U.S. patent application number 13/541191 was filed with the patent office on 2013-07-25 for processing method for wafer.
This patent application is currently assigned to DISCO CORPORATION. The applicant listed for this patent is Hitoshi Hoshino. Invention is credited to Hitoshi Hoshino.
Application Number | 20130189806 13/541191 |
Document ID | / |
Family ID | 48797550 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130189806 |
Kind Code |
A1 |
Hoshino; Hitoshi |
July 25, 2013 |
PROCESSING METHOD FOR WAFER
Abstract
A wafer has, on a front face thereof, a device region in which a
device is formed in regions partitioned by a plurality of scheduled
division lines. An outer peripheral region surrounds the device
region. A reflecting film of a predetermined width is formed from
the outermost periphery of the wafer on a rear face of the wafer
corresponding to the outer peripheral region. The front face side
of the wafer is held in a chuck table, and a focal point of a
pulsed laser beam of a wavelength having permeability through the
wafer is positioned in the inside of the wafer corresponding to the
scheduled division lines. The pulsed laser beam is irradiated from
the rear face side of the wafer to form modified layers
individually serving as a start point of division along the
scheduled division lines in the inside of the wafer.
Inventors: |
Hoshino; Hitoshi; (Ota-Ku,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hoshino; Hitoshi |
Ota-Ku |
|
JP |
|
|
Assignee: |
DISCO CORPORATION
Tokyo
JP
|
Family ID: |
48797550 |
Appl. No.: |
13/541191 |
Filed: |
July 3, 2012 |
Current U.S.
Class: |
438/29 ;
257/E33.072 |
Current CPC
Class: |
B28D 5/0011 20130101;
H01L 33/0095 20130101; B23K 26/009 20130101; B23K 26/0624 20151001;
B23K 26/53 20151001; B23K 26/142 20151001; H01L 33/60 20130101;
B23K 2103/50 20180801; B23K 26/0853 20130101; B23K 26/40
20130101 |
Class at
Publication: |
438/29 ;
257/E33.072 |
International
Class: |
H01L 33/60 20100101
H01L033/60 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 24, 2012 |
JP |
2012-011925 |
Claims
1. A processing method for a wafer which has, on a front face
thereof, a device region in which a device is formed in each of
regions partitioned by a plurality of scheduled division lines and
an outer peripheral region which surrounds the device region, the
processing method comprising: a reflecting film forming step of
forming a reflecting film of a predetermined width from the
outermost periphery of the wafer on a rear face of the wafer
corresponding to the outer peripheral region; a modified layer
forming step of holding, after the reflecting film forming step is
carried out, the front face side of the wafer by a chuck table,
positioning a focal point of a pulsed laser beam of a wavelength
having permeability through the wafer in the inside of the wafer
corresponding to the scheduled division lines and irradiating the
pulsed laser beam from the rear face side of the wafer to form
modified layers individually serving as a start point of division
along the scheduled division lines in the inside of the wafer; and
a transporting step of taking out, after the modified layer forming
step is carried out, the wafer from the chuck table and
transporting the wafer to a next step.
2. The processing method for a wafer according to claim 1, wherein
the wafer is an optical device wafer in which a semiconductor layer
is laminated on a front face of a sapphire substrate and a
plurality of optical devices are formed on the semiconductor layer
such that the optical devices are partitioned by the scheduled
division lines, and at the transporting step, the wafer is
transported to a rear face processing step at which a reflecting
film is laminated on the rear face of the wafer.
3. The processing method for a wafer according to claim 2, further
comprising a rear face processing step of laminating the reflecting
film over the overall area of the rear face of the wafer.
4. The processing method for a wafer according to claim 1, further
comprising a dividing step of applying, after the modified layer
forming step is carried out, external force to the scheduled
division lines of the wafer to divide the wafer into the individual
devices.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a processing method for a wafer
wherein a laser beam is irradiated upon a wafer such as an optical
device wafer to form a modified layer in the inside of the wafer
and then external force is applied to the wafer to divide the wafer
into individual devices.
