WO2025227707A1 - Wafer wet etching method and wafer produced thereby - Google Patents

Abstract

The present application relates to the technical field of semiconductor integrated circuit manufacturing, and in particular to a wafer wet etching method and a wafer produced thereby. The wafer comprises a substrate and a composite metal layer; the composite metal layer covers a preset surface of the substrate; the composite metal layer comprises a first metal layer and a second metal layer; and the first metal layer covers the surface of the second metal layer. By means of the wet etching process provided by the present invention, different masks are provided for different metal layers and the widths of transparent areas of the masks are controlled, so that the problem of dimensional distortion of a bottom metal layer when a conventional process is used for wet etching of a composite metal film is effectively solved, thereby improving the dimensional precision of the bottom layer during wet etching of the composite metal film, and also improving the yield rate and reliability of wafer production.

Description

A wet etching method for wafers and the wafer thereof Technical Field

This application relates to the field of semiconductor integrated circuit manufacturing technology, and in particular to a wafer wet etching method and a wafer thereof.

Background Technology

As electronic device designs become increasingly complex, the demands on the integration, miniaturization, and performance of semiconductor components are rising. Consequently, a large number of semiconductor components are manufactured using MEMS technology. Micro-Electro-Mechanical Systems (MEMS), as an advanced manufacturing technology platform, integrates microcircuits and micromechanics onto chips according to functional requirements. The dimensions are typically controlled at the millimeter or micrometer level. MEMS has already been applied to various branches of physics, including force, electricity, optics, magnetism, and acoustics, at the microscale in many disciplines such as microelectronics, materials science, mechanics, chemistry, and mechanical engineering. Etching, in particular, is based on MEMS technology. Etching is an indispensable process in the manufacturing of semiconductor devices. It is one of the core steps in realizing the microstructure and circuit patterning of semiconductor devices. After the photolithography step, the image of the circuit design is formed on the photoresist layer on the wafer surface. The etching process uses chemical or physical means to retain the material in the areas protected by the photoresist, while selectively removing thin film materials such as silicon, metals, and dielectrics from the substrate in the areas not covered by photoresist. This process accurately transfers the pattern on the photomask to the semiconductor substrate. Etching technology is used to create various microstructures of microelectronic devices, such as the gate, source, and drain of transistors, interconnect wires, contact holes, capacitors, and other key components.

Etching processes are mainly divided into wet etching and dry etching. Dry etching is usually carried out in a gaseous environment, using chemical reactions or physical collisions between the gas and the substrate surface to remove material. Wet etching uses chemical solutions to remove unwanted parts of the material surface. In semiconductor manufacturing, silicon wafers are immersed in specific chemical solvents, selectively dissolving the target material layer through chemical reactions. Wet etching has several advantages over dry etching: 1. The equipment used in wet etching is usually relatively simple and inexpensive, and the operation and maintenance costs are easier to control. Moreover, since it does not involve complex plasma or high vacuum systems, its initial investment and operating costs may be lower than those of dry etching; 2. Wet etching relies on special... The selective etching process allows for precise etching of target materials without damaging adjacent protective layers, thanks to the selective solubility of the chemical solution. Furthermore, wet etching provides good uniformity across the entire wafer surface, especially in batch processing, where the liquid medium helps ensure all etched areas receive similar chemical treatment. The etching rate and depth can be flexibly controlled by adjusting parameters such as solution concentration, temperature, pH, and immersion time. However, it's important to note that despite these advantages, wet etching also has significant limitations in modern semiconductor manufacturing processes, particularly in applications requiring extremely high precision, aspect ratios, and complex three-dimensional structures.

1. Wet etching is generally isotropic, meaning the etching rates in the vertical and parallel directions are similar, resulting in insufficient sidewall steepness, which is not conducive to forming high aspect ratio structures; 2. Since liquid etchants can diffuse into the substrate material under the mask, it may cause lateral drilling, affecting pattern fidelity and linewidth control, and even causing the hierarchical structure to collapse, leading to wafer scrap; 3. Wet etching uses a large amount of corrosive chemicals, and the waste liquid generated poses an environmental challenge and increases operating costs.

Referring to Figure 4, when etching composite metal films on wafers using wet etching, existing techniques typically involve continuously etching the composite metal film by fabricating a photoresist mask 4. This results in the bottom metal film 6 being etched using the top metal 5 as a mask. However, wet etching produces side etching, causing the etched groove size of the top metal 5 to be larger than the designed size (i.e., the size of the photoresist mask 4) after wet etching. When the bottom metal 6 is then wet-etched again, using the top metal 5 as a mask, its size will increase further on top of the side etching of the top metal 5, leading to distortion in the etched size of the bottom metal 6. At the same time, there is a problem that the etching status of the bottom metal 6 cannot be observed; only by etching the top metal 5 can the wet-etched appearance of the bottom metal 6 be observed.

Therefore, improving the dimensional accuracy of the substrate in wet etching of composite metal thin films is a technical problem that engineers need to solve.

Summary of the Invention

To overcome the problems existing in the related technologies, this application provides a wafer wet etching method and wafer thereof to improve the dimensional accuracy of the bottom metal wet etching and solve the technical problem of the distortion of the bottom metal size when wet etching composite metal films is performed using traditional wet etching processes.

