stress sensing element

Abstract

This invention provides a stress sensing element comprising a first silicon element layer, a second silicon element layer, a substrate connection layer, and a substrate. The first silicon element layer has a suspended membrane region and at least one stress sensing unit for sensing stress changes in the suspended membrane region. The second silicon element layer is connected to the bottom surface of the first silicon element layer and includes a bump unit and an outer frame located outside the suspended membrane region, with the bump unit and the outer frame separated by a gap. The substrate connection layer is located on the surface of the outer frame opposite to the first silicon element layer. The substrate is connected to the outer frame via the substrate connection layer and has at least one opening penetrating the substrate and communicating with the gap, thereby providing a stress sensing element with good sensing characteristics.

Description

[Technical Field]

[0001] This invention relates to a sensing element, and more particularly to a stress sensing element. [Previous Technology]

[0002] Stress sensing elements can be used for many applications such as pressure sensing and vibration sensing. Taking a piezoresistive sensing element that senses changes in piezoresistive resistance as an example, it mainly utilizes a diaphragm or cantilever structure, on which a sensor containing piezoresistive sensing material is set. By sensing the pressure difference between the two ends of the diaphragm or cantilever or by bearing external force, the diaphragm or cantilever deforms, generating corresponding stress, thereby changing the resistance value of the sensor located on the diaphragm or cantilever. The changed electrical signal is read by the pickup circuit, which can then be converted into sensed pressure or external force.

[0003] However, when it is necessary to sense relatively small physical quantities (external force, pressure), a highly sensitive piezoresistive sensor needs to be designed to sense the minute changes. Therefore, the diaphragm or cantilever used in the sensing application is usually designed to be thinner or longer. However, increasing the size or decreasing the thickness can easily cause large deformation of the structure, degrade linearity, and is also easy to damage during the manufacturing process, resulting in low yield and manufacturing difficulties. Therefore, the art has proposed different methods to improve this problem. [Summary of the Invention]

[0004] Therefore, the object of the present invention is to provide a stress sensing element with good sensing characteristics.

[0005] Thus, the stress sensing element of the present invention includes a first silicon element layer, a second silicon element layer, a substrate connection layer, and a substrate.

[0006] The first silicon element layer has a surface and a bottom surface that are opposite to each other, includes a suspended membrane region, and at least one stress sensing unit for sensing stress changes in the suspended membrane region.

[0007] The second silicon element layer is connected to the bottom surface of the first silicon element layer, includes a bump unit, and an outer frame located outside the suspension membrane area, and the bump unit and the outer frame are separated by a gap.

[0008] The substrate connection layer is located on the surface of the outer frame opposite to the first silicon element layer.

[0009] The substrate is connected to the outer frame via the substrate connection layer and has at least one opening that penetrates the substrate and communicates with the gap.

[0010] In addition, another object of the present invention is to provide a stress sensing element with good sensing characteristics and low cost.

[0011] Thus, the stress sensing element includes a first silicon element layer, a silicon element connection layer, a second silicon element layer, and a substrate.

[0012] The first silicon element layer has a surface and a bottom surface that are opposite to each other, includes a suspended membrane region, and at least one stress sensing unit for sensing stress changes in the suspended membrane region.

[0013] The second silicon element layer includes an outer frame located on the opposite outer side of the suspension membrane region and including a gap. The outer frame is connected to the bottom surface of the first silicon element layer by the silicon element connecting layer. The silicon element connecting layer is located on the surface of the first silicon element layer in the same direction as the outer frame and is located within the orthographic projection range of the outer frame.

[0014] The substrate is connected to the outer frame of the second silicon element layer and has at least one opening that penetrates the substrate and communicates with the gap.

[0015] The advantages of this invention are that by setting an independent central bump on the bottom surface of the first silicon element layer and corresponding to the center of the suspended membrane area to maintain the flatness of the suspended membrane area, large deformation of the center of the suspended membrane can be avoided, thereby reducing nonlinear output; and by using side bumps distributed around the outer periphery of the central bump to adjust the stress concentration area, the sensing sensitivity of the stress sensing element can be improved; and by using the bump units formed before the substrate is opened during the process to fix the suspended membrane, the deformation of the suspended membrane caused by the high temperature step during the process can be greatly reduced, thereby reducing zero offset. By designing a substrate connection layer, it can serve as an etching termination layer when the substrate is opened during the process, enabling the fabrication of good bump structure uniformity, thereby achieving consistent output of the sensing element. In addition, by designing a silicon element connection layer, non-uniform bump structures during the process can be selectively removed, thereby achieving good consistent output of the sensing element with lower manufacturing cost. In addition, the design of the opening positions formed on the substrate can reduce the impact of packaging stress on the chip during the packaging process and avoid the problem of failure caused by overpressure rupture of the suspension area during the pressure test.

Implementation Method

[0017] Before the present invention is described in detail, it should be noted that similar elements are represented by the same numbers in the following description.

[0018] The stress sensing element of the present invention is a pressure sensing element or a vibration sensing element that can be used to sense pressure or vibration.

