TWI534973B - Chip bonding structure and bonding method thereof - Google Patents

Description

Wafer bonding structure and bonding method thereof

The present disclosure relates to a wafer structure, particularly a wafer bonding structure and bonding method thereof.

Today's electronic products are developing in a light, short, high-efficiency, highly integrated system and wireless direction. The three-dimensional integrated circuit (3D IC) is a three-dimensional stack integration mode of the wafer, which not only shortens the length of the metal wire and the wiring resistance, but also reduces the wafer area, and has the characteristics of small accumulation, high integration, low power consumption, low cost, and the like. It is considered to be the next generation of semiconductor new technology.

The three-dimensional integrated circuit stack has high requirements for electrical contact reliability of internal circuits between components to ensure that the integrated system operates normally. However, the stacking of integrated circuits at the wafer level suffers from a problem that the bonding surface is not flat enough, making it difficult for manufacturers to implement a wafer-level integrated circuit stacking process. Among them, the problem of unevenness of the bonding surface is particularly likely to occur in a hybrid wafer bonding process. Hybrid wafer bonding means that the wafer has both a dielectric layer and a metal. When the hybrid wafer is bonded, the dielectric layer is butted to the metal, and the height of the dielectric layer and the metal are not uniform, or the metal or the dielectric layer is likely to be recessed, resulting in insufficient wafer bonding degree (adhesion). problem. When the wafer bonding is insufficient, a gap is formed at the wafer joint, and a space at the metal joint causes an electrical open circuit, and a gap at the dielectric layer increases the probability of the wafer being broken in a subsequent thermal process. As a result, wafer bonding is caused. The yield is reduced.

The wafer bonding method of one embodiment of the present disclosure includes the steps of providing two wafers. The method of fabricating each wafer includes forming a first dielectric layer on the substrate. A plurality of metal pads are mated on the first dielectric layer. Forming a plurality of first dielectric layers recessed in at least one of the wafers. These depressions are respectively between these metal pads. A second dielectric layer is formed on the first dielectric layer of the wafer having the recesses and overlying the recesses of the wafer and the metal pads. The two wafers are bonded such that the metal pads of the two wafers are in contact with each other, and the recesses of one of the wafers and the surface of the other wafer form a plurality of cavities, and the second dielectric layer is located in the cavities. The second dielectric layer is filled with mechanical cavities to fill the cavities. The two wafers are pressed together, and the second dielectric layer is cured, and the two wafers are fixed to each other.

In a wafer bonding method according to another embodiment of the present disclosure, the method includes the steps of providing two wafers. The method of fabricating each wafer includes forming a first dielectric layer on the substrate. A plurality of metal pads are mated on the first dielectric layer, and each of the metal pads includes a base and a protrusion. The base is fitted to the first dielectric layer. The projection is connected to the base. A second dielectric layer is formed on the first dielectric layer. A second dielectric layer covers the bases, and the protrusions penetrate the second dielectric layer and form a plurality of recesses between the protrusions. The two wafers are bonded such that the metal pads of the two wafers are in contact with each other, and the recesses of the two wafers form a plurality of cavities, and the second dielectric layer is located in the cavities. The second dielectric layer is filled with mechanical cavities to fill the cavities. The two wafers are pressed together, and the second dielectric layer is cured, and the two wafers are fixed to each other.

The wafer bonding structure of one embodiment of the present disclosure includes a second wafer and a second dielectric layer. Each wafer includes a substrate, a first dielectric layer, and a plurality of metal pads. First dielectric layer On the substrate. The first dielectric layer has a surface. These metal pads are embedded on the surface of the first dielectric layer. The first dielectric layer of at least one of the wafers has a plurality of recesses. These depressions are located on the surface and between these metal pads. A second dielectric layer is interposed between the first dielectric layers of the two wafers and overlies the surface of the first dielectric layer and the recesses. The second dielectric layer has opposing two bonding faces. The two bonding faces of the second dielectric layer and the two first dielectric layers are in contact with each other and adhere to each other to fix the two wafers to each other, and the metal pads of one of the wafers are in contact with the metal pads of the other wafer.

