JP4373936B2 - Thin film piezoelectric resonator and manufacturing method thereof - Google Patents

Description

  The present invention relates to a thin film piezoelectric resonator and a manufacturing method thereof, and more particularly to a thin film piezoelectric resonator using a longitudinal vibration in a thickness direction of a piezoelectric thin film and a manufacturing method thereof.

  A surface acoustic wave (RF) is used for a high frequency filter (RF) or an intermediate frequency (IF) filter for constructing a mobile communication device or a high frequency oscillator (Voltage Controlled Oscillator: simply referred to as “VCO” hereinafter). Hereinafter, the device is simply referred to as “SAW”. The resonance frequency of the SAW element is inversely proportional to the inter-comb electrode distance, and the inter-comb electrode distance is 1 μm or less in a frequency region exceeding 1 GHz. For this reason, it is difficult for a SAW element to cope with a higher frequency of use.

  As a resonator that has recently attracted attention in place of the SAW element, there is a thin film piezoelectric resonator using a longitudinal vibration mode in a film thickness direction of a thin film piezoelectric body. This thin film piezoelectric resonator is also called an FBRA (Film Bulk Acoustic Resonator) or BAW (Bulk Acoustic Wave) element. In this thin film piezoelectric resonator, the resonance frequency is determined by the sound speed and film thickness of the thin film piezoelectric body. Usually, a resonance frequency of 2 GHz is obtained when the film thickness of the thin film piezoelectric body is 1 μm to 2 μm, and a resonance frequency of 5 GHz is obtained when the film thickness of the thin film piezoelectric body is 0.4 μm to 0.8 μm. In this film forming technique, it is possible to realize a high frequency up to several tens of GHz. Further, for example, FIG. 1A of Non-Patent Document 1 below discloses a circuit configuration of a ladder filter that can incorporate this type of thin film piezoelectric resonator and is suitable for miniaturization.

  On the other hand, the following patent document 1 discloses the most typical structure of a thin film piezoelectric resonator and a manufacturing method thereof. The manufacturing method of the thin film piezoelectric resonator is as follows. First, a recess is formed on the silicon (Si) substrate surface using anisotropic etching, and a sacrificial layer is subsequently formed on the substrate. As the sacrificial layer, for example, a silicate glass (BPSG) layer doped with boron and phosphorus is used. Thereafter, the surface of the sacrificial layer is polished until the surface of the Si substrate is exposed, and the surface of the sacrificial layer is planarized. As a result, a sacrificial layer can be embedded in the depression formed in advance in the Si substrate, and the surface of the Si substrate can be exposed in the periphery thereof. Subsequently, the lower electrode, the piezoelectric film, and the upper electrode are sequentially formed on the sacrificial layer. Thereafter, a hole is drilled until reaching the sacrificial layer, and the sacrificial layer is removed by selective etching through the hole, thereby forming a cavity corresponding to a depression formed in advance between the Si substrate and the lower electrode. When these series of manufacturing steps are completed, the thin film piezoelectric resonator is completed.

  A piezoelectric crystal film such as aluminum nitride (AlN) or zinc oxide (ZnO) is often used for the piezoelectric film of the thin film piezoelectric resonator manufactured by such a manufacturing method. Non-Patent Document 2 discusses that in a thin film piezoelectric resonator (FBAR), there is a strong correlation between the c-axis orientation half width of an AlN piezoelectric crystal film and the electromechanical coupling coefficient.

  One method for increasing the orientation of the piezoelectric crystal film is to epitaxially grow an AlN piezoelectric crystal film on the substrate. Patent Document 2 listed below discloses a manufacturing method in which an AlN piezoelectric crystal film is epitaxially grown and a thin film piezoelectric resonator is manufactured using the AlN piezoelectric crystal film. According to this manufacturing method, the AlN piezoelectric crystal film can be epitaxially grown in the (0001) crystal orientation on the Si substrate having the (111) crystal orientation on the surface.

  Furthermore, in Patent Document 2, an upper electrode is formed on an epitaxially grown AlN piezoelectric crystal film, and then a via hole is formed by performing anisotropic etching on the Si substrate until the AlN piezoelectric crystal film is exposed from the back surface. A manufacturing method for forming a lower electrode through a via hole on an exposed surface of an AlN piezoelectric crystal film is disclosed. According to such a manufacturing method, a thin film piezoelectric resonator in which both the upper surface and the lower surface of the AlN piezoelectric crystal film are in contact with the air layer can be manufactured.

As a method for forming a via hole, for example, a silicon deep reactive ion etching (Si-Deep-RIE (Reactive Ion Etching)) method disclosed in Non-Patent Document 3 below can be used. According to this etching method, a via hole can be formed in a direction substantially perpendicular to the back surface of the Si substrate.
JP 2000-69594 A JP 2001-94373 A IEEE TRANSECTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 43, NO.12, p.2933, DECEMBER 1995. Rajan S. Nik et al., “Measurements of Bulk, C-Axis Electromechanical Coupling Constant as a Function of AlN Film Quality”, IEEE TRNSACTIONS ON ULTRASONICS, FEROELECTRICS, AND FREQUENCY CONTROL, p292-296, VOL.47, NO.1, JANUARY 2000. MJ Walker, “Comparison of Bosh and cryogenic process for patterning high aspect ratio feature in silicon” Proc. SPIE Vol.4407, 2001, p.89-99.

  In the thin film piezoelectric resonator disclosed in Patent Document 2, the orientation of the piezoelectric crystal film can be increased by epitaxial growth, but the following points have not been considered. In a thin film piezoelectric resonator, a piezoelectric crystal film and an upper electrode are sequentially formed on a Si substrate, and then a via hole is formed on the back surface of the Si substrate, and a lower electrode is formed through the via hole. By using the etching method disclosed in Non-Patent Document 3 described above for forming the via hole, the via hole can be formed in an ideal shape in which the inner wall of the via hole is substantially perpendicular to the back surface of the Si substrate. . Therefore, it is possible to reduce the size of the thin film piezoelectric resonator. However, a lower electrode layer is formed on a steep stepped portion from the back surface of the Si substrate to the inner wall of the via hole, and this lower electrode layer is patterned in the steep stepped portion and the via hole to form a lower electrode. This is extremely difficult in the manufacturing process.

  On the other hand, in order to easily realize the manufacturing process of the lower electrode, it is effective to increase the angle of the inner wall of the via hole so as to spread from the Si substrate surface toward the back surface. Specifically, for example, by performing anisotropic etching on the back surface of the Si substrate using a strong alkaline solution such as potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) in a strong acid containing hydrofluoric acid, The angle of the inner wall of the via hole can be increased. However, since the via hole diameter is effectively increased and the occupied area of the via hole is increased, the thin film piezoelectric resonator cannot be reduced in size.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the crystallinity of a thin film piezoelectric body and to easily realize microfabrication. It is to provide a manufacturing method.

  Furthermore, an object of the present invention is to provide a thin film piezoelectric resonator capable of increasing the frequency and realizing a reduction in size.

A first feature according to an embodiment of the present invention is that, in the method of manufacturing a thin film piezoelectric resonator, a step of forming a first electrode layer on a substrate, and a hexagonal crystal structure on the first electrode layer. forming a first piezoelectric layer having a first piezoelectric layer to form a first piezoelectric body is patterned to form the first electrode by patterning the first electrode layer A step of cleaning the surface of the first piezoelectric body, and forming a second piezoelectric body having a hexagonal crystal structure on the cleaned surface of the first piezoelectric body. And a step of forming a piezoelectric body in which the second piezoelectric body is laminated, and a step of forming a second electrode on the piezoelectric body.

A second feature according to the embodiment of the present invention is that, in a thin film piezoelectric resonator, the first electrode on the substrate, the first electrode on the substrate, and the upper surface shape of the first electrode are the same. A first piezoelectric body having a lower surface shape, a piezoelectric body including a second piezoelectric body laminated on the first piezoelectric body, and a second electrode on the piezoelectric body , the first electrode The crystal grains of the first piezoelectric body and the crystal grains of the first piezoelectric body have the same crystal orientation at positions adjacent to each other, and the crystal grains of the first piezoelectric body and the crystal grains of the second piezoelectric body respectively. Means having the same crystal orientation at positions adjacent to each other .

