Metal working – Piezoelectric device making
Reexamination Certificate
2001-03-05
2002-04-09
Hall, Carl E. (Department: 3729)
Metal working
Piezoelectric device making
C310S334000, C427S100000
Reexamination Certificate
active
06367133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
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.
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.
FIGS. 10A
to
10
E 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.
10
A). Dry etching forms electrodes
101
a
of a first surface acoustic wave device (FIG.
10
B). 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.
10
C). 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
102
a
of the second surface acoustic wave device.
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 &mgr;m, the efficiency percentage of manufacturing the apparatus can be increased.
However, in the method described in the related art, dry etching which is performed when the electrodes
101
a
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.
Generally, when dry etching is performed in a case in which an electrode finger pitch is approximately 1 &mgr;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.
Therefore, when the electrodes
101
a
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.
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.
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.
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
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.
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 t
Ikada Katsuhiro
Sakaguchi Kenji
Takamiya Miki
Hall Carl E.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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