[0003] 2. Description of the Related Art
[0004] An optical device wafer wherein a semiconductor layer
(epitaxial layer) of gallium nitride (GaN) or the like is formed on
a substrate for crystal growth such as a sapphire substrate or a
SiC substrate and a plurality of optical devices such as LEDs are
partitioned by streets (scheduled division lines) formed in a
lattice shape and formed in the semiconductor layer, is
comparatively high in Mohs hardness and difficult to divide by
means of a cutting blade. Therefore, the optical device wafer is
divided into individual optical devices by irradiation of a laser
beam, and the divided optical devices are utilized in various
electric apparatus such as portable telephone sets, lighting
systems, liquid crystal television sets and personal computers.
[0005] As a method for dividing an optical device wafer into
individual optical devices using a laser beam, first and second
processing methods to be described below are known. The first
processing method is a method wherein the focal point of a laser
beam of a wavelength (for example, 1064 nm) having permeability
through a substrate is positioned in the inside of a substrate
corresponding to a scheduled division line. Then, the laser beam is
irradiated along such scheduled division lines from the rear face
side, on which no semiconductor layer is formed, to form a modified
layer in the inside of the substrate. Thereafter, external force is
applied to divide the optical device wafer into individual optical
devices (refer to, for example, Japanese Patent No. 3408805).
[0006] The second processing method is a method wherein a laser
beam of a wavelength (for example, 355 nm) having absorbability by
a substrate is irradiated upon a region corresponding to scheduled
division lines from the front face side to form dividing starting
grooves which serve as start points of division by abrasion
processing. Thereafter, external force is applied to divide the
optical device wafer into individual optical devices (refer to, for
example, Japanese Patent Laid-open No. Hei 10-305420). Any of the
processing methods can divide an optical device wafer with
certainty into individual optical devices.
[0007] Generally, on the rear face of an optical device such as an
LED (Light Emitting Diode), a reflecting film is formed in order to
enhance the extraction efficiency of light. This reflecting film is
formed on the rear face of a wafer by sputtering, CVD (Chemical
Vapor Deposition) or the like in a state of an optical device
wafer. Where a reflecting film configured from gold, aluminum or
the like is formed on the rear face of an optical device wafer in
this manner, there is a problem that a laser beam cannot be
irradiated from the rear face side of the optical device wafer. In
order to solve this problem, a dividing method for a sapphire wafer
wherein, before a reflecting film is formed on the rear face of a
wafer, a laser beam is irradiated from the rear face side of the
wafer to form a modified layer serving as a start point of division
along a scheduled division line in the inside of the substrate is
disclosed in Japanese Patent Laid-open No. 2011-243875.
SUMMARY OF THE INVENTION
[0008] However, the dividing method for a sapphire wafer just
described has a problem in that, in the middle of a procedure
wherein an optical device wafer in which a modified layer is formed
is taken out from a laser processing apparatus and transported to a
reflecting film forming apparatus for forming a reflecting film on
the rear face of the optical device wafer or when such optical
device wafer is taken out from the laser processing apparatus, the
optical device wafer is sometimes broken.
[0009] Therefore, it is an object of the present invention to
provide a processing method for a wafer wherein the wafer is not
broken along a modified layer when the wafer is taken out from a
laser processing apparatus and transported to a next stage and has
a reflecting film on the rear face thereof.
[0010] In accordance with an aspect of the present invention, there
is provided a processing method for a wafer which has, on a front
face thereof, a device region in which a device is formed in each
of regions partitioned by a plurality of scheduled division lines
and an outer peripheral region which surrounds the device region,
the processing method for a wafer including: a reflecting film
forming step of forming a reflecting film of a predetermined width
from the outermost periphery of the wafer on a rear face of the
wafer corresponding to the outer peripheral region; a modified
layer forming step of holding, after the reflecting film forming
step is carried out, the front face side of the wafer by a chuck
table, positioning a focal point of a pulsed laser beam of a
wavelength having permeability through the wafer in the inside of
the wafer corresponding to the scheduled division lines and
irradiating the pulsed laser beam from the rear face side of the
wafer to form modified layers individually serving as a start point
of division along the scheduled division lines in the inside of the
wafer; and a transporting step of taking out, after the modified
layer forming step is carried out, the wafer from the chuck table
and transporting the wafer to a next step.
