JP2008079328A - Piezoelectric thin film resonator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and miniaturized piezoelectric thin film resonator and its manufacturing method having superior characteristics, easy to be manufactured, and having a high yield. <P>SOLUTION: In the piezoelectric thin film resonator (FBAR) 1A in which a lower electrode 13, a piezoelectric thin film 12 formed of an aluminum nitride, and an upper electrode 14 are formed on a substrate 11, and an air gap 15 is formed at an area to be positioned under the lower electrode 13, each of the lower electrode 13 and the upper electrode 14 includes a layer of ruthenium or an alloy of the ruthenium, and the lower electrode is configured to be exposed to the air gap which is formed under it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric thin film resonator and a method for manufacturing the same, and more particularly to a piezoelectric thin film resonator in which voids are formed by etching with a fluorine-based gas and a method for manufacturing the same.

  2. Description of the Related Art In recent years, with the rapid spread of mobile communication devices typified by mobile phones, the demand for small and lightweight filters composed of surface acoustic wave (SAW) elements and the like is rapidly increasing. Among these, a surface acoustic wave filter (hereinafter referred to as a SAW filter) has a steep cut-off characteristic, and is small and light. Therefore, it is widely used particularly as an RF (Radio Frequency) filter and an IF (Intermediate Frequency) filter in mobile phones. ing.

  The SAW filter includes a piezoelectric element substrate (hereinafter referred to as a piezoelectric substrate) and a comb electrode (InterDigital Transducer: IDT) provided on one main surface of the piezoelectric substrate. According to the alternating voltage applied to the piezoelectric substrate, an elastic wave in a specific frequency band is excited on the surface of the piezoelectric substrate.

  In such a SAW filter, when a large electric power is applied to the comb-shaped electrode, the comb-shaped electrode itself is physically disconnected due to the distortion of the substrate due to the elastic wave. This defect becomes more prominent as the electrode finger width of the comb-shaped electrode becomes narrower, that is, the higher the frequency filter.

  As described above, the surface acoustic wave filter has a problem in power durability, and particularly has a problem when used as a filter in a front end portion of an antenna duplexer or the like.

  On the other hand, a piezoelectric thin film resonator (hereinafter referred to as “FBAR”) has conventionally existed as an effective means for configuring a filter suitable for a large power application. A piezoelectric thin film resonator has a substrate and a piezoelectric thin film sandwiched from above and below by an upper electrode and a lower electrode, which are metal thin films, and has a structure in which a gap is provided below the lower electrode in contact with the substrate Have In this configuration, when a potential difference is applied to the upper electrode and the lower electrode, the piezoelectric thin film sandwiched between them vibrates in the thickness direction due to the piezoelectric effect, and exhibits electrical resonance characteristics.

  A bandpass filter can be configured by connecting FBARs having such characteristics to a ladder type. At present, it is known that an FBAR filter represented by such a band-pass filter has extremely excellent power durability as compared with, for example, a SAW filter.

  The band-pass filter is required to have a low loss with respect to the pass frequency band and a large degree of suppression with respect to frequencies outside the pass frequency band. Therefore, when realizing a band-pass filter using FBAR, selection of the electrode material used for the upper electrode and the lower electrode is one of the important factors.

  The electrode material needs to be a film having a low resistance and a large acoustic impedance. Conventionally, an electrode structure as described below has been disclosed.

  For example, Patent Document 1 discloses an electrode structure using molybdenum (Mo) as an electrode material. Since a film formed of molybdenum (Mo) has low resistance and high acoustic impedance, excellent resonance characteristics can be obtained by using it for a piezoelectric thin film resonator.

  However, since molybdenum (Mo) is easily etched with a fluorine-based gas or an acid-based chemical, a method for forming a void under the lower electrode is limited. Here, several methods for providing a gap under the lower electrode will be described below.

  One of them is the method disclosed in Patent Document 2 shown below. In this method, a single crystal silicon substrate is anisotropically etched with a KOH solution or the like to open a through hole from the back surface of the substrate. Since molybdenum (Mo) is not etched with a KOH solution, this method can be used to easily form voids without damaging the lower electrode even when molybdenum (Mo) is used as the electrode material. .

As another method, there is a method disclosed in Patent Document 3 shown below. In this method, a sacrificial layer is deposited in a depression formed on a substrate, and after the lower electrode, piezoelectric thin film, and upper electrode are formed, the sacrificial layer is removed. More specifically, as a first step, for example, a recess is formed on the surface of a silicon (Si) substrate by etching. Next, as a second step, a thermal oxide film is formed on the silicon substrate surface. This is to prevent phosphorus (P) in PSG (phosphorus quartz glass) used as a sacrificial layer from diffusing into silicon (Si). When the thermal oxide film is thus formed, PSG is deposited as a third step to form a sacrificial layer. Next, as a fourth step, the surface of the deposited sacrificial layer is mirror-finished using polishing and cleaning, so that the sacrificial layer other than the depression is removed. Subsequently, as a fifth step, a lower electrode, a piezoelectric thin film, and an upper electrode are sequentially deposited on the surface of the silicon substrate including the sacrificial layer exposed flush with the surface of the silicon substrate. Finally, as the sixth step, the sacrificial layer is removed. To do. Thereby, an air gap is formed under the lower electrode. For example, a diluted H ₂ O: HF solution can be used for removing the sacrificial layer (PSG) in the sixth step. Thereby, since PSG can be etched at a very high etching rate, even when molybdenum (Mo) is used as an electrode material, it is possible to provide a gap below the lower electrode.

