Bonding method, bonding structure, MEMS device and manufacturing method thereof

Abstract

The invention discloses a bonding method, a bonding structure, an MEMS device and a manufacturing method thereof. The bonding method comprises the following steps: providing a first substrate; etching the front surface of the first substrate, and forming a first boss structure and a second boss structure on the front surface of the first substrate; forming a germanium layer on the top surface of the first boss structure; providing a second substrate, and forming an aluminum layer on the front surface of the second substrate; patterning the aluminum layer, and forming a first aluminum pad corresponding to the first boss structure and a second aluminum pad corresponding to the second boss structure on the front surface of the second substrate; and executing a eutectic bonding process, so that the germanium layer and the first aluminum pad are mutually fused to form an aluminum-germanium mutual fusion bonding layer, and the surface of the second boss structure is in contact with the surface of the second aluminum pad. According to the invention, the consistency of aluminum-germanium bonding can be improved, so that the performance of the MEMS device is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor device manufacturing, and in particular to a bonding method, a bonding structure, a MEMS device and a manufacturing method thereof. Background Art

[0002] MEMS (micro-electro-mechanical system) gyroscopes are very susceptible to dust, water vapor, mechanical factors and other factors during the dicing and packaging process due to their movable microstructures, which can cause device damage or device performance degradation. Therefore, MEMS gyroscopes require airtight packaging to prevent damage to the movable microstructure, and at the same time maintain a stable gas damping coefficient to improve device performance.

[0003] Eutectic bonding is a wafer-level vacuum packaging technology that has been widely used in sensors such as accelerometers, gyroscopes, and pressure gauges in recent years, and has become a key technology for the development and practical application of MEMS devices. Eutectic bonding uses a metal layer as the intermediate bonding medium layer, taking advantage of the low melting temperature of some eutectic alloys, and heats and melts the two metals to tightly combine together to achieve bonding. Compared with other bonding methods commonly used in MEMS devices (anodic bonding, silicon-silicon direct bonding, and adhesive bonding), due to the use of metal dielectric materials, eutectic bonding sheets have lower permeability, so they can provide better airtightness levels. At the same time, the sealing metal ring required for eutectic bonding is narrower, so that new MEMS devices can meet smaller packaging size requirements. While forming a sealing metal ring, the eutectic bonding technology also provides an electrical path for the chip, which can easily introduce a vertical interconnected metal layer to realize wafer stacking packaging technology, thereby further reducing chip manufacturing and packaging costs.

[0004] The aluminum-germanium eutectic bonding process is often used in the production of MEMS gyroscopes. The principle of aluminum-germanium eutectic bonding is: by sputtering or evaporating aluminum-germanium metal layers of a certain thickness ratio on the surfaces of the two silicon wafers to be bonded, the aluminum-germanium metals melt and contact each other at a lower temperature. After mutual diffusion, an aluminum-germanium liquid alloy with a eutectic component is formed. As the diffusion time increases, the liquid alloy layer continues to thicken. After cooling, the aluminum-germanium metal in the liquid alloy layer grows based on its original solid phase, and the two metals are continuously and alternately precipitated to form a more stable crystal structure, thereby achieving bonding.

[0005] However, affected by the bonding machine, the current aluminum-germanium eutectic bonding process has poor bonding consistency. The total thickness of the AL / Ge bond varies in different areas of the entire wafer, affecting device performance. In addition, when the total thickness of the AL / Ge bond is too thin, that is, in an over-bonded state, the overflow of the AL / Ge in a molten state will cause a circuit short, resulting in device failure and affecting device yield. Summary of the invention

[0006] The object of the present invention is to provide a bonding method, a bonding structure, a MEMS device and a manufacturing method thereof, which can improve the consistency of aluminum-germanium bonding and thus improve the performance of the MEMS device.

[0007] To achieve the above object, in a first aspect, the present invention provides a bonding method, comprising:

[0008] providing a first substrate;

[0009] Etching the front surface of the first substrate to form a first boss structure and a second boss structure on the front surface of the first substrate;

[0010] forming a germanium layer on a top surface of the first boss structure;

[0011] Providing a second substrate, and forming an aluminum layer on the front side of the second substrate; patterning the aluminum layer, and forming a first aluminum pad corresponding to the first boss structure and a second aluminum pad corresponding to the second boss structure on the front side of the second substrate;

[0012] The front side of the first substrate is opposite to the front side of the second substrate, the germanium layer is aligned with the first aluminum pad, and the second boss structure is aligned with the second aluminum pad;

[0013] A eutectic bonding process is performed to melt the germanium layer and the first aluminum pad to form an aluminum-germanium mutual melting bonding layer, and the surface of the second boss structure is in contact with the surface of the second aluminum pad. The temperature of the eutectic bonding process is lower than the melting point of aluminum.

[0014] In a second aspect, the present invention provides a bonding structure, comprising:

[0015] A first substrate, wherein a bottom surface of the first substrate has a first boss structure and a second boss structure;

[0016] A second substrate is located below the first substrate, the top surface of the second substrate and the bottom surface of the first boss structure are bonded together through an aluminum-germanium mutual melting bonding layer, and the aluminum-germanium mutual melting bonding layer is formed by mutual melting of a germanium layer located on the surface of the first boss structure and a first aluminum pad located on the top surface of the second substrate;

[0017] A second aluminum pad is also disposed on the top surface of the second substrate, and the top surface of the second aluminum pad contacts the bottom surface of the second boss structure.

