JP2007019758A - Thin film piezo-electricity resonant element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a lower part cavity whose shape control is good when a thin film piezo-electricity resonant element is formed on a high resistance Si substrate which has high resistivity of 100 Ω cm or more. <P>SOLUTION: The thin film piezo-electricity resonant element FRi is formed on an Si substrate 1 with high resistivity of 100 Ω cm or more; and has a first electrode 2, a piezo-electric film 4, and a second electrode 3. In its manufacturing method, the cavity is adjusted and formed so that an etching speed of a central part of a penetrating bottom plane becomes large by repeating etching of mainly SF<SB>6</SB>gas and deposition of mainly C<SB>4</SB>F<SB>8</SB>gas, and adjusting bias voltage to be impressed on the substrate when a through-hole 5 is formed as the lower cavity 4 of the thin film piezo-electricity resonant element FRi, so as to penetrate through the Si substrate in the Si substrate 1 just under the thin film piezo-electricity resonant element FRi. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a thin film piezoelectric resonator element and a thin film piezoelectric resonator element, and more particularly to a method for manufacturing a thin film piezoelectric resonator element used as a passive component such as a high-frequency band filter or an oscillator and a thin film piezoelectric resonator element.

  2. Description of the Related Art In recent years, a radio communication system having a frequency in the GHz band has been actively developed, represented by a hot spot service of a mobile phone that has been rapidly spread and a notebook personal computer (notebook PC) that has recently started up. The use frequency of these wireless communication systems tends to increase with the demand for the amount of information to be transmitted and received, and is practically used up to 5 GHz. In a high frequency circuit in a wireless communication system, a filter is used in an analog circuit portion. Ceramic filters and SAW filters have been conventionally used in this high-frequency circuit, but it is difficult to reduce the size of the circuit with ceramic filters, and SAW filters (Surface Acoustic Wave) are used due to problems with power durability at high frequencies. The upper limit of the frequency is suppressed to about 1 GHz, and further, it is becoming difficult to cope with the portable radio communication system in the GHz band because these devices cannot be integrated on Si.

  There is a strong demand for downsizing, thinning, and weight reduction of these high-frequency communication devices. It is very important that high-frequency communication devices for mobile phones and personal computers (PCs) are manufactured with the aim of reducing volume in order to be built in or to be mounted in a PC card slot. Wireless devices mounted on these devices are generally classified into an RF front-end unit that processes high-frequency (RF) signals and a baseband unit that performs digital signal processing. Of these, the baseband portion is a portion that performs signal modulation / demodulation by digital signal processing, and can basically be constituted by an LSI chip based on a silicon substrate. For this reason, the height of a baseband part can be easily reduced to less than 1 mm. On the other hand, the RF front end unit is a portion that performs amplification, frequency conversion, and the like using a high-frequency signal as an analog signal. For this reason, a complicated configuration including many passive components such as an oscillator and a filter is required, and it is difficult to configure the RF front end portion only with an LSI chip. Among passive components, a dielectric filter or an LC filter has been conventionally used as a filter. Since these filters filter high-frequency signals using the passband characteristics of a cavity resonator or an LC circuit, it is essentially difficult to reduce the size, and it is extremely difficult to reduce the height to several millimeters or less. For this reason, there has been a limit to the reduction in size and thickness of these high-frequency devices, in particular, volume saving by combining them.

  In order to solve such problems, a thin film piezoelectric resonator (FBAR) is drawing attention. This thin film piezoelectric resonator is a thin film piezoelectric resonator formed by sandwiching a thin film piezoelectric body made of aluminum nitride (AlN) or zinc oxide (ZnO) between two electrodes and straddling a cavity formed in a substrate. . This cavity may penetrate to the back surface of the substrate, or may be just under the first electrode. The thin-film piezoelectric resonance element confines vibration energy in the piezoelectric film by the action of the cavity, and obtains frequency resonance in the thickness direction of the first and second electrodes in contact with the air layer and the piezoelectric film.

Further, instead of the cavity directly under the thin film piezoelectric resonator, a reflector is formed by alternately laminating a layer having a high acoustic impedance and a layer having a low acoustic impedance at a thickness of λ / 4 of the resonance frequency of the thin film piezoelectric resonator. In some cases, vibration energy is confined in the piezoelectric film, and frequency resonance is obtained in the thickness direction of the first electrode, the second electrode, and the piezoelectric film. In this case, the reflector uses a multilayer film in which tungsten (W) is laminated as a high impedance layer and silicon dioxide (SiO ₂ ) is laminated as a low impedance layer.

