阅读说明：本技术 铟柱焊点的制备方法、芯片衬底及芯片 (Indium column welding spot preparation method, chip substrate and chip ) 是由 张文龙 杨楚宏 郑亚锐 张胜誉 于 2020-07-01 设计创作，主要内容包括：本申请公开了一种铟柱焊点的制备方法、芯片衬底及芯片。所述方法包括：在衬底上涂敷第一光刻胶层,进行第一烘烤；在第一光刻胶层上涂敷第二光刻胶层,进行第二烘烤；对第二光刻胶层进行欠曝光,进行第三烘烤；对经欠曝光和第三烘烤后的第二光刻胶层进行显影和定影,以在第二光刻胶层上形成底切结构,该衬底带有光刻胶结构；对带有光刻胶结构的衬底进行泛曝光,进行第四烘烤；在经泛曝光和第四烘烤之后,刻蚀第一光刻胶层形成图形限制层；在图形限制层的定义图形位置处沉积铟材料形成铟柱焊点；将第一光刻胶层和第二光刻胶层从衬底上剥离,得到带有铟柱焊点的衬底。本申请能够避免铟柱底部产生侧向扩散的问题,保护衬底其他位置不受影响。(The application discloses a preparation method of an indium column welding spot, a chip substrate and a chip. The method comprises the following steps: coating a first photoresist layer on a substrate, and carrying out first baking; coating a second photoresist layer on the first photoresist layer, and carrying out second baking; underexposure is carried out on the second photoresist layer, and third baking is carried out; developing and fixing the underexposed and third baked second photoresist layer to form an undercut structure on the second photoresist layer, the substrate having a photoresist structure; carrying out flood exposure on the substrate with the photoresist structure, and carrying out fourth baking; after flood exposure and fourth baking, etching the first photoresist layer to form a pattern limiting layer; depositing an indium material at the defined pattern position of the pattern limiting layer to form an indium column welding spot; and stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the indium stud welding points. The problem that the bottom of the indium column generates lateral diffusion can be avoided, and other positions of the protective substrate are not affected.)

1. A method for preparing an indium stud solder joint, the method comprising:

coating a first photoresist layer on a substrate, and then carrying out first baking;

coating a second photoresist layer on the first photoresist layer, and then carrying out second baking;

performing third baking after underexposure on the second photoresist layer;

developing and fixing the second photoresist layer after the underexposure and the third baking to form an undercut structure on the second photoresist layer, wherein the substrate is provided with a photoresist structure; wherein the photoresist structure comprises the first photoresist layer and a second photoresist layer with the undercut structure;

carrying out flood exposure on the substrate with the photoresist structure, and then carrying out fourth baking;

after the flood exposure and the fourth baking, etching the first photoresist layer to form a pattern limiting layer;

depositing an indium material at the defined pattern position of the pattern limiting layer to form an indium column welding spot;

and stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the indium column welding points.

2. The method of claim 1, wherein the underexposed exposure time is less than an exposure time for which the second photoresist layer is fully exposed.

3. The method of claim 1 wherein the developing time t1 for the second photoresist layer is greater than the developing time t2 for the second photoresist layer under full exposure conditions.

4. The method of claim 3, wherein t1 is t2+15 seconds.

5. The method of claim 1, wherein the developer used to develop the second photoresist layer does not react with the first photoresist layer.

6. The method of claim 1, wherein depositing indium material at the defined pattern locations of the pattern-limiting layer to form indium stud bumps comprises:

and depositing an indium material on the second photoresist layer with the undercut structure and the exposed substrate by adopting an evaporation method, and forming the indium stud welding point at the position of the defined pattern of the pattern limiting layer.

7. The method of claim 1 wherein said stripping said first photoresist layer and said second photoresist layer from said substrate to provide a substrate with said indium stud bumps comprises:

and placing the substrate deposited with the indium stud welding points in glue stripping liquid, and stripping the first photoresist layer and the second photoresist layer from the substrate at the temperature of 20-80 ℃ to obtain the substrate with the indium stud welding points.

8. The method of claim 1, wherein the etching comprises at least one of: physical etching and chemical etching.

9. The method of claim 1, wherein the first photoresist layer is a single layer of glue or the first photoresist layer comprises multiple layers of glue.

