U.S. patent application number 15/373735 was filed with the patent office on 2017-06-22 for protective film detecting method for laser processing.
The applicant listed for this patent is DISCO CORPORATION. Invention is credited to Yukinobu Ohura, Senichi Ryo.
Application Number | 20170176331 15/373735 |
Document ID | / |
Family ID | 59067054 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170176331 |
Kind Code |
A1 |
Ryo; Senichi ; et
al. |
June 22, 2017 |
PROTECTIVE FILM DETECTING METHOD FOR LASER PROCESSING
Abstract
Disclosed herein is a protective film detecting method of
detecting the formed condition of a protective film formed on the
front side of a workpiece. The protective film detecting method
includes a fluorescence intensity measuring step of forming a
plurality of reference protective films having different
thicknesses on the front sides of a plurality of reference
workpieces, next applying excitation light absorbable by an
absorbing agent contained in each reference protective film to each
reference protective film, and next measuring the intensity of
fluorescence emitted from the absorbing agent due to the absorption
of the excitation light, and a threshold deciding step of deciding
a threshold of the fluorescence intensity corresponding to a
desired one of the different thicknesses of the reference
protective films according to the fluorescence intensity measured
above.
Inventors: |
Ryo; Senichi; (Tokyo,
JP) ; Ohura; Yukinobu; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DISCO CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
59067054 |
Appl. No.: |
15/373735 |
Filed: |
December 9, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2021/8427 20130101;
G01N 2021/6495 20130101; G01N 21/8422 20130101; G01N 21/64
20130101; H01L 22/12 20130101; H01L 21/67253 20130101; G03F 7/70608
20130101; G01N 21/645 20130101; C23C 16/52 20130101; H01L 22/26
20130101; G01B 11/0658 20130101 |
International
Class: |
G01N 21/64 20060101
G01N021/64 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2015 |
JP |
2015-247143 |
Claims
1. A protective film detecting method of detecting the formed
condition of a protective film formed on a front side of a
workpiece, so as to protect the front side of said workpiece from
processing dust generated in laser-processing said workpiece by
applying a pulsed laser beam having a wavelength in an ultraviolet
region or visible region to said workpiece, said protective film
being formed of a water-soluble resin containing an absorbing agent
capable of absorbing said pulsed laser beam, said protective film
detecting method comprising: a fluorescence intensity measuring
step of forming a plurality of reference protective films having
different thicknesses on the front sides of a plurality of
reference workpieces, next applying excitation light absorbable by
said absorbing agent to said reference protective films, and next
measuring the intensity of fluorescence emitted from said absorbing
agent contained in each reference protective film due to the
absorption of said excitation light; a threshold deciding step of
deciding a threshold of the fluorescence intensity corresponding to
a desired one of said different thicknesses of said reference
protective films according to the fluorescence intensity measured
in said fluorescence intensity measuring step; and a determining
step of applying said excitation light to said protective film
formed on the front side of said workpiece, next measuring the
intensity of fluorescence emitted from said absorbing agent
contained in said protective film due to the absorption of said
excitation light, next comparing the fluorescence intensity from
said absorbing agent contained in said protective film with said
threshold decided in said threshold deciding step, and next
determining whether or not said protective film has said desired
thickness.
2. The protective film detecting method according to claim 1,
wherein the wavelength of said pulsed laser beam is 355 nm; the
wavelength of said excitation light is in the range of 355 to 400
nm; and the peak wavelength of said fluorescence at which the
fluorescence intensity becomes a peak value is longer than the
wavelength of said excitation light and falls within the range of
365 to 600 nm.
3. The protective film detecting method according to claim 1,
wherein the wavelength of said pulsed laser beam is 532 nm; the
wavelength of said excitation light is in the range of 480 to 600
nm; and the peak wavelength of said fluorescence at which the
fluorescence intensity becomes a peak value is longer than the
wavelength of said excitation light and falls within the range of
570 to 700 nm.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates to a method of determining
whether or not a protective film has a desired thickness, the
protective film being formed on the front side of a workpiece such
as a semiconductor wafer in dividing the workpiece by laser
processing.
[0003] Description of the Related Art
[0004] As a method of dividing a workpiece such as a semiconductor
wafer along streets (division lines), there is a method of
laser-processing the workpiece along the streets to thereby divide
the workpiece (see Japanese Patent Laid-open No. 1994-120334, for
example). In the laser processing method described in Japanese
Patent Laid-open No. 1994-120334, a laser beam is applied to the
semiconductor wafer along the streets to generate thermal energy on
the semiconductor wafer in an area corresponding to the streets,
thereby continuously processing the semiconductor wafer in this
area irradiated with the laser beam. There is a case that the
thermal energy may be concentrated in this laser irradiated area on
the semiconductor wafer to cause the generation of debris
(processing dust). Accordingly, there is a problem such that this
debris may adhere to bonding pads or the like on large scale
integrations (LSIs) formed on the semiconductor wafer, causing a
reduction in quality of semiconductor chips.
[0005] To solve this problem, the present applicant has proposed a
laser processing method including the steps of forming a
water-soluble protective film on the front side of a semiconductor
wafer and next applying a laser beam through this protective film
to the semiconductor wafer (see Japanese Patent Laid-open No.
2004-322168, for example). In the laser processing method described
in Japanese Patent Laid-open No. 2004-322168, the semiconductor
wafer is processed through the protective film, so that the debris
scattered in laser processing can be made to adhere to the
protective film. Thereafter, in a cleaning step, the protective
film is removed together with the debris. Accordingly, the adhesion
of the debris to the front side of the semiconductor wafer can be
suppressed to prevent a reduction in quality of the semiconductor
chips.
SUMMARY OF THE INVENTION
[0006] However, in processing the semiconductor wafer through the
protective film by using a laser beam, it is preferable to set the
thickness of the protective film evenly to a predetermined value.
That is, the thickness of the protective film has an effect on the
result of laser processing. If the thickness of the protective film
is less than the predetermined value, there is a possibility that
the wafer cannot be sufficiently protected from the debris, whereas
if the thickness of the protective film is greater than the
predetermined value, there is a possibility that laser processing
may be hindered by the protective film. It is therefore desired to
accurately measure the thickness of the protective film formed on
the semiconductor wafer before laser processing. Further, if much
time is required for the measurement of the thickness of the
protective film, the productivity in laser processing is
reduced.
[0007] It is therefore an object of the present invention to
provide a protective film detecting method which can accurately and
simply detect the formed condition of a protective film formed on
the front side of a workpiece.