To achieve the above objectives, this application provides a wafer wet etching method. The wafer includes a substrate and a composite metal layer. The composite metal layer covers a predetermined surface of the substrate. The composite metal layer includes, from top to bottom, a first metal layer, a second metal layer, ..., an Nth metal layer, where N ≥ 2. The first metal layer covers the surface of the second metal layer, the second metal layer covers the surface of the third metal layer, ..., and the (N-1)th metal layer covers the surface of the Nth metal layer. The wet etching method includes the following steps:

S1. Coating the surface of the first metal layer with photoresist to form a first photoresist layer;

S2. Photolithography is performed on the first photoresist layer to form a first mask;

S3. Etch the first metal layer;

S4. Remove the first mask;

S5. Coat the surface of the first metal layer and the surface of the second metal layer exposed after etching with photoresist to form a second photoresist layer, and ensure that the surface of the second photoresist layer is flat, that is, ensure that the upper surface of the second photoresist layer covering the surface of the first metal layer and the surface of the second metal layer is at the same horizontal height. The same method is used to coat the photoresist below to ensure that the surface of the Nth photoresist layer is flat, so that the upper surface of the Nth photoresist layer covering the surface of the first metal layer and the surface of the Nth metal layer is at the same horizontal height.

S6. Photolithography is performed on the second photoresist layer to form a second mask, wherein the mask corresponding to the first photoresist layer has a first transparent area with a width of _d1 , and the mask corresponding to the second photoresist layer has a second transparent area with a width of _d2 , where _d1 ≥ _d2 ; wherein the first transparent area is directly above the second transparent area;

S7. Etch the second metal layer;

S8. Remove the second mask;

...;

The process is performed sequentially, coating the surface of the first metal layer and the surfaces of the second, ..., and/or the exposed Nth metal layer with photoresist to form the Nth photoresist layer, ensuring that the upper surface of the Nth photoresist layer is flat, so that the upper surface of the Nth photoresist layer covering the surface of the first metal layer and the surfaces of the other metal layers is at the same horizontal height; the mask corresponding to the Nth photoresist layer has an Nth transparent area with a width of d_{_n}, where d _₁ ≥ d_₂ … ≥ d_{_n};

The Nth photoresist layer is photolithographically etched to form the Nth mask; the Nth metal layer is etched.

Remove the Nth mask. Further, before step S1, the process includes:

The wafer is cleaned;

The wafer is dried.

Furthermore, after coating the surface of the Nth metal layer with photoresist to form the Nth photoresist layer, and before photolithography is performed on the Nth photoresist layer to form the Nth mask, the following processing steps are also included:

The Nth photoresist layer is subjected to soft baking, wherein the soft baking temperature is the evaporation temperature of the solvent of the photoresist in the Nth photoresist layer.

Furthermore, the process of photolithography to form the Nth mask from the Nth photoresist layer specifically includes the following sub-steps:

The Nth photoresist layer is exposed;

The wafer is then post-baked;

The wafer is immersed in a developing solution to form the Nth mask.

Further, etching the (N-1)th metal layer specifically includes immersing the wafer in the (N-1)th etching solution to etch the (N-1)th metal layer, ensuring that the (N-1)th etching solution does not react with the (N-1)th mask and the Nth metal layer; or ensuring that the (N-1)th etching solution does not react with the (N-1)th mask and the remaining metal layers that have been etched.

Further, removing the Nth mask specifically includes: immersing the wafer in a resist remover to remove the Nth mask;

The residual adhesive on the wafer is rinsed off with a cleaning solution.

Furthermore, the photoresist in the Nth photoresist layer has a lower viscosity than the photoresist in the (N-1)th photoresist layer.

Furthermore, the N-1th photoresist layer and the Nth photoresist layer are made of the same material, the exposure time of the Nth photoresist layer is longer than that of the N-1th photoresist layer, and/or the exposure light intensity of the Nth photoresist layer is greater than that of the N-1th photoresist layer.

Further, etching of the (N-1)th metal layer specifically includes immersing the wafer in the (N-1)th etching solution to etch the (N-1)th metal layer. The (N-1)th etching solution does not react with the (N-1)th mask, the Nth metal layer, or the already etched metal layer.

More specifically, the composite metal layer includes a first metal layer and a second metal layer, with the first metal layer covering the surface of the second metal layer. The wet etching method specifically includes the following steps:

S1. A first photoresist layer is formed by coating photoresist onto the surface of the first metal layer;

S2. Photolithography is performed on the first photoresist layer to form a first mask;

S3. Etch the first metal layer;

S4. Remove the first mask;

S5. Coat the first metal layer and the second metal layer exposed after etching with photoresist to form a second photoresist layer, and ensure that the surface of the second photoresist layer is flat.

S6. Photolithography is performed on the second photoresist layer to form a second mask, wherein the transparent area widths of the masks corresponding to the first photoresist layer and the second photoresist layer are equal or the transparent area width of the mask corresponding to the second photoresist layer is narrower than the transparent area width of the mask corresponding to the first photoresist layer.

S7. Etch the second metal layer;

S8. Remove the second mask.

Specifically, the composite metal layer includes a first metal layer, a second metal layer, and a third metal layer. From top to bottom, the first metal layer covers the surface of the second metal layer, and the second metal layer covers the surface of the third metal layer. The wet etching method includes the following steps:

S1. Coating the first metal layer with photoresist to form a first photoresist layer;

S2. Photolithography is performed on the first photoresist layer to form a first mask;

S3. Etch the first metal layer;

S4. Remove the first mask;

S5. Coat the first metal layer and the second metal layer exposed after etching with photoresist to form a second photoresist layer, and ensure that the upper surface of the second photoresist layer is flat;

S6. Photolithography is performed on the second photoresist layer to form a second mask, wherein the transparent area widths of the masks corresponding to the first photoresist layer and the second photoresist layer are equal or the transparent area width of the mask corresponding to the second photoresist layer is narrower than the transparent area width of the mask corresponding to the first photoresist layer.

