U.S. patent application number 14/997198 was filed with the patent office on 2016-05-12 for semiconductor substrate and method of fabricating the same.
The applicant listed for this patent is Seoul Viosys Co., Ltd. Invention is credited to Shiro Sakai.
Application Number | 20160133792 14/997198 |
Document ID | / |
Family ID | 47072538 |
Filed Date | 2016-05-12 |
United States Patent
Application |
20160133792 |
Kind Code |
A1 |
Sakai; Shiro |
May 12, 2016 |
SEMICONDUCTOR SUBSTRATE AND METHOD OF FABRICATING THE SAME
Abstract
A semiconductor substrate includes a substrate including a
plurality of semispherical protrusions disposed at an interval on a
first plane of the substrate, and a first semiconductor layer
disposed on the first plane of the substrate.
Inventors: |
Sakai; Shiro;
(Tokushima-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seoul Viosys Co., Ltd |
Ansan-si |
|
KR |
|
|
Family ID: |
47072538 |
Appl. No.: |
14/997198 |
Filed: |
January 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14114124 |
Oct 25, 2013 |
9299779 |
|
|
PCT/KR2011/005019 |
Jul 8, 2011 |
|
|
|
14997198 |
|
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Current U.S.
Class: |
257/76 ;
257/618 |
Current CPC
Class: |
H01L 21/02458 20130101;
H01L 33/22 20130101; H01L 21/02664 20130101; H01L 33/32 20130101;
H01L 21/0242 20130101; H01L 33/007 20130101; H01L 33/20 20130101;
H01L 21/02647 20130101; H01L 21/02658 20130101; H01L 33/0093
20200501; H01L 21/0243 20130101; H01L 21/02639 20130101; H01L
29/0688 20130101; H01L 21/0254 20130101 |
International
Class: |
H01L 33/32 20060101
H01L033/32; H01L 33/20 20060101 H01L033/20 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2011 |
JP |
2011-100321 |
Jun 3, 2011 |
JP |
10-2011-0053952 |
Claims
1. A semiconductor substrate, comprising: a substrate comprising a
plurality of semispherical protrusions disposed at an interval on a
first plane of the substrate; and a first semiconductor layer
disposed on the first plane of the substrate.
2. The semiconductor substrate of claim 1, wherein the ratio of the
total surface area of the plurality of semispherical protrusions to
the surface area of the first plane is at least one.
3. The semiconductor substrate of claim 2, wherein the
semispherical protrusions have a bottom surface width of 5 .mu.m or
less.
4. The semiconductor substrate of claim 1, wherein the substrate
comprises sapphire and the first semiconductor layer comprises
gallium nitride.
5. The semiconductor substrate of claim 4, further comprising: a
second semiconductor layer disposed on a first surface of the first
semiconductor layer opposite to the first plane of the substrate;
and cavities disposed in portions of the first semiconductor layer
and the second semiconductor layer.
6. The semiconductor substrate of claim 5, wherein the cavities
comprise a width equal to the interval between semispherical
protrusions, respectively, and the cavities are disposed on the
first surface of the first semiconductor layer and between the
semispherical protrusions.
7. The semiconductor substrate of claim 5, wherein the cavities
comprise a plurality of rectangles each comprising a long side
disposed in a first direction, and the cavities are spaced apart
from each other in a second direction orthogonal to the first
direction.
8. The semiconductor substrate of claim 7, wherein the first
direction is a {1-100} direction of the first semiconductor layer
or an equivalent direction to the {1-100} direction.
9. A semiconductor substrate, comprising: a substrate comprising a
plurality of curved concavities disposed at an interval on a first
plane of the substrate; and a first semiconductor layer disposed on
the first plane of the substrate.
10. The semiconductor substrate of claim 9, wherein the curved
concavities have a bottom surface width of 5 .mu.m or less.
11. The semiconductor substrate of claim 9, wherein the substrate
comprises sapphire and the first semiconductor layer comprises
gallium nitride.
12. A semiconductor device, comprising: the first semiconductor
layer lifted-off from the semiconductor substrate of claim 1; a
first compound semiconductor layer disposed on the first
semiconductor layer; an active layer disposed on the first compound
semiconductor layer; and a second compound semiconductor layer
disposed on the active layer.
13. A semiconductor device, comprising: the second semiconductor
layer lifted-off from the semiconductor substrate of claim 5; a
first compound semiconductor layer disposed on the second
semiconductor layer; an active layer disposed on the first compound
semiconductor layer; and a second compound semiconductor layer
disposed on the active layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/114,124, filed on Oct. 25, 2013, which is the National
Stage entry of International Application PCT/KR2011/005019, filed
on Jul. 8, 2011, and claims priority from and the benefit of
Japanese Patent Application No. 2011-100321, filed on Apr. 28,
2011, and Korean Patent Application No. 10-2011-0053952, filed on
Jun. 3, 2011, which are incorporated herein by reference for all
purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field
[0003] The present invention relates to a semiconductor substrate,
a semiconductor device, and a method of fabricating the same. More
particularly, the present invention relates to a process of
lifting-off a gallium nitride layer from a sapphire substrate, a
semiconductor substrate and a semiconductor device fabricated
through the lift-off process, and a method of fabricating the
same.
[0004] 2. Discussion of the Background
[0005] Gallium nitride (GaN) based light emitting diodes (LEDs)
have been used in a wide range of applications including signals, a
backlight unit of a liquid crystal panel, etc.
[0006] Since fabrication of a gallium nitride (GaN) substrate is
very difficult and requires high manufacturing costs, semiconductor
devices such as LEDs or laser diodes are generally fabricated by
growing a GaN layer on a heterogeneous substrate such as sapphire.
One example of crystal growth of GaN is disclosed in
"Polycrystalline GaN for light emitter and field electron emitter
applications" (S. Hasegawa, S. Nishida, T. Yamashita, H. Asahi,
Thin Solid Films 487 (2005), pp. 260-267). In this document, a GaN
crystal is grown on a quartz substrate, a high melting-point metal
substrate of W, Mo, Ta and Nb, and a Si substrate through
plasma-assisted molecular beam epitaxy.
[0007] However, lattice mismatch and different coefficients of
thermal expansion between the GaN layer and the substrate cause
high dislocation density or increases defects, obstructing
improvement of luminous efficiency of an LED. Although mechanical
polishing or laser ablation is performed to strip a GaN bulk
crystal into a GaN substrate, it is very difficult to obtain a GaN
substrate with practical size and good reproducibility. In
addition, since a sapphire substrate has lower thermal conductivity
than the GaN substrate, the sapphire substrate deteriorates heat
dissipation of a semiconductor device. Further, when a thin GaN
layer is formed on the sapphire substrate, it is very difficult to
lift-off the GaN layer from the sapphire substrate.
SUMMARY
[0008] Exemplary embodiments of the invention provide a flat and
thin semiconductor substrate, which is formed on a heterogeneous
substrate to be easily lifted-off from the heterogeneous substrate,
a semiconductor device including the same, and a method of
fabricating the same.