US Pat. No. 5,587,620 Japanese Patent Laid-Open No. 6-204776 JP 2000-69594 A

  However, a substrate having a through-hole formed by the method disclosed in Patent Document 2 has very low mechanical strength. For this reason, there is a problem that the manufacturing yield is lowered and the dicing process from the wafer and the mounting process on the package are extremely difficult. Further, since a through hole having an inclination angle of about 55 ° is formed in anisotropic etching, it is difficult to make a resonator-type connection by bringing the resonator close to each other, which is disadvantageous in terms of miniaturization of the element. Is also present.

  Furthermore, the method disclosed in Patent Document 3 has a very large number of steps and is difficult to manufacture at a low cost. In addition, there is a problem that the yield is low because the polishing process includes many problems such as slurry remaining.

  In view of the above problems, an object of the present invention is to provide an inexpensive and miniaturized piezoelectric thin film resonator having excellent characteristics, easy to manufacture, having a high yield, and a method for manufacturing the same. To do.

  In order to achieve this object, the present invention provides a piezoelectric thin film resonator having a piezoelectric thin film formed on a first surface of a substrate, and a lower electrode and an upper electrode formed so as to sandwich the piezoelectric thin film. The piezoelectric thin film is formed of aluminum nitride, the upper electrode and the lower electrode each include a layer of ruthenium or a ruthenium alloy, and the lower electrode is exposed to a gap formed thereunder. . The resistance value of the lower electrode and / or the upper part contributes to loss of resonance characteristics, and the acoustic impedance of the lower electrode and / or the upper electrode also contributes to anti-resonance characteristics. Therefore, by providing ruthenium or ruthenium alloy, which has low resistance and large acoustic impedance characteristics compared to commonly used electrode materials, on the lower electrode and the upper electrode, respectively, low loss and excellent anti-resonance characteristics are achieved. A piezoelectric thin film resonator can be obtained. In addition, ruthenium or ruthenium alloys are stable against fluorine-based gases and acid-based chemicals generally used in etching, that is, have a characteristic that they are not easily etched. Alternatively, by including a ruthenium alloy layer, it is possible to reduce the damage of the lower electrode and the upper electrode due to etching, and it is possible to improve the yield of the piezoelectric thin film resonator. Further, for the same reason, it is not necessary to use a special process, etching method, gas, chemicals, or the like, so that the manufacturing is easy and the manufacturing cost is low. Furthermore, since the gap can be formed so that the side surface is substantially perpendicular to the main surface of the substrate, a layout in which a plurality of resonators are close to each other can be achieved, resulting in miniaturization. A device can be obtained.

  The piezoelectric thin film resonator can be configured such that the aluminum nitride forming the piezoelectric thin film has an orientation with the (002) direction as the main axis. By setting the orientation of the piezoelectric thin film to the (002) direction, a piezoelectric thin film resonator exhibiting good resonance characteristics can be obtained.

  The piezoelectric thin film resonator may be configured such that the lower electrode includes the ruthenium or ruthenium alloy layer, and the ruthenium or ruthenium alloy layer has orientation with a (002) direction as a main axis. By setting the orientation of the piezoelectric thin film to the (002) direction, a piezoelectric thin film resonator exhibiting good resonance characteristics can be obtained. However, the orientation of the piezoelectric thin film largely depends on the orientation of the lower electrode formed thereunder. Therefore, by setting the orientation of the lower electrode in the (002) direction, the orientation of the piezoelectric thin film can be easily set in the (002) direction, and as a result, a piezoelectric thin film resonator having good resonance characteristics can be obtained. Can do.

  The piezoelectric thin film resonator may be configured such that a ratio d1 / d2 between a sum d1 of film thicknesses of the lower electrode and the upper electrode and a film thickness d2 of the piezoelectric thin film is 1/12 or more and 1 or less. By setting the ratio d1 / d2 to be 1/12 or more and 1 or less, it is possible to obtain a piezoelectric thin film resonator corresponding to a partial band at a frequency of about 100 MHz to about 100 GHz.

  The present invention also includes a first step of forming a lower electrode on the substrate, a second step of forming a piezoelectric thin film of aluminum nitride on the substrate so as to cover the lower electrode, and the piezoelectric thin film on the piezoelectric thin film. A method of manufacturing a piezoelectric thin film resonator having a third step of forming an upper electrode, wherein the first step includes a step of forming the lower electrode including a layer of ruthenium or a ruthenium alloy, Step 3 includes the step of forming the upper electrode including a layer of ruthenium or a ruthenium alloy, and the manufacturing method further includes a step of forming a void exposing the lower electrode under the lower electrode. It is a manufacturing method of a thin film resonator. Ruthenium or ruthenium alloy is stable against fluorine-based gas and acid-based chemicals that are generally used in etching, that is, has a characteristic that it is difficult to be etched. By including this layer, for example, it is possible to reduce damage to the first electrode due to etching when forming a void, and it is possible to improve the yield of the piezoelectric thin film resonator. Further, for the same reason, it is not necessary to use a special process, etching method, gas, chemicals, or the like, so that the manufacturing is easy and the manufacturing cost is low. Furthermore, since the gap can be formed so that the side surface is substantially perpendicular to the main surface of the substrate, a layout in which a plurality of resonators are close to each other can be achieved, resulting in miniaturization. A device can be manufactured. In addition, the piezoelectric thin film resonator manufactured in this way has low loss and excellent anti-resonance characteristics.

  In the manufacturing method, the first step forms the ruthenium or ruthenium alloy layer having an orientation with the (002) direction as the main axis, and the second step has an orientation with the (002) direction as the main axis. The aluminum nitride layer may be formed. By setting the orientation of the piezoelectric thin film to the (002) direction, a piezoelectric thin film resonator exhibiting good resonance characteristics can be obtained. However, the orientation of the piezoelectric thin film largely depends on the orientation of the lower electrode formed thereunder. Therefore, by setting the orientation of the lower electrode in the (002) direction, the orientation of the piezoelectric thin film can be easily set in the (002) direction, and as a result, a piezoelectric thin film resonator having good resonance characteristics can be obtained. Can do.

