U.S. patent application number 12/561237 was filed with the patent office on 2010-01-14 for method for fabricating a nitride-based semiconductor light emitting device.
This patent application is currently assigned to FOXSEMICON INTEGRATED TECHNOLOGY, INC.. Invention is credited to WEN-JANG JIANG.
Application Number | 20100009483 12/561237 |
Document ID | / |
Family ID | 40264112 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100009483 |
Kind Code |
A1 |
JIANG; WEN-JANG |
January 14, 2010 |
METHOD FOR FABRICATING A NITRIDE-BASED SEMICONDUCTOR LIGHT EMITTING
DEVICE
Abstract
An exemplary method includes the following steps. First, a
substrate is provided. Second, a nitride-based multi-layered
structure is epitaxially grown on the substrate. The multi-layered
structure includes a first-type layer, an active layer, and a
second-type layer arranged one on the other in that order along a
direction away from the substrate. A crystal growth orientation of
the multi-layered structure intersects with a <0001> crystal
orientation thereof. Thirdly, the multi-layered structure is
patterned to form a mesa structure thereof, wherein the first-type
layer is partially exposed to form an exposed portion. The mesa
structure has a top surface facing away from the substrate, and
side surfaces adjacent to the top surface. Fourthly, a first-type
electrode and a second-type electrode are formed in ohmic contact
with the first-type layer and the second-type layer, respectively.
Finally, the top and side surfaces of the patterned multi-layered
structure are wet etched.
Inventors: |
JIANG; WEN-JANG; (Miao-Li
Hsien, TW) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
288 SOUTH MAYO AVENUE
CITY OF INDUSTRY
CA
91789
US
|
Assignee: |
FOXSEMICON INTEGRATED TECHNOLOGY,
INC.
Miao-Li Hsien
TW
|
Family ID: |
40264112 |
Appl. No.: |
12/561237 |
Filed: |
September 16, 2009 |
Current U.S.
Class: |
438/39 ;
257/E33.006 |
Current CPC
Class: |
H01L 33/32 20130101;
H01L 33/16 20130101; H01L 33/22 20130101 |
Class at
Publication: |
438/39 ;
257/E33.006 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2007 |
CN |
200710201125.0 |
Claims
1. A method for fabricating a nitride-based semiconductor light
emitting device, the method comprising: providing a substrate;
epitaxially growing a nitride-based multi-layered structure on the
substrate, the multi-layered structure comprising a first-type
layer, an active layer and a second-type layer arranged in that
order along a direction away from the substrate, wherein a crystal
growth orientation of the multi-layered structure intersects with a
<0001> crystal orientation of the multi-layered structure;
patterning the multi-layered structure to form a mesa structure
thereof, wherein the first-type layer is partially exposed to form
an exposed portion, and the mesa structure has a top surface facing
away from the substrate and a plurality of side surfaces adjacent
to the top surface; forming a first-type electrode and a
second-type electrode on the exposed portion and the top surface,
respectively, wherein the first-type electrode is in ohmic contact
with the first-type layer and the second-type electrode is in ohmic
contact with the second-type layer; and wet etching the patterned
multi-layered structure to roughen the top surface and the side
surfaces of the mesa structure.
2. The method of claim 1, wherein the substrate is a single crystal
plate, the single crystal plate has a crystal face on which the
multi-layered is epitaxially grown, and the crystal growth
orientation of the multi-layered structure matches a crystal
orientation of the crystal face.
3. The method of claim 1, wherein the first-type layer, the active
layer and the second-type layer are made from one or more group
III-nitride compound materials.
4. The method of claim 3, further comprising irradiating the mesa
structure with electromagnetic waves during the wet etching,
wherein an energy of the electromagnetic waves is equal to or
higher than an energy gap of at least one group III-nitride
compound material which is etched.
5. The method of claim 1, wherein the crystal growth orientation of
the multi-layered structure is substantially perpendicular to the
<0001> crystal orientation of the multi-layered
structure.
6. The method of claim 1, wherein the wet etching is performed by
one of an acid etching solution containing phosphoric acid and
sulfuric acid, and an alkaline etching solution containing
potassium hydroxide.
