U.S. patent application number 09/799438 was filed with the patent office on 2001-10-18 for method of manufacturing surface acoustic wave apparatuses.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Ikada, Katsuhiro, Sakaguchi, Kenji, Takamiya, Miki.
Application Number | 20010029648 09/799438 |
Document ID | / |
Family ID | 18590736 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010029648 |
Kind Code |
A1 |
Ikada, Katsuhiro ; et
al. |
October 18, 2001 |
Method of manufacturing surface acoustic wave apparatuses
Abstract
A method of manufacturing a surface acoustic wave apparatus
including the steps of forming a first conductive film, depositing
a first resist on the first conductive film and patterning the
first resist, dry-etching the first conductive film using the
patterned first resist to form IDT electrodes, a short-circuit
wiring electrode for establishing electrical connection between IDT
electrodes, and a second conductive film provided where the second
surface acoustic wave device is constructed, removing the second
conductive film, depositing a second resist and heating the second
resist, patterning the second resist on the electrodes, forming a
second conductive film having a thickness which is different from
the first conductive film, removing the second resist to form the
electrodes of the second surface acoustic wave device and to expose
the electrodes of the first surface acoustic wave device, and
disconnecting the short-circuit wiring electrode.
Inventors: |
Ikada, Katsuhiro;
(Ishikawa-ken, JP) ; Sakaguchi, Kenji;
(Ishikawa-ken, JP) ; Takamiya, Miki;
(Kanazawa-shi, JP) |
Correspondence
Address: |
Keating & Bennett LLP
10400 Eaton Place, Suite 312
Fairfax
VA
22030
US
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
26-10 Tenjin 2-chome
Nagaokakyo-shi
JP
617-8555
|
Family ID: |
18590736 |
Appl. No.: |
09/799438 |
Filed: |
March 5, 2001 |
Current U.S.
Class: |
29/25.35 |
Current CPC
Class: |
H03H 3/08 20130101; Y10T
29/42 20150115 |
Class at
Publication: |
29/25.35 |
International
Class: |
H04R 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2000 |
JP |
2000-072300 |
Claims
What is claimed is:
1. A method of manufacturing a surface acoustic wave apparatus
including first and second surface acoustic wave devices having
interdigital transducers with different thicknesses from each other
on a single piezoelectric substrate, the method comprising the
steps of: providing a piezoelectric substrate; forming a first
conductive film on the entire surface of the piezoelectric
substrate; depositing a first resist on the entire surface of the
first conductive film and patterning the first resist; dry-etching
the first conductive film using the patterned first resist to form
on the piezoelectric substrate IDT electrodes of a first surface
acoustic wave device, a short-circuit wiring electrode for
establishing electrical connection between comb-shaped electrodes
of the IDT electrodes, and a conductive film provided in a region
including the entire area in which the second surface acoustic wave
device is constructed; removing the conductive film in the region
including the entire area in which the second surface acoustic wave
device is constructed; depositing a second resist on the entire
surface of the piezoelectric substrate and heating the second
resist; patterning the second resist at a portion in which the
electrodes of the second surface acoustic wave device are formed;
forming on the entire surface of the piezoelectric substrate, a
second conductive film having a thickness which is different from
that of the first conductive film and having substantially the same
film thickness as the electrode film thickness of the second
surface acoustic wave device; removing the second resist by a
lift-off method to form the electrodes of the second surface
acoustic wave device and to expose the electrodes of the first
surface acoustic wave device; and disconnecting the short-circuit
wiring electrode in the first surface acoustic wave device.
2. The method according to claim 1, wherein the step of removing
the conductive film in the region including the entire area in
which the second surface acoustic wave device is constructed is
performed via wet etching.
3. The method according to claim 2, wherein the wet etching is
performed using an etchant that can remove the conductive film
without affecting the second resist.
4. The method according to claim 1, wherein the piezoelectric
substrate is made of one of a piezoelectric single crystal, a
piezoelectric ceramic, and an insulating substrate with a
piezoelectric thin film disposed thereon.
5. A method according to claim 1, wherein the step of forming the
first conductive film on the entire surface of the piezoelectric
substrate is performed via one of evaporation, sputtering, and
plating.
6. A method of manufacturing a surface acoustic wave apparatus
including first and second surface acoustic wave devices having
interdigital transducers with different thicknesses from each other
on a single piezoelectric substrate, the method comprising the
steps of: providing a piezoelectric substrate; depositing a first
resist on the entire surface of the piezoelectric substrate;
removing the first resist at an area in which electrodes of the
first surface acoustic wave device are to be formed and an area in
which a wiring electrode for short-circuiting between the
comb-shaped electrodes of the IDT electrodes of the first surface
acoustic wave device is to be formed; forming on the entire surface
of the piezoelectric substrate a first conductive film having
substantially the same film thickness as the electrode film
thickness of the first surface acoustic wave device; lifting off
the first resist and the first conductive film deposited on the
first resist so as to form the electrodes of the first surface
acoustic wave device and the wiring electrode; depositing a second
resist on the entire surface of the piezoelectric substrate and
heating the piezoelectric substrate; removing the second resist at
an area in which the electrodes of the second surface acoustic wave
device are formed; depositing on the entire surface of the
piezoelectric surface a second conductive film having substantially
the same film thickness as the electrode film thickness of the
second surface acoustic wave device; lifting off the second resist
and the second conductive film deposited on the second resist so as
to form the electrodes of the second surface acoustic wave device;
and disconnecting the short-circuit wiring electrode in the first
surface acoustic wave device.
