JP2005210614A - Thin-film bulk acoustic resonator manufacturing method, piezoelectric film forming method and non-reactive sputtering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric film forming method which can manufacture a high membranous piezoelectric film with high productivity, a manufacturing method of an FBAR, and a non-reactive sputtering device realizing the methods. <P>SOLUTION: In a thin-film bulk acoustic resonator manufacturing method having an elastic resonant film in which at least a lower part electrode, a piezoelectric film and an upper part electrode are laminated, a lower part electrode 12 is firstly formed on a substrate 10, and a piezoelectric film 13 is formed by a non-reactive sputtering which targets compound materials expressing piezoelectric property on an upper layer of the lower part electrode 12. Then, an upper part electrode 14 is formed on an upper layer of the piezoelectric film 13. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a thin film bulk acoustic wave resonator (FBAR), a method of forming a piezoelectric film used in the FBAR, and a non-reactive sputtering apparatus used in these manufacturing method and forming method. It is about.

In the field of electronic devices, the frequency of radio communication and electrical circuits is increasing, and parts with extremely thin thickness such as mobile terminals and IC cards such as mobile phones and PDAs (Personal Digital Assistants) are used. The required products have emerged, and there is a strong demand for miniaturization and thinning of parts, and their development is actively underway.
Among the electronic devices described above, development of a thin-film bulk acoustic resonator (FBAR) that can be reduced in size and thickness and is compatible with a high frequency is being promoted particularly as a piezoelectric resonator.

  As a conventional FBAR, for example, in Non-Patent Document 1, as shown in FIG. 10, a lower electrode 102, a piezoelectric film 103, and an upper electrode are provided via a gap V that forms a predetermined resonance region on a substrate 100 such as silicon. An FBAR in which an elastic resonance film 105 made of a laminate of 104 is formed is disclosed. The lower electrode 102 and the upper electrode 104 are made of a conductive material such as molybdenum, and the piezoelectric film 103 is made of a piezoelectric material such as aluminum nitride. The gap V is supported by a leg formed by bending at the end of the lower electrode 102.

  Here, a difference occurs in the acoustic impedance at the interface between the air gap V and the elastic resonance film 105, so that the vibration of the elastic resonance film 105 is reflected to the elastic resonance film 105 side without being transmitted to the substrate 100, and particularly in the elastic resonance film. If the standing wave condition is satisfied in FIG. The piezoelectric film 103 is a very important element because the crystalline orientation determines resonance characteristics.

  As a method of forming the FBAR having the above-described configuration, for example, a sacrificial layer for forming the void V is formed on the substrate 100 such as silicon, and this is covered, and the lower electrode 102, the piezoelectric film 103, and the upper portion are covered by, for example, sputtering. The electrodes 104 are sequentially stacked and processed into a predetermined shape, and then the sacrificial layer is removed by etching or the like to form a void V.

Here, as a method of depositing the piezoelectric film 103, chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) is used, but the most widely used. The method that has been described is the reactive sputtering method.
The target material used for the formation of the compound piezoelectric film by the conventional reactive sputtering method is a high-purity metal material (high-purity aluminum when forming an aluminum nitride film), and a rare gas such as argon or xenon and nitrogen or Sputtering is performed with a reactive gas such as oxygen (nitrogen in the case of forming aluminum nitride) to form a compound piezoelectric film on the substrate.

The reaction mechanism of the above-described conventional reactive sputtering method can be roughly explained by two models depending on the difference in flow rate corresponding to the concentration of the reaction gas.
FIG. 11 is a diagram in which the deposition rate of aluminum nitride is plotted against the flow rate of nitrogen, which is a reactive gas, in a reactive sputtering method in which aluminum nitride is deposited by supplying nitrogen gas as a target. 11 explains the above two models.
In the first model M1, metal atoms sputtered from a high-purity metal target react in the substrate surface or plasma in a low concentration region where the nitrogen flow rate is small, and deposit on the substrate as a compound piezoelectric material. Model. This model explains when the nitrogen flow rate is increased from a low region to a high region.
The second model M2 is a model in which a compound piezoelectric material is generated on the surface of a high-purity metal target in a high-concentration region where the nitrogen flow rate is high, and is sputtered by a rare gas and deposited on a substrate. . This model explains when the nitrogen flow rate is reduced from a high region to a low region.

  When the piezoelectric film is formed by the above-described CVD method or MBE method, although there is an advantage that a highly crystalline film can be obtained, a film forming temperature of 800 ° C. or higher is required. In the manufacturing process for forming the FBAR, the process temperature is required to be 300 ° C. or lower, and it is difficult to adopt the CVD method or the MBE method as a method for forming a piezoelectric film.