[0019] The first embodiment is described using the stress sensing element as a pressure sensing element for sensing pressure.

[0020] Referring to Figures 1 and 2, the first embodiment of the stress sensing element of the present invention includes a first silicon element layer 2, a second silicon element layer 3, a silicon element connection layer 4, a substrate connection layer 5, and a substrate 6.

[0021] The first silicon element layer 2 has a silicon substrate 21 and at least one stress sensing unit 22. The silicon substrate 21 has a surface 211 opposite to each other, a bottom surface 212, a suspended membrane groove 216 formed downward from the surface 211 and located in a suspended membrane region 213, a peripheral region 214 surrounding the suspended membrane region 213 and located outside the suspended membrane region 213, and a plurality of edge ribs 215 symmetrically distributed in the suspended membrane region 213 and adjacent to the peripheral region 214. In some embodiments, the suspended membrane region 213 is generally square.

[0022] Multiple stress sensing units 22 are provided corresponding to the edge ribs 215 and are used to sense stress changes in the suspension region 213. Each stress sensing unit 22 includes a sensing layer 221 made of piezoresistive material, an insulating protective layer 222 covering the sensing layer 221, and a metal trace 223 passing through the insulating protective layer 222 and electrically connected to the sensing layer 221. The metal trace 223 will cooperate to transmit the electrical signal sensed by the sensing layer 221 to the outside. Since the relevant materials and structures of the stress sensing unit 22 are known to those skilled in the art and are not the focus of this invention, they will not be described in detail here.

[0023] The second silicon element layer 3 is in contact with the bottom surface 212 of the silicon substrate 21 and includes a bump unit 31 and an outer frame 32. The bump unit 31 has a central bump 311 located at the center of the suspended membrane region 213 and a plurality of side bumps 312 located outside the central bump 311 and spaced apart by a gap G1. The outer frame 32 is located in the peripheral region 214, and the orthographic projection directions of its boundaries coincide, and it is connected to the bottom surface 212 of the silicon substrate 21 by the silicon element connecting layer 4. The silicon element connecting layer 4 is made of silicon dioxide, and the distance S between the side bumps 312 and the corresponding boundary of the suspended membrane region 213 is between 5 and 200 micrometers.

[0024] As mentioned above, the central protrusion 311 can be a symmetrical structure such as square, X-shaped, or cross-shaped, and the outer frame 32 can be a frame-like structure surrounding the suspension membrane area 213. In this embodiment, the central protrusion 311 has an X-shaped structure, the outer frame 32 is a frame-like structure surrounding the suspension membrane area 213, and there are four side protrusions 312, which are symmetrically arranged between the central protrusion 311 and the adjacent outer frame 32, and each side protrusion 312 is a square structure. However, in actual implementation, this structure, number, and distribution pattern are not limited.

[0025] Furthermore, it should be noted that the first embodiment is illustrated by the example of the first silicon element layer 2 and the second silicon element layer 3 being connected by the silicon element connection layer 4. However, in some embodiments, the first silicon element layer 2 and the second silicon element layer 3 can also be directly connected by silicon fusion bonding without the silicon element connection layer 4.

[0026] Furthermore, to achieve structural uniformity and output consistency, the bump unit 31 needs to have a flat bottom surface and its thickness needs to be precisely controlled. In some embodiments, the total thickness variation (TTV) of the central bump 311 and the side bumps 312 is less than 1 micrometer.

[0027] In some embodiments, the area of ​​the central protrusion 311 is 5 to 20% of the area of ​​the suspension membrane region 213.

[0028] In some embodiments, the thickness of the central protrusion 311 and the side protrusions 312 is no more than 100 micrometers, which can have a smaller vibration sensitivity and reduce noise error.

[0029] The substrate 6 is connected to the outer frame 32 via the substrate connecting layer 5, and has at least one opening 62 that penetrates the substrate 6 and communicates with the gaps between the gaps G1 and the gaps between the side protrusions 312 and the corresponding suspension membrane area 213.

[0030] In some embodiments, the substrate connection layer 5 is recessed and located within the orthographic projection range of the outer frame 32, and the recessed width is not less than 2 micrometers.

[0031] In detail, the substrate 6 has a plate body 61, and the openings 62 penetrate the plate body 61. The plate body 61 can be made of materials such as silicon, glass, or ceramic, and the substrate connecting layer 5 can be made of insulating materials such as silicon nitride, silicon dioxide, or polymers. In this embodiment, the plate body 61 is made of silicon, and the substrate connecting layer 5 is made of silicon dioxide as an example.

[0032] More specifically, the plate body 61 has a frame 611 connected to the outer frame 32. The openings 62 penetrate the plate body 61 and are located within the projection range of the suspended membrane area 213. The central protrusion 311 and the side protrusions 312 are located within the orthographic projection range of the corresponding openings 62, and the diameter of the openings 62 is slightly larger than the size of the corresponding side protrusions 312 and the central protrusion 311 to form gaps. Accordingly, the openings 62 can be connected to the gaps G1 and the gaps between the side protrusions 312 and the boundary of the corresponding suspended membrane area 213 through the gaps, which can avoid the problem of direct impact on the suspended membrane area 213 when pressure is applied through the openings 62.

