U.S. patent application number 11/251810 was filed with the patent office on 2006-05-18 for protective film agent for laser dicing and wafer processing method using the protective film agent.
This patent application is currently assigned to Tokyo Ohka Kogyo Co., Ltd.. Invention is credited to Atsushi Kawakami, Nobuyasu Kitahara, Hiroshi Takanashi, Toshiyuki Yoshikawa.
Application Number | 20060105544 11/251810 |
Document ID | / |
Family ID | 36273953 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060105544 |
Kind Code |
A1 |
Takanashi; Hiroshi ; et
al. |
May 18, 2006 |
Protective film agent for laser dicing and wafer processing method
using the protective film agent
Abstract
A protective film agent for laser dicing according to the
present invention comprises a solution having, dissolved therein, a
water-soluble resin and at least one laser light absorber selected
from the group consisting of a water-soluble dye, a water-soluble
coloring matter, and a water-soluble ultraviolet absorber. The
protective film agent is coated on a surface of a wafer, which is
to be processed, and is then dried to form a protective film. Laser
dicing through the protective film produces chips from the wafer.
As a result, deposition of debris can be effectively prevented on
the entire face of the chips, including their peripheral edge
portions.
Inventors: |
Takanashi; Hiroshi;
(Kanagawa-ken, JP) ; Kawakami; Atsushi;
(Kanagawa-ken, JP) ; Yoshikawa; Toshiyuki; (Tokyo,
JP) ; Kitahara; Nobuyasu; (Tokyo, JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Assignee: |
Tokyo Ohka Kogyo Co., Ltd.
Disco Corporation
|
Family ID: |
36273953 |
Appl. No.: |
11/251810 |
Filed: |
October 18, 2005 |
Current U.S.
Class: |
438/460 |
Current CPC
Class: |
B23K 2103/50 20180801;
B23K 26/40 20130101; H01L 21/67092 20130101; C09D 5/32 20130101;
B23K 2101/40 20180801 |
Class at
Publication: |
438/460 |
International
Class: |
H01L 21/78 20060101
H01L021/78 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 12, 2004 |
JP |
2004-328400 |
Claims
1. A protective film agent for laser dicing, comprising a solution
having, dissolved therein, a water-soluble resin and at least one
water-soluble laser light absorber selected from the group
consisting of a water-soluble dye, a water-soluble coloring matter,
and a water-soluble ultraviolet absorber.
2. The protective film agent for laser dicing according to claim 1,
wherein solids of the solution have a g absorption coefficient k,
for laser light with a wavelength of 355 nm, within a range of
3.times.10.sup.-3 to 2.5.times.10.sup.-1 absL/g (abs:
absorbance).
3. The protective film agent for laser dicing according to claim 1,
wherein the laser light absorber is contained in an amount of 0.01
to 10 parts by weight based on 100 parts by weight of the
water-soluble resin.
4. A processing method for a wafer, comprising: coating a surface
of the wafer, which is to be processed, with the protective film
agent for laser dicing according to claim 1, followed by drying, to
form a protective film; and irradiating the surface, which is to be
processed, with laser light via the protective film to perform
processing.
5. The processing method according to claim 4, wherein a wavelength
of the laser light is 355 nm.
6. The processing method according to claim 4, wherein a plurality
of semiconductor chips partitioned by streets arranged in a lattice
pattern are formed in the wafer, and the streets are irradiated
with the laser light via the protective film to form grooves.
7. The processing method according to claim 4, wherein the
protective film is removed by washing with water after irradiation
with the laser light.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a protective film agent for use in
laser dicing which applies a laser beam to a predetermined region
of a wafer, such as a semiconductor wafer, to carry out
predetermined processing, and a processing method by laser dicing
using the protective film agent.
[0003] 2. Description of the Related Art
[0004] As is well known among those skilled in the art, a wafer
formed in a semiconductor device manufacturing process has a
laminate, which comprises an insulating film and a functional film
stacked on the face of a semiconductor substrate, such as silicon,
partitioned by a lattice of scheduled division lines, called
streets. Respective regions partitioned by the streets define
semiconductor chips such as IC's or LSI's. That is, a plurality of
semiconductor chips are obtained by cutting the wafer along the
streets. An optical device wafer has a laminate, which comprises a
gallium nitride-based compound semiconductor or the like stacked on
the face of a sapphire substrate or the like, partitioned into a
plurality of regions by streets. When cut along these streets, the
optical device wafer is divided into optical devices, such as light
emitting diodes or laser diodes. These optical devices find wide
use in electrical equipment.
[0005] Such cutting of the wafer along the streets is usually
performed by a cutting device called a dicer. This cutting device
comprises a chuck table for holding the wafer, which is a
workpiece, cutting means for cutting the wafer held on the chuck
table, and moving means for moving the chuck table and the cutting
means relative to each other. The cutting means includes a rotating
spindle to be rotated at a high speed, and a cutting blade mounted
on the spindle. The cutting blade comprises a disk-shaped base, and
an annular cutting edge mounted on an outer peripheral portion of
the side surface of the base. The cutting edge, for example,
comprises diamond abrasive grains, which have a grain size of the
order of 3 .mu.m, fixed to the outer peripheral portion of the side
surface of the base by electroforming, and is formed in a thickness
of the order of 20 .mu.m.
[0006] The wafer having the above-described laminated structure is
a high brittleness material. Thus, the wafer has posed the problems
that when the wafer is cut into semiconductor chips by the cutting
blade (cutting edge), flaws, scratches or chipping occurs, causing
the peeling of the insulating film required of circuit elements
formed on the faces of the chips.
[0007] To avoid the above problems, it is currently becoming common
practice to apply laser light along the streets prior to cutting
with the cutting blade, thereby forming grooves commensurate with
the width of the cutting blade (cutting edge), and then to perform
cutting with the blade.
