperatures Tj
of up to 240.degree. C. are measured at the diode. In practice, the
diodes are subjected to many temperature cycles. For example, 3000
temperature cycles are to be withstood with a failure rate less
than 1%. The situation is exacerbated by the increased use of
modern start-stop or recuperation systems, in the case of which
approximately 0.2-2 million temperature cycles of approximately
40.degree. C. to 80.degree. C., which are superimposed on the mean
diode temperature, may additionally occur.
[0013] Of course, connecting layers 4, 5 used cannot melt at the
high temperatures. If a solder is used for connecting layers 4, 5,
a solder is thus used, melting temperature Ts of which is
preferable as high as possible above maximum occurring barrier
layer temperature Tj. Thus, solders having a high lead content have
generally been used up to this point, solidus temperature Ts of
which is greater than 300.degree. C. Such diodes are known, for
example, from DE 19549202.
[0014] The materials which are combined in the diode, silicon,
connecting layers 4, 5 having a lead-containing solder in
particular, and copper, have large differences in the physical
material properties. Thus, for example, coefficients of expansion
and moduli of elasticity are very different. In the event of
temperature changes, high mechanical tensions therefore occur. The
mechanical tension arising in connecting layers 4,5 during the
temperature variations rapidly reach and exceed the elasticity
limit of connecting layers 4, 5, i.e., connecting layers 4, 5 begin
to deform plastically. A procedure occurs, which is referred to as
creep. Connecting layers 4, 5 swell up out of their original
positions in the course of time and creep into the area between
copper or chip sides (2, 6 or 3, respectively) and plastic layer 7.
The creep of connecting layers 4, 5 finally results in
short-circuits. The described effect also fundamentally occurs in
the case of lead-free soft solders.
[0015] In addition, errors may occur during the mounting and the
soldering of base (1), small solder plate (4, 5), semiconductor
chip (3), and copper wire. For example, the solder may not be
correctly placed during the mounting, or may run out during
soldering. In the case of joining methods which do not use soft
solder--for example, in the case of low-temperature silver
sintering (NTV)--the joining layer may also be incorrectly placed
during the construction, inter alia. The silver layer may be
located too close to the chip edge or may even protrude beyond the
chip edge, for example.
[0016] A first exemplary embodiment of the present invention is
shown in FIG. 2. A detail is shown in FIG. 2, in which only
semiconductor element 3, first connecting layer 5, and first
metallic contact 6 are shown. Second connecting layer 4 and second
metallic contact 2 are not shown in this view, since they are not
significant for comprehending the present invention. In FIG. 2, the
internal structure of semiconductor element 3 is also shown in
particular. Semiconductor element 3 is implemented as a
plate-shaped semiconductor element, which has a first side, which
faces toward first metallic contact 6. Furthermore, plate-shaped
semiconductor element 3 has a second side, which faces toward
second connecting layer 4 or second metallic contact 2. Second
metal plating 2 and second connecting layer 4 are not shown in FIG.
2.
[0017] On the first side of plate-shaped semiconductor element 3,
which is referred to as the upper side hereafter, a p-doping 16 is
provided in a middle area and a p-doping 14 is provided in an edge
area. P-doping 16 forms, together with n-doping 13 of plate-shaped
semiconductor element 3, a p-n diode, which represents the actual
diode for the rectifier. P-doping 14, which is situated in the edge
area, also forms, with n-material 13 of plate-shaped semiconductor
element 3, a further diode, which is situated in the edge area. The
upper side of semiconductor element 3 is provided in an area
between p-doping 16 and p-doping 14 with a dielectric layer 17, for
example, a silicon oxide layer. A contact metal plating 15 is
provided on p-doping 16, which includes, for example, the
above-described layer sequence of chromium, nickel, and silver and
establishes a good ohmic contact to p-doping 16. Furthermore, this
metal plating layer 15 establishes a good electrical contact to
connecting layer 5. A good ohmic contact between metal contact 6
and the p-n diode, formed from p- doping 16 and n-material 13, is
established by this metal plating layer 15 and connecting layer 5.
P-doping 16 is provided in a middle area, i.e., this p-doping does
not reach the lateral edge of plate-shaped semiconductor element 3
at any point. P-doping 14 completely encloses p-doping 16, i.e.,
the entire edge area around the middle area is provided with a
p-doping 14 and completely encloses the middle area.
[0018] Edge area 18 of plate-shaped semiconductor element 3 is
typically produced in that a plurality of semiconductor elements 3
are manufactured on a large plate, in particular a silicon wafer,
and then this large plate is cut into a plurality of individual
semiconductor elements 3 by a sawing process. A plurality of
mechanical micro-cracks is introduced by this sawing process into
the edge area, i.e., in lateral edge 18, which results in a change
of the electrical semiconductor properties of the material. In
particular, such micro-cracks also extend into the area in which
the further diodes, formed by p-doping 14 and n-doping 13, extend.
The electrical properties of this further diode therefore differ
significantly from the electrical properties of the diode which are
produced by p-doping 16 and n-silicon 13. For an approximately 20
mm.sup.3 diode in the middle area having a breakthrough voltage in
the range of 20 V, the blocking current, i.e., the current which
flows upon the application of a blocking voltage for the diode in
the middle area (p-doping 16-n-doping 13), is generally less than
100 nA. The blocking current of the further diode in the edge area
(p-doping 14-n-doping 13), in contrast, is in the order of
magnitude of 10 to 100 .mu.A. Therefore, by measuring the blocking
current, it may be determined whether only the diode in the middle
area (p-doping 16-n-doping 13) or also the diode in the edge area
(p-doping 14-n-doping 13) was contacted by connecting layer 5.
