Package structure and method of manufacturing the same

Abstract

A package structure and a manufacturing method thereof are provided. The package structure includes: a pair of substrates (20, 30) arranged opposite to each other; a bonding portion (H) that seals an element (10) in an internal space surrounded by the pair of substrates (20, 30); an adsorption layer (72) provided in at least one substrate (30) of the pair of substrates (20, 30) and located in the internal space, which at least adsorbs hydrogen; and a diffusion prevention layer (71) provided between the at least one substrate (30) and the adsorption layer (72), in which hydrogen is less likely to diffuse compared to the at least one substrate (30).

Description

Technical Field

[0001] This invention relates to packaging structures and their manufacturing methods. Background Technology

[0002] Electronic components, mechanical components, and optical components are susceptible to performance degradation due to contact with oxygen and water vapor, and are therefore often housed within a hermetically sealed encapsulation structure. In such cases, to increase the vacuum level of the internal space, a layer called a getter is placed inside the internal space to adsorb gas molecules.

[0003] For example, Patent Document 1 discloses a packaging structure comprising: a lower cover that forms a MEMS substrate together with a resonator; an upper cover that forms a vibration space for the resonator between the lower cover and the upper cover; and a getter layer disposed on the upper cover and located within the internal space, which adsorbs escaping gases. By providing a getter layer within the internal space of the packaging structure, the vacuum level of the internal space can be increased, suppressing performance degradation of the device. In particular, in a piezoelectric vibrating element utilizing the piezoelectric effect as described in Patent Document 1, fluctuations in frequency characteristics can be suppressed due to the adsorption of gas molecules.

[0004] Patent Document 1: International Publication No. 2019 / 155663

[0005] However, in the packaging structure described in Patent Document 1, if hydrogen contained in the substrate constituting the top cover invades the getter layer and increases the hydrogen storage capacity of the getter layer, there is a possibility that a hydrogen desorption reaction occurs from the getter layer, and a high vacuum cannot be maintained. Summary of the Invention

[0006] The present invention was made in view of the following circumstances, and the object of the present invention is to provide a packaging structure and a method thereof that can easily maintain a high vacuum level.

[0007] One embodiment of the packaging structure of the present invention comprises: a pair of substrates disposed opposite to each other; a joint of the pair of substrates for sealing an element in an internal space surrounded by the pair of substrates; an adsorption layer disposed on at least one of the pair of substrates and located in the internal space, for adsorbing at least hydrogen; and an anti-diffusion layer disposed between the at least one substrate and the adsorption layer, wherein hydrogen is less likely to diffuse compared to the at least one substrate.

[0008] Another aspect of the present invention provides a method for manufacturing a packaging structure comprising: a step of preparing a pair of substrates; a step of providing an adsorption layer for adsorbing at least hydrogen on at least one of the substrates; and a step of configuring the pair of substrates such that the adsorption layer provided on at least one substrate faces the other substrate, and providing a joint for sealing an element in an internal space surrounded by the pair of substrates, and further comprising: a step of providing an anti-diffusion layer on at least one substrate that is less prone to hydrogen diffusion than the at least one substrate.

[0009] According to the present invention, a packaging structure capable of easily maintaining a high vacuum level and a method thereof can be provided. Attached Figure Description

[0010] Figure 1 This is a perspective view schematically showing the appearance of the resonant device according to the first embodiment.

[0011] Figure 2 This is an exploded perspective view schematically showing the structure of the resonant device according to the first embodiment.

[0012] Figure 3 This is a top view schematically showing the structure of the resonator in the first embodiment.

[0013] Figure 4 It is a schematic representation Figure 1 A cross-sectional view along the X-axis of the stacked structure of the resonant device shown.

[0014] Figure 5 It is a schematic representation Figure 1 A cross-sectional view along the Y-axis of the stacked structure of the resonant device shown.

[0015] Figure 6 This is a flowchart schematically illustrating the manufacturing method of the resonant device according to the first embodiment.

[0016] Figure 7 It is a cross-sectional view schematically showing the process of setting the anti-diffusion layer.

[0017] Figure 8 It is a cross-sectional view schematically representing the process of setting the adsorption layer.

[0018] Figure 9 This is a cross-sectional view schematically illustrating the process of setting the adsorption layer in the manufacturing method of the resonant device in the second embodiment.

[0019] Figure 10 This is a cross-sectional view schematically illustrating the process of setting the anti-diffusion layer in the manufacturing method of the resonant device according to the second embodiment.

[0020] Figure 11 This is a cross-sectional view schematically showing the structure of the top cover in the third embodiment.

[0021] Figure 12 This is a cross-sectional view schematically illustrating the process of setting the adsorption layer in the manufacturing method of the resonant device according to the fourth embodiment.

[0022] Figure 13 This is a cross-sectional view schematically illustrating the process of setting an anti-diffusion layer in the manufacturing method of the resonant device according to the fourth embodiment. Detailed Implementation

[0023] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The drawings for each embodiment are illustrative, and the dimensions and shapes of the parts are schematic and should not be construed as limiting the technical scope of the present invention to these embodiments.

[0024] As one embodiment of the present invention, a resonant device with a built-in MEMS resonator will be used as an example for explanation. The MEMS resonator corresponds to the component housed in the packaging structure of one embodiment of the present invention, and the lower cover and upper cover correspond to a pair of substrates constituting the packaging structure of one embodiment of the present invention. The packaging structure of one embodiment of the present invention is not limited to MEMS resonators; it can be appropriately applied to various electronic components, optical components, mechanical components, etc., as long as it houses components requiring high vacuum or low hydrogen partial pressure within an internal space.

[0025] <First Implementation>

[0026] First, refer to Figure 1 and Figure 2 The structure of the resonant device 1 according to the first embodiment of the present invention will be described. Figure 1 This is a perspective view schematically showing the appearance of the resonant device according to the first embodiment. Figure 2 This is an exploded perspective view schematically showing the structure of the resonant device according to the first embodiment.

[0027] The following describes the structure of the resonant device 1. To clarify the relationships between the various figures and aid in understanding the positional relationships of the components, for convenience, an orthogonal coordinate system consisting of the X-axis, Y-axis, and Z-axis is used in the figures. The directions parallel to the X-axis, Y-axis, and Z-axis are referred to as the X-axis direction, Y-axis direction, and Z-axis direction, respectively. The surface defined by the X-axis and Y-axis is called the XY plane, and the same applies to the YZ plane and ZX plane. Furthermore, in the following description, the direction parallel to the Z-axis and the direction of the arrow on the Z-axis (+Z-axis direction) will be described above, and the direction parallel to the Z-axis and opposite to the arrow on the Z-axis (-Z-axis direction) will be described below.

[0028] The resonant device 1 includes a resonator 10, a lower cover 20 and an upper cover 30 disposed opposite to each other with the resonator 10 sandwiched between them. The lower cover 20, the resonator 10 and the upper cover 30 are stacked in this order along the Z-axis. The resonator 10 and the lower cover 20 are joined together, and the resonator 10 and the upper cover 30 are joined together. A vibration space for the resonator 10 is formed between the lower cover 20 and the upper cover 30, which are joined together via the resonator 10. In other words, the lower cover 20 and the upper cover 30 are indirectly joined together to form an internal space for housing the resonator 10, which is equivalent to a piezoelectric vibrating element. Moreover, the lower cover 20 and the upper cover 30 constitute an encapsulation structure for housing the resonator 10.

[0029] The resonator 10 is a MEMS resonant element manufactured using MEMS technology. The resonator 10 includes a resonating section 110, a holding section 140, and a holding arm 150. The resonator 110 is held in a vibration space. The vibration mode of the resonator 110 is not limited; for example, it can be an out-of-plane bending vibration mode relative to the XY plane, but it can also be an in-plane bending vibration mode relative to the XY plane. The holding section 140 is, for example, configured as a rectangular frame to surround the resonator 110. The holding arm 150 connects the resonator 110 and the holding section 140.

[0030] The frequency band of the resonator 10 is, for example, above 1 kHz and below 1 MHz. For the vibration mode of such a resonator 10, the frequency variation caused by the mass change of the vibrating part 110 is relatively large. Therefore, by increasing the vacuum level of the vibration space of the resonant device 1, the deviation of the initial frequency and the frequency variation over time can be reduced.

