U.S. patent application number 14/511610 was filed with the patent office on 2015-01-22 for power module substrate, power module, and method for manufacturing power module substrate.
The applicant listed for this patent is MITSUBISHI MATERIALS CORPORATION. Invention is credited to Kazuhiro Akiyama, Takeshi Kitahara, Yoshirou Kuromitsu, Yoshiyuki Nagatomo, Hiroshi Tonomura.
Application Number | 20150022977 14/511610 |
Document ID | / |
Family ID | 43589695 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150022977 |
Kind Code |
A1 |
Kuromitsu; Yoshirou ; et
al. |
January 22, 2015 |
POWER MODULE SUBSTRATE, POWER MODULE, AND METHOD FOR MANUFACTURING
POWER MODULE SUBSTRATE
Abstract
A power module substrate includes: a ceramics substrate having a
surface; and a metal plate connected to the surface of the ceramics
substrate, composed of aluminum, and including Cu at a joint
interface between the ceramics substrate and the metal plate,
wherein a Cu concentration at the joint interface is in the range
of 0.05 to 5 wt %.
Inventors: |
Kuromitsu; Yoshirou;
(Saitama-shi, JP) ; Nagatomo; Yoshiyuki;
(Saitama-shi, JP) ; Kitahara; Takeshi;
(Gotenba-shi, JP) ; Tonomura; Hiroshi; (Naka-gun,
JP) ; Akiyama; Kazuhiro; (Naka-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI MATERIALS CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
43589695 |
Appl. No.: |
14/511610 |
Filed: |
October 10, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14027601 |
Sep 16, 2013 |
|
|
|
14511610 |
|
|
|
|
12737042 |
Dec 3, 2010 |
8564118 |
|
|
PCT/JP2009/060392 |
Jun 5, 2009 |
|
|
|
14027601 |
|
|
|
|
Current U.S.
Class: |
361/748 ;
228/122.1; 428/552; 428/614; 428/627; 428/632 |
Current CPC
Class: |
C04B 2237/128 20130101;
C04B 2237/343 20130101; H05K 1/0306 20130101; C04B 2237/72
20130101; C04B 2237/86 20130101; C04B 2237/366 20130101; H01L
23/3735 20130101; H05K 1/0271 20130101; C04B 37/026 20130101; H05K
1/181 20130101; B23K 1/20 20130101; C04B 35/645 20130101; H01L
21/76838 20130101; C04B 2237/124 20130101; Y10T 29/49117 20150115;
C04B 2237/704 20130101; H01L 2224/29111 20130101; H01L 24/32
20130101; H05K 1/09 20130101; C04B 2237/55 20130101; B23K 1/0016
20130101; C04B 2237/706 20130101; C04B 2237/60 20130101; C04B
2235/6581 20130101; H01L 24/29 20130101; Y10T 428/12611 20150115;
C04B 2237/121 20130101; H01L 2924/01322 20130101; H01L 2224/32225
20130101; C04B 2237/402 20130101; H01L 23/498 20130101; B23K 1/0008
20130101; C04B 2237/708 20130101; Y10T 428/12486 20150115; Y10T
428/12056 20150115; Y10T 428/12576 20150115; H01L 2224/29111
20130101; H01L 2924/01047 20130101; H01L 2224/29111 20130101; H01L
2924/01049 20130101; H01L 2224/29111 20130101; H01L 2924/01047
20130101; H01L 2924/01029 20130101; H01L 2924/01322 20130101; H01L
2924/00 20130101 |
Class at
Publication: |
361/748 ;
228/122.1; 428/627; 428/632; 428/614; 428/552 |
International
Class: |
H05K 1/02 20060101
H05K001/02; H05K 1/18 20060101 H05K001/18; H05K 1/03 20060101
H05K001/03; H05K 1/09 20060101 H05K001/09; B23K 1/00 20060101
B23K001/00; B23K 1/20 20060101 B23K001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2008 |
JP |
2008-149902 |
Mar 17, 2009 |
JP |
2009-065033 |
Mar 26, 2009 |
JP |
2009-075315 |
Mar 31, 2009 |
JP |
2009-086247 |
Mar 31, 2009 |
JP |
2009-086248 |
Claims
1-29. (canceled)
30. A power module substrate comprising: a ceramics substrate
having a surface; a metal plate connected to the surface of the
ceramics substrate via a brazing filler metal including Si,
composed of aluminum; Cu introduced into the joint interface
between the ceramics substrate and the metal plate, wherein the
metal plate includes Si and Cu; and a Si concentration is in the
range of 0.05 to 0.5 wt % and a Cu concentration is in the range of
0.05 to 1.0 wt %, in a portion which is close to the joint
interface of the metal plate.
31. The power module substrate according to claim 30, wherein a
width of the ceramics substrate is greater than a width of the
metal plate; an aluminum phase in which Si and Cu are included in
aluminum, a Si phase in which a content rate of Si is greater than
or equal to 98 wt %, and an eutectic phase composed of a ternary
eutectic structure including Al, Cu, and Si, are formed at an end
portion in a width direction of the metal plate.
32. The power module substrate according to claim 31, wherein
precipitate particles composed of a compound including Cu
precipitate in the eutectic phase.
33. The power module substrate according to claim 30, further
comprising: a high-Si concentration section formed at the joint
interface between the metal plate and the ceramics substrate,
having a Si concentration that is more than five times the Si
concentration in the metal plate, wherein the ceramics substrate is
composed of AlN or Al.sub.2O.sub.3.
34. The power module substrate according to claim 30, further
comprising: a high-oxygen concentration section formed at the joint
interface between the metal plate and the ceramics substrate,
having an oxygen concentration that is greater than oxygen
concentrations in the metal plate and in the ceramics substrate,
and having a thickness of less than or equal to 4 nm, wherein the
ceramics substrate is composed of AlN or Si.sub.3N.sub.4.
35. A power module comprising: a power module substrate according
to claim 30; and an electronic component mounted on the power
module substrate.
36. A method for manufacturing a power module substrate,
comprising: preparing a ceramics substrate having a connection
face, a metal plate composed of aluminum, and a brazing filler
metal including Si; stacking the ceramics substrate and the metal
plate in layers with the brazing filler metal interposed
therebetween; heating the ceramics substrate, the brazing filler
metal, and the metal plate which are stacked in layers in a state
where a pressure is applied thereon; forming a fusion aluminum
layer at a boundary face between the ceramics substrate and the
metal plate by melting the brazing filler metal; and solidifying
the fusion aluminum layer, wherein Cu is adhered to at least one of
the connection face of the ceramics substrate and a face of the
brazing filler metal opposing the ceramics substrate before
stacking the ceramics substrate and the metal plate in layers with
the brazing filler metal interposed therebetween.
37. The method for manufacturing a power module substrate according
to claim 36, wherein Cu is adhered to at least one of the
connection face of the ceramics substrate and a face of the brazing
filler metal opposing the ceramics substrate by an evaporation
method or a sputtering method in the adhering of Cu.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a power module substrate,
which is employed in a semiconductor device controlling a large
amount of high voltage electrical current, a power module including
the power module substrate, and a method for manufacturing the
power module substrate.
[0003] This application is based on and claims priority from
Japanese Patent Application No. 2008-149902, filed on Jun. 6, 2008,
Japanese Patent Application No. 2009-065033, filed on Mar. 17,
2009, Japanese Patent Application No. 2009-075315, filed on Mar.
26, 2009, Japanese Patent Application No. 2009-086247, filed on
Mar. 31, 2009, and Japanese Patent Application No. 2009-086248,
filed on Mar. 31, 2009, the contents of which are incorporated
herein by reference.
[0004] 2. Background Art
[0005] Conventionally, in all of semiconductor elements, a power
module is used for the power supply.
[0006] The amount of heat generated by the power module is
relatively high.
[0007] Consequently, as a substrate on which the power module is
mounted, a power module substrate is used in which a metal plate
made of Al (aluminum) is joined to a ceramics substrate composed
of, for example, AlN (aluminum nitride), Si.sub.3N.sub.4 (silicon
nitride), or Al.sub.2O.sub.3 (aluminum oxide), with an Al--Si
system brazing filler metal interposed therebetween.
[0008] In addition, the metal plate is formed as a circuit layer,
and a semiconductor chip that is a power element is mounted on the
metal plate with a solder material interposed therebetween.
[0009] In addition, in order to improve the heat radiation
efficiency, a structure in which a metal layer is formed by
connecting a metal plate composed of Al or the like with a lower
face of a ceramics substrate, and the entire power module substrate
is joined to a heat radiation plate with the metal layer interposed
therebetween has been proposed.
[0010] Conventionally, in order to reliably obtain the joint
strength between metal plates which serve as the circuit layer and
the metal layer, and a ceramics substrate, for example, technique
of having the surface roughness of the ceramics substrate being
less than 0.5 .mu.m has been known, as disclosed in Japanese
Unexamined Patent Application, First Publication No. H3-234045.
[0011] However, when the metal plate is joined to the ceramics
substrate, even if the roughness surface of the ceramics substrate
is simply reduced, sufficient high joint strength is not obtained
and there is a disadvantage in that the reliability thereof cannot
be improved.
[0012] Even if, for example, a honing treatment is performed on the
surface of the ceramics substrate by use of Al.sub.2O.sub.3
particles in a dry method and the roughness surface Ra thereof is
made 0.2 .mu.m, peeling may occur at an interface thereof in a
peeling test.
[0013] In addition, even if a ceramics substrate is polished by use
of a polishing method so that the roughness surface Ra is made less
than or equal to 0.1 .mu.m, there is a case where peeling occurs at
the interface in the same manner as described above.
[0014] In addition, in a case where a power module substrate is
subjected to a heat-load cycle, not only peeling at an interface
but also cracks being generated in the ceramics substrate is
known.
[0015] Specifically, recently, in power modules, downsizing and
reducing of thickness has been required, and the usage environment
has become severe.
[0016] The power module is used under a usage environment in which,
for example, heat stress is repeatedly generated.
[0017] In addition, recently, the amount of heat generated in an
electronic component has tended to increase, so it is necessary to
dispose a power module substrate on a heat radiation plate as
described above.
[0018] In this case, since the power module substrate is rigidly
fixed to the heat radiation plate, a large shear force is generated
at a joint interface between the metal plate and the ceramics
substrate when the substrate is subjected to a heat-load cycle.
[0019] As a result, improvement of the joint strength and
reliability are further required.
SUMMARY OF THE INVENTION
[0020] The present invention was conceived in view of the
above-described circumstances and it is an object thereof to
provide a power module substrate, a power module including the
power module substrate, and a method for manufacturing the power
module substrate, in which a metal plate is reliably connected to a
ceramics substrate and the heat-load cycle reliability thereof is
high.
[0021] In order to solve the foregoing problem and achieve the
object, a power module substrate of a first aspect of the present
invention includes: a ceramics substrate having a surface; and a
metal plate connected to the surface of the ceramics substrate,
composed of aluminum, and including Cu at a joint interface between
the ceramics substrate and the metal plate, wherein a Cu
concentration at the joint interface is in the range of 0.05 to 5
wt %.
[0022] In the power module substrate having the above-described
structure, since Cu is diffused in the metal plate and Cu
concentration in the joint interface is in the range of 0.05 to 5
wt %, the joint interface of the metal plate is solid-solution
strengthened.
[0023] Therefore, when a heat-load cycle or the like is performed,
cracks are prevented from being generated and propagated in the
metal plate, it is possible to improve the junction
reliability.
[0024] In the power module substrate of the first aspect of the
present invention, it is preferable that an aluminum phase in which
Cu is included in aluminum, and an eutectic phase composed of a
binary eutectic structure including Al and Cu be formed at an end
portion in a width direction of the metal plate.
[0025] In this case, since the eutectic phase composed of a binary
eutectic structure including Al and Cu is formed at the end portion
in the width direction of the metal plate, it is possible to
further strengthen the end portion in the width direction of the
metal plate.
[0026] Consequently, it is possible to prevent cracks from being
generated and propagated at the end portion in the width direction
of the metal plate, and it is possible to improve the junction
reliability.
[0027] In the power module substrate of the first aspect of the
present invention, it is preferable that precipitate particles
composed of a compound including Cu precipitate in the eutectic
phase.
[0028] In this case, since the precipitate particles composed of a
compound including Cu precipitate in the eutectic phase formed at
the end portion in the width direction of the metal plate, it is
possible to further realize precipitation strengthening of the end
portion in the width direction of the metal plate.
[0029] Consequently, it is possible to prevent cracks from being
generated and propagated at the end portion in the width direction
of the metal plate, and it is possible to reliably improve the
junction reliability.
[0030] In the power module substrate of the first aspect of the
present invention, it is preferable that the metal plate include: a
concentration-gradient section in which the Cu concentration
gradually decreases in a manner so as to separate from the joint
interface in a direction in which the metal plate and the ceramics
substrate are stacked in layers; and a soft layer formed at an
opposite side of the ceramics substrate relative to the
concentration-gradient section, having a degree of hardness lower
than that of a near joint interface.
[0031] In this case, Cu concentration is high in the metal plate
adjacent to the joint interface, and is hardened due to solid
solution strengthening.
[0032] On the other hand, in the soft layer, Cu concentration is
low, the degree of hardness is low, and the deformation resistance
is low.
[0033] Therefore, due to the soft layer, it is possible to absorb
heat strain (heat stress) which is caused by the difference of the
coefficient of thermal expansion between the metal plate and the
ceramics substrate, and it is possible to considerably improve the
heat-load cycle reliability.
[0034] A power module of a second aspect of the present invention
is provided with: the power module substrate of the above-described
first aspect; and an electronic component mounted on the power
module substrate.
[0035] According to the power module having the above-described
structure, since the joint strength between the ceramics substrate
and the metal plate is high, even if the power module is used under
a severe usage environment in which, for example, heat stress is
repeatedly generated, it is possible to significantly improve the
reliability thereof.
[0036] A method for manufacturing a power module substrate of a
third aspect of the present invention includes: preparing a
ceramics substrate, a metal plate composed of aluminum, and a
Cu-layer having a thickness of 0.15 .mu.m to 3 .mu.m; stacking the
ceramics substrate and the metal plate in layers with the Cu-layer
interposed therebetween (stacking step); pressing the ceramics
substrate, the Cu-layer, and the metal plate which were stacked in
layers in a stacked direction, and heating the ceramics substrate,
the Cu-layer, and the metal plate; forming a fusion metal layer at
a boundary face between the ceramics substrate and the metal plate
(melting step); solidifying the fusion metal layer by cooling the
fusion metal layer (solidifying step); and making Cu to be included
into the metal plate adjacent to the joint interface between the
ceramics substrate and the metal plate in the melting step and the
solidifying step so that a Cu concentration is in the range of 0.05
to 5 wt %.
[0037] In the method for manufacturing a power module substrate,
the ceramics substrate and the metal plate stacked in layers with
the Cu-layer interposed therebetween, and the ceramics substrate
and the metal plate which were stacked in layers is pressed in the
stacked direction and heated.
[0038] Because of this, due to the eutectic reaction of Cu of the
Cu-layer and Al of the metal plate, the melting point of the near
joint interface is lowered, even under relatively low-temperature,
it is possible to form the fusion metal layer at the boundary face
between the ceramics substrate and the metal plate, and it is
possible to connect the ceramics substrate to the metal plate.
[0039] Namely, without using a brazing filler metal composed of
Al--Si alloy or the like, it is possible to connect the ceramics
substrate to the metal plate.
[0040] As described above, since the ceramics substrate is bonded
to the metal plate without using a brazing filler metal, a brazing
filler metal does not penetrate to a surface of the circuit layer,
and it is possible to reliably form a Ni-plated layer on the
surface of the circuit layer.
[0041] Here, when the thickness of the Cu-layer is less than 0.15
.mu.m, there is a concern that a fusion metal layer cannot be
sufficiently formed at the boundary face between the ceramics
substrate and the metal plate.
[0042] In addition, when the thickness of the Cu-layer exceeds 3
.mu.m, reactant of Cu and Al is excessively generated at the joint
interface, the near joint interface of the metal plate is
strengthened more than necessary, and there is a concern that
cracks are generated at the ceramics substrate when the ceramics
substrate is subjected to a heat-load cycle.
[0043] Consequently, it is preferable that the thickness of the
Cu-layer be 0.15 .mu.m to 3 .mu.m.
[0044] In addition, in order to reliably obtain the above-described
action and effect, it is preferable that the thickness of the
Cu-layer be 0.5 .mu.m to 2.5 .mu.m.
[0045] In the method for manufacturing a power module substrate of
the third aspect of the present invention, it is preferable that
the Cu-layer be adhered to at least one of the ceramics substrate
and the metal plate before stacking the ceramics substrate, the
Cu-layer, and the metal plate in layers.
[0046] In this case, since Cu is adhered to a face of the metal
plate (connection face) facing the ceramics substrate or a face of
the ceramics substrate (connection face) facing the metal plate, it
is possible to stack the ceramics substrate and the metal plate in
layers with the Cu-layer reliably interposed therebetween, and it
is possible to reliably connect the ceramics substrate to the metal
plate.
