Method for improving morphology of photoresist layer and preparation method of semiconductor device

Abstract

According to the method for improving the morphology of the photoresist layer and the preparation method of the semiconductor device provided by the invention, in the process of the photoresist layer needing to be specifically thickened, the method for coating the double-layer photoresist is selected, and the first photoresist layer and the second photoresist layer have the properties of different refractive indexes n and light absorbance k; the thickness of the first photoresist layer and the thickness of the second photoresist layer are reasonably controlled, so that the appearance of the side face of the first groove formed after exposure and development becomes more vertical, the CD white edge is reduced, the requirement for thickening of the photoresist layers in the photoetching process is met, the problem of photoresist residues at the bottom of the first groove can be reduced, and the yield of the semiconductor device is improved. And meanwhile, the first photoresist layer and the second photoresist layer allow photoresist with different properties to be used in the photoetching process, so that the requirements of different processes can be met, a foundation is laid for the subsequent etching process, and the quality and the stability of the formed device are further improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor manufacturing technology, and in particular to a method for improving the morphology of a photoresist layer and a method for preparing a semiconductor device. Background Art

[0002] The photolithography process is an important step in the manufacturing process of chips and integrated circuits. The process is as follows: first, spray the photoresist evenly on the wafer substrate, bake and dry the photoresist to form a dense, uniformly thick photosensitive film, then expose and develop the photoresist layer to engrave a geometric pattern on the photoresist layer, and then use the photoresist layer as a mask to transfer the above geometric pattern to the wafer substrate through an etching process.

[0003] However, researchers have found that in some semiconductor processes that require a specific thickened photoresist, after the photoresist layer is exposed, it is easy to cause uneven light exposure at the bottom of the photoresist layer, which makes it difficult to completely remove the photoresist at the bottom of the photoresist layer when the photoresist layer is subsequently developed, and eventually forms photoresist residue. In addition, for thickened photoresists, there is also a risk of photoresist backflow. Although the above problem can be solved by increasing the exposure dose, increasing the exposure dose will cause the line width to become larger, which does not meet the semiconductor process specifications.

[0004] Therefore, how to increase the thickness of the photoresist layer that needs to be thickened specifically while reducing the risk of backflow and bottom photoresist residue without changing the line width has become a problem that needs to be solved urgently. Summary of the invention

[0005] In view of the shortcomings of the prior art mentioned above, the purpose of the present application is to provide a method for improving the morphology of a photoresist layer and a method for preparing a semiconductor device, so as to solve the problem in the prior art that it is impossible to increase the thickness of the photoresist layer that needs to be thickened specifically and reduce the risk of backflow and bottom photoresist residue without changing the line width.

[0006] In order to achieve the above-mentioned purpose and other related purposes, the present application provides a method for improving the morphology of a photoresist layer in the process of preparing a semiconductor structure, and the method for improving the morphology of a photoresist layer comprises the following steps:

[0007] Providing a substrate, spin coating a first photoresist on the substrate and performing a first pre-bake on the first photoresist to form a first photoresist layer, wherein the first photoresist is a negative photoresist;

[0008] Spin coating a second photoresist on the first photoresist layer and pre-baking the second photoresist for a second time to form a second photoresist layer, wherein the second photoresist is a positive photoresist;

[0009] Placing a first mask on the second photoresist layer, and accurately exposing and developing the second photoresist layer to form a first groove;

[0010] The second photoresist layer at the bottom of the first trench and the exposed first photoresist layer are further developed to remove the second photoresist remaining at the bottom of the first trench and the first photoresist directly below the bottom of the first trench.

[0011] Optionally, the pre-baking temperature after spin coating the first photoresist is 100-130° C., and the baking time is 60-120 s.

[0012] Optionally, the pre-baking temperature after spin coating the second photoresist is 100-130° C., and the baking time is 60-120 s.

[0013] Optionally, a ratio of a thickness of the first photoresist layer to a thickness of the second photoresist layer is 1:10 to 1:20.

[0014] Optionally, the thickness of the first photoresist layer is The thickness of the second photoresist layer is

[0015]

[0016] Optionally, the refractive index n of the first photoresist is 1.4-1.9, and the absorbance k is 0.005-0.6.