S7. Etch the second metal layer;

S8. Remove the second mask;

S9. Coat the first metal layer and the third metal layer exposed after etching with photoresist to form a third photoresist layer, and ensure that the upper surface of the third photoresist layer is flat;

S10. Photolithography is performed on the third photoresist layer to form a third mask, wherein the transparent area widths of the masks corresponding to the first photoresist layer, the second photoresist layer, and the third photoresist layer are equal, or the transparent area width of the mask corresponding to the second photoresist layer is narrower than the transparent area width of the mask corresponding to the first photoresist layer, and the transparent area width of the mask corresponding to the third photoresist layer is narrower than the transparent area width of the mask corresponding to the second photoresist layer;

S11. Etch the third metal layer;

S12. Remove the third mask.

Furthermore, prior to step S1, the following steps are also included:

Clean the wafer;

The wafer is then dried.

Furthermore, after step S1 and before step S2, the following steps are also included:

The first photoresist layer is subjected to soft baking at a temperature equal to the evaporation temperature of the solvent in the photoresist.

Further, step S2 includes:

Expose the first photoresist layer;

The wafer was then post-baked.

The wafer is immersed in a developing solution to form the first mask.

Further, step S3 includes:

The wafer is immersed in a first etching solution to etch the first metal layer, wherein the first etching solution does not react with the second metal layer and the first mask.

Further, step S4 includes:

The wafer is immersed in a resist remover to remove the first mask.

The residual adhesive on the wafer was rinsed off using a cleaning solution.

Furthermore, it is ensured that the photoresist in the second photoresist layer has a lower viscosity than the photoresist in the first photoresist layer.

Furthermore, the first photoresist layer and the second photoresist layer are made of the same material, the exposure time of the second photoresist layer is longer than that of the first photoresist layer, and/or the exposure light intensity of the second photoresist layer is greater than that of the first photoresist layer.

Further, step S7 includes:

The wafer is immersed in a second etching solution to etch the second metal layer. The second etching solution does not react with the first metal layer and the second mask.

This application also provides a wafer, comprising:

It is produced using the wet etching method described above in this invention.

The technical solution provided in this application has the following beneficial effects:

1. In this technical solution, the wafer includes a substrate and a composite metal layer. The composite metal layer covers a predetermined surface of the substrate. The composite metal layer includes a first metal layer, a second metal layer, ..., an Nth metal layer. For example, when there are two metal layers, the first metal layer covers the upper surface of the second metal layer. When etching the wafer, photoresist is first coated on the first metal layer to form a first photoresist layer. Then, photolithography is performed on the first photoresist layer to form a first mask. Circuit patterns are etched on the first mask. Then, the first metal layer is etched. During the etching process, the first mask... The area covered by the film protects the underlying first metal layer from etching, while the unprotected areas are etched, thereby transferring the circuit pattern on the first mask to the first metal layer. After etching, the first mask is removed, and then photoresist is applied again to the first metal layer, filling the etched areas (grooves) with photoresist. It is ensured that the surface of the second photoresist layer is smooth to prevent image transfer distortion due to unevenness. Then, photolithography is performed on the second photoresist layer to form the second mask. During this process, it is ensured that the first photoresist... When the transparent area widths of the masks corresponding to the first and second photoresist layers are equal, or the transparent area width of the mask corresponding to the second photoresist layer is narrower than that of the mask corresponding to the first photoresist layer, the groove size obtained by etching the first metal layer will be larger than the size on the first mask due to the side etching problem during the etching of the first metal layer. When the second photoresist layer is photolithographically etched using a mask with a transparent area width equal to or narrower than that corresponding to the first photoresist layer, the formed second mask can fill the groove size etched on the first metal layer to a size equal to that of the first photoresist layer. The dimensions on the mask are equal to or smaller than those on the first mask. Then, the second metal layer is etched, so that the size of the groove etched on the second metal layer is equal to or smaller than the size of the groove on the first metal layer. Finally, the second mask is removed, thus completing the etching of the wafer. This method solves the problem of dimensional distortion of the second metal layer caused by using the first metal layer as a mask for etching the composite metal thin film on the wafer when using the traditional wet etching process. It improves the dimensional accuracy of the wet etching of the second metal layer and also improves the yield and reliability of wafer production.

2. The wafer wet etching method provided by this invention can process wafers with more than or equal to two metal composite layers, and has universality for etching multi-layer composite metal layers. When the composite metal layer also includes a third metal layer, and the second metal layer covers the surface of the third metal layer, this wet etching method can also be applied to the etching of the third metal layer. The first metal layer and the second metal layer are wet etched according to S1 to S7. After etching, the first metal layer and the second metal layer are combined and regarded as the "first metal layer", and the third metal layer is regarded as the "second metal layer". Wet etching is then performed according to S5 to S8, which can realize the etching of the third metal layer and improve the etching dimensional accuracy when etching multi-layer metal layers.

3. In the wafer wet etching method provided by the present invention, when the second photoresist layer is photolithographically etched using a mask with a narrower width than the transparent area corresponding to the first photoresist layer, a second mask is formed at the sidewall of the groove on the first metal layer. The thickness of the second mask is thicker than the etched portion of the first metal layer. After the second mask fills the etched portion of the first metal layer, the second mask further reduces the size of the groove to be smaller than the size of the groove on the first mask. Then, the second metal layer is etched. The size of the groove formed in the second metal layer is smaller than the size of the groove on the first metal layer. After the composite metal layer is etched layer by layer by the above repeated etching method, the operator can observe from the first metal layer to the bottom layer of the etched area using an observation device. The corresponding dimensions of each etched area of the composite metal layer can be observed and measured, solving the problem that the other metal layers of the composite metal layer, except for the first metal layer, cannot be observed.

It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application.

Attached Figure Description

The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments thereof.

Figure 1 is a schematic diagram of the wafer wet etching process shown in an embodiment of this application;

Figure 2 is a detailed schematic diagram of the wafer wet etching process shown in an embodiment of this application;

Figure 3 is a schematic diagram of the structure during the wet etching process of a wafer, as shown in an embodiment of this application;

Figure 4 is a schematic diagram of the structure during the wet etching process of a wafer, as shown by existing technology;

Figure 5 is a schematic diagram showing the dimensional relationship of the widths _d1 , d2 _, ..., _{dn of} the transparent areas of each metal layer mask during the wet etching process of the wafer, as illustrated in an embodiment of this application.