[0008] In accordance with an aspect of the present invention, there
is provided a protective film detecting method of detecting the
formed condition of a protective film formed on the front side of a
workpiece, so as to protect the front side of the workpiece from
processing dust generated in laser-processing the workpiece by
applying a pulsed laser beam having a wavelength in an ultraviolet
region or visible region to the workpiece, the protective film
being formed of a water-soluble resin containing an absorbing agent
capable of absorbing the pulsed laser beam, the protective film
detecting method including a fluorescence intensity measuring step
of forming a plurality of reference protective films having
different thicknesses on the front sides of a plurality of
reference workpieces, next applying excitation light absorbable by
the absorbing agent to the reference protective films, and next
measuring the intensity of fluorescence emitted from the absorbing
agent contained in each reference protective film due to the
absorption of the excitation light; a threshold deciding step of
deciding a threshold of the fluorescence intensity corresponding to
a desired one of the different thicknesses of the reference
protective films according to the fluorescence intensity measured
in the fluorescence intensity measuring step; and a determining
step of applying the excitation light to the protective film formed
on the front side of the workpiece, next measuring the intensity of
fluorescence emitted from the absorbing agent contained in the
protective film due to the absorption of the excitation light, next
comparing the fluorescence intensity from the absorbing agent
contained in the protective film with the threshold decided in the
threshold deciding step, and next determining whether or not the
protective film has the desired thickness.
[0009] Preferably, the wavelength of the pulsed laser beam is 355
nm; the wavelength of the excitation light is in the range of 350
to 400 nm; and the peak wavelength of the fluorescence at which the
fluorescence intensity becomes a peak value is longer than the
wavelength of the excitation light and falls within the range of
365 to 600 nm. Alternatively, the wavelength of the pulsed laser
beam is 532 nm; the wavelength of the excitation light is in the
range of 480 to 600 nm; and the peak wavelength of the fluorescence
at which the fluorescence intensity becomes a peak value is longer
than the wavelength of the excitation light and falls within the
range of 570 to 700 nm.
[0010] According to the present invention, the protective film is
formed of a water-soluble resin containing an absorbing agent. This
protective film is formed on the front side of the workpiece, and
the excitation light is applied to the protective film. At this
time, the absorbing agent contained in the protective film absorbs
the excitation light to emit fluorescence. Then, the intensity of
this fluorescence is measured and it is determined whether or not
the protective film has a desired thickness according to the
fluorescence intensity measured above. Accordingly, the thickness
of the protective film can be measured accurately and easily by
using the excitation light having an absorption wavelength to the
absorbing agent contained in the protective film. Further, as the
excitation light for the detection of the protective film,
continuous-wave light having a single wavelength is used.
Accordingly, damage to the protective film due to the excitation
light can be suppressed and it can be accurately determined whether
or not the protective film has a desired thickness.
[0011] 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 a preferred embodiment
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view of a laser processing apparatus
for use in performing the present invention;
[0013] FIG. 2 is a perspective view of protective film forming
means included in the laser processing apparatus shown in FIG.
1;
[0014] FIG. 3A is a schematic view showing the configuration of a
protective film detecting unit included in the laser processing
apparatus shown in FIG. 1 in the case of detecting fluorescence at
a certain position on the front side of a workpiece W;
[0015] FIG. 3B is a schematic view similar to FIG. 3A, showing the
case that a fiber is used;
[0016] FIG. 3C is a schematic view showing the configuration of the
protective film detecting unit in the case of detecting
fluorescence on a large area of the front side of the workpiece
W;
[0017] FIG. 3D is a schematic view similar to FIG. 3C, showing the
case that a doughnut-shaped pumping source is used;
[0018] FIG. 4A is a sectional view showing a condition where a
water-soluble liquid resin is applied to the front side of a wafer
to form a protective film;
[0019] FIG. 4B is a sectional view showing a condition where the
protective film formed on the front side of the wafer is dried;
[0020] FIG. 5 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 365 nm is applied to a
pattern wafer;
[0021] FIG. 6 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 365 nm is applied to a bump
wafer;
[0022] FIG. 7 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 385 nm is applied to a
pattern wafer;
[0023] FIG. 8 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 385 nm is applied to a bump
wafer;
[0024] FIG. 9 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 405 nm is applied to a
pattern wafer;
[0025] FIG. 10 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 405 nm is applied to a bump
wafer;
[0026] FIG. 11 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 532 nm is applied to a bump
wafer;
[0027] FIG. 12 is a graph showing a fluorescence spectrum in the
case that light having a wavelength of 570 nm is applied to a bump
wafer;
[0028] FIG. 13A is a photograph in the case that light having a
wavelength of 365 nm is applied to a bump wafer having a protective
film containing an absorbing agent capable of absorbing a laser
beam;
[0029] FIG. 13B is a photograph similar to FIG. 13A, showing the
case that the protective film does not contain the absorbing
agent;
[0030] FIG. 13C is a binary image of the photograph shown in FIG.
13A;
[0031] FIG. 13D is a binary image of the photograph shown in FIG.
13B;
[0032] FIG. 14A is a photograph in the case that light having a
wavelength of 365 nm is applied to a pattern wafer having a
protective film containing an absorbing agent capable of absorbing
a laser beam;
[0033] FIG. 14B is a photograph similar to FIG. 14A, showing the
case that the protective film does not contain the absorbing
agent;
[0034] FIG. 14C is a binary image of the photograph shown in FIG.
14A; and
[0035] FIG. 14D is a binary image of the photograph shown in FIG.
14B.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0036] Referring to FIG. 1, there is shown a laser processing
apparatus 1 for use in performing the present invention. The laser
processing apparatus 1 shown in FIG. 1 has a function of forming a
protective film on the front side Wa of a workpiece W, a function
of determining whether or not the protective film formed has a
desired thickness, and a function of laser-processing the workpiece
W. The laser processing apparatus 1 includes a cassette mounting
area 6 for mounting a cassette 60 storing the workpiece W as a
target to be laser-processed, workpiece handling means 7 for
handling the workpiece W to take it out of the cassette 60 before
laser processing or store it into the cassette 60 after laser
processing, protective film forming means 8 for forming a
protective film on the front side Wa of the workpiece W taken out
of the cassette 60, a chuck table 2 for holding the workpiece W on
which the protective film has been formed, and laser beam applying
means 3 for applying a laser beam to the workpiece W held on the
chuck table 2.
[0037] The cassette mounting area 6 is vertically movable. A
plurality of slots for receiving a plurality workpieces W are
formed in the cassette 60 so as to be vertically arranged at
different levels. By vertically moving the cassette mounting area
6, a desired one of the slots can be positioned at a predetermined
height in taking the workpiece W out of the cassette 60 or storing
it into the cassette 60. A plurality of crossing division lines L
are formed on the front side Wa of the workpiece W stored in the
cassette 60 to thereby partition the front side Wa into a plurality
of separate regions where a plurality of devices D are formed. The
back side Wb of the workpiece W is attached to a tape T supported
at its peripheral portion to a frame F. Accordingly, the workpiece
W stored in the cassette 60 is supported through the tape T to the
frame F in the condition where the front side Wa of the workpiece W
is exposed.
[0038] The workpiece handling means 7 is movable in the
longitudinal direction (Y direction) of the apparatus 1. The
workpiece handling means 7 includes a holding (pinching) portion 70
for holding the frame F supporting the workpiece W. In the
condition where the frame F is held by the holding portion 70, the
workpiece W supported to the frame F can be taken out of the
cassette 60 by operating the workpiece handling means 7.
