Functional oxide film based on hard mask stripping technology and high-temperature patterning preparation method

Abstract

The invention discloses a functional oxide film based on a hard mask stripping technology and a high-temperature patterning preparation method, and belongs to the technical field of semiconductor films. The invention provides a stripping process based on a double-layer metal hard mask to solve the problem that high-quality patterning of an oxide film with a high-temperature deposition function is difficult to realize in a traditional process. According to the method, a nickel metal layer which is resistant to high temperature and stable in temperature serves as a bearing layer so as to adapt to the high-temperature environment in the thin film deposition process; and meanwhile, aluminum sensitive to a specific corrosive is adopted as a sacrificial layer, so that subsequent selective wet etching treatment is facilitated. Through the process, after the high-quality functional oxide thin film is deposited at a high temperature, nondestructive stripping of the metal hard mask and the thin film covered by the metal hard mask can be realized by utilizing selective corrosion on the aluminum sacrificial layer, so that the graphical functional oxide thin film which is sharp in edge and free of damage is obtained. The method is simple and convenient in process, low in cost and excellent in compatibility, and an effective technical approach is provided for manufacturing of high-performance oxide electronic devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor thin films, and particularly relates to a functional oxide thin film and a high-temperature patterning preparation method based on a hard mask stripping technology. BACKGROUND

[0002] Functional oxide thin films have a wide application potential in the fields of microelectronics, optoelectronics and sensors due to their unique electrical, optical and magnetic properties. In order to achieve excellent crystalline quality and device performance, functional oxide thin films usually need to be deposited at high temperature (generally 300-1000℃). Therefore, the selected substrate material must have good high-temperature stability, which can maintain structural integrity and chemical stability in a high-temperature environment, so oxide substrates (such as perovskite oxides, aluminum oxide, sapphire, etc.) or silicon substrates are often used. In contrast, organic substrates (such as polyimide PI, etc.) are difficult to meet the needs of high-temperature processes due to their low thermal decomposition temperature. Compared with thin films deposited at room temperature or low temperature, high-temperature growth has irreplaceable advantages: thin films deposited at room temperature or low temperature usually have amorphous or poor crystalline quality due to insufficient migration energy of film-forming atoms, and have loose structure and insufficient density, a large number of microscopic defects and difficult to accurately control the stoichiometric ratio, resulting in poor physical properties such as electrical, optical and other physical properties, and low stability and repeatability. High-temperature growth provides sufficient migration energy for atoms in the thin film, which is beneficial to form a dense and stoichiometrically accurate crystalline structure. Even if it fails to achieve single-crystal epitaxy due to lattice mismatch and other factors, its high-quality polycrystalline structure is far superior to amorphous, and effectively reduces the lattice defect density. This significantly improves the key physical properties of the thin film such as carrier mobility, electrical conductivity and optical transparency, and enhances its environmental stability and device operation reliability. However, because the high-temperature grown thin film has dense and stable excellent characteristics, the subsequent patterning process becomes extremely complex, which is a major challenge in the current technical field.

