U.S. patent application number 11/054409 was filed with the patent office on 2005-07-07 for semiconductor light-emitting element and method of manufacturing the same.
Invention is credited to Akaike, Yasuhiko, Asakawa, Koji, Egashira, Katsumi, Fujimoto, Akira, Ohashi, Kenichi, Sugiyama, Hitoshi, Washizuka, Shoichi, Yamashita, Atsuko, Yoshitake, Shunji.
Application Number | 20050145864 11/054409 |
Document ID | / |
Family ID | 19191603 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145864 |
Kind Code |
A1 |
Sugiyama, Hitoshi ; et
al. |
July 7, 2005 |
Semiconductor light-emitting element and method of manufacturing
the same
Abstract
There is disclosed a semiconductor light-emitting element
comprising a substrate having a first surface and a second surface,
a semiconductor laminate formed on the first surface of the
substrate and containing a light-emitting layer and a current
diffusion layer having a light-extracting surface. The
light-emitting element is provided with a light-extracting surface
which is constituted by a finely recessed/projected surface, 90% of
which is constructed such that the height of the projected portion
thereof having a cone-like configuration is 100 nm or more, and the
width of the base of the projected portion is within the range of
10-500 nm.
Inventors: |
Sugiyama, Hitoshi;
(Ashigarashimo-gun, JP) ; Ohashi, Kenichi;
(Kawasaki-shi, JP) ; Yamashita, Atsuko;
(Yokosuka-shi, JP) ; Washizuka, Shoichi;
(Yokohama-shi, JP) ; Akaike, Yasuhiko;
(Kawasaki-shi, JP) ; Yoshitake, Shunji;
(Kawasaki-shi, JP) ; Asakawa, Koji; (Kawasaki-shi,
JP) ; Egashira, Katsumi; (Kitakyushu-shi, JP)
; Fujimoto, Akira; (Kawasaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
19191603 |
Appl. No.: |
11/054409 |
Filed: |
February 10, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11054409 |
Feb 10, 2005 |
|
|
|
10346108 |
Jan 17, 2003 |
|
|
|
Current U.S.
Class: |
257/95 ;
257/E33.074; 438/29 |
Current CPC
Class: |
H01L 33/22 20130101 |
Class at
Publication: |
257/095 ;
438/029 |
International
Class: |
H01L 033/00; H01L
021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2002 |
JP |
2002-010571 |
Claims
1. A semiconductor light-emitting element comprising: a substrate
having a first surface and a second surface; and a semiconductor
laminate formed on said first surface of said substrate and
containing a light-emitting layer; wherein said light-emitting
element is provided with a light-extracting surface which is
constituted by a finely recessed/projected surface, at least 90% of
which is constructed such that the height of the projected portion
thereof having a cone-like configuration is 100 nm or more, and the
width of the base of the projected portion is within the range of
10-500 nm.
2. The semiconductor light-emitting element according to claim 1,
wherein said light-extracting surface is constituted by said second
surface of substrate.
3. The semiconductor light-emitting element according to claim 2,
wherein said substrate is formed of a transparent substrate.
4. The semiconductor light-emitting element according to claim 1,
wherein said light-extracting surface is constituted by an
outermost surface of said semiconductor laminate.
5. The semiconductor light-emitting element according to claim 1,
wherein at least one of said projected portions is formed of a
cone-shaped configuration having an apex angle ranging from 20 to
80 degrees.
6. The semiconductor light-emitting element according to claim 1,
wherein at least one of said projected portions is provided, at the
apex thereof, with a very small transparent portion constituted by
a material which differs in kind from the material of said
light-extracting surface.
7. The semiconductor light-emitting element according to claim 1,
wherein at least one of said projected portions is provided with a
flat apex.
8. The semiconductor light-emitting element according to claim 1,
wherein at least one of said projected portions is provided with a
flat apex, on which a very small transparent portion is disposed,
said very small transparent portion being formed of a material
differing in kind from the material of said light-extracting
surface.
9. The semiconductor light-emitting element according to claim 2,
wherein said substrate is provided, on said second surface, with a
transparent oxide film or a transparent nitride film, and said
finely recessed/projected portions are constituted by a surface of
said transparent oxide film or of said transparent nitride
film.
10. The semiconductor light-emitting element according to claim 4,
wherein said semiconductor laminate comprises a current diffusion
layer is disposed at the uppermost layer of said semiconductor
laminate, and said finely recessed/projected portions exists on an
exposed surface of said current diffusion layer.
11. The semiconductor light-emitting element according to claim 10,
wherein said current diffusion layer is provided, on the exposed
surface thereof, with a transparent oxide film or a transparent
nitride film, and said finely recessed/projected portions are
formed on a surface of said transparent oxide film or of said
transparent nitride film.
12-23. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No.
2002-010571, filed Jan. 18, 2002, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a semiconductor
light-emitting element such as a light-emitting diode (LED), a
semiconductor laser (LD), etc., and to a method of manufacturing
the semiconductor light-emitting element.
[0004] 2. Description of the Related Art
[0005] A light-emitting diode of high luminance is conventionally
constructed such that a light-emitting portion constituted by a
double-hetero structure, etc., is disposed on the surface of a
semiconductor substrate, and a current diffusion layer is deposited
on the light-emitting portion. As this light-emitting diode is
packaged by resin, the upper portion of the current diffusion layer
is covered with a transparent resin layer to protect the
light-emitting element.