10. The method of claim 1, wherein the second photoresist is an inverse or negative photoresist.

11. The method of claim 1,

the first baking is the soft baking temperature of the first photoresist layer;

the second baking is the soft baking temperature of the second photoresist layer;

the third baking is the pre-baking temperature of the second photoresist layer;

and the fourth baking comprises baking at the pre-baking temperature and the hardening temperature of the second photoresist layer in sequence.

12. A chip substrate having indium stud bumps thereon, said indium stud bumps being prepared by a method according to any one of claims 1 to 11.

13. A die having indium stud bumps on a substrate, said indium stud bumps being prepared by a method according to any one of claims 1 to 11.

14. The chip of claim 13, wherein the chip is a quantum chip.

15. A method of preparing a solder joint, the method comprising:

coating a first photoresist layer on a substrate;

coating a second photoresist layer on the first photoresist layer;

underexposing the second photoresist layer;

developing and fixing the second photoresist layer after the underexposure to form an undercut structure on the second photoresist layer, wherein the substrate is provided with a photoresist structure; wherein the photoresist structure comprises the first photoresist layer and a second photoresist layer with the undercut structure;

performing flood exposure on the substrate with the photoresist structure;

after the flood exposure, etching the first photoresist layer to form a pattern limiting layer;

depositing materials at the defined pattern positions of the pattern limiting layer to form welding spots;

and stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the welding spots.

Technical Field

The embodiment of the application relates to the technical field of quantum technology and micro-nano processing, in particular to a preparation method of an indium column welding spot, a chip substrate and a chip.

Background

The indium column welding spot refers to column indium metal deposited on a specific position of a substrate sample by using an evaporation coating mode and the like, and is used as a welding spot.

The traditional process for preparing the indium column welding spot is mainly based on a stripping process of single-layer glue, a single photoresist is used, an indium column graph is defined through one-time exposure and development, then metal indium is deposited and stripped, the scheme generally requires that the thickness of a glue layer at least reaches three times of the height of the indium column, and because the glue side wall of a graph area can be directly contacted with the deposited indium, the indium on the side wall and the deposited indium are mutually adhered, the stripping is difficult, and the appearance of the indium column welding spot is poor.

Later researchers developed improved processes that were mainly based on the lift-off process of making undercut structures by bonding multiple glues, mainly two glues, such as a combination of positive and negative glues. The improved process has a bottom cutting structure, so that the deposited indium, the side wall of the glue and the indium on the top of the glue are prevented from being contacted and adhered with each other, and the problems of difficult stripping and poor appearance existing in the traditional process are solved to a certain extent.

However, due to the existence of the undercut structure, the bottom of the indium column can diffuse to the area of the undercut structure in the indium plating process, and the lateral diffusion can cause the position of the substrate where indium should not be originally deposited to deposit a thin layer of indium, thereby affecting the structures or devices at other positions of the substrate.

Disclosure of Invention

The embodiment of the application provides a preparation method of an indium column welding spot, a chip substrate and a chip, which can avoid the problem of lateral diffusion generated at the bottom of an indium column. The technical scheme is as follows:

according to an aspect of an embodiment of the present application, there is provided a method for preparing an indium stud solder, the method including:

coating a first photoresist layer on a substrate, and then carrying out first baking;

coating a second photoresist layer on the first photoresist layer, and then carrying out second baking;

performing third baking after underexposure on the second photoresist layer;

developing and fixing the second photoresist layer after the underexposure and the third baking to form an undercut structure on the second photoresist layer, wherein the substrate is provided with a photoresist structure; wherein the photoresist structure comprises the first photoresist layer and a second photoresist layer with the undercut structure;

carrying out flood exposure on the substrate with the photoresist structure, and then carrying out fourth baking;

after the flood exposure and the fourth baking, etching the first photoresist layer to form a pattern limiting layer;

depositing an indium material at the defined pattern position of the pattern limiting layer to form an indium column welding spot;

and stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the indium column welding points.

According to one aspect of the embodiment of the application, a chip substrate is provided, wherein the chip substrate is provided with indium stud welding points, and the indium stud welding points are prepared by adopting the method.

According to one aspect of the embodiment of the application, the chip is provided with the indium stud welding points on the substrate, and the indium stud welding points are prepared by adopting the method.

