MEMS vibrator, MEMS resonator and manufacturing method therefor

Abstract

To provide a MEMS vibrator which is highly sensitive, small in size, and low in manufacturing cost, and capable of securing long-term stability of vibration.SOLUTION: A MEMS vibrator includes: a substrate having a front surface and a back surface; a cavity provided in the substrate; a MEMS structure held in the cavity, where the MEMS structure includes: an anchor having a first end and a second end, the first end being connected to the substrate; a vibrator connected to the second end of the anchor and held in a hollow; counter electrodes disposed to face each other, with the vibrator interposed therebetween, the vibrator and the counter electrodes forming an electrostatic capacitance type vibrator; and a cap layer formed on the surface of the substrate and encapsulating the MEMS structure therein. The anchor includes an insulating isolation joint disposed to electrically insulate between the first end and the second end, and the counter electrode is electrically connected to a back-surface electrode provided on the back surface of the substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a MEMS vibrator, a MEMS resonator, and a method for manufacturing the same, and more particularly to a MEMS vibrator, a MEMS resonator, and a method for manufacturing the same that use an isolation joint. [Background technology]

[0002] In MEMS resonators, it is important to use materials with stable material properties (e.g., Young's modulus, modulus of rigidity, Poisson's ratio, etc.), and single-crystal silicon is used, for example. In this case, the silicon substrate is etched to create the electrodes of the MEMS structure, but electrical insulation is required between this electrode and the silicon substrate. For this reason, an SOI (Silicon on Insulator) substrate is usually used, and the electrodes are created on the silicon layer on top of the insulating layer.

[0003] In addition, for MEMS resonators, after the MEMS structure is fabricated on the silicon layer, a separate silicon substrate is prepared and then bonded to the SOI substrate using glass frit bonding, sealing the MEMS structure between the two substrates. This glass frit bonding is performed at a relatively low temperature, such as 450°C. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-134376

[0005] [overview] However, SOI substrates are more expensive than regular silicon single crystal substrates, resulting in higher manufacturing costs. Furthermore, while it is important to remove impurities such as organic matter adhering to the surface of the MEMS structure at high temperatures to ensure long-term vibration stability in MEMS resonators, glass frit bonding, which uses relatively low temperatures, does not adequately remove these impurities, making it impossible to guarantee long-term vibration stability.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a MEMS vibrator and a MEMS resonator that are highly sensitive, compact, inexpensive to manufacture, and capable of ensuring long-term vibration stability.

[0007] One aspect of the present disclosure is A MEMS resonator that vibrates at a predetermined resonant frequency, a substrate having a front surface and a back surface; a cavity provided in the substrate; a MEMS structure held within the cavity, an anchor having a first end and a second end, the first end connected to the substrate; a vibrator connected to the second end of the anchor and held in the air; the MEMS structure including opposing electrodes disposed opposite to each other with the vibrator sandwiched therebetween, the vibrator and the opposing electrodes forming a capacitive vibrator; a cap layer formed on a surface of the substrate and sealing the MEMS structure therein; the anchor includes an insulating isolation joint disposed to provide electrical insulation between the first end and the second end; The counter electrode is a MEMS resonator electrically connected to a back electrode provided on the back surface of the substrate.