7. The method of claim 1, wherein an etching temperature during the
wet etching is higher than 150 degrees Celsius.
8. A method for fabricating a nitride-based semiconductor light
emitting device, the method comprising: providing a single crystal
substrate having a crystal face, wherein the crystal face is one of
a non-polar face and a semi-polar face; epitaxially growing a
nitride-based multi-layered structure on the crystal face, wherein
a crystal growth orientation of the multi-layered structure matches
a crystal orientation of the crystal face, and the multi-layered
structure includes an N-type layer and a P-type layer; treating the
multi-layered structure to form a mesa structure thereof; forming a
pair of electrodes on the multi-layered structure, the electrodes
being electrically connected with the N-type layer and the P-type
layer, respectively; and wet etching the multi-layered structure to
roughen at least one surface selected from the group consisting of
a top surface and side surfaces of the mesa structure.
9. The method of claim 8, further comprising irradiating the mesa
structure with electromagnetic waves during the wet etching,
wherein the multi-layered structure is made from one or more group
III-nitride compound materials, and an energy of the
electromagnetic waves is equal to or higher than an energy gap of
at least one group III-nitride compound material which is
etched.
10. The method of claim 8, wherein the top surface faces away from
the single crystal substrate, the side surfaces are adjacent to the
top surface, and the top surface and all the side surfaces are
roughened during the wet etching.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims foreign priority based on
Chinese Patent Application No. 200710201125.0, filed in China on
Jul. 19, 2007; and the present application is a divisional
application of U.S. patent application Ser. No. 12/102,617, filed
on Apr. 14, 2008. The entire contents of the aforementioned related
applications are incorporated by reference herein.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure generally relates to methods for
fabricating a nitride-based semiconductor light emitting device
with relatively low cost and high light extraction efficiency.
[0004] 2. Description of Related Art
[0005] Nowadays, nitride-based semiconductor light emitting devices
such as gallium nitride light emitting diodes (LEDs) have the
advantages of low power consumption and long life span, etc, and
thus are widely used for display, backlighting, outdoor
illumination, automobile illumination, etc. However, in order to
achieve high luminous brightness, an improvement of the light
extraction efficiency of the conventional nitride-based LEDs is
required.
[0006] Kao et al. have published a paper in IEEE photonics
technology letters, vol. 19, No. 11, pages 849-851 (June, 2007),
entitled "light-output enhancement of nano-roughened GaN laser
lift-off light-emitting diodes formed by ICP dry etching," the
disclosure of which is fully incorporated herein by reference. Kao
et al. have proposed an approach for the improvement of the light
extraction efficiency of the GaN LED, by way of roughening a
light-emitting region of the GaN LED via an ICP-RIE (i.e.,
inductively coupled plasma-reactive ion etching) dry etching
process. In particular, firstly, a GaN-based layer structure is
epitaxially grown on a c-face sapphire substrate. The GaN-based
layer structure is then placed into a vacuum chamber which is fed
with chlorine and argon for ICP-RIE dry etching. Consequently, a
light-emitting region of the GaN-based layer structure is given a
nano-roughened surface which facilitates improvement of the light
extraction efficiency of the GaN LED.
[0007] However, the use of the c-face sapphire substrate would
force the epitaxial growth of the GaN-based layer structure to be
oriented along a c-axis <0001> crystal orientation. As a
result, the surface atoms of the resultant GaN-based layer
structure are entirely gallium metal atoms. Such configuration of
the surface atoms results in the GaN-based layer structure
exhibiting a very strong polarity defect. Such polarity defect is
liable to cause at least the following two difficulties. First, a
quantum well structure in the GaN-based layer structure which is
oriented along the c-axis <0001> crystal orientation is
liable to encounter a significantly strong quantum-confined stark
effect (QCSE), so that an internal quantum efficiency of the GaN
LED is lowered and thus the light extraction efficiency is reduced.
Second, in order to roughen the surface of the light-emitting
region, a relatively high cost dry etching process with strong
etching capability (e.g., an ICP-RIE etching process) is needed.
Furthermore, due to the inherent selective etching characteristic
of the dry etching process, it is difficult to roughen sidewalls of
the GaN-based layer structure. Therefore further improvement of the
light extraction efficiency of the GaN LED is limited.
