JP5786393B2 - Quartz device manufacturing method - Google Patents

Description

  The present invention relates to a quartz crystal device using a quartz thin film and a method for manufacturing the quartz crystal device.

  Conventionally, a piezoelectric device having a piezoelectric thin film has been manufactured. The piezoelectric device has a thinner piezoelectric thin film as the operating frequency band is higher, and the thickness of the thin film is 100 μm or less in the MHz band and several μm or less in the GHz band.

As a method for manufacturing a piezoelectric device including a piezoelectric thin film, there has been a method of polishing a quartz substrate bonded to a semiconductor substrate (see, for example, Patent Document 1). In addition, there is a type in which ions are implanted into an LT (LiTaO ₃ ) substrate or an LN (LiNbO ₃ ) substrate to generate a microcavity, and the microcavity is grown by heating to thermally peel the piezoelectric thin film from the piezoelectric single crystal. (For example, refer to Patent Document 2).

JP-A-5-327383 US Pat. No. 6,767,749

  However, in the invention described in Patent Document 1, as described in paragraph [0020] of Patent Document 1, since it is 10 μm or more that can be accurately mechanically polished, when a quartz thin film of several μm or less is manufactured, There was a problem that the quality was not stable due to variations in thickness.

  Further, in the invention described in Patent Document 2, when a crystal substrate is used as the piezoelectric substrate, a microcavity is not formed even if ions are implanted, and the crystal thin film does not peel even when the crystal substrate is heated. There was a problem that it could not be obtained.

  Accordingly, an object of the present invention is to provide a method of manufacturing a quartz device that can stably manufacture a very thin quartz thin film having a thickness of several μm or less, and a quartz device manufactured by this manufacturing method.

  (1) The manufacturing method of the quartz crystal device of this invention is equipped with the amorphous layer formation process and the isolation | separation process. In the amorphous layer forming step, ions or atoms are implanted into the quartz substrate to form an amorphous layer in the quartz substrate. In the separation step, the amorphous layer is removed by etching to separate the quartz thin film from the quartz substrate.

  When hydrogen ions, rare gas ions, or hydrogen atoms are implanted into the quartz substrate, the quartz substrate and ions (or atoms) react to become amorphous, so that an amorphous layer is formed in the quartz substrate. The depth at which the amorphous layer is formed is determined by ion or atom implantation conditions (implantation energy and dose). Depending on the implantation conditions, a flat amorphous layer having no variation is formed at a depth of 1 μm to several μm from the implantation surface. Since the crystal amorphous has a higher etching rate than the crystal, the crystal thin film can be separated from the crystal substrate by removing the amorphous layer by etching. Therefore, a quartz thin film having a thickness of several μm or less can be stably manufactured.

  In addition, the crystal substrate may be ion-implanted by cutting into a crystal orientation optimal for the vibration mode to be used. As a result, an amorphous layer is formed at a certain depth from the surface of the quartz single crystal substrate, so that the cut surface of the quartz membrane can be arbitrarily selected, and a quartz resonator having excellent performance can be manufactured according to the application. .

  (2) In (1), it is preferable that the separation step is a step of removing a part of the amorphous layer by etching to form a space between the quartz thin film and the quartz substrate. By removing a part of the amorphous layer by etching, it can be used as a vibration space of the crystal thin film separated from the crystal substrate. In addition, by leaving a part of the amorphous layer around the vibration space without removing it, the crystal thin film can be supported by the remaining amorphous layer without providing a separate support portion. Therefore, it is possible to manufacture a crystal device having a vibration space of a crystal thin film by separating the crystal thin film from the crystal substrate by a simple process.

  The portion where the amorphous layer is left is preferably a region having a small vibration displacement (for example, a vibration node point) when the crystal thin film is used as a vibration body. The deterioration of the Q value can be suppressed by mechanically connecting the crystal thin film and the crystal substrate while leaving the amorphous layer in contact with the region where the vibration displacement is small.

  (3) In (1), before the amorphous layer forming step, a resist film that blocks ion or atom implantation is formed on a part of the surface on the ion or atom implantation side. It is preferable to inject atoms from the surface on the injection side to form an amorphous layer in the quartz substrate, and to remove the resist film after the amorphous layer forming step.

  When a resist film is formed on the surface of the quartz substrate on the ion or atom implantation side, ions or atoms are not implanted from the portion where the resist film is formed. Therefore, after forming a resist film in a region other than the region where the crystal thin film is to be formed, ions or atoms are implanted from the surface on the ion or atom implantation side, thereby forming an amorphous layer only in the region where the crystal thin film needs to be formed. it can. Therefore, compared with the case where an amorphous layer is formed on the entire quartz substrate and etching is performed, the formation of the amorphous layer and the removal of the amorphous layer by etching can be performed efficiently. Further, since the region where the amorphous layer is etched and the amorphous layer is not formed is not etched, a support made of quartz can be formed in the vicinity of the region where the electrode is formed. That is, since the quartz thin film (membrane) can be formed with a minimum area, the usage efficiency of the quartz substrate can be increased and the quartz device can be miniaturized.