  In addition, in the reactive sputtering method, the formation of the piezoelectric film by the model (model M1) when increasing from the low nitrogen flow region to the high flow region has an advantage of high film formation speed, but there is a problem in composition reproducibility. And there is a problem that the internal stress of the film becomes high. This is presumably because even rare gas atoms are taken in during film formation.

On the other hand, in the reactive sputtering method, the piezoelectric film is formed by the model (model M2) when the flow rate of nitrogen is decreased from a large region to a small region, and there is an advantage that the composition is stable and the internal stress is small. However, there is a problem that the deposition rate is slow and the productivity is poor.
Motoaki Hara et al., `` Alminium Nitride Thin Film 2 GHz Resonator Using Germanium Sacrificial Layer Etching '', Mems Symposium 2002 Tohoku Univ. Motoaki Hara et al., `` MEMS Based Thin Film 2 GHz Resonator for CMOS Integration '', 2003 IEEE MTT-S Digest, 1797-1800. Published by Nikkan Kogyo Shimbun, “Basics of Thin Film Creation” by Tatsuo Maya Richard C. Ruby et al., `` Thin Film Bulk Wave Acoustic Resonators (FBAR) for Wireless Applications '', 2001 IEEE URTRASONICS SYMPOSIUM, 813-821. QX Su et al., `` EDGE SUPPORTED ZnO THIN FILM BILK ACOUSTIC WAVERESONATORS AND FILTER DESIGN '', 2000 IEEE / EIA International Frequency Control Symposiomand Exhibition, 434-440. KM Lakin et al., `` Improved Bulk Wave Resonator Coupling Coefficient For Wide Bandwidth Filters '', 2001 IEEE URTRASONICS SYMPOSIUM, 827-831. Chien-Chuan Cheng et al., `` Highly c-axis oriented AlN films deposited on LiNbO substrate for surface acoustic wave devices '', 2001 IEEE, 439-442.

  The problem to be solved is that it is difficult to manufacture a high quality piezoelectric film with high productivity in the piezoelectric film forming method in the FBAR manufacturing method or the like.

  A method of manufacturing a thin film bulk acoustic resonator according to the present invention is a method of manufacturing a thin film bulk acoustic resonator having an elastic resonant film formed by laminating at least a lower electrode, a piezoelectric film, and an upper electrode. A step of forming, a step of forming a piezoelectric film on the upper layer of the lower electrode by non-reactive sputtering using a compound material that exhibits piezoelectricity, and a step of forming an upper electrode on the upper layer of the piezoelectric film; Have

  The method for manufacturing a thin film bulk acoustic resonator according to the present invention is a method for manufacturing a thin film bulk acoustic resonator having an elastic resonant film formed by laminating at least a lower electrode, a piezoelectric film, and an upper electrode. A lower electrode is formed, and a piezoelectric film is formed on the upper layer of the lower electrode by non-reactive sputtering using a compound material that exhibits piezoelectricity as a target. Next, an upper electrode is formed on the upper layer of the piezoelectric film.

  The method for forming a piezoelectric film of the present invention includes a step of forming a piezoelectric film on a substrate by non-reactive sputtering using a compound material that exhibits piezoelectricity as a target.

  In the method for forming a piezoelectric film of the present invention, the piezoelectric film is formed on the substrate by non-reactive sputtering using a compound material that exhibits piezoelectricity as a target.

  Further, the non-reactive sputtering apparatus of the present invention is disposed in the non-reactive sputtering processing chamber, the non-reactive sputtering processing chamber, a substrate holding unit for holding the substrate, and the non-reactive sputtering processing chamber. And a target made of a compound material that exhibits piezoelectricity, and a power source for applying a voltage to the substrate and the target, and applying a predetermined voltage to the substrate and the target to perform non-reactive sputtering of the target. A compound material is deposited on the substrate to form a piezoelectric film.

In the non-reactive sputtering apparatus of the present invention, a substrate holding unit for holding a substrate and a target made of a compound material that exhibits piezoelectricity are arranged in the non-reactive sputtering chamber.
When a predetermined voltage is applied to the substrate and target by the power source, a piezoelectric film is formed by non-reactive sputtering.

