JP2007288645A - Piezoelectric thin film resonator and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric thin film resonator which suppresses horizontal mode spurious and can be miniaturized and a manufacturing method thereof. <P>SOLUTION: A top electrode 5 which demarcates a resonation region of a bulk acoustic wave resonator 10 has the approximate rectangular parallelpiped shape and each end face of two sides opposite to each other of one of two sets of two sides opposite to each other of its circumference is formed by having the irregular approximate saw-tooth shape which is not linear. Thus, acoustic waves in a horizontal mode emitted from a certain point on the end faces of the approximate saw-tooth shape are propagated in irregular directions, directions of the acoustic waves to be reflected also become irregular since the end face of the opposite side is also in the approximate saw-tooth shape and propagation paths having resonation paths with the same length hardly exist. Consequently, the horizontal mode spurious is suppressed without generating shrinking at high level. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric thin film resonator using bulk acoustic waves, and more particularly to a piezoelectric thin film resonator in which transverse mode spurious is suppressed and a method for manufacturing the same.

  Conventionally, using a thin film semiconductor process, a piezoelectric thin film resonator called FBAR (Film Bulk Acoustic Resonator) as a resonator of a metal-dielectric-metal laminated structure has been used for a duplexer, a bandpass filter, and the like. This makes it possible to reduce the size and cost. Further, it is excellent in filter characteristics and low power consumption in a high frequency band of several GHz band, and is attracting attention because it is suitable for application to high-speed wireless communication applications.

  However, although the fundamental vibration mode of the bulk acoustic wave resonator is propagated in the direction perpendicular to the electrode surface, there are other vibration modes that are excited, and this vibration mode propagates parallel to the electrode surface. Such vibration parallel to the electrode surface is noise with respect to the fundamental mode, which is called transverse mode spurious, and causes a problem in a circuit using a duplexer, a bandpass filter, an oscillator, a sensor, and the like.

  As means for suppressing the above-described transverse mode spurious, a part of the overlapping portion of the top electrode and the bottom electrode provided on the front and back surfaces of the piezoelectric body (dielectric material) is part of a non-rectangular irregular polygon. A bulk acoustic wave resonator having an outer peripheral portion is known (see, for example, Patent Document 1).

  In addition, in the overlapping portion of the top electrode and the bottom electrode provided on the front and back surfaces of the piezoelectric body (dielectric material), an additional wall-shaped electrode is provided on the outer peripheral edge of the top electrode to suppress transverse mode spurious. A so-called acoustic resonator is also known (see, for example, Non-Patent Document 1).

JP 2000-332568 A (3rd and 4th pages, FIGS. 4 and 5) G. G. Fattinger, S.M. Marksteiner, J. et al. Kaitila, and R.K. Aigner, “Optimization of Acoustic Dispersion for High Performance Thin Film BAW Resonators”, 2005 Ultrasonic Symposium (Rotterdam).

  In such a patent document 1, since it forms a part of a non-rectangular irregular polygon, a high-level degeneration is reduced by repeating the reflection of the sound wave in the transverse mode irregularly at the outer periphery. It is possible to suppress transverse mode spurious, but the area of the overlapping portion of the top electrode and the bottom electrode is required to have a predetermined size, and the irregular non-rectangular shape in the overlapping portion of the top electrode and the bottom electrode is required. In order to obtain the outer peripheral shape, a discarded area is generated, so that the area must be increased, and there is a problem that the planar size is increased.

  Further, according to Non-Patent Document 1, by providing a further stepped electrode on the outer peripheral edge of the top electrode and providing a step with a higher peripheral edge, the cutoff frequency of the boundary characteristic of sound wave propagation in this step Although it is possible to suppress the transverse mode spurious by changing the dispersion characteristics, an additional layer of electrodes is provided on the outer periphery of the top electrode, which necessitates an increase in the number of masks and manufacturing processes, which is disadvantageous in terms of cost. It is.

  An object of the present invention is to provide a piezoelectric thin film resonator that can suppress the transverse mode spurious and can be miniaturized, and a method for manufacturing the same, in order to solve the above-described problems.

  In order to solve the above-described problems, the present invention provides a substrate, a bottom electrode stacked on the substrate, a piezoelectric body stacked on the bottom electrode, a top electrode stacked on the piezoelectric body, and substantially rectangular in plan view. A photoresist film forming step of forming a photoresist film on a laminate formed by sequentially laminating a bottom electrode and a piezoelectric body on a substrate; An exposure process for exposing the photoresist film using an exposure mask having a light-shielding pattern in which at least two opposite end faces of the outer periphery of the top electrode have a substantially sawtooth shape; and developing the exposed photoresist film A developing process for forming a photoresist pattern having a shape corresponding to the light shielding pattern, a metal film forming process for forming a metal film on the laminate on which the photoresist pattern is formed, and a photoresist. With dissolving the pattern, and the gist in that it comprises a top electrode portion forming step of forming all or part of the top electrode by removing the metal film on the photoresist pattern.

