U.S. patent application number 10/611898 was filed with the patent office on 2004-12-09 for method for manufacturing vertical gan light emitting diodes.
Invention is credited to Hahm, Hun Joo, Kim, In Eung, Na, Jeong Seok, Park, Young Ho, Yoo, Seung Jin.
Application Number | 20040248377 10/611898 |
Document ID | / |
Family ID | 33411747 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040248377 |
Kind Code |
A1 |
Yoo, Seung Jin ; et
al. |
December 9, 2004 |
METHOD FOR MANUFACTURING VERTICAL GAN LIGHT EMITTING DIODES
Abstract
A method for manufacturing vertical GaN light emitting diodes is
provided. The method comprises the steps of: forming a light
emitting structure on a sapphire substrate, said light emitting
structure including a first conductive GaN clad layer, an active
layer and a second conductive GaN clad layer. The light emitting
structure is divided into plural units so that the first conductive
GaN clad layer of a thickness of at least approximately 100 .ANG.
remains. A conductive substrate is attached to the divided upper
surface of the light emitting structures using a conductive
adhesive layer. A lower surface of the sapphire substrate is
irradiated by laser beam so that the sapphire substrate is removed
from the unit light emitting structures. First and second contacts
are formed respectively on the surfaces of the first conductive
clad layer and the conductive substrate. Finally, The resulting
structure is cut into plural unit light emitting diodes.
Inventors: |
Yoo, Seung Jin; (Kyungki-do,
KR) ; Kim, In Eung; (Kyungki-do, KR) ; Hahm,
Hun Joo; (Kyungki-do, KR) ; Park, Young Ho;
(Kyungki-do, KR) ; Na, Jeong Seok; (Seoul,
KR) |
Correspondence
Address: |
LOWE HAUPTMAN GOPSTEIN GILMAN & BERNER, LLP
Suite 310
1700 Diagonal Road
Alexandria
VA
22314
US
|
Family ID: |
33411747 |
Appl. No.: |
10/611898 |
Filed: |
July 3, 2003 |
Current U.S.
Class: |
438/458 |
Current CPC
Class: |
Y10S 438/977 20130101;
H01L 33/0093 20200501 |
Class at
Publication: |
438/458 |
International
Class: |
H01L 021/46 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2003 |
KR |
2003-35766 |
Claims
What is claimed is:
1. A method for manufacturing GaN light emitting diodes, comprising
the steps of: (a) forming a light emitting structure on a sapphire
substrate, said light emitting structure including a first
conductive GaN clad layer, an active layer and a second conductive
GaN clad layer sequentially stacked on the sapphire substrate; (b)
dividing the light emitting structure into plural units with a
designated size so that the first conductive GaN clad layer of a
thickness of at least approximately 100 .ANG. remains; (c)
attaching a conductive substrate to exposed upper surfaces of the
unit light emitting structures using a conductive adhesive layer;
(d) irradiating a laser beam on a lower surface of the sapphire
substrate so that the sapphire substrate is removed from the unit
light emitting structures, wherein the residual first conductive
GaN clad layer is removed so that the light emitting structure is
perfectly divided into the unit light emitting structures with a
size the same as that of light emitting diodes to be finally
manufactured; (e) forming first and second contacts respectively on
the surface of the first conductive clad layer, from which the
sapphire substrate is removed, and the exposed surface of the
conductive substrate; and (f) cutting the resulting structure along
the divided lines of the unit light emitting structures into plural
unit light emitting diodes.
2. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein in the step (b), the thickness of the
residual first conductive GaN clad layer is less than approximately
2 .mu.m.
3. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein in the step (b), the thickness of the
residual first conductive GaN clad layer is less than approximately
1 .mu.m.
4. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein the step (a) includes the step of forming
a reflective layer made of a conductive material on the second
conductive GaN clad layer.
5. The method for manufacturing GaN light emitting diodes as set
forth in claim 4, wherein the reflective layer is made of a
material selected from the group consisting of Au, Ni, Ag, Al and
their alloys.
6. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein the step (c) includes the sub-steps of:
(c-1) forming the conductive adhesive layer on the lower surface of
the conductive substrate; and (c-2) attaching the lower surface of
the conductive substrate provided with the conductive adhesive
layer to the exposed upper surfaces of the unit light emitting
structures.
7. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein the step (c) includes the sub-steps of:
(c') forming the conductive adhesive layer on the upper surfaces of
the unit light emitting structures; and (c") attaching the
conductive substrate to the upper surfaces of the unit light
emitting structures provided with the conductive adhesive
layer.
8. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein the conductive substrate is made of a
material selected from the group consisting of silicon (Si),
germanium (Ge), SiC, ZnO, diamond, and GaAs.
9. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein the conductive adhesive layer is made of
a material selected from the group consisting of Au--Sn, Sn, In,
Au--Ag, Ag--In, Ag--Ge, Ag--Cu and Pb--Sn.
10. The method for manufacturing GaN light emitting diodes as set
forth in claim 1, wherein the first conductive GaN clad layer is a
GaN crystalline layer doped with an n-type impurity, and the second
conductive GaN clad layer is a GaN crystalline layer doped with a
p-type impurity.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for manufacturing
vertical GaN light emitting diodes, and more particularly to a
method for manufacturing vertical GaN light emitting diodes, from
which an insulating sapphire substrate with low thermal
conductivity is removed and in which a conductive substrate such as
a silicon substrate is installed so as to have improved luminance
and reliability.
[0003] 2. Description of the Related Art
[0004] Generally, light emitting diodes (LEDs) are semiconductor
elements, which emit light based on the recoupling of electrons and
holes, and are widely used as various types of light sources in
optical communication and electronic equipment. GaN serves as a
compound for manufacturing blue-light emitting diodes.
[0005] Frequency (or wavelength) of light emitted from the light
emitting diode is functionally related to a band gap of a
semiconductor material to be used. When the band gap is small,
photons with low energy and a longer wavelength are generated. In
order to generate photons with a shorter wavelength, there is
required a semiconductor material with a broader band gap.
[0006] For example, AlGaInP commonly used in lasers emits light
corresponding to visible red light (approximately 600.about.700 m).
On the other hand, silicon carbide (SiC) and Group III nitride
semiconductor materials such as gallium nitride (GaN) with a
comparatively broad band gap emit light corresponding to visible
blue light or ultraviolet rays. A short wavelength LED has an
advantage in increasing a storage space of an optical storage
(approximately 4 times as large as that of a general LED emitting
red light).
[0007] The same as other Group III nitride semiconductor materials
for emitting blue light, there is no practical technique for
forming a bulk single crystal made of GaN. Accordingly, there is
required a substrate suitable for growing a GaN crystal thereon.
Sapphire, i.e., aluminum oxide (Al.sub.2O.sub.3), is typically used
as such a substrate for growing the GaN crystal thereon.
[0008] However, a sapphire substrate has an insulating property,
thus limiting the structure of a GaN light emitting diode. With
reference to FIG. 1, the structure of a conventional GaN light
emitting diode is will be described in detail.
[0009] FIG. 1 is a cross-sectional view of a conventional GaN light
emitting diode 10. The GaN light emitting diode 10 comprises a
sapphire substrate 11 and a GaN light emitting structure 15 formed
on the sapphire substrate 11.
[0010] The GaN light emitting structure 15 includes an n-type GaN
clad layer 15a, an active layer 15b formed to have a multi-quantum
well structure, and a p-type GaN clad layer 15c. Here, the n-type
GaN clad layer 15a, the active layer 15b and the p-type GaN clad
layer 15c are sequentially formed on the sapphire substrate 11. The
light emitting structure 15 may be grown on the sapphire substrate
11 using MOCVD (metal-organic chemical vapor deposition), etc.
Here, in order to improve the lattice matching of the light
emitting structure 15 and the sapphire substrate 11, a buffer layer
(not shown) made of AlN/GaN may be formed on the sapphire substrate
11 before the growing of the n-type GaN clad layer 15a.