[0017] Optionally, the refractive index n of the second photoresist is 1.4-1.9, and the absorbance k is 0.005-0.6.

[0018] Optionally, the developer used when developing the second photoresist layer is a positive photoresist developer, and the developer used when developing the first photoresist layer is a negative photoresist developer.

[0019] Optionally, the inclination angle of the sidewall of the first groove is 85 to 90 degrees.

[0020] The present invention also provides a method for preparing a semiconductor device, wherein the method for preparing a semiconductor device comprises any of the above methods for improving the morphology of a photoresist layer.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: in the case of a photoresist layer that needs to be specifically thickened, a double-layer photoresist coating method is selected, different photoresists have different refractive indices n and absorbances k, and the thickness of the double-layer photoresist is reasonably controlled, so that the side morphology of the photoresist becomes more vertical, the CD white edge is reduced, the requirement for thickening the photoresist layer during the photolithography process and the problem of reducing the residual photoresist at the bottom are solved, thereby improving the performance of the photoresist and being more conducive to the subsequent etching process. At the same time, the double-layer photoresist allows different photoresists to be used during the photolithography process to adapt to the requirements of different processes, laying the foundation for the subsequent etching process, and thereby improving the quality and stability of the formed device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown is a process flow chart of the method for improving the morphology of the photoresist layer in the present invention.

[0023] Figure 2 It is a schematic diagram of the cross-sectional structure after forming the first photoresist layer in the present invention.

[0024] Figure 3 It is a schematic diagram of the cross-sectional structure after forming the second photoresist layer in the present invention.

[0025] Figure 4 It is a schematic diagram of the cross-sectional structure after the second photoresist layer is developed in the present invention.

[0026] Figure 5 It is a schematic diagram of the cross-sectional structure after the first photoresist layer is developed in the present invention.

[0027] Figure 6 Shown is a comparison of the morphology of using a single-layer photoresist and a double-layer photoresist.

[0028] Description of Reference Numerals

[0029] 10. Substrate; 11. First photoresist layer; 12. Second photoresist layer; 13. First trench; S1-S4: steps. DETAILED DESCRIPTION

[0030] The following describes the implementation of the present invention in detail in conjunction with specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the schematic diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0032] For convenience of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings.

[0033] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0034] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0035] This embodiment provides a method for improving the morphology of a photoresist layer during the preparation of a semiconductor structure. Figure 1 , showing a process flow chart of a method for improving the morphology of a photoresist layer, comprising the following steps:

[0036] S1: providing a substrate 10, spin coating a first photoresist on the substrate 10 and performing a first pre-bake on the first photoresist to form a first photoresist layer 11, wherein the first photoresist is a negative photoresist;

[0037] S2: Spin-coating a second photoresist on the first photoresist layer 11 and pre-baking the second photoresist for a second time to form a second photoresist layer 12, wherein the second photoresist is a positive photoresist;

[0038] S3: placing a first mask on the second photoresist layer 12, and accurately exposing and developing the second photoresist layer 12 to form a first groove 13;

[0039] S4: continuing to develop the second photoresist layer 12 and the exposed first photoresist layer 11 at the bottom of the first groove 13 to remove the second photoresist remaining at the bottom of the first groove 13 and the first photoresist directly below the bottom of the first groove 13 .

[0040] Optionally, the substrate 10 may be a silicon substrate 10, a silicon germanium substrate 10, or a silicon carbide substrate 10. Before the first photoresist is spin-coated on the substrate 10, the substrate 10 may be cleaned first, for example, by sequentially using an organic solvent such as acetone and deionized water to remove pollutants on the surface of the substrate 10, and then drying, or first using a dilute acid solution to remove a natural oxide layer on the surface of the substrate 10, then using deionized water to clean, and finally drying, or using the aforementioned cleaning methods for multiple cleanings to obtain a clean substrate 10.