[0047] In the method for manufacturing a power module substrate of
the third aspect of the present invention, it is preferable that,
when the Cu is adhered to at least one of the ceramics substrate
and the metal plate, Cu be adhered to at least one of the ceramics
substrate and the metal plate, by a method selected from an
evaporation method, a sputtering method, a plating method, and a
method of applying a Cu-paste.
[0048] In this case, it is possible to form reliably the Cu-layer
by a method selected from the evaporation method, the sputtering
method, the plating method, and the method of applying a Cu-paste,
and it is possible to connect the ceramics substrate to the metal
plate.
[0049] In the method for manufacturing a power module substrate of
the third aspect of the present invention, it is preferable that,
when stacking the ceramics substrate and the metal plate in layers
with the Cu-layer interposed therebetween, the Cu-layer be disposed
by inserting a copper foil between the ceramics substrate and the
metal plate.
[0050] In this case, due to inserting of Cu-foil, it is possible to
form the Cu-layer on the face of the metal plate (connection face)
facing the ceramics substrate or the face of the ceramics substrate
(connection face) facing the metal plate.
[0051] Therefore, it is possible to tightly connect the ceramics
substrate to the metal plate.
[0052] A power module substrate of a fourth aspect of the present
invention includes: a ceramics substrate composed of AlN or
Si.sub.3N.sub.4, having a surface; a metal plate connected to the
surface of the ceramics substrate, composed of pure aluminum; and a
high-Cu concentration section formed at a joint interface between
the metal plate and the ceramics substrate, having a Cu
concentration that is more than twice the Cu concentration in the
metal plate.
[0053] In the power module substrate having the above-described
structure, since the high-Cu concentration section having a Cu
concentration that is more than twice the Cu concentration in the
metal plate is formed at the joint interface between the ceramics
substrate composed of AlN or Si.sub.3N.sub.4 and the metal plate
composed of pure aluminum, it is possible to improve the joint
strength between the ceramics substrate and the metal plate due to
a Cu atom existing at the near boundary face.
[0054] In addition, Cu concentration in the metal plate means a Cu
concentration in the portion that is positioned separately from the
joint interface in the metal plate by a predetermined distance (for
example, 50 nm or more).
[0055] In the power module substrate of the fourth aspect of the
present invention, it is preferable that an oxygen concentration in
the high-Cu concentration section be greater than oxygen
concentrations in the metal plate and the ceramics substrate.
[0056] In this case, due to oxygen intervening the joint interface,
it is possible to further improve the joint strength between the
ceramics substrate composed of AlN or Si.sub.3N.sub.4 and the metal
plate composed of pure aluminum.
[0057] In addition, it is thought that the oxygen existing at the
joint interface with a high degree of concentration is oxygen
existing at a surface of the ceramics substrate and oxygen taken
from an oxide film formed on a surface of a metal plate.
[0058] Here, the oxygen existing at the joint interface with a high
degree of concentration, this means the oxide film or the like
being sufficiently heated so as to be reliably removed.
[0059] Therefore, it is possible to tightly connect the ceramics
substrate to the metal plate.
[0060] In the power module substrate of the fourth aspect of the
present invention, it is preferable that the ceramics substrate be
composed of AlN; and the mass ratio of Al, Cu, O, and N be
Al:Cu:O:N=50 to 90 wt %:1 to 10 wt %:2 to 20 wt %:25 wt % or less
when the joint interface including the high-Cu concentration
section is analyzed by an energy dispersive X-ray spectroscopy.
[0061] In the power module substrate of the fourth aspect of the
present invention, it is preferable that the ceramics substrate be
composed of Si.sub.3N.sub.4; and the mass ratio of Al, Si, Cu, O,
and N be Al:Si:Cu:O:N=15 to 45 wt %:15 to 45 wt %:1 to 10 wt %:2 to
20 wt %:25 wt % or less when the joint interface including the
high-Cu concentration section is analyzed by an energy dispersive
X-ray spectroscopy.
[0062] When the mass ratio of Cu atom existing at the joint
interface exceeds 10 wt %, the reactant of Cu and Al is excessively
generated, there is a concern that the reactant interferes the
junction.
[0063] In addition, the near joint interface of the metal plate is
strengthened more than necessary due to the reactant, a stress
operates in the ceramics substrate when the ceramics substrate is
subjected to a heat-load cycle, and there is a concern that the
ceramics substrate is cracked.
[0064] On the other hand, when the mass ratio of Cu atom is less
than 1 wt %, there is a concern that it is impossible to
sufficiently improve the joint strength due to a Cu atom.
[0065] Therefore, it is preferable that the mass ratio of Cu atom
be in the range of 1 to 10 wt % at the joint interface.
[0066] In addition, when the mass ratio of oxygen atom including
the high-Cu concentration section and existing at the joint
interface exceeds 20 wt %, the thickness of portion in which the
oxygen concentration is high increases, and cracks are generated at
the high-concentration section when a heat-load cycle is
performed.
[0067] Because of this, there is a concern that, junction
reliability is degraded.
[0068] Therefore, it is preferable that the oxygen concentration be
2 to 20 wt %.
[0069] Here, when analyzation is performed by an energy dispersive
X-ray spectroscopy, since the diameter of the spot therefor is
extremely small, a plurality of points are measured on the joint
interface (for example, 10 to 100 points), and the average of the
points is calculated.
[0070] In addition, when the measuring is performed, the joint
interface between the crystalline grain and the ceramics substrate
is only measured, and the joint interface between the crystalline
grain boundary of the metal plate and the ceramics substrate is not
measured.
[0071] In addition, in this specification, analytical values are
obtained by use of an energy dispersive X-ray spectroscopy under
the condition where an acceleration voltage is set to 200 kV by use
of an energy-dispersive X-ray fluorescence spectrometer, NORAN
System 7 produced by Thermo Fisher Scientific Inc., the
spectrometer being mounted on an electron microscope, JEM-2010F
produced by JEOL Ltd.
[0072] A power module of a fifth aspect of the present invention is
provided with: the power module substrate of the above-described
fourth aspect; and an electronic component mounted on the power
module substrate.
[0073] According to the power module having the above-described
structure, the joint strength between the ceramics substrate and
the metal plate is high, and even if the power module is used under
a severe usage environment in which, for example, heat stress is
repeatedly generated, it is possible to significantly improve the
reliability thereof.
[0074] A method for manufacturing a power module substrate of a
sixth aspect of the present invention includes: preparing a
ceramics substrate composed of AlN, a metal plate composed of pure
aluminum, and a Cu-layer having a thickness of 0.15 .mu.m to 3
.mu.m; stacking the ceramics substrate and the metal plate in
layers with the Cu-layer interposed therebetween (stacking step);
pressing the ceramics substrate, the Cu-layer, and the metal plate
which were stacked in layers in a stacked direction, and heating
the ceramics substrate, the Cu-layer, and the metal plate; forming
a fusion aluminum layer at a boundary face between the ceramics
substrate and the metal plate (melting step); solidifying the
fusion aluminum layer by cooling the fusion aluminum layer
(solidifying step); and forming a high-Cu concentration section at
a joint interface between the ceramics substrate and the metal
plate in the melting step and the solidifying step, the high-Cu
concentration section having a Cu concentration that is more than
twice the Cu concentration in the metal plate.
[0075] In the method for manufacturing a power module substrate,
the ceramics substrate and the metal plate stacked in layers with
the Cu-layer interposed therebetween, and the ceramics substrate
and the metal plate which were stacked in layers is pressed in the
stacked direction and heated.
[0076] Because of this, due to the eutectic reaction of Cu of the
Cu-layer and Al of the metal plate, the melting point of the near
joint interface is lowered, even under relatively low-temperature,
it is possible to form the fusion aluminum layer at the boundary
face between the ceramics substrate and the metal plate, and it is
possible to connect the ceramics substrate to the metal plate.
[0077] Namely, without using a brazing filler metal composed of
Al--Si alloy or the like, it is possible to connect the ceramics
substrate to the metal plate.
[0078] In addition, when the thickness of the Cu-layer is less than
0.15 .mu.m, there is a concern that a fusion aluminum layer cannot
be sufficiently formed at the boundary face between the ceramics
substrate and the metal plate.
[0079] In addition, when the thickness of the Cu-layer exceeds 3
.mu.m, reactant of Cu and Al is excessively generated at the joint
interface, the near joint interface of the metal plate is
strengthened more than necessary, and there is a concern that
cracks are generated at the ceramics substrate composed of AlN when
the ceramics substrate is subjected to a heat-load cycle.
[0080] Consequently, in a case where the ceramics substrate is
composed of AlN, it is preferable that the thickness of the
Cu-layer be 0.15 .mu.m to 3 .mu.m.
[0081] A method for manufacturing a power module substrate of a
seventh aspect of the present invention includes: preparing a
ceramics substrate composed of Si.sub.3N.sub.4, a metal plate
composed of pure aluminum, and a Cu-layer having a thickness of
0.15 .mu.m to 3 .mu.m; stacking the ceramics substrate and the
metal plate in layers with the Cu-layer interposed therebetween
(stacking step); pressing the ceramics substrate, the Cu-layer, and
the metal plate which were stacked in layers in a stacked
direction, and heating the ceramics substrate, the Cu-layer, and
the metal plate; forming a fusion aluminum layer at a boundary face
between the ceramics substrate and the metal plate (melting step);
solidifying the fusion aluminum layer by cooling the fusion
aluminum layer (solidifying step); and forming a high-Cu
concentration section at a joint interface between the ceramics
substrate and the metal plate in the melting step and the
solidifying step, the high-Cu concentration section having a Cu
concentration that is more than twice the Cu concentration in the
metal plate.
[0082] In the method for manufacturing a power module substrate,
the ceramics substrate and the metal plate stacked in layers with
the Cu-layer interposed therebetween, and the ceramics substrate
and the metal plate which were stacked in layers is pressed in the
stacked direction and heated.
[0083] Because of this, due to the eutectic reaction of Cu of the
Cu-layer and Al of the metal plate, the melting point of the near
joint interface is lowered, even under relatively low-temperature,
it is possible to form the fusion aluminum layer at the boundary
face between the ceramics substrate and the metal plate, and it is
possible to connect the ceramics substrate to the metal plate.
[0084] Namely, without using a brazing filler metal composed of
Al--Si alloy or the like, it is possible to connect the ceramics
substrate to the metal plate.
[0085] In addition, when the thickness of the Cu-layer is less than
0.15 .mu.m, there is a concern that a fusion aluminum layer cannot
be sufficiently formed at the boundary face between the ceramics
substrate and the metal plate.
[0086] In addition, when the thickness of the Cu-layer exceeds 3
.mu.m, the reactant of Cu and Al is excessively generated at the
joint interface, there is a concern that the reactant interferes
the junction.
[0087] Consequently, in a case where the ceramics substrate is
composed of Si.sub.3N.sub.4, it is preferable that the thickness of
the Cu-layer be 0.15 .mu.m to 3 .mu.m.
[0088] In the method for manufacturing a power module substrate of
the sixth aspect or the seventh aspect of the present invention, it
is preferable that, when stacking the ceramics substrate and the
metal plate in layers with the Cu-layer interposed therebetween,
the Cu-layer be disposed by inserting a copper foil between the
ceramics substrate and the metal plate.
[0089] In the method for manufacturing a power module substrate of
the sixth aspect or the seventh aspect of the present invention, it
is preferable that the Cu-layer be adhered to at least one of the
ceramics substrate and the metal plate before stacking the ceramics
substrate, the Cu-layer, and the metal plate in layers.
[0090] In the method for manufacturing a power module substrate of
the sixth aspect or the seventh aspect of the present invention, it
is preferable that, when the Cu is adhered to at least one of the
ceramics substrate and the metal plate, Cu be adhered to at least
one of the ceramics substrate and the metal plate, by a method
selected from an evaporation method, a sputtering method, a plating
method, and a method of applying a Cu-paste.
[0091] According to the methods, between the ceramics substrate and
the metal plate, it is possible to form a Cu-layer having a desired
thickness, and it is possible to reliably connect the ceramics
substrate to the metal plate.
[0092] A power module substrate of an eighth aspect of the present
invention includes: a ceramics substrate composed of
Al.sub.2O.sub.3, having a surface; a metal plate connected to the
surface of the ceramics substrate, composed of pure aluminum; and a
high-Cu concentration section formed at a joint interface between
the metal plate and the ceramics substrate, having a Cu
concentration that is more than twice the Cu concentration in the
metal plate.
[0093] In the power module substrate having the above-described
structure, since the high-Cu concentration section having a Cu
concentration that is more than twice the Cu concentration in the
metal plate is formed at the joint interface between the ceramics
substrate composed of Al.sub.2O.sub.3 and the metal plate composed
of pure aluminum, it is possible to improve the joint strength
between the ceramics substrate and the metal plate due to a Cu atom
existing at the near boundary face.
[0094] In addition, Cu concentration in the metal plate means a Cu
concentration in the portion that is positioned separately from the
joint interface in the metal plate by a predetermined distance (for
example, 50 nm or more).
[0095] In the power module substrate of the eighth aspect of the
present invention, it is preferable that the mass ratio of Al, Cu,
and O be Al:Cu:O=50 to 90 wt %:1 to 10 wt %:0 to 45 wt % when the
joint interface including the high-Cu concentration section is
analyzed by an energy dispersive X-ray spectroscopy.
[0096] When the mass ratio of Cu atom existing at the joint
interface exceeds 10 wt %, the reactant of Cu and Al is excessively
generated, there is a concern that the reactant interferes the
junction.
[0097] On the other hand, when the mass ratio of Cu atom is less
than 1 wt %, there is a concern that it is impossible to
sufficiently improve the joint strength due to a Cu atom.
[0098] Therefore, it is preferable that the mass ratio of Cu atom
be in the range of 1 to 10 wt % at the joint interface.
[0099] Here, when analyzation is performed by an energy dispersive
X-ray spectroscopy, since the diameter of the spot therefor is
extremely small, a plurality of points are measured on the joint
interface (for example, 10 to 100 points), and the average of the
points is calculated.
[0100] In addition, when the measuring is performed, the joint
interface between the crystalline grain and the ceramics substrate
is only measured, and the joint interface between the crystalline
grain boundary of the metal plate and the ceramics substrate is not
measured.
[0101] A power module of a ninth aspect of the present invention is
provided with: the power module substrate of the above-described
eighth aspect; and an electronic component mounted on the power
module substrate.
[0102] According to the power module having the above-described
structure, the joint strength between the ceramics substrate and
the metal plate is high, and even if the power module is used under
a severe usage environment in which, for example, heat stress is
repeatedly generated, it is possible to significantly improve the
reliability thereof.
[0103] A method for manufacturing a power module substrate of a
tenth aspect of the present invention includes: preparing a
ceramics substrate composed of Al.sub.2O.sub.3, a metal plate
composed of pure aluminum, and a Cu-layer having a thickness of
0.15 .mu.m to 3 um; stacking the ceramics substrate and the metal
plate in layers with the Cu-layer interposed therebetween (stacking
step); pressing the ceramics substrate, the Cu-layer, and the metal
plate which were stacked in layers in a stacked direction, and
heating the ceramics substrate, the Cu-layer, and the metal plate;
forming a fusion aluminum layer at a boundary face between the
ceramics substrate and the metal plate (melting step); solidifying
the fusion aluminum layer by cooling the fusion aluminum layer
(solidifying step); and forming a high-Cu concentration section at
a joint interface between the ceramics substrate and the metal
plate in the melting step and the solidifying step, the high-Cu
concentration section having a Cu concentration that is more than
twice the Cu concentration in the metal plate.
[0104] In the method for manufacturing a power module substrate,
the ceramics substrate and the metal plate stacked in layers with
the Cu-layer interposed therebetween, and the ceramics substrate
and the metal plate which were stacked in layers is pressed in the
stacked direction and heated.
[0105] Because of this, due to the eutectic reaction of Cu of the
Cu-layer and Al of the metal plate, the melting point of the near
joint interface is lowered, even under relatively low-temperature,
it is possible to form the fusion aluminum layer at the boundary
face between the ceramics substrate and the metal plate, and it is
possible to connect the ceramics substrate to the metal plate.
[0106] Namely, without using a brazing filler metal composed of
Al--Si alloy or the like, it is possible to connect the ceramics
substrate to the metal plate.
[0107] In addition, when the thickness of the Cu-layer is less than
0.15 .mu.m, there is a concern that a fusion aluminum layer cannot
be sufficiently formed at the boundary face between the ceramics
substrate and the metal plate.
[0108] In addition, when the thickness of the Cu-layer exceeds 3
.mu.m, reactant of Cu and Al is excessively generated at the joint
interface, the near joint interface of the metal plate is
strengthened more than necessary, and there is a concern that
cracks are generated at the ceramics substrate composed of
Al.sub.2O.sub.3 when the ceramics substrate is subjected to a
heat-load cycle.