In the figure: 1. Wafer; 10. Composite metal layer; 100. First metal layer; 101. Second metal layer; 11. Substrate; 2. First photoresist layer; 20. First mask; 3. Second photoresist layer; 30. Second mask; 4. Photoresist mask; 5. Top metal layer; 6. Bottom metal layer.

Detailed Implementation

To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

Example 1:

This application provides a wet etching method for a wafer, wherein the wafer 1 includes a substrate 11 and a composite metal layer 10, the composite metal layer 10 covering a predetermined surface of the substrate 11, the composite metal layer 10 including a first metal layer 100 and a second metal layer 101, the first metal layer 100 covering the surface of the second metal layer 101, and the wet etching method includes:

S1. Photoresist is coated onto the first metal layer 100 to form a first photoresist layer 2;

S2. The first photoresist layer 2 is photolithographically formed to form a first mask 20, wherein the first mask 20 has a first transparent area with a width of _d1 ;

S3. Etch the first metal layer 100;

S4. Remove the first mask 20;

S5. Photoresist is coated on the first metal layer 100 and the second metal layer 101 exposed after etching to form a second photoresist layer 3, and the surface of the second photoresist layer 3 is made flat. The second photoresist layer 3 covers the unetched first metal layer 100 and the groove of the first metal layer 100 exposed after etching and the second metal layer 101, so that the second photoresist layer 3 can cover the sidewall of the first metal layer 100 that has been etched and side-etched.

S6. The second photoresist layer 3 is photolithographically formed to form a second mask 30. A second transparent area is formed on the second mask 30. The width of the transparent area of the _mask corresponding to the first photoresist layer 2 and the second photoresist layer 3 is equal or the width of the transparent area of the mask corresponding to the second photoresist layer 3 is narrower than the width of the transparent area of the mask corresponding to the first photoresist layer 2, i.e., _d1 ≥ _d2 . In this way, a second transparent area is set corresponding to the first transparent area, and the width of the second transparent area _d2 is ensured to be ≤ the width of the first transparent area _d1 . Therefore, when etching the second metal layer, the groove width of the etched second metal layer 101 can be effectively prevented from being greater than the groove width of the etched first metal layer 100. This effectively overcomes the technical problem of the etching size increase caused by the continued side etching of the first metal layer 100 and the distortion of the etching size of the second metal layer. At the same time, it overcomes the technical problem that the etching of the bottom metal of the composite metal film cannot be observed, and the wet etching appearance of the bottom metal can only be observed by etching the top metal.

S7. Etch the second metal layer 101;

S8. Remove the second mask 30.

In the prior art, when etching the composite metal layer 10 on wafer 1 using wet etching, a photoresist mask is generally used to continuously etch the composite metal layer 10. As a result, the etching of the second metal layer 101 is performed using the first metal layer 100 as a mask. However, wet etching will produce side etching, which will cause the size of the etched groove after the first metal layer 100 is wet etched to be larger than the design size (i.e., the size of the photoresist mask). When the second metal layer 101 is wet etched again, the size will be further increased on the basis of the side etching of the first metal layer 100, resulting in the distortion of the etching size of the second metal layer 101.

Referring to Figures 1 and 3, in this embodiment, wafer 1 includes a substrate 11 and a composite metal layer 10. The composite metal layer 10 covers a predetermined surface of the substrate 11 and includes a first metal layer 100 and a second metal layer 101. The first metal layer 100 covers the surface of the second metal layer 101. When etching the wafer 1, photoresist is first coated on the first metal layer 100 to form a first photoresist layer 2. Then, photolithography is performed on the first photoresist layer 2 to form a first mask 20. Circuit patterns are etched on the first mask 20. Then, the first metal layer 100 is etched. During the etching process, the area covered by the first mask 20 can protect the underlying first metal layer 100 from being etched, while the unprotected area is etched, thereby transferring the circuit patterns on the first mask 20 to the first metal layer 100. After etching, the first mask 20 is removed, and then the first... Photoresist is coated again on the metal layer 100, and the area to be etched is filled with photoresist to ensure that the surface of the second photoresist layer 3 is flat. Unevenness on the surface of the photoresist layer can cause differences in light intensity and penetration depth during exposure, leading to deformation or dimensional deviations in the formed circuit pattern. The flatness of the second photoresist layer 3 prevents image transfer distortion. Then, photolithography is performed on the second photoresist layer 3 to form the second mask 30. The transparent area widths of the masks corresponding to the first photoresist layer 2 and the second photoresist layer 3 are equal, or the transparent area width of the mask corresponding to the second photoresist layer 3 is narrower than that of the mask corresponding to the first photoresist layer 2. Because the first metal layer 100 experiences side etching during etching, the groove size obtained from the etching of the first metal layer 100 will be larger than the size on the first mask 20. When the second photoresist layer 3 is photolithographically etched... When photolithography is performed using a mask with a width equal to the transparent area corresponding to the first photoresist layer 2, a second mask 30 is formed on the sidewall of the groove on the first metal layer 100. The second mask 30 fills in the eroded portion of the first metal layer 100, thereby reducing the size of the groove. This makes the size of the groove covered by the second mask 30 equal to the size of the first mask 20. Then, the second metal layer 101 is etched, and the size of the groove formed on the second metal layer 101 is equal to the size of the groove on the first metal layer 100. This solves the problem of severe erosion of the second metal layer 101 during wet etching of the composite metal layer 10, which leads to dimensional distortion. When photolithography is performed using a mask with a narrower transparent area than the first photoresist layer 2, a second mask 30 is formed on the sidewall of the groove on the first metal layer 100. The thickness of the second mask 30 is greater than the width of the transparent area corresponding to the first metal layer 100. The etched portion needs to be thicker. After the second mask 30 fills the etched portion of the first metal layer 100, the second mask 30 further reduces the size of the groove to be smaller than the size of the first mask 20. Then, the second metal layer 101 is etched. The size of the groove formed in the second metal layer 101 is smaller than the size of the groove on the first metal layer 100, so the etching condition of the second metal layer 101 can be directly observed. This solves the problem that the second metal layer 101 of the composite metal film cannot be observed. Finally, the second mask 30 is removed, thus completing the etching of wafer 1. This method solves the problem of dimensional distortion of the second metal layer 101 caused by using the first metal layer 100 as a mask for etching the composite metal film on wafer 1 when using wet etching. It improves the dimensional accuracy of the second metal layer wet etching and also improves the yield and reliability of wafer 1 production.