  Among these, the thin film piezoelectric resonator element formed so as to straddle the cavity formed in the substrate forms a reflector in which layers with high and low acoustic impedance, which require high-precision film thickness control, are alternately stacked. Compared to a thin film piezoelectric resonator, the manufacturing is much easier industrially. Further, the method of forming the cavity from the back surface of the substrate to the position immediately below the first electrode is different from the method in which the cavity is only directly below the first electrode, in that the first electrode called sticking during the wet process or the subsequent use and the portion immediately below the first electrode. It has the feature that there is no defect such as sticking, and the production yield can be easily increased.

  The thickness of the piezoelectric film of 0.5 μm to several μm, which is an easy range for forming these thin film piezoelectric resonator elements, corresponds to a resonance frequency of several GHz, and resonance in the high frequency region of the GHz band. Is advantageous.

  By arranging a plurality of these thin film piezoelectric resonance elements in series or in parallel to form a ladder type filter, it can be used as an RF filter for a mobile communication device. Further, by combining a thin film piezoelectric resonance element, a variable capacitor, and an amplifier, it can be used as a voltage controlled oscillator (VCO) of a mobile communication device. An example of a filter using this thin film piezoelectric resonator is a publication of “IEEE Transactions on ultrasonics, ferroelectrics, and frequency control, Vol. 47, No. 1, p. 292, January 2000” (Non-patent Document 1). Is disclosed. This non-patent document 1 discloses that a ladder filter 102 as shown in FIG. 9 can be used as an RF filter of a mobile communication device. The ladder filter 102 is configured by arranging a plurality of thin film piezoelectric resonance elements 101 in series-parallel connection. Further, the thin film piezoelectric resonance element 101 may be used in a voltage controlled oscillator (VCO) 103 of a mobile communication device in combination with a variable capacitor 104 and an amplifier 105 as shown in FIG. In FIG. 10, 106 is a feedback resistor and 107 is a damping resistor. The structure of a conventional typical thin film piezoelectric resonator element is disclosed in Japanese Patent Laid-Open No. 2000-69594 (Patent Document 1).

  Since this thin film piezoelectric resonant element is formed as a thin film on a semiconductor substrate, it is very easy to reduce the size, particularly to reduce the volume. In particular, regarding the height of the element, it is possible to easily realize a dimension of less than 1 mm, which is difficult with an existing filter. Also, it can be easily formed on a semiconductor substrate together with a transistor, IC, and LSI, and can be formed together with these elements by omitting mounting on the same plane.

However, when a thin film piezoelectric resonant element is fabricated on a Si substrate via SiO ₂ and a cavity is formed from the back surface of the Si substrate to the SiO ₂ film immediately below the first electrode, the shape inside the cavity is not controlled appropriately. It is difficult to obtain a thin film piezoelectric resonance element having sufficient high frequency characteristics and reliability. A BOSCH deep-RIE (Reactive Ion Etching) apparatus is used for such deep Si etching from the back surface of the substrate. This etching is performed by sequentially repeating two steps consisting of a step of forming a protective film on the cavity side wall using C ₄ F ₈ gas and an isotropic etching step of Si using SF ₆ gas, so that the selectivity ratio with respect to the photoresist is increased. Has a high value of about 50 to 200, and the Si etching rate per minute is as fast as 5 to 10 μm. Since this Si etching has a high selection ratio with the SiO ₂ film as in the photoresist, the SiO ₂ film immediately below the first electrode acts as an etching stop layer. Further, in this Si etching process, etching process marks called scallops are formed on the side walls of the Si cavity by two processes including a protective film forming process and an isotropic etching process. Since this is formed on the peripheral side wall of the cavity, it can be observed as a horizontal striped pattern in the longitudinal section of the cavity.

The thin film piezoelectric resonance element is used in a high frequency band where the resonance frequency is several GHz as described above. The circuit pattern is formed on SiO ₂ formed on the surface of the Si substrate. However, since the circuit pattern is used in a high frequency band of several GHz, there is a problem that the SiO ₂ film acts as a capacitance between the circuit patterns and deteriorates high frequency characteristics. is there. In order to avoid this, there is no problem if the Si ₂ film thickness is set to 5 μm or more or a Si substrate having a high resistivity exceeding 100 Ω · cm is used. In a high frequency circuit of several GHz band, a dense SiO ₂ film having a thermal oxidation level is required, so that it is not practical to form a SiO ₂ film having a thickness exceeding 5 μm. For this reason, use of a high resistance Si substrate is inevitable.