[0109] Consequently, in a case where the ceramics substrate is
composed of Al.sub.2O.sub.3, it is preferable that the thickness of
the Cu-layer be 0.15 .mu.m to 3 .mu.m.
[0110] In the method for manufacturing a power module substrate of
the tenth aspect of the present invention, it is preferable that,
when stacking the ceramics substrate and the metal plate in layers
with the Cu-layer interposed therebetween, the Cu-layer be disposed
by inserting a copper foil between the ceramics substrate and the
metal plate.
[0111] In the method for manufacturing a power module substrate of
the tenth aspect of the present invention, it is preferable that
the Cu-layer be adhered to at least one of the ceramics substrate
and the metal plate before stacking the ceramics substrate, the
Cu-layer, and the metal plate in layers.
[0112] In the method for manufacturing a power module substrate of
the tenth aspect of the present invention, it is preferable that,
when the Cu is adhered to at least one of the ceramics substrate
and the metal plate, Cu be adhered to at least one of the ceramics
substrate and the metal plate, by a method selected from an
evaporation method, a sputtering method, a plating method, and a
method of applying a Cu-paste.
[0113] According to the methods, between the ceramics substrate and
the metal plate, it is possible to form a Cu-layer having a desired
thickness, and it is possible to reliably connect the ceramics
substrate to the metal plate.
[0114] A power module substrate of an eleventh aspect of the
present invention includes: a ceramics substrate having a surface;
a metal plate connected to the surface of the ceramics substrate
via a brazing filler metal including Si, composed of aluminum; Cu
introduced into the joint interface between the ceramics substrate
and the metal plate, wherein the metal plate includes Si and Cu;
and a Si concentration is in the range of 0.05 to 0.5 wt % and a Cu
concentration is in the range of 0.05 to 1.0 wt %, in a portion
which is close to the joint interface of the metal plate.
[0115] In the power module substrate having the above-described
structure, the ceramics substrate is bonded to the metal plate
composed of aluminum by use of the brazing filler metal including
Si, and Cu is introduced into the joint interface between the metal
plate and the ceramics substrate.
[0116] Here, since Cu is chemical element having the reactivity
that is greater than that of Al, due to Cu existing at the joint
interface, a surface of the metal plate composed of aluminum is
activated.
[0117] Therefore, even if the connecting is performed under the
junction condition where a temperature is relatively low in a short
time by use of a commonly-used Al--Si system brazing filler metal,
it is possible to tightly connect the ceramics substrate to the
metal plate.
[0118] In addition, in a method for introducing Cu into the joint
interface, Cu may be adhered to a surface of the ceramics substrate
and the brazing filler metal by an evaporation method, a sputtering
method, a plating method, or the like, or Cu may be included in a
Al--Si system brazing filler metal.
[0119] In addition, since Cu is diffused in the metal plate and the
Cu concentration in the portion which is close to the joint
interface is in the range of 0.05 to 1.0 wt %, the portion which is
close to the joint interface of the metal plate is solid-solution
strengthened.
[0120] Consequently, it is possible to prevent fractures from being
generated in the metal plate part, and it is possible to improve
the junction reliability.
[0121] Furthermore, the ceramics substrate is bonded to the metal
plate composed of aluminum by use of the brazing filler metal
including Si, Si is diffused in the metal plate, the Si
concentration in portion which is close to the joint interface is
in the range of 0.05 to 0.5 wt %.
[0122] For this reason, the brazing filler metal is reliably molten
and in a solid-solution state, Si is sufficiently diffused in the
metal plate, and the ceramics substrate is tightly connected to the
metal plate.
[0123] In the power module substrate of the eleventh aspect of the
present invention, it is preferable that a width of the ceramics
substrate be greater than a width of the metal plate; an aluminum
phase in which Si and Cu are included in aluminum, a Si phase in
which a content rate of Si is greater than or equal to 98 wt %, and
an eutectic phase composed of a ternary eutectic structure
including Al, Cu, and Si be formed at an end portion in a width
direction of the metal plate.
[0124] In this case, since not only the aluminum phase in which Si
and Cu are diffused in aluminum but also the Si phase in which the
content rate of Si is greater than or equal to 98 wt %, and the
eutectic phase composed of the ternary eutectic structure including
Al, Cu, and Si are formed at the end portion in the width direction
of the metal plate, it is possible to strengthen the end portion in
the width direction of the metal plate.
[0125] In the power module substrate of the eleventh aspect of the
present invention, it is preferable that precipitate particles
composed of a compound including Cu precipitate in the eutectic
phase.
[0126] In this case, in the eutectic phase formed at the end
portion in the width direction of the metal plate, since the
precipitate particles composed of a compound including Cu
precipitate, it is possible to further realize precipitation
strengthening of the end portion in the width direction of the
metal plate.
[0127] Consequently, it is possible to prevent fractures from being
generated at the end portion in the width direction of the metal
plate, and it is possible to improve the junction reliability.
[0128] The power module substrate of the eleventh aspect of the
present invention may include a high-Si concentration section
formed at the joint interface between the metal plate and the
ceramics substrate, having a Si concentration that is more than
five times the Si concentration in the metal plate, and the
ceramics substrate may be composed of AlN or Al.sub.2O.sub.3.
[0129] In this case, since the high-Si concentration section having
the Si concentration that is more than five times the Si
concentration in the metal plate is formed at the joint interface
between the metal plate and the ceramics substrate, due to a Si
atom existing the joint interface, the joint strength between the
ceramics substrate composed of AlN or Al.sub.2O.sub.3 and the metal
plate composed of aluminum is improved.
[0130] In addition, here, Si concentration in the metal plate means
a Si concentration in the portion that is positioned separately
from the joint interface in the metal plate by a predetermined
distance (for example, 50 nm or more).
[0131] it is thought that the Si existing at the joint interface
with a high degree of concentration is Si mainly included in a
brazing filler metal.
[0132] When the connecting is performed, Si is diffused in aluminum
(metal plate), the amount thereof decreases at the joint interface,
a boundary face portion between the ceramics and aluminum (metal
plate) becomes a site of nonuniform nucleation, Si atoms remain at
the boundary face portion, and the high-Si concentration section
having the Si concentration that is more than five times the Si
concentration in the metal plate is formed.
[0133] The power module substrate of the eleventh aspect of the
present invention may include a high-oxygen concentration section
formed at the joint interface between the metal plate and the
ceramics substrate, having an oxygen concentration that is greater
than oxygen concentrations in the metal plate and in the ceramics
substrate, and having a thickness of less than or equal to 4 nm,
and the ceramics substrate may be composed of AlN or
Si.sub.3N.sub.4.
[0134] In this case, since the high-oxygen concentration section
having the oxygen concentration that is greater than the oxygen
concentrations in the metal plate and in the ceramics substrate at
the joint interface between the ceramics substrate composed of AlN
or Si.sub.3N.sub.4 and the metal plate composed of aluminum, the
joint strength between the ceramics substrate composed of AlN or
Si.sub.3N.sub.4 and the metal plate composed of aluminum is
improved due to the oxygen existing at the joint interface.
[0135] Moreover, since the thickness of the high-oxygen
concentration section is less than or equal to 4 nm, generation of
crack is suppressed in the high-oxygen concentration section due to
the stress when a heat-load cycle is performed.
[0136] In addition, here, oxygen concentrations in the metal plate
and in the ceramics substrate means an oxygen concentration in the
portion that is positioned separately from the joint interface in
the metal plate and in the ceramics substrate by a predetermined
distance (for example, 50 nm or more).
[0137] In addition, it is thought that the oxygen existing at the
joint interface with a high degree of concentration is oxygen
existing at a surface of the ceramics substrate and oxygen taken
from an oxide film formed on a surface of a brazing filler
metal.
[0138] Here, the oxygen existing at the joint interface with a high
degree of concentration, this means that the oxide film or the like
is sufficiently heated so as to be reliably removed.
[0139] Therefore, it is possible to tightly connect the ceramics
substrate to the metal plate.
[0140] A power module of a twelfth aspect of the present invention
is provided with: the power module substrate of the above-described
eleventh aspect; and an electronic component mounted on the power
module substrate.
[0141] According to the power module having the above-described
structure, the joint strength between the ceramics substrate and
the metal plate is high, and even if the power module is used under
a severe usage environment in which, for example, heat stress is
repeatedly generated, it is possible to significantly improve the
reliability thereof.
[0142] A method for manufacturing a power module substrate of a
thirteenth aspect of the present invention includes: preparing a
ceramics substrate having a connection face, a metal plate composed
of aluminum, and a brazing filler metal including Si; stacking the
ceramics substrate and the metal plate in layers with the brazing
filler metal interposed therebetween (stacking step); heating the
ceramics substrate, the brazing filler metal, and the metal plate
which are stacked in layers in a state where a pressure is applied
thereon; forming a fusion aluminum layer at a boundary face between
the ceramics substrate and the metal plate by melting the brazing
filler metal (melting step); and solidifying the fusion aluminum
layer (solidifying step), wherein Cu is adhered to at least one of
the connection face of the ceramics substrate and a face of the
brazing filler metal opposing the ceramics substrate before
stacking the ceramics substrate and the metal plate in layers with
the brazing filler metal interposed therebetween (adhering
step).
[0143] The method for manufacturing a power module substrate has a
Cu-adhering step in which Cu is adhered to at least one of the
connection face of the ceramics substrate and a face of the brazing
filler metal opposing the ceramics substrate, before performing the
stacking step in which the ceramics substrate and the metal plate
are stacked in layers with the brazing filler metal including Si
interposed therebetween.
[0144] Consequently, Cu is reliably introduced into the joint
interface between the ceramics substrate and the metal plate, the
surface of the metal plate is activated due to Cu, even if the
ceramics substrate is bonded to the metal plate under the junction
condition where a temperature is relatively low in a short time by
use of a commonly-used Al--Si system brazing filler metal, it is
possible to tightly connect the ceramics substrate to the metal
plate.
[0145] In the method for manufacturing a power module substrate of
the thirteenth aspect of the present invention, it is preferable
that Cu be adhered to at least one of the connection face of the
ceramics substrate and a face of the brazing filler metal opposing
the ceramics substrate by an evaporation method or a sputtering
method in the adhering of Cu.
[0146] In this case, Cu is reliably adhered to at least one of the
connection face of the ceramics substrate and the face of the
brazing filler metal by the evaporation method or the sputtering
method, and Cu can reliably exist at the joint interface between
the ceramics substrate and the metal plate.
[0147] For this reason, the surface of the metal plate is activated
due to Cu, and it is possible to tightly connect the ceramics
substrate to the metal plate.
Effects of the Present Invention
[0148] According to the present invention, it is possible to
provide a power module substrate in which a metal plate is reliably
connected to a ceramics substrate and heat-load cycle reliability
is high, a power module which is provided with the power module
substrate, and a method for manufacturing the power module
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0149] FIG. 1 is a schematic cross-sectional view showing a power
module in which a power module substrate of a first embodiment of
the present invention is employed.
[0150] FIG. 2 is an explanatory diagram showing a Cu concentration
distribution in a circuit layer and a metal layer of the power
module substrate of the first embodiment of the present
invention.
[0151] FIG. 3 is an explanatory diagram showing an end portion in a
width direction of the circuit layer and the metal layer (metal
plate) of the power module substrate of the first embodiment of the
present invention.
[0152] FIGS. 4A to 4C are cross-sectional views showing a method
for manufacturing a power module substrate of the first embodiment
of the present invention.
[0153] FIGS. 5A to 5C are cross-sectional views showing a near
joint interface between the metal plate and the ceramics substrate
in FIGS. 4A to 4C.
[0154] FIG. 6 is a diagram showing an evaluation result of junction
reliability in a first example.
[0155] FIG. 7 is a diagram showing an evaluation result of junction
reliability in the first example.
[0156] FIG. 8 is a schematic cross-sectional view showing a power
module in which a power module substrate of a second embodiment of
the present invention is employed.
[0157] FIG. 9 is a schematic cross-sectional view showing the joint
interface between a circuit layer, a metal layer (metal plate), and
a ceramics substrate of the power module substrate of the second
embodiment of the present invention.
[0158] FIGS. 10A to 10C are cross-sectional views showing a method
for manufacturing a power module substrate of the second embodiment
of the present invention.
[0159] FIGS. 11A to 11C are cross-sectional views showing a near
joint interface between the metal plate and the ceramics substrate
in FIGS. 10A to 10C.
[0160] FIG. 12 is a schematic cross-sectional view showing a power
module in which a power module substrate of a third embodiment of
the present invention is employed.
[0161] FIG. 13 is a schematic cross-sectional view showing the
joint interface between a circuit layer, a metal layer (metal
plate), and a ceramics substrate of the power module substrate of
the third embodiment of the present invention.
[0162] FIGS. 14A to 14D are cross-sectional views showing a method
for manufacturing a power module substrate of the third embodiment
of the present invention.
[0163] FIGS. 15A to 15C are cross-sectional views showing a near
joint interface between the metal plate and the ceramics substrate
in FIGS. 14A to 14D.
[0164] FIGS. 16A and 16B are diagrams showing an evaluation result
of cracking in a ceramics substrate in a second example.
[0165] FIGS. 17A and 17B are diagrams showing an evaluation result
of junction reliability in the second example.
[0166] FIGS. 18A and 18B are diagrams showing an evaluation result
of cracking in a ceramics substrate in a third example.
[0167] FIGS. 19A and 19B are diagrams showing an evaluation result
of junction reliability in the third example.
[0168] FIG. 20 is a schematic cross-sectional view showing a power
module in which a power module substrate of a fourth embodiment of
the present invention is employed.
[0169] FIG. 21 is a schematic cross-sectional view showing the
joint interface between a circuit layer, a metal layer (metal
plate), and a ceramics substrate of the power module substrate of
the fourth embodiment of the present invention.
[0170] FIGS. 22A to 22C are cross-sectional views showing a method
for manufacturing a power module substrate of the fourth embodiment
of the present invention.
[0171] FIGS. 23A to 23C are cross-sectional views showing a near
joint interface between the metal plate and the ceramics substrate
in FIGS. 22A to 22C.
[0172] FIGS. 24A and 24B are diagrams showing an evaluation result
of cracking in a ceramics substrate in a fourth example.
[0173] FIGS. 25A and 25B are diagrams showing an evaluation result
of junction reliability in the fourth example.
[0174] FIG. 26 is a schematic cross-sectional view showing a power
module in which a power module substrate of a fifth embodiment of
the present invention is employed.
[0175] FIG. 27 is an explanatory diagram showing a Si concentration
distribution and a Cu concentration distribution in a circuit layer
and a metal layer of the power module substrate of the fifth
embodiment of the present invention.
[0176] FIG. 28 is an explanatory diagram showing an end portion in
a width direction of the joint interface between the circuit layer,
the metal layer (metal plate), and the ceramics substrate of the
power module substrate of the fifth embodiment of the present
invention.
[0177] FIG. 29 is a schematic cross-sectional view showing the
joint interface between a circuit layer, a metal layer (metal
plate), and a ceramics substrate of the power module substrate of
the fifth embodiment of the present invention.
[0178] FIGS. 30A to 30C are cross-sectional views showing a method
for manufacturing a power module substrate of the fifth embodiment
of the present invention.
[0179] FIGS. 31A to 31C are cross-sectional views showing a near
joint interface between the metal plate and the ceramics substrate
in FIG. 29.
[0180] FIG. 32 is a schematic cross-sectional view showing a power
module in which a power module substrate of a sixth embodiment of
the present invention is employed.
[0181] FIG. 33 is a schematic cross-sectional view showing the
joint interface between a circuit layer, a metal layer (metal
plate), and a ceramics substrate of the power module substrate of
the sixth embodiment of the present invention.
[0182] FIG. 34 is a cross-sectional view showing a power module
substrate used for a comparison experiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0183] Hereinafter, embodiments of the present invention will be
described with reference to attached drawings.
First Embodiment
[0184] FIG. 1 shows a power module substrate and a power module of
a first embodiment of the present invention.
[0185] The power module 1 includes a power module substrate 10 on
which a circuit layer 12 is disposed, a semiconductor chip 3 which
is bonded to a top face of the circuit layer 12 with a solder layer
2 interposed therebetween, and a heatsink 4.
[0186] Here, the solder layer 2 is a solder material, for example,
a Sn--Ag system, a Sn--In system, or a Sn--Ag--Cu system.
[0187] In addition, in the first embodiment, a Ni plated layer (not
shown in the figure) is provided between the circuit layer 12 and
the solder layer 2.
[0188] The power module substrate 10 includes a ceramics substrate
11, the circuit layer 12 that is disposed on a first face of the
ceramics substrate 11 (upper face in FIG. 1) and a metal layer 13
that is disposed on a second face of the ceramics substrate 11
(lower face in FIG. 1).