[0031] The lower cover 20 has a rectangular flat base plate 22 arranged along the XY plane, and a sidewall 23 extending from the periphery of the base plate 22 along the Z-axis. The sidewall 23 engages with the holding portion 140 of the resonator 10. In the lower cover 20, a recess 21 formed by the base plate 22 and the sidewall 23 is formed on the surface opposite to the vibrating portion 110 of the resonator 10. The recess 21 is an upward-opening cuboid opening, forming part of the vibration space of the resonator 10. In other words, the lower cover 20 has an inner wall 25 constituting the recess 21, which corresponds to part of the internal space of the encapsulation structure. On the inner surface of the lower cover 20, a protrusion 50 protruding into the vibration space is formed on the upper surface of the base plate 22.

[0032] The structure of the upper cover 30, except for the protrusion 50 provided on the lower cover 20, is symmetrical to the structure of the lower cover 20 with respect to the resonator 10. That is, the upper cover 30 has a rectangular flat plate base 32 disposed along the XY plane, and a sidewall 33 extending from the periphery of the base plate 32 along the Z-axis direction, the sidewall 33 engaging with the holding portion 140 of the resonator 10. In the upper cover 30, a recess 31 is formed on the surface opposite to the vibrating portion 110 of the resonator 10. The recess 31 is a downward-opening cuboid opening, forming part of the vibration space of the resonator 10. In other words, the upper cover 30 has an inner wall 35 constituting the recess 31, and the recess 31 corresponds to part of the internal space of the packaging structure.

[0033] Furthermore, the structures of the lower cover 20 and the upper cover 30 are not limited to the aforementioned configurations; for example, they may be asymmetrical. For instance, one of the lower cover 20 or the upper cover 30 may be dome-shaped. The shapes of the recess 21 in the lower cover 20 and the recess 31 in the upper cover 30 may differ from each other; for example, the depths of the recesses 21 and 31 may differ.

[0034] Next, refer to Figure 3 The structure of the resonator 10, the vibration part 110, the holding part 140, and the holding arm 150 of the resonator 10 according to the embodiment of the present invention will be described in more detail. Figure 3 This is a top view schematically showing the structure of the resonator in the first embodiment.

[0035] When viewed from the top cover 30 side, the vibrating part 110 is disposed inside the holding part 140. A space is formed between the vibrating part 110 and the holding part 140 at a predetermined interval. The vibrating part 110 has an excitation part 120 composed of four vibrating arms 121A, 121B, 121C, and 121D, and a base 130 connected to the excitation part 120. Furthermore, the number of vibrating arms is not limited to four, and can be set to any number of more than one. In this embodiment, the excitation part 120 and the base 130 are integrally formed.

[0036] Vibration arms 121A, 121B, 121C, and 121D extend along the Y-axis and are arranged side-by-side at predetermined intervals along the X-axis. One end of vibration arm 121A is a fixed end connected to the front end portion 131A of the base 130 (described later), and the other end of vibration arm 121A is an open end separate from the front end portion 131A of the base 130. Vibration arm 121A has a mass attachment portion 122A and an arm portion 123A arranged in the extending direction of vibration arm 121A. The mass attachment portion 122A is formed on the open end side, and the arm portion 123A extends from the fixed end and is connected to the mass attachment portion 122A. In other words, the mass attachment portion 122A is located at a position in the vibration section 110 where the displacement is relatively large. Similarly, vibration arms 121B, 121C, and 121D each have mass attachment portions 122B, 122C, and 122D and arm portions 123B, 123C, and 123D, respectively. Furthermore, the width of arms 123A to 123D is approximately 50 μm in the X-axis direction and the length is approximately 450 μm in the Y-axis direction, respectively.

[0037] Vibration arms 121A and 121D are outer vibration arms positioned on the outer side in the X-axis direction, while vibration arms 121B and 121C are inner vibration arms positioned on the inner side in the X-axis direction. As an example, the width (hereinafter referred to as the "release width") W1 of the gap formed between the arm portions 123B and 123C of each of the inner vibration arms 121B and 121C is set to be greater than the release width W2 between the arm portions 123A and 123B of each of the adjacent outer vibration arms 121A and inner vibration arms 121B in the X-axis direction, and also greater than the release width W2 between the arm portions 123D and 123C of each of the adjacent outer vibration arms 121D and inner vibration arms 121C in the X-axis direction. By setting the release width W1 to be larger than the release width W2, vibration characteristics and durability can be improved. The values ​​of release widths W1 and W2 are not limited; for example, release width W1 is approximately 25 μm and release width W2 is approximately 10 μm. Furthermore, the release width W1 between the inner vibrating arms and the release width W2 between the inner and outer vibrating arms are not limited to... Figure 3 As shown, the release width W1 can also be set to be smaller than the release width W2, or they can be set to be at equal intervals.

[0038] The mass augmentation portions 122A to 122D each have mass augmentation films 125A to 125D on their respective surfaces. In other words, when viewed from the top cover 30 side, the portion containing each of the mass augmentation films 125A to 125D is the mass augmentation portion 122A to 122D. The weight per unit length of each of the mass augmentation portions 122A to 122D (hereinafter referred to simply as "weight") is greater than the weight of each of the arm portions 123A to 123D due to the presence of the mass augmentation films 125A to 125D. As a result, the vibration unit 110 can be miniaturized, and the vibration characteristics can be improved. In addition, the mass augmentation films 125A to 125D not only have the function of increasing the weight of the front end portion of the vibration arms 121A to 121D respectively, but also have the function of serving as a so-called frequency adjustment film, which adjusts the resonant frequency of the vibration arms 121A to 121D by cutting a portion of it.

[0039] In this embodiment, the width of each of the mass attachments 122A to 122D along the X-axis is greater than the width of each of the arms 123A to 123D along the X-axis. This allows for a further increase in the weight of each of the mass attachments 122A to 122D. However, as long as the weight per unit length of each of the mass attachments 122A to 122D is greater than the weight per unit length of each of the arms 123A to 123D, the width of each of the mass attachments 122A to 122D along the X-axis is not limited to the above-described case. The width of each of the mass attachments 122A to 122D along the X-axis may also be the same as, or less than, the width of each of the arms 123A to 123D along the X-axis.

[0040] When viewed from the top cover 30 side, each of the mass attachments 122A to 122D is a generally rectangular shape with curved surfaces (e.g., so-called R-shapes) at its four corners. Each of the arms 123A to 123D is a generally rectangular shape with an R-shape near the fixed end connected to the base 130 and near the connecting portion connected to each of the mass attachments 122A to 122D. However, the shapes of the mass attachments 122A to 122D and each of the arms 123A to 123D are not limited to the above description. For example, each of the mass attachments 122A to 122D may also be trapezoidal or L-shaped. Furthermore, each of the arms 123A to 123D may also be trapezoidal or have slits, etc.

[0041] When viewed from the top cover 30 side, a protrusion 50 protruding from the bottom cover 20 is formed between the arm portions 123B and 123C of each of the inner vibrating arms 121B and 121C. The protrusion 50 extends parallel to the arm portions 123B and 123C along the Y-axis. The length of the protrusion 50 in the Y-axis direction is approximately 240 μm, and the length in the X-axis direction is approximately 15 μm. By forming the protrusion 50, the twisting of the bottom cover 20 is suppressed.

[0042] like Figure 3 As shown, when viewed from the top cover 30 side, the base 130 has a front end portion 131A, a rear end portion 131B, a left end portion 131C, and a right end portion 131D. The front end portion 131A, rear end portion 131B, left end portion 131C, and right end portion 131D are all parts of the outer edge of the base 130. Specifically, the front end portion 131A is the end portion extending along the X-axis direction on the side of the vibration arms 121A to 121D. The rear end portion 131B is the end portion extending along the X-axis direction on the side opposite to the vibration arms 121A to 121D. The left end portion 131C is the end portion extending along the Y-axis direction on the side of the vibration arm 121A when viewed from the vibration arm 121D. The right end portion 131D is the end portion extending along the Y-axis direction on the side of the vibration arm 121D when viewed from the vibration arm 121A.

[0043] The two ends of the left end 131C are connected to one end of the front end 131A and one end of the rear end 131B, respectively. The two ends of the right end 131D are connected to the other ends of the front end 131A and the rear end 131B, respectively. The front end 131A and the rear end 131B are opposite each other in the Y-axis direction. The left end 131C and the right end 131D are opposite each other in the X-axis direction. Vibration arms 121A to 121D are connected to the front end 131A.