  According to the method for manufacturing a thin film bulk acoustic resonator of the present invention, the piezoelectric film constituting the thin film bulk acoustic resonator is formed by non-reactive sputtering targeting a compound material that expresses piezoelectricity that has been previously compounded. Therefore, a high quality piezoelectric film can be manufactured with high productivity.

  According to the method for forming a piezoelectric film of the present invention, a piezoelectric film is formed by non-reactive sputtering using a compound material that expresses a piezoelectric property that is a compound in advance, so that a high-quality piezoelectric film can be produced with high productivity. Can be manufactured.

  According to the non-reactive sputtering apparatus of the present invention, a non-reactive sputtering process can be performed using a compound material that expresses piezoelectricity that has been previously compounded, and a high-quality piezoelectric film is formed with high productivity. be able to.

  Embodiments of a method for manufacturing a thin film bulk acoustic resonator (FBAR), a method for forming a piezoelectric film, and a non-reactive sputtering apparatus according to the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a schematic sectional view showing the structure of an FBAR according to this embodiment.
For example, an elastic resonance film 15 made of a laminate of a lower electrode 12, a piezoelectric film 13 and an upper electrode 14 is formed on a substrate 10 made of a high-resistance material such as silicon or sapphire via a gap V constituting a predetermined resonance area. Is formed.
The lower electrode 12 and the upper electrode 14 are made of a conductive material such as Al, Pt, Au, Cu, W, Mo, and Ti, and are formed with a film thickness of 0.1 to 0.5 μm, for example.
The piezoelectric film 13 is made of a piezoelectric material such as aluminum nitride or zinc oxide, is a dense film highly oriented in the c-axis, and has excellent piezoelectric characteristics and elastic characteristics. It is formed with a film thickness of 5 μm or less.
The gap V is supported by a leg formed by bending at the end of the lower electrode 12, and the height of the gap V is, for example, about several μm.
The film thickness of the lower electrode 12, the upper electrode 14, and the piezoelectric film 13, the height of the gap V, and the like can be appropriately adjusted in accordance with the resonance frequency.

  Here, a difference occurs in the acoustic impedance at the interface between the gap V and the elastic resonance film 15, so that the vibration of the elastic resonance film 15 is reflected to the elastic resonance film 15 side without being transmitted to the substrate 10, and particularly in the elastic resonance film. If the standing wave condition is satisfied in FIG. That is, since the acoustic wave generated by the longitudinal vibration of the thickness of the elastic resonance film 15 is efficiently confined inside the elastic resonance film 15, the loss of vibration energy can be reduced, and a small piezoelectric resonator can be realized.

Next, a method for manufacturing the FBAR according to the present embodiment will be described.
First, as shown in FIG. 2A, a material that can be selectively removed from the substrate 10 and the elastic resonance film 15, such as silicon oxide or germanium, by a CVD method or the like on the substrate 10, for example. The sacrificial layer 11 is formed by depositing and patterning. At this time, for example, the side surface of the sacrificial layer 11 is processed so as to have a forward tapered shape with respect to the substrate 10.

Next, as shown in FIG. 2B, the sacrificial layer 11 is covered, and the lower electrode 12 is formed on the entire surface by a vapor phase synthesis method such as a CVD method, a sputtering method, or a vacuum evaporation method. Pattern the shape.
In particular, for a substrate having a three-dimensional complicated shape, a CVD method represented by an MOCVD (organometallic CVD) method or the like that can obtain a relatively uniform film thickness even with a complicated shape is preferable. For a flat substrate having a layered structure, a sputtering method or a vacuum deposition method is preferable from the viewpoint of cost and simplicity.

  Next, as shown in FIG. 2C, the piezoelectric film 13 is formed on the lower electrode 12 by non-reactive sputtering using, for example, a compound material that exhibits piezoelectricity such as aluminum nitride or zinc oxide. .

Non-reactive sputtering in the step of forming the piezoelectric film 13 is performed by using a compound material that exhibits piezoelectricity as a target and depositing the target material without reacting in a commonly used sputtering apparatus. Can do.
That is, in the non-reactive sputtering apparatus, a substrate holding unit for holding a substrate and a target made of a compound material that exhibits piezoelectricity are arranged in a non-reactive sputtering processing chamber, and a power source for applying a voltage to the substrate and the target is provided. It is set as the provided structure.
A non-reactive sputtering chamber is set to a predetermined pressure atmosphere as described below, and a predetermined rare gas such as argon or xenon and a sputtering auxiliary gas such as nitrogen are supplied at a predetermined flow rate as described below. A predetermined voltage is applied to the substrate and the target. For example, since aluminum nitride is an insulator, an RF or DC pulse voltage is applied.
By non-reactive sputtering as described above, a target compound material is deposited on a substrate to form a piezoelectric film.