[0189] The ceramics substrate 11 is a substrate used for preventing
an electrical connection between the circuit layer 12 and the metal
layer 13, and is made of MN (aluminum nitride) with a high level of
insulation.
[0190] In addition, the thickness of the ceramics substrate 11 is
in a range of 0.2 to 1.5 mm, and is 0.635 mm in the first
embodiment.
[0191] In addition, as shown in FIG. 1, the width of the ceramics
substrate 11 is greater than the widths of the circuit layer 12 and
the metal layer 13 in the first embodiment.
[0192] By connecting a metal plate 22 having a conductive property
to the first face of the ceramics substrate 11, the circuit layer
12 is formed.
[0193] In the first embodiment, by connecting the metal plate 22
constituted of a rolled plate composed of aluminum having a purity
of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 11, the circuit layer 12 is formed thereon.
[0194] By connecting a metal plate 23 to the second face of the
ceramics substrate 11, the metal layer 13 is formed.
[0195] In the first embodiment, due to connecting the metal plate
23 constituted of a rolled plate composed of aluminum having a
purity of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 11, the metal layer 13 is formed in a manner similar to
the circuit layer 12.
[0196] The heatsink 4 is a component for cooling the
above-described power module substrate 10, and provided with a top
panel section 5 connected to the power module substrate 10, and a
flow passage 6 through which a cooling medium (for example, cooling
water) flows.
[0197] The heatsink 4 (top panel section 5) is desirably composed
of a material having excellent thermal conductivity, composed of
A6063 (aluminum alloy) in the first embodiment.
[0198] In addition, in the first embodiment, a buffer layer 15
composed of aluminum, an aluminum alloy, or a combination of
materials including aluminum (for example, AlSiC or the like) is
provided between the top panel section 5 of the heatsink 4 and the
metal layer 13.
[0199] Consequently, as shown in FIGS. 1 and 2, in the center
portion in the width direction of the joint interface 30 between
the ceramics substrate 11 and the circuit layer 12 (metal plate
22), and in the center portion (portion A in FIG. 1) in the width
direction of the joint interface 30 between the ceramics substrate
11 and the metal layer 13 (metal plate 23), Cu is diffused in the
circuit layer 12 (metal plate 22) and in the metal layer 13 (metal
plate 23), and a concentration-gradient layer 33
(concentration-gradient section) is formed in which the Cu
concentration gradually decreases with increases in the distance
from the joint interface 30 in a stacked direction.
[0200] In addition, in this specification, "stacked direction"
represents the direction in which the ceramics substrate 11, the
circuit layer 12, and the metal layer 13 are stacked in layers.
[0201] Here, the Cu concentration in the portion which is close to
the joint interface 30 of the concentration-gradient layer 33 is in
the range of 0.05 to 5 wt %.
[0202] In addition, the Cu concentration in the portion which is
close to the joint interface 30 of the concentration-gradient layer
33 is the average value of five points which are measured in the
range from the joint interface 30 to 50 .mu.m by use of an EPMA
analyzation (diameter of spot is 30 .mu.m).
[0203] In addition, a soft layer 34 which has a Cu concentration
lower than the Cu concentration in the near joint interface 30 and
has a low degree of hardness is formed at the opposite side of the
ceramics substrate 11 in the concentration-gradient layer 33 (lower
side in FIG. 2).
[0204] In addition, in the end portion in the width direction of
the joint interface 30 between the ceramics substrate 11 and the
circuit layer 12 (metal plate 22), and in the end portion (portion
B in FIG. 1) in the width direction of the joint interface 30
between the ceramics substrate 11 and the metal layer 13 (metal
plate 23), as shown in FIG. 3, an aluminum phase 41 in which Cu is
diffused in aluminum in a solid-solution state, and an eutectic
phase 42 composed of a binary eutectic structure including Al and
Cu are formed.
[0205] In addition, precipitate particles composed of a compound
including Cu (for example, CuAl.sub.2) precipitate in the eutectic
phase 42.
[0206] The foregoing power module substrate 10 is manufactured as
described below.
[0207] At first, as shown in FIGS. 4A and 5A, a ceramics substrate
11 composed of AlN, a metal plate 22 (rolled plate made of 4N
aluminum) that becomes a circuit layer 12, and a metal plate 23
(rolled plate made of 4N aluminum) that becomes a metal layer 13
are prepared.
[0208] Thereafter, Cu is adhered to both faces of the ceramics
substrate 11 due to a sputtering, and Cu-layers 24 and 25 having a
film thickness of 0.15 .mu.m to 3 .mu.m are thereby formed
(Cu-adhering step).
[0209] Consequently, the ceramics substrate 11, the metal plates 22
and 23, and the Cu-layers 24 and 25 are prepared.
[0210] Subsequently, as shown in FIG. 4B, the metal plate 22 is
stacked on a first face of the ceramics substrate 11, and the metal
plate 23 is stacked on a second face of the ceramics substrate 11
(stacking step).
[0211] Therefore, a layered body 20 is formed.
[0212] Next, the layered body 20 that was formed in the
above-described manner is heated in a state where the layered body
20 is pressed in the stacked direction thereof (pressure is 1 to 5
kgf/cm.sup.2) and is set inside a vacuum furnace.
[0213] Here, in the vacuum furnace, the degree of vacuum is
10.sup.-3 Pa to 10.sup.-5 Pa, and the heating temperature is
610.degree. C. to 650.degree. C.
[0214] Due to the pressing-heating step, as shown in FIG. 5B,
surface layers of the metal plates 22 and 23, which become the
circuit layer 12 and the metal layer 13, and the Cu-layers 24 and
25 are melted, and fusion metal layers 26 and 27 are formed on the
surface of the ceramics substrate 11 (melting step).
[0215] Subsequently, as shown in FIGS. 4C and 5C, by cooling the
layered body 20, the fusion metal layers 26 and 27 are solidified
(solidifying step).
[0216] Due to the melting step and the solidifying step, Cu is
diffused in the vicinity of the joint interface between the metal
plate 22 that becomes the circuit layer 12 and the ceramics
substrate 11, or in the vicinity of the joint interface between the
metal plate 23 that becomes the metal layer 13 and the ceramics
substrate 11, so that the Cu concentration is in the range of 0.05
to 5 wt %.
[0217] In the above-described manner, the metal plates 22 and 23
that become the circuit layer 12 and the metal layer 13 are
connected to the ceramics substrate 11, and the power module
substrate 10 of the first embodiment is manufactured.
[0218] In the power module substrate 10 and the power module 1 of
the first embodiment having the above-described structure, Cu is
diffused in the circuit layer 12 (metal plate 22) and the metal
layer 13 (metal plate 23) in a solid-solution state.
[0219] In addition, since the Cu concentration in the joint
interface 30 between the circuit layer 12 and the ceramics
substrate 11 or in the joint interface 30 between the metal layer
13 and the ceramics substrate 11 is in the range of 0.05 to 5 wt %,
the joint interface 30 between the circuit layer 12 (metal plate
22) and the metal layer 13 (metal plate 23) is solid-solution
strengthened.
[0220] Because of this, when a heat-load cycle or the like is
performed, cracks are prevented from being propagated in the
portions of the circuit layer 12 (metal plate 22) and the metal
layer 13 (metal plate 23), and it is thereby possible to
considerably improve the reliability of the power module substrate
10 and the power module 1.
[0221] In addition, since the aluminum phase 41 in which Cu is
diffused in aluminum, and the eutectic phase 42 composed of the
binary eutectic structure including Al and Cu are formed in the end
portions in the width direction of the circuit layer 12 (metal
plate 22) and the metal layer 13 (metal plate 23), it is possible
to further strengthen the end portions in the width direction of
the circuit layer 12 (metal plate 22) and the metal layer 13 (metal
plate 23).
[0222] Consequently, it is possible to prevent fractures from being
generated at the end portions in the width direction of the circuit
layer 12 (metal plate 22) and the metal layer 13 (metal plate 23),
and it is possible to improve the junction reliability of the power
module substrate 10.
[0223] Furthermore, in the first embodiment, since precipitate
particles composed of a compound including Cu (for example,
CuAl.sub.2) precipitate in the eutectic phase 42, it is possible to
realize precipitation strengthening of the end portions in the
width direction of the circuit layer 12 (metal plate 22) and the
metal layer 13 (metal plate 23), and it is possible to reliably
prevent cracks from being propagated in the end portions in the
width direction of the circuit layer 12 (metal plate 22) and the
metal layer 13 (metal plate 23).
[0224] In addition, in the center portion in the width direction of
the joint interface 30 between the ceramics substrate 11 and the
circuit layer 12 (metal plate 22), and in the center portion
(portion A in FIG. 1) in the width direction of the joint interface
30 between the ceramics substrate 11 and the metal layer 13 (metal
plate 23), Cu is diffused in the circuit layer 12 (metal plate 22)
and in the metal layer 13 (metal plate 23) in a solid-solution
state, and a concentration-gradient layer 33 is formed in which the
Cu concentration gradually decreases with increases in the distance
from the joint interface 30 in a stacked direction; furthermore,
the soft layer 34 which has a Cu concentration lower than the Cu
concentration in the near joint interface 30, which has a low
degree of hardness, and which has a deformation resistance, is
formed at the opposite side of the ceramics substrate 11 in the
concentration-gradient layer 33 (lower side in FIG. 2).
[0225] In this structure, due to the soft layer 34, it is possible
to absorb heat strain (heat stress) which is caused by the
difference of the coefficient of thermal expansion between the
circuit layer 12 (metal plate 22) and the ceramics substrate 11 and
by the difference of the coefficient of thermal expansion between
the metal layer 13 (metal plate 23) and the ceramics substrate 11,
and it is possible to considerably improve the heat-load cycle
reliability of the power module substrate 10.
[0226] According to the method for manufacturing a power module
substrate of the first embodiment, since the ceramics substrate 11,
the metal plate 22 that becomes the circuit layer 12, and the metal
plate 23 that becomes the metal layer 13 are stacked in layers with
the Cu-layers 24 and 25 interposed therebetween, and the ceramics
substrate 11 and the metal plates 22 and 23 which were stacked in
layers are pressed in the stacked direction and heated, the melting
point of the near joint interface 30 is lowered due to the eutectic
reaction of Cu included in the Cu-layers 24 and 25 and Al included
in the metal plates 22 and 23. Therefore, even under relatively
low-temperature, it is possible to form the fusion metal layers 26
and 27 at the boundary face between the ceramics substrate 11 and
the metal plates 22 and 23, and it is possible to connect the
ceramics substrate 11 to the metal plates 22 and 23.
[0227] Since it is possible to connect the ceramics substrate 11 to
the metal plates 22 and 23 without using a brazing filler metal
composed of Al--Si alloy or the like in the above-described manner,
there is not a concern that a brazing filler metal penetrates to a
surface of the circuit layer 12, and it is possible to prevent the
Ni-plating formed on the surface of the circuit layer 12 from
peeling.
[0228] Consequently, it is possible to reliably form the solder
layer 2 on the circuit layer 12 with the Ni-plating interposed
therebetween.
[0229] In addition, since the thickness of the Cu-layers 24 and 25
is 0.15 .mu.m to 3 .mu.m, the fusion metal layers 26 and 27 are
reliably formed at the boundary face between the ceramics substrate
11 and the metal plates 22 and 23, and it is possible to connect
the ceramics substrate 11 to the metal plates 22 and 23.
[0230] In addition, it is possible to prevent reactants of Cu and
Al from being excessively generated at the near joint interface 30,
and it is possible to prevent cracks from being generated in the
ceramics substrate 11 when the ceramics substrate 11 is subjected
to a heat-load cycle.
[0231] Furthermore, since the Cu-layers 24 and 25 are formed on the
first face and the second face of the ceramics substrate 11 (i.e.,
connection face, faces opposed to the metal plates 22 and 23),
respectively, in the Cu-adhering step in which Cu is adhered
thereto by a sputtering, it is possible to reliably stack the
ceramics substrate 11 and the metal plates 22 and 23 in layers with
the Cu-layers 24 and 25 interposed therebetween, the ceramics
substrate 11 is reliably bonded to the metal plates 22 and 23, and
it is thereby possible to manufacture the power module substrate 10
of the first embodiment.
[0232] As described above, the first embodiment of the present
invention is described, the technical scope of the present
invention is not limited to the above embodiment, and various
modifications may be made without departing from the scope of the
present invention.
[0233] In the first embodiment of the present invention, the
manufacturing method is described having the Cu-adhering step in
which Cu is adhered to a surface of the ceramics substrate, it is
not limited to this method, Cu may be adhered to a face of the
metal plate facing to the ceramics substrate 11 (connection
face).
[0234] In addition, in the stacking step, the Cu-layer may be
formed by inserting a copper foil between the ceramics substrate
and the metal plate.
[0235] In addition, the method for forming the Cu-layer by a
sputtering method is described, it is not limited to this method,
Cu may be adhered thereto by an evaporation method, a plating
method, a method of applying a paste, or the like.
Second Embodiment
[0236] FIG. 8 shows a power module substrate 60 and a power module
51 of a second embodiment of the present invention.
[0237] In the second embodiment, identical symbols are used for the
elements which are identical to those of the first embodiment, and
the explanations thereof are omitted or simplified.
[0238] The power module 51 includes a power module substrate 60 on
which a circuit layer 62 is disposed, a semiconductor chip 3 which
is bonded to a top face of the circuit layer 62 with a solder layer
2 interposed therebetween, and a heatsink 4.
[0239] The power module substrate 60 includes a ceramics substrate
61, the circuit layer 62 that is disposed on a first face of the
ceramics substrate 61 (upper face in FIG. 8) and a metal layer 63
that is disposed on a second face of the ceramics substrate 61
(lower face in FIG. 8).
[0240] The ceramics substrate 61 is a substrate used for preventing
an electrical connection between the circuit layer 62 and the metal
layer 63, and is made of MN (aluminum nitride) with a high level of
insulation.
[0241] In addition, the thickness of the ceramics substrate 61 is
in a range of 0.2 to 1.5 mm, and is 0.635 mm in the second
embodiment.
[0242] By connecting a metal plate 72 having a conductive property
to the first face of the ceramics substrate 61, the circuit layer
62 is formed.
[0243] In the second embodiment, by connecting the metal plate 72
constituted of a rolled plate composed of aluminum having a purity
of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 61, the circuit layer 62 is formed thereon.
[0244] By connecting a metal plate 73 to the second face of the
ceramics substrate 61, the metal layer 63 is formed.
[0245] In the second embodiment, due to connecting the metal plate
73 constituted of a rolled plate composed of aluminum having a
purity of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 61, the metal layer 63 is formed in a manner similar to
the circuit layer 62.
[0246] Consequently, when the joint interface 80 between the
ceramics substrate 61 and the circuit layer 62 (metal plate 72) and
the joint interface 80 between the ceramics substrate 61 and the
metal layer 63 (metal plate 73) are observed using a transmission
electron microscope, a high-Cu concentration section 82 in which Cu
is concentrated is formed at the joint interface 80 as shown in
FIG. 9.
[0247] The Cu concentration in the high-Cu concentration section 82
is more than the Cu concentrations in the circuit layer 62 (metal
plate 72) and in the metal layer 63 (metal plate 73).
[0248] Specifically, the Cu concentration in the joint interface 80
is more than twice the Cu concentrations in the circuit layer 62
and in the metal layer 63.
[0249] Here, in the second embodiment, the thickness H of the
high-Cu concentration section 82 is less than or equal to 4 nm.
[0250] Furthermore, the oxygen concentration in the high-Cu
concentration section 82 is greater than the oxygen concentrations
in the circuit layer 62 and in the metal layer 63.
[0251] Here, in the joint interface 80 that is observed by a
transmission electron microscope, the center between an end portion
of the boundary face of the grid image of the circuit layer 62
(metal plate 72) and the metal layer 63 (metal plate 73), and an
end portion of the boundary face of the grid image of the ceramics
substrate 61, is defined as reference face S as shown in FIG.
9.
[0252] In addition, the Cu concentrations and the oxygen
concentrations in the circuit layer 62 (metal plate 72) and in the
metal layer 63 (metal plate 73) mean the Cu concentrations and the
oxygen concentrations at the positions that are separated from the
joint interface 80 by a predetermined distance (50 nm or more in
the second embodiment) in the circuit layer 62 (metal plate 72) or
the metal layer 63 (metal plate 73).
[0253] In addition, when the joint interface 80 is analyzed by
energy dispersive X-ray spectroscopy (EDS), the mass ratio of Al,
Cu, O, and N is in the range of Al:Cu:O:N=50 to 90 wt %:1 to 10 wt
%:2 to 20 wt %:25 wt % or less.
[0254] In addition, when the analyzation is performed by the EDS,
the diameter of the spot therefor is 1 to 4 nm, a plurality of
points (for example, 100 points in the second embodiment) is
measured at the joint interface 80, and the average value thereof
is calculated.