[0011] The p-type GaN clad layer 15c and the active layer 15b are
removed at designated portions by dry etching so as to selectively
expose the upper surface of the n-type GaN clad layer 15a. An
n-type contact 19 is formed on the exposed upper surface of the
n-type GaN clad layer 15a, and a p-type contact 17 is formed on the
upper surface of the p-type GaN clad layer 15c. A designated
voltage is applied to the n-type contact 19 and the p-type contact
17. Generally, in order to increase a current injection area while
not negatively affecting luminance, a transparent electrode 16 may
be formed on the upper surface of the p-type GaN clad layer 15c
before forming the p-type contact 17 on the p-type GaN clad layer
15c.
[0012] As described above, since the conventional GaN light
emitting diode 10 uses the insulating sapphire substrate 11, the
two contacts 17 and 19 are formed on the sapphire substrate so that
the contacts 17 and 19 are nearly horizontal with each other.
Accordingly, when a voltage is applied to the conventional GaN
light emitting diode 10, a current flows over a narrow area from
the n-type contact 19 to the p-type contact 17 via the active layer
15b in a horizontal direction. Since a forward voltage (V.sub.f) of
the light emitting diode 10 is increased due to this narrow current
flow, the current efficiency of the light emitting diode 10 is
lowered and an electrostatic discharge effect is weak.
[0013] Further, the conventional GaN light emitting diode 10 emits
a great amount of heat in proportion to the increase of the current
density. On the other hand, the sapphire substrate 11 has low
thermal conductivity, thus not rapidly dissipating heat.
Accordingly, mechanical stress is exerted between the sapphire
substrate 11 and the GaN light emitting structure 15 due to the
increased temperature, thus causing the GaN light emitting diode 10
to be unstable.
[0014] Moreover, in order to form the n-type contact 19, a portion
of the active layer 15b with a size at least larger than that of
the contact 19 to be formed must be removed. Accordingly, a light
emitting area is reduced, and the luminous efficiency according to
the luminance relative to the size of the diode 10 is lowered.
[0015] In order to solve this problem, there is required a vertical
light emitting diode. A method for manufacturing the vertical light
emitting diode must comprise a step of removing a sapphire
substrate from a GaN light emitting structure so as to form a
contact layer on upper and lower surfaces of the vertical light
emitting diode.
[0016] The sapphire substrate may be removed from the GaN light
emitting structure using several conventional techniques. Since the
sapphire substrate has a high strength, there is a limit to the
ability to remove the sapphire substrate from the GaN light
emitting structure using mechanical polishing. Further, the removal
of the sapphire substrate from the GaN light emitting structure
using a laser beam may cause damage to the GaN single crystal plane
of the GaN light emitting structure due to the lattice mismatching
and the difference of thermal coefficient of expansion (TCE)
between the sapphire substrate and the light emitting structure
during exposure to the laser beam.
[0017] More specifically, when the laser beam is irradiated on the
lower surface of the sapphire substrate in order to remove the
sapphire substrate from a GaN single crystalline layer, residual
stress occurs due to the difference of thermal coefficient of
expansion between the sapphire substrate and the GaN single
crystalline layer, and the lattice mismatching thereof. That is,
the thermal coefficient of expansion of sapphire is approximately
7.5.times.10.sup.-6/K, while the thermal coefficient of expansion
of GaN single crystal is approximately 5.9.times.10.sup.-6/K. In
this case, the rate of the lattice mismatching is approximately
16%. In case that a GAN/AlN buffer layer is formed on the sapphire
substrate prior to the growing of the GaN single crystalline layer,
the rate of the lattice mismatching is several percent (%).
Accordingly, when the heat is generated by exposure to the laser
beam, large-sized compressive stress is exerted on the surface of
the sapphire substrate and large-sized tensile stress is exerted on
the surface of the GaN single crystalline layer. Particularly,
since the area of the irradiation of the laser beam is narrow
(maximally 10 mm.times.10 mm), the laser beam is repeatedly
irradiated on sectional areas of the sapphire substrate so that the
laser beam can be irradiated on the entire surface of the sapphire
substrate. Thereby, the level of stress becomes more serious, thus
excessively damaging the surface of the GaN single crystalline
layer.
