Preparation method of multilayer EUV photoresist

Abstract

The invention discloses a preparation method of a multilayer EUV photoresist, and relates to the technical field of photoresists, the multilayer EUV photoresist comprises an EUV photoresist and a covering structure or an intercalation structure formed by at least one layer of antireflection film, the covering structure is a single-layer or multi-layer film covering structure formed by covering one or more layers of antireflection films on the EUV photoresist; the intercalation structure is a multilayer film structure formed by inserting one or more layers of antireflection films into EUV photoresist and overlapping the antireflection film layers and the photoresist. The invention has the technical effect that the obtained photoresist has higher exposure efficiency on extreme ultraviolet light with a certain wavelength or a certain wave band. The heat stability, the chemical stability and the mechanical stability are higher; cracks and defects are more difficult to generate; thermal expansion resistance is better; and the reaction with water in air is difficult.

Description

Technical Field

[0001] The present invention relates to the technical field of photoresists, and particularly to a method for preparing a multilayer EUV photoresist. Background Art

[0002] Photoresist is an important photosensitive material used in semiconductor manufacturing and micro-nano processing. Its key role is to achieve high-resolution and high-precision pattern transfer, thereby manufacturing complex micro-nano structures. When exposed to a light source of a specific wavelength, the chemical properties of the photoresist change, allowing fine patterns to be formed on its surface. These patterns are then transferred to the substrate material, and the required microelectronic structures are generated through subsequent etching or deposition processes. Photoresists are widely used in fields such as semiconductor manufacturing, microelectromechanical systems, optoelectronic devices, and display manufacturing.

[0003] With the continuous progress of integrated circuit manufacturing technology, the critical dimensions of the lithography process are continuously shrinking. Today's lithography frontier technologies are deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography technologies. EUV lithography technology is bound to replace DUV lithography technology. Because the wavelength of EUV lithography is shorter, its resolution is higher. EUV can achieve the same line width with fewer process steps and lower costs without using multiple patterning like DUV lithography technology. Therefore, EUV lithography is crucial for the production of advanced nodes (such as 5 nm, 3 nm).

[0004] The requirements for photoresists in EUV lithography technology are also getting higher and higher. EUV light with a wavelength of 13.5 nm has fewer photons compared to DUV light and a shorter penetration depth in photoresist materials. In thick photoresists, most EUV photons are absorbed on the surface, and the absorbed EUV light will scatter in the lower layer, resulting in incomplete or uneven exposure in the depth of the photoresist. This uneven exposure will lead to a decrease in pattern fidelity, and the top of the resist layer will be exposed more than the bottom. Therefore, using a thick resist will result in unclear, blurred, or thinned patterns, which are not suitable for high-resolution feature requirements. And the photon dose of EUV is low, and random effects occur. These reasons will increase the line edge roughness (LER) and line width roughness (LWR). High-resolution EUV lithography for advanced nodes (such as 7 nm, 5 nm and below) requires extremely precise control of pattern edges and line widths. Thinner resists can reduce the line edge roughness (LER) and line width roughness (LWR), thereby helping to improve the accuracy of small feature patterns. And thinner resists can reduce the amount of outgassing materials, reduce the risk of contamination, and better meet the high requirements for EUV tool maintenance.

[0005] Therefore, the thickness of EUV photoresist is usually between 20 nanometers and 50 nanometers. This is much thinner than the traditional resist layers used in deep ultraviolet (DUV) lithography, whose thickness is usually between 80 nanometers and 100 nanometers. It can be predicted that the thickness of photoresist for future EUV should be controlled below 20 nm or even below 10 nanometers.

[0006] Photosensitivity refers to the sensitivity of photoresist to light, that is, the ability to undergo chemical reactions under the irradiation of light with a specific wavelength. If the photosensitivity of the photoresist is low, then higher light intensity or longer exposure time is required during the lithography process to achieve the desired exposure effect. Different photoresists have different photosensitivities to light of different wavelengths. For example, some photoresists have high photosensitivity under deep ultraviolet light (DUV, 193 nm), while they may have low photosensitivity under extreme ultraviolet light (EUV, 13.5 nm). This poses challenges for photoresist technology in promoting the development of semiconductor manufacturing towards smaller sizes and higher densities.