Conversely, when the frame F is pushed by the workpiece handling
means 7 in the Y direction toward the front side of the apparatus
1, the workpiece W can be stored into a desired slot in the
cassette 60. A temporary setting area 61 for temporarily setting
the workpiece W after taking it out of the cassette 60 or before
storing it into the cassette 60 is defined on the rear side of the
cassette mounting area 6 in the Y direction. The temporary setting
area 61 is provided with a guide portion 62 for guiding the frame F
and setting the workpiece W at a predetermined position.
[0039] As shown in FIG. 2, the protective film forming means 8
includes a rotatable holding table 80 for holding the workpiece W
supported to the frame F under suction, a water-soluble liquid
resin nozzle 81 for dispensing a water-soluble liquid resin to the
workpiece W held on the holding table 80, a cleaning liquid nozzle
82 for discharging a cleaning liquid to the workpiece W, and an air
nozzle 85 for discharging air under high pressure. The holding
table 80 includes a porous holding member 800 connected to a vacuum
source (not shown). The holding table 80 is vertically movable by
an elevating portion 83 and rotatable by a motor 84. A receptacle
portion 88 for receiving the water-soluble liquid resin or the
cleaning liquid is provided below the holding table 80 so as to
surround the holding table 80. The bottom of the receptacle portion
88 is formed with a drain opening 880 for draining the
water-soluble liquid resin or the cleaning liquid.
[0040] The elevating portion 83 is composed of a plurality of air
cylinders 830 fixed to the side surface (cylindrical outer surface)
of the motor 84 and a plurality of rods 831 corresponding to the
plural air cylinders 830. When the air cylinders 830 are operated,
the motor 84 and the holding table 80 can be vertically moved
together.
[0041] As shown in FIG. 1, a transfer mechanism 9 is provided
between the temporary setting area 61 and the protective film
forming means 8. The transfer mechanism 9 includes a rotating shaft
90 having an axis extending in a vertical direction (Z direction),
an expansion arm 91 horizontally extending from the upper end of
the rotating shaft 90, and a suction holding portion 92 provided at
the front end of the expansion arm 91 for holding the frame F under
suction. The suction holding portion 92 can be adjusted in position
in an X-Y plane by the rotation of the rotating shaft 90 and the
expansion/contraction of the expansion arm 91. The suction holding
portion 92 can also be adjusted in position in the vertical
direction (Z direction) by the vertical movement of the rotating
shaft 90.
[0042] The chuck table 2 includes a suction holding portion 20 for
holding the workpiece W under suction. A fixing portion 21 for
fixing the frame F supporting the workpiece W is provided around
the suction holding portion 20. The fixing portion 21 includes a
pressing portion 210 for pressing the frame F from the upper side
thereof.
[0043] The chuck table 2 is supported by feeding means 4 so as to
be movable in a feeding direction (X direction) and also supported
by indexing means 5 so as to be movable in an indexing direction (Y
direction).
[0044] The feeding means 4 is composed of a ball screw 40 having an
axis extending in the X direction, a pair of guide rails 41
parallel to the ball screw 40, a motor 42 connected to one end of
the ball screw 40, and a slide portion 43 having an internal nut
(not shown) threadedly engaged with the ball screw 40 and having a
lower portion slidably engaged with the guide rails 41.
Accordingly, when the ball screw 40 is rotated by the motor 42, the
slide portion 43 is slidingly moved on the guide rails 41 in the X
direction to thereby move the chuck table 2 in the X direction.
[0045] The chuck table 2 and the feeding means 4 are supported by
the indexing means 5 so as to be movable in the Y direction. The
indexing means 5 is composed of a ball screw 50 having an axis
extending in the Y direction, a pair of guide rails 51 parallel to
the ball screw 50, a motor 52 connected to one end of the ball
screw 50, and a platelike base 53 having an internal nut (not
shown) threadedly engaged with the ball screw 50 and having a lower
portion slidably engaged with the guide rails 51. Accordingly, when
the ball screw 50 is rotated by the motor 52, the base 53 is
slidingly moved on the guide rails 51 in the Y direction to thereby
move the chuck table 2 and the feeding means 4 in the Y
direction.
[0046] The laser beam applying means 3 includes a base 30 fixed to
a rear wall la of the apparatus 1 and a laser head 31 fixed to the
front end of the base 30. The laser head 31 functions to radiate a
laser beam along an optical path extending in the Z direction.
[0047] While the feeding means 4 and the indexing means 5 are so
configured as to move the chuck table 2 in the X direction and the
Y direction, respectively, and the laser beam applying means 3 is
not moved in the laser processing apparatus 1 shown in FIG. 1, the
configuration is not limited to that shown in FIG. 1, provided that
the chuck table 2 and the laser beam applying means 3 are
relatively moved in the X direction and in the Y direction. For
example, the chuck table 2 may be moved in the X direction and the
laser beam applying means 3 may be moved in the Y direction. As
another configuration, the chuck table 2 may not be moved and the
laser beam applying means 3 may be moved both in the X direction
and in the Y direction.
[0048] The laser processing apparatus 1 further includes a
protective film detecting unit 10 for applying light to the
protective film formed on the workpiece W by the protective film
forming means 8 and detecting fluorescence emitted from the
protective film to thereby detect whether or not the protective
film formed on the workpiece W has a desired thickness. The
protective film detecting unit 10 may be provided in the same space
as that of the protective film forming means 8 or in the same space
as that of the laser beam applying means 3 as in this preferred
embodiment. Alternatively, the protective film detecting unit 10
may be provided independently of the laser processing apparatus 1.
As shown in FIG. 3A, the protective film detecting unit 10 includes
a pumping source 100, an optical filter 101 for preventing that
light emitted from the pumping source 100 may enter a photodetector
102, the photodetector 102 for detecting fluorescence emitted from
a protective film 86 formed on the workpiece W, and a controller
103 for receiving information from the photodetector 102 and
performing processing according to the information received.
[0049] As the pumping source 100 for use in detecting fluorescence
at a certain position on the workpiece W as shown in FIG. 3A, a
light-emitting diode (LED) or a continuous-wave (CW) laser may be
used, for example. Further, as a method of detecting fluorescence
at a certain position on the workpiece W, a method (configuration)
shown in FIG. 3B may be used. The configuration shown in FIG. 3B
includes a pumping source 100, a fiber 104 for guiding light
emitted from the pumping source 100 to a protective film 86 present
on the workpiece W, a probe 105 for convergently applying the light
guided by the fiber 104 to the protective film 86 and guiding
reflected light and fluorescence from the protective film 86 to an
optical filter 101, the optical filter 101 for blocking only the
reflected light from the probe 105, a photodetector 102 for
detecting only the fluorescence from the protective film 86, and a
controller 103 for receiving information from the photodetector 102
and performing processing according to the information
received.
[0050] As a method of detecting fluorescence on a large area or the
whole surface of the front side of the workpiece W, a method
(configuration) shown in FIG. 3C may be used. The configuration
shown in FIG. 3C includes a pumping source 110, an optical filter
101 for preventing that light emitted from the pumping source 110
may enter a photodetector 102, the photodetector 102 for detecting
fluorescence from a protective film 86 formed on the workpiece W,
and a controller 103 for receiving information from the
photodetector 102 and performing processing according to the
information received. As the pumping source 110, an LED array is
preferably used.