[0008] Accordingly, what is needed is an inexpensive method for
fabricating a nitride-based semiconductor light emitting device
with high extraction efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Many aspects of the disclosure can be better understood with
reference to the following drawings. The components in the drawings
are not necessarily drawn to scale, the emphasis instead being
placed upon clearly illustrating the principles of the disclosure.
Moreover, in the drawings, all the views are schematic, and like
reference numerals designate corresponding parts throughout the
several views.
[0010] FIG. 1 is a cross-sectional view of a nitride-base
semiconductor light emitting device manufactured in accordance with
an exemplary embodiment of a method of the present invention.
[0011] FIG. 2 is a schematic, cross-sectional view of a single
crystal plate used in the method of the exemplary embodiment.
[0012] FIG. 3 shows a nitride-based multi-layered structure
epitaxially formed on the single crystal plate of FIG. 2.
[0013] FIG. 4 shows the multi-layered structure of FIG. 3 having
been patterned to form a mesa structure.
[0014] FIG. 5 shows an N-type electrode and a P-type electrode
formed on the patterned multi-layered structure of FIG. 4.
[0015] FIG. 6 is a photograph of the multi-layered structure of
FIG. 5 after it has been treated by a wet etching process, the
photograph obtained by a Scanning Electron Microscope (SEM).
[0016] The exemplifications set out herein illustrate various
exemplary and preferred embodiments, in various forms, and such
exemplifications are not to be construed as limiting the scope of
the present method in any manner.
DETAILED DESCRIPTION
[0017] Referring to FIG. 1, a nitride-based semiconductor light
emitting device 20, in accordance with a present embodiment, is
shown. The nitride-based semiconductor light emitting device 20 can
for example be a gallium nitride light emitting diode (GaN LED).
The nitride-based semiconductor light emitting device 20 includes a
substrate 22, a nitride-based multi-layered structure 24
epitaxially formed on the substrate 22, an N-type electrode 26, and
a P-type electrode 28.
[0018] The substrate 22 beneficially is a single crystal plate, and
can be made from material selected from the group consisting of
sapphire, silicon carbide (SiC), silicon (Si), gallium arsenide
(GaAs), lithium aluminate (LiAlO.sub.2), magnesium oxide (MgO),
zinc oxide (ZnO), GaN, aluminum nitride (AlN), indium nitride
(InN), etc. The substrate 22 has a crystal face 222, which
facilitates the epitaxial growth of the multi-layered structure 24
thereon. A crystal orientation of the crystal face 222 matches with
a crystal growth orientation of the multi-layered structure 24.
[0019] The multi-layered structure 24 includes an N-type layer 241,
an active layer 242 and a P-type layer 243 arranged in that order
one on top of the other along a direction away from substrate 22.
That is, the active layer 242 is sandwiched between the N-type
layer 241 and the P-type layer 243. The N-type layer 241 is made of
semiconductor material in which charge is carried by electrons, and
the P-type layer 243 is made of semiconductor material in which
charge is carried by holes. Each of the N-type layer 241, the
active layer 242 and the P-type layer 243 can be a single layer
structure or a multi-layered structure, and each of the N-type
layer 241, the active layer 242 and the P-type layer 243 can
suitably made from group III-nitride compound materials. The group
III element can be aluminum (Al), gallium (Ga), indium (In), and so
on. For illustration purposes, the N-type layer 241, the active
layer 242 and the P-type layer 243 are an N-type GaN layer, an
InGaN layer and a P-type GaN layer, respectively.
[0020] The multi-layered structure 24 has a crystal growth
orientation intersecting with a <0001> crystal orientation
thereof. That is, crystal growth orientations of the N-type layer
241, the active layer 242 and the P-type layer 243 respectively
intersect with respective <0001> crystal orientations
thereof. Beneficially, the multi-layered structure 24 has a crystal
growth orientation such as a <11 20> crystal orientation or a
<10 10> crystal orientation substantially perpendicular to
the <0001> crystal orientation thereof.
