U.S. patent application number 12/687510 was filed with the patent office on 2011-07-14 for patterned sapphire substrate manufacturing method.
Invention is credited to Chi-Hao Cheng, Szu-Hua Ho, Wen-Ching Hsu, Bo-Wen Lin, Yew-Chung Sermon Wu.
Application Number | 20110168670 12/687510 |
Document ID | / |
Family ID | 44257729 |
Filed Date | 2011-07-14 |
United States Patent
Application |
20110168670 |
Kind Code |
A1 |
Wu; Yew-Chung Sermon ; et
al. |
July 14, 2011 |
Patterned Sapphire Substrate Manufacturing Method
Abstract
A patterned sapphire substrate manufacturing method uses
two-section dip etching procedure to improve the lateral etching
rate at each etching position, so as to produce a concave-convex
pattern composed of a plurality of triangular pyramid structures
protruded from a surface onto an upper surface of a sapphire
substrate, such that less planar area of the sapphire substrate
surface will remain, and a mixed solution of sulfuric acid and
phosphoric acid is used in a first dip etching step, and pure
phosphoric acid or a mixed solution of sulfuric acid and phosphoric
acid is used in a second dip etching step for etching the sapphire
substrate to control the inclination of each triangular pyramid
structure precisely, and providing a better light extraction rate
for later manufactured light emitting diodes.
Inventors: |
Wu; Yew-Chung Sermon;
(Hsinchu, TW) ; Cheng; Chi-Hao; (Hsinchu, TW)
; Lin; Bo-Wen; (Hsinchu, TW) ; Hsu; Wen-Ching;
(Hsinchu, TW) ; Ho; Szu-Hua; (Hsinchu,
TW) |
Family ID: |
44257729 |
Appl. No.: |
12/687510 |
Filed: |
January 14, 2010 |
Current U.S.
Class: |
216/51 ;
216/41 |
Current CPC
Class: |
G03F 7/00 20130101 |
Class at
Publication: |
216/51 ;
216/41 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1. A patterned sapphire substrate manufacturing method, and the
sapphire substrate having an upper surface with a crystal
orientation (0001), and the method comprising the steps of: (a)
selectively forming an etching barrier onto the upper surface of
the sapphire substrate, such that a portion of the upper surface is
exposed; (b) using a first etching solution to etch the exposed
portion of the upper surface of the sapphire substrate, such that a
plurality of triangular pyramid frustum structures are formed onto
the upper surface of the sapphire substrate, wherein each
triangular pyramid structure of the plurality of triangular pyramid
frustum structures has a first crystal face with an orientation
(1012), a second crystal face with an orientation (0112), and a
third crystal face with an orientation (1102), and the first
etching solution is a mixed solution of sulfuric acid and
phosphoric acid used for performing a first etch, and the ratio of
the sulfuric acid and the phosphoric acid is 3:1; (c) using the
first etching solution to etch the exposed portion on the upper
surface of the sapphire substrate, such that the plurality of
triangular pyramid frustum structures are formed into the whole
triangular pyramid structures, and the second etching solution is
pure phosphoric acid.
2. The patterned sapphire substrate manufacturing method of claim
1, wherein the first etch is preferably performed at a temperature
of 270.degree. C.
3. The patterned sapphire substrate manufacturing method of claim
1, wherein the second etch is preferably performed at a temperature
of 270.degree. C.
4. The patterned sapphire substrate manufacturing method of claim
1, wherein the etching barrier is formed by silicon oxide.
5. The patterned sapphire substrate manufacturing method of claim
1, wherein the etching barrier is formed onto the upper surface of
the sapphire substrate by a chemical vapor deposition process or a
sputtering process.
6. A patterned sapphire substrate manufacturing method, and the
sapphire substrate having an upper surface with a crystal
orientation (0001), and the method comprising the steps of: (a)
selectively forming an etching barrier onto the upper surface of
the sapphire substrate, such that a portion of the upper surface is
exposed; (b) using a first etching solution to etch the exposed
portion of the upper surface of the sapphire substrate, such that a
plurality of triangular pyramid frustum structures are formed onto
the upper surface of the sapphire substrate, wherein each
triangular pyramid structure of the plurality of triangular pyramid
frustum structures has a first crystal face with an orientation
(1012), a second crystal face with an orientation (0112), and a
third crystal face with an orientation (1102), and the first
etching solution is a mixed solution of sulfuric acid and
phosphoric acid used for performing a first etch, and the ratio of
the sulfuric acid and the phosphoric acid is 5:1; (c) using the
first etching solution to etch the exposed portion on the upper
surface of the sapphire substrate, such that the plurality of
triangular pyramid frustum structures are formed into the whole
triangular pyramid structures, and the second etching solution is a
mixed solution of sulfuric acid and phosphoric acid, and the ratio
of the sulfuric acid and the phosphoric acid is 5:1.