According to an aspect of an embodiment of the present application, there is provided a solder joint preparation method, including:

coating a first photoresist layer on a substrate;

coating a second photoresist layer on the first photoresist layer;

underexposing the second photoresist layer;

developing and fixing the second photoresist layer after the underexposure to form an undercut structure on the second photoresist layer, wherein the substrate is provided with a photoresist structure; wherein the photoresist structure comprises the first photoresist layer and a second photoresist layer with the undercut structure;

performing flood exposure on the substrate with the photoresist structure;

after the flood exposure, etching the first photoresist layer to form a pattern limiting layer;

depositing materials at the defined pattern positions of the pattern limiting layer to form welding spots;

and stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the welding spots.

According to an aspect of the embodiments of the present application, there is provided a chip substrate, where the chip substrate has solder joints, and the solder joints are prepared by the above method.

According to an aspect of the embodiments of the present application, there is provided a chip, on a substrate of which a solder joint is provided, the solder joint being prepared by the above method.

The technical scheme provided by the embodiment of the application can bring the following beneficial effects:

coating a first photoresist layer on a substrate to serve as a protective adhesive layer, then coating a second photoresist layer on the first photoresist layer, forming an undercut structure on the second photoresist layer by carrying out underexposure, development and fixation treatment on the second photoresist layer, then etching the first photoresist layer to form a pattern limiting layer, and depositing indium column welding spots at the pattern defining positions of the pattern limiting layer; according to the preparation method of the indium column welding spot, on one hand, due to the fact that the undercut structure exists on the second photoresist layer, the indium material on the substrate cannot be in contact adhesion with the indium material on the second photoresist layer and the side wall of the second photoresist layer in the indium plating process due to the undercut structure, and the problems of difficult stripping and poor appearance in the traditional process are solved; on the other hand, the first photoresist layer is etched to form the pattern limiting layer, and the pattern limiting layer can effectively limit bottom lateral diffusion of the indium material deposited on the substrate, so that structures or devices at other positions of the substrate are protected from being influenced.

In addition, the pattern limiting layer can enable the size of the indium columns formed by deposition to be consistent with the size of the defined pattern, and the preparation quality of the indium column welding spots is effectively improved. Therefore, the technical scheme provided by the embodiment of the application can be suitable for preparing the indium column welding spots with different heights and excellent appearance.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a flow chart of a method for fabricating an indium stud solder joint according to one embodiment of the present application;

FIG. 2 shows a side view and a top view of an indium stud bump made using the improved process mentioned in the background;

FIG. 3 shows a side view and a top view of an indium stud solder joint made using the teachings of the present application;

FIG. 4 is a schematic flow chart of a method for fabricating an indium stud solder joint according to an embodiment of the present disclosure;

FIG. 5 is a flowchart of a method for manufacturing solder joints according to an embodiment of the present application.

Detailed Description

To make the objects, technical solutions and advantages of the present application more clear, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

Cloud technology (cloud technology) refers to a hosting technology for unifying series of resources such as hardware, software, network and the like in a wide area network or a local area network to realize calculation, storage, processing and sharing of data.

The cloud technology is a general term of network technology, information technology, integration technology, management platform technology, application technology and the like applied based on a cloud computing business model, can form a resource pool, is used as required, and is flexible and convenient. Cloud computing technology will become an important support. Background services of the technical network system require a large amount of computing and storage resources, such as video websites, picture-like websites and more web portals. With the high development and application of the internet industry, each article may have its own identification mark and needs to be transmitted to a background system for logic processing, data in different levels are processed separately, and various industrial data need strong system background support and can be realized through cloud computing.

Cloud technology relates to basic technologies such as cloud computing, cloud storage, databases and big data, and cloud applications provided based on the cloud technology include medical cloud, cloud internet of things, cloud security, cloud calling, private cloud, public cloud, hybrid cloud, cloud games, cloud education, cloud conference, cloud social contact, artificial intelligent cloud service and the like. With the development of cloud technology and the application of cloud technology in different fields, more and more cloud applications will appear.

