U.S. patent application number 12/729721 was filed with the patent office on 2011-09-22 for method of fabricating a light emitting diode chip having phosphor coating layer.
This patent application is currently assigned to Everlight Electronics Co., Ltd.. Invention is credited to Chung-Chuan Hsieh.
Application Number | 20110229993 12/729721 |
Document ID | / |
Family ID | 44647566 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110229993 |
Kind Code |
A1 |
Hsieh; Chung-Chuan |
September 22, 2011 |
METHOD OF FABRICATING A LIGHT EMITTING DIODE CHIP HAVING PHOSPHOR
COATING LAYER
Abstract
A method of fabricating light emitting diode chips having a
phosphor coating layer comprises providing a substrate having a
plurality of light emitting diodes formed thereon; forming a
conductive bump on at least one of the plurality of light emitting
diodes; forming a phosphor coating layer over the substrate and the
light emitting diodes; cutting the phosphor coating layer by a
point cutter to remove an upper portion of the phosphor coating
layer, so as to reduce a thickness of the phosphor coating layer
and expose the conductive bump; and forming a plurality of
individual light emitting diode chips having the phosphor coating
layer by separating the plurality of light emitting diodes.
Inventors: |
Hsieh; Chung-Chuan;
(Tucheng, TW) |
Assignee: |
Everlight Electronics Co.,
Ltd.
|
Family ID: |
44647566 |
Appl. No.: |
12/729721 |
Filed: |
March 23, 2010 |
Current U.S.
Class: |
438/29 ;
257/E21.599; 257/E33.061; 438/33 |
Current CPC
Class: |
H01L 2224/48091
20130101; H01L 33/508 20130101; H01L 2933/0041 20130101; H01L
2224/48091 20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
438/29 ; 438/33;
257/E21.599; 257/E33.061 |
International
Class: |
H01L 33/00 20100101
H01L033/00; H01L 21/78 20060101 H01L021/78 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2010 |
TW |
099108042 |
Claims
1. A method of fabricating a plurality of light emitting diode
chips having a phosphor coating layer, comprising: providing a
substrate having a plurality of light emitting diodes formed
thereon; forming a conductive bump on at least one of the plurality
of light emitting diodes; forming the phosphor coating layer over
the substrate and the light emitting diodes; cutting the phosphor
coating layer with a point cutter to remove an upper portion of the
phosphor coating layer, so as to reduce a thickness of the phosphor
coating layer and expose the conductive bump; and forming a
plurality of individual light emitting diode chips having the
phosphor coating layer by separating the plurality of light
emitting diodes.
2. The method of claim 1, wherein the point cutter is a diamond
cutter or a Tungsten Carbide(WC) cutter.
3. The method of claim 1, wherein the point cutter cuts the upper
portion of the phosphor coating layer in a horizontal
direction.
4. The method of claim 1, further comprising cutting an upper
portion of the conductive bump by the point cutter.
5. The method of claim 4, wherein, after cutting, an upper surface
of the phosphor coating layer is substantially at the same level as
an upper surface of the conductive bump.
6. The method of claim 1, wherein cutting the phosphor coating
layer comprises: cutting the phosphor coating layer to remove a
surface layer of the phosphor coating layer; checking whether the
conductive bump is exposed; and if the conductive bump is not
exposed, repeating the cutting step until the conductive bump is
exposed.
7. The method of claim 1, wherein cutting the phosphor coating
layer is performed by: rotating the point cutter about a rotation
axis in a vertical direction; and moving the substrate relative to
the point cutter in a horizontal direction.
8. The method of claim 1, wherein the phosphor coating layer is
formed by one of transfer molding, compressing molding, screen
printing, spin coating, dispensing, electrophoresis and spray
coating.
9. The method of claim 1, wherein forming the plurality of
individual light emitting diode chips having the phosphor coating
layer comprises dicing the phosphor coating layer, the light
emitting diodes, and the substrate.
10. The method of claim 9, wherein the step of dicing is performed
by a blade or a laser.