[0011] Preferably, the wafer is an optical device wafer in which a
semiconductor layer is laminated on a front face of a sapphire
substrate and a plurality of optical devices are formed on the
semiconductor layer such that the optical devices are partitioned
by the scheduled division lines, and at the transporting step, the
wafer is transported to a rear face processing step at which a
reflecting film is laminated on the rear face of the wafer.
Preferably, the processing method for a wafer further includes a
dividing step of applying, after the modified layer forming step is
carried out, external force to the scheduled division lines of the
wafer to divide the wafer into the individual devices.
[0012] With the processing method for a wafer of the present
invention, before a reflecting film is laminated over the overall
area of the rear face of the wafer, when the focal point of the
pulsed laser beam of the wavelength having permeability through the
wafer is positioned in the inside of the wafer corresponding to the
scheduled division lines and the pulsed laser beam is irradiated
from the rear face side of the wafer to form modified layers in the
inside of the wafer, since the reflecting film of the predetermined
width is formed on the outermost periphery of the rear face of the
wafer corresponding to the outer peripheral region, the modified
layers are not formed in the outer peripheral region.
[0013] Accordingly, the outer peripheral region of the wafer serves
as a reinforcing portion, and when the wafer is taken out from the
chuck table and transported to the next step, the wafer is not
broken along a modified layer. Further, even if the wafer has a
reflecting film on the rear face thereof, the modified layers can
be formed along the scheduled division lines.
[0014] The above and other objects, features and advantages of the
present invention and the manner of realizing them will become more
apparent, and the invention itself will best be understood, from a
study of the following description and appended claims with
reference to the attached drawings showing some preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of a laser processing
apparatus;
[0016] FIG. 2 is a block diagram of a laser beam generation
unit;
[0017] FIG. 3 is a perspective view of an optical device wafer;
[0018] FIG. 4A is an exploded perspective view illustrating a
manner in which a protective tape is adhered to a front face of the
optical device wafer;
[0019] FIG. 4B is a perspective view of the rear face side of the
optical device wafer having the protective tape adhered to the
front face thereof;
[0020] FIG. 5 is a perspective view of the rear face side of the
optical device wafer which has a reflecting film of a predetermined
width from an outermost periphery of the optical device wafer
formed on the rear face of the optical device wafer by a reflecting
film forming step;
[0021] FIG. 6 is a perspective view illustrating a modified layer
forming step;
[0022] FIG. 7 is a perspective view illustrating a transporting
step;
[0023] FIG. 8 is a perspective view of the rear face side of the
optical device wafer which has a reflecting film on the overall
rear face thereof formed by a rear face processing step;
[0024] FIG. 9 is a perspective view of the optical device wafer
supported on an annular frame through an adhesive tape; and
[0025] FIG. 10 is a vertical sectional view illustrating a dividing
step.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] In the following, an embodiment of the present invention is
described in detail with reference to the drawings. FIG. 1 shows a
schematic block diagram of a laser processing apparatus 2 suitable
for carrying out a modified layer forming step in a wafer
processing method of the present invention. The laser processing
apparatus 2 includes a first slide block 6 mounted for movement in
an X-axis direction on a stationary base 4. The first slide block 6
is moved in a processing feeding direction, that is, in the X-axis
direction, along a pair of guide rails 14 by processing feeding
means 12 configured from a ball screw 8 and a step motor 10.
[0027] A second slide block 16 is mounted for movement in a Y-axis
direction on the first slide block 6. In particular, the second
slide block 16 is moved in an indexing direction, that is, in the
Y-axis direction, along a pair of guide rails 24 by indexing
feeding means 22 configured from a ball screw 18 and a step motor
20. A chuck table 28 is mounted on the second slide block 16 with a
cylindrical support member 26 interposed therebetween and can be
moved in the X-axis direction and the Y axis direction by the
processing feeding means 12 and the indexing feeding means 22,
respectively. A clamp 30 for clamping an annular frame which
supports a wafer sucked to and held by the chuck table 28 is
provided on the chuck table 28.