[0008] Another aspect of the present disclosure is providing a substrate having a front surface and a back surface; a step of etching the substrate from the surface to fabricate a lower cavity and a MEMS structure held in the lower cavity in a hollow state, the MEMS structure having a vibrator and a counter electrode disposed opposite to each other with the vibrator sandwiched therebetween; depositing a sacrificial oxide film on a surface of the substrate; Etching a portion of the sacrificial oxide film to create an upper cavity, and creating a cavity from the lower cavity and the upper cavity in which the MEMS structure is held; depositing a cap layer of polycrystalline silicon over the surface of the substrate to encapsulate the MEMS structure; and an electrode forming step of forming a back electrode electrically connected to the counter electrode on the back surface of the substrate. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a plan view illustrating an outline of a MEMS resonator according to a first embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the MEMS resonator taken along line A1-A2 of FIG. 1. [Figure 3] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 4] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 5] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 6] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 7] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 8] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 9] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 10] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 11] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 12] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 13] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 14]3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 15] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 16] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 17] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 18] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 19] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 20] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 21] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 22] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 23] 3A to 3C are cross-sectional views illustrating a manufacturing process of the MEMS vibrator according to the first embodiment of the present invention. [Figure 24] FIG. 4 is a cross-sectional view of a modified example of the MEMS vibrator according to the first embodiment of the present invention. [Figure 25] FIG. 4 is a cross-sectional view of a modified example of the MEMS vibrator according to the first embodiment of the present invention. [Figure 26] FIG. 4 is a cross-sectional view of a modified example of the MEMS vibrator according to the first embodiment of the present invention. [Figure 27] FIG. 10 is a cross-sectional view of a MEMS resonator according to a second embodiment of the present invention. [Figure 28] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 29] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 30] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 31] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 32] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 33] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 34] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS vibrator according to a second embodiment of the present invention. [Figure 35] FIG. 10 is a cross-sectional view of a MEMS resonator according to a third embodiment of the present invention. [Figure 36] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 37] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 38] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 39] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 40] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 41] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 42] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 43] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 44] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 45] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 46] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 47] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 48] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 49] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 50] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 51] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 52] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 53] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 54] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 55] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 56] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 57] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 58] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 59] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention. [Figure 60] 10A to 10C are cross-sectional views illustrating a manufacturing process of a MEMS resonator according to a third embodiment of the present invention.

[0010] [Detailed explanation] <First Embodiment> (1) Structure FIG. 1 is a plan view showing an outline of a MEMS resonator according to a first embodiment of the present invention, generally designated 100. FIG. 2 is a cross-sectional view of the MEMS resonator taken along line A1-A2 of FIG. 1. Since FIG. 1 is a schematic view, the dimensions and the like do not necessarily match those of FIG. 2. For ease of explanation, a cap layer, electrode pads, and the like are omitted from FIG. 1.

[0011] The MEMS resonator 100 includes a substrate 10 made of, for example, single crystal silicon. A lower cavity 20 is provided in a portion of the substrate 10. A pair of anchors 40 extending in the X-axis direction and held in midair are provided above the lower cavity 20. The anchors 40 are MEMS structures fabricated by etching the substrate 10, and are connected to opposing side surfaces of the cavity 20. An isolation joint (IJ) 15 made of, for example, silicon oxide is provided midway along the anchor 40. Furthermore, although the anchor 40 in FIG. 1 has a portion with an elliptical structure to facilitate deformation, the elliptical structure may be omitted.

[0012] The MEMS resonator 100 further includes a resonator 50 held above the lower cavity 20 by a pair of anchors 40. The resonator 50 is also a MEMS structure fabricated by etching the substrate 10, and has a structure that is mirror-symmetric (or point-symmetric) with respect to the XZ plane that includes the X axis along which the anchors 40 extend. While FIG. 1 shows a structure with two annular portions arranged in mirror symmetry, the annular portions may have shapes other than circles, such as ellipses. The resonator 50 may also have other mirror-symmetric shapes, such as a figure-eight shape.

[0013] Two counter electrodes 61 and 63 are provided around the vibrator 50 so as to surround the two annular portions of the vibrator 50 from the outside. The counter electrodes 61 and 63 are also made of MEMS structures fabricated by etching the substrate 10, and an isolation joint (IJ) is provided midway so that they are electrically insulated from the substrate 10.

[0014] Furthermore, counter electrodes 62 and 64 are provided inside the vibrator 50 and are surrounded by the annular portion of the vibrator 50. The counter electrodes 62 and 64 are also made of MEMS structures fabricated by etching the substrate 10, and are provided with isolation joints (IJ) surrounding their peripheries, thereby electrically insulating them from the substrate 10. In this way, the anchor 40, the vibrator 50, and the counter electrodes 61 to 64 form a MEMS structure held in midair above the lower cavity 20.

[0015] Wiring layers 70-74 and electrodes 80-84 made of, for example, polycrystalline silicon are provided on the substrate 10. As can be seen from Fig. 2, an oxide film 12 made of silicon oxide is provided on the substrate 10, electrically insulating the wiring layers 71-73 from the substrate 10. In addition, IJs 15 are provided to surround the electrodes 80-84, electrically insulating the electrodes 80-84 from the substrate 10. The portions surrounded by the IJs 15 become TSVs (Through Silicon Vias) 13, which will be described later.