[0006] In the light-emitting diode constructed in this manner, the
critical angle between the current diffusion layer (refractive
index 3.1-3.5) and the layer of the transparent resin (refractive
index about 1.5) is within the range of 25 to 29 degrees. Light
having a larger incidence angle than this critical angle is totally
reflected, thus greatly degrading the probability of the light
being emitted from the light-emitting element. Therefore, the
extraction efficiency of the light that can be actually generated
from the light-emitting diode is as low as 20% or so at
present.
[0007] Incidentally, as for the method of roughening the surface of
the current diffusion layer, there is known a technique of treating
the surface of the current diffusion layer with hydrochloric acid,
sulfuric acid, hydrogen peroxide or a mixed solution comprising
these chemicals, thereby obtaining a surface-roughened chip
(Japanese Patent Unexamined Publication (Kokai) 2000-299494 and
Japanese Patent Unexamined Publication (Kokai) H4-354382). These
methods are however accompanied by the problem that due to the
influence of the crystallinity of the substrate, the roughening of
the surface of the current diffusion layer may become impossible
depending on the orientation of the surface being exposed.
Therefore, roughening of the surface of the chip may not
necessarily be possible, so that, the extraction efficiency of the
light is prevented from being improved, thus making it difficult to
enhance the luminance of the light-emitting diode.
[0008] As described above, the conventional light-emitting diode
packaged by resin is accompanied by the problem that the incident
light to be entered obliquely into the interface between the
uppermost layer of the semiconductor multi-layer including a
light-emitting layer and a transparent resin is totally reflect
from the interface, thus degrading the light extraction efficiency
of the light. Further, this problem is not limited to a
light-emitting diode, but is also applicable to a surface-emitting
type semiconductor laser.
BRIEF SUMMARY OF THE INVENTION
[0009] A semiconductor light-emitting element according to one
embodiment of the present invention comprises:
[0010] a substrate having a first surface and a second surface;
and
[0011] a semiconductor laminate formed on the first surface of the
substrate and containing a light-emitting layer and a current
diffusion layer;
[0012] wherein the light-emitting element is provided with a
light-extracting surface which is constituted by a finely
recessed/projected surface, 90% of which is constructed such that
the height of the projected portion thereof having a cone-like
configuration is 100 nm or more, and the width of the base of the
projected portion is within the range of 10-500 nm.
[0013] A method of manufacturing a semiconductor light-emitting
element according to one embodiment of the present invention
comprises:
[0014] forming a semiconductor laminate on a first surface of a
substrate having a first surface and a second surface, the
semiconductor laminate containing a light-emitting layer and a
current diffusion layer;
[0015] determining a light-extracting surface for extracting light
from the light-emitting layer;
[0016] forming a polymer film comprising a diblock copolymer on the
light-extracting surface;
[0017] subjecting the polymer film to an annealing treatment,
thereby phase-separating the diblock copolymer into two phases;
[0018] eliminating one of the phases of the diblock copolymer that
has been phase-separated to form a mask material layer having a
pattern constituted by the other phase; and
[0019] transferring the pattern of the mask material layer to the
light-extracting surface to form finely recessed/projected portions
on the light-extracting surface.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0020] FIG. 1 is a cross-sectional view illustrating the element
structure of an LED according to one embodiment of the present
invention;
[0021] FIGS. 2A to 2D are cross-sectional views each illustrating
the state of finely recessed/projected portions according to one
embodiment of the present invention;
[0022] FIGS. 3A to 3D are cross-sectional views each illustrating,
stepwise, the manufacturing steps of an LED according to one
embodiment of the present invention;
[0023] FIGS. 4A to 4D are cross-sectional views each illustrating,
stepwise, the manufacturing steps of an LED according to another
embodiment of the present invention;
[0024] FIGS. 5A and 5B are cross-sectional views each illustrating
the element structure of an LED according to a further embodiment
of the present invention;
[0025] FIGS. 6A and 6B are cross-sectional views each illustrating
the element structure of an LED according to a further embodiment
of the present invention;
[0026] FIG. 7 is a cross-sectional view illustrating the element
structure of an LED according to a further embodiment of the
present invention;
[0027] FIGS. 8A to 8C are cross-sectional views each illustrating,
stepwise, the manufacturing steps of an LED according to a further
embodiment of the present invention;
[0028] FIGS. 9A to 9C are cross-sectional views each illustrating,
stepwise, the manufacturing steps of an LED according to a further
embodiment of the present invention;
[0029] FIG. 10 is a microphotograph illustrating the features of
the recessed/projected surface according to one embodiment of the
present invention; and
[0030] FIGS. 11A to 11C are cross-sectional views each
illustrating, stepwise, the manufacturing steps of an LED according
to a further embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Next, the embodiments of the present invention will be
explained in detail with reference to drawings.
First Embodiment
[0032] FIG. 1 is a cross-sectional view illustrating the element
structure of an LED according to a first embodiment of the present
invention.