[0009] According to an exemplary embodiment of the present
invention, a semiconductor substrate includes a substrate including
a plurality of semispherical protrusions disposed at an interval on
a first plane of the substrate, and a first semiconductor layer
disposed on the first plane of the substrate.
[0010] According to an exemplary embodiment of the present
invention, a semiconductor substrate includes a substrate including
a plurality of curved concavities disposed at an interval on a
first plane of the substrate, and a first semiconductor layer
disposed on the first plane of the substrate.
[0011] According to the exemplary embodiments, there are provided a
flat and thin semiconductor substrate, which is formed on a
heterogeneous substrate to be easily lifted-off from the
heterogeneous substrate, a semiconductor device including the same,
and a method of fabricating the same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate exemplary
embodiments of the invention, and together with the description
serve to explain the principles of the invention.
[0013] FIG. 1(a) and FIG. 1(b) show a semiconductor substrate 100
according to one exemplary embodiment of the present invention, in
which FIG. 1(a) is a plan view of the semiconductor substrate 100
and FIG. 1(b) is a partially cross-sectional view taken along a
dotted line of FIG. 1(a).
[0014] FIG. 2 is a diagram of a pattern of semispherical
protrusions 11 according to the exemplary embodiment of the present
invention.
[0015] FIG. 3(a), FIG. 3(b), and FIG. 3(c) show sectional views of
a method of fabricating the semiconductor substrate 100 according
to the exemplary embodiment of the present invention.
[0016] FIG. 3(d), FIG. 3(e), and FIG. 3(f) show sectional views of
the method of fabricating the semiconductor substrate 100 according
to the exemplary embodiment of the present invention.
[0017] FIG. 4(a) and FIG. 4(b) show a semiconductor substrate 200
according to another exemplary embodiment of the present invention,
in which FIG. 4(a) is a plan view of the semiconductor substrate
200 and FIG. 4(b) is a sectional view taken along a dotted line of
FIG. 4(a).
[0018] FIG. 5(a), FIG. 5(b), FIG. 5(c), FIG. 5(d), and FIG. 5(e)
show sectional views of a method of fabricating the semiconductor
substrate 200 according to the exemplary embodiment of the present
invention.
[0019] FIG. 5(f), FIG. 5(g), FIG. 5(h), and FIG. 5(i) show
sectional views of the method of fabricating the semiconductor
substrate 200 according to the exemplary embodiment of the present
invention.
[0020] FIG. 6(a) and FIG. 6(b) show a semiconductor substrate 300
according to a further exemplary embodiment of the present
invention, in which FIG. 6(a) is a plan view of the semiconductor
substrate 300 and FIG. 6(b) is a sectional view taken along a
dotted line of FIG. 6(a).
[0021] FIG. 7(a), FIG. 7(b), FIG. 7(c), FIG. 7(d), and FIG. 7(e)
show sectional views of a method of fabricating the semiconductor
substrate 300 according to the exemplary embodiment of the present
invention.
[0022] FIG. 7(f), FIG. 7(g), FIG. 7(h), and FIG. 7(i) show
sectional views of the method of fabricating the semiconductor
substrate 300 according to the exemplary embodiment of the present
invention.
[0023] FIG. 8(a) and FIG. 8(b) show a semiconductor substrate 400
according to still another exemplary embodiment of the present
invention, in which FIG. 8(a) is a plan view of the semiconductor
substrate 400 and FIG. 8(b) is a sectional view taken along a
dotted line of FIG. 8(a).
[0024] FIG. 9(a), FIG. 9(b), and FIG. 9(c) show sectional views of
a method of fabricating the semiconductor substrate 400 according
to the exemplary embodiment of the present invention.
[0025] FIG. 9(d), FIG. 9(e), and FIG. 9(f) show sectional views of
the method of fabricating the semiconductor substrate 400 according
to the exemplary embodiment of the present invention.
[0026] FIG. 10(a) and FIG. 10(b) show a semiconductor substrate 500
according to still another exemplary embodiment of the present
invention, in which FIG. 10(a) is a plan view of the semiconductor
substrate 500 and FIG. 10(b) is a sectional view taken along a
dotted line of FIG. 10(a).
[0027] FIG. 11(a), FIG. 11(b), and FIG. 11(c) show sectional views
of a method of fabricating the semiconductor substrate 500
according to the exemplary embodiment of the present invention.
[0028] FIG. 11(d), FIG. 11(e), and FIG. 11(f) show sectional views
of the method of fabricating the semiconductor substrate 500
according to the exemplary embodiment of the present invention.
[0029] FIG. 12 is a partial sectional view of a semiconductor
device 1000 according to one exemplary embodiment of the present
invention.
[0030] FIG. 13 is a partial sectional view of a semiconductor
device 2000 according to another exemplary embodiment of the
present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0031] The invention is described more fully hereinafter with
reference to the accompanying drawings, in which exemplary
embodiments of the invention are shown. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the exemplary embodiments set forth herein.
Further, like reference numerals denote like elements through the
specification and the accompanying drawings.
[0032] As described above, conventionally, it is difficult to
lift-off a thin semiconductor substrate from a heterogeneous
substrate when the semiconductor substrate is grown on a
heterogeneous substrate. For example, when a GaN layer of about 10
um is formed on a sapphire substrate, it is difficult to lift-off
the GaN layer from the sapphire substrate only through application
of stress. Thus, conventionally, a GaN layer is further formed to a
thickness of about 100 um thereon. The inventors of the present
invention found that, when a GaN layer is formed to a thickness of
about 10 um by metal organic chemical vapor deposition (MOCVD)
using a PSS substrate, which is a sapphire substrate having a
specific pattern, the GaN layer can be lifted-off from the PSS
substrate.
[0033] A first exemplary embodiment of the invention will be
described.
[0034] FIGS. 1(a) and 1(b) show a semiconductor substrate 100
according to a first exemplary embodiment of the present invention.
Here, FIG. 1(a) is a plan view of the semiconductor substrate 100
and FIG. 1(b) is a partially cross-sectional view taken along a
dotted line of FIG. 1(a). The semiconductor substrate 100 includes
a PSS substrate 110 (hereinafter, referred to as a "substrate 110")
and a first semiconductor layer 20. In this embodiment, the
substrate 110 may have a different composition from the first
semiconductor layer 20. Although the first semiconductor layer 20
is illustrated as being formed of GaN in this embodiment, the
invention is not limited thereto and any material may be used for
the first semiconductor layer so long as the material may be
applicable to light emitting devices (LEDs). The c-plane of the
substrate, that is, a first plane 10a of the substrate on which the
first semiconductor layer 20 will be formed, has a plurality of
semispherical protrusions 11 arranged at an interval (i) and each
having a bottom surface width (w). Herein, the interval (i) means
the shortest distance between two semispherical protrusions 11.