In the BOSCH type Deep-RIE, when an ordinary Si substrate having a low resistivity is used, etching can be performed while controlling the shape inside the cavity, and the formation of the cavity is easy. However, when cavitation etching is applied to the high-resistance high-resistance Si substrate described above, there is a problem that charge-up occurs during etching due to an increase in substrate resistance, and shape control inside the cavity becomes extremely difficult. . FIG. 11 shows typical defects due to difficulty in shape control, such as a wall surface roughness 112, a notch, and a taper 113 generated by the charge-up 111 when the cavity 110 is formed. Among them, a notch, a taper 113 is the largest influence on the cavity area immediately below the thin-film piezoelectric resonator element, frequency characteristics of the thin film piezoelectric resonator element, the deterioration of the quality factor Q and coupling coefficient k ^2, which leads to spurious. Moreover, since the wall surface roughness 112 increases the surface area of the wall surface, F gas during etching is adsorbed, causing a decrease in reliability. Thus, the deterioration of the shape controllability in the cavity formation has a very important influence on the characteristics of the thin film piezoelectric resonance device, and it has been desired to solve the above problems.
JP 2000-69594 A “IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control”, Vol. 47, no. 1, p. 292, January 2000.

  The present invention has been made in view of the above-described conventional technical problems, and is a thin film capable of forming a cavity with particularly good shape controllability when forming a thin film piezoelectric resonant element on a high resistance Si substrate having a high resistivity. An object of the present invention is to provide a method for manufacturing a piezoelectric resonant element and a thin film piezoelectric resonant element.

The present invention relates to a method of manufacturing a thin film piezoelectric resonance element having a first electrode, a piezoelectric film, and a second electrode, wherein the thin film piezoelectric element penetrates the Si substrate directly under the thin film piezoelectric resonance element. When forming a through-hole serving as a lower cavity of the resonant element, by repeatedly performing etching mainly using SF ₆ gas and depositing mainly containing C ₄ F ₈ gas, and adjusting the bias power applied to the Si substrate The through hole is formed such that the etching rate of the central portion of the bottom surface of the through portion is higher than that of the surrounding portion.

In the method for manufacturing a thin film piezoelectric resonator of the present invention, the bias power voltage applied to the Si substrate may be a rectangular wave. Further, in the thin film piezoelectric resonator, by supplying an etching gas mainly composed of SF ₆ gas and a deposition gas mainly composed of C ₄ F ₈ gas, the step of the side wall is viewed from the bottom of the Si substrate, and the thin film piezoelectric resonance is observed. The through hole can be formed so as to be convex toward the element side.

  In the method for manufacturing a thin film piezoelectric resonator of the present invention, a plurality of thin film piezoelectric resonators are simultaneously formed in parallel or in series on the high-resistance Si substrate, and the Si substrate immediately below each of the thin film piezoelectric resonators is formed on the Si substrate. A through hole serving as a lower cavity of each of the thin film piezoelectric resonator elements may be formed so as to penetrate the Si substrate.

In the method of manufacturing the thin-film piezoelectric resonator element of the present invention, furthermore, the etching mainly the SF ₆ gas, SF ₆ gas flow rate 10 to 1000 sccm, the chamber gas pressure 0.1～30Pa, etching time 0.1 30 s, RF (13.56 MHz) power 0.1 to 100 kW, bias (300 kHz) applied power 5 to 1000 W, bias rectangular wave maximum power 10 to 500 W, bias rectangular wave maximum power holding time 5 to 500 ms, bias rectangular wave minimum power 0～250W, conducted under conditions of bias square wave minimum power retention time 1～100Ms, deposited mainly the _C 4 _{F 8 gas,} C 4 _{F 8} gas flow rate 5～900Sccm, the gas pressure of the chamber 0.1 ~ 27Pa, etching time 0.3 ~ 28s, RF (13.56MHz) power 0 1 to 100 kW, bias (300 kHz) applied power 5 to 200 W, bias rectangular wave maximum power 10 to 450 W, bias rectangular wave maximum power holding time 5 to 500 ms, bias rectangular wave minimum power 0 to 250 W, bias rectangular wave minimum power holding time The etching is performed under the condition of 1 to 120 ms, and the repetition time of the etching mainly including the SF ₆ gas and the deposition mainly including the C ₄ F ₈ gas may be 5 to 240 minutes.

  In the thin film piezoelectric resonator of the present invention, a first electrode, a piezoelectric film, and a second electrode are sequentially stacked on a Si substrate, a cavity is formed in a portion immediately below the first electrode on the Si substrate, and A step is formed on the side wall of the cavity so as to protrude toward the first electrode and the piezoelectric film when the Si substrate is viewed from the bottom.