  When the shape of the intersection region of the bottom electrode and the top electrode is a square, the transverse mode sound wave emitted from one point on the outer periphery of the intersection region is reflected perpendicularly to the opposite parallel side and returns to the original point. . In this way, when there are a plurality of the same reciprocal resonance paths of the sound wave, a high level of degeneracy occurs and appears as an unnecessary spurious.

  Here, when a substantially square top electrode with good space efficiency is formed in the intersecting region, the sound wave of the transverse mode emitted from a certain point is propagated in an irregular direction by making the end face into a substantially sawtooth shape. Even if it is reflected by the opposite parallel side, it does not return to the original point, and there is almost no same resonance path. The top electrode formed by the above manufacturing method can have a substantially saw-tooth shape on at least two opposing end surfaces of the outer periphery. Therefore, it is possible to suppress spuriousness without causing high-level degeneration without increasing the planar size as in the structure in which the outer peripheral shape of the intersecting region is non-rectangular as in Patent Document 1 described above.

  In the method for manufacturing a piezoelectric thin film resonator according to the present invention, it is desirable that the light shielding pattern of the exposure mask is formed of a light shielding material for discharging a droplet.

  According to this configuration, an exposure mask in which a light-shielding pattern corresponding to the shape of the top electrode is formed by a droplet discharge method such as an ink jet method can be produced, and the top electrode can be formed using this exposure mask. When a rectangular drawing pattern is formed using the inkjet method, the end face of the drawing pattern in the scanning direction of the droplet discharge head is formed substantially linearly by droplets discharged from the same nozzle. On the other hand, the end face of the drawing pattern formed in the pitch feed direction perpendicular to the scanning direction of the droplet ejection head is uneven due to the difference in the landing positions of the droplets ejected from the ink nozzles while being pitch fed. An end face shape approximate to the sawtooth shape is formed. As a result, the end surfaces of at least two opposing sides of the top electrode can be formed in a substantially sawtooth shape, and the transverse mode spurious of the piezoelectric thin film resonator can be reduced by the effect that the same resonance path in the substantially rectangular crossing region is almost eliminated. Can be suppressed.

  Further, according to the above configuration, when a top electrode having a square shape with a flat end surface is formed, a step portion made of the same metal material as the top electrode is formed on the end surface portion of the top electrode. It is also possible to suppress transverse mode spurious. For example, an exposure mask is prepared in which a light-shielding pattern corresponding to a band-like region covering the end face of the top electrode having a flat end face shape and the periphery thereof is formed using a droplet discharge light-shielding material using an ink-jet droplet discharge device. . The end face of the band-shaped light shielding pattern is formed in a substantially sawtooth shape in the process of forming the drawing pattern end face shape by the ink jet method described above. When a step portion is formed on the end surface portion of the top electrode by photolithography using this exposure mask, the end surface of the step portion has an irregular, substantially serrated shape. Thereby, since at least a part of the outer peripheral shape of the intersecting region of the top electrode and the bottom electrode formed by the step portion has a substantially sawtooth shape, it is possible to suppress transverse mode spurious. Furthermore, the step formed on the top electrode serves as a weight, which also has the effect of suppressing transverse mode sound waves that leak outside the intersecting region, so that the resonance path with the disconnected portion outside the intersecting region is also ineffective. It becomes a rule and transverse mode spurious can be suppressed.

  In addition, since the exposure mask can be manufactured at a low cost by a simple process compared to the conventional method of forming a light shielding pattern on the exposure mask by vapor deposition or sputtering, it is possible to reduce the cost of manufacturing the piezoelectric thin film resonator. it can.

  In the method for manufacturing a piezoelectric thin film resonator according to the present invention, of the four sides of the outer periphery of the light shielding pattern, one opposite two sides are formed substantially in parallel, and the other two opposite sides are in relation to the one opposite two sides. It is good also as a structure formed so that it may not orthogonally cross.

  As described above, when a substantially rectangular drawing pattern is formed using the ink jet method, the end face shape of the drawing pattern in the scanning direction of the droplet discharge head is formed with a substantially straight line by the same nozzle. The shape of the end face in the direction orthogonal to the scanning direction of the droplet discharge head has a substantially sawtooth shape. By making a predetermined angle between the two sides corresponding to the direction corresponding to the scanning direction of the droplet discharge head so as not to be parallel to the scanning direction of the droplet discharge head, the end surface shape of the drawing pattern is substantially sawtooth shape. Is possible. Thereby, the end face shape of the substantially square light-shielding pattern can be made into a substantially serrated shape on all four sides. The top electrode formed using the exposure mask having such a light-shielding pattern has a further effect of suppressing transverse mode spurious without increasing the electrode area.

  The main purpose of the piezoelectric thin film resonator of the present invention is to have all or part of the top electrode manufactured by using the above-described method for manufacturing a piezoelectric thin film resonator.

  The top electrode manufactured by using the above-described manufacturing method is formed to have a substantially saw-tooth shape in which at least two opposing sides of the outer periphery are irregular. Thereby, since the same resonance path hardly exists in the region intersecting with the bottom electrode, it is possible to provide a piezoelectric thin film resonator in which transverse mode spurious is suppressed.