[0044] When viewed from the top cover 30 side, the base 130 is approximately rectangular with the front end 131A and rear end 131B as its long sides and the left end 131C and right end 131D as its short sides. The base 130 is approximately symmetrical with respect to the virtual plane P defined by the perpendicular bisectors of the front end 131A and rear end 131B. Furthermore, the base 130 is not limited to… Figure 3 The rectangle shown can also be other shapes that are approximately symmetrical with respect to the virtual plane P. For example, the shape of the base 130 can also be a trapezoidal shape in which one of the front end 131A and the rear end 131B is longer than the other. In addition, at least one of the front end 131A, the rear end 131B, the left end 131C, and the right end 131D can be bent or curved.

[0045] Furthermore, the virtual plane P corresponds to the plane of symmetry of the entire vibrating section 110. Therefore, the virtual plane P is also a plane passing through the center of the vibrating arms 121A to 121D in the X-axis direction, and is located between the inner vibrating arms 121B and 121C. Specifically, each of the adjacent outer vibrating arms 121A and inner vibrating arms 121B is separated by the virtual plane P, and is formed symmetrically with each of the adjacent outer vibrating arms 121D and inner vibrating arms 121C.

[0046] In the base 130, as an example, the longest distance in the Y-axis direction between the front end portion 131A and the rear end portion 131B, i.e., the base length, is approximately 40 μm. Additionally, as an example, the longest distance in the X-axis direction between the left end portion 131C and the right end portion 131D, i.e., the base width, is approximately 300 μm. Furthermore, in... Figure 3 In the structural example shown, the base length is equivalent to the length of the left end 131C or the right end 131D, and the base width is equivalent to the length of the front end 131A or the rear end 131B.

[0047] The retaining part 140 is a portion used to hold the vibrating part 110 in the vibration space formed by the lower cover 20 and the upper cover 30, for example, surrounding the vibrating part 110. Figure 3 As shown, when viewed from the top cover 30 side, the holding part 140 has a front frame 141A, a rear frame 141B, a left frame 141C, and a right frame 141D. The front frame 141A, rear frame 141B, left frame 141C, and right frame 141D are each part of a generally rectangular frame surrounding the vibrating part 110. Specifically, the front frame 141A is the portion extending along the X-axis direction on the excitation part 120 side when viewed from the base 130. The rear frame 141B is the portion extending along the X-axis direction on the base 130 side when viewed from the excitation part 120. The left frame 141C is the portion extending along the Y-axis direction on the vibrating arm 121A side when viewed from the vibrating arm 121D. The right frame 141D is the portion extending along the Y-axis direction on the vibrating arm 121D side when viewed from the vibrating arm 121A. The holding part 140 is formed symmetrically with respect to the virtual plane P.

[0048] The two ends of the left frame 141C are connected to one end of the front frame 141A and one end of the rear frame 141B, respectively. The two ends of the right frame 141D are connected to the other ends of the front frame 141A and the rear frame 141B, respectively. The front frame 141A and the rear frame 141B are positioned opposite each other in the Y-axis direction, separated by the vibrating part 110. The left frame 141C and the right frame 141D are positioned opposite each other in the X-axis direction, separated by the vibrating part 110. Furthermore, the holding part 140 may be provided in at least a portion around the vibrating part 110, and is not limited to a continuous frame shape in the circumferential direction.

[0049] A retaining arm 150 is disposed inside the retaining portion 140, connecting the base 130 and the retaining portion 140. For example... Figure 3 As shown, when viewed from the top cover 30 side, the retaining arm 150 has a left retaining arm 151A and a right retaining arm 151B. The left retaining arm 151A connects the rear end portion 131B of the base 130 and the left frame 141C of the retaining portion 140. The right retaining arm 151B connects the rear end portion 131B of the base 130 and the right frame 141D of the retaining portion 140. The left retaining arm 151A has a retaining rear arm 152A and a retaining side arm 153A, and the right retaining arm 151B has a retaining rear arm 152B and a retaining side arm 153B. The retaining arm 150 is formed symmetrically with respect to the virtual plane P.

[0050] The retaining arms 152A and 152B are located between the rear end portion 131B of the base 130 and the retaining portion 140, extending from the rear end portion 131B of the base 130. Specifically, the retaining arm 152A extends and protrudes from the rear end portion 131B of the base 130 toward the rear frame 141B, bends, and extends toward the left frame 141C. The retaining arm 152B extends and protrudes from the rear end portion 131B of the base 130 toward the rear frame 141B, bends, and extends toward the right frame 141D.

[0051] The retaining side arm 153A extends parallel to the outer vibrating arm 121A between the outer vibrating arm 121A and the retaining portion 140. The retaining side arm 153B extends parallel to the outer vibrating arm 121D between the outer vibrating arm 121D and the retaining portion 140. Specifically, the retaining side arm 153A extends from the end of the retaining rear arm 152A on the left frame 141C side toward the front frame 141A, bends, and connects to the left frame 141C. The retaining side arm 153B extends from the end of the retaining rear arm 152B on the right frame 141D side toward the front frame 141A, bends, and connects to the right frame 141D.

[0052] Furthermore, the retaining arm 150 is not limited to the structure described above. For example, the retaining arm 150 may also be connected to the left end portion 131C and the right end portion 131D of the base 130. Alternatively, the retaining arm 150 may also be connected to the front frame 141A of the retaining portion 140.

[0053] Next, refer to Figure 4 and Figure 5 The stacked structure of the resonant device 1 in the first embodiment will be described. Figure 4 It is a schematic representation Figure 1 A cross-sectional view along the X-axis of the stacked structure of the resonant device shown. Figure 5 It is a schematic representation Figure 1 The diagram shows a cross-sectional view along the Y-axis of the stacked structure of the resonant device. Furthermore, Figure 4The illustration of the arms 123A-123D, leads C2 and C3, and through electrodes V2 and V3 is merely a schematic representation of the stacked structure of the resonant device 1; these structures may not necessarily be located on the same plane. For example, the through electrodes V2 and V3 could also be formed in the Y-axis direction at a position away from the cross-section that is parallel to the ZX plane defined by the Z-axis and X-axis and cuts off the arms 123A-123D. Similarly, Figure 5 The diagram is merely a schematic representation of the cross-sections of the mass addition 122A, arm 123A, leads C1, C2, and through electrodes V1, V2, etc., for the purpose of illustrating the stacked structure of the resonant device 1. These structures may not be located on the same plane.

[0054] For the resonant device 1, the holding portion 140 of the resonator 10 is joined to the side wall 23 of the lower cover 20, and the holding portion 140 of the resonator 10 is further joined to the side wall 33 of the upper cover 30. In this way, the resonator 10 is held between the lower cover 20 and the upper cover 30, and a vibration space for the vibration of the resonator 110 is formed by the lower cover 20, the upper cover 30, and the holding portion 140 of the resonator 10. As an example, the resonator 10, the lower cover 20, and the upper cover 30 are each formed using a silicon (Si) substrate (hereinafter referred to as "Si substrate"). Alternatively, the resonator 10, the lower cover 20, and the upper cover 30 may also be formed using an SOI (Silicon On Insulator) substrate with a silicon layer and a silicon oxide film stacked on it. Furthermore, the resonator 10, the lower cover 20, and the upper cover 30 may also be formed using substrates other than Si substrates, such as compound semiconductor substrates, glass substrates, ceramic substrates, resin substrates, etc., as long as the substrates can be processed using microfabrication techniques.

[0055] Next, the structure of resonator 10 will be described.

[0056] The resonator 10's vibrating portion 110, holding portion 140, and holding arm 150 are integrally formed using the same process. The resonator 10 has a metal film E1 stacked on a Si substrate F2, which is an example of a substrate. Furthermore, a piezoelectric film F3 is stacked on the metal film E1 to cover it, and a metal film E2 is further stacked on the piezoelectric film F3. A protective film F5 is stacked on the metal film E2 to cover it. In the mass-added portions 122A to 122D, the aforementioned mass-added films 125A to 125D are further stacked on the protective film F5, respectively. The respective shapes of the vibrating portion 110, holding portion 140, and holding arm 150 are formed by removing and patterning the laminate composed of the Si substrate F2, metal film E1, piezoelectric film F3, metal film E2, and protective film F5 using dry etching irradiation with, for example, an argon (Ar) ion beam.