The first step may be configured to form the ruthenium or ruthenium alloy layer using a sputtering method with a sputtering pressure of 0.5 Pa or more. A piezoelectric thin film resonator having an internal stress including a ruthenium layer or a ruthenium layer greater than 3 GPa has a high possibility of breaking when a high-frequency input signal is applied. Further, the ruthenium film formed under the condition that the sputtering pressure during sputtering is less than 0.5 Pa has a large internal stress. For this reason, the internal pressure in the layer of ruthenium or a ruthenium alloy is reduced by setting the sputtering pressure at the time of sputtering to 0.5 Pa or more. As a result, a piezoelectric thin film resonator that is less likely to break can be manufactured.
Further, the step of forming the gap may be configured to form the lower electrode so that the entire lower electrode is exposed to the gap.

  According to the present invention, it is possible to realize an inexpensive and miniaturized piezoelectric thin film resonator having excellent characteristics, easy to manufacture, having a high yield, and a manufacturing method thereof.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  First, Embodiment 1 according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows a basic configuration of a piezoelectric thin film resonator (FBAR) 1A according to this embodiment. In FIG. 1, (a) is a plan view of the FBAR 1A, and (b) is a cross-sectional view taken along the line AA of (a).

  As shown in FIGS. 1A and 1B, the FBAR 1 </ b> A has a configuration in which a piezoelectric thin film 12 is formed on one main surface of a substrate 11. For example, a silicon (Si) substrate is used as the substrate 11. In the region where the resonator is formed in the piezoelectric thin film 12, a lower electrode 13 and an upper electrode 14 are formed at positions where the piezoelectric thin film 12 is sandwiched from above and below. A space (cavity) 15 is formed in the substrate 11, and the entire surface of the lower electrode 13 faces the space 15. The air gap 15 is for preventing vibration of the piezoelectric thin film 12 from being hindered when a high frequency signal is applied to the lower electrode 13 and the upper electrode 14.

  In such a configuration, the piezoelectric thin film 12 and the lower electrode 13 and the upper electrode 14 sandwiching the piezoelectric thin film 12 are as follows in order to realize excellent resonance characteristics and easy manufacturing.

For the piezoelectric thin film 12, for example, a thin film of lead titanate (PbTiO ₃ ), PZT, aluminum nitride (AlN) or the like can be used, but an AlN thin film is preferably used. This is due to the fact that PbTiO ₃ and PZT have a large number of components such as three or more elements and lead (Pb) diffuses, so that there is a drawback that the composition is very difficult to control and the mass productivity is poor. Because. On the other hand, since AlN has two elements and a small number of components and does not have the problem of lead diffusion, the use of this makes it possible to facilitate the manufacturing method and improve the yield.

  In this embodiment, for example, the ratio d1 / d2 between the sum d1 of the film thicknesses of the lower electrode 13 and the upper electrode 14 and the film thickness d2 of the piezoelectric thin film 12 is included in the range of 1/12 or more and 1 or less. By configuring, the pass frequency band of the FBAR 1A can be part of the frequency band included in 100 MHz to 10 GHz.

  Here, for the patterning of the piezoelectric thin film 12 and the formation of the gap 15, a fluorine-based gas or an acid-based chemical suitable for etching AlN (piezoelectric thin film 12) or silicon (substrate 11) is usually used. However, some commonly used electrode materials, such as molybdenum (Mo), are vulnerable to fluorine-based gases and acid-based chemicals, that is, those that are easily etched by these. Therefore, in this embodiment, ruthenium or a ruthenium alloy is used as an electrode material resistant to fluorine-based gas or acid-based chemicals, and at least one of the lower electrode and the upper electrode includes a thin film layer of ruthenium or ruthenium alloy. Specifically, a configuration in which at least one of the lower electrode and the upper electrode includes a thin film layer of ruthenium or a ruthenium alloy, specifically, one or both of the lower electrode and the upper electrode are formed as a single layer film of ruthenium or a ruthenium alloy. This means a configuration in which one or both of the lower electrode and the upper electrode are formed as a multilayer film, and a ruthenium or ruthenium alloy film is included in the multilayer film.

  The ruthenium alloy is a material containing ruthenium as a main component, for example, an alloy containing about 2% of copper (Cu) in ruthenium, an alloy containing about 2% of aluminum (Al) in ruthenium, or ruthenium. And an alloy containing about 2% of chromium (Cr).

  Further, the resistance of the lower electrode 13 and the upper electrode 14 contributes to loss of resonance characteristics, and the acoustic impedance of the lower electrode 13 and the upper mirror 14 also contributes to anti-resonance characteristics. Therefore, the present inventors have found that the lower electrode 13 and / or the upper electrode 14 are controlled so as to satisfy the following conditions in order to obtain good resonance characteristics and anti-resonance characteristics.

  First, since the specific resistance of the lower electrode 13 and the upper electrode 14 causes a loss of the input signal, it is controlled to be a sufficiently small value, for example, 50 μΩ · cm or less. By satisfying this condition, it is possible to reduce the loss of the input signal, which is a high-frequency signal, and obtain good resonance characteristics. The lower limit can be set to 1 μΩ · cm, for example.