  The piezoelectric thin film resonator of the present invention may have a configuration in which a cavity is formed in the approximate center of the substrate.

  According to this configuration, the piezoelectric body formed above the substrate and sandwiched between the top electrode and the bottom electrode is in a state of being bridged on the cavity, so that the piezoelectric body freely vibrates so-called FBAR ( A film bulk acoustic resonator (piezoelectric thin film resonator) type piezoelectric thin film resonator can be provided while suppressing transverse mode spurious.

  The piezoelectric thin film resonator of the present invention may be configured such that the substrate has an acoustic multilayer film in which a metal layer and an insulating layer are sequentially laminated.

  According to this configuration, a so-called SMR (Solid Mounted Resonator) type piezoelectric thin film in which a longitudinal elastic wave excited from a piezoelectric body sandwiched between a top electrode and a bottom electrode is reflected and confined by an acoustic multilayer film. A resonator can be provided with reduced transverse mode spurs. Further, the SMR type piezoelectric thin film resonator does not need to be provided with a cavity in the substrate unlike the FBAR type piezoelectric resonator, and can be formed only by a thin film semiconductor process.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments in which a piezoelectric thin film resonator of the present invention is embodied in a bulk acoustic wave resonator will be described with reference to the drawings.

(First embodiment)
First, a first embodiment of the present invention will be described.
1A and 1B show a bulk acoustic wave resonator 10 according to the first embodiment, in which FIG. 1A is a plan view schematically showing the schematic structure, and FIG. 1B is a cross-sectional view taken along line AA in FIG. It is.

1 (b), the bulk acoustic wave resonator 10 is laminated on the upper surface of the support frame 1 as a substrate made of Si, the insulating layer 2 made of SiO _2, the bottom electrode 3, the piezoelectric elements 4, and a top electrode 5 in this order Has been configured.

  The support frame 1 has a cavity 9 formed by etching and removing a part of the approximate center of the Si substrate from the back surface side in a state where the above-described components are stacked. The piezoelectric body 4 includes a top electrode 5 and a bottom electrode 3 sandwiching a part of the piezoelectric body 4, and is bridged on the cavity 9 so that an air / electric field surface is formed at the bottom of the piezoelectric body 4. It is. The piezoelectric thin film resonator configured as described above is generally called an FBAR (Film Bulk Acoustic Resonator). In such an FBAR bulk acoustic wave resonator 10, it is more desirable that the piezoelectric body 4 is within the region of the cavity 9 because vibration energy leaks less.

  The insulating layer 2 is an extremely thin layer formed as an etching stopper when the cavity 9 is formed on the upper surface of the support frame 1 made of a Si substrate by etching.

  The bottom electrode 3 is made of aluminum (Al), tungsten (W), molybdenum (Mo), or the like. Further, as the material of the piezoelectric body 4, AlN (aluminum nitride), ZnO, PZT (registered trademark) or the like is adopted, and is formed by means such as sputtering or vapor deposition.

  In this embodiment, the top electrode 5 has a substantially rectangular shape in plan view, and is formed of aluminum (Al), tungsten (W), molybdenum (Mo), or the like. In addition, among the four side end faces that form the outer shape of the top electrode 5, the two opposite end faces are formed to have an irregular substantially sawtooth shape.

  In the present embodiment, the bottom electrode 3 is provided on the entire surface of the support frame 1, and the area thereof is sufficiently larger than the area of the top electrode 5. Therefore, the intersection region between the bottom electrode 3 and the top electrode 5 corresponds to the shape of the top electrode 5.

  In the desired resonance mode of the bulk acoustic wave resonator 10, the bulk compression wave is designed to propagate in the piezoelectric body 4 parallel to the axis in the thickness direction. When an electric field is generated between two electrodes by applying voltage (between the top electrode 5 and the bottom electrode 3), the piezoelectric body 4 converts electrical energy into mechanical energy in the form of sound waves, and the sound waves are in the same direction as the electric field. Propagated and reflected at the electrode / air interface. The frequency of the fundamental longitudinal resonance mode of the cavity 9 of the support frame 1 is centered on CL / 2t. CL is the speed of sound in the longitudinal propagation mode, and t is the thickness of the piezoelectric body 4.

  When a potential is applied in the thickness direction of the piezoelectric body 4, lateral mechanical distortion may occur, which may excite sound waves that move laterally in the piezoelectric body 4. Such lateral movement of sound waves is referred to as a transverse mode.

  Here, the sound waves in the transverse mode emitted from one point on the outer periphery of the intersecting region of the top electrode 5 and the bottom electrode 3, that is, the end face of the top electrode 5, are reflected vertically by the wall of the end face of the facing side. When the end face shape of the outer periphery of the top electrode 5 formed in a substantially rectangular shape having the most space efficiency is substantially a straight line, the sound wave in the transverse mode emitted from a certain point on the outer periphery of the top electrode 5 It is reflected vertically by the wall and returns to a certain point on the original outer periphery where the transverse mode sound wave is emitted. Assuming that the width of the top electrode 5 serving as a propagation path of the transverse mode sound wave is W, the sound wave has a resonance path having a length of 2W. As described above, when there are a plurality of the same reciprocal resonance paths of sound waves in the same element, a high level of degeneration occurs, and unnecessary lateral mode spurious is generated.