[0018] As a result, the damaged GaN single crystalline plane
drastically reduces the electric characteristics of the finally
manufactured GaN light emitting diode.
SUMMARY OF THE INVENTION
[0019] Therefore, the present invention has been made in view of
the above problems, and it is an object of the present invention to
provide a method for manufacturing GaN blue light emitting diodes
with improved luminance and reliability obtained by stably removing
a sapphire substrate from a GaN light emitting structure.
[0020] In accordance with the present invention, the above and
other objects can be accomplished by the provision of a method for
manufacturing GaN light emitting diodes, comprising the steps of:
(a) forming a light emitting structure on a sapphire substrate,
said light emitting structure including a first conductive GaN clad
layer, an active layer and a second conductive GaN clad layer
sequentially stacked on the sapphire substrate; (b) dividing the
light emitting structure into plural units with a designated size
so that the first conductive GaN clad layer of a thickness of at
least approximately 100 .ANG. remains; (c) attaching a conductive
substrate to exposed upper surfaces of the unit light emitting
structures using a conductive adhesive layer; (d) irradiating a
laser beam on a lower surface of the sapphire substrate so that the
sapphire substrate is removed from the unit light emitting
structures, wherein the residual first conductive GaN clad layer is
removed so that the light emitting structure is perfectly divided
into the unit light emitting structures with a size the same as
that of light emitting diodes to be finally manufactured; (e)
forming first and second contacts respectively on the surface of
the first conductive clad layer, from which the sapphire substrate
is removed, and the exposed surface of the conductive substrate;
and (f) cutting the resulting structure along the divided lines of
the unit light emitting structures into plural unit light emitting
diodes.
[0021] In the step (b), the thickness of the residual first
conductive GaN clad layer may be preferably less than approximately
2 .mu.m, and more preferably less than approximately 1 .mu.m.
[0022] Further, in order to improve the luminance of light emitted
from the upper surface of the diode, a reflective layer made of a
conductive material may be formed between the second conductive GaN
clad layer and the conductive adhesive layer. Preferably, the
reflective layer may be made of a material selected from the group
consisting of Au, Ni, Ag, Al and their alloys.
[0023] Preferably, the conductive substrate may be made of a
material selected from the group consisting of silicon (Si),
germanium (Ge), SiC, ZnO, diamond, and GaAs, and the conductive
adhesive layer may be made of a material selected from the group
consisting of Au--Sn, Sn, In, Au--Ag, Ag--In, Ag--Ge, Ag--Cu and
Pb--Sn.
[0024] Further, in order to obtain an improved current density
distribution, the first conductive GaN clad layer may be a GaN
crystalline layer doped with an n-type impurity, and the second
conductive GaN clad layer may be a GaN crystalline layer doped with
a p-type impurity.
[0025] Moreover, preferably, in the step (c), the conductive
adhesive layer may be formed on the lower surface of the conductive
substrate in advance, and then the lower surface of the conductive
substrate provided with the conductive adhesive layer may be
attached to the exposed upper surfaces of the unit light emitting
structures. Alternatively, in the step (c), the conductive adhesive
layer may be formed on the upper surfaces of the unit light
emitting structures, and then the conductive substrate may be
attached to the upper surfaces of the unit light emitting
structures provided with the conductive adhesive layer.
[0026] In the method for manufacturing vertical GaN Light emitting
diodes of the present invention, the GaN single crystalline light
emitting structure is grown on the sapphire substrate and the
conductive substrate such as a silicon substrate is attached to the
other surface of the light emitting structure using the conductive
adhesive layer. Subsequently, the sapphire substrate is removed
from the light emitting structure using the laser beam.
Accordingly, it is possible to more easily manufacture the vertical
GaN Light emitting diodes.
[0027] Further, in the method for manufacturing vertical GaN Light
emitting diodes of the present invention, the light emitting
structure is divided into plural units with a designated size so
that the first conductive GaN clad layer of a thickness of at least
approximately 100 .ANG. remains on the sapphire substrate.