  ADVANTAGE OF THE INVENTION According to this invention, while being able to improve the crystallinity of a thin film piezoelectric material, the manufacturing method of the thin film piezoelectric resonator which can implement | achieve fine processing easily can be provided.

  Furthermore, according to the present invention, it is possible to provide a thin film piezoelectric resonator capable of increasing the frequency and realizing a reduction in size.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
[Structure of thin film piezoelectric resonator]
As shown in FIG. 1, a thin film piezoelectric resonator 1 according to a first embodiment of the present invention includes a substrate 2, a first electrode (lower electrode) 5 on the substrate 2, and a first electrode 5. And a piezoelectric body (piezoelectric crystal) including a first piezoelectric body 61 having a bottom surface shape identical to the top surface shape of the first electrode 5 and a second piezoelectric body 63 on the first piezoelectric body 61. Thin film) 6 and a second electrode 82 on the piezoelectric body 6. Further, the thin film piezoelectric resonator 1 includes an insulator 3 on the substrate 2, a base layer 4 disposed between the insulator 3 and the first electrode 5, and a part (side surface) of the first electrode 5. And a spacer 7 having an insulating property disposed between a part of the side surface of the piezoelectric body 6 and the second electrode 82, and below the piezoelectric body 6. , A hole (via hole) 9 that penetrates the substrate 2 and the insulator 3 and exposes the back surface of the base layer 4 is provided.

  The performance of the thin film piezoelectric resonator 1 can be expressed by an electromechanical coupling coefficient kt2 and a quality factor Q value. As the electromechanical coupling coefficient kt2 is larger, a broadband filter and a VCO having a larger variable range of oscillation frequency can be configured. In order to increase the electromechanical coupling coefficient kt2, it is effective to use the piezoelectric body 6 having a large electromechanical coupling coefficient kt2 unique to the crystal and align the polarization axis of the crystal in the thickness direction of the film. The Q value is related to the sharpness of oscillation of the thin film piezoelectric resonator 1, and affects the insertion loss and skirt characteristics when a filter is constructed, and affects the phase noise when applied to a VCO circuit. Various phenomena such as absorption of elastic waves are related to the fluctuation of the Q value, and the crystal purity of the piezoelectric body 6 is increased, the crystal orientation of the piezoelectric body 6 is aligned, and the piezoelectric body 6 having the same polarization direction is used. By doing so, a large Q value can be obtained.

  As the piezoelectric body 6, a piezoelectric crystal thin film having a hexagonal crystal structure such as AlN or ZnO can be practically used. A piezoelectric crystal thin film having a hexagonal crystal structure is inherently easy to be c-axis oriented, and can be aligned with a single axis in the c-axis direction, ie, the (0001) crystal axis direction, which is the polarization direction. . By aligning the polarization axes in this way, it is possible to configure the piezoelectric body 6 in which the electromechanical coupling coefficient kt2 and the quality coefficient Q value are optimally ensured.

  In the first embodiment, the piezoelectric body 6 is laminated on the first piezoelectric body 61 and the first piezoelectric body 61 formed on the first electrode 5 in order to improve the c-axis orientation. A plurality of layers (in the first embodiment, two layers) are formed with the second piezoelectric body 63 formed. The first piezoelectric body 61 can prevent the formation of a surface oxide film of the first electrode 5 in the patterning process of the manufacturing process that determines the planar shape of the first electrode 5, and further the first electrode 5. The second piezoelectric body 63 can be formed with the crystal orientation of the crystal grains on the surface thereof maintained in a high orientation, and has a function as a relay layer.

  The inventors of the present application take over the crystal orientation on the surface of the first electrode 5 without using an epitaxial growth technique for growing a piezoelectric film on the surface of the substrate using the crystallinity. As a result of extensive theoretical and experimental studies on the method for growing the film, the orientation of the piezoelectric film 6 has been greatly improved by adopting a manufacturing method including at least the following steps (1) to (4). Found a fact that can be improved.

(1) First, on the surface of the electrode layer (formation layer of the first electrode 5), a first piezoelectric layer (formation layer of the first piezoelectric body 61) is continuously formed after the formation of this electrode layer. Form a film. The electrode layer is formed over the entire surface of the substrate 2, and the first piezoelectric layer is similarly formed over the entire surface of the electrode layer.

(2) Subsequently, the first piezoelectric layer 61 is patterned to form the first piezoelectric body 61, and the electrode layer is patterned to form the first electrode 5. Each of the first piezoelectric body 61 and the first electrode 5 is basically patterned by a method of overlapping cutting with the same manufacturing mask, and a connection portion between the first electrode 5 and the extraction electrode 81 shown in FIG. Except for this, at least the upper surface shape of the first electrode 5 and the lower surface shape of the first piezoelectric body 61 are the same.

(3) After this patterning, the surface of the first piezoelectric body 61 is appropriately washed by cleaning.

(4) The second piezoelectric body 63 is formed on the cleaned surface of the first piezoelectric body 61, and the piezoelectric body 6 in which the second piezoelectric body 63 is laminated on the first piezoelectric body 61 is formed. To do.

  The AlN piezoelectric crystal thin film used as the piezoelectric body 6 has a hexagonal crystal structure. In order to improve the c-axis orientation, the (111) orientation of the fcc crystal structure having a good lattice matching with the first electrode 5 is used. It is necessary to use a conductive thin film having a (110) orientation of a bcc crystal structure. For example, the first electrode 5 having high crystal orientation can be formed by previously forming the base film 4 for improving the flatness of the substrate 2 or improving the lattice matching, and this first electrode 5 can be formed. The first piezoelectric body 61 can be formed so as to inherit the crystal orientation of the surface of the electrode 5. The piezoelectric body 6 formed with such a manufacturing process can have a much improved c-axis orientation as compared with the case where the crystal orientation of the first electrode 5 is not inherited.

  In order to take over the crystal orientation of the base, the presence of substances that hinder the transmission of crystal information of the base, such as oxide films and organic contaminants, is not permitted, and a clean base surface is essential. Therefore, it is ideal to continuously form the first piezoelectric body 61 on the surface of the first electrode 5 having high crystal orientation in a high vacuum.

  However, in the manufacturing process of the thin film piezoelectric resonator 1, the step of patterning the first electrode 5 using the photolithography technique is essential. When this patterning process is performed, a surface oxide film is generated on the surface of the first electrode 5 or organic contamination occurs. The surface oxide film and organic contaminants are removed if sputter cleaning is performed on the surface of the first electrode 5 immediately after forming the piezoelectric body 6 after forming the first electrode 5 by the patterning process. Can do. In order not to impair the flatness of the surface of the first electrode 5 and to damage the crystal structure, sputter cleaning using low energy ions is necessary.

  In sputter cleaning using low energy ions, when a strong oxide film such as aluminum is used for the first electrode 5, alumina cannot be removed. Cannot take over to 6. On the other hand, when sputter cleaning using high energy ions is used, the flatness and crystallinity of the surface of the first electrode 5 are deteriorated, so that the crystallinity of the surface of the first electrode 5 is inherited by the piezoelectric body 6. I can't.

  Further, in order to improve the c-axis orientation of the piezoelectric body 6, the first electrode 5 is formed over the entire surface of the substrate 2 without patterning, and the piezoelectric material is applied over the entire surface of the first electrode 5 surface. There is a method of continuously forming body layers. The piezoelectric layer is patterned and formed as a piezoelectric body 6 that is isolated from the surroundings. A second electrode 82 is formed on the piezoelectric body 6. However, since the first electrode 5 is formed over the entire surface of the substrate 2, an interlayer insulating film having an electrical isolation function is required between the first electrode 5 and the second electrode 82. The number of processes increases.

  When the shape of the piezoelectric body 6 is not isolated without patterning, the parasitic capacitance added to each of the first electrode 5 and the second electrode 82 increases, and the characteristics of the thin film piezoelectric resonator 1 are improved. It will deteriorate. Therefore, in the thin film piezoelectric resonator 1, the shape of the piezoelectric body 6 is isolated from the surroundings, and the planar shape is the same as or similar to the planar shape of the piezoelectric body 6, that is, at least the same as the bottom surface shape of the piezoelectric body 6. It is preferable to constitute the first electrode 5 having the upper surface shape.

