U.S. patent application number 14/224634 was filed with the patent office on 2014-07-24 for semiconductor light emitting device and method for manufacturing same.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yasuharu SUGAWARA.
Application Number | 20140203296 14/224634 |
Document ID | / |
Family ID | 48609220 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140203296 |
Kind Code |
A1 |
SUGAWARA; Yasuharu |
July 24, 2014 |
SEMICONDUCTOR LIGHT EMITTING DEVICE AND METHOD FOR MANUFACTURING
SAME
Abstract
According to an embodiment, a semiconductor light emitting
device includes a light emitting body including a semiconductor
light emitting layer, a support substrate supporting the light
emitting body, and a bonding layer provided between the light
emitting body and the support substrate, the bonding layer bonding
the light emitting body and the support substrate together. The
device also includes a first barrier metal layer provided between
the light emitting body and the bonding layer, and an electrode
provided between the light emitting body and the first barrier
metal layer. The first barrier layer includes a first layer made of
nickel and a second layer made of a metal having a smaller linear
expansion coefficient than nickel, and the first layer and the
second layer are alternately disposed in a multiple-layer
structure. The electrode is electrically connected to the light
emitting body.
Inventors: |
SUGAWARA; Yasuharu;
(Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Tokyo |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
48609220 |
Appl. No.: |
14/224634 |
Filed: |
March 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13472310 |
May 15, 2012 |
8723336 |
|
|
14224634 |
|
|
|
|
Current U.S.
Class: |
257/76 ;
257/99 |
Current CPC
Class: |
H01L 33/0093 20200501;
H01L 33/40 20130101; H01L 33/32 20130101; H01L 33/387 20130101;
H01L 33/405 20130101 |
Class at
Publication: |
257/76 ;
257/99 |
International
Class: |
H01L 33/40 20060101
H01L033/40; H01L 33/32 20060101 H01L033/32 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2011 |
JP |
2011-276137 |
Claims
1-20. (canceled)
21. A semiconductor light emitting device comprising: a light
emitting body including a semiconductor light emitting layer; a
substrate; a bonding layer between the light emitting body and the
substrate, the bonding layer bonding the light emitting body to the
substrate; a first barrier metal layer between the light emitting
body and the bonding layer, the first barrier metal layer including
at least one of a first layer made of a first metal and at least
one of a second layer made of a second metal having a linear
expansion coefficient that is less than the first metal; and an
electrode between the light emitting body and the first barrier
metal layer, the electrode comprising a metal having a linear
expansion coefficient between that of the first metal and that of
the second metal.
22. The device according to claim 21, wherein the electrode
includes silver (Ag).
23. The device according to claim 21, wherein the linear expansion
coefficient of the metal of the electrode is closer to the linear
expansion coefficient of the first metal than the linear expansion
coefficient of the second metal.
24. The device according to claim 21, wherein the first metal and
the second metal each comprise at least one metal selected from
titanium (Ti), platinum (Pt), tantalum (Ta), and tungsten (W).
25. The device according to claim 21, wherein the first barrier
metal layer alternatively includes three or more of the first layer
and three or more of the second layer.
26. The device according to claim 21, wherein the second layer is
provided between the electrode and a first layer.
27. The device according to claim 21, wherein the first layer is
provided between the bonding layer and a second layer.
28. The device according to claim 21, wherein a thickness of each
of the first layer and the second layer is not less than 50 nm and
not more than 500 nm.
29. The device according to claim 21, wherein the bonding layer
comprises at least one of gold (Au) and tin (Sn).
30. The device according to claim 21, wherein the bonding layer
comprises Au and Sn, and a portion of the bonding layer nearer the
first barrier metal layer than the substrate has a smaller ratio of
Sn to Au than a portion of the bonding layer nearer to the
substrate than the first barrier metal layer.
31. The device according to claim 21, wherein the light emitting
body includes a p-type GaN layer and an n-type GaN layer, and the
semiconductor light emitting layer is between the p-type GaN layer
and the n-type GaN layer.