7. The method according to claim 6, wherein the piezoelectric
substrate is made of one of a piezoelectric single crystal, a
piezoelectric ceramic, and an insulating substrate with a
piezoelectric thin film disposed thereon.
8. A method according to claim 6, wherein after the step of
removing the first resist at an area in which electrodes of the
first surface acoustic wave device are to be formed and an area in
which a wiring electrode for short-circuiting between the
comb-shaped electrodes of the IDT electrodes of the first surface
acoustic wave device is to be formed, the first resist remains at a
portion including the entire area in which the electrodes of the
second surface acoustic wave filter device are formed.
9. A method according to claim 6, wherein the first resist has a
reverse tapered cross section.
10. A method of manufacturing a surface acoustic wave apparatus
including first and second surface acoustic wave devices having
interdigital transducers with different thicknesses from each other
on a single piezoelectric substrate, the method comprising the
steps of: providing a piezoelectric substrate; depositing a first
resist on the entire surface of the piezoelectric substrate;
removing the first resist at an area in which electrodes of the
first and second surface acoustic wave devices are to be formed;
forming on the entire surface of the piezoelectric substrate a
first conductive film having substantially the same film thickness
as the electrode film thickness of the second surface acoustic wave
device; depositing a second resist on the entire surface of the
piezoelectric surface; removing the second resist at an area in
which at least the electrodes of the first surface acoustic wave
device are formed, except a portion in which the second surface
acoustic wave device is located; depositing a second conductive
film on the first conductive film using the first and second
resists; and removing by a lift-off method, the first resist and
the second resist to form interdigital transducers of the first and
second surface acoustic wave devices
11. The method according to claim 10, wherein the piezoelectric
substrate is made of one of a piezoelectric single crystal, a
piezoelectric ceramic, and an insulating substrate with a
piezoelectric thin film disposed thereon.
12. A method according to claim 10, wherein the first resist is a
negative-type resist.
13. A method according to claim 10, wherein the first resist is a
positive-type resist, the second resist is a negative-type resist,
and only one separating liquid is used for lifting off the first
and second resists.
14. A method according to claim 10, further comprising the step of
forming additional conductive films, in addition to the first and
second conductive films, on the piezoelectric substrate.
15. A method according to claim 14, wherein the total thickness of
all of the conductive films is substantially equal to the thickness
of the IDT electrodes of the first surface acoustic wave filter
device.
16. A method according to claim 10, further comprising the step of
forming an intermediate layer between the first conductive film and
the second conductive film.
17. A method according to claim 14, wherein the total thickness of
the first and second conductive films and the intermediate layer is
substantially equal to the thickness of the IDT electrodes of the
first surface acoustic wave filter device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to methods of manufacturing
surface acoustic wave apparatuses constructed by forming a
plurality of surface acoustic wave devices having electrode films
with different thicknesses on the same piezoelectric substrate,
and, for example, relates to a method of manufacturing a surface
acoustic wave apparatus in which a plurality of surface acoustic
wave filter devices having different bands, are disposed on the
piezoelectric substrate.
[0003] 2. Description of the Related Art
[0004] Recently, in mobile communication apparatuses such as mobile
phones, the apparatuses that support multi-band transmissions have
been considered in order to achieve high-performance. In addition,
the transmission frequencies of the mobile phones are getting
higher.
[0005] Therefore, a mobile phone that can operate at an 800 MHz
band as well as one having a 1.5 GHz or greater frequency band
requires RF band-pass filters each corresponding to the two
different frequency bands.
[0006] In order to achieve miniaturization and low overall weight
of a terminal apparatus such as this type of a mobile phone,
miniaturization of the components mounted therein must be achieved.
However, since there is the limit as to how small the components
can be, it is strongly desired that a single component perform the
functions of the two RF band-pass filters.
[0007] In Japanese Unexamined Patent Application Publication No.
10-190390, there is disclosed a method of manufacturing a surface
acoustic wave apparatus in which a plurality of surface acoustic
wave filter devices are disposed on the same piezoelectric
substrate.
[0008] FIGS. 10A to 10E are cross-sectional views illustrating the
method of manufacturing the surface acoustic wave apparatus
according to the above-described related art. In the method
described in this related art, a conductive film 104 is formed on a
piezoelectric substrate 103 and then a resist is formed along the
entire surface of the conductive film 104. Patterning of the resist
is performed to form a resist layer 105 (FIG. 10A). Dry etching
forms electrodes 101a of a first surface acoustic wave device (FIG.
10B). Thereafter, deposition of the resist and patterning of the
resist form a resist layer 106' at a portion in which a second
surface acoustic wave device is provided. In this case, a portion
in which the first surface acoustic wave device is provided is
coated with a resist layer 106 (FIG. 10C). Furthermore, as shown in
FIGS. 10D and 10E, a conductive film 107 is entirely formed and
then lift-off is performed on the resist layers 106 and 106', and
the conductive film 107 is laminated thereon to form electrodes
102a of the second surface acoustic wave device.
[0009] According to this method, in a state in which the electrodes
of the first electric component device are protected by the resist,
the electrodes of the second electric component device are formed
by photolithography or etching. Accordingly, when the electrodes of
the first and second electric component devices are formed, high
accuracy is not required. Therefore, when this method is used for
manufacturing a surface acoustic wave apparatus, even though the
width of the electrode fingers are as fine as approximately 1
.mu.m, the efficiency percentage of manufacturing the apparatus can
be increased.
[0010] However, in the method described in the related art, dry
etching which is performed when the electrodes 101a of a first
surface acoustic wave device are initially formed is also performed
on a region where a second surface acoustic wave device is
constructed on a piezoelectric substrate 103. That is, a region
indicated by an arrow A in FIG. 10(b) is also subject to dry
etching.