[Basic manufacturing method of thin film piezoelectric resonator]
In the thin film piezoelectric resonator 1 according to the first embodiment, an optimum metal material (conductive material) that improves the c-axis orientation of the piezoelectric body 6 is formed as a base layer 4, and the first layer is formed on the base layer 4. 1 is formed using a manufacturing method in which the piezoelectric body 6 formed on the surface of the first electrode layer has high crystal orientation on the surface of the first electrode layer. ing. That is, the basic outline of this manufacturing method is as follows.

(1) First, a first electrode layer (formation layer of the first electrode 5) that is highly oriented in a crystal orientation with good lattice matching with the (0001) crystal plane of the AlN piezoelectric crystal thin film is formed.

(2) Subsequently, a first piezoelectric layer (forming layer of the first piezoelectric body 61) is continuously formed on the first electrode layer. The film formation of the first piezoelectric layer is preferably performed in the same vacuum system as the film formation of the first electrode layer. Since the first piezoelectric layer is formed as a part of the film thickness necessary for the final piezoelectric body 6, the thickness of the first piezoelectric layer is naturally compared with the thickness of the piezoelectric body 6. Become thinner.

(3) The first piezoelectric body layer and the first electrode layer are patterned, and the first piezoelectric body 61 is formed from the first piezoelectric body layer by the electrode shape processing by the patterning. The first electrode 5 is formed from the electrode layer.

(4) Thereafter, in the high vacuum system, the surface of the first piezoelectric body 61 is cleaned by performing sputter cleaning on the surface of the first piezoelectric body 61 using low energy ions. Subsequently, a second piezoelectric layer (forming layer of the second piezoelectric body 63) is formed on the surface of the first piezoelectric body 61 where the sputter cleaning has been performed. The second piezoelectric layer is formed as the remaining film thickness that is the final film thickness required for the piezoelectric body 6. Then, patterning is performed on the second piezoelectric layer, and the second piezoelectric body 63 is formed by shape processing of the electrode by this patterning. By forming the second piezoelectric body 63, the piezoelectric body 6 including the first piezoelectric body 61 and the second piezoelectric body 63 stacked on the cleaning surface can be formed.

(5) Thereafter, the second electrode 82 is formed on the second piezoelectric body 63 of the piezoelectric body 6.

  When the first electrode layer is formed of, for example, a metal material whose main component is aluminum, an oxide film is easily generated on the surface of the first electrode layer when the first electrode layer is opened to the atmosphere during the manufacturing process. In addition, the oxide film cannot be removed unless sputtering cleaning with high energy ions is used. However, if the first piezoelectric layer is continuously formed on the first electrode layer in the same vacuum system or without opening to the atmosphere, the clean surface of the first electrode layer is formed. The first piezoelectric layer is formed. The first piezoelectric layer inherits the crystal orientation on the surface of the first electrode layer, and the c-axis orientation of the first piezoelectric layer is increased. In this state, the first electrode layer is patterned to form the first electrode 5 having an appropriate planar shape, and the first piezoelectric layer is patterned to form the first piezoelectric body 61. . Here, the metal material mainly composed of aluminum is used in the sense of including aluminum or an aluminum alloy containing an additive substance such as Ni, Ta, Si, or Cu.

  In the manufacturing process of the first electrode 5, that is, patterning, the surface of the first electrode layer is covered and protected by the first piezoelectric layer, so that the crystal orientation of the surface of the first electrode 5 is maintained. ing. The surface of the first piezoelectric body 61 can be made a clean surface by performing sputter cleaning of low energy ions in a high vacuum. An oxide film is generated on the surface of the first piezoelectric body 61 during the manufacturing process of the first electrode 5, but this oxide film can be easily obtained by sputtering cleaning using low energy ions unless exposed to a strong oxidizing atmosphere. Can be removed.

  Since the second piezoelectric body 63 is formed on the clean surface of the first piezoelectric body 61 by taking over the crystal orientation, the c-axis orientation of the second piezoelectric body 63 is increased. As a result, the orientation of the crystal grains of the first electrode 5, the first piezoelectric body 61 of the piezoelectric body 6, and the second piezoelectric body 63 share an interface and are in an aligned state. Become.

  Thus, in the thin film piezoelectric resonator 1 according to the first embodiment, the c-axis orientation half-value width is small on the substrate 2 without using an expensive and complicated thin film growth technique such as an epitaxial growth method. Since the piezoelectric film 6 can be formed, the electromechanical coupling coefficient can be increased.

[Evaluation of orientation of piezoelectric body of thin film piezoelectric resonator]
Next, the evaluation results of the crystal orientation of the piezoelectric body 6 used in the thin film piezoelectric resonator 1 will be described with reference to FIG.

  In FIG. 2, Examples 1 to 4 are all evaluation results of crystal orientation to which the manufacturing method of the thin film piezoelectric resonator 1 according to the first embodiment is applied. That is, in each of Examples 1 to 4, the piezoelectric body 6 was formed on the first electrode layer under the processing conditions shown in FIG. It is a measurement result of a price range. On the other hand, Comparative Examples 1 to 6 are evaluation results of crystal orientation in which the manufacturing method of the thin film piezoelectric resonator 1 according to the first embodiment is not applied.

  The first electrode layer is aluminum having (111) crystal orientation in all of Examples 1 to 4 and Comparative Examples 1 to 6. In Examples 1 to 4, all the half widths of the (111) crystal orientation of the first electrode layer are 1.0 °. In Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 6, the orientation half width of the (111) crystal orientation of the first electrode layer is 1.0 °. In Comparative Example 4 and Comparative Example 5, the first half-width of the (111) crystal orientation of the first electrode layer is 4.0 °.

  The piezoelectric body 6 is an AlN piezoelectric body, and the film thickness (nm) of the first piezoelectric body 61 and the film thickness (nm) of the second piezoelectric body 63 are as shown in FIG. The total film thickness of the piezoelectric body 6 is 1 μm. The piezoelectric body 63 is formed by high frequency magnetron sputtering at room temperature. The half width of orientation of the piezoelectric body 6 is the half width of orientation of the (0002) crystal orientation of the second piezoelectric body 63 finally formed.

                   Sputter cleaning (surface cleaning) is cleaning of the surface of the first piezoelectric body 61 and is performed in an argon atmosphere. The speed (nm / s) is the cleaning speed (etching speed) of the first piezoelectric body 61, and is a value converted into the cleaning speed of the silicon dioxide film grown by the thermal oxidation method. Similarly, the time (s) is the cleaning time (etching time) of the first piezoelectric body 61 and is a value converted into the cleaning time of the silicon dioxide film grown by the thermal oxidation method.

  As shown in FIG. 2, in Example 1, after the first piezoelectric layer is formed, a resist mask is formed on the first piezoelectric layer, and the first piezoelectric layer is patterned by RIE. Then, the first piezoelectric body 61 is formed, the first electrode layer is subsequently patterned to form the first electrode 5, the resist mask is peeled off, and then the surface of the first piezoelectric body 61 is sputter cleaned. Since the second piezoelectric body 63 is formed on the clean surface of the first piezoelectric body 61, the orientation half width of the (0002) crystal orientation of the piezoelectric body 6 (second piezoelectric body 63) is This is equivalent to the full width at half maximum of the (111) crystal orientation of the first electrode 5. Similar to the first embodiment, in any of the second to third embodiments, the orientation half width of the piezoelectric body 6 is equal to the orientation half width of the first electrode 5. That is, the film thickness of the first piezoelectric body 61 of the first to fourth embodiments is oscillated within the range of 30 nm to 500 nm, that is, within the range of 3% to 50% of the total film thickness of the piezoelectric body 6. However, in this wide range, the crystal orientation of the first electrode 5 can be inherited by the crystal orientation of the second piezoelectric body 63.

  On the other hand, Comparative Example 1 forms the first electrode 5 by directly patterning the first electrode layer without forming the first piezoelectric layer on the first electrode layer. In this example, the second piezoelectric layer (1000 nm) corresponding to the final film thickness of the piezoelectric body 6 is formed after the sputtering cleaning. In Comparative Example 1, the orientation half-value width of the (0002) crystal orientation of the piezoelectric body 6 was a large value close to 10 °. The inventors of the present application could not remove the oxide film formed on the surface of the first electrode 5 by sputtering cleaning, and could not take over the crystal orientation of the surface of the first electrode 5 to the piezoelectric body 6. In addition, it is considered that the numerical value of the half width of orientation has increased.