32. The device according to claim 21, wherein the electrode is
electrically connected to the p-type GaN layer.
33. The device according to claim 21, wherein the electrode
includes a plurality of portions disposed between the light
emitting body and the first barrier metal layer, and each of the
portions is separated from one another along a direction
substantially parallel to a plane of the substrate.
34. The device according to claim 33, wherein at least one portion
among the plurality of portions of the electrode has an end portion
inclined at an angle that is less than perpendicular with respect
to the plane of the substrate such that a width of the at least one
portion decreases in a direction from the light emitting body to
the first barrier metal layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2011-276137, filed on
Dec. 16, 2011; the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments are related generally to a semiconductor light
emitting device and a method for manufacturing the same.
BACKGROUND
[0003] A semiconductor light emitting device having a thin-film
structure is provided through the manufacturing processes, where a
light emitting body including a semiconductor light emitting layer
is bonded to a support substrate via a bonding metal. In the
bonding process, metal atoms contained in the bonding metal
sometimes penetrate into the interface between an electrode
connected to the light emitting body and the light emitting body,
causing degradation in contact resistance etc. To prevent this, a
barrier metal is interposed between the electrode and the bonding
metal to suppress movement of metal atoms. However, it is not
sufficient to suppress the penetration of the metal atoms.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a schematic cross-sectional view illustrating a
semiconductor light emitting device according to a first
embodiment;
[0005] FIG. 2A to FIG. 4B are schematic cross-sectional views
illustrating manufacturing processes of the semiconductor light
emitting device according to the first embodiment;
[0006] FIGS. 5A to 5D are partial cross-sectional views
schematically illustrating bonding structures of the semiconductor
light emitting devices and plan photographs of the bonding
structures; and
[0007] FIGS. 6A and 6B are schematic cross-sectional views
illustrating a semiconductor light emitting device according to a
second embodiment.
DETAILED DESCRIPTION
[0008] According to one embodiment, a semiconductor light emitting
device includes a light emitting body including a semiconductor
light emitting layer, a support substrate supporting the light
emitting body, and a bonding layer provided between the light
emitting body and the support substrate, the bonding layer bonding
the light emitting body and the support substrate together. The
device also includes a first barrier metal layer provided between
the light emitting body and the bonding layer, and an electrode
provided between the light emitting body and the first barrier
metal layer. The first barrier layer includes a first layer made of
nickel and a second layer made of a metal having a smaller linear
expansion coefficient than nickel, and the first layer and the
second layer are alternately disposed in a multiple-layer
structure. The electrode is electrically connected to the light
emitting body.
[0009] Hereinbelow, embodiments of the invention are described with
reference to the drawings. Identical components in the drawings are
marked with the same reference numerals, and a detailed description
thereof is omitted as appropriate and different components are
described.
First Embodiment
[0010] FIG. 1 is a schematic cross-sectional view showing a
semiconductor light emitting device 100 according to a first
embodiment. The semiconductor light emitting device 100 is, for
example, a light emitting diode (LED) made of a GaN-based nitride
semiconductor. The semiconductor light emitting device 100 is an
LED having so called a thin-film structure, and includes a light
emitting body 10 including a semiconductor light emitting layer and
a support substrate 20 supporting the light emitting body 10.
[0011] As shown in FIG. 1, a bonding layer 30 is provided between
the light emitting body 10 and the support substrate 20, in order
to make the bond therebetween. Furthermore, a first barrier metal
layer 40a is provided between the light emitting body 10 and the
bonding layer 30. The first barrier metal layer 40a includes a
multiple-layer structure in which a first layer made of nickel (Ni)
and a second layer made of a metal having a smaller linear
expansion coefficient than nickel are alternately disposed.
[0012] An electrode 50 electrically connected to the light emitting
body 10 is provided between the light emitting body 10 and the
first barrier metal layer 40a.
[0013] The configuration of the semiconductor light emitting device
100 will now be specifically described below.