A wafer bonding structure according to another embodiment of the present disclosure includes two wafers. Each of the wafers includes a substrate, a first dielectric layer, a plurality of metal pads, and a second dielectric layer. The first dielectric layer is placed on the substrate. The first dielectric layer has a surface. Each metal pad includes a base and a protrusion. These bases are fitted to the first dielectric layer. The projection is attached to the base and protrudes from the surface. A second dielectric layer is disposed between the first dielectric layers of the two wafers and overlying the surfaces of the two first dielectric layers and the bases. The second dielectric layer has opposing two bonding faces. The two bonding faces of the second dielectric layer and the two first dielectric layers are in contact with each other and adhere to each other to fix the two wafers to each other, and wherein the protrusions of one of the wafers are in contact with the protrusions of the other wafer .

The above description of the disclosure and the following description of the embodiments are intended to illustrate and explain the principles of the disclosure, and to provide a further explanation of the scope of the disclosure.

5, 5', 5" ‧ ‧ wafer bonding structure

10, 10'‧‧‧ wafer

20, 20’‧‧‧ cavity

100‧‧‧Substrate

200‧‧‧First dielectric layer

210‧‧‧ surface

220‧‧‧ dent

300, 300’‧‧‧Metal pads

310‧‧‧ base

320‧‧‧protrusion

400‧‧‧Second dielectric layer

410‧‧‧ joint surface

1 is a schematic cross-sectional view of a wafer bonding structure in accordance with an embodiment of the present disclosure.

2A to 2E are schematic views showing a bonding method of the wafer bonding structure of Fig. 1.

3A is a cross section of one step of a wafer bonding method according to another embodiment of the present disclosure. schematic diagram.

Fig. 3B is a schematic cross-sectional view showing the wafer bonding structure of Fig. 3A.

4 is a cross-sectional view showing one step of a wafer bonding method according to still another embodiment of the present disclosure.

FIG. 5 is a cross-sectional view of a wafer bonding structure according to still another embodiment of the present disclosure.

6A to 6D are schematic views showing a bonding method of the wafer bonding structure of Fig. 5.

Figure 7 is a cross-sectional view showing a wafer bonding structure according to still another embodiment of the present disclosure.

Please refer to Figures 1 to 2E. 1 is a schematic cross-sectional view of a wafer bonding structure in accordance with an embodiment of the present disclosure. 2A to 2E are schematic views showing a bonding method of the wafer bonding structure of Fig. 1.

The steps of the wafer bonding method of this embodiment are as follows: Two wafers 10 are provided, and each wafer 10 is manufactured as follows: As shown in FIG. 2A, a first dielectric layer 200 is formed on a substrate 100. The method of forming the first dielectric layer 200 includes chemical vapor deposition (CVD), printing, or spin on. The material of the first dielectric layer 200 is ceria (SiO ₂ ), tantalum nitride (SiN) or low dielectric material (Low-K material), and may also be a combination of multilayer dielectric materials. The first dielectric layer 200 has a surface 210. Next, a plurality of metal pads 300 are fitted on the first dielectric layer 200. The material of the metal pad 300 may comprise a conductive material such as copper, aluminum, tungsten or the like or a combination thereof.

As shown in FIG. 2B, a plurality of recesses 220 are formed on the first dielectric layer surface 210. These recesses 220 are interposed between these metal pads 300, respectively. Wherein, forming a plurality of recesses 220 The method can be selected from one of the group consisting of, for example, grinding, etching etch back, wet etching, or selective etching, and combinations thereof.

As shown in FIG. 2C, a second dielectric layer 400 is formed over one of the wafers 10, and the second dielectric layer 400 covers the recesses 220 and the metal pads 300. The method of forming the second dielectric layer 400 is, for example, chemical vapor deposition, spin coating or printing. The material of the second dielectric layer 400 is, for example, liquid cerium oxide (SOG), benzocyclobutene (BCB) or lead oxide (PBO), but the disclosure is not limited thereto.

As shown in FIG. 2D, the two wafers 10 are bonded, and the second dielectric layer 400 has opposing two bonding faces 410. The two bonding faces 410 are respectively in contact with the first dielectric layer of the two wafers 10 such that the metal pads 300 of the two wafers 10 are in contact with each other, and the recesses 220 of the two wafers 10 constitute a plurality of cavities 20, and the second dielectric layer Electrical layer 400 is located within these cavities 20.

It should be noted that, in this embodiment, the first dielectric layer of the two wafers 10 has a plurality of recesses 220, but is not limited thereto. In other embodiments, the recesses 220 may be formed only in the other embodiments. On one of the wafers 10, the recesses 220 on one of the wafers and the surface 210 of the other wafer form a plurality of cavities 20.