Furthermore, when the composite metal layer 10 also includes a third metal layer, and the second metal layer 101 covers the surface of the third metal layer, the wet etching method can also be applied to the etching of the third metal layer. The first metal layer 100 and the second metal layer 101 are wet etched according to S1 to S7. After etching, the first metal layer 100 and the second metal layer 101 are combined and regarded as "first metal layer 100", and the third metal layer is regarded as "second metal layer 101". Wet etching is performed according to S5 to S8, which can realize the etching of the third metal layer and also improve the etching dimensional accuracy when etching multiple metal layers.

Example 2:

The wet etching method for wafer 1, prior to S1, also includes:

The wafer 1 is cleaned;

The wafer 1 is dried.

The period between S1 and S2 also includes:

The first photoresist layer 2 is subjected to soft baking, and the temperature of soft baking is the evaporation temperature of the solvent of the photoresist.

Referring to Figure 2, in this embodiment, to avoid contaminants on the surface of wafer 1 affecting the photoresist photolithography, the surface of wafer 1 needs to be cleaned before the photoresist is coated on the first metal layer 100. During the manufacturing process, the surface of wafer 1 may be contaminated with organic contaminants (such as grease, solvent residue, particulate matter, etc.), inorganic contaminants (such as metal ions, oxides), and other impurities. These contaminants will reduce the adhesion of the photoresist, making it prone to peeling and detachment in subsequent development and etching steps, thus damaging the integrity of the circuit pattern. They will also cause unevenness or defects in the formed photoresist layer, altering the thickness distribution and photosensitive reaction of the photoresist on the surface of wafer 1. This prevents light from accurately passing through the photoresist and reaching the surface of the composite metal layer 10 during exposure, causing pattern transfer distortion, affecting the accuracy and resolution of circuit lines, and reducing the performance and yield of the chip fabricated from wafer 1. Therefore, cleaning wafer 1 is necessary. First, a pre-cleaning process is performed to remove oily stains, particles, and loose impurities from the surface of wafer 1 using solvents (such as isopropanol (IPA), ethanol, or other organic solvents). Then, wafer 1 is rinsed with deionized water (a highly pure water that has undergone a special purification process to almost completely remove dissolved mineral ions. Deionized water has good compatibility with various semiconductor materials and will not cause adverse chemical reactions or physical damage, thus avoiding circuit defects) to remove residual solvents and other soluble substances. Next, an ultrasonic cleaner (which uses the cavitation effect generated by ultrasound in a liquid to clean the object) is used to peel off the fine particles attached to the surface of wafer 1. Finally, a high-pressure nitrogen gas stream is used to blow away the liquid on the surface to prevent the liquid from leaving stains on the surface after drying, reducing the risk of re-contamination. This process cleans wafer 1 and avoids the adverse effects of contaminants on the photoresist on the photolithography.

After the photoresist is coated on the first metal layer 100 and before photolithography, the wafer 1 needs to be placed in an oven to perform soft baking on the first photoresist layer 2. The temperature set in the oven is the evaporation temperature of the photoresist solvent. Soft baking of the photoresist can evaporate and remove the solvent in the photoresist layer, which improves the adhesion and stability of the photoresist to the composite metal layer 10, prevents subsequent peeling and detachment, and also avoids solvent residue in the first photoresist layer 2, which would cause deformation of the transferred circuit pattern during photolithography. At the same time, it can prevent solvent vapor from interfering with the photochemical reaction of the photoresist during exposure, thereby causing adverse effects on subsequent development.

Example 3:

The wet etching method for wafer 1, S2, includes:

The first photoresist layer 2 is exposed;

The wafer 1 is then post-baked;

The wafer 1 is immersed in a developing solution to form the first mask 20.

S3 includes:

The wafer 1 is immersed in the first etching solution to etch the first metal layer 100. The first etching solution does not react with the second metal layer 101 and the first mask 20.

S4 includes:

The wafer 1 is immersed in a resist remover to remove the first mask 20;

The residual adhesive on the wafer 1 is rinsed off with a cleaning solution.

Referring to Figure 2, in this embodiment, to transfer the circuit pattern on the photomask to the first photoresist layer 2, specifically, the first photoresist layer 2 is exposed. A light source (such as ultraviolet light, deep ultraviolet light, or extreme ultraviolet light) irradiates the photomask and then passes through the transparent area of the photomask to irradiate the first photoresist layer 2. A chemical reaction occurs in the area irradiated by the light, making the exposed area soluble in the developer or insoluble in the developer. Then, the wafer 1 is sent into an oven for post-baking to accelerate the chemical reaction inside the photoresist and enhance the contrast between the exposed and unexposed areas. Next, the wafer 1 is immersed in the developer. When the exposed area becomes soluble in the developer, the developer will dissolve the exposed area, leaving the remaining area to form the first photomask 20; when the exposed area becomes insoluble in the developer, the developer will dissolve the unexposed area, leaving the exposed area to form the first photomask 20, thereby transferring the circuit pattern on the photomask to the first photoresist layer 2.

