Method of solder preparation in wafer level vacuum packaging and wafer with solder

Abstract

The application relates to the field of wafer-level vacuum packaging, and discloses a solder preparation method in wafer-level vacuum packaging, which comprises the following steps: aligning a solder mask plate with a soldering surface of a wafer to be bonded, so that through holes on the solder mask plate are respectively aligned with bonding metal areas on the soldering surface; placing pre-prepared solder pieces in the through holes, so that the pre-prepared solder pieces are aligned with the bonding metal areas; soldering the pre-prepared solder pieces and the bonding metal areas, and removing the solder mask plate to obtain a wafer with solder. According to the application, the pre-prepared solder pieces are aligned with the bonding metal areas of the wafer to be bonded through the solder mask plate, that is, a plurality of pre-prepared solder pieces can be aligned at one time through the solder mask plate, the process difficulty is reduced, the production speed is improved, and the production cost is reduced. Moreover, the pre-prepared solder pieces do not need to be aligned one by one through optical alignment, the alignment precision is improved, the qualified rate of the wafer with solder is improved, and the production cost is reduced.

Description

Technical Field

[0001] This application relates to the field of wafer-level vacuum packaging, and in particular to a solder preparation method and a wafer with solder in wafer-level vacuum packaging. Background Technology

[0002] Wafer-level chip vacuum packaging enables miniaturization, integration, and cost reduction of devices, and is widely used in MEMS (Micro-Electro-Mechanical System) devices such as gyroscopes, pressure sensors, and microbolometers.

[0003] Solder bonding is a bonding technology used in wafer-level vacuum packaging, characterized by low processing temperature, high strength, and minimal impact from surface roughness. Currently, pre-fabricated solder sheets can be bonded to wafers using optical alignment technology to align the pre-fabricated solder sheets with the metallized areas on the wafer before bonding. However, this process has several drawbacks: First, only one pre-fabricated solder sheet can be aligned at a time, requiring multiple alignments and bonding operations, resulting in cumbersome and inefficient operations and high manufacturing costs. Second, the optical alignment accuracy is insufficient for wafer-level vacuum packaging requirements, leading to potential misalignment of the pre-fabricated solder sheets, which can severely damage the product. Third, the high cost of optical alignment equipment further contributes to the high manufacturing cost.

[0004] Therefore, how to solve the above-mentioned technical problems should be a key focus for those skilled in the art. Summary of the Invention

[0005] The purpose of this application is to provide a solder preparation method and a wafer with solder in a circular vacuum package, so as to improve solder preparation efficiency and alignment accuracy and reduce manufacturing cost.

[0006] To address the aforementioned technical problems, this application provides a method for preparing solder in wafer-level vacuum packaging, comprising:

[0007] Align the solder mask with the bonding surface of the wafer to be bonded, so that each through-hole on the solder mask is aligned with the corresponding bonding metal area on the bonding surface;

[0008] Each pre-made solder sheet is placed in each of the through holes, so that each pre-made solder sheet is aligned with the corresponding bonding metal region;

[0009] The pre-fabricated solder sheets and the corresponding bonding metal regions are soldered together, and the solder mask is removed to obtain a wafer with solder.

[0010] Optionally, aligning the solder mask with the bonding surface of the wafer to be bonded includes:

[0011] The solder mask is aligned with the bonding face of the wafer to be bonded using mechanical and optical alignment devices, and / or a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask; wherein the first alignment mark corresponds to the second alignment mark.

[0012] Optionally, of the first alignment mark and the second alignment mark, one is a raised mark and the other is a recessed mark.

[0013] Optionally, welding the preformed solder sheet and the bonding metal region includes:

[0014] The preformed solder sheet is welded to the bonding metal region by laser welding or spot welding.

[0015] Optionally, before aligning the solder mask with the bonding faces of the wafer to be bonded, the following steps are also included:

[0016] Fabricate a solder mask that matches the bonding metal region on the bonding surface of the wafer to be bonded.

[0017] Optionally, before aligning the solder mask with the bonding surface of the wafer to be bonded, the bonding metal region is formed on the bonding surface of the wafer to be bonded, specifically including:

[0018] A patterned photoresist is formed on the bonding surface of the wafer to be bonded;

[0019] A metal layer is deposited on the patterned photoresist;

[0020] The patterned photoresist is stripped away to form the bonding metal region on the welding surface.

[0021] Optionally, depositing a metal layer on the patterned photoresist includes:

[0022] An adhesion layer is deposited on the patterned photoresist;

[0023] A barrier layer is deposited on the surface of the adhesive layer.