[0008] When laser light is applied along the streets of the wafer,
however, the new problem has arisen that the laser light is
absorbed, for example, into the silicon substrate, and its thermal
energy leads to the melting or thermal decomposition of silicon,
thus generating a silicon vapor, etc., which are condensed and
deposited on the faces of the chips. The resulting condensation
deposit (debris) of the silicon vapor, etc. markedly deteriorates
the quality of the semiconductor chips.
[0009] To resolve the problem due to debris, Japanese Patent
Application Laid-Open No. 1978-8634 (hereinafter referred to as
Patent Document 1) and Japanese Patent Application Laid-Open No.
1993-211381 (hereinafter referred to as Patent Document 2) propose
methods in which a protective film comprising a water-soluble resin
is formed on a surface of a wafer to be processed, and this surface
is irradiated with laser light via the protective film.
[0010] According to the methods of Patent Documents 1 and 2, the
chip faces are protected with the protective film. Thus, even if a
silicon vapor or the like, which is the thermal decomposition
product of the substrate upon laser irradiation, scatters and
condenses, its condensate (debris) deposits on the surface of the
protective film, and does not deposit on the chip faces. Since the
protective film is water-soluble, moreover, it can be easily
removed by washing with water. That is, the debris on the
protective film is washed away simultaneously with the washing of
the protective film with water. As a result, deposition of the
debris on the chip faces can be prevented.
[0011] With the foregoing methods, however, it is still impossible
to prevent the deposition of debris completely, and the problem
occurs that debris deposits on peripheral edge portions of the
chips, in particular. The following mechanism may be involved: Upon
irradiation with laser light, thermal decomposition of the
substrate proceeds prior to the thermal decomposition of the
protective film, and the pressure of a silicon vapor or the like,
which is its thermal decomposition product, causes voids to be
formed between the protective film and the peripheral edge portions
of the chip faces (in the vicinity of the street lines) (in other
words, partial peeling of the protective film takes place at the
peripheral edge portions). As a result, debris deposition occurs at
the peripheral edge portions of the chip faces. The problem also
exists that the adhesion of the protective film to the wafer face
is so low that the protective film is prone to peel off. Such
peeling is another factor for easy deposition of debris on the
peripheral edge portions of the chip faces.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention, therefore, to
provide a protective film agent for laser dicing, which can form a
protective film having high adhesion to the face of a wafer, and
being capable of effectively preventing deposition of debris on the
entire face of chips, including their peripheral edge portions, in
producing the chips from the wafer by laser dicing, and also to
provide a method for processing the wafer with the use of the
protective film agent.
[0013] According to an aspect of the present invention, there is
provided a protective film agent for laser dicing, comprising a
solution having, dissolved therein, a water-soluble resin and at
least one laser light absorber selected from the group consisting
of a water-soluble dye, a water-soluble coloring matter, and a
water-soluble ultraviolet absorber.
[0014] In the protective film agent of the present invention, it is
preferred that
[0015] (1) the g absorption coefficient k, for laser light with a
wavelength of 355 nm, of the solids of the solution be within the
range of 3.times.10.sup.-3 to 2.5.times.10.sup.-1 absL/g (abs:
absorbance); and
[0016] (2) the laser light absorber be contained in an amount of
0.01 to 10 parts by weight based on 100 parts by weight of the
water-soluble resin.
[0017] According to another aspect of the present invention, there
is provided a processing method for a wafer, comprising coating a
surface of the wafer, which is to be processed, with the
above-mentioned protective film agent for laser dicing, followed by
drying, to form a protective film, and irradiating the surface,
which is to be processed, with laser light via the protective film
to perform processing.
[0018] The processing method of the present invention may generally
adopt the following measures:
[0019] (3) The wavelength of the laser light is 355 nm.
[0020] (4) In the wafer, a plurality of semiconductor chips
partitioned by streets arranged in a lattice pattern are formed,
and the streets are irradiated with the laser light via the
protective film to form grooves.
[0021] (5) After irradiation with the laser light, the protective
film is removed by washing with water.
[0022] The protective film agent for laser dicing according to the
present invention contains the water-soluble laser light absorber
in addition to the water-soluble resin. Thus, a protective film,
which is formed on the face of the wafer by coating and drying the
protective film agent, shows high absorption of laser light and,
when irradiated with laser light, is promptly thermally decomposed
to be laser-processed along the street lines. Hence, peeling of the
protective film, which occurs under the pressure of a vapor, etc.
of the thermal decomposition product of the substrate upon exposure
to laser light, can be effectively prevented. Furthermore, the
water-soluble dye, etc., which are used as the water-soluble laser
light absorbers, all have high affinity for the wafer face. Thus,
the adhesion of the protective film has been enhanced, and peeling
of the protective film from the wafer face, particularly, in the
vicinity of the street lines is effectively suppressed.
Accordingly, the protective film is formed by the protective film
agent of the present invention, and laser dicing is performed by
irradiation with laser light, whereby the deposition of debris can
be effectively prevented throughout the faces of the diced
chips.
[0023] Generally, laser light having a wavelength of 355 nm is
used. In performing dicing with the use of such laser light, the
amount of the laser light absorber used is adjusted such that the g
absorption coefficient k of the protective film (the solids of the
above solution) is within the range of 3.times.10.sup.-3 to
2.5.times.10.sup.-1 absL/g (abs: absorbance). By so doing, uniform
processing can be achieved along the street lines of a fine line
width.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a perspective view showing a semiconductor wafer
which is processed by the wafer processing method using the
protective film agent of the present invention.
[0025] FIG. 2 is an enlarged sectional view of the semiconductor
wafer shown in FIG. 1.
[0026] FIG. 3 is an explanation drawing showing an embodiment of a
protective film formation step in the wafer processing method
according to the present invention.
[0027] FIG. 4 is an enlarged sectional view of essential parts of
the semiconductor wafer having a protective film formed thereon by
the protective film formation step shown in FIG. 3.
[0028] FIG. 5 is a perspective view showing a state in which the
semiconductor wafer having the protective film formed thereon is
supported by an annular frame via a protective tape.
[0029] FIG. 6 is a perspective view of essential parts of a laser
processing apparatus for performing a laser light application step
in the wafer processing method according to the present
invention.
