CN115838156A - Method for preparing solder in wafer-level vacuum packaging and wafer with solder - Google Patents

Abstract

The application relates to the field of wafer-level vacuum packaging, and discloses a method for preparing solder in wafer-level vacuum packaging, which comprises the following steps: aligning the solder mask plate with the welding surface of the wafer to be bonded, and respectively aligning the through holes on the solder mask plate with the bonding metal areas on the welding surface; placing the prefabricated solder piece in the through hole to align the prefabricated solder piece with the bonding metal area; and welding the prefabricated solder sheet and the bonding metal area, and removing the solder mask to obtain the wafer with the solder. The prefabricated solder pieces are aligned with the bonding metal area of the wafer to be bonded through the solder mask, namely, the prefabricated solder pieces can be aligned through the solder mask at one time, the process difficulty is reduced, the manufacturing speed is increased, and the manufacturing cost is reduced. Moreover, the alignment of the prefabricated solder sheet single piece is not needed by optical alignment, the alignment precision is improved, the qualification rate of the wafer with the solder is improved, and the manufacturing cost can be reduced.

Description

Method for preparing solder in wafer-level vacuum packaging and wafer with solder

Technical Field

The present disclosure relates to the field of wafer-level vacuum packaging, and more particularly, to a method for preparing solder in wafer-level vacuum packaging and a wafer with solder.

Background

The wafer level chip vacuum package has the characteristics of realizing miniaturization, integration and low cost of devices, and is widely applied to the field of Micro-Electro-Mechanical systems (MEMS) devices such as gyroscopes, pressure sensors, microbolometers and the like.

Solder bonding is a bonding technology in the wafer-level vacuum packaging process, and has the characteristics of low process temperature, high strength and small influence of surface roughness. Currently, a pre-fabricated solder sheet can be soldered to a wafer, and the pre-fabricated solder sheet can be aligned to a metalized area on the wafer by an optical alignment technique, followed by soldering. Firstly, only one prefabricated solder sheet can be aligned at a time, then welding is carried out until all the prefabricated solder sheets are aligned and welded, the material swinging process is complex in operation and low in efficiency, and further the manufacturing cost is high; secondly, the optical alignment precision is difficult to meet the requirement of vacuum packaging of the wafer-level chip, and the prefabricated solder sheet is easy to misplace, which can lead to product scrapping in serious cases; third, the optical alignment equipment is expensive, making manufacturing cost high.

Therefore, how to solve the above technical problems should be a great concern to those skilled in the art.

Disclosure of Invention

The purpose of the application is to provide a solder preparation method in the circular vacuum packaging and a wafer with solder, so as to improve the solder manufacturing efficiency and the alignment precision and reduce the manufacturing cost.

In order to solve the above technical problem, the present application provides a method for preparing solder in wafer-level vacuum package, including:

aligning a solder mask plate with a welding surface of a wafer to be bonded, and aligning each through hole on the solder mask plate with a corresponding bonding metal area on the welding surface respectively;

respectively placing each prefabricated solder sheet into each through hole, and aligning each prefabricated solder sheet with the corresponding bonding metal area;

and welding each prefabricated solder sheet and the corresponding bonding metal area, and removing the solder mask to obtain the wafer with the solder.

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

aligning the solder mask plate with the welding surface of the wafer to be bonded through a mechanical and optical aligner and/or a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask plate; wherein the first alignment mark corresponds to the second alignment mark.

Optionally, one of the first alignment mark and the second alignment mark is a protrusion type mark, and the other is a groove type mark.

Optionally, the soldering the pre-fabricated solder sheet and the bonding metal region includes:

and welding the prefabricated welding flux sheet and the bonding metal area through laser welding or spot welding.

Optionally, before aligning the solder mask with the bonding surface of the wafer to be bonded, the method further includes:

and manufacturing the solder mask matched with the bonding metal area on the welding surface of the wafer to be bonded.

Optionally, before aligning the solder mask with the bonding surface of the wafer to be bonded, forming the bonding metal region on the bonding surface of the wafer to be bonded, specifically including:

forming a patterned photoresist on the welding surface of the wafer to be bonded;

depositing a metal layer on the patterned photoresist;

and stripping the patterned photoresist to form the bonding metal area on the welding surface.

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

depositing an adhesion layer on the patterned photoresist;

and depositing a barrier layer on the surface of the adhesion layer.

Optionally, after depositing the barrier layer on the surface of the adhesion layer, the method further includes:

and depositing an anti-oxidation wetting layer on the surface of the barrier layer.