[0014] The light emitting body 10 includes, for example, an n-type
GaN layer 3, a light emitting layer 5, and a p-type GaN layer. The
light emitting layer 5 has a multi-quantum well (MQW) structure
composed of an InGaN well layer and a GaN barrier layer, and emits
blue light, for example.
[0015] The electrode 50 contains, for example, silver (Ag), and
reflects the light emitted from the light emitting layer 5 toward a
light emitting surface 10a. In the following, the electrode 50 is
referred to as a reflection electrode 50.
[0016] The bonding layer 30 includes a first bonding metal layer
30a and a second bonding metal layer 30b. The first bonding metal
layer 30a is provided on the reflection electrode 50 via the first
barrier metal layer 40a. The second bonding metal layer 30b is
provided on the support substrate 20 via a second barrier metal
layer 40b. As described later, the light emitting body 10 and the
support substrate 20 are bonded together by bonding the first
bonding metal layer 30a and the second bonding metal layer 30b
together using a thermocompression method.
[0017] The second barrier metal layer 40b includes multiple-layer
structure in which a Ni layer 41 and, for example, a titanium (Ti)
layer 43 having a smaller linear expansion coefficient than Ni are
alternately disposed.
[0018] An n electrode 60 is selectively provided on the light
emitting surface 10a of the light emitting body 10. The n electrode
60 is in ohmically contact with the n-type GaN layer 3. A back
surface electrode 70 is provided on the back surface 20b of the
support substrate 20.
[0019] Next, a method for manufacturing the semiconductor light
emitting device 100 according to the first embodiment is described
with reference to FIG. 2A to FIG. 4B. FIG. 2A to FIG. 4B are
schematic cross-sectional views showing the manufacturing
processes.
[0020] A wafer 90 including the light emitting body 10 and the
support substrate 20 are prepared as shown in FIG. 2A. The wafer 90
includes a growth substrate 80, the n-type GaN layer 3 epitaxially
grown thereon, the light emitting layer 5, and the p-type GaN layer
7. The reflection electrode 50 is provided on the p-type GaN layer
7.
[0021] A sapphire substrate, for example, is used as the growth
substrate 80. The n-type GaN layer 3, the light emitting layer 5,
and the p-type GaN layer 7 can be formed using the MOCVD (metal
organic chemical vapor deposition) method, the MBE (molecular beam
epitaxy) method, etc. The reflection electrode 50 is, for example,
an Ag layer, and is formed using the vacuum deposition method. The
support substrate 20 is, for example, a p-type silicon wafer.
[0022] Next, the first barrier metal layer 40a and the first
bonding metal layer 30a are sequentially formed on the wafer 90.
The second barrier metal layer 40b and the second bonding metal
layer 30b are sequentially formed on the support substrate 20.
[0023] The first and second barrier metal layers can be formed
using, for example, the sputtering method. It is also possible to
set the wafer 90 and the support substrate 20 in the same
apparatus, and form the first barrier metal layer 40a and the
second barrier metal layer 40b simultaneously. That is, the first
barrier metal layer 40a may have the same configuration as the
second barrier metal layer 40b.
[0024] The first barrier metal layer 40a has a multiple-layer
structure in which, for example, the Ti layer 43 that is the second
layer and the Ni layer 41 that is the first layer are alternately
stacked in this order from the reflection electrode 50 side. The
linear expansion coefficient of Ti is 8.4.times.10.sup.-6/.degree.
C., which is smaller than the linear expansion coefficient of Ni,
1.33.times.10.sup.-5/.degree. C.
[0025] For example, a Ti layer 43 with a thickness of 50 to 500
nanometers (nm) and a Ni layer 41 with a thickness of 50 to 500 nm
are alternately stacked. Preferably a Ti layer 43 of 50 to 200 nm
and a Ni layer 41 of 50 to 200 nm are alternately stacked. Also the
second barrier metal layer 40b is similarly formed on the support
substrate 20. The second barrier metal layer 40b may includes the
Ni layer 41 as a third layer and the Ti layer 43 as a fourth
layer.