  (4) In (1) to (3), it is preferable that a support substrate is provided on the side of the crystal substrate ion or atom implantation surface after the amorphous layer formation step and before the separation step. By providing the support substrate on the ion or atom implantation surface side, the crystal thin film can be supported by the support substrate. Further, by providing the support substrate so that a space having an arbitrary width is formed between the quartz substrate and the support substrate, an oscillation space having an arbitrary width can be formed between the crystal thin film and the support substrate. In order to form the vibration space, for example, a sacrificial layer may be provided between the quartz substrate and the support substrate, and the sacrificial layer may be removed.

  (5) In (1) to (4), it is preferable to perform the groove forming step after the amorphous layer forming step and before the separating step. In the groove forming step, a plurality of grooves are provided in the quartz substrate to expose the side surfaces of the amorphous layer. The separation step is preferably a step of introducing an etching solution into the plurality of grooves to remove the amorphous layer between the grooves.

  When the quartz substrate is provided with a plurality of grooves to expose the side surfaces of the amorphous layer and etching is performed from each groove, the etching is performed compared to the case where etching is performed from the end of the quartz substrate without providing the grooves on the quartz substrate. The distance can be shortened. Therefore, the etching time can be shortened and the quartz crystal device can be manufactured efficiently.

  (6) In (5), the groove forming step is preferably a step of forming a plurality of grooves in line symmetry with respect to an axis passing through the center along the surface of the crystal thin film.

  When a groove is formed on a quartz substrate as described above, when the amorphous layer is removed by etching in the separation step, the axis portion passing through the center along the surface of the quartz thin film is thicker than the end portion. It can be formed into a shape. This is because the end portion of the crystal thin film is close to the groove, and the time during which the crystal thin film is touched (soaked) is longer than the center portion of the crystal thin film. By making the quartz thin film into a mountain shape as described above, an energy confinement structure in which the wave number of the main vibration mode in the central part is real and the wave number in the peripheral part is imaginary can be configured in the operating frequency band. Since the quartz thin film has an energy confinement structure, vibration energy does not leak at the time of resonance, so that a quartz device having a high Q value and stable characteristics can be manufactured.

  (7) In (1) to (6), the separating step is preferably a step of further removing a part of the quartz substrate by etching.

  By adjusting the mixing ratio of the etching liquid, it is possible to remove part of the quartz crystal substrate together with the amorphous layer by etching. Since the end of the crystal thin film is close to the groove and the etching liquid is in contact with (dipped) for a longer time than the center of the crystal thin film, the crystal thin film is removed closer to the end of the crystal thin film. In this way, when not only the amorphous layer of crystal but also the crystal thin film is removed, the crystal thin film has the thickest mountain shape at the center and can form an energy confinement structure. You can get a device.

  (8) The crystal device of the present invention is manufactured by the manufacturing method according to any one of the above (1) to (7), and the crystal thin film includes electrodes for applying voltages to both sides thereof, and one surface of the crystal thin film Is opposed to the support substrate in a vibration space, and the quartz crystal thin film vibrates in the vibration space when a voltage is applied between the electrodes.

  The sensitivity of the frequency fluctuation of the quartz thin film is inversely proportional to the thickness. Since the quartz crystal device is provided with a very thin quartz thin film of several μm or less manufactured by the above method, it can be used as a very sensitive sensor.

  When the quartz thin film is configured in the X-cut bending vibration mode, the resonance frequency at the time of bending vibration is proportional to the thickness and inversely proportional to the length. Since the quartz device includes a very thin quartz thin film manufactured by the above method, the resonance frequency can be lowered. In addition, when the frequency is the same, if the length of the quartz thin film manufactured by the above method is shortened, the reduction of the resonance frequency due to the thinning is canceled by the shortening of the quartz thin film, resulting in the miniaturization of the quartz thin film. be able to. Therefore, the crystal device provided with such a crystal thin film can be used as a small sensor.

  (9) The quartz crystal thin film can be configured to undergo surface vibration in the vibration space when a voltage is applied between the electrodes. A crystal device including a crystal thin film having such characteristics can be used as a resonator of about 10 to 100 MHz. When the quartz thin film is configured to be in the GT-cut coupled vibration mode, the CT-cut / DT-cut contour vibration mode, that is, the surface vibration mode, the thickness can be reduced, so that the impedance of the crystal device can be reduced. In addition, the entire quartz crystal device including the package can be thinned by thinning the quartz crystal thin film.

  (10) The crystal thin film can be configured to vibrate in thickness in the vibration space when a voltage is applied between the electrodes.

  A crystal device including a crystal thin film having such characteristics can be used as a resonator of 1 GHz to 2 GHz. This resonator has a higher Q value and a stable frequency-temperature characteristic than a resonator using a conventional AlN film.

  (11) A quartz crystal device of the present invention is manufactured by the manufacturing method according to any one of (1) to (7) above, and the quartz crystal thin film includes a pair of comb-shaped electrodes for applying a voltage to the first surface, The surface of 2 faces the quartz substrate with a vibration space, and the quartz thin film generates a plate wave when a voltage is applied between the pair of comb electrodes.

  A crystal device including a crystal thin film having such characteristics can be used as a plate wave resonator. When this crystal device is used as a solution concentration sensor or gas sensor, the thickness of the crystal thin film is very thin, so that the concentration of the solution or gas can be detected with high sensitivity.

  (12) The quartz crystal thin film can be configured to generate a surface wave when a voltage is applied to the pair of comb electrodes. A crystal device including a crystal thin film having such characteristics can be used as a surface wave device.