[0033] In addition, it should be noted that although the closer the edge of the side protrusion 312 is to the boundary of the suspension membrane region 213, the more significant the stress output can be. However, considering the manufacturing process and performance, the distance S between the edge of the corresponding side protrusion 312 and the boundary of the adjacent suspension membrane region 213 can be further controlled to be in the range of 5 to 200 micrometers. This can achieve relatively high sensitivity and avoid the manufacturing process problem of the side protrusion 312 being too close to the boundary of the suspension membrane region 213.

[0034] In some other embodiments, the plate body 61 may have only one opening 62 corresponding to the suspension membrane area 213, instead of having multiple openings 62. As long as the opening 62 is located within the orthographic projection range of either the central protrusion 311 or the side protrusions 312, and is offset from the position of the gaps G1 and not directly connected, and the distance between the boundary of each opening 62 and the boundary of either the central protrusion 311 or the side protrusions 312 in the orthographic projection direction is not greater than 100 micrometers.

[0035] The stress sensing element of the present invention utilizes an independent central bump 311 disposed on the bottom surface 212 of the first silicon element layer 2 and at the position of the suspended film region 213. This maintains the flatness of the suspended film region 213, thereby reducing the nonlinearity of the element output. Simultaneously, before the board body 61 is drilled during manufacturing, the bump unit 31 fixes the suspended film region 213, significantly reducing the deformation of the suspended film caused by high-temperature steps during the process and maintaining the flatness of the suspended film, thus reducing the zero-offset output variation caused by the deformation of the suspended film. Furthermore, independently distributed side bumps 312 disposed on the outer side of the central bump 311 adjust the stress concentration area, thereby enabling the stress sensing element to have better sensing sensitivity. By designing a substrate connection layer 5, it can serve as an etching termination layer when the substrate is drilled during the process, enabling the fabrication of good bump structure uniformity, thereby achieving consistent output of the sensing element. Furthermore, by matching the positions of the openings 62 formed on the substrate 6 with the bump unit 31, the problem of the suspended film area 213 being directly impacted by the openings 62 during pressure injection can be avoided, which could lead to the suspended film area 213 failing due to overpressure. This can also reduce packaging process failures and the impact of packaging stress on the wafer.

[0036] Referring to Figure 3, in some embodiments, the central protrusion 311 and the side protrusions 312 can be an inverted trapezoidal structure that is wider at the top and narrower at the bottom. The stress distribution can be adjusted by designing the shape of the central protrusion 311 and the side protrusions 312.

[0037] Referring to FIG4, in some embodiments, the first silicon element layer 2 may further have a protrusion 23 protruding upward from the bottom of the suspension membrane groove 216 in the suspension membrane region 213. The protrusion 23 can be used to locally reinforce the structure of the suspension membrane region 213 and further change the rigidity of the suspension membrane and the stress distribution when the suspension membrane is deformed under pressure. FIG4 is an example with the position of the protrusion 23 corresponding to the central protrusion 311. However, in actual implementation, it is not limited to this position.

[0038] Referring to FIG5, in some embodiments, the first silicon element layer 2 may be planar in the suspension region 213 and the peripheral region 214 without having the groove structure shown in FIG1. ​​This structure can simplify the manufacturing process and can also achieve the pressure sensing result of the present invention.

[0039] Referring to FIG6, in some embodiments, the lateral protrusions 312 may be distributed in multiple rows between the central protrusion 311 and the outer frame 32, and the distance S between the lateral protrusions 312 closest to the outer frame 32 and the boundary of the corresponding suspension region 213 is between 5 and 200 micrometers. The multi-layered distribution of the lateral protrusions 312 can increase design flexibility and adjust the characteristics of the stress sensing element.

[0040] Referring to FIG7, in some embodiments, the bump unit 31 further includes a plurality of limiting bumps 313. The substrate 6 may also have a frame extension area 612 extending from the frame 611 toward the suspended membrane area 213 and not connected to the outer frame 32, such that the overall surface area of ​​the substrate 6 and the outer frame 32 (the surface area of ​​the frame 611 plus the surface area of ​​the frame extension area 612) is larger than the surface area of ​​the outer frame 32. The limiting bumps 313 are connected to the bottom surface 212 of the silicon substrate 21 and are located within the projection range of the frame extension area 612. The limiting bumps 313 and the surface of the frame extension area 612 are separated by an air gap G2 with a vertical distance of no more than 5 micrometers. The limiting bumps 313 can achieve the function of limiting the vertical displacement of the suspended membrane when the suspended membrane area 213 is compressed, thereby avoiding the problem of the suspended membrane area 213 breaking and failing due to excessive deformation caused by overpressure. In this embodiment, there are four limiting protrusions 313, which are distributed in the suspension membrane area 213 and located within the orthographic projection range of the border extension area 612.