[0051] As another method of detecting fluorescence on a large area
or the whole surface of the front side of the workpiece W, a method
(configuration) shown in FIG. 3D may be used. The configuration
shown in FIG. 3D includes a pumping source 120, an optical filter
101 for preventing that light emitted from the pumping source 120
may enter a photodetector 102, the photodetector 102 for detecting
fluorescence from a protective film 86 formed on the workpiece W,
and a controller 103 for receiving information from the
photodetector 102 and performing processing according to the
information received. As the pumping source 120, an LED array
having a central hole (e.g., a doughnut-shaped LED array) is
preferably used.
[0052] In performing laser processing to the workpiece W by using
the laser processing apparatus 1 shown in FIG. 1, a protective film
is preliminarily formed on the front side Wa of the workpiece W and
it is determined whether or not this protective film has a desired
thickness before laser processing according to the following
method. When the protective film has a desired thickness, the
workpiece W is laser-processed.
[0053] (1) Preparation Step
[0054] Prior to inspecting the thickness of a protective film to be
actually formed on the front side Wa of the workpiece W to be
laser-processed, data as a criterion for determination is obtained
in advance.
[0055] (1a) Reference Spectrum Making Step
[0056] A plurality of workpieces W are prepared. A tape T is
attached to the back side Wb of each workpiece W, and a ring frame
F is attached to the peripheral portion of the tape T. In this
manner, each workpiece W is supported through the tape T to the
frame F so as to form a unit. These plural workpieces W supported
to the frames F are stored in the cassette 60. Each workpiece W
stored in the cassette 60 is taken out by the workpiece handling
means 7 in such a manner that the frame F is held by the holding
portion 70 of the workpiece handling means 7. The workpiece W is
then carried to the temporary setting area 61 by the workpiece
handling means 7. After setting the workpiece W at a predetermined
position in the temporary setting area 61, the workpiece W is
transferred to the protective film forming means 8 by operating the
transfer mechanism 9. In the protective film forming means 8, the
workpiece W is held through the tape T on the holding table 80 in
the condition where the front side Wa of the workpiece W is exposed
upward.
[0057] As shown in FIG. 4A, the holding table 80 is next rotated
and a water-soluble liquid resin 810 is dropped from the liquid
resin nozzle 81 onto the front side Wa of the workpiece W at the
center thereof. The water-soluble liquid resin 810 is a material
for forming a protective film. This material is not especially
limited, provided that it is soluble in water or the like and can
be formed into a film after coating and drying. Examples of the
water-soluble liquid resin 810 include polyvinyl alcohol, polyvinyl
pyrrolidone, polyethylene glycol having 5 or more repetition units
of oxyethylene, polyethylene oxide, methyl cellulose, ethyl
cellulose, hydroxypropyl cellulose, polyacrylic acid, block
copolymer of polyvinyl alcohol and polyacrylic acid, block
copolymer of polyvinyl alcohol and polyacrylate, and polyglycerol.
These materials may be used solely or in combination.
[0058] The water-soluble liquid resin 810 contains an absorbing
agent for absorbing light having a wavelength equal to the
wavelength of a laser beam to be applied from the laser beam
applying means 3. The absorbing agent is contained in an amount of
about 0.01 to 10 parts by weight per 100 parts by weight of
water-soluble resin. For example, in the case of using a laser beam
having an ultraviolet region (e.g., a wavelength of 355 nm) in a
laser processing step to be hereinafter described, an ultraviolet
absorbing agent for absorbing light having a wavelength in the
ultraviolet region (e.g., in the wavelength range of 250 to 400 nm)
is used as the absorbing agent to be added to the water-soluble
liquid resin 810. Examples of this ultraviolet absorbing agent
include a plastic additive such as benzophenone series,
benzotriazole series, triazine series, and benzoate series. In the
case of using a laser beam having a visible region (e.g., a
wavelength of 532 nm), a visible light absorbing agent for
absorbing light in the visible region (e.g., in the wavelength
range of 480 to 600 nm) is used as the absorbing agent to be added
to the water-soluble liquid resin 810. Examples of this visible
light absorbing agent include a coloring matter such as
phthalocyanine series, quinacridone series, pigment red series,
pigment blue series, and malachite green series.
[0059] When the holding table 80 is rotated, the water-soluble
liquid resin 810 dropped onto the front side Wa of the workpiece W
at the center thereof is radially spread on the whole surface of
the front side Wa by a centrifugal force. At the time the
water-soluble liquid resin 810 is applied by a predetermined
amount, the supply of the water-soluble liquid resin 810 from the
liquid resin nozzle 81 is stopped. After applying the predetermined
amount of water-soluble liquid resin 810 to the front side Wa of
the workpiece W as mentioned above, the water-soluble liquid resin
810 is dried by the rotation of the holding table 80 as shown in
FIG. 4B, thereby solidifying the water-soluble liquid resin 810 to
form a protective film 86 on the front side Wa of the workpiece
W.
[0060] The water-soluble liquid resin 810 may be dried by applying
light from a lamp (e.g., infrared lamp, halogen lamp, tungsten
lamp, or mercury lamp), LED, pulsed laser, or xenone pulse lamp. In
this case, pulse light from a pulsed laser or xenone pulse lamp is
preferably applied, so as to avoid a rise in temperature of the
protective film 86. In the case that the temperature rise is small,
the light may be applied at a time. In the case that the
temperature rise is large, the light is applied plural times. In
the case of applying the light plural times, the protective film 86
may be allowed to stand until the temperature is naturally
decreased or may be cooled by air. Further, the water-soluble
liquid resin 810 applied to the workpiece W may be subjected to
baking by using a hot plate. Further, the water-soluble liquid
resin 810 may be applied by a spin coating method as in this
preferred embodiment or by a spray coating method. Further, the
water-soluble liquid resin 810 may be discharged from a slit-shaped
nozzle. In the case that a surface active agent is contained in the
water-soluble liquid resin 810, it is unnecessary to dry the
water-soluble liquid resin 810 applied to the workpiece W. By using
such a drying method, a protective film having a thickness of 2
.mu.m or more can be dried in a short time. In such a case of large
film thickness, it is difficult to dry the protective film by using
a centrifugal force. By increasing the thickness of the protective
film, fluorescence intensity can be increased and it can be
accurately determined whether or not the protective film has a
desired thickness. Further, by increasing the thickness of the
protective film on a wafer with bumps, the protective film can be
easily formed on a highest part of each bump. In general, when a
wafer as a workpiece is laser-processed, a plasma is generated from
the material of the wafer to break a thin part of the protective
film, so that there is a possibility that a residue may be
deposited on the front side of the wafer. This residue is not
water-soluble and it is therefore difficult to remove this residue
together with the protective film after performing laser
processing. Accordingly, it is necessary to form a protective film
having a thickness capable of resisting the breakage by the laser
processing and the plasma generated thereby.