  In Comparative Example 2, a first piezoelectric layer having a thickness of 50 nm is formed on the first electrode layer, and the first piezoelectric body 61 and the first electrode 5 are formed by patterning. In this example, the second piezoelectric layer is formed on the surface of the piezoelectric body 61 without performing sputter cleaning. In Comparative Example 2, the full width at half maximum of the (0002) crystal orientation of the piezoelectric body 6 was 6.6 °. Since the inventors of the present application have not performed the sputter cleaning on the surface of the first piezoelectric body 61, the surface of the first piezoelectric body 61 is in a state where the resist mask is peeled off, and as a result, the surface of the first electrode 5 is not exposed. It is considered that the numerical value of the orientation half-value width has increased because the crystal orientation cannot be inherited by the piezoelectric body 6.

  In the third comparative example, the basic parameters are the same as in the first embodiment. The first piezoelectric layer is formed on the first electrode layer with a thickness of 50 nm, and the first piezoelectric layer is patterned. After patterning the first piezoelectric body 61 and the first electrode layer to form the first electrode 5, the first piezoelectric body 61 is sputter-cleaned, and then the second piezoelectric body having a thickness of 950 nm is formed. This is an example in which a layer is formed. In the comparative example 3, the sputter cleaning using high energy is used as compared with the sputter cleaning used in the first embodiment. The sputter cleaning rate is about 2.5 times faster than the sputter cleaning rate used in Example 1 in terms of the etching rate of the silicon dioxide film. In Comparative Example 3, the full width at half maximum of the (0002) crystal orientation of the piezoelectric body 6 is 6.0 °. The inventors of the present application lose the flatness of the first piezoelectric body 61 when the sputter cleaning is set to high energy, and as a result, take over the crystal orientation of the surface of the first electrode 5 to the piezoelectric body 6. It is considered that the numerical value of the alignment half-value width has increased due to the failure to achieve the above.

  In Comparative Example 4, a first piezoelectric layer having a thickness of 50 nm was formed on a first electrode layer having an orientation half width of 4.0 °, and the first piezoelectric layer was patterned to form a first piezoelectric layer. After patterning the first piezoelectric body 61 and the first electrode layer to form the first electrode 5 and performing the sputter cleaning on the first piezoelectric body 61, the second piezoelectric body layer having a thickness of 950 nm is formed. Is an example of forming a film. In Comparative Example 4, sputter cleaning using low energy set under the same conditions as the low sputter cleaning used in Example 4 is used. In Comparative Example 4, the full width at half maximum of the (0002) crystal orientation of the piezoelectric body 6 is 4.5 °. The inventors of the present application considered that the piezoelectric body 6 took over the crystal orientation of the first electrode 5 to some extent because the half width of the first electrode 5 was previously set to 4.0 °. ing.

  Comparative Example 5 is an example in which the surface of the first piezoelectric body 61 is not subjected to low energy sputter cleaning in Comparative Example 4. In Comparative Example 5, the full width at half maximum of the (0002) crystal orientation of the piezoelectric body 6 is a large value of 12.5 °.

  Comparative Example 6 is an example in which the time of low energy sputter cleaning performed on the surface of the first piezoelectric body 61 in Example 1 is shortened to 35 (s). In Comparative Example 6, the full width at half maximum of the (0002) crystal orientation of the piezoelectric body 6 is 6.4 °. The inventors of the present application have the same basic parameters as in the first embodiment, but the sputter cleaning time is short and the surface of the first piezoelectric body 61 is not sufficiently cleaned. As a result, the first electrode 5 It is considered that since the crystal orientation of the surface could not be inherited by the piezoelectric body 6, the numerical value of the alignment half width increased. As is apparent from Comparative Example 6 and Example 1, the sputter cleaning is set to low energy, and the crystal orientation of the surface of the first piezoelectric body 61 is changed to the second unless the sufficient time is implemented. The crystal orientation of the piezoelectric body 63 cannot be inherited.

[Specific First Manufacturing Method of Thin Film Piezoelectric Resonator]
Next, a specific method for manufacturing the thin film piezoelectric resonator 1 according to Example 1 will be described. First, a Si substrate having a high specific resistance value of 1 kΩcm or more is prepared as the substrate 2, and the insulator 3 is formed over the entire (100) crystal surface of the substrate 2 (see FIG. 3). For the insulator 3, a silicon oxide film having a thickness of 1 μm, for example, formed by a thermal oxidation method is used.

Next, as shown in FIG. 3, a base layer 4 is formed over the entire surface of the insulator 3. As the underlayer 4, an amorphous Al _0.5 Ta _0.5 film formed by a high frequency magnetron sputtering method is used, and the film thickness is set to 30 nm.

  Next, the first electrode layer 50 is formed over the entire surface of the base layer 4, and subsequently, the first piezoelectric layer 610 is formed over the entire surface of the first electrode layer 50 as shown in FIG. Film. As the first electrode layer 50, an aluminum film formed by a high frequency magnetron sputtering method is used, and the film thickness is set to 250 nm. The half width of the (111) crystal orientation of this aluminum film is controlled to 1.0 °. As the first piezoelectric layer 610, an AlN film formed by a reactive high-frequency magnetron sputtering method is used, and the film thickness is set to 50 nm.

  Although not shown, an etching mask (resist mask) is formed on the surface of the first piezoelectric layer 610 by photolithography. By using this etching mask, the first piezoelectric layer 61 is patterned to form the first piezoelectric body 61. As shown in FIG. 5, the first piezoelectric body 61 is subsequently used as a substantial etching mask. The first electrode 5 is formed by patterning the first electrode layer 50. For patterning, for example, a magnetron RIE method can be used practically. By tapering the side surface shape of the etching mask and optimizing the etching conditions, the end surface shape of the first electrode 5 and the end surface shape of the first piezoelectric body 61 can be tapered as shown in FIG. This taper angle is preferably set to 30 degrees or less with respect to the surface of the substrate 2. In removing the etching mask (resist stripping), ashing is not performed to avoid oxidation of the surface of the first piezoelectric body 61.

  Next, in the film forming apparatus (reactive high-frequency magnetron sputtering apparatus), as shown in FIG. 6, surface cleaning is performed on the surface of the first piezoelectric body 61. Reactive high-frequency sputter cleaning controlled to low energy can be used practically for surface cleaning. This surface cleaning is performed until the clean (0001) crystal plane of the surface of the first piezoelectric body 61 is exposed. Therefore, the first piezoelectric body 61 needs to have a minimum thickness enough to obtain a clean crystal plane.

  Next, as shown in FIG. 7, a second piezoelectric layer 630 is formed over the entire surface of the substrate 2 including the surface of the first piezoelectric body 61. An AlN film formed by reactive high-frequency magnetron sputtering is used for the second piezoelectric layer 630, and the film thickness is set to 2250 nm. Here, as shown in FIG. 7 and Example 1 of FIG. 2 described above, in the part 631 of the second piezoelectric layer 630 formed on the surface of the first piezoelectric member 6, the first The crystal orientation of the piezoelectric body 61 is sufficiently inherited, and the orientation half-value width of the (0001) crystal orientation remains within a range of about 1 °. On the other hand, the other part 632 of the second piezoelectric layer 630 is formed on the side surface (tapered surface) of the first electrode 5, the side surface of the base layer 4, and the surface of the insulator 3. , (0001) crystal orientation has a full width at half maximum of about 10 °.

  Next, although not shown, an etching mask is formed on the surface of the second piezoelectric layer 630 using photolithography. Using this etching mask, the second piezoelectric layer 630 is patterned to form a second piezoelectric body 63 as shown in FIG. For example, magnetron reactive etching can be used for patterning. By forming the second piezoelectric body 63, the piezoelectric body 6 including the first piezoelectric body 61 and the second piezoelectric body 63 laminated on the surface of the first piezoelectric body 61 can be completed. it can. As a result, the piezoelectric body 6 has a crystal orientation that sufficiently inherits the crystal orientation of the surface of the first electrode 5.

  Next, an insulator is formed, and the insulator 7 is patterned by using an etching mask formed using photolithography and magnetron reactive ion etching, so that a spacer 7 is formed on a part of the side wall of the piezoelectric body 6. (See FIG. 9). For example, a silicon oxide film can be used practically for the spacer 7. In the first embodiment, the spacer 7 is formed of a material different from that of the second piezoelectric body 63, but will be described in the method for manufacturing the thin film piezoelectric resonator 1 according to the second embodiment to be described later. In addition, the etching mask for patterning the second piezoelectric layer 630 may be extended to the region where the spacer 7 is formed, and the spacer 7 may be formed by the second piezoelectric layer 630 (632). In this case, the film forming process and the patterning process of the spacer 7 can be combined with the film forming process and the patterning process of the second piezoelectric body 63, so that the number of manufacturing processes can be reduced.