[0019] In FIG. 2, a correct arrangement of connecting layer 5 in
relation to the diode in the middle area (16-13) is shown by
reference numeral 5. A flawed arrangement of connecting layer 5 in
relation to plate-shaped semiconductor element 3 is shown by
reference numeral 5a, in such a way that electrical contacting of
the exposed contact of p-doping 14 also takes place via connecting
layer 5a, which is now incorrectly situated. Due to incorrectly
situated connecting layer 5a, the upper side of p-doping 14 and
therefore the exposed electrical contact of the further diode in
the edge area is therefore contacted. A current flow may therefore
also take place via the further diode in the edge area (14-13),
which has an influence on the electrical properties of the overall
semiconductor element or the diode. If a current is applied in the
forward direction to first metallic contact 6 and second metallic
contact 2, the current will thus predominantly flow via the diode
in the middle area (16-13) and an increased current of the further
diode in the edge area (14-13) through the crystal defects will not
have further influence. However, if a voltage is applied in the
blocking direction, the current flow via the diode in the middle
area (16-13) will only be slight, while the current flow via the
further diode in the edge area (14-13) will have significantly
greater influence than the current flow via the diode in the middle
area (16-13). A possibility is thus provided of determining, by
applying a blocking voltage, whether the first connecting layer
only contacts the diode in the middle area (16-13) or also contacts
the further diode in the edge area (14-13). To reliably ensure by a
simple measurement whether the first connecting layer is correctly
embodied between the first metallic contact and the first side of
the semiconductor element, the diode and the further diode are to
have a lateral distance from one another which is greater than the
range of the space charge zone propagating from the diode in case
of blocking, so that the space charge zone of the diode does not
extend up to the further diode element. The blocking case is
understood here as the extension of the space charge zone in the
case of the maximum applicable blocking voltage. The maximum
applicable blocking voltage is limited to a maximum value by a
breakthrough of the diode in the middle area of the semiconductor
element due to the avalanche effect. Also in this case (or up to a
somewhat higher voltage), the space charge zone is also not to
extend up to the further diode in the edge area. Alternatively, a
circumferential, highly-doped semiconductor layer having inverted
polarity, which delimits the extension of the space charge zone,
may also be located between the two diodes on the semiconductor
surface.
[0020] FIG. 3 shows another exemplary embodiment of the present
invention. The specific embodiment in FIG. 3 essentially
corresponds to the specific embodiment according to FIG. 2, and
reference numerals 3, 5, 6, 13, 14, 15, 16, 17, and 18 also
identify the same objects in FIG. 3 as in FIG. 2. However, in
contrast to FIG. 2, a further metal plating 15a is provided, which
is constructed with regard to the materials precisely like metal
plating 15. However, metal plating 15a is situated in the edge area
above further diode 14-13, so that the exposed contact of this
further diode is now no longer formed by the surface of p-doping
14, but rather by metal plating 15a. Particularly simple contacting
of the further diode is ensured by this measure, since an
electrical contact of incorrectly situated connecting layer 5a to
metal plating layer 15a is ensured. It is thus ensured that
contacting of incorrectly situated connecting layer 5a to further
diode 14-13 is ensured. The recognition in principle of an
incorrectly situated connecting layer 5 is thus further
improved.
[0021] FIG. 4 shows another exemplary embodiment of the diode
according to the present invention. Reference numerals 3, 5, 6, 13,
14, 15, 16, 17, 18, 5a, and 15a again represent the same objects as
in FIGS. 2 and 3. In contrast to FIGS. 2 and 3, however, a
plurality of different metal platings 15a, 15b, and 15c are
provided in the edge area, which are each situated in the edge area
and each completely enclose the middle area in a ring. These metal
layers 15a, 15b, and 15c are again metal contacts of further diode
14-13 in the edge area. Since these individual metal platings are
separate from one another, however, and an area is provided in each
case between individual metal platings 15a, 15b, 15c, in which no
metal is provided, a further propagation of flawed connecting layer
5a is prevented. Specifically, it has been shown that in the event
of thermally related creep of metal layer 5a, surfaces which are
already covered with metal are very easily covered, and then at the
end of such a superficial metal plating 15a, 15b, 15c, further
creep is prevented. Therefore, further thermally related creep of
connecting layer 5 is prevented by the arrangement as the multiple
ring type structures of metal platings 15a, 15b, 15c.
Alternatively, additional dielectric layers (similarly to layer 17)
may also be located between metal layers 15a, 15b, and 15c.
[0022] FIG. 5 shows another exemplary embodiment of the present
invention. Reference numerals 3, 5, 6, 13, 14, 15, 15a, 17, 5a, and
18 again identify the same objects as in FIG. 3. In contrast to
FIG. 3, however, a continuous p-doping 16, which forms a first p-n
diode in a middle area, is not provided. Instead, a plurality of
individual p-areas 19 is provided. In these p-areas 19, flat,
highly n-doped areas 20 are introduced, which form the source zones
of MOS transistors. A thin gate oxide 21 is then provided on the
upper side, which extends on the upper side of semiconductor
element 3 from superficially exposed areas 13 via p-doped areas 19
up to strongly n-doped source areas 20. Thin gate oxide 21 is then
covered with an n-doped polysilicon gate 22, which is in turn
completely covered by metal plating 15. An MOS transistor is thus
provided in the middle area of semiconductor element 3, in which
the gate, body region, and source region are electrically
short-circuited with one another. Such a component also behaves
like a diode having a very low forward voltage and also only has a
very small current flow in the blocking direction. In the case of
such a component according to FIG. 2, it may therefore also be
established by measuring a blocking current whether an incorrect
arrangement of connecting layer 5 or 5a has occurred. The MOS
transistors in FIG. 5 may also be embodied in other variations
corresponding to the related art.
* * * * *