[0033] As shown in FIG. 1, on the top surface (the first surface)
of an n-type GaP substrate 10 are deposited semiconductor laminated
layers comprising a hetero structure portion 14 which is
constituted by an n-type InAlP clad layer 11, an InGaAlP activated
layer 12 and a p-type InAlP clad layer 13; and a p-type GaP current
diffusion layer 15. A p-side electrode (upper electrode) 16 is
formed on part of the surface of the current diffusion layer 15
with the remaining portion of the surface of the current diffusion
layer 15 being left exposed. On the other hand, an n-side electrode
(lower electrode) 17 is formed on the bottom surface (the second
surface) of the substrate 10. The light emitted from the activated
layer 12 is taken up from the exposed surface of the current
diffusion layer 15. Namely, the exposed surface of the current
diffusion layer 15 is employed as a light-extracting surface.
[0034] On this exposed surface of the current diffusion layer 15,
there are formed finely recessed/projected portions 18. These
finely recessed/projected portions 18 are formed by a diblock
copolymer as explained hereinafter, and configured as shown in FIG.
2A, for instance. In FIG. 2A, "h" is the height of the projected
portion of the recessed/projected portions 18, while "d" is the
length (width) of the base of the projected portion.
[0035] This projected portion is triangular in cross section with
the width of the base thereof (d) ranging from 10 to 500 nm, the
height thereof (h) being 100 nm or more, and the apex angle thereof
ranging from 25 to 80 degrees, these numerical limitations being
admitted as effective in securing a sufficient effect to improve
the light extraction efficiency. The non-uniformity in
configuration of the projected portion within the element was
found, for example, 100.+-.50 nm in width and 200.+-.100 nm in
height (i.e. the distribution of width within the element: .+-.50%,
and the distribution of height within the element: .+-.50%).
[0036] At least part of the recessed/projected portions 18 may be
constructed such that the tip end of the projected portion is
provided with a fine transparent portion as shown in FIG. 2B.
Alternatively, the tip end of the projected portion may be
flattened as shown in FIG. 2C. Further, the tip end of the
projected portion may be flattened and provided thereon with a fine
transparent portion as shown in FIG. 2D.
[0037] Next, the process of manufacturing the LED according to this
embodiment will be explained with reference to FIGS. 3A to 3D.
[0038] First of all, as shown in FIG. 3A, the hetero structure
portion 14 and the current diffusion layer 15 were successively
epitaxially grown on the top surface of the n-type GaP substrate
10. Then, the p-side electrode 16 was formed on a desired region of
the surface of the current diffusion layer 15, and the n-side
electrode 17 was formed on the bottom surface of the substrate
10.
[0039] Meanwhile, a 1:2.5 diblock copolymer comprising polystyrene
(PS) and poly(methyl methacrylate)(PMMA) was dissolved in a solvent
formed of ethylcellosolve acetate (ECA) to prepare a solution of
the copolymer. A 1:2-3 diblock copolymer comprising PS and PMMA may
be used, and it is possible to use propylene glycol monomethyl
ether acetate (PGMEA) or ethyl lactate (EL) as a solvent.
[0040] This solution was then spin-coated over the current
diffusion layer 15 and the p-side electrode 16 at a rotational
speed of 2500 rpm to form a coated film, which was then pre-baked
at a temperature of 110.degree. C. for 90 seconds to volatilize the
solvent to form a polymer layer 31 as shown in FIG. 3B. Thereafter,
the polymer layer 31 was subjected to annealing in a nitrogen gas
atmosphere at a temperature of 210.degree. C. for 4 hours to permit
the diblock copolymer to take place the phase separation thereof
into PS and PMMA.
[0041] The polymer layer containing this phase-separated diblock
copolymer was then subjected to etching by RIE using CF.sub.4 (30
sccm) under the conditions of 1.33 Pa in pressure and 100 W in
power output. As a result, it was possible to selectively remove
the PMMA phase by a difference in etching rate between PS and PMMA,
thereby allowing a pattern 32 of PS to remain as shown in FIG. 3C.
This PS pattern 32 was subsequently employed as a mask material
layer. More specifically, this PS pattern 32 was transcribed onto
the surface of the current diffusion layer 15 by RIE using
BCl.sub.3 (23 sccm) and N.sub.2 (7 sccm). This transcription was
performed for about 100 seconds under the conditions of: 0.2 Pa in
pressure, and 500 W in power output. As a result, it was possible
to form a finely recessed/projected pattern on the surface of the
current diffusion layer 15 as shown in FIG. 3D. Alternatively, the
aforementioned RIE may be performed by using BCl.sub.3 (8 sccm),
Cl.sub.2 (5 sccm) and Ar (37 sccm) with other conditions being the
same as described above. Thereafter, the remaining PS pattern was
removed by an O.sub.2 asher to obtain a structure as shown in FIG.
1.
[0042] In this embodiment, it was possible to uniformly form finely
recessed/projected portions each projected portion having a
cone-like configuration on the exposed surface of the current
diffusion layer 15, this exposed surface being functioning as a
light-extracting surface. More specifically, the projected portion
of the recessed/projected portions was about 100.+-.50 nm in base
length, about 200.+-.100 nm in height and 20 to 40 degrees in apex
angle. Due to the existence of these finely recessed/projected
portions, it is now possible to take up light out of the current
diffusion layer 15 even if the incidence angle at the
light-extracting surface is increased. Further, even if the
light-extracting surface is sealed with a transparent resin, it is
possible to improve the light extraction efficiency.