[0018] In a third aspect, the present invention provides a method for manufacturing a MEMS device, comprising:

[0019] Providing a cap wafer, wherein a plurality of openings are formed on the front side of the cap wafer;

[0020] Providing a device wafer, bonding the front side of the device wafer to the front side of the cap wafer, wherein the device wafer closes the opening to form a cavity;

[0021] Etching the back side of the device wafer to form a first boss structure and a second boss structure on the back side of the device wafer;

[0022] forming a germanium layer on a top surface of the first boss structure;

[0023] forming an interdigitated electrode structure in the device wafer, wherein the interdigitated electrode structure is located above the cavity;

[0024] Providing a base wafer, wherein an insulating layer is formed on the front side of the base wafer, and a wiring layer is formed in the insulating layer;

[0025] forming an aluminum layer on the insulating layer;

[0026] Patterning the aluminum layer to form a first aluminum pad corresponding to the first boss structure and a second aluminum pad corresponding to the second boss structure on the insulating layer;

[0027] The back side of the device wafer is opposite to the front side of the substrate wafer, the first boss structure is aligned with the first aluminum pad, and the second boss structure is aligned with the second aluminum pad;

[0028] A eutectic bonding process is performed to melt the germanium layer and the first aluminum pad to form an aluminum-germanium mutual melting bonding layer, and the surface of the second boss structure is in contact with the surface of the second aluminum pad. The temperature of the eutectic bonding process is lower than the melting point of aluminum.

[0029] In a fourth aspect, the present invention provides a MEMS device, comprising:

[0030] A cap wafer, wherein the bottom surface of the cap wafer has a plurality of openings;

[0031] A device wafer is located below the cap wafer, the top surface of the device wafer is bonded to the bottom surface of the cap wafer, and the device wafer closes the opening to form a cavity;

[0032] The bottom surface of the device wafer has a first boss structure and a second boss structure, and the device wafer has an interdigitated electrode structure inside, and the interdigitated electrode structure is located below the cavity;

[0033] A base wafer is located below the device wafer, the top surface of the base wafer has an insulating layer, and the insulating layer has a wiring layer;

[0034] The surface of the insulating layer and the bottom surface of the first boss structure are bonded together through an aluminum-germanium mutual melting bonding layer, the aluminum-germanium mutual melting bonding layer is electrically connected to the wiring layer, and the aluminum-germanium mutual melting bonding layer is formed by mutual melting of a germanium layer located on the surface of the first boss structure and a first aluminum pad located on the insulating layer in the first region of the base wafer;

[0035] A second aluminum pad is also disposed on the insulating layer, and a top surface of the second aluminum pad contacts a bottom surface of the second boss structure.

[0036] The beneficial effects of the present invention are:

[0037] The bonding method of the present invention forms a first boss structure and a second boss structure on the front side of the first substrate, and forms a germanium layer only on the surface of the first boss structure, and then forms a first aluminum pad corresponding to the first boss structure and a second aluminum pad corresponding to the second boss structure on the front side of the second substrate through a patterned aluminum layer, and then bonds the first aluminum pad to the germanium layer on the first boss structure through a eutectic bonding process to form an aluminum-germanium mutual melting bonding layer, and makes the surface of the second boss structure contact and adhere to the surface of the second aluminum pad. Since the temperature of the eutectic bonding process is lower than the melting point of aluminum, the second substrate is located at the edge of the second substrate. The second aluminum pad will not melt during the bonding process, so the second aluminum pad and the second boss structure can limit the height of the aluminum-germanium mutual melting during the mutual melting of the first aluminum pad and the germanium layer, that is, during the bonding process, as the aluminum-germanium mutual melting, the distance between the first substrate and the second substrate can only be compressed to a state where the second aluminum pad and the second boss structure are in contact with each other, so the height of the aluminum-germanium mutual melting is the original thickness of the germanium layer. Thus, by adding the second boss structure and the second aluminum pad, the height of the AL / Ge mutual melting is limited, and the consistency of the thickness of the AL / Ge mutual melting bonding layer in different regions on the wafer is effectively improved. At the same time, due to the low hardness of metal aluminum, the second boss structure and the second aluminum pad are contacted to limit the position during the bonding process, which can reduce the stress between the bonded wafers, thereby reducing the probability of wafer breakage and improving the quality of the bonding process and the yield of the device.

[0038] Furthermore, the bonding method of the present invention forms a passivation layer surrounding the first aluminum pad. The passivation layer can block the AL / Ge mutual melting overflow to the device area during the bonding process, thereby effectively avoiding the problem of circuit short circuit caused by the AL / Ge mutual melting overflow during bonding, resulting in device failure, thereby improving the yield of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figures 1 to 3 The device structure schematic diagram corresponding to each step of the existing MEMS gyroscope device manufacturing method is shown.

[0041] Figures 4 to 8 A schematic diagram of the device structure corresponding to each step in a bonding method according to embodiment 1 of the present invention is shown.

[0042] Figures 9 to 16 A schematic diagram of the device structure corresponding to each step in a method for manufacturing a MEMS device according to embodiment 3 of the present invention is shown. DETAILED DESCRIPTION

[0043] The existing manufacturing process of MEMS gyroscope is as follows: Figure 1-Figure 3 As shown, first, a cap wafer is provided, the cap wafer has an opening, an oxide layer is deposited on the surface of the cap wafer, a device wafer is bonded to the cap wafer, a cavity is formed between the device wafer and the cap wafer, and the structure after bonding is as shown in FIG. Figure 1 As shown; then the top surface of the device wafer is thinned, a boss structure is etched on the top surface of the device wafer, and then a germanium layer of a certain thickness is formed on the boss by deposition and patterning processes, and then the device wafer above the cavity is etched to form an interdigitated electrode structure. The structure formed is as shown Figure 2 After that, the structure is flipped over and the germanium layer on the boss is bonded to the aluminum layer on the top surface of the substrate wafer. The device structure is as shown in FIG. Figure 3 shown.

[0044] The above-mentioned aluminum-germanium eutectic bonding process is affected by the bonding machine, and the total thickness of AL / Ge bonding varies in different areas on the entire wafer. In some areas, AL / Ge over-bonding may occur, resulting in the total thickness of AL / Ge melt being too thin, and the distance (h) from the end of the fork finger to the top metal on the base wafer is affected by the bonding thickness, so capacitance and frequency failures may occur. At the same time, when the total thickness of AL / Ge bonding is too thin, the overflow of AL / Ge in a molten state may cause a circuit short circuit, resulting in failure.