[0057] The Si substrate F2 is formed, for example, from a degenerate n-type silicon (Si) semiconductor with a thickness of about 6 μm, and may include phosphorus (P), arsenic (As), antimony (Sb), etc., as n-type dopants. The resistivity of the degenerate silicon (Si) used in the Si substrate F2 is, for example, less than 16 mΩ·cm, more preferably less than 1.2 mΩ·cm. Furthermore, a temperature characteristic correction layer F21, for example made of silicon oxide such as SiO2, is formed on the lower surface of the Si substrate F2.

[0058] The temperature characteristic correction layer F21 is a layer that has the function of reducing the temperature coefficient of the resonant frequency of the resonant 10, i.e., the rate of change of the resonant frequency per unit temperature, at least near room temperature. Since the oscillating part 110 has the temperature characteristic correction layer F21, the temperature characteristics of the resonant 10 are improved. In addition, the temperature characteristic correction layer may also be formed on the upper surface of the Si substrate F2, or it may be formed on both the upper and lower surfaces of the Si substrate F2.

[0059] The temperature characteristic correction layer F21 of the preferred mass additions 122A to 122D is formed with a uniform thickness. Furthermore, the term "uniform thickness" means that the deviation of the thickness of the temperature characteristic correction layer F21 is within ±20% of the average thickness.

[0060] Metal films E1 and E2 each have excitation electrodes for exciting vibrating arms 121A to 121D and lead-out electrodes for electrically connecting the excitation electrodes to an external power supply. The portions of metal films E1 and E2 that function as excitation electrodes are sandwiched between piezoelectric films F3 and opposite each other in the arm portions 123A to 123D of vibrating arms 121A to 121D. The portions of metal films E1 and E2 that function as lead-out electrodes are, for example, led out from the base 130 to the holding portion 140 via the holding arm 150. Metal film E1 is electrically continuous throughout the resonator 10. Metal film E2 is electrically separated in the portions formed in the outer vibrating arms 121A and 121D and in the portions formed in the inner vibrating arms 121B and 121C. Metal film E1 corresponds to the lower electrode, and metal film E2 corresponds to the upper electrode.

[0061] The thicknesses of metal films E1 and E2 are, for example, approximately 0.1 μm to 0.2 μm. After deposition, metal films E1 and E2 are patterned into excitation electrodes, lead-out electrodes, etc., through etching or other removal processes. Metal films E1 and E2 are formed, for example, from a metal material with a body-centered cubic crystal structure. Specifically, metal films E1 and E2 are formed using molybdenum (Mo) or tungsten (W). Furthermore, if the Si substrate F2 is a degenerate semiconductor substrate with high conductivity, metal film E1 can be omitted, and the Si substrate F2 can serve as the lower electrode.

[0062] The piezoelectric film F3 is a thin film formed by a piezoelectric material that converts electrical energy and mechanical energy into each other. Based on the electric field generated within the piezoelectric film F3 by the metal films E1 and E2, the piezoelectric film F3 expands and contracts along the Y-axis in the in-plane direction of the XY plane. Through this expansion and contraction of the piezoelectric film F3, the vibrating arms 121A to 121D are displaced with their open ends toward the base plate 22 of the lower cover 20 and the base plate 32 of the upper cover 30, respectively. Therefore, the resonator 10 vibrates in an out-of-plane bending vibration mode.

[0063] The piezoelectric film F3 is formed from a material with a wurtzite hexagonal crystal structure, such as aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), gallium nitride (GaN), indium nitride (InN), or other nitrides or oxides as the main components. Furthermore, scandium aluminum nitride is formed by replacing a portion of the aluminum in aluminum nitride with scandium, or it can be replaced by magnesium (Mg) and niobium (Nb), or magnesium (Mg) and zirconium (Zr), or two elements such as zirconium (Zr). The thickness of the piezoelectric film F3 is, for example, about 1 μm, but can also be about 0.2 μm to 2 μm.

[0064] The protective film F5 protects the metal film E2 from oxidation. Furthermore, if the protective film F5 is disposed on the side of the upper cover 30, it may not be exposed relative to the base plate 32 of the upper cover 30. For example, a parasitic capacitance reducing film, which reduces the capacitance of the wiring formed on the resonator 10, may be formed to cover the protective film F5. The protective film F5 may be, for example, made of aluminum nitride (AlN) or silicon nitride (SiN). X Nitrided films, or aluminum oxide (Al2O3), tantalum pentoxide (Ta2O5), silicon oxide (SiO2), etc. X Oxide films are formed, such as those formed by oxidation.

[0065] The mass-adding films 125A to 125D constitute the surface of the upper cover 30 side of each of the mass-adding portions 122A to 122D, corresponding to the frequency adjustment film of each of the vibrating arms 121A to 121D. The frequency of the resonator 10 is adjusted by a trimming process that removes a portion of each of the mass-adding films 125A to 125D. From the perspective of frequency adjustment efficiency, it is preferable that the mass-adding films 125A to 125D are formed of a material whose mass reduction rate due to etching is faster than that of the protective film F5. The mass reduction rate is expressed as the product of the etching rate and the density. The etching rate is the thickness removed per unit time. If the relationship between the mass reduction rates of the protective film F5 and the mass-adding films 125A to 125D is as described above, then the magnitude relationship of the etching rates is arbitrary. Furthermore, from the viewpoint of effectively increasing the weight of the mass-adding portions 122A to 122D, it is preferable that the mass-adding films 125A to 125D are formed of a material with a higher specific gravity. For these reasons, the mass-added films 125A to 125D are formed from metallic materials such as molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), and titanium (Ti). Furthermore, during the finishing process, a portion of the protective film F5 can be removed. In such cases, the protective film F5 also functions as a frequency-adjusting film.

[0066] A portion of the upper surface of each of the mass-added films 125A to 125D is removed during the frequency adjustment process by a finishing treatment. The finishing treatment of the mass-added films 125A to 125D is, for example, dry etching by irradiation with an argon (Ar) ion beam. While the ion beam provides excellent processing efficiency due to its ability to irradiate a wide area, there is a concern that the mass-added films 125A to 125D may become charged. To prevent changes in the vibration trajectory of the vibrating arms 121A to 121D and deterioration of the vibration characteristics of the resonator 10 due to Coulomb interactions caused by the charging of the mass-added films 125A to 125D, it is preferable to ground the mass-added films 125A to 125D.

[0067] exist Figure 5 In the structural example shown, the mass-adding film 125A is electrically connected to the metal film E1 via a through electrode that penetrates the piezoelectric film F3 and the protective film F5. Similarly, the mass-adding films 125B to 125D (not shown) are electrically connected to the metal film E1 via through electrodes. Furthermore, the grounding method for each of the mass-adding films 125A to 125D is not limited to the above-described case; for example, it can also be electrically connected to the metal film E1 via side electrodes provided on the sides of the mass-adding portions 122A to 122D. Additionally, as long as the effect of the charge on the mass-adding films 125A to 125D can be reduced, the electrical connection object for the mass-adding films 125A to 125D is not limited to the metal film E1; for example, it can also be the metal film E2.

[0068] Lead wires C1, C2, and C3 are formed on the protective film F5 of the holding part 140. Lead wire C1 is electrically connected to the metal film E1 through a through hole formed in the piezoelectric film F3 and the protective film F5. Lead wire C2 is electrically connected to the portions of the outer vibrating arms 121A and 121D formed in the metal film E2 through a through hole formed in the protective film F5. Lead wire C3 is electrically connected to the portions of the inner vibrating arms 121B and 121C formed in the metal film E2 through a through hole formed in the protective film F5. Lead wires C1 to C3 are formed of metallic materials such as aluminum (Al), germanium (Ge), gold (Au), and tin (Sn).

[0069] Next, the structure of the lower cover 20 will be explained.