In the step of forming the piezoelectric film 13 by the above-described non-reactive sputtering, it is preferable to use a target having a density of 90% or more of the theoretical density as a target, and also to use a target formed by a melting method. Is preferred.
In the non-reactive sputtering for forming the piezoelectric film, since the target compound material that exhibits piezoelectricity is deposited without reacting, the lower the concentration of impurities in the target, the better, for example, the theory High purity is preferable so that the density is 90% or more of the density. This target is preferably formed by a melting method because it is possible to realize the formation of a high-purity target as described above. Moreover, as long as the high purity target as described above can be realized, a sintering method may be used.

Further, in the step of forming the piezoelectric film, it is preferable to form by non-reactive sputtering using a non-metallic component of the compound material as a sputtering auxiliary gas.
Sputtering auxiliary gas does not primarily contribute to sputtering, but prevents non-metallic components from escaping from the compound material released from the target by sputtering, and maintains the composition ratio of the compound target. It is a gas for deposition.
Here, as the sputtering auxiliary gas, nitrogen gas is used when aluminum nitride is deposited, and oxygen gas is used when zinc oxide is deposited.
The sputtering auxiliary gas is preferably used at a flow rate of 10% by flow or more with respect to the total sputtering gas. If it is less than 10% by flow rate, the function as a sputtering auxiliary gas is insufficient, and there is a possibility that a nonmetallic component may escape from the compound material as a gas.

Further, it is preferable that the step of forming the piezoelectric film is performed in a high vacuum atmosphere of 10 ⁻⁵ Pa or less.
In the high vacuum or ultra-high vacuum atmosphere as described above, the composition ratio of the compound target can be maintained, and it is possible to prevent the impurities such as oxygen remaining in the sputtering atmosphere from being taken in and deposited. it can.

After the piezoelectric film 13 is formed as described above, the upper electrode 14 is formed on the piezoelectric film 13 in the same manner as the lower electrode 12 as shown in FIG.
Further, as shown in FIG. 3B, the upper electrode 14 and the piezoelectric film 13 are patterned as necessary. In the drawing, the upper electrode 14 and the piezoelectric film 13 have the same pattern, but may have different patterns.

As the subsequent step, for example, an opening (not shown) that reaches the sacrificial layer 11 through the piezoelectric film 13 and the lower electrode 12 is opened, and an etching solution is introduced from the opening by wet etching such as HF solution, for example. The sacrificial layer 11 is removed.
Thus, the FBAR having the structure shown in FIG. 1 according to the present embodiment can be formed.

  In addition, as the structure and manufacturing method of the FBAR, the structure and manufacturing method of the FBAR according to the present embodiment can be applied to the structure and manufacturing method described in Non-Patent Documents 1 and 2.

According to the FBAR manufacturing method of the present embodiment described above, when forming a piezoelectric film, not a high-purity metal target but a compound target such as aluminum nitride or zinc oxide is used as a sputtering target. The piezoelectric film can be formed at a low temperature.
Since the target of each of the above compound materials is a high melting point material, composition deformation hardly occurs, and a film having the same composition as the target can be formed even at low temperature film formation of 300 ° C. or lower.

  In addition, unlike reactive sputtering, the compound target has a composition ratio that is reduced until the sputtered atomic group reaches the substrate simply by introducing a sputtering auxiliary gas of, for example, 10% by flow or more because of its high melting point. In contrast to the conventional sputtering model M1 shown in FIG. 11, variations in the composition of the piezoelectric film can be suppressed.

Further, the main gas of sputtering is a rare gas similar to conventional metal sputtering, that is, argon or xenon, and the non-metallic component gas which is a sputtering auxiliary gas can be suppressed to about 10% by flow rate. As compared with the conventional sputtering model M2 shown in FIG.
This is due to the sputtering rate of sputtered ions (see Non-Patent Document 3).
For example, when the sputtering rate of argon is normalized to 1, the sputtering rate of nitrogen (N ₂ ) or oxygen (O ₂ ) is about 0.45. In the reactive sputtering of the conventional method (the above model M2), the non-metallic sputtering gas is 70% by flow and the rare gas is 30% by flow, so that the overall sputtering rate is (1 × 0.3 + 0.45 × 0. 7) = 0.615.
On the other hand, in the above embodiment, when the nonmetallic sputtering gas (auxiliary gas) is 10 flow% and the rare gas is 90 flow%, the total sputtering rate is (1 × 0.9 + 0.45 × 0.1) = 0.945.
That is, since the ratio of the sputtering rate (0.945 / 0.615) = 1.54, the sputtering rate can be improved by 50% or more, even if estimated to be 40% or less.
Further, the film internal stress can be formed at 100 MPa or less.

