Method for improving topography of photoresist layer and method for manufacturing semiconductor device

Abstract

The application provides a method for improving the morphology of a photoresist layer and a preparation method of a semiconductor device. In a process requiring a specific thickened photoresist layer, a method for coating a double-layer photoresist is selected, the first photoresist layer and the second photoresist layer have different refractive indexes n and light absorption rates k, and the thicknesses of the first photoresist layer and the second photoresist layer are reasonably controlled, so that the side surface morphology of the first trench formed after exposure and development treatment becomes more vertical, CD white edges are reduced, the requirement of the photoresist layer thickening in the photoetching process is solved, and the problem of the photoresist residue at the bottom of the first trench is reduced, thereby being more beneficial to the subsequent etching process. Meanwhile, the first photoresist layer and the second photoresist layer allow different photoresists to be used in the photoetching process, thereby being able to adapt to the requirements of different processes, laying a foundation for the subsequent etching process, and further improving the quality and stability of the formed device.

Description

TECHNICAL FIELD

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

[0002] As an important step in the manufacturing process of chips and integrated circuits, the photoetching process is as follows: first, photoresist is uniformly sprayed on a wafer substrate, the photoresist is baked and dried to form a dense, uniform-thickness photosensitive film, the photoresist layer is then exposed and developed to draw geometric patterns on the photoresist layer, and then the photoresist layer is used as a mask to transfer the geometric patterns to the wafer substrate through an etching process.

[0003] However, researchers have found that in some semiconductor processes that require a specific thickening of the photoresist, after the photoresist layer is exposed, the bottom of the photoresist layer is prone to uneven light exposure, which makes it difficult to completely remove the photoresist at the bottom of the photoresist layer during subsequent development of the photoresist layer, ultimately resulting in photoresist residues. In addition, for thickened photoresist, there is also a risk of reverse glue. Although the above problems can be solved by increasing the exposure dose, increasing the exposure dose will cause the line width to become larger, thus not meeting the specifications of the semiconductor process.

[0004] Therefore, how to increase the thickness of the photoresist layer that needs to be thickened without changing the line width, while reducing the risk of reverse glue and bottom photoresist residues, has become a problem that needs to be solved. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a method for improving the morphology of a photoresist layer and a method for manufacturing a semiconductor device to solve the problem that the prior art cannot increase the thickness of the photoresist layer that needs to be thickened without changing the line width, and reduce the risk of reverse glue and bottom photoresist residues.

[0006] 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 manufacturing a semiconductor structure, which comprises the following steps:

[0007] A substrate is provided, a first photoresist is spin-coated on the substrate, and the first photoresist is subjected to a first pre-baking to form a first photoresist layer, the first photoresist being a negative photoresist;

[0008] A second photoresist is spin-coated on the first photoresist layer, and the second photoresist is subjected to a second pre-baking to form a second photoresist layer, the second photoresist being a positive photoresist;

[0009] placing a first mask on the second photoresist layer, performing accurate exposure and development on the second photoresist layer to form a first trench;

[0010] continuing to develop the second photoresist layer at the bottom of the first trench and the exposed first photoresist layer, and removing the second photoresist layer remaining at the bottom of the first trench and the first photoresist layer directly below the bottom of the first trench.

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

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

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

[0014] Optionally, the thickness of the first photoresist layer is 100-200nm. Optionally, the thickness of the second photoresist layer is 100-200nm.

[0015] Optionally, the refractive index n of the first photoresist layer is 1.4-1.9, and the light absorption rate k is 0.005-0.6.

[0016] Optionally, the refractive index n of the second photoresist layer is 1.4-1.9, and the light absorption rate k is 0.005-0.6.

[0017] Optionally, the developing solution used for developing the second photoresist layer is a positive photoresist developing solution, and the developing solution used for developing the first photoresist layer is a negative photoresist developing solution.

[0018] Optionally, the inclination angle of the sidewall of the first trench is 85-90 degrees.

[0019] The application further provides a semiconductor device preparation method, which comprises the above-mentioned method for improving the morphology of a photoresist layer.