[0070] The bottom plate 22 and sidewall 23 of the lower cover 20 are integrally formed from a Si substrate P10. The Si substrate P10 is formed from undegenerate silicon and has a resistivity of, for example, 10 Ω·cm or higher. The Si substrate P10 is exposed on the inner wall 25 of the recess 21 of the lower cover 20. A temperature characteristic correction layer F21 is formed on the upper surface of the protrusion 50. However, from the viewpoint of suppressing the charging of the protrusion 50, a conductive layer can be formed on the upper surface of the protrusion 50, where the resistivity of the Si substrate P10, which is lower than that of the temperature characteristic correction layer F21, can be exposed. The lower cover 20 corresponds to one of a pair of substrates.

[0071] The thickness of the lower cover 20 in the Z-axis direction is approximately 150 μm, and similarly, the depth D1 of the recess 21 is approximately 100 μm. Since the amplitude of each of the vibrating arms 121A to 121D is limited to the depth D1, the maximum amplitude on the side of the lower cover 20 is approximately 100 μm.

[0072] Furthermore, the lower cover 20 can also be considered as part of the SOI substrate. When the resonator 10 and the lower cover 20 are considered as a MEMS substrate formed from a single SOI substrate, the Si substrate P10 of the lower cover 20 corresponds to the support substrate of the SOI substrate, the temperature characteristic correction layer F21 of the resonator 10 corresponds to the BOX layer of the SOI substrate, and the Si substrate F2 of the resonator 10 corresponds to the active layer of the SOI substrate. In this case, various semiconductor elements, circuits, etc., can be formed on the outside of the resonant device 1 using a portion of a continuous MEMS substrate.

[0073] Next, the structure of the top cover 30 will be explained.

[0074] The bottom plate 32 and sidewall 33 of the top cover 30 are integrally formed from a Si substrate Q10. Preferably, the surface, back surface, and inner surface of the through holes of the top cover 30 are covered with a silicon oxide film Q11. The silicon oxide film Q11 is formed on the surface of the Si substrate Q10, for example, by oxidation or chemical vapor deposition (CVD) of the Si substrate Q10. The Si substrate Q10 is exposed on the inner wall 35 of the recess 31 of the top cover 30. The top cover 30 corresponds to one of a pair of substrates, and the substrate Q10 corresponds to the silicon layer.

[0075] The thickness of the top cover 30 in the Z-axis direction is specified to be approximately 150 μm, and similarly, the depth D2 of the recess 31 is specified to be approximately 100 μm. The amplitude of each of the vibrating arms 121A to D is limited to the depth D2, so the maximum amplitude on the side of the top cover 30 is approximately 100 μm.

[0076] An anti-diffusion layer 71 and an adsorption layer 72 are provided in the recess 31 of the upper cover 30.

[0077] An anti-diffusion layer 71 is disposed on the inner wall 35 of the base plate 32, and is located between the Si substrate Q10 and the adsorption layer 72. Compared to the Si substrate Q10, hydrogen is less likely to diffuse into the anti-diffusion layer 71, and compared to the adsorption layer 72, hydrogen is less likely to diffuse into it. The anti-diffusion layer 71 inhibits the diffusion of hydrogen contained in the substrate Q10 to the adsorption layer 72, reducing the hydrogen storage capacity of the adsorption layer 72. The anti-diffusion layer 71 may, for example, comprise a titanium-silicon (Ti-Si) alloy. An anti-diffusion layer 71 with titanium-silicon alloy as its main component may also comprise silicon oxide or titanium oxide. Figure 4 and Figure 5 In the example shown, the anti-diffusion layer 71 is disposed on a portion of the inner wall 35, but it may also be disposed on the entire inner wall 35. The anti-diffusion layer 71 may be a metal layer, but it may also be a semiconductor layer or an insulating layer. The anti-diffusion layer 71 may also be a laminated structure.

[0078] An adsorption layer 72 is disposed on the base plate 32 and located in the vibration space. The adsorption layer 72 adsorbs hydrogen, allowing the adsorbed hydrogen to diffuse inward and be stored. Therefore, the adsorption layer 72, with its ample hydrogen storage, reduces the hydrogen partial pressure in the vibration space, increasing the vacuum level of the vibration space. The adsorption layer 72 may contain, for example, titanium (Ti). Figure 4 and Figure 5In the example shown, when viewed from above the inner wall 35 of the base plate 32, the end of the adsorption layer 72 substantially overlaps with the end of the anti-diffusion layer 71. As long as the end of the adsorption layer 72 overlaps with the anti-diffusion layer 71, it is not limited to the above situation and can also be located inside the end of the anti-diffusion layer 71. Furthermore, the material constituting the adsorption layer 72 is not limited to titanium, as long as it can adsorb hydrogen; it can also include zirconium (Zr), vanadium (V), niobium (Nb), tantalum (Ta), or alloys containing at least one of these, or oxides of alkali metals, or oxides of alkaline earth metals. The adsorption layer 72 can also contain materials that adsorb oxygen, water vapor, etc., other than hydrogen. Furthermore, the adsorption and desorption of hydrogen in the adsorption layer 72 is an equilibrium reaction, and the hydrogen partial pressure in the vibration space is proportional to the hydrogen storage capacity of the adsorption layer 72.

[0079] Terminals T1, T2, and T3 are formed on the upper surface of the cover 30 (the side opposite to the resonator 10). Terminal T1 is a mounting terminal for grounding the metal film E1. Terminal T2 is a mounting terminal for electrically connecting the metal film E2 of the outer vibrating arms 121A and 121D to an external power supply. Terminal T3 is a mounting terminal for electrically connecting the metal film E2 of the inner vibrating arms 121B and 121C to an external power supply. Terminals T1 to T3 are formed, for example, by plating nickel (Ni), gold (Au), silver (Ag), or copper (Cu) onto a metallization layer (base layer) such as chromium (Cr), tungsten (W), or nickel (Ni). In addition, in order to adjust parasitic capacitance and mechanical strength balance, dummy terminals electrically insulated from the resonator 10 may also be formed on the upper surface of the cover 30.

[0080] Through electrodes V1, V2, and V3 are formed inside the sidewall 33 of the upper cover 30. Through electrode V1 electrically connects terminal T1 and lead C1, through electrode V2 electrically connects terminal T2 and lead C2, and through electrode V3 electrically connects terminal T3 and lead C3. Through electrodes V1 to V3 are formed by filling conductive material through through holes in the sidewall 33 of the upper cover 30 in the Z-axis direction. The conductive material used is, for example, polysilicon (Poly-Si), copper (Cu), or gold (Au).

[0081] A joint H is formed between the sidewall 33 of the upper cover 30 and the holding portion 140 to join the sidewall 33 of the upper cover 30 and the holding portion 140 of the resonator 10. The joint H is formed in a closed loop surrounding the vibrating portion 110 in the XY plane to hermetically seal the vibration space of the resonator 10 under vacuum. The joint H is formed, for example, from a metal film stacked and eutecticly bonded in the order of aluminum (Al) film, germanium (Ge) film, and aluminum (Al) film. In addition, the joint H may also have a film appropriately selected from gold (Au), tin (Sn), copper (Cu), titanium (Ti), aluminum (Al), germanium (Ge), silicon (Si), and alloys containing at least one of them. The joint H may also contain a eutectic metal containing at least one of aluminum, copper, silicon, germanium, and titanium. In addition, to improve the tightness, the joint H may also have an insulating film made of metal compounds such as titanium nitride (TiN) and tantalum nitride (TaN).

[0082] Next, refer to Figure 4 and Figure 5 The operation of the resonant device 1 will be explained.

[0083] In this embodiment, terminal T1 is grounded, and alternating voltages with opposite phases are applied to terminals T2 and T3. Therefore, the phases of the electric fields of the piezoelectric films F3 formed on the outer vibrating arms 121A and 121D and the inner vibrating arms 121B and 121C are opposite to each other. Consequently, the outer vibrating arms 121A and 121D and the inner vibrating arms 121B and 121C vibrate in opposite phases. For example, when the mass attachments 122A and 122D of each of the outer vibrating arms 121A and 121D displace toward the inner wall 35 of the upper cover 30, the mass attachments 122B and 122C of each of the inner vibrating arms 121B and 121C displace toward the inner wall 25 of the lower cover 20. As described above, vibrating arms 121A and 121B vibrate in opposite directions about a central axis r1 extending along the Y-axis between adjacent vibrating arms 121A and 121B. Similarly, vibrating arms 121C and 121D vibrate in opposite directions about a central axis r2 extending along the Y-axis between adjacent vibrating arms 121C and 121D. This generates torsional moments in opposite directions on the central axes r1 and r2, resulting in bending vibration in the base 130. The maximum amplitude of vibrating arms 121A to D is approximately 100 μm, and the amplitude during normal operation is approximately 10 μm.