  According to the present invention, it is possible to stably manufacture a crystal device including a very thin crystal thin film having a thickness of several μm or less.

It is a flowchart which shows the manufacturing method of the piezoelectric device which concerns on 1st Embodiment of this invention. It is a figure which shows typically the manufacturing process of the piezoelectric device formed with the manufacturing flow shown in FIG. It is a flowchart which shows the manufacturing method of the piezoelectric device which concerns on 2nd Embodiment of this invention. It is a figure which shows typically the manufacturing process of the piezoelectric device formed with the manufacturing flow shown in FIG. It is a flowchart which shows the manufacturing method of the piezoelectric device which concerns on 3rd Embodiment of this invention. It is a figure which shows typically the manufacturing process of the piezoelectric device formed with the manufacturing flow shown in FIG. It is a flowchart which shows the manufacturing method of the piezoelectric device which concerns on 4th Embodiment of this invention. It is a figure which shows typically the manufacturing process of the piezoelectric device formed with the manufacturing flow shown in FIG.

[First Embodiment]
In the first embodiment, an example in which a crystal thin film is provided on a crystal single crystal substrate will be described.

  FIG. 1 is a flowchart showing a method for manufacturing a quartz crystal device according to a first embodiment of the present invention. FIG. 2 is a diagram schematically showing a manufacturing process of the quartz crystal device formed by the manufacturing flow shown in FIG.

  As shown in FIG. 2A, a quartz single crystal substrate 1 having a predetermined thickness is prepared. As the quartz single crystal substrate 1, a substrate whose surface 1A is mirror-polished and on which a plurality of quartz thin films can be arranged is used. FIG. 2 shows a part of the quartz single crystal substrate 1.

  As shown in FIG. 2 (B), resist films 11A and 11B are formed on the surface 1A, which is the surface on the ion implantation side of the quartz single crystal substrate 1, on the portion where the quartz thin film is not formed (FIG. 1: S101). The resist films 11A and 11B are formed by, for example, a photolithography method.

As shown in FIG. 2C, hydrogen ions 12 are implanted from the surface 1A of the quartz single crystal substrate 1. When hydrogen ions 12 are implanted into the quartz single crystal substrate 1, layers (hereinafter referred to as amorphous layers) 13A to 13C in which quartz (SiO ₂ ) is amorphized are formed at a certain depth from the surface 1A (see FIG. 1: S102 [amorphous layer forming step]). At this time, since the resist films 11A and 11B provided on the surface 1A of the quartz single crystal substrate 1 block ion implantation, an amorphous layer is not formed immediately below the resist film 11A and the resist film 11B. Note that ion implantation can be prevented even if a metal film is provided instead of the resist films 11A and 11B.

When the hydrogen ion implantation conditions are set to an implantation energy of 110 keV and a dose (ion implantation density) of 5.0 × 10 ¹⁶ atoms / cm ² , the depth from the surface 1A of the quartz single crystal substrate 1 is 1.25 μm. Amorphous layers 13 </ b> A to 13 </ b> C having a thickness of 0.1 μm are formed at the positions to be formed.

  As a material to be injected into the quartz single crystal substrate 1, in addition to hydrogen ions 12, rare gas ions such as helium ions and argon ions, and atoms such as hydrogen can be used. The depth at which the amorphous layers 13A to 13C are formed can be adjusted by changing the implantation conditions of the hydrogen ions 12 and the substances (ions and atoms) implanted into the quartz substrate.

  As shown in FIG. 2D, the resist films 11A and 11B are removed (FIG. 1: S103). The resist films 11A and 11B are removed by RIE (Reactive Ion Etching) method or the like.

  As shown in FIG. 2 (E), a plurality of grooves 14 </ b> A to 14 </ b> D are formed in the surface 1 </ b> A of the quartz single crystal substrate 1. The grooves 14A to 14D are formed by dicing or dry etching so that the side surfaces of the amorphous layers 13A to 13C are exposed (FIG. 1: S104 [groove forming step]).

  Subsequently, the amorphous layer is removed by etching, and the quartz thin film is separated from the quartz single crystal substrate 1 (FIG. 1: S105 [separation step]). Specifically, first, an etching solution is introduced into the plurality of grooves 14 </ b> A to 14 </ b> D formed on the surface 1 </ b> A of the crystal single crystal substrate 1. The amorphous layer of quartz has a higher etching rate than the quartz single crystal. Therefore, etching is started from the exposed side surface of the amorphous layer. As the etching proceeds, the amorphous layer between the grooves is removed, and a space (vibration space) is formed in the crystal single crystal substrate 1. As a result, a quartz thin film having a thickness of about 1.2 μm is formed on the surface 1A of the quartz single crystal substrate 1, for example.

  Basically, since the amorphous layer is etched and the region where the amorphous layer is not formed is not etched, a support made of a crystal single crystal can be formed in the vicinity of a region where a comb electrode described later is formed. That is, since the quartz thin film (membrane) can be formed with a minimum area, the usage efficiency of the quartz substrate can be increased and the quartz device can be miniaturized.

  For example, BHF (buffered hydrofluoric acid) is used as the etchant. BHF is a mixture of hydrofluoric acid, water, and ammonium fluoride. By adjusting these mixing ratios and changing the ratio of the etching rate of crystal single crystal and crystal amorphous (quartz glass), the crystal thin film can be formed in a mountain shape or a flat shape.