[0007] The research and optimization of photoresist have always been an important research direction in the field of materials science and engineering. By improving the photosensitive performance, heat resistance performance, and resolution of photoresist, the performance and integration of microelectronic devices can be further improved.

[0008] One disadvantage of the ultra-thin EUV photoresist is that due to its very thin thickness, the volume capable of participating in the exposure reaction is much smaller than that of DUV, which requires increasing the absorption rate of EUV photoresist.

[0009] Reflections on the surface and inside of the photoresist will result in the loss of a part of the light energy. The reflected light cannot effectively participate in the exposure process, thus reducing the light energy utilization rate. These factors jointly affect the efficiency and accuracy of the lithography process. Therefore, in the design and optimization of photoresist, how to reduce reflections and increase the light absorption rate is an important research direction.

[0010] EUV photoresist also requires higher thermal stability, chemical stability, and mechanical stability. The high energy of EUV light will generate local heating, which requires the photoresist to be able to withstand these conditions without reducing or losing its resolution. They must also be resistant to chemical swelling during the development process to maintain the authenticity of the fine patterns. If the mechanical properties of the photoresist are poor, defects may occur during the coating process, or fractures or peeling may occur during the development process. Summary of the Invention

[0011] The objective of the present invention is to solve the technical problem of low absorption efficiency of ultra-thin EUV photoresist, improve the stability of EUV photoresist, and propose a preparation method for multi-layer EUV photoresist. By covering the EUV photoresist with one or more anti-reflection film layers, the light intensity acting on the photoresist is increased, thereby improving the light source utilization rate of the photoresist. Or by inserting one or more anti-reflection film layers into the photoresist, the absorption rate of the photoresist for the exposure light is increased. The photoresist prepared by the method of the present invention solves the technical problem of low absorption efficiency of the existing photoresist for the lithography light source and improves the stability of the photoresist.

[0012] To solve the above technical problems. The technical solution adopted by the present invention is:

[0013] A preparation method for multi-layer EUV photoresist, comprising an EUV photoresist and a covering structure or an intercalation structure formed by at least one anti-reflection film layer. The covering structure is one or more anti-reflection film layers covering on the EUV photoresist to form a covering structure of a single-layer or multi-layer film; the intercalation structure is one or more anti-reflection film layers inserted into the EUV photoresist to form a multi-layer film structure in which the anti-reflection film layer and the photoresist are superimposed on each other.

[0014] Further, in the single-layer or multi-layer film covering structure, the single-layer film is formed by alternately introducing trimethylaluminum and water as precursors, using an inert gas as the carrier gas, and performing atomic layer deposition at room temperature or below 100°C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds; the introduction time of water is 50 milliseconds and the purge time is 30 seconds.

[0015] Further, in the single-layer or multi-layer film covering structure, for the multi-layer film, first, an alumina layer with an optical thickness of a half-wavelength layer is grown by atomic layer deposition technology at room temperature or below 100°C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds, and the introduction time of water is 50 milliseconds and the purge time is 30 seconds; then a hafnium oxide layer with a thickness of half a wavelength is grown, using hafnium tetrakis(dimethylamide) and ozone as precursors and alternately introducing them, using an inert gas as the carrier gas, and performing atomic layer deposition at room temperature or below 100°C. Among them, the introduction time of hafnium tetrakis(dimethylamide) is 50 milliseconds and the purge time is 30 seconds, and the introduction time of ozone is 50 milliseconds and the purge time is 30 seconds.

[0016] Furthermore, the antireflection film layer and the photoresist are stacked on top of each other into a multi-layer film structure by inserting one or more antireflection films into the EUV photoresist. Among them, for a single layer film, trimethylaluminum and water are used as precursors and alternately introduced, with an inert gas as the carrier gas, and atomic layer deposition is carried out at room temperature or below 100°C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds; the introduction time of water is 50 milliseconds and the purge time is 30 seconds. For a multi-layer film, first, a layer of alumina with an optical thickness of a half-wavelength layer is grown using atomic layer deposition technology at room temperature or below 100°C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds, the introduction time of water is 50 milliseconds and the purge time is 30 seconds; then a hafnium oxide layer with a thickness of half a wavelength is grown, using tetrakis(dimethylamino)hafnium and ozone as precursors and alternately introduced, with an inert gas as the carrier gas, and atomic layer deposition is carried out at room temperature or below 100°C. Among them, the introduction time of tetrakis(dimethylamino)hafnium is 50 milliseconds and the purge time is 30 seconds, and the introduction time of ozone is 50 milliseconds and the purge time is 30 seconds.