  A second electrode layer is formed over the entire surface of the substrate 2 including the surface of the spacer 7. For example, an aluminum film formed by sputtering is used for the second electrode layer, and the thin film is set to 250 nm. Although not shown in the drawing, an etching mask is formed on the surface of the second electrode layer using photolithography, and the second electrode layer is patterned using this etching mask, as shown in FIG. An electrode 81 and a second electrode 82 can be formed. One end of the extraction electrode 81 is connected to the surface of the first electrode 5 at a part of the peripheral edge of the first electrode 5, and the other end extends on the surface of the insulator 3. One end of the second electrode 82 is connected to the surface of the piezoelectric body 6 (second piezoelectric body 63), and the other end passes over the spacer 7 and extends on the surface of the insulator 2.

  Next, in the region where the first electrode 5 of the substrate 2 is formed, at least the substrate 2 and the insulator 3 are removed from the back surface of the substrate 2 to the front surface, and as shown in FIG. Forms a hole 9 for vibrating in the film thickness direction. In forming the holes 9, for example, an inductively coupled plasma (ICP) -RIE can be used for removing the substrate 2, and a magnetron RIE can be used practically for removing the insulator 3. . When the step of forming the hole 9 is completed, the thin film piezoelectric resonator 1 according to the first embodiment is completed.

[Characteristic evaluation of thin film piezoelectric resonator]
As a result of measuring the frequency characteristics in the thin film piezoelectric resonator 1 manufactured as described above, the resonance frequency is 2.0 GHz, the electromechanical coupling coefficient is 6.0%, the quality factor Q is 720 at the resonance point, and the antiresonance is achieved. In this respect, an extremely excellent frequency characteristic of 650 could be obtained. This mechanical coupling coefficient value is 91% of the maximum value theoretically expected from the AlN piezoelectric material.

  FIG. 10 is a cross-sectional transmission electron micrograph of the vicinity of the interface between the first electrode 5 and the piezoelectric body 6 of the thin film piezoelectric resonator 1. As shown in FIG. 10, in the vicinity of the interface between the first electrode (aluminum electrode) 5 and the piezoelectric body (AlN) 6, the size of the crystal grains in the horizontal direction of the first electrode 5 and the first piezoelectric body 61. The horizontal crystal grain size and the horizontal crystal grain size of the second piezoelectric body 63 are substantially the same.

  FIG. 11 shows a microscopic part electron beam diffraction pattern, which is a diffraction pattern of crystal particles obtained by irradiating a specific region of crystal particles with an electron beam with a diameter of 1 nm. Each of “a” to “f” shown in FIG. 11 corresponds to each of “a” to “f” shown in FIG. “A” shown in FIG. 11 is a [0-11] incident pattern on the (111) crystal plane of the first electrode (aluminum) 5. “B” shown in FIG. 11 is a [−1-120] incident pattern on the (0001) crystal plane of the first piezoelectric body (AlN) 61, and “c” is (0001) of the second piezoelectric body (AlN) 63. ) [-1-120] incident pattern on the crystal plane. Therefore, in the orientation relationship of Al [0-11] // AlN [-1-120], both are locally epitaxial. Similarly, in each of the incident patterns “d” to “f” shown in FIG.

  As described above, in the method of manufacturing the thin film piezoelectric resonator 1 according to the first embodiment, the first piezoelectric layer 610 is continuously formed on the surface of the first electrode layer 50, and these The first piezoelectric body 61 and the first electrode 5 are formed by patterning, and then the surface of the first piezoelectric body 61 is cleaned, and then the second piezoelectric body layer 630 is formed. ing. As a result, the crystal orientation on the surface of the first electrode 5 can be sufficiently inherited by the piezoelectric body 6. Further, the first electrode 5 is formed by patterning, and the first electrode 5 and the extraction electrode 81 can be connected on the surface of the substrate 2. That is, it is not necessary to connect the first electrode 5 and the extraction electrode 81 on the back surface of the substrate 2, and the hole 9 of the substrate 2 can be finely processed. Therefore, it is possible to obtain the thin-film piezoelectric resonator 1 that can implement a higher frequency and can be downsized.

[Application examples of thin film piezoelectric resonators]
The above-described thin film piezoelectric resonator 1 can be provided in, for example, the high frequency filter 100 shown in FIG. 12 and the VCO shown in FIG. The high frequency filter 100 shown in FIG. 12 is inserted in parallel with input terminals P1 and P2, output terminals P3 and P4, and thin film piezoelectric resonators 1 (1) and 1 (2) inserted in series. Thin film piezoelectric resonators 1 (3) and 1 (4) are provided.

  A VCO 200 shown in FIG. 13 includes a thin film piezoelectric resonator 1, an inverter 201, resistance elements 202 and 203, a capacitive element 204, and a variable capacitive element 205.

  Since both the high-frequency filter 100 and the VCO 200 include the thin film piezoelectric resonator 1 described above, high-frequency characteristics can be improved and downsizing can be realized.

(Second Embodiment)
The second embodiment of the present invention describes an example in which the second electrode structure connected to the piezoelectric body 6 is changed in the thin film piezoelectric resonator 1 according to the first embodiment described above. In the second embodiment and the subsequent embodiments, the description of the first embodiment has been made unless there is a description of the material, film thickness, film forming conditions, etc. of each component. It is the same as or equivalent to the material, film thickness, film forming conditions, etc. of each component given the same symbol.

[Specific Second Manufacturing Method of Thin Film Piezoelectric Resonator]
In the method of manufacturing the thin film piezoelectric resonator 1 according to the second embodiment, first, the substrate 2 is prepared, and the insulator 3 is formed over the entire surface of the substrate 2 (see FIG. 3 described above). . As shown in FIG. 3 described above, the base layer 4 is formed over the entire surface of the insulator 3. As the underlayer 4, an amorphous Al _0.6 Ta _0.4 film formed by a high frequency magnetron sputtering method is used, and the film thickness is set to 30 nm.

  Next, the first electrode layer 50 is formed over the entire surface of the underlayer 4, and subsequently the first piezoelectric layer 610 is formed over the entire surface of the first electrode layer 50 as shown in FIG. Film.

  Although not shown, an etching mask is formed on the surface of the first piezoelectric layer 610 by photolithography. Using this etching mask, the first piezoelectric body 61 is patterned to form the first piezoelectric body 61. As shown in FIG. 15, the first piezoelectric body 61 continues to be a substantial etching mask. The first electrode 5 is formed by patterning the first electrode layer 50. For patterning, for example, the ICP-RIE method can be used practically. By tapering the side surface shape of the etching mask and optimizing the etching conditions, the end surface shape of the first electrode 5 and the end surface shape of the first piezoelectric member 61 can be tapered as shown in FIG. The taper angle is preferably set to 20 degrees or less with respect to the surface of the substrate 2. In removing the etching mask, ashing is not performed to avoid oxidation of the surface of the first piezoelectric body 61.

  Next, surface cleaning is performed on the surface of the first piezoelectric body 61 in the film forming apparatus (see FIG. 6 described above). For the surface cleaning, reactive high-frequency sputter cleaning controlled to low energy under the conditions of the above-described Example 4 can be used practically. This surface cleaning is performed until the clean (0001) crystal plane of the surface of the first piezoelectric body 61 is exposed.

  Next, a second piezoelectric layer 630 is formed on the entire surface of the substrate 2 including the surface of the first piezoelectric body 61, and the second piezoelectric layer is continuously continuously formed as shown in FIG. An electrode layer 85 is formed over the entire area of the surface of 630. As the second piezoelectric layer 630, an AlN film formed by reactive high-frequency magnetron sputtering is used, and the film thickness is set to 1970 nm. The electrode layer 85 uses a molybdenum film formed by the same sputtering, and its film thickness is set to 200 nm. In the second embodiment, the electrode layer 85 is used as a part of the second electrode 82.