Further, the acoustic impedance of the lower electrode 13 and the upper electrode 14 needs to be increased in order to obtain good anti-resonance characteristics. Here, the acoustic impedance is expressed by the square root of the product of elastic modulus and density. That is, a film having a large elastic modulus has a large acoustic impedance. Therefore, by using an electrode film having a large elastic modulus for the lower electrode 13 and the upper electrode 14, a resonator having excellent antiresonance characteristics can be obtained. For example, good anti-resonance characteristics can be obtained by forming the lower electrode 13 and / or the upper electrode 14 using an electrode film having an elastic modulus of 4 × 10 ¹¹ N / m or more.

  Since ruthenium and ruthenium alloys used in this embodiment have characteristics of lower resistance and higher acoustic impedance than commonly used electrode materials, it is possible to easily obtain an electrode film that satisfies the above conditions. . That is, in this embodiment, by forming at least one of the lower electrode 13 and the upper electrode 14 by using an electrode film partially including a film made of at least one of ruthenium and a ruthenium alloy, good resonance characteristics and anti-resonance are achieved. It is possible to obtain an FBAR indicating the characteristics.

  However, when AlN is used as the piezoelectric thin film 12, it is important that this exhibits (002) orientation in order to obtain good resonance characteristics. In order to make the piezoelectric thin film 12 have the (002) orientation, the orientation of the lower electrode 13 is the key. This is because the orientation of the lower electrode 13 greatly affects the orientation of the piezoelectric thin film 12 because the piezoelectric thin film 12 is formed on the lower electrode 13. Therefore, the lower electrode 13 is oriented with the (002) direction as the main axis, like the piezoelectric thin film 12. As a result, an AlN thin film exhibiting a good (002) orientation can be obtained.

  Further, as shown in FIG. 1B, a gap 15 is formed under the lower electrode 13. At this time, the substrate 11 used as the base of the lower electrode 13 and the piezoelectric thin film 12 is etched with an acid-based chemical such as a fluorine-based gas or buffered hydrofluoric acid as described above, but ruthenium or a ruthenium alloy. Is very stable against this fluorine-based gas and acid-based chemicals. Therefore, by forming the lower electrode 13 using this film, the lower electrode 13 can be prevented from being etched and stable. FBAR1A can be manufactured.

  In particular, when the substrate 11 is formed of a silicon substrate, a method of dry etching the substrate 11 in a direction perpendicular to the main surface of the substrate 11 (in other words, the substrate 11 is formed in a direction perpendicular to the main surface of the substrate 11). Fluorine-based gas is used in the method of forming the side surface of the gap 15 approximately perpendicularly to the main surface of the substrate 11 by dry etching. Even in such a case, the lower electrode 13 is made of ruthenium or a ruthenium alloy. By using the electrode film, the gap 15 can be easily formed, and it is possible to suppress a decrease in yield due to the etching of the lower electrode 13.

  As described above, ruthenium and ruthenium alloys are stable against fluorine-based gas and acid-based chemicals. Therefore, anisotropic etching using a KOH solution or the like is performed when forming the void 15 in the substrate 11. There is no need to use it. For this reason, it is possible to use dry etching using a fluorine-based gas that can make the side surface of the gap 15 a surface substantially perpendicular to the main surface of the substrate 11. Therefore, the resonator can be laid out closer to the layout than in the case of using anisotropic etching in which the side surface of the gap 15 is inclined with respect to the main surface of the substrate 11, and as a result, the device can be miniaturized. Become. In addition, since a step of forming a sacrificial layer for forming the void 15 and a step of polishing the sacrificial layer are not required, manufacturing can be facilitated and manufacturing cost can be reduced.

  However, for example, a method is used in which a sacrificial layer is formed in advance on the substrate 11, the lower electrode 13, the piezoelectric thin film 12, and the upper electrode 14 are formed thereon, and then the sacrificial layer is removed to form the void 15. Even in this case, by using an electrode film made of ruthenium or a ruthenium alloy, the lower electrode 13 can be similarly prevented from being etched, and can be stably manufactured without lowering the yield. Even when wet etching is used for patterning the piezoelectric thin film 12, the electrode film made of ruthenium or a ruthenium alloy is not etched, so that the yield does not decrease and the electrode film can be manufactured stably. Further, the same effect can be obtained even when dry etching is used for patterning the piezoelectric thin film 12.

  In this embodiment, the gap 15 needs to be formed to a size that allows the lower electrode 13 to be completely exposed. That is, all the substrate 11 under the lower electrode 13 is removed by etching. Thereby, it can prevent that the board | substrate 11 becomes the obstruction of excitation. However, the piezoelectric thin film 12 needs to be larger than the size of the gap 15 in order to fix it on the substrate 11.

  Next, a method for manufacturing FBAR 1A according to the present embodiment will be described in detail with reference to the drawings. In the following description, the upper electrode 14 is formed as a single layer film of ruthenium (Ru) from the top, the lower electrode 13 is formed as a multilayer film of molybdenum (Mo) and aluminum (Al) from the top, and the piezoelectric thin film 12 An example will be described in the case where is formed of aluminum nitride (AlN) and a silicon substrate is used as the substrate 11.

  In this manufacturing method, first, as shown in FIG. 2A, a silicon substrate 11A is used, and a conductive film 13A for patterning to the lower electrode 13 is formed on one main surface of the silicon substrate 11A by using, for example, a sputtering method. (See FIG. 2 (b)). The conductor film 13A has a multilayer structure in which, for example, a 50 nm (nanometer) aluminum (Al) film is formed on a silicon substrate 11A, and a 100 nm molybdenum (Mo) film is formed thereon.

  Next, a resist having a predetermined shape (a shape for leaving the lower electrode 13) is formed on the conductor film 13A using, for example, photolithography, and then patterned using, for example, dry etching or wet etching. Thus, as shown in FIG. 2C, the lower electrode 13 having a desired shape is formed. At this time, other wiring patterns, ground patterns, and the like may be patterned at the same time. For dry etching or wet etching, a fluorine-based gas or an acid-based chemical as described above can be used.