[0043] It was confirmed that the improvement of the light
extraction efficiency was dependent on the height of the projected
portion in the finely recessed/projected portions. More
specifically, it was found that when the height of the projected
portion in the finely recessed/projected portions was 100 nm (h=100
nm), the light extraction efficiency could be enhanced by a
magnitude of about 1.3 times higher as compared with there was no
finely recessed/projected portions, and when the height of the
projected portion was 200 nm (h=200 nm), the light extraction
efficiency could be enhanced by a magnitude of about 1.5 times
higher. Namely, it was confirmed that the light extraction
efficiency could be significantly enhanced (enhancement by 10% or
more) when the height of the projected portion was 100 nm or more.
When the height "h" was increased over 200 nm, this enhancement was
increased to 1.5 to 1.6 times at most, and any further enhancement
could not be obtained. It was also recognized that as long as the
width "d" of the base of the projected portion was confined within
the range of 10 to 500 nm, it was possible to expect a sufficient
enhancement of the light extraction efficiency.
[0044] It was also found possible to obtain a sufficient
enhancement of the light extraction efficiency as long as at least
90% of the finely recessed/projected portions formed on the surface
of the current diffusion layer 15 satisfied the aforementioned
conditions. The creation of these finely recessed/projected
portions would be possible only when the current diffusion layer 15
was subjected to the aforementioned treatment, using the
aforementioned diblock copolymer. Namely, it would be impossible to
obtain these finely recessed/projected portions by the conventional
roughening work or etching work. It may be possible to form finely
recessed/projected portions having almost the same features as
described above by using a micro-lithographic technique such as EB,
it would lead to a prominent increase in manufacturing cost.
Whereas, it is now possible according to this embodiment to form
these finely recessed/projected portions more cheaply and
easily.
[0045] As for the diblock copolymer having a polymer chain which is
capable of exhibiting a sufficiently large difference in dry
etching rate, it is possible to employ a diblock copolymer having
an aromatic ring-containing polymer chain and an acrylic polymer
chain. As for the aromatic ring-containing polymer chain, it is
possible to employ a polymer chain which can be synthesized through
the polymerization of at least one monomer selected from the group
consisting of vinyl naphthalene, styrene and derivatives thereof.
As for the acrylic polymer chain, it is possible to employ a
polymer chain which can be obtained through the polymerization of
at least one monomer selected from the group consisting of acrylic
acid, methacrylic acid, crotonic acid, and derivatives thereof. A
typical example of the diblock copolymer is a 1:2.5 diblock
copolymer comprising polystyrene and poly(methyl methacrylate),
which was employed in this embodiment.
[0046] According to this embodiment, since the finely
recessed/projected portions can be uniformly created on the
light-extracting surface, it is now possible to prevent the
degrading of the light extraction efficiency that may be caused due
to the influence by the total reflection of light. As a result, it
is now possible to enhance the light extraction efficiency and
hence to enhance the luminance of LED. In contrast to the
conventional surface-roughening treatment, of substrate using
hydrochloric acid, sulfuric acid, hydrogen peroxide or a mixed
solution comprising these chemicals, the method of this embodiment
enables to form finely recessed/projected portions in a very
efficient manner irrespective of the orientation of the crystal
plane of substrate.
[0047] Moreover, due to the finely recessed/projected portions that
have been formed on the light-extracting surface, even the light
that has been re-absorbed by the activated layer due to the
internal multi-reflection can be taken up out of the
light-extracting surface, so that it is now possible to operate an
LED at a relatively high temperature (up to 100.degree. C. or
more).
Second Embodiment
[0048] A PS pattern was formed by RIE under the same conditions as
described in the aforementioned first embodiment except that
O.sub.2 was substituted for CF.sub.4.
[0049] In the same manner as described in the first embodiment, a
polymer layer 31 containing a diblock copolymer was formed on the
surface of the current diffusion layer 15 and then, the diblock
copolymer was subjected to phase separation. Then, the polymer
layer 31 was subjected to etching by RIE using O.sub.2 gas (30
sccm) under the conditions of 13.3 Pa in pressure and 100 W in
power output. In contrast with the etching using CF.sub.4, although
it was impossible, in this case where O.sub.2 was employed, to etch
the polymer layer 31 down to the underlying substrate, it was
possible to relatively accurately remove the PMMA phase of the
PS-PMMA block, thereby forming a PS pattern.
[0050] This PS pattern was then transcribed onto the surface of the
current diffusion layer 15 by RIE under the same conditions as
described in the aforementioned first embodiment except that
Cl.sub.2 (5 to 40 sccm) was employed as an etching gas. Thereafter,
the PS pattern left remained was removed by using an O.sub.2
asher.
[0051] As a result, in the same manner as in the aforementioned
first embodiment, it was possible to form a pattern of
recessed/projected portions on the exposed surface of the current
diffusion layer 15 constituting a light-extracting surface with the
projected portion thereof being about 100.+-.50 nm in base length
and about 200.+-.100 nm in height. Accordingly, it was possible to
obtain almost the same effects as those obtained in the first
embodiment.
Third Embodiment
[0052] In this embodiment, a PS pattern was formed through the
scission of the main chain of polymer by the irradiation of
electron beam.