[0255] In addition, the joint interface 80 between the crystalline
grain of the metal plates 72 and 73 constituting the circuit layer
62 and the metal layer 63, and the ceramics substrate 61 is only
measured, and the joint interface 80 between the crystalline grain
boundary of the metal plates 72 and 73 constituting the circuit
layer 62 and the metal layer 63, and the ceramics substrate 61 is
not measured.
[0256] The foregoing power module substrate 60 is manufactured as
described below.
[0257] As shown in FIGS. 10A and 11A, the ceramics substrate 61
composed of AlN, a metal plate 72 (rolled plate made of 4N
aluminum) that becomes a circuit layer 62, a copper foil 74 having
a thickness of 0.15 .mu.m to 3 .mu.m (3 .mu.m in the second
embodiment), a metal plate 73 (rolled plate made of 4N aluminum)
that becomes a metal layer 63, and a copper foil 75 having a
thickness of 0.15 .mu.m to 3 .mu.m (3 .mu.m in the second
embodiment) are prepared.
[0258] Next, as shown in FIGS. 10B and 11B, the metal plate 72 is
stacked on a first face of the ceramics substrate 61 with the
copper foil 74 interposed therebetween, and the metal plate 73 is
stacked on a second face of the ceramics substrate 61 with the
copper foil 75 interposed therebetween.
[0259] Consequently, a layered body 70 is formed.
[0260] Next, the layered body 70 is heated in a state where the
layered body 70 is pressed in the stacked direction thereof
(pressure is 1 to 5 kgf/cm.sup.2) and is set inside a vacuum
furnace (pressing-heating step).
[0261] Here, in the vacuum furnace, the degree of vacuum is
10.sup.-3 Pa to 10.sup.-5 Pa, and the heating temperature is
610.degree. C. to 650.degree. C.
[0262] Due to the pressing-heating step, as shown in FIG. 11B, the
surface layers of metal plates 72 and 73 that become the circuit
layer 62 and the metal layer 63 are melted with the copper foils 74
and 75, and fusion aluminum layers 76 and 77 are formed on the
surface (the first face and the second face) of the ceramics
substrate 61.
[0263] Subsequently, as shown in FIGS. 10C and 11C, by cooling the
layered body 70, the fusion aluminum layers 76 and 77 are
solidified (solidifying step).
[0264] Due to the pressing-heating step and the solidifying step, a
high-Cu concentration section 82 having a Cu concentration and an
oxygen concentration that are greater than the Cu concentrations
and the oxygen concentrations in the metal plates 72 and 73
constituting the circuit layer 62 and the metal layer 63 is
generated in the joint interface 80.
[0265] In the above-described manner, a power module substrate 60
of the second embodiment is manufactured.
[0266] In the power module substrate 60 and the power module 51
having the above-described structure in the second embodiment, the
high-Cu concentration section 82 having a Cu concentration that is
more than twice the Cu concentrations in the circuit layer 62 and
in the metal layer 63 is formed at the joint interface 80 between
the circuit layer 62, the metal layer 63, and the ceramics
substrate 61; furthermore, the oxygen concentration in the high-Cu
concentration section 82 is greater than the oxygen concentrations
in the circuit layer 62 and in the metal layer 63.
[0267] Because of this, oxygen atom and Cu atom intervene in the
joint interface 80, and it is possible to improve the joint
strength between the ceramics substrate 61 composed of AlN and the
circuit layer 62, and the joint strength between the ceramics
substrate 61 and the metal layer 63.
[0268] Furthermore, in the second embodiment, when the joint
interface 80 is analyzed by energy dispersive X-ray spectroscopy,
the mass ratio of Al, Cu, O, and N is in the range of Al:Cu:O:N=50
to 90 wt %:1 to 10 wt %:2 to 20 wt %:25 wt % or less.
[0269] As a result, it is possible to prevent reactants of Cu and
Al interfering the joint from being excessively generated in the
joint interface 80, it is possible to sufficiently obtain the
effect that the joint strength is improved due to a Cu atom.
[0270] In addition, the thickness of a portion in which the oxygen
concentration is high is prevented from increasing in the joint
interface 80, and it is possible to suppress cracks from being
generated when a heat-load cycle is performed.
[0271] In addition, the metal plate 72 that becomes the circuit
layer 62 is stacked on the first face of the ceramics substrate 61
composed of AlN with the copper foil 74 having a thickness of 0.15
.mu.m to 3 .mu.m (3 .mu.m in the second embodiment) interposed
therebetween, and the metal plate 73 (rolled plate made of 4N
aluminum) that becomes the metal layer 63 is stacked on the second
face of the ceramics substrate 61 with the copper foil 75 having a
thickness of 0.15 .mu.m to 3 .mu.m (3 .mu.m in the second
embodiment) interposed therebetween, and the layered body is
pressed and heated.
[0272] As a result, eutectic reaction of Cu of the copper foils 74
and 75 and Al of the metal plates 72 and 73 is generated, and the
melting point of surface layer portions between the copper foils 74
and 75, and the metal plates 72 and 73 is lowered.
[0273] Consequently, even under relatively low-temperatures
(610.degree. C. to 650.degree. C.), it is possible to form the
fusion aluminum layers 76 and 77 at the boundary face between the
ceramics substrate 61 and the metal plates 72 and 73, and it is
possible to connect the ceramics substrate to the metal plate, and
it is possible to connect the ceramics substrate 61 to the metal
plates 72 and 73.
Third Embodiment
[0274] Next, a third embodiment of the present invention will be
described.
[0275] FIG. 12 shows a power module substrate 110 and a power
module 101 of a third embodiment of the present invention.
[0276] In the third embodiment, identical symbols are used for the
elements which are identical to those of the first and the second
embodiments, and the explanations thereof are omitted or
simplified.
[0277] The power module substrate 110 includes a ceramics substrate
111, the circuit layer 112 that is disposed on a first face of the
ceramics substrate 111 (upper face in FIG. 12) and a metal layer
113 that is disposed on a second face of the ceramics substrate 111
(lower face in FIG. 12).
[0278] The ceramics substrate 111 is a substrate used for
preventing an electrical connection between the circuit layer 112
and the metal layer 113, and is made of Si.sub.3N.sub.4 (silicon
nitride) with a high level of insulation.
[0279] In addition, the thickness of the ceramics substrate 111 is
in a range of 0.2 to 1.5 mm, and is 0.32 mm in the third
embodiment.
[0280] By connecting a metal plate 122 having a conductive property
to the first face of the ceramics substrate 111, the circuit layer
112 is formed.
[0281] In the third embodiment, by connecting the metal plate 22
constituted of a rolled plate composed of aluminum having a purity
of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 111, the circuit layer 112 is formed thereon.
[0282] By connecting a metal plate 123 to the second face of the
ceramics substrate 111, the metal layer 113 is formed.
[0283] In the third embodiment, due to connecting the metal plate
123 constituted of a rolled plate composed of aluminum having a
purity of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 111, the metal layer 113 is formed in a manner similar to
the circuit layer 112.
[0284] Consequently, when the joint interface 130 between the
ceramics substrate 111 and the circuit layer 112 (metal plate 122)
and the joint interface 130 between the ceramics substrate 111 and
the metal layer 113 (metal plate 123) are observed using a
transmission electron microscope, a high-Cu concentration section
132 in which Cu is concentrated is formed at the joint interface
130 as shown in FIG. 13.
[0285] The Cu concentration in the high-Cu concentration section
132 is more than the Cu concentrations in the circuit layer 112
(metal plate 122) and in the metal layer 113 (metal plate 123).
[0286] Specifically, the Cu concentration in the joint interface
130 is more than twice the Cu concentrations in the circuit layer
112 and in the metal layer 113.
[0287] Here, in the third embodiment, the thickness H of the
high-Cu concentration section 132 is less than or equal to 4
nm.
[0288] Furthermore, the oxygen concentration in the high-Cu
concentration section 132 is greater than the oxygen concentrations
in the circuit layer 112 and in the metal layer 113.
[0289] Here, in the joint interface 130 that is observed by a
transmission electron microscope, the center between an end portion
of the boundary face of the grid image of the circuit layer 112
(metal plate 122) and the metal layer 113 (metal plate 123), and an
end portion of the boundary face of the grid image of the ceramics
substrate 111, is defined as reference face S as shown in FIG.
13.
[0290] In addition, the Cu concentrations and the oxygen
concentrations in the circuit layer 112 and in the metal layer 113
mean the Cu concentrations and the oxygen concentrations at the
positions that are separated from the joint interface 130 by a
predetermined distance (50 nm or more in the third embodiment) in
the circuit layer 112 or the metal layer 13.
[0291] In addition, when the joint interface 130 is analyzed by
energy dispersive X-ray spectroscopy (EDS), the mass ratio of Al,
Si, Cu, O, and N is in the range of Al:Si:Cu:O:N=15 to 45 wt %:15
to 45 wt %:1 to 10 wt %:2 to 20 wt %:25 wt % or less.
[0292] In addition, when the analyzation is performed by the EDS,
the diameter of the spot therefor is 1 to 4 nm, a plurality of
points (for example, 100 points in the third embodiment) is
measured at the joint interface 130, and the average value thereof
is calculated.
[0293] In addition, the joint interface 130 between the crystalline
grain of the metal plates 122 and 123 constituting the circuit
layer 112 and the metal layer 113, and the ceramics substrate 111
is only measured, and the joint interface 130 between the
crystalline grain boundary of the metal plates 122 and 123
constituting the circuit layer 112 and the metal layer 113, and the
ceramics substrate 111 is not measured.
[0294] The foregoing power module substrate 110 is manufactured as
described below.
[0295] As shown in FIG. 14A, Cu is adhered to the both faces of the
ceramics substrate 111 composed of Si.sub.3N.sub.4 by a vacuum
deposition method, and Cu-adhesion layers 124 and 125 having a
thickness of 0.15 .mu.m to 3 .mu.m are formed (Cu-adhering
step).
[0296] Next, as shown in FIGS. 14B and 14C, and FIGS. 15A and 15B,
the metal plate 122 (rolled plate made of 4N aluminum) that becomes
the circuit layer 112 is stacked on the first face of the ceramics
substrate 111 on which the Cu-adhesion layers 124 and 125 are
formed, and the metal plate 123 (rolled plate made of 4N aluminum)
that becomes the metal layer 113 is stacked on the second face of
the ceramics substrate 111 (stacking step).
[0297] The layered body 120 that was formed in the above-described
manner is heated in a state where the layered body 120 is pressed
in the stacked direction thereof (pressure is 1 to 5 kgf/cm.sup.2)
and is set inside a vacuum furnace (pressing-heating step).
[0298] Here, in the vacuum furnace, the degree of vacuum is
10.sup.-3 Pa to 10.sup.-5 Pa, and the heating temperature is
610.degree. C. to 650.degree. C.
[0299] Due to the pressing-heating step, as shown in FIG. 15, the
surface layers of metal plates 122 and 123 that become the circuit
layer 112 and the metal layer 113 are melted with the Cu-adhesion
layers 124 and 125, and fusion aluminum layers 126 and 127 are
formed on the surface of the ceramics substrate 111.
[0300] Subsequently, as shown in FIGS. 14D and 15C, by cooling the
layered body 120, the fusion aluminum layers 126 and 127 are
solidified (solidifying step).
[0301] Due to the pressing-heating step and the solidifying step, a
high-Cu concentration section 132 having a Cu concentration and an
oxygen concentration that are greater than the Cu concentrations
and the oxygen concentrations in the metal plates 122 and 123
constituting the circuit layer 112 and the metal layer 113 is
generated in the joint interface 130.
[0302] In the above-described manner, a power module substrate 110
of the third embodiment is manufactured.
[0303] In the power module substrate 110 having the above-described
structure in the third embodiment, the high-Cu concentration
section 132 having a Cu concentration that is more than twice the
Cu concentrations in the circuit layer 112 and in the metal layer
113 is formed at the joint interface 130 between the circuit layer
112, the metal layer 113, and the ceramics substrate 111.
[0304] Furthermore, the oxygen concentration in the high-Cu
concentration section 132 is greater than the oxygen concentrations
in the circuit layer 112 and in the metal layer 113.
[0305] Because of this, oxygen atom and Cu atom intervene in the
joint interface 130, and it is possible to improve the joint
strength between the ceramics substrate 111 composed of
Si.sub.3N.sub.4, the circuit layer 112, and the metal layer
113.
[0306] Furthermore, in the third embodiment, since the mass ratio
of Al, Si, Cu, O, and N is in the range of Al:Si:Cu:O:N=15 to 45 wt
%:15 to 45 wt %:1 to 10 wt %:2 to 20 wt %:25 wt % or less when the
joint interface 130 is analyzed by energy dispersive X-ray
spectroscopy (EDS), it is possible to prevent reactants of Cu and
Al interfering the joint from being excessively generated in the
joint interface 130, it is possible to sufficiently obtain the
effect that the joint strength is improved due to a Cu atom.
[0307] In addition, the thickness of a portion in which the oxygen
concentration is high is prevented from increasing in the joint
interface 130, and it is possible to suppress cracks from being
generated when a heat-load cycle is performed.
[0308] In addition, Cu is adhered to the both faces of the ceramics
substrate 111 composed of Si.sub.3N.sub.4 by a vacuum deposition
method, and the metal plate 122 (rolled plate made of 4N aluminum)
that becomes the circuit layer 112 is stacked on the first face of
the ceramics substrate 111 on which the Cu-adhesion layers 124 and
125 are formed, and the metal plate 123 (rolled plate made of 4N
aluminum) that becomes the metal layer 113 is stacked on the second
face of the ceramics substrate 111, and the layered body is pressed
and heated.
[0309] As a result, due to the eutectic reaction of Cu of
Cu-adhesion layers 124 and 125 and Al of the metal plates 122 and
123, the melting point of the surface layer portions of the metal
plates 122 and 123 is lowered, even under relatively
low-temperatures (610.degree. C. to 650.degree. C.), it is possible
to form the fusion aluminum layers 126 and 127 at the boundary face
between the ceramics substrate 111 and the metal plates 122 and
123, and it is possible to connect the ceramics substrate 111 to
the metal plates 122 and 123.
[0310] As described above, the second and the third embodiments of
the present invention are described, the technical scope of the
present invention is not limited to the above embodiment, and
various modifications may be made without departing from the scope
of the present invention.
[0311] In the third embodiment, the manufacturing method is
described for adhering Cu to the both-faces of the ceramics
substrate, it is not limited to this method, Cu may be adhered to a
face of the metal plate facing to the ceramics substrate 11
(connection face), and Cu may be adhered to both of the metal plate
and the ceramics substrate.
[0312] In addition, the method for adhering Cu by a vacuum
deposition method is described, it is not limited to this method,
Cu may be adhered thereto by a sputtering method, a plating method,
a method of applying a Cu-paste, or the like.
Fourth Embodiment
[0313] FIG. 20 shows a power module substrate 160 and a power
module 151 of a fourth embodiment of the present invention.
[0314] In the fourth embodiment, identical symbols are used for the
elements which are identical to those of the first to the third
embodiments, and the explanations thereof are omitted or
simplified.
[0315] The power module 151 includes a power module substrate 160
on which a circuit layer 162 is disposed, a semiconductor chip 3
which is bonded to a top face of the circuit layer 162 with a
solder layer 2 interposed therebetween, and a heatsink 4.
[0316] The power module substrate 160 includes a ceramics substrate
161, the circuit layer 162 that is disposed on a first face of the
ceramics substrate 161 (upper face in FIG. 20) and a metal layer
163 that is disposed on a second face of the ceramics substrate 161
(lower face in FIG. 20).
[0317] The ceramics substrate 161 is a substrate used for
preventing an electrical connection between the circuit layer 162
and the metal layer 163, and is made of Al.sub.2O.sub.3 (alumina)
with a high level of insulation.
[0318] In addition, the thickness of the ceramics substrate 161 is
in a range of 0.2 to 1.5 mm, and is 0.635 mm in the fourth
embodiment.
[0319] By connecting a metal plate 172 having a conductive property
to the first face of the ceramics substrate 161, the circuit layer
162 is formed.
[0320] In the fourth embodiment, by connecting the metal plate 172
constituted of a rolled plate composed of aluminum having a purity
of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 161, the circuit layer 162 is formed thereon.
[0321] By connecting a metal plate 173 to the second face of the
ceramics substrate 161, the metal layer 163 is formed.
[0322] In the fourth embodiment, due to connecting the metal plate
173 constituted of a rolled plate composed of aluminum having a
purity of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 161, the metal layer 163 is formed in a manner similar to
the circuit layer 162.
[0323] Consequently, when the joint interface 180 between the
ceramics substrate 161 and the circuit layer 162 (metal plate 172)
and the joint interface 180 between the ceramics substrate 161 and
the metal layer 163 (metal plate 173) are observed using a
transmission electron microscope, a high-Cu concentration section
182 in which Cu is concentrated is formed at the joint interface
180 as shown in FIG. 21.
[0324] The Cu concentration in the high-Cu concentration section
182 is more than the Cu concentrations in the circuit layer 162
(metal plate 172) and in the metal layer 163 (metal plate 173).