  For example, when the mixing ratio (weight ratio) of hydrofluoric acid: water: ammonium fluoride is 1:59:40, the ratio of the crystal single crystal to the amorphous etching rate is about 200 times. In this case, when the etching time becomes long, not only the amorphous layer but also a part of the crystal single crystal is removed by etching. That is, the end portions of the crystal thin films 16A to 16C are close to the grooves 14A to 14D and have a long time of being touched (immersed) in the etching solution. The part is also removed by etching. On the other hand, in the central part of the crystal thin films 16A to 16C, the time during which the etching liquid is touched is shorter than the end part, so that a part of the amorphous layers 13A to 13C remains. Therefore, the difference in thickness between the central portion and the end portion of each of the crystal thin films 16A to 16C is increased. That is, like the crystal thin film 16B shown in FIG. 2 (F), the end portion is the thinnest, the thickness gradually increases as the distance from the end portion increases, and the central portion has the thickest mountain shape.

  The Q value can be increased by forming the quartz thin film in a mountain shape. It is known that the bulk vibrator is in an energy confined state in the operating frequency band by setting the wave number of the main vibration mode in the central part as a real number and the wave number in the peripheral part as an imaginary number. Many bulk vibration modes represented by the thickness-shear vibration mode of AT-cut quartz have low-frequency cutoff type dispersion characteristics. In the vibration mode having a low-frequency cutoff type dispersion characteristic, the energy confinement structure can be configured by slightly reducing the thickness of the end portion with respect to the central portion.

  On the other hand, when the mixing ratio (weight ratio) of hydrofluoric acid: water: ammonium fluoride is 6:64:30, the ratio of the crystal single crystal to the amorphous etching rate is about 500 times. In this case, since the quartz single crystal substrate 1 is hardly etched, the difference in thickness between the central portion and the end portion of the quartz thin film is small.

  Since the amorphous layers 13A to 13C formed on the crystal single crystal substrate 1 are dense and flat, the surfaces of the crystal thin films 16A to 16C can be kept smooth even after the amorphous layer is removed by etching. Therefore, when the amorphous layer is removed by etching, the surface of the quartz thin film can be smoothed, and a flat shape is obtained as in the quartz thin film 18B shown in FIG.

  As described above, the shape of the quartz thin film can be adjusted by changing the mixing ratio (weight ratio) of hydrofluoric acid: water: ammonium fluoride. In addition, by setting the ratio of hydrofluoric acid / ammonium fluoride to a range of 1 to 20, a preferable shape can be obtained as a crystal resonator. That is, since leakage of vibration energy is eliminated, a crystal device having a high Q value and stable characteristics can be obtained.

  It is to be noted that by adjusting the mixing ratio of the etching solution, the quartz thin film can be formed in a mountain shape by removing the amorphous layer without removing the quartz single crystal substrate 1.

  2H is a plan view of the quartz single crystal substrate 1, FIG. 2I is a BB cross-sectional view of the quartz single crystal substrate 1 shown in FIG. 2H, and FIG. It is AA sectional drawing of the quartz single crystal substrate 1 shown to 2 (H).

  As shown in FIG. 2H, an electrode for driving as a vibrator is formed on the surface of the crystal thin film 18 on the crystal thin film (FIG. 1: S106).

A pair of IDT (Interdigital Transducer) electrodes 19 and reflectors 20A and 20B are formed on the upper surface of the crystal thin film 18B. The reflectors 20A and 20B are formed at both ends of the pair of IDT electrodes 19 in the surface wave propagation direction. A plate wave resonator that generates a plate wave can be formed by forming a pair of IDT electrodes 19 on a quartz crystal thin film 18B held hollow in the quartz single crystal substrate 1 and applying a voltage between the pair of IDT electrodes 19.

  Since the vibration displacement of the plate wave resonator is small, there is no problem even if the spaces 15A to 15C or the spaces 17A to 17C formed by removing the amorphous layer are used as the vibration space.

  Next, the quartz single crystal substrate 1 is cut to cut out individual quartz devices (FIG. 1: S107). Through the above steps, a quartz crystal device having a comb-shaped electrode on one side of a quartz crystal thin film can be manufactured.

  Since the crystal device manufactured in this way has a plate wave resonator as described above, when used as a solution concentration sensor or a gas sensor, the thickness of the crystal thin film is very thin. Can be detected with high sensitivity.

  In the first embodiment, in the flowchart shown in FIG. 1, the resist films 11A and 11B are provided on the surface 1A of the crystal single crystal substrate 1 before ion implantation. However, the resist films 11A and 11B are not provided. In addition, it is possible to form the crystal thin films 18A to 18C. That is, steps S102 and S104 and subsequent steps can be performed without performing steps S101 and S103.

  In this case, in step S102, hydrogen ions are implanted into the entire crystal single crystal substrate 1 from the surface 1A of the crystal single crystal substrate 1. In step S104, the length in the vertical direction in FIG. 2H is formed shorter than the groove shown in FIG. In step 105, the mixing ratio of the etching solution and the etching time are adjusted so that the amorphous layer 13 immediately below the portion where the IDT 19 and the reflectors 20A and 20B are formed is mainly removed. Steps S106 and S107 are processed in the same manner as described above.

  As a result, the etching is stopped when the amorphous layer immediately below the IDT and the reflector is removed, so that the region away from the IDT and the reflector is not removed by etching and the amorphous layer remains. That is, the crystal thin film is held by the amorphous layer.

