Sealed-liquid sealing structure and pressure sensor

Abstract

To provide a sealing structure of a sealed liquid and a pressure sensor which improve pressure resistance reliability at a high temperature.SOLUTION: The semiconductor device includes a device body 2 formed of Si, and a sealing part 4 which has an exposed surface 3 exposed continuously with an outer surface 2a of the device body 2, is formed of Au, Sn, and Si as main components, and is included inside the device body 2. And a sealing hole 5 which is formed inside the device body 2, extends from a sealed end 5a closed by the sealing part 4 to the opposite side of the exposed surface 3, and is filled with sealing liquid 6. The sealing portion 4 is joined to the device main body 2 by diffusion bonding and is integrated with the device main body 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sealing structure for sealing a sealed liquid that seals an opening of a sealing hole, and to a pressure sensor. [Background technology]

[0002] A conventional sealing structure for sealing the opening of the sealing hole for the sealed liquid is described, for example, in Patent Document 1. Patent Document 1 discloses a sealing structure for the sealed liquid that is applied to a pressure sensor of a differential pressure transmitter. The pressure sensor disclosed in Patent Document 1 has two diaphragms on which the pressure to be measured acts, a pair of pressure chambers formed with these diaphragms as part of their walls, a communication passage connecting the pair of pressure chambers, and a sealing hole extending from the communication passage to the outer surface of the pressure sensor chip.

[0003] The sealing hole is opened on the outer surface of the pressure sensor, and after being filled with a fill liquid, is sealed using a conventional sealing structure. This sealing structure is configured by forming a metal layer at the opening of the sealing hole, and then melting and solidifying a metal ball into this metal layer to seal the opening. The metal ball used for sealing is often made of an alloy whose main component is AuSn. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-159593 Summary of the Invention [Problem to be solved by the invention]

[0005] It is generally known that metallic materials undergo creep over time, even under load conditions that do not cause deformation or fracture at room temperature, above a certain temperature. As deformation due to creep progresses, creep fracture occurs, leading to fracture. This creep phenomenon and creep fracture also occur in sealing materials made of AuSn, which is formed by melting and solidifying sealing balls. Above a certain temperature, AuSn loses sufficient hardness and may be destroyed by creep and creep fracture. In other words, conventional sealing structures for sealed liquids may have low pressure resistance reliability at high temperatures.

[0006] An object of the present invention is to provide a sealing structure for a sealed liquid and a pressure sensor that have high pressure resistance reliability at high temperatures. [Means for solving the problem]

[0007] In order to achieve this object, the sealing structure for the sealed liquid according to the present invention comprises a device body formed of Si, a sealing part formed mainly of Au, Sn, and Si and contained inside the device body, which has an exposed surface that is continuous with the outer surface of the device body, and a sealing hole formed inside the device body, extending from a sealing end that is closed by the sealing part to the opposite side of the exposed surface and filled with the sealed liquid, and the sealing part is joined to the device body by diffusion bonding to be integrated with the device body.

[0008] In the sealing structure for sealing a sealed liquid according to the present invention, the sealing portion may be formed in a shape that gradually becomes larger from the sealing end of the sealing hole toward the exposed surface.

[0009] In the sealing structure for sealing a sealed liquid according to the present invention, a width of the exposed surface of the sealing portion may be longer than a distance between the sealed end of the sealing hole and the exposed surface.