  As described above, according to the method for manufacturing an FBAR according to the present embodiment, the piezoelectric film constituting the thin film bulk acoustic resonator is formed by non-reactive sputtering using a compound material that expresses piezoelectricity, which is a compound in advance, as a target. Since it is formed, a high-quality piezoelectric film having high uniformity and high c-axis orientation can be manufactured with high productivity.

Second Embodiment FIG. 4 is a schematic sectional view showing the structure of an FBAR according to the embodiment.
For example, the substrate 10 made of a high resistance material such as silicon or sapphire is formed with a recess 10a that becomes a gap V that constitutes a predetermined resonance region, and is in contact with both ends of the recess 10a to hold the gap V. An elastic resonance film 15 made of a laminate of the lower electrode 12, the piezoelectric film 13 and the upper electrode 14 is formed.
The lower electrode 12, the piezoelectric film 13, and the upper electrode 14 can be made of the same material and film thickness as in the first embodiment.
The depth of the recess 10a that becomes the gap V is, for example, about several μm, and the film thickness of the lower electrode 12, the upper electrode 14, and the piezoelectric film 13, the height of the gap V, and the like can be appropriately adjusted according to the resonance frequency. it can.

  Here, as in the first embodiment, there is a difference in acoustic impedance at the interface between the gap V and the elastic resonance film 15, so that the vibration of the elastic resonance film 15 is not transmitted to the substrate 10 and is moved to the elastic resonance film 15 side. In particular, when reflecting and satisfying the standing wave condition in the elastic resonance film, it is in a resonance state and a piezoelectric resonator can be realized.

Next, a method for manufacturing the FBAR according to the present embodiment will be described.
First, as shown in FIG. 5A, a resist film that opens a pattern of a recess is formed on the substrate 10 and etching such as wet etching is performed to form the recess 10a.
Next, a material that can be selectively removed by etching with respect to the substrate 10 and the elastic resonance film 15, such as silicon oxide or germanium, is deposited on the entire surface by embedding the recess 10a by, for example, the CVD method. The deposited portion is removed by etching to form a sacrificial layer 11 embedded in the recess 10 a of the substrate 10.

  Next, as shown in FIG. 5B, the sacrificial layer 11 is covered, and the lower electrode 12 is formed by a vapor phase synthesis method such as a CVD method, a sputtering method, or a vacuum evaporation method. In the same manner as described above, the piezoelectric film 13 is formed on the lower electrode 12 by non-reactive sputtering using, for example, a compound material that exhibits piezoelectricity such as aluminum nitride or zinc oxide. Thus, the upper electrode 14 is formed on the piezoelectric film 13. Further, the upper electrode 14, the piezoelectric film 13, and the lower electrode 12 are patterned as necessary.

Next, for example, an opening (not shown) that reaches the sacrificial layer 11 through the upper electrode 14, the piezoelectric film 13, the lower electrode 12, and the like is opened, and an etching solution is infiltrated from the opening by, for example, wet etching such as HF solution The sacrificial layer 11 is removed.
As described above, the FBAR having the structure shown in FIG. 4 according to this embodiment can be formed.

  In addition, as the FBAR structure and manufacturing method, the FBAR structure and manufacturing method according to this embodiment can be applied to the structure and manufacturing method described in Non-Patent Document 4.

  According to the FBAR manufacturing method of the present embodiment described above, as in the first embodiment, the thin film bulk acoustic resonator is formed by non-reactive sputtering using a compound material that expresses a piezoelectric property that is a compound in advance. Since the piezoelectric film is formed, a high-quality piezoelectric film can be manufactured with high productivity.

Third Embodiment FIG. 6 is a schematic sectional view showing the structure of an FBAR according to the embodiment.
For example, coating layers (10b, 10c) made of silicon oxide or the like are formed on both surfaces of a substrate 10 made of a high resistance material such as silicon or sapphire, and the lower electrode 12 and the piezoelectric film 13 are formed on one coating layer 10b. An elastic resonance film 15 made of a laminate of the upper electrode 14 is formed.
The lower electrode 12, the piezoelectric film 13, and the upper electrode 14 can be made of the same material and film thickness as in the first embodiment.
The substrate 10 is formed with an opening 10d that penetrates the substrate 10 from the surface of the other coating layer 10c and exposes the surface of the elastic resonance film 15 on the lower electrode 12 side (actually the coating layer 10b). It is a substrate with a diaphragm structure.