[0053] In the same manner as described in the first embodiment, a
polymer layer 31 containing a diblock copolymer was formed on the
surface of the current diffusion layer 15 and then, the diblock
copolymer was subjected to phase separation. Then, an electron beam
was irradiated the entire surface of the polymer layer 31 to cut
the main chain of PMMA. On this occasion, the conditions of
irradiating the electron beam were set to 2 eV. Thereafter, the
polymer layer 31 was subjected to development by using a developing
solution (for example, a mixed solution comprising MIBK
(methylisobutyl ketone) and IPA (isopropanol)). The resultant
surface of the polymer layer 31 was then rinsed by IPA or ethanol
to selectively dissolve and remove the PMMA, thereby leaving a
pattern 32 of PS.
[0054] This PS pattern was then transcribed onto the surface of the
current diffusion layer 15 by RIE under the same conditions as
described in the aforementioned first embodiment except that
Cl.sub.2 (5 to 40 sccm) was employed as an etching gas. Thereafter,
the PS pattern left remained was removed by using an O.sub.2
asher.
[0055] As a result, in the same manner as in the aforementioned
first embodiment, it was possible to form a pattern of
recessed/projected portions on the exposed surface of the current
diffusion layer 15 constituting a light-extracting surface with the
projected portion thereof being about 100.+-.50 nm in base length
and about 200.+-.100 nm in height. Accordingly, it was possible to
obtain almost the same effects as those obtained in the first
embodiment.
Fourth Embodiment
[0056] In this embodiment, a material containing an aromatic
ring-containing polymer chain and an aliphatic double-bond polymer
chain was employed as a diblock copolymer.
[0057] This aliphatic double-bond polymer is a polymer containing a
double-bond in the main chain of the polymer, wherein the
double-bond is cut off by the effect of oxidation using ozone for
instance. Therefore, it is possible, in the case of a diblock
copolymer containing an aromatic ring-containing polymer chain and
an aliphatic double-bond polymer chain, to selectively remove the
aliphatic double-bond polymer chain. As for specific examples of
the aliphatic double-bond polymer chain, it is possible to employ
polydiene-based polymer and derivatives thereof. As for specific
examples of the diblock copolymer containing an aromatic
ring-containing polymer chain and an aliphatic double-bond polymer
chain, it is possible to employ a diblock copolymer comprising
polystyrene and polybutadiene, a diblock copolymer comprising
polystyrene and polyisoprene, etc.
[0058] In this embodiment, a 1:2.5 diblock copolymer comprising
polystyrene (PS)-polyisoprene was employed to form a polymer layer
on the current diffusion layer 15 in the same manner as described
in the first embodiment, and then, the diblock copolymer was
subjected to phase separation. Subsequently, this phase-separated
diblock copolymer was left to stand in an ozone atmosphere for 5
minutes, thereby removing the polyisoprene, thus forming a pattern
of PS. Thereafter, by the same procedures as described in the
aforementioned first embodiment, the pattern of PS was transcribed
onto the surface of the current diffusion layer 15.
[0059] As a result, it was possible to form a pattern of
recessed/projected portions on the exposed surface of the current
diffusion layer 15 constituting a light-extracting surface with the
projected portion thereof being about 100.+-.50 nm in base length
and about 200.+-.100 nm in height. Accordingly, it was possible to
obtain almost the same effects as those obtained in the first
embodiment. Even when a copolymer comprising polystyrene and
polybutadiene was employed as a diblock copolymer, it was possible,
through the same process as described above, to form
recessed/projected portions having almost the same features as
described above.
Fifth Embodiment
[0060] FIGS. 4A to 4D are cross-sectional views each illustrating,
stepwise, the manufacturing steps of an LED according to a fifth
embodiment of the present invention. Incidentally, the same
portions as those of FIGS. 3A to 3D will be identified by the same
reference numbers in FIGS. 4A to 4D, thereby omitting the detailed
explanation thereof.
[0061] In this embodiment, the finely recessed/projected portions
were formed on the surface of a transparent layer formed on the
current diffusion layer.
[0062] First of all, after a laminate having the same structure as
that of FIG. 3A was formed, a transparent film 41 was formed on the
surface of the current diffusion layer 15. This transparent film 41
can be formed, for example, by a sputtering method, a CVD method or
a coating method by SiO.sub.2, SiN.sub.2, TiO.sub.2, etc.
[0063] Then, by using a solution of the same copolymer and by the
same procedures as employed in the aforementioned first embodiment,
a polymer film 31 was formed on the transparent film 41.
Thereafter, the polymer film 31 was subjected to annealing in a
nitrogen atmosphere at a temperature of 210.degree. C. for 4 hours
to permit the diblock copolymer to take place the phase separation
thereof.
[0064] The polymer layer containing this phase-separated diblock
copolymer was then subjected to etching by RIE to form a pattern 32
of PS, which was subsequently transcribed onto the surface of the
transparent film 41 as shown in FIG. 4C. The RIE in this case can
be performed using an etching gas such as CF.sub.4, CHF.sub.3,
C.sub.4F.sub.8, SF.sub.6, etc. and under the conditions of: 5-10 Pa
in pressure, and 100-1000 W in power output.
[0065] Thereafter, the PS pattern remaining was removed by using an
O.sub.2 asher to form finely recessed/projected portions on the
surface of the transparent film 41 as shown in FIG. 4D. These
finely recessed/projected portions were found excellent in
uniformity as those of the first embodiment with the projected
portion thereof being about 100.+-.50 nm in base length, about
200.+-.100 nm in height.