As shown in FIG. 2E, the second dielectric layer 400 located in the cavities 20 is filled with mechanical cavities to fill the cavities 20. Wherein, the mechanical driving mode can be, for example, rotating, flipping or oscillating, and the embodiment adopts flipping (in the direction indicated by the arrow a). In one embodiment, the mechanically driven manner allows the second dielectric layer 400 located within the cavities 20 to fill the cavity 20 in an operating environment that can be a vacuum environment.

The two wafers 10 are pressed (the pressing force F is applied), and the second dielectric layer 400 is cured to fill the cavity 20 with the second dielectric layer 400 so that the two wafers 10 can be fixed to each other. among them, The method of curing the second dielectric layer 400 is, for example, heating the two wafers 10. In an embodiment, a gap may exist in the cavity 20 before the wafer 10 is cured. During the heating of the wafer 10, the metal pad 300 may be melted, so that the two wafers 10 are closer to each other and the cavity 20 is narrowed. The volume, while the volume of the second dielectric layer 400 fills the cavities 20 by curing expansion. In another embodiment, before the wafer 10 is cured, the second dielectric layer 400 in the cavity 20 is filled in the cavity 20 due to surface tension or capillary phenomenon after mechanically driving, and then on the wafer 10. During the heating process, the second dielectric layer 400 is cured. As a result, the bonding degree (adhesion) of the two wafers 10 can be increased by the second dielectric layer 400, thereby improving the bonding yield of the two wafers 10.

As shown in FIG. 1, the wafer bonding structure 5 formed by the above wafer bonding method includes two wafers 10, each of which includes a substrate 100, a first dielectric layer 200, a plurality of metal pads 300, and at least one wafer. A second dielectric layer 400.

The first dielectric layer 200 is disposed on the substrate 100. As shown in FIG. 2B, the first dielectric layer 200 has a surface 210 and a plurality of recesses 220. These recesses 220 are located on the surface 210. The spacing between the recess 220 of one of the wafers 10 and the recess 220 of the other wafer 10 is between 1 and 2 microns. In the present embodiment, the surface of the recess 220 is a curved surface.

The metal pads 300 are embedded in the surface 210 of the first dielectric layer 200, and the recesses 220 are located between the metal pads 300. The edges of the recesses 220 may be, for example, two metal pads 300 contacting the opposite sides.

In the embodiment, the second dielectric layer 400 is disposed on the surface 210 of the first dielectric layer 200 and the recesses 220. The second dielectric layer 400 has a bonding surface 410. The bonding surface 410 is located on a side of the second dielectric layer 400 that is relatively far from the first dielectric layer 200. The two bonding surfaces 410 of the second dielectric layer 400 of the two wafers 10 are in contact with each other and adhere to each other to make the two wafers 10 The metal pads 300 of one of the wafers 10 are electrically connected to the metal pads 300 of the other wafer 10.

Please refer to FIGS. 3A and 3B. FIG. 3A is a schematic cross-sectional view showing one step of the wafer bonding method according to another embodiment of the present disclosure. Fig. 3B is a schematic cross-sectional view showing the wafer bonding structure of Fig. 3A.

In order to make the metal pads 300 of the two wafers 10 have better electrical contact effects, the first embodiment removes the contact with the metal pads 300 after the step of forming the second dielectric layer 400 on the first dielectric layer 200. The two dielectric layers 400 (shown in FIG. 3A) are such that the metal pads 300 of one of the wafers 10 can be in direct contact with the metal pads 300 of the other wafer 10 (as shown in FIG. 3B), thereby enhancing The electrical contact effect of the two wafers 10.

Please refer to FIG. 4, which is a cross-sectional view showing a step of the wafer bonding method according to still another embodiment of the present disclosure.

If a plurality of recesses 220 are formed on the first dielectric layer 200, it is still considered that the recess 220 may be further etched when the depth is insufficient to deepen the depth of the recess 220, thereby allowing the recess 220 to accommodate a larger amount of the second dielectric layer. 400.

The top surface of the metal pad 300 of the wafer 10 is coplanar with the surface 210 of the first dielectric layer 200, but is not limited thereto. In other embodiments, the metal pad 300 may also protrude from the surface 210 of the first dielectric layer 200.