[0016] The wiring layer 70 runs from the electrode 80 over the substrate 10 and is electrically connected to the anchor 40 and the vibrator 50. The wiring layers 71 and 73 electrically connect the electrodes 81 and 83 to the counter electrodes 61 and 63, respectively. On the other hand, the wiring layers 72 and 74 electrically connect the electrodes 82 and 84 provided inside the vibrator 50 to the counter electrodes 62 and 64 around them, respectively.

[0017] The electrodes 80 to 83 are connected to rear electrodes 85 to 89 via TSVs 13 made of a silicon substrate surrounded by IJs 15, respectively.

[0018] As shown in FIG. 2, the substrate 10 is covered with a cap layer 95 to seal the resonator 50 within the upper cavity 27 .

[0019] (2) Operation The operation of the MEMS vibrator 100 will be described. As described above, in the MEMS vibrator 100, the vibrator 50 having two annular portions is provided so as to surround the counter electrodes 62 and 64, and the counter electrodes 61 and 63 are further provided around the vibrator 50. As a result, the counter electrodes 61 and 62 are arranged opposite each other with the vibrator 50 in between, and the counter electrodes 63 and 64 are arranged opposite each other with the vibrator 50 in between, each forming a capacitive vibrator.

[0020] The vibrator 50 is supported in the air by a pair of anchors 40 within the cavities 20 and 27. Therefore, the annular portions at both ends (top and bottom ends in FIG. 1) are also held in the air.

[0021] The capacitive vibrator is driven by electrostatic attraction generated by a potential applied between the opposing electrodes 61 to 64 and the vibrator 50. For example, electrode 80 connected to vibrator 50 is set to a constant voltage (reference voltage: for example, 18 V), and a rectangular voltage is applied to electrodes 81 and 82. The applied voltage is, for example, a rectangular wave that periodically changes between +0.1 V and -0.1 V, and voltages of opposite phases are applied to the two electrodes 81 and 82. As a result, electrostatic attraction acts alternately between the opposing electrode 61 and the vibrator 50 and between the opposing electrode 62 and the vibrator 50, causing the annular portion of the vibrator 50 to expand (expand outward from the center of the annular portion) and contract (contract toward the center of the annular portion).

[0022] When vibrator 50 is vibrated (expanded / contracted) using counter electrodes 61 and 62, the resonant frequency generated by counter electrodes 63 and 64 is measured. Because counter electrodes 63 and 64 are arranged opposite each other with vibrator 50 in between to form a capacitive vibrator, the resonant frequency of vibrator 50 can be detected by measuring the change in capacitance between counter electrodes 63 and 64 and vibrator 50. Here, the difference between the capacitance between counter electrode 63 and vibrator 50 and the capacitance between counter electrode 64 and vibrator 50 is used, making it possible to detect the resonant frequency with higher accuracy.

[0023] Counter electrodes 63 and 64 may be used to drive vibrator 50, and counter electrodes 61 and 62 may be used to measure the resonant frequency of the vibrator, or all of counter electrodes 61 to 64 may be used by switching between a drive mode for vibrator 50 and a measurement mode for the resonant frequency.

[0024] In the MEMS vibrator 100 according to the first embodiment of the present invention, by arranging the counter electrodes 62 and 63 inside the vibrator 50, it is possible to increase the opposing area between each of the counter electrodes 61 to 64 and the vibrator 50 compared to, for example, a case in which the counter electrodes 61 to 64 are all arranged outside the vibrator 50. This makes it possible to improve the driving efficiency of the vibrator 50 and the measurement accuracy of the resonance frequency. It also becomes possible to miniaturize the MEMS vibrator 100.

[0025] (3) Manufacturing method A method for manufacturing MEMS resonator 100 according to the first embodiment of the present invention will be described with reference to Figures 3 to 24. The manufacturing method includes the following steps 1 to 21. In Figures 3 to 24, the same reference numerals as in Figures 1 and 2 indicate the same or corresponding parts.

[0026] Step 1: As shown in FIG. 3, a substrate 10 made of, for example, single crystal silicon is prepared.

[0027] Step 2: As shown in FIG. 4, an oxide film 12 made of, for example, silicon oxide is formed by thermal oxidation.

[0028] 5, the oxide film 12 is patterned using a resist mask (not shown), and then the oxide film 12 is used as a hard mask to form trenches 14 in the substrate 10. The depth of the trenches 14 is, for example, 30 μm.