[0066] Alternatively, the finely recessed/projected portions formed
in the transparent film 41 may be transcribed onto the current
diffusion layer 15 subsequent to the formation of the structure
shown in FIG. 4D, and then, the transparent film 41 may be removed
by a chemical solution such as HF, NH.sub.4F, etc. In this case,
the finely recessed/projected portions can be formed on the surface
of the current diffusion layer 15 in the same manner as described
in the first embodiment.
[0067] As explained above, according to this embodiment, since
finely recessed/projected portions can be uniformly formed on the
surface of the transparent film 41 or the current diffusion layer
15, both functioning as a light-extracting surface, it is possible
to prevent the degrading of light extraction efficiency that may be
otherwise caused to occur due to the influence of the total
reflection of light. Accordingly, it was possible to obtain almost
the same effects as those obtained in the first embodiment.
Sixth Embodiment
[0068] FIGS. 5A and 5B are cross-sectional views each illustrating
the element structure of an LED according to a sixth embodiment of
the present invention.
[0069] The LED shown in FIG. 5A is a Junction Up type LED where the
light is extracted from a surface located opposite to the substrate
50. In this case, an n-type GaN buffering layer 51, an n-type GaN
clad layer 52, an MQW activated layer 53 containing InGaN/GaN, a
p-type AlGaN cap layer 54, and a p-type GaN contact layer 55 are
successively deposited on the surface of an n-type GaN substrate
50. A p-side electrode 57 is formed on part of the surface of the
contact layer 55 with the remaining portion of the surface of the
contact layer 55 being left exposed. On the other hand, an n-side
electrode 58 is formed on the bottom surface of the substrate 50.
Finely recessed/projected portions 55a are formed on the exposed
surface of the contact layer 55 by the same procedures as explained
above. Alternatively, the finely recessed/projected portions may be
formed in the dielectric film which is disposed on the exposed
surface of the contact layer 55.
[0070] Since these finely recessed/projected portions 55a can be
uniformly formed on the surface of the light-extracting surface, it
is possible to enhance the light extraction efficiency.
[0071] The LED shown in FIG. 5B is a Junction Down type LED where
the light is extracted from the substrate 50 side. In this case
also, the same kinds of layers as those of FIG. 5A, i.e. the layers
51, 52, 53, 54 and 55 are successively deposited on the surface of
an n-type GaP substrate 50. A p-side electrode 57 is formed on the
surface of the contact layer 55, and an n-side electrode 58 which
has been patterned is formed partially on the bottom surface of the
substrate 50. The remaining region of the bottom surface of the
substrate 50 is left exposed and provided with finely
recessed/projected portions 50a which have been formed by the same
procedures as explained above.
[0072] Since these finely recessed/projected portions 50a can be
uniformly formed on the bottom surface of the substrate 50
functioning as a light-extracting surface, it is possible to
enhance the light extraction efficiency.
[0073] In the case of the LED shown in FIG. 5B, the light emitted
from the MQW activated layer 53 is reflected by each of the end
faces, thus enabling the light to be extracted from the finely
recessed/projected portions 50a which are formed on the top surface
of the substrate, thereby making it possible to minimize the
density of light at the sidewall of chip. As a result, it is
possible to prevent the degrading of the resin located on the
sidewall of chip and hence to prevent the discoloration of the
resin even if the LED is actuated for a long period of time.
Seventh Embodiment
[0074] FIGS. 6A and 6B are cross-sectional views each illustrating
the element structure of an LED according to a seventh embodiment
of the present invention.
[0075] The LED shown in FIG. 6A is a Junction Up type LED where the
light is extracted from a surface located opposite to the substrate
60. In this case, an AlGaN buffering layer 61, an n-type GaN
contact layer 62, an MQW activated layer 63 containing InGaN/GaN, a
p-type AlGaN cap layer 64, a p-type GaN contact layer 65 and a
transparent electrode 66 made of ITO for instance are successively
deposited on the top surface of a sapphire substrate 60. This
laminate is partially etched in such a manner that the etched
region is extended from the transparent electrode 66 down to an
intermediate portion of the n-type GaN contact layer 62.
[0076] A p-side electrode 67 is formed on part of the surface of
the transparent electrode 66 with the remaining portion of the
surface of the transparent electrode 66 being left exposed. On the
exposed surface of the contact layer 62, there is formed an n-side
electrode 68. Finely recessed/projected portions 66a are formed on
the exposed surface of the transparent electrode 66 by using the
same procedures as explained above.
[0077] Since these finely recessed/projected portions 66a can be
uniformly formed on the surface of the transparent electrode 66
constituting a light-extracting surface, it is possible to enhance
the light extraction efficiency.
[0078] The LED shown in FIG. 6B is a Junction Down type LED where
the light is extracted from the substrate 60 side. In this case
also, the same kinds of layers as those of FIG. 6A, i.e. the layers
61, 62, 63, 64 and 65 are successively deposited on the surface of
a sapphire substrate 60. This laminate is partially etched in such
a manner that the etched region is extended from the p-type contact
layer 65 up to an intermediate portion of the n-type contact layer
62. A p-side electrode 67 is formed on the surface of the p-type
contact layer 65, and an n-side electrode 68 is formed on the
exposed surface of the n-type contact layer 62. Finely
recessed/projected portions 60a are formed the entire surface of
the substrate 60 by using the same procedures as explained
above.