  Here, as in the first embodiment, a difference occurs in acoustic impedance on the surface of the elastic resonance film 15 on the side of the opening 10d (actually, the surface of the coating layer 10b). 10 is reflected to the side of the elastic resonance film 15 without being transmitted, and in particular, when the standing wave condition is satisfied in the elastic resonance film, it enters a resonance state and a piezoelectric resonator can be realized.

Next, a method for manufacturing the FBAR according to the present embodiment will be described.
First, coating layers (10b, 10c) such as silicon oxide are formed on both surfaces of the substrate 10, and the lower layer is formed on the upper layer of one coating layer 10b by a vapor phase synthesis method such as a CVD method, a sputtering method, or a vacuum deposition method. The electrode 12 is formed, and in the same manner as in the first embodiment, the piezoelectric film 13 is formed on the lower electrode 12 by non-reactive sputtering using, for example, a compound material that exhibits piezoelectricity such as aluminum nitride or zinc oxide. Further, the upper electrode 14 is formed on the piezoelectric film 13 in the same manner as the lower electrode 12. Further, the upper electrode 14, the piezoelectric film 13, and the lower electrode 12 are patterned as necessary.
Next, a resist film that opens a region for forming a diaphragm structure is formed on the coating layer 10c on the back surface side of the surface on which the elastic resonance film 15 is formed, and this is used as a mask and etching using the other coating layer 10b as an etching stopper. Thus, an opening 10d that penetrates through the substrate 10 and exposes the surface of the elastic resonance film 15 on the lower electrode 12 side (actually the coating layer 10b) is formed, thereby obtaining a substrate having a diaphragm structure.
As described above, the FBAR having the structure shown in FIG. 6 according to the present embodiment can be formed.

  In addition, as the structure and manufacturing method of the FBAR, the structure and manufacturing method of the FBAR according to the present embodiment can be applied to the structure and manufacturing method described in Non-Patent Document 5.

  According to the FBAR manufacturing method of the present embodiment described above, as in the first embodiment, the thin film bulk acoustic resonator is formed by non-reactive sputtering using a compound material that expresses a piezoelectric property that is a compound in advance. Since the piezoelectric film is formed, a high-quality piezoelectric film can be manufactured with high productivity.

Fourth Embodiment FIG. 7 is a schematic sectional view showing the structure of an FBAR according to the embodiment.
For example, the first reflection film 16a, the second reflection film 16b, the third reflection film 16c, the fourth reflection film 16d, the fifth reflection film 16e, and the sixth reflection are formed on the substrate 10 made of a high resistance material such as silicon or sapphire. An acoustic reflection film 16 composed of a laminate of seven layers such as a film 16f and a seventh reflection film 16g is formed, and an elastic resonance film 15 composed of a laminate of the lower electrode 12, the piezoelectric film 13 and the upper electrode 14 is formed thereon. Is formed.

The FBAR has no vibration space, and an acoustic reflection film 16 is formed between the substrate 10 and the lower electrode 12.
Here, the first reflection film 16a to the seventh reflection film 16g constituting the acoustic reflection film 16 are configured by alternately laminating materials having different specific acoustic resistance values, but in order to increase the reflectance. The effect is insufficient by simply laminating multiple layers, and in order to reflect efficiently, each film thickness is a value (λ / 4) of ¼ of the resonance frequency λ.

  Here, as in the first embodiment, since a difference in acoustic impedance occurs at the interface between the acoustic reflection film 16 and the elastic resonance film 15, the vibration of the elastic resonance film 15 is not transmitted to the substrate 10 and the elastic resonance film 15. When the standing wave condition is satisfied in the elastic resonance film, a resonance state is obtained and a piezoelectric resonator can be realized.

Next, a method for manufacturing the FBAR according to the present embodiment will be described.
First, materials having different specific acoustic resistance values are alternately stacked on the substrate 10 with a film thickness having a value of ¼ of the resonance frequency λ (λ / 4) by a known method, and a CVD method, a sputtering method, or the like is formed thereon. The lower electrode 12 is formed by a vapor phase synthesis method such as a vacuum deposition method, and further, in the same manner as in the first embodiment, on the lower electrode 12, for example, a compound material that exhibits piezoelectricity such as aluminum nitride or zinc oxide The piezoelectric film 13 is formed by non-reactive sputtering using as a target, and the upper electrode 14 is formed on the piezoelectric film 13 in the same manner as the lower electrode 12. Further, the upper electrode 14, the piezoelectric film 13, the lower electrode 12, and the acoustic reflection film 16 are patterned as necessary.
As described above, the FBAR having the structure shown in FIG. 7 according to this embodiment can be formed.