[0028] A column 32 is provided uprightly on the stationary base 4,
and a casing 35 for accommodating a laser beam generation unit 37
shown in FIG. 2 therein is attached to the column 32. Reference
numeral 34 denotes a laser beam irradiation unit which is
configured from the laser beam generation unit 37 shown in FIG. 2
and a condenser (laser head) 36 attached to an end of the casing
35.
[0029] As shown in FIG. 2, the laser beam generation unit 37
includes a laser oscillator 62 for oscillating YAG laser or YVO4
laser, repetition frequency setting means 64, pulse width
adjustment means 66, and power adjustment means 68. A pulsed laser
beam whose power is adjusted to predetermined power by the power
adjustment means 68 of the laser beam generation unit 37 is
reflected by a mirror 70 of the condenser 36 attached to the end of
the casing 35, condensed by a condensing objective lens 72 and
irradiated upon an optical device wafer 11 held on the chuck table
28.
[0030] At an end portion of the casing 35, image pickup means 38
for detecting a processing region to be laser processed is disposed
in alignment with the condenser 36 in the X-axis direction. The
image pickup means 38 includes an image pickup element such as an
ordinary CCD element for picking up an image of the processing
region of the optical device wafer 11 using visible light. The
image pickup means 38 further includes infrared irradiation means
for irradiating infrared rays on the optical device wafer 11, an
optical system for catching infrared rays irradiated by the
infrared irradiation means, and infrared image pickup means
configured from an infrared image pickup element such as an
infrared CCD element which outputs an electric signal corresponding
to the infrared rays caught by the optical system. The image signal
obtained by the image pickup is transmitted to a controller
(control means) 40.
[0031] The controller 40 is configured from a computer and includes
a central processing unit (CPU) 42 for carrying out an arithmetic
operation process in accordance with a control program, a read only
memory (ROM) 44 for storing the control program and so forth, a
readable and writable random access memory (RAM) 46 for storing an
arithmetic operation result and so forth, a counter 48, an input
interface 50, and an output interface 52.
[0032] Reference numeral 56 denotes processing feed amount
detection means configured from a linear scale 54 disposed along
the guide rails 14, and a reading head not shown disposed on the
first slide block 6. A detection signal of the processing feed
amount detection means 56 is inputted to the input interface 50 of
the controller 40. Reference numeral 60 denotes indexing feed
amount detection means configured from a linear scale 58 disposed
along the guide rails 24, and a reading head not shown disposed on
the second slide block 16, and a detection signal of the indexing
feed amount detection means 60 is inputted to the input interface
50 of the controller 40. Also an image signal obtained by image
pickup by the image pickup means 38 is inputted to the input
interface 50 of the controller 40. Meanwhile, from the output
interface 52 of the controller 40, control signals are outputted to
the step motor 10, step motor 20, laser beam generation unit 37 and
so forth.
[0033] Referring to FIG. 3, there is shown a surface side
perspective view of the optical device wafer 11 used as a
processing object of the processing method of the present
invention. The optical device wafer 11 is configured by laminating
an epitaxial layer (semiconductor layer) 15 of gallium nitride
(GaN) or the like on a sapphire substrate 13. The optical device
wafer 11 has a front face 11a on which the epitaxial layer 15 is
laminated, and a rear face 11b to which the sapphire substrate 13
is exposed. The rear face 11b is formed as a mirror. The sapphire
substrate 13 has a thickness of, for example, 120 .mu.m, and the
epitaxial layer 15 has a thickness of, for example, 5 .mu.m. The
epitaxial layer 15 has a plurality of optical devices 19 such as
LEDs formed thereon and partitioned by scheduled division lines
(streets) formed in a lattice pattern.