[0003] The current mainstream patterning technology has the following problems: (1) "deposition after etching" process, that is, first depositing a functional oxide film on the entire substrate by high-temperature deposition, and then forming the required pattern by using photolithography and dry or wet etching. The disadvantage of this method is that the oxide film after high-temperature deposition has high hardness and stable chemical properties, resulting in high etching difficulty, especially in fine pattern processing, which is prone to defects such as rough edges and line breakage. Although dry etching (such as ion beam etching) can realize pattern transfer, it has high equipment cost and is prone to process damage, thereby affecting the performance of the film. (2) "low-temperature deposition and then annealing" process, that is, first depositing and patterning the oxide film at low temperature, and then improving the crystalline quality of the film by high-temperature annealing. The defect of this method is that the low-temperature deposited film is usually loose in structure and lacks compactness, and may crack, shrink or react with the substrate in the annealing process, making it difficult to obtain a film with excellent performance. (3) Hard mask stripping process, which uses a metal or silicon oxide hard mask to replace the traditional photoresist for pattern transfer. However, the selection of hard mask material is challenging, and a single material cannot meet the requirements of resistance to high-temperature deposition environment and subsequent selective etching removal. For example, some metals are prone to oxidation in a high-temperature oxygen-rich environment, forming a dense and difficult-to-remove oxide, which leads to failure of the stripping process; ordinary metal masks may not withstand high-temperature deposition, and the etchant used to remove the hard mask may also corrode the functional oxide film or the substrate, limiting its application range. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provide a functional oxide film and high-temperature patterning preparation method based on hard mask stripping technology, so as to ensure that the film has excellent physical properties brought by high-temperature growth and is subjected to high-precision patterning processing. This method avoids direct etching of hard high-temperature deposited films, is simple in process, low in cost, and can obtain patterned functional oxide films with steep edges and excellent performance.

[0005] To achieve the above-mentioned purpose, the present application provides a functional oxide film high-temperature patterning preparation method based on hard mask stripping technology, comprising the following steps: 1) Forming a patterned photoresist layer on a hard substrate; 2) Depositing a hard mask layer on the patterned photoresist layer and the exposed substrate surface; 3) Removing the photoresist layer and stripping the hard mask layer covering it, thereby forming a patterned hard mask on the substrate; 4) High-temperature deposition of a functional oxide film on the substrate and the patterned hard mask surface; 5) removing the patterned hard mask and peeling off the functional oxide film thereon, thereby obtaining a patterned functional oxide film on the substrate.

[0006] As a preferred technical solution, the hard mask layer is a double-layer composite structure, comprising a sacrificial layer arranged at the bottom and a high-temperature-resistant metal layer arranged above the sacrificial layer. Specifically, the sacrificial layer can be an aluminum layer with a thickness of 50-200 nm, and the high-temperature-resistant metal layer can be a nickel layer with a thickness of 20-50 nm.

[0007] In the method, the high-temperature deposition process of step 4) can be performed at a temperature ranging from 300°C to 1000°C. In order to obtain better film quality, the step can include: first depositing a seed layer with a thickness of 1-5 nm at a low temperature ranging from room temperature to 300°C, and then continuing to grow at a high temperature, so that the final total thickness of the film reaches 5-100 nm.

[0008] In order to ensure the cleanliness and success rate of the process, the substrate can be cleaned and surface treated before step 1). In addition, when the patterned hard mask is removed in step 5), a protective layer can be first spin-coated on the surface of the functional oxide film, and then the sacrificial layer is selectively etched using an etching solution, thereby completing the peeling.

[0009] The hard substrate can be a substrate capable of withstanding high temperature and corrosion resistant, such as an oxide substrate or a silicon substrate, and the oxide substrate includes a ternary perovskite ABO3 material, aluminum oxide, silicon oxide, and a sapphire substrate.

[0010] The application also provides a functional oxide film prepared by any of the above methods, which has a thickness of 1-100 nm and a planar size of a pattern of 1-1000 µm.

[0011] Compared with the prior art, the application has at least the following beneficial technical effects: (1) Direct etching of the hard and dense oxide film after high-temperature deposition is avoided, the process is simplified, and the damage introduced by etching is reduced.

[0012] (2) A high-temperature-resistant hard mask is used, so that the film can be grown at an optimal high temperature, ensuring the crystalline quality and performance of the film.

[0013] (3) Precise pattern transfer is achieved by using a double-layer hard mask and selective wet etching, the process has good compatibility, is easy to operate, and has low cost.

[0014] (4) The method is versatile and suitable for high-temperature patterning preparation of various high-temperature-resistant substrates (such as oxide substrates and silicon substrates) and functional oxide film materials, but is not suitable for low-thermal-stability materials such as organic substrates.