  The region that remains without removing a part of the amorphous layer is preferably a region where vibration displacement is small (for example, a vibration node point) when the crystal thin film is used as a vibration body. The deterioration of Q can be suppressed by mechanically connecting the crystal thin film and the crystal substrate while leaving the amorphous layer in contact with the region where the vibration displacement is small. For example, in the above configuration, it is preferable to have a structure in which the quartz thin film is held by the IDT and the portion around the reflector (outside) without vibration displacement.

[Second Embodiment]
FIG. 3 is a flowchart showing a method for manufacturing a quartz crystal device according to the second embodiment of the present invention. FIG. 4 is a diagram schematically showing a manufacturing process of the quartz crystal device formed by the manufacturing flow shown in FIG.

  As shown in FIG. 4A, hydrogen ions 32 are implanted from the surface 3A, which is an implantation surface of the crystal single crystal substrate 3, and an amorphous layer 33 is formed in the crystal single crystal substrate 3 (FIG. 3: S201). . The implantation conditions of the hydrogen ions 32 may be the same as those in the first embodiment.

  As shown in FIG. 4B, lower electrodes 31A to 31C are formed to a predetermined thickness on the surface 3A of the crystal single crystal substrate 3 after the amorphous layer 33 is formed (FIG. 3: S202). When Al (aluminum) is used as an electrode material, resist formation, Al vapor deposition, and lift-off are performed, and electrode patterning of the Al film is performed. As the material for the lower electrodes 31A to 31C, a material that is resistant to an etching solution is used when the membrane sacrificial layer described later is etched.

  As shown in FIG. 4C, membrane sacrificial layers 34A to 34C are formed so as to cover the periphery of the lower electrodes 31A to 31C (FIG. 3: S203). When Cu (copper) is used as the material of the membrane sacrificial layers 34A to 34C, patterning is performed by resist formation, Cu vapor deposition, and lift-off.

  Since the membrane sacrificial layers 34 </ b> A to 34 </ b> C become membrane space portions by processing described later, they are formed to have a thickness corresponding to the required size of the membrane space portions. For example, it is formed to a thickness of about 2 μm. For the membrane sacrificial layers 34 </ b> A to 34 </ b> C, a material capable of obtaining selectivity with the lower electrode when the membrane sacrificial layer described later is etched. As the sacrificial layer material, in addition to Cu, a metal such as Ni · W or a dielectric such as AlN can be used. By creating the membrane sacrificial layers 34A to 34C by vapor deposition lift-off, the size and shape of the crystal thin film (membrane) can be made with high accuracy.

  As shown in FIG. 4D, the membrane support layer 35 is formed so as to cover the membrane sacrificial layers 34A to 34C and the surface 3A of the crystal single crystal substrate 3 (FIG. 3: S204). Aluminum nitride is used as the material of the membrane support layer 35, and the membrane support layer 35 is formed by sputtering so as to have a thickness of 3 times or more the thickness of the sacrificial layer. In addition, as a material of the membrane support layer 35, a material having resistance to each etching solution is used at the time of etching an amorphous layer 33 described later and at the time of etching the membrane sacrificial layers 34A to 34C. In addition to aluminum nitride, for example, silicon nitride, aluminum oxide, aluminum nitride, tantalum oxide and the like are preferable.

  As shown in FIG. 4E, the surface of the membrane support layer 35 is planarized by CMP using silica slurry (FIG. 3: S205). At this time, the surface roughness Ra is finished to 1 nm or less.

  As shown in FIG. 4F, groove processing is performed on the membrane support layer 35 and a part of the quartz single crystal substrate 1 (FIG. 3: S206). That is, a resist pattern is formed on the membrane support layer 35 by photolithography, and grooves 36A to 36D are formed from the surface of the membrane support layer 35 to a position deeper than the amorphous layer of the crystal single crystal substrate 1 by dry etching or wet etching. Form. The grooves 36A to 36D are formed so as to be line symmetric with respect to an axis passing through the center along the surface of the quartz crystal thin film. That is, it forms so that it may become line symmetrical with respect to the axis which passes along the center along the surface of lower electrode 31A-31C. Thereby, as described in detail in the first embodiment, the shape of the crystal thin film can be formed into a mountain shape where the center of the lower electrodes 31A to 31C is thickest and becomes thinner toward the end.

  Further, when a plurality of grooves are provided in the quartz single crystal substrate 1, the etching distance can be shortened compared to the case where etching is performed from the end of the quartz substrate without providing the grooves in the quartz substrate. Therefore, the time for etching can be shortened.

As shown in FIG. 4G, the membrane support layer 35 and the support substrate 37 are directly bonded in a vacuum using a cleaning bonding technique (FIG. 3: S207). As a material of the support substrate 37, LT (LiTaO ₃ ), LN (LiNbO ₃ ), Si, glass, or the like is used.

  As shown in FIG. 4H, the amorphous layer 33 is removed by etching, and the crystal thin films 39A to 39C are separated from the crystal single crystal substrate 3 (FIG. 3: S208). That is, an etching solution is introduced from the grooves 36 </ b> A to 36 </ b> D, and the amorphous layer 33 is removed to form the membrane space 38. As described in the first embodiment, the mixing ratio of the etching liquid is set so that the ratio of the etching rate between the crystal and the amorphous layer is about 200 times. Thereby, the crystal thin films 39A to 39C have the thickest mountain shape along the axis passing through the center along the surface of the crystal thin film (see FIG. 4I).