[0021] The multi-layered structure 24 includes a developed mesa
structure 244. At a bottom of the mesa structure 244, the N-type
layer 241 is stepped at a side thereof facing away from the
substrate 22. Thereby, the N-type layer 241 defines an exposed
portion 245 thereof. The bottom of the mesa structure 244
terminates at a plane as denoted by the broken line in FIG. 1. The
mesa structure 244 includes but is not limited to the P-type layer
243, the active layer 242 and a top portion of the N-type layer
241. The mesa structure 244 has a top surface 247 and a plurality
of side surfaces 246 adjoining the top surface 247. The side
surfaces 246 are located generally between the top surface 247 and
the exposed portion 245. The top surface 247 and the side surfaces
246 are roughened surfaces and include a plurality of recesses (or
pits) 248 formed therein. The roughened surfaces are microstructure
in form. The roughened surfaces can help transmit light emitted
from the active layer 242 through the side surfaces 246, so as to
provide the nitride-based semiconductor light emitting device 20
with an improved light field distribution. That is, the divergence
angle of light emitted from the nitride-based semiconductor light
emitting device 20 is widened.
[0022] The N-type electrode 26 is formed on the exposed portion
245, so as to electrically connect with (e.g., ohmically contact)
the N-type layer 241. The N-type electrode 26 usually includes at
least one metallic layer which is in ohmic contact with the N-type
layer 241.
[0023] The P-type electrode 28 is formed on the top surface 247 of
the mesa structure 244 so as to electrically connect with (e.g.,
ohmically contact) the P-type layer 243. The P-type electrode 28
can be a single metallic layer or a multi-layered structure. When
the P-type electrode 28 is a multi-layered structure, it
essentially includes a metallic layer and a transparent conductive
film.
[0024] Referring to FIGS. 2 through 6, an exemplary method for
fabricating the nitride-based semiconductor light emitting device
20 will be described in detail, with reference to the accompanying
drawings.
[0025] As illustrated in FIG. 2, a substrate 12 is provided. The
substrate 12 is a single crystal plate and can be made from
sapphire, SiC, Si, GaAs, LiAlO.sub.2, MgO, ZnO, GaN, AlN, InN, etc.
The single crystal substrate 12 has a crystal face 122, which
facilitates a nitride-based multi-layered structure 14 being
epitaxially grown thereon (see FIG. 3). A crystal orientation of
the crystal face 122 matches with a crystal growth orientation of
the multi-layered structure 14 epitaxially grown on the substrate
12. The crystal face 122 can be a non-polar face or a semi-polar
face. In particular, the non-polar face is a type of crystal face
having a crystal orientation substantially perpendicular to the
<0001> crystal orientation of the crystal face 122. The
semi-polar face is a type of crystal face having a crystal
orientation obliquely intersecting the <0001> crystal
orientation of the crystal face 122.
[0026] Referring to FIG. 3, the multi-layered structure 14 is
epitaxially formed on the crystal face 122 of the single crystal
substrate 12. The multi-layered structure 14 includes an N-type
layer 141, an active layer 142 and a P-type layer 143 arranged one
on top of the other in that order along a direction away from the
single crystal substrate 12. That is, the active layer 142 is
sandwiched between the N-type layer 141 and the P-type layer 143.
The N-type layer 141 is made of semiconductor material in which
charge is carried by electrons, and the P-type layer 143 is made of
semiconductor material in which charge is carried by holes. In the
illustrated embodiment, the N-type layer 141, the active layer 142
and the P-type layer 143 are suitably made from group III-nitride
compound materials. For the purpose of illustration, the N-type
layer 141, the active layer 142 and the P-type layer 143 are an
N-type GaN layer, an InGaN layer and a P-type GaN layer,
respectively.
[0027] The multi-layered structure 14 has a crystal growth
orientation such as a <11 20> crystal orientation or a <10
10> crystal orientation, which intersects with a <0001>
crystal orientation of the multi-layered structure 14. As such,
surface atoms of the N-type layer 141, the active layer 142 and the
P-type layer 143 are not entirely metal atoms. That is, the surface
atoms include metal atoms and nitrogen atoms. Due to the presence
of the nitrogen atoms, the very strong polarity defect found in
conventional multi-layered structures can be effectively minimized
or even eliminated. Accordingly, a wet etching process is feasible
for carrying out roughening of the surfaces of the multi-layered
structure 14.