7. The patterned sapphire substrate manufacturing method of claim
6, wherein the etching barrier is made of silicon oxide.
8. The patterned sapphire substrate manufacturing method of claim
6, wherein the etching barrier is formed onto the upper surface of
the sapphire substrate by a chemical vapor deposition process or a
sputtering process.
Description
BACKGROUND OF THE INVENTION
[0001] (a) Field of the Invention
[0002] The present invention relates to a method of patternizing a
sapphire substrate surface, and more particularly to an etching
method of producing concave-convex patterns onto a sapphire
substrate surface effectively up to the manufacturing quality.
[0003] (b) Description of the Related Art
[0004] In general, a light emitting diode comprises a substrate, a
first semiconductor layer, an electrode, a light emitting layer, a
second semiconductor layer, an ohmic contact layer, and another
electrode, wherein the first semiconductor layer, light emitting
layer, second semiconductor layer, ohmic contact layer and
electrodes are installed sequentially on the substrate, and the
light emitting layer is just covered onto a portion of the first
semiconductor layer, and the electrodes are installed onto the
first semiconductor layer not covered by the light emitting
layer.
[0005] Sapphire or silicon carbide (SiC) is usually used as a
substrate for performing a direct epitaxial growth of a first
semiconductor layer on the substrate. Since the epitaxial growing
surface of the substrate is in a planar shape, its misalignment
defect is extended to quantum wells and the crystalline quality is
affected when the epitaxy is performed directly on the plane. Such
result only affects the yield rate of the fabricated devices, but
also reduces the light emitting efficiency and the electron
mobility, and fails to produce light emitting diodes with a higher
light emitting efficiency.
[0006] Therefore, roughening an epitaxial substrate surface is
considered as one of the effective ways of improving the light
emitting efficiency of the light emitting diode, and a light
emitting device having a surface texturing substrate as disclosed
in U.S. Pat. No. 6,091,085 comprises a sapphire substrate, and a
rough surface composed of a plurality of protrusions and a
plurality of recessions randomly formed on a contact surface of the
sapphire substrate with a semiconductor layer by a mechanical
polishing method or an ion etching method, so as to improve the
light extraction efficiency.
[0007] Although the aforementioned method can improve the light
extraction efficiency by roughening the sapphire substrate surface,
the sapphire substrate surface is damaged easily due to a
composition change and a lattice distortion occurred at the
sapphire substrate surface and caused by ion bombardments occurred
during the roughening process. Furthermore, some mask materials or
reacting ions are sputtered and subsided into a certain depth from
the substrate surface during the process, so that the quality of
epitaxial layer formed at a later stage will be affected.
Similarly, the lattice structure of the sapphire substrate surface
is damaged in the mechanical polishing process, and thus the
quality of semiconductor layer grown at a later stage will be
affected, and the internal quantum efficiency will be lowered.
[0008] Thereafter, a dry etching method and a wet etching method
for producing a concave-convex pattern on a sapphire substrate
surface without damaging a lattice structure of the sapphire
substrate surface were disclosed. In similar etching methods, a
photosensitive material (or photoresist) is coated onto a sapphire
substrate surface first, and then a mask is placed onto the
sapphire substrate, wherein the mask has a pattern corresponding to
the concave-convex pattern, and then an exposure procedure is
carried out for performing a selective light sensing to the light
sensitive material, such that the pattern on the mask is
transferred onto the sapphire substrate. After the exposure
procedure is completed, a photolithography is performed, so that
the photoresist obtains a same or complementary pattern of the mask
pattern, and finally an etching reaction is performed to produce an
expected pattern on the sapphire substrate surface.
[0009] Although the principle of using an etching reaction to
produce an expected concave-convex pattern on a sapphire substrate
surface is well known, there are many parameters affecting the
quality of the concave-convex pattern finally formed onto the
sapphire substrate surface, and these parameters include the
photoresist material, mask pattern ratio, exposure time, selection
of chemical solution for dipping the sapphire substrate,
composition proportion of chemical solution, dipping temperature,
dipping time, and even frequency of dipping in the chemical
solution, etc.
[0010] Therefore, we are unable to predict necessary conditions
from a single parameter condition during the process of perceiving
the patterned sapphire substrate manufacturing method, but we can
do the evaluations indirectly in the complicated manufacturing
process to learn the necessary conditions. It is the best measure
to explore possible characteristics by continuously and gradually
varying the parameter conditions of similar nature.
[0011] The inventor of the present invention based on years of
experience in the related industry to conduct extensive researches
and experiments, and finally invented a patterned sapphire
substrate manufacturing method to overcome the shortcomings of the
prior art.