[0030] FIG. 7 is a block diagram schematically showing the
configuration of laser light application means installed in the
laser processing apparatus shown in FIG. 6.
[0031] FIG. 8 is a schematic view for illustrating the focus spot
diameter of laser light.
[0032] FIGS. 9(a) and 9(b) are explanation drawings of the laser
light application step in the wafer processing method according to
the present invention.
[0033] FIG. 10 is an explanation drawing showing the position of
laser light application in the laser light application step of the
wafer processing method according to the present invention.
[0034] FIG. 11 is an enlarged sectional view of essential parts of
the semiconductor wafer showing a laser-processed groove formed in
the semiconductor wafer by the laser light application step in the
wafer processing method according to the present invention.
[0035] FIG. 12 is an enlarged sectional view of the essential parts
of the semiconductor wafer showing a state in which the protective
film coated on the face of the semiconductor wafer has been removed
by a protective film removal step in the wafer processing method
according to the present invention.
[0036] FIG. 13 is a perspective view of essential parts of a
cutting device for performing a cutting step in the wafer
processing method according to the present invention.
[0037] FIGS. 14(a) and 14(b) are explanation drawings of the
cutting step in the wafer processing method according to the
present invention.
[0038] FIGS. 15(a) and 15(b) are explanation drawings showing a
state in which the semiconductor wafer is cut along the
laser-processed groove by the cutting step in the wafer processing
method according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
(Protective Film Agent)
[0039] The protective film agent of the present invention comprises
a solution containing a water-soluble resin and a water-soluble
laser light absorber.
[0040] The water-soluble resin serves as a matrix for a protective
film, and is not limited, if it is a material which can form a film
when dissolved in a solvent, such as water, coated and dried. Its
examples include polyvinyl alcohol, polyvinyl pyrrolidone,
polyethylene glycol with 5 or more oxyethylene recurring units,
polyethylene oxide, methylcellulose, ethylcellulose, hydroxypropyl
cellulose, polyacrylic acid, polyvinyl alcohol-polyacrylic acid
block copolymer, polyvinyl alcohol-polyacrylic acid ester block
copolymer, and polyglycerin. These resins can be used alone or in
combination of two or more.
[0041] The protective film formed on the wafer face in the present
invention is removed by washing with water after laser processing.
If the water-washability of the protective film is taken into
consideration, it is preferred to use a resin having only an ether
linkage or a hydroxyl group as a polar group, for example,
polyvinyl alcohol or polyethylene glycol, as the aforementioned
water-soluble resin. This is because a water-soluble resin having a
polar group, such as a carboxyl group or a tertiary amine, tends to
bind firmly to the wafer face (chip face), and is likely to remain
on the wafer face after washing with water. The resin having only
an ether linkage or a hydroxyl group, on the other hand, has
relatively weak adhesiveness, and its remaining after washing with
water can be effectively avoided. In terms of the washability with
water, the polymerization degree or molecular weight of the
water-soluble resin used is preferably lower. If polyvinyl alcohol
is taken as an example, its polymerization degree is preferably of
the order of 300. However, the water-soluble resin with a high
polymerization degree or a high molecular weight has low
washability with water, but in this case, a decline in
water-washability can be avoided by using a plasticizer (to be
described later) concomitantly.
[0042] As the laser light absorber used in combination with the
above-mentioned water-soluble resin, a water-soluble dye, a
water-soluble coloring matter, and a water-soluble ultraviolet
absorber are used. These agents are all water-soluble, and are
advantageously present uniformly in the protective film. Moreover,
they show high affinity for the wafer face, and can form a
protective film highly adherent to the wafer face. Furthermore,
they are advantageous in that their solutions have high storage
stability and, during storage, cause no disadvantage, such as phase
separation or sedimentation, and can ensure satisfactory coating
properties. If a water-insoluble laser light absorber, such as a
pigment, is used, for example, there will be variations in the
laser absorption capacity of the protective film, or storage
stability or coating properties will be poor, making it difficult
to form a uniformly thick protective film.
[0043] As the above water-soluble dye in the present invention, a
water-soluble dye is selected, for example, from among azo dyes
(monoazo and polyazo dyes, metal complex salt azo dyes, pyrazolone
azo dyes, stilbene azo dyes, thiazole azo dyes), anthraquinone dyes
(anthraquinone derivatives, anthrone derivatives), indigoid dyes
(indigoid derivatives, thioindigoid derivatives), phthalocyanine
dyes, carbonium dyes (diphenylmethane dyes, triphenylmethane dyes,
xanthene dyes, acridine dyes), quinoneimine dyes (azine dyes,
oxazine dyes, thiazine dyes), methine dyes (cyanine dyes,
azomethine dyes), quinoline dyes, nitroso dyes, benzoquinone dyes
and naphthoquinone dyes, naphthalimide dyes, perinone dyes, and
other dyes.
[0044] As the water-soluble dyes, dyes as food additives, for
example, Food Red No. 2, Food Red No. 40, Food Red No. 102, Food
Red No. 104, Food Red No. 105, Food Red No. 106, Food Yellow NY,
Food Yellow No. 4 tartrazine, Food Yellow No. 5, Food Yellow No. 5
Sunset Yellow FCF, Food Orange AM, Food Vermillion No. 1, Food
Vermillion No. 4, Food Vermillion No. 101, Food Blue No. 1, Food
Blue No. 2, Food Green No. 3, Food Melon Color B, and Food Egg
Color No. 3 are preferred from the viewpoint of environmental load,
etc.
[0045] Examples of the water-soluble ultraviolet absorber are
4,4'-dicarboxybenzophenone, benzophenone-4-carboxylic acid,
2-carboxyanthraquinone, 1,2-naphthalenedicarboxylic acid,
1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid,
2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic
acid and sodium salt, potassium salt, ammonium salt, and quaternary
ammonium salt thereof, 2,6-anthraquinonedisulfonic acid sodium
salt, 2,7-anthraquinonedisulfonic acid sodium salt, and ferulic
acid. Of these substances, ferulic acid is preferred.