[0084] Next, refer to Figures 6-8 The manufacturing method of the resonant device 1 according to the first embodiment will be described. Figure 6 This is a flowchart schematically illustrating the manufacturing method of the resonant device according to the first embodiment. Figure 7 It is a cross-sectional view schematically showing the process of setting the anti-diffusion layer. Figure 8 It is a cross-sectional view schematically representing the process of setting the adsorption layer.

[0085] First, prepare a pair of silicon substrates (S10). A pair of silicon substrates is equivalent to Si substrates P10 and Q10.

[0086] Next, the silicon substrate is oxidized (S20). This forms a silicon oxide film Q11 on the surface of the Si substrate Q10 and a temperature characteristic correction layer F21 on the surface of the Si substrate P10. Alternatively, only the silicon oxide film Q11 may be formed in this step, while the temperature characteristic correction layer F21 may be formed in other steps.

[0087] Next, a pair of recesses are formed (S30). A portion of the upper surface of the Si substrate P10 is removed by etching to form a recess 21 surrounded by the inner wall 25. Similarly, a portion of the upper surface of the Si substrate Q10 is removed by etching to form a recess 31 surrounded by the inner wall 35. Furthermore, the method for forming the recesses 21 and 31 is not limited to etching. Alternatively, the recess 21 may be formed after the resonator 10 is bonded to the lower cover 20.

[0088] Next, the resonator is bonded to the lower cover (S40). The lower cover 20 and the resonator 10 are heated below their melting points, and the side wall 23 of the lower cover 20 and the holding portion 140 of the resonator 10 are pressurized together. The bonding method between the lower cover 20 and the resonator 10 is not limited to the heat-pressing method described above; for example, it can also be bonding using adhesives, brazing filler metal, solder, etc.

[0089] Next, an anti-diffusion layer (S50) is installed. For example... Figure 7 As shown, particles 71p are deposited on the inner wall 35 of the top cover 30 to form an anti-diffusion layer 71 on the Si substrate Q10. The particles 71p are, for example, vapors of titanium-silicon alloy, or a mixture of titanium vapor and silicon vapor. The anti-diffusion layer 71 is patterned using a metal mask MK.

[0090] Next, the adsorption layer (S60) is set. For example... Figure 8 As shown, particles 72p are deposited on the anti-diffusion layer 71 to form an adsorption layer 72. Particles 72p are, for example, titanium vapor. The adsorption layer 72 is patterned, for example, using a metal mask MK, the same metal mask used in the patterning of the anti-diffusion layer 71. Furthermore, in forming the patterned anti-diffusion layer 71 and adsorption layer 72, the patterning method is not limited to patterning; it can also be an etching method using photoresist or a stripping method.

[0091] Next, the adsorption layer is activated (S70). By heating the adsorption layer 72, the hydrogen adsorbed on its surface is desorbed, restoring the hydrogen adsorption effect of the adsorption layer 72. The activation of the adsorption layer 72 is performed through a heat treatment. This heat treatment is performed, for example, at a temperature of 350°C or higher and 500°C or lower, for a heating time of 5 minutes or higher and 30 minutes or lower. This is because heating below 350°C and for a duration shorter than 5 minutes will not sufficiently activate the adsorption layer 72. Furthermore, heating above 500°C and for a duration longer than 30 minutes will decrease the efficiency of activation and prolong the manufacturing preheating time.

[0092] Next, the joint (S80) is formed. The metallization layers of the lower cover 20 and the upper cover 30 are metal-bonded under reduced pressure. The resulting joint H is an airtight seal within a vacuum-sealed vibration space. The joint H is formed by heat treatment. This heat treatment is performed, for example, at a temperature of 400°C or higher and 500°C or lower, for a heating time of 1 minute or higher and 30 minutes or less. This is because if the temperature is below 400°C and the heating time is less than 1 minute, sufficient bonding strength and sealing cannot be obtained. Furthermore, if the temperature is above 500°C and the heating time is longer than 30 minutes, the energy efficiency for bonding deteriorates, and the manufacturing lead time is extended.

[0093] As described above, in this embodiment, an anti-diffusion layer 71, which is less prone to hydrogen diffusion than the Si substrate Q10, is provided between the Si substrate Q10 of the upper cover 30 and the adsorption layer 72.

[0094] Accordingly, since the diffusion of hydrogen from the Si substrate Q10 to the adsorption layer 72 can be suppressed, the hydrogen storage capacity of the adsorption layer 72 can be reduced. Because the hydrogen storage capacity of the adsorption layer 72 is reduced, the desorption of hydrogen from the adsorption layer 72 can be suppressed. Therefore, by reducing the initial hydrogen storage capacity of the adsorption layer 72, the decrease in the hydrogen adsorption capacity of the adsorption layer 72 over time can be suppressed, and a high vacuum level can be easily maintained. Furthermore, the hydrogen partial pressure in the vibration space can be reduced, increasing the initial vacuum level. If such a packaging structure is applied to the resonant device 1, the frequency variation over time and the initial frequency deviation can be reduced.

[0095] Compared to the adsorption layer 72, hydrogen is less likely to diffuse in the anti-diffusion layer 71.

[0096] Accordingly, since the diffusion of hydrogen from the Si substrate Q10 to the adsorption layer 72 can be further suppressed, the deterioration of the vacuum degree over time can be suppressed, and the initial vacuum degree of the vibration space can be improved.

[0097] The anti-diffusion layer 71 may contain a titanium-silicon alloy or titanium oxide.

[0098] Compared to silicon, titanium-silicon alloys require higher energy for hydrogen diffusion, thus effectively suppressing hydrogen diffusion.

[0099] The adsorption layer 72 contains titanium. The top cover 30 contains a silicon layer.

[0100] Accordingly, a titanium alloy can be formed by heat treatment to create a silicon layer on the top cover 30 and an adsorption layer 72.

[0101] As an example, an anti-diffusion layer 71 is disposed on the inner wall 35 of the top cover 30. The joint H comprises at least one of aluminum, copper, silicon, germanium, titanium, gold, and tin.

[0102] The frequency band of resonator 10 is above 1 kHz and below 1 MHz.

[0103] Therefore, even for vibration elements in frequency bands where the vacuum level of the vibration space has a significant impact, the initial frequency deviation and the frequency change over time can be reduced.

[0104] Furthermore, in the first embodiment, the anti-diffusion layer 71 and the adsorption layer 72 are disposed on a portion of the inner wall 35 of the upper cover 30, but the anti-diffusion layer 71 and the adsorption layer 72 may also be disposed on the entire surface of the inner wall 35. Alternatively, the anti-diffusion layer 71 and the adsorption layer 72 may also be disposed on a portion or all of the inner wall 25 of the lower cover 20, or may be disposed on both the lower cover 20 and the upper cover 30.

[0105] The structure of the resonator according to other embodiments of the present invention will be described below. Furthermore, in the following embodiments, descriptions of matters identical to those in the first embodiment described above are omitted, and only the differences are explained. In particular, the same effects produced by the same structure are not mentioned sequentially.

[0106] <Second Implementation>

[0107] Next, refer to Figures 9-10 The resonant device 2 of the second embodiment and its manufacturing method will be described. Figure 9 This is a cross-sectional view schematically illustrating the process of setting the adsorption layer in the manufacturing method of the resonant device in the second embodiment. Figure 10 This is a cross-sectional view schematically illustrating the process of setting the anti-diffusion layer in the manufacturing method of the resonant device according to the second embodiment.

[0108] In the second embodiment, after the adsorption layer 72 is provided, an anti-diffusion layer 71 is provided. Specifically, as follows: Figure 9 As shown, particles 72p are deposited on the inner wall 35 of the upper cover 30, and an adsorption layer 72 is formed on the Si substrate Q10. Next, as... Figure 10As shown, an anti-diffusion layer 71 is formed between the Si substrate Q10 and the adsorption layer 72 through heat treatment. To prevent oxidation of the adsorption layer 72, for example, heat treatment is performed by applying heat Q to the upper cover 30 and the adsorption layer 72 using an external heater in a vacuum or an atmosphere of inert gas such as nitrogen. During this process, an anti-diffusion layer 71, made of a titanium-silicon alloy, is formed at the boundary between the Si substrate Q10 and the adsorption layer 72, using silicon contained in the Si substrate Q10 and titanium contained in the adsorption layer 72 as raw materials. Therefore, a portion of the anti-diffusion layer 71 is positioned to penetrate the Si substrate Q10 of the upper cover 30.