Accordingly, it is possible to prevent the laser beam passing
through the sapphire substrate from reaching and melting the
conductive adhesive layer, during the step of removing the sapphire
substrate from the light emitting structure using the laser
beam.
[0028] Here, the residual first conductive GaN clad layer may be
removed by mechanical impact indispensably generated when the laser
beam is irradiated on the sapphire substrate so as to remove
sapphire substrate from the light emitting structure. The thickness
of the residual first conductive GaN clad layer may be preferably
less than approximately 2 .mu.m, and more preferably less than
approximately 1 .mu.m, so that the residual first conductive GaN
clad layer can be removed by small mechanical impact.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] 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:
[0030] FIG. 1 is a schematic cross-sectional view of a conventional
GaN light emitting diode;
[0031] FIG. 2 is a schematic cross-sectional view of a vertical GaN
light emitting diode manufactured in accordance with the present
invention; and
[0032] FIGS. 3a to 3f are cross-sectional views illustrating a
method for manufacturing vertical GaN light emitting diodes in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Now, preferred embodiments of the present invention will be
described in detail with reference to the annexed drawings.
[0034] FIG. 2 is a cross-sectional view of a vertical GaN light
emitting diode 20 manufactured in accordance with the present
invention.
[0035] The vertical GaN light emitting diode 20 comprises a light
emitting structure 25 including a p-type GaN clad layer 25a, an
active layer 25b, and an n-type GaN clad layer 25c. Further, the
GaN light emitting diode 20 selectively comprises a reflective
layer 22 formed on the lower surface of the p-type GaN clad layer
25a. The reflective layer 22 is attached to a silicon substrate 21
using a conductive adhesive layer 24. The reflective layer 22
serves to improve the effective luminance depending on light
emitted from the upper surface of the GaN light emitting diode 20,
and is made of a metal with high reflectivity. Preferably, the
reflective layer 22 is made of a material selected from the group
consisting of Au, Ni, Ag, Al and their alloys.
[0036] That is, the conductive adhesive layer 24 is formed on the
lower surface of the reflective layer 22. First, the GaN single
crystalline light emitting structure 25 of the present invention is
grown on a sapphire substrate, and a conductive substrate is
attached to the other side of the light emitting structure 25.
Then, the vertical GaN light emitting diode 20 shown in FIG. 2 is
obtained by removing the sapphire substrate from the light emitting
structure 25.
[0037] Here, the conductive adhesive layer 24 is used to attach the
silicon substrate 21 to the light emitting structure 25. The
conductive adhesive layer 24 used in the present invention must be
made of a conductive material with an adhesive property.
Preferably, such a conductive material is a metal adhesive selected
from the group consisting of Au--Sn, Sn, In, Au--Ag, Ag--In,
Ag--Ge, Ag--Cu, and Pb--Sn. As described above, the conductive
adhesive layer 24 is made of a metal or an alloy, thus having
comparatively high reflectivity. Accordingly, although the
reflective layer 22 is omitted, the luminance of the GaN light
emitting diode 20 of the present invention can be improved by the
reflectivity of the conductive adhesive layer 24.
[0038] This embodiment employs the silicon substrate 21 as a
conductive substrate. However, various conductive substrates rather
than the insulating sapphire substrate may be used in the present
invention. Here, the conductive substrate of the present invention
may be made of silicon, germanium (Ge), Sic, ZnO, diamond, GaAs,
etc.
[0039] The vertical GaN light emitting diode 20 of this embodiment
is designed so that the upper and lower portions of the light
emitting diode 20 are electrically connected to each other. A
p-type contact 27 is formed on the entire lower surface of the
silicon substrate 21, and an n-type contact 29 is formed on a
portion of the upper surface of the n-type GaN clad layer 25c.
Thereby, the vertical GaN light emitting diode shown in FIG. 2 is
completely manufactured.
[0040] Compared to the vertical structure of the conventional GaN
light emitting diode, the GaN light emitting diode 20 of this
embodiment provides several advantages. First, since the GaN light
emitting diode 20 of this embodiment uses the silicon substrate 21
instead of the sapphire substrate, the GaN light emitting diode 20
has improved heat emission efficiency, reduced forward voltage
(V.sub.f) by the current flowing over a broader area than the
conventional vertical light emitting diode, and enhanced
electrostatic discharge efficiency.