[0046] In the present invention, the above-mentioned water-soluble
laser light absorber is used in such an amount that the desired
laser light absorption capacity can be ensured. If processing is
performed using laser light with a wavelength of 355 nm, for
example, the water-soluble laser light absorber is preferably used
in such an amount that the g absorption coefficient k of the
protective film (the solids of the solution) is within the range of
3.times.10.sup.-3 to 2.5.times.10.sup.-1 absL/g (abs: absorbance).
If this g absorption coefficient k is lower than the above range,
the laser light absorption capacity of the protective film is so
low that the thermal decomposition of the protective film by
irradiation with laser light lags considerably behind the substrate
such as silicon. As a result, peeling of the film and so on due to
the pressure of a vapor of the thermal decomposition product are
apt to occur, and debris tends to form at the peripheral edge
portions of the chips. If the g absorption coefficient k is higher
than the above range, the thermal decomposition of the protective
film easily takes place even owing to the reflection of laser light
from the substrate upon laser light application. Thus, the
processing width of laser becomes larger than the laser spot
diameter. This is likely to be unsuitable, particularly, for dicing
along the streets of a very small line width.
[0047] If the laser light absorber, in whose maximum absorption
wavelength region the wavelength of laser light used belongs, is
selected and used, the use of its small amount enables the g
absorption coefficient k within the above-described range to be
secured. If the laser light absorber, which fails to meet this
condition, is chosen and used, it has to be used in a large amount
in order to secure the g absorption coefficient k within the
above-described range. However, if the amount of the laser light
absorber used is too large, phase separation may be caused between
the laser light absorber and the water-soluble resin, when the
solution containing it is coated and dried to form the protective
film. If the amount of the laser light absorber used is too small,
the laser light absorber may be unevenly distributed in the
protective film. Generally, therefore, it is preferred to select
the laser light absorber so that its amount used of 0.01 to 10
parts by weight based on 100 parts by weight of the water-soluble
resin enables the g absorption coefficient k within the
above-described range to be secured.
[0048] In the present invention, other compounding agents can be
dissolved, in addition to the above-mentioned water-soluble resin
and laser light absorber, in the solution for use as the protective
film agent. For example, a plasticizer and a surface active agent
can be used.
[0049] The plasticizer is used to enhance the water-washability of
the protective film after laser processing. The plasticizer is
preferably used, particularly when the water-soluble resin with a
high molecular weight is used. The use of the plasticizer is also
advantageous in that it can suppress the carbonization of the
water-soluble resin due to irradiation with laser light. A
water-soluble, low molecular weight compound is preferred as such a
plasticizer. Its examples include ethylene glycol, triethylene
glycol, tetraethylene glycol, ethanolamine, and glycerin. These
compounds can be used alone or in combination of two or more. Such
a plasticizer is used in such an amount that after coating and
drying of the solution, phase separation does not occur between the
plasticizer and the water-soluble resin. For example, its
recommendable amount used is 75 parts by weight or less, especially
20 to 75 parts by weight, based on 100 parts by weight of the
water-soluble resin.
[0050] The surface active agent is used to enhance the coating
properties, and further to enhance the storage stability of the
solution. Any surface active agents of the nonionic, cationic,
anionic or ampholytic type can be used, if they are
water-soluble.
[0051] Examples of the nonionic surface active agent are nonyl
phenol-based, higher alcohol-based, polyhydric alcohol-based,
polyoxyalkylene glycol-based, polyoxyethylene alkyl ester-based,
polyoxyethylene alkyl ether-based, polyoxyethylene alkylphenol
ether-based, and polyoxyethylene sorbitan alkyl ester-based surface
active agents. Examples of the cationic surface active agent are
quaternary ammonium salts and amine salts. Examples of the anionic
surface active agent are alkylbenzenesulfonic acids and their
salts, alkylsulfuric ester salts, methyltaurates, and ether
sulfonates. Examples of the ampholytic surface active agent are
imidazoliniumbetaine-based, amidopropylbetaine-based, and
aminodipropionate-based surface active agents. One of, or a
combination of two or more of, these surface active agents may be
selected. The amount of any such surface active agent may be
several tens of ppm or several hundred ppm based on the
solution.
[0052] In the protective film agent for laser dicing of the present
invention, which comprises the solution having the above-mentioned
components dissolved therein, the solids content in the solution
should be set in accordance with the type, the polymerization
degree or the molecular weight of the water-soluble resin used so
that the solution may have moderate coating properties. If the
solids content is too high, for example, coating is difficult,
resulting in a tendency toward an uneven thickness or entrapment of
air bubbles. If the solids content is low, the solution, when
coated on the wafer face, tends to drip, and the film thickness
after drying (thickness of the protective film) is difficult to
adjust. Thus, the solids content (the total content of the
respective ingredients) in the solution is preferably set at a
value of the order of 3 to 30% by weight, although it is different
according to the water-soluble resin, etc. used. The amount of the
water-soluble resin in the solids is generally 5% by weight or
more. This is preferred in rendering the strength of the protective
film appropriate, and preventing the deposition of debris on the
chip faces.
[0053] The solvent for use in preparing the solution, which is the
protective film agent of the present invention, may be a solvent in
which the aforementioned water-soluble resin and water-soluble
laser light absorber dissolve. Examples of the solvent are water,
alcohols, esters, alkylene glycols, alkylene glycol monoalkyl
ethers, and alkylene glycol monoalkyl ether acetates. Of them,
water and alkylene glycol monoalkyl ethers are preferred. As the
alkylene glycol monoalkyl ether, propylene glycol monomethyl ether
(PGME) is preferred. The most preferred solvent for the work
environment is water, or a mixed solvent containing water.