[0010] The pressure sensor according to the present invention is a pressure sensor equipped with a sealing structure for the sealed liquid, and comprises a pressure sensor chip constituting the device main body, a pair of pressure chambers formed in the pressure sensor chip with a diaphragm on which the pressure to be measured acts as part of the wall, a communicating passage formed in the pressure sensor chip to connect the pressure chambers, and a pressure transmitting structure for transmitting the pressure to be measured to the diaphragm, wherein the sealing portion has an exposed surface continuous with the outer surface of the pressure sensor chip and is formed so as to be contained inside the pressure sensor chip, the sealing hole is formed so as to extend from the communicating passage to the sealing portion, and the sealed liquid is sealed in the entire area from the pressure chamber through the communicating passage and the sealing hole to the sealing portion. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a sealing structure for a sealed liquid and a pressure sensor that have high pressure resistance reliability at high temperatures. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a sealing structure for a sealed liquid according to the present invention. [Figure 2] Figure 2 is a micrograph of the main part. [Figure 3] FIG. 3 is a plan view of the sealing structure. [Figure 4] FIG. 4 is a cross-sectional view showing the main part of the device body. [Figure 5] FIG. 5 is a cross-sectional view showing the main part of the device body and the AuSn balls. [Figure 6] FIG. 6 is a cross-sectional view of the main part of the device body and the AuSn balls irradiated with laser light. [Figure 7] FIG. 7 is a cross-sectional view of the main part of the device body showing the state in which the AuSn balls are melted. [Figure 8] FIG. 8 is a cross-sectional view of the main part of the device body showing the state where the diffusion bonded portion is formed. [Figure 9] FIG. 9 is a graph showing the relationship between the silicon weight ratio and hardness. [Figure 10] FIG. 10 is a graph showing the relationship between the weld diameter and the hardness. [Figure 11] FIG. 11 is a cross-sectional view showing the configuration of the pressure sensor. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) Hereinafter, one embodiment of a sealing structure for sealed liquid according to the present invention will be described in detail with reference to FIGS. The sealing structure 1 for the enclosed liquid shown in Figure 1 comprises a device main body 2, a sealing portion 4 having an exposed surface 3 that is continuous with and exposed to the outer surface 2a of the device main body 2, and an enclosure hole 5 having one end closed by the sealing portion 4.

[0014] The device body 2 is made of Si and has a flat outer surface. The sealing portion 4 is made of an alloy containing Au, Sn, and Si as its main components, and is diffusion-bonded to the device body 2 and is contained within the device body 2. In Figure 1, the boundary between the device body 2 and the sealing portion 4 is indicated by a two-dot chain line, but since this is a diffusion-bonded boundary, in reality, no clear bonding interface separating the device body 2 and the sealing portion 4 is visible at this point. Figure 2 shows a micrograph of a cross-section of this sealing structure 1.

[0015] As shown in FIG. 2, no clear bonding interface is observed between the device body 2 and the sealing portion 4, and it can be seen that the sealing portion 4 is bonded to the device body 2 by diffusion bonding and is integrated with the device body 2. The encapsulation hole 5 is formed so as to extend from the part of the sealing portion 4 farthest from the exposed surface 3 in the opposite direction to the exposed surface 3. In other words, the encapsulation hole 5 extends from the sealing end 5a closed by the sealing portion 4 to the side opposite to the exposed surface 3. The inside of the encapsulation hole 5 is filled with the encapsulated liquid 6.

[0016] 1, i.e., in a cross section viewed from a direction perpendicular to the outer surface 2a of the device body 2, the shape of the sealing portion 4 is formed so that it gradually becomes larger from the sealing end 5a of the encapsulation hole 5 toward the exposed surface 3. Furthermore, in the cross section shown in FIG. 1, the formation width W of the exposed surface 3 of the sealing portion 4 is longer than the distance D between the sealing end 5a of the encapsulation hole 5 and the exposed surface 3. As shown in Fig. 3, the shape of the exposed surface 3 of the sealing portion 4 is approximately circular when viewed from a position facing the outer surface of the device body 2. In other words, the sealing portion 4 is formed in a solid bowl shape, and the bottom of the sealing portion 4 closes the encapsulation hole 5. The opening shape of the encapsulation hole 5 is approximately circular when viewed from the opening direction as shown in Fig. 3.

[0017] Next, a procedure for realizing the above-described sealing structure 1 will be described. First, as shown in Fig. 4, the encapsulation hole 5 and the recess 11 are formed in the device body 2. The recess 11 is formed so that it opens to the outer surface 2a of the device body 2, with the encapsulation hole 5 opening in the center. The opening shape of the recess 11 is circular when viewed from a position facing the outer surface 2a of the device body 2. After the recess 11 is formed, an Au film 12 is formed on the inner surface of the recess 11 and on the outer surface 2 a of the device body 2 in the vicinity of the periphery of the recess 11 .