[0035] FIG. 2 is a diagram of a pattern of semispherical
protrusions 11 according to one exemplary embodiment of the
invention. When each of the semispherical protrusions 11 has a
circular bottom surface having a radius of w/2, the centers of the
semispherical protrusions 11 are respectively located at vertexes
of an equilateral triangle, each side of which has a length of w+i.
Specifically, in the pattern of semispherical protrusions 11
according to this embodiment, sets of three semispherical
protrusions 11 are repeatedly arranged in a first direction and a
second direction orthogonal to the first direction on the first
plane 10a of the substrate 110.
[0036] On the c-plane of the substrate 110, the first semiconductor
layer 20 is not easily lifted-off from the substrate 110 due to a
high bonding force between the substrate 110 and the first
semiconductor layer 20. However, since curved surfaces of the
semispherical protrusions 11 allow the first semiconductor layer 20
to be simply seated on the substrate 110 with very low bonding
force, the first semiconductor layer 20 can be easily lifted-off
from the substrate 110. Thus, in this embodiment, the semispherical
protrusions 11 are arranged at a predetermined interval (i) on the
c-plane 10a of the substrate 110, thereby allowing the first
semiconductor layer 20 to be easily lifted-off from the substrate
110. Here, for the substrate 110 according to this embodiment, the
ratio of the total surface area of the semispherical protrusions 11
to the area of the c-plane of the substrate 110 may be 1 or more.
The substrate 110 having such a ratio of the total surface area of
the semispherical protrusions 11 to the area of the c-plane of the
substrate 110 allows the first semiconductor layer 20 to be easily
lifted-off from the substrate 110.
[0037] In this embodiment, the area of the c-plane of the substrate
110, the width (w) of the bottom surface of each of the
semispherical protrusions 11, and the interval (i) of the
semispherical protrusions 11 may be arbitrarily set to obtain the
ratio described above. According to this embodiment, the bottom
surface width of each of the semispherical protrusions 11 may be 5
um or less. When the bottom surface width of each of the
semispherical protrusions 11 is set to 5 um or less, the first
semiconductor layer 20 may be easily lifted-off from the substrate
110. Such a pattern of semispherical protrusions 11 may be formed
by etching the substrate, for example, through photolithography.
Photolithography is generally used for formation of a pattern, but
is limited up to a line width of 1 um to ensure good quality of the
pattern. Thus, when forming the pattern of semispherical
protrusions 11 on the substrate 110 according to this embodiment,
the interval (i) of the semispherical protrusions 11 may be set to
1 um or more. For example, on the substrate 110 shown in FIGS. 1(a)
and 1(b), when the interval (i) between two semispherical
protrusions 11 is set to 1 um, the bottom surface width of each of
the semispherical protrusions 11 is set to 3 um in order to have
the ratio described above.
[0038] Next, a method of fabricating the semiconductor substrate
100 according to this embodiment will be described. FIGS. 3(a) to
3(f) show sectional views illustrating the method of fabricating
the semiconductor substrate 100. A matrix 10 is prepared (FIG.
3(a)) and subjected to etching to form a pattern of semispherical
protrusions 11 on the c-plane of the substrate 110 (FIG. 3(b)). As
described above, photolithography may be used when forming the
pattern on the substrate 110 according to this embodiment. On the
substrate 110 according to this embodiment, the semispherical
protrusions 11 are arranged at a predetermined interval (i) on the
c-plane 10a of the substrate 110 such that the ratio of the total
surface area of the semispherical protrusions 11 to the area of the
c-plane of the substrate 110 becomes 1 or more. The arrangement of
this pattern facilitates separation of a first semiconductor layer
20 from the substrate 110 in a lift-off process described
below.
[0039] Then, the first semiconductor layer 20 is formed on an upper
surface (that is, c-plane) of the substrate 110 having the pattern
of semispherical protrusions 11 (FIG. 3(c)). The first
semiconductor layer 20 may be formed by metal organic chemical
vapor deposition (MOCVD). The conditions for forming the first
semiconductor layer 20 may be arbitrarily set depending on the
thickness of a material or layer to be used for the first
semiconductor layer 20. The formation of the first semiconductor
layer 20 is performed until an upper surface of the first
semiconductor layer 20 (second plane opposite the first plane
defined as the c-plane of the substrate 110) becomes flat. For
example, when forming the pattern of semispherical protrusions 11
each having a bottom surface width of 3 um on the substrate 110 to
be arranged at an interval of 1 um, the first semiconductor layer
20 can be flattened by forming the first semiconductor layer 20 to
a thickness of 10 um. As a result, it is possible to manufacture a
semiconductor substrate 100 according to the embodiment.
[0040] The prepared semiconductor substrate 100 allows the
substrate 110 to be easily lifted-off therefrom. Then, a second
substrate 170 is attached to an upper surface of the first
semiconductor layer 20 of the semiconductor substrate 100 via a
bonding layer 180 (FIG. 3(d)). The second substrate 170 may be
formed of, for example, silicon (Si) substrate, silicon carbide
(SiC), or metal. Further, the bonding layer 180 may be formed of,
for example, gallium (Ga), indium (In), aluminum (Al), gold (Au),
an alloy of gold and tin (Sn), or adhesives known in the art.
[0041] Then, the substrate 110 is lifted-off from the semiconductor
substrate 100, to which the second substrate 170 is bonded (FIG.
3(e)). Separation of the first semiconductor layer 20 from the
substrate 110 may be performed by, for example, a laser lift-off
process. In a fabricated semiconductor substrate 101, the first
semiconductor layer 20 has concavities at portions adjoining the
semispherical protrusions 11. When a semiconductor device such as
an LED is manufactured using the semiconductor substrate 101 that
has the first semiconductor layer 20 having such concavities formed
therein, the semiconductor device exhibits about two times higher
light extraction efficiency than semiconductor devices known in the
art.
[0042] Further, in the semiconductor substrate 101, the first
semiconductor layer 20 may be flattened by a polishing process
(FIG. 3(f)). In this embodiment, the first semiconductor layer 20
may be lifted-off from the substrate 110 using mechanical lift-off
instead of laser lift-off. Consequently, it is possible to obtain a
flat and thin semiconductor substrate 105.
[0043] As such, according to this embodiment, the first
semiconductor layer is formed on the substrate having a plurality
of semispherical protrusions arranged at a predetermined interval
on the first plane thereof, so that it is possible to fabricate a
thin and flat semiconductor substrate which can be easily
lifted-off from the substrate.
[0044] Next, a second exemplary embodiment of the invention will be
described.
[0045] In the first exemplary embodiment, the first semiconductor
layer is formed on the substrate having the semispherical
protrusions. In the second exemplary embodiment, a metallic
material layer having a pattern of predetermined shapes is formed
on an upper surface of the first semiconductor layer (on a second
plane opposite the first plane of the substrate 110, that is, the
c-plane of the substrate 110), followed by forming a second
semiconductor layer on the metallic material layer using MOCVD to
form cavities in the first semiconductor layer. In the
semiconductor substrate according to this embodiment, when the
first semiconductor layer is thinly formed to be less than 10 um on
a substrate, it is possible to easily lift-off the first
semiconductor layer from the substrate.