  Next, although not shown, an etching mask is formed on the surface of the electrode layer 85 by photolithography. As shown in FIG. 17, the electrode layer 85 is patterned using an etching mask, and an extraction electrode 84 is formed from the electrode layer 85. For patterning, for example, chemical dry etching can be practically used.

  Next, although not shown, an etching mask is formed on the surface of the second piezoelectric layer 630 including the surface of the extraction electrode 84 by photolithography. As shown in FIG. 18, the second piezoelectric layer 630 is patterned using the etching mask so that a part 631 below the extraction electrode 84 and a part of the other part 632 remain, and a part 631 is formed. Then, the second piezoelectric body 63 is formed, and the spacer 7 is formed from a part of the other portion 632. When the second piezoelectric body 63 is formed, the piezoelectric body 6 including the first piezoelectric body 61 and the second piezoelectric body 63 laminated on the surface thereof can be formed. Magnetron RIE can be used practically for patterning.

  A second electrode layer is formed over the entire surface of the substrate 2 including the surface of the spacer 7. For the second electrode layer, for example, an aluminum film formed by sputtering is used, and the thin film is set to 500 nm. Although not shown in the drawing, an etching mask is formed on the surface of the second electrode layer by using a photolithography technique, and the second electrode layer is patterned using the etching mask, as shown in FIG. An extraction electrode 81 and a second electrode 82 can be formed. One end of the extraction electrode 84 is connected to the second piezoelectric body 63 on the surface of the second piezoelectric body 63 of the piezoelectric body 6, and the other end of the extraction electrode 84 is connected to the second electrode 82 on the surface of the spacer 7. The Magnetron RIE can be used practically for patterning.

  Next, as shown in FIG. 20, the substrate 2 is polished from its back surface toward its surface. For example, chemical mechanical polishing (CMP) is used for polishing, and polishing is performed until the thickness of the substrate 2 becomes, for example, 200 μm.

  Next, in the region where the first electrode 5 of the substrate 2 is formed, at least the substrate 2 and the insulator 3 are removed from the back surface to the front surface of the substrate 2 to form holes 9 as shown in FIG. . In forming the holes 9, for example, ICP-RIE can be used for removing the substrate 2, and magnetron RIE can be used for removing the insulator 3. When the step of forming the hole 9 is completed, the thin film piezoelectric resonator 1 according to the second embodiment is completed.

[Characteristic evaluation of thin film piezoelectric resonator]
As a result of measuring the frequency characteristics in the thin film piezoelectric resonator 1 manufactured as described above, the resonance frequency is 2.0 GHz, the electromechanical coupling coefficient is 6.65%, the quality factor Q is 900 at the resonance point, and anti-resonance. In this respect, an extremely excellent frequency characteristic of 790 was obtained. This mechanical coupling coefficient value is comparable to the maximum value theoretically expected from the AlN piezoelectric material.

  FIG. 22 is a cross-sectional transmission electron micrograph of the vicinity of the interface between the first electrode 5 and the piezoelectric body 6 of the thin film piezoelectric resonator 1, and FIG. 23 is an enlarged cross-sectional transmission electron micrograph. As shown in FIGS. 22 and 23, in the vicinity of the interface between the first electrode (aluminum electrode) 5 and the piezoelectric body (AlN) 6, the size of the crystal grains in the horizontal direction of the first electrode 5 and the first The size of the crystal grains in the horizontal direction of the piezoelectric body 61 and the size of the crystal grains in the horizontal direction of the second piezoelectric body 63 are substantially uniform.

  FIG. 24 is a microscopic part electron beam diffraction pattern, which is a diffraction pattern of crystal grains obtained by irradiating a specific region of crystal grains with an electron beam focused to a diameter of 1 nm. Each of “a” to “f” shown in FIG. 24 corresponds to each of “a” to “f” shown in FIG. “A” shown in FIG. 24 is a [−1-12] incident pattern on the (111) crystal plane of the first electrode (aluminum) 5. “B” shown in FIG. 11 is a [1-100] incidence pattern on the (0001) crystal plane of the first piezoelectric body (AlN) 61, and “c” is (0001) of the second piezoelectric body (AlN) 63. It is a [1-100] incidence pattern to a crystal plane. Therefore, in the orientation relationship of Al [-1-12] // AlN [1-100], both are locally epitaxial. Similarly, in each of the incident patterns “d” to “f” shown in FIG.

  Note that the AlN columnar crystals of the piezoelectric body 6 are aligned in a region where the second piezoelectric body 63 is formed on the surface of the first electrode 5 with the first piezoelectric body 61 interposed. On the other hand, the portion where the first piezoelectric layer 610 is removed from the tapered portion of the end face of the first electrode 5 and the surface of the insulator 3 where the first electrode layer 50 is removed by patterning (or The columnar crystals of the second piezoelectric body 63 formed on the surface of the underlayer 4 are disturbed. However, since the region where the first electrode 5 does not exist is not related to piezoelectric resonance, it does not lead to deterioration of resonance characteristics. In addition, the width dimension of the tapered portion of the end face of the first electrode 5 is 1 μm or less, and the total area of the end face of the first electrode 5 is about 1% of the proportion of the thin film piezoelectric resonator 1. The resonator 1 has almost no effect on the deterioration of the resonance characteristics.

  As described above, in the method for manufacturing the thin film piezoelectric resonator 1 according to the second embodiment, the same effects as those obtained by the method for manufacturing the thin film piezoelectric resonator 1 according to the first embodiment described above are obtained. There is an effect. Therefore, it is possible to obtain the thin-film piezoelectric resonator 1 that can implement a higher frequency and can be downsized.

(Third embodiment)
In the third embodiment of the present invention, in the thin film piezoelectric resonator 1 according to the first embodiment described above, a cavity is provided instead of the hole 9 provided under the first electrode 5. Is described.

[Specific Third Manufacturing Method of Thin Film Piezoelectric Resonator]
In the method of manufacturing the thin film piezoelectric resonator 1 according to the third embodiment, first, the substrate 2 is prepared, and the insulator 3 is formed over the entire surface of the substrate 2 (see FIG. 25). Although not shown, an etching mask is formed on the surface of the insulator 3 by a photolithography technique, and the insulator 3 is patterned using the etching mask to form the first electrode 5 as shown in FIG. A part of the insulator 3 is selectively removed in the region to be formed, and a groove 30 is formed in the insulator 3. The groove 30 is a portion that will become a cavity in the future. For patterning, wet etching with an ammonium fluoride solution can be used practically.

  Next, a sacrificial layer 31 is formed on the surface of the insulator 3 so that the groove 30 is embedded. For the sacrificial layer 31, for example, a molybdenum film formed by high-frequency magnetron sputtering can be used practically, and the film thickness is set to 1.2 μm. Further, as shown in FIG. 27, the sacrificial layer 31 is buried in the groove 30, and the sacrificial layer 31 is removed until the surface of the insulator 3 is exposed. CMP can be used to remove the sacrificial layer 31. By using CMP, the surface of the insulator 3 and the surface of the sacrificial layer 31 can be planarized.

  As shown in FIG. 28, an insulator 32 is further formed on the entire surface of the insulator 3 including the surface of the sacrificial layer 31. By forming the insulator 32, the sacrificial layer 31 is completely embedded. As the insulator 32, for example, a silicon dioxide film formed by high frequency magnetron sputtering is used, and the film thickness is set to 50 nm.

Next, the base layer 4 is formed over the entire surface of the insulator 32 (see FIG. 29). As the underlayer 4, an amorphous Al _0.5 Ta _0.5 film formed by a high frequency magnetron sputtering method is used, and the film thickness is set to 30 nm.

  Next, the first electrode layer 50 is formed over the entire surface of the underlayer 4, and the first piezoelectric layer 610 is subsequently formed over the entire surface of the first electrode layer 50 as shown in FIG. Film. Then, similarly to the method of manufacturing the thin film piezoelectric resonator 1 according to the second embodiment described above, the first piezoelectric body 61 is patterned by patterning the first piezoelectric layer 610 as shown in FIG. In addition, the first electrode 5 is formed by patterning the first electrode layer 50.

  Next, surface cleaning is performed on the surface of the first piezoelectric body 61 in the film forming apparatus (see FIG. 6 described above). For the surface cleaning, reactive high-frequency sputter cleaning controlled to low energy under the conditions of the above-described Example 4 can be used practically. This surface cleaning is performed until the clean (0001) crystal plane of the surface of the first piezoelectric body 61 is exposed.