Please refer to Figures 5 to 6D. FIG. 5 is a cross-sectional view of a wafer bonding structure according to still another embodiment of the present disclosure. 6A to 6D are schematic views showing a bonding method of the wafer bonding structure of Fig. 5.

The steps of the wafer bonding method of this embodiment are as follows: Two wafers 10' are provided, and each wafer 10' is manufactured as follows: As shown in FIG. 6A, a first dielectric layer 200 is formed on a substrate 100. Among them, the method of forming the first dielectric layer 200 includes chemical vapor deposition, printing or spin coating, and the like. The material of the first dielectric layer 200 is ceria (SiO ₂ ), tantalum nitride (SiN) or low dielectric material (Low-K material), and may also be a combination of multilayer dielectric materials. Next, a plurality of metal pads 300' are fitted on the first dielectric layer 200. Each metal pad 300 ′ includes a base portion 310 and a protrusion portion 320 . The base 310 is fitted to the first dielectric layer 200. The projection 320 is coupled to the base 310. The material of the metal pad 300' may comprise a conductive material such as copper, aluminum, tungsten or the like or a combination thereof. It should be noted that the protrusion 320 and the base 310 may be the same or different conductive materials.

As shown in FIG. 6B, a second dielectric layer 400 is formed on the first dielectric layer 200. The second dielectric layer 400 covers the base portion 310 of the metal pads 300', and the height of the second dielectric layer 400 is close to or equal to the height of the protruding portion 320 protruding from the first dielectric layer 200. The height of the second dielectric layer 400 of the present embodiment is slightly smaller than the height of the protruding portion 320 of the metal pad 300' protruding from the first dielectric layer 200. That is, the projections 320 of the metal pads 300' penetrate the second dielectric layer 400. The method of forming the second dielectric layer 400 is, for example, chemical vapor deposition, spin coating or printing. The material of the second dielectric layer 400 is liquid cerium oxide (SOG), benzocyclobutene (BCB) or lead oxide (PBO).

As shown in FIG. 6C, the two wafers 10' are bonded such that the projections 320 of the metal pads 300' of the two wafers 10' are in contact with each other, and the plurality of cavities are formed between the metal pads 300' of the two wafers 10'. 20', and the second dielectric layer 400 of the two wafers 10' is located within the cavities 20'.

The two protrusions 320 of the embodiment protrude from the joint surface of the second dielectric layer 400. 410, so that there is no need to remove the second dielectric layer 400 over the metal pad 300' before bonding the two wafers 10', so that a good electrical contact effect between the two wafers 10' can be ensured.

As shown in Fig. 6D, the second dielectric layer 400 is filled with the cavities 20' by mechanical driving. Wherein, the mechanical driving mode can be, for example, rotating, flipping or oscillating, and the embodiment adopts flipping (in the direction indicated by the arrow a). In one embodiment, the mechanically driven manner allows the operating environment of the second dielectric layer 400 located within the cavities 20' to fill the cavities 20' to be a vacuum environment.

The two wafers 10 are pressed (the pressing force F is applied), and the second dielectric layers 400 are cured to fill the cavities 20' with the second dielectric layer 400 so that the two wafers 10' can be fixed to each other. Among them, the method of curing the second dielectric layer 400 is, for example, heating the two wafers 10'. In one embodiment, there may be voids in the cavity 20' before the wafer 10' is cured. During the heating of the wafer 10', the metal pad 300' may melt, causing the two wafers 10' to be closer to each other. The volume of the cavity 20' is reduced, and the volume of the second dielectric layer 400 is filled with these cavities 20' by curing expansion. As a result, the bonding degree (adhesion) of the two wafers 10' can be increased by the second dielectric layer 400, thereby improving the bonding yield of the two wafers 10'.

As shown in FIG. 5, the wafer bonding structure 5' formed by the above wafer bonding method includes two wafers 10'. Each wafer 10' includes a substrate 100, a first dielectric layer 200, and a plurality of metal pads 300'. A second dielectric layer 400.

The first dielectric layer 200 is disposed on the substrate 100. These first dielectric layers 200 have a surface 210.

These metal pads 300' are embedded in the surface 210 of the first dielectric layer 200. Each metal pad 300' includes a base portion 310 and a projection portion 320. The base 310 is fitted to the first dielectric layer 200. The protrusion 320 is connected to the base 310 and protrudes from the first dielectric layer 200. The surface of the two wafers 10' has a pitch of from 1 to 10 μm.