[0045] To solve the above problems, the present invention provides a bonding method, a bonding structure, a MEMS device and a manufacturing method thereof, which can improve the control of aluminum-germanium bonding consistency, and is beneficial to improving device yield and bonding process control.

[0046] The following is a further detailed description of a bonding method, bonding structure, MEMS device and its manufacturing method of the present invention in combination with the accompanying drawings and specific embodiments. According to the following description and drawings, the advantages and features of the present invention will be clearer. However, it should be noted that the concept of the technical solution of the present invention can be implemented in a variety of different forms and is not limited to the specific embodiments described herein. The drawings are all in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0047] The terms "first", "second", "upper", "lower", "top surface", "bottom surface", etc. in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe a specific order, a temporal sequence or a specific spatial position. It is to be understood that, where appropriate, these terms used in this way are interchangeable, for example, so that the embodiments of the present invention described herein can be operated in an order other than that described or shown herein. Similarly, if the method described herein includes a series of steps, the order of these steps presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described may be omitted and / or some other steps not described herein may be added to the method. If the components in a certain figure are the same as the components in other figures, although these components can be easily identified in all figures, in order to make the description of the figures clearer, this specification will not mark all the same component numbers in each figure.

[0048] Example 1

[0049] like Figure 4-Figure 8 As shown, this embodiment provides a bonding method, including:

[0050] like Figure 4 As shown, a first substrate 100 is provided; the front side of the first substrate 100 is etched to form a first boss structure 101 and a second boss structure 102 on the front side of the first substrate 100 .

[0051] The etching process for forming the first boss structure 101 and the second boss structure 102 can be a wet etching process or a dry etching process, wherein the dry etching process is preferably used, and the dry etching includes but is not limited to reactive ion etching (RIE), ion beam etching, plasma etching or laser cutting. The dry etching can be, for example, inductively coupled plasma (ICP) etching, reactive ion etching (RIE), etc. The top surface of the first boss structure 101 is used as a bonding surface, and the second boss structure 102 is used to limit the bonding height. The height of the first boss structure 101 and the second boss structure 102 can be set according to the bonding requirements. The shape of the first boss structure 101 and the second boss structure 102 is not limited, and can be annular, circular, rectangular, etc., which can be selected according to the specific bonding requirements of the device. Preferably, the top surface of the first boss structure 101 is flush with the top surface of the second boss structure 102, so that it is convenient to form them simultaneously through a single etching process. Meanwhile, the position distribution of the first boss structure 101 and the second boss structure 102 is not limited and can be selected according to the process requirements. Figure 5 As shown, a germanium layer 103 is formed on the top surface of the first boss structure 101;

[0052] The germanium layer 103 can be formed on the front of the first substrate 100 by physical vapor deposition or chemical vapor deposition methods such as magnetron sputtering and evaporation, and then the germanium layer 103 is patterned by a patterning process. The patterned germanium layer 103 only covers the surface of the first boss structure 101 as a metal bonding layer. Preferably, the thickness of the germanium layer 103 is

[0053] like Figure 6 As shown, a second substrate 200 is provided, and an aluminum layer is formed on the front surface of the second substrate 200; the aluminum layer is patterned to form a first aluminum pad 201 corresponding to the first boss structure 101 and a second aluminum pad 202 corresponding to the second boss structure 102 on the front surface of the second substrate 200; preferably, the top surface of the first aluminum pad 201 is flush with the top surface of the second aluminum pad 202;

[0054] An aluminum layer can be formed on the front side of the second substrate 200 by physical vapor deposition or chemical vapor deposition methods such as magnetron sputtering and evaporation, and then the aluminum layer is patterned by a patterning process to form a first aluminum pad 201 and a second aluminum pad 202 on the second substrate 200, respectively, wherein the first aluminum pad 201 serves as a metal bonding layer corresponding to the germanium layer 103, and the second aluminum pad 202 is used to cooperate with the second boss structure 102 to limit the height of the aluminum-germanium mutual melting during the bonding process. The thickness of the aluminum layer can be selected to be

[0055] like Figure 7As shown, a passivation layer 203 is formed on the front surface of the second substrate 200 and distributed circumferentially along the first aluminum pad 201 .

[0056] The method for forming the passivation layer 203 includes:

[0057] Depositing a passivation layer material on the front side of the second substrate 200 to cover the first aluminum pad 201, the second aluminum pad 202 and the exposed surface of the second substrate 200;

[0058] The first aluminum pad 201, the second aluminum pad 202, and part of the passivation layer material on the surface of the second substrate 200 are removed by etching, and only the passivation layer material on the surface of the second substrate 200 around the first aluminum pad 201 is retained, and the remaining passivation layer material forms a passivation layer 203 surrounding the first aluminum pad 201 along the circumference of the first aluminum pad 201. The passivation layer 203 can be used to prevent aluminum-germanium from melting and overflowing to the area with circuits on the substrate during the bonding process.

[0059] Preferably, the thickness of the passivation layer 203 is greater than the thickness of the first aluminum pad 201, and less than the sum of the thicknesses of the second aluminum pad 202 and the second boss structure 102. The material of the passivation layer 203 can be a dielectric material such as silicon oxide and silicon nitride.

[0060] like Figure 8 As shown, the front side of the first substrate 100 is opposite to the front side of the second substrate 200, the germanium layer 103 is aligned with the first aluminum pad 201, and the second boss structure 102 is aligned with the second aluminum pad 202;

[0061] A eutectic bonding process is performed to melt the germanium layer 103 and the first aluminum pad 201 to form an aluminum-germanium mutual melting bonding layer 204, and the surface of the second boss structure 102 is in contact with the surface of the second aluminum pad 202. The temperature of the eutectic bonding process is lower than the melting point of aluminum.