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

carrying out primary alignment on the welding mask and the welding surface of the wafer to be bonded;

observing the alignment effect of the solder mask and the wafer to be bonded through a camera;

and if the welding flux mask and the wafer to be bonded are staggered, adjusting the positions of the welding flux mask and/or the wafer to be bonded until alignment is realized.

The application also provides a wafer with solder, and the wafer is prepared by adopting any one of the methods.

The application provides a method for preparing solder in wafer-level vacuum packaging, which comprises the following steps: aligning a solder mask plate with a welding surface of a wafer to be bonded, and aligning each through hole on the solder mask plate with a corresponding bonding metal area on the welding surface respectively; respectively placing each prefabricated solder piece into each through hole to enable each prefabricated solder piece to be aligned with the corresponding bonding metal area; welding each prefabricated solder sheet and the corresponding bonding metal area, and removing the solder mask to obtain the wafer with the solder

Therefore, when the solder is manufactured on the wafer, the solder mask is aligned with the welding surface of the wafer to be bonded, so that each through hole of the solder mask is aligned with the corresponding bonding metal area, and then the prefabricated solder piece is directly placed in the through hole to be aligned with the bonding metal area and then is welded. Namely, the plurality of prefabricated solder pieces can be aligned at one time through the solder mask, the process difficulty is reduced, the manufacturing speed is increased, and the manufacturing cost is reduced. Moreover, alignment of the single solder sheet is not needed, so that the alignment precision is improved, the qualification rate of the wafer with the solder is improved, and the manufacturing cost can be reduced.

In addition, the application also provides a wafer with the solder, which has the advantages.

Drawings

For a clearer explanation of the embodiments or technical solutions of the prior art of the present application, the drawings needed for the description of the embodiments or prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a flowchart of a solder preparation method in a wafer level vacuum package according to an embodiment of the present disclosure;

FIG. 2 is a schematic view of a solder mask provided in an embodiment of the present disclosure;

fig. 3 is a schematic view of a wafer to be bonded according to an embodiment of the present disclosure;

fig. 4 is a schematic view of a prefabricated solder sheet provided in accordance with an embodiment of the present application;

fig. 5 is an exploded view of a pre-fabricated solder sheet, a solder mask and a wafer to be bonded according to an embodiment of the present application;

FIG. 6 is a schematic view of a solder joint on a pre-fabricated solder wafer according to an embodiment of the present application;

FIG. 7 is a flow chart of another method for preparing solder in a wafer level vacuum package according to an embodiment of the present disclosure;

FIG. 8 is an enlarged view of a metal layer according to an embodiment of the present disclosure;

in the figure, 1, a wafer to be bonded, 2, a bonding metal area, 3, a first alignment mark, 4, a solder mask, 5, a second alignment mark, 6, a prefabricated solder sheet, 7, a welding point, 8, a through hole, 2a, an anti-oxidation wetting layer, 2b, a barrier layer, 2c and an adhesion layer.

Detailed Description

In order that those skilled in the art will better understand the disclosure, the following detailed description will be given with reference to the accompanying drawings. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced otherwise than as specifically described herein, and it will be appreciated by those skilled in the art that the present invention may be practiced without departing from the spirit and scope of the present invention and that the present invention is not limited by the specific embodiments disclosed below.

As described in the background section, when soldering is performed on a wafer by using solder pads, only one solder pad can be aligned at a time and then soldered, which has the disadvantages of low manufacturing efficiency and high cost.

In view of the above, the present application provides a method for preparing solder in wafer level vacuum package, please refer to fig. 1, which includes:

step S101: aligning a solder mask plate with a welding surface of a wafer to be bonded, and aligning each through hole on the solder mask plate with a corresponding bonding metal area on the welding surface respectively.

Fig. 2 shows a schematic diagram of a solder mask, in which a plurality of through holes 8 are formed in the solder mask 4, and the distribution manner of the through holes 8 is the same as that of the bonding metal regions on the bonding surface of the wafer to be bonded, that is, the through holes 8 in the solder mask 4 correspond to the bonding metal regions on the wafer to be bonded one by one.

The material of the solder mask can be quartz or metal, and the application is not limited.

Optionally, before aligning the solder mask with the bonding surface of the wafer to be bonded, the method further includes:

and manufacturing the solder mask matched with the bonding metal area on the welding surface of the wafer to be bonded.

The manufacturing method of the solder mask can be etching and the like, and is not particularly limited in the application.