According to the present invention, in etching for forming a cavity opened from the back surface of a high-resistance Si substrate having a high resistivity of 100 Ω · cm or more directly below the thin-film piezoelectric resonator, the cavity wall surface roughness and notch caused by charge-up are formed. prevents a decrease in k ² and Q shows the performance of the thin film piezoelectric resonator element tapered and leads, it is possible to provide a further method of manufacturing highly reliable after mounting can be manufactured FBAR element can be maintained, also such It is possible to provide a thin film piezoelectric resonance element having excellent characteristics.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. A thin film piezoelectric resonant element manufactured by a manufacturing method according to one embodiment of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). The thin film piezoelectric resonant element shown in FIGS. 1A and 1B is a thin film piezoelectric resonant element having a cavity 4 immediately below the first electrode 3. 1A and 1B, a cavity 4 penetrating to the back surface of the substrate 1 is opened, and the first electrode 3, the piezoelectric film 7, and the second electrode 8 are formed on the substrate 1 across the cavity 4. Is formed on the oxide film 2 as an insulating film.

  FIG. 2 shows an RF filter as a thin film piezoelectric resonance device, in which nine thin film piezoelectric resonance elements shown in FIG. 1 are connected in series or in parallel. The circuit configuration of the RF filter is shown in FIG. An oxide film 2 made of, for example, silicon oxide is provided on the silicon substrate 1 as an insulating film, and a first electrode 3 of a thin film piezoelectric resonance element is provided on the oxide film 2. Three first electrodes 3 are provided, and each of the first electrodes 3 is configured to be a common first electrode for the three thin film piezoelectric resonance elements. A cavity 4 penetrating the oxide film 2 and the silicon substrate 1 is provided immediately below the first electrode 3 at a position where each thin film piezoelectric resonance element is provided.

  On the other hand, a piezoelectric film 7 is provided on the front surface of the silicon substrate 1 provided with the oxide film 2 so as to cover the three first electrodes 3. On the piezoelectric film 7, there are provided second electrodes 8 of nine thin film piezoelectric resonance elements that also serve as wirings for connecting the nine thin film piezoelectric resonance elements in series or in parallel. In the thin film piezoelectric resonator according to the present embodiment, seven second electrodes 8 are provided. An insulating film 9 made of, for example, silicon nitride SiNx is provided on the piezoelectric film 7 so as to cover the second electrodes 8. A wiring electrode 10 electrically connected to the second electrode 8 serving as a terminal of an RF filter in which nine thin film piezoelectric resonance elements are connected in series or in parallel is provided on the side of the piezoelectric film 7. The electrode 10 is configured to extend on the oxide film 2.

  Next, a method for manufacturing a thin film piezoelectric resonance element for manufacturing the thin film piezoelectric resonance device having the above configuration will be described with reference to FIGS. First, a material film for the first electrode 3 such as Mo, Al, Ir, etc. on a high resistance silicon substrate 1 having a resistivity of 100 to 2000 Ω · cm and a substrate thickness of 25 to 900 μm on which an oxide film 2 as an insulating film is formed. As shown in FIG. 3A, a metal film is formed by sputtering, a pattern using, for example, a positive resist (OFPR-5000) made by Tokyo Ohka is formed by lithography, and the electrode material film is patterned. The first electrode 3 is formed. The patterning is performed by wet etching or dry etching. For example, it can be processed by dry etching using a chlorine gas and a boron trichloride gas by a magnetron-type M-RIE (Magnetron-reactive ion etching apparatus). In the present embodiment, three first electrodes 3 are formed as shown in FIG. The film thickness of the first electrode 3 is 20 to 900 nm.

  Subsequently, as shown in FIG. 3B, for example, AlN, ZnO, PZT or the like is formed by sputtering as a film of a piezoelectric material so as to cover the first electrode 3 so as to have a film thickness of 0.4 to 10 μm. Then, the piezoelectric film 7 is formed by patterning the film of the piezoelectric material using a lithography technique. Here, in the case of an AlN piezoelectric material film, the sputtering is performed by RF sputtering using an Al target and nitrogen gas. In addition, the AlN film is processed by forming a pattern using a positive resist (PEMR P-LA900PM) made by Tokyo Ohka by lithography, and dry etching using chlorine gas and boron trichloride gas by the same M-RIE as above. To process.