In the bulk acoustic wave resonator 10 of the present embodiment, each of the two opposing sides of the outer periphery of the top electrode 5 formed in a substantially rectangular shape is not linear. It is formed with a regular substantially serrated shape. As a result, the sound wave in the transverse mode emitted from one point on the substantially serrated end surface is propagated in an irregular direction, and the sound wave emitted from one point is reflected on one point on another adjacent end surface. Further, since the end faces of the opposing sides are also substantially serrated, the direction of the reflected sound wave is irregular, and there are almost no propagation paths having the same length of the resonance path. Therefore, transverse mode spurious can be suppressed without causing high-level degeneration.
Moreover, in this embodiment, since the top electrode 5 used as the outer periphery of a cross | intersection area | region has a substantially rectangular shape, compared with the structure where the outer periphery shape of a cross | intersection area | region like the patent document 1 mentioned above is non-rectangular, This is advantageous in reducing the planar size of the resonator 10.

  (Second Embodiment)

Next, the manufacturing method of the bulk acoustic wave resonator 10 of 1st Embodiment is demonstrated along drawing.
2A and 2B show an exposure mask 100 used for manufacturing the bulk acoustic wave resonator 10 of the present embodiment, in which FIG. 2A is a schematic plan view and FIG. 2B is a schematic cross-sectional view. FIG. 3 is a flowchart for explaining a process of forming the top electrode 5 having an end surface having a substantially serrated shape, which is a feature of the present invention.

The bulk acoustic wave resonator 10 shown in FIG. 1 is formed using a thin film semiconductor process.
First, the insulating layer 2 made of silicon oxide (SiO ₂ ) is formed on the surface of a silicon (Si) substrate 1a for forming the support frame 1 by thermal oxidation or the like.
Next, the bottom electrode 3 made of aluminum (Al), molybdenum (Mo), or the like is formed on the upper surface of the insulating layer 2 by sputtering or vapor deposition. In the first embodiment, the example in which the bottom electrode 3 is formed on the entire upper surface of the support frame 1 is shown. However, the present invention is not limited to this, and the bottom electrode 3 may be formed with a predetermined surface area.

  Next, the piezoelectric body 4 made of AlN (aluminum nitride), ZnO (zinc oxide) or the like is formed on the upper surface of the bottom electrode 3 by sputtering, vapor deposition, or the like. In the present embodiment, for convenience of explanation, a laminated body formed by sequentially laminating the insulating layer 2, the bottom electrode 3, and the piezoelectric body 4 on the silicon substrate 1a is referred to as a piezoelectric element laminated body, and is denoted by reference numeral 14. 3 (a) to 3 (c).

Next, a method for forming the top electrode 5 on the piezoelectric element laminate 14 will be described.
First, as shown in FIG. 3A, a photoresist film 90 is formed on the entire upper surface of the piezoelectric element laminate 14 formed as described above by spin coating or the like. Then, exposure is performed by irradiating exposure light from above the photoresist film 90 through the exposure mask 100 in which the light shielding pattern 150 having the same shape as the top electrode pattern 5 is formed. In the present embodiment, the structure of the negative photoresist film 90 that remains after development after the portion irradiated with the exposure light is cured by photoreaction and the exposure mask 100 corresponding thereto is described. It is also possible to apply a photoresist and a corresponding exposure mask.

  Next, the photoresist film 90 is developed with a predetermined developer to remove a portion that has not been irradiated with exposure light during exposure, thereby forming a photoresist pattern 90a shown in FIG.

  Next, as shown in FIG. 3C, a metal layer 5a which is a prototype of the top electrode 5 made of aluminum (Al), molybdenum (Mo) or the like is formed by sputtering or vapor deposition. The metal layer 5a is formed by being deposited along the surface of the piezoelectric body 4 exposed by removing the photoresist film 90 by development and the surface of the photoresist pattern 90a.

  Next, as shown in FIG. 3D, a so-called lift-off is performed in which the unnecessary metal layer 5a stacked on the photoresist pattern 90a is simultaneously removed by peeling the photoresist pattern 90a with a predetermined stripping solution. Do. Thereby, only the metal layer on the piezoelectric body 4 remains and the top electrode 5 is formed.

Although not shown in FIGS. 3A to 3C, the substantially central portion on the back surface side of the silicon substrate 1a is selectively removed by etching with an etchant such as hydrofluoric acid. The support frame 1 is formed by forming the cavity 9 shown in d). Etching at this time is stopped by the insulating layer 2 which is an etching stopper, and the piezoelectric body 4 sandwiched between the bottom electrode 3 and the top electrode 5 is bridged on the cavity 9 of the support frame 1. Is formed.
The formation of the cavity 9 of the support frame 1 can also be performed after the above-described bottom electrode 3 is formed or after the top electrode 5 described later is formed.
As described above, the series of manufacturing steps of the bulk acoustic wave resonator 10 is completed by the manufacturing steps described above.