[0062] The bonding between the second germanium pad and the germanium layer 103 is completed by a eutectic bonding process, and the specific method is as follows:

[0063] The germanium layer 103 on the first boss structure 101 of the first substrate 100 and the first aluminum pad 201 on the second substrate 200 are aligned and contacted, and then the first substrate 100 and the second substrate 200 are pressurized and heated for a set time, so that the metal germanium in the germanium layer 103 and the aluminum in the first aluminum pad 201 melt and diffuse with each other to form a liquid alloy layer. During the bonding process, as the aluminum and germanium melt together, the germanium layer 103 is gradually consumed, and the distance between the first substrate 100 and the second substrate 200 is compressed until the second boss contacts the surface of the second aluminum pad 202, and the first aluminum pad 201 and the germanium layer 103 are connected. 3, the mutual melting height cannot be further compressed, forming an aluminum-germanium mutual melting layer of a specific thickness, and after cooling, it forms a stable aluminum-germanium mutual melting bonding layer 204 together with the remaining germanium layer and the aluminum layer, that is, the aluminum-germanium mutual melting bonding layer 204 as a whole includes an aluminum-germanium mutual melting layer, a germanium layer remaining after mutual melting, and a remaining first aluminum pad, a total of three layers. In this solution, there is no restriction on the thickness of the germanium layer and the aluminum layer (first aluminum pad) remaining after mutual melting. In some cases, the thickness of the remaining germanium layer or aluminum layer can also be zero (that is, completely consumed). In this embodiment, the thickness of the aluminum-germanium mutual melting bonding layer 204 is preferably Preferably, the process conditions adopted in the eutectic bonding process include: bonding temperature: 400-500° C.; bonding time: 5-15 min; bonding pressure: 5000-7000 MPa.

[0064] Compared with the existing method of directly eutectic bonding thicker aluminum layer and germanium layer, this method adds a second boss structure 102 on the first substrate 100 and adds a second aluminum pad 202 on the second substrate 200, and limits the mutual melting compression height of the first aluminum pad 201 and the germanium layer 103 through the second boss structure 102 and the second aluminum pad 202. After bonding, the height consumed by the aluminum-germanium mutual melting is the original thickness of the germanium layer 103, so that the AL / Ge mutual melting height is limited, and the consistency of the thickness of the AL / Ge mutual melting bonding layer in different regions on the wafer is effectively improved. At the same time, this method forms a passivation layer 203 surrounding the first aluminum pad 201 around the first aluminum pad 201, and the passivation layer 203 can block the AL / Ge mutual melting overflow to the device area during the bonding process, thereby effectively avoiding the problem of circuit short circuit caused by the AL / Ge mutual melting overflow during bonding, resulting in device function failure, thereby improving the device yield.

[0065] At the same time, since the hardness of metal aluminum is relatively low, the stress between the bonded wafers can be reduced by limiting the contact between the second boss structure and the second aluminum pad during the bonding process, thereby reducing the probability of wafer breakage and improving the quality of the bonding process and the yield of the device.

[0066] Furthermore, the method is highly feasible. On the basis of the existing process, the second boss structure 102 and the second aluminum pad 202 can be added only by modifying the mask, without redesigning the product. At the same time, no mask materials and process steps are added, and the cost is low.

[0067] It should be noted that the method of this embodiment can be applied to the preparation of any semiconducting device that requires an aluminum-germanium bonding process. Therefore, this embodiment does not limit the types of the first substrate 100 and the second substrate 200. The first substrate 100 and the second substrate 200 can be any suitable substrate known to those skilled in the art, for example, at least one of the following materials: silicon (Si), germanium (Ge), silicon germanium (SiGe), carbon silicon (SiC), carbon germanium silicon (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP) or other III / V compound semiconductors, including multilayer structures composed of these semiconductors, or silicon on insulator (SOI), stacked silicon on insulator (SSOI), stacked silicon germanium on insulator (S-SiGeOI), silicon germanium on insulator (SiGeOI) and germanium on insulator (GeOI), or double-sided polished silicon wafers (Double Side Polished Wafers, DSP), or ceramic substrates such as aluminum oxide, quartz or glass substrates, etc. The first substrate 100 may have device structures such as cavities and functional devices, and the second substrate 200 may also have semiconductor device structures such as wiring layers and electrical connection structures.

[0068] Example 2

[0069] like Figure 8 As shown, this embodiment provides a bonding structure, which can be formed by the bonding method of embodiment 1, and the bonding structure includes:

[0070] A first substrate 100, wherein the bottom surface of the first substrate 100 has a first boss structure 101 and a second boss structure 102;

[0071] A second substrate 200 is located below the first substrate 100, and the top surface of the second substrate 200 is bonded to the bottom surface of the first boss structure 101 through an aluminum-germanium mutual melting bonding layer 204, and the aluminum-germanium mutual melting bonding layer 204 is formed by mutual melting of the germanium layer 103 located on the surface of the first boss structure 101 and the first aluminum pad 201 located in the first area of ​​the top surface of the second substrate 200;

[0072] A second aluminum pad 202 is further disposed on the top surface of the second substrate 200 , and the top surface of the second aluminum pad 202 contacts the bottom surface of the second boss structure 102 .

[0073] Preferably, the bottom surface of the first boss structure 101 is flush with the bottom surface of the second boss structure 102, and before bonding, the top surface of the first aluminum pad is flush with the top surface of the second aluminum pad; the thickness of the germanium layer 103 before bonding is preferably The thickness of the first aluminum pad before bonding can be selected as The thickness of the Al-Ge inter-melting bonding layer 204 is

[0074] In this embodiment, a passivation layer 203 is provided on the top surface of the second substrate 200 and is distributed circumferentially along the aluminum-germanium mutual melting bonding layer 204 .