[0018] The Au film 12 can be, for example, a Ti-Au film with a Ti base. A Ti-Pt-Au film can also be used instead of the Ti-Au film. However, because Pt inhibits diffusion, it is preferable to use a Ti-Au film that does not contain Pt. When using a Ti-Pt-Au film, a larger amount of heat is required for diffusion compared to when using a Ti-Au film, so the thermal impact on the electronic components and the enclosed liquid 6 that employ this sealing structure 1 can be minimized.

[0019] 5, after the Au film 12 is formed in the recess 11, the sealing hole 5 is filled with the sealing liquid 6, and the AuSn ball 13 is inserted and placed in the recess 11. The AuSn ball 13 is a ball made of AuSn. After placing the AuSn ball 13 in the recess 11, a laser beam 14 is irradiated toward the outer surface 2a of the device body 2, as shown in Fig. 6. In this embodiment, the laser beam 14 is schematically shown by hatching consisting of vertical dashed lines. The area irradiated with the laser beam 14 is a circular area with a predetermined radius centered on the AuSn ball 13. Therefore, the laser beam 14 is irradiated onto the outer surface 2a of the device body 2 around the recess 11, the recess 11, and the AuSn ball 13.

[0020] The conditions for irradiating the laser beam 14 are set so that the device body 2 and the AuSn ball 13 around the recess 11 melt. The area of ​​the device body 2 that is irradiated with the laser beam 14 and melted is a range that is approximately three to four times the outer diameter of the AuSn ball 13. For example, if the outer diameter of the AuSn ball 13 is 220 μm, the device body 2 is melted in a circular range with an outer diameter of 600 μm to 900 μm, centered on the AuSn ball 13.

[0021] When the laser beam 14 is irradiated, the AuSn balls 13 melt and spread along the Au film 12, as shown in FIG. 7. When all of the AuSn balls 13 melt, the recess 11 is filled with molten AuSn 15 consisting of the molten AuSn balls 13. Then, as the AuSn balls 13 melt, the device body 2 melts, and Si, a material constituting the device body 2, diffuses into the molten AuSn 15 via the Au film 12. This diffusion creates a diffusion region 16 between the device body 2 and the molten AuSn 15, as shown in FIG. 8. The Au constituting the Au film 12 diffuses into this diffusion region 16, and the Au film 12 disappears.

[0022] Diffusion portion 16 spreads over the entire area of ​​molten AuSn 15 and also over the entire area of ​​the melted portion of device body 2. The irradiation of laser light 14 is stopped when diffusion portion 16 has spread over the entire area of ​​the melted portion of device body 2. Diffusion portion 16 then cools and solidifies, forming sealing portion 4 shown in FIG. 1 . Therefore, sealing portion 4 is formed from an alloy primarily composed of Au, Sn, and Si, which is generated when Si, the material of device body 2, diffuses into Au film 12 and molten AuSn 15.

[0023] In the sealing structure 1 for the sealed liquid configured in this manner, the sealing hole 5 is sealed by the sealing part 4 formed by mutual diffusion of Si, which is the material of the device body 2, and AuSn, which is the material of the AuSn ball 13. Therefore, compared to conventional sealing parts formed by melting and solidifying AuSn, the sealing part 4 has a higher hardness and is firmly bonded to the device body 2, so it is possible to provide a sealing structure for the sealed liquid that has high pressure resistance reliability at high temperatures.

[0024] When the hardness of the sealing portion 4 according to this embodiment was compared with that of a conventional sealing portion, the results shown in Figures 9 and 10 were obtained. Figure 9 is a graph showing the relationship between the Si weight ratio of the sealing portion and hardness, and Figure 10 is a graph showing the relationship between the weld diameter (fusion diameter) of the sealing portion and hardness. These graphs show the results of measuring the hardness of multiple samples prepared for a fusion-bonded product having a conventional sealing structure in which the sealing portion is formed by melting and solidifying AuSn, and a diffusion-bonded product having the sealing structure of the present invention in which the sealing portion is formed by diffusion bonding. As can be seen from FIGS. 9 and 10, the sealing portion according to this embodiment has a larger Si weight ratio, a larger weld diameter, and higher hardness than the conventional sealing portion.