[0034] The optical device wafer 11 has, on the front face thereof,
a device region 21 in which a plurality of optical devices 19 are
formed and an outer peripheral region 23 which surrounds the device
region 21. It is to be noted that the outer peripheral region 23 in
the present embodiment is a region on the inner side by 0.2 to 2 mm
with respect to an outermost periphery of the optical device wafer
11 and sometimes includes part of an outer periphery of the device
region 21.
[0035] In the processing method for a wafer of the present
invention, in order to protect the optical devices 19 formed on the
front face, a protective tape 25 is adhered to the front face 11a
of the optical device wafer 11 as shown in FIGS. 4A and 4B. Then, a
reflecting film forming step of forming a reflecting film 27 of a
predetermined width W1 from the outermost periphery on the rear
face 11b of the optical device wafer 11 corresponding to the outer
peripheral region 23 as shown in FIG. 5 is carried out. At this
reflecting film forming step, a mask equivalent to the optical
device wafer 11 from which the predetermined width W1 from the
outermost periphery is removed is placed on the rear face 11b of
the optical device wafer 11 to form the reflecting film 27 of the
predetermined width W1 from the outermost periphery by a sputtering
method, a CVD method or the like. The predetermined width W1 is 0.2
to 2 mm and preferably is 1 to 2 mm.
[0036] After the reflecting film forming step is carried out, a
modified layer forming step of forming a modified layer in the
inside of the optical device wafer 11 is carried out. At this
modified layer forming step, the optical device wafer 11 is sucked
and held at the protective tape 25 side adhered to the front face
thereof to and by the chuck table 28 of the laser processing
apparatus 2, and the rear face 11b of the optical device wafer 11
is exposed. Then, alignment of picking up an image of the optical
device wafer 11 from the rear face 11b side of the same by the
infrared image pickup element of the image pickup means 38 to
detect a region corresponding to a scheduled division line 17 is
carried out. For this alignment, a well-known pattern matching
method is utilized.
[0037] At this modified layer forming step, as shown in FIG. 6, the
focal point of a laser beam 69 having a wavelength having
permeability through the sapphire substrate 13 from the rear face
11b side, formed as a mirror, of the optical device wafer 11 is
positioned in the inside of the sapphire substrate 13 corresponding
to a scheduled division line 17 by the condenser 36. Then, the
laser beam 69 is irradiated along the scheduled division line 17 to
form a modified layer 29 which is used as a start point of division
in the inside of the sapphire substrate 13. Although the pulsed
laser beam is irradiated also upon the outermost peripheral region
of the optical device wafer 11 in which the reflecting film 27 is
formed, since penetration of the laser beam 69 is prevented by the
reflecting film 27, the modified layer 29 is not formed in the
outermost peripheral region in which the reflecting film 27 is
formed.
[0038] At this modified layer forming step, while the chuck table
28 is fed for processing in the direction indicated by an arrow
mark X1, the modified layer 29 is formed along the scheduled
division line 17 extending in the first direction. The modified
layer 29 is formed in the inside of the sapphire substrate 13 along
all scheduled division lines 17 of the optical device wafer 11
extending in the first direction while the chuck table 28 is
successively fed for indexing. Then, the chuck table 28 is rotated
by 90 degrees, and a similar modified layer 29 used as a start
point of division is formed along all of the scheduled division
lines 17 extending in the second direction crossing with the first
direction. A rear face side perspective view of the optical device
wafer 11 in a state in which a modified layer 29 serving as a start
point of division is formed along all of the scheduled division
lines 17 is shown in FIG. 7.
[0039] Processing conditions of the modified layer forming step are
set, for example, in the following manner.