[0109] Accordingly, the tightness of the seal between the top cover 30 and the anti-diffusion layer 71, and the tightness of the seal between the anti-diffusion layer 71 and the adsorption layer 72 are improved.

[0110] The heating treatment used to impart heat Q can be performed, for example, in the process of activating the adsorption layer 72. The heating temperature is 450°C or higher and 700°C or lower, and the heating time is 1 hour or more. Thus, when the process of activating the adsorption layer 72 also serves as the process of setting the anti-diffusion layer 71, compared to the process of activating only the adsorption layer, the heating time is longer and the heating temperature is higher, but accordingly, the adsorption layer 72 can be activated and the anti-diffusion layer 71 can be set. Therefore, the manufacturing process can be simplified and manufacturing costs can be reduced.

[0111] The heat treatment used to impart heat Q can be performed, for example, in the process of setting the joint H. The heating temperature is 450°C or higher and 700°C or lower, and the heating time is 1 hour or more. Thus, when the process of setting the joint H also serves as the process of setting the anti-diffusion layer 71, the heating time is longer than that of the process of setting only the joint, but this allows the adsorption layer 72 to be activated and the joint H to be set. Therefore, the manufacturing process can be simplified, and manufacturing costs can be reduced.

[0112] Furthermore, the heat treatment used to impart heat Q can be performed separately from the process of activating the adsorption layer 72 and the process of setting the joint H.

[0113] Accordingly, changes in the piezoelectric characteristics of the resonator 10 caused by heat treatment can be suppressed. That is, changes in the characteristics of components housed in the package structure can be suppressed.

[0114] <Third Implementation Method>

[0115] Next, refer to Figure 11 The resonant device 3 of the third embodiment and its manufacturing method will be described. Figure 11 This is a cross-sectional view schematically showing the structure of the top cover in the third embodiment.

[0116] The third embodiment differs from the first embodiment in that it has a silicon oxide film Q12 that corresponds to a silicon oxide layer. The silicon oxide film Q12 is disposed on the adsorption layer 72 side of the Si substrate Q10, and the surface of the silicon oxide film Q12 corresponds to the inner wall 35.

[0117] In the third embodiment, the silicon oxide film Q12 is disposed in the region between the Si substrate Q10 and the anti-diffusion layer 71 and the region outside thereof. In other words, the anti-diffusion layer 71 is disposed on a portion of the silicon oxide film Q12.

[0118] <Fourth Implementation>

[0119] Next, refer to Figure 12 and Figure 13 The resonant device 4 of the fourth embodiment and its manufacturing method will be described. Figure 12 This is a cross-sectional view schematically illustrating the process of setting the adsorption layer in the manufacturing method of the resonant device according to the fourth embodiment. Figure 13 This is a cross-sectional view schematically illustrating the process of setting an anti-diffusion layer in the manufacturing method of the resonant device according to the fourth embodiment.

[0120] In the fourth embodiment, before forming the anti-diffusion layer 71 and the adsorption layer 72, a silicon oxide film Q12 is formed on the side of the Si substrate Q10 opposite to the silicon oxide film Q11. The silicon oxide film Q12 is formed, for example, by oxygen plasma treatment of the Si substrate Q10. The thickness of the silicon oxide film Q12 is preferably thin, for example, 5 nm or less. Next, as... Figure 12 As shown, particles 72p are deposited on the inner wall 35 formed by the silicon oxide film Q12, and an adsorption layer 72 is patterned on the Si substrate Q10. Next, as... Figure 13 As shown, an anti-diffusion layer 71 is formed between the Si substrate Q10 and the adsorption layer 72 through heat treatment. At this time, using silicon oxide from the silicon oxide film Q12 and titanium from the adsorption layer 72 as raw materials, an anti-diffusion layer 71 composed of a titanium-silicon alloy and titanium oxide is formed. Since the silicon oxide film Q12 in the region in contact with the adsorption layer 72 is consumed during the formation of the titanium-silicon alloy and titanium oxide, the anti-diffusion layer 71 is adjacent to the silicon oxide film Q12 in a direction parallel to the interface between the anti-diffusion layer 71 and the adsorption layer 72.

[0121] The heat treatment for imparting heat Q is the same as in the second embodiment, and can be performed in the process of activating the adsorption layer 72 or in the process of setting the bonding portion H. However, in the fourth embodiment, due to the presence of the silicon oxide film Q12, the heating temperature required to form the titanium-silicon alloy is lower. In the fourth embodiment, the heating temperature for setting the anti-diffusion layer 71 is 400°C or higher and 700°C or lower, and the heating time is 1 hour or higher. Therefore, compared with the second embodiment, the energy required for manufacturing can be reduced.

[0122] The following describes some or all of the embodiments of the present invention and their effects. However, the present invention is not limited to the following descriptions.

[0123] According to one aspect of the present invention, the packaging structure comprises: a pair of substrates disposed opposite to each other; a joint of the pair of substrates for sealing an element in an internal space surrounded by the pair of substrates; an adsorption layer disposed on at least one of the pair of substrates and located in the internal space, for adsorbing at least hydrogen; and an anti-diffusion layer disposed between the at least one substrate and the adsorption layer, wherein hydrogen is less likely to diffuse compared to the at least one substrate.

[0124] Accordingly, since the diffusion of hydrogen from at least one substrate to the adsorption layer can be suppressed, the hydrogen storage capacity of the adsorption layer can be reduced. Because the hydrogen storage capacity of the adsorption layer is reduced, the desorption of hydrogen from the adsorption layer can be suppressed. Therefore, by reducing the initial hydrogen storage capacity of the adsorption layer, the decrease in the hydrogen adsorption capacity of the adsorption layer over time can be suppressed, and a high vacuum level can be easily maintained. Furthermore, the hydrogen partial pressure in the internal space can be reduced, increasing the initial vacuum level. If such a packaging structure is applied to a resonant device, the frequency variation over time and the initial frequency deviation can be reduced.

[0125] As a means, hydrogen is less likely to diffuse compared to the adsorption layer.

[0126] Accordingly, since the diffusion of hydrogen from at least one substrate to the adsorption layer can be further suppressed, the deterioration of the vacuum degree over time can be suppressed, and the initial vacuum degree of the internal space can be improved.

[0127] As one approach, the anti-diffusion layer comprises a titanium-silicon alloy.

[0128] Compared to silicon, titanium-silicon alloys require higher energy for hydrogen diffusion, thus effectively suppressing hydrogen diffusion.

[0129] As one method, the anti-diffusion layer contains titanium oxide.

[0130] In one approach, the adsorption layer contains titanium.

[0131] In one manner, at least one substrate comprises a silicon layer.

[0132] Accordingly, a titanium alloy is capable of forming at least one substrate silicon layer and adsorption layer by heat treatment.

[0133] In one embodiment, at least one substrate further comprises a silicon oxide layer disposed on the adsorption layer side of the silicon layer.

[0134] As one approach, the thickness of the silicon oxide layer is less than 5 nm.

[0135] As one approach, an anti-diffusion layer is disposed on the surface of at least one substrate.

[0136] In one approach, at least a portion of the anti-diffusion layer is configured to penetrate into at least one substrate.

[0137] Accordingly, the adhesion between at least one substrate and the anti-diffusion layer, and the adhesion between the anti-diffusion layer and the adsorption layer are improved.

[0138] In one manner, the joint comprises at least one material selected from aluminum, copper, silicon, germanium, titanium, gold, and tin.

[0139] As one approach, the element is a vibrating element with a frequency band above 1 kHz and below 1 MHz. Accordingly, even for vibrating elements in frequency bands where the vacuum level of the internal space has a significant impact, it is possible to reduce frequency changes over time and initial frequency deviations.