[0041] like Figure 2 As shown, in an optional embodiment, the first photoresist selected in step S1 is a negative photoresist, and the first photoresist is spin-coated on the substrate 10 using a spin coating process with a rotation speed of 3000 rpm and a time of 20 seconds. The first photoresist is subjected to a first pre-bake process to form a first photoresist layer 11. Since the negative photoresist has a non-photosensitive property, the first photoresist layer 11 can be used as a sacrificial layer for subsequent photolithography processes. Specifically, the temperature of the first pre-bake is 100-130°C, and the drying time is 60-120 seconds. For example, the pre-bake temperature is 120°C, and the drying time is 60 seconds, thereby ensuring that the formed first photoresist layer 11 can be fully dried and has a good bond with the substrate 10.

[0042] like Figure 3 As shown, in an optional embodiment, the second photoresist selected in step S2 is a positive photoresist, and the second photoresist is spin-coated on the first photoresist layer 11 using a spin coating process with a rotation speed of 3000 rpm and a time of 20 s. The second photoresist is subjected to a second pre-bake process to form a second photoresist layer 12. Since the positive photoresist has a photosensitive property, the second photoresist layer 12 can form a geometric pattern with the same shape as the first mask under exposure to ultraviolet light. Specifically, the temperature of the second pre-bake is 100-130°C, and the drying time is 60-120 s. For example, the pre-bake temperature is 120°C, and the drying time is 60 s, thereby ensuring that the formed second photoresist layer 12 can be fully dried and has good bonding with the first photoresist layer 11.

[0043] Optionally, the refractive index n of the first photoresist is 1.4-1.9, and the absorbance k is 0.005-0.6; the refractive index n of the second photoresist is 1.4-1.9, and the absorbance k is 0.005-0.6. For example, the refractive index n of the first photoresist is 1.6, and the absorbance k is 0.2; the refractive index n of the second photoresist is 1.5, and the absorbance k is 0.4. This can effectively prevent ultraviolet light from penetrating during exposure and significantly improve the resolution of the pattern formed after the photoresist is developed.

[0044] Optionally, the thickness ratio of the first photoresist layer 11 to the second photoresist layer 12 is 1:10 to 1:20, and the thickness of the first photoresist layer 11 is The thickness of the second photoresist layer 12 is By reasonably controlling the thickness ratio of the first photoresist layer 11 to the second photoresist layer 12, the side morphology of the photoresist layer after exposure and development can be significantly improved, the photoresist residue at the bottom after exposure and development can be eliminated, and the risk of photoresist backflow caused by the increase in the thickness of the second photoresist layer 12 can be reduced. In addition, the formed first photoresist layer 11 can also improve the adhesion and corrosion resistance between the photoresist and the substrate 10.

[0045] In step S3, see Figure 1 and Figure 4 , placing a first mask on the second photoresist layer 12 , and accurately exposing and developing the second photoresist layer 12 to form a first groove 13 .

[0046] Specifically, the second photoresist layer 12 and the first photoresist layer 11 are exposed successively using the first mask, such as Figure 4 As shown, the second photoresist layer 12 is precisely exposed and developed to form a first groove 13. During the precise exposure process, the second photoresist layer 12, which is a positive photoresist, will undergo a photoreaction. The substrate 10 after precise exposure is then treated with a developer. The developer used for developing the second photoresist layer 12 is generally a positive photoresist developer. The positive photoresist developer opens the illuminated area of ​​the second photoresist layer 12 to form the first groove 13. If the first photoresist layer 11 is not subsequently developed, the positive photoresist developer here cannot completely remove the photoresist in the first groove 13, so that some photoresist remains at the bottom of the first groove 13.

[0047] In step S4, see Figure 1 and Figure 5 , developing the first photoresist layer 11 exposed by the first groove 13 to completely eliminate the second photoresist remaining at the bottom of the first groove 13 .

[0048] Specifically, the formed first groove 13 exposes the first photoresist layer 11. Since the first photoresist layer 11, which is a negative photoresist, does not undergo photoreaction, a new developer is replaced on the basis of step S3 to continue developing the first photoresist layer 11. The developer used for developing the first photoresist layer 11 here is generally a negative photoresist developer, and since the negative photoresist developer has an isotropic property, it is easier to eliminate the photoresist residue at the bottom of the first groove 13.