SUMMARY OF THE INVENTION
[0012] Therefore, it is a primary objective of the present
invention to overcome the aforementioned shortcoming and deficiency
of the prior art by providing a patterned sapphire substrate
manufacturing method for controlling the manufacturing quality of
producing a concave-convex pattern onto a sapphire substrate
surface effectively.
[0013] To achieve the aforementioned objective, the present
invention uses a wet etching process to effectively produce a
concave-convex pattern on a sapphire substrate surface during a
manufacturing process. Since the temperature of the etching process
keeps decreasing, and the etching rate tends to become slower to
affect the angle, and thus a two-section dip etching procedure is
adopted to improve the lateral etching rate at each etching
position, so as to produce a concave-convex pattern having a
plurality of triangular pyramid structures protruded from the
sapphire substrate upper surface, such that a smaller planar area
of the sapphire substrate surface will remain, and it helps
improving the yield rate of producing devices on the surface of the
sapphire substrate at later processes.
[0014] A mixed solution of sulfuric acid and phosphoric acid is
used in the first dip etching step, and a pure phosphoric acid or a
mixed solution of sulfuric acid and phosphoric acid is used in the
second dip etching step for etching the sapphire substrate to
control the inclination of each triangular pyramid structure
precisely, such that the light emitting diode manufactured at a
later process can obtain a better light extraction rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a cross-sectional view of a sapphire substrate of
the present invention;
[0016] FIG. 2 is a cross-sectional view of an etching barrier
coated onto an upper surface of a sapphire substrate in accordance
with the present invention;
[0017] FIG. 3 is a cross-sectional view of a photoresist coated
onto an etching barrier together with a mask for performing a
yellow light lithography process in accordance with the present
invention;
[0018] FIG. 4 is a cross-sectional view of a photoresist used for
completing a yellow light lithography process in accordance with
the present invention;
[0019] FIG. 5 is a cross-sectional view of a structure after a
photoresist is removed in accordance with the present
invention;
[0020] FIG. 6 is a cross-sectional view of producing a plurality of
triangular pyramid frusta on a sapphire substrate after a first
etch takes place in accordance with the present invention; and
[0021] FIG. 7 is a cross-sectional view of producing a plurality of
whole triangular pyramids on a sapphire substrate after a second
etch takes place in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The technical characteristics of the present invention will
become apparent with the detailed description of the preferred
embodiments and the illustration of the related drawings as
follows.
[0023] The present invention provides an etching method with a
manufacturing quality capable of enhancing the manufacturing
production capability to effectively produce a concave-convex
pattern on a sapphire substrate surface and controlling the
concave-convex pattern produced on the sapphire substrate surface.
A chemical wet etching method is used for etching the sapphire
substrate into a specific concave-convex pattern, wherein the
specific concave-convex pattern is composed of a plurality of whole
triangular pyramid structures protruded from the surface, and a
two-section etching procedure is adopted, and the effect of
different chemical solutions to different etching rates of each
specific crystal face of the sapphire is used for controlling the
angle of the triangular pyramid structures of the patterned
sapphire substrate.
[0024] With reference to FIGS. 1 to 7 for a patterned sapphire
substrate manufacturing method in accordance with the present
invention, the patterned sapphire substrate manufacturing method
comprises the following steps:
[0025] (a) Prepare a sapphire substrate 10 as shown in FIG. 1,
wherein the sapphire substrate 10 has an upper surface 11 with a
crystal orientation (0001). In other words, a C-plane sapphire
substrate 10 is prepared first.
[0026] (b) Coat an etching barrier 12 as shown in FIG. 2 onto the
upper surface 11 of the sapphire substrate 10, wherein the etching
barrier 12 is made of silicon oxide, and the etching barrier 12 is
formed onto the upper surface 11 of the sapphire substrate 10 by a
chemical vapor deposition (CVD) process or a sputtering process in
accordance with a preferred embodiment.
[0027] (c) Prepare a mask 20 as shown in FIG. 3, wherein the mask
20 has a plurality of square patterns arranged with a predetermined
interval apart from each other.
[0028] (d) Coat a layer of photoresist 13 as shown in FIG. 3 onto
the etching barrier 12, and perform a yellow light lithography
process to transfer a pattern of the mask 20 onto the photoresist
13.
[0029] (e) Remove the exposed area of the etching barrier 12 which
is not covered by the photoresist 13 as shown in FIG. 4, such that
the portion not covered by the etching barrier 12 is exposed from
the upper surface 11 of the sapphire substrate 10 (which is also
the target of the etching process), wherein a buffer oxide etching
solution (BOE) is used for removing the exposed etching barrier 12
in the preferred embodiment.
[0030] (f) Remove the photoresist on the etching barrier 12 as
shown in FIG. 5, wherein the photoresist is removed by dipping the
photoresist into an acetone solution.