Referring to Figure 3, in order to etch the first metal layer 100, specifically, in this example, the wafer 1 is immersed in the first etching solution. The first etching solution is selective; it only reacts strongly with the first metal layer 100 and dissolves it, while it does not react with the second metal layer 101 and the first mask 20. Therefore, the area covered by the first mask 20 will not be etched by the first etching solution. Even after the first etching solution etches through the first metal layer 100, it will not etch the second metal layer 101, thus completing the etching of the first metal layer 100 and transferring the circuit pattern on the first mask 20 to the first metal layer 100, while also preventing damage to the second metal layer 101.

Referring to Figures 2 and 3, the first mask 20 needs to be removed next. Since the material of the first mask 20 is actually photoresist, the wafer 1 can be immersed in an ultrasonic cleaning tank containing a photoresist remover to dissolve and remove the first mask 20. The photoresist remover can be a solvent such as acetone, isopropanol (IPA), or N-methylpyrrolidone (NMP). In the ultrasonic cleaning tank, the photoresist will be quickly detached due to the action of the solvent and ultrasonic vibration. Then, the photoresist remover on the wafer 1 is rinsed with deionized water. Finally, the liquid on the surface of the wafer 1 is blown off with a high-pressure nitrogen gas flow to dry the wafer 1 and prevent residual solvent from affecting the coating of the next photoresist layer, thus completing the removal of the first mask 20.

Example 4:

The wet etching method for wafer 1

The photoresist in the second photoresist layer 3 has a lower viscosity than the photoresist in the first photoresist layer 2.

Specifically, when the first photoresist layer and the second photoresist layer are made of the same material, the exposure time of the second photoresist layer is longer than that of the first photoresist layer, and/or the exposure light intensity of the second photoresist layer is greater than that of the first photoresist layer.

In addition, S7 includes:

The wafer 1 is immersed in the second etching solution to etch the second metal layer 101. The second etching solution does not react with the first metal layer 100 and the second mask 30.

Referring to Figures 2 and 3, in this embodiment, wafer 1 needs to be coated with photoresist twice. When the photoresist is coated to form the first photoresist layer 2, the surface of the first metal layer 100 is a flat surface, and the surface of the coated photoresist is easy to form a flat surface. However, after the first metal layer 100 is etched, the circuit pattern is transferred to the surface of the first metal layer 100, causing the surface of the first metal layer 100 to become uneven. When the photoresist is coated on the first metal layer, it needs to fill the etched grooves on the first metal layer 100. If the surface of the formed second photoresist layer 3 is not flat, it will lead to a decrease in the resolution of photolithography and the edge quality of the pattern formed after development, and deformation of the circuit pattern. Therefore, the second photoresist layer 3 needs to use a photoresist with a lower viscosity than the first photoresist layer 2 to improve the fluidity of the photoresist during the coating process, so that the photoresist has better filling performance and ensures that the photoresist can quickly fill the grooves when the photoresist is coated, so that the surface of the formed second photoresist layer 3 is flat.

Referring to Figures 2 and 3, since the second etching is performed on the second metal layer 101 based on the first etching, the exposure area of the second photoresist layer 3 is actually located within the groove etched in the first metal layer 100. This results in the exposure area of the second photoresist layer 3 being thicker than the exposure area of the first photoresist layer 2. The photoresist reacts with light because it contains specific photosensitive components. These components undergo chemical reactions under light of a specific wavelength, achieving control over the solubility of the photoresist. Increasing the thickness of the photoresist layer reduces the exposure sensitivity of the photoresist (exposure sensitivity refers to the photochemical reaction that occurs per unit time under a specific light source, reflecting the photoresist's response speed and efficiency to light energy) and increases the exposure dose of the underlying photoresist (when light passes through the photoresist layer, the light intensity decreases due to absorption and scattering). (Due to the depth of the photoresist layer, the light intensity needs to be increased to produce a chemical reaction on the bottom photoresist.) If the viscosity of the photoresist used in the first photoresist layer 2 is sufficient to fill the groove of the first metal layer 100, and the surface of the second photoresist layer 3 formed after filling is flat, the photoresist used in the second photoresist layer 3 is the same as that in the first photoresist layer. In this case, more time needs to be spent exposing the exposure area, or the exposure light intensity of the second photoresist layer can be adjusted to make the exposure light intensity of the second photoresist layer greater than that of the first photoresist layer. Alternatively, the exposure time and the exposure light intensity can be increased simultaneously to prevent the photoresist in the area to be etched from being completely removed during development, which would result in the inability to complete the etching of the second metal layer 101 and the inability to completely transfer the circuit pattern to the second metal layer 101.

Referring to Figures 2 and 3, in order to etch the second metal layer 101, specifically, in this example, the wafer 1 is immersed in the second etching solution. The second etching solution is selective; it only reacts strongly with the second metal layer 101 and dissolves it, while it does not react with the first metal layer 100 and the second mask 30. Therefore, the area covered by the second mask 30 will not be etched by the second etching solution. Even after the second etching solution etches through the second metal layer 101, it will not etch the bottom metal layer or substrate 11, thereby completing the etching of the second metal layer 101 and transferring the circuit pattern on the second mask 30 to the second metal layer 101, while also preventing damage to the first metal layer 100.