  As shown in FIG. 4J, upper electrodes 40A to 40C are formed on the upper surfaces of the crystal thin films 39A to 39C (FIG. 3: S209). As with the lower electrodes 31A to 31C, the electrode material forms an electrode pattern with Al.

  Subsequently, in order to open windows at the ends of the crystal thin films 39A to 39C on which the upper electrodes 40A to 40C are formed, a resist pattern (not shown) is formed by photolithography in addition to the areas to be opened (FIG. 3). : S210).

  As shown in FIG. 4K, the quartz thin films 39A to 39C are opened (FIG. 3: S211). That is, etching windows 41A to 41C for removing the membrane sacrificial layers 34A to 34C are formed by dry etching in regions where the resist patterns (not shown) at the ends of the crystal thin films 39A to 39C are not formed. Since the thickness of the crystal thin film is as very thin as about 1.2 μm, even if dry etching is performed, the etched portion is not tapered, and the processing accuracy is good.

  Subsequently, an etching solution is introduced from the etching windows 41A to 41C to remove the membrane sacrificial layers 34A to 34C (FIG. 3: S212). Thereby, the vibration spaces 42A to 42C are formed below the crystal thin films 39A to 39C. Note that an etching solution that does not affect the membrane support layer 35, the upper electrode 60, and the lower electrodes 31A to 31C is selected.

  As shown in FIG. 4L, the quartz single crystal substrate 3 is cut to cut out individual quartz devices (FIG. 3: S213). Through the above steps, the crystal device 44 (44A to 44C) having electrodes on both sides of the crystal thin film can be manufactured.

  When a quartz crystal device is manufactured as described above, ion implantation is performed on a quartz single crystal substrate cut out in a crystal orientation (referred to as a cut surface or a cut angle) optimum for a vibration mode to be used. As a result, an amorphous layer is formed at a certain depth from the surface of the crystal single crystal substrate, so the cut surface of the crystal thin film (membrane) can be selected arbitrarily, and a crystal resonator with excellent performance can be selected according to the application. Can be manufactured.

  The crystal resonator selects a vibration mode such as thickness sliding or contour vibration according to required characteristics such as resonance frequency, impedance, frequency temperature stability, and required dimensions. Each vibration mode has a crystal orientation in which spurious characteristics, electromechanical coupling coefficient, frequency temperature characteristics, etc. are optimal.

(1) Bending vibration mode (including not only quadratic prisms but also vibrations of triangular prisms, cylinders, tuning forks, tridents, etc.)
As described above, a quartz crystal device in which metal electrodes are formed on both opposing surfaces (upper and lower surfaces) of a quartz crystal thin film, when an alternating voltage having a resonance frequency in a bending vibration mode is input to an external connection terminal (not shown). The thin film vibrates with the bending vibration mode as the main mode. The crystal thin film becomes a bending vibration mode by X cut. When the crystal thin film (membrane) is resonated in the bending vibration mode, it is possible to detect fluctuations in the resonance frequency caused by pressure, impact, and strain due to acceleration. Therefore, the crystal device 44 can be used as a pressure sensor, an impact sensor, an acceleration sensor, or the like.

  In addition, since the thickness of the quartz thin film can be made very thin, about 1 μm, the sensor can have the following characteristics.

  A. Since the sensitivity of the frequency fluctuation of the quartz thin film is inversely proportional to the thickness, a very sensitive sensor can be configured by thinning the quartz thin film.

  B. The resonance frequency when the quartz crystal thin film vibrates is proportional to the thickness and inversely proportional to the length. The resonance frequency can be lowered by thinning the quartz thin film. In addition, by thinning and shortening the quartz thin film, the reduction of the resonance frequency due to the thinning is canceled by shortening the quartz thin film, and the resonance frequency is increased, but the quartz thin film can be miniaturized. Therefore, it can be used as a small sensor.

(2) Surface vibration (area vibration, radial vibration, contour vibration (ramé mode, coupled mode))
As described above, in a quartz crystal device in which metal electrodes are formed on both opposing surfaces (upper surface and lower surface) of the quartz crystal thin film of the quartz device, an alternating voltage having a resonance frequency in the plane vibration mode is input to an external connection terminal (not shown). Then, the crystal thin film vibrates with the plane vibration mode as the main mode. Thereby, it can be used as a resonator of about 10 to 100 MHz. The surface vibration mode is a general term for an area vibration mode, a radial vibration mode, and a contour vibration mode (rame mode, coupled vibration mode). The crystal single crystal substrate is cut out by GT cut or NS-GT cut in the coupled vibration mode, and by CT cut or DT cut in the contour vibration mode.

  By reducing the thickness of the quartz thin film, the impedance of the quartz thin film is lowered, and a quartz device including the entire package can be provided. Moreover, when this quartz crystal device is used for detection of air gas or liquid solution concentration, it can be detected with high sensitivity. This is because the sensitivity of frequency change when mass change occurs due to gas adhesion or modification in the vibration region of the crystal thin film is improved in inverse proportion to the thickness of the crystal thin film. Therefore, the sensitivity can be remarkably improved as compared with a quartz crystal resonator having a quartz crystal thin film having a thickness of about 100 μm.