[0017] Furthermore, the inert gas is nitrogen or argon.

[0018] Furthermore, the thickness of the alumina film layer is 2.1 + 4.1k nanometers, where k = 0, 1, 2, 3.

[0019] A multi-layer EUV photoresist is prepared by the above method, and the photoresist has a covering structure or an intercalated structure formed by at least one antireflection film.

[0020] The principle of the present invention is:

[0021] The emergence of EUV technology requires the thickness of the photoresist to be controlled below 50 nanometers, and it may be developed to below 10 nanometers in the future. Therefore, in EUV lithography, the reaction volume of the photoresist is much smaller than that in DUV lithography, and it is urgent to improve the exposure sensitivity of the EUV photoresist.

[0022] When light passes through the interface of different media, due to the difference in refractive index, partial reflection will occur. By designing an antireflection film with appropriate materials and thickness, it is possible to make the reflected light generated at the interface between the antireflection film layer and the photoresist and the reflected light on the surface of the antireflection film layer have opposite phases, so that they interfere with each other and cancel each other out, reducing the intensity of the reflected light. Since the reflected light is reduced, more light can enter the photoresist through the antireflection film layer, thereby increasing the intensity of the transmitted light. Therefore, the role of the antireflection film layer is to optimize the distribution of light, so that more light can be effectively utilized by the photoresist.

[0023] The metal oxide coating is very dense, which can effectively enhance the stability of the photoresist. The presence of the photoresist during exposure isolates the air, avoiding unnecessary chemical reactions between the photoresist and air during non-exposure processes (such as during wafer transfer). The metal oxide coating has a small coefficient of thermal expansion, which can offset the thermal expansion during the lithography process.

[0024] The material of the antireflection film layer can be selected from oxides, photoresists of different materials, etc. The antireflection film layer can be grown by spin coating, chemical vapor deposition (MOCVD, ALD, etc.), and molecular layer deposition (MLD). The thickness of the antireflection film layer needs to be determined according to the refractive index of the antireflection film layer and the wavelength of the exposure light source.

[0025] The technical effects of the present invention are:

[0026] 1. The photoresist with an antireflection film layer has a higher exposure efficiency for extreme ultraviolet light of a certain wavelength or a certain wavelength band than the photoresist without a film layer.

[0027] 2. The photoresist with an antireflection film layer has higher thermal stability, chemical stability, and mechanical stability than the photoresist without a film layer: it is less likely to crack and have defects; it is more resistant to thermal expansion; it is less likely to react with water in the air. Brief Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the photoresist with a multi-layer antireflection film layer in Embodiment 1 of the present invention;

[0029] Figure 2 It is a schematic diagram of the photoresist with an intercalated antireflection film layer in Embodiment 2 of the present invention.

[0030] Figure 3 It is a comparison schematic diagram of the photoresist with and without a coating layer.

[0031] In the figure: 1. Exposure light; 2. Antireflection film layer; 3. Photoresist; 4. Reflected light. Detailed Embodiments

[0032] The technical solution of the present invention will be further described below with reference to the drawings. The highly stable photoresist described in the present invention is as Figure 1-2 shown.

[0033] As the first embodiment, the coating layer adopts a multi-layer film scheme and an intercalated scheme to form the photoresist structures shown in Embodiment 1 and Embodiment 2. Among them, the multi-layer film scheme: a layer or multiple layers of antireflection film are covered on the surface of the photoresist. The intercalated scheme: the antireflection film layer and the photoresist are stacked on top of each other to form a multi-layer film structure.

[0034] Embodiment 1

[0035] Multi-layer film solution: Cover the surface of the photoresist with one or more anti-reflection films.