[0046] FIGS. 4(a) and 4(b) show a semiconductor substrate 200
according to the second exemplary embodiment of the invention, in
which FIG. 4(a) is a plan view of the semiconductor substrate 200
and FIG. 4(b) is a sectional view taken along a dotted line of FIG.
4(a). The semiconductor substrate 200 includes a substrate 210, a
first semiconductor layer 220, a second semiconductor layer 240 and
cavities 250. In this embodiment, the substrate 210 may have a
different composition from the first semiconductor layer 220.
Although the first semiconductor layer 220 is illustrated as being
formed of GaN in this embodiment, the invention is not limited
thereto and any material may be used for the first semiconductor
layer so long as the material may be applicable to LEDs. Further,
the second semiconductor layer 240 may have the same or different
composition from the first semiconductor layer 220. As in the
semiconductor substrate 100, the c-plane of the substrate 210 for
the semiconductor substrate 200, that is, the first plane of the
substrate 210 on which the first semiconductor layer 220 will be
formed, has a plurality of semispherical protrusions 21 arranged at
an interval (i) and each having a bottom surface width (w).
[0047] The cavities 250 are formed to surround the semispherical
protrusions 21 of the first semiconductor layer 220 and the second
semiconductor layer 240. In this embodiment, the cavities 250 are
formed at positions corresponding to the interval (i) between two
semispherical protrusions 21. As shown in FIG. 4(a), the cavities
250 are arranged such that the centers of the cavities are
respectively located at vertexes of a hexagonal shape, the center
of which is coincident with the center of the semispherical
protrusion 21 and which is disposed to fill the first plane of the
substrate 210, that is, the c-plane of the substrate 210, like a
cross-section of a honeycomb structure. The other configurations of
the semiconductor substrate 200 are the same as those of the
semiconductor substrate 100, and detailed descriptions thereof will
be omitted herein.
[0048] Next, a method of fabricating the semiconductor substrate
200 according to this embodiment will be described. FIGS. 5(a) to
5(i) show sectional views illustrating the method of fabricating
the semiconductor substrate 200. The processes shown in FIGS. 5(a)
to 5(c) are the same as those of the semiconductor substrate 100,
and detailed descriptions thereof will be omitted herein. A
metallic material layer 230 having a pattern of predetermined
shapes is formed on an upper surface of the first semiconductor
layer 220 (FIG. 5(d)). The metallic material layer 230 is composed
of cylindrical metal islands each having a width (a bottom surface
width thereof), which is the same as the predetermined interval
(i). The metallic material layer 230 may be formed of metal which
reacts with components used for the first semiconductor layer 220.
For example, when the first semiconductor layer 220 is formed of
GaN, tantalum, titanium or chromium may be suitably used for the
metallic material layer 230. The metallic material layer 230 may be
formed using an electron beam (EB) deposition or lift-off process.
Then, in the metallic material layer 230, the cylindrical metal
islands each having a width (the bottom surface width) which is the
same as the predetermined interval (i), are formed at positions
corresponding to the interval between the semispherical protrusions
21 to surround the semispherical protrusions 21. Further, in the
metallic material layer 230, the metal islands are disposed such
that the centers of the metal islands are respectively located at
vertexes of a hexagonal shape.
[0049] Next, a second semiconductor layer 240 is formed. The second
semiconductor layer 240 is formed by MOCVD. The conditions for
forming the second semiconductor layer 240 may be arbitrarily set
depending on the thickness of a material or layer to be used for
the second semiconductor layer 240. When the second semiconductor
layer 240 is formed, the metallic material layer 230 reacts with a
component constituting the first semiconductor layer 220, so that
some of the first semiconductor layer 220 adjoining the bottom
surface of the metallic material layer 230 is decomposed, forming
cavities 250 (FIG. 5(e)). For example, if the first semiconductor
layer 220 is formed of GaN and the metallic material layer 230 is
formed of tantalum, nitrogen in the first semiconductor layer 220
reacts with tantalum to form tantalum nitride (TaN), so that GaN of
the first semiconductor layer 220 is decomposed, whereby the
cavities 250 are formed on part of the first semiconductor layer
220 adjoining the bottom surface of the metallic material layer
230. Here, the second semiconductor layer 240 is formed on an upper
surface of the first semiconductor layer 220 and a lateral surface
of the metallic material layer 230.
[0050] After the cavities 250 are formed, the metallic material
layer 230 is removed. If the metallic material layer 230 is formed
of, for example, Ta, removal of the metallic material layer may be
achieved by etching using hydrogen fluoride (HF). For example,
removal of the metallic material layer may be achieved by immersing
the semiconductor substrate having the cavities 250 in a 50% HF
aqueous solution. For example, the semiconductor substrate may be
immersed in the solution for 25 hours. Although this embodiment is
illustrated as using HF for etching, any solution may be used to
etch the metallic material layer 230 so long as the solution is
capable of dissolving the metallic material layer without
dissolving the first semiconductor layer 220 and the second
semiconductor layer 240. After removing the metallic material layer
230, the second semiconductor layer 240 is further grown to
fabricate the semiconductor substrate 200 according to this
embodiment (FIG. 5(f)).
[0051] The prepared semiconductor substrate 200 allows the
substrate 210 to be easily lifted-off therefrom. Then, a second
substrate 170 is attached to an upper surface of the first
semiconductor layer 220 of the semiconductor substrate 200 via a
bonding layer 180 (FIG. 5(g)). The second substrate 170 and the
bonding layer 180 in this embodiment are the same as those of the
first exemplary embodiment, and detailed descriptions thereof will
be omitted herein. The semiconductor substrate 200 may be easily
lifted-off from the semispherical protrusions 21 and is torn near
the bottom surfaces of the cavities 250, thereby allowing the
substrate 210 to be easily lifted-off therefrom (FIG. 5(h)). To
lift-off the first semiconductor layer 220 and the second
semiconductor layer 240 from the substrate 210, for example, a
laser lift-off process may be used. In a prepared semiconductor
substrate 201, the first semiconductor layer 220 has concavities at
portions adjoining the semispherical protrusions 21. When a
semiconductor device such as an LED is manufactured using the
semiconductor substrate 201 that has the first semiconductor layer
220 having such concavities formed therein, the semiconductor
device exhibits about two times higher light extraction efficiency
than semiconductor devices known in the art.
[0052] Further, in the semiconductor substrate 201, the first
semiconductor layer 220 may be flattened by a polishing process
(FIG. 5(i)). In this embodiment, the first semiconductor layer 20
may be lifted-off from the substrate 210 using mechanical lift-off
instead of laser lift-off. Consequently, it is possible to obtain a
flat and thin semiconductor substrate 205.