[0029] Step 4: As shown in FIG. 6, the inner wall of the trench 14 is thermally oxidized to fill the inside of the trench 14 with an oxide film 12.

[0030] 7, the oxide film 12 on the surface of the substrate 10 is etched using a resist mask (not shown) to form an opening 16. At the bottom of the opening 16, the surface of the substrate 10 is exposed.

[0031] Step 6: As shown in Figure 8, a polycrystalline silicon film, for example, 0.5 µm thick, is formed on the oxide film 12 by thermal CVD, and then etched using a resist mask (not shown) to form wiring layers 70, 71, and 72. The polycrystalline silicon is doped with impurities to make it conductive. The wiring layers 70, 71, and 72 are connected to the substrate 10 in the openings 16, forming contacts.

[0032] 9, the oxide film 12 and the substrate 10 are etched by DRIE using a resist mask (not shown) to form openings 18 around the area that will become the MEMS structure (structure etch). The depth of the openings 18 is, for example, 28 μm, and the width is, for example, 1 to 3 μm.

[0033] 10, an oxide film 22 made of, for example, silicon oxide is formed on the entire surface by plasma CVD. In this step 8, the oxide film 22 is also formed on the side and bottom surfaces of the opening 18.

[0034] 11, the oxide film 22 on the bottom surface of the opening 18 is removed by, for example, RIE to expose the surface of the substrate 10. In this case, the side surface of the opening 18 remains covered with the oxide film 22.

[0035] Step 10: As shown in Figure 12, the substrate 10 is etched through the opening 18 using SF6 gas to form a lower cavity 20. The depth of the lower cavity 20 is, for example, 25 µm. In this step, the sidewall of the opening 18 is not etched because it is covered with an oxide film 22, and a MEMS structure is formed that is held in the air above the lower cavity 20 (structure release). In addition, the lower end of the oxide film 12 embedded in the trench 14 is exposed, forming an isolation joint (IJ) 15.

[0036] Step 11: As shown in Fig. 13, the oxide film 22 is removed using, for example, hydrofluoric acid vapor. Prior to the next step 12, an ALD film such as Al2O3 may be deposited to protect the isolation joint (IJ) 15 from the hydrofluoric acid.

[0037] Step 12: As shown in Fig. 14, a sacrificial oxide film 25 made of silicon oxide is formed on the entire surface by plasma CVD. The thickness of the sacrificial oxide film 25 is, for example, 3 to 5 µm.

[0038] Step 13: As shown in FIG. 15, the surface of the sacrificial oxide film 25 is planarized by etching back using RIE or CMP.

[0039] Step 14: As shown in FIG. 16, the sacrificial oxide film 25 (or the sacrificial oxide film 25 and the ALD film if an ALD film was deposited prior to step 12) on the periphery of the substrate 10 is etched using a resist mask (not shown) to expose the surface of the substrate 10.

[0040] Step 15: As shown in FIG. 17, a polycrystalline silicon film 90 having a thickness of, for example, 1 μm is formed on the entire surface by thermal CVD.

[0041] 18, a resist mask (not shown) is used to form a plurality of release openings 93 in the polycrystalline silicon film 90. The diameter of each release opening 93 is, for example, 0.1 μm.

[0042] 19, the sacrificial oxide film 25 is etched using hydrofluoric acid vapor to partially remove the sacrificial oxide film 25 above the lower cavity 20, thereby forming an upper cavity 27. As a result, the MEMS structure, including the anchor 40, the vibrator 50, and the counter electrodes 61 to 64, is held in midair between the lower cavity 20 and the upper cavity 27.

[0043] Step 18: As shown in FIG. 20, a cap layer 95 made of polycrystalline silicon is formed on the entire surface by epitaxial growth. The film thickness of the cap layer 95 is, for example, 5 to 30 μm. By using epitaxial growth, the cap layer 95 is formed on the polycrystalline silicon film 90 so as to cover the release opening 93. By forming the cap layer 95, the MEMS structure is sealed inside. Furthermore, since the epitaxial growth is performed at a high temperature of about 600°C to 1400°C, impurities such as organic matter adhering to the surface of the MEMS structure can be removed.

[0044] Step 19: As shown in Fig. 21, the substrate 10 is ground from the backside using, for example, CMP. For example, if the thickness of the substrate 10 is 725µ, it is ground by about 100 to 150µm.