[0041] The manufacturing method of the aforementioned first embodiment will be described below.

[0042] Referring to Figures 2, 8, and 9, the manufacturing method of the first embodiment of the present invention will be described below.

[0043] First, a substrate 100 to be etched, as shown in FIG8(a), is provided, including a first substrate 101, a second substrate 102, and an etch stop layer 5a between the first substrate 101 and the second substrate 102. The second substrate 102 is used to define the bump unit 31. Therefore, the thickness of the second substrate 102 can be matched with the thickness of the bump unit 31 to be formed, and the etch stop layer 5a becomes the substrate connection layer 5 after the process. The substrate 100 to be etched can be an SOI (Silicon on Insulator) wafer.

[0044] Next, the second substrate 102 is etched downwards from the surface of the first substrate 101 to the etch stop layer 5a, so as to form the second substrate 102 with the central bump 311, the symmetrical side bumps 312 located on the symmetrical side of the central bump 311, and the outer frame 32 surrounding the symmetrical side bumps 312, to obtain the second silicon element layer 3, which has the structure shown in FIG8(b).

[0045] Then, a temporary substrate 900 including the third substrate 103 is bonded to the second silicon element layer 3 opposite to the surface of the first substrate 101 via an etch stop layer 4a. The bonding method can be silicon-to-silicon oxide fusion bonding (Si-SiO2 fusion bonding), resulting in the structure shown in FIG8(c). The temporary substrate 900 includes a support substrate 901 and the third substrate 103 bonded to the surface of the support substrate 901.

[0046] Then, using a layer transfer process, the support substrate 901 is removed, exposing the surface 211 of the third substrate 103, resulting in the structure shown in 8(d). The temporary substrate 900 can be a general silicon wafer or an SOI silicon wafer, and the etch stop layer 4a becomes the silicon device connection layer 4 after the process.

[0047] Next, a portion of the material is selectively removed from the surface 211 of the third substrate 103 to form the suspension groove 216, and the third substrate 103 is defined to obtain the suspension region 213, the peripheral region 214, and the edge ribs 215, to obtain the structure shown in FIG9(e). As mentioned above, the selective removal of the material of the third substrate 103 can be performed by etching (dry etching or wet etching) or laser, etc.

[0048] Furthermore, it should be noted that in this first embodiment, the third substrate 103 is bonded to the second silicon element layer 3 using the etch stop layer 4a, and the etch stop layer 4a becomes the silicon element connection layer 4 as shown in FIG2 after the process is completed. However, in some embodiments, the third substrate 103 and the second silicon element layer 3 can also be directly bonded through silicon-to-silicon fusion bonding, without the need for the etch stop layer 4a.

[0049] Next, the stress sensing unit 22 is formed on the surface of the third substrate 103 to obtain a structure as shown in FIG9(f).

[0050] Specifically, the stress sensing unit 22 is formed by ion-bonding a sensing layer 221 made of piezoresistive material at the location of the peripheral region 214 of the third substrate 103 near the edge ribs 215, and a protective layer 222 covering the sensing layer 221. Then, a metal trace 223 is formed that passes through the protective layer 222 and is electrically connected to the sensing layer 221, thus completing the stress sensing unit 22 and obtaining the first silicon element layer 2. Since the relevant structure, material selection and related process control of the stress sensing unit 22 are known in the art, they will not be described in detail.

[0051] Then, the openings 62 penetrating the first substrate 101 are formed on the first substrate 101 with the structure shown in FIG9(f), so that the first substrate 101 is transformed into a substrate 6 containing the openings 62. At this time, the position of the openings 62 will stop on the etch stop layer 5a, so that the openings 62 are still not connected to the gaps G1. Then, the exposed portion of the etch stop layer 5a connected to the openings 62 and the gaps G1 is removed to obtain the structure shown in FIG9(g) to complete the fabrication of the stress sensing element.

[0052] Specifically, the aforementioned openings 62 can be formed by dry etching, wet etching, laser, CNC, or sandblasting, etc., and the openings 62 can correspond to the positions of the central protrusion 311 and the side protrusions 312 (as shown in Figure 2). The etch termination layer 5a can be removed by dry etching, wet etching, etc.

[0053] Referring to Figure 10, which shows the actual fabricated sensing element, a scanning electron microscope image of the bump unit 31 (central bump 311, side bump 312) is taken out of the suspension region 213 of the stress sensing element and observed. Figure 10(a) is an image of the bump unit 31 without the etch stop layer 5a, and Figure 10(b) is an image of the bump unit 31 with the etch stop layer 5a introduced using the present invention. As can be seen from Figure 10, the bump unit 31 without the etch stop layer 5a has uneven thickness and poor surface flatness of each bump, which can easily cause poor and inconsistent output characteristics of the manufactured stress sensing element, such as zero-point offset and nonlinearity. The present invention, through a layer transfer process, pre-controls the thickness of the second substrate 102 (as shown in FIG. 8) defining the central bump 311 and the side bumps 312, thereby precisely controlling the thickness of the bump unit 31 made from the second substrate 102, so that the thickness difference of each individual bump of the bump unit 31 is no more than 5 micrometers. By introducing the etch stop layer 5a as an etch barrier material for the bump unit 31 during the manufacturing process, the total thickness variation (TTV) of each bump can be controlled to be less than 1 micrometer. Under such a small thickness variation, the manufactured stress sensing element can have excellent and consistent output characteristics.