Generally, a system constructed based on cloud technology includes a server and a terminal. The server may be an independent physical server, a server cluster or a distributed system formed by a plurality of physical servers, or a cloud server providing basic cloud computing services such as a cloud service, a cloud database, cloud computing, a cloud function, cloud storage, a Network service, cloud communication, a middleware service, a domain name service, a security service, a CDN (Content Delivery Network), a big data and artificial intelligence platform. The terminal may be, but is not limited to, a smart phone, a tablet computer, a laptop computer, a desktop computer, a smart speaker, a smart watch, and the like. The terminal and the server may be directly or indirectly connected through wired or wireless communication, and the application is not limited herein.

Quantum computers (quantum computers) are a class of physical devices that perform high-speed mathematical and logical operations, store, and process quantum information following quantum mechanics laws. When a device processes and calculates quantum information and runs quantum algorithms, the device is a quantum computer. The quantum computer is characterized by high running speed, strong information processing capability, wide application range and the like. Compared with a classical computer, the more information processing amount is, the more beneficial the quantum computer to implement operation is, and the more accurate the operation can be ensured.

Quantum chips are the core components of quantum computers. The quantum chip integrates quantum circuits on a substrate, and further bears the function of quantum information processing. In view of the development process of the conventional computer, the research on the quantum computer needs to be integrated to realize commercialization and industrial upgrading after overcoming the bottleneck technology. Superconducting systems, semiconductor quantum dot systems, micro-nano photonics systems, and even atomic and ionic systems, all want to go the path of chipization. From the development point of view, superconducting quantum chip systems are technically moved in front of other physical systems; the traditional semiconductor quantum dot system is also an object of research, because after all, the traditional semiconductor industry has developed well, for example, once a semiconductor quantum chip breaks through a threshold value of fault-tolerant quantum computation in the phase-coherent time and the control precision, the traditional semiconductor quantum dot system is expected to integrate the existing achievement of the traditional semiconductor industry, and the development cost is saved.

In view of the advantages of quantum computers, quantum computers may be used for some processing and computation in future systems built based on cloud technology to provide better services.

The embodiment of the application provides a preparation method of an indium column welding spot, a chip substrate and a chip. In the following, the technical solution of the present application will be described by several embodiments.

Referring to fig. 1, a flow chart of a method for fabricating an indium stud solder joint according to an embodiment of the present application is shown, where the method includes the following steps (101-108):

step 101: after a first photoresist layer is coated on a substrate, a first baking is performed.

The substrate is a base material for preparing indium stud welding spots, and can be a substrate of a chip for mounting components of the chip.

And coating a first photoresist on the cleaned substrate to form a first photoresist layer, wherein the first photoresist layer is used as a protective adhesive layer and plays a role in protecting the substrate. In the embodiment of the present application, the method of applying the first photoresist is not limited, and for example, a spin coating method may be used. The developing solution used in the developing process of the photoresist is mainly divided into organic solution and alkaline solution, the organic solution and the alkaline solution can possibly react with the substrate, and the developing solution can be prevented from corroding the substrate by adding a protective glue layer between the substrate and the photoresist.

Optionally, the first photoresist layer is a single layer of photoresist, or the first photoresist layer includes multiple layers of photoresist. In the case of multiple layers of glue, the layers of glue are in a stacked configuration over the substrate. In addition, whether a single layer of glue or multiple layers of glue, each layer of glue should be as uniform and flat as possible.

After a first photoresist layer is coated on a substrate, a first baking is performed on the first photoresist layer. Optionally, the first baking is a soft baking temperature of the first photoresist layer. The soft-baking temperature refers to the temperature used for soft-baking. The soft baking is to evaporate the solvent of the photoresist layer to improve the adhesion, light absorption and corrosion resistance between the photoresist layer and the substrate.

Step 102, after coating a second photoresist layer on the first photoresist layer, performing a second baking.

And coating a second photoresist on the first photoresist layer subjected to the first baking to form a second photoresist layer. In the embodiment of the present application, the manner of applying the second photoresist is also not limited, and for example, a spin coating manner may be adopted.

Optionally, the second photoresist layer is a single layer of photoresist, or the second photoresist layer includes multiple layers of photoresist. In the case of a multi-layer resist, the multi-layer resist is in a stacked configuration over the first photoresist layer. In addition, whether a single layer of glue or multiple layers of glue, each layer of glue should be as uniform and flat as possible.