[0011] Generally, when dry etching is performed in a case in which
an electrode finger pitch is approximately 1 .mu.m or less, due to
a micro loading phenomena, a micro-gap portion is the last to be
etched. In the dry etching, after etching is performed on the
electrodes, generally over-etching follows.
[0012] Therefore, when the electrodes 101a of the first surface
acoustic wave device are formed, etching is finished earlier in the
region indicated by the arrow A. Accordingly, it takes a longer
time for the surface of the piezoelectric substrate of the region
indicated by the arrow A to be exposed to the plasma, such as F,
which is used when dry etching including over-etching is performed.
Since the surface of the substrate indicated by the arrow A is
exposed to the plasma for the comparatively longer time, there is a
problem that the insertion loss of the second surface acoustic wave
device is degraded and VSWR is increased.
[0013] Furthermore, since the region indicated by the arrow A is
also etched, the area of the etched region is increased.
Accordingly, when a plurality of surface acoustic wave apparatuses
is constructed from a mother piezoelectric substrate, there is a
problem that a variation in the characteristic of the surface
acoustic wave apparatus in the mother piezoelectric substrate
increases.
[0014] In addition, when the manufacturing method according to the
above-described related art is applied to a method of manufacturing
the surface acoustic wave apparatus using a piezoelectric substrate
having pyroelectricity, the following problem arises.
[0015] That is, generally, when the resist is deposited, the resist
is often heated in order to improve adhesion and resistance to
plasma of the resist pattern. However, when the piezoelectric
substrate having the pyroelectricity is used, due to a temperature
change during heating of the resist, a voltage drop occurs between
a pair of comb-shaped electrodes which constitute the IDT
electrodes of the first surface acoustic wave device, causing
discharge. This discharge sometimes produces pyroelectric
destruction in the electrodes. Even though discharge is too small
to cause the pyroelectric destruction, the resist is sometimes
broken, which causes a short circuit in the IDT electrodes of the
first surface acoustic wave device after the lift-off process for
constructing the electrodes of the surface acoustic wave
device.
SUMMARY OF THE INVENTION
[0016] In order to overcome the problems described above, preferred
embodiments of the present invention provide a method of
manufacturing a surface acoustic wave apparatus which, even when a
pyroelectric substrate is used in constructing a plurality of
surface acoustic wave devices by forming electrodes having
different thicknesses on the same piezoelectric substrate, short
circuits or other defects are prevented from occurring, and
degradation of the piezoelectric substrate is prevented from
occurring in an electrode region of the subsequently formed surface
acoustic wave device, and degradation of the insertion loss and
degradation of the VSWR characteristics are prevented from
occurring.
[0017] According to a first preferred embodiment of the present
invention, a method of manufacturing a surface acoustic wave
apparatus including first and second surface acoustic wave devices
having different electrode film thicknesses on a piezoelectric
substrate, the method including the steps of providing a
piezoelectric substrate, forming a first conductive film on an
entire surface of the piezoelectric substrate, depositing a first
resist on the entire surface of the first conductive film,
performing patterning and dry etching on the first resist to form
on the piezoelectric substrate IDT electrodes of the first surface
acoustic wave device, a short-circuit wiring electrode for
establishing electrical connection between comb-shaped electrodes
of the IDT electrodes, and a conductive film provided in a region
including the entire area in which the second surface acoustic wave
device is constructed, performing wet etching to remove the
conductive film provided in the region including the entire area in
which the second surface acoustic wave device is constructed,
depositing a second resist on the entire surface of the
piezoelectric substrate and heating the substrate, removing the
second resist at a location in which the electrodes of the second
surface acoustic wave device are located, forming a second
conductive film having the same film thickness as the electrode
film thickness of the second surface acoustic wave device, lifting
off the second resist and the second conductive film deposited on
the second resist, forming the electrodes of the second surface
acoustic wave device while exposing the electrodes of the first
surface acoustic wave device, and disconnecting the short-circuit
wiring electrode in the first surface acoustic wave device.
[0018] A second preferred embodiment of the present application
provides a method of manufacturing a surface acoustic wave
apparatus including first and second surface acoustic wave devices
having different electrode film thicknesses on a piezoelectric
substrate, the method including the steps of providing a
piezoelectric substrate, depositing a first resist on an entire
surface of the piezoelectric substrate, removing the first resist
at an area in which electrodes of the first surface acoustic wave
device are to be formed and an area in which a wiring electrode for
short-circuiting between the comb-shaped electrodes of the IDT
electrodes of the first surface acoustic wave device is to be
formed, forming a first conductive film having substantially the
same film thickness as the electrode film thickness of the first
surface acoustic wave device, lifting off the first resist and the
first conductive film deposited on the first resist, forming the
electrodes of the first surface acoustic wave device and the wiring
electrode, depositing a second resist on the entire surface of the
piezoelectric substrate and heating the substrate, removing the
second resist at an area in which the electrodes of the second
surface acoustic wave device are formed, depositing a second
conductive film having substantially the same film thickness as the
electrode film thickness of the second surface acoustic wave
device, lifting off the second resist and the second conductive
film deposited on the second resist, forming the electrodes of the
second surface acoustic wave device, and disconnecting the
short-circuit wiring electrode in the first surface acoustic wave
device.