In this embodiment, the second dielectric layer 400 is disposed on the surface 210 of the first dielectric layer 200 and the base portion 310 of the metal pads 300', and the protrusions 320 may penetrate the second dielectric layer 400. The second dielectric layer 400 has a bonding surface 410. The bonding surface 410 is located on a side of the second dielectric layer 400 that is relatively far from the first dielectric layer 200. The two bonding surfaces 410 of the second dielectric layer 400 of the two wafers 10' are in contact with each other and adhere to each other, so that the two wafers 10' are fixed to each other, and the metal pads 300 of one wafer 10' and another wafer are These metal pads 300' of 10' are in electrical contact.

The wafer bonding structure 5, 5' is a symmetric structure (butting the wafers 10 of the same structure or docking the wafers 10 of the same structure), but not limited thereto. In other embodiments, the wafer bonding structure 5, 5' can also be an asymmetric structure. Please refer to Figure 7. Figure 7 is a cross-sectional view showing a wafer bonding structure according to still another embodiment of the present disclosure. The wafer bonding structure 5" of the present embodiment is abutting the two wafers 10, 10' of the different structures. In detail, in the embodiment, one wafer 10 has the same structure as the wafer 10 of the first drawing, and the other wafer 10' The structure is the same as the wafer 10' of the above fifth drawing.

According to the wafer bonding structure and the bonding method thereof according to the embodiment of the present disclosure, the second dielectric layer is accommodated in each of the recesses between the dielectric layers, and in the process of curing the wafer (curing), The metal pad may melt, causing the two wafers to be closer to each other to reduce the volume of the cavity, and the volume of the second dielectric layer may expand to fill the cavity, or the second dielectric in the recess before the wafer is cured After mechanically driving, the electrical layer is filled with recesses due to surface tension or capillary phenomena, and then the second dielectric layer is cured during wafer warming. In this way, you can The bonding degree (adhesion) of the two wafers is increased by the second dielectric layer, thereby improving the bonding yield of the two wafers.

While the embodiments of the present disclosure are disclosed as described above, it is not intended to limit the scope of the present disclosure, and the scope, structure, and features described in the scope of the application of the present disclosure, without departing from the spirit and scope of the disclosure. And the number of modifications may be made, and the scope of patent protection of this disclosure is subject to the scope of the patent application attached to this specification.

5‧‧‧ wafer bonding structure

10‧‧‧ wafer

100‧‧‧Substrate

200‧‧‧First dielectric layer

300‧‧‧Metal pad

400‧‧‧Second dielectric layer

410‧‧‧ joint surface

Claims (26)