[0075] Preferably, the thickness of the passivation layer 203 is greater than the thickness of the first aluminum pad 201, and the thickness of the passivation layer 203 is less than the sum of the thicknesses of the second aluminum pad 202 and the second boss structure 102. The annular passivation layer 203 surrounding the aluminum-germanium intermelting bonding layer 204 can prevent the Al / Ge intermelting from overflowing to the circuit area on the second substrate 200 when the first aluminum pad 201 and the germanium layer 103 are intermelted, thereby avoiding circuit short circuit.

[0076] Since the bonding structure of this embodiment is formed by the bonding method of embodiment 1, during the bonding process, the second boss structure 102 and the second aluminum pad 202 limit the compressible height of the eutectic bonding between the germanium layer 103 and the first aluminum pad 201, so that the thickness of the AL / Ge mutual melting bonding layer in different regions on the wafer has a high consistency. At the same time, due to the presence of the passivation layer 203, the AL / Ge mutual melting overflow to the device area during the bonding process can be blocked, avoiding the short circuit problem, so the device has a high yield and good performance.

[0077] Example 3

[0078] like Figure 9-Figure 16 As shown, this embodiment provides a method for manufacturing a MEMS device, the method comprising:

[0079] like Fig. 9 As shown, a cap wafer 300 is provided, and a plurality of openings are formed on the front side of the cap wafer 300;

[0080] The material of the cap wafer 300 refers to the material of the first substrate 100 or the second substrate 200 in Example 1. The material of the cap wafer 300 of this embodiment is single crystal silicon. The opening on the front of the cap wafer 300 can be formed by an etching process, and the shape of the bottom surface of the opening is preferably rectangular. A dielectric layer 301 is also formed on the front of the cap wafer 300. The material of the dielectric layer 301 can be any suitable dielectric material, including but not limited to at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbonitride and the like. The dielectric layer 301 can be formed by depositing silicon oxide.

[0081] like Fig.10 As shown, a device wafer 400 is provided, and the front side of the device wafer 400 is bonded to the front side of the cap wafer 300 . The device wafer 400 closes the opening to form a cavity; the cavity is used to form a working space for the interdigitated electrode structure 401 to be formed subsequently.

[0082] The device wafer 400 is used as a device structure layer for subsequently forming a boss structure and an interdigitated electrode structure 401 . In this embodiment, the material of the device wafer 400 is preferably single crystal silicon.

[0083] like Fig.11 As shown, the back side of the device wafer 400 is thinned and then etched to form a first boss structure 101 and a second boss structure 102 on the back side of the device wafer 400; preferably, the top surface of the first boss structure 101 is flush with the top surface of the second boss structure 102.

[0084] The first boss structure 101 and the second boss structure 102 do not overlap with the cavity in a direction perpendicular to the surface of the device wafer 400. In this embodiment, the first boss structure 101 is located at the edge region of the cavity, and the second boss structure 102 is located at the edge region of the device wafer 400.

[0085] The first boss structure 101 and the second boss structure 102 can be formed simultaneously by an etching process, and the etching process for forming the first boss structure 101 and the second boss structure 102 can be a wet etching process or a dry etching process, wherein a dry etching process is preferably used, and dry etching includes but is not limited to reactive ion etching (RIE), ion beam etching, plasma etching or laser cutting. The dry etching may be, for example, inductively coupled plasma (ICP) etching, reactive ion etching (RIE), and the like. Among them, the top surface of the first boss structure 101 is used as a bonding surface, and the second boss structure 102 is used to limit the aluminum-germanium bonding height in the subsequent bonding process. The height of the first boss structure 101 and the second boss structure 102 can be set according to the capacitance value required between the interdigitated electrode and the top metal (i.e., the aluminum layer) on the base wafer 500.

[0086] like Fig.12 As shown, a germanium layer 103 is formed on the top surface of the first boss structure 101;

[0087] The method of forming the germanium layer 103 includes:

[0088] A germanium layer 103 is formed on the back side of the device wafer 400 to cover the first boss structure, the second boss structure 102 and the surface of the device wafer 400. The germanium layer 103 is then patterned to remove the second boss structure 102 and the germanium layer 103 on the surface of the device wafer 400, leaving only the germanium layer 103 on the top surface of the first boss structure 101.

[0089] The germanium layer 103 may be formed by physical vapor deposition such as magnetron sputtering or evaporation or chemical vapor deposition. Preferably, the thickness of the germanium layer 103 is

[0090] like Fig.13 As shown, an interdigitated electrode structure 401 is formed in the device wafer 400, and the interdigitated electrode structure 401 is located above the cavity;

[0091] The device wafer 400 above the cavity can be etched by an etching process to form an interdigitated electrode structure 401, and the gaps between the interdigitated electrodes in the interdigitated electrode structure 401 are connected to the cavity. The etching process preferably adopts a dry etching process.

[0092] like Fig.14 As shown, a base wafer 500 is provided, an insulating layer 501 is formed on the front side of the base wafer 500, and a wiring layer 502 is formed in the insulating layer 501;

[0093] forming an aluminum layer on the insulating layer 501;

[0094] The aluminum layer is patterned to form a first aluminum pad 201 and a second aluminum pad 202 with top surfaces flush with each other on the insulating layer 501. In this embodiment, the first aluminum pad 201 is located in the central area of ​​the base wafer 500 and corresponds to the first boss structure 101, and the second aluminum pad 202 is located in the edge area of ​​the base wafer 500 and corresponds to the second boss structure 102.

[0095] The aluminum layer can be formed by physical vapor deposition such as magnetron sputtering or evaporation or chemical vapor deposition. Preferably, the thickness of the aluminum layer (the first aluminum pad 201 and the second aluminum pad 202) is The thickness ratio of the germanium layer 103 to the aluminum layer can be selected according to process requirements.

[0096] The material of the base wafer 500 refers to the material of the first substrate 100 in Example 1. <100> P-type high-resistance single-crystal silicon wafer with different crystal orientations.