[0025] The sealing portion 4 according to the above-described embodiment is formed in a shape that gradually becomes larger from the sealing end 5a of the encapsulation hole 5 toward the exposed surface 3. Therefore, the pressure applied to the sealing portion 4 from the enclosed liquid 6 in the encapsulation hole 5 can be dispersed radially outward from the encapsulation hole 5, thereby making it possible to seal the encapsulation hole 5 more reliably.

[0026] Furthermore, in the above-described embodiment, the formation width W of the exposed surface 3 of the sealing portion 4 is longer than the distance D between the sealing end 5a of the encapsulation hole 5 and the exposed surface 3. This allows a larger area to be secured over which the sealing portion 4 and the device body 2 are joined by diffusion bonding, thereby enabling even stronger sealing.

[0027] (Second embodiment) The sealing structure for sealed liquid according to the present invention can be applied to a pressure sensor as shown in Fig. 11. In Fig. 11, members that are the same as or equivalent to those described with reference to Figs. 1 to 8 are given the same reference numerals, and detailed descriptions thereof will be omitted where appropriate.

[0028] The pressure sensor 21 shown in Fig. 11 includes a pressure sensor chip 22 that is depicted at the top in Fig. 11. The pressure sensor chip 22 constitutes the device body 2 of the sealing structure 1 for sealed liquid according to the present invention. The sealing portion 4 according to this embodiment has an exposed surface 3 that is continuous with the outer surface 22a of one end (the upper end in Fig. 11) of the pressure sensor chip 22, and is formed so as to be included inside the pressure sensor chip 22.

[0029] A first recess 24 and a second recess 25 are formed on the main surface 23 on the other end side (the lower side in FIG. 11) of the pressure sensor chip 22. These first and second recesses 24, 25 are in communication with each other via a communication path 26 formed in the pressure sensor chip 22. The communication path 26 is connected to the encapsulation hole 5. The encapsulation hole 5 is formed to extend from the communication path 26 to the sealing portion 4 and is sealed by the sealing portion 4.

[0030] A plate-shaped sensor diaphragm 27, on which the pressure to be measured acts, is bonded to the other end of the pressure sensor chip 22. The openings of the first recess 24 and the second recess 25 are closed by the sensor diaphragm 27. The inside of the first recess 24 forms a first pressure chamber 28 with the sensor diaphragm 27 as part of its wall, and the inside of the second recess 25 forms a second pressure chamber 29 with the sensor diaphragm 27 as part of its wall. In this embodiment, the filled liquid 6 is filled in the entire area extending from the first and second pressure chambers 28 and 29 through the communication passage 26 and the filling hole 5 to the sealing portion 4 .

[0031] The sensor diaphragm 27 is provided with bridge circuits 30 in a portion facing the first recess 24 and a portion facing the second recess 25, respectively, for converting the displacement of the sensor diaphragm 27 into an electrical signal. These bridge circuits 30 constitute detection members that detect pressure based on changes in the sensor diaphragm 27. These bridge circuits 30 are also electrically connected to electrode pads 31 provided on the sides of the sensor diaphragm 27. The electrode pads 31 are electrically connected to other circuits, such as a signal processing circuit and a power supply circuit (not shown), via conductors and external output pins (not shown). As a result, the displacement of each pressure chamber of the sensor diaphragm 27 is output as an electrical signal.

[0032] A pressure transmission structure 32 that transmits the pressure to be measured to the sensor diaphragm 27 is connected to a main surface 27 a of the sensor diaphragm 27 opposite to the pressure sensor chip 22 . The pressure transmission structure 32 includes a support member 33 joined to the sensor diaphragm 27, an insulating member 34 joined to the support member 33, and a diaphragm base 36 adhered to the insulating member 34 with adhesive 35. Pressure guide paths 37 and 38 are formed in the support member 33, the insulating member 34, and the diaphragm base 36, respectively, for the first and second pressure chambers 28 and 29 described above.

