U.S. patent application number 11/458938 was filed with the patent office on 2006-12-28 for nitride semiconductor light emitting diode and fabrication method thereof.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. Invention is credited to Jong Ho JANG, Jun Ho SEO.
Application Number | 20060292804 11/458938 |
Document ID | / |
Family ID | 34675943 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060292804 |
Kind Code |
A1 |
SEO; Jun Ho ; et
al. |
December 28, 2006 |
NITRIDE SEMICONDUCTOR LIGHT EMITTING DIODE AND FABRICATION METHOD
THEREOF
Abstract
The invention relates to a nitride semiconductor LED and a
fabrication method thereof. In the LED, a first nitride
semiconductor layer, an active region a second nitride
semiconductor layer of a light emitting structure are formed in
their order on a transparent substrate. A dielectric mirror layer
is formed on the underside of the substrate, and has at least a
pair of alternating first dielectric film of a first refractivity
and a second dielectric film of a second refractivity larger than
the first refractivity. A lateral insulation layer is formed on the
side of the substrate and the light emitting structure. The LED of
the invention effectively collimate undesirably-directed light
rays, which may be otherwise extinguished, to maximize luminous
efficiency, and are protected by the dielectric mirror layer formed
on the side thereof to remarkably improve ESD characteristics.
Inventors: |
SEO; Jun Ho; (KYUNGKI-DO,
KR) ; JANG; Jong Ho; (KYUNGKI-DO, KR) |
Correspondence
Address: |
LOWE HAUPTMAN BERNER, LLP
1700 DIAGONAL ROAD
SUITE 300
ALEXANDRIA
VA
22314
US
|
Assignee: |
SAMSUNG ELECTRO-MECHANICS CO.,
LTD.
314 MAETAN-3-DONG, YOUNGTONG-KU, SUWON
KYUNGKI-DO
KR
|
Family ID: |
34675943 |
Appl. No.: |
11/458938 |
Filed: |
July 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10870467 |
Jun 18, 2004 |
|
|
|
11458938 |
Jul 20, 2006 |
|
|
|
Current U.S.
Class: |
438/287 ;
257/E33.068 |
Current CPC
Class: |
Y10S 257/918 20130101;
H01L 2224/48091 20130101; H01L 2224/49107 20130101; H01L 2224/73265
20130101; H01L 33/46 20130101; H01L 2224/48091 20130101; H01L
2924/00014 20130101 |
Class at
Publication: |
438/287 |
International
Class: |
H01L 21/336 20060101
H01L021/336 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2003 |
KR |
2003-95172 |
Claims
1. A wafer-level fabrication method of nitride semiconductor Light
Emitting Diodes (LEDs), the method comprising the following steps
of: preparing a transparent wafer for growing single crystal
nitride semiconductor thereon; forming a light emitting structure
including a first nitride semiconductor layer, an active layer and
a second nitride semiconductor layer laminated in their order on
the wafer; cutting the wafer together with the light emitting
structure into the size of LED to expose the side of each LED; and
laminating at least one alternating pair of first and second
dielectric materials on the side and the underside of the LED, the
first dielectric material having a first refractivity and the
second dielectric material having a second refractivity larger than
the first refractivity, whereby the first and second dielectric
materials are laminated at least on the underside of the LED to
form a dielectric mirror layer.
2. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 1, wherein the step of cutting the wafer
together with the light emitting structure into the size of LED
includes: attaching a tape on the light emitting structure, cutting
the wafer from the underside into LEDs and stretching the tape to
sufficiently expose the side of the cut LEDs.
3. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 1, wherein the first and second dielectric
materials are laminated on the side of the LED at substantially
same thickness and number as the first and second dielectric
materials on the underside of the LED to form a dielectric mirror
layer.
4. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 1, wherein the first and second dielectric
materials comprise oxide or nitride containing one element selected
from a group including Si, Zr, Ta, Ti and Al.
5. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 1, wherein each of the first and second
dielectric films forms a film having a thickness of about 300 to
900 .ANG..
6. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 1, wherein each of the first and second
dielectric materials comprises a SiO.sub.2 film or a
Si.sub.3N.sub.4 film.
7. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 5, wherein the SiO.sub.2 film has a thickness of
about 600 to 600 .ANG., and the Si.sub.3N.sub.4 film has a
thickness of about 400 to 600 .ANG..
8. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 1, wherein the dielectric mirror layer has a
reflectivity of at least 90%.
9. The wafer-level fabrication method of nitride semiconductor LEDs
according to claim 8, wherein the dielectric mirror layer has a
reflectivity of at least 95%.