[0045] Step 20: As shown in FIG. 22, aluminum is evaporated onto the entire back surface of the substrate 10, and then patterned using a resist mask (not shown) to form a back electrode 85 of aluminum.

[0046] Step 21: As shown in FIG. 23, using a resist mask (not shown), the substrate 10 around the back electrode (excluding the substrate contact electrode) is etched to expose the IJ 15. This forms a TSV 13 that is surrounded by the insulating IJ 15 and connects the electrodes 80, 81, and 82 to the back electrode 85. The TSV 13 is formed from a part of the substrate 10 and is made of, for example, conductive silicon.

[0047] Through the above steps, the MEMS vibrator 100 according to the first embodiment of the present invention shown in FIGS. 1 and 2 is completed.

[0048] In the MEMS vibrator 100 according to the first embodiment of the present invention, the electrodes 80 to 84 are electrically connected to the back electrode 85 using the TSV 13 surrounding the IJ 15. However, instead of the IJ 15, the TSV 13 may be formed by etching the substrate 10 from the back surface to the oxide film 12 on the front surface, and forming a trench 17 surrounding the back electrode 85, as shown in FIG. 24.

[0049] Furthermore, as shown in FIG. 25, an insulating layer 19 such as an oxide film such as silicon oxide or a photoresist may be deposited on the entire back surface so as to fill the trench 17 in FIG. 24, and then the insulating layer 19 on the back surface electrode 85 may be removed to form a wiring layer 88.

[0050] 26, instead of IJ15, the substrate 10 may be etched from the back surface until the electrodes 80 to 84 are exposed to form a trench 17, and then an insulating layer 19 such as an oxide film or photoresist may be formed on the back surface of the substrate 10 and the side walls of the trench 17 for protection, followed by plating with copper or the like, to form a plated layer 89 electrically connected to the electrodes 80 to 84 to form a TSV13.

[0051] The TSV structure shown in FIGS. 24 to 26 may be applied to the MEMS vibrator 200 and the MEMS resonator 300 according to the second and third embodiments described below.

[0052] <Embodiment 2> (1) Structure Fig. 27 is a cross-sectional view of a MEMS resonator according to a second embodiment of the present invention, generally designated 200, as viewed in the same direction as A1-A2 in Fig. 1. In Fig. 27, the same reference numerals as in Figs. 1 and 2 indicate the same or corresponding parts.

[0053] 27, in MEMS resonator 200 according to the second embodiment of the present invention, the back surface of MEMS resonator 100 is covered with mold layer 96, and wiring layer 88 connected to back surface electrode 85 is provided thereon. Mold layer 96 is made of, for example, epoxy resin, and wiring layer 88 is made of, for example, copper.

[0054] Furthermore, the surface is covered with a solder resist 98. Openings are provided in the solder resist 98, exposing the wiring layer 88 for connection to the outside. For example, bumps may be provided on the exposed wiring layer 88.

[0055] (2) Operation In the MEMS vibrator 200 according to the second embodiment of the present invention, the wiring layer 88 connected to the back electrode 85 is already provided on the back surface of the MEMS vibrator 200, so that the MEMS vibrator 200 can be driven simply by connecting the wiring layer 88 exposed in the opening or the bumps thereon to an external control circuit or the like.

[0056] (3) Manufacturing method 28 to 34, a method for manufacturing MEMS vibrator 200 according to the first embodiment of the present invention will be described. In the method for manufacturing MEMS vibrator 200, steps 1 to 21 are the same as those for MEMS vibrator 200 according to the first embodiment, followed by the following steps 22 to 28. In Figs. 28 to 34, the same reference numerals as those in Figs. 1 and 2 indicate the same or corresponding parts.

[0057] 28, a photosensitive dry film 97 is attached to the rear surface of the substrate 10. Photoresist may be applied instead of the photosensitive dry film.

[0058] Step 23: As shown in FIG. 29, the photosensitive dry film 97 above the rear electrode 85 is opened.

[0059] 30, pillars 87 are formed on the back surface electrode 85 so as to fill the openings by, for example, immersion in a plating solution. The pillars 87 are made of, for example, copper.

[0060] 31, after removing the photosensitive dry film 27, a mold layer 96 made of, for example, epoxy resin is formed on the entire surface. The mold layer 96 is formed by, for example, compression molding.

[0061] Step 26: As shown in FIG. 32, the mold layer 96 is ground away, for example by CMP, to expose the pillars.