[0024] Optionally, after depositing a barrier layer on the surface of the adhesive layer, the method further includes:

[0025] An anti-oxidation wetting layer is deposited on the surface of the barrier layer.

[0026] Optionally, aligning the solder mask with the bonding surface of the wafer to be bonded includes:

[0027] The solder mask is initially aligned with the bonding surface of the wafer to be bonded;

[0028] The alignment effect between the solder mask and the wafer to be bonded is observed using a camera.

[0029] If there is a misalignment between the solder mask and the wafer to be bonded, adjust the position of the solder mask and / or the wafer to be bonded until alignment is achieved.

[0030] This application also provides a wafer with solder, prepared using any of the methods described above.

[0031] This application provides a method for preparing solder in wafer-level vacuum packaging, comprising: aligning a solder mask with the bonding surfaces of a wafer to be bonded, such that each via on the solder mask is aligned with a corresponding bonding metal region on the bonding surface; placing each pre-made solder sheet into each of the vias, such that each pre-made solder sheet is aligned with its corresponding bonding metal region; bonding each pre-made solder sheet to its corresponding bonding metal region; and removing the solder mask to obtain a wafer with solder.

[0032] As can be seen, in this application, when fabricating solder on a wafer, the solder mask is aligned with the bonding surfaces of the wafer to be bonded, ensuring that each via of the solder mask aligns with its corresponding bonding metal region. Then, the pre-fabricated solder sheet is directly placed within the via to achieve alignment with the bonding metal region before soldering. This allows multiple pre-fabricated solder sheets to be aligned simultaneously using the solder mask, reducing process complexity, increasing fabrication speed, and lowering manufacturing costs. Furthermore, it eliminates the need for individual alignment of each pre-fabricated solder sheet, improving alignment accuracy, increasing the yield of wafers with solder, and further reducing manufacturing costs.

[0033] In addition, this application also provides a solder-coated wafer with the above-mentioned advantages. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A flowchart illustrating a solder preparation method in wafer-level vacuum packaging provided in this application embodiment;

[0036] Figure 2 A schematic diagram of a solder mask provided in an embodiment of this application;

[0037] Figure 3 A schematic diagram of a wafer to be bonded, provided for an embodiment of this application;

[0038] Figure 4A schematic diagram of a pre-fabricated solder sheet provided in an embodiment of this application;

[0039] Figure 5 Exploded views of the preformed solder sheet, solder mask, and wafer to be bonded provided in the embodiments of this application;

[0040] Figure 6 This is a schematic diagram of a welding point on a prefabricated solder sheet provided in an embodiment of this application;

[0041] Figure 7 A flowchart illustrating another method for solder preparation in wafer-level vacuum packaging provided in this application embodiment;

[0042] Figure 8 This is an enlarged schematic diagram of a metal layer provided in an embodiment of this application;

[0043] In the figure, 1. Wafer to be bonded, 2. Bonding metal area, 3. First alignment mark, 4. Solder mask, 5. Second alignment mark, 6. Pre-made solder sheet, 7. Solder joint, 8. Through hole, 2a. Anti-oxidation wetting layer, 2b. Barrier layer, 2c. Adhesive layer. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0046] As described in the background section, when soldering pre-made solder sheets to wafers, only one pre-made solder sheet can be aligned and soldered at a time, which has the disadvantages of low production efficiency and high cost.

[0047] In view of this, this application provides a method for solder preparation in wafer-level vacuum packaging. Please refer to [the relevant documentation]. Figure 1 ,include:

[0048] Step S101: Align the solder mask with the bonding surface of the wafer to be bonded, so that each through hole on the solder mask is aligned with the corresponding bonding metal area on the bonding surface.

[0049] A schematic diagram of a solder mask is shown below. Figure 2 As shown, the solder mask 4 has multiple through holes 8. The distribution of the through holes 8 is the same as the distribution of the bonding metal area on the bonding surface of the wafer to be bonded. That is, the through holes 8 on the solder mask 4 correspond one-to-one with the bonding metal area on the wafer to be bonded.

[0050] The solder mask can be made of quartz or metal, and this application does not limit the material.

[0051] Optionally, before aligning the solder mask with the bonding faces of the wafer to be bonded, the following steps are also included:

[0052] Fabricate a solder mask that matches the bonding metal region on the bonding surface of the wafer to be bonded.

[0053] The solder mask can be fabricated by methods such as etching, and this application does not specify any particular method.

[0054] A schematic diagram of the wafer to be bonded is shown below. Figure 3 As shown, bonding metal regions 2 are distributed in an array on the bonding surface of the wafer 1 to be bonded, and the bonding metal regions 2 are in a ring shape. The shape of the bonding metal regions 2 includes, but is not limited to, square rings and circular rings. Figure 3 It is shown in a square ring.