[0041] Further, in view of a manufacturing process, the GaN light
emitting diode 20 of this embodiment has remarkably improved
current density distribution, thus not requiring a step of forming
a transparent electrode. Further, since the sapphire substrate is
removed from the light emitting structure, a step of cutting the
light emitting diode into a plurality of units can be simplified.
Moreover, in view of the luminance of the light emitting diode,
differently from the conventional vertical light emitting diode,
the vertical light emitting diode of this embodiment does not
require a step of selectively etching the active layer, thus
obtaining a large-sized light emitting area and improved
luminance.
[0042] Hereinafter, with reference to FIGS. 3a to 3f, a method for
manufacturing vertical GaN light emitting diodes of the present
invention is described in detail.
[0043] FIGS. 3a to 3f are cross-sectional views illustrating each
step of the method for manufacturing vertical GaN light emitting
diodes in accordance with a preferred embodiment of the present
invention.
[0044] With reference to FIG. 3a, a light emitting structure 125
made of a GaN single crystalline layer is formed on a sapphire
substrate 121. The GaN single crystalline layer of the light
emitting diode 125 comprises an n-type GaN clad layer 125a, an
active layer 125b, and a p-type GaN clad layer 125c. Although not
shown in FIG. 3a, a reflective layer made of a material selected
from the group consisting of Au, Ni, Ag, Al and their alloys may be
additionally formed on the upper surface of the light emitting
structure 125 so as to improve the reflective effect.
[0045] Subsequently, as shown in FIG. 3b, a first cutting step of
the GaN light emitting structure 125 is preformed. Here, the GaN
light emitting structure 125 is cut into a plurality of units with
a designated size (S) so that the n-type GaN clad layer 125a of a
thickness (t) of at least approximately 100 .ANG. remains. In this
first cutting step, in order to minimize the level of stress
exerted on the unit light emitting structure by irradiating a laser
beam thereon, the GaN light emitting structure 125 is cut so that
the size (S) of each of the unit light emitting structures 125'
corresponds to the size of a final light emitting diode to be
manufactured. However, the GaN light emitting structure 125 is not
perfectly cut so that the residual n-type GaN clad layer 125'a is
of a thickness (t) of at least approximately 100 .ANG..
[0046] When a laser beam is irradiated on the rear surface of the
sapphire substrate 121 so as to remove the sapphire substrate 121
from the unit light emitting structures 125' (shown in FIG. 3d),
the residual n-type GaN clad layer 125"a serves as a cut-off layer
for preventing the laser beam passing through the sapphire
substrate 121 from affecting the unit light emitting structures
125'. The detailed description of this step will be given
later.
[0047] Then, as shown in FIG. 3c, a conductive substrate 131 is
attached to the upper surfaces of the first cut unit light emitting
structures 125' using a conductive adhesive layer 124. This step
may be achieved by forming the conductive adhesive layer 124 on the
lower surface of the conductive substrate 131 and then attaching
the other surface of the conductive adhesive layer 124 to the unit
light emitting structures 125' (specifically, to the unit p-type
GaN clad layers 125'c). Alternatively, this step may be achieved by
forming the conductive adhesive layer 124 on an attaching surface
of the conductive substrate 131 and attaching the conductive
substrate 131 to the upper surfaces of the unit light emitting
structures 125'. The conductive adhesive layer 124 is made of a
material such as Au--Sn, Sn, In, Au--Ag, Ag--In, Ag--Ge, Ag--Cu, or
Pb--Sn. The conductive adhesive layer 124 is made of a metal or
alloy with comparatively high reflectivity; thus having a desired
reflective effect without use of an additional reflective layer (22
of FIG. 2).
[0048] In this step, since the conductive substrate 131 is attached
to the upper surfaces of the unit light emitting structures 125',
which are imperfectly cut from the light emitting structure 125
shown in FIG. 3b, although the sapphire substrate 121 is separated
from the unit light emitting structures 125', the unit light
emitting structures 125' can be stably arranged and maintained.