[0031] (g) Perform a first etch, wherein the first etching solution
is used for etching an exposed portion of the upper surface 11 of
the sapphire substrate 10 which is not covered by the etching
barrier 12 as shown in FIG. 6, such that the plurality of
triangular pyramid frustum structures 111 are formed onto the upper
surface 11 of the sapphire substrate 10, and the etching barrier 12
is coated onto a flat top of each triangular pyramid frustum
structures 111.
[0032] (h) Perform a second etch, wherein the second etching
solution is used for etching an exposed portion of the upper
surface 11 of the sapphire substrate 10 which is not covered by the
etching barrier 12 as shown in FIG. 7, such that the plurality of
triangular pyramid frustum structures are formed into the whole
triangular pyramid structure 112, and the etching barrier 12 is
removed at the same time, or the etching barrier 12 is removed
before the second etch as described in step (h) takes place, such
that the whole triangular pyramid structure can be formed.
[0033] In a preferred embodiment, the first etching solution used
for the first etch is a mixed solution of sulfuric acid and
phosphoric acid. In the mixed solution, the ratio of sulfuric acid
and phosphoric acid is 3:1. In addition, the first etch is
preferably conducted at a temperature of 270.degree. C. The second
etching solution used for the second etch is a pure phosphoric
acid, and the second etch is preferably conducted at a temperature
of 270.degree. C.
[0034] In another preferred embodiment, the first etching solution
used for the first etch is a mixed solution of sulfuric acid and
phosphoric acid, and the ratio of sulfuric acid and phosphoric acid
in the mixed solution is 5:1. In addition, the first etch is
preferably conducted at a temperature range between 150.degree. C.
and 350.degree. C. The second etching solution used for the second
etch is a mixed solution of sulfuric acid and phosphoric acid, and
the ratio of sulfuric acid and phosphoric acid in the mixed
solution is 5:1,and the second etch is preferably conducted at a
temperature range between 150.degree. C. and 350.degree. C.
[0035] If different parameter conditions of the aforementioned
preferred embodiments are used for completing the first etch, there
will be some places on the etching barrier 12 not etched by the
first etching solution, such that an original C-plane sapphire
substrate 10 will remain. Since the etching solution has a slower
etching rate on the r-plane of the sapphire substrate 10, therefore
there will be three inclined r-planes in three different
orientations remained at the periphery of an area covered by the
etching barrier 12, after the sapphire substrate (which is also an
exposed portion of the upper surface 11) not protected by the
etching barrier 12 is etched.
[0036] After the etching process by the first etching solution
takes place, a plurality of triangular pyramid frustum structures
111 as shown in FIG. 6 will be formed on the upper surface 11 of
the sapphire substrate 10, wherein the triangular pyramid frustum
structures 111 have a first crystal face with an orientation
(1012), a second crystal face with an orientation (0112) and a
third crystal face with an orientation (1102), wherein the three
crystal faces are the aforementioned three inclined r-planes.
[0037] The second etching solution has a slower etching rate on the
C-plane of the sapphire substrate 10, and thus the aforementioned
triangular pyramid frustum structures 101 will be formed into the
whole triangular pyramid structure 112 as shown in FIG. 7 after the
etching process by the second etching solution takes place. Here,
the "whole triangular pyramid structure" is defined with respect to
the triangular pyramid frustum structure. Even there are minor
flaws in the triangular pyramid structure formed after the etching
process performed by the second etching solution, such triangular
pyramid structure is still considered as the whole triangular
pyramid structure 112 defined by the present invention.
[0038] In the whole triangular pyramid structure formed on the
upper surface of the sapphire substrate by the patterned sapphire
substrate manufacturing method in accordance with the present
invention, the second etching solution is used for the etching and
formation, wherein the included angle between the inclined surface
and the horizontal surface is equal to 37 degrees. Since the
lateral etching rate of the second etching solution is faster, the
inclination of the inclined plane of the triangular pyramid gone
through etches with different time durations can be controlled.
Particularly, optoelectronic semiconductor devices such as light
emitting diodes can be manufactured by using the patterned sapphire
substrate of the present invention. The patterned sapphire
substrate can effectively reduce the density of internal defectives
(such as dislocation) occurred during the epitaxial process of the
light emitting diode to enhance internal quantum efficiency and
light extraction rate of the light emitting diode.
[0039] In summation of the description above, the present invention
can improve the epitaxial quality of an optoelectronic
semiconductor device to enhance the optoelectric properties of the
optoelectronic semiconductor device when the patterned sapphire
substrate of the present invention is applied for manufacturing the
optoelectronic semiconductor device, and the present invention also
complies with the patent application requirements, and thus the
invention is duly filed for patent application.
[0040] While the invention has been described by device of specific
embodiments, numerous modifications and variations could be made
thereto by those generally skilled in the art without departing
from the scope and spirit of the invention set forth in the
claims.
* * * * *