[0054] Referring to FIG11, a second embodiment of the stress sensing element of the present invention has a structure that is substantially the same as that of the first embodiment. The difference is that the central protrusion 311 of the second embodiment has a hollow structure 314 formed by multiple grooves formed downward from the surface adjacent to the suspension membrane region 213. A plurality of side protrusions 312 are spaced apart between the central protrusion 311 and the adjacent outer frame 32 (FIG11 illustrates two side protrusions 312 as an example). The substrate 6 has openings 62 at positions corresponding to the central protrusion 311 and the side protrusions 312. By forming the hollow structure 314 with the central protrusion 311, in addition to maintaining the rigidity of the central protrusion 311, it can also reduce the mass of the central protrusion 311 to adjust the sensitivity of the stress sensing element to vibration, thereby avoiding the influence of excessive vibration sensitivity on the pressure sensing results.

[0055] It should be noted that the aforementioned second embodiment is illustrated by the example of the central protrusion 311 having a hollow structure 314. However, in actual implementation, at least one of the central protrusion 311 and the side protrusions 312 can have the hollow structure 314 as required, and there are no particular restrictions.

[0056] The manufacturing method of the aforementioned second embodiment is largely the same as that of the first embodiment, except that when defining the central bump 311, the trenches can be designed to have a smaller width. This allows the aspect-ratio dependent etching characteristic during dry etching to simultaneously etch the bump (such as the central bump 311) and the trenches within the central bump 311 without etching through the bump (central bump 311). Then, the same steps as in the first embodiment are performed to complete the manufacturing of the second embodiment.

[0057] Referring to FIG12, a third embodiment of the stress sensing element of the present invention has a structure that is substantially the same as that of the first embodiment. The difference is that, in addition to having the openings 62, the substrate 6 also has a substrate groove 63 that communicates with the openings 62, and the second silicon element layer 3 does not have the substrate connection layer 5 between it and the substrate 6.

[0058] Specifically, in this third embodiment, the substrate 6 has a substrate body 61, a substrate groove 63 formed downward from the surface of the substrate body 61 adjacent to the protrusion unit 31, a frame 611 surrounding the substrate groove 63 and connected to the second silicon element layer 3, and the orthographic projection range of the substrate groove 63 at least covers the protrusion unit 31 and communicates with the gap G1. The opening 62 is formed in the orthographic projection range of the peripheral region 214, and the second silicon element layer 3 is integrally formed with the substrate 6 or is formed by silicon-to-silicon fusion bonding. Therefore, there is no substrate connecting layer 5, and it has the structure shown in FIG12. FIG12 is an example of an opening 62 formed in the peripheral region 214; however, in actual implementation, the number is not limited to this. By positioning the opening 62 below the peripheral area 214 and offset from the suspension membrane area 213, damage to the suspension membrane area 213 and / or the protrusion unit 31 can be further avoided when the opening 62 is formed. It can also effectively reduce the impact force on the suspension membrane when air pressure suddenly enters from the opening 62.

[0059] Referring to FIG13, in some embodiments, when the substrate 6 of the stress sensing element has the substrate groove 63, the openings 62 can also be located within the orthographic projection range of the substrate groove 63. The substrate groove 63 increases the buffer space when pressure is introduced from the openings 62, reducing the impact force on the suspension membrane when air pressure suddenly enters from the openings 62, and increasing the design flexibility of the opening positions 62. FIG13 shows an example where the openings 62 are located below the gap G1 between the central protrusion 311 and the side protrusions 312. However, in actual implementation, the openings 62 can also be located below the positions of the central protrusion 311 and the side protrusions 312, as shown in the first embodiment.

[0060] Referring to FIG14, the manufacturing method of the aforementioned third embodiment is similar to that of the first embodiment, except that: after the second silicon element layer 3 is formed on the first substrate 101, the subsequent formation order of the first silicon element layer 2 and the substrate 6 is different, including the following steps.

[0061] First, step (a) is performed, in which a temporary substrate 900 is bonded to the second silicon element layer 3 against the surface of the first substrate 101, resulting in the structure shown in FIG. 14(a). The temporary substrate 900 includes a support substrate 901 and a third substrate 103 bonded to the surface of the support substrate 901, and the third substrate 103 is bonded to the second silicon element layer 3. The temporary substrate 900 may be an SOI wafer, and the first substrate 101 and the second silicon element layer 3 may be the handle layer and device layer of another SOI wafer, respectively.

[0062] Next, step (b) is performed, in which the first substrate 101 is removed using a layer transfer process, exposing the second silicon element layer 3, to obtain the structure shown in FIG14(b).