[0020] Compared with the prior art, the present application has the beneficial effects that in the case of facing the requirement of thickening the photoresist layer, the method of selecting double-layer photoresist is used, the different photoresists have different refractive index n and light absorption rate k, and the thickness of the double-layer photoresist is reasonably controlled, so that the photoresist side appearance becomes more vertical, the CD white edge is reduced, the requirement of thickening the photoresist layer in the photoetching process is solved, and the problem of photoresist residue at the bottom is reduced, thereby improving the performance of the photoresist and being more beneficial to the subsequent etching process. Meanwhile, the double-layer photoresist allows different photoresists to be used in the photoetching process to adapt to the requirements of different processes, lays a foundation for the subsequent etching process, and further improves the quality and stability of the formed device. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A process flow diagram of the method for improving the photoresist layer appearance in the present application is shown.

[0022] Figure 2 A cross-sectional structure schematic diagram after forming the first photoresist layer in the present application is shown.

[0023] Figure 3 A cross-sectional structure schematic diagram after forming the second photoresist layer in the present application is shown.

[0024] Figure 4 A cross-sectional structure schematic diagram after developing the second photoresist layer in the present application is shown.

[0025] Figure 5 A cross-sectional structure schematic diagram after developing the first photoresist layer in the present application is shown.

[0026] Figure 6 A comparison diagram of the appearance of using single-layer photoresist and double-layer photoresist is shown.

[0027] BRIEF DESCRIPTION OF DRAWINGS

[0028] 10, substrate; 11, first photoresist layer; 12, second photoresist layer; 13, first trench; S1-S4: steps. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below with specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied by different specific embodiments, and the details in the present specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0030] As illustrated in the embodiments of the present application, the schematic views of the device structure are partially enlarged without the general proportion for the convenience of illustration, and the schematic views are only examples which should not limit the scope of protection of the present application. In addition, the three-dimensional spatial dimensions including length, width and depth should be included in the actual production.

[0031] For the convenience of description, spatial relationship words such as "under", "below", "lower", "underneath", "above", "upper" and the like can be used herein to describe the relationship of one element or feature with other elements or features shown in the drawings. It should be understood that these spatial relationship words are intended to include other orientations of the device in use or operation in addition to the orientations depicted in the drawings.

[0032] In the context of the present application, the structure described as "on" the first feature can include the embodiment in which the first and second features form direct contact, and can also include the embodiment in which another feature is formed between the first and second features, so that the first and second features can not be in direct contact.

[0033] It should be noted that the diagrams provided in the embodiments only schematically illustrate the basic concept of the present application, and only the components related to the present application are shown in the diagrams, not the number, shape and size of the components when actually implemented. The actual implementation of each component can be a random change, and the component layout pattern can be more complex.

[0034] The embodiments provide a method for improving the topography of a photoresist layer in a semiconductor structure preparation process. Referring to Figure 1 , a process flow diagram of the method for improving the topography of a photoresist layer is shown, which includes the following steps:

[0035] S1: providing a substrate 10, spin-coating a first photoresist on the substrate 10 and performing a first pre-baking on the first photoresist to form a first photoresist layer 11, the first photoresist being a negative photoresist;

[0036] S2: spin-coating a second photoresist on the first photoresist layer 11 and performing a second pre-baking on the second photoresist to form a second photoresist layer 12, the second photoresist being a positive photoresist;

[0037] S3: placing a first mask on the second photoresist layer 12, performing a precise exposure and development on the second photoresist layer 12 to form a first trench 13;

[0038] S4: Continue to develop the second photoresist layer 12 at the bottom of the first trench 13 and the exposed first photoresist layer 11 to remove the second photoresist remaining at the bottom of the first trench 13 and the first photoresist directly below the bottom of the first trench 13.

[0039] Optionally, the substrate 10 can be a silicon substrate 10, a germanium-silicon substrate 10, or a silicon carbide substrate 10. Before spin-coating the first photoresist onto the substrate 10, the substrate 10 can be cleaned, for example, by sequentially cleaning with an organic solvent such as acetone and deionized water to remove contaminants from the surface of the substrate 10, followed by drying; or by first removing the natural oxide layer on the surface of the substrate 10 with a diluted acid solution, then cleaning with deionized water, and finally drying; or by performing multiple cleaning methods as described above to obtain a clean substrate 10.