[0062] Step 27: As shown in FIG. 33, a metal layer such as copper is formed on the entire surface by evaporation or sputtering, and then the metal layer is patterned using a resist mask (not shown) to form a wiring layer 88. The wiring layer 88 can be formed at a desired position.

[0063] Step 28: As shown in Fig. 34, solder resist 98 is applied to the entire surface, and then openings are made at desired positions to expose wiring layer 88. If necessary, solder bumps may be formed on the exposed wiring layer 88. Through the above steps, MEMS resonator 200 according to the second embodiment shown in Fig. 27 is completed.

[0064] <Third Embodiment> (1) Structure Fig. 35 is a cross-sectional view of a MEMS resonator according to a third embodiment of the present invention, generally designated 300, as viewed in the same direction as A1-A2 in Fig. 1. In Fig. 35, the same reference numerals as in Figs. 1 and 2 indicate the same or corresponding parts.

[0065] 35, MEMS resonator 300 according to the third embodiment of the present invention has a structure in which ASIC 500 is connected to the back surface of MEMS vibrator 100. That is, back surface electrode 85 of MEMS vibrator 100 is connected to electrode 585 of the ASIC, thereby forming MEMS resonator 300.

[0066] (2) Operation In the MEMS resonator 300 according to the third embodiment of the present invention, the MEMS resonator 300 is formed integrally with the ASIC 500 that controls the MEMS resonator 300, so that wiring such as wire bonding between the MEMS resonator 300 and the ASIC 500 is not required, making it possible to provide a highly reliable and compact MEMS resonator 300.

[0067] (3) Manufacturing method A manufacturing method for MEMS resonator 300 according to the third embodiment of the present invention will be described with reference to Figures 36 to 60. The manufacturing method includes the following steps 1 to 25. In Figures 36 to 60, the same reference numerals as in Figures 1 and 2 indicate the same or corresponding parts.

[0068] Steps 1 to 13: As shown in Figures 36 to 48, after forming an oxide film 12 on the substrate 1 and in the trench 14, wiring layers 70 to 72, 75 and a lower cavity 20 are formed, and a sacrificial oxide film 25 is further deposited on the surface. These steps 1 to 13 are almost the same as steps 1 to 13 (Figures 3 to 15) in the first embodiment. However, in the third embodiment, an electrode layer 75 for connection to an ASIC is also formed in the same steps.

[0069] Step 14: As shown in FIG. 49, using a resist mask (not shown), the sacrificial oxide film 25 (or the sacrificial oxide film 25 and the ALD film, if an ALD film was deposited prior to step 12) on the peripheral portion of the substrate 10 and on the electrode layer 75 is etched to expose the surface of the substrate 10.

[0070] 50 to 52, a polycrystalline silicon film 90 is formed on the entire surface, and after forming a plurality of release openings 93, the sacrificial oxide film 25 is etched using hydrofluoric acid vapor to form the upper cavity 27. As a result, the MEMS structure, including the anchor 40, the vibrator 50, and the counter electrodes 61 to 64, is held in midair between the lower cavity 20 and the upper cavity 27.

[0071] 53 and 54, after forming a cap layer 95 on the entire surface, the back surface of the substrate 10 is ground using CMP. Steps 15 to 19 are almost the same as steps 15 to 19 (FIGS. 17 to 21) in the first embodiment.

[0072] 55, aluminum is evaporated onto the entire rear surface of substrate 10, and then germanium is evaporated onto the rear surface, followed by patterning using a resist mask (not shown) to form rear surface electrode 85. Here, rear surface electrode 85 has a two-layer structure of an aluminum layer and a germanium layer, with the aluminum layer being 0.2 μm thick and the germanium layer being 1.0 μm thick, for example.

[0073] Step 21: As shown in FIG. 56, using a resist mask (not shown), the substrate 10 around the back electrode (excluding the substrate contact electrode) is etched to expose the IJ 15. This forms a TSV 13 surrounded by the IJ 15 and connecting the wiring layers 70, 71, 72, and 75 to the back electrode 85. In this step, the IJ 15 is also formed around the electrode 75, forming the TSV 13 connecting the electrode 71 to the back electrode 85.