[0019] A third preferred embodiment of the present invention
provides a method of manufacturing a surface acoustic wave
apparatus including first and second surface acoustic wave devices
having different electrode film thicknesses on a piezoelectric
substrate, the method including the steps of providing a
piezoelectric substrate, depositing a first resist on an entire
surface of the piezoelectric substrate, removing the first resist
at an area in which electrodes of the first and second surface
acoustic wave devices are to be formed, forming a first conductive
film having substantially the same film thickness as the electrode
film thickness of the second surface acoustic wave device,
depositing a second resist, removing the second resist at an area
in which at least the electrodes of the first surface acoustic wave
device are formed, except an area in which the second surface
acoustic wave device is constructed, depositing a second conductive
film having substantially the same film thickness as the electrode
film thickness of the first surface acoustic wave device, and
lifting off the first resist, the second resist, and the conductive
films laminated thereon at the same time.
[0020] It is preferred that a negative-type resist is used as the
first resist in the third preferred embodiment of the present
invention.
[0021] In another modification of the third preferred embodiment of
the present invention, a positive-type resist is preferably used as
the first resist and the negative-type resist is used as the second
resist. In the lift-off process, the separating liquid for
separating the first and second resists is shared.
[0022] In manufacturing methods of surface acoustic wave
apparatuses according to various preferred embodiments of present
invention, when first and second surface acoustic wave devices
having different electrode film thicknesses are formed on a common
piezoelectric substrate, a short-circuit wiring electrode for
electrically connecting between input/output terminals of the IDT
electrodes and ground terminals is formed while the IDT electrodes
of the first surface acoustic wave device are formed. After the IDT
electrodes of the second surface acoustic wave filter device are
formed, the short-circuit wiring electrode is disconnected. Hence,
even though the second resist is deposited and adhesion and
resistance to heat of the second resist are increased due to
heating, the short circuit in the IDT electrodes of the first
surface acoustic wave filter device is positively prevented.
[0023] Therefore, while malfunction of the IDT electrodes of the
first surface acoustic wave filter device is prevented, the
electrodes of the second surface acoustic wave filter can be highly
accurately formed.
[0024] In the first preferred embodiment of the present invention,
when dry etching is performed during formation of the IDT
electrodes of the first surface acoustic wave filter device, a
piezoelectric substrate portion in which the second surface
acoustic wave filter device is formed is protected by the first
resist. After the dry etching, a conductive film which is provided
at a region including the portion in which the second surface
acoustic wave device is formed is removed using a wet etching
method. Accordingly, the region in which the second surface
acoustic wave filter device of the piezoelectric substrate is
formed can be prevented from being subjected to plasma such as F
used in the dry etching. This enables the insertion loss and VSWR
of the second surface acoustic wave filter device to be reliably
and positively prevented from being degraded.
[0025] In manufacturing methods according to the second and third
preferred embodiments of the present invention, when the first and
second surface acoustic wave devices having different electrode
film thicknesses are formed on the piezoelectric substrate,
formation of the electrodes of the first surface acoustic wave
filter device are performed using the lift-off method and the
region in which the second surface acoustic wave filter device is
formed is protected by the resist. Hence, compared with the
conventional method in which the first surface acoustic wave filter
device is formed using the dry etching method, degradation of the
insertion loss and VSWR of the second surface acoustic wave filter
device is reliably prevented.
[0026] Furthermore, according to the third preferred embodiment of
the present invention, since there is no need to increase the
accuracy during the second photolithography process, the heating
temperature of the resist can be very low, which prevents the
occurrence of pyroelectric destruction. Therefore, since formation
of the short-circuit wiring electrode and a disconnection process
are not required, simplification of the manufacturing processes can
be achieved.
[0027] In addition, since the lift-off is simultaneously performed
during the last process of which the electrodes of the first and
second surface acoustic wave filter devices are formed,
simplification of the processes can be achieved.
[0028] By causing the polarities of the first and second resists to
be different, when patterning is performed on the second resist,
deformation of the first resist can be prevented. This increases
the electrode accuracy of the first surface acoustic wave filter
device.
[0029] For the purpose of illustrating the present invention, there
is shown in the drawings several forms that are presently
preferred, it being understood, however, that the present invention
is not limited to the precise arrangements and instrumentalities
shown.
[0030] Other features, characteristics, elements and advantages of
the present invention will become more apparent from the following
detailed description of preferred embodiments thereof with
reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIGS. 1A to 1F are cross sectional views illustrating a
manufacturing method according to the first preferred embodiment of
the present invention.
[0032] FIGS. 2A to 2D are plan views illustrating each step of the
manufacturing method according to the first preferred embodiment of
the present invention.
[0033] FIG. 3 is a graph illustrating the insertion loss-frequency
characteristic of a second surface acoustic wave filter device of a
surface acoustic wave apparatus obtained according to a
conventional method.
[0034] FIG. 4 is a graph illustrating the VSWR characteristic of
the second acoustic wave filter device of the surface acoustic wave
apparatus obtained using the conventional method.
[0035] FIG. 5 is a graph illustrating the insertion loss-frequency
characteristics of the second surface acoustic wave filter device
of the surface acoustic wave apparatus according to the first
preferred embodiment of the present invention.
[0036] FIG. 6 is a graph illustrating the VSWR characteristic of
the surface acoustic wave filter device of the surface acoustic
wave apparatus according to the first preferred embodiment of the
present invention.
[0037] FIGS. 7A to 7F are of schematically cross sectional views
each illustrating the manufacturing method according to the second
preferred embodiment of the present invention.
[0038] FIG. 8 is a schematically side view illustrating a
preferable shape of a resist, in the second preferred embodiment,
in a case in which the resist is formed.
[0039] FIGS. 9A to 9E are schematically cross sectional views
illustrating the manufacturing method according to the third
preferred embodiment of the present invention.