  Next, as shown in FIG. 31, a second piezoelectric layer 630 is formed over the entire surface of the substrate 2 including the surface of the first piezoelectric body 61. As the second piezoelectric layer 630, an AlN film formed by reactive high-frequency magnetron sputtering is used, and the film thickness is set to 2270 nm.

  Next, although not shown, an etching mask is formed on the surface of the second piezoelectric layer 630 by photolithography. Similar to the method of manufacturing the thin film piezoelectric resonator 1 according to the second embodiment described above, the second piezoelectric layer 630 is patterned using an etching mask, and the second piezoelectric body 63 is formed from a part 631. And the spacer 7 is formed from a part of the other portion 632 (see FIG. 32). When the second piezoelectric body 63 is formed, the piezoelectric body 6 including the first piezoelectric body 61 and the second piezoelectric body 63 laminated on the surface thereof can be formed. Magnetron RIE can be used practically for patterning.

  A second electrode layer is formed over the entire surface of the substrate 2 including the surface of the piezoelectric body 6 and the surface of the spacer 7. For example, an aluminum film formed by sputtering is used for the second electrode layer, and the thin film is set to 250 nm. Although not shown, an etching mask is formed on the surface of the second electrode layer using a photolithography technique, and the second electrode layer is patterned using this etching mask, as shown in FIG. An extraction electrode 81 and a second electrode 82 can be formed.

  Next, although not shown, a plurality of through holes reaching the surface of the sacrificial layer 31 are formed in the insulator 32 around the first electrode 5 on the sacrificial layer 31 buried in the already formed groove 30. . This through hole can be formed, for example, by forming an etching mask using a photolithography technique and patterning the insulator 32 using this etching mask. The number of through holes may be about 2 to 4, for example, and the diameter of the through holes is set to 5 μm, for example.

  Then, by immersing in an aqueous hydrogen peroxide solution heated to 50 degrees Celsius for about 20 minutes, the aqueous solution penetrates into the sacrificial layer 31 through the through holes, and the sacrificial layer 31 is selectively removed, as shown in FIG. A cavity 35 surrounded by the substrate 2, the insulator 3, and the insulator 32 can be formed. By forming the cavity 35, the thin film piezoelectric resonator 1 according to the third embodiment is completed.

[Characteristic evaluation of thin film piezoelectric resonator]
In the thin film piezoelectric resonator 1 manufactured as described above, the frequency characteristics were measured. As a result, the resonance frequency was 2.0 GHz, the electromechanical coupling coefficient was 6.5%, the quality factor Q was 820 at the resonance point, and anti-resonance. In this respect, an extremely excellent frequency characteristic of 750 could be obtained. This mechanical coupling coefficient value is comparable to the maximum value theoretically expected from the AlN piezoelectric material.

  As described above, in the method of manufacturing the thin film piezoelectric resonator 1 according to the third embodiment, the thin film piezoelectric resonator 1 according to the first embodiment or the second embodiment described above. The effect similar to the effect acquired by a manufacturing method can be show | played. Therefore, it is possible to obtain the thin-film piezoelectric resonator 1 that can implement a higher frequency and can be downsized.

(Fourth embodiment)
In the fourth embodiment of the present invention, in the thin film piezoelectric resonator 1 according to the second embodiment described above, an acoustic mirror reflective layer is arranged in place of the hole 9 disposed under the first electrode 5. An example will be described.

[Specific Third Manufacturing Method of Thin Film Piezoelectric Resonator]
In the method of manufacturing the thin film piezoelectric resonator 1 according to the fourth embodiment, first, the substrate 2 is prepared, and the first insulator 101, the second insulator 102, Each of the third insulator 103 and the fourth insulator 104 is sequentially formed (see FIG. 34). A silicon nitride film formed by thermal CVD (Chemical Vapor Deposition) is used for each of the first insulator 101 and the third insulator 103, and the second insulator 102 and the fourth insulator 104 are used. Each of these uses a silicon oxide film formed by plasma CVD.

  Next, although not shown, an etching mask is formed on the surface of the fourth insulator 104 by a photolithography technique, and the fourth insulator 104 is patterned using the etching mask, as shown in FIG. Next, a groove 105 is formed. The groove 105 is a portion that will be a region where an acoustic mirror reflection layer is to be disposed in the future. For patterning, wet etching with an ammonium fluoride solution can be used practically. The third insulator 103 has a function as an etching stopper layer when the fourth insulator layer 104 is etched.

  Next, as shown in FIG. 35, the high acoustic mirror layer 110, the low acoustic mirror layer 111, and the high acoustic mirror layer are formed on the surface of the third insulator 103 and the surface of the fourth insulator 104 exposed inside the groove 105. 112 and the low acoustic mirror layer 113 are sequentially formed. For each of the high acoustic mirror layers 110 and 112, a tungsten film having high acoustic impedance characteristics can be used practically. For each of the low acoustic mirror layers 111 and 113, a silicon dioxide film having low acoustic impedance characteristics can be practically used. The film thicknesses of the high-acoustic mirror layer 110, the low-acoustic mirror layer 111, the high-acoustic mirror layer 112, and the low-acoustic mirror layer 113 are set to λ / 4 of 2.0 GHz, for example.

  Next, the low-acoustic mirror layer 113, the high-acoustic mirror layer 112, the low-acoustic mirror layer 111, and the high-acoustic mirror layer 110 are sequentially polished until the height becomes equal to the surface of the fourth insulator 104. As shown in FIG. 36, the acoustic mirror reflecting layer 10 including the high acoustic mirror layer 110, the low acoustic mirror layer 111, the high acoustic mirror layer 112, and the low acoustic mirror layer 113 embedded in the groove 105 is formed. CMP can be used for polishing.

  As shown in FIG. 37, an insulator 32 is further formed on the entire surface of the fourth insulator 104 including the surface of the acoustic mirror reflective layer 10. By forming the insulator 32, the acoustic mirror reflective layer 10 is completely embedded.

Next, the base layer 4 is formed over the entire surface of the insulator 32 (see FIG. 38). As the underlayer 4, an amorphous Al _0.5 Ta _0.5 film formed by a high frequency magnetron sputtering method is used, and the film thickness is set to 30 nm.

  Next, the first electrode layer 50 is formed over the entire surface of the underlayer 4, and the first piezoelectric layer 610 is subsequently formed over the entire surface of the first electrode layer 50 as shown in FIG. Film.

  Although not shown, an etching mask is formed on the surface of the first piezoelectric layer 610 by photolithography. Using this etching mask, the first piezoelectric layer 61 is patterned to form the first piezoelectric body 61. As shown in FIG. 39, the first piezoelectric body 61 is subsequently used as a substantial etching mask. The first electrode 5 is formed by patterning the first electrode layer 50. For patterning, for example, the ICP-RIE method can be used practically. By tapering the side surface shape of the etching mask and optimizing the etching conditions, the end surface shape of the first electrode 5 and the end surface shape of the first piezoelectric body 61 can be tapered as shown in FIG. This taper angle is preferably set to 35 degrees or less with respect to the surface of the substrate 2. In removing the etching mask, ashing is not performed to avoid oxidation of the surface of the first piezoelectric body 61.

  Next, surface cleaning is performed on the surface of the first piezoelectric body 61 in the film forming apparatus (see FIG. 6 described above). For the surface cleaning, reactive high-frequency sputter cleaning controlled to low energy under the conditions of the above-described Example 4 can be used practically. This surface cleaning is performed until the clean (0001) crystal plane of the surface of the first piezoelectric body 61 is exposed.

  Next, a second piezoelectric layer 630 is formed over the entire surface of the substrate 2 including the surface of the first piezoelectric body 61, and as shown in FIG. An electrode layer 85 is formed over the entire area of the surface of 630. An AlN film formed by reactive high-frequency magnetron sputtering is used for the second piezoelectric layer 630, and the film thickness is set to 1900 nm. The electrode layer 85 uses a molybdenum film formed by the same sputtering, and its film thickness is set to 200 nm.

  Next, although not shown, an etching mask is formed on the surface of the electrode layer 85 by photolithography. As shown in FIG. 41, the electrode layer 85 is patterned using an etching mask, and the extraction electrode 84 is formed from the electrode layer 85.