[0074] 57, the substrate 10 is turned over, and the electrode 585 on the surface of the ASIC 500 is bonded to the back electrode 85 of the MEMS resonator 100. The electrode 585 is, for example, an aluminum layer of 0.8 μm, and has a two-layer structure of an aluminum layer and a germanium layer, so that it can be placed on the back electrode 85 and heated to achieve eutectic bonding.

[0075] Step 23: As shown in FIG. 58, the cap layer 95 on the surface of the MEMS vibrator 100 is planarized by, for example, the CMP method.

[0076] Step 24: As shown in FIG. 59, a polycrystalline silicon layer is formed on the cap layer 95, and then patterned using a resist mask (not shown) to form a pad electrode 580 above the electrode 75.

[0077] Step 25: As shown in FIG. 60 , the cap layer 95 and the polycrystalline silicon film 90 are etched using a resist mask (not shown) to form a trench 517 surrounding the pad electrode 580. This forms a TSV 513 that connects the electrode 75 and the pad electrode 580. As a result, the electrode 75 of the ASIC 500 is electrically connected to the pad electrode 580 via the TSV 13, the electrode 80, and the TSV 513.

[0078] Through the above steps, the MEMS resonator 300 according to the third embodiment of the present invention shown in FIG. 35 is completed.

[0079] <Additional Notes> The present disclosure provides: A MEMS resonator that vibrates at a predetermined resonant frequency, a substrate having a front surface and a back surface; a cavity provided in the substrate; A MEMS structure held within a cavity, comprising: an anchor having a first end and a second end, the first end connected to the substrate; a vibrator connected to a second end of the anchor and held in the hollow; a MEMS structure including opposing electrodes disposed opposite to each other with a vibrator therebetween, the vibrator and the opposing electrodes forming a capacitive vibrator; a cap layer formed on the surface of the substrate and sealing the MEMS structure therein; the anchor includes an insulating isolation joint arranged to provide electrical insulation between the first end and the second end; The counter electrode is a MEMS resonator electrically connected to a back electrode provided on the back surface of the substrate. By using an isolation joint for insulation and a back electrode, a small, high-performance MEMS resonator can be provided at low cost.

[0080] In the present disclosure, the vibrator has an annular portion, and opposing electrodes are disposed opposite to each other across the annular vibrator. Compared to when all the opposing electrodes are arranged on one side of the vibrator, the opposing area between the opposing electrodes and the vibrator can be made larger, and the driving efficiency of the vibrator and the measurement accuracy of the resonance frequency can be improved.

[0081] In the present disclosure, the opposing electrodes arranged opposite each other across the vibrator are arranged concentrically. Such a structure can be made compact and the opposing area between the opposing electrode and the vibrator can be increased.

[0082] In the present disclosure, the counter electrode is connected to the back electrode through a substrate surrounded by an insulating isolation joint. By using a substrate surrounded by insulating isolation joints, TSVs can be easily formed.

[0083] In the present disclosure, a solder resist is further provided on the rear surface of the substrate. By simply connecting an external control circuit, the MEMS vibrator can be driven.

[0084] The present disclosure is a MEMS resonator that includes a MEMS vibrator and an ASIC connected to a back electrode of the MEMS vibrator. This eliminates the need for wiring such as wire bonding between the MEMS resonator and the ASIC, making it possible to provide a highly reliable and compact MEMS resonator.

[0085] The present disclosure provides: providing a substrate having a front surface and a back surface; a step of etching the substrate from the surface to fabricate a lower cavity and a MEMS structure held in the lower cavity in a hollow state, the MEMS structure having a vibrator and a counter electrode disposed opposite to each other with the vibrator sandwiched therebetween; depositing a sacrificial oxide film on a surface of the substrate; Etching a portion of the sacrificial oxide film to create an upper cavity, and creating a cavity from the lower cavity and the upper cavity in which the MEMS structure is held; depositing a cap layer of polycrystalline silicon over the surface of the substrate to encapsulate the MEMS structure; and an electrode forming step of forming a back electrode electrically connected to the counter electrode on the back surface of the substrate. This process allows for low-cost, small-sized, and high-performance devices.

[0086] The electrode formation process of the present disclosure includes: forming an annular trench in a surface of a substrate, the trench being filled with an insulator; forming a back surface electrode on the back surface of the substrate; Selectively etching the substrate from the backside until the insulator-filled trench is exposed, leaving the substrate surrounded by the annular insulator and with the backside electrode. Back electrodes can be easily formed using TSVs.