[0040] FIGS. 10A to 10E are cross sectional views illustrating the
manufacturing method of the conventional surface acoustic wave
apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0041] Hereinafter, preferred embodiments of the present invention
are illustrated with reference to drawings, for describing the
present invention.
[0042] FIGS. 1A to 1F are each cross-sectional views illustrating a
method of manufacturing a surface acoustic wave apparatus according
to a preferred embodiment of the present invention.
[0043] In the present preferred embodiment, the surface acoustic
wave apparatus which is schematically shown in a cross sectional
manner in FIG. 1F is manufactured. As shown in FIG. 1F, in this
surface acoustic wave apparatus, a surface acoustic wave filter
device 1 includes electrodes 1a and a second surface acoustic wave
filter device 2 including electrodes 2a, wherein the surface
acoustic wave devices 1 and 2 including the electrodes 1a and 2a
are disposed on a common piezoelectric substrate 3.
[0044] The surface acoustic wave filter devices 1 and 2, which are
schematically shown in FIG. 1, preferably have substantially planar
shapes shown in FIG. 2D. That is, the IDT electrodes 1a and
reflectors 1c and 1d located at both ends of the propagation
direction of a surface wave of the IDT electrodes 1a are disposed
on the piezoelectric substrate 3, thereby defining the first
surface acoustic filter device 1. The IDT electrodes 2a, and
reflectors 2c and 2d arranged at both ends of the propagation
direction of a surface wave of the IDT electrodes 2a are disposed
on the piezoelectric substrate 3, thereby defining the second
surface acoustic filter device.
[0045] The thickness of each of the IDT electrodes 1a is preferably
thicker than the thickness of each of the IDT electrodes 2a.
[0046] The IDT electrodes 1a and 2a include a pair of comb-shaped
electrodes which have electrode fingers that are interdigitated
with each other. A wiring electrode 1b is disposed in the surface
acoustic wave filter device 1. In FIG. 2D, the wiring electrode 1b
is disconnected. In a state shown in FIG. 2C, as described below,
the wiring electrode 1b is electrically connected to both of the
comb-shaped electrodes of the IDT electrodes 1a and the
reflectors.
[0047] Initially, as shown in FIG. 1A, a conductive film 4 having
substantially the same film thickness as that of each of the IDT
electrodes 1a of the first surface acoustic wave filter device 1 is
formed on the entire surface of the piezoelectric substrate 3. The
piezoelectric substrate 3 can be constructed of a piezoelectric
single crystal, such as LiTaO.sub.3, LiNbO.sub.3, crystal, lithium
tetraborate, or langasite, or piezoelectric ceramic such as lead
zirconium titanate series ceramics.
[0048] Alternatively, the piezoelectric substrate 3 may be
constructed by forming a piezoelectric thin film such as ZnO on an
insulation substrate made of an insulating material such as alumina
or other suitable material.
[0049] The conductive film 4 can be constructed using a conductive
material such as Al. In order to form the conductive film 4, an
appropriate method such as evaporation, sputtering, or plating can
be used.
[0050] Next, a positive-type first photo-resist layer is formed on
the entire top surface of the conductive film 4. The first
photo-resist layer is exposed using a mask having a shielding
portion that corresponds to the shape of each of the IDT electrodes
1a of the first surface acoustic wave filter device and the entire
region of the second surface acoustic wave filter device 2
including a portion in which all electrodes including the
reflectors of the second surface acoustic wave filter device 2 are
formed. Thereafter, the exposed resist portion is removed.
[0051] As a result, as is shown in FIG. 1A, the resist 5 having
patterning can be obtained. As is obvious from FIG. 1A, patterning
is performed so that the resist 5 have a shape corresponding to a
part in which the IDT electrodes 1a of the surface acoustic wave
filter device 1 (see FIG. 1F) and the wiring electrode 1b are
formed and so that the resist 5 remains in a region including the
entire region having the electrodes of the acoustic wave filter
device 2 formed thereon, as shown on the right part of FIG. 1A.
[0052] Next, etching is performed using etchant that can remove the
conductive film 4 without affecting the resist 5. Thereafter,
removing the resist 5 leads to formation of the IDT electrodes 1a,
the wiring electrode 1b, and the conductive film 2b, as shown in
FIG. 1B. FIG. 2A shows a plan view of this state.
[0053] As is obvious from FIGS. 1B and FIG. 2A, subsequent to the
above process, the IDT electrodes 1a of the first surface acoustic
wave filter device 1, the reflectors 1c and 1d, and the wiring
electrode 1b are formed. The conductive film 2b is formed on the
entire region of the surface acoustic wave filter device 2
including a region in which the electrodes thereof are formed. The
etching can be performed via dry etching using the plasma, such as
F or Cl, or other suitable material.
[0054] When the etching is performed, a region in which the
electrodes of the second surface acoustic wave filter device of the
piezoelectric substrate 3 are formed is coated with the conductive
film 2b. Accordingly, the portion of the top surface of the
piezoelectric substrate 3 which is coated with the conductive film
2b is unlikely to be damaged when the dry etching is performed.
[0055] Next, a positive-type photo resist is deposited on the
entire surface of the piezoelectric substrate 3. On the side in
which the second surface acoustic wave filter device 2 is
constructed, a mask in which a region corresponding to the
conductive film 2b is set as an opening is laminated on the resist
and is exposed. The exposed resist portion is removed and,
moreover, the conductive film 2b is removed by wet etching. In
addition, removal of the remained resist enables the conductive
film 2b to be removed, as shown in FIG. 1C. Since, as described
above, removal of the conductive film 2b is performed using the wet
etching, the top surface of the piezoelectric substrate 3 is hardly
damaged in the region in which the conductive film 2b is formed.