[0061] Further, in the case that the protective film is deposited
to the frame F, it may be dried by using the lamp mentioned above
or may be removed from the frame F by discharging water to only the
frame F.
[0062] In this manner, the protective film 86 is formed on the
front side Wa of each workpiece W, wherein the plural protective
films 86 formed in this step have different thicknesses. The
thickness of each protective film 86 may be changed according to
the rotational speed of the holding table 80 and the duration of
rotation thereof in performing the spin coating. For example, five
kinds of workpieces W with the protective films 86 having different
thicknesses of 1.2 .mu.m, 2.3 .mu.m, 2.7 .mu.m, 3.1 .mu.m, and 5.0
.mu.m are prepared. Alternatively, a plurality of protective films
having different thicknesses may be formed at plural portions on
one workpiece rather than preparing a plurality of workpieces with
plural protective films having different thicknesses.
[0063] After preparing the plural workpieces W with the protective
films 86 having different thicknesses, a fluorescence spectrum is
made for each of the plural workpieces W with the protective films
86 having different thicknesses, by using the protective film
detecting unit 10.
[0064] Referring back to FIG. 1, each workpiece W having the
protective film 86 is transferred to the chuck table 2 by operating
the transfer mechanism 9. The workpiece W is held through the tape
T on the suction holding portion 20 of the chuck table 2.
Thereafter, the chuck table 2 is moved in the -X direction (to the
left side as viewed in FIG. 1) until reaching a position directly
below the protective film detecting unit 10.
[0065] When the chuck table 2 is positioned directly below the
protective film detecting unit 10, the light emitted from the
pumping source 100 shown in FIG. 3A, for example, is applied to the
protective film 86. The light emitted from the pumping source 100
is ultraviolet light or visible light, which is continuous-wave
light having a single wavelength. The light having a single
wavelength means light having a limited wavelength component. That
is, this light may have a certain wavelength range. For example, in
the case that the absorbing agent contained in the protective film
has absorptivity to ultraviolet light, the light (excitation light)
to be emitted from the pumping source 100 is ultraviolet light. For
example, in the case that the wavelength of a pulsed laser beam to
be used in laser processing of the workpiece W is 355 nm, light
having a longer wavelength (e.g., 355 to 410 nm) is preferably used
as the excitation light. For example, ultraviolet light having a
peak wavelength of 365.+-.10 nm or a peak wavelength of 385.+-.10
nm may be used. Although light having a wavelength less than or
equal to 355 nm may be used, there is a technical problem such that
high power cannot be obtained or the protective film may be
modified. The power of this ultraviolet light is set to 10 to 100
mW/cm.sup.2, for example.
[0066] In the case that the wavelength of the pulsed laser beam to
be used in laser processing of the workpiece W is 532 nm, light
having a wavelength of 480 to 600 nm, for example, is preferably
used as the excitation light. For example, visible light having a
peak wavelength of 532.+-.10 nm or a peak wavelength of 570.+-.10
nm may be used. In the case of excitation by visible light, the
wavelength of the visible light is not especially limited, but the
wavelength may be changed according to the absorbing agent to be
added to the protective film. The power of this visible light is
set to 10 to 100 mW/cm.sup.2, for example. The continuous-wave
light having a single wavelength is used for the following reason.
The reason why continuous-wave light is used is to suppress the
modification of the protective film. Further, the reason why light
having a single wavelength is used is to accurately determine
whether or not the protective film has a desired thickness. That
is, if any light other than fluorescence enters a photodetector in
measuring the fluorescence emitted from the protective film, it is
impossible to distinguish the fluorescence from the other light.
The continuous-wave light may be provided by a lamp such as a
halogen lamp, tungsten lamp, and mercury lamp, a CW laser, or an
LED. In the case of using a lamp such as a halogen lamp, tungsten
lamp, and mercury lamp, the light having a single wavelength can be
obtained by using an optical component such as a filter. The light
emitted from an LED slightly contains a wavelength component other
than a peak wavelength. Accordingly, in the case of using an LED,
the wavelength component other than the peak wavelength may be
removed by using an optical component. From the viewpoint of
applying the light to a large area with high intensity, an LED is
preferably used to generate the continuous-wave light having a
single wavelength.
[0067] When the light applied to the protective film 86 is absorbed
by the absorbing agent, the molecules of the absorbing agent in a
ground state are excited and the energy of the molecules therefore
becomes a high unstable state. Thereafter, the state of the
molecules is dropped to a relaxation caused electronic singlet
state. Thereafter, the molecules of the absorbing agent emit light
having a wavelength longer than that of the light emitted from the
pumping source 100 and dissipate energy to restore the ground
state. This light emitted from the molecules of the absorbing agent
in restoring the ground state is fluorescence. The fluorescence
emitted from the protective film 86 is detected by the
photodetector 102. To detect only the fluorescence, the reflected
light from the protective film 86 is blocked by the optical filter
101 located before the photodetector 102. The intensity of the
fluorescence detected by the photodetector 102 is measured by the
controller 103. In the controller 103, a fluorescence spectrum
showing the relation between the wavelength of the fluorescence and
the intensity of the fluorescence is made as shown in FIG. 5 or a
value for the fluorescence intensity at a certain wavelength can be
recognized. Such a fluorescence spectrum or fluorescence intensity
is made for each of the plural workpieces W with the protective
films 86 having different thicknesses. The fluorescence intensity
may be measured on the whole surface of each workpiece W or at only
a predetermined position on each workpiece W. In the fluorescence
spectrum, the fluorescence intensity (along the vertical axis of
the graph shown in FIG. 5) increases with an increase in thickness
of the protective film 86.
[0068] The fluorescence spectrum as a reference is made according
to the kind of the workpiece W. For example, a fluorescence
spectrum for an ordinary pattern wafer with no bumps formed on the
front side (FIG. 5) and a fluorescence spectrum for a bump wafer
with bumps formed on the front side (FIG. 6) are made because the
peak intensity is different. Accordingly, the fluorescence spectrum
for the pattern wafer and the fluorescence spectrum for the bump
wafer are made for the protective films 86 having different
thicknesses and then stored into the controller 103 in advance.
[0069] Each of the fluorescence spectra shown in FIGS. 5 and 6
shows the dependence of the fluorescence intensity upon the
thickness of the protective film 86 in the case that the wavelength
of the light to be applied to the protective film 86 is set to 365
nm. Also in the case that the wavelength of the light to be applied
to the protective film 86 is different, the fluorescence spectrum
is measured and stored into the controller 103. For example, FIG. 7
shows a fluorescence spectrum in the case that the protective film
86 is formed on the ordinary pattern wafer with no bumps formed on
the front side and the wavelength of the light to be applied to the
protective film 86 is set to 385 nm. FIG. 8 shows a fluorescence
spectrum in the case that the protective film 86 is formed on the
bump wafer with bumps formed on the front side and the wavelength
of the light to be applied to the protective film 86 is set to 385
nm. Further, FIG. 9 shows a fluorescence spectrum in the case that
the protective film 86 is formed on the ordinary pattern wafer with
no bumps formed on the front side and the light to be applied to
the protective film 86 is LED light having a wavelength of 405 nm.