[0063] Then, in step (c), a substrate 902 to be drilled is bonded to the exposed surface of the second silicon element layer 3. The substrate 902 to be drilled has a substrate groove 63 formed from the surface adjacent to the second silicon element layer 3. Afterwards, the support substrate 901 is removed using a layer transfer process, exposing the third substrate 103, resulting in the structure shown in FIG14(c). At this time, the substrate 902 to be drilled is considered as the first substrate 101 as shown in FIG8.

[0064] It should be noted that the bonding between the aforementioned second silicon element layer 3 and the substrate 902 to be opened can be directly bonded through silicon-to-silicon fusion bonding, but it can also be bonded through other wafer bonding methods containing intermediate layers, such as silicon-to-silicon oxide fusion bonding, without any particular limitation.

[0065] Then, step (d) is performed to selectively remove part of the material of the third substrate 103 downward from the surface of the third substrate 103 to form the suspension groove 216 on the third substrate 103, thereby obtaining the structure shown in FIG14(d) to define the suspension region 213, the peripheral region 214, and the edge ribs 215.

[0066] Subsequently, the same steps as in the first embodiment can be used to form the stress sensing unit 22 on the third substrate 103 to obtain the first silicon element layer 2. Then, the opening 62, which communicates with the substrate groove 63 and is located in the peripheral area 214, is etched from the substrate 902 to be opened to obtain the substrate 6, thus completing the fabrication of the third embodiment as shown in FIG12. Wherein, when the opening 62 is set as shown in FIG12, located below the peripheral area 214 and offset from the suspension film area 213, it can further avoid damage to the suspension film area 213 and / or the bump unit 31 when the opening 62 is formed. Therefore, it is not necessary to introduce the etching stop layer 5a or remove the etching stop layer 5a.

[0067] Referring to FIG15, a fourth embodiment of the stress sensing element of the present invention has a main structure that is generally the same as that of the first embodiment. The difference is that the suspension membrane area 213 of the first silicon element layer 2 does not contain the suspension membrane groove 216 and is coplanar with the peripheral area 214. Multiple side protrusions 312 are distributed between the central protrusion 311 of the protrusion unit 31 and the outer frame 32. The first silicon element layer 2 also has multiple suspension membrane perforations 24, and the substrate 6 also has a central mass block 64 connected to the central protrusion 311.

[0068] In detail, the suspended membrane perforations 24 are distributed between the central protrusion 311 and the adjacent side protrusions 312. The openings 62 of the substrate 6 are annular and are located in the area below the side protrusions 312. The plate body 61 also has a central mass block 64 defined by the annular openings 62, located below the central protrusion 311 and connected to the central protrusion 311. The vibration sensitivity of the stress sensing element can be adjusted by using the suspended membrane perforations 24 and the central mass block 64 connected to the central protrusion 311, and the stress sensing element can be used as an accelerometer independently.

[0069] Furthermore, referring to FIG16, in some embodiments, the stress sensing element structure shown in the first embodiment and the fourth embodiment can be integrated to obtain a composite sensor that integrates an accelerometer and a pressure gauge.

[0070] Referring to FIG17, a fifth embodiment of the present invention has a structure similar to the first embodiment, including the first silicon element layer 2, the second silicon element layer 3, the silicon element connection layer 4, and the substrate 6. The difference is that the second silicon element layer 3 does not have the bump unit 31, the silicon element connection layer 4 used to connect the first silicon element layer 2 and the outer frame 32 is made of silicon oxide and is recessed within the orthographic projection range of the outer frame 32, and the second silicon element layer 3 and the substrate 6 are integrally formed or formed by silicon-to-silicon fusion bonding. Therefore, the substrate connection layer 5 shown in FIG2 is not present.

[0071] In some embodiments, the silicon element connection layer 4 is recessed and located within the orthographic projection range of the outer frame 32, and the recessed width is not less than 2 micrometers.

[0072] In some embodiments, the second silicon element layer 3 may also have the bump unit 31 as shown in FIG2, but unlike the first embodiment, the bump unit 31 will only have a central bump 311 with a larger area, and will not have the side bumps 312.

[0073] The manufacturing method of the fifth embodiment is described below.

[0074] Referring to FIG18, firstly, a silicon substrate 903 is prepared, and a plurality of bumps 300 are defined by etching downward from the surface of the silicon substrate 903 to a predetermined depth, and the outer frame 32 surrounding the bumps 300 is defined to obtain the structure shown in FIG18(a).

[0075] Next, the bumps 300 and the outer frame 32 are connected to a thin silicon substrate 904 using a silicon element connection layer 4 to obtain the structure shown in FIG18(b).

[0076] Then, selective etching is performed from the thin silicon substrate 904 in the opposite direction to the surface of the bumps 300 to form the suspension groove 216, so as to define the suspension area 213, the peripheral area 214 and the edge ribs 215, to obtain the structure shown in FIG18(c).