FIG. 2B shows a plan view of this state.
[0056] Next, the positive-type second photo resist is deposited on
the entire surface of the piezoelectric substrate 3. On the side in
which the second surface acoustic wave filter device 2 is
constructed, a mask in which electrode formed components such as
the IDT electrodes or the reflectors are an opening part is
laminated on the photo resist and is exposed. At this stage,
adhesion and resistance to heat of the photo resist is greatly
increased.
[0057] Since the wiring electrode 1b short-circuits a pair of
comb-shaped electrodes of the IDT electrodes 1a, discharge does not
occur between the comb-shaped electrodes of the IDT electrodes.
Accordingly, damage to the IDT electrodes 1a and the resist is
prevented.
[0058] More specifically, the wiring electrode 1b is connected to
input/output pads 13 and 14 and the reflector 1d. Each of the
input/output pads 13 and 14 is electrically connected to the
corresponding comb-shaped electrodes of the IDT electrodes 1a.
[0059] Thereafter, the exposed resist portion is removed, whereby,
as shown in FIG. 1D, a second photo resist 6 having patterning can
be obtained. As is obvious from FIG. 1D, on the side of the first
surface acoustic wave filter device 1, the IDT electrodes 1a, the
wiring electrode 1b, and other elements are coated and protected by
the photo resist 6 having patterning. On the side of the second
surface acoustic wave filter device, the photo resist 6 having
patterning is formed except the portion having the IDT electrodes
2a of the second surface acoustic wave filter device formed
thereon.
[0060] Thereafter, as shown in FIG. 1E, a conductive film 7 is
laminated on the entire surface of the photo resist 6 and
preferably has substantially the same film thickness of each of the
IDT electrodes 2a of the second surface acoustic wave filter device
2.
[0061] Next, the conductive film 7 deposited on the photo resist 6
is removed via lift-off along with the photo resist 6. This state
is shown in a plan view of FIG. 2C.
[0062] As described above, on the second surface acoustic wave
filter device 2 side, the IDT electrodes 2a, the reflectors 2c and
2d, and the input/output pads 23 and 24 are formed.
[0063] Next, as shown in FIG. 2D, the wiring electrode 1b is
disconnected at a portion indicated by an arrow B. Thus, the
surface acoustic wave filter apparatus according to the present
preferred embodiment can be obtained, which is schematically shown
in the cross-sectional view in FIG. 1F and which is shown in the
plan view in FIG. 2D.
[0064] The wiring electrode 1b can be disconnected using the photo
resist via a photolithography etching method or via a laser or
other suitable method.
[0065] As described above, the first and second surface acoustic
wave filters 1 and 2 including IDT electrodes with different
thicknesses from each other are disposed on the same piezoelectric
substrate 3.
[0066] Furthermore, in the manufacturing method according to the
present preferred embodiment, when the electrodes 1a of the first
surface acoustic wave filter device 1 are formed, the dry etching
is preferably performed using the plasma. During this process, the
region in which the second surface acoustic wave filter device is
formed is coated with the conductive film 2b so as to be protected.
Accordingly, degradation of the piezoelectric substrate hardly
occurs.
[0067] In addition, in forming the first and second surface
acoustic wave filters 1 and 2, initially, the IDT electrodes 1a of
the first surface acoustic wave filter device are formed. The
wiring electrode 1b causes a pair of comb-shaped electrodes and the
reflectors of the IDT electrodes 1a to be electrically connected to
each other and be short-circuit. Therefore, even though adhesion
and resistance to heat are increased due to heating or other
conditions, since discharging hardly occurs, disconnect or short
circuit or other defects of the IDT electrodes 1a are reliably
prevented.
[0068] As described above, the surface acoustic wave apparatus is
obtained by forming the surface acoustic wave filter devices 1 and
2 having certain dimensions (e.g., 1.5 mm.times.2.1 mm.times.0.35
mm=1.10 mm.sup.3) on the piezoelectric substrate 3. The amplitude
characteristic and the reflection characteristic of the second
surface acoustic wave filter device are measured. For comparison,
in the surface acoustic wave apparatus obtained using the
above-described conventional method, the amplitude characteristic
and the reflection characteristic of the second surface acoustic
wave filter device are measured. The results are shown in FIG. 3 to
FIG. 6. The dashed lines in FIG. 3 and FIG. 5 represent
characteristics expanded by the scales on the right hand of the
vertical axis. In FIG. 4 and FIG. 6, the solid lines represent
characteristics of the input port and the dashed lines represent
characteristics of the output port.
[0069] FIG. 3 and FIG. 4 show the amplitude characteristic and the
reflection characteristic of the second surface acoustic wave
filter device of the surface acoustic wave apparatus obtained using
the conventional method, the apparatus which is provided for
comparison. FIG. 5 and FIG. 6 show the amplitude characteristic and
the reflection characteristic of the second surface acoustic wave
filter device of the surface acoustic wave apparatus obtained in
the above-described preferred embodiment.
[0070] As is obvious from comparison of the results shown in FIG.
3, FIG. 4, FIG. 5, and FIG. 6, according to the manufacturing
method of the present preferred embodiment, it is clear that
insertion loss and VSWR are greatly improved. The results indicated
in FIG. 3 to FIG. 6 are shown in the below table 1.