After coating a second photoresist layer on the first photoresist layer, a second baking is performed on the second photoresist layer. Optionally, the second bake is a soft bake temperature of the second photoresist layer.

Optionally, the second photoresist is an inverse or negative photoresist.

The photoresist includes various types such as positive photoresist, negative photoresist, pattern reversal photoresist, and the like. The positive photoresist is insoluble to a developing solution before exposure and becomes soluble after exposure, and can obtain the same pattern as a shading area of a mask plate, and the positive photoresist is called as the positive photoresist for short. The negative photoresist is soluble to a developing solution before exposure and becomes insoluble after exposure, and can obtain a pattern opposite to a shading area of a mask plate, and the negative photoresist is called negative photoresist for short. The pattern reversal glue is a photoresist which can realize the performance of positive glue or negative glue by adjusting process parameters, and the pattern reversal glue is called as the reversal glue for short.

And 103, performing third baking after underexposure on the second photoresist layer.

The exposure and development is a micro-nano processing technology, which mainly relates to ultraviolet lithography, namely coating photoresist on the surface of a substrate, irradiating the ultraviolet light to the surface of the substrate through a mask, changing the property of the irradiated part of the photoresist by photochemical reaction (the process is an exposure process), and dissolving the area which reacts with the light into a specific solution (called a developing solution) to achieve the purpose of making a specific pattern on the surface of the substrate (the process is a development process).

In photolithography, the exposure time greatly affects the result, and a full exposure time, that is, a time in which a photoresist of a specific thickness sufficiently reacts with light, is generally used. However, sometimes, an underexposure or overexposure exposure time is intentionally used in order to produce a particular structure. Wherein, under exposure means that the exposure time is shorter than the complete exposure time, and the photoresist close to the bottom does not react with light sufficiently to generate a special structure. Therefore, the exposure time for underexposing the second photoresist layer is less than the exposure time for fully exposing the second photoresist layer.

Optionally, the third bake is a pre-bake temperature of the second photoresist layer. In the present embodiment, the prebaking means baking after exposure before development to evaporate a substance generated by a reaction between the glue and light.

And 104, developing and fixing the underexposed and third baked second photoresist layer to form an undercut structure on the second photoresist layer, wherein the substrate is provided with a photoresist structure.

An undercut (undercut) structure is a photoresist structure, which usually means that the bottom of the photoresist is wider than the top, the sidewall gradually expands outward from the top to the bottom, and the photoresist profile is in a regular trapezoid shape, and also appears in a "convex" shape after process improvement. The structure is commonly used for the stripping technology in the field of micro-nano processing.

In the embodiment of the application, the second photoresist layer after the underexposure and the third baking is developed by using the developing solution, and then is fixed by using the fixing solution, so that the undercut structure is formed on the second photoresist layer.

Optionally, the developer used for developing the second photoresist layer does not react with the first photoresist layer, so as to prevent the developer from dissolving the first photoresist layer.

Optionally, the developing time t1 for developing the second photoresist layer is greater than the developing time t2 of the second photoresist layer under full exposure conditions. Since the second photoresist layer is underexposed in the step 103, the bottom of the second photoresist layer does not sufficiently react with light, and the bottom region of the second photoresist layer can be dissolved by controlling t1 > t2, so as to form an undercut structure. Illustratively, t1 ≧ t2+15 seconds.

After forming the undercut structure on the second photoresist layer, the photoresist structure over the substrate includes a first photoresist layer and a second photoresist layer with an undercut structure.

Step 105, after performing flood exposure on the substrate with the photoresist structure, performing a fourth baking.

Optionally, the fourth baking comprises baking at a pre-bake temperature and a hard-film temperature of the second photoresist layer in sequence. That is, the pre-baking temperature of the second photoresist layer is used for baking, and then the baking is performed at the hardening temperature of the second photoresist layer.

And 106, etching the first photoresist layer to form a pattern limiting layer after flood exposure and fourth baking.

In the embodiment of the application, the first photoresist layer (namely, the protective adhesive layer) is etched to become the pattern limiting layer, so that the adhesive film structure for coating and stripping is obtained.