[0026] The first bonding metal layer 30a and the second bonding
metal layer 30b are formed using, for example, the vacuum
deposition method or the sputtering method. It is also possible to
form the first bonding metal layer 30a and the second bonding metal
layer 30b simultaneously into the same configuration. The first
bonding metal layer 30a has, for example, a structure in which gold
(Au) and gold tin (AuSn) are stacked in this order from the first
barrier metal layer 40a side. The thickness of the Au is, for
example, 10 to 400 nm, and the thickness of the AuSn is 100 to 5000
nm. Also the second bonding metal layer 30b is similarly formed on
the second barrier metal layer 40b.
[0027] As a modification example of the embodiment, the second
barrier metal layer 40b may have a different configuration from the
first barrier metal layer 40a. Furthermore, also a configuration is
possible in which one of the first bonding metal layer 30a and the
second bonding metal layer 30b has a stacked structure of Au/AuSn
and the other is a single layer of Au.
[0028] Next, as shown in FIG. 3A, the wafer 90 is stacked on the
support substrate 20, and the bonding surface 30x of the first
bonding metal layer 30a and the bonding surface 30y of the second
bonding metal layer 30b are brought into contact with each other.
Furthermore, in a state where pressure is applied from the back
surface side of the growth substrate 80 and the back surface side
of the support substrate 20, the temperature is increased to bond
the first bonding metal layer 30a and the second bonding metal
layer 30b together by thermocompression.
[0029] For example, the temperature of the support substrate 20 and
the wafer 90 is set not less than 220.degree. C. and not more than
350.degree. C., and they are kept under pressure for not less than
1 minute and not more than 20 minutes. Thereby, as shown in FIG.
3B, the wafer 90 and the support substrate 20 can be bonded
together via the bonding layer 30.
[0030] Next, as shown in FIG. 4A, the growth substrate 80 is
separated from the light emitting body 10. For example, laser light
is applied from the back surface side of the growth substrate 80 to
dissociate GaN near the interface between the growth substrate 80
and the n-type GaN layer 3. Thereby, the growth substrate 80 can be
removed, leaving the light emitting body 10 on the support
substrate 20. The light emitting body 10 is bonded to the support
substrate 20 via the bonding layer 30 placed between the first
barrier metal layer 40a and the second barrier metal layer 40b.
[0031] Next, as shown in FIG. 4B, the n electrode 60 is selectively
formed on the light emitting surface 10a of the light emitting body
10 from which the growth substrate 80 has been removed. The n
electrode 60 is formed using, for example, the vacuum deposition
method, and has a stacked structure of Al/Ti/Au. The back surface
electrode 70 is formed on the back surface 20b of the support
substrate 20, and the semiconductor light emitting device 100 is
thus completed.
[0032] FIGS. 5A to 5D are schematic cross-sectional views showing
parts of the bonding structures of semiconductor light emitting
devices and plan photographs thereof. FIG. 5A and FIG. 5B show a
bonding structure according to the embodiment, and FIG. 5C and FIG.
5D show a bonding structure according to a comparative example.
[0033] FIG. 5A is a cross-sectional structure taken along line A-A
shown in FIG. 5B. In the embodiment, the first barrier metal layer
40a is provided so as to cover the reflection electrode 50. The
first barrier metal layer 40a has a configuration in which the Ti
layer 43 that is the second layer and the Ni layer 41 that is the
first layer are alternately stacked in this order from the
reflection electrode 50 side. Three Ti layers 43 and three Ni
layers 41 are stacked. In addition, an Au layer 31 and an AuSn
layer 33 are stacked in this order on the first barrier metal layer
40a.
[0034] FIG. 5B is a photograph showing the reflection surface of
the reflection electrode 50 as viewed from the back surface side of
the growth substrate 80 after the wafer 90 and the support
substrate 20 are bonded together. Since the sapphire substrate and
the GaN-based nitride semiconductor are transparent to visible
light, the reflection surface can be directly observed as shown in
FIG. 5B.