  Next, for the purpose of making the resonance frequency different between the thin film piezoelectric resonator elements connected in series and the thin film piezoelectric resonator elements connected in parallel, as shown in FIG. On top of this, for example, a load electrode 15 is formed using a metal film of Mo, Al, and Ir. When a Mo film is used for the load electrode 15, the film is formed by sputtering. In this process, a pattern using a positive resist (OFPR-5000) manufactured by Tokyo Ohka is formed by lithography, and four films are formed by M-RIE. Processed by dry etching using methane gas. Thereafter, a metal film such as Al, Mo, Ir or the like is formed on the entire surface of the substrate 1 as an electrode material film, and the electrode material film is patterned using a lithography technique, thereby forming a first film as shown in FIG. Two electrodes 8 are formed. The method for forming and processing the second electrode 8 is the same as that for the first electrode 3. The film thickness is 20 nm to 900 nm. As a result, nine thin film piezoelectric resonance elements FR1 to FR9 in which the piezoelectric film 7 is sandwiched between the first electrode 3 and the second electrode 8 are formed. Seven second electrodes 8 are formed, and one of the seven second electrodes 8 also serves as a wiring for connecting the thin film piezoelectric resonance element FR2 and the thin film piezoelectric resonance element FR3, and the other second electrode 8 Reference numeral 8 also serves as a wiring for connecting the thin film piezoelectric resonance element FR4 and the thin film piezoelectric resonance element FR5. In FIG. 3 (d), the thin film piezoelectric resonance element FRi is shown surrounded by a dashed-dotted line.

  Next, as shown in FIGS. 4A and 4B, a metal film of Al, Au, Cu or the like is formed as a wiring electrode material on the entire surface of the substrate 1, and the above electrode material is used by using a lithography technique. By patterning the film, five wiring electrodes 10 respectively connected to the second electrodes 8 of the thin film piezoelectric resonance elements FR1, FR6, FR7, FR8, FR9 are formed on the side portion of the piezoelectric film 7. These wiring electrodes 10 extend not only on the sides of the piezoelectric film 7 but also on the oxide film 2. The method for forming and processing the wiring electrode 10 is the same as that for the first electrode 3. The film thickness is 500 nm to 20 μm. After the formation of the wiring electrode 10, the back surface of the silicon substrate 1 is polished so that the thickness of the silicon substrate 1 is 25 μm to 400 μm.

  Next, as shown in FIG. 5, a film such as silicon nitride SiNx, SiO2, or AlN is formed to have a thickness of about 10 to 900 nm using CVD (Chemical Vapor Deposition) so as to cover the second electrode 8 on the piezoelectric film 7. A passivation film 9 is formed by forming a film and patterning the film using a lithography technique. The passivation film 9 is not formed on the wiring electrode 10.

  Next, etching is performed from the back surface of the silicon substrate 1 using a BOSCH-type ICP-RIE (Inductively coupled plasma-reactive ion etching) apparatus shown in FIG. The silicon substrate 1 and the oxide film 2 immediately below are removed, and cavities 4 are formed immediately below the thin film piezoelectric resonance elements FRi. In the RIE apparatus shown in FIG. 7, 51 is a laser spectroscopic observation window, 52 is an alumina container, 53 is an RF coil antenna, and 54 is a wafer gripping apparatus.

A method for forming a cavity in the silicon substrate 1 immediately below each of the thin film piezoelectric resonance elements FRi will be described in detail below. The pattern of the cavity 4 is formed by a lithography technique using a positive resist (PEMR P-LA900PM) manufactured by Tokyo Ohka. Next, the Si cavity 4 is formed by the ICP-RIE apparatus described above, but etching mainly including SF ₆ gas and deposition mainly including C ₄ F ₈ gas are repeated, and the bias voltage applied to the substrate 1 is adjusted. By doing so, the cavity 4 is formed so that the etching rate of the central portion of the bottom surface of the penetrating portion is higher than that of the surrounding portion.

Etching mainly composed of SF ₆ gas includes SF ₆ gas flow rate of 10 to 1000 sccm, chamber gas pressure of 0.1 to 30 Pa, etching time of 0.1 to 30 s, RF (13.56 MHz) power of 0.1 to 100 kW, bias (300 kHz) Applied power 5 to 1000 W, bias rectangular wave maximum power 10 to 500 W, bias rectangular wave maximum power holding time 5 to 500 ms, bias rectangular wave minimum power 0 to 250 W, bias rectangular wave minimum power holding time 1 to 100 ms It is preferable to carry out at.

The deposition mainly composed of C ₄ F ₈ gas has a C ₄ F ₈ gas flow rate of 5 to 900 sccm, a chamber gas pressure of 0.1 to 27 Pa, an etching time of 0.3 to 28 s, and an RF (13.56 MHz) power of 0.1. -100 kW, bias (300 kHz) applied power 5 to 200 W, bias rectangular wave maximum power 10 to 450 W, bias rectangular wave maximum power holding time 5 to 500 ms, bias rectangular wave minimum power 0 to 250 W, bias rectangular wave minimum power holding time 1 It is preferable to carry out under the condition of ~ 120 ms. The repetition time of etching mainly composed of SF ₆ gas and deposition mainly composed of C ₄ F ₈ gas is preferably 5 to 240 minutes.