Accordingly, it is possible to easily perform a subsequent step
such as the forming of contacts using a mask under the condition
that the unit light emitting structures 125' are arranged.
[0049] As shown in FIG. 3d, a laser beam is irradiated on the lower
surface of the sapphire substrate 121 so that the sapphire
substrate 121 is removed from the imperfectly cut unit light
emitting structures 125' The laser beam passes through the sapphire
substrate 121, divides the residual n-type GaN clad layer 125"a
contacting the sapphire substrate 121 into gallium (Ga) and
nitrogen (N.sub.2), and then melts gallium (Ga) by heat of a
designated temperature, thus easily removing the sapphire substrate
121 from the unit light emitting structures 125'.
[0050] The laser beam used in the step passes through the sapphire
substrate 121, and then may melt the conductive adhesive layer 124.
In case that the conductive adhesive layer 124 is melted by the
laser beam, the adhesive force between the conductive substrate 131
and the unit light emitting structures 125' may be weakened,
thereby causing the detachment of the conductive substrate 131 from
the unit light emitting structures 125'. In order to prevent the
laser beam passing through the sapphire substrate 121 from reaching
the conductive adhesive layer 124, the light emitting structure 125
is imperfectly cut into the unit light emitting structures 125' so
that the residual n-type GaN clad layer 125"a is of a thickness (t)
of at least approximately 100 .ANG.. In order to cut off the laser
beam passing through the sapphire substrate 121, the thickness (t)
of the residual n-type GaN clad layer 125"a must be at least
approximately 100 .ANG..
[0051] Since the thickness (t) of the residual n-type GaN clad
layer 125"a disposed between the unit light emitting structures
125' is very small, the stress exerted on the interface between the
sapphire substrate 121 and the residual n-type GaN clad layer 125"a
is consumed for removing the residual n-type GaN clad layer 125"a.
Accordingly, the actual stress acting on the interface between the
sapphire substrate 121 and the unit light emitting structures 125'
is exerted only on the small-sized (S) unit light emitting
structures 125'. Thereby, it is possible to reduce the level of the
stress acting on the unit light emitting structures 125'.
[0052] The residual n-type GaN clad layer 125"a is removed by
mechanical polishing. At this time, the imperfectly cut unit light
emitting structures 125' are perfectly cut into a plurality of
light emitting diodes. That is, a self-dicing of the light emitting
structures 125' is carried out.
[0053] In order to reduce the level of stress and obtain the
self-dicing effect, the thickness (t) of the residual n-type GaN
clad layer 125"a in FIG. 3a may be modified depending on the
irradiation amount and time of the laser beam. Preferably, the
thickness (t) of the residual n-type GaN clad layer 125"a is less
than approximately 2 .mu.m, and more preferably less than
approximately 1 .mu.m.
[0054] As shown in FIG. 3e, a contact forming step is performed on
both surfaces of the resulting structure. FIG. 3e shows the
inverted state of the resulting structure of FIG. 3d. Here,
contacts are formed only on the upper surfaces of the n-type GaN
clad layer 125"a of the unit light emitting structures 125' and the
lower surface of the conductive substrate 131. An n-type contact
139 is formed on a designated area of the upper surface of each
n-type GaN clad layer 125"a (generally, the center of the upper
surface), and a p-type contact 137 serving as a rear electrode is
formed on the entire lower surface of the conductive substrate
131.
[0055] Finally, as shown in FIG. 3f, vertical GaN light emitting
diodes 130 are obtained by perfectly cutting the resulting
structure of FIG. 3e into plural units. Generally, a silicon
substrate with strength smaller than that of the sapphire
substrate. 121 is used as the conductive substrate 131, thus being
easily cut by a conventional cutting step.
[0056] As apparent from the above description, the present
invention provides a method for manufacturing vertical GaN light
emitting diodes with improved luminous efficiency, in which a
sapphire substrate is easily removed from a light emitting
structure using a laser beam and the melting of a conductive
adhesive layer due to the exposure to the laser beam passing
through the sapphire substrate is prevented.
[0057] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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