[0040] Light source: LD-pumped Q switch Nd: YAG
[0041] Wavelength: 1064 nm
[0042] Average output: 0.4 W
[0043] Repetition frequency: 100 kHz
[0044] Collected spot diameter: 1 .mu.m
[0045] Pulse width: 100 ps
[0046] Working feed speed: 100 to 200 mm/second
[0047] Sapphire substrate: 120 .mu.m thick
[0048] Position of focal point: 60 .mu.m from rear face
[0049] Width of modified layer: 30 .mu.m
[0050] After the modified layer forming step is carried out, as
shown in FIG. 7, a transporting step of cancelling the holding of
the chuck table 28 by the suction, taking out the optical device
wafer 11 from the chuck table 28 and transporting the optical
device wafer 11 to a next step is carried out. Since the modified
layer 29 is not formed in the outermost peripheral portion of the
optical device wafer 11 in which the reflecting film 27 is formed,
the outermost peripheral portion serves as a kind of reinforcing
portion and prevents the optical device wafer 11 from being broken
along a modified layer 29 during the transporting step of
transporting the optical device wafer 11 to a next step.
[0051] In the wafer processing method of the present embodiment,
the next step to which the optical device wafer 11 is transported
at the transporting step is a rear face processing step (reflecting
film forming step) of forming a reflecting film on the rear face
11b of the optical device wafer 11. Referring to FIG. 8, there is
shown a rear face side perspective view of the optical device wafer
11 which has the modified layers 29 in the inside thereof and has a
reflecting film 31 formed over the overall area of the rear face
11b. The reflecting film 31 is formed in an overlapping
relationship also in the reflecting film 27. The reflecting film 31
is configured from gold, aluminum or the like and is formed by a
well-known sputtering method, a well-known CVD method or the
like.
[0052] After the rear face processing step is carried out, a
dividing step of dividing the optical device wafer 11, in which the
modified layers 29 are formed, into individual chips 33 each having
an optical device 19 is carried out. As a preceding step to this
dividing step, the optical device wafer 11 is adhered to an
adhesive tape T which is adhered at an outer peripheral portion
thereof to an annular frame F as seen in FIG. 9. Then, the annular
frame F is placed on a receiving face of a cylinder 80 and clamped
by a clamp 82 as shown in FIG. 10. Then, a dividing jig 84 in the
form of a bar is disposed into the cylinder 80. The dividing jig 84
has an upper stage holding face 86a and a lower stage holding face
86b and has a vacuum suction path 88 formed therein which is open
to the lower stage holding face 86b. A detailed structure of the
dividing jig 84 is disclosed in Japanese Patent No. 4361506 and
incorporated as a reference in the present specification.
[0053] In order to carry out the dividing step by the dividing jig
84, while the vacuum suction path 88 of the dividing jig 84 carries
out vacuum suction as indicated by an arrow mark 90, the upper
stage holding face 86a and the lower stage holding face 86b of the
dividing jig 84 are brought into contact with the adhesive tape T
from the lower side and the dividing jig 84 is moved in the
direction indicated by an arrow mark A. In other words, the
dividing jig 84 is moved in a direction perpendicular to the
scheduled division line 17 along which division is to be carried
out. If a modified layer 29 comes to a position just above an inner
side edge of the upper stage holding face 86a of the dividing jig
84 as a result of the movement, then bending stress is generated in
a concentrated manner at the position of the scheduled division
line 17 which has the modified layer 29, and the optical device
wafer 11 is cut along the scheduled division line 17 by the bending
stress.
[0054] After the division along all of the scheduled division lines
17 extending in the first direction comes to an end, the dividing
jig 84 is rotated by 90 degrees or the cylinder 80 is rotated by 90
degrees, and the scheduled division lines 17 extending in the
second direction perpendicular to the scheduled division lines 17
extending in the first direction are cut similarly. Consequently,
the optical device wafer 11 is divided into the individual chips
33.
[0055] Although the modified layer 29 is not formed in the inside
of the sapphire substrate 13 corresponding to the reflecting film
27, since this portion has a very small width, the sapphire
substrate 13 can be cut readily along extension lines of the
scheduled division lines 17 which have the modified layers 29 by
the dividing jig 84.
[0056] The present invention is not limited to the details of the
above described preferred embodiment. The scope of the invention is
defined by the appended claims and all changes and modifications as
fall within the equivalence of the scope of the claims are
therefore to be embraced by the invention.
* * * * *