[0077] Next, referring to FIG19, stress sensing units 22 are formed in the peripheral area 214 of the thin silicon substrate 904 near the edge ribs 215 to obtain the first silicon element layer 2, forming the structure shown in FIG19(d).

[0078] Then, back etching is performed from the silicon substrate 903 toward the surface of the first silicon element layer 2 to form the openings 62. Since there is no etch stop layer after the openings 62 are formed by back etching, when over-etching continues, the bumps 300 will continue to be etched and produce an uneven surface R, as shown in FIG19(e).

[0079] Next, after forming the openings 62, isotropic etching is performed on the silicon element connection layer 4 to remove the portion of the silicon element connection layer 4 connecting the bumps 300 and the first silicon element layer 2, thereby peeling off the bumps 300, as shown in FIG19(f), thus completing the fabrication of the fifth embodiment. The silicon element connection layer 4 connecting the outer frame 32 and the first silicon element layer 2 is also removed from the outermost side inwards due to isotropic undercut etching, resulting in an inward-shrinking structure for the silicon element connection layer 4.

[0080] It should be noted that the silicon element connection layer 4 and the substrate connection layer 5 in the aforementioned embodiments (Figures 2-15) are schematic structures that are flush with the outer edge of the corresponding connection structure. However, in actual implementation, the silicon element connection layer 4 and the substrate connection layer 5 may have an inwardly recessed structure similar to that in Figure 17 due to different etching methods.

[0081] The stress sensing element described in this fifth embodiment can reduce the use of high-cost SOI wafers and utilize a lower-cost process. Forming the bumps 300 during the process helps provide suspension support during the process to prevent deformation. Even if the bumps 300 have issues such as uneven thickness or flatness during fabrication, due to their small size, they can be removed by isotropic undercut etching of the silicon element connection layer 4 during the etching process. Therefore, this structure simplifies the process, reduces costs, and avoids performance variations in the final stress sensing element due to the uniformity of the bump units 31. Regarding the recessed structure of the silicon element connection layer 4 between the outer frame 32 and the first silicon element layer 2, which generally requires a recess of at least 2 micrometers for process control, the width of the bumps 300 to be removed needs to be designed to be less than twice the recessed distance, such as approximately 4 micrometers.

[0082] Furthermore, it should be noted that when the fifth embodiment intends to retain the central bump 311 as shown in FIG2, it is only necessary to design the bump 300 located in the center to have a larger area when forming the bumps 300. Therefore, after isotropic undercut etching, the bump 300 with a larger area will be retained, and the central bump 311 as shown in FIG2 will be formed.

[0083] In summary, the stress sensing element of the present invention, as described in the first to fourth embodiments, provides support for the first silicon element layer 2 and prevents deformation of the first silicon element layer 2 through the bump unit 31 of the second silicon element layer 3. Since the stress sensing element can be fabricated using two SOI wafer processes, the thickness and bottom surface flatness of the bump unit 31 can be effectively controlled, ensuring that the thickness of the bump unit 31 is no greater than 100 micrometers, and the thickness variation of each bump (central bump 311, side bump 312) of the bump unit 31 is less than 5 micrometers, and the total thickness deviation of each bump (central bump 311, side bump 312) is less than 1 micrometer. This improves overall performance, including linearity, zero-point output, and yield, and effectively reduces vibration noise errors. Furthermore, the stress distribution can be adjusted by designing the shape, structure, and number of the bump unit 31 to obtain a more stable stress sensing element with better sensing sensitivity. In other implementations, the stress sensing element of the fifth embodiment, through the design of the silicon element connection layer 4, can selectively peel off and remove the bump unit 31 with an uneven bottom surface during the manufacturing process, eliminating the need to use the more expensive SOI wafer to fabricate the bump structure, and instead utilizing a lower-cost process. The present invention can also reduce performance variations in the resulting stress sensing element by retaining the central bump 311 portion, thus effectively achieving the objectives of the present invention.

[0084] However, the above description is only an embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the patent specification shall still fall within the scope of the patent of the present invention. [Simplified Explanation of the Diagram]

[0016] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, wherein: FIG1 is a top view illustrating the top structure of a first embodiment of the stress sensing element of the present invention; FIG2 is a cross-sectional view illustrating the cross-sectional structure along section line II-II of FIG1; FIG3 is a cross-sectional view illustrating another structural form of the bump unit of the first embodiment; FIG4 is a cross-sectional view illustrating another structural form of the first silicon element layer of the first embodiment; FIG5 is a cross-sectional view illustrating yet another structural form of the first silicon element layer of the first embodiment; FIG6 is a cross-sectional view illustrating another structural form of the bump unit of the first embodiment; FIG7 is a cross-sectional view illustrating another structural form of the bump unit and the substrate of the first embodiment; FIG8-9 are flowcharts illustrating the manufacturing process of the first embodiment; FIG10 is a SEM image illustrating scanning electron microscope (SEM) images of the bump unit in contact with the suspension membrane obtained by different processes; FIG11 is a cross-sectional view illustrating a second embodiment of the stress sensing element of the present invention. Figure 12 is a cross-sectional schematic diagram illustrating a third embodiment of the stress sensing element of the present invention; Figure 13 is a cross-sectional schematic diagram illustrating another structural state of the substrate of the third embodiment; Figure 14 is a flowchart illustrating some of the manufacturing process steps of the third embodiment; Figure 15 is a cross-sectional schematic diagram illustrating a fourth embodiment of the stress sensing element of the present invention; Figure 16 is a cross-sectional schematic diagram illustrating a composite sensor obtained by integrating the first embodiment and the fourth embodiment; Figure 17 is a cross-sectional schematic diagram illustrating a fifth embodiment of the stress sensing element of the present invention; and Figures 18-19 are flowcharts illustrating the manufacturing process of the fifth embodiment.