[0053] In this embodiment, when the first semiconductor layer is
formed to a small thickness of less than 10 um, semispherical
protrusions 21 each having a bottom surface width of 1 um are
formed, for example, on the substrate 210 shown in FIG. 4(b). After
the first semiconductor layer 220 is grown to a thickness of 2 um,
a metallic material layer 230 is formed by forming metal islands
each having a width of 1 um on the first semiconductor layer 220,
and a second semiconductor layer 240 is grown to a thickness of 3
um thereon, thereby forming a semiconductor substrate 200 having a
flat surface.
[0054] As described above, according to this embodiment, the first
semiconductor layer is formed on the substrate having a plurality
of semispherical protrusions arranged at a predetermined interval
on the first plane, the metallic material layer having a pattern of
predetermined shapes is formed on the second plane of the first
semiconductor layer, and the second semiconductor layer is formed
on the second plane, so that the cavities are formed in the first
semiconductor layer adjoining the metallic material layer. As a
result, it is possible to provide a flat and thin semiconductor
substrate which can be easily lifted-off from the substrate through
the semispherical protrusions formed on the substrate and the
cavities formed in the first semiconductor layer. According to this
embodiment, when the first semiconductor layer is thinly formed to
a thickness of less than 10 um, the first semiconductor layer can
be easily lifted-off from the substrate.
[0055] Next, a third exemplary embodiment of the invention will be
described.
[0056] In the second exemplary embodiment, the cavities are formed
by positioning the cylindrical metal islands at positions
corresponding to the interval between the semispherical protrusions
to surround the semispherical protrusions. In the third exemplary
embodiment, a metallic material layer is formed in a pattern of
predetermined shapes that is composed of a plurality of rectangles
each having a long side disposed in a first direction and arranged
in a second direction orthogonal to the first direction. In the
semiconductor substrate according to this embodiment, when a first
semiconductor layer is thinly formed to be less than 10 um on a
substrate, it is possible to easily lift-off the first
semiconductor layer from the substrate.
[0057] FIGS. 6(a) and 6(b) show a semiconductor substrate 300
according to the third exemplary embodiment of the invention. Here,
FIG. 6(a) is a plan view of the semiconductor substrate 300 and
FIG. 6(b) is a sectional view taken along a dotted line of FIG.
6(a). The semiconductor substrate 300 includes a substrate 210, a
first semiconductor layer 320, a second semiconductor layer 340,
and cavities 350. In this embodiment, the substrate 210 may have a
different composition from the first semiconductor layer 320.
Although the first semiconductor layer 320 is illustrated as being
formed of GaN in this embodiment, the invention is not limited
thereto and any material may be used for the first semiconductor
layer so long as the material is applicable to LEDs. Further, the
second semiconductor layer 340 has the same or different
composition from the first semiconductor layer 320. As in the
semiconductor substrate 100, the c-plane of the substrate 210 for
the semiconductor substrate 300, that is, a first plane of the
substrate 210 on which the first semiconductor layer 320 will be
formed, has a plurality of semispherical protrusions 21 arranged at
an interval (i) and each having a bottom surface width (w).
[0058] The first semiconductor layer 320 and the second
semiconductor layer 340 have a plurality of cavities 350, which
have a rectangular shape with a long side disposed in a first
direction and are arranged in a second direction orthogonal to the
first direction. The other configurations of the semiconductor
substrate 300 are the same as those of the semiconductor substrate
100 or 200, and detailed descriptions thereof will be omitted
herein.
[0059] Next, a method of fabricating the semiconductor substrate
300 according to this embodiment will be described. FIGS. 7(a) to
7(i) show sectional views illustrating the method of fabricating
the semiconductor substrate 300. The processes shown in FIGS. 7(a)
to 7(c) are the same as those of the semiconductor substrate 100,
and detailed descriptions thereof will be omitted herein. A
metallic material layer 330 having a pattern of predetermined
shapes is formed on an upper surface of the first semiconductor
layer 320 (FIG. 7(d)). The metallic material layer 330 may be
formed using an electron beam (EB) deposition or lift-off process.
In this embodiment, the metallic material layer 330 is formed by
placing a plurality of rectangular metal stripes each having a long
side disposed in a {1-100} direction of the first semiconductor
layer 320 or in an equivalent direction to the {1-100} direction on
the first semiconductor layer 320 to be arranged in a direction
orthogonal to the {1-100} direction or to the equivalent direction
to the {1-100} direction or to be arranged in an equivalent
direction to this direction. For example, when forming a pattern of
semispherical protrusions 21 arranged at an interval (i) of 1 um,
and a bottom surface width (w) of 3 um on the substrate 210,
rectangular metal stripes having a thickness of about 50 um and a
width of 5 um are arranged at an interval of 5 um, thereby forming
the metallic material layer. Here, the metallic material may be
tantalum (Ta). In addition, the thickness of the metallic material
layer 330 may vary depending on the kind of metallic material for
the metallic material layer and may be as high as possible.
[0060] Next, a second semiconductor layer 340 is formed on the
metallic material layer using MOCVD. The conditions for forming the
second semiconductor layer 340 may be arbitrarily set depending on
the thickness of a material or layer to be used for the second
semiconductor layer 340. When the second semiconductor layer 340 is
formed, the metallic material layer 330 reacts with a component
constituting the first semiconductor layer 320, so that some of the
first semiconductor layer 320 adjoining the bottom surface of the
metallic material layer 330 is decomposed, forming cavities 350
(FIG. 7(e)).
[0061] In this embodiment, when the metallic material layer 330 is
formed to have a long side disposed in the {1-100} direction of the
first semiconductor layer 320 or in an equivalent direction to the
{1-100}, reaction between components constituting the first
semiconductor layer 320 and the metallic material layer 330 is
facilitated, and decomposition of portions of the first
semiconductor layer 320 adjoining the bottom surface of the
metallic material layer 330 is also facilitated. This is because a
growth rate in a direction parallel to the substrate is higher than
the growth rate in a second direction of the metallic material
layer 330. Thus, advantageously, the cavities 350 are efficiently
formed in the first semiconductor layer 320. The material for the
metallic material layer 330 in this embodiment is the same as that
for the metallic material layer 230, and a detailed description
thereof will be omitted herein.
[0062] After the cavities 350 are formed, the metallic material
layer 330 is removed. Since removal of the metallic material layer
may be achieved by the same process as in the second embodiment, a
detailed description thereof will be omitted. After removing the
metallic material layer 330, the second semiconductor layer 340 is
further grown to fabricate the semiconductor substrate 200
according to this embodiment (FIG. 7(f)).