Next, a detailed configuration and a manufacturing method of the exposure mask 100 used in FIG. 3A will be described with reference to FIG.
The exposure mask 100 is configured by forming a light shielding pattern 150 made of a droplet discharge light shielding material having the same shape as the top electrode 5 on the surface of a transparent glass plate 110 such as synthetic quartz glass.

  The light shielding pattern 150 is formed by applying a droplet discharge light shielding material to the upper surface of the glass plate 110 using a droplet discharge method. In this embodiment, a predetermined amount of a droplet discharge light-shielding material containing, for example, a black pigment is applied to a predetermined position at a substantially central portion on the glass plate 110 using an inkjet droplet discharge apparatus. The application amount and application position of the droplet discharge light-shielding material are stored as drawing data in the memory of the droplet discharge device, and a coating pattern for the light-shielding pattern 150 is formed by the droplet discharge device based on the drawing data. The

  In FIG. 2, the application pattern of the droplet discharge light-shielding material, which is the prototype of the light-shielding pattern 150, is applied with the X direction in the figure as the scanning direction of the ink jet head of the droplet discharge device and the Y direction in the figure as the pitch feed direction. Thereafter, the light-shielding pattern 150 is solidified and formed. As for the droplets ejected in the scanning direction of the droplet ejection head, the end face shape of the coating pattern becomes a substantially straight line when the same ink nozzle is landed on the coating surface along the scanning direction. On the other hand, the coating pattern end face in the pitch feeding direction of the droplet ejection head orthogonal to the scanning direction has irregularities due to the difference in the landing positions of the droplets ejected from the ink nozzles while being pitch fed, and has a substantially sawtooth shape. An end face shape is formed.

  Next, the light-shielding pattern 150 is formed by solidifying the coating pattern of the light-shielding pattern 150 formed of the conductive material for discharging droplets, and the exposure mask 100 is completed. The solidification method at this time, for example, when using a light-blocking material for discharging droplets using an organic solvent as a solvent, removes the solvent by putting it in a constant temperature layer and heating it at a predetermined temperature for a predetermined time. Form a film. In addition to this, by selecting the type of curing material for the light-blocking material for droplet ejection, such as using a light-blocking material for droplet ejection containing an ultraviolet curing material and irradiating the coating pattern with ultraviolet light to solidify it. Then, a curing method corresponding to that is taken.

  According to the manufacturing method of the bulk acoustic wave resonator 10 using the exposure max 100 described above, the light-shielding pattern is formed by applying a liquid material for ejecting liquid droplets using an ink-jet type liquid droplet ejection apparatus and solidifying the coating pattern. An exposure mask 100 having 150 formed thereon is used. The coating pattern of the droplet discharge light-shielding material discharged by the droplet discharge device is such that the end surface in the direction orthogonal to the scanning direction of the droplet discharge head is the position of the landing position of the droplet discharged from the ink nozzle while being pitch-fed. Due to the difference, it is formed with an irregular, substantially serrated shape that is not linear. In the bulk acoustic wave resonator 10 having the top electrode 5 formed thereby, it opposes the transverse mode sound wave emitted from one point on the end face of the top electrode 5 at the intersection region between the top electrode 5 and the bottom electrode 3. The direction of the sound wave reflected from the side becomes irregular. Therefore, since the same resonance path hardly exists, transverse mode spurious can be suppressed.

  Further, the light shielding pattern 150 is formed by directly drawing a light-shielding material for discharging droplets on the glass plate 110. This makes it possible to produce an exposure mask with a simpler manufacturing process and at a lower cost than the conventional method of forming a light-shielding pattern made of a metal such as chromium (Cr) by vapor deposition or sputtering. Accordingly, it is possible to provide the bulk acoustic wave resonator 10 capable of suppressing the transverse mode spurious while suppressing the manufacturing cost.

(Third embodiment)
In the bulk acoustic wave resonator 10 of the above embodiment, the top electrode 5 is formed on the glass plate 110 by using the exposure mask 100 in which the light shielding pattern 150 having the same shape as the top electrode 5 made of a light-shielding material for droplet discharge is formed. Not limited to this. A configuration in which a step is formed on the end surface of the top electrode using an exposure mask provided with a light-shielding pattern for forming an end surface corresponding to the position of the end surface portion after forming the majority of the top electrode by a normal thin film semiconductor process It is good.

  Hereinafter, the bulk acoustic wave resonator 40 of the present embodiment will be described with reference to the drawings. In the configuration of the present embodiment, the electrode step portion 37 is formed on the end surface portion of the top electrode main body portion 36 which is the majority of the top electrode 35, and the other configurations are the same as those of the above-described embodiment. Since it is the same, description of a common part is abbreviate | omitted.