Example 5:

The composite metal layer includes a first metal layer, a second metal layer, and a third metal layer. From top to bottom, the first metal layer covers the surface of the second metal layer, and the second metal layer covers the surface of the third metal layer. The wet etching method includes the following steps:

S1. Coating the first metal layer with photoresist to form a first photoresist layer;

S2. Photolithography is performed on the first photoresist layer to form a first mask;

S3. Etch the first metal layer;

S4. Remove the first mask;

S5. Photoresist is coated on the first metal layer and the second metal layer exposed after etching to form a second photoresist layer, and the upper surface of the second photoresist layer is made flat. The second photoresist layer covers the first metal layer, the groove of the first metal layer exposed after etching, and the second metal layer. Thus, the second photoresist layer can also cover the sidewall of the first metal layer that has been etched during the etching process.

S6. Photolithography is performed on the second photoresist layer to form a second mask, wherein the transparent area widths of the masks corresponding to the first photoresist layer and the second photoresist layer are equal or the transparent area width of the mask corresponding to the second photoresist layer is narrower than the transparent area width of the mask corresponding to the first photoresist layer.

S7. Etch the second metal layer;

S8. Remove the second mask;

S9. Photoresist is coated on the first metal layer, the etched first metal layer groove, the second metal layer groove and the third metal layer to form a third photoresist layer, and the upper surface of the third photoresist layer is made flat. The third photoresist layer covers the first metal layer, the groove of the first metal layer and the second metal layer exposed after etching and the third metal layer. In this way, the third photoresist layer can also cover the sidewalls corresponding to the grooves of the first metal layer and the second metal layer that have been etched.

S10. Photolithography is performed on the third photoresist layer to form a third mask, wherein the transparent area widths of the masks corresponding to the first photoresist layer, the second photoresist layer, and the third photoresist layer are equal, or the transparent area width of the mask corresponding to the second photoresist layer is narrower than the transparent area width of the mask corresponding to the first photoresist layer, and the transparent area width of the mask corresponding to the third photoresist layer is narrower than the transparent area width of the mask corresponding to the second photoresist layer;

S11 etches the third metal layer;

S12. Remove the third mask.

Example 6:

A wet etching method for wafers, the wafer comprising a substrate and a composite metal layer, the composite metal layer covering a predetermined surface of the substrate, the composite metal layer comprising, from top to bottom, a first metal layer, a second metal layer, ..., an Nth metal layer, where N≥4, wherein the first metal layer covers the surface of the second metal layer, the second metal layer covers the surface of the third metal layer, ..., the (N-1)th metal layer covers the surface of the Nth metal layer, the wet etching method comprising the following steps:

S1. Coating the surface of the first metal layer with photoresist to form a first photoresist layer;

S2. Photolithography is performed on the first photoresist layer to form a first mask;

S3. Etch the first metal layer;

S4. Remove the first mask;

S5. Coat the surface of the first metal layer and the surface of the second metal layer exposed after etching with photoresist to form a second photoresist layer, and ensure that the surface of the second photoresist layer is flat, that is, ensure that the upper surface of the second photoresist layer covering the surface of the first metal layer and the surface of the second metal layer is at the same horizontal height. The same method is used to coat the photoresist below to ensure that the surface of the Nth photoresist layer is flat, so that the upper surface of the Nth photoresist layer covering the surface of the first metal layer and the surface of the Nth metal layer is at the same horizontal height.

S6. Photolithography is performed on the second photoresist layer to form a second mask, wherein the mask corresponding to the first photoresist layer has a first transparent area with a width of _d1 , and the mask corresponding to the second photoresist layer has a second transparent area with a width of _d2 , where _d1 ≥ _d2 ; wherein the first transparent area is directly above the second transparent area;

S7. Etch the second metal layer;

S8. Remove the second mask;

...;

The process proceeds sequentially, coating the surface of the first metal layer and the surfaces of the second, ..., and/or the exposed Nth metal layer with photoresist to form the Nth photoresist layer. The upper surface of the Nth photoresist layer is ensured to be flat, so that the upper surface of the Nth photoresist layer covering the surface of the first metal layer, the grooves of the other etched metal layers, and the metal layers is at the same horizontal level. The mask corresponding to the Nth photoresist layer has an Nth transparent region with a width of d _{_n} , where d _₁ ≥ d_₂ ... ≥ d_n . Figure 5 shows the wafer of the N-layer metal composite layer, with the widths of the transparent regions d _₁ , d _₂, ..., d_n of each mask in each process step. The diagram of _n ; in this way, it can be ensured that each time the photoresist layer is applied, the photoresist layer can cover the sidewall of the groove with the corresponding metal layer that has been etched, preventing it from being further laterally etched. In addition, by setting the width of the transparent area, it can also effectively prevent the actual width of the groove in the lower metal layer from being greater than the width of the groove in the upper metal layer after lateral etching, or the overall etching size distortion from occurring.

The Nth photoresist layer is photolithographically etched to form the Nth mask; the Nth metal layer is etched.

Remove the Nth mask.

Furthermore, prior to step S1, the following steps are also included:

The wafer is cleaned;

The wafer is dried.

Furthermore, after coating the surface of the Nth metal layer with photoresist to form the Nth photoresist layer, and before photolithography is performed on the Nth photoresist layer to form the Nth mask, the following processing steps are also included:

The Nth photoresist layer is subjected to soft baking, wherein the soft baking temperature is the evaporation temperature of the solvent of the photoresist in the Nth photoresist layer.

Furthermore, the process of photolithography to form the Nth mask from the Nth photoresist layer specifically includes the following sub-steps:

The Nth photoresist layer is exposed;

The wafer is then post-baked;

The wafer is immersed in a developing solution to form the Nth mask.

Further, etching the (N-1)th metal layer specifically includes immersing the wafer in the (N-1)th etching solution to etch the (N-1)th metal layer, ensuring that the (N-1)th etching solution does not react with the (N-1)th mask and the Nth metal layer; or ensuring that the (N-1)th etching solution does not react with the (N-1)th mask and the remaining metal layers that have been etched.