[0063] The prepared semiconductor substrate 300 allows the
substrate 210 to be easily lifted-off therefrom. Then, a second
substrate 170 is attached to an upper surface of the second
semiconductor layer 340 of the semiconductor substrate 300 via a
bonding layer 180 (FIG. 7(g)). The second substrate 170 and the
bonding layer 180 are the same as those of the first exemplary
embodiment, and a detailed description thereof will be omitted
herein. The semiconductor substrate 300 may be easily lifted-off
from the semispherical protrusions 21 and is torn near the bottom
surfaces of the cavities 350, thereby allowing the substrate 210 to
be easily lifted-off therefrom (FIG. 7(h)). To lift-off the first
semiconductor layer 320 and the second semiconductor layer 340 from
the substrate 210, for example, a laser lift-off process may be
used. In a prepared semiconductor substrate 301, the first
semiconductor layer 320 has concavities at portions adjoining the
semispherical protrusions 21. When a semiconductor device such as
an LED is manufactured using the semiconductor substrate 301 that
has the first semiconductor layer 320 having such concavities
formed therein, the semiconductor device exhibits about two times
higher light extraction efficiency than semiconductor devices known
in the art.
[0064] Further, in the semiconductor substrate 301, the first
semiconductor layer 320 may be flattened by a mechanical lift-off
process (FIG. 7(i)). In this embodiment, the first semiconductor
layer 220 may be lifted-off from the substrate 210 using mechanical
lift-off instead of laser lift-off. Consequently, it is possible to
obtain a flat and thin semiconductor substrate 305.
[0065] In this embodiment, when the first semiconductor layer is
formed to a small thickness of less than 10 um, semispherical
protrusions 21 each having a bottom surface width of 1 um are
formed, for example, on the substrate 210 shown in FIG. 6(b). After
the first semiconductor layer 320 is grown to a thickness of 2 um,
a metallic material layer 330 is formed by placing a plurality of
rectangular metal stripes each having a long side disposed in a
{1-100} direction of the first semiconductor layer or in an
equivalent direction to the {1-100} direction to be arranged in a
second direction orthogonal to the first direction, and a second
semiconductor layer is formed on a second plane, so that the
cavities are formed at portions of the first semiconductor layer
adjoining the metallic material layer. As a result, it is possible
to provide a flat and thin semiconductor substrate which can be
easily lifted-off from the substrate through the semispherical
protrusions formed on the substrate and the cavities formed in the
first semiconductor layer. According to this embodiment, when the
first semiconductor layer is thinly formed to a thickness less than
10 um, the first semiconductor layer can be easily lifted-off from
the substrate.
[0066] Next, a fourth exemplary embodiment of the invention will be
described.
[0067] In the first to third exemplary embodiment, the first
semiconductor layer is formed on the substrate having the
semispherical protrusions. In the fourth exemplary embodiment, the
first semiconductor layer is formed on a substrate having a
plurality of curved concavities arranged at a predetermined
interval on a first plane of the substrate.
[0068] FIGS. 8(a) and 8(b) show a semiconductor substrate 400
according to the fourth exemplary embodiment of the invention. FIG.
8(a) is a plan view of the semiconductor substrate 400 and FIG.
8(b) is a sectional view taken along a dotted line of FIG. 8(a).
The semiconductor substrate 400 includes a PSS substrate 410
(hereinafter, referred to as a "substrate 410") and a first
semiconductor layer 420. In this embodiment, the substrate 410 may
have a different composition from the first semiconductor layer
420. Although the first semiconductor layer 420 is illustrated as
being formed of GaN in this embodiment, the invention is not
limited thereto and any material may be used for the first
semiconductor layer so long as the material is applicable to LEDs.
The c-plane of the substrate 410, that is, the first plane 10a of
the substrate 410 on which the first semiconductor layer 420 will
be formed, has a plurality of curved concavities 460 arranged at a
predetermined interval (i). Herein, the interval (i) means the
shortest distance between two curved concavities 460. In this
embodiment, as the pattern of curved concavities is formed at a
predetermined interval on the c-plane of the substrate 410, that
is, on the first plane of the substrate, the first semiconductor
layer 420 may be easily lifted-off from the substrate 410.
[0069] On the c-plane of the substrate 410, the first semiconductor
layer 420 is not easily lifted-off from the substrate 410 due to a
high bonding force between the substrate 410 and the first
semiconductor layer 420. However, since the curved concavities 460
allow the first semiconductor layer 420 to be simply seated on the
substrate 410 with very low bonding force, the first semiconductor
layer 420 can be easily lifted-off from the substrate 410. Thus, in
this embodiment, the curved concavities 460 are arranged at a
predetermined interval (i) on the c-plane 10a of the substrate 410,
thereby allowing the first semiconductor layer 420 to be easily
lifted-off from the substrate 410. Although the curved concavities
460 are illustrated as having a semispherical shape in FIG. 8(b),
it is necessary for the curved concavities 460 to have a flat
bottom surface. Further, the curved concavities 460 may have any
suitable shape. For example, the curved concavities 460 may have a
mortar shape or a conical shape.
[0070] For example, if the curved concavities 460 are semispherical
concavities as shown in FIGS. 8(a) and 8(b), the ratio of the total
surface area of the curved concavities 460 to the area of the
c-plane of the substrate 410 may be 1 or more. The substrate 40
having such a ratio of the total surface area of the curved
concavities 460 to the area of the c-plane of the substrate 410
allows the first semiconductor layer 420 to be easily lifted-off
from the substrate 410. When each of the curved concavities 460 has
a circular bottom surface having a radius of w/2, the centers of
the curved concavities 460 are respectively located at vertexes of
an equilateral triangle, each side of which has a length of w+i.
Specifically, in the pattern of curved concavities 460 according to
this embodiment, sets of three curved concavities 460 are
repeatedly arranged in a first direction and a second direction
orthogonal to the first direction on the first plane 10a of the
substrate 410.
[0071] In this embodiment, the area of the c-plane of the substrate
410, the width (w) of the bottom surface of each of the curved
concavities 460, and the interval (i) of the curved concavities 460
may be arbitrarily set to obtain the ratio described above.
[0072] According to this embodiment, the bottom surface width of
each of the curved concavities 460 may be 5 um or less. When the
bottom surface width of each of the curved concavities 460 is set
to 5 um or less, the first semiconductor layer 420 may be easily
lifted-off from the substrate 410. Such a pattern of curved
concavities 460 may be formed by etching a matrix 10, for example,
through photolithography. Photolithography is generally used for
formation of a pattern, but is limited up to a line width of 1 um
to ensure good pattern quality. Thus, when forming the pattern of
curved concavities 460 according to this embodiment on the
substrate 410, the interval (i) of the curved concavities 460 may
be set to 1 um or more. For example, on the substrate 410 shown in
FIG. 8(b), when the interval (i) between two curved concavities 460
is set to 1 um, the bottom surface width of each of the curved
concavities 460 is set to 3 um in order to obtain the ratio
described above.
[0073] Next, a method of fabricating the semiconductor substrate
400 according to this embodiment will be described. FIGS. 9(a) to
9(f) show sectional views illustrating the method of fabricating
the semiconductor substrate 400. A matrix 10 is prepared (FIG.