  5A and 5B show a bulk acoustic wave resonator 40 according to the third embodiment, in which FIG. 5A is a plan view schematically showing a schematic structure thereof, and FIG. 5B is a cross-sectional view taken along line BB in FIG. It is. FIG. 6 is a schematic plan view of an exposure mask 300 for forming the electrode step 37 constituting the end face portion of the top electrode 35 of the present embodiment.

  In FIG. 5B, the bulk acoustic wave resonator 40 of the present embodiment includes an insulating layer 32, a bottom electrode 33, a piezoelectric body 34, and a top electrode on the upper surface of a support frame 31 in which a cavity 39 is formed at the approximate center of the lower surface. The main body 36 is sequentially stacked. Furthermore, an electrode step portion 37 is formed so as to border two end face portions on the long side in the drawing of the substantially rectangular top electrode main body portion 36 in plan view, and the top electrode main portion 36, the electrode step portion 37, Thus, the top electrode 35 is constituted.

  Each end surface of the outer periphery of the top electrode main body portion 36 formed in a substantially rectangular shape has a smooth substantially linear shape. An electrode step 37 made of the same metal material as that of the top electrode main body 36 is formed on each end surface portion of two opposite sides on the long side in the figure of the top electrode main body 36. A top electrode 35 is constituted by the top electrode main body 36 and the electrode step portion 37, and an irregular substantially serrated end surface of the electrode step portion 37 forms an end surface in the longitudinal direction of the top electrode 35 in the drawing. .

Next, a manufacturing method of the bulk acoustic wave resonator 40 will be described focusing on a method for forming the electrode step portion 37, which is a feature of the present embodiment, and a configuration and a manufacturing method for the exposure mask 300 used therefor.
The bulk acoustic wave resonator 40 shown in FIG. 5 is manufactured by the same thin film semiconductor process as in the second embodiment. First, the insulating layer 32 made of silicon oxide (SiO ₂ ) is formed on the surface of the silicon substrate for forming the support frame 31 by thermal oxidation. The support frame 31 is formed by selectively removing the substantially central portion on the back surface side of the silicon substrate by etching with hydrofluoric acid or the like to form the cavity 39.
On the upper surface of the insulating layer 32, a bottom electrode 33 made of aluminum or molybdenum, a piezoelectric body 34 made of aluminum nitride, ZnO (zinc oxide), or the like, and a top electrode made of the same material as the bottom electrode 33 are formed by sputtering or vapor deposition. The main body 36 is formed by sequentially laminating. The piezoelectric body 34 and the top electrode main body 36 are each formed in a desired shape by photolithography. At this time, each end surface of the outer periphery of the top electrode main body portion 36 formed in a substantially rectangular shape has a smooth substantially linear shape.

  Next, electrode step portions 37 made of the same metal material as that of the top electrode main body portion 36 are formed on the respective end surface portions of two opposite sides on the long side of the top electrode main body portion 36. In this embodiment, in order to form the electrode step part 37, the exposure mask 300 shown in FIG. 6 is used.

Here, the configuration and the production method of the exposure mask 300 will be described.
The exposure mask 300 is configured by forming a light shielding pattern 350 having the same shape as the electrode step portion 37 on a glass plate 310.
In the present embodiment, the light shielding pattern 350 is formed by applying a liquid droplet ejection light shielding material to the upper surface of the glass plate 310 by an ink jet type liquid droplet ejection apparatus and solidifying it. At this time, the application pattern of the droplet discharge light-shielding material forming the light-shielding pattern 350 was applied with the X direction in the figure as the scanning direction of the ink jet head of the droplet discharge device and the Y direction in the figure as the pitch feed direction. After that, a state in which the light shielding pattern 350 is solidified and formed is illustrated. The droplets ejected in the scanning direction of the droplet ejection head (the X direction in the figure) are substantially linear in the end face shape of the coating pattern when the same ink nozzles land on the coating surface along the scanning direction. It becomes. On the other hand, the coating pattern end face in the pitch feed direction (Y direction in the figure) of the droplet discharge head orthogonal to the scanning direction is uneven due to the difference in the landing positions of the droplets discharged from the ink nozzles while being pitch-fed. As a result, an irregular substantially serrated end surface shape is formed.
Then, the light-shielding pattern 350 is formed by removing the solvent from the coating pattern of the light-shielding pattern 350 using the droplet discharge light-shielding material thus formed, for example, by heating, and the exposure mask 300 is completed. .

Returning to the description of the method for forming the electrode step 37 again.
After the top electrode body 36 is laminated and formed, a negative photoresist film is formed by spin coating or the like, and then light is irradiated from above the photoresist film through the exposure mask 300. To expose.

  Next, the photoresist film is developed with a predetermined developer to form a photoresist pattern. This photoresist pattern is formed by removing a portion that is not irradiated by light shielding by the light shielding pattern 350 of the exposure mask 300 at the time of exposure, that is, a portion having the same shape as the electrode step portion 37.

  Next, an electrode step metal layer that is a prototype of the electrode step 37 made of the same conductive material as the bottom electrode 33 is formed by sputtering or vapor deposition. The electrode step metal layer is deposited along the edge of the top electrode body 36 exposed by developing the photoresist film removed by development, the surface of the piezoelectric body 34 in the vicinity thereof, and the surface of the photoresist pattern of the photoresist. To be formed.