Description
CROSS REFERENCE
[0001] This application is a divisional application of U.S.
application Ser. No. 10/870,467 filed Jun. 18, 2004, which claims
priority from Korean Patent Application No. 2003-95172 filed Dec.
23, 2003, which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a nitride semiconductor
light emitting diode, and more particularly, to a nitride
semiconductor light emitting diode and a fabrication method
thereof, in which a high reflectivity layer is formed to minimize
light loss as well as achieve excellent electrostatic discharge
characteristics.
[0004] 2. Description of the Related Art
[0005] As well-known in the art, Nitride semiconductor Light
Emitting Diodes (LEDs) are being spotlighted as high power optical
devices capable of generating single wavelength light such as blue
or green light to realize full color display. A nitride
semiconductor LED is made by growing single crystal semiconductor
expressed as a formula of Al.sub.xIn.sub.yGa.sub.(1-x-y)N (wherein
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and 0.ltoreq.x+y.ltoreq.1)
on a specific substrate of for example sapphire for growing
GaN.
[0006] Unlike a GaAs-based red LED that has electrodes formed on
the underside of a substrate, the sapphire substrate as a
representative substrate for growing GaN has two electrodes formed
on crystallized semiconductor layers as shown in FIG. 1a because it
is insulated.
[0007] Referring to FIG. 1a, a nitride semiconductor LED 10
includes a sapphire substrate 11, a first nitride semiconductor
layer 13, an active layer 15 and a second nitride semiconductor
layer 17 formed in their order on the sapphire substrate 11.
Further, in order to form two electrodes on the semiconductor
layers as described above, predetermined regions of the second
nitride semiconductor layer 17 and the active layer 15 are etched
to form a general mesa structure. The first electrode 18a is
arranged on the exposed region of the first nitride semiconductor
layer 13, and the second electrode 18b is arranged on the second
nitride semiconductor 17.
[0008] The nitride semiconductor LED 10, as shown in FIG. 1a, can
be loaded on a Printed Circuit Board (PCB) 21 and then covered with
resin 28 to form an LED package 20. A circuit pattern including
first and second conductive patterns 22a and 22b are formed on the
PCB 21, the LED 10 is attached to the second conductive pattern 22b
via a conductive paste layer 16, and the electrodes 18b and 18a of
the LED 10 are connected to the first and second conductive
patterns 22a and 22b via the wires 24a and 24b.
[0009] In the package shown in FIG. 1b, light rays generated from
the nitride semiconductor LED are projected not only in desirable
upward directions but also in downward directions through the
transparent sapphire substrate. Light rays directed downward are
partially absorbed and extinguished or partially reach the
conductive paste layer 16 bonding the LED 10 with the second
conductive pattern 22b that reflects the light rays upward.
However, because the conductive paste layer 16 itself does not
define an irregular surface, high reflectivity can be rarely
expected from the conductive paste layer 16 even though it is made
of a high reflectivity material such as Ag. Rather, the light rays
are scattered from the irregular surface to disappear.
[0010] Accordingly, there have been required in the art nitride
semiconductor LEDs and a fabrication method thereof which can
minimize light loss as well as maximize luminous efficiency by
using a suitable reflector structure.
SUMMARY OF THE INVENTION
[0011] Therefore the present invention has been made to solve the
foregoing problems of the prior art.
[0012] It is therefore an object of the present invention to
provide a nitride semiconductor LED which can utilize high
reflectivity characteristics of a dielectric mirror layer to
minimize light loss as well as insulation properties thereof to
remarkably improve electrostatic discharge characteristics.
[0013] It is another object of the present invention to provide a
wafer-level fabrication method of nitride semiconductor LEDs.
[0014] According to an aspect of the invention for realizing the
above objects, there is provided a nitride semiconductor Light
Emitting Diode (LED) comprising: a transparent substrate for
growing nitride semiconductor single crystal thereon; a light
emitting structure including a first nitride semiconductor layer,
an active region a second nitride semiconductor layer formed in
their order on the substrate; a dielectric mirror layer formed on
the underside of the substrate and having at least a pair of first
dielectric film of a first refractivity and a second dielectric
film of a second refractivity larger than the first refractivity,
the first and second dielectric films being laminated on each other
in an alternating fashion; and a lateral insulation layer formed on
the side of the substrate and the light emitting structure.
[0015] It is preferred that the lateral insulation layer comprises
a dielectric mirror layer equal to the dielectric mirror layer
formed on the underside of the substrate. It is preferred that the
first and second dielectric films comprise oxide or nitride
containing one element selected from a group including Si, Zr, Ta,
Ti and Al. It is also preferred that each of the first and second
dielectric films has a thickness of about 300 to 900 .ANG..
