Test structure for wafer bonding process detection

Abstract

The utility model relates to a test structure for wafer bonding process detection, and the structure comprises a bonding unit which is of a multi-layer stacked structure and comprises a top layer which comprises a first metal wire, a first through hole and a first bonding pad, and the first through hole is connected with the first metal wire and the first bonding pad; the bottom layer comprises a second metal wire, a second through hole and a second bonding pad, and the second through hole is respectively connected with the second metal wire and the second bonding pad; wherein the second bonding pad is connected with the first bonding pad in a bonding mode, and the two ends of the testing structure are connected out for testing through the first metal wire on the top layer or the second metal wire on the bottom layer. According to the test structure, the efficiency and the accuracy of process monitoring are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, in particular to a test structure for wafer bonding process detection. BACKGROUND

[0002] In the post-Moore era, the difficulty and cost of size reduction are greatly increased. In order to improve the energy efficiency of chips and reduce costs from other angles, the concept of chiplet has been very popular in recent years. Specifically, a chip die with rich functions and large area is divided into multiple chiplets, which are produced separately and then integrated and packaged together through advanced packaging methods (such as 3D packaging) to form a system chip. This method is called Chiplet Design.

[0003] Wafer-on-Wafer bonding process is an important technology for realizing advanced packaging. It is to connect two or more wafers together to realize the integration of different materials and form a complex structure. Wafer-on-Wafer bonding process includes metal hybrid bonding, oxide bonding, multiple stack bonding, etc. As shown in the figure, metal hybrid bonding can use thermal compression bonding to make the bonding surfaces of two or more wafers in contact to achieve the purpose of combining wafers. Figure 1

[0004] Currently, the effect of wafer-on-wafer bonding is mainly observed by scanning the metal hybrid bonding interface through a Sonoscan. If there is a gap in the interface, the Sonoscan will show a high light. This method has low precision. SUMMARY

[0005] Therefore, it is necessary to provide a test structure for wafer bonding process detection to solve the problem of low precision in detecting the effect of wafer-on-wafer bonding in the prior art.

[0006] In order to achieve the above purpose, the present application provides a test structure for wafer bonding process detection, characterized in that it comprises a bonding unit arranged in a multi-layer stacked structure, which comprises a top layer and a bottom layer.

[0007] The top layer comprises a first metal line, a first via and a first pad, and the first via is connected to the first metal line and the first pad respectively. ​

[0008] The bottom layer comprises a second metal line, a second via and a second pad, the second via connecting the second metal line and the second pad respectively; wherein,

[0009] The second pad is bonded to the first pad, and the two ends of the test structure are connected out for testing through the first metal line of the top layer or the second metal line of the bottom layer respectively.

[0010] In some embodiments, the test structure for wafer bonding process detection comprises a bonding chain formed by at least two bonding units connected in sequence, wherein two first metal lines in the top layer or two second metal lines in the bottom layer of adjacent bonding units in the bonding chain are connected;

[0011] The two bonding units at the chain end of the bonding chain connect the first metal line of the top layer or the second metal line of the bottom layer as a pin for testing.

[0012] In some embodiments, the bonding chain is in the shape of a long chain or a snake.

[0013] In some embodiments, the test structure for wafer bonding process detection comprises a plurality of bonding chains, wherein,

[0014] The plurality of bonding chains are in the shape of a long chain, and the distance between the center points of adjacent bonding units in different long chain-shaped bonding chains is different.

[0015] In some embodiments, the test structure for wafer bonding process detection comprises a plurality of bonding chains, wherein,

[0016] The plurality of bonding chains are in the shape of a snake, the distance between adjacent line segments in different snake-shaped bonding chains is different, and / or the distance between the center points of adjacent bonding units in different snake-shaped bonding chains is different.

[0017] In some embodiments, the test structure for wafer bonding process detection comprises a plurality of bonding chains, wherein,

[0018] The size of the first pad is the same, the size of the second pad is the same, and the size of the first pad is larger than the size of the second pad between different bonding units in the same bonding chain.