  Next, so-called lift-off is performed in which the photoresist pattern is stripped with a predetermined stripping solution to simultaneously remove unnecessary electrode stepped metal layers stacked on the photoresist pattern. Thereby, the electrode step portion metal layer only on the end portion of the top electrode main body portion 36 and the surface of the piezoelectric body 34 in the vicinity thereof remains, and the electrode step portion 37 as shown in FIGS. It is formed.

According to the configuration of the bulk acoustic wave resonator 40 described above, the end surface in the Y direction in FIG. 6 of the electrode step portion 37 is formed in an irregular substantially saw-tooth shape, so that the top electrode main body portion 36 and the electrode step portion 37 are formed. The top electrode 35 constituted by can be used for suppressing transverse mode spurious. Moreover, the electrode step part 37 becomes a weight, and there also exists an effect which suppresses the sound wave of the transverse mode which leaks to the outer side of a cross | intersection area | region.
In addition, the light shielding pattern 350 of the exposure mask 300 of the present embodiment is formed by applying a liquid droplet ejection shading material using a droplet ejection apparatus. As a result, it is possible to form a light-shielding pattern having a substantially serrated end surface at a lower cost compared to a conventional method of forming a light-shielding pattern of a metal such as chromium (Cr) by vapor deposition or sputtering. .

(Fourth embodiment)
In the above embodiment, the configuration in which the end face shape of the top electrode of the FBAR (Film Bulk Acoustic Resonator) type piezoelectric thin film resonator is formed in a substantially sawtooth shape and the manufacturing method thereof are shown, but the present invention is not limited thereto. The same transverse mode spurious effect can be obtained by applying to a SMR (Solded Mounted Resonator) type piezoelectric thin film resonator.

Hereinafter, a fourth embodiment in which the present invention is applied to an SMR bulk acoustic wave resonator 80 will be described with reference to the drawings.
As shown in FIGS. 7A and 7B, the SMR type bulk acoustic wave resonator 80 includes an AlN / W (aluminum nitride / tungsten) layer 62, 64, 66, 68 and SiO ₂ on a silicon substrate 71. Insulating layers 63, 65, 67, 72, etc., have acoustic multilayer films (mirror layers) that are alternately and sequentially stacked. A bottom electrode 73, a piezoelectric body 74, and a top electrode 75 are sequentially stacked on the insulating layer 72 as the uppermost layer of the acoustic multilayer film. The element configured as described above may be generally referred to as SMR (Solid Mounted Resonator). The SMR type piezoelectric thin film resonator has a structure in which the FBAR type piezoelectric thin film resonator of each of the embodiments described above freely vibrates the piezoelectric film by a membrane structure in which a cavity is provided in a support frame. Therefore, the elastic wave is reflected.

In such a configuration of the SMR type bulk acoustic wave resonator 80, the top electrode 75 is formed by a method similar to that in each of the above-described embodiments, thereby having a substantially serrated shape with an irregular end face shape.
According to this configuration, in the intersecting region between the top electrode 75 and the bottom electrode 73, the transverse mode sound wave emitted from one point on the end surface of the top electrode 75 having a substantially sawtooth shape and the sound wave reflected from the opposite side Since the directions become irregular and the same resonance path hardly exists, the transverse mode spurious of the SMR type bulk acoustic wave resonator 80 can be suppressed.

  The present invention is not limited to the above-described embodiments, and the following modifications can also be implemented.

  (Modification) In the first and second embodiments described above, the planar shape of the top electrode 5 of the bulk acoustic wave resonator 10 is a substantially rectangular shape, and the opposite end faces of the two sides are formed in a substantially sawtooth shape, and Although the manufacturing method was shown, it is not restricted to this. By making the planar shape of the top electrode parallel to the two opposite sides and being square with the other two opposite sides that are not orthogonal thereto, transverse mode spurious can be further suppressed while minimizing an increase in the planar size. .

  FIG. 4 shows an exposure used for manufacturing a bulk acoustic wave resonator according to this modification, in which the planar shape of the top electrode is a square with the other two opposite sides that are not orthogonal to the opposite two sides in parallel. 3 is a schematic plan view illustrating a mask 200. FIG.

  In FIG. 4, the exposure mask 200 has a light shielding pattern 250 for forming a substantially square top electrode on a glass plate 210. In the light shielding pattern 250, two opposite sides in the Y direction in the figure are formed substantially in parallel among the four outer sides, and the two opposite sides in the X direction in the figure are orthogonal to the two opposite sides in the X direction in the figure. It has a substantially rectangular shape with an angle so that it does not. The light shielding pattern 250 of this modification is a substantially parallelogram.