11. The method of claim 9, wherein the step of dicing further
comprises: dicing the phosphor coating layer and the light emitting
diodes with a blade, and dicing the substrate with a laser.
12. The method of claim 1, wherein: the plurality of light emitting
diodes comprises a plurality of light emitting diode dies formed
separately on the substrate, and wherein the step of forming the
phosphor coating layer further comprises filling a space between
the dies.
13. The method of claim 12, wherein forming the plurality of
individual light emitting diode chips having the phosphor coating
layer comprises dicing the phosphor coating layer and the
substrate.
14. The method of claim 13, wherein the step of dicing is performed
by a blade or laser.
15. The method of claim 14, wherein the step of dicing further
comprises: dicing the phosphor coating layer and the light emitting
diodes with a blade, and dicing the substrate with a laser.
16. The method of claim 1, wherein the step of cutting results in
an upper surface of the phosphor coating layer having a rough
surface with regular patterns.
17. The method of claim 1, wherein the step of cutting results in
the phosphor coating layer having a substantially uniform
thickness.
19. The method of claim 1, wherein the step of forming the phosphor
coating layer further comprises mixing at least a phosphor powder
and a resin, the resin being a silicone or an epoxy.
20. The method of claim 1, wherein the step of forming the
conductive bump further comprises forming the conductive bump from
Au or alloy of Au.
21. The method of claim 1, wherein the substrate is a SiC
substrate, a Si substrate, a sapphire substrate, a ZnO substrate, a
GaAs substrate, a spinelle substrate, or a metal substrate.
22. The method of claim 12, wherein the substrate is a printed
circuit board, a ceramic substrate, a silicon substrate, or a metal
substrate.
Description
RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority to Taiwan Patent Application No. 099108042, filed Mar. 18,
2010, the entire content of which is incorporated by reference
herein in its entirety.
TECHNOLOGY FIELD
[0002] The present invention relates to a method of fabricating a
light emitting diode chip, and particularly to a method of
fabricating a light emitting diode chip having a uniform phosphor
coating layer.
BACKGROUND
[0003] Due to their long lifetime, small size, high resistance to
shock and vibration, low heat generation, and low power
consumption, light emitting diodes (LEDs) have been widely used in
display or as light source in various consumer electronic devices,
electrical appliances, and apparatuses. Recently, multi-color and
high brightness LEDs have also been used in out-door large-screen
displays, traffic lights, etc. In the future, LEDs may act as the
major illumination light source, with the advantages of energy
saving as well as environment protection.
[0004] One common type of LED is the white LED, which is capable of
emitting white light. Different approaches can be implemented to
realize white light emitting from an LED. One approach is to use
the combination of a blue LED chip and yellow phosphor. FIG. 1
shows the cross-sectional view of a prior art white LED. The
conventional white LED 100 shown in FIG. 1 comprises a blue LED
chip 110 arranged on a base 120. The blue LED chip 110 is
electrically connected to the base 120 by electrical wires W. A
yellow phosphor resin 130 is formed to cover the blue LED chip 110
and the wires W by dispensing, for example. A lens 140 is formed
over the yellow phosphor resin 130. The blue light emitted by the
blue LED chip 110 is partially absorbed by the yellow phosphor
powders in the yellow phosphor resin 130 and converted to yellow
light. Unabsorbed blue light mixes with the yellow light so as to
generate a white light.
[0005] However, there are problems with such convention LEDs in
that it is often difficult for the yellow phosphor resin 130 formed
by dispensing to evenly cover the LED chip. A thicker portion of
the yellow phosphor resin 130 absorbs more blue light and emits
more yellow light than a thinner portion. Accordingly, it is
difficult for such an LED 100 to emit light with uniform color. For
example, while it may be possible to realize white light in the
center portion of the yellow phosphor resin 130, light emitted from
other portion of the yellow phosphor resin 130 may undesirably
appear yellowish.