[0055] Step S102: Place each pre-made solder sheet into each of the through holes, so that each pre-made solder sheet is aligned with the corresponding bonding metal area.

[0056] Since the via is aligned with the bonding metal area, placing the pre-made solder sheet inside the via achieves alignment with the bonding metal area.

[0057] It should be noted that this application does not limit the method of placing the pre-fabricated solder sheet in the through-hole, but depends on the circumstances. For example, the pre-fabricated solder sheet can be placed in the through-hole by automated feeding equipment or by manual placement.

[0058] The purpose of the pre-formed solder sheet is to perform vacuum sealing between two wafers.

[0059] The materials for pre-formed solder sheets can be AuSn-based solders, such as Au80Sn20 and Au10Sn90; In-based solders, such as In97Ag3 and In52Sn48; SAC-based solders, such as Sn96.5Ag3.0Cu0.5 and Sn95.5Ag3.8Cu0.7; SnAg-based solders, etc. The pre-formed solder sheets offer greater choice in material composition and a wider variety of materials.

[0060] Pre-fabricated solder sheets are formed by melting an alloy, which reduces the complexity of the target material composition, allows for greater component selectivity, and eliminates the need for flux. In contrast, solder in some related technologies is formed by printing solder paste, which is limited by the solder paste composition and requires flux. Furthermore, the thickness and size of the pre-fabricated solder sheets in this application are flexible and controllable.

[0061] Pre-fabricated solder sheet 6 is a pre-made, single-piece solder sheet, such as... Figure 4 As shown. It should be emphasized that alignment is achieved using a solder mask in this application, but the thickness of the solder mask does not limit the thickness of the pre-formed solder sheet. The thickness of the pre-formed solder sheet in this application can be flexibly selected during fabrication as needed. Therefore, both the material and thickness of the pre-formed solder sheet in this application can be flexibly selected. For example, the pre-formed solder sheet can be made thicker, thereby increasing the spacing between the two wafers and improving the window height.

[0062] After the pre-formed solder sheet is placed in the through-hole of the solder mask, the exploded view of the pre-formed solder sheet 6, the solder mask 4, and the wafer 1 to be bonded is shown below. Figure 5 As shown.

[0063] Step S103: Solder each of the pre-made solder sheets and the corresponding bonding metal regions, and remove the solder mask to obtain a wafer with solder.

[0064] Optionally, as one possible implementation, welding the pre-formed solder sheet and the bonding metal region includes: welding the pre-formed solder sheet to the bonding metal region by laser welding. However, this application does not specifically limit this; as another possible implementation, welding the pre-formed solder sheet and the bonding metal region includes: welding the pre-formed solder sheet to the bonding metal region by spot welding.

[0065] For example, when the bonding metal area 2 and the preformed solder sheet 6 form a square ring, welding can be performed along the center line of the width on each of the four sides of the preformed solder sheet 6. A schematic diagram of the welding point 7 on the preformed solder sheet 6 is shown below. Figure 6 As shown, the number of solder joints 7 depends on the size of the preformed solder sheet. When the bonding metal area and the preformed solder sheet form a ring, equidistant or non-equidistant soldering can be performed along the center line of the width of the preformed solder sheet, and the number of solder joints depends on the size of the preformed solder sheet.

[0066] This application describes a method for fabricating solder on a wafer. By aligning a solder mask with the bonding surfaces of the wafer to be bonded, the vias of the solder mask are aligned with their corresponding bonding metal regions. The pre-fabricated solder sheet is then directly placed within the vias to achieve alignment with the bonding metal regions before soldering. This allows for the simultaneous alignment of multiple pre-fabricated solder sheets using a solder mask, reducing process complexity, increasing fabrication speed, and lowering manufacturing costs. Furthermore, it eliminates the need for individual optical alignment of each pre-fabricated solder sheet, improving the yield rate of wafers with solder and further reducing manufacturing costs.

[0067] Based on the above embodiments, in one embodiment of this application, aligning the solder mask with the bonding surface of the wafer to be bonded includes:

[0068] The solder mask is aligned with the bonding face of the wafer to be bonded using mechanical and optical alignment devices, and / or a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask; wherein the first alignment mark corresponds to the second alignment mark.

[0069] There are three alignment methods: First, aligning the solder mask with the bonding surface of the wafer to be bonded using mechanical and optical alignment devices; second, aligning the solder mask with the bonding surface of the wafer to be bonded using a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask; third, aligning the solder mask with the bonding surface of the wafer to be bonded using mechanical and optical alignment devices and the first alignment mark on the wafer to be bonded and the second alignment mark on the solder mask.