Further, removing the Nth mask specifically includes: immersing the wafer in a resist remover to remove the Nth mask;

The residual adhesive on the wafer is rinsed off with a cleaning solution.

Furthermore, the photoresist in the Nth photoresist layer has a lower viscosity than the photoresist in the (N-1)th photoresist layer.

Furthermore, the N-1th photoresist layer and the Nth photoresist layer are made of the same material, the exposure time of the Nth photoresist layer is longer than that of the N-1th photoresist layer, and/or the exposure light intensity of the Nth photoresist layer is greater than that of the N-1th photoresist layer.

Further, etching of the (N-1)th metal layer specifically includes immersing the wafer in the (N-1)th etching solution to etch the (N-1)th metal layer. The (N-1)th etching solution does not react with the (N-1)th mask, the Nth metal layer, or the already etched metal layer.

Example 7:

This application also provides a wafer 1 produced using the wet etching method described above.

In this embodiment, wafer 1 is produced using the aforementioned wet etching method. The wet etching process is simpler than dry etching, and the equipment used in wet etching is less expensive, which can reduce the equipment cost investment in the wafer 1 production process. At the same time, the wet etching rate is faster than dry etching, which can improve the production rate of wafer 1. In addition, the aforementioned wet etching method also solves the problem of poor etching dimensional accuracy of the second metal layer 101 of the composite metal layer 10, so that the performance and reliability of wafer 1 mass-produced by this wet etching method are improved, making it more competitive than wafers produced by existing wet etching methods.

The solution of this application has been described in detail above with reference to the accompanying drawings. In the above embodiments, the descriptions of each embodiment have different emphases; for parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. Those skilled in the art should also understand that the actions and modules involved in the specification are not necessarily essential to this application. Furthermore, it is understood that the steps in the method of this application embodiment can be adjusted, combined, and deleted according to actual needs, and the structure in the device of this application embodiment can be combined, divided, and deleted according to actual needs.

The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims (10)

A wet etching method for wafers, the wafer comprising a substrate and a composite metal layer, the composite metal layer covering a predetermined surface of the substrate, the composite metal layer comprising, from top to bottom, a first metal layer, a second metal layer, ..., an Nth metal layer, where N≥2, wherein the first metal layer covers the surface of the second metal layer, the second metal layer covers the surface of the third metal layer, ..., the (N-1)th metal layer covers the surface of the Nth metal layer, characterized in that the wet etching method comprises the following steps: S1. Coating the surface of the first metal layer with photoresist to form a first photoresist layer; S2. Photolithography is performed on the first photoresist layer to form a first mask; S3. Etch the first metal layer; S4. Remove the first mask; S5. Coat the surface of the first metal layer and the surface of the second metal layer exposed after etching with photoresist to form a second photoresist layer, and ensure that the surface of the second photoresist layer is flat; S6. Photolithography is performed on the second photoresist layer to form a second mask, wherein the mask corresponding to the first photoresist layer has a first transparent area with a width of _d1 , and the mask corresponding to the second photoresist layer has a second transparent area with a width of _d2 , wherein _d1 ≥ _d2 ; S7. Etch the second metal layer; S8. Remove the second mask; ...; A photoresist layer is formed by coating the surface of the first metal layer and the surfaces of the second metal layer, ..., and/or the exposed surface of the Nth metal layer after etching with photoresist, and ensuring that the surface of the Nth photoresist layer is flat. The mask corresponding to the Nth photoresist layer has an Nth transparent area with a width of d _{_n}, where d _₁ ≥ d_₂ … ≥ d _{_n}. The Nth photoresist layer is photolithographically etched to form the Nth mask; the Nth metal layer is etched. Remove the Nth mask. According to claim 1, a wafer wet etching method is characterized in that, before step S1, it further includes: The wafer is cleaned; The wafer is dried. A wafer wet etching method according to claim 1, characterized in that: After coating the surface of the Nth metal layer with photoresist to form the Nth photoresist layer, and before photolithography is performed on the Nth photoresist layer to form the Nth mask, the following processing steps are also included: The Nth photoresist layer is subjected to soft baking, wherein the soft baking temperature is the evaporation temperature of the solvent of the photoresist in the Nth photoresist layer. According to claim 3, the wafer wet etching method is characterized in that the photolithography of the Nth photoresist layer to form the Nth mask specifically includes the following sub-steps: The Nth photoresist layer is exposed; The wafer is then post-baked; The wafer is immersed in a developing solution to form the Nth mask. A wafer wet etching method according to claim 1 or 2, characterized in that, Etching the (N-1)th metal layer specifically involves immersing the wafer in the (N-1)th etching solution to etch the (N-1)th metal layer, wherein the (N-1)th etching solution does not react with the (N-1)th mask and the Nth metal layer. A wafer wet etching method according to claim 1 or 2, characterized in that, Removing the Nth mask specifically includes: immersing the wafer in a resist remover to remove the Nth mask; The residual adhesive on the wafer is rinsed off with a cleaning solution. A wafer wet etching method according to claim 1 or 2, characterized in that, The photoresist in the Nth photoresist layer has a lower viscosity than the photoresist in the (N-1)th photoresist layer. A wafer wet etching method according to claim 1 or 2, characterized in that, The N-1th photoresist layer and the Nth photoresist layer are made of the same material, the exposure time of the Nth photoresist layer is longer than that of the N-1th photoresist layer, and/or the exposure light intensity of the Nth photoresist layer is greater than that of the N-1th photoresist layer. A wafer wet etching method according to claim 1 or 2, characterized in that, Etching the (N-1)th metal layer specifically involves immersing the wafer in the (N-1)th etching solution to etch the (N-1)th metal layer. The (N-1)th etching solution does not react with the (N-1)th mask, the Nth metal layer, or the already etched metal layer. A wafer, characterized in that it comprises: Produced using the wet etching method as described in any one of claims 1 to 9.