Next, the oxide film 2 is removed with C ₄ F ₈ gas and oxygen gas under conditions of RF (13.56 MHz) power 0.01 to 1 kW and etching time 5 to 500 minutes at a pressure of 0.1 to 10 Pa. To do.

In the thin-film piezoelectric resonator manufactured by the above-described method for manufacturing a thin-film piezoelectric resonator, as shown in FIG. 8, step 12 of the side wall 11 that protrudes toward the thin-film piezoelectric resonator FRi when the Si substrate 1 is viewed from the bottom. Is obtained. This step 12 shows the tip of the cavity etching in which etching mainly composed of SF ₆ gas and deposition mainly composed of C ₄ F ₈ gas were repeated. As a result, the cavity 4 is formed so as to increase the etching rate at the central portion of the bottom surface of the penetrating portion, and the shape defect inside the cavity 101 due to the charge-up 106 specific to the high resistance Si substrate shown in FIG. 11 can be prevented. it can. For this reason, in the thin film piezoelectric resonance device manufactured by the manufacturing method of the present embodiment, k ² = 4.00% to 7.79% (6.5%) and Q = 450 to 1900 (1500) are high frequency characteristics. Further, in the high-temperature and high-humidity test at high temperature and high humidity (80 ° C., 95%), no deterioration of characteristics is observed even after about 100 hours, and the reliability is excellent.

  An embodiment of the method for manufacturing a thin film piezoelectric resonance element of the present invention will be described. First, Al is formed by sputtering as a material film of the first electrode 3 on a silicon substrate 1 having a resistivity of 200 Ω · cm and a substrate thickness of 200 μm on which an oxide film 2 as an insulating film is formed, and is manufactured by Tokyo Ohka Kogyo by lithography technology. By forming a pattern using a positive resist (OFPR-5000) and patterning the electrode material film, the first electrode 3 was formed as shown in FIG. This patterning was performed by dry etching using chlorine gas and boron trichloride gas with a magnetron M-RIE apparatus. As shown in FIG. 3A, three first electrodes 3 were formed.

  Subsequently, as shown in FIG. 3B, AlN is formed by sputtering as a film of piezoelectric material so as to cover the first electrode 3 so as to have a film thickness of 1.5 μm, and the piezoelectric body is formed by using a lithography technique. The piezoelectric film 7 was formed by patterning the material film. Sputtering of the AlN piezoelectric material film was performed by RF sputtering using an Al target and nitrogen gas. For the processing of the AlN film, a pattern using a positive resist made by Tokyo Ohka (PEMR P-LA900PM) is formed by lithography technology, and dry etching using chlorine gas and boron trichloride gas by the same M-RIE apparatus as above. It processed by.

  Next, for the purpose of making the resonance frequency different between the thin film piezoelectric resonator elements connected in series and the thin film piezoelectric resonator elements connected in parallel, as shown in FIG. A load electrode 15 was formed on the top using a Mo film. This Mo film is formed by sputtering, and this processing is performed by forming a pattern using a positive resist (OFPR-5000) made by Tokyo Ohka by lithography technology, and dry etching using tetrafluoromethane gas by an M-RIE apparatus. It processed by. Thereafter, an Al film was formed as an electrode material film on the entire surface of the substrate 1, and the electrode material film was patterned using a lithography technique, thereby forming the second electrode 8 as shown in FIG. The method for forming and processing the second electrode 8 is the same as that for the first electrode 3. As a result, nine thin film piezoelectric resonance elements FR1 to FR9 in which the piezoelectric film 7 was sandwiched between the first electrode 3 and the second electrode 8 were formed. Seven second electrodes 8 are formed, and one of the seven second electrodes 8 also serves as a wiring for connecting the thin film piezoelectric resonance element FR2 and the thin film piezoelectric resonance element FR3, and the other second electrode 8 Reference numeral 8 also serves as a wiring for connecting the thin film piezoelectric resonance element FR4 and the thin film piezoelectric resonance element FR5.