9(a)) and subjected to etching to form a pattern of curved
concavities 460 on the c-plane of the substrate 410 (FIG. 9(b)). As
described above, photolithography may be used when forming the
pattern on the substrate 410 according to this embodiment. On the
substrate 410 according to this embodiment, the curved concavities
460 are arranged at a predetermined interval (i) on the c-plane 10a
of the substrate 410 such that the ratio of the total surface area
of the curved concavities 460 to the area of the c-plane of the
substrate 410 becomes 1 or more. The arrangement of this pattern
facilitates separation of a first semiconductor layer 420 from the
substrate 410 in a lift-off process described below.
[0074] Then, the first semiconductor layer 420 is formed on an
upper surface (that is, c-plane) of the substrate 410 having the
pattern of curved concavities 460 (FIG. 9(c)). The first
semiconductor layer 420 may be formed by MOCVD. The conditions for
forming the first semiconductor layer 420 may be arbitrarily set
depending on the thickness of a material or layer to be used for
the first semiconductor layer 420. The formation of the first
semiconductor layer 420 is performed until an upper surface of the
first semiconductor layer 420 (second plane opposite the first
plane defined as the c-plane of the substrate 410) becomes flat.
For example, when forming the pattern of curved concavities 460
each having a bottom surface width of 3 um on the substrate 410 to
be arranged at an interval of 1 um, the first semiconductor layer
420 can be flattened by forming the first semiconductor layer 20 to
a thickness of 410 um. As a result, it is possible to manufacture a
semiconductor substrate 400 according to the embodiment.
[0075] The prepared semiconductor substrate 400 allows the
substrate 410 to be easily lifted-off therefrom. Then, a second
substrate 170 is attached to an upper surface of the first
semiconductor layer 420 of the semiconductor substrate 400 via a
bonding layer 180 (FIG. 9(d)). The second substrate 170 and the
bonding layer 180 in this embodiment are the same as those of the
first exemplary embodiment, and detailed descriptions thereof will
be omitted herein. The prepared semiconductor substrate 400 allows
the substrate 410 to be easily lifted-off therefrom (FIG. 9(e)).
Separation of the first semiconductor layer 420 from the substrate
410 may be performed by, for example, a laser lift-off process. In
a fabricated semiconductor substrate 401, the first semiconductor
layer 420 has protrusions at portions adjoining the curved
concavities 460. When a semiconductor device such as an LED is
manufactured using the semiconductor substrate 401 that has the
first semiconductor layer 420 having such protrusions formed
thereon, the semiconductor device exhibits about two times higher
light extraction efficiency than semiconductor devices known in the
art.
[0076] Further, the semiconductor substrate 401 may be flattened by
a polishing process (FIG. 9(f)). In this embodiment, the first
semiconductor layer 420 may be lifted-off from the substrate 410
using mechanical lift-off instead of laser lift-off. Consequently,
it is possible to obtain a flat and thin semiconductor substrate
405.
[0077] As such, according to the present embodiment, the first
semiconductor layer is formed on the substrate having a plurality
of curved concavities arranged at a predetermined interval on the
first plane thereof, so that it is possible to fabricate a thin and
flat semiconductor substrate which can be easily lifted-off from
the substrate.
[0078] Next, a fifth exemplary embodiment of the invention will be
described.
[0079] In the fourth exemplary embodiment, the first semiconductor
layer is formed on the substrate having a plurality of curved
concavities. On the contrary, in the fifth embodiment of the
invention, the first semiconductor layer is formed on a substrate
having a plurality of troughs arranged at a predetermined interval
on a first plane of the substrate.
[0080] FIGS. 10(a) and 10(b) show a semiconductor substrate 500
according to the fifth exemplary embodiment of the invention. FIG.
10(a) is a plan view of the semiconductor substrate 500 and FIG.
10(b) is a sectional view taken along a dotted line of FIG. 10(a).
The semiconductor substrate 500 includes a PSS substrate 510
(hereinafter, referred to as a "substrate 510") and a first
semiconductor layer 520. In this embodiment, the substrate 510 may
have a different composition from the first semiconductor layer
520. Although the first semiconductor layer 520 is illustrated as
being formed of GaN in this embodiment, the invention is not
limited thereto and any material may be used for the first
semiconductor layer so long as the material may be applicable to
LEDs. The c-plane of the substrate 510, that is, the first plane
10a of the substrate 510 on which the first semiconductor layer 520
will be formed, has a plurality of troughs 560 arranged at a
predetermined interval (i). In this embodiment, as the pattern of
troughs is formed at a predetermined interval on the c-plane of the
substrate 510, that is, on the first plane of the substrate 510,
the first semiconductor layer 520 may be easily lifted-off from the
substrate 510.
[0081] In this embodiment, the troughs 560 are formed to have a
sufficiently narrow width (w) to prevent the first semiconductor
layer 520 from being grown on the bottom surfaces (that is,
c-plane) of the troughs 560. Further, as shown in FIG. 10(b),
according to this embodiment, cavities 555 are formed at upper
portions of the troughs 560 to extend towards a second plane
opposite the first plane of the first semiconductor layer 520
adjoining the c-plane of the substrate 510. The extended portion of
the cavity 520 is formed by gradually growing the first
semiconductor layer, which is grown on the c-plane of the substrate
510, in a direction parallel to the c-plane.
[0082] According to this embodiment, the bottom surface width (w)
of each of the troughs 560 may be 5 um or less. When the bottom
surface width (w) of the trough 560 is set to 5 um or less, the
troughs 560 prevent the first semiconductor layer 520 from growing
on the bottom surfaces thereof while allowing the cavities to be
grown thereon, thereby facilitating separation of the first
semiconductor layer 520 from the substrate 510. If the bottom
surface width (w) of the troughs 560 is greater than 5 um, the
first semiconductor layer 520 is grown on the bottom surfaces of
the troughs 560, making it difficult to lift-off the first
semiconductor layer 520 from the substrate 510. Further, such a
pattern of troughs 560 may be formed by etching the matrix 10, for
example, through photolithography. Photolithography is generally
used for formation of a pattern, but is limited up to a line width
of 1 um to ensure good pattern quality. Thus, when forming the
pattern of troughs 560 according to this embodiment on the
substrate 510, the width (w) of the troughs 560 may be set to 1 um
or more.
[0083] Next, a method of fabricating the semiconductor substrate
500 according to this embodiment will be described. FIGS. 11(a) to
11(f) show sectional views illustrating the method of fabricating
the semiconductor substrate 500. A matrix 10 is prepared (FIG.
11(a)) and subjected to etching to form a pattern of troughs 560 on
the c-plane of the substrate 510 (FIG. 11(b)). As described above,
photolithography may be used when forming the pattern on the
substrate 510 according to this embodiment. According to this
embodiment, the troughs 560 may have a width (w) of 5 um or less.