[0016] Representatively, each of the first and second dielectric
films may comprise a SiO.sub.2 film or a Si.sub.3N.sub.4 film,
wherein the SiO.sub.2 film may have a thickness of about 600 to 600
.ANG., and the Si.sub.3N.sub.4 film has a thickness of about 400 to
600 .ANG..
[0017] According to the present invention, the dielectric mirror
layer preferably may have a reflectivity of at least 90%, and more
preferably a reflectivity of at least 95%.
[0018] According to an aspect of the invention for realizing the
above objects, there is provided a wafer-level fabrication method
of nitride semiconductor Light Emitting Diodes (LEDs), the method
comprising the following steps of: preparing a transparent wafer
for growing single crystal nitride semiconductor thereon; forming a
light emitting structure including a first nitride semiconductor
layer, an active layer and a second nitride semiconductor layer
laminated in their order on the wafer; cutting the wafer together
with the light emitting structure into the size of LED to expose
the side of each LED; and laminating at least one alternating pair
of first and second dielectric materials on the side and the
underside of the LED, the first dielectric material having a first
refractivity and the second dielectric material having a second
refractivity larger than the first refractivity, whereby the first
and second dielectric materials are laminated at least on the
underside of the LED to form a dielectric mirror layer.
[0019] It is preferred that the step of cutting the wafer together
with the light emitting structure into the size of LED may include:
attaching a tape on the light emitting structure, cutting the wafer
from the underside into LEDs and stretching the tape to
sufficiently expose the side of the cut LEDs.
[0020] It is also preferred that the first and second dielectric
materials are laminated on the side of the LED at substantially
same thickness and number as the first and second dielectric
materials on the underside of the LED to form a dielectric mirror
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0022] FIG. 1a is a sectional view illustrating a conventional
nitride semiconductor LED;
[0023] FIG. 1b is an LED package incorporating the LED in FIG.
1a;
[0024] FIG. 2a is a sectional view illustrating a nitride
semiconductor LED according to a first embodiment of the
invention;
[0025] FIG. 2b is a magnification of the part A in FIG. 2a for
illustrating the sectional configuration of a multilayer mirror
structure adopted to the LED;
[0026] FIG. 3 is a sectional view illustrating a package having the
semiconductor LED according to the invention; and
[0027] FIGS. 4a to 4e are sectional views illustrating a
fabrication method of nitride semiconductor LEDs according to the
invention.
[0028] FIG. 5 is a graph showing Optical Power of the present
example and the comparative example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] Hereinafter the present invention will be described in more
detail with reference to the accompanying drawings.
[0030] FIG. 2a is a sectional view illustrating a nitride
semiconductor LED according to a first embodiment of the
invention.
[0031] Referring to FIG. 2a, a nitride semiconductor LED 30
includes a transparent substrate 31 for growing nitride
semiconductor thereon, a first nitride semiconductor substrate 33,
an active region or layer 35 and a second nitride semiconductor
layer 37 formed in their order on the substrate 31. The first and
second electrodes 38a and 38b are formed respectively on a
predetermined region of the first nitride semiconductor layer 33
exposed by mesa etching and the second semiconductor layer 35.
[0032] For example, the transparent substrate 31 may be made of
sapphire, and the first nitride semiconductor layer 33 may be
formed of an n-doped GaN layer. The active layer 35 maybe formed of
an undoped InGaN layer of a multi-quantum well structure, and the
second nitride semiconductor layer 37 may be formed of a p-doped
GaN layer and a p-doped AlGaN layer.
[0033] The nitride semiconductor LED 30 of the invention includes a
dielectric mirror layer 39 formed on both the side and the
underside. As shown in FIG. 3b, the dielectric mirror layer 39 has
three pairs of alternating first and second dielectric materials or
films 39a and 39b, but is not limited thereto. The first dielectric
films 39a have a first refractivity, and the second dielectric
films 39b have a second refractivity higher than the first
refractivity. The material type, thickness and alternating number
(i.e., the number of pairs) of the dielectric mirror layer 39 can
be so set that the dielectric mirror layer 39 has a suitable
reflectivity according to oscillation wavelength.