[0019] The size of the first pad is different and the size of the second pad is the same between different bonding units in different bonding chains, or the size of the second pad is different and the size of the first pad is the same between different bonding units in different bonding chains.

[0020] In some embodiments, the size of the first pad and the size of the second pad are the projected areas.

[0021] In some embodiments, the first pad and the second pad have a size ranging from 0.8a to 1.2a, where a is a process window of the first pad or the second pad.

[0022] In some embodiments, the first pad and the second pad include copper, tungsten, or aluminum.

[0023] The test structure for wafer bonding process detection described above includes a bonding unit arranged as a multi-layer stacked structure, which includes a top layer including a first metal line, a first via, and a first pad, the first via connecting the first metal line and the first pad respectively; and a bottom layer including a second metal line, a second via, and a second pad, the second via connecting the second metal line and the second pad respectively. By bonding and connecting the first pad of the top layer and the second pad of the bottom layer, and connecting the two ends of the test structure through the first metal line of the top layer or the second metal line of the bottom layer respectively for testing, the effect of the Wafer-on-Wafer bonding connection of the top layer and the bottom layer can be quickly measured through electrical testing, and the efficiency and accuracy of process monitoring are improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0025] Figure 1 A structural diagram of a metal hybrid bonding process provided in the related art;

[0026] Figure 2 A process flow diagram of a metal hybrid bonding process provided in the related art;

[0027] Figure 3 A cross-sectional schematic diagram of a test structure for wafer bonding process detection provided in an embodiment of the present application;

[0028] Figure 4 A structural schematic diagram of a test structure for wafer bonding process detection provided in an embodiment of the present application;

[0029] Figure 5 A structural schematic diagram of a long-chain bonding chain provided in an embodiment of the present application;

[0030] Figure 6 A structural schematic diagram of a snake-shaped bonding chain provided in an embodiment of the present application;

[0031] Figure 7 A structure diagram of a top wafer or a bottom wafer;

[0032] Figure 8 A structure diagram of a top wafer and a bottom wafer before a bonding process;

[0033] Figure 9 A structure diagram of a serpentine bonding chain with different PitchX, PitchY is provided for another embodiment of the present application;

[0034] Figure 10 A structure diagram of a test structure with different first pad or second pad sizes is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present application, the present application will be described in more detail below with reference to the relevant drawings. The drawings show embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the specification of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0037] It should be understood that although the terms first, second, third, etc. are used to describe various elements, components, regions, layers, doping types and / or parts, these elements, components, regions, layers, doping types and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, doping type or part from another element, component, region, layer, doping type or part. Therefore, the first element, component, region, layer, doping type or part discussed below can be represented as the second element, component, region, layer or part without departing from the teachings of the present application.

[0038] As used herein, the singular forms "a", "an" and "the" can include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "comprise / comprises" or "have / having" specifies the presence of stated features, integers, steps, operations, components, parts or combinations thereof, but does not exclude the presence or addition of one or more other features, integers, steps, operations, components, parts or combinations thereof. At the same time, in the specification, the term "and / or" includes any and all combinations of the related listed items.

[0039] Wafer-on-Wafer (WoW) bonding is an advanced semiconductor manufacturing process that aims to stack two or more wafers together to achieve higher integration and performance. Among them, Metal Hybrid Bonding is an advanced process that combines metal bonding technology, widely used in 3D integrated circuits (3D IC) and other high-density packaging technologies.

[0040] Figure 2 The process flow chart for Metal Hybrid Bonding. Specifically, first prepare two wafers with metal (such as Cu) and dielectric material (Dielectric, such as SiO2) interfacial interface, generally speaking, Cu interface will be slightly lower than SiO2. Then use plasma to perform surface activation treatment, align the two wafers at room temperature, due to van der Waals force, the two wafers can have certain bonding strength at this time. Then, at 100℃, the condensation reaction between Dielectric is carried out, forming strong covalent bond to improve the bonding strength. Finally, the temperature is raised to 300℃ to 400℃, at this time, due to the larger thermal expansion coefficient of Cu than Dielectric, the Cu surface will be in contact and naturally subjected to compressive stress, promoting the diffusion of Cu joints.