[0140] As another aspect of the present invention, a method for manufacturing a packaging structure includes: a step of preparing a pair of substrates; a step of providing an adsorption layer on at least one of the pair of substrates, wherein the adsorption layer adsorbs at least hydrogen; a step of configuring the pair of substrates such that the adsorption layer provided on at least one substrate faces the other substrate, and providing a joint for sealing an element in an internal space surrounded by the pair of substrates; and a step of providing an anti-diffusion layer on at least one substrate that is less prone to hydrogen diffusion than the at least one substrate.

[0141] Therefore, a packaging structure that can easily maintain a high vacuum level can be provided.

[0142] In one approach, during the process of setting the adsorption layer, the adsorption layer is set on at least one substrate. In the process of setting the anti-diffusion layer, after the process of setting the adsorption layer, an anti-diffusion layer is formed between at least one substrate and the adsorption layer by heat treatment. The anti-diffusion layer is formed from the material contained in at least one substrate and the material contained in the adsorption layer.

[0143] As a method, the heat treatment should be carried out for at least 1 hour.

[0144] As another method, there is also a step to activate the adsorption layer, in which heat treatment is performed.

[0145] Accordingly, the adsorption layer can be activated, and an anti-diffusion layer can be provided. This simplifies the manufacturing process and reduces manufacturing costs.

[0146] As one method, heat treatment is performed during the process of setting the joint.

[0147] Accordingly, the adsorption layer can be activated, and the bonding portion can be formed. Therefore, the manufacturing process can be simplified, and the manufacturing cost can be reduced.

[0148] In one approach, at least one substrate comprises a silicon layer, and the process of setting the adsorption layer includes setting titanium on the silicon layer and performing heat treatment at a temperature above 450°C and below 700°C.

[0149] In one embodiment, at least one substrate comprises a silicon layer and a silicon oxide layer disposed on the silicon layer, and the process of setting the adsorption layer includes setting titanium on the silicon oxide layer and performing heat treatment at a temperature above 400°C and below 700°C.

[0150] Because of the presence of the silicon oxide layer, the heating temperature required to form the titanium-silicon alloy is reduced. Therefore, the energy required for manufacturing can be reduced.

[0151] As described above, according to one aspect of the present invention, a packaging structure capable of easily maintaining a high vacuum level and a method thereof can be provided.

[0152] Furthermore, the embodiments described above are for ease of understanding of the present invention and are not intended to limit or interpret the scope of the present invention. The present invention can be modified / improved without departing from its spirit, and the present invention also includes its equivalents. That is, any design modifications appropriately applied to the various embodiments by those skilled in the art that possess the features of the present invention are included within the scope of the present invention. For example, the elements, their configurations, materials, conditions, shapes, dimensions, etc., of each embodiment are not limited to the illustrated contents and can be appropriately modified. For example, the vibration element and oscillator of the present invention can be used in timing devices or load sensors. In addition, the elements of each embodiment can be combined as much as technically possible, and the structure formed by combining these elements is included within the scope of the present invention as long as it contains the features of the present invention.

[0153] Explanation of reference numerals in the attached figures

[0154] 1…Resonant device; 10…Resonator; 20…Lower cover; 30…Upper cover; Q10, P10…Silicon (Si) substrate; 21, 31…Recess; 22, 32…Bottom plate; 23, 33…Side wall; 25, 35…Inner wall; 71…Anti-diffusion layer; 72…Adsorption layer.

Claims

1. A packaging structure comprising: A pair of substrates are arranged opposite each other; The joint of the aforementioned pair of substrates seals the component within the internal space surrounded by the aforementioned pair of substrates; An adsorption layer, disposed on at least one of the pair of substrates and located in the internal space, adsorbs at least hydrogen; and An anti-diffusion layer is disposed between the at least one substrate and the adsorption layer, wherein hydrogen is less likely to diffuse compared to the at least one substrate. The aforementioned anti-diffusion layer is made from the material contained in at least one of the aforementioned substrates and the material contained in the aforementioned adsorption layer.

2. The packaging structure according to claim 1, wherein, Compared to the adsorption layer, hydrogen is less likely to diffuse through the aforementioned anti-diffusion layer.

3. The packaging structure according to claim 1 or 2, wherein, The aforementioned anti-diffusion layer comprises a titanium-silicon alloy.

4. The packaging structure according to claim 1 or 2, wherein, The aforementioned anti-diffusion layer contains titanium oxide.

5. The packaging structure according to claim 1 or 2, wherein, The aforementioned adsorption layer contains titanium.

6. The packaging structure according to claim 1 or 2, wherein, At least one of the aforementioned substrates comprises a silicon layer.

7. The packaging structure according to claim 6, wherein, The at least one substrate further includes a silicon oxide layer, which is disposed on the adsorption layer side of the silicon layer.

8. The packaging structure according to claim 7, wherein, The thickness of the aforementioned silicon oxide layer is less than 5 nm.

9. The packaging structure according to claim 1 or 2, wherein, The aforementioned anti-diffusion layer is disposed on the surface of at least one of the aforementioned substrates.

10. The packaging structure according to claim 1 or 2, wherein, At least a portion of the aforementioned anti-diffusion layer is configured to penetrate into at least one of the aforementioned substrates.

11. The packaging structure according to claim 1 or 2, wherein, The aforementioned joint comprises at least one of aluminum, copper, silicon, germanium, titanium, gold, and tin.

12. The packaging structure according to claim 1 or 2, wherein, The aforementioned components are vibration components with a frequency band of 1 kHz or higher and 1 MHz or lower.

13. A method for manufacturing a packaging structure, comprising: The process of preparing a pair of substrates; In the process of providing an adsorption layer on at least one of the aforementioned pair of substrates, wherein... The above-mentioned adsorption layer adsorbs at least hydrogen; and The process involves configuring the pair of substrates such that the adsorption layer disposed on at least one of the substrates faces the other substrate, and performing a step of sealing the element in a joint within the internal space surrounded by the pair of substrates. The manufacturing method of the above-mentioned packaging structure further includes the step of providing an anti-diffusion layer on at least one substrate, which is less prone to hydrogen diffusion than the at least one substrate. The aforementioned anti-diffusion layer is disposed between the at least one substrate and the aforementioned adsorption layer. In the process of setting the adsorption layer, the adsorption layer is set on at least one substrate. In the process of setting the above-mentioned anti-diffusion layer, after the process of setting the above-mentioned adsorption layer, the above-mentioned anti-diffusion layer is formed between the above-mentioned at least one substrate and the above-mentioned adsorption layer by heat treatment. The above-mentioned anti-diffusion layer is made of the material contained in the above-mentioned at least one substrate and the material contained in the above-mentioned adsorption layer.

14. The method for manufacturing the packaging structure according to claim 13, wherein, The above heat treatment shall be carried out for at least 1 hour.

15. The method for manufacturing the packaging structure according to claim 13 or 14, wherein, It also includes a process for activating the aforementioned adsorption layer. The above-mentioned heat treatment is performed in the process of activating the above-mentioned adsorption layer.

16. The method for manufacturing the packaging structure according to claim 13 or 14, wherein, The above-mentioned heat treatment is performed during the process of setting the above-mentioned joint.

17. The method for manufacturing the packaging structure according to claim 15, wherein, At least one of the aforementioned substrates comprises a silicon layer. The process of setting the above-mentioned adsorption layer includes setting titanium on the above-mentioned silicon layer. The above-mentioned heat treatment is performed at a temperature above 450°C and below 700°C.

18. The method for manufacturing the packaging structure according to claim 16, wherein, At least one of the aforementioned substrates comprises a silicon layer. The process of setting the above-mentioned adsorption layer includes setting titanium on the above-mentioned silicon layer. The above-mentioned heat treatment is performed at a temperature above 450°C and below 700°C.

19. The method for manufacturing the packaging structure according to claim 15, wherein, The at least one substrate mentioned above includes a silicon layer and a silicon oxide layer disposed on the silicon layer. The process of setting the adsorption layer includes setting titanium on the silicon oxide layer. The above-mentioned heat treatment is performed at a temperature above 400°C and below 700°C.

20. The method for manufacturing the packaging structure according to claim 16, wherein, The at least one substrate mentioned above includes a silicon layer and a silicon oxide layer disposed on the silicon layer. The process of setting the adsorption layer includes setting titanium on the silicon oxide layer. The above-mentioned heat treatment is performed at a temperature above 400°C and below 700°C.

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