1 TABLE 1 Present Conventional Preferred Method Embodiment Process
(Average/.sigma.) (Average/.sigma.) Difference Minimum 1.42 dB/0.06
1.27 dB/0.06 0.15 dB Insertion Loss VSWR 2.30/0.11 1.87/0.05
0.43
[0071] FIGS. 7A to 7F are each cross-sectional views illustrating
the manufacturing method of the surface acoustic wave apparatus
according to a second preferred embodiment of the present
invention. Elements that are identical to their counterparts in the
first preferred embodiment are assigned to have the same reference
numerals as those corresponding elements, and the detailed
description of the identical elements is omitted.
[0072] In the second preferred embodiment, the surface acoustic
wave apparatus having the same electrode construction as in the
first preferred embodiment is manufactured.
[0073] Initially, a negative-type first photo resist is deposited
on the entire top surface of the piezoelectric substrate. A mask in
which a shielding portion is the portion in which the electrodes 1a
of the first surface acoustic wave filter device 1 are formed is
laminated on this resist layer and is exposed. Next, by removing
the exposed resist portion, as shown in FIG. 7A, the resist 5
having the patterning is obtained. Patterning is performed so that
this resist 5 does not exist at a portion in which the
short-circuit wiring electrode 1b is provided. The resist 5 remains
at a portion including the entirety of the region in which the
electrodes of the second surface acoustic wave filter device are
formed.
[0074] Next, a conductive film having substantially the same film
thickness as those of the IDT electrodes 1a of the first surface
acoustic wave filter device is formed on the entire surface of the
piezoelectric substrate 3 (FIG. 7B).
[0075] Thereafter, the conductive film 4 laminated on the resist 5
is removed via lift-off along with the resist 5, forming the IDT
electrodes 1a as well as the wiring electrode 1b (FIG. 7C). In this
case, although not shown in FIG. 7, the reflectors 1c and 1d shown
in FIG. 2D are formed in the same manner. The electrode film is not
formed in the region in which the second surface acoustic wave
filter device 2 is constructed.
[0076] Since, as described above, the IDT electrodes 1a of the
first surface acoustic wave filter device 1 and the wiring
electrode 1b are formed using the lift-off method, the region in
which the electrodes of the second surface acoustic wave filter
device of the piezoelectric substrate 3 are formed is not subject
to the dry etching, which eliminates any damage to the
piezoelectric substrate 3.
[0077] Thereafter, the positive-type second photo resist is
preferably deposited on the entire top surface of the piezoelectric
substrate 3. Next, on the side in which the second surface acoustic
wave filter device 2 is formed, the mask in which a pattern
portion, such as each of the IDT electrodes 2a, or the reflector 2c
or 2d, functions as the opening is laminated on the resist and is
exposed. At this stage, heat treatment on the resist 6 greatly
increases adhesion and resistance to heat thereof.
[0078] During the heating of this resist 6, since the electrodes on
the side of the first surface acoustic wave filter device 1, such
as the IDT electrodes 1a and the wiring electrode 1b, are coated
with the resist 6, the top surface of the piezoelectric substrate 3
is hardly damaged on the side of the first surface acoustic wave
filter device 1.
[0079] In the same manner as in the first preferred embodiment,
since the wiring electrode 1b causes the input/output pads 13 and
14, and the reflectors 1c and 1d to be short-circuited, discharging
is prevented from occurring during the heating. Accordingly, damage
to the IDT electrodes 1a and to the resist 6 is prevented.
[0080] Thereafter, by removing the exposed resist, the resist 6
having patterning can be obtained as shown in FIG. 7D.
[0081] Next, the conductive film 7 preferably having substantially
the same film thickness as the thickness of each of the IDT
electrodes 2a of the second surface acoustic wave filter device is
entirely deposited. In this case, due to deposition of the
conductive film 7, the IDT electrodes 2a including the conductive
film 7, and, though not shown in FIG. 7, the reflectors 2c and 2d,
and the electrode pads 23 and 24 are formed in a region in which
the resist 6 does not exist. Thus, the electrode construction on
the side of the second surface acoustic wave filter device 2 is
formed. Thereafter, by lifting off the resist 6 and the conductive
film 7 on the resist 6, and disconnecting the wiring electrode 1b
in the same manner as in the first preferred embodiment, the
surface acoustic wave apparatus can be obtained.
[0082] In the second preferred embodiment, formation of the
electrodes of the first surface acoustic wave filter device can be
performed using the lift-off method. Therefore, during the process
of forming the electrodes on the side of the first surface acoustic
wave filter device, due to the dry etching or other suitable
process, there is no risk of degrading the piezoelectric substrate
portion on the side in which the second surface acoustic wave
filter device is constructed. Accordingly, compared with the
conventional method, degradation of the insertion loss or the VSWR
can be prevented on the second surface acoustic wave filter device
side.
[0083] In the manufacturing method according to the second
preferred embodiment, preferably, by eliminating burrs at the edge
portion of the IDT electrodes to improve the ease of lift-off, it
is preferable that the resist 5 be constructed so as to have a
reverse tapered cross section, as shown in FIG. 8A. That is, as the
resist 5 moves closer to the piezoelectric substrate 3 side, the
resist 5 is preferably formed so that the width of each of the
electrode fingers expands.
[0084] In the manufacturing method according to the second
preferred embodiment, dry etching is not required. Only execution
of two-stage lift-off method is necessary. Accordingly,
simplification of the processes can be achieved compared to the
first preferred embodiment.
[0085] FIGS. 9A to 9E each are cross-sectional views illustrating a
manufacturing method of the surface acoustic wave apparatus
according to a third preferred embodiment of the present
invention.
[0086] Elements that are identical to their counterparts in the
first preferred embodiment are illustrated by the same reference
numerals as those of the counterpart elements, and the detailed
description thereof is omitted.