  Next, as shown in FIG. 2D, a piezoelectric thin film 12A is formed on the lower electrode 13 and the silicon substrate 11A by using, for example, a sputtering method, and further, as shown in FIG. 2E. Then, a conductor layer 14A for patterning on the upper electrode 14 is formed by using, for example, a sputtering method. The piezoelectric thin film 12A includes, for example, 500 nm of aluminum nitride (AlN). The conductor layer 14A has a single layer structure in which, for example, 100 nm of ruthenium (Ru) is formed on the piezoelectric thin film 12A.

  Next, after a resist having a predetermined shape (a shape for leaving the upper electrode 14 and the piezoelectric thin film 12) is formed on the conductor layer 14A by using, for example, a photolithography technique, dry etching or wet etching is performed thereon. By patterning, the upper mirror 14 (see FIG. 3A) and the piezoelectric thin film (see FIG. 3B) having a desired shape are formed. At this time, fluorine-based gas or acid-based chemical as described above can be used for dry etching or wet etching. In this step, lift-off may be used to form the upper electrode 14.

  When the resonator including the lower electrode 13, the piezoelectric thin film 12, and the upper electrode 14 is formed in this way, finally, a predetermined shape (a shape for forming the air gap 15) is formed on the back surface of the silicon substrate 11A using, for example, a photolithography technique. The substrate 11 in which the air gap 15 is formed is produced by performing dry etching from above. Thereby, FBAR1A as shown in FIG.1 and FIG.3 (c) is obtained.

When forming the gap 15, etching with CF _6, which is a fluorine-based gas, and side wall protective film formation with C ₄ F ₈ are alternately repeated, so that the side surface of the gap 15 is in contact with the back surface of the silicon substrate 11A. Thus, the gap 15 can be formed so as to be substantially vertical. However, it is not limited to this method, and other methods may be used.

  In the above, the ruthenium or ruthenium alloy layer contained in the lower electrode 13 and / or the upper electrode 14 may be formed by, for example, vacuum deposition, wet etching, ion milling, oxygen gas, etc. in addition to the sputtering method described above. It is possible to form by using reactive ion etching using a gas containing hydrogen, or a method combining two or more of these. Note that nitric acid or dicerium / ammonium nitrate can be used as an etchant when forming by wet etching.

  FIG. 4 shows the suppression at the attenuation pole of the FBAR 1A manufactured by the manufacturing method as described above. In FIG. 4, the resonance frequency is 5 GHz, and the cross section of the lower electrode 13 and the upper electrode 14 (cross section in a plane parallel to the main surface of the substrate 11) in the excitation unit is circular, and the radius of the cross sectional shape FBAR1A having a thickness of 80 μm (micrometer), and the electrode material of the upper electrode 14 is aluminum (Al), titanium (Ti), copper (Cu), chromium (Cr), molybdenum (Mo) or ruthenium (Ru) In this case, the suppression of the attenuation pole is shown.

  As can be seen from FIG. 4, the resonance characteristics of the FBAR 1 </ b> A vary greatly depending on the type of electrode material used for the upper electrode 14. More specifically, it can be seen that the suppression of the attenuation pole is increased by forming the upper electrode 14 with an electrode material having a large acoustic impedance. Therefore, by using ruthenium having high acoustic impedance as an electrode material, an FBAR having excellent resonance characteristics can be manufactured.

  Next, the band-pass filter 10 manufactured using the FBAR 1A according to this embodiment will be described in detail with reference to the drawings. FIG. 5 is a plan view showing the configuration of the bandpass filter 10 according to the present embodiment. FIG. 6 is a cross-sectional view of the bandpass filter 10 shown in FIG. FIG. 7 is a circuit diagram showing an equivalent circuit of the bandpass filter 10 shown in FIGS.

  As shown in FIGS. 5 and 7, the bandpass filter 10 includes four resonators (hereinafter referred to as series resonators) S1 to S4 connected in series and three resonances connected in parallel. This is configured to have children (hereinafter referred to as parallel resonators) P1 to P3. Each of the series resonators S1 to S4 and the parallel resonators P1 to P3 has the same configuration as the FBAR 1A shown in FIG. 1 as shown in FIGS.

  The upper electrodes 14 of the series resonators S1 and S4 provided at the input end and the output end in the band pass filter 10 are connected to the wiring 24, respectively. On this wiring 24, for example, a bump connection pad 22 having a laminated structure of a gold layer and a titanium layer is formed. Metal bumps 23 are formed on the bump connection pads 22 and can be connected to signal output terminals or signal input terminals on a die attach surface of a package (not shown), for example. The band-pass filter 10 is face-down bonded to the die attach surface of the package.

  The wiring 24 between the input end and the series resonator S1 is branched, and the upper electrode 14 of the parallel resonator P1 is connected. The lower electrode 13 in the parallel resonator P <b> 1 is connected to a wiring 21 that extends to a region other than the lower portion of the piezoelectric thin film 12. A bump connection pad 22 similar to that described above is formed on the wiring 21 in a region other than the lower portion of the piezoelectric thin film 12, and is configured to be connectable to a ground terminal on the die attach surface. Similarly, the wiring 24 between the series resonator S4 and the output end is branched, and the upper electrode 14 of the parallel resonator P3 is connected. The lower electrode 13 in the parallel resonator P3 is connected to a wiring 21 extending to a region other than the lower portion of the piezoelectric thin film 12. A bump connection pad 22 similar to the above is formed on the wiring 21 in a region other than the lower part of the piezoelectric thin film 12, and is configured to be connectable to the ground terminal on the die attach surface.