When MOCVD is performed at 500 Torr or more, the width (w) of the
troughs may be set to 2 um or less. The arrangement of this pattern
facilitates separation of a first semiconductor layer 520 from the
substrate 510 in a lift-off process described below.
[0084] Then, the first semiconductor layer 520 is formed on an
upper surface (that is, c-plane) of the substrate 510 having the
pattern of troughs 560 (FIG. 11(c)). The first semiconductor layer
520 may be formed by MOCVD. The conditions for forming the first
semiconductor layer 520 may be arbitrarily set depending on the
thickness of a material or layer to be used for the first
semiconductor layer 520. The formation of the first semiconductor
layer 520 is performed until an upper surface of the first
semiconductor layer 520 (second plane opposite the first plane
defined as the c-plane of the substrate 510) becomes flat. As a
result, it is possible to manufacture a semiconductor substrate 500
according to the embodiment.
[0085] The prepared semiconductor substrate 500 allows the
substrate 510 to be easily lifted-off therefrom. Then, a second
substrate 170 is attached to an upper surface of the first
semiconductor layer 520 of the semiconductor substrate 500 via a
bonding layer 180 (FIG. 11(d)). The second substrate 170 and the
bonding layer 180 in this embodiment are the same as those of the
first exemplary embodiment, and detailed descriptions thereof will
be omitted herein. The prepared semiconductor substrate 500 allows
the substrate 510 to be easily lifted-off therefrom (FIG. 11(e)).
Separation of the first semiconductor layer 520 from the substrate
510 may be performed by, for example, a laser lift-off process. In
a fabricated semiconductor substrate 501, the first semiconductor
layer 520 has concavities at portions adjoining the troughs 560.
When a semiconductor device such as an LED is manufactured using
the semiconductor substrate 501 that has the first semiconductor
layer 420 having such concavities formed therein, the semiconductor
device exhibits about two times higher light extraction efficiency
than semiconductor devices known in the art.
[0086] Further, the semiconductor substrate 501 may be flattened by
a polishing process (FIG. 11(f)). In this embodiment, the first
semiconductor layer 520 may be lifted-off from the substrate 510
using mechanical lift-off instead of laser lift-off. Consequently,
it is possible to obtain a flat and thin semiconductor substrate
505.
[0087] As such, according to the present embodiment, the first
semiconductor layer is formed on the substrate having a plurality
of troughs 560 having a predetermined width on the first plane
thereof, so that it is possible to fabricate a thin and flat
semiconductor substrate which can be easily lifted-off from the
substrate.
[0088] Next, a semiconductor device according one exemplary
embodiment of the invention will be described.
[0089] A semiconductor device, such as an LED, may be fabricated
using one of the semiconductor substrates 100 to 500 according to
the embodiments of the invention described above. Herein, a
semiconductor device 1000 fabricated using the semiconductor
substrate 105 will be described as one example. FIG. 12 is a
sectional view of the semiconductor device 1000 according to one
exemplary embodiment of the invention. The semiconductor device
1000 includes an ohmic contact layer 1110 on a surface of the first
semiconductor layer 20 of the semiconductor substrate 105 and an
ohmic contact layer 1130 on a surface of a second substrate.
[0090] The ohmic contact layer 1110 may be formed by stacking, for
example, a 10 nm Ti layer, a 10 nm Al layer, and a 10 um Al layer.
Further, the ohmic contact layer 1130 may be formed by stacking,
for example, a 50 nm Au layer and a 50 nm Sb layer when the second
substrate 170 is a Si substrate. A bonding layer 180 may be, for
example, a 3 um Au layer. Here, although not shown in the drawings,
an ohmic contact layer composed of a 10 nm Au layer and a 10 nm
nickel layer is formed between the first semiconductor layer 20 and
the bonding layer 180. An N-type semiconductor is provided to the
ohmic contact layer 1110 side of the first semiconductor layer 20,
and a P-type semiconductor is provided to the bonding layer 180
side of the first semiconductor layer 20.
[0091] Further, an active layer may be located between the N-type
semiconductor and the P-type semiconductor. The N-type
semiconductor, the active layer and the P-type semiconductor may be
formed before attaching the second substrate.
[0092] As such, when fabricating the semiconductor device 1000
using the semiconductor substrate 105, it is possible to reduce
manufacturing costs of the LED. Further, although the semiconductor
device 1000 is illustrated as being formed on the semiconductor
substrate 105 prepared from the semiconductor substrate 100 in this
embodiment, the semiconductor device 1000 may be suitably formed
using any one selected from the semiconductor substrates
200.about.500, a substrate lifted-off therefrom, a flattened
substrate, and the like.
[0093] On the other hand, it is possible to fabricate the
semiconductor device using the first semiconductor layer as a
growth substrate after lifting-off the first semiconductor layer 20
or the second semiconductor layer 240 from the semiconductor
substrate.
[0094] FIG. 13 is a sectional view of a semiconductor device 2000
according to another exemplary embodiment of the invention. The
first semiconductor layer 20 is a semiconductor layer lifted-off
from the semiconductor substrate 100. The semiconductor device 2000
includes a first compound semiconductor layer 930, an active layer
950 and a second compound semiconductor layer 970 on an upper
surface of the first semiconductor layer 20. One ohmic contact
layer is formed under the first semiconductor layer 20, and another
ohmic contact layer is formed on the second compound semiconductor
layer 970. Here, the first compound semiconductor layer 930 and the
first semiconductor layer 20 may be the same conductive type
semiconductor layers.
[0095] The semiconductor device 2000 may be fabricated by lifting
off the first semiconductor layer 20 from the semiconductor
substrate 100 and sequentially forming the first compound
semiconductor layer 930, the active layer 950, and the second
compound semiconductor layer 970 on the first semiconductor layer
20.
[0096] Here, although the semiconductor device 2000 of this
embodiment is illustrated as being formed by sequentially forming
the first compound semiconductor layer, the active layer and second
compound semiconductor layer on the first semiconductor layer 20
lifted-off from the semiconductor substrate 100, the semiconductor
device 2000 may be formed by sequentially forming the first
compound semiconductor layer, the active layer and the second
compound semiconductor layer on the first semiconductor layer 420
or 520, which is lifted-off from the semiconductor substrate 400 or
500. Alternatively, the semiconductor device 2000 may be formed by
sequentially forming the first compound semiconductor layer, the
active layer and the second compound semiconductor layer on the
second semiconductor layer 240 or 340, which is lifted-off from the
semiconductor substrate 200 or 300.
[0097] Although the invention has been illustrated with reference
to some exemplary embodiments in conjunction with the drawings, it
will be apparent to those skilled in the art that various
modifications and changes can be made to the invention without
departing from the spirit and scope of the invention. Therefore, it
should be understood that the exemplary embodiments are provided by
way of illustration only and are given to provide complete
disclosure of the invention and to provide thorough understanding
of the invention to those skilled in the art. Thus, it is intended
that the invention covers the modifications and variations provided
they fall within the scope of the appended claims and their
equivalents.
* * * * *