[0015] (5) The method has excellent size compatibility, and can be used for manufacturing high-precision devices such as microelectronic devices and microelectromechanical systems (MEMS). BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings required to be used in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0017] Figure 1 Structure diagram for forming a photoresist pattern on an oxide substrate.

[0018] Figure 2 Structure diagram for depositing a hard mask layer on a sample surface.

[0019] Figure 3 Structure diagram for forming a patterned hard mask on a substrate after the first peeling.

[0020] Figure 4 Structure diagram for depositing a functional oxide film at high temperature on a sample surface.

[0021] Figure 5 Structure diagram for spin-coating a PMMA protective layer on a sample surface.

[0022] Figure 6 Structure diagram for removing a sacrificial layer by wet etching.

[0023] Figure 7 Structure diagram for peeling off a PMMA protective layer.

[0024] Figure 8 Structure diagram of a patterned functional oxide film finally obtained.

[0025] Figure 9 SEM characterization diagram of a clear patterned functional oxide film finally obtained.

[0026] BRIEF DESCRIPTION OF DRAWINGS: 1-oxide substrate, 2-photoresist, 3-Al sacrificial layer, 4-Ni high-temperature resistant metal layer, 5-functional oxide film, 6-PMMA protective layer. DETAILED DESCRIPTION

[0027] In the following, certain exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are to be regarded as illustrative in nature rather than restrictive.

[0028] In the description of the present application, it is to be understood that the terms "including", "comprising", "having" and "with" when used in this specification and in the following claims indicate the presence of the stated features, integers, steps, operations, elements, and / or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0029] It is also to be understood that the terminology used in the description of the present application is for the purpose of describing certain embodiments only and is not intended to be limiting of the present application. As used in this description and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0030] It will be further understood that the terms "and / or", as used in the specification and in the claims, indicate one or more of the associated listed items, and include all possible combinations of one or more of the associated listed items.

[0031] Various structural diagrams according to the disclosed embodiments of the present application are shown in the drawings. These diagrams are not drawn to scale, in which certain details are exaggerated for clarity and others are omitted. The shapes and relative sizes of the various regions, layers, and elements illustrated in the drawings are exemplary only and can vary depending on the manufacturing techniques used to produce the structures, and the intended design of the structures. The skilled person can design regions / layers with different shapes, sizes, relative positions according to the actual needs.

[0032] Embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0033] Embodiment 1 The present application provides a functional oxide thin film high-temperature patterning method based on hard mask lift-off technology, comprising the following steps: 1) Forming a patterned photoresist layer on a hard substrate by a photolithography process; 2) Depositing a hard mask layer on the patterned photoresist layer and the exposed substrate surface; 3) Removing the photoresist layer by a lift-off process, thereby forming a patterned hard mask on the substrate which is opposite to the photoresist pattern; 4) On the substrate and patterned hard mask surface, deposit functional oxide films by physical vapor deposition or other methods in a high-temperature environment; 5) Optionally remove the patterned hard mask, thereby stripping the functional oxide films above the hard mask, and finally obtain the desired pattern of functional oxide films on the substrate.

[0034] Preferably, the hard mask layer is a sacrificial bilayer structure, stacked by an easily soluble lift-off layer at the bottom and a shape-defining rigid layer at the top.

[0035] In the present application, the shape-defining rigid layer at the top is made of nickel (Ni), and the easily soluble lift-off layer at the bottom is made of aluminum (Al). This design of Al / Ni bilayer metal film structure has unique and key advantages.

[0036] The Al layer at the bottom is chosen as the lift-off layer, which is based on the following key reasons: First, aluminum is a typical amphoteric metal, which can react rapidly with strong alkali solutions (such as KOH, NaOH) and be dissolved. This extremely high selectivity allows for the rapid and complete removal of the Al lift-off layer without damaging the precise functional oxide film patterns and the underlying substrate that we want to keep. However, other key materials in the present system, such as the Ni rigid layer at the top, most functional oxide films (such as SRO, BTO, and other perovskite structure oxides), and oxide substrates (such as STO, Al2O3, SiO2), all show excellent chemical inertness to strong alkali. This large difference in reactivity provides almost perfect etching selectivity, ensuring that the lift-off process can accurately and cleanly remove the sacrificial layer without damaging any functional structures. Second, strong alkali solution as an etchant, with low cost, mature technology, easy to obtain and process, has high industrial application value and mass production.