SUMMARY
[0006] In the following description, certain aspects and
embodiments will become evident. It should be understood that the
aspects and embodiments, in their broadest sense, could be
practiced without having one or more features of these aspects or
embodiments. Thus, it should be understood that these aspects and
embodiments are merely exemplary and not restrictive.
[0007] In accordance with one aspect of the disclosure describing
embodiments of the present invention, there is provided a method of
fabricating light emitting diode chips having a phosphor coating
layer. In the fabrication method, a substrate is provided having a
plurality of light emitting diodes formed thereon. A conductive
bump is formed on at least one of the plurality of light emitting
diodes. A phosphor coating layer is formed over the substrate and
the light emitting diodes and is cut by a point cutter to remove an
upper portion of the phosphor coating layer, so as to reduce a
thickness of the phosphor coating layer and expose the conductive
bump. A plurality of individual light emitting diode chips having
the phosphor coating layer are formed by separating the plurality
of light emitting diodes.
[0008] Features and advantages consistent with the invention will
be set forth in part in the description which follows, and in part
will be obvious from the description, or may be learned by practice
of the invention. Such features and advantages will be realized and
attained by means of the elements and combinations particularly
pointed out in the appended claims.
[0009] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
[0010] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate several
embodiments of the invention and together with the description,
serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a cross-sectional view showing a prior art white
light emitting diode.
[0012] FIGS. 2A-2E are cross-sectional views showing an exemplary
process of fabricating light emitting diode chips according to one
embodiment of the invention.
[0013] FIGS. 3A-3B are a plan view and a side view, respectively,
illustrating the rotating direction of the diamond cutter and the
moving direction of the semiconductor wafer during the cutting step
shown in FIG. 2C.
[0014] FIGS. 4A-4E are cross-sectional views showing an exemplary
process of fabricating light emitting diode chips according to
another embodiment of the invention.
[0015] FIG. 5 is a enlarged view illustrating an exemplary light
emitting diode chip shown in FIG. 4A.
DETAILED DESCRIPTION
[0016] Embodiments consistent with the invention include methods of
fabricating one or more light emitting diode chips having a uniform
phosphor coating layer. Hereinafter, embodiments consistent with
the present invention will be described with reference to the
drawings. Wherever possible, the same reference numbers will be
used throughout the drawings to refer to the same or like
parts.
[0017] FIGS. 2A-2E show an exemplary process of fabricating one or
more light emitting diode chips according to one embodiment of the
invention. Referring now to FIG. 2A, an exemplary substrate C is
first provided. A light emitting unit 210 is formed over the
substrate C. The light emitting unit 210 may comprise a first
semiconductor layer 212 with a first conductivity type, a light
emitting layer 214, and a second semiconductor layer 216 with a
second conductivity type. The light emitting layer 214 may be
sandwiched between the first semiconductor layer 212 and the second
semiconductor layer 216. The substrate C may be made of, for
example, silicon carbide (SiC), silicon (Si), sapphire, zinc oxide
(ZnO), gallium arsenide (GaAs), spinelle (MgAl.sub.2O.sub.4), or
metal (such as copper). A plurality of electrodes 220 are formed on
the second semiconductor layer 216 and a plurality of conductive
bumps 230 are then formed on the electrodes 220. The conductive
bumps may be made of, for example, gold (Au) or gold alloy.
[0018] Referring now to FIG. 2B, a phosphor coating layer 240 is
formed over the second semiconductor layer 216 and the conductive
bumps 230. The phosphor coating layer 240 may cover the conductive
bumps 230. In some embodiments, the phosphor coating layer 240 may
be formed by, for example, transfer molding, compressing molding,
screen printing, spin coating, dispensing, electrophoresis, spray
coating, or any other suitable methods. In one embodiment, the
phosphor coating layer 240 may be a mixture of at least one type of
phosphor powder and a resin. The resin may be, for example,
silicone or epoxy resin.