[0097] The method for forming the insulating layer 501 and the wiring layer 502 on the base wafer 500 includes:

[0098] forming a first insulating layer on the base wafer 500, and then patterning the first insulating layer;

[0099] A conductive metal layer is formed on the first insulating layer, and then the conductive metal layer is patterned to form a wiring layer 502 .

[0100] A second insulating layer is formed on the wiring layer 502, and then the second insulating layer is patterned to expose the underlying wiring layer 502.

[0101] The first insulating layer and the second insulating layer together constitute the insulating layer 501. The first insulating layer and the second insulating layer are made of the same material, which can be any suitable dielectric material, including but not limited to at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbonitride, etc. In this embodiment, it is silicon oxide. The material of the wiring layer 502 can be any conductive metal material, such as copper, aluminum, gold, silver, etc. In this embodiment, the material of the wiring layer 502 is aluminum. The thickness of the wiring layer 502 can be selected to be The first insulating layer and the second insulating layer can be formed by any suitable deposition method known to those skilled in the art, such as chemical vapor deposition, physical vapor deposition or atomic layer deposition. The wiring layer 502 can be formed by physical vapor deposition or chemical vapor deposition methods such as magnetron sputtering and evaporation.

[0102] like Fig.15 As shown, a passivation layer 203 is formed on the insulating layer 501 and distributed circumferentially along the first aluminum pad 201. Preferably, the thickness of the passivation layer 203 is greater than the thickness of the first aluminum pad 201, and the thickness of the passivation layer 203 is less than the sum of the thicknesses of the second aluminum pad 202 and the second boss structure 102. The method for forming the passivation layer 203 is referred to Example 1.

[0103] like Fig.16 As shown, the back side of the device wafer 400 is placed opposite to the front side of the substrate wafer 500 , the first boss structure 101 is aligned with the first aluminum pad 201 , and the second boss structure 102 is aligned with the second aluminum pad 202 ;

[0104] A eutectic bonding process is performed to make the germanium layer 103 and the first aluminum pad 201 mutually melt to form an aluminum-germanium mutual melting bonding layer 204, and the surface of the second boss structure 102 is in contact with the surface of the second aluminum pad 202. The temperature of the eutectic bonding process is lower than the melting point of aluminum. The thickness of the aluminum-germanium mutual melting bonding layer 204 is preferably The sum of the thickness of the AlGe interfusion bonding layer 204 and the thickness of the first boss structure corresponds to the distance between the end of the interdigitated electrode and the top metal of the front surface of the base wafer 500 (ie Figure 3 The distance h) is shown.

[0105] The MEMS device finally formed in this embodiment is a gyroscope, in which the bonding between the second aluminum pad 202 and the germanium layer 103 is completed by a eutectic bonding process, and the specific method is:

[0106] The back side of the device wafer 400 is placed opposite to the front side of the base wafer 500, the first boss structure 101 is aligned with the pattern of the first aluminum pad 201, and the second boss structure 102 is aligned with the pattern of the second aluminum pad 202, and the germanium layer 103 on the first boss structure 101 is in contact with the first aluminum pad 201, and then the cap wafer 300, the device wafer 400 and the base wafer 500 are pressurized and heated for a set time, so that the metal germanium in the germanium layer 103 and the aluminum in the second aluminum pad 202 melt and diffuse with each other to form a liquid alloy layer, and a stable aluminum-germanium intermelting bonding layer 204 is formed after cooling; preferably, the process conditions adopted in the eutectic bonding process include: bonding temperature: 400-500°C; bonding time: 5-15min; bonding pressure: 5000-7000mpa.

[0107] Compared with the existing method of directly eutectic bonding the thicker aluminum layer and the germanium layer 103, in this method, a second protrusion structure is added to the device wafer 400, and a second aluminum pad 202 structure is added to the base wafer 500. Since the bonding temperature is lower than the melting point of aluminum, only the first aluminum pad 201 and the germanium layer 103 melt during the bonding process, while the second aluminum pad 202 does not melt. Therefore, the compressible height of the aluminum-germanium mutual melting is limited by the second protrusion and the second aluminum pad 202. The bonding process ends when the surfaces of the second boss structure 102 and the second aluminum pad 202 contact each other. Therefore, the height of the aluminum-germanium bonding compression can be guaranteed to be the thickness of the germanium layer 103 (the germanium layer 103 after bonding is completely consumed and the thickness is zero), which can avoid the aluminum-germanium mutual melting bonding layer 204 formed at the end being too thick, and at the same time improve the consistency of the bonding height of different regions on the wafer, thereby effectively controlling the distance between the end of the finger electrode and the top metal on the base wafer 500, and avoiding its capacitance and frequency failure. At the same time, due to the limiting effect of the second boss and the second aluminum pad 202, the overflow of the molten aluminum germanium metal during the bonding process can be reduced. At the same time, due to the low hardness of metallic aluminum, the stress between the bonded wafers can be reduced by limiting the contact between the second boss structure and the second aluminum pad during the bonding process, thereby reducing the probability of wafer breakage and improving the quality of the bonding process and the yield of the device.

[0108] Furthermore, by providing a passivation layer 203 around the first aluminum pad 201, the short circuit problem caused by excessive overflow of molten metal on the circuit can be avoided, thereby avoiding device failure and improving the yield of the gyroscope device.

[0109] Secondly, the method is highly feasible. On the basis of the existing process, the second boss structure 102 and the second aluminum pad 202 can be added only by modifying the mask, without redesigning the product. At the same time, no mask materials and process steps are added, and the cost is low.

[0110] In other embodiments, the second boss structure 102 can also be selected to be set in the edge area of ​​the cavity, and the first boss structure 101 can be set in the area on the back side of the device wafer 400 away from the cavity, and the first aluminum pad 201 and the second aluminum pad 202 on the base wafer 500 are adjusted in position accordingly. During the bonding process, since gas is generated when the first aluminum pad 201 and the germanium layer 103 on the first boss structure 101 are mutually melted, the cavity can be sealed by the contact between the second boss structure 102 located at the edge of the cavity and the second aluminum pad 202, thereby reducing the gas generated by the mutual melting of aluminum and germanium entering the cavity, thereby improving the vacuum degree of the working cavity in the MEMS device and improving the device performance.