[0070] The shapes of the first alignment mark and the second alignment mark include, but are not limited to, cross, grid, and star shapes.

[0071] like Figure 3 As shown, the first alignment mark 3 can be located at the edge of the wafer 1 to be bonded, or it can be located at any position in the center. The number of the first alignment marks 3 can be set by the user. Correspondingly, when the first alignment mark 3 is located at the edge of the wafer 1 to be bonded, as shown... Figure 2 As shown, the second alignment mark 5 is also located at the edge of the solder mask 4, and the number is equal to that of the first alignment mark 3.

[0072] To facilitate alignment using the first alignment mark and the second alignment mark, one of the first alignment mark and the other is a raised mark, and the other is a recessed mark. That is, the first alignment mark is a raised mark, and the second alignment mark is a recessed mark; or, the first alignment mark is a recessed mark, and the second alignment mark is a raised mark.

[0073] Based on any of the above embodiments, in one embodiment of this application, please refer to Figure 7 The solder preparation methods in wafer-level vacuum packaging include:

[0074] Step S201: A patterned photoresist is formed on the bonding surface of the wafer to be bonded.

[0075] Photoresist is coated onto the bonding surface of the wafer to be bonded, and then exposed and developed to complete the patterning of the photoresist.

[0076] Step S202: Deposit a metal layer on the patterned photoresist.

[0077] The metal layer can be deposited by magnetron sputtering or physical vapor deposition (i.e., S2021, S2022, and S2023 mentioned below, each of which can be achieved by magnetron sputtering or thermal evaporation). This application does not make any specific limitations.

[0078] Optionally, as one possible implementation, depositing a metal layer on the patterned photoresist includes:

[0079] Step S2021: Deposit an adhesion layer on the patterned photoresist;

[0080] Step S2022: Deposit a barrier layer on the surface of the adhesive layer.

[0081] The thermal expansion coefficient of the adhesive layer is similar to that of the wafer to be bonded. The material of the adhesive layer can be metals such as Cr (chromium), Ti (titanium), and V (vanadium), and the thickness can be 10nm to 1μm.

[0082] The barrier layer can be made of Ni (nickel) and its thickness can be 50 nm to 1 μm.

[0083] Optionally, as another possible implementation, depositing a metal layer on the patterned photoresist includes:

[0084] Step S2021: Deposit an adhesion layer on the patterned photoresist;

[0085] Step S2022: Deposit a barrier layer on the surface of the adhesive layer.

[0086] Step S2023: Deposit an anti-oxidation wetting layer on the surface of the barrier layer.

[0087] The material of the anti-oxidation wetting layer can be a metal with strong stability such as Au (gold), and the thickness can be 10nm to 1μm, in order to protect the metal layer and prevent oxidation.

[0088] In this embodiment, the enlarged view of the metal layer, that is... Figure 3 A magnified view of region a in the middle is shown below. Figure 8As shown, in the direction away from the wafer to be bonded, the metal layer 2 includes an adhesion layer 2c, a barrier layer 2b, and an anti-oxidation wetting layer 2a.

[0089] Step S203: Strip the patterned photoresist to form the bonding metal region on the welding surface.

[0090] The patterned photoresist is stripped using a lift-off process, and the metal layer on the patterned photoresist is also stripped off, thus forming a bonding metal region.

[0091] It should be noted that when a raised first alignment mark is provided on the wafer to be bonded, the first alignment mark is fabricated together with the metal layer.

[0092] Step S204: Align the solder mask with the bonding surface of the wafer to be bonded, so that each through hole on the solder mask is aligned with the corresponding bonding metal area on the bonding surface.

[0093] Step S205: Place each pre-made solder sheet into each of the through holes, so that each pre-made solder sheet is aligned with the corresponding bonding metal area.

[0094] Step S206: Solder each of the pre-made solder sheets and the corresponding bonding metal regions, and remove the solder mask to obtain a wafer with solder.

[0095] Based on any of the above embodiments, in one embodiment of this application, aligning the solder mask with the bonding surface of the wafer to be bonded includes:

[0096] The solder mask is initially aligned with the bonding surface of the wafer to be bonded;

[0097] The alignment effect between the solder mask and the wafer to be bonded is observed using a camera.

[0098] If there is a misalignment between the solder mask and the wafer to be bonded, adjust the position of the solder mask and / or the wafer to be bonded until alignment is achieved.