(3) Thickness vibration mode (thickness longitudinal vibration, thickness sliding vibration)
As described above, in a quartz crystal device in which metal electrodes are formed on both opposing surfaces (upper surface and lower surface) of the quartz crystal device, an alternating voltage having a resonance frequency in the thickness vibration mode is input to an external connection terminal (not shown). Then, the crystal thin film vibrates with the thickness vibration mode as the main mode. Thereby, it can be used as a resonator of 1 GHz to 2 GHz. The thickness vibration mode is a general term for the thickness longitudinal vibration mode and the thickness shear vibration mode. In the thickness-shear vibration mode, the quartz single crystal substrate is cut out by AT cut.

  This resonator has a higher Q value than a conventional FBAR (thin film bulk resonator) using an AlN film, and has a stable frequency temperature characteristic. Further, by etching the membrane from the outer periphery to slightly bulge the central portion, in the thickness-shear vibration mode such as AT cut having a low-frequency cutoff type dispersion characteristic, the energy is confined and the Q value is improved. Moreover, since vibration does not leak to the outer periphery, it becomes easy to hold.

  Moreover, when this quartz crystal device is used as a QCM (quartz crystal sensor) for detection of air gas or liquid solution concentration, it can be detected with high sensitivity. This is because the sensitivity of the frequency change when a mass change occurs due to gas adhesion or modification in the vibration region of the crystal thin film is improved in inverse proportion to the thickness of the crystal thin film. Therefore, the sensitivity can be remarkably improved as compared with the conventional QCM provided with a crystal thin film having a thickness of about 100 μm.

  The present invention is not necessarily limited to these vibration modes, and for example, various vibration modes described in Table 2.11. In any vibration mode, along with the thinning of the crystal, the resonance frequency of the vibrator, the higher frequency of the fundamental mode oscillation of the oscillator (frequency constant in Table 2.11), the mass load, the viscosity of the fluid or gas, With respect to pressure, it is possible to configure a sensor that is more sensitive than conventional elements created by cutting. In addition, since the depth variation due to ion implantation is extremely uniform as compared with a device formed by combining conventional cutting and etching, a device having a small thickness distribution can be manufactured.

[Third Embodiment]
FIG. 5 is a flowchart showing a method for manufacturing a quartz crystal device according to the third embodiment of the present invention. FIG. 6 is a diagram schematically showing a manufacturing process of the quartz crystal device formed by the manufacturing flow shown in FIG.

  The crystal device manufacturing method according to the third embodiment is different in steps S206 to S208 in the crystal device manufacturing method according to the second embodiment shown in FIG. 3, and the other processes are the same. Therefore, in the following description, a different part from 2nd Embodiment is mainly demonstrated.

  FIG. 6 (A) shows the same state as FIG. 4 (E), in which the surface of the membrane support layer 35 is planarized by CMP using silica slurry (FIG. 5: S205).

  Then, as shown in FIG. 6B, a support substrate 37 (corresponding to the support substrate) is prepared, and the membrane support layer 35 and the support substrate 37 are directly bonded in vacuum using a cleaning bonding technique ( FIG. 5: S306).

  Further, as shown in FIG. 6C, grooves 36A to 36D are formed in the crystal single crystal substrate 3 and the membrane support layer 35 from the surface 3B of the crystal single crystal substrate 3 (FIG. 5: S307). The grooves 36A to 36D are formed by half-cutting with a dicer using a blade or by sandblasting.

  The grooves 36A to 36D may be formed in the same manner as in the second embodiment. Thereby, a quartz crystal thin film can be made into a mountain shape.

  Then, as shown in FIG. 6D, an etching solution is introduced from the previously formed groove and the amorphous layer is removed by etching to form a membrane space 38 (FIG. 5: S308). Thereby, the quartz thin films 39A to 39C are separated from the quartz single crystal substrate 3, and the state shown in FIG. This state is the same as that shown in FIG. Thereafter, similarly to the second embodiment, a quartz crystal device is obtained by performing each process of opening a window, removing the membrane sacrificial layer, and separating.

[Fourth Embodiment]
FIG. 7 is a flowchart showing a method for manufacturing a quartz crystal device according to the fourth embodiment of the present invention. FIG. 8 is a diagram schematically showing the manufacturing process of the quartz crystal device formed by the manufacturing flow shown in FIG.

  As shown in FIG. 8A, hydrogen ions 52 are implanted from the surface 5A, which is the implantation surface of the crystal single crystal substrate 5, thereby forming an amorphous layer 53 in the crystal single crystal substrate 5 (FIG. 7: S401). . By making the implantation conditions of the hydrogen ions 52 the same as in the first embodiment, an amorphous layer having a thickness of 0.1 μm can be formed centering on a depth of 1.25 μm from the surface 3A of the crystal single crystal substrate 5.

  As shown in FIG. 8B, a membrane support layer 55 is formed on the top surface 5A of the quartz single crystal substrate 5 (FIG. 7: S402).

  Subsequently, the surface of the membrane support layer 55 is planarized by CMP using a silica slurry (FIG. 7: S403). At this time, the surface roughness Ra is finished to 1 nm or less.