[0019] After forming the phosphor coating layer 240 over the second
semiconductor layer 216 and the conductive bumps 230, the phosphor
coating layer 240 may be subjected to curing. Then, as shown in
FIG. 2C, an upper portion of the cured phosphor coating layer 240'
is removed by cutting the phosphor coating layer 240' using a point
cutter, e.g., a diamond cutter or a Tungsten Carbide(WC) cutter
(not shown), to reduce the thickness of the cured phosphor coating
layer 240' so that the conductive bumps 230 are exposed. The
conductive bumps 230 are exposed so as to facilitate the subsequent
wire bonding process. It is to be noted that the step of cutting
the phosphor coating layer 240' may be performed multiple times.
After each cutting step, the wafer may be checked to see whether
the conductive bumps 230 are exposed. If the conductive bumps 230
are not exposed, the cutting step is repeated. Such procedure may
be repeatedly performed until the conductive bumps 230 are
exposed.
[0020] Referring now to FIGS. 3A and 3B, a plan view and a side
view, respectively, of the phosphor coating layer 240' of FIG. 2C
are shown to illustrate how the diamond cutter moves relative to
the semiconductor wafer during cutting of the phosphor coating
layer 240'. In one embodiment, when cutting the phosphor coating
layer 240', the diamond cutter 250 may rotate clockwise about a
rotation axis in the vertical direction. The wafer may move
relative to the diamond cutter 250 in the horizontal direction
indicated by V. However, the rotation direction of the diamond
cutter 250 and the moving direction of the wafer are not limited to
those described above. For example, the diamond cutter 250 may also
rotate counter-clockwise. In some embodiments, the diamond cutter
250 may also cut the conductive bumps 230, and in the meantime, an
upper portion of the conductive bumps 230 is removed.
[0021] It is to be noted that, in a conventional chemical
mechanical polishing method, polishing slurry comprising abrading
particles and a polishing pad having abrading particles are needed.
During polishing, the polishing slurry and the material polished
from the polishing surface cannot be removed instantaneously.
Therefore, when a chemical mechanical polishing method is used to
polish the phosphor coating layer, it is difficult to keep the
upper surface of the phosphor coating layer at the same level as
the upper surface of the conductive bumps due to the different
degree of hardness between the phosphor coating layer and the
conductive bumps. On the other hand, consistent with an embodiment
and principles of the present invention, the diamond cutter 250 may
cut the phosphor coating layer 240' and the conductive bumps 230 at
the same time, and may push away the material cut from the phosphor
coating layer 240' and/or that cut from the conductive bumps 230
immediately. In such a manner, the upper surface of the phosphor
coating layer 240' and that of the conductive bumps 230 may be kept
at the same height level after the cutting step, as shown in FIGS.
2C-2E and 3B.
[0022] Consistent with an embodiment and principles of the present
invention, the diamond cutter 250 cuts the phosphor in the
horizontal direction. Therefore, the phosphor layer 240' after
cutting has a substantially uniform thickness, which may be about 5
.mu.m to about 40 .mu.m. For example, the thickness of the phosphor
layer 240' after cutting may be about 30 .mu.m.
[0023] Due to the rotation of the diamond cutter 250, the tip of
the diamond cutter moves in a circle when cutting the phosphor
coating layer 240', and then forming a curved cutting line on the
surface of the wafer as shown in FIG. 3. In addition, since the
wafer moves relative to the diamond cutter 250 in the direction V,
the cutting line is then expanded to a cutting surface, so that the
entire phosphor coating layer 240' is subjected to cutting and an
upper portion of the entire phosphor coating layer 240' may be
removed by the cutting step. The surface 244 of the phosphor
coating layer 240' after cutting may have regular patterns. These
patterns may help to reduce the total reflection of the light
emitted from the light emitting layer 214 and/or that emitted by
the phosphor coating layer 240 at the surface 244 of the phosphor
coating layer 240', and thus may improve the extraction
efficiency.