[0036] In the current chip manufacturing process, in the lithography process, the photoresist is first spin-coated on the wafer and then sent for exposure. Taking the EUV light source as an example, the wavelength of the exposure light source is 13.5 nm. The spin-coating method cannot meet the requirements of EUV photoresist because defects and fractures are likely to occur when spin-coating a photoresist with a thickness of dozens of nanometers. At present, some people try to deposit EUV photoresist by means of atomic layer deposition. The present invention can cooperate with this method to improve the absorption efficiency of EUV photoresist. After the photoresist is deposited by atomic layer deposition, atomic layer deposition (ALD) can be carried out in-situ. According to the idea of this invention patent, a layer of aluminum oxide can be grown on the surface of the photoresist by ALD process as an anti-reflection film. The specific growth process is as follows: trimethylaluminum and water are used as precursors and alternately introduced, and inert gases (nitrogen, argon) are used as carrier gases. To prevent the photoresist from denaturing due to rising temperature, atomic layer deposition can be carried out at room temperature or below 100 °C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds; the introduction time of water is 50 milliseconds and the purge time is 30 seconds. Atomic layer deposition technology can precisely control the thickness of the grown film layer, making it possible to control the thickness of the aluminum oxide film layer to the nanometer level. The refractive index of aluminum oxide n = 1.63. According to the anti-reflection film formula D = (2k + 1)λ / 4n, it can be seen that when the thickness of the aluminum oxide film layer is 2.1 + 4.1k (k = 0, 1, 2, 3) nanometers, it has the effect of increasing the transmitted light. Due to the existence of the anti-reflection film, on the one hand, it can increase the exposure efficiency of the photoresist, and on the other hand, the dense aluminum oxide film layer can enhance the stability of the photoresist, preventing the wafer from cracking and having defects due to reasons such as vibration and thermal expansion, and can isolate water and oxygen in the air.

[0037] The selection of the single-layer film can also be a hybrid graded-index thin film, which is based on metal organic chemical vapor deposition (MOCVD). During the MOCVD deposition process, two thin films are deposited simultaneously, one with a low refractive index and the other with a high refractive index. By controlling the deposition rates of the two thin films, it is theoretically possible to obtain any thin film with a refractive index between the above high and low refractive index values.

[0038] If the broadening of the exposure light source is relatively wide, the single-layer film can only enhance the transmission of light of a certain wavelength, and the energy of other wavelength bands is wasted. In this case, a multi-layer film solution can be used, such as the λ / 4-λ / 2W film and the λ / 4-λ / 4V film and their deformed forms. For example, on the surface of the photoresist, a layer of aluminum oxide with an optical thickness of a half-wavelength layer is first grown by atomic layer deposition (using trimethylaluminum and water as precursors and alternately introducing them, with an inert gas (nitrogen, argon) as the carrier gas. To prevent the photoresist from denaturing due to the increase in temperature, atomic layer deposition can be carried out at room temperature or below 100°C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds; the introduction time of water is 50 milliseconds and the purge time is 30 seconds.). Then, a hafnium oxide layer with a thickness of half a wavelength is grown (using hafnium tetrakis(dimethylamide) and ozone as precursors and alternately introducing them, with an inert gas (nitrogen, argon) as the carrier gas. To prevent the photoresist from denaturing due to the increase in temperature, atomic layer deposition can be carried out at room temperature or below 100°C. The introduction time of hafnium tetrakis(dimethylamide) is 50 milliseconds and the purge time is 30 seconds; the introduction time of ozone is 50 milliseconds and the purge time is 30 seconds.). Since the refractive indices of aluminum oxide and hafnium oxide are different, their combination can achieve enhanced transmission across the entire wavelength band. This multi-layer film solution improves the exposure efficiency of the photoresist.

[0039] Example 2

[0040] Intercalation scheme: Stack the anti-reflection film layer and the photoresist to form a multi-layer film structure.

[0041] If there are two photoresists that are sensitive to a certain wavelength of UV light source, namely photoresist A and photoresist B, with different compositions and refractive indices. Compared with a single photoresist A and photoresist B, photoresist A and photoresist B can be cross-covered on the wafer, with photoresist A - photoresist B - photoresist A from top to bottom. Therefore, photoresist A serves as an anti-reflection film for photoresist B, and photoresist A + photoresist B can serve as an anti-reflection film for the underlying photoresist A, thereby improving the performance of the overall photoresist.