[0037] However, if only Al single layer is used as a hard mask, it will face serious technical obstacles: First, Al has limited temperature resistance, and in a high-temperature environment exceeding 700℃, Al atoms may evaporate or diffuse into the substrate and deposited films, thereby contaminating the functional layer. Second, and more critically, in a high-temperature oxygen-rich deposition atmosphere, the Al surface will rapidly oxidize to form a dense, corrosion-resistant aluminum oxide (Al2O3) passivation layer, which will completely fail the subsequent stripping step.

[0038] The top Ni layer introduced by the present application solves the above problems perfectly. The Ni layer plays multiple key roles: it is a protective layer and isolation barrier layer, which completely isolates the underlying Al stripping layer from the high-temperature oxygen-rich deposition environment, effectively preventing Al oxidation and diffusion. It is a pattern definition rigid layer, which has excellent mechanical strength and high-temperature stability, effectively preventing thermal deformation during high-temperature growth, ensuring the accuracy of the final film pattern.

[0039] In summary, through the ingenious combination of the bottom easy-etch layer and the top rigid protective layer, the double-layer mask structure of the present application ensures that the Al stripping layer still maintains its chemical activity at the end of the process, thereby ensuring the success rate and cleanliness of the final stripping step. This design is the core of realizing a reliable stripping process at high temperature.

[0040] Preferably, when performing step 4) high-temperature deposition of functional oxide thin film, a two-step growth method can be used: first, deposit a thin seed layer at a relatively low temperature to enhance the adhesion of the thin film to the substrate, and then grow at high temperature for a long time to ensure high crystalline quality of the thin film. The low temperature generally refers to room temperature to a temperature lower than the high temperature, for example, room temperature to 300°C.

[0041] Preferably, when performing step 5) removing the hard mask, a protective glue such as PMMA can be first spin-coated on the surface of the sample, and then a specific etching solution (such as strong alkali solution KOH or NaOH) is used to laterally etch the sacrificial layer, so that the overlying high-temperature-resistant metal layer and functional oxide thin film are completely stripped.

[0042] Example 2 The present embodiment provides a method for preparing a patterned SRO (strontium rubidate) or ITO (indium tin oxide) thin film on an oxide substrate 1, and the process flow is as shown in Figures 1-8 .

[0043] Step 1: Provide a high-temperature-resistant substrate 1 (such as STO single crystal substrate, sapphire substrate, aluminum oxide substrate, silicon substrate, etc.), and perform ultrasonic cleaning in acetone, anhydrous ethanol, and deionized water in sequence, and then dry. The substrate must be able to withstand the subsequent high-temperature deposition process (such as 700°C), and not be attacked by strong alkali etching solution. To enhance the adhesion of the subsequent thin film, the surface of the substrate can be treated with oxygen plasma to activate the surface.

[0044] Step 2: As shown in Figure 1 , form a photoresist layer 2 with the required pattern on the surface of the cleaned oxide substrate 1 through standard spin coating, pre-baking, post-baking, exposure, development, and other photolithography processes. The minimum feature size of the pattern can be in the micrometer range. The thickness of the photoresist can be selected to be 1-2 μm.