[0024] Referring now to FIG. 2D, a plurality of individual light
emitting diode chips 200 having a phosphor coating layer 240' may
be formed by cutting or otherwise separating the phosphor coating
layer 240', the light emitting unit 210, and the substrate C along
the vertical dashed lines in the spaces G between the conductive
bumps 230. Such separating may be accomplished via, for example,
dicing with a blade or laser cutting. FIG. 2E is an enlarged view
showing such a light emitting diode chip 200 after the separating
step. The light emitting diode chip 200 shown in FIG. 2E comprises
two conductive bumps. However, it is noted that the number of
conductive bumps comprised in one light emitting diode chip may not
be limited to two. A light emitting diode chip consistent with an
embodiment and principles of the present invention may comprise,
e.g., one, three, or more conductive bumps. A larger light emitting
diode chip may have more conductive bumps, so that uniformity of
the current distribution may be improved.
[0025] Consistent with principles of the present invention,
different equipment may be used to dice the phosphor coating layer
240', the light emitting unit 210, and the substrate C. For
example, the phosphor coating layer 240', the light emitting unit
210, and the substrate C may be diced using a blade. Alternatively,
the phosphor coating layer 240' and the light emitting unit 210 may
be diced using a blade, and the substrate C may be diced using a
laser. As another alternative, the phosphor coating layer 240', the
light emitting unit 210, and the substrate C may be diced using a
laser.
[0026] Consistent with principles of the present invention, since
the phosphor coating layer 240' is first formed over the light
emitting unit 210 and then cutting is performed on the phosphor
coating layer 240' to reduce its thickness, the phosphor coating
layer may be controlled to form only on the upper surface of the
light emitting unit 210. Moreover, the thickness of the phosphor
coating layer formed on the upper surface of the light emitting
unit may have a substantially uniform thickness. Therefore, the
light emitted by the light emitting diode chip in an embodiment of
the invention may have better uniformity. That is, uniform white
color may be emitted from the entire upper surface of the phosphor
coating layer of the light emitting diode chip.
[0027] FIGS. 4A-4E show an exemplary process of fabricating light
emitting diode chips according to another embodiment of the
invention. FIG. 5 is an enlarged view of a light emitting diode
shown in FIG. 4A.
[0028] Referring to FIGS. 4A and 5, a submount 410 is provided with
a plurality of light emitting diodes 420 formed thereon. Each light
emitting diode 420 may comprise a substrate 422, a first
semiconductor layer 424 with a first conductivity type, a light
emitting layer 426, and a second semiconductor layer 428 with a
second conductivity type. The light emitting layer 426 may be
sandwiched between the first semiconductor layer 424 and the second
semiconductor layer 428. The submount 410 may be print circuit
board, ceramic submount, silicon submount, or metal submount. The
substrate 422 may be made of, for example, sapphire.
[0029] As shown in FIG. 4A, a recess R may be formed in the light
emitting diode 420, exposing portion of the first semiconductor
layer 424. A first electrode P1 is formed over the portion of the
first semiconductor layer 424 exposed in the recess R. A second
electrode P2 is formed over the second semiconductor layer 424.
[0030] Next, referring to FIG. 4B, a first conductive bump 432 and
a second conductive 434 are formed over the first electrode P1 and
the second electrode P2, respectively. The top point of the first
conductive bump 432 and that of the of the second conductive bump
434 may be kept at approximately the same height level.
[0031] Referring to FIG. 4C, a phosphor coating layer 440 is then
formed over the submount 410, the light emitting diode chips 420,
the first conductive bumps 432 and the second conductive bumps 434.
The phosphor coating layer 440 may fill the spaces G1 between the
light emitting diode chips. In some embodiments, the phosphor
coating layer 440 may be formed by, for example, transfer molding,
compressing molding, screen printing, spin coating, dispensing,
electrophoresis, spray coating, or any other suitable methods. The
phosphor coating layer 440 may be a mixture of at least one type of
phosphor powder and a resin. The resin may be, for example,
silicone or epoxy resin.