[0087] The present disclosure further includes a step of providing a solder resist on the back surface of the substrate. By simply connecting an external control circuit, the MEMS vibrator can be driven.

[0088] The present disclosure provides a method for manufacturing a MEMS resonator, comprising: providing an ASIC with electrodes; The method also includes a step of connecting the back electrode of the MEMS vibrator to an electrode of the ASIC. This eliminates the need for wiring such as wire bonding between the MEMS resonator and the ASIC, making it possible to provide a highly reliable and compact MEMS resonator. [Industrial Applicability]

[0089] The MEMS vibrator and MEMS resonator according to the present invention can be applied to oscillation circuits and filters that utilize the resonance frequency, and temperature sensors, pressure sensors, mass sensors, and the like that utilize the shift in the resonance frequency. [Explanation of symbols]

[0090] 10 Substrate 12 Oxide film 13 TSV 14 Trench 15 Oxide film 16 Opening 17 Trench 18 Opening 19 Insulating layer 15 Isolation Joint (IJ) 20 Lower cavity 22 Oxide film 25 Sacrificial oxide film 27 Upper cavity 40 Anchor 50 oscillators 61~64 Counter electrode 70~74 wiring layer 80~84 electrode 85 Back electrode 86 Electrode 87 Pillar 88 Wiring layer 89 plating layer 90 Polycrystalline silicon film 93 Release opening 95 Cap Layer 96 mold layer 97 Photosensitive dry film 98 Solder Resist 100, 200 MEMS resonators 300 MEMS resonators 500 ASIC 513 TSV 517 Trench 580 Pad Electrode 585 Electrode

Claims

1. A MEMS vibrator that vibrates at a predetermined resonant frequency, a substrate having a front surface and a back surface; a cavity provided in the substrate; a MEMS structure held within the cavity, an anchor having a first end and a second end, the first end connected to the substrate; a vibrator connected to the second end of the anchor and held in the air; the MEMS structure including: opposing electrodes disposed opposite to each other with the vibrator interposed therebetween, the vibrator and the opposing electrodes forming a capacitive vibrator; a cap layer formed on a surface of the substrate and sealing the MEMS structure therein; the anchor includes an insulating isolation joint disposed to provide electrical isolation between the first end and the second end; The counter electrode is electrically connected to a back surface electrode provided on the back surface of the substrate.

2. The MEMS vibrator according to claim 1 , wherein the vibrator has an annular portion, and the counter electrodes are disposed opposite to each other with the annular portion of the vibrator sandwiched therebetween.

3. The MEMS vibrator according to claim 1 or 2, wherein the vibrator and the counter electrode disposed opposite to each other across the vibrator are arranged on concentric circles.

4. 3. The MEMS vibrator according to claim 1, wherein the counter electrode is connected to the rear electrode via a substrate surrounded by an insulating isolation joint.

5. 3. The MEMS vibrator according to claim 1, further comprising a solder resist provided on the rear surface of the substrate.

6. A MEMS resonator comprising: the MEMS vibrator according to claim 1 or 2; and an ASIC connected to a back electrode of the MEMS vibrator.

7. providing a substrate having a front surface and a back surface; a step of etching the substrate from the surface to fabricate a lower cavity and a MEMS structure held in the lower cavity in a hollow state, the MEMS structure having a vibrator and a counter electrode disposed opposite to each other with the vibrator sandwiched therebetween; depositing a sacrificial oxide layer on a surface of the substrate; etching a portion of the sacrificial oxide film to form an upper cavity, and forming a cavity from the lower cavity and the upper cavity into which the MEMS structure is held; depositing a cap layer of polycrystalline silicon on the surface of the substrate to encapsulate the MEMS structure; and forming an electrode on the back surface of the substrate, the back surface electrode being electrically connected to the counter electrode.

8. The electrode forming step includes: forming an annular trench in a surface of the substrate, the trench being filled with an insulator; forming the back surface electrode on the back surface of the substrate; and selectively etching the substrate from the backside until the trench filled with the insulator is exposed, leaving a substrate surrounded by the annular insulator and provided with the backside electrode.

9. The manufacturing method according to claim 7 or 8, further comprising the step of providing a solder resist on the rear surface of the substrate.

10. a step of preparing the MEMS vibrator according to claim 7 or 8; providing an ASIC with electrodes; and connecting a rear electrode of the MEMS vibrator to an electrode of the ASIC.

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