[0111] Example 4

[0112] like Fig.16 As shown, this embodiment provides a MEMS device, which can be prepared by the method of embodiment 3. The MEMS device includes:

[0113] A cap wafer 300, wherein the bottom surface of the cap wafer 300 has a plurality of openings;

[0114] The device wafer 400 is located below the cap wafer 300, the top surface of the device wafer 400 is bonded to the bottom surface of the cap wafer 300, and the device wafer 400 closes the opening to form a cavity;

[0115] The bottom surface of the device wafer 400 has a first boss structure 101 and a second boss structure 102; in this embodiment, the top surface of the first boss structure 101 is flush with the top surface of the second boss structure 102; the first boss structure 101 is located at the edge area of ​​the cavity, and the second boss structure 102 is located at the edge area of ​​the device wafer 400; the device wafer 400 has an interdigital electrode structure 401, and the interdigital electrode structure 401 is located below the cavity;

[0116] In this embodiment, the surface of the insulating layer 501 located in the central area of ​​the base wafer 500 is bonded to the bottom surface of the first boss structure 101 through an aluminum-germanium mutual melting bonding layer 204, and the aluminum-germanium mutual melting bonding layer 204 is electrically connected to the wiring layer 502; the aluminum-germanium mutual melting bonding layer 204 is formed by mutual melting of the germanium layer 103 located on the surface of the first boss structure 101 and the first aluminum pad 201 located on the insulating layer 501 in the first area of ​​the base wafer 500;

[0117] A second aluminum pad 202 is further disposed on the insulating layer 501 at the edge of the base wafer 500 , and the top surface of the second aluminum pad 202 is in contact with the bottom surface of the second boss structure 102 .

[0118] refer to Figure 13-Figure 16 The Al-Ge intermelting bonding layer 204 in this embodiment is formed by the intermelting of the Ge layer 103 located on the surface of the first boss structure 101 and the first Al pad 201 located on the insulating layer 501 in the central area of ​​the base wafer 500 .

[0119] The thickness of the germanium layer 103 before bonding is The thickness of the first aluminum pad 201 before bonding can be selected as The thickness of the Al-Ge inter-melting bonding layer 204 is

[0120] In other embodiments, the positions of the first boss structure 101 and the second boss structure 102 may also be set in other areas, and the positions may be adjusted according to specific process requirements. For example, the second boss structure 102 is set in the edge area of ​​the cavity, and the first boss structure 101 is set in an area away from the cavity on the back side of the device wafer 400, and the first aluminum pad 201 and the second aluminum pad 202 on the base wafer 500 are adjusted accordingly.

[0121] Preferably, in this embodiment, a passivation layer 203 is further provided on the insulating layer 501 and is distributed circumferentially along the aluminum-germanium mutual melting bonding layer 204. The thickness of the passivation layer 203 is greater than the thickness of the first aluminum pad 201, and the thickness of the passivation layer 203 is less than the sum of the thicknesses of the second aluminum pad 202 and the second boss structure 102.

[0122] The MEMS device of this embodiment is a gyroscope. In the MEMS device of this embodiment, by adding a second aluminum pad 202 on the base wafer 500 and adding a second boss structure 102 on the back of the device wafer 400, the second aluminum pad 202 and the second boss structure 102 do not participate in eutectic bonding, but are only used to limit the compression height of the aluminum-germanium bonding between the first aluminum pad 201 and the germanium layer 103 on the first boss. Through the bonding height limiting effect of the second boss structure 102 and the second aluminum pad 202, it is ensured that the height of the aluminum-germanium mutual melting is equal to the thickness of the germanium layer 103, thereby controlling the thickness consistency of the aluminum-germanium mutual melting bonding layer 204 in different areas on the wafer, and then effectively controlling the distance between the end of the finger and the top metal, ensuring that the capacitance and frequency will not fail. In addition, it is less likely to produce excessive metal overflow during the bonding process, which can avoid problems such as circuit short circuit caused by overflow, and the device function is not easy to fail.

[0123] Furthermore, by providing a passivation layer 203 around the first aluminum pad 201, the circuit short circuit problem caused by the overflow generated by the mutual melting of aluminum and germanium can be further ensured. At the same time, during the bonding process, the second boss structure is contacted with the second aluminum pad for limiting, which can reduce the stress between the bonded wafers. Therefore, the MEMS device of this embodiment can have a higher yield and better functional stability.

[0124] It should be noted that the various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the structural embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0125] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A bonding method, characterized in that: include: providing a first substrate; Etching the front surface of the first substrate to form a first boss structure and a second boss structure on the front surface of the first substrate; forming a germanium layer on a top surface of the first boss structure; Providing a second substrate, and forming an aluminum layer on the front side of the second substrate; Patterning the aluminum layer to form a first aluminum pad corresponding to the first boss structure and a second aluminum pad corresponding to the second boss structure on the front side of the second substrate; The front side of the first substrate is opposite to the front side of the second substrate, and the germanium layer is aligned with the first aluminum pad, and the second boss structure is aligned with the second aluminum pad; A eutectic bonding process is performed to melt the germanium layer and the first aluminum pad to form an aluminum-germanium mutual melting bonding layer, and the surface of the second boss structure is in contact with the surface of the second aluminum pad. The temperature of the eutectic bonding process is lower than the melting point of aluminum.

2. The bonding method according to claim 1, characterized in that: The top surface of the first boss structure is flush with the top surface of the second boss structure; Before bonding, a top surface of the first aluminum pad is flush with a top surface of the second aluminum pad.

3. The bonding method according to claim 1, characterized in that: Before placing the front surface of the first substrate opposite to the front surface of the second substrate, aligning the germanium layer with the first aluminum pad, and aligning the second boss structure with the second aluminum pad, the method further includes: A passivation layer is formed on the front surface of the second substrate and distributed circumferentially along the first aluminum pad.