[0032] After forming, the phosphor coating layer 440 is subjected
to curing. Then, as shown in FIGS. 4C and 4D, an upper portion of
the cured phosphor coating layer 440' is removed by cutting the
phosphor coating layer 440' using a point cutter, e.g., a diamond
cutter 450, to reduce the thickness of the phosphor layer 440' so
that the first conductive bumps 432 and the second conductive bumps
434 are exposed. In some embodiments, when cutting the phosphor
coating layer 440', the diamond cutter 450 may also cut the first
upper end portions 432a of the first conductive bumps 432 and the
second upper end portions 434a of the second conductive bumps
434.
[0033] Consistent with the present invention, since the diamond
cutter 450 may cut the phosphor coating layer 440', the first upper
end portions 432a of the first conductive bumps 432, and the second
upper end portions 434a of the second conductive bumps 434 at the
same time, the upper surface 444 of the phosphor coating layer
440', the first upper surfaces 432b of the first conductive bumps
432, and the second upper surfaces 434b of the second conductive
bumps 434 may be kept at substantially the same height level after
the cutting step, as shown in FIG. 4D.
[0034] Consistent with principles of the present invention, since
the diamond cutter 450 cuts the phosphor coating layer 440 in a
rotation manner (same to that shown in FIGS. 2C, 3A, and 3B), the
surface 444 of the phosphor coating layer 440' after cutting may
have regular patterns. These patterns may help to reduce the total
reflection of the light emitted from the light emitting diode chips
420 and/or that emitted by the phosphor coating layer 440' at the
surface 444 of the phosphor coating layer 440', and thus may
improve the extraction efficiency.
[0035] Then, referring to FIG. 4D, the phosphor coating layer 440'
and the submount 410 are diced along the vertical dashed lines in
the spaces G1 between the light emitting diode chips 420, so as to
form a plurality of individual light emitting diode chips 400
having a phosphor coating layer. One of the light emitting diode
chips 400 is shown in FIG. 4E. Consistent with principles of the
present invention, different equipment may be used to dice the
phosphor coating layer 440' and the submount 410. For example, the
phosphor coating layer 440' and the submount 410 may be diced using
a blade. Alternatively, the phosphor coating layer 440' may be
diced using a blade, and the submount 410 may be diced using a
laser. As another alternative, the phosphor coating layer 440' and
the submount 410 may be diced using a laser.
[0036] In one embodiment, since the phosphor coating layer 440' is
first formed over the light emitting diode chips 420 and then
cutting is performed on the phosphor coating layer 440' to reduce
its thickness, the phosphor coating layer thus formed on the light
emitting diode chips may have a substantially uniform thickness.
Therefore, the light emitted by the light emitting diode chip
consistent with the present invention may have better
uniformity.
[0037] In one embodiment, since the light emitting diode chips 420
are provided over the submount 410, the phosphor coating layer 440'
may fully fill the space between the chips. Therefore, the phosphor
coating layer may also be formed on the side surface S of the light
emitting diode chip 420. The thickness of the phosphor coating
layer formed on the side surface S may be controlled to be smaller
than the thickness of the phosphor coating layer formed on the
upper surface of the light emitting chip. Since the light emitted
from the side surface S of the light emitting diode chip 420 is
relatively weaker, thinner phosphor coating layer on the side
surface may help to ensure better uniformity and higher brightness
across the entire light emitting diode chip including the upper
surface and the side surface.
[0038] In summary, an embodiment of the present invention may use a
diamond cutter to cut the phosphor coating layer so as to reduce
the thickness of the phosphor coating layer. The formed phosphor
coating layer after cutting has very uniform thickness. Therefore,
the light emitted from the light emitting diode chip having
phosphor coating layer consistent with the present invention may
have good uniformity. In another embodiment, since the ratio
between the vertical thickness and the lateral thickness of the
phosphor coating layer on the upper surface and the side surface,
respectively, of the light emitting diode chip may be controlled,
good light uniformity may be achieved across the entire light
emitting diode chip. Moreover, since the surface of the phosphor
coating layer after cutting may have regular patterns, the total
reflection at the surface of the phosphor coating layer may be
reduced, so that the extraction efficiency of the light emitting
diode chip may be improved.
[0039] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
* * * * *