A wafer bonding method, the method comprising: providing two wafers, each of the wafer manufacturing methods comprising: forming a first dielectric layer on a substrate; and fitting a plurality of metal pads on the first dielectric layer; Forming a plurality of recesses on the first dielectric layer of the at least one of the wafers, the recesses being respectively between the metal pads; forming a second dielectric layer on the first dielectric layer of the one of the wafers And overlying the recesses of the wafer and the metal pads; bonding the two wafers to contact the metal pads of the two wafers, and causing the recesses of one of the wafers and the other wafer The surface forms a plurality of cavities, and the second dielectric layer is located in the cavities; the second dielectric layer is mechanically driven to fill the cavities; and the two wafers are pressed and cured The second dielectric layer and the two wafers are fixed to each other. The method of claim 1 , after the step of forming the second dielectric layer on the first dielectric layer and the metal pads, further comprising: removing the second dielectric contacting the surface of the metal pad Electrical layer. The wafer bonding method of claim 1, wherein the step of pressing the two wafers and curing the second dielectric layer further comprises: melting the metal pads to bond the two wafers. The wafer bonding method of claim 1, wherein the operating environment in which the second dielectric layer fills the cavities by mechanical driving is a vacuum environment. The wafer bonding method according to claim 1, wherein the method of forming the first dielectric layer comprises chemical vapor deposition (CVD), printing, or spin on. The wafer bonding method of claim 1, the method of forming the recesses comprises grinding, etching etch back, wet etching, selective etching, or a combination thereof. The method of forming the second dielectric layer is the chemical vapor deposition (CVD), spin on or printing. The wafer bonding method of claim 1, wherein the mechanical driving method is rotation, inversion, or oscillation. The wafer bonding method of claim 1, wherein the material of the first dielectric layer comprises hafnium oxide (SiO ₂ ), tantalum nitride (SiN), low dielectric material (Low-K material), or a combination thereof. The wafer bonding method of claim 1, wherein the material of the metal pad comprises copper, aluminum, tungsten or a combination thereof. The wafer bonding method of claim 1, wherein the material of the second dielectric layer comprises liquid cerium oxide (SOG), benzocyclobutene (BCB) or lead oxide (PBO). The wafer bonding method of claim 1, wherein the cavities of the two wafers have a pitch of 1 to 5 μm. The wafer bonding method of claim 1, wherein the depressions constituting the cavities are a curved surface. The wafer bonding method of claim 1, wherein the metal pads on the wafer without the recesses each comprise a base and a protrusion, the protrusion being connected to the base. A wafer bonding method, the method comprising: providing two wafers, each of the wafer manufacturing methods comprising: forming a first dielectric layer on a substrate; A plurality of metal pads are mounted on the first dielectric layer, and each of the metal pads includes a base portion and a protrusion portion, the base portion is fitted to the first dielectric layer, and the protrusion portion is coupled to the base portion And forming a second dielectric layer on the first dielectric layer, the second dielectric layer covering the base portions, and the protruding portions penetrating the second dielectric layer; bonding the two wafers The protrusions of the two wafers are in contact with each other, and the plurality of cavities are formed between the metal pads of the two wafers, and the second dielectric layer is located in the cavities; The second dielectric layer fills the cavities; and presses the two wafers, and cures the second dielectric layer, and fixes the two wafers to each other. The wafer bonding method of claim 15, wherein the step of pressing the two wafers and curing the two second dielectric layers further comprises: melting the metal pads to bond the two wafers. The wafer bonding method of claim 15, wherein the operating environment in which the second dielectric layer fills the cavities by mechanical driving is a vacuum environment. A wafer bonding structure comprising: two wafers, each wafer comprising: a substrate; a first dielectric layer disposed on the substrate, the first dielectric layer having a surface; and a plurality of metal pads embedded in the substrate The surface of the first dielectric layer, the first dielectric layer of the at least one of the wafers has a plurality of recesses, the recesses being located on the surface and located between the metal pads; a second dielectric layer disposed between the first dielectric layer of the two wafers and covering the surface of the first dielectric layer, the second dielectric layer having opposite two bonding surfaces, the first The two bonding surfaces of the two dielectric layers and the two first dielectric layers are in contact with each other and adhere to each other to fix the two wafers to each other, and one of the metal pads of the wafer and the other of the wafers Some metal pads are in contact. The wafer bonding structure of claim 18, wherein the two dielectric layers of the second dielectric layer have a pitch of between 1 and 5 microns. The wafer bonding structure of claim 18, wherein the recess is a curved surface, the edge of the recess contacting the two metal pads on opposite sides. The wafer bonding structure of claim 18, wherein the material of the first dielectric layer comprises hafnium oxide (SiO ₂ ), tantalum nitride (SiN), low dielectric material (Low-K material), or a combination thereof. The wafer bonding structure of claim 18, wherein the material of the metal pad comprises copper, aluminum, tungsten, or a combination thereof. The wafer bonding structure of claim 18, wherein the material of the second dielectric layer comprises liquid cerium oxide (SOG), benzocyclobutene (BCB) or lead oxide (PBO). The wafer bonding structure of claim 18, wherein the metal pads on the wafer without the recesses each comprise a base and a protrusion, the protrusion being connected to the base. A wafer bonding structure comprising: two wafers, each wafer comprising: a substrate; a first dielectric layer disposed on the substrate, the first dielectric layer having a surface; a plurality of metal pads, each of the metal The pad includes a base and a protrusion, and the base Embedded in the first dielectric layer, the protrusion is connected to the base and protrudes from the surface; and a second dielectric layer is disposed between the first dielectric layer of the two wafers and covered The surface of the two first dielectric layers is opposite to the base portions, and the second dielectric layer has opposite opposing surfaces; wherein the two bonding surfaces of the second dielectric layer and the first dielectric layer The electrical layers are in contact with each other and adhere to each other to fix the two wafers to each other, and the projections of one of the wafers are in contact with the projections of the other of the wafers. The wafer bonding structure of claim 25, wherein the surface of the two wafers has a pitch of between 1 and 10 microns.