[0034] Preferably, the dielectric films 39a and 39b may be made of
oxide or nitride containing one element selected from the group
consisting of Si, Zr, Ta, Ti and Al. The dielectric material shows
substantially no light loss owing to its low absorptivity nearing
zero, and can realize high reflectivity based upon the refractivity
difference of the multilayer dielectric films of the dielectric
mirror layer. The dielectric mirror layer 39 adopted in the
invention can have a reflectivity of about 80%, preferably 90%, and
more preferably 98%.
[0035] Each of the first and second dielectric films 39a and 39b
preferably has a thickness of about 300 to 900 .ANG. regarding a
typical wavelength range (e.g., about 350 to 550 mm) oscillated
from the nitride semiconductor LED. Representative examples of the
dielectric films may include a SiO.sub.2 film and a Si.sub.3N.sub.4
film. The SiO.sub.2 film is used to form a lower refractivity layer
with relation to that formed by the Si.sub.3N.sub.4 film. It is
preferred that the SiO.sub.2 film has a thickness of about 600 to
800 .ANG. and the Si.sub.3N.sub.4 film has a thickness of about 400
to 600 .ANG.. Table 1 below illustrates a dielectric mirror layer
structure for realizing high reflectivity of at least 98%:
TABLE-US-00001 TABLE 1 Oscillation Re- Number of Re- wavelength
Material Thickness fractivity Pairs flectivity 390 nm SiO.sub.2 663
1.47 6 98 Si.sub.3N.sub.4 469 2.0787 450 nm SiO.sub.2 765 1.47 6
98.5 Si.sub.3N.sub.4 547 2.0547 470 nm SiO.sub.2 799 1.47 6 98
Si.sub.3N.sub.4 573 2.0489
[0036] It is reported that the dielectric mirror layer 39 composed
according to conditions in Table 1 above has a high reflectivity of
at least 98% with respect to an oscillation wavelength range from
390 to 470 nm. Instead of being scattered or absorbed from/into a
defective reflective surface, the most of light directed downward
in the diode is reflected upward by the dielectric mirror layer of
the invention.
[0037] The semiconductor LED of the invention also has an
insulation layer formed on the side. This lateral insulation layer
provides protection to the outside surface of the diode as well as
the electrically-insulated dielectric mirror layer. That is,
although an LED with an exposed lateral portion may be destructed
by surge voltage, the LED 30 shown in FIG. 2a can have excellent
reliability of fine Electrostatic Discharge (ESD) characteristics
because the insulation layer is formed also on the side.
[0038] The lateral insulation layer may be formed of an insulating
material different from that of the dielectric mirror layer only on
the side of the LED, separate from the formation of the dielectric
mirror layer. Alternatively, the lateral insulation layer on the
side of the LED may be formed simultaneous with the dielectric
mirror layer 39, with the same dielectric mirror layer as the
dielectric mirror layer 39.
[0039] FIG. 3 is a sectional view illustrating a package having the
semiconductor LED according to the invention.
[0040] Referring to FIG. 3, a nitride semiconductor LED package 40
includes a PCB 41, a nitride semiconductor LED 30 mounted on the
PCB 41 and 1 transparent resin structure 48 formed around the LED
30 mounted on the PCB 41.
[0041] The PCB 41 includes first and second conductive patterns 42a
and 42b formed thereon. The LED 30 has a dielectric mirror layer 39
formed beneath and around the LED 30, and is bonded onto the second
conductive pattern 42b via an adhesive (not shown) made of
conductive paste such as Ag. Further, the LED 30 has electrodes
(e.g., 38b and 38a in FIG. 2a) which are connected respectively to
the first and second conductive patterns 42a and 42b.
[0042] In the package 40 adopting the LED 30 of the invention, even
if directed downward through a transparent sapphire substrate, a
light ray a generated from the nitride semiconductor LED 30 is not
scattered or absorbed from/into a reflective surface, which is
uneven owing to the adhesive, but reflects upward from the high
reflectivity dielectric mirror layer 39. Also, because the
dielectric mirror layer 39 is formed around the lateral portion of
the LED 30 of the invention, a light ray b directed toward the
lateral portion can be re-reflected upward. Therefore, the
invention effectively forms the high reflectivity dielectric mirror
layer also on the side of the LED
[0043] As a result, the LED of the invention has the high
reflectivity dielectric mirror layer formed up to the side of the
LED to minimize substantial extinction of undesirably directed
light rays thereby maximizing resultant luminous efficiency.
Further, the LED of the invention is protected at both the side and
the underside by the electrically-insulated dielectric mirror layer
to improve ESD characteristics.
[0044] FIGS. 4a to 4e are sectional views illustrating a
fabrication method of a plurality of nitride semiconductor LEDs
according to the invention. The wafer-level fabrication process of
nitride semiconductor LEDs will provide more apparent understanding
to an advantage of the invention that further facilitates the
formation of the dielectric mirror layer of the invention.