[0087] In the present preferred embodiment, as shown using the
schematically cross sectional view in FIG. 9E, the first and second
surface acoustic wave filter devices 1 and 2 are constructed on the
piezoelectric substrate 3. The IDT electrodes 1a of the first
surface acoustic wave filter device 1 have a construction in which
a plurality of electrode films are laminated, whereby the electrode
film of each of the IDT electrodes 1a of the first surface acoustic
wave filter device 1 is preferably thicker than that of each of the
IDT electrodes 2a of the second surface acoustic wave filter device
2.
[0088] Initially, a negative-type first resist is deposited on the
entirety of the top face of the piezoelectric substrate 3. A mask,
in which a shielding portion is a portion in which the IDT
electrodes 1a of the first surface acoustic wave filter device 1,
the IDT electrodes 2a of the second surface acoustic wave filter
device, and the reflectors of these surface acoustic wave filter
devices are formed, is laminated on this first resist and exposed.
Thereafter, by removing the exposed first resist part, the first
resist layer 5 having the patterning shown in FIG. 9A is
obtained.
[0089] Next, the conductive film 4 having substantially the same
film thickness as that of each of the IDT electrodes 2a of the
second surface acoustic wave filter device 2 is formed on the
entire surface of the piezoelectric substrate 3 (FIG. 9B).
[0090] Thereafter, the positive-type second resist is deposited on
the entire surface of the piezoelectric substrate 3. Thereafter, a
mask is laminated and exposed in which an opening portion is a
region excluding a region in which the electrodes of the second
surface acoustic wave filter device are provided and including a
region in which at least the first surface acoustic wave filter
device is formed. By removing the exposed resist portion, the
second resist layer 6 having patterning is obtained (FIG. 9C).
[0091] Since patterning of this second resist layer 6 is not
patterning for forming the IDT electrode portion, high accuracy may
not be required.
[0092] As shown in FIG. 9C, the IDT electrodes 2a are protected by
the second resist 6 on the second surface acoustic wave filter
device 2 side.
[0093] Next, the second conductive film 7 is laminated on the
entire surface of the conductive film 4. The thickness of the
second conductive film 7 is preferably selected so that the total
thickness of the second conductive film 7 and the conductive film 4
is substantially equal to the thickness of the IDT electrodes 1a of
the first surface acoustic wave filter device, or that of the
reflector 1c or 1d (FIG. 9D).
[0094] The number of laminated conductive films is not particularly
limited. Other conductive films may also be formed on the
conductive film 7.
[0095] Alternatively, an intermediate layer including Ti, NiCr, or
other suitable material may be disposed between the conductive film
4 and the conductive film 7 in order to increase the adhesion
thereof.
[0096] In either case, the total thickness of the laminated
conductive films which may include an intermediate layer is
preferably substantially equal to the thickness of the IDT
electrodes 1a of the first surface acoustic wave filter device.
[0097] Thereafter, the conductive films 4 and 7 deposited on the
first and second resists 5 and 6 are removed via lift off along
with the first and second resists 5 and 6. In this manner, as shown
in FIG. 9E, the IDT electrodes 1a of the first surface acoustic
wave filter device 1 are formed. In this case, when lift-off is
performed, a separating liquid functioning the positive-type resist
as well as the negative-type resist is desired to be used in order
to simplify the processes.
[0098] Although the first resist is the negative-type and the
second resist is the positive-type, alternatively, the first resist
can be the positive-type resist and the second resist can be the
negative-type resist. In this case, when patterning is performed on
the second resist, the region in which the electrodes of the first
surface acoustic wave filter device 1 are formed is shielded with
the mask, the exposure of the first resist is prevented, which
prevents deformation of the first resist 5.
[0099] In the manufacturing method according to the present
preferred embodiment, since formation of the electrodes of the
first surface acoustic wave filter device is performed using the
lift-off method, when the electrodes of the first surface acoustic
wave filter device are formed, the region in which the
piezoelectric substrate of the second surface acoustic wave filter
device is formed is protected by the resist. Accordingly, compared
with the conventional method in which formation of the first
surface acoustic wave filter device is performed using the dry
etching method, degradation of the insertion loss and VSWR of the
second surface acoustic wave filter device 2 is prevented.
[0100] In addition, since, during the second photolithography
process, only pattering is performed to protect the second surface
acoustic wave filter device side, there is no need to increase the
accuracy during the second photolithography process. Accordingly,
the heating temperature of the resist 6 can be comparatively low so
as to prevent pyroelectric destruction of the IDT electrodes.
Therefore, although the wiring electrode is preferably formed and
disconnected in the first and second preferred embodiments, there
is no need to form such a short-circuit wiring electrode and thus,
no need to execute the disconnecting process.
[0101] However, in the third preferred embodiment, in the same
manner as in the first and second preferred embodiments, the
process may be executed in which the short-circuit wiring electrode
is formed and are finally disconnected.
[0102] Furthermore, in the manufacturing method according to the
third preferred embodiment, since the resists on the electrode
construction of the first and second surface acoustic wave filter
devices and the conductive films thereon are simultaneously removed
via lift-off, the processes can be simplified.
[0103] When the first resist 5 is the positive-type resist,
deformation of the first resist is reliably prevented during
patterning of the second resist by having the second resist be the
negative-type.
[0104] While preferred embodiments of the present invention have
been disclosed, various modes of carrying out the principles
disclosed herein are contemplated as being within the scope of the
following claims. Therefore, it is understood that the scope of the
present invention is not to be limited except as otherwise set
forth in the claims.
* * * * *