[0099] It is understandable that if there is no misalignment between the solder mask and the wafer to be bonded, it indicates that the solder mask and the wafer to be bonded are already aligned, and there is no need to adjust the position of the solder mask and / or the wafer to be bonded.

[0100] During initial alignment, alignment can be performed using mechanical and optical alignment devices, and / or by using a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask.

[0101] The camera can be an infrared camera.

[0102] To further verify the alignment effect and improve the alignment accuracy, after the initial alignment, the alignment of the solder mask and the wafer to be bonded is checked again using a camera. If there is an alignment deviation, the position of the solder mask and / or the wafer to be bonded is adjusted, and then the camera is used to observe again until the solder mask and the wafer to be bonded are completely aligned.

[0103] In summary, the solder preparation method for wafer-level vacuum packaging in this application has the following advantages:

[0104] First, by aligning the solder mask with the bonding surface of the wafer to be bonded, the through holes of the solder mask are aligned with the bonding metal area. Then, the pre-made solder sheet is placed directly into the through hole to achieve alignment with the bonding metal area, which improves the alignment speed and accuracy between the pre-made solder sheet and the bonding metal area, reduces the process difficulty and manufacturing cost, and can reduce the investment in semiconductor equipment costs.

[0105] Second, this application uses pre-fabricated solder sheets in sheet shape to bond with the wafers to be bonded. The thickness of the pre-fabricated solder sheets can also be flexibly selected and is not limited by the solder mask. For example, the pre-fabricated solder sheets can be made thicker, thereby increasing the spacing between the two wafers and increasing the window height.

[0106] Third, the materials used for the prefabricated solder sheets in this application are diverse and can be selected flexibly.

[0107] This application also provides a wafer with solder, which is prepared using the method described in any of the above embodiments.

[0108] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0109] The solder preparation method and the solder-coated wafer in wafer-level vacuum packaging provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing solder in wafer-level vacuum packaging, characterized in that, include: Align the solder mask with the bonding surface of the wafer to be bonded, so that each through-hole on the solder mask is aligned with the corresponding bonding metal area on the bonding surface; Each pre-made solder sheet is placed in each of the through holes, so that each pre-made solder sheet is aligned with the corresponding bonding metal region; The pre-fabricated solder sheets and the corresponding bonding metal regions are soldered together, and the solder mask is removed to obtain a wafer with solder. The bonding metal region is ring-shaped; The pre-made solder sheet is used for vacuum sealing of two wafers; the pre-made solder sheet is a pre-made single-piece solder, and the thickness of the pre-made solder sheet is not limited by the thickness of the solder mask. Welding the preformed solder sheet and the bonding metal region includes: The preformed solder sheet is welded to the bonding metal region by laser welding or spot welding.

2. The method as described in claim 1, characterized in that, Aligning the solder mask with the bonding face of the wafer to be bonded includes: The solder mask is aligned with the bonding face of the wafer to be bonded using mechanical and optical alignment devices, and / or a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask; wherein the first alignment mark corresponds to the second alignment mark.

3. The method as described in claim 2, characterized in that, Of the first alignment mark and the second alignment mark, one is a raised mark and the other is a recessed mark.

4. The method as described in claim 1, characterized in that, Before aligning the solder mask with the bonding face of the wafer to be bonded, the process also includes: Fabricate a solder mask that matches the bonding metal region on the bonding surface of the wafer to be bonded.

5. The method as described in claim 1, characterized in that, Before aligning the solder mask with the bonding surface of the wafer to be bonded, the bonding metal region is formed on the bonding surface of the wafer to be bonded, specifically including: A patterned photoresist is formed on the bonding surface of the wafer to be bonded; A metal layer is deposited on the patterned photoresist; The patterned photoresist is stripped away to form the bonding metal region on the welding surface.

6. The method as described in claim 5, characterized in that, Depositing a metal layer on the patterned photoresist includes: An adhesion layer is deposited on the patterned photoresist; A barrier layer is deposited on the surface of the adhesive layer.

7. The method as described in claim 6, characterized in that, After depositing a barrier layer on the surface of the adhesive layer, the method further includes: An anti-oxidation wetting layer is deposited on the surface of the barrier layer.

8. The method according to any one of claims 1 to 7, characterized in that, Aligning the solder mask with the bonding face of the wafer to be bonded includes: The solder mask is initially aligned with the bonding surface of the wafer to be bonded; The alignment effect between the solder mask and the wafer to be bonded is observed using a camera. If there is a misalignment between the solder mask and the wafer to be bonded, adjust the position of the solder mask and / or the wafer to be bonded until alignment is achieved.

9. A wafer with solder, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

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