  As shown in FIG. 8C, groove processing is performed on the membrane support layer 55 and the single crystal crystal substrate 5 (FIG. 7: S404). That is, a resist pattern is formed on the membrane support layer 55 by photolithography, and the grooves 54A to 54D are formed from the surface of the membrane support layer 55 to a position deeper than the amorphous layer 53 of the quartz single crystal substrate 5 by dry etching or wet etching. 54D is formed. The grooves 54 </ b> A to 54 </ b> D can be formed in a mountain shape by forming the grooves 54 </ b> A to 54 </ b> D so as to be line symmetric with respect to an axis passing through the center along the crystal thin film surface (axis passing through the center along the crystal thin film surface). .

As shown in FIG. 8D, the membrane support layer 55 and the support substrate 57 are directly bonded in a vacuum using a cleaning bonding technique (FIG. 7: S405). As a material for the support substrate 57, LT (LiTaO ₃ ), LN (LiNbO ₃ ), Si, glass, or the like is used.

  As shown in FIG. 8E, the amorphous layer is etched to separate the quartz thin film from the quartz substrate (FIG. 7: S406). That is, the etching solution is introduced from the plurality of grooves formed in step S404 to remove the amorphous layer, and the crystal thin film is separated from the crystal substrate. As described in the first embodiment, the mixing ratio of the etching liquid is set so that the ratio of the etching rate between the crystal and the amorphous layer is about 200 times. Thereby, as described above, the portion along the central axis becomes the highest mountain shape (see FIG. 8F).

  As shown in FIG. 8G, upper electrodes (comb electrodes) 60A to 60C are formed on the upper surfaces of the crystal thin films 59A to 59C (FIG. 7: S407). For example, an Al thin film is patterned.

As shown in FIG. 8H, SiO ₂ layers 61A to 61C are formed so as to cover the comb electrodes 60A to 60C over the entire surfaces of the quartz thin films 59A to 59C.

When a part of the amorphous layer remains on the surfaces of the quartz thin films 59A to 59C, the frequency temperature coefficient TCF of the quartz glass is a negative value. On the other hand, the frequency temperature coefficient TCF of the SiO ₂ layer is a positive value. Therefore, the absolute value of the frequency temperature coefficient can be reduced as a whole by forming the SiO ₂ layer as described above. That is, frequency fluctuation due to temperature change can be reduced.

  Next, as shown in FIG. 8I, the crystal single crystal substrate 3 is cut to cut out individual crystal devices (FIG. 7: S408). Through the above steps, quartz crystal devices (surface wave devices) 65A to 65C having a pair of comb-shaped electrodes on one side of the quartz crystal thin film can be manufactured.

  In addition, when using a vibration mode in which vibration energy reaches the surface of the crystal, which is a vibrating body, such as a vibration mode in the thickness direction, a vibration mode in the plane direction, a bending mode, a plate wave, etc. In order to improve the Q value, it is desirable to form a space filled with vacuum, air, or nitrogen gas to form a vibration space and suppress leakage loss of elastic waves.

DESCRIPTION OF SYMBOLS 1,3,5 ... Crystal single crystal substrate 11A, 11B ... Resist film 12, 32, 52 ... Hydrogen ion 13A-13C, 33, 53 ... Amorphous layer 14A-14D, 36A-36D, 54A-54D ... Groove 15A-15C ... Spaces 16A to 16C, 18A to 18C, 39A to 39C, 59A to 59C ... Quartz thin film 17A to 17C ... Space 19 ... IDT (comb electrode)
20A, 20B ... Reflectors 31A-31C ... Lower electrodes 34A-34C ... Membrane sacrificial layers 35, 55 ... Membrane support layers 37, 57 ... Support substrate 38 ... Membrane spaces 40A-40C, 60A-60C ... Upper electrodes 41A-41C ... Etching windows 42A to 42C ... Vibration space 44 (44A to 44C) ... Quartz devices 61A to 61C ... SiO ₂ layers 65A to 65C ... Quartz devices (surface wave devices)

Claims (7)

An amorphous layer forming step of injecting ions or atoms into the quartz substrate to form an amorphous layer in the quartz substrate;
A separation step of removing the amorphous layer by etching to separate the quartz thin film from the quartz substrate;
A method of manufacturing a crystal device comprising:   2. The method of manufacturing a quartz device according to claim 1, wherein the separating step is a step of removing a part of the amorphous layer to form a space between the quartz thin film and the quartz substrate. Before the amorphous layer forming step, a step of forming a resist film for blocking the implantation of ions or atoms on a part of the surface on the ion or atom implantation side;
Removing the resist film after the amorphous layer forming step;
The manufacturing method of the crystal device of Claim 1 provided with these. After the amorphous layer forming step and before the separating step,
4. The method of manufacturing a crystal device according to claim 1, further comprising a step of providing a support substrate on an ion or atom implantation surface side of the crystal substrate. 5. After the amorphous layer forming step and before the separating step,
Providing a plurality of grooves in the quartz substrate and exposing a side surface of the amorphous layer;
5. The method for manufacturing a crystal device according to claim 1, wherein the separation step is a step of introducing an etching solution into the plurality of grooves to remove an amorphous layer between the grooves. 6. .   6. The method for manufacturing a crystal device according to claim 5, wherein the groove forming step is a step of forming a plurality of grooves in line symmetry with respect to an axis passing through a center along the surface of the crystal thin film. The method for manufacturing a quartz device according to claim 1, wherein the separation step is a step of further removing a part of the quartz substrate by etching .

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