[0033] These pressure guide paths 37, 38 are formed so that the portions of the sensor diaphragm 27 that form the first and second pressure chambers 28, 29 form walls at one end, and a pair of barrier diaphragms 39, 40 provided on the diaphragm base 36 form walls at the other end, and are filled with a pressure transmission medium 41. A first fluid to be measured (not shown) contacts the surface of one barrier diaphragm 39 opposite to the pressure guide path 37, and a second fluid to be measured (not shown) contacts the surface of the other barrier diaphragm 40 opposite to the pressure guide path 38. Therefore, the pressure of the first fluid to be measured (measurement pressure) acts on one barrier diaphragm 39, and the pressure of the second fluid to be measured (measurement pressure) acts on the other barrier diaphragm 40.

[0034] In the pressure sensor 21 configured in this manner, the pressure of the fluid to be measured applied to one barrier diaphragm 39 is transmitted to the first pressure chamber 28 via the pressure transmission medium 41 and the sensor diaphragm 27. Furthermore, the pressure of the fluid to be measured applied to the other barrier diaphragm 40 is transmitted to the second pressure chamber 29 via the pressure transmission medium 41 and the sensor diaphragm 27. In this way, the sensor diaphragm 27 is displaced in the process of transmitting the pressure to the first pressure chamber 28 and the second pressure chamber 29, and the pressure sensor 21 detects the differential pressure between the pressure of the first fluid to be measured and the pressure of the second fluid to be measured.

[0035] The pressure sensor chip 22 of the pressure sensor 21 shown in the second embodiment is provided with the sealing structure 1 for the sealed liquid according to the present invention. Therefore, according to the second embodiment, it is possible to provide a pressure sensor that has high pressure resistance reliability at high temperatures. [Explanation of symbols]

[0036] 1...sealing structure, 2...device body, 3...exposed surface, 4...sealing portion, 5...sealing hole, 5a...sealing end, 6...sealed liquid, 21...pressure sensor, 22...pressure sensor chip, 26...communicating passage, 27...sensor diaphragm (diaphragm), 28...first pressure chamber, 29...second pressure chamber, 32...pressure transmission structure.

Claims

1. a device body formed of Si; a sealing portion having an exposed surface that is continuous with and exposed to the outer surface of the device body, the sealing portion being formed mainly of Au, Sn, and Si and being included inside the device body; a sealing hole formed inside the device body, extending from a sealing end closed by the sealing portion to a side opposite the exposed surface, and filled with a sealing liquid; The sealing structure for sealed liquid is characterized in that the sealing portion is joined to the device body by diffusion bonding and is integrated with the device body.

2. 2. The sealing structure for sealed liquid according to claim 1, The sealing structure for a sealed liquid, wherein the sealing portion is formed in a shape that gradually becomes larger from the sealing end of the sealing hole toward the exposed surface.

3. 3. The sealing structure for sealed liquid according to claim 2, A sealing structure for sealing a sealed liquid, wherein a width of the exposed surface of the sealing portion is longer than a distance between the sealing end of the sealing hole and the exposed surface.

4. A pressure sensor equipped with the sealing structure for sealed liquid according to any one of claims 1 to 3, a pressure sensor chip constituting the device body; a pair of pressure chambers formed in the pressure sensor chip, the diaphragms being part of the walls of which act the pressure to be measured; a communication path formed in the pressure sensor chip so as to communicate the pressure chambers with each other; a pressure transmission structure that transmits a pressure to be measured to the diaphragm, the sealing portion has an exposed surface that is continuous with an outer surface of the pressure sensor chip, and is formed so as to be included inside the pressure sensor chip; the sealing hole is formed to extend from the communication path to the sealing portion, The pressure sensor is characterized in that the enclosed liquid is enclosed in the entire area from the pressure chamber through the communication path and the enclosure hole to the sealing portion.

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