[0041] The effect of Metal Hybrid Bonding interface is crucial to ensure the quality and reliability of wafer stacking. In related technologies, in order to detect the bonding effect of Metal Hybrid interface, the main technical means is to use ultrasonic scanner (Sonoscan) to scan the Metal Hybrid bonding interface to observe the effect of wafer stacking bonding. If there is a gap in the interface, the ultrasonic scanner will show high light, and this method has low accuracy.

[0042] Please refer to Figure 3 The present application provides a test structure for wafer bonding process detection, which comprises a bonding unit arranged as a multi-layer stacked structure, each bonding unit is provided with a top layer and a bottom layer, the top layer and the bottom layer belong to different wafers (Top wafer and Bottom wafer), and the top layer and the bottom layer are connected by bonding process. Specifically, in this embodiment, the top layer includes a first metal line (TW TM), a first via (TW Via) and a first pad (TW Pad), the first via TW Via is connected with the first metal line TW TM and the first pad TW Pad respectively. The bottom layer includes a second metal line (BWTM), a second via (BW Via) and a second pad (BW Pad), the second via BW Via is connected with the second metal line BW TM and the second pad respectively.

[0043] In order to adapt to different conditions, in the embodiment, the material, direction, length and width of the first metal line TW TM and the second metal line BW TM, the size of the first via TW Via, the second via BW Via, the first pad TW Pad and the second pad BW Pad, the distance from the end of the first metal line TW TM / second metal line BW TM, and the like in the test structure can be designed under the premise of satisfying the design rule, which is not limited herein.

[0044] In the embodiment, in the bonding unit, the second pad BW Pad and the first pad TW Pad are arranged opposite to each other and are bonded to be connected, so that the top layer and the bottom layer are bonded to be connected. The first metal line TW TM and the second metal line BW TM are arranged in the top layer and the bottom layer respectively, so that the first metal line TW TM and the second metal line BW TM do not contact each other, that is, the first metal line TW TM, the first via TW Via and the first pad TW Pad of the top layer, and the second pad BW Pad, the second via BW Via and the second metal line BW TM of the bottom layer are sequentially stacked in series to form an electrical interconnection structure.

[0045] In order to test the metal mixed bonding interface, the two ends of the test structure can be respectively connected out for testing by the first metal line TW TM of the top layer or the second metal line BW TM of the bottom layer. In the test, the pins snakePin1 and snakePin2 connected out for testing by the first metal line TW TM of the top layer or the second metal line BW TM of the bottom layer can measure the resistance value of the test link formed by the top layer and the bottom layer stacked in series by two-end method. By measuring the resistance value, the bonding connection success or failure and the bonding contact degree can be evaluated, and then the bonding effect can be reflected, and further the process window of the bonding connection can be obtained, and the electrical continuity and overall quality of the bonding interface can be evaluated.

[0046] Generally, high voltage can be applied to the pin snakePin1, low voltage can be applied to the pin snakePin2, the current between the two pins can be measured, and the resistance between the two pins can be calculated. The resistance value R of the bonding unit measured under different bonding effects is different. When the resistance value R is A (more than 10 times of the normal value), it means that the test link is open, which is most likely caused by the bonding failure between the first pad TW Pad of the top layer and the second pad BW Pad of the bottom layer. When the resistance value R is B (normal value), it means that the bonding is successful. When the resistance value R is C (2-10 times of the normal value), it means that the test link is partially contacted, and there may be a situation of partial contact without complete open.

[0047] In the embodiment, the bonding unit is provided with one or more.

[0048] As shown in Figure 4 , when the test structure for wafer bonding process detection includes one bonding unit, the first pad TW Pad of the top layer of the bonding unit is bonded and connected with the second pad BW Pad of the bottom layer, the first metal line TW TM of the top layer and the second metal line BW TM of the bottom layer are respectively connected with the pins snakePin1 and snakePin2, the resistance value R is measured by two-end method, and then the bonding effect is judged.