[0035] FIG. 5C shows a cross section of the bonding structure
according to the comparative example. A barrier metal layer 45
covering the reflection electrode 50 includes the Ti layer 43 and a
platinum (Pt) layer 47 in the comparative example. The Ti layer 43
and the Pt layer 47 are stacked in this order from the reflection
electrode 50 side. The Au layer 31 and the AuSn layer 33 are
stacked in this order on the barrier metal layer 45.
[0036] FIG. 5D is a photograph showing the reflection surface after
the wafer 90 and the support substrate 20 are bonded together. In
the example, migration of tin (Sn) contained in the first bonding
metal layer 30a is seen along the outer periphery and inner
periphery of the pattern of the reflection electrode 50. That is,
Su has penetrated into the interface between the reflection
electrode 50 and the p-type GaN layer 7. Consequently, the
reflectance is reduced at the reflection surface of the reflection
electrode 50, and further the ohmic contact is also degraded
between the p-type GaN layer 7 and the reflection electrode 50.
Thus, the light emitting efficiency is reduced in the semiconductor
light emitting device.
[0037] In contrast, as shown in FIG. 5B, in the embodiment,
migration of Sn is not seen, exhibiting the higher blocking
performance of the first barrier metal layer 40a. That is, the
penetration of Sn can be prevented by alternately stacking the Ti
layer 43 and the Ni layer 41 to form a multiple-layer structure.
Thereby, degradation in the reflectance and the ohmic contact of
the reflection electrode 50 can be suppressed.
[0038] It may be presumed that, for example, also in the barrier
metal layer 45 in the comparative example, the barrier properties
to Sn can be improved by thickening the Ti layer 43 and the Pt
layer 47 or employing a multiple-layer structure. However, both Ti
and Pt have a smaller linear expansion coefficient than Ag
contained in the reflection electrode 50. Therefore, when the Ti
layer 43 and the Pt layer 47 are formed to be thicker, the thermal
stress applied to the reflection electrode 50 becomes larger, and
peeling at the interface between the reflection electrode 50 and
the p-type GaN layer 7 is likely to occur.
[0039] The first barrier metal layer 40a according to the
embodiment contains Ni having a linear expansion coefficient
(1.33.times.10.sup.-5/.degree. C.) near that of Ag. Therefore, the
stress applied to the reflection electrode 50 is reduced, and
peeling of the reflection electrode 50 from the p-type GaN layer 7
is suppressed. Thereby, the barrier properties to Sn can be
improved.
[0040] Table 1 shows relationships between the numbers of Ti layers
43 and Ni layers 41 and the barrier properties to Sn. Even in the
first barrier metal layer 40a according to the embodiment,
migration of Sn will occur in the case where the number of layers
is small. That is, in the case where the numbers of Ti layers 43
and Ni layers 41 are both set to two or less, migration of Sn
occurs. On the other hand, in the case where the numbers of stacked
Ti layers 43 and Ni layers 41 are both set to three or more,
migration of Sn does not occur.
TABLE-US-00001 TABLE 1 Number of Ti/Ni layers Barrier properties 1
X 2 X 3 .largecircle. 5 .largecircle. 7 .largecircle.
[0041] That is, the first barrier metal layer 40a preferably
includes three or more Ti layers 43 and three or more Ni layers 41
alternately disposed. Furthermore, the numbers are both preferably
set to seven or less from the viewpoint of reducing manufacturing
costs.
[0042] Ni has the property of easily reacting with Au and Sn.
Therefore, the Ni layer 41 by itself has a limited capability of
retaining the barrier properties to Sn. Hence, a structure in which
the Ti layer 43 and the Ni layer 41 are alternately disposed is
employed. However, the metal combined with the Ni layer 41 is not
limited to Ti, and any metal less likely to react with the first
bonding metal layer 30a may be used.
TABLE-US-00002 TABLE 2 Melting point Linear expansion Material Use
(.degree. C.) coefficient Ti Barrier metal 1660 8.9 .times.