FIG. 10 shows a fluorescence spectrum in the case that the
protective film 86 is formed on the bump wafer with bumps formed on
the front side and the light to be applied to the protective film
86 is LED light having a wavelength of 405 nm.
[0070] FIG. 11 shows a fluorescence spectrum in the case that the
wavelength of the light to be applied to the protective film 86 is
set to 532 nm. Also in the case that the wavelength of the light to
be applied to the protective film 86 is different, the fluorescence
spectrum is measured and stored into the controller 103. For
example, FIG. 11 shows a fluorescence spectrum in the case that the
protective film 86 is formed on the bump wafer with bumps formed on
the front side and the wavelength of the light to be applied to the
protective film 86 is set to 532 nm. FIG. 12 shows a fluorescence
spectrum in the case that the protective film 86 is formed on the
bump wafer with bumps formed on the front side and the wavelength
of the light to be applied to the protective film 86 is set to 570
nm.
[0071] (1b) Threshold Deciding Step
[0072] Thereafter, the threshold of a predetermined fluorescence
intensity corresponding to a predetermined thickness of the
protective film 86 is determined according to the fluorescence
spectra obtained above. That is, this step is a step of determining
the threshold of the fluorescence intensity as the criterion for
determination of whether or not the protective film 86 has a
predetermined thickness. For example, as the threshold to be used
as the criterion for determination of whether or not the thickness
of the protective film 86 is sufficient, a peak value for the
fluorescence intensity in each of the fluorescence spectra shown in
FIGS. 5 to 10 is stored into the controller 103 shown in FIG. 3A.
For example, in the case that the wavelength of the light to be
applied to the protective film 86 is set to 365 nm, a peak value
for the fluorescence intensity in the fluorescence spectrum shown
in FIG. 5 is used as the threshold. More specifically, in the case
that the thickness of the protective film 86 is 5.0 .mu.m, the
threshold is set to 350. In the case that the thickness of the
protective film 86 is 3.1 .mu.m, the threshold is set to 200. In
the case that the thickness of the protective film 86 is 2.7 .mu.m,
the threshold is set to 110. In the case that the thickness of the
protective film 86 is 2.3 .mu.m, the threshold is set to 90. In the
case that the thickness of the protective film 86 is 1.2 .mu.m, the
threshold is set to 70. When a protective film is actually formed
on the workpiece W later and the intensity of the fluorescence
emitted from the protective film by the application of ultraviolet
light is not less than the threshold set above, it is determined
that the thickness of the protective film is sufficient. As the
threshold to be used as the criterion for determination, an
integral value in a predetermined range may be used instead of the
peak value for the fluorescence spectrum mentioned above. In this
case, this integral value is compared with an integral value in the
predetermined range in the fluorescence spectrum actually measured
later.
[0073] (2) Spectrum measuring step
[0074] Thereafter, a protective film is formed on the front side Wa
of the workpiece W to be laser-processed, and a fluorescence
spectrum is measured for the protective film formed on the
workpiece W, so as to determine whether or not the protective film
has a predetermined thickness. Prior to forming the protective
film, the back side Wb of the workpiece W is ground by using a
grinding wheel or the like to reduce the thickness of the workpiece
W to a predetermined thickness.
[0075] In this step, the protective film is formed on the front
side Wa of the workpiece W in a manner similar to that in the
reference spectrum making step mentioned above. Further, the
fluorescence spectrum for the protective film formed on the
workpiece W is measured in a manner similar to that in the
reference spectrum making step mentioned above. The predetermined
thickness of the protective film to be formed in this step is equal
to the thickness of any one of the plural protective films formed
in the reference spectrum making step mentioned above. In the case
that the fluorescence spectra shown in FIGS. 5 to 10 are made, the
thickness of the protective film to be actually formed on the
workpiece W is set to any one of 1.2 .mu.m, 2.3 .mu.m, 2.7 .mu.m,
3.1 .mu.m, and 5.0 .mu.m. In this step, every time the protective
film is formed on the workpiece W by the protective film forming
means 8 shown in FIG. 1, the workpiece W is next transferred to the
position directly below the protective film detecting unit 10 to
obtain a fluorescence spectrum for this workpiece W.
[0076] (3) Determining Step
[0077] Thereafter, the controller 103 shown in FIG. 3A, for
example, compares the fluorescence spectrum (not shown) obtained in
the above spectrum measuring step with the fluorescence spectrum
obtained in the reference spectrum making step mentioned above and
then determines whether or not the peak value for the fluorescence
intensity measured in the spectrum measuring step is not less than
the threshold decided in the threshold deciding step mentioned
above.
[0078] For example, in the case that the workpiece with the
protective film actually formed thereon is an ordinary pattern
wafer with no bumps, that the wavelength of the LED light applied
to the protective film in measuring the fluorescence spectrum is
365 nm, and that the desired thickness is 5.0 .mu.m, it is
determined that the thickness of the protective film is sufficient
if the peak value for the fluorescence intensity obtained in the
spectrum measuring step and shown in FIG. 5 is not less than 350.
Conversely, if the peak value for the fluorescence intensity
obtained in the spectrum measuring step is less than 350, it is
determined that the thickness of the protective film is
insufficient. In the case that the thickness of the protective film
is insufficient, the workpiece W is returned to the holding table
80 of the protective film forming means 8 by operating the transfer
mechanism 9 to form a protective film on this workpiece W again in
the case that the protective film detecting unit 10 is not present
in the same space as that of the protective film forming means 8 as
in this preferred embodiment. In the case that the protective film
detecting unit 10 is present in the same space as that of the
protective film forming means 8 (e.g., in the case that the
detecting unit 10 is located directly above the forming means 8),
the transfer of the workpiece W to the chuck table 2 is not
required, but the excitation light may be applied to the workpiece
W held on the holding table 80. In forming a protective film again,
the previous protective film may be first removed by cleaning and a
new protective film may be next formed. Alternatively, a new
protective film may be formed on the previous protective film.
After forming the protective film again, the spectrum measuring
step and the determining step are performed again.
[0079] In the case of detecting a portion having an insufficient
thickness of the protective film formed on one workpiece, LED light
is applied to the whole surface of the protective film and the
fluorescence emitted from the whole surface of the protective film
is detected by the photodetector 102 shown in FIG. 3C, for example.
Thereafter, a fluorescence image obtained is binarized by the
controller 103. For example, in the case that the fluorescence from
the protective film is blue, the controller 103 compares RG and B
in quantity of RGB constituting the image. For example, for each
pixel composed of 8-bit information in the image, it is determined
whether or not the following relation of Eq. (1) holds.
{[R(0-255)+G(0-255)]/2+Q}<{B(0-255)} (1)
where 0-255 are pixel values and Q is an arbitrary value, which is
decided according to the shape and condition of the workpiece, such
as bumps.