  Each of the series resonators S1 and S2 and the series resonators S3 and S4 has a lower electrode 13 connected via a wiring 21. Further, the upper electrodes 14 of the series resonators S <b> 2 and S <b> 3 are connected via a wiring 24.

  The wiring 24 connecting the series resonators S2 and S3 is branched, and the upper electrode 14 of the parallel resonator P2 is connected. The lower electrode 13 in the parallel resonator P2 is connected to a wiring 21 extending to a region other than the lower portion of the piezoelectric thin film 12. A bump connection pad 22 similar to that described above is formed on the wiring 21 in a region other than the lower portion of the piezoelectric thin film 12, and is configured to be connectable to a ground terminal on the die attach surface.

  As described above, by manufacturing the bandpass filter 10 using the FBAR 1A according to the present embodiment, a bandpass filter having a small insertion loss and good filter characteristics can be obtained.

  In the above description, the piezoelectric thin film 12 may be formed using, for example, zinc oxide (ZnO) instead of AlN. The lower electrode 13 and the upper electrode 14 may be formed using iridium (Ir), iridium alloy, rhodium (Rh), or rhodium alloy instead of ruthenium or a ruthenium alloy.

  Next, a second embodiment of the present invention will be described in detail with reference to the drawings. In Example 1 described above, the case where an electrode film including a layer of ruthenium or a ruthenium alloy is used as at least one of the lower electrode 13 and the upper electrode 14 is taken as an example. Therefore, in this embodiment, a case where an electrode film including a layer of ruthenium or a ruthenium alloy is used for both the lower electrode 13 and the upper electrode 14 is shown. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  8A and 8B are diagrams showing the configuration of the FBAR 1B according to the present embodiment. FIG. 8A is a plan view of the FBAR 1B, and FIG. 8B is a cross-sectional view taken along the line BB in FIG.

  As shown in FIGS. 8A and 8B, the FBAR 1B according to the present embodiment uses an electrode film in which the lower electrode 13 and the upper electrode 14 both include a layer of ruthenium or a ruthenium alloy in the FBAR 1A according to the first embodiment. The lower electrode 13b and the upper electrode 14b are formed. Other configurations are the same as those of the FBAR 1A according to the first embodiment.

  With the configuration described above, according to the present embodiment, the upper electrode 14b and the lower electrode in both the etching for forming the piezoelectric thin film 12 (including the upper electrode 14b) and the etching for forming the gap 15 are performed. Since the damage of 13b can be suppressed, the yield can be further improved.

  FIG. 9 shows the resonance characteristics (S (2, 1)) of the FBAR 1B according to this example. FIG. 9 shows an example in which the upper electrode 14b is formed with a 100 nm ruthenium film, the piezoelectric thin film 12 is formed with a 430 nm AlN film, and the lower electrode 13b is formed with a 100 nm ruthenium film.

  As is apparent from FIG. 9, in the FBAR 1B, the suppression at the resonance point is −3 dB or less, indicating a good resonance characteristic. On the other hand, the suppression at the antiresonance point is -20 dB or more, indicating a good antiresonance characteristic. Thus, by forming the lower electrode 13b and the upper electrode 14b with an electrode film including a layer of ruthenium or a ruthenium alloy, an FBAR exhibiting good resonance characteristics and anti-resonance characteristics can be obtained. Further, as described in the first embodiment, the loss can be reduced by using an electrode film including a layer of ruthenium or a ruthenium alloy.

  Other configurations and manufacturing methods are the same as those in the first embodiment, and thus the description thereof is omitted here.

  Next, a third embodiment of the present invention will be described in detail with reference to the drawings. In Example 1 described above, the case where an electrode film including a layer of ruthenium or a ruthenium alloy is used as at least one of the lower electrode 13 and the upper electrode 14 is taken as an example. In contrast, in this embodiment, a case where a thin film layer for preventing damage to the lower electrode 13 due to etching is provided on the gap 15 side of the lower electrode 13 is taken as an example. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 10 is a diagram showing a basic configuration of the FBAR 1C according to the present embodiment, in which (a) is a plan view of the FBAR 1C, and (b) is a cross-sectional view taken along the line CC of (a).

  As shown in FIGS. 10A and 10B, the FBAR 1C according to the present embodiment has the same configuration as the FBAR 1A according to the first embodiment, and the thin film layer 16 is formed below the lower electrode 13, that is, on the gap 15 side. It has a configuration. This prevents the lower electrode 13 from being exposed to the gap 15 and prevents the lower electrode 13 from being damaged during the etching for forming the gap 15. Other configurations are the same as those of the FBAR 1A according to the first embodiment.

The material of the thin film layer 16 is, for example, a pure metal of aluminum (Al), copper (Cu) or chromium (Cr), an alloy of aluminum (Al), copper (Cu) or chromium (Cr), or aluminum (Al). , Copper (Cu) or chromium (Cr) oxide, aluminum (Al), copper (Cu) or chromium (Cr) nitride, or the like can be applied. However, the present invention is not limited to these, and any material can be used as long as it is a material that is relatively stable with respect to etching using a fluorine-based gas. In the following description, a case where the thin film layer 16 is formed of alumina (Al ₂ O ₃ ) is taken as an example.

  With the configuration as described above, it is possible to reliably prevent damage to the lower electrode 13 due to etching when the air gap 15 is formed, so that the yield can be further improved.

  Next, the manufacturing method of FBAR1C according to the present embodiment will be described in detail with reference to the drawings. In the following description, the thin film layer 16 is formed of alumina, and the other configuration is an example in which the same configuration as the configuration described in FIGS. 2 and 3 is used.