Optionally, the etching position of the first photoresist layer is an exposed position on the first photoresist layer, and the exposed position may also be referred to as a region position defined by the pattern of the second photoresist layer, that is, a region position on the first photoresist layer that can be observed when viewed from top down.

Etching refers to a process of removing a thin film layer not masked by a resist to obtain exactly the same pattern on the thin film as on the resist film. In the embodiment of the application, the indium stud welding point is deposited and formed at the exposed position by etching the first photoresist layer to expose partial position of the substrate. Optionally, the etching comprises at least one of: physical etching and chemical etching. Physical etching refers to etching by physical means, and chemical etching refers to etching by chemical reaction. Through etching, a region with a non-undercut structure can be formed on the first photoresist layer, for example, the upper width and the lower width of a tangent plane of an etched part are the same or close, so that the bottom of the indium column can be prevented from generating lateral diffusion.

And step 107, depositing an indium material at the defined pattern position of the pattern limiting layer to form an indium stud welding spot.

The pattern position defined by the pattern limiting layer is the etched position, and because the substrate area at the position is exposed, indium material can be deposited on the substrate at the position by indium plating, so that an indium stud welding point is formed.

Optionally, an evaporation method is used to deposit the indium material on the second photoresist layer with the undercut structure and on the exposed substrate. The indium material deposited on the second photoresist layer is removed along with the stripping of the photoresist layer. The indium material deposited on the exposed substrate forms indium stud pads.

In the embodiment of the application, on one hand, due to the existence of the undercut structure on the second photoresist layer, the existence of the undercut structure can prevent the indium material on the substrate from contacting and adhering with the indium material on the second photoresist layer and the side wall of the second photoresist layer in the indium plating process, so that the problems of difficult stripping and poor appearance in the traditional process are solved; on the other hand, the first photoresist layer is etched to form the pattern limiting layer, and the pattern limiting layer can effectively limit bottom lateral diffusion of the indium material deposited on the substrate, so that structures or devices at other positions of the substrate are protected from being influenced.

Referring to fig. 2 and fig. 3, a comparison graph of the effect of the improved process mentioned in the technical solution and the background of the present application is shown. Fig. 2 shows a side view and a top view of an indium stud bump prepared using the improved process mentioned in the background, and fig. 3 shows a side view and a top view of an indium stud bump prepared using the teachings of the present application. As is evident from fig. 2, there is significant lateral diffusion at the bottom of the indium stud 21, as indicated by region 22 in fig. 2. However, as shown in fig. 3, the indium stud solder joint prepared by the technical solution of the present application has better quality because lateral diffusion does not exist at the bottom of the indium stud 31.

And step 108, stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the indium column welding points.

And finally, stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the indium column welding points. Optionally, placing the substrate deposited with the indium stud welding points in a glue stripping liquid, and stripping the first photoresist layer and the second photoresist layer from the substrate at the temperature of 20-80 ℃ to obtain the substrate with the indium stud welding points. In the embodiment of the application, the first photoresist layer and the second photoresist layer can be simultaneously stripped from the substrate only by one-step stripping operation, the first photoresist layer and the second photoresist layer do not need to be stripped respectively, and the method is simple and efficient.

To sum up, in the technical solution provided in the embodiment of the present application, a first photoresist layer is coated on a substrate as a protective photoresist layer, a second photoresist layer is then coated on the first photoresist layer, an undercut structure is formed on the second photoresist layer by performing underexposure, development and fixing treatment on the second photoresist layer, then the first photoresist layer is etched to form a pattern limiting layer, and an indium column solder joint is deposited at a defined pattern position of the pattern limiting layer; according to the preparation method of the indium column welding spot, on one hand, due to the fact that the undercut structure exists on the second photoresist layer, the indium material on the substrate cannot be in contact adhesion with the indium material on the second photoresist layer and the side wall of the second photoresist layer in the indium plating process due to the undercut structure, and the problems of difficult stripping and poor appearance in the traditional process are solved; on the other hand, the first photoresist layer is etched to form the pattern limiting layer, and the pattern limiting layer can effectively limit bottom lateral diffusion of the indium material deposited on the substrate, so that structures or devices at other positions of the substrate are protected from being influenced.