[0054] The above-described protective film agent of the present
invention is coated on the surface of the wafer to be processed,
for example, the surface of the wafer to be processed, where a
plurality of semiconductor chips partitioned by streets arranged in
a lattice layout are formed, followed by drying the coating,
whereby the protective film is formed. The streets are irradiated
with laser light via the protective film to form grooves (carry out
laser dicing). The recommendable thickness of the protective film
(the dry thickness of the protective film agent) is usually of the
order of 0.1 to 5 .mu.m on the streets. The reasons are as follows:
Such a surface of the wafer to be processed has many dents and
projections, and the streets are formed in these dents. Thus, if
the above thickness is too small, the thickness of the protective
film in the projections is so small that debris may enter the
protective film and deposit on the chip faces. An unnecessarily
large thickness, on the other hand, would bring no particular
advantages, but would cause only such a disadvantage that washing
with water after processing takes time.
[0055] An explanation will be offered below for the processing of
the wafer by laser dicing with the use of the protective film agent
according to the present invention.
[0056] FIG. 1 shows a perspective view of a semiconductor wafer
which is processed in accordance with the present invention. FIG. 2
shows an enlarged sectional view of the essential parts of the
semiconductor wafer shown in FIG. 1. The semiconductor wafer 2
shown in FIGS. 1 and 2 has a plurality of semiconductor chips 22,
such as IC's and LSI's, formed in a matrix form from a laminate 21,
which comprises an insulating film and a circuit-forming functional
film stacked on the face 20a of a semiconductor substrate 20 of
silicon or the like. The respective semiconductor chips 22 are
partitioned by streets 23 formed in a lattice pattern. In the
illustrated embodiment, the insulating film constituting the
laminate 21 is a low dielectric constant insulator film (Low-k
film) comprising an SiO.sub.2 film, or a film derived from an
inorganic material such as SiOF or BSG (SiOB), or a film from an
organic material which is a polymer such as polyimide or
Parylene.
[0057] To perform laser processing along the streets 23 of the
above-mentioned semiconductor wafer 2, the first step is to form a
protective film on the face 2a, a surface of the semiconductor
wafer 2 to be processed, with the use of the aforementioned
protective film agent.
[0058] In this protective film formation step, the protective film
agent is coated on the face 2a of the semiconductor wafer 2 by a
spin coater 4 as shown in FIG. 3. The-spin coater 4 is furnished
with a chuck table 41 having suction/holding means, and a nozzle 42
disposed above the center of the chuck table 41. The semiconductor
wafer 2 is laid, with its face 2a pointed upward, on the chuck
table 41 and, with the chuck table 41 being rotated, the protective
film agent in liquid form is dripped through the nozzle 42 onto the
center of the face of the semiconductor wafer 2. By this procedure,
the liquid protective film agent flows to an outer peripheral
portion of the semiconductor wafer 2 under centrifugal force,
covering the face of the semiconductor wafer 2. The liquid
protective film agent is moderately heated to be dried, whereby a
protective film 24 with a thickness of the order of 0.1 to 5 .mu.m
(thickness on the street 23) is formed on the face 2a of the
semiconductor wafer 2, as shown in FIG. 4.
[0059] Once the protective film 24 is formed in this manner on the
face 2a of the semiconductor wafer 2, a protective tape 6 mounted
on an annular frame 5 is stuck to the back of the semiconductor
wafer 2, as shown in FIG. 5.
[0060] Then, the face 2a (streets 23) of the semiconductor wafer 2
is irradiated with laser light through the protective film 24. This
laser light irradiation or application step is performed using a
laser processing apparatus as shown in FIGS. 6 to 8.
[0061] The laser processing apparatus 7 shown in FIGS. 6 to 8
comprises a chuck table 71 for holding a workpiece, laser light
application means 72 for applying laser light to the workpiece held
on the chuck table 71, and imaging means 73 for imaging the
workpiece held on the chuck table 71. The chuck table 71 is
constructed so as to suck and hold the workpiece, and is moved by a
moving mechanism (not shown) in a processing feed direction
indicated by an arrow X and an indexing feed direction indicated by
an arrow Y in FIG. 6.
[0062] As shown in FIG. 7, the laser light application means 72
includes a cylindrical casing 721 disposed substantially
horizontally. Pulsed laser light oscillation means 722 and a
transmission optical system 723 are disposed within the casing 721.
The pulsed laser light oscillation means 722 is composed of a
pulsed laser light oscillator 722a comprising a YAG laser
oscillator or a YVO4 laser oscillator, and a pulse repetition
frequency setting means 722b annexed thereto. The transmission
optical system 723 includes a suitable optical element such as a
beam splitter. A focusing device 724 accommodating condenser lenses
(not shown) composed of a lens assembly, which may itself be in a
well-known shape, is mounted at the front end of the casing 721.
Laser light, oscillated by the pulsed laser light oscillation means
722, arrives at the focusing device 724 via the transmission
optical system 723, and is directed from the focusing device 724 at
the workpiece, which is held on the chuck table 71, with a
predetermined focus spot diameter D.
[0063] The focus spot diameter D is defined by the following
equation, if pulsed laser light showing Gaussian distribution is
applied through an objective focusing lens 724a of the focusing
device 724 as shown in FIG. 8:
D(.mu.m)=4.times..lamda..times.f/(.pi..times.W) where .lamda.
represents the wavelength (.mu.m) of a pulsed laser beam,
[0064] W represents the diameter (mm) of pulsed laser light
incident on the objective focusing lens 724a, and
[0065] f represents the focal length (mm) of the objective focusing
lens 724a.
[0066] The imaging means 73, mounted at a front end portion of the
casing 721 constituting the laser light application means 72, is
composed of an infrared illumination means for directing infrared
rays at the workpiece, an optical system for catching infrared rays
applied by the infrared illuminations means, and an imaging device
(infrared CCD) for outputting an electrical signal corresponding to
the infrared rays caught by the optical system, in addition to an
ordinary imaging device (CCD) for taking an image with the use of
visible rays, in the illustrated embodiment. The imaging means 73
sends image signals obtained to a control means (not shown).
[0067] The laser light application step to be performed using the
above-described laser processing apparatus 7 will be described with
reference to FIG. 6 and FIGS. 9(a), 9(b) to 11.