  In this manufacturing method, first, as shown in FIG. 11A, a silicon substrate 11A is used, and on one main surface thereof, a thin film layer 16C for patterning to the thin film layer 16 and patterning to the lower electrode 13 are performed. The conductor film 13C is formed using, for example, a sputtering method (see FIG. 11B). The thin film layer 16C has, for example, a single layer structure in which 50 nm of alumina is formed on the silicon substrate 11A. The conductor film 13C has a single layer structure in which, for example, 100 nm of ruthenium is formed on the thin film layer 16C.

  Next, after a resist having a predetermined shape (a shape for leaving the lower electrode 13 and the thin film layer 16) is formed on the thin film layer 16C by using, for example, a photolithography technique, dry etching or wet etching is used on the resist. By patterning, the thin film layer 16 and the lower electrode 13 having a desired shape are formed as shown in FIG. At this time, other wiring patterns, ground patterns, and the like may be patterned at the same time. For dry etching or wet etching, a fluorine-based gas or an acid-based chemical as described above can be used.

  Next, as shown in FIG. 11 (d), a piezoelectric thin film 12A is formed on the lower electrode 13 and the silicon substrate 11A by using, for example, a sputtering method, and further, as shown in FIG. 11 (e). Then, a conductor layer 14A for patterning on the upper electrode 14 is formed by using, for example, a sputtering method. The piezoelectric thin film 12A has, for example, 420 nm of aluminum nitride (AlN). The conductor layer 14A has a single layer structure in which, for example, 100 nm of ruthenium (Ru) is formed on the piezoelectric thin film 12A.

  Next, after a resist having a predetermined shape (a shape for leaving the upper electrode 14 and the piezoelectric thin film 12) is formed on the conductor layer 14A by using, for example, a photolithography technique, dry etching or wet etching is performed thereon. By patterning, the upper mirror 14 (see FIG. 12A) and the piezoelectric thin film (see FIG. 12B) having a desired shape are formed. At this time, fluorine-based gas or acid-based chemical as described above can be used for dry etching or wet etching. In this step, lift-off may be used to form the upper electrode 14.

  When the resonator including the thin film layer 16, the lower electrode 13, the piezoelectric thin film 12, and the upper electrode 14 is formed in this manner, finally, a predetermined shape (gap 15 is formed on the back surface of the silicon substrate 11A by using, for example, a photolithography technique. The substrate 11 in which the air gap 15 is formed is manufactured by performing dry etching on the resist. Thereby, FBAR1C as shown in FIG.10 and FIG.12 (c) is obtained.

  FIG. 13 shows the resonance characteristics (S (2, 1)) of the FBAR 1C according to this example. In FIG. 13, the upper electrode 14 is formed of a 100 nm ruthenium film, the piezoelectric thin film 12 is formed of a 420 nm AlN film, the lower electrode 13 is formed of a 100 nm ruthenium film, and the thin film layer 16 is formed of a 50 nm alumina film. Take the case of

  As apparent from FIG. 13, in the FBAR 1C, the suppression at the resonance point is −3 dB or less, and a good resonance characteristic is shown. On the other hand, the suppression at the antiresonance point is -20 dB or more, indicating a good antiresonance characteristic. Thus, the lower electrode 13 and the upper electrode 14 are formed of an electrode film including a layer of ruthenium or a ruthenium alloy, and the thin film layer 16 for protecting the lower electrode 13 from etching is provided under the lower electrode 13. FBAR exhibiting excellent resonance characteristics and anti-resonance characteristics can be obtained. Further, as described in the first embodiment, the loss can be reduced by using an electrode film including a layer of ruthenium or a ruthenium alloy.

  Since other configurations are the same as those of the first embodiment, the description thereof is omitted here.

  Next, the relationship between the elastic modulus of the ruthenium film used for the lower electrode and / or the upper electrode and the suppression of the attenuation pole will be described in detail as Example 4 with reference to the drawings. In the following description, an example is given in which the elastic modulus of the ruthenium film forming the lower electrode 13b and the upper electrode 14b of the FBAR 1B described in the second embodiment is changed.

  FIG. 14 is a graph showing the relationship between the elastic modulus of the ruthenium film and suppression of the attenuation pole. As apparent from FIG. 14, the suppression of the attenuation pole increases as the elastic modulus of the ruthenium film increases. That is, the larger the elastic modulus of the lower electrode 13b and the upper electrode 14b, the better characteristics can be obtained.

  The elastic modulus of the ruthenium film can be controlled by changing the conditions for forming the ruthenium film, and the manufacturing method thereof is the same as the process described in the first embodiment.

  Other configurations and manufacturing methods are the same as those in the first embodiment, and thus the description thereof is omitted here.

  Next, when the lower electrode 13 and / or the upper electrode 14 are formed of ruthenium, the influence of the internal stress of the ruthenium film on the strength of the device (FBAR or a filter produced using the same) will be described in the following examples. 5 will be described in detail. In the present embodiment, description will be given using the FBAR 1A shown in the first embodiment.

  In this embodiment, by changing the film formation conditions of the ruthenium film, a plurality of FBARs 1A including the ruthenium film having different internal stresses in the lower electrode 13 and / or the upper electrode 14 are produced, and these are used to form the interior of the ruthenium film. The relationship between stress and device failure was investigated.

  As a result, for example, when an input signal of about 5 GHz was given, most of the FBAR 1A having a ruthenium film having an internal stress greater than 3 GPa was destroyed. In particular, it has been found that a ruthenium film formed under a condition where the sputtering pressure during sputtering is less than 0.5 Pa has a large internal stress, and the device is frequently destroyed.