4. The bonding method according to claim 3, characterized in that: The thickness of the passivation layer is greater than the thickness of the first aluminum pad, and the thickness of the passivation layer is less than the sum of the thicknesses of the second aluminum pad and the second boss structure.

5. The bonding method according to claim 1, characterized in that: The process conditions adopted in the eutectic bonding process include: Bonding temperature: 400-500℃; Bonding time: 5-15min; Bonding pressure: 5000-7000mpa.

6. A bonding structure, characterized in that: include: A first substrate, wherein a bottom surface of the first substrate has a first boss structure and a second boss structure; A second substrate is located below the first substrate, the top surface of the second substrate and the bottom surface of the first boss structure are bonded together through an aluminum-germanium mutual melting bonding layer, and the aluminum-germanium mutual melting bonding layer is formed by mutual melting of a germanium layer located on the surface of the first boss structure and a first aluminum pad located on the top surface of the second substrate; A second aluminum pad is also disposed on the top surface of the second substrate, and the top surface of the second aluminum pad contacts the bottom surface of the second boss structure.

7. The bonding structure according to claim 6, characterized in that: The bottom surface of the first boss structure is flush with the bottom surface of the second boss structure; Before bonding, top surfaces of the first aluminum pad and the second aluminum pad are flush.

8. The bonding structure according to claim 6, characterized in that: The top surface of the second substrate is also provided with a passivation layer distributed along the circumference of the aluminum-germanium mutual melting bonding layer.

9. The bonding structure according to claim 8, characterized in that: The thickness of the passivation layer is greater than the thickness of the first aluminum pad, and the thickness of the passivation layer is less than the sum of the thicknesses of the second aluminum pad and the second boss structure.

10. A method for manufacturing a MEMS device, characterized in that: include: Providing a cap wafer, wherein a plurality of openings are formed on the front side of the cap wafer; Providing a device wafer, bonding the front side of the device wafer to the front side of the cap wafer, wherein the device wafer closes the opening to form a cavity; Etching the back side of the device wafer to form a first boss structure and a second boss structure on the back side of the device wafer; forming a germanium layer on a top surface of the first boss structure; forming an interdigitated electrode structure in the device wafer, wherein the interdigitated electrode structure is located above the cavity; Providing a base wafer, wherein an insulating layer is formed on the front side of the base wafer, and a wiring layer is formed in the insulating layer; forming an aluminum layer on the insulating layer; Patterning the aluminum layer to form a first aluminum pad corresponding to the first boss structure and a second aluminum pad corresponding to the second boss structure on the insulating layer; The back side of the device wafer is opposite to the front side of the substrate wafer, the first boss structure is aligned with the first aluminum pad, and the second boss structure is aligned with the second aluminum pad; A eutectic bonding process is performed to melt the germanium layer and the first aluminum pad to form an aluminum-germanium mutual melting bonding layer, and the surface of the second boss structure is in contact with the surface of the second aluminum pad. The temperature of the eutectic bonding process is lower than the melting point of aluminum.

11. The method for manufacturing a MEMS device according to claim 10, characterized in that: The top surface of the first boss structure is flush with the top surface of the second boss structure; Before bonding, a top surface of the first aluminum pad is flush with a top surface of the second aluminum pad.

12. The method for manufacturing a MEMS device according to claim 10, characterized in that: Before placing the back side of the device wafer opposite to the front side of the substrate wafer, aligning the first boss structure with the first aluminum pad, and aligning the second boss structure with the second aluminum pad, the method further includes: A passivation layer is formed on the insulating layer and distributed circumferentially along the first aluminum pad.

13. The method for manufacturing a MEMS device according to claim 12, characterized in that: The thickness of the passivation layer is greater than the thickness of the first aluminum pad, and the thickness of the passivation layer is less than the sum of the thicknesses of the second aluminum pad and the second boss structure.

14. The method for manufacturing a MEMS device according to claim 10, characterized in that: The process conditions adopted in the eutectic bonding process include: Bonding temperature: 400-500℃; Bonding time: 5-15min; Bonding pressure: 5000-7000mpa.

15. A MEMS device, characterized in that: include: A cap wafer, wherein the bottom surface of the cap wafer has a plurality of openings; A device wafer is located below the cap wafer, the top surface of the device wafer is bonded to the bottom surface of the cap wafer, and the device wafer closes the opening to form a cavity; The bottom surface of the device wafer has a first boss structure and a second boss structure, and the device wafer has an interdigitated electrode structure inside, and the interdigitated electrode structure is located below the cavity; A base wafer is located below the device wafer, the top surface of the base wafer has an insulating layer, and the insulating layer has a wiring layer; The surface of the insulating layer and the bottom surface of the first boss structure are bonded together through an aluminum-germanium mutual melting bonding layer, the aluminum-germanium mutual melting bonding layer is electrically connected to the wiring layer, and the aluminum-germanium mutual melting bonding layer is formed by mutual melting of a germanium layer located on the surface of the first boss structure and a first aluminum pad located on the insulating layer in the first region of the base wafer; A second aluminum pad is also disposed on the insulating layer, and a top surface of the second aluminum pad contacts a bottom surface of the second boss structure.

16. The MEMS device according to claim 15, characterized in that: The top surface of the first boss structure is flush with the top surface of the second boss structure; Before bonding, a top surface of the first aluminum pad is flush with a top surface of the second aluminum pad.

17. The MEMS device according to claim 15, characterized in that: A passivation layer is also provided on the insulating layer and distributed along the circumference of the aluminum-germanium mutual melting bonding layer.

18. The MEMS device according to claim 17, characterized in that: The thickness of the passivation layer is greater than the thickness of the first aluminum pad, and the thickness of the passivation layer is less than the sum of the thicknesses of the second aluminum pad and the second boss structure.

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