[0325] Specifically, the Cu concentration in the joint interface
180 is more than twice the Cu concentrations in the circuit layer
162 and in the metal layer 163.
[0326] Here, in the fourth embodiment, the thickness H of the
high-Cu concentration section 182 is less than or equal to 4
nm.
[0327] Here, in the joint interface 180 that is observed by a
transmission electron microscope, the center between an end portion
of the boundary face of the grid image of the circuit layer 162
(metal plate 172) and the metal layer 163 (metal plate 173), and an
end portion of the boundary face of the grid image of the ceramics
substrate 161, is defined as reference face S as shown in FIG.
21.
[0328] In addition, the Cu concentrations in the circuit layer 162
(metal plate 172) and in the metal layer 163 (metal plate 173) mean
the Cu concentrations at the positions that are separated from the
joint interface 180 by a predetermined distance (50 nm or more in
the fourth embodiment) in the circuit layer 162 (metal plate 172)
or the metal layer 163 (metal plate 173).
[0329] In addition, when the joint interface 180 is analyzed by
energy dispersive X-ray spectroscopy (EDS), the mass ratio of Al,
Cu, and O is in the range of Al:Cu:O=50 to 90 wt %:1 to 10 wt %:0
to 45 wt %.
[0330] In addition, when the analyzation is performed by the EDS,
the diameter of the spot therefor is 1 to 4 nm, a plurality of
points (for example, 100 points in the fourth embodiment) is
measured at the joint interface 180, and the average value thereof
is calculated.
[0331] In addition, the joint interface 180 between the crystalline
grain of the metal plates 172 and 173 constituting the circuit
layer 162 and the metal layer 163, and the ceramics substrate 161
is only measured, and the joint interface 180 between the
crystalline grain boundary of the metal plates 172 and 173
constituting the circuit layer 162 and the metal layer 163, and the
ceramics substrate 161 is not measured.
[0332] The foregoing power module substrate 160 is manufactured as
described below.
[0333] As shown in FIGS. 22A and 23A, the ceramics substrate 161
composed of Al.sub.2O.sub.3, a metal plate 172 (rolled plate made
of 4N aluminum) that becomes a circuit layer 162, a copper foil 174
having a thickness of 0.15 .mu.m to 3 .mu.m (3 .mu.m in the fourth
embodiment), a metal plate 173 (rolled plate made of 4N aluminum)
that becomes a metal layer 163, and a copper foil 175 having a
thickness of 0.15 .mu.m to 3 .mu.m (3 .mu.m in the fourth
embodiment) are prepared.
[0334] Next, as shown in FIGS. 22B and 23B, the metal plate 172 is
stacked on a first face of the ceramics substrate 161 with the
copper foil 174 interposed therebetween, and the metal plate 173 is
stacked on a second face of the ceramics substrate 161 with the
copper foil 175 interposed therebetween.
[0335] Consequently, a layered body 170 is formed.
[0336] Next, the layered body 170 is heated in a state where the
layered body 170 is pressed in the stacked direction thereof
(pressure is 1 to 5 kgf/cm.sup.2) and is set inside a vacuum
furnace (pressing-heating step).
[0337] Here, in the vacuum furnace, the degree of vacuum is
10.sup.-3 Pa to 10.sup.-5 Pa, and the heating temperature is
610.degree. C. to 650.degree. C.
[0338] Due to the pressing-heating step, as shown in FIG. 23, the
surface layers of metal plates 172 and 173 that become the circuit
layer 162 and the metal layer 163 are melted with the copper foils
174 and 175, and fusion aluminum layers 176 and 177 are formed on
the surface of the ceramics substrate 161.
[0339] Subsequently, as shown in FIGS. 22C and 23C, by cooling the
layered body 170, the fusion aluminum layers 176 and 177 are
solidified (solidifying step).
[0340] Due to the pressing-heating step and the solidifying step, a
high-Cu concentration section 182 having a Cu concentration that is
greater than the Cu concentrations in the metal plates 172 and 173
constituting the circuit layer 162 and the metal layer 163 is
generated in the joint interface 180.
[0341] In the above-described manner, a power module substrate 160
of the fourth embodiment is manufactured.
[0342] In the power module substrate 160 and the power module 151
having the above-described structure in the fourth embodiment, the
high-Cu concentration section 182 having a Cu concentration that is
more than twice the Cu concentrations in the circuit layer 162 and
in the metal layer 163 is formed at the joint interface 180 between
the circuit layer 162, the metal layer 163, and the ceramics
substrate 161.
[0343] Because of this, Cu atom intervenes in the joint interface
180, and it is possible to improve the joint strength between the
ceramics substrate 161 composed of Al.sub.2O.sub.3 and the circuit
layer 162, and the joint strength between the ceramics substrate
161 and the metal layer 163.
[0344] Furthermore, in the fourth embodiment, when the joint
interface 180 is analyzed by energy dispersive X-ray spectroscopy,
the mass ratio of Al, Cu, and O is in the range of Al:Cu:O=50 to 90
wt %:1 to 10 wt %:0 to 45 wt %.
[0345] As a result, it is possible to prevent reactants of Cu and
Al interfering the joint from being excessively generated in the
joint interface 180, it is possible to sufficiently obtain the
effect that the joint strength is improved due to a Cu atom.
[0346] In addition, the metal plate 172 that becomes the circuit
layer 162 is stacked on the first face of the ceramics substrate
161 composed of Al.sub.2O.sub.3 with the copper foil 174 having a
thickness of 0.15 .mu.m to 3 .mu.m (3 .mu.m in the fourth
embodiment) interposed therebetween, and the metal plate 173
(rolled plate made of 4N aluminum) that becomes the metal layer 163
is stacked on the second face of the ceramics substrate 161 with
the copper foil 175 having a thickness of 0.15 .mu.m to 3 .mu.m (3
.mu.m in the fourth embodiment) interposed therebetween, and the
layered body is pressed and heated.
[0347] As a result, eutectic reaction of Cu of the copper foils 174
and 175 and Al of the metal plates 172 and 173 is generated, and
the melting point of surface layer portions between the copper
foils 174 and 175, and the metal plates 172 and 173 is lowered.
[0348] Consequently, even under relatively low-temperatures
(610.degree. C. to 650.degree. C.), it is possible to form the
fusion aluminum layers 176 and 177 at the boundary face between the
ceramics substrate 161 and the metal plates 172 and 173, and it is
possible to connect the ceramics substrate to the metal plate, and
it is possible to connect the ceramics substrate 161 to the metal
plates 172 and 173.
[0349] As described above, the fourth embodiment of the present
invention is described, the technical scope of the present
invention is not limited to the above embodiment, and various
modifications may be made without departing from the scope of the
present invention.
[0350] In the fourth embodiment of the present invention, the
method for inserting the copper foil between the ceramics substrate
and the metal plate in the stacking step, it is not limited to this
method, before the stacking step, a Cu-layer may be formed by a
Cu-adhering step for adhering Cu to at least one of a face of the
metal plate (connection face) opposed to the ceramics substrate and
a face of the ceramics substrate (connection face) opposed to the
metal plate.
[0351] In addition, as a method for adhering Cu, for example, a
vacuum deposition method, a sputtering method, a plating method, a
method of applying a Cu-paste, or the like may be adopted.
Fifth Embodiment
[0352] FIG. 26 shows a power module substrate and a power module of
a fifth embodiment of the present invention.
[0353] In the fifth embodiment, identical symbols are used for the
elements which are identical to those of the first to the fourth
embodiments, and the explanations thereof are omitted or
simplified.
[0354] The power module 201 includes a power module substrate 210
on which a circuit layer 212 is disposed, a semiconductor chip 3
which is bonded to a top face of the circuit layer 212 with a
solder layer 2 interposed therebetween, and a heatsink 4.
[0355] The power module substrate 210 includes a ceramics substrate
211, the circuit layer 212 that is disposed on a first face of the
ceramics substrate 211 (upper face in FIG. 26) and a metal layer
213 that is disposed on a second face of the ceramics substrate 211
(lower face in FIG. 26).
[0356] The ceramics substrate 211 is a substrate used for
preventing an electrical connection between the circuit layer 212
and the metal layer 213, and is made of MN (aluminum nitride) with
a high level of insulation.
[0357] In addition, the thickness of the ceramics substrate 211 is
in a range of 0.2 to 1.5 mm, and is 0.635 mm in the fifth
embodiment.
[0358] In addition, as shown in FIG. 26, the width of the ceramics
substrate 211 is greater than the widths of the circuit layer 212
and the metal layer 213 in the fifth embodiment.
[0359] By connecting a metal plate 222 having a conductive property
to the first face of the ceramics substrate 211, the circuit layer
212 is formed.
[0360] In the fifth embodiment, by connecting the metal plate 222
constituted of a rolled plate composed of aluminum having a purity
of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 211, the circuit layer 212 is formed thereon.
[0361] Here, an Al--Si system brazing filler metal including Si
that is a melting-point lowering element is used for connecting the
ceramics substrate 211 to the metal plate 222.
[0362] By connecting a metal plate 223 to the second face of the
ceramics substrate 211, the metal layer 213 is formed.
[0363] In the fifth embodiment, due to connecting the metal plate
223 constituted of a rolled plate composed of aluminum having a
purity of 99.99% or more (a so-called 4N aluminum) to the ceramics
substrate 211, the metal layer 213 is formed in a manner similar to
the circuit layer 212.
[0364] Here, an Al--Si system brazing filler metal including Si
that is a melting-point lowering element is used for connecting the
ceramics substrate 211 to the metal plate 223.
[0365] Consequently, as shown in FIG. 27, in the center portion in
the width direction of the joint interface 230 between the ceramics
substrate 211 and the circuit layer 212 (metal plate 222), and in
the center portion (portion A in FIG. 26) in the width direction of
the joint interface 230 between the ceramics substrate 211 and the
metal layer 213 (metal plate 223), Si and Cu are diffused in the
circuit layer 212 (metal plate 222) and in the metal layer 213
(metal plate 223), and a concentration-gradient layer 233 is formed
in which the Si concentration and the Cu concentration gradually
decrease with increasing the distance from the joint interface 230
in a stacked direction.
[0366] Here, in the portion which is close to the joint interface
230 of the concentration-gradient layer 233, the Si concentration
is in the range of 0.05 to 0.5 wt % wt %, and the Cu concentration
is in the range of 0.05 to 1.0 wt %.
[0367] In addition, the Si concentration and the Cu concentration
in the portion which is close to the joint interface 230 of the
concentration-gradient layer 233 is the average value of five
points which are measured in the range from the joint interface 230
to 50 .mu.m by use of an EPMA analyzation (diameter of spot is 30
.mu.m).
[0368] In addition, in the end portion 235 in the width direction
of the joint interface 230 between the ceramics substrate 211 and
the circuit layer 212 (metal plate 222), and in the end portion 235
(portion B in FIG. 26) in the width direction of the joint
interface 230 between the ceramics substrate 211 and the metal
layer 213 (metal plate 223), as shown in FIG. 28, an aluminum phase
241 in which Si and Cu are diffused in aluminum in a solid-solution
state, a Si phase 242 in which the content rate of Si is greater
than or equal to 98 wt %, and an eutectic phase 243 composed of a
ternary eutectic structure including Al, Cu, and Si are formed.
[0369] In addition, precipitate particles composed of a compound
including Cu (for example, CuAl.sub.2) precipitate in the eutectic
phase 243.
[0370] In addition, when the joint interface 230 between the
ceramics substrate 211 and the circuit layer 212 (metal plate 222)
and the joint interface 230 between the ceramics substrate 211 and
the metal layer 213 (metal plate 223) are observed using a
transmission electron microscope, a high-Si concentration section
232 in which Si is concentrated is formed at the joint interface
230 as shown in FIG. 29.
[0371] The Si concentration in the high-Si concentration section
232 is more than five times the Si concentrations in the circuit
layer 212 (metal plate 222) and in the metal layer 213 (metal plate
223).
[0372] In addition, the thickness H of the high-Si concentration
section 232 is less than or equal to 4 nm.
[0373] Here, in the joint interface 230 that is observed by a
transmission electron microscope, the center between an end portion
of the boundary face of the grid image of the circuit layer 212
(metal plate 222) and the metal layer 213 (metal plate 223), and an
end portion of the boundary face of the grid image of the ceramics
substrate 211, is defined as reference face S as shown in FIG.
29.
[0374] The foregoing power module substrate 210 is manufactured as
described below.
[0375] At first, Cu is adhered to the both faces of the ceramics
substrate 211 composed of AlN by a sputtering method (Cu-adhering
step).
[0376] Subsequently, as shown in FIGS. 30A and 31A, the ceramics
substrate 211 composed of AlN to which was Cu was adhered, a metal
plate 222 (rolled plate made of 4N aluminum) that becomes a circuit
layer 212, a brazing filler metal foil 224 having a thickness of 10
to 30 .mu.m (20 .mu.m in the fifth embodiment), a metal plate 223
(rolled plate made of 4N aluminum) that becomes a metal layer 213,
and a brazing filler metal foil 225 having a thickness of 10 to 30
.mu.m (20 .mu.m in the fifth embodiment) are prepared.
[0377] Next, as shown in FIGS. 30B and 31B, the metal plate 222 is
stacked on a first face of the ceramics substrate 211 with the
brazing filler metal foil 224 interposed therebetween, and the
metal plate 223 is stacked on a second face of the ceramics
substrate 211 with the brazing filler metal foil 225 interposed
therebetween (stacking step).
[0378] Therefore, a layered body 220 is formed.
[0379] Next, the layered body 220 is heated in a state where the
layered body 220 is pressed in the stacked direction thereof
(pressure is 1 to 5 kgf/cm.sup.2) and is set inside a vacuum
furnace, and the brazing filler metal foils 224 and 225 are melted
(melting step).
[0380] Here, the degree of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa
in the vacuum furnace.
[0381] Due to the melting step, as shown in FIG. 31B, a part of the
metal plates 222 and 223, which become the circuit layer 212 and
the metal layer 213, and the brazing filler metal foils 224 and 225
are melted, and fusion aluminum layers 226 and 227 are formed on
the surface of the ceramics substrate 211.
[0382] Subsequently, as shown in FIGS. FIGS. 30C and 31C, by
cooling the layered body 220, the fusion metal layers 226 and 227
are solidified (solidifying step).
[0383] In the above-described manner, the metal plates 222 and 223
that become the circuit layer 212 and the metal layer 213 are
connected to the ceramics substrate 211, and the power module
substrate 210 of the fifth embodiment is manufactured.
[0384] In the power module substrate 210 and the power module 201
of the fifth embodiment having the above-described structure, the
circuit layer 212 (metal plate 222) and the metal layer 213 (metal
plate 223) are connected to the ceramics substrate 211 by use of
the Al--Si system brazing filler metal, and Cu is introduced into
the joint interface 230 between the circuit layer 212 (metal plate
222), the metal layer 213 (metal plate 223), and the ceramics
substrate 211.
[0385] Consequently, Cu and Al existing at the joint interface 230
are melted and reacted, even if the connecting is performed under
the junction condition where a temperature is relatively low in a
short time, it is possible to tightly connect the ceramics
substrate 211 to the circuit layer 212 (metal plate 222) and the
metal layer 213 (metal plate 223), and it is possible to
considerably improve junction reliability.
[0386] In addition, in the center portion in the width direction of
the joint interface 230 between the ceramics substrate 211 and the
circuit layer 212 (metal plate 222), and in the center portion
(portion A in FIG. 26) in the width direction of the joint
interface 230 between the ceramics substrate 211 and the metal
layer 213 (metal plate 223), Si and Cu are diffused in the circuit
layer 212 (metal plate 222) and in the metal layer 213 (metal plate
223), and a concentration-gradient layer 233 is formed in which the
Si concentration and the Cu concentration gradually decrease with
increasing the distance from the joint interface 230 in a stacked
direction.
[0387] In addition, since the Cu concentration in the portion of
the concentration-gradient layer 233 which is close to the joint
interface 230 is in the range of 0.05 to 1.0 wt %, the portions of
the circuit layer 212 (metal plate 222) and the metal layer 213
(metal plate 223) which are close to the joint interface 230 are
solid-solution strengthened, it is possible to prevent fractures
from being generated at the circuit layer 212 (metal plate 222) and
the metal layer 213 (metal plate 223).
[0388] In addition, since the Si concentration in the portion of
the concentration-gradient layer 233 which is close to the joint
interface 230 is in the range of 0.05 to 0.5 wt %, Si is
sufficiently diffused in the circuit layer 212 (metal plate 222)
and the metal layer 213 (metal plate 223).
[0389] For this reason, since the brazing filler metal is reliably
melted and solidified, it is possible to tightly connect the
ceramics substrate 211 to the circuit layer 212 (metal plate 222),
and connect the ceramics substrate 211 to the metal layer 213
(metal plate 223).