Claims

1. A stress sensing element, comprising: a first silicon element layer having a surface and a bottom surface opposite to each other, including a suspended membrane region, and at least one stress sensing unit for sensing stress changes in the suspended membrane region; a second silicon element layer connected to the bottom surface of the first silicon element layer, including a bump unit and an outer frame located outside the suspended membrane region, wherein the bump unit and the outer frame are separated by a gap; a substrate connecting layer located on the surface of the outer frame opposite to the first silicon element layer; and a substrate connected to the outer frame via the substrate connecting layer, having at least one opening penetrating the substrate and communicating with the gap.

2. The stress sensing element as claimed in claim 1 further includes a silicon element connection layer for connecting the first silicon element layer and the second silicon element layer.

3. The stress sensing element as claimed in claim 1, wherein, The substrate connection layer is located within the orthographic projection range of the outer frame.

4. The stress sensing element as claimed in claim 1, wherein, The first silicon element layer also has a suspended membrane groove formed downward from the surface and located in the suspended membrane region, and a plurality of edge ribs symmetrically distributed around the suspended membrane groove.

5. The stress sensing element as claimed in claim 1, wherein, The bump unit includes a central bump with a thickness of no more than 100 micrometers and a total thickness deviation of less than 1 micrometer.

6. The stress sensing element as claimed in claim 1, wherein, The suspended membrane region is generally square, and the bump unit includes at least four side bumps symmetrically distributed on the boundaries of the four sides adjacent to the suspended membrane region. The thickness of the side bumps is no more than 100 micrometers, the total thickness deviation is less than 1 micrometer, and the distance between the side bumps and the corresponding boundary of the suspended membrane region is between 5 and 200 micrometers.

7. The stress sensing element as claimed in claim 1, wherein, The bump unit includes at least four limiting bumps. The substrate also has a frame connected to the outer frame and a frame extension surface extending from the frame toward the suspension membrane area without being connected to the outer frame. The at least four limiting bumps are distributed in the suspension membrane area and are located within the orthographic projection range of the frame extension surface, and are separated from the surface of the opposite frame by an air gap of no more than 5 micrometers.

8. The stress sensing element as claimed in claim 1, wherein, At least one of the bumps in the bump unit has a hollow structure.

9. The stress sensing element as claimed in claim 5, wherein, The opening is annular, and the substrate also has a frame surrounding the opening and connected to the outer frame, and a mass surrounded by the opening. The annular opening communicates with the gaps, and the mass is connected to the central protrusion.

10. The stress sensing element as claimed in claim 1, wherein, The substrate has a plurality of openings, the number and position of which correspond to the number and position of the bumps of the bump unit. The diameter of the openings is larger than that of the corresponding bumps, and the distance between the boundary of each opening and the boundary of the corresponding bump in the orthographic projection direction is no more than 100 micrometers.

11. The stress sensing element as claimed in claim 1, wherein, The substrate has a substrate groove formed downward from the surface of the adjacent bump unit, the orthographic projection direction of the substrate groove covers the bump unit and communicates with the gap, and the at least one opening communicates with the substrate groove.

12. The stress sensing element as claimed in claim 11, wherein, At least one opening is located outside the orthographic projection range of the suspended membrane area.

13. A stress sensing element, comprising: a first silicon element layer having a surface and a bottom surface opposite to each other, including a suspended membrane region, and at least one stress sensing unit for sensing stress changes in the suspended membrane region; a silicon element connecting layer connected to the bottom surface of the first silicon element layer; a second silicon element layer including an outer frame located on the opposite outer side of the suspended membrane region and including a gap, the outer frame being connected to the bottom surface of the first silicon element layer via the silicon element connecting layer, and the silicon element connecting layer being located within the orthographic projection range of the outer frame; and a substrate connected to the outer frame of the second silicon element layer, having at least one opening penetrating the substrate and communicating with the gap.

14. The stress sensing element as claimed in claim 13, wherein, The inward width of the silicon element connection layer within the orthographic projection range of the outer frame is not less than 2 micrometers.

15. The stress sensing element as claimed in claim 14, wherein, The second silicon element layer also includes a bump unit having a central bump located in the center of the suspension region and having a total thickness deviation of less than 1 micrometer, and the central bump being connected to the bottom surface of the first silicon element layer via the silicon element connection layer.

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