[0049] As shown in Figure 5 and Figure 6 , in order to realize large-area monitoring and improve test speed, the test structure for wafer bonding process detection includes a bonding chain formed by at least two bonding units connected in sequence. Please refer to Figure 3 , the two first metal lines TW TM in the top layer or the two second metal lines BW TM in the bottom layer of adjacent bonding units in the bonding chain are connected, so that the plurality of bonding units are connected in sequence through the first metal line TW TM or the second metal line BW TM. In the bonding chain, the first metal line TW TM, the first via TW Via, the first pad TW Pad, the second pad BW Pad, the second via BW Via and the second metal line BW TM of different bonding units are respectively located in the same stack layer. By bonding and connecting a plurality of groups of first pads TW Pad and second pads BW Pad of the plurality of bonding units, a large-area metal hybrid bonding interface can be monitored at the same time, the detection sensitivity can be improved, and the detection efficiency of process problems can be effectively improved.

[0050] The two bonding units at the chain end of the bonding chain respectively connect the first metal line TW TM of the top layer or the second metal line BW TM of the bottom layer with the pins snakePin1 and snakePin2, measure the resistance value R' by two-end method, average the resistance value R' to each bonding unit to obtain the resistance value R (R=R' / n, n is the number of bonding units), and then judge the bonding effect.

[0051] In the embodiment, the bonding chain is in a long chain shape or a snake shape. Of course, in other embodiments, when the bonding unit is provided with a plurality of bonding units, the bonding chain can be other various types of design patterns, which are not limited herein.

[0052] Please continue to refer to Figure 7 , Figure 7Fig. 1 is a schematic diagram of a structure of a top wafer or a bottom wafer. As shown, a metal (e.g., Cu) and a dielectric material (not shown) are embedded in a back-end-of-line (BEOL) structure. Before wafer hybrid bonding, the top wafer and the bottom wafer need to be planarized by chemical mechanical planarization (CMP) to process the bonding interface. Since the bonding interface is the embedded interface of Cu and the dielectric material, the selection of the two by CMP is different. Generally, the metal Cu is more easily polished, so the surface height of the metal Cu is slightly lower than that of the dielectric material, forming a height difference ΔH. As shown in Fig. 2, when the metal Cu density of the bonding interface of the top wafer and the bottom wafer is different, the degree of polishing of the bonding interface is different, so after the bonding interface is polished by CMP, the metal Cu and the dielectric material of the bonding interface of the top wafer and the bottom wafer bonded before processing are also different, forming different height differences ΔH1 and ΔH2, which will affect the success of the subsequent bonding process. Figure 8

[0053] According to different test purposes, the test structure for wafer bonding process detection can include one or more bonding chains. In order to further monitor the influence of different metal pad densities of the metal hybrid bonding interface on the bonding process and detect the bonding effect, the following test structure is designed:

[0054] As shown in Fig. 3, in an embodiment, when the test structure includes a plurality of bonding chains, the plurality of bonding chains are in the shape of long chains, and the distance PitchY between the center points of adjacent bonding units in different long chain-shaped bonding chains is different. The resistance values of the two bonding units of the top wafer of each bonding chain chain end can be measured, and the resistance values of the first metal line TW TM or the second metal line BWTM of the bottom wafer of each bonding chain chain end can be measured, and then the bonding effect of the bonding interface under different metal pad densities can be judged. Figure 5

[0055] As shown in Fig. 4, in an embodiment, when the test structure includes a plurality of bonding chains, the plurality of bonding chains are in the shape of long chains, and the distance PitchY between the center points of adjacent bonding units in different long chain-shaped bonding chains is different. The resistance values of the two bonding units of each bonding chain chain end can be measured, and the resistance values of the first metal line TW TM or the second metal line BWTM of the bottom wafer of each bonding chain chain end can be measured, and then the bonding effect of the bonding interface under different metal pad densities can be judged. Figure 6 Figure 9 ​​​In another embodiment, as shown, when the test structure includes a plurality of the bonding chains, the plurality of the bonding chains are serpentine, the distance PitchX between adjacent line segments in different serpentine bonding chains is different, and / or the distance PitchY between adjacent bonding unit center points in different serpentine bonding chains is different. By setting different PitchX and PitchY in different bonding chains, a plurality of different experimental examples are set for different bonding interface metal pad densities along the direction perpendicular to the extension direction of the bonding chain and the extension direction of the bonding chain, respectively, so as to more comprehensively detect the bonding effect under different test conditions, so as to obtain the process window of the bonding interface pad density.

[0056] Alternatively, the distance PitchX between adjacent line segments in different serpentine bonding chains (No. 1-No. 5) and the distance PitchY between adjacent bonding unit center points in different serpentine bonding chains can be set with reference to the minimum distance (min pitch), as shown in the following table:

[0057]

[0058] In metal hybrid bonding, the size relationship of the upper layer and the lower layer metal is a key design consideration to ensure good bonding quality and electrical performance. In order to detect the influence of the size and relative arrangement of the first pad TW Pad of the top layer and the second pad BW Pad of the bottom layer in the bonding unit on the metal hybrid bonding process interface, the following test structure is provided.

[0059] In some embodiments, the test structure for wafer bonding process detection includes a plurality of the bonding chains, wherein the size of the first pad TW Pad is the same and the size of the second pad BW Pad is the same between different bonding units in the same bonding chain.

[0060] Considering that the metal hybrid bonding process combines the direct bonding of metal and insulating dielectric material, especially for high-density interconnection, extremely high alignment accuracy is required. In the actual bonding process, temperature changes can cause thermal expansion or contraction of materials, or applied pressure can cause slight displacement of the chip, which are all direct sources of alignment error. In this embodiment, in order to compensate for the alignment error and reduce its influence on the bonding process detection result, the size of the first pad TW Pad is larger than the size of the second pad BW Pad between different bonding units in the same bonding chain, or vice versa. This overlap can ensure good contact even under alignment deviation.

[0061] As Figure 10As shown, multiple bonding chains are also provided as experimental examples. In some embodiments, the size of the first pad (TW Pad) is different between different bonding units in different bonding chains, while the size of the second pad (BW Pad) is the same. In other embodiments, the size of the second pad (BW Pad) is different between different bonding units in different bonding chains, while the size of the first pad (TW Pad) is the same.

[0062] In the above embodiments, the first solder pad (TW Pad) and the second solder pad (BW Pad) can be made of copper, tungsten, or aluminum. They can be selected to suit different process conditions, and this application is not limited thereto.

[0063] It is understood that in other embodiments, as long as the size of either the first pad TW Pad or the second pad BW Pad remains unchanged, multiple bonding chains can be set up according to testing requirements by changing the other, and the specific size settings can be adjusted under the premise of meeting the design rule.

[0064] Wherein, the dimensions of the first solder pad (TW Pad) and the second solder pad (BW Pad) are projected areas. For example, the dimensions of the first solder pad (TW Pad) and the second solder pad (BW Pad) range from 0.8a to 1.2a, where 'a' is the process window of the first solder pad (TW Pad) or the second solder pad (BW Pad). The process window refers to the range of process parameters allowed to vary during manufacturing, within which the product can still meet design specifications and performance requirements. For example, such as... Figure 10 As shown, the standard size of the first TW Pad (top layer), i.e., the TWPad rule size, is a*a, and the standard size of the second BW Pad (bottom layer), i.e., the BWPad rule size, is b*b. In the test structure of this application, the size of the first TW Pad (top layer) of the bonding unit can be 0.8a*0.8a, 1.2a*1.2a, or any value between 0.8a*0.8a and 1.2a*1.2a; the size of the second BW Pad (bottom layer) can be 0.8a*0.8a, 1.2a*1.2a, or any value between 0.8a*0.8a and 1.2a*1.2a.