[0390] Furthermore, the width of the ceramics substrate 211 is
greater than the widths of the circuit layer 212 (metal plate 222)
and the metal layer 213 (metal plate 223); the aluminum phase 241
in which Si and Cu are diffused in aluminum, the Si phase 242 in
which the content rate of Si is greater than or equal to 98 wt %,
and the eutectic phase 243 composed of a ternary eutectic structure
including Al, Cu, and Si are formed at the end portion 235 in the
width direction of the circuit layer 212 (metal plate 222) and the
metal layer 213 (metal plate 223).
[0391] Consequently, the strength of the end portion 235 in the
width direction of the circuit layer 212 (metal plate 222) and the
metal layer 213 (metal plate 223) is improved.
[0392] Furthermore, since precipitate particles composed of a
compound including Cu (for example, CuAl.sub.2) precipitate in the
eutectic phase 243, it is possible to further realize precipitation
strengthening of the end portion 235 in the width direction.
[0393] As a result, it is possible to prevent fractures from being
generated at the end portion 235 in the width direction of the
circuit layer 212 (metal plate 222) and the metal layer 213 (metal
plate 223).
[0394] In addition, in the fifth embodiment, the ceramics substrate
211 is composed of AlN, and the high-Si concentration section 232
having the Si concentration that is more than five times the Si
concentrations in the circuit layer 212 (metal plate 222) and in
the metal layer 213 (metal plate 223) is formed at the joint
interface 230 between the metal plates 222 and 223 and the ceramics
substrate 211.
[0395] Because of this, due to Si existing at the joint interface
230, it is possible to improve the joint strength between the
ceramics substrate 211 and the metal plates 222 and 223.
Sixth Embodiment
[0396] Next, a sixth embodiment of the present invention will be
described with reference to FIGS. 32 and 33.
[0397] In the sixth embodiment, identical symbols are used for the
elements which are identical to those of the first to the fifth
embodiments, and the explanations thereof are omitted or
simplified.
[0398] The power module substrate 260 of the sixth embodiment is
different from the fifth embodiment in terms of the ceramics
substrate 261 being composed of Si.sub.3N.sub.4.
[0399] Here, when the joint interface 280 between the ceramics
substrate 261 and the circuit layer 262 (metal plate 272) and the
joint interface 280 between the ceramics substrate 261 and the
metal layer 263 (metal plate 273) are observed using a transmission
electron microscope, a high-oxygen concentration section 282 in
which oxygen is concentrated is formed at the joint interface 280
is observed as shown in FIG. 33.
[0400] The oxygen concentration in the high-oxygen concentration
section 282 is greater than the oxygen concentrations in the
circuit layer 262 (metal plate 272) and in the metal layer 263
(metal plate 273).
[0401] In addition, the thickness H of the high-oxygen
concentration section 282 is less than or equal to 4 nm.
[0402] Here, in the joint interface 280 that is observed by a
transmission electron microscope, the center between an end portion
of the boundary face of the grid image of the circuit layer 262
(metal plate 272) and the metal layer 263 (metal plate 273), and an
end portion of the joint boundary face of the grid image of the
ceramics substrate 261, is defined as reference face S as shown in
FIG. 33.
[0403] In the power module substrate 260 of the sixth embodiment
having the above-described structure, since the high-oxygen
concentration section 282 in which the oxygen concentration thereof
is greater than the oxygen concentrations in the metal plates 272
and 273 that constitute the circuit layer 262 and the metal layer
263 is formed in the joint interface 280 between the ceramics
substrate 261 and the metal plates 272 and 273 that become the
circuit layer 262 and the metal layer 263, due to oxygen, it is
possible to improve the joint strength between the ceramics
substrate 261 and the metal plates 272 and 273.
[0404] In addition, since the thickness of the high-oxygen
concentration section 282 is less than or equal to 4 nm, generation
of crack is suppressed in the high-oxygen concentration section 282
due to the stress when a heat-load cycle is performed.
[0405] As described above, the first to the sixth embodiments of
the present invention are described, the technical scope of the
present invention is not limited to the above embodiment, and
various modifications may be made without departing from the scope
of the present invention.
[0406] For example, the case where a rolled plate composed of
aluminum having a purity of 99.99% is adopted as a metal plate
constituting the circuit layer and the metal layer is described,
however, it is not limited to this method, and aluminum having a
purity of 99% (2N aluminum) may be used.
[0407] In addition, the case where the buffer layer composed of
aluminum, an aluminum alloy, or a combination of materials
including aluminum (for example, AlSiC or the like) is provided
between the top panel section of the heatsink and the metal layer
is described, however, it is not necessary to provide the buffer
layer.
[0408] Moreover, the structure in which the heatsink is formed of
aluminum is described, however, a structure in which the heatsink
is formed of an aluminum alloy, a composite material including
aluminum, copper, a copper alloy or the like may be employed.
[0409] Furthermore, the structure having the flow passage of
cooling medium as a heatsink is described, however, the structure
of the heatsink is not limited.
[0410] In addition, in the fifth embodiment, the case where the
ceramics substrate composed of AlN is used is described, it is not
limited to this structure, and a ceramics composed of
Al.sub.2O.sub.3 or the like may be used.
[0411] In addition, the manufacturing method is described having
the Cu-adhering step in which Cu is adhered to a surface of the
ceramics substrate, it is not limited to this method, and Cu may be
adhered to a surface of a brazing filler metal foil.
[0412] In addition, not only a sputtering method, but also Cu may
be adhered thereto by an evaporation method, a plating method, or
the like.
[0413] In addition, Cu may be introduced into an Al--Si system
brazing filler metal.
EXAMPLES
[0414] Next, the results of confirmatory experiments which were
performed in order to confirm the effectivity of the power module
substrate (power module) of the above-described first to sixth
embodiments are described.
Example 1
[0415] In the example 1 described below, with reference to FIGS. 6
and 7, the results of confirmatory experiments which were performed
in order to confirm the effectivity of the power module substrate
of the first embodiment are described.
[0416] Firstly, as the power module substrate used for the
experiment, a power module substrate was manufactured by the
following method of manufacturing.
[0417] Specifically, a ceramics substrate composed of AlN having 40
mm square and a thickness of 0.635 mm, and two metal plates
composed of aluminum 4N having a thickness of 0.6 mm were
prepared.
[0418] Thereafter, Cu was adhered to the both faces of the ceramics
substrate by a vacuum deposition, and a layered body was formed by
stacking the metal plates on both faces of the ceramics
substrate.
The layered body was heated in a vacuum furnace (the degree of
vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a pressure
of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked direction,
and a power module substrate provided with a ceramics substrate, a
circuit layer, and a metal layer was manufactured.
[0419] In a way similar to the above-described manner, a ceramics
substrate composed of AlN having 40 mm of square and a thickness of
0.635 mm, and two metal plates composed of aluminum 4N having a
thickness of 0.6 mm were prepared.
[0420] Thereafter, Cu was adhered to one of the faces of each metal
plate by a vacuum deposition, the metal plate was stacked on the
both faces of the ceramics substrate so that the face of the metal
plate on which the evaporation is performed faces the ceramics
substrate, and thereby a layered body is formed.
[0421] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0422] As described above, in the example 1, two kinds of power
module substrates were employed.
[0423] Here, adherence amounts of the adhered Cu (thickness of Cu)
by vacuum deposition were different from each other by five
parameters (five levels), and were 0.1 .mu.m, 0.5 .mu.m, 1.0 .mu.m,
2.0 .mu.m, and 3.0 .mu.m.
[0424] In addition, the heating temperatures were different from
each other by three parameters (three levels), and were 610.degree.
C., 630.degree. C., and 650.degree. C.
[0425] Consequently, a total of thirty kinds of power module
substrates were prepared.
[0426] An aluminum plate (A6063) was connected to the metal layer
of the power module substrate that were formed in this manner with
a buffer layer composed of AlSiC and having a thickness of 0.9 mm
interposed therebetween, the aluminum plate corresponding to a top
panel of a heatsink, and having lengths of 50 mm and 60 mm and a
thickness of 5 mm.
[0427] Consequently, a total of thirty kinds of test pieces were
prepared.
[0428] Subsequently, before the thirty kinds of test pieces being
subjected to a heat-load cycle test, the percentage of
connected-surface area (junction rate) in the joint interface
between the ceramics substrate and the metal plate was
determined.
[0429] Specifically, by use of an ultrasonic imaging device
(frequency of transducer is 15 MHz), the joint interface between
the ceramics substrate and the metal plate was captured, the data
that has been obtained by the capturing was binarized, the junction
rate was calculated by obtaining the surface area of a bonded
portion of the entirety of the joint interface.
[0430] In addition, the junction rate between a ceramics substrate
and a metal plate was 100%, before a heat-load cycle test is
performed.
[0431] Subsequently, a total of thirty kinds of test pieces were
subjected to heat-load cycles of -40.degree. C. to 105.degree. C.
by 3000 times under load.
[0432] Thereafter, by the same method as the above-described method
in which the ultrasonic imaging device was used, the junction rate
between a ceramics substrate and a metal plate, that is, the
junction rate after the 3000 heat-load cycles were performed, was
determined.
[0433] As a result, evaluation results of the power module
substrate were obtained.
[0434] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 6.
[0435] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 7.
[0436] In addition, in FIGS. 6 and 7, the power module substrate is
represented by the symbol ".largecircle.", in which the junction
rate was 85% or more after the power module substrate is subjected
to a 3000 cyclical thermal load; the power module substrate is
represented by the symbol ".DELTA.", in which the junction rate was
greater than or equal to 70% and less than 85% after the power
module substrate is subjected to a 3000 cyclical thermal load; and
the power module substrate is represented by the symbol "X", in
which the junction rate was less than 70% after the power module
substrate is subjected to a 3000 cyclical thermal load.
[0437] As shown in FIGS. 6 and 7, it was confirmed that, as the
heating temperature increases, the junction reliability was
improved.
[0438] In addition, in the case where the thickness of the Cu-layer
is approximately 1.0 .mu.m to 2.0 .mu.m, even if the heating
temperature is low, it was confirmed that the junction reliability
was improved.
[0439] Furthermore, FIGS. 6 and 7 shows the same tendency, it was
not confirmed that the difference between the case where Cu was
adhered to the ceramics substrate and the case where Cu was adhered
to the metal plate.
Example 2
[0440] In the example 2 described below, with reference to FIGS.
16A, 16B, 17A, and 17B, the results of confirmatory experiments
which were performed in order to confirm the effectivity of the
power module substrate of the second embodiment are described.
[0441] Firstly, as the power module substrate used for the
experiment, a power module substrate was manufactured by the
following method of manufacturing.
[0442] Specifically, a ceramics substrate composed of AlN having 40
mm square and a thickness of 0.635 mm, and two metal plates
composed of aluminum 4N having a thickness of 0.6 mm were
prepared.
[0443] Thereafter, Cu was adhered to the both faces of the ceramics
substrate by a vacuum deposition, and a layered body was formed by
stacking the metal plates on both faces of the ceramics
substrate.
[0444] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0445] In a way similar to the above-described manner, a ceramics
substrate composed of AlN having 40 mm of square and a thickness of
0.635 mm, and two metal plates composed of aluminum 4N having a
thickness of 0.6 mm were prepared.
[0446] Thereafter, Cu was adhered to one of the faces of each metal
plate by a vacuum deposition, the metal plate was stacked on the
both faces of the ceramics substrate so that the face of the metal
plate on which the evaporation is performed faces the ceramics
substrate, and thereby a layered body is formed.
[0447] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0448] As described above, in the example 2, two kinds of power
module substrates were employed.
[0449] Here, adherence amounts of the adhered Cu (thickness of Cu)
by vacuum deposition were different from each other by five
parameters (five levels), and were 0.1 .mu.m, 0.5 .mu.m, 1.0 .mu.m,
2.0 .mu.m, and 3.0 .mu.m.
[0450] In addition, the heating temperatures were different from
each other by three parameters (three levels), and were 610.degree.
C., 630.degree. C., and 650.degree. C.
[0451] Consequently, a total of thirty kinds of power module
substrates were formed.
[0452] An aluminum plate (A6063) was connected to the metal layer
of the power module substrate that were formed in this manner with
a buffer layer composed of 4N aluminum and having a thickness of
0.9 mm interposed therebetween, the aluminum plate corresponding to
a top panel of a heatsink, and having lengths of 50 mm and 60 mm
and a thickness of 5 mm.
[0453] Consequently, a total of thirty kinds of test pieces were
prepared.
[0454] Subsequently, before the thirty kinds of test pieces being
subjected to a heat-load cycle test, the percentage of
connected-surface area (junction rate) in the joint interface
between the ceramics substrate and the metal plate was
determined.
[0455] As a method for calculating the junction rate, the method
for calculating the junction rate by use of an ultrasonic imaging
device (frequency of transducer is 15 MHz) was adopted as described
in Example 1.
[0456] In addition, the junction rate between a ceramics substrate
and a metal plate was 100%, before a heat-load cycle test is
performed.
[0457] Subsequently, a total of thirty kinds of test pieces were
subjected to heat-load cycles of -40.degree. C. to 105.degree. C.
by 3000 times under load, and the presence or absence of cracks in
the ceramics substrate was confirmed.
[0458] In addition, in this experiment, two sets of thirty kinds of
test pieces were prepared, and the presence or absence of cracks in
the ceramics substrate was confirmed.
[0459] The results were shown in FIGS. 16A and 16B.
[0460] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 16A.
[0461] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 16B.
[0462] In addition, the power module substrate is represented by
the symbol ".largecircle.", in which cracks were not generated in
the ceramics substrate in both two test pieces, the power module
substrate is presented by the symbol ".DELTA.", in which cracks
were generated in the ceramics substrate in one of two test pieces,
and the power module substrate is represented by the symbol "X", in
which cracks were generated in the ceramics substrate in both two
test pieces.
[0463] In addition, the junction rate of a total of thirty kinds of
test pieces was determined after the 3000 heat-load cycles
described above were performed.
[0464] Specifically, by the same method as the above-described
method in which the ultrasonic imaging device was used, the
junction rate between a ceramics substrate and a metal plate, that
is, the junction rate after the 3000 heat-load cycles were
performed, was determined.
[0465] As a result, evaluation results of the power module
substrate were obtained.
[0466] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 17A.
[0467] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 17B.
[0468] In addition, in FIGS. 17A and 17B, the power module
substrate is represented by the symbol ".largecircle.", in which
the junction rate is 85% or more after the power module substrate
is subjected to a 3000 cyclical thermal load; the power module
substrate is represented by the symbol ".DELTA.", in which the
junction rate is greater than or equal to 70% and less than 85%
after the power module substrate is subjected to a 3000 cyclical
thermal load; and the power module substrate is represented by the
symbol "X", in which the junction rate is less than 70% after the
power module substrate is subjected to a 3000 cyclical thermal
load.
[0469] As shown in FIGS. 16A and 16B, it was confirmed that, as the
thickness of Cu formed in a Cu-adhering step increases, cracks in
the ceramics substrate composed of AlN are easily generated.
[0470] In addition, in the test piece in which the thickness of Cu
is 2 .mu.m, it was confirmed that, as the heating temperature
increases, cracks in the ceramics are suppressed more.
[0471] In addition, as shown in FIGS. 17A and 17B, it was confirmed
that, as the heating temperature increases, the junction
reliability was improved.
[0472] In addition, in the case where the thickness of Cu is
approximately 2 .mu.m, even if the heating temperature is low, it
was confirmed that the junction reliability was improved.
[0473] According to the test result, in the ceramics substrate
composed of AlN, it is confirmed that the thickness of Cu existing
at the boundary face between the metal plate and the ceramics
substrate is preferably less than or equal to 2.5 .mu.m at the time
of connecting.
Example 3
[0474] In the example 3 described below, with reference to FIGS.
18A and 18B, and FIGS. 19A and 19B, the results of confirmatory
experiments which were performed in order to confirm the
effectivity of the power module substrate of the third embodiment
are described.
[0475] Firstly, as the power module substrate used for the
experiment, a power module substrate was manufactured by the
following method of manufacturing.
[0476] Specifically, a ceramics substrate composed of
Si.sub.3N.sub.4 having 40 mm square and a thickness of 0.32 mm, and
two metal plates composed of aluminum 4N having a thickness of 0.6
mm were prepared.
[0477] Thereafter, Cu was adhered to the both faces of the ceramics
substrate by a vacuum deposition, and a layered body was formed by
stacking the metal plates on both faces of the ceramics
substrate.
[0478] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0479] In a way similar to the above-described manner, a ceramics
substrate composed of Si.sub.3N.sub.4 having 40 mm of square and a
thickness of 0.32 mm, and two metal plates composed of aluminum 4N
having a thickness of 0.6 mm were prepared.
[0480] Thereafter, Cu was adhered to one of the faces of each metal
plate by a vacuum deposition, the metal plate was stacked on the
both faces of the ceramics substrate so that the face of the metal
plate on which the evaporation is performed faces the ceramics
substrate, and thereby a layered body is formed.