[0042] The specific preparation method of this embodiment is the same as that of Embodiment 1. The difference is that this embodiment adopts an intercalated structure setting. Specifically, one or more antireflection films are inserted into the EUV photoresist. Among them, the single-layer film is formed by alternately introducing trimethylaluminum and water as precursors, with an inert gas as the carrier gas, and atomic layer deposition is carried out at room temperature or below 100 °C. The introduction time of trimethylaluminum is 50 milliseconds, and the purge time is 30 seconds; the introduction time of water is 50 milliseconds, and the purge time is 30 seconds. For the multi-layer film, first, an aluminum oxide layer with an optical thickness of half a wavelength layer is grown by atomic layer deposition at room temperature or below 100 °C. The introduction time of trimethylaluminum is 50 milliseconds, and the purge time is 30 seconds. The introduction time of water is 50 milliseconds, and the purge time is 30 seconds. Then, a hafnium oxide layer with a thickness of half a wavelength is grown. Tetrakis(dimethylamino)hafnium and ozone are alternately introduced as precursors, with an inert gas as the carrier gas, and atomic layer deposition is carried out at room temperature or below 100 °C. Among them, the introduction time of tetrakis(dimethylamino)hafnium is 50 milliseconds, and the purge time is 30 seconds. The introduction time of ozone is 50 milliseconds, and the purge time is 30 seconds.

[0043] EUV lithography requires the thickness of the photoresist to be in the order of dozens of nanometers. When the exposure light irradiates the photoresist, part of the light enters the photoresist and participates in the lithography reaction, while the other part of the light is reflected. Since the reflected light fails to participate in the lithography reaction, it is wasted. In this embodiment, one or more antireflection film layers are inserted into the photoresist to increase the absorption rate of the photoresist for the exposure light.

[0044] See Appendix Figure 3 , when light passes through the interface of different media, due to the difference in refractive index, partial reflection will occur. By designing an antireflection film with appropriate materials and thickness, the reflected light generated at the interface between the antireflection film layer and the photoresist and the reflected light on the surface of the antireflection film layer can be made to have opposite phases, so that they interfere with each other and cancel each other out, reducing the intensity of the reflected light. Since the reflected light is reduced, more light can enter the photoresist through the antireflection film layer, thereby increasing the intensity of the transmitted light. Therefore, the antireflection film layer optimizes the distribution of light, enabling more light to be effectively utilized by the photoresist.

[0045] The present invention proposes to cover one or more antireflection film layers on the photoresist. The thickness of the antireflection film layer is determined according to the refractive index of the antireflection film layer and the wavelength of the exposure light source. The antireflection film can make the reflected light interfere and cancel each other out, so that more light can pass through the antireflection film layer and enter the photoresist. This improves the utilization rate of the photoresist for the exposure light source. In addition, the presence of the antireflection film layer enhances the transmission of light of a specific wavelength and weakens the light source outside the specific wavelength, thus avoiding unnecessary photochemical reactions during the non-exposure process and increasing the exposure accuracy.

[0046] The multilayer antireflection film of the present invention is composed of multiple layers of thin films with different refractive indices and thicknesses to achieve the antireflection effect for light of multiple wavelengths. Since the refractive indices of light of different wavelengths in a medium are different, a single-layer antireflection film can only achieve the best antireflection effect for light of a specific wavelength. However, the multilayer antireflection film can achieve a better antireflection effect within a relatively wide wavelength range through the interaction of different layers of films, thereby reducing the requirements for the light source in the lithography process. Therefore, the lithography efficiency can be greatly improved. In addition, the antireflection film layer is not limited to being coated on the surface of the photoresist, but can also be inserted into the photoresist. The design of the multilayer film structure of the present invention can significantly improve the efficiency and precision of the lithography process.