[0028] Referring to FIG. 4, the multi-layered structure 14 is
patterned and developed to form a mesa structure 144. In
particular, a top surface (not labeled) of the N-type layer 141 is
partially exposed to form an exposed portion 145. In detail, a hard
mask layer (not shown), for example a patterned nickel layer, is
firstly disposed on the multi-layered structure 14. A dry etching
operation such as an RIE etching process is then implemented to
remove part of the P-type layer 143, part of the active layer 142,
and a top surface portion of the N-type layer 141. Thus, an exposed
portion 145 of the N-type layer 141 is formed. The hard mask layer
is then removed so that the mesa structure 144 formed on the
multi-layered structure 14 is obtained. The mesa structure 144 at
least includes but is not limited to the P-type layer 143, the
active layer 142 and a top portion of the N-type layer 141. A
bottom of the mesa structure 144 terminates at a plane as denoted
by the broken line of FIG. 4. The mesa structure 144 includes a top
surface 147 facing away from the substrate 12, and a plurality of
side surfaces 146 adjoining the top surface 147. The side surfaces
146 are located generally between the top surface 147 and the
exposed portion 145.
[0029] Referring to FIG. 5, an N-type electrode 16 and a P-type
electrode 18 are respectively formed on and electrically
(ohmically) contact the N-type layer 141 and the P-type layer 143.
In particular, the N-type electrode 16 is formed on the exposed
portion 145 of the N-type layer 141, and the P-type electrode 18 is
formed on the top surface 147 of the mesa structure 144.
[0030] After the formation of the N-type electrode 16 and the
P-type electrode 18, a wet etching process is carried out for
roughening the top surface 147 and the side surfaces 146 of the
mesa structure 144. In particular, the patterned multi-layered
structure 14 is dipped or immersed into an acid etching solution,
such as a solution containing a mixture of phosphoric acid and
sulfuric acid. A molar ratio of the phosphoric acid to the sulfuric
acid is 1:1, and an etching temperature is above 150 degrees
Celsius. In one embodiment, the wet etching process is only applied
to one of the top surfaces and the side surfaces at a time, with
all the other surfaces being suitably protected from etching at
that time. The etching rate, the etching selectivity and the
roughness of each etched surface can be controlled by adjusting any
one or more of the etching temperature, the composition of the
etching solution, and the concentration of the etching solution. As
a result of the wet etching process, a nitride-based semiconductor
light emitting device 20, as illustrated in FIG. 1, is obtained. An
SEM photograph of the multi-layered structure 14 after treatment
with the wet etching process is shown in FIG. 6.
[0031] Advantageously, in order to accelerate the etching rate of
the wet etching process, electromagnetic waves having a
predetermined energy can be employed to irradiate etching areas
such as the side surfaces 146. The energy of the electromagnetic
waves generally is higher than an energy gap of the nitride-based
semiconductor material being etched, so that the nitride-based
semiconductor material can absorb the energy of the electromagnetic
waves. It is understood that the irradiation using the
electromagnetic waves not only can accelerate the etching rate, but
also can be utilized to reduce the etching temperature.
[0032] The chemical etching solution is not limited to an acid
etching solution. Other etching solutions such as an alkaline
etching solution containing potassium hydroxide (KOH) can be
employed, as long as the same or a similar etching effect is
achieved.
[0033] In addition, a person skilled in the art can perform various
changes within the spirit of the present embodiments. For example,
any of the material of the substrates 12, 22, the composition of
the multi-layered structure 14, 24, the composition of the etching
solution, and the etching temperature, etc, can be suitably
changed. In one particular example, the N-type layer 141, 241 is
instead a P-type layer, the N-type electrode 16, 26 is instead a
P-type electrode, the P-type layer 143, 243 is instead an N-type
layer, and the P-type electrode 18, 28 is instead an N-type
electrode.
[0034] It is believed that the present embodiments and their
advantages will be understood from the foregoing description, and
it will be apparent that various changes may be made thereto
without departing from the spirit and scope of the invention or
sacrificing all of its material advantages, the examples
hereinbefore described merely being preferred or exemplary
embodiments of the present invention.
* * * * *