  Next, as shown in FIGS. 4A and 4B, an Al film is formed on the entire surface of the substrate 1 as a wiring electrode material, and the electrode material film is patterned using a lithography technique to form a thin film. Five wiring electrodes 10 respectively connected to the second electrodes 8 of the piezoelectric resonant elements FR1, FR6, FR7, FR8, and FR9 were formed on the sides of the piezoelectric film 7. These wiring electrodes 10 extend not only on the sides of the piezoelectric film 7 but also on the oxide film 2. The method for forming and processing the wiring electrode 10 is the same as that for the first electrode 3. After the formation of the wiring electrode 10, the back surface of the silicon substrate 1 was polished so that the thickness of the silicon substrate 1 was 50 μm to 200 μm.

  Next, as shown in FIG. 5, a film made of silicon nitride SiNx is formed to 100 nm by CVD so as to cover the second electrode 8 on the piezoelectric film 7, and the silicon nitride film is made by using a lithography technique. A passivation film 9 was formed by patterning. The passivation film 9 is not formed on the wiring electrode 10.

  Next, by etching from the back surface of the silicon substrate 1 using the BOSCH type ICP-RIE apparatus shown in FIG. 7, the silicon substrate 1 and the oxide film immediately below each of the thin film piezoelectric resonance elements FRi as shown in FIG. 2 was removed, and a cavity 4 was formed immediately below each of the thin film piezoelectric resonator elements FRi.

The pattern of the cavity 4 was formed using a positive resist (PEMR P-LA900PM) made by Tokyo Ohka by lithography technique. Next, Si cavities were formed by the ICP-RIE apparatus described above. For this purpose, etching mainly with SF ₆ gas and deposition mainly containing C ₄ F ₈ gas are repeated, and the bias voltage applied to the substrate 1 is adjusted so that the etching rate of the central portion of the bottom surface of the penetrating portion is reduced. The cavity 4 was formed while adjusting to be larger than the surrounding portion.

Etching mainly using SF ₆ gas is SF ₆ gas flow rate 300 sccm, chamber gas pressure 5 Pa, etching time 7 s, RF (13.56 MHz) power 1.6 kW, bias (300 kHz) applied power 50 W, bias rectangular wave maximum power. The measurement was performed under the conditions of 50 W, bias rectangular wave maximum power holding time 30 ms, bias rectangular wave minimum power 10 W, and bias rectangular wave minimum power holding time 25 ms.

The deposition mainly composed of C ₄ F ₈ gas is C ₄ F ₈ gas flow rate 90 sccm, chamber gas pressure 1.5 Pa, etching time 3 s, RF (13.56 MHz) power 1.2 kW, bias (300 kHz) applied power 15 W. , Bias rectangular wave maximum power 15 W, bias rectangular wave maximum power holding time 30 ms, bias rectangular wave minimum power 2 W, bias rectangular wave minimum power holding time 25 ms. The repetition time of etching mainly composed of SF ₆ gas and deposition mainly composed of C ₄ F ₈ gas was set to 65 minutes.

Next, the oxide film 2 is subjected to a condition of RF (13.56 MHz) power 1.2 kW, bias (13.56 MHz) applied power 300 W, and etching time 10 minutes using C ₄ F ₈ gas and oxygen gas at a pressure of 3 Pa. Removed.

In the thin-film piezoelectric resonator manufactured by the above-described method for manufacturing a thin-film piezoelectric resonator, as shown in FIG. 8, step 12 of the side wall 11 that protrudes toward the thin-film piezoelectric resonator FRi when the Si substrate 1 is viewed from the bottom. was gotten. This step 12 shows the tip of the cavity etching in which etching mainly composed of SF ₆ gas and deposition mainly composed of C ₄ F ₈ gas were repeated. As a result, the cavity 4 is formed so as to increase the etching rate at the central portion of the bottom surface of the penetrating portion, and the shape defect inside the cavity 101 due to the charge-up 106 specific to the high resistance Si substrate shown in FIG. 11 is prevented. . For this reason, the thin-film piezoelectric resonator manufactured by the manufacturing method of the present example shows k ² = 6.5% and Q = 1500 as high-frequency characteristics, and further, high temperature and humidity resistance at high temperature and high humidity (80 ° C., 95%). The test showed no deterioration in properties even after 100 hours and was excellent in reliability.