  As is clear from these results, when the lower electrode 13 and / or the upper electrode 14 are produced using an electrode film containing a ruthenium or ruthenium alloy layer, the internal stress of the layer made of ruthenium or ruthenium alloy is 3 GPa or less. It is preferable that As a result, an FBAR with reduced device breakdown can be obtained.

  In order to control the internal stress of the lower electrode 13, a pure metal such as aluminum (Al), copper (Cu) or chromium (Cr), or aluminum (Al) is provided below the lower electrode 13 (on the gap 15 side). , Copper (Cu) or chromium (Cr) alloy, aluminum (Al), copper (Cu) or chromium (Cr) oxide, or aluminum (Al), copper (Cu) or chromium (Cr) nitride A thin film layer may be formed. Thereby, the same effect as the case where the internal stress of the lower electrode 13 is controlled to 3 GPa or less can be obtained.

  Since other configurations and manufacturing methods in the fifth embodiment are the same as those in the first embodiment, description thereof is omitted here.

  In addition, the first to fifth embodiments described above are merely examples for carrying out the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention. It is obvious from the above description that various other embodiments are possible within the scope of the present invention.

It is a figure which shows the basic composition of FBAR1A by Example 1 of this invention, (a) is a top view of FBAR1A, (b) is AA sectional drawing of (a). It is a figure which shows the manufacturing method of FBAR1A by Example 1 of this invention (1). It is a figure which shows the manufacturing method of FBAR1A by Example 1 of this invention (2). It is a figure which shows suppression in the attenuation pole of FBAR1A by Example 1 of this invention. It is a top view which shows the structure of the band pass filter 10 by Example 1 of this invention. It is A'-A 'sectional drawing of the band pass filter 10 shown in FIG. FIG. 7 is a circuit diagram showing an equivalent circuit of the bandpass filter 10 shown in FIGS. 5 and 6. It is a figure which shows the basic composition of FBAR1B by Example 2 of this invention, (a) is a top view of FBAR1B, (b) is BB sectional drawing of (a). It is a figure which shows the resonance characteristic (S (2, 1)) of FBAR1B by Example 2 of this invention. It is a figure which shows the basic composition of FBAR1C by Example 3 of this invention, (a) is a top view of FBAR1C, (b) is CC sectional drawing of (a). It is a figure which shows the manufacturing method of FBAR1C by Example 3 of this invention (1). It is a figure which shows the manufacturing method of FBAR1C by Example 3 of this invention (2). It is a figure which shows the resonance characteristic (S (2, 1)) of FBAR1C by Example 3 of this invention. It is a graph which shows the relationship between the elasticity modulus of the ruthenium film | membrane in Example 4 of this invention, and suppression of an attenuation pole.

Explanation of symbols

1A, 1B, 1C FBAR
DESCRIPTION OF SYMBOLS 10 Band pass filter 11 Substrate 11A Silicon substrate 12, 12A Piezoelectric thin film 13, 13b Lower electrode 13A, 14A Conductive film 14, 14b Upper electrode 15 Air gap 16, 16C Thin film layer 21, 24 Wiring 22 Bump connection pad 23 Metal bump P1 P3 parallel resonator S1-S4 series resonator

Claims (10)

A piezoelectric thin film resonator having a piezoelectric thin film formed on a first surface of a substrate, and a lower electrode and an upper electrode formed so as to sandwich the piezoelectric thin film,
The piezoelectric thin film is formed of aluminum nitride;
Each of the upper and lower electrodes includes a layer of ruthenium or ruthenium alloy,
The piezoelectric thin film resonator according to claim 1, wherein the lower electrode is exposed to a gap formed thereunder. 2. The piezoelectric thin film resonator according to claim 1, wherein the entire lower electrode is exposed in the gap. 3. The piezoelectric thin film resonator according to claim 1, wherein each of the upper electrode and the lower electrode includes a ruthenium alloy layer. 4. The piezoelectric thin film resonator according to claim 1, wherein the aluminum nitride forming the piezoelectric thin film has an orientation having a (002) direction as a main axis. 5. The lower electrode comprises the ruthenium or ruthenium alloy layer;
4. The piezoelectric thin film resonator according to claim 1, wherein the ruthenium or ruthenium alloy layer has an orientation with a (002) direction as a main axis. 5. The ratio d1 / d2 between the sum d1 of the film thicknesses of the lower electrode and the upper electrode and the film thickness d2 of the piezoelectric thin film is 1/12 or more and 1 or less. The piezoelectric thin film resonator as described. A first step of forming a lower electrode on the substrate; a second step of forming a piezoelectric thin film of aluminum nitride on the substrate so as to cover the lower electrode; and a second step of forming an upper electrode on the piezoelectric thin film. A method of manufacturing a piezoelectric thin film resonator having three steps,
The first step includes forming the lower electrode including a layer of ruthenium or a ruthenium alloy,
The third step includes forming the upper electrode including a layer of ruthenium or a ruthenium alloy,
The method for manufacturing a piezoelectric thin film resonator according to claim 1, further comprising a step of forming a gap in which the lower electrode is exposed under the lower electrode. The first step includes a step of forming a layer of the ruthenium or ruthenium alloy having orientation with a (002) direction as a main axis,
8. The method of manufacturing a piezoelectric thin film resonator according to claim 7, wherein the second step includes a step of forming the aluminum nitride layer having an orientation with a (002) direction as a main axis. 9. The piezoelectric thin film resonance according to claim 7, wherein in the first step, the ruthenium or ruthenium alloy layer is formed using a sputtering method with a sputtering pressure of 0.5 Pa or more. Child manufacturing method. 10. The method of manufacturing a piezoelectric thin film resonator according to claim 7, wherein the step of forming the gap forms the lower electrode so that the entire lower electrode is exposed to the gap. Method.

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