[0080] When the above Eq. (1) holds, the image is made black in the
controller 103, whereas when the above Eq. (1) does not hold, the
image is made white in the controller 103. Then, either color is
mapped on one screen to form a binary image. The controller 103
determines that a black part of this binary image corresponds to a
portion of the protective film where the thickness is sufficient
and that a white part of this binary image corresponds to a portion
of the protective film where the thickness is insufficient. Thus,
whether of not the protective film is formed is determined. Prior
to forming the protective film, ultraviolet light may be applied to
the front side of the workpiece W to thereby improve hydrophilicity
and uniformly form the protective film.
[0081] (4) Laser Processing Step
[0082] After performing the determining step to determine that the
thickness of the protective film 86 formed on the workpiece W is
sufficient, the chuck table 2 holding the workpiece W is moved in
the X direction and then positioned directly below the laser beam
applying means 3. The workpiece W includes a silicon substrate and
a dielectric film (one or more films of SiO.sub.2, SiN.sub.x, or
polyimide) formed on the silicon substrate.
[0083] After detecting the division line L to be processed, the
chuck table 2 is fed in the X direction and at the same time a
laser beam is applied from the laser head 31 along this division
line L, thereby performing ablation along this division line L.
This laser processing is performed under the following conditions,
for example.
[0084] Wavelength: 550 nm or less
[0085] Pulse width: 10 fs to 500 ns
[0086] Power: 0.1 to 100 W
[0087] Repetition frequency: 10 kHz to 1 GHz
[0088] Spot diameter: 2 to 70 .mu.m
[0089] Feed speed: 100 to 5000 mm/second
[0090] Processing mode: single pulse or burst pulse
[0091] Beam shape: Gaussian type or top-hat type
[0092] For example, in the case that the wavelength of the laser
beam for processing the workpiece W is 355 nm, the laser processing
is performed in plural passes along this division line L under the
following conditions shown in Table 1.
Table 1
TABLE-US-00001 [0093] TABLE 1 Pulse Repetition Spot Feed width
Power frequency diameter speed Index [ns] [W] [kHz] [.mu.m] [mm/s]
[mm] First pass 100 1.5 200 8 200 0.02 Second pass 100 1.5 200 8
200 -0.02 Third pass 100 5.9 40 30 100 0.00 Fourth pass 100 5.9 40
30 100 0.00
[0094] In the first pass and the second pass, the laser processing
is performed with low intensity to form two parallel grooves on the
dielectric film, so as to prevent delamination (separation of the
dielectric film). In the third pass, the laser processing is
performed with high intensity to form a groove on the silicon
substrate. That is, in the third pass, the groove is formed on the
silicon substrate along this division line L so as to overlap the
two parallel grooves formed in the first pass and the second pass.
In the case that a low-permittivity insulator film (low-k film) or
a passivation film is not formed on the front side of the workpiece
(especially on each division line), the first pass and the second
pass are not essential, but only the third and fourth passes may be
performed. Further, the intensity of the laser beam in the first
pass may be made lower than that of the laser beam in the second
pass. Conversely, the intensity of the laser beam in the first pass
may be made higher than that of the laser beam in the second pass.
Further, the two parallel grooves to be formed in the first and
second passes may be overlapped or separated. Further, any other
various manners of laser processing may be adopted. That is, the
manner of laser processing is not especially limited, but optimum
processing conditions may be selected by adjusting variable laser
parameters according to the material to be processed. Further,
light emitted from a light source for laser processing may be
branched into two or more laser beams. In the case of two laser
beams, they may be used in simultaneously performing the first pass
and the second pass. In the case of three or more laser beams, they
may be applied in different directions parallel, perpendicular, and
oblique to the processing direction. The spacing between these
branched beams is preferably made sufficient to relax a thermal
effect.
[0095] In the case that the pulse width is subnano second, the beam
spots are preferably overlapped at a high rate of 50% or more, so
as to prevent the delamination. To prevent the delamination and
achieve high-speed processing, a laser oscillator having a high
repetition frequency of MHz or more is used. Further, in the case
of high-speed processing, a polygon mirror may be used to apply a
laser beam along the division line linearly or nonlinearly. Also in
the case that the pulse width is subnano second, various manners of
laser processing may be adopted as in the nano-second laser
processing mentioned above. That is, also in this case, optimum
processing conditions may be selected by adjusting variable laser
parameters according to the material to be processed.
[0096] The groove to be formed in this laser processing preferably
has a shape such that the lateral center of the groove is deeper
than the other portion. In performing the laser processing, an
assist gas such as oxygen, nitrogen, argon, and helium may be
discharged to remove a substance melted and evaporated.
Alternatively, such a substance may be sucked by using a suction
nozzle or the like.
[0097] After performing the laser processing (ablation) along the
above predetermined division line L, the indexing means 5 is
operated to move the chuck table 2 in the Y direction and then
similarly perform the laser processing along the next division line
L. After performing the laser processing along all of the other
division lines L extending in a first direction, the chuck table 2
is rotated 90 degrees to similarly perform the laser processing
along all of the other division lines L extending in a second
direction perpendicular to the first direction. In this manner, a
plurality of laser processed grooves are formed along all of the
division lines L.
[0098] Debris generated and scattered by the ablation adheres to
the upper surface of the protective film 86. In the determining
step mentioned above, it is determined that the protective film 86
formed on the workpiece W to be laser-processed has a sufficient
thickness. Accordingly, it is possible to prevent that the debris
may adhere to the devices D.
[0099] Although the protective film 86 is formed on the whole
surface of the front side Wa of a workpiece W having high bumps,
the debris of silicon may react with oxygen in the air to produce a
residue such as silicon oxide (SiO.sub.x), which cannot be removed
by cleaning with water, and this residue may adhere to the surface
of each bump and it is difficult to remove. In this case, isotropic
plasma etching is performed to remove the residue adhering to the
surface of each bump.
[0100] Further, metal oxide such as TiO.sub.2 may be mixed in the
water-soluble liquid resin 810 for forming the protective film 86,
so as to promote the laser processing. Further, in the case that
silica (SiO.sub.2) is mixed in the water-soluble liquid resin 810,
delamination can be suppressed owing to the low expansion
coefficient and high thermal diffusivity of silica. The metal oxide
to be mixed has a particle size of 10 to 200 nm, and it is mixed in
an amount of about 0.01 to 10 parts by weight per 100 parts by
weight of water-soluble resin. The shape of the particles of the
metal oxide may be circular or elongated like a needle.
[0101] In this manner, the spectrum measuring step, the determining
step, and the laser processing step are repeated for all of the
workpieces W stored in the cassette 60 shown in FIG. 1. As a
result, it is possible to obtain the devices with no debris from
each workpiece W.
[0102] After dividing each workpiece W along the division lines L
to obtain the individual devices attached to the tape T, the
individual devices attached to the tape T are transferred from the
chuck table 2 to the protective film forming means 8 by operating
the transfer mechanism 9. In the protective film forming means 8, a
cleaning water is discharged from the cleaning liquid nozzle 82
toward the protective film 86 formed on the workpiece W held on the
holding table 80, thereby removing the protective film 86 formed on
the front side of each device.