  In addition, as the FBAR structure and manufacturing method, the FBAR structure and manufacturing method according to this embodiment can be applied to the structure and manufacturing method described in Non-Patent Document 6.

  According to the FBAR manufacturing method of the present embodiment described above, as in the first embodiment, the thin film bulk acoustic resonator is formed by non-reactive sputtering using a compound material that expresses a piezoelectric property that is a compound in advance. Since the piezoelectric film is formed, a high-quality piezoelectric film can be manufactured with high productivity.

(Example)
FIG. 8 is a graph showing the relationship between the XRD intensity indicating the c-axis orientation of the piezoelectric film and the nitrogen concentration at the time of formation when the aluminum nitride piezoelectric film is formed by reactive sputtering according to the conventional example. This is a graph obtained by extracting the XRD intensity indicating the c-axis orientation from the data described in Non-Patent Document 7.
As described above, when a piezoelectric film is formed by reactive sputtering according to the conventional example, the c-axis orientation of aluminum nitride greatly depends on the nitrogen concentration. When the nitrogen concentration is lowered, the c-axis orientation is also lowered and the film quality is lowered. It was confirmed that.

On the other hand, FIG. 9 is a graph obtained by simulating the relationship between the XRD intensity indicating the c-axis orientation of the piezoelectric film and the nitrogen concentration during formation when the aluminum nitride piezoelectric film is formed by non-reactive sputtering according to the present embodiment. It is.
As described above, when the piezoelectric film is formed by the non-reactive sputtering according to the present embodiment, the dependency of the aluminum nitride on the c-axis orientation with respect to the nitrogen concentration is reduced, and a high c-axis orientation is achieved regardless of the nitrogen concentration process. It was confirmed that the film quality could be maintained and the film quality could be improved.

The present invention is not limited to the above embodiment.
For example, the present invention is not limited to the FBAR manufacturing method, but can be applied as a method for forming a piezoelectric film used for an element other than the FBAR.
In addition, various modifications can be made without departing from the scope of the present invention.

  The method for manufacturing a thin film bulk acoustic resonator according to the present invention can be applied to a method for manufacturing an FBAR used in a circuit such as a transmission filter or a duplexer in a wireless communication system such as a mobile phone or a wireless sensing system.

  The method for forming a piezoelectric film of the present invention can be applied to a method for forming a piezoelectric film used in a manufacturing process of an element including an FBAR or other piezoelectric film.

  The non-reactive sputtering apparatus of the present invention can be applied to an apparatus for forming a piezoelectric film by non-reactive sputtering in a manufacturing process of an element including an FBAR or other piezoelectric film.

FIG. 1 is a schematic cross-sectional view showing the configuration of the FBAR according to the first embodiment. 2A to 2C are schematic cross-sectional views illustrating manufacturing steps of the FBAR manufacturing method according to the first embodiment. FIG. 3A and FIG. 3B are schematic cross-sectional views illustrating manufacturing steps of the method for manufacturing an FBAR according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing the configuration of the FBAR according to the second embodiment. FIG. 5A and FIG. 5B are schematic cross-sectional views illustrating manufacturing steps of the method for manufacturing an FBAR according to the second embodiment. FIG. 6 is a schematic cross-sectional view showing the configuration of the FBAR according to the third embodiment. FIG. 7 is a schematic cross-sectional view showing the configuration of the FBAR according to the fourth embodiment. FIG. 8 is a graph showing the relationship between the XRD intensity indicating the c-axis orientation of the piezoelectric film and the nitrogen concentration at the time of formation when the piezoelectric film is formed by reactive sputtering according to the conventional example. FIG. 9 is a graph showing the relationship between the XRD intensity indicating the c-axis orientation of the piezoelectric film and the nitrogen concentration during formation when the piezoelectric film is formed by non-reactive sputtering according to the present invention. FIG. 10 is a schematic cross-sectional view showing a configuration of an FBAR according to a conventional example. FIG. 11 is a graph showing the relationship between the deposition rate of the piezoelectric film and the nitrogen concentration during deposition by the conventional FBAR manufacturing method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,100 ... Board | substrate, 10a ... Recessed part, 10b, 10c ... Silicon nitride film, 10d ... Back surface via, 11 ... Sacrificial film, 12, 102 ... Lower electrode, 13, 103 ... Piezoelectric film, 14, 104 ... Upper electrode, 15 , 105 ... elastic resonance film, 16 ... acoustic reflection film, 16a ... first reflection film, 16b ... second reflection film, 16c ... third reflection film, 16d ... fourth reflection film, 16e ... fifth reflection film, 16f ... Sixth reflective film, 16g ... seventh reflective film, V ... air gap