[0047] The presence of the capping layer can also increase the mechanical stability of the photoresist. The photoresist needs to be uniformly coated on the substrate. If the coating is uneven or defective, it will affect the lithography effect. After a capping layer is covered on the surface of the photoresist, the photoresist needs to overcome the capping layer tension to break. Therefore, a dense capping layer (such as an oxide) can increase the mechanical stability and thermal stability of the photoresist.

[0048] It should be further noted that the above embodiments are only used for understanding the technical solution of the present invention and are not used to limit the protection scope of the present invention. Any obvious adjustments and modifications made to the above technical solutions belonging to the technical concept of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a multilayer EUV photoresist, characterized in that: The invention comprises a EUV photoresist and a covering structure or an intercalation structure formed by at least one layer of anti-reflection film. The covering structure is a covering structure in which one or more layers of anti-reflection film are covered on the EUV photoresist to form a single-layer or multi-layer film; the intercalation structure is a multi-layer film structure in which one or more layers of anti-reflection film are inserted into the EUV photoresist to form an anti-reflection film layer and a photoresist are superimposed on each other.

2. The method for preparing a multilayer EUV photoresist according to claim 1, characterized in that: In the single-layer or multi-layer film covering structure, the single-layer film is formed by alternately introducing trimethylaluminum and water as precursors, using inert gas as carrier gas, and performing atomic layer deposition at room temperature or below 100°C. The introduction time of trimethylaluminum is 50 milliseconds and the purge time is 30 seconds; the introduction time of water is 50 milliseconds and the purge time is 30 seconds.

3. The method for preparing a multilayer EUV photoresist according to claim 1, characterized in that: In the single-layer or multi-layer film covering structure, the multi-layer film is first grown using atomic layer deposition technology to grow a layer of aluminum oxide with an optical thickness of half a wavelength layer, and the atomic layer deposition is carried out at room temperature or below 100°C, the introduction time of trimethylaluminum is 50 milliseconds, the purge time is 30 seconds, the introduction time of water is 50 milliseconds, and the purge time is 30 seconds; then grow a half-wavelength thick layer of hafnium oxide, use tetrakis(dimethylamine)hafnium and ozone as precursors alternately introduced, and use inert gas as carrier gas, and carry out atomic layer deposition at room temperature or below 100°C, wherein the introduction time of tetrakis(dimethylamine)hafnium is 50 milliseconds, the purge time is 30 seconds, the introduction time of ozone is 50 milliseconds, and the purge time is 30 seconds.

4. The method for preparing a multilayer EUV photoresist according to claim 1, wherein: The anti-reflection film layer and the photoresist are superimposed on each other in a multi-layer film structure, which is to insert one or more layers of anti-reflection film into the EUV photoresist, wherein the single-layer film is made by alternately introducing trimethylaluminum and water as precursors, using inert gas as carrier gas, and performing atomic layer deposition at room temperature or below 100°C, the trimethylaluminum introduction time is 50 milliseconds and the purge time is 30 seconds; the water introduction time is 50 milliseconds and the purge time is 30 seconds; the multi-layer film is firstly grown by atomic layer deposition technology with an optical thickness of half a wavelength layer of aluminum oxide, and then grown at room temperature. Atomic layer deposition is performed at or below 100° C., the trimethylaluminum is introduced for 50 milliseconds and the purge time is 30 seconds, the water is introduced for 50 milliseconds and the purge time is 30 seconds; then a half-wavelength thick layer of hafnium oxide is grown, tetrakis(dimethylamine)hafnium and ozone are alternately introduced as precursors, and an inert gas is used as a carrier gas. Atomic layer deposition is performed at room temperature or below 100° C., wherein the tetrakis(dimethylamine)hafnium is introduced for 50 milliseconds and the purge time is 30 seconds, the ozone is introduced for 50 milliseconds and the purge time is 30 seconds.

5. The method for preparing a multilayer EUV photoresist according to claim 2, 3 or 4, characterized in that: The inert gases are nitrogen and argon.

6. The method for preparing a multilayer EUV photoresist according to claim 3 or 4, characterized in that: The thickness of the aluminum oxide film is 2.1+4.1k nanometers, k=0,1,2,3.

7. A multi-layer EUV photoresist prepared by the method according to any one of claims 1 to 6, wherein the photoresist has a covering structure or an intercalation structure formed by at least one anti-reflection film.

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