Fig. 3 shows a schematic diagram of a wafer to be bonded, bonding metal regions 2 distributed in an array are distributed on a welding surface of the wafer 1 to be bonded, and the bonding metal regions 2 are annular. The shape of the bond metal region 2 includes, but is not limited to, a square ring, a circular ring, shown as a square ring in fig. 3.

Step S102: and respectively placing each prefabricated solder sheet in each through hole to enable each prefabricated solder sheet to be aligned with the corresponding bonding metal area.

Since the through-holes are aligned with the bond metal regions, placing the pre-formed solder sheet in the through-holes achieves alignment with the bond metal regions.

It should be noted that the manner in which the pre-fabricated solder sheet is placed within the through-hole is not limited in this application, as the case may be. For example, the pre-formed solder sheets can be placed in the through holes by automated feeding equipment or manually by hand.

The function of the pre-formed solder sheet is to vacuum seal the two wafers.

The prefabricated solder sheet can be made of AuSn solder, such as Au80Sn20, au10Sn90 and the like; in-based solders such as In97Ag3, in52Sn48, and the like; SAC-based solders such as sn96.5ag3.0cu0.5, sn95.5ag3.8cu0.7, and the like; snAg series solder, etc., the prepared solder sheet has better material component selectivity and abundant material types.

The prefabricated solder sheet is formed by melting alloy, has low requirement on the complexity of target components, has more component selectivity, and does not need soldering flux, while the solder in some related technologies is formed by printing solder paste, is limited by the components of the solder paste, and needs the soldering flux. And, the thickness and the size of prefabricated solder piece are nimble controllable in this application.

The pre-fabricated solder sheet 6 is a single piece of solder that has been fabricated in advance, as shown in fig. 4. It should be emphasized that the alignment is performed through the solder mask in the present application, but the thickness of the solder mask has no limitation on the thickness of the prefabricated solder sheet, and the thickness of the prefabricated solder sheet in the present application can be flexibly selected according to the requirement during the manufacturing. Therefore, the material and the thickness of prefabricated solder piece all can select in a flexible way in this application, for example prefabricated solder piece can make thickly to increase the interval between two wafers, promote the window height.

After placing the prefabricated solder pieces in the through holes of the solder mask, the explosion diagram of the prefabricated solder pieces 6, the solder mask 4 and the wafer 1 to be bonded is shown in fig. 5.

Step S103: and welding each prefabricated solder sheet and the corresponding bonding metal area, and removing the solder mask to obtain the wafer with the solder.

Optionally, as an embodiment, the soldering the pre-fabricated solder sheet and the bonding metal region includes: and welding the prefabricated solder sheet and the bonding metal area through laser welding. However, the present application is not limited thereto, and as another possible embodiment, the soldering the pre-solder sheet and the bonding metal region includes: and welding the prefabricated solder sheet and the bonding metal area through spot welding.

For example, when the metal area 2 to be bonded and the preformed solder sheet 6 are in the form of square loops, soldering can be performed on each of the four sides of the preformed solder sheet 6 along the center line of the width, and the solder joints 7 on the preformed solder sheet 6 are schematically shown in fig. 6, where the number of solder joints 7 depends on the size of the preformed solder sheet. When the metal area to be bonded and the prefabricated solder sheet are in a circular ring shape, the prefabricated solder sheet can be welded at equal intervals or welded at unequal intervals along the central line of the width, and the number of the welding points is determined according to the size of the prefabricated solder sheet.

When the solder is manufactured on the wafer, the solder mask is aligned with the welding surface of the wafer to be bonded, so that each through hole of the solder mask is aligned with the corresponding bonding metal area, then the prefabricated solder piece is directly placed in the through hole to be aligned with the bonding metal area, and then welding is carried out. Namely, the plurality of prefabricated solder pieces can be aligned at one time through the solder mask, the process difficulty is reduced, the manufacturing speed is increased, and the manufacturing cost is reduced. Moreover, the alignment of the prefabricated solder sheet single piece is not needed by optical alignment, the optical alignment is not needed, the qualification rate of the wafer with the solder is improved, and the manufacturing cost can be reduced.

On the basis of the above embodiments, in one embodiment of the present application, aligning the solder mask with the bonding surface of the wafer to be bonded includes:

aligning the solder mask plate with the welding surface of the wafer to be bonded through a mechanical and optical aligner and/or a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask plate; wherein the first alignment mark corresponds to the second alignment mark.