  In the exposure mask 200 of the present modification, the light shielding pattern 250 is made of a light emitting material for ejecting droplets, and is formed using a droplet ejecting apparatus using an ink jet method. At this time, the light shielding material for droplet discharge is applied so that the X direction of the light shielding pattern 250 in the drawing is parallel to the scanning direction of the droplet discharge head. The end faces of the two opposite sides in the Y direction in the drawing of the light shielding pattern correspond to the pitch feed direction of the droplet discharge head described above, so that a substantially sawtooth shape is formed. Since the end face in the X direction in the drawing of the light shielding pattern 250 is formed with an angle that is not parallel to the scanning direction of the liquid droplet ejection head, the end face is separated from the separate ink nozzles of the plurality of ink nozzles provided in the inkjet head. Formed by ejected droplets. Due to the difference in the landing positions of the droplets discharged from the different nozzles, the end surface in the X direction of the light shielding pattern 250 can also be formed in an irregular substantially sawtooth shape.

  A bulk acoustic wave resonator having a top electrode formed by using lift-off in the same manner as in each of the above-described embodiments using the above-described exposure mask 200 has a substantially saw-tooth shape in which the end face shape of the substantially square top electrode is irregular on all four sides. It can be shaped. Thereby, compared with the substantially rectangular top electrode of each of the above-described embodiments, the effect of suppressing transverse mode spurious is further exhibited while suppressing an increase in the electrode area.

  The piezoelectric thin film resonator of the present invention described above is suitable for use in a duplexer, a bandpass filter, an oscillator, a sensor, etc. in high-speed wireless communication.

The bulk acoustic wave resonator which concerns on the 1st Embodiment of this invention is shown, (a) is a top view which shows the schematic structure, (b) is the sectional view on the AA line of Fig.1 (a). The exposure mask used for manufacture of the bulk acoustic wave resonator which concerns on the 2nd Embodiment of this invention is shown, (a) is a schematic plan view, (b) is a schematic sectional drawing. The flowchart figure explaining the process in which a top electrode is formed among the manufacturing methods of the bulk acoustic wave resonator of this invention. The schematic plan view of the exposure mask used for formation of the top electrode based on the modification of the bulk acoustic wave resonator of this invention. The bulk acoustic wave resonator which concerns on the 3rd Embodiment of this invention is shown, (a) is a top view which shows the schematic structure, (b) is the BB sectional drawing of Fig.5 (a). The schematic plan view of the exposure mask used for manufacture of the bulk acoustic wave resonator of the 3rd Embodiment of this invention. The bulk acoustic wave resonator which concerns on the 4th Embodiment of this invention is shown, (a) is a top view explaining the schematic structure, (b) is CC sectional view taken on the line of Fig.7 (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,31 ... Support frame as a substrate, 71 ... Silicon substrate, 3, 33, 73 ... Bottom electrode, 4, 34, 74 ... Piezoelectric body, 5, 35, 75 ... Top electrode, 36 ... Main body of top electrode Top electrode body 37, electrode step forming end of top electrode, 90a ... photoresist pattern, 100, 200, 300 ... exposure mask, 150, 250, 350 ... light shielding pattern, 10, 40 ... piezoelectric thin film resonance Bulk acoustic wave resonator as a child, 80... SMR type bulk acoustic wave resonator as a piezoelectric thin film resonator.

Claims (6)

A substrate,
A bottom electrode laminated on the substrate;
A piezoelectric body laminated on the bottom electrode;
A method of manufacturing a piezoelectric thin film resonator having a top electrode that is stacked on the piezoelectric body and has a substantially square shape in plan view,
A photoresist film forming step of forming a photoresist film on a laminate formed by sequentially laminating the bottom electrode and the piezoelectric body on the substrate;
An exposure step of exposing the photoresist film using an exposure mask having a light-shielding pattern in which end faces of at least two opposite sides of the outer periphery of the top electrode have a substantially sawtooth shape;
Developing the exposed photoresist film to form a photoresist pattern having a shape corresponding to the light shielding pattern; and
A metal film forming step of forming a metal film on the laminate on which the photoresist pattern is formed;
And a top electrode portion forming step of forming all or part of the top electrode by dissolving the photoresist pattern and removing the metal film on the photoresist pattern. Child manufacturing method. In the manufacturing method of the piezoelectric thin film resonator according to claim 1,
A method of manufacturing a piezoelectric thin film resonator, wherein the light shielding pattern of the exposure mask is formed of a light shielding material for discharging a droplet. In the manufacturing method of the piezoelectric thin film resonator according to claim 2,
Of the four sides of the outer periphery of the light shielding pattern, one opposite two sides are formed substantially in parallel, and the other two opposite sides are formed so as not to be orthogonal to the one opposite two sides. A method for manufacturing a piezoelectric thin film resonator.   A piezoelectric thin film resonator comprising all or part of a top electrode manufactured using the method for manufacturing a piezoelectric thin film resonator according to claim 1. The piezoelectric thin film resonator according to claim 4, wherein
A piezoelectric thin film resonator having a cavity formed substantially in the center of the substrate. The piezoelectric thin film resonator according to claim 4, wherein
The piezoelectric thin film resonator, wherein the substrate has an acoustic multilayer film in which a metal layer and an insulating layer are sequentially laminated.

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