Claims (15)

A method of manufacturing a thin film bulk acoustic resonator having an elastic resonance film formed by laminating at least a lower electrode, a piezoelectric film, and an upper electrode,
Forming a lower electrode on the substrate;
Forming a piezoelectric film on the upper layer of the lower electrode by non-reactive sputtering using a compound material that exhibits piezoelectricity as a target;
Forming a top electrode on an upper layer of the piezoelectric film. A method of manufacturing a thin film bulk acoustic resonator. The method for manufacturing a thin film bulk acoustic resonator according to claim 1, wherein a target formed by a melting method is used as the target in the step of forming the piezoelectric film. The method for manufacturing a thin film bulk acoustic resonator according to claim 1, wherein in the step of forming the piezoelectric film, a target having a density of 90% or more with respect to a theoretical density is used as the target. The method of manufacturing a thin film bulk acoustic resonator according to claim 1, wherein in the step of forming the piezoelectric film, the compound material is aluminum nitride or zinc oxide. The method of manufacturing a thin film bulk acoustic resonator according to claim 1, wherein in the step of forming the piezoelectric film, the piezoelectric material is formed by non-reactive sputtering using a non-metallic component of the compound material as a sputtering auxiliary gas. The method for manufacturing a thin film bulk acoustic resonator according to claim 5, wherein in the step of forming the piezoelectric film, nitrogen gas or oxygen gas is used as the sputtering auxiliary gas. The method for manufacturing a thin film bulk acoustic resonator according to claim 5, wherein in the step of forming the piezoelectric film, the sputtering auxiliary gas is used at a flow rate of 10 flow% or more. The method for manufacturing a thin film bulk acoustic resonator according to claim 1, wherein the step of forming the piezoelectric film is performed in a high vacuum atmosphere of 10 ⁻⁵ Pa or less. Before the step of forming the lower electrode, further comprising the step of forming a sacrificial layer on the substrate;
In the step of forming the lower electrode, the sacrificial layer is covered so as to be in contact with the substrate at both ends of the sacrificial layer,
The method for manufacturing a thin film bulk acoustic resonator according to claim 1, further comprising a step of removing the sacrificial layer after the step of forming the upper electrode. After the step of forming the upper electrode and before the step of removing the sacrificial layer, the method further includes the step of forming an opening that penetrates at least the piezoelectric film and the lower electrode and reaches the sacrificial layer,
The method for manufacturing a thin film bulk acoustic resonator according to claim 9, wherein the sacrificial layer is removed through the opening. Before the step of forming the sacrificial layer, and further, forming a recess in the substrate,
The method for manufacturing a thin film bulk acoustic resonator according to claim 9, wherein the sacrificial layer is formed so as to be embedded in the recess. After the step of forming the upper electrode, an opening that penetrates the substrate from the back surface side of the formation surface of the elastic resonance film and exposes the lower electrode side surface of the elastic resonance film is formed to form a diaphragm structure. The method for manufacturing a thin film bulk acoustic resonator according to claim 1, further comprising a step of forming a substrate. Before the step of forming the lower electrode, further comprising the step of forming an acoustic reflection film on the substrate,
The method for manufacturing a thin film bulk acoustic resonator according to claim 1, wherein in the step of forming the lower electrode, the lower electrode is formed in an upper layer of the acoustic reflection film. A method for forming a piezoelectric film, comprising: forming a piezoelectric film on a substrate by non-reactive sputtering using a compound material that exhibits piezoelectricity as a target. A non-reactive sputtering chamber;
A substrate holding unit disposed in the non-reactive sputtering chamber and holding a substrate;
A target made of a compound material that expresses piezoelectricity disposed in the non-reactive sputtering chamber;
A power source for applying a voltage to the substrate and the target, applying a predetermined voltage to the substrate and the target, and depositing a compound material of the target on the substrate by non-reactive sputtering to form a piezoelectric film Non-reactive sputtering equipment to be formed.

Images