[0079] Since these finely recessed/projected portions 60a can be
uniformly formed on the bottom surface of the substrate 60
functioning as a light-extracting surface, it is possible to
enhance the light extraction efficiency.
Eighth Embodiment
[0080] FIG. 7 is a cross-sectional view illustrating the element
structure of an LED according to an eighth embodiment of the
present invention.
[0081] In this LED shown in FIG. 7, a p-type GaP buffering layer
71, a p-type InGaP adhesion layer 72, a p-type InAlP clad layer 73,
an InGaAlP activated layer 74, an n-type InAlP clad layer 75 and an
n-type InGaAlP current diffusion layer 76 are successively
deposited on the surface of a p-type GaP substrate 70.
[0082] At the central region of the surface of the current
diffusion layer 76 is formed a laminate containing an n-type GaAs
contact layer 77, an i-type InAlP block layer 78, an i-type GaAs
block cover layer 79 and an n-side electrode 81. On the peripheral
region of the surface of the current diffusion layer 76, there are
deposited the n-type GaAs contact layer 77 and the n-side electrode
81. On the other hand, a p-side electrode 82 which has been
patterned is formed on the bottom surface of the substrate 70.
Finely recessed/projected portions 83 are formed on the exposed
surface of the current diffusion layer 75 by the same procedures as
explained above.
[0083] Next, the process of manufacturing the LED according to this
embodiment will be explained with reference to FIGS. 8A to 8C.
[0084] First of all, as shown in FIG. 8A, an n-type GaAs buffering
layer 91 (0.5 .mu.m in thickness; 4.times.10.sup.17 cm.sup.-3 in
carrier concentration), an i-type InGaP etch-stop layer 92 (0.2
.mu.m), an i-type GaAs block cover layer 79 (0.1 .mu.m), an i-type
InAlP block layer 78 (0.2 .mu.m), an n-type GaAs contact layer 77
(0.1 .mu.m in thickness; 1.times.10.sup.18 cm.sup.-3 in carrier
concentration), an n-type InGaAlP current diffusion layer 76 (1.5
.mu.m in thickness; 4.times.10.sup.17 cm.sup.-3 in carrier
concentration), an n-type InAlP clad layer 75 (0.6 .mu.m in
thickness; 4.times.10.sup.17 cm.sup.-3 in carrier concentration),
an InGaAlP-MQW activated layer 74 (0.72 .mu.m in thickness; 621 nm
in wavelength), a p-type InAlP clad layer 73 (1 .mu.m in thickness;
4.times.10.sup.17 cm.sup.-3 in carrier concentration), a p-type
InGaP adhesion layer 72 (0.05 .mu.m in thickness; 3.times.10.sup.18
cm.sup.-3 in carrier concentration), and an n-type InAlP cap layer
95 (0.15 .mu.m in thickness; 2.times.10.sup.15 cm.sup.-3 in carrier
concentration) were successively formed on the top surface of the
n-type GaAs substrate 90.
[0085] Then, the cap layer 95 was removed to expose the adhesion
layer 72. On the other hand, a p-type GaP layer 71 (0.2 .mu.m in
thickness; 3.times.10.sup.18 cm.sup.-3 in carrier concentration)
was allowed to grow on the surface of a p-type GaP substrate 70
having a thickness of 150 .mu.m to prepare a supporting substrate.
Then, this supporting substrate was adhered onto the adhesion layer
72. Thereafter, the GaAs substrate 90, the buffering layer 91 and
the etch-stop layer 92 were etched away to obtain a structure as
shown in FIG. 8B.
[0086] Then, as shown in FIG. 8C, the block cover layer 79, the
block layer 78 and the contact layer 77 were etched so as to form a
pattern of electrode. On this occasion, the central portion of
these layers was patterned into a circular configuration, and the
peripheral portion thereof was formed into a pattern of fine linear
configuration, and at the same time, the block cover layer 79 and
the block layer 78 were removed. In either of patterns, an n-side
electrode 81 was formed on the uppermost layer thereof, while a
p-side electrode 82 was formed on the bottom surface of the
substrate 70. Although not clearly shown in the drawings, the
p-side electrode 82 was formed as a circular pattern at four
locations of the substrate excluding the central region of the
substrate in order to enhance the light extraction efficiency of
the region immediately below the portion where the n-side electrode
81 was not located. This p-side electrode 82 can be formed all over
the bottom surface of the substrate 70.
[0087] Thereafter, finely recessed/projected portions were formed
on the surface of the current diffusion layer 76 by using a diblock
copolymer and by using the same procedures as explained above,
thereby obtaining a structure as shown in FIG. 7.
[0088] Since these finely recessed/projected portions 83 can be
uniformly formed the entire surface of the current diffusion layer
76 functioning as a light-extracting surface except the region
where the electrode 81 was formed, it is possible to enhance the
light extraction efficiency.
Ninth Embodiment
[0089] A method of working an underlying film by using an oxide
film (such as SiO.sub.2) or a nitride film (such as SiN) as a mask
will be explained with reference to FIGS. 9A to 9C.