  Next, although not shown, an etching mask is formed on the surface of the second piezoelectric layer 630 including the surface of the extraction electrode 84 by photolithography. As shown in FIG. 42, by using an etching mask, the second piezoelectric layer 630 is patterned so that a part 631 below the extraction electrode 84 and a part of the other part 632 remain, and a part 631 is formed. Then, the second piezoelectric body 63 is formed, and the spacer 7 is formed from a part of the other portion 632. When the second piezoelectric body 63 is formed, the piezoelectric body 6 including the first piezoelectric body 61 and the second piezoelectric body 63 laminated on the surface thereof can be formed.

  A second electrode layer is formed over the entire surface of the substrate 2 including the surface of the spacer 7. For the second electrode layer, for example, an aluminum film formed by sputtering is used, and the thin film is set to 500 nm. Although not shown in the figure, an etching mask is formed on the surface of the second electrode layer by using a photolithography technique, and the second electrode layer is patterned using this etching mask, as shown in FIG. An extraction electrode 81 and a second electrode 82 can be formed. One end of the extraction electrode 84 is connected to the second piezoelectric body 63 on the surface of the second piezoelectric body 63 of the piezoelectric body 6, and the other end of the extraction electrode 84 is connected to the second electrode 82 on the surface of the spacer 7. The Magnetron RIE can be used practically for patterning. By forming the extraction electrode 81 and the second electrode 82, the thin film piezoelectric resonator 1 according to the fourth embodiment is completed.

[Characteristic evaluation of thin film piezoelectric resonator]
As a result of measuring the frequency characteristics in the thin film piezoelectric resonator 1 manufactured as described above, the resonance frequency is 2.0 GHz, the electromechanical coupling coefficient is 5.5%, the quality factor Q is 600 at the resonance point, and anti-resonance. In this respect, an extremely excellent frequency characteristic of 550 could be obtained. The mechanical coupling coefficient value is comparable to the maximum value theoretically expected from the AlN piezoelectric material for the thin film piezoelectric resonator 1 including the acoustic mirror reflecting layer 10.

  As described above, in the method for manufacturing the thin film piezoelectric resonator 1 according to the fourth embodiment, the thin film piezoelectric resonator 1 according to the first embodiment or the second embodiment described above. The effect similar to the effect acquired by a manufacturing method can be show | played. Therefore, it is possible to obtain the thin-film piezoelectric resonator 1 that can implement a higher frequency and can be downsized.

  The present invention is not limited to the above-described embodiment, and can be changed without departing from the gist thereof.

1 is a cross-sectional view of a thin film piezoelectric resonator according to a first embodiment of the present invention. It is a figure which shows the orientation evaluation result of the thin film piezoelectric resonator which concerns on 1st Embodiment. FIG. 6 is a first process cross-sectional view illustrating a first manufacturing method of the thin film piezoelectric resonator shown in FIG. 1. It is 2nd process sectional drawing. It is 3rd process sectional drawing. It is a 4th process sectional view. FIG. 10 is a fifth process cross-sectional view. It is 6th process sectional drawing. It is 7th process sectional drawing. 2 is a cross-sectional transmission electron micrograph of the main part of the thin film piezoelectric resonator shown in FIG. It is a figure which shows the micro part electron beam diffraction pattern of the principal part of the thin film piezoelectric resonator shown in FIG. It is a circuit diagram of the high frequency filter concerning a 1st embodiment. 1 is a circuit diagram of a VCO according to a first embodiment. FIG. It is 1st process sectional drawing explaining the manufacturing method of the thin film piezoelectric resonator which concerns on the 2nd Embodiment of this invention. It is 2nd process sectional drawing. It is 3rd process sectional drawing. It is a 4th process sectional view. FIG. 10 is a fifth process cross-sectional view. It is 6th process sectional drawing. It is 7th process sectional drawing. It is 8th process sectional drawing. It is a cross-sectional transmission electron micrograph of the principal part of the thin film piezoelectric resonator shown in FIG. It is an expanded cross-sectional transmission electron micrograph of the principal part of the thin film piezoelectric resonator shown in FIG. It is a figure which shows the micro part electron beam diffraction pattern of the principal part of the thin film piezoelectric resonator shown in FIG. It is a 1st process sectional view explaining the manufacturing method of the thin film piezoelectric resonator concerning a 3rd embodiment of the present invention. It is 2nd process sectional drawing. It is 3rd process sectional drawing. It is a 4th process sectional view. FIG. 10 is a fifth process cross-sectional view. It is 6th process sectional drawing. It is 7th process sectional drawing. It is 8th process sectional drawing. It is 9th process sectional drawing. It is a 1st process sectional view explaining the manufacturing method of the thin film piezoelectric resonator concerning a 4th embodiment of the present invention. It is 2nd process sectional drawing. It is 3rd process sectional drawing. It is a 4th process sectional view. FIG. 10 is a fifth process cross-sectional view. It is 6th process sectional drawing. It is 7th process sectional drawing. It is 8th process sectional drawing. It is 9th process sectional drawing. It is 10th process sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin film piezoelectric resonator 2 Board | substrate 35 Cavity 4 Underlayer 5 1st electrode 6 Piezoelectric body 7 Spacer 61 1st piezoelectric body 63 2nd piezoelectric body 81 Extraction electrode 82 2nd electrode 9 Hole 10 Acoustic mirror reflective layer

Claims (12)

Forming a first electrode layer on a substrate;
Forming a first piezoelectric layer having a hexagonal crystal structure on the first electrode layer;
Patterning the first piezoelectric layer to form a first piezoelectric body, patterning the first electrode layer to form a first electrode;
Cleaning the surface of the first piezoelectric body;
A second piezoelectric body having a hexagonal crystal structure is formed on the cleaned surface of the first piezoelectric body, and a piezoelectric body is formed by laminating the second piezoelectric body on the first piezoelectric body. And a process of
Forming a second electrode on the piezoelectric body;
A method for manufacturing a thin film piezoelectric resonator, comprising:   The step of forming the first piezoelectric body is a step of forming a first aluminum nitride piezoelectric body, and the step of forming the second piezoelectric body is a step of forming a second aluminum nitride piezoelectric body. The method for manufacturing a thin film piezoelectric resonator according to claim 1, wherein:   3. The method of manufacturing a thin film piezoelectric resonator according to claim 2, wherein the step of forming the first electrode is a step of forming an electrode mainly composed of aluminum.   4. The step of cleaning the surface of the first piezoelectric body is a step of exposing a clean surface of the first piezoelectric body using ion sputtering. Manufacturing method for a thin film piezoelectric resonator.   The step of forming the first piezoelectric layer on the first electrode layer is a step of forming the first piezoelectric layer having a crystal orientation aligned on the first electrode layer according to the (111) orientation. The method for manufacturing a thin film piezoelectric resonator according to claim 3, wherein:   In the step of forming the piezoelectric body, the piezoelectric body is formed by laminating the second piezoelectric body including crystal grains that inherit crystal orientations of crystal grains on the surface of the first piezoelectric body layer. 6. The method for manufacturing a thin film piezoelectric resonator according to claim 5, wherein the method is a process. Further comprising a step of forming an underlayer for adjusting the orientation of the first electrode layer on the substrate,
The step of forming the first electrode layer on the substrate is a step of forming the first electrode layer on the underlayer after forming the underlayer. Item 7. A method for manufacturing a thin film piezoelectric resonator according to Item 6.   8. The method for manufacturing a thin film piezoelectric resonator according to claim 1, further comprising a step of forming a cavity on the surface of the substrate under the first electrode.   8. The method for manufacturing a thin film piezoelectric resonator according to claim 1, further comprising a step of forming an acoustic mirror between the substrate and the first electrode. A substrate,
A first electrode on the substrate;
A piezoelectric element provided with a first piezoelectric body disposed on the first electrode and having a lower surface shape identical to the upper surface shape of the first electrode, and a second piezoelectric body laminated on the first piezoelectric body. Body,
A second electrode on the piezoelectric body ,
Each crystal particle of the first electrode and each crystal particle of the first piezoelectric body have the same crystal orientation at positions adjacent to each other,
Each of the crystal grains of the first piezoelectric body and each of the crystal grains of the second piezoelectric body have the same crystal orientation at positions adjacent to each other . The thin-film piezoelectric resonator according to claim 10 , further comprising a cavity below the first electrode on the surface of the substrate. The thin film piezoelectric resonator according to claim 10 , further comprising an acoustic mirror between the substrate and the first electrode.