[0068] In this laser light application step, the semiconductor
wafer 2 is laid on the chuck table 71 of the laser processing
apparatus 7 shown in FIG. 6, with the side, where the protective
film 24 is formed, being pointed upward. In this condition, the
semiconductor wafer 2 is attracted to and held on the chuck table
71. In FIG. 6, the annular frame 5, on which the protective tape 6
is mounted, is not shown. However, the annular frame 5 is held by a
suitable frame holding means disposed on the chuck table 71.
[0069] The chuck table 71 sucking and holding the semiconductor
wafer 2 as mentioned above is positioned directly below the imaging
means 73 by the moving mechanism (not shown). When the chuck table
71 is located directly below the imaging means 73, an alignment
operation for detecting the processing zone of the semiconductor
wafer 2 to be laser-processed is carried out by the imaging means
73 and the control means (not shown). That is, the imaging means 73
and the control means (not shown) perform image processing, such as
pattern matching, for aligning the street 23, formed in the
predetermined direction of the semiconductor wafer 2, with the
focusing device 724 of the laser light application means 72 for
applying laser light along the street 23, thereby implementing
alignment of the laser light application position. For the street
23 extending perpendicularly to the above predetermined direction
of the semiconductor wafer 2, alignment of the laser light
application position is performed similarly. At this time, the
protective film 24 basically opaque is formed on the face 2a of the
semiconductor wafer 2, where the streets 23 are formed, but the
street 23 can be imaged with infrared rays and alignment can be
performed from above the face 2a.
[0070] In the manner described above, the street 23 formed on the
semiconductor wafer 2 held on the chuck table 71 is detected, and
the alignment of the laser light application position is carried
out. Upon completion of alignment, the chuck table 71 is moved to a
laser light application zone where the focusing device 724 of the
laser light application means 72 is located, as shown in FIG. 9(a).
In the laser light application zone, one end (left end in FIG. 9)
of the predetermined street 23 is positioned directly below the
focusing device 724 of the laser light application means 72. With
pulsed laser light 725 being applied from the focusing device 724,
the chuck table 71, namely, the semiconductor wafer 2, is moved at
a predetermined feed speed in a direction indicated by an arrow X1
in FIG. 9(a). When the application position of the laser light
application means 7 reaches the position of the other end (right
end in FIGS. 9(a), 9(b)) of the street 23, as shown in FIG. 9(b),
application of the pulsed laser light 725 is stopped, and the
movement of the chuck table 71, namely, the semiconductor wafer 2,
is terminated.
[0071] Then, the chuck table 71, namely, the semiconductor wafer 2,
is moved by about 10 to 20 .mu.m in a direction perpendicular to
the sheet face of the drawing (i.e., in the indexing feed
direction). Then, with pulsed laser light 725 being applied from
the laser light application means 72, the chuck table 71, namely,
the semiconductor wafer 2, is moved at a predetermined feed speed
in a direction indicated by an arrow X2 in FIG. 9(b). When the
laser light application means 72 reaches the position shown in FIG.
9(a), application of the pulsed laser light 725 is stopped, and the
movement of the chuck table 71, namely, the semiconductor wafer 2,
is terminated.
[0072] As described above, during the reciprocating movement of the
chuck table 71, namely, the semiconductor wafer 2, the pulsed laser
light 725 is applied to the street 23, with its focus spots P in
alignment with areas in the vicinity of the upper surface of the
street 23, the spacing between P's being wider than the width of a
cutting blade (to be described later), as shown in FIG. 10.
[0073] The laser light application step is performed, for example,
under the following processing conditions:
[0074] Source of laser light: YVO4 laser or YAG laser
[0075] Wavelength: 355 nm
[0076] Pulse repetition frequency: 50 to 100 kHz
[0077] Output: 0.3 to 4.0 W
[0078] Focus spot diameter: 9.2 .mu.m
[0079] Processing feed speed: 1 to 800 mm/second
[0080] By performing the above-described laser light application
step, a laser-processed groove 25 having a larger width than the
width of the cutting blade (to be described later) is formed along
the street 23 in the laminate 21 of the semiconductor wafer 2 where
the street 23 has been formed, as shown in FIG. 11. The
laser-processed groove 25 reaches the semiconductor substrate 20 to
remove the laminate 21. When, in this laser light application step,
the pulsed laser light 725 is applied via the protective film 24 to
the laminate 21 having the street 23 formed therein, thermal
decomposition of the protective film 24 occurs nearly
simultaneously with (or prior to) the thermal decomposition of the
laminate 21 and the semiconductor substrate 20, since the
protective film 24 has a high laser light absorption capacity. As a
result, film rupture takes place at the site of laser application.
That is, the protective film 24 becomes the starting point of
processing. After the starting point of processing is formed in the
protective film 24 in this manner, or nearly at the same time as
the formation of the starting point of processing, the laminate 21
and the semiconductor substrate 20 are processed by application of
the pulsed laser light 725. Thus, the protective film 24 is
prevented from being peeled off under the pressure of a vapor of
the thermal decomposition product of the laminate 21 or the
semiconductor substrate 20. Hence, the deposition of debris onto
the peripheral edge portion of the semiconductor chip 22 due to
such peeling of the protective film 24 can be effectively
prevented. Furthermore, the adhesion of the protective film 24 to
the wafer face 20a (face of the semiconductor chip 22) is so high
that the peeling of the protective film 24 during processing, for
example, minimally occurs. Consequently, the deposition of debris
due to such peeling of the protective film 24 is effectively
avoided. That is, as shown in FIG. 11, since the above-mentioned
protective film 24 is formed, debris 26 deposits on the surface of
the protective film 24, and does not deposit on the semiconductor
chips 22. Accordingly, deterioration of the quality of the
semiconductor chips 22 due to deposition of the debris 26 can be
avoided effectively.