In addition, the pattern limiting layer can enable the size of the indium columns formed by deposition to be consistent with the size of the defined pattern, and the preparation quality of the indium column welding spots is effectively improved. Therefore, the technical scheme provided by the embodiment of the application can be suitable for preparing the indium column welding spots with different heights and excellent appearance.

In addition, the undercut structure in the embodiment of the present application is made by using a single negative or inverse photoresist, and only one development process using a single developing solution is needed, and the size of the undercut structure can be controlled by the development time.

In addition, the protective glue layer is coated on the substrate in advance, so that the corrosion damage of the developing solution to the substrate material during development can be avoided.

Referring to fig. 4 in combination, a flow chart of a method for manufacturing an indium stud solder joint according to an embodiment of the present application is shown. The process may include the steps of:

1. obtaining a cleaned substrate;

2. coating a first photoresist layer on the cleaned substrate, and soft baking to evaporate a solvent of the first photoresist layer;

3. coating a second photoresist layer on the first photoresist layer, wherein the developing solution of the second photoresist layer does not react with the first photoresist layer, and then soft baking to evaporate the solvent of the second photoresist layer;

4. performing an underexposure operation on the second photoresist layer by using a mask, and then performing a pre-baking;

5. developing, wherein areas which are not reacted with light in the second photoresist layer are dissolved in a developing solution, and an undercut structure is formed on the second photoresist layer by underexposure, wherein the transverse size of the undercut structure can be adjusted by controlling the developing time, and the first photoresist layer is not reacted with the developing solution, so that the substrate can be protected from being contacted with the developing solution; then, carrying out flood exposure and post baking, and carrying out film hardening treatment on the photoresist structure;

6. introducing etching gas to etch the first photoresist layer by using equipment such as a photoresist remover and the like, so that the first photoresist layer is completely etched in the defined pattern region to form a pattern limiting adhesive layer;

7. the metal indium is deposited by using a film coating method such as electron beam evaporation, the side wall of the deposited indium cannot be adhered to the side wall of the photoresist, the bottom of the deposited indium is blocked by the pattern limiting glue layer, and transverse diffusion cannot be generated;

8. and placing the substrate on which the metal indium is deposited into a glue removing solution, releasing the two layers of glue, stripping the metal indium in the non-pattern-defining area cleanly along with the release of the photoresist, and leaving the metal indium columns in the pattern-defining area on the substrate, namely the indium column welding points.

In an example, the indium stud bump preparation process provided by the embodiment of the present application is described by taking a first photoresist as a PMMA (Polymethyl Methacrylate) photoresist and a second photoresist as a KMP E3150A negative photoresist as an example:

1. placing the cleaned aluminum substrate on a spin-coating type spin coater, sucking PMMA glue by a dropper, dripping the PMMA glue on the center of the aluminum substrate, operating for 5 seconds at 500rpm (revolutions per minute) and then operating for 40 seconds at 5000rpm, then placing the aluminum substrate on a heating plate after glue homogenizing, and baking for a period of time at 180 ℃;

2. placing the aluminum substrate subjected to the step 1 on a spin-coating type spin coater, sucking E3150A negative glue by a dropper, dripping the negative glue at the center of the aluminum substrate, operating at 500rpm for 5s, then operating at 4000rpm for 45s, then placing the aluminum substrate subjected to spin coating on a heating plate, and baking for a period of time at 95-120 ℃;

3. performing underexposure on the aluminum substrate coated with the double-layer glue by using an ultraviolet photoetching machine, and then placing the underexposed substrate on a hot plate to bake for a period of time at the temperature in the step 2;

4. placing the aluminum substrate subjected to the step 3 in an alkaline developing solution for developing for 80-150 s, then placing the substrate in deionized water for fixing for 30-180 s, wherein PMMA is used as a protective adhesive layer and does not react with the alkaline solution in the process, and the aluminum substrate is prevented from reacting with alkali;

5. performing flood exposure on the aluminum substrate subjected to the step 4 by using an ultraviolet lithography machine, and then placing the substrate on a hot plate to bake for a period of time at the temperature in the step 2;

6. placing the substrate subjected to the step 5 in a photoresist remover, etching under the conditions of certain power and oxygen environment, completely etching the PMMA layer in each defined pattern within the defined pattern size, and reserving PMMA at other positions to serve as a pattern limiting glue layer;