[0049] like Figure 6 As shown, it is a morphology comparison diagram of using a single-layer photoresist and a double-layer photoresist with different ratios of the thickness of the second photoresist layer 12 and the first photoresist layer 11. Figure 6 It can be seen that compared with forming only a single photoresist layer, the side profile of the first groove 13 formed after forming the first photoresist layer 11 and the second photoresist layer 12 on the substrate 10 and then undergoing exposure and development becomes more vertical and can also reduce the CD white edge.

[0050] In another embodiment, a method for preparing a semiconductor device is also provided, and the method for preparing a semiconductor device includes the above-mentioned method for improving the morphology of the photoresist layer, that is, the above-mentioned method for improving the morphology of the photoresist layer can adapt to the requirements of different processes and can improve the quality and stability of the formed device.

[0051] In summary, the present invention provides a method for improving the morphology of a photoresist layer and a method for preparing a semiconductor device. In a process that requires a specific thickened photoresist layer, a method for coating a double layer of photoresist is selected, and the properties of different refractive indices n and absorbance k of the first photoresist layer and the second photoresist layer are utilized, and by reasonably controlling the thickness of the first photoresist layer and the second photoresist layer, the side morphology of the first groove formed after exposure and development becomes more vertical, and the CD white edge is reduced, which solves the requirement of thickening the photoresist layer during the photolithography process and can reduce the problem of residual photoresist at the bottom of the first groove, thereby being more conducive to the subsequent etching process. At the same time, the first photoresist layer and the second photoresist layer allow the use of photoresists of different properties during the photolithography process, thereby being able to adapt to the requirements of different processes, laying the foundation for subsequent etching processes, and thereby improving the quality and stability of the formed device.

[0052] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Anyone familiar with the technology may modify, change or combine the above embodiments without violating the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present application shall still be covered by the claims of the present application.

Claims

1. A method for improving the morphology of a photoresist layer in the process of preparing a semiconductor structure, characterized in that: The method for improving the morphology of the photoresist layer comprises the following steps: Providing a substrate, spin coating a first photoresist on the substrate and performing a first pre-bake on the first photoresist to form a first photoresist layer, wherein the first photoresist is a negative photoresist; Spin coating a second photoresist on the first photoresist layer and pre-baking the second photoresist for a second time to form a second photoresist layer, wherein the second photoresist is a positive photoresist; Placing a first mask on the second photoresist layer, and accurately exposing and developing the second photoresist layer to form a first groove; The second photoresist layer at the bottom of the first trench and the exposed first photoresist layer are further developed to remove the second photoresist remaining at the bottom of the first trench and the first photoresist directly below the bottom of the first trench.

2. The method for improving the morphology of a photoresist layer according to claim 1, characterized in that: The pre-baking temperature after spin coating the first photoresist is 100-130° C., and the baking time is 60-120 seconds.

3. The method for improving the morphology of a photoresist layer according to claim 1, characterized in that: The pre-baking temperature after spin coating the second photoresist is 100-130° C., and the baking time is 60-120 seconds.

4. The method for improving the morphology of a photoresist layer according to claim 1, characterized in that: The ratio of the thickness of the first photoresist layer to the thickness of the second photoresist layer is 1:10 to 1:

20.

5. The method for improving the morphology of a photoresist layer according to claim 4, characterized in that: The thickness of the first photoresist layer is The thickness of the second photoresist layer is 6. The method for improving the morphology of a photoresist layer according to any one of claims 1 to 5, characterized in that: The refractive index n of the first photoresist is 1.4-1.9, and the absorption rate k is 0.005-0.

6.

7. The method for improving the morphology of a photoresist layer according to any one of claims 1 to 5, characterized in that: The refractive index n of the second photoresist is 1.4-1.9, and the absorption rate k is 0.005-0.

6.

8. The method for improving the morphology of a photoresist layer according to claim 6, characterized in that: The developer used when developing the second photoresist layer is a positive photoresist developer, and the developer used when developing the first photoresist layer is a negative photoresist developer.

9. The method for improving the morphology of a photoresist layer according to claim 1, characterized in that: The inclination angle of the side wall of the first groove is 85-90 degrees.

10. A method for preparing a semiconductor device, characterized in that: The method for preparing the semiconductor device comprises the method for improving the morphology of the photoresist layer according to any one of claims 1 to 9.

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