[0045] As shown in FIG. 4a, a light emitting structure 105
including a first nitride semiconductor layer, an active layer and
a second nitride semiconductor layer is formed on a transparent
wafer 101 of for example sapphire for growing nitride thereon. In a
following step, the sapphire wafer 101 together with the light
emitting structure 105 can be divided into respective unit LEDs 110
as indicated with dotted lines.
[0046] Then, in each unit LED 110, a first electrode 111a is formed
on an exposed region of the first nitride semiconductor layer,
which is exposed via mesa etching, and a second electrode 111b is
formed on the second nitride semiconductor layer as shown in FIG.
4b. For example, a p-electrode can be provided by forming a
transparent electrode layer on the p-doped nitride semiconductor
layer and then a bonding metal on the transparent electrode
layer.
[0047] Then, the wafer having the light emitting structure is cut
according to the size of unit LED exposing the side of the unit
LEDs, which in turn are provided at the side and the underside with
suitable dielectric mirror layers made of a desired dielectric
material. Preferably, this process can be performed according to
the steps as shown in FIGS. 4c to 4e, starting with the step of
attaching a tape 120 on the light emitting structure. A resultant
structure attached with the tape 120 is placed with the upside down
so as to facilitate the following cutting step.
[0048] Then, as shown in FIG. 4d, the cutting step is performed
from the underside of the wafer to divide the resultant structure
into the unit LEDs, and the tape is stretched to expose the side of
the cut unit LEDs. A first dielectric film of a first refractivity
and a second dielectric film of a second refractivity larger than
the first refractivity are laminated alternating with each other
for at least one time on the side and the underside of the unit
LEDs. The lamination is performed to suitably form the first and
second dielectric films with a desired thickness in order to
realize the dielectric mirror layers.
[0049] The dielectric layer lamination as shown in FIG. 4d provides
a plurality of LEDs 110 each having a dielectric mirror layer 119
on the side and the underside, in which the dielectric mirror layer
119 includes the first dielectric film of the first refractivity
and the second dielectric film of the second refractivity. This
embodiment illustrates that the same dielectric mirror layer 119 is
also formed on the side of the each LED by adopting a desired
process and material capable of sufficiently overcoming step
coverage. This structure can improve the reflectivity at the side
of the LED to further raise the luminous efficiency. On the other
hand, although the reflection effect of the dielectric mirror layer
cannot be expected because the dielectric films are not formed with
suitable thickness on the side of the LED, the dielectric mirror
layer coated on the side of the LED can function as a desirable
insulation layer to improve ESC characteristics of the LED so that
high reliability LEDs can be expected.
EXAMPLE
[0050] To demonstrate the improvement of brightness in the present
invention, GaN LED according to the present invention was
produced.
[0051] First, n-type GaN layer, InGaN/GaN MQW active layer and
p-type GaN layer were grown on a sapphire substrate sequentially.
Then, 7 pairs of Al.sub.2O.sub.3 film and Si.sub.3N.sub.4 film were
formed as the present dielectric mirror layer on bottom and side
surfaces of the resulting structure as the LED shown in FIG. 2A. In
this example, the thickness of Al.sub.2O.sub.3 film was about 700
.ANG. and the thickness of Si.sub.3N.sub.4 film was about 540
.ANG..
COMPARATIVE EXAMPLE
[0052] GaN LED of this comparative example is made in the same
manner and material as the above example except that the dielectric
mirror layer was employed.
[0053] Then, the optical power of each LED was measured using a
chip prober(OPTO corp. Japan). The result is shown in FIG. 5.
Referring to FIG. 5, it can be observed that the LED according to
the present example shows more optical power(increased about 90.2%)
than that of the comparative example.
[0054] While the present invention has been described with
reference to the particular illustrative embodiments and the
accompanying drawings, it is not to be limited thereto but will be
defined by the appended claims. It is to be appreciated that those
skilled in the art can substitute, change or modify the embodiments
into various forms without departing from the scope and spirit of
the present invention.
[0055] According to the present invention as set forth above, the
high reflectivity dielectric mirror layer including the alternating
pair of dielectric films having different refractivities is formed
on both the side and the underside of the LED to effectively
collimate undesirably-directed light rays, which may be otherwise
extinguished, thereby maximizing luminous efficiency. Furthermore,
the dielectric mirror layer can also protect the side of the LED to
remarkably improve ESD characteristics of the LED.
* * * * *