The first method is to align the solder mask plate with the welding surface of the wafer to be bonded by a mechanical aligner and an optical aligner; secondly, aligning the solder mask plate with the welding surface of the wafer to be bonded through the first alignment mark on the wafer to be bonded and the second alignment mark on the solder mask plate; thirdly, the solder mask is aligned with the welding surface of the wafer to be bonded through a mechanical and optical aligner and the first alignment mark on the wafer to be bonded and the second alignment mark on the solder mask.

The shape of the first alignment mark and the second alignment mark includes, but is not limited to, a cross, a field, a star.

As shown in fig. 3, the first alignment mark 3 may be disposed at the edge of the wafer 1 to be bonded, or may be disposed at any position of the center, and the number of the first alignment marks 3 may be set by itself. Accordingly, when the first alignment marks 3 are disposed at the edge of the wafer 1 to be bonded, as shown in fig. 2, the second alignment marks 5 are also correspondingly disposed at the edge of the solder mask 4, and the number of the second alignment marks is equal to that of the first alignment marks 3.

In order to facilitate alignment by the first and second alignment marks, one of the first and second alignment marks is a protrusion-type mark, and the other is a groove-type mark. Namely, the first alignment mark is a convex mark, and the second alignment mark is a concave mark; alternatively, the first alignment mark is a groove-type mark, and the second alignment mark is a protrusion-type mark.

On the basis of any of the above embodiments, in an embodiment of the present application, referring to fig. 7, a method for preparing solder in a wafer-level vacuum package includes:

step S201: and forming a patterned photoresist on the welding surface of the wafer to be bonded.

And coating photoresist on the welding surface of the wafer to be bonded, and carrying out exposure and development to complete the patterning of the photoresist.

Step S202: and depositing a metal layer on the patterned photoresist.

The deposition method of the metal layer may be a physical vapor deposition method such as a magnetron sputtering method or a thermal evaporation method (i.e., the following S2021, S2022, and S2023, each step may be implemented by a magnetron sputtering method or a thermal evaporation process), and the application is not limited specifically.

Optionally, as an implementation manner, the depositing a metal layer on the patterned photoresist includes:

step S2021: depositing an adhesion layer on the patterned photoresist;

step S2022: and depositing a barrier layer on the surface of the adhesion layer.

The thermal expansion coefficient of the adhesion layer is similar to that of the wafer to be bonded, the material of the adhesion layer can be Cr (chromium), ti (titanium), V (vanadium) and other metals, and the thickness can be 10 nm-1 μm.

The material of the barrier layer may be Ni (nickel), and the thickness may be 50nm to 1 μm.

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

step S2021: depositing an adhesion layer on the patterned photoresist;

step S2022: and depositing a barrier layer on the surface of the adhesion layer.

Step S2023: and depositing an anti-oxidation wetting layer on the surface of the barrier layer.

The material of the anti-oxidation wetting layer can be metal with strong stability such as Au (gold), and the thickness can be 10 nm-1 μm, so as to protect the metal layer and avoid oxidation.

In the present embodiment, an enlarged view of the metal layer, that is, a partial enlarged view of a region a in fig. 3 is shown in fig. 8, and the metal layer 2 includes an adhesion layer 2c, a barrier layer 2b, and an oxidation-preventing wetting layer 2a in a direction away from the wafer to be bonded.

Step S203: and stripping the patterned photoresist to form the bonding metal area on the welding surface.

And stripping the patterned photoresist by a Lift-off process, and stripping the metal layer on the patterned photoresist together to form a bonding metal region.

It should be noted that, when the wafer to be bonded is further provided with the raised first alignment mark, the first alignment mark is manufactured together with the metal layer.

Step S204: aligning a solder mask plate with a welding surface of a wafer to be bonded, and aligning each through hole on the solder mask plate with a corresponding bonding metal area on the welding surface respectively.

Step S205: and respectively placing each prefabricated solder sheet in each through hole to enable each prefabricated solder sheet to be aligned with the corresponding bonding metal area.

Step S206: and welding each prefabricated solder sheet and the corresponding bonding metal area, and removing the solder mask to obtain the wafer with the solder.

On the basis of any one of the above embodiments, in an embodiment of the present application, aligning the solder mask with the bonding surface of the wafer to be bonded includes:

carrying out primary alignment on the welding mask and the welding surface of the wafer to be bonded;

observing the alignment effect of the solder mask and the wafer to be bonded through a camera;

and if the welding flux mask and the wafer to be bonded are staggered, adjusting the positions of the welding flux mask and/or the wafer to be bonded until alignment is realized.

It can be understood that when 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 aligned, and there is no need to adjust the positions of the solder mask and/or the wafer to be bonded.

The alignment may be performed by mechanical and optical aligners, and/or by a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask during the first alignment.