7. placing the substrate sample after the step 6 in a thermal evaporation coating device with the vacuum degree of 9 multiplied by 10^-4Pa, evaporating metal indium, and due to a bottom cutting structure, the side wall of the indium metal and the double-layer adhesive film cannot be adhered;

8. and (3) placing the substrate subjected to indium evaporation in acetone for soaking to release two layers of glue of PMMA and E3150A, stripping for 24h at room temperature, and then ultrasonically cleaning the sample by using acetone, isopropanol and deionized water in sequence to obtain the indium columns in the defined pattern area, wherein the edges of the bottoms of the indium columns are clearly visible and do not laterally diffuse as shown in figure 3.

The above embodiment shows that the method for preparing the indium stud solder joint by using the PMMA photoresist and the KMP E3150A negative photoresist can prepare the indium stud solder joint with excellent appearance and no lateral diffusion at the bottom, and does not damage the substrate in the preparation process.

An exemplary embodiment of the present application further provides a chip substrate, where the chip substrate has indium stud bumps, and the indium stud bumps are prepared by the method provided in the above embodiment.

An exemplary embodiment of the present application further provides a chip, wherein the chip has an indium stud pad on a substrate, and the indium stud pad is prepared by the method provided in the above embodiment.

Optionally, the chip is a quantum chip. A quantum chip is a chip integrated with quantum wires (or called quantum circuits). Because the quantum chip is widely used with indium materials to generate welding spots, and the quality of the indium column welding spots can directly influence the processing performance of the quantum chip, the scheme provided by the application is adopted to prepare the indium column welding spots, which is beneficial to producing the quantum chip with high quality.

Of course, in some other embodiments, the chip may also be a common ic (integrated circuit) chip, which is not limited in this embodiment.

Referring to fig. 5, a flow chart of a solder joint manufacturing method according to another embodiment of the present application is shown, where the method may include the following steps (501-508):

step 501, coating a first photoresist layer on a substrate;

step 502, coating a second photoresist layer on the first photoresist layer;

step 503, underexposing the second photoresist layer;

step 504, developing and fixing the underexposed second photoresist layer to form an undercut structure on the second photoresist layer, the substrate having a photoresist structure; the photoresist structure comprises a first photoresist layer and a second photoresist layer with an undercut structure;

step 505, performing flood exposure on the substrate with the photoresist structure;

step 506, after the flood exposure, etching the first photoresist layer to form a pattern limiting layer;

step 507, depositing materials at the defined pattern position of the pattern limiting layer to be used as welding spots;

in this embodiment, the solder joint material may be a metal material such as copper, indium, etc., which is not limited in this embodiment.

And step 508, stripping the first photoresist layer and the second photoresist layer from the substrate to obtain the substrate with the welding spots.

For details which are not described in detail in the embodiment of fig. 5, reference is made to the description in the embodiment of fig. 1.

According to the method for preparing the welding spot, on one hand, due to the existence of the undercut structure on the second photoresist layer, the welding spot material on the substrate cannot be contacted and adhered with the welding spot material on the second photoresist layer and the side wall of the second photoresist layer in the evaporation process of the welding spot material, so that the problems of difficult stripping and poor appearance in the traditional process are solved; on the other hand, the first photoresist layer is etched to form the pattern limiting layer, and the pattern limiting layer can effectively limit the lateral diffusion of the bottom of the welding spot material deposited on the substrate, so that structures or devices at other positions of the substrate are protected from being influenced.

An exemplary embodiment of the present application further provides a chip substrate, where the chip substrate has solder joints, and the solder joints are prepared by the above method.

An exemplary embodiment of the present application further provides a chip, which has a pad on a substrate, and the pad is prepared by the above method.

It should be understood that reference to "a plurality" herein means two or more. In addition, the step numbers described herein only exemplarily show one possible execution sequence among the steps, and in some other embodiments, the steps may also be executed out of the numbering sequence, for example, two steps with different numbers are executed simultaneously, or two steps with different numbers are executed in a reverse order to the order shown in the figure, which is not limited by the embodiment of the present application.

The above description is only exemplary of the present application and should not be taken as limiting the present application, and any modifications, equivalents, improvements and the like that are made within the spirit and principle of the present application should be included in the protection scope of the present application.