[0081] After the laser light application step is carried out along
the street in the above manner, the chuck table 71, accordingly,
the semiconductor wafer 2 held thereon, is indexed by a spacing
between the streets in a direction indicated by an arrow Y
(indexing step), and the laser light application step is performed
again. After the laser light application step and the indexing step
are performed in this manner for all the streets extending in the
predetermined direction, the chuck table 71, accordingly, the
semiconductor wafer 2 held thereon, is turned 90 degrees. Then, the
laser light application step and the indexing step are performed,
as above, along each street extending perpendicularly to the above
predetermined direction, whereby the laser-processed grooves 25 can
be formed in all the streets 23 formed in the semiconductor wafer
2.
[0082] Then follows the removal of the protective film 24 coated on
the face 2a of the semiconductor wafer 2 stuck to the protective
tape 6 mounted on the annular frame 5. For this protective film
removal step, the protective film 24 can be washed off with water
(or hot water) as shown in FIG. 12, because the protective film 24
has been formed from the water-soluble resin (the other component
is also water-soluble), as stated earlier. At this time, the debris
26 on the protective film 24 generated during the aforementioned
laser light application step is also washed away along with the
protective film 24. As shown here, removal of the protective film
24 can be performed very easily.
[0083] After the protective film 24 is removed in the above manner,
a cutting step is performed for cutting the semiconductor wafer 2
along the laser-processed grooves 25 formed in the streets 23 of
the semiconductor wafer 2. This cutting step can be carried out
using a cutting device 8, which is generally used as a dicing
device, as shown in FIG. 13. The cutting device 8 comprises a chuck
table 81 equipped with suction/holding means, cutting means 82
furnished with a cutting blade 821, and imaging means 83 for
imaging the workpiece held on the chuck table 81.
[0084] The cutting step to be performed using the above-described
cutting device 8 will be described with reference to FIGS. 13 to
15(a), 15(b).
[0085] The semiconductor wafer 2 deprived of the protective film 24
is laid on the chuck table 81 of the cutting device 6, with the
face 2a of the semiconductor wafer 2 being pointed upward, as shown
in FIG. 13. In this condition, the semiconductor wafer 2 is held on
the chuck table 81 by suction means (not shown). The chuck table 81
sucking and holding the semiconductor wafer 2 is positioned
directly below the imaging means 83 by a moving mechanism (not
shown).
[0086] When the chuck table 81 is located directly below the
imaging means 83, an alignment operation for detecting a zone of
the semiconductor wafer 2 to be cut is carried out by the imaging
means 83 and control means (not shown). That is, the imaging means
83 and the control means (not shown) perform image processing, such
as pattern matching, for aligning the street 23, formed in the
predetermined direction of the semiconductor wafer 2, with the
cutting blade 821 for cutting the semiconductor wafer 2 along the
laser-processed groove 25, thereby implementing alignment of the
cutting zone. For the street 23 extending perpendicularly to the
above predetermined direction of the semiconductor wafer 2,
alignment of the cutting zone is performed similarly.
[0087] In the manner described above, the street 23 formed on the
semiconductor wafer 2 held on the chuck table 81 is detected, and
the alignment of the cutting zone is carried out. Upon completion
of this alignment, the chuck table 81 holding the semiconductor
wafer 2 is moved to a cutting start position in the cutting zone.
At this time, the semiconductor wafer 2 is positioned such that one
end (left end in FIGS. 14(a), 14(b)) of the street 23 to be cut is
positioned rightwardly, by a predetermined amount, of a position
directly below the cutting blade 821, as shown in FIG. 14(a). The
semiconductor wafer 2 is also positioned such that the cutting
blade 821 is located at the center of the laser-processed groove 25
formed in the street 23.
[0088] When the chuck table 81, namely, the semiconductor wafer 2,
has been brought to the cutting start position in the cutting zone,
the cutting blade 821 is moved downward in a depth setting motion
from a standby position indicated by double-dotted chain lines in
FIG. 14(a), and is thereby brought to a predetermined infeed
position as indicated by solid lines in FIG. 14(a). This infeed
position is set such that the lower end of the cutting blade 821
reaches the protective tape 6 stuck to the back of the
semiconductor wafer 2, as shown in FIG. 14(a) and FIG. 15(a).
[0089] Then, the cutting blade 821 is rotated at a predetermined
rotational speed, and the chuck table 81, namely, the semiconductor
wafer 2, is moved at a predetermined cutting feed speed in a
direction indicated by an arrow X1 in FIG. 14(a). When the chuck
table 81, namely, the semiconductor wafer 2, comes to such a
position that the other end (right end in FIGS. 14(a) and 14(b)) of
the street 23 is located a predetermined amount leftwardly of the
position directly below the cutting blade 821, as shown in FIG.
14(b), the movement of the chuck table 81, namely, the
semiconductor wafer 2, is stopped. By so feeding the chuck table
81, namely, the semiconductor wafer 2, for feeding, a cut groove 27
reaching the back of the semiconductor wafer 2 is formed along the
laser-processed groove 25 formed in the street 23, whereby the
semiconductor wafer 2 is cut, as shown in FIG. 15(b). In this
cutting step, only the semiconductor substrate 20 is cut by the
cutting blade 821. This can prevent the peeling of the laminate 21
which is caused by cutting the laminate 21, formed on the face of
the semiconductor substrate 20, by the cutting blade 821.
[0090] The above-described cutting step is performed, for example,
under the following conditions: [0091] Cutting blade: Outer
diameter 52 mm, thickness 20 .mu.m [0092] Rotational speed of
cutting blade: 30,000 rpm [0093] Cutting feed speed: 50
mm/second
[0094] Then, the cutting blade 821 is brought to a standby position
indicated by dashed double-dotted lines in FIG. 14(b), and the
chuck table 81, namely, the semiconductor wafer 2, is moved in a
direction indicated by an arrow X2 in FIG. 14(b) until it is
returned to the position shown in FIG. 14(a). Then, the chuck table
81, namely, the semiconductor wafer 2, is indexed, by an amount
corresponding to the spacing between the streets 23, in a direction
perpendicular to the sheet face in the drawing (i.e., in an
indexing feed direction), whereby the street 23 to be cut next is
brought to the position opposed to the cutting blade 821. When the
street 23 to be cut next has been located at the position opposed
to the cutting blade 821, the above-described cutting step is
performed.