[0090] First of all, as shown in FIG. 9A, an SOG film 93 having a
thickness of 0.1 .mu.m and comprising an SiO.sub.2 film was formed
on the surface of the InGaAlP current diffusion layer 76 of the
laminate structure shown in FIG. 7 by a spin-coating method. Then,
a polymer film containing a diblock copolymer was formed on the
surface of the SOG film 93 in the same manner as described in the
first embodiment, and the polymer layer was allowed to take place
the phase separation thereof. Thereafter, this phase-separated
polymer film was subjected to etching for 30 seconds by RIE using
O.sub.2 gas (30 sccm) under the conditions of 13 Pa in pressure and
100 W in power output, thereby forming a polymer pattern 94.
[0091] This polymer pattern 94 was then employed as a mask to etch
the SOG film 93 for about 100 seconds by RIE using CF.sub.4 gas (30
sccm) under the conditions of 1.3 Pa in pressure and 100 W in power
output, thereby forming a pattern of SOG as shown in FIG. 9B.
[0092] Then, the resultant surface was subjected to etching for
about 100 seconds by RIE using BCl.sub.3 (8 sccm), Cl.sub.2 (5
sccm) and Ar (37 sccm) under the conditions of: 0.2 Pa in pressure,
and 500 W in power output. As a result, it was possible, as shown
in FIG. 9C, to form finely recessed/projected portions 83 with the
projected portion having a minute cone-like configuration 50-300 nm
in width and 100-500 nm in height on the surface of the InGaAlP
current diffusion layer 76. In this case, the SOG (oxide film) 93
may be left at the apex portion of the finely recessed/projected
portions, i.e. no trouble would be raised even if the SOG is left
in this manner.
[0093] It was possible in this manner to uniformly form finely
recessed/projected portions on the surface of the InGaAlP current
diffusion layer 76, each projected portion having a cone-like
configuration about 100.+-.50 nm in base length and about
200.+-.100 nm in height. FIG. 10 shows an electron microphotograph
of the finely recessed/projected portions.
Tenth Embodiment
[0094] A method of working an underlying substrate by using a
multi-layer resist system will be explained with reference to FIGS.
11A to 11C.
[0095] First of all, as shown in FIG. 11A, an underlying resist
film (positive novolac resist) 95 having a thickness of 0.1 .mu.m
was formed on the surface of the InGaAlP current diffusion layer
76. The resist to be employed in this case may not contain a
photosensitive agent. Then, an SOG film 93 and a polymer film were
formed on the surface of the underlying resist film 95 in the same
manner as described above. After the diblock copolymer contained in
the polymer layer was allowed to underego phase separation thereof,
this phase-separated polymer film was subjected to etching for 30
seconds by RIE using O.sub.2 gas (30 sccm) under the conditions of
13 Pa in pressure and 100 W in power output, thereby forming a
polymer pattern 94.
[0096] This polymer pattern 94 was then employed as a mask to etch
the SOG film 93 by RIE, and the underlying resist film 95 was
etched by RIE using O.sub.2 gas (8 sccm) and N.sub.2 gas (80 sccm)
under the conditions of 2 Pa in pressure and 300 W in power output,
thereby forming a resist pattern 95a as shown in FIG. 11B.
[0097] Then, after the InGaAlP current diffusion layer 76 was
etched by RIE under the same conditions as described in the ninth
embodiment, a resist pattern 95a was peeled off by using an O.sub.2
asher, thereby forming, as shown in FIG. 1C, finely
recessed/projected portions 83 on the surface of the InGaAlP
current diffusion layer 76, each projected portion thereof having a
cone-like configuration about 50-200 nm in width and 100-500 nm in
height.
[0098] It was possible in this manner to uniformly form finely
recessed/projected portions on the surface of the InGaAlP current
diffusion layer 76, each projected portion having a cone-like
configuration 100.+-.50 nm in base length and 300.+-.150 nm in
height.
[0099] According to this embodiment, since the finely
recessed/projected portions that have been defined as mentioned
above are formed on the light-extracting surface, it is now
possible to prevent the degrading of the light extraction
efficiency that may be caused due to the influence by the total
reflection of light. As a result, it is now possible to enhance the
light extraction efficiency. Furthermore, it is now possible to
minimize the internal absorption loss that may be caused by the
multi-reflection in the interior of the semiconductor layer,
thereby making it possible to realize a light-emitting element
capable of extremely minimizing temperature increase. Additionally,
since the surface-roughening treatment using a diblock copolymer is
applied to the light-extracting surface, it is now possible to
uniformly form finely recessed/projected portions without depending
on the crystal orientation of the underlying layer.
[0100] The present invention should not be construed as being
limited to the aforementioned embodiments. For example, as for the
materials for forming the polymer layer, it is possible to employ
any diblock copolymer as long as they are capable of selectively
removing one of the components that have been phase-separated. The
finely recessed/projected portions can be formed on any desired
layer as long as it is located at an uppermost layer of the
light-extracting side and at the same time, capable of being worked
through etching using a phase-separated polymer film as a mask.
[0101] Further, as far as the projected portion of the finely
recessed/projected portions is formed of a cone-like configuration,
it is possible to obtain the advantages as mentioned above.
Furthermore, the finely recessed/projected portions having a
cone-like configuration may be formed on each of the surfaces (top
and side surfaces) of the chip other than the portions where
electrodes are formed. The aforementioned advantages would not be
hindered even if the electrodes are formed after the finely
recessed/projected portions have been formed all over the
light-extracting surface. The present invention can be executed by
modifying it in various ways as long as such variations do not
exceed the subject matter of the present invention.
[0102] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *