Wafer bonding method and wafer bonding structure

Abstract

The application provides a wafer bonding method and a wafer bonding structure. The bonding method comprises the following steps: providing a first wafer, forming a first bonding ring layer on a bonding surface of the first wafer; providing a second wafer, forming a second bonding ring layer on a bonding surface of the second wafer, the second bonding ring layer corresponding to the first bonding ring layer; forming a first cavity in the second bonding ring layer of the second wafer; forming a gas path channel penetrating through at least one wafer, the gas path channel being located in a non-functional device area of the wafer; and bonding and forming a bonding ring. The wafer bonding structure comprises a first wafer, a second wafer, a first cavity, a gas path channel and a bonding ring. Compared with a conventional device, the application forms a gas path channel on a wafer, so that when vacuumizing and backfilling gas, the gas exchange is more sufficient, the vacuum degree is closer to the true value and is more uniform, the backfilled gas is purer, the packaging gas pressure can be lower, and the performance of the device is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor technology, in particular to a wafer bonding method and wafer bonding structure. BACKGROUND

[0002] Wafer level packaging technology is the main solution to realize high performance, low cost and batch production, wafer level packaging can be achieved by wafer level bonding technology, for example, a cap is installed on a MEMS device and the two are bonded to complete the packaging, thus having the advantage of batch and reducing packaging cost.

[0003] Wafer level bonding technology is to combine two wafers with each other, and make the surface atoms react with each other, so that the bonding energy between the surfaces reaches a certain strength, thereby combining the two wafers into one. There are many methods for wafer level bonding, such as fusion bonding, hot pressing bonding, low temperature vacuum bonding, anode bonding and eutectic bonding. Wafer level bonding is an important process in MEMS technology, and its main functions include mechanical protection of the movable device (such as movable comb teeth), specific gas backfilling (such as inert protection) or sealing under high vacuum degree (such as resonator). An important indicator of the bonding process is the vacuum degree, which directly determines the Q value of the device, and the Q value will affect the sensitivity, bandwidth, resolution, range and other parameters of the device.

[0004] The bonding method of the existing bonding process is to use an external alignment and an internal bonding of the machine. Specifically, a flag is inserted between the two wafers to be bonded, as shown in Figure 2 The wafer 201 is separated by the flag 202, and three flags 202 are usually used. The flag 202 can be a wedge-shaped iron piece of about 100 μm. During vacuum pumping and air exchange, the gas enters and exits from the gap between the wafers, as shown in Figure 3 The cap wafer 302 and the MEMS wafer 301 are aligned on the alignment module, the flag 303 is inserted between the two wafers, and after the alignment is completed, the clamp clamps and fixes the two wafers, and then they are transmitted to the bonding cavity. In the cavity, vacuum pumping and air exchange, heating and pressurization are performed to bond.

[0005] The wafers are aligned before entering the bonding cavity, and the two wafers are clamped and separated by the flag. During the vacuum pumping process, the air charging and pumping between the wafers can only be transmitted through the edge of the wafer, which will have the following disadvantages:

[0006] Disadvantage 1: The actual bonding vacuum degree of the wafer is quite different from the set vacuum degree of the cavity, and cannot reach the set value of the machine;

[0007] Disadvantage 2: The uniformity of the vacuum degree in the wafer is poor, the vacuum near the edge of the wafer is high, and the closer to the center, the lower, as shown in Figure 2 ​

[0008] Disadvantage 3: The first step of the bonding process is to replace the air with backfill gas. The air between the wafers cannot be completely exchanged, and air remains in the wafers, leading to oxidation.

[0009] Therefore, in order to improve the gas exchange efficiency in the bonding process, a wafer bonding method and a wafer bonding structure are designed. SUMMARY

[0010] A series of simplified concepts are introduced in the summary section, which will be further described in detail in the specific embodiments section. The summary section of the present application does not mean to attempt to limit the key features and essential technical features of the claimed technical solutions, nor to determine the protection scope of the claimed technical solutions.

[0011] The present application provides a wafer bonding method, comprising the following steps: providing a first wafer, forming a first bonding ring layer on the bonding surface of the first wafer; providing a second wafer, forming a second bonding ring layer on the bonding surface of the second wafer, the second bonding ring layer corresponding to the first bonding ring layer; forming a first cavity in the second bonding ring layer of the second wafer; forming a gas path channel penetrating at least one wafer, the gas path channel being located in the non-functional device area of the wafer; bonding the first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer to form a bonding ring.

[0012] Optionally, the method further comprises: before bonding, forming a first sealing ring layer on the bonding surface of the first wafer, the first sealing ring layer being located at the periphery of the first bonding ring layer and surrounding the gas path channel, and forming a second sealing ring layer corresponding to the first sealing ring layer on the bonding surface of the second wafer, to form a sealing ring during bonding.

[0013] Optionally, the gas path channel comprises a second cavity and a gas hole connected in communication.

[0014] Optionally, the gas path channel penetrates only the second wafer, and the first cavity and the second cavity are formed synchronously.

[0015] Optionally, the gas hole is obtained by etching from the second cavity, or obtained by etching inwardly from a position corresponding to the second cavity on the non-bonding surface of the second wafer to the second cavity.

[0016] Optionally, the maximum width of the gas hole is less than or equal to the width of the second cavity.

[0017] Optionally, the method further comprises: before forming the first bonding ring layer or the second bonding ring layer with aluminum, forming an adhesion barrier layer on the surface of the wafer to prevent the diffusion of aluminum into the wafer.

[0018] A wafer bonding structure includes: a first wafer having a first bonding ring layer on its bonding surface; a second wafer having a second bonding ring layer on its bonding surface, the second bonding ring layer corresponding to the first bonding ring layer; a first cavity located within the second bonding ring layer of the second wafer; a gas passage extending through at least one wafer, the gas passage being located in a non-functional device region of the wafer; and a bonding ring formed by bonding the first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer together.

[0019] Optionally, the wafer bonding structure also includes a sealing ring located around the bonding ring and surrounding the gas passage.

[0020] Optionally, the air passage includes a connected second cavity and a vent.

[0021] This invention provides a wafer bonding method and wafer bonding structure. Compared with traditional devices, by forming gas channels on the wafer, gas exchange is more complete during vacuuming and backfilling, and the vacuum degree is closer to the true value, i.e., reaching the set value of the machine. The vacuum degree uniformity is better, making the vacuum degree of the wafer edge and center close. The backfill gas is purer, making it easier to replace air with backfill gas and reduce air residue. The packaging gas pressure can be lower, improving the performance of the device. Attached Figure Description

[0022] The following drawings, which are incorporated herein by reference as part of this invention, are provided for understanding the invention. The drawings illustrate embodiments of the invention and their descriptions, serving to explain the principles of the invention.

[0023] In the attached image:

[0024] Figure 1 A flowchart of a wafer bonding method according to an embodiment of the present invention is shown;

[0025] Figure 2 A top view (diagram of air pressure distribution) of the insertion of markings between discs in the prior art is shown;

[0026] Figure 3 A side view is shown of the insertion of markings between discs in the prior art;

[0027] Figure 4A A schematic cross-sectional view of a semiconductor structure in which a first bonding ring layer is formed on the bonding surface of a first wafer is shown according to an embodiment of the present invention.

[0028] Figure 4B This illustrates the formation of bonding surfaces on a second wafer according to an embodiment of the present invention. Figure 4A A schematic cross-sectional view of the semiconductor structure of the second bonding ring layer corresponding to the first bonding ring layer;

[0029] Figure 4CAn embodiment of the present invention is shown in Figure 4B A schematic cross-sectional view of a semiconductor structure in which a first cavity is formed in the second bonding ring layer and a second cavity is formed in the second sealing ring layer.

[0030] Figure 4D An embodiment of the present invention is shown in Figure 4C A cross-sectional schematic diagram of a semiconductor structure with ventilation holes formed on a wafer;

[0031] Figure 4E An embodiment of the present invention is shown. Figure 4D and Figure 4A A cross-sectional schematic diagram of a semiconductor structure bonded to a wafer;

[0032] Figure 5 A schematic cross-sectional view of a semiconductor structure is shown, according to an embodiment of the present invention, wherein a wafer having a gas passage is bonded to a wafer having an adhesion barrier layer.

[0033] Figure 6 A cross-sectional schematic diagram and a top view of a semiconductor structure according to an embodiment of the present invention are shown in comparison.

[0034] Figure 7 A top view of a circular disc having a gas exchange channel structure according to an embodiment of the present invention is shown;

[0035] Figure 8 A top view of a circular sheet having a bonding structure according to an embodiment of the present invention is shown. Detailed Implementation

[0036] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0037] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated. The same reference numerals denote the same elements throughout.

[0038] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this invention, the first element, component, area, layer, or portion discussed below may be referred to as the second element, component, area, layer, or portion.

[0039] Spatial relation terms such as "below," "under," "below," "below," "above," "over," etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as "below" or "under" or "below" of the other element or feature will be oriented "above" the other element or feature. Therefore, the exemplary terms "below" and "under" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprise” and / or “comprising,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups. When used herein, the terms “and / or” include any and all combinations of the associated listed items.

[0041] Embodiments of the invention are described herein with reference to cross-sectional views that serve as schematic diagrams of ideal embodiments (and intermediate structures). Thus, variations from the shapes shown can be anticipated due to, for example, manufacturing techniques and / or tolerances. Therefore, embodiments of the invention should not be limited to the specific shapes of the regions shown herein, but include shape deviations due to, for example, manufacturing processes. The regions shown in the figures are substantially schematic, and their shapes are not intended to show the actual shapes of regions of the device and are not intended to limit the scope of the invention.

[0042] To fully understand this invention, detailed structures and steps will be presented in the following description to illustrate the technical solution proposed by this invention. Preferred embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0043] This invention provides a wafer bonding method, such as... Figure 1 As shown, the method includes the following steps:

[0044] 101. Provide a first wafer, and form a first bonding ring layer on the bonding surface of the first wafer;

[0045] 102. A second wafer is provided, and a second bonding ring layer is formed on the bonding surface of the second wafer, the second bonding ring layer corresponding to the first bonding ring layer;

[0046] 103. A first cavity is formed within the second bonding ring layer of the second wafer;

[0047] 104. Form a gas path that runs through at least one wafer, the gas path being located in the non-functional device region of the wafer;

[0048] 105. The first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer are bonded together to form a bonding ring.

[0049] Before bonding, a first sealing ring layer is formed on the bonding surface of the first wafer, located outside the first bonding ring layer and surrounding the gas passage, and a second sealing ring layer corresponding to the first sealing ring layer is formed on the bonding surface of the second wafer, so as to form a sealing ring during bonding.

[0050] During the evacuation and backfilling process, gas exchanges with the edges of the first and second wafers and the gas passage. The sealing ring surrounds the gas passage, which prevents moisture from entering the wafer and corroding the aluminum pad during subsequent processes.

[0051] The gas path can include a connected second cavity and a vent. When forming a gas path that only penetrates the second wafer, the first and second cavities can be formed simultaneously without additional process steps. The vent can be obtained by etching from the second cavity, or by etching inward from the unbonded surface of the second wafer corresponding to the second cavity. The vent can be located on the area to be diced on the second wafer, making dicing easier and not affecting the overall wafer structure. The width of the vent can be less than or equal to the width of the second cavity. By setting the second cavity, the aspect ratio of the vent can be reduced, making etching easier, allowing the hole to be made smaller, and simplifying the process.

[0052] By increasing the gas path channels, gas exchange is more complete during vacuuming and inert gas backfilling, the vacuum level inside the wafer is closer to the true value, the vacuum uniformity is better, the backfill gas is purer, the packaging gas pressure can be lower, and the device performance is improved.

[0053] Example 1

[0054] like Figures 4A-4E As shown, taking the fabrication of MEMS as an example, the specific method is as follows:

[0055] like Figure 4A As shown, a first wafer 400 is provided. Here, the first wafer can be a capping wafer or a MEMS wafer. A first bonding ring layer 402 and a first sealing ring layer 404 are formed on the bonding surface of the first wafer. Here, the first sealing ring layer 404 can also be omitted. The first bonding ring layer is made of aluminum or germanium, and the thickness of the first bonding ring layer is 0.3μm to 0.7μm. In one example, the first bonding ring layer is made of aluminum and the thickness is 0.5μm.

[0056] like Figure 4B As shown, a second wafer 406 is provided, and a second bonding ring layer 408 and a second sealing ring layer 410 are formed on the bonding surface of the second wafer. Here, the second sealing ring layer 410 can also be omitted. The second bonding ring layer is made of germanium or aluminum, and the thickness of the second bonding ring layer is 0.8μm to 1.2μm. In one example, the second bonding ring layer is made of germanium and the thickness is 1.0μm.

[0057] like Figure 4C As shown, a first cavity 412 is formed in the second bonding ring layer of the second wafer, and a second cavity 414 is formed in the second sealing ring layer. The first cavity 412 and the second cavity 414 can be formed simultaneously or asynchronously. The width of the second cavity can be 40 to 70 μm. In one example, the width of the second cavity is 60 μm.

[0058] like Figure 4DAs shown, the second cavity 414 is etched through to form a vent 416. The etching can be done by dry etching, such as plasma etching. The width of the vent is 20-40 μm. In one example, the width of the vent is 30 μm. The second cavity 414 and the vent 416 form a gas passage.

[0059] like Figure 4E As shown, the first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer are bonded together to form a bonding ring, wherein the gas passage can be set on the periphery of the bonding ring to form a ring.

[0060] In one example, the method further includes: forming a first sealing ring layer on the bonding surface of the first wafer, located around the first bonding ring layer and surrounding the gas passage, prior to bonding; and forming a second sealing ring layer on the bonding surface of the second wafer, corresponding to the first sealing ring layer, to form a sealing ring during bonding. During evacuation and backfilling, gas exchange occurs from the edges of the first and second wafers and the gas passage.

[0061] In one example, the vent is located on the dicing area of ​​the second wafer.

[0062] In one example, the vent hole is obtained by etching from the second cavity.

[0063] In one example, the vent holes are etched inward from the unbonded surface of the second wafer.

[0064] In one example, the maximum width of the vent is less than or equal to the width of the second cavity.

[0065] Example 2

[0066] like Figure 5 As shown, before forming the bonding ring layer 502 and sealing ring layer 504 with aluminum, an adhesion barrier layer 501 is formed on the surface of the wafer 500 to prevent aluminum from diffusing into the wafer. When the first recess 512 is made on the back side of the vent hole of the sealing cap, the second recess 514 is also made simultaneously. Then, the second recess 514 is etched through from the front side to form a vent hole 516. The width of the second recess 514 is the same as that of the vent hole 516, ensuring that gas can be extracted from the gas passage during bonding. Then, a bonding sealing ring layer 510 is formed around the gas passage. After bonding, the gas passage is sealed by the sealing ring, ensuring that there is no water leakage during subsequent trimming, grinding, and other processes, and reducing the impact of aluminum pad corrosion. The specific steps are as follows:

[0067] First, an adhesion barrier layer 501 is formed on the MEMS surface. This adhesion barrier layer can be a single-layer titanium Ti layer or a double-layer TiTiN layer, wherein in the double-layer TiTiN layer, Ti is a titanium dioxide layer. TiN is Then, aluminum is deposited to create a bonding ring, a gas passage sealing ring, and an aluminum pad. Processes unrelated to this patent, including electrode and wiring steps performed before and after aluminum deposition, are omitted.

[0068] Secondly, the cap surface and the MEMS need to be bonded. In the corresponding area, a germanium bonding ring 508 and a gas passage sealing ring 510 need to be fabricated. Then, the first cavity 512 is fabricated on the cap surface, and the second cavity 514 is also etched at the position of the gas passage.

[0069] Next, the vent hole 516 is etched on the non-bonded side of the cap surface to pierce through the wafer and open the gas passage structure.

[0070] Finally, the MEMS and the cap are bonded with aluminum-germanium. During the evacuation and backfilling process, gas is exchanged from the edge and the gas passage. After bonding, the gas passage is blocked by the sealing ring around it, so moisture will not enter the wafer to etch the aluminum pad during subsequent processes such as trimming, grinding, and photolithography.

[0071] Example 3

[0072] like Figures 6-8 As shown, the present invention also provides a wafer bonding structure, comprising: a first wafer having a first bonding ring layer on its bonding surface; a second wafer having a second bonding ring layer on its bonding surface, the second bonding ring layer corresponding to the first bonding ring layer; a first cavity located within the second bonding ring layer of the second wafer; a gas passage extending through at least one wafer, the gas passage being located in a non-functional device region of the wafer; and a bonding ring formed by bonding the first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer together.

[0073] In at least one embodiment, such as Figure 6 As shown, a gas exchange channel, i.e. a gas path channel 600, is made in the area to be cut 610 on the capping surface of the chip. The gas path channel 600 corresponds to the second cavity 414 and the vent 416. Firstly, during the evacuation and backfilling process of bonding, the gas can not only be exchanged from the edge of the wafer, but also from the gas path channel, ensuring that the gas can be fully exchanged. Secondly, it can also improve the uniformity of the bonding vacuum degree throughout the entire wafer area.

[0074] The second cavity 414 is formed simultaneously with the first cavity 412. Here, the first cavity 412 corresponds to 604, and the bonding ring layer 408 corresponds to 602. In at least one embodiment, a through-hole is then cut from the front, and a bonded sealing ring 410 is formed around the gas passage. Here, 410 corresponds to 606. After bonding, the gas passage will be sealed by the sealing ring 606, ensuring that there is no water leakage during subsequent trimming, grinding, and other processes, and reducing the impact on the corrosion of the aluminum pad.

[0075] Gas exchange channels are fabricated on the outer surface of the chip's cap or the chip area of ​​the MEMS surface. The number, size, and distribution of these channels can be customized as needed. Figure 6 This is a cross-sectional view of the gas path structure. Figure 7 This is one type of distribution method. During the bonding process, gas exchange can occur through the gas exchange channel, changing the existing method of exchange from the edge of the wafer, thus improving gas exchange efficiency. The uniformity of gas pressure throughout the entire wafer range is improved, and there is no residual air in the backfill atmosphere, making the bonding gas pressure more closely match the machine settings.

[0076] This invention provides a wafer bonding method and wafer bonding structure. Compared with traditional devices, by forming gas channels on the wafer, gas exchange is more complete during vacuuming and backfilling, the vacuum degree is closer to the true value, the vacuum degree uniformity is better, the backfill gas is purer, and the packaging gas pressure can be lower, thereby improving the performance of the device.

[0077] The present invention has been described through the above embodiments. However, it should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the invention to the scope of the described embodiments. Furthermore, those skilled in the art will understand that the present invention is not limited to the above embodiments, and many more variations and modifications can be made based on the teachings of the present invention, all of which fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wafer bonding method, characterized in that, Includes the following steps: A first wafer is provided, and a first bonding ring layer and a first sealing ring layer are formed on the bonding surface of the first wafer; A second wafer is provided, and a second bonding ring layer and a second sealing ring layer are formed on the bonding surface of the second wafer, wherein the second bonding ring layer corresponds to the first bonding ring layer and the second sealing ring layer corresponds to the first sealing ring layer; A first cavity is formed in the second bonding ring layer of the second wafer, and a second cavity is formed in the second sealing ring layer, wherein the first cavity and the second cavity are formed simultaneously. A gas path channel is formed through the second wafer, the gas path channel being located in the non-functional device area of ​​the wafer, wherein the gas path channel includes a second cavity and a vent hole that are connected to each other; The first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer are bonded together to form a bonding ring, wherein the first sealing ring layer and the second sealing ring layer form a sealing ring during bonding, and the sealing ring is located outside the bonding ring and surrounds the gas passage.

2. The wafer bonding method as described in claim 1, characterized in that, The vent hole is obtained by further etching from the second cavity, or by etching inward from the position corresponding to the second cavity on the non-bonded surface of the second wafer to the second cavity.

3. The wafer bonding method as described in claim 1, characterized in that, The maximum width of the vent hole is less than or equal to the width of the second cavity.

4. The wafer bonding method as described in claim 1, characterized in that, The method further includes forming an adhesion barrier layer on the surface of the wafer before forming a first bonding ring layer or a second bonding ring layer having aluminum.

5. A wafer bonding structure, characterized in that, include: The first wafer has a first bonding ring layer on the bonding surface of the first wafer; The second wafer has a second bonding ring layer on its bonding surface, the second bonding ring layer corresponding to the first bonding ring layer; The first cavity is located within the second bonding ring layer of the second wafer; A gas path channel that extends through at least one wafer, the gas path channel being located in the non-functional device region of the wafer; A bonding ring is formed by bonding the first bonding ring layer of the first wafer and the second bonding ring layer of the second wafer to each other; A sealing ring, which is located around the bonding ring and surrounds the gas passage; The air passage includes a second concave cavity and a vent hole that are connected to each other.

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