[0095] The foregoing cutting step is performed for all the streets
23 formed in the semiconductor wafer 2. As a result, the
semiconductor wafer 2 is cut along the laser-processed grooves 25
formed in the streets 23, and is thereby separated into individual
semiconductor chips 20. In the cutting step, cutting is carried
out, with cutting water (pure water) being supplied. Thus, the
protective film 24 can be removed by cutting water supplied,
without the need to provide the aforementioned protective film
removal step individually. As noted here, the cutting step may be
performed while concurrently serving as the protective film removal
step.
[0096] While the wafer processing method of the present invention
has been described based on the embodiments in which the
semiconductor wafer is divided, it is to be understood that the
present invention can be applied to various types of laser
processing for other wafers. For example, the present invention can
be applied to the division of optical device wafers.
EXAMPLES
[0097] The specifications for the laser processing apparatus used
in the following examples are as follows:
[0098] Source of laser light: YVO4 laser
[0099] Wavelength: 355 nm
[0100] Pulse repetition frequency: 50 to 100 kHz
[0101] Output: 0.3 to 4.0 W
[0102] Focus spot diameter: 9.2 .mu.m
[0103] Processing feed speed: 1 to 800 mm/second
Example 1
[0104] A protective film agent of the following composition was
prepared:
[0105] Water-soluble resin: 20 g [0106] Polyvinyl alcohol having a
saponification degree of 88% and a polymerization degree of 300
[0107] Water-soluble laser light absorber: 0.2 g [0108] Ferulic
acid
[0109] Water: 80 g
[0110] g absorption coefficient k of the
solids=1.56.times.10.sup.-1
[0111] The above protective film agent was coated on a silicon
wafer by a spinner, and dried to form a protective film having a
thickness on the street of 0.5 to 1.5 .mu.m. Then, the silicon
wafer having the protective film formed thereon was mounted on the
laser processing apparatus complying with the above specifications,
and was subjected to laser processing. Then, the protective film
was washed off with pure water, and the surroundings of the laser
scans were observed. Bulges of the edge areas were observed, but no
deposition of debris on the surroundings was noted. Thus, the
silicon wafer was at a usable level. The width of processing was
comparable to the laser spot diameter without having influence from
the thickness of the coating film.
Example 2
[0112] A protective film agent was prepared in exactly the same
manner as in Example 1, except that the amount of ferulic acid, a
water-soluble laser light absorber, was changed to 0.8 g. The g
absorption coefficient k of the solids of the protective film agent
was 5.61.times.10.sup.-1.
[0113] Using the above protective film agent, a protective film
having a thickness of 0.2 .mu.m was formed on a silicon wafer in
the same manner as in Example 1. Laser processing was performed in
the same manner, and the protective film was washed off with water.
Observation of the surroundings of the laser scans, which was made
in the same manner as in Example 1, showed no deposition of debris.
The width of processing was slightly larger than the laser spot
diameter, but the silicon wafer was at a usable level.
Example 3
[0114] A protective film agent was prepared in the same manner as
in Example 1, except that polyvinyl alcohol having a saponification
degree of 75% and a polymerization degree of 500 was used as the
water-soluble resin. The g absorption coefficient k of the solids
of the protective film agent was 1.56.times.10.sup.-1 as in Example
1.
[0115] Using the above protective film agent, a protective film
having a thickness of 0.5 to 1.5 .mu.m was formed on a silicon
wafer in the same manner as in Example 1. Laser processing was
performed in the same manner, and the protective film was washed
off with water. Observation of the surroundings of the laser scans,
which was made in the same manner as in Example 1, showed no
deposition of debris. The width of processing was comparable to the
laser spot diameter without having influence from the thickness of
the coating film.
Example 4
[0116] A protective film agent was prepared in exactly the same
manner as in Example 3, except that a water-soluble monoazo dye
(AIZEN SWTW3, Hodogaya Chemical Co., Ltd.) was used, instead of
ferulic acid, as the water-soluble laser light absorber. The g
absorption coefficient k of the solids of the protective film agent
was 7.9.times.10.sup.-2.
[0117] Using the above protective film agent, a protective film
having a thickness of 0.5 to 1.5 .mu.m was formed on a silicon
wafer in the same manner as in Example 1. Laser processing was
performed in the same manner, and the protective film was washed
off with water. Observation of the surroundings of the laser scans,
which was made in the same manner as in Example 1, showed no
deposition of debris. The width of processing was comparable to the
laser spot diameter without having influence from the thickness of
the coating film.
Example 5
[0118] A protective film agent was prepared in exactly the same
manner as in Example 5, except that 15 g of glycerin was added as a
plasticizer. The g absorption coefficient k of the solids of the
protective film agent was 7.9.times.10.sup.-2 as in Example 5.
[0119] Using the above protective film agent, a protective film
having a thickness of 0.5 to 1.5 .mu.m was formed on a silicon
wafer in the same manner as in Example 1. Laser processing was
performed in the same manner, and the protective film was washed
off with water. Observation of the surroundings of the laser scans,
which was made in the same manner as in Example 1, showed no
deposition of debris. The width of processing was comparable to the
laser spot diameter without having influence from the thickness of
the coating film.
Comparative Example 1
[0120] A protective film agent was prepared in exactly the same
manner as in Example 1, except that ferulic acid, a water-soluble
laser light absorber, was not used. The g absorption coefficient k
of the solids of the protective film agent was
1.94.times.10.sup.-3.
[0121] Using the above protective film agent, a protective film
having a thickness of 0.5 to 1.5 .mu.m was formed on a silicon
wafer in the same manner as in Example 1. Laser processing was
performed in the same manner, and the protective film was washed
off with water. Observation of the surroundings of the laser scans,
which was made in the same manner as in Example 1, showed marked
deposition of debris, and peeling of the film.
* * * * *