[0065] In the embodiment, the size of the first pad TW Pad between different bonding units in the same bonding chain is larger than the size of the second pad BW Pad, or vice versa. The size of the first pad TW Pad and the second pad BW Pad can be adaptively adjusted according to the process window. Of course, in the present application, in order to ensure good bonding quality and avoid the influence of other factors on the bonding effect, the size of the top layer and the bottom layer metal needs to be within the alignment tolerance range to ensure effective contact and bonding. In addition, the top layer and the bottom layer metal need to be size matched to provide the maximum contact area, which helps to improve the bonding strength and the reliability of the electrical connection of the bonding chain.

[0066] For a plurality of bonding chains with different sizes of the first pad TW Pad or the second pad BW Pad, the two bonding units at the chain end of each bonding chain respectively connect the first metal wire TW TM of the top layer or the second metal wire BW TM of the bottom layer to the pin snakePin1 and snakePin2, and the resistance value R' is measured by the two-end method. The resistance value R' is averaged to obtain the resistance value R (R=R' / n, n is the number of bonding units), the bonding effect is judged according to the resistance value R, the influence of the size of the first pad TW Pad or the second pad BW Pad on the bonding effect is obtained, and the process window is further obtained.

[0067] It can be understood that in other embodiments, the difference between a plurality of bonding chains can be a plurality of variables, such as the line width, length of the first metal wire TW TM and the second metal wire BW TM, the number of the first via TW Via and the second via BW Via, etc. By setting a combination of a plurality of bonding chains with different metal pad densities, the process safety window can be effectively obtained.

[0068] In the description of the present specification, the description of the terms "some embodiments", "other embodiments", "ideal embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example.

[0069] The technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features of the above-described embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present specification.

[0070] The above embodiments only express several implementation ways of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation to the patent scope of the application. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A test structure for inspecting wafer bonding processes, characterized in that, include: The bonding unit is configured as a multi-layer stacked structure, including: The top layer includes a first metal line, a first through-hole, and a first pad, wherein the first through-hole is connected to the first metal line and the first pad respectively; The bottom layer includes a second metal line, a second via, and a second pad, wherein the second via connects the second metal line and the second pad, respectively; wherein... The second pad is bonded to the first pad, and the two ends of the test structure are respectively connected to the test via the first metal line of the top layer or the second metal line of the bottom layer.

2. The test structure for wafer bonding process inspection according to claim 1, characterized in that, It includes a bonding chain formed by sequentially connecting at least two of the bonding units, wherein two first metal wires in the top layer or two second metal wires in the bottom layer of adjacent bonding units in the bonding chain are connected. The two bonding units at the ends of the bonding chain respectively connect the first metal wire of the top layer or the second metal wire of the bottom layer as pins for testing.

3. The test structure for wafer bonding process inspection according to claim 2, characterized in that, The bonding chain is long and serpentine.

4. The test structure for wafer bonding process inspection according to claim 3, characterized in that, Including multiple of the aforementioned bonding chains, wherein, The multiple bonding chains are long chains, and the distance between the center points of adjacent bonding units in different long chain shapes is different.

5. The test structure for wafer bonding process inspection according to claim 3, characterized in that, Including multiple of the aforementioned bonding chains, wherein, The multiple bonding chains are serpentine, and the distance between adjacent segments in different serpentine bonding chains is different, and / or the distance between the center points of adjacent bonding units in different serpentine bonding chains is different.

6. The test structure for wafer bonding process inspection according to claim 3, characterized in that, Including multiple of the aforementioned bonding chains, wherein, In the same bonding chain, among different bonding units, the first pad has the same size, the second pad has the same size, and the first pad has a larger size than the second pad. In different bonding units of different bonding chains, the size of the first pad is different and the size of the second pad is the same, or the size of the second pad is different and the size of the first pad is the same in different bonding chains.

7. The test structure for wafer bonding process inspection according to claim 6, characterized in that, The dimensions of the first pad and the second pad are projected areas.

8. The test structure for wafer bonding process inspection according to claim 6, characterized in that, The size range of the first pad and the second pad is 0.8a to 1.2a, where a is the process window of the first pad or the second pad.

9. The test structure for wafer bonding process inspection according to claim 1, characterized in that, The first pad and the second pad comprise copper, tungsten, or aluminum.

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