The camera may be an infrared camera.

In order to further check the alignment effect and improve the alignment precision, the alignment condition of the solder mask and the wafer to be bonded is checked by using the camera after the primary alignment, when the alignment deviation exists, the positions of the solder mask and/or the wafer to be bonded are adjusted, and then the camera is used again for observation until the solder mask and the wafer to be bonded are completely aligned.

In summary, the solder preparation method in the wafer level vacuum package in the present application has the following advantages:

firstly, aligning a solder mask with a welding surface of a wafer to be bonded to align a through hole of the solder mask with a bonding metal area, and then directly placing a prefabricated solder sheet in the through hole to align with the bonding metal area, so that the alignment speed and the alignment precision of the prefabricated solder sheet and the bonding metal area are improved, the process difficulty and the manufacturing cost are reduced, and the investment of the cost of semiconductor equipment can be reduced;

secondly, the prefabricated welding flux sheet which is prefabricated into a sheet shape is welded with the wafer to be bonded, the thickness of the prefabricated welding flux sheet can be flexibly selected and is not limited by a welding flux mask; for example, the prefabricated solder sheet can be made thicker, so that the distance between two wafers is increased, and the height of the window is increased;

thirdly, the prefabricated solder piece of this application's material is abundant in kind, can select in a flexible way.

The application further provides a wafer with solder, and the wafer is manufactured by the method of any one of the above embodiments.

The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same or similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The method for preparing the solder in the wafer-level vacuum package and the wafer with the solder provided by the application are described in detail above. The principles and embodiments of the present application are explained herein using specific examples, which are provided only to help understand the method and the core idea of the present application. It should be noted that, for those skilled in the art, it is possible to make several improvements and modifications to the present application without departing from the principle of the present application, and such improvements and modifications also fall within the scope of the claims of the present application.

Claims (10)

1. A method for preparing solder in wafer-level vacuum packaging is characterized by comprising the following steps:

aligning a solder mask plate with a welding surface of a wafer to be bonded, and aligning each through hole on the solder mask plate with a corresponding bonding metal area on the welding surface respectively;

respectively placing each prefabricated solder piece into each through hole to enable each prefabricated solder piece to be aligned with the corresponding bonding metal area;

and welding each prefabricated solder sheet and the corresponding bonding metal area, and removing the solder mask to obtain the wafer with the solder.

2. The method of claim 1, wherein aligning the solder mask to the bonding side of the wafers to be bonded comprises:

aligning the solder mask plate with the welding surface of the wafer to be bonded through a mechanical aligner and an optical aligner and/or a first alignment mark on the wafer to be bonded and a second alignment mark on the solder mask plate; wherein the first alignment mark corresponds to the second alignment mark.

3. The method of claim 2, wherein one of the first alignment mark and the second alignment mark is a protrusion-type mark and the other is a groove-type mark.

4. The method of claim 1, wherein soldering the pre-formed solder sheet and the bonding metal region comprises:

and welding the prefabricated welding flux sheet and the bonding metal area through laser welding or spot welding.

5. The method of claim 1, wherein prior to aligning the solder mask with the bonding surface of the wafer to be bonded, further comprising:

and manufacturing the solder mask matched with the bonding metal area on the welding surface of the wafer to be bonded.

6. The method of claim 1, wherein forming the bonding metal region on the bonding surface of the wafer to be bonded before aligning the solder mask with the bonding surface of the wafer to be bonded comprises:

forming a patterned photoresist on the welding surface of the wafer to be bonded;

depositing a metal layer on the patterned photoresist;

and stripping the patterned photoresist to form the bonding metal area on the welding surface.

7. The method of claim 6, wherein depositing a metal layer on the patterned photoresist comprises:

depositing an adhesion layer on the patterned photoresist;

and depositing a barrier layer on the surface of the adhesion layer.

8. The method of claim 7, wherein after depositing the barrier layer on the adhesion layer surface, further comprising:

and depositing an oxidation-resistant wetting layer on the surface of the barrier layer.

9. The method of any of claims 1 to 8, wherein aligning the solder mask with the bonding surface of the wafer to be bonded comprises:

carrying out primary alignment on the welding mask and the welding surface of the wafer to be bonded;

observing the alignment effect of the solder mask and the wafer to be bonded through a camera;

and if the welding flux mask and the wafer to be bonded are staggered, adjusting the positions of the welding flux mask and/or the wafer to be bonded until alignment is realized.

10. A wafer with solder, characterized in that it is manufactured by a method according to any one of claims 1 to 9.

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