[0040] like Figure 2 As shown, in an optional embodiment, the first photoresist selected in step S1 is a negative photoresist. The first photoresist is spin-coated onto the substrate 10 using a spin-coating process with a rotation speed of 3000 rpm and a time of 20 s. The first photoresist is then subjected to a first pre-baking process to form a first photoresist layer 11. Since the negative photoresist has non-photosensitive properties, the first photoresist layer 11 can serve as a sacrificial layer for subsequent photolithography processes. Specifically, the temperature of the first pre-baking is 100-130°C, and the drying time is 60-120 s. For example, the pre-baking temperature is 120°C, and the drying time is 60 s, thereby ensuring that the formed first photoresist layer 11 can be fully dried and has a good bond with the substrate 10.

[0041] like Figure 3 As shown, in an optional embodiment, the second photoresist selected in step S2 is a positive photoresist. A spin-coating process with a rotation speed of 3000 rpm and a time of 20 seconds is used to spin-coat the second photoresist onto the first photoresist layer 11. A second pre-baking process is then performed on the second photoresist to form the second photoresist layer 12. Since the positive photoresist has photosensitive properties, the second photoresist layer 12 can form a geometric pattern with the same shape as the first photomask under ultraviolet light exposure. Specifically, the temperature of the second pre-baking is 100–130°C, and the drying time is 60–120 seconds. For example, the pre-baking temperature is 120°C, and the drying time is 60 seconds, thereby ensuring that the formed second photoresist layer 12 can be fully dried and has good adhesion to the first photoresist layer 11.

[0042] Optionally, the first photoresist has a refractive index n of 1.4-1.9 and an optical absorption k of 0.005-0.6, and the second photoresist has a refractive index n of 1.4-1.9 and an optical absorption k of 0.005-0.6, for example, the first photoresist has a refractive index n of 1.6 and an optical absorption k of 0.2, and the second photoresist has a refractive index n of 1.5 and an optical absorption k of 0.4, which can effectively prevent the penetration of ultraviolet light during exposure and significantly improve the resolution of the pattern formed after the development of the photoresist.

[0043] Optionally, the thickness ratio of the first photoresist layer 11 to the second photoresist layer 12 is 1:10-1:20, and the thickness of the first photoresist layer 11 is 0.5-5 microns. The thickness of the second photoresist layer 12 is 5-50 microns. By reasonably controlling the thickness ratio of the first photoresist layer 11 to the second photoresist layer 12, the side profile of the photoresist layer after exposure and development can be significantly improved, the residual photoresist at the bottom after exposure and development can be eliminated, and the risk of reverse glue caused by the increase in the thickness of the second photoresist layer 12 can be reduced. In addition, the first photoresist layer 11 formed can also improve the adhesion and etch resistance between the photoresist and the substrate 10.

[0044] In step S3, please refer to Figure 1 and Figure 4 , place a first mask on the second photoresist layer 12, and perform precise exposure and development on the second photoresist layer 12 to form a first trench 13.

[0045] Specifically, the first mask is used to perform exposure on the second photoresist layer 12 and the first photoresist layer 11 in sequence, as shown in Figure 4 , the second photoresist layer 12 is precisely exposed and developed to form a first trench 13. In the process of precise exposure, the second photoresist layer 12 of positive photoresist will undergo a photochemical reaction. The substrate 10 after precise exposure is treated by a developing solution. The developing solution used for developing the second photoresist layer 12 is generally a positive photoresist developing solution. The positive photoresist developing solution opens the light-exposed area of the second photoresist layer 12 to form the first trench 13. If the subsequent development of the first photoresist layer 11 is not performed, the positive photoresist developing solution cannot completely remove the photoresist in the first trench 13, so that part of the photoresist remains at the bottom of the first trench 13.

[0046] In step S4, please refer to Figure 1 and Figure 5 , the first photoresist layer 11 exposed by the first trench 13 is developed to completely remove the residual second photoresist at the bottom of the first trench 13.

[0047] Specifically, the first trench 13 exposes the first photoresist layer 11. Since the first photoresist layer 11, which is a negative photoresist, will not undergo photoreaction, a new developer is used to continue developing the first photoresist layer 11 based on step S3. The developer used to develop the first photoresist layer 11 is generally a negative photoresist developer. Since the negative photoresist developer has isotropic properties, it is easier to eliminate photoresist residue at the bottom of the first trench 13.

[0048] like Figure 6 As shown, it displays a morphology comparison image of using a single-layer photoresist and a double-layer photoresist, with the second photoresist layer 12 and the first photoresist layer 11 having different thicknesses. Figure 6 It can be seen that, compared with forming only a single layer of photoresist, the side morphology of the first trench 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 processes becomes more vertical, and can also reduce the white edge of the CD.

[0049] In another embodiment, a method for fabricating a semiconductor device is also provided, the method for improving the morphology of the photoresist layer described above, that is, the method for improving the morphology of the photoresist layer can adapt to different process requirements and can improve the quality and stability of the formed device.

[0050] In summary, the present invention provides a method for improving the morphology of a photoresist layer and a method for fabricating a semiconductor device. In processes requiring a specific thickness of the photoresist layer, a double-layer photoresist coating method is chosen. Utilizing the different refractive indices (n) and absorbance (k) of the first and second photoresist layers, and by rationally controlling the thicknesses of the first and second photoresist layers, the side morphology of the first trench formed after exposure and development becomes more vertical, reducing CD white edges. This solves the requirement for photoresist layer thickness during photolithography and reduces the problem of photoresist residue at the bottom of the first trench, thus facilitating subsequent etching processes. Furthermore, the first and second photoresist layers allow the use of photoresists with different properties during photolithography, adapting to different process requirements and laying the foundation for subsequent etching processes, thereby improving the quality and stability of the formed device.

[0051] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify, alter, or combine the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A method for improving photoresist layer topography during the fabrication of a semiconductor structure, comprising: The method for improving the topography of a photoresist layer comprises the following steps: providing a substrate, spin-coating a first photoresist on the substrate and performing a first pre-baking 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 performing a second pre-baking on the second photoresist to form a second photoresist layer, wherein the second photoresist is a positive photoresist, and the thickness ratio of the first photoresist layer to the second photoresist layer is 1:10-1:20; placing a first mask on the second photoresist layer, performing a precise exposure and development on the second photoresist layer to form a first trench; continuing the development on the second photoresist layer and the first photoresist layer exposed at the bottom of the first trench 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 of claim 1, wherein, The pre-baking temperature after spin-coating the first photoresist is 100-130℃, and the drying time is 60-120s.

3. The method of claim 1, wherein the photoresist layer is formed by a spin coating process. The pre-baking temperature after spin-coating the second photoresist is 100-130℃, and the drying time is 60-120s.

4. The method of claim 1, wherein the photoresist layer is formed by a spin coating process. The thickness of the first photoresist layer is 4000-8000Å, and the thickness of the second photoresist layer is 40000-50000Å.

5. The method of claim 1-4, wherein, The refractive index n of the first photoresist is 1.4-1.9, and the light absorption rate k is 0.005-0.

6.

6. The method of claim 1-4, wherein The refractive index n of the second photoresist is 1.4-1.9, and the light absorption rate k is 0.005-0.

6.

7. The method of claim 5, wherein the photoresist layer is exposed to the plasma. The developer used for developing the second photoresist layer is a positive photoresist developer, and the developer used for developing the first photoresist layer is a negative photoresist developer.

8. The method of claim 1, wherein the photoresist layer is formed by a spin coating process. The inclination angle of the sidewall of the first trench is 85-90 degrees.

9. A method of manufacturing a semiconductor device, characterized by, The method for preparing a semiconductor device comprises the method for improving the topography of a photoresist layer according to any one of claims 1-8.

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