1 shows the structure of one thin film piezoelectric resonator element in a thin film piezoelectric resonator manufactured by the method of manufacturing a thin film piezoelectric resonator element according to one embodiment of the present invention. FIG. 1 (a) is a plan view and FIG. 1 (b). FIG. 2 is a cross-sectional view taken along line AA ′ in FIG. FIGS. 2A and 2B show a structure of the thin film piezoelectric resonator manufactured according to the above embodiment, and FIG. 2B is a cross-sectional view taken along line BB ′ in FIG. The top view which shows the manufacturing process 1 of the thin film piezoelectric resonance apparatus by the said embodiment. FIGS. 4A and 4B show a manufacturing process part 2 of the thin film piezoelectric resonator according to the above embodiment, FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along the line CC ′ in FIG. Sectional drawing which shows the manufacturing process 3 of the thin film piezoelectric resonance apparatus by the said embodiment. Sectional drawing which shows the manufacturing process part 4 of the thin film piezoelectric resonance apparatus by the said embodiment. Sectional drawing of the ICP-RIE apparatus used for the manufacturing process of the thin film piezoelectric resonance apparatus by the said embodiment. Sectional drawing which shows the step of the cavity part side wall surface of the thin film piezoelectric resonance apparatus after the ICP-RIE etching in the said embodiment. The circuit diagram of a general RF filter. The circuit diagram of a general voltage controlled oscillator. Explanatory drawing which shows the generation | occurrence | production principle of the shape defect by the charge up peculiar to a high resistance Si board | substrate generate | occur | produced when a cavity part is formed in a high resistance Si board | substrate by an etching with the manufacturing method of the conventional thin film piezoelectric resonance element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Oxide film 3 First electrode 4 Cavity 7 Piezoelectric film 8 Second electrode 9 Insulating film (SiN _x film)
10 Wiring electrodes FR1 to FR9 Thin film piezoelectric resonance element

Claims (6)

In a method of manufacturing a thin film piezoelectric resonance element having a first electrode, a piezoelectric film, and a second electrode,
When forming a through-hole serving as a lower cavity of the thin film piezoelectric resonator element so as to penetrate the Si substrate directly under the thin film piezoelectric resonator element, etching mainly using SF ₆ gas and C ₄ F ₈ gas are performed. The through hole is formed such that the etching rate of the central portion of the bottom of the through portion is larger than that of the surrounding portion by repeating the deposition mainly consisting of and adjusting the bias power applied to the Si substrate. A manufacturing method of a thin film piezoelectric resonance element characterized by the above.   2. The method of manufacturing a thin film piezoelectric resonance element according to claim 1, wherein the bias power voltage applied to the Si substrate is a rectangular wave. By supplying an etching gas mainly composed of SF ₆ gas and a deposition gas mainly composed of C ₄ F ₈ gas in the thin film piezoelectric resonator element, the step of the side wall is viewed from the bottom of the Si substrate and the thin film piezoelectric resonator side The method of manufacturing a thin film piezoelectric resonance element according to claim 1, wherein the through hole is formed so as to be convex.   A plurality of thin film piezoelectric resonator elements are simultaneously formed in parallel or in series on the high-resistance Si substrate, and each of the thin film piezoelectric resonator elements passes through the Si substrate directly below the Si substrate. The method for manufacturing a thin film piezoelectric resonance element according to claim 1, wherein a through-hole serving as a lower cavity is formed. Etching mainly composed of SF ₆ gas includes SF ₆ gas flow rate of 10 to 1000 sccm, chamber gas pressure of 0.1 to 30 Pa, etching time of 0.1 to 30 s, RF (13.56 MHz) power of 0.1 to 100 kW, Bias (300 kHz) applied power 5 to 1000 W, bias rectangular wave maximum power 10 to 500 W, bias rectangular wave maximum power holding time 5 to 500 ms, bias rectangular wave minimum power 0 to 250 W, bias rectangular wave minimum power holding time 1 to 100 ms Under the conditions
The _C 4 _{F 8} gas deposits mainly composed of _the, C 4 _{F 8} gas flow rate 5～900Sccm, chamber gas pressure 0.1～27Pa, etching time 0.3~28s, RF (13.56MHz) power 0. 1 to 100 kW, bias (300 kHz) applied power 5 to 200 W, bias rectangular wave maximum power 10 to 450 W, bias rectangular wave maximum power holding time 5 to 500 ms, bias rectangular wave minimum power 0 to 250 W, bias rectangular wave minimum power holding time 1 to 120 ms, and
5. The thin film piezoelectric resonance according to claim 1, wherein a repetition time of etching mainly composed of the SF ₆ gas and deposition mainly composed of the C ₄ F ₈ gas is set to 5 to 240 minutes. Device manufacturing method. A thin film piezoelectric resonance element in which a first electrode, a piezoelectric film, and a second electrode are sequentially stacked on a Si substrate, and a cavity is formed immediately below the first electrode in the Si substrate. The side wall of the thin film piezoelectric resonance element is characterized in that a step is formed which protrudes toward the first electrode and the piezoelectric film when the Si substrate is viewed from the bottom.