[0103] While the laser processing apparatus 1 has a function of
forming a protective film on the front side Wa of the workpiece W,
a function of determining whether or not the protective film formed
has a desired thickness, and a function of laser-processing the
workpiece W in the above preferred embodiment, these functions may
be separately performed by individual apparatuses. Further, while
the unit for measuring a fluorescence spectrum and the unit for
forming a protective film are provided adjacent to each other in
the same space in this preferred embodiment, these units may be
provided in different spaces.
[0104] The fluorescence spectra shown in FIGS. 5 to 10 show the
measurement results in the case that Hogomax as a water-soluble
resin provided by DISCO Corporation is used as the water-soluble
liquid resin 810 shown in FIG. 4A and the water-soluble liquid
resin 810 contains an absorbing agent (ferulic acid) capable of
absorbing a pulsed laser beam having a wavelength of 355 nm (the
water-soluble liquid resin 810 showing no color to pale yellow
color in appearance). This water-soluble liquid resin 810 is formed
on the front side of each wafer. The fluorescence spectra shown in
FIGS. 11 and 12 show the measurement results in the case that the
absorbing agent contained in Hogomax is changed to an absorbing
agent (blue coloring matter) capable of absorbing a pulsed laser
beam having a wavelength of 532 nm (this water-soluble liquid resin
810 showing red to blue color in appearance).
[0105] More specifically, the fluorescence spectra shown in FIGS. 5
and 6 are those in the case that the wavelength of excitation light
to be applied to the protective film is 365 nm. As apparent from
FIGS. 5 and 6, there is a correlation between the thickness of the
protective film and the fluorescence intensity. Accordingly, these
fluorescence spectra can be used for the determination of whether
or not the protective film has a desired thickness.
[0106] The fluorescence spectrum shown in FIG. 7 is that in the
case that the wavelength of the excitation light is 385 nm and the
protective film is formed on a pattern wafer. As apparent from FIG.
7, the fluorescence intensity increases with an increase in
thickness of the protective film. Accordingly, in determining the
thickness of an actual protective film formed on a pattern wafer,
it is possible to determine whether or not the actual protective
film has a predetermined thickness by comparing the fluorescence
spectra according to the thickness.
[0107] The fluorescence spectrum shown in FIG. 8 is that in the
case that the wavelength of the excitation light is 385 nm and the
protective film is formed on a bump wafer. As apparent from FIG. 8,
there is no correlation between the thickness of the protective
film and the fluorescence intensity in the case that the protective
film is thin. However, in the case that the protective film is
thick (5.0 .mu.m or 3.1 .mu.m), there is a correlation between the
thickness of the protective film and the fluorescence intensity.
Accordingly, in the case that the actual protective film is thick
(e.g., 3.1 .mu.m or more), it is possible to determine whether or
not the thickness of the actual protective film has a predetermined
thickness by comparing the fluorescence spectra according to the
thickness.
[0108] The fluorescence spectra shown in FIGS. 9 and 10 are those
in the case that the wavelength of the excitation light is 405 nm.
As apparent from FIGS. 9 and 10, there is no correlation between
the thickness of the protective film and the fluorescence
intensity. Accordingly, these fluorescence spectra are not used for
the determination of the thickness of the protective film.
[0109] The fluorescence spectra shown in FIGS. 11 and 12 are those
in the case that the wavelength of the excitation light is set to
532 nm and 570 nm, respectively, and the protective film is formed
on a bump wafer. As apparent from FIGS. 11 and 12, the fluorescence
intensity increases with an increase in thickness of the protective
film. Accordingly, in determining the thickness of an actual
protective film on a bump wafer, it is possible to determine
whether or not the actual protective film has a predetermined
thickness by comparing the fluorescence spectra according to the
thickness.
[0110] FIGS. 13A and 13B are real images (photographs) and FIGS.
13C and 13D are binary images respectively corresponding to FIGS.
13A and 13B in the case of a bump wafer. On the other hand,
FIGS.14A and 14B are real images (photographs) and FIGS. 14C and
14D are binary images respectively corresponding to FIGS. 14A and
14B in the case of a pattern wafer. FIG. 13A is the real image in
the case that the protective film contains the absorbing agent, and
FIG. 13B is the real image in the case that the protective film
does not contain the absorbing agent. Similarly, FIG. 14A is the
real image in the case that the protective film contains the
absorbing agent, and FIG. 14B is the real image in the case that
the protective film does not contain the absorbing agent. FIGS. 13A
to 14D are shown to verify the effectiveness of the present
invention by the comparison between the case that the absorbing
agent is present in the protective film and the case that the
absorbing agent is absent in the protective film. In the case that
the protective film containing the absorbing agent is formed on the
bump wafer, blue fluorescence is emitted from an area where the
protective film is formed by applying LED light having a wavelength
of 365.+-.10 nm. As shown in FIG. 13A, this blue fluorescence is
shown as a pale white area. On the other hand, in the case that the
protective film not containing the absorbing agent is formed on the
bump wafer, the blue fluorescence is not emitted and no white area
is shown in FIG. 13B.
[0111] Similarly, in the case that the protective film containing
the absorbing agent is formed on the pattern wafer, blue
fluorescence is emitted from an area where the protective film is
formed by applying LED light having a wavelength of 365.+-.10 nm.
As shown in FIG. 14A, this blue fluorescence is shown as a pale
white area. On the other hand, in the case that the protective film
not containing the absorbing agent is formed on the pattern wafer,
the blue fluorescence is not emitted and no white area is shown in
FIG. 14B.
[0112] The real images obtained above were subjected to binary
image analysis by Eq. (1) mentioned above. By adjusting the
arbitrary value Q in Eq. (1), the protective film containing the
absorbing agent was displayed in black as shown in FIGS. 13C and
14C, whereas the protective film not containing the absorbing agent
was displayed in white as shown in FIGS. 13D and 14D. In this
manner, the present invention is a measuring method derived from
the fluorescence due to the absorbing agent contained in the
protective film.
[0113] In FIGS. 13A and 14A, the formed area of the protective film
was artificially prepared. This formed area is a lower area on each
wafer. As shown in FIGS. 13A and 14A, no fluorescence was seen in
this formed area. Further, as shown in FIGS. 13C and 14C, this
formed area was displayed in white as a binary image. In this
manner, by measuring the fluorescence due to the absorbing agent
contained in the protective film, it is possible to determine
whether or not the protective film is present.
[0114] In this preferred embodiment, the continuous-wave light
having a single wavelength used for measurement of the fluorescence
intensity in an ultraviolet region includes light having a
wavelength of 365 nm and light having a wavelength of 385 nm. In
the case of using the light having a wavelength of 365 nm, there is
a definite correlation between the thickness of the protective film
and the fluorescence intensity. That is, a large optical absorption
coefficient can be obtained, so that the fluorescence intensity due
to the absorbing agent can be increased. Accordingly, it can be
easily determined whether or not the protective film is present.
Further, in the fluorescence spectra shown in FIGS. 5 to 8 which
can be used for the determination of the thickness of the
protective film, it is apparent that the peak wavelength as a
reference for setting of the threshold is longer than the
wavelength of the excitation light and falls within the range of
400 to 500 nm.
[0115] 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.
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