[0481] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0482] As described above, in the example 3, two kinds of power
module substrates were employed.
[0483] Here, adherence amounts of the adhered Cu (thickness of Cu)
by vacuum deposition were different from each other by five
parameters (five levels), and were 0.1 .mu.m, 0.5 .mu.m, 1.0 .mu.m,
2.0 .mu.m, and 3.0 .mu.m.
[0484] In addition, the heating temperatures were different from
each other by three parameters (three levels), and were 610.degree.
C., 630.degree. C., and 650.degree. C.
[0485] Consequently, a total of thirty kinds of power module
substrates were formed.
[0486] An aluminum plate (A6063) was connected to the metal layer
of the power module substrate that were formed in this manner with
a buffer layer composed of 4N aluminum and having a thickness of
0.9 mm interposed therebetween, the aluminum plate corresponding to
a top panel of a heatsink, and having lengths of 50 mm and 60 mm
and a thickness of 5 mm.
[0487] Consequently, a total of thirty kinds of test pieces were
prepared.
[0488] Subsequently, before the thirty kinds of test pieces being
subjected to a heat-load cycle test, the percentage of
connected-surface area (junction rate) in the joint interface
between the ceramics substrate and the metal plate was
determined.
[0489] As a method for calculating the junction rate, the method
for calculating the junction rate by use of an ultrasonic imaging
device (frequency of transducer is 15 MHz) was adopted as described
in Example 1.
[0490] In addition, the junction rate between a ceramics substrate
and a metal plate was 100%, before a heat-load cycle test is
performed.
[0491] Subsequently, a total of thirty kinds of test pieces were
subjected to heat-load cycles of -40.degree. C. to 105.degree. C.
by 3000 times under load, and the presence or absence of cracks in
the ceramics substrate was confirmed.
[0492] In addition, in this experiment, two sets of thirty kinds of
test pieces were prepared, and the presence or absence of cracks in
the ceramics substrate was confirmed.
[0493] The results were shown in FIGS. 18A and 18B.
[0494] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 18A.
[0495] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 18B.
[0496] In addition, the power module substrate is represented by
the symbol ".largecircle.", in which cracks were not generated in
the ceramics substrate in both two test pieces, the power module
substrate is presented by the symbol ".DELTA.", in which cracks
were generated in the ceramics substrate in one of two test pieces,
and the power module substrate is represented by the symbol "X", in
which cracks were generated in the ceramics substrate in both two
test pieces.
[0497] In addition, the junction rate of a total of thirty kinds of
test pieces was determined after the 3000 heat-load cycles
described above were performed.
[0498] Specifically, by the same method as the above-described
method in which the ultrasonic imaging device was used, the
junction rate between a ceramics substrate and a metal plate, that
is, the junction rate after the 3000 heat-load cycles were
performed, was determined.
[0499] As a result, evaluation results of the power module
substrate were obtained.
[0500] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 19A.
[0501] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 19B.
[0502] In addition, in FIGS. 19A and 19B, the power module
substrate is represented by the symbol ".largecircle.", in which
the junction rate is 85% or more after the power module substrate
is subjected to a 3000 cyclical thermal load; the power module
substrate is represented by the symbol ".DELTA.", in which the
junction rate is greater than or equal to 70% and less than 85%
after the power module substrate is subjected to a 3000 cyclical
thermal load; and the power module substrate is represented by the
symbol "X", in which the junction rate is less than 70% after the
power module substrate is subjected to a 3000 cyclical thermal
load.
[0503] As shown in FIGS. 18A and 18B, in the ceramics substrate
composed of Si.sub.3N.sub.4, cracks in the ceramics substrate were
not confirmed under the condition of the present experiment.
[0504] In addition, as shown in FIGS. 19A and 19B, it was confirmed
that, as the heating temperature increases, the junction
reliability was improved.
[0505] In addition, in the case where the thickness of Cu is
approximately 2.0 .mu.m, even if the heating temperature is low, it
was confirmed that the junction reliability was improved.
[0506] According to the test result, in the ceramics substrate
composed of Si.sub.3N.sub.4, it is confirmed that the thickness of
Cu existing at the boundary face between the metal plate and the
ceramics substrate is preferably 0.15 .mu.m to 3 .mu.m at the time
of connecting.
Example 4
[0507] In the example 4 described below, with reference to FIGS.
24A, 24B, 25A, and 25B, the results of confirmatory experiments
which were performed in order to confirm the effectivity of the
power module substrate of the fourth embodiment are described.
[0508] Firstly, as the power module substrate used for the
experiment, a power module substrate was manufactured by the
following method of manufacturing.
[0509] Specifically, a ceramics substrate composed of
Al.sub.2O.sub.3 having 40 mm square and a thickness of 0.635 mm,
and two metal plates composed of aluminum 4N having a thickness of
0.6 mm were prepared.
[0510] Thereafter, Cu was adhered to the both faces of the ceramics
substrate by a vacuum deposition, and a layered body was formed by
stacking the metal plates on both faces of the ceramics
substrate.
[0511] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0512] In a way similar to the above-described manner, a ceramics
substrate composed of Al.sub.2O.sub.3 having 40 mm of square and a
thickness of 0.635 mm, and two metal plates composed of aluminum 4N
having a thickness of 0.6 mm were prepared.
[0513] Thereafter, Cu was adhered to one of the faces of each metal
plate by a vacuum deposition, the metal plate was stacked on the
both faces of the ceramics substrate so that the face of the metal
plate on which the evaporation is performed faces the ceramics
substrate, and thereby a layered body is formed.
[0514] The layered body was heated in a vacuum furnace (the degree
of vacuum is 10.sup.-3 Pa to 10.sup.-5 Pa) in a state where a
pressure of 1 to 5 kgf/cm.sup.2 was applied thereto in a stacked
direction, and a power module substrate provided with a ceramics
substrate, a circuit layer, and a metal layer was manufactured.
[0515] As described above, in the example 4, two kinds of power
module substrates were employed.
[0516] Here, adherence amounts of the adhered Cu (thickness of Cu)
by vacuum deposition were different from each other by five
parameters (five levels), and were 0.1 .mu.m, 0.5 .mu.m, 1.0 .mu.m,
2.0 .mu.m, and 3.0 .mu.m.
[0517] In addition, the heating temperatures were different from
each other by three parameters (three levels), and were 610.degree.
C., 630.degree. C., and 650.degree. C.
[0518] Consequently, a total of thirty kinds of power module
substrates were formed.
[0519] An aluminum plate (A6063) was connected to the metal layer
of the power module substrate that were formed in this manner with
a buffer layer composed of 4N aluminum and having a thickness of
0.9 mm interposed therebetween, the aluminum plate corresponding to
a top panel of a heatsink, and having lengths of 50 mm and 60 mm
and a thickness of 5 mm.
[0520] Consequently, a total of thirty kinds of test pieces were
prepared.
[0521] Subsequently, before the thirty kinds of test pieces being
subjected to a heat-load cycle test, the percentage of
connected-surface area (junction rate) in the joint interface
between the ceramics substrate and the metal plate was
determined.
[0522] As a method for calculating the junction rate, the method
for calculating the junction rate by use of an ultrasonic imaging
device (frequency of transducer is 15 MHz) was adopted as described
in Example 1.
[0523] In addition, the junction rate between a ceramics substrate
and a metal plate was 100%, before a heat-load cycle test is
performed.
[0524] Subsequently, a total of thirty kinds of test pieces were
subjected to heat-load cycles of -40.degree. C. to 105.degree. C.
by 3000 times under load, and the presence or absence of cracks in
the ceramics substrate was confirmed.
[0525] In addition, in this experiment, two sets of thirty kinds of
test pieces were prepared, and the presence or absence of cracks in
the ceramics substrate was confirmed.
[0526] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 24A.
[0527] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 24B.
[0528] In addition, the power module substrate is represented by
the symbol ".largecircle.", in which cracks were not generated in
the ceramics substrate in both two test pieces, the power module
substrate is presented by the symbol ".DELTA.", in which cracks
were generated in the ceramics substrate in one of two test pieces,
and the power module substrate is represented by the symbol "X", in
which cracks were generated in the ceramics substrate in both two
test pieces.
[0529] In addition, the junction rate of a total of thirty kinds of
test pieces was determined after the 3000 heat-load cycles
described above were performed.
[0530] Specifically, by the same method as the above-described
method in which the ultrasonic imaging device was used, the
junction rate between a ceramics substrate and a metal plate, that
is, the junction rate after the 3000 heat-load cycles were
performed, was determined.
[0531] As a result, evaluation results of the power module
substrate were obtained.
[0532] An evaluation result of the power module substrate that is
obtained by evaporating and adhering Cu to the ceramics substrate
is shown in FIG. 25A.
[0533] In addition, an evaluation result of the power module
substrate that is obtained by evaporating and adhering Cu to the
metal plate is shown in FIG. 25B.
[0534] In addition, in FIG. 25B, the power module substrate is
represented by the symbol ".largecircle.", in which the junction
rate is 85% or more after the power module substrate is subjected
to a 3000 cyclical thermal load; the power module substrate is
represented by the symbol ".DELTA.", in which the junction rate is
greater than or equal to 70% and less than 85% after the power
module substrate is subjected to a 3000 cyclical thermal load; and
the power module substrate is represented by the symbol "X", in
which the junction rate is less than 70% after the power module
substrate is subjected to a 3000 cyclical thermal load.
[0535] As shown in FIGS. 25A and 25B, it was confirmed that, as the
thickness of Cu formed in a Cu-adhering step increases, cracks in
the ceramics substrate composed of Al.sub.2O.sub.3 are easily
generated.
[0536] In addition, in the test piece in which the thickness of Cu
is 2 .mu.m, it was confirmed that, as the heating temperature
increases, cracks in the ceramics are suppressed more.
[0537] In addition, as shown in FIGS. 25A and 25B, it was confirmed
that, as the heating temperature increases, the junction
reliability was improved.
[0538] In addition, in the case where the thickness of Cu is
approximately 1 .mu.m, even if the heating temperature is low, it
was confirmed that the junction reliability was improved.
[0539] According to the test result, in the ceramics substrate
composed of Al.sub.2O.sub.3, it is confirmed that the thickness of
Cu existing at the boundary face between the metal plate and the
ceramics substrate is preferably less than or equal to 2.5 .mu.m at
the time of connecting.
Example 5
[0540] In the examples 5 and 6 described below, with reference to
FIG. 34 and Table 1, the results of confirmatory experiments which
were performed in order to confirm the effectivity of the power
module substrate of the fifth and sixth embodiments are
described.
[0541] As shown in FIG. 34, confirmatory experiment was performed
by use of a power module substrate having: a ceramics substrate 211
composed of AlN having a thickness of 0.635 mm; a circuit layer 212
composed of 4N aluminum having a thickness of 0.6 mm; a metal layer
213 composed of 4N aluminum having a thickness of 0.6 mm; a top
panel section 5 composed of an aluminum alloy (A6063) having a
thickness of 5 mm; and a buffer layer 15 composed of 4N aluminum
having a thickness of 1.0 mm, as common power module substrates in
the comparative example and example 5.
[0542] In example 5, metal plates that become the circuit layer 212
and the metal layer 213 were connected to the ceramics substrate
211 by use of an Al--Si system brazing filler metal, after Cu was
adhered to the surface of the ceramics substrate 211 by a
sputtering.
[0543] In contrast, in the comparative example, Cu was not
introduced into the joint interfaces between the ceramics substrate
211 and the metal plates, and the metal plates that become the
circuit layer 212 and the metal layer 213 were connected to the
ceramics substrate 211 by use of an Al--Si system brazing filler
metal.
[0544] Consequently, a test piece of example 5 and a test piece of
the comparative example were prepared.
[0545] Subsequently, before the test pieces being subjected to a
heat-load cycle test, the percentage of connected-surface area
(junction rate) in the joint interface between the ceramics
substrate and the metal plate was determined.
[0546] As a method for calculating the junction rate, the method
for calculating the junction rate by use of an ultrasonic imaging
device (frequency of transducer is 15 MHz) was adopted as described
in Example 1.
[0547] In addition, before a heat-load cycle test is performed, the
junction rate between a ceramics substrate and a metal plate of the
test piece of example 5 was 100%, and the junction rate between a
ceramics substrate and a metal plate of the test piece of the
comparative example was 99.8%.
[0548] Next, evaluation of the junction reliability by use of the
test pieces was performed.
[0549] In the evaluation of the junction reliability, regarding the
junction rate at which after heat-load cycles (-45.degree. C. to
125.degree. C.) were repeatedly performed, the comparative example
was compared to example 5.
[0550] Specifically, by the same method as the above-described
method in which the ultrasonic imaging device was used, junction
rate between the ceramics substrate and the metal plate in the
comparative example and example 5 was determined.
[0551] Furthermore, the junction rates were determined after each
of heat-load cycles of 1000 times, 2000 times, and 3000 times is
performed.
[0552] Consequently, the evaluation result of the power module
substrate was obtained.
[0553] The evaluation result was shown in Table 1.
TABLE-US-00001 TABLE 1 JUNCTION RATE AFTER BEING SUBJECTED
INTRODUCING OF TO HEAT-LOAD CYCLE Cu INTO JOINT 1000 2000 3000
INTERFACE TIMES TIMES TIMES EXAMPLE 5 PRESENCE 100% 100% 99.2%
COMPARATIVE ABSENCE 99.8% 94.2% 91.5% EXAMPLE
[0554] In the comparative example, in which connection is performed
by use of an Al--Si system brazing filler metal without introducing
Cu into the joint interface, the junction rate was near 100%
(99.8%) after 1000 heat-load cycles.
[0555] However, it was confirmed that the junction rate decreases
after 2000 heat-load cycles (94.2%), and the junction rate
decreased to 91.5% after the 3000 heat-load cycles.
[0556] On the other hand, in example 5, in which Cu was introduced
into the joint interface, even if the heat-load cycles were
performed 2000 times, the junction rate did not decrease.
[0557] The junction rate was 99.2% after the 3000 heat-load
cycles.
[0558] According to the confirmatory experiment, it was confirmed
that the heat-load cycle reliability is improved by introducing Cu
into the joint interface.
Example 6
[0559] Subsequently, assay result of component of the metal layer
in the power module substrates of the fifth and sixth embodiments
is described.
[0560] The circuit layer 212 composed of 4N aluminum having a
thickness of 0.6 mm and the metal layer 213 composed of 4N aluminum
having a thickness of 0.6 mm were connected to the ceramics
substrate 211 composed of AlN having a thickness of 0.635 mm, and
the power module substrate was manufactured.
[0561] Here, in examples 6A to 6C, a Cu-layer having a thickness of
1.5 .mu.m was formed on the surface of a brazing filler metal
having Si including Al-7.5 wt %, and the circuit layer 212 and the
metal layer 213 were connected to the ceramics substrate 211 by use
of the brazing filler metal having Si including Al-7.5 wt %.
[0562] In addition, the connection temperatures were different from
each other by three parameters (3 levels), and were 610.degree. C.,
630.degree. C., and 650.degree. C.
[0563] Here, in examples 6D to 6F, a Cu-layer having a thickness of
1.5 .mu.m was formed on the surface of the ceramics substrate 211,
and the circuit layer 212 and the metal layer 213 were connected to
the ceramics substrate 211 by use of a brazing filler metal having
Si including Al-7.5 wt %.
[0564] In addition, the connection temperatures were different from
each other by three parameters (3 levels), and were 610.degree. C.,
630.degree. C., and 650.degree. C.
[0565] Regarding the examples 6A to 6F, quantitative analysis was
performed for the Cu concentration and the Si concentration by use
of EPMA, at a center portion in a width direction of the boundary
face between the metal layer and the ceramics substrate, and at the
end portion in the width direction of the boundary face.
[0566] The result was shown in Table 2.
TABLE-US-00002 TABLE 2 Si (wt %) Cu (wt %) CONNECTION END END
TEMPERATURE CENTER POR- CENTER POR- (.degree. C.) PORTION TION
PORTION TION EXAMPLE 6A 610 0.084 1.091 0.481 0.943 EXAMPLE 6B 630
0.113 1.455 0.457 0.854 EXAMPLE 6C 650 0.106 1.243 0.418 0.933
EXAMPLE 6D 610 0.102 1.314 0.634 1.066 EXAMPLE 6E 630 0.108 1.257
0.370 1.043 EXAMPLE 6F 650 0.087 1.066 0.355 1.320
[0567] According to the result of quantitative analysis, in the
case where the Cu-layer was formed and the ceramics substrate was
connected to the metal plate by use of an Al--Si system brazing
filler metal, it was confirmed that the Si concentration of the
portion which is close to the joint interface is 0.05 to 0.5 wt %
and the Cu concentration thereof was in the range of 0.05 to 1.0 wt
% at the center portion of the width direction.
[0568] In addition, it is confirmed that Si and Cu exist at the end
portion in the width direction with a high level of
concentration.
* * * * *