10.sup.-6 Pt Barrier metal 1770 9.0 .times. 10.sup.-6 Ag
p-electrode 961.9 1.91 .times. 10.sup.-5 Ni Barrier metal 1455 1.33
.times. 10.sup.-5 Ta Barrier metal 2990 6.5 .times. 10.sup.-6 W
Barrier metal 3400 4.5 .times. 10.sup.-6
[0043] Table 2 illustrates materials that can be used for the
electrode of the semiconductor light emitting device. Among the
materials shown in the table, Ag has the largest linear expansion
coefficient, and Ni has the second largest linear expansion
coefficient. Ti and Pt have almost the same linear expansion
coefficient. Tantalum (Ta) and tungsten (W) having high melting
points have small & linear expansion coefficients than Ti and
Pt.
[0044] Ni has an intermediate linear expansion coefficient between
Ag and other high melting point metals, and may constitute the
first barrier metal layer 40a according to the embodiment by being
combined with a high melting point metal shown in the table. That
is, the first barrier metal layer 40a may contain at least one
metal selected from titanium (Ti), platinum (Pt), tantalum (Ta),
and tungsten (W) as the second layer.
Second Embodiment
[0045] FIG. 6A is a schematic cross-sectional view showing a
semiconductor light emitting device 200 according to a second
embodiment. FIG. 6B is a partial cross-sectional view showing a
reflection electrode 55 and a portion therearound of the
semiconductor light emitting device 200.
[0046] The semiconductor light emitting device 200 includes the
light emitting body 10 and the support substrate 20 supporting the
light emitting body. The bonding layer 30 bonding the light
emitting body 10 and the support substrate 20 together is provided
between the light emitting body 10 and the support substrate 20.
Furthermore, the first barrier metal layer 40a is provided between
the light emitting body 10 and the bonding layer 30. The first
barrier metal layer 40a includes a multiple-layer structure in
which the first layer 41 made of nickel (Ni) and the second layer
43 made of a metal having a smaller linear expansion coefficient
than nickel are alternately disposed.
[0047] The reflection electrode 55 of the embodiment is provided as
a plurality of portions being away from one another between the
light emitting body 10 and the first barrier metal layer 40a. Such
a configuration is advantageous to, for example, the case where the
adhesion strength between the reflection electrode 55 and the
p-type GaN layer 7 is weak. That is, the p-type GaN layer 7 and the
first barrier metal layer 40a are in contact with each other
between the adjacent portions of the reflection electrode 55.
Therefore, when the adhesion strength between the first barrier
metal layer 40a and the p-type GaN layer 7 is higher than that
between the reflection electrode 55 and the p-type GaN layer 7, the
adhesion between the reflection electrode 55 and the p-type GaN
layer 7 is reinforced to improve the barrier properties to Sn.
Thereby, degradation can be suppressed in the reflectance and the
ohmic contact of the reflection electrode 55.
[0048] Furthermore, as shown in FIG. 6B, an end 55a of each portion
may be inclined in the reflection electrode 55. Thereby, step
cutting of the first barrier metal layer 40a can be suppressed at
the end 55a of the portion. That is, migration of Sn via a crack of
the first barrier metal layer 40a can be suppressed. Furthermore,
by eliminating the step of the end 55a, the stress can be relaxed
in the direction of peeling the reflection electrode 55 from the
p-type GaN layer 7. Thereby, degradation can be suppressed in light
emitting efficiency, improving reliability in the semiconductor
light emitting device 200.
[0049] The "nitride semiconductor" referred to herein includes
group III-V compound semiconductors of BxInyAlzGa1-x-y-zN
(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1,
0.ltoreq.x+y+z.ltoreq.1), and also includes mixed crystals
containing a group V element besides N (nitrogen), such as
phosphorus (P) and arsenic (As). Furthermore, the "nitride
semiconductor" also includes those further containing various
elements added to control various material properties such as
conductivity type, and those further containing various unintended
elements.
[0050] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
invention.
* * * * *