[0045] Step 3: As shown in Figure 2As shown, the sample with photoresist pattern is put into a physical vapor deposition device (such as an electron beam evaporation system) to deposit the hard mask layer. In this embodiment, the hard mask layer is a double-layer structure, first depositing a layer of Al with a thickness of 80-100 nm as a sacrificial layer 3, and then depositing a layer of Ni with a thickness of 20-50 nm as a high-temperature-resistant metal layer 4. The thicker Al layer is selected to provide a stable and uniform lateral etching channel in the subsequent stripping step, and the 20-50 nm thickness of the Ni layer is sufficient to form a continuous and dense protective layer, effectively isolating the Al layer from the high-temperature oxygen-rich environment.

[0046] Step 4: As shown in Figure 3 , the above sample is immersed in a hot acetone solution (for example, 60°C) and ultrasonically treated. The photoresist 2 is dissolved, and the metal double-layer film (sacrificial layer 3 and high-temperature-resistant metal layer 4) above it is lifted off. Finally, an Al / Ni double-layer hard mask with the desired pattern is obtained on the oxide substrate 1.

[0047] Step 5: As shown in Figure 4 , the sample with the patterned hard mask is again put into a physical vapor deposition device (such as pulsed laser deposition (PLD) or magnetron sputtering) to grow an SRO functional oxide film or a general ITO conductive oxide electrode 5. To improve the crystalline quality of the film, a two-step growth method can be used: first, deposit a layer of SRO or ITO film with a thickness of 1-5 nm as a seed layer at a relatively low temperature (such as room temperature to 300°C) to enhance adhesion and induce orientation; then rapidly increase the temperature to a high-temperature (for example, 700°C) environment for continued epitaxial growth. The final total thickness of the SRO or ITO film can be 25-30 nm and will be deposited on the exposed substrate surface and the surface of the Ni hard mask.

[0048] Step 6: As shown in Figure 5 , in order to protect the SRO film that has been grown on the substrate during the subsequent wet etching process, a layer of PMMA protective layer 6 can be spin-coated on the surface of the sample. The PMMA protective layer has two main functions: (1) to prevent the Ni layer and functional oxide film fragments that are stripped off during the wet etching process from scattering in the etching solution, avoiding the re-deposition of these fragments on the sample surface causing contamination; (2) to "pack and take away" the stripped film fragments as a carrier, preventing them from adhering to the substrate surface due to static electricity or intermolecular forces, ensuring the edge cleanliness of the final pattern.

[0049] Step 7: As shown in Figure 6As shown, the sample is immersed in an etching solution that can selectively etch the sacrificial layer 3 without etching the high-temperature-resistant metal layer 4, the functional oxide film 5, and the substrate 1. For example, for an Al sacrificial layer, a strong alkali solution (such as KOH solution, concentration of 0.1-2 mol / L) can be selected, the etching temperature can be room temperature to 60°C, and the etching time is determined according to the thickness of the Al layer, usually 5-30 minutes. The etching solution will invade from the side of the hard mask and laterally etch the Al sacrificial layer 3. As the sacrificial layer 3 is completely removed, the Ni high-temperature-resistant metal layer 4 and the SRO functional oxide film or the general ITO conductive electrode oxide 5 above it are completely peeled off.

[0050] Step 8: As shown in Figure 7 and Figure 8 , the PMMA protective layer 6 is removed using solvents such as acetone, and the sample is cleaned and dried. In this process, the PMMA protective layer is completely removed along with the peel-off film fragments it carries, ensuring the cleanliness of the substrate surface. Finally, a high-quality SRO film or a patterned ITO film with clear edges is obtained on the oxide substrate 1. Through this method, any pattern with steep sidewalls and line width in the micron range (such as 1-10 μm) can be accurately prepared, and the film thickness can be accurately controlled in the nanometer range.

[0051] Step 9: As shown in Figure 9 , the pre-patterned hard mask layer is successfully removed by the optimized peeling process described above. The hard mask layer has been processed by photolithography into various fine geometric shapes (including micron-level bar-shaped, circular, and rectangular structures), and the pattern accuracy directly determines the final morphology of the functional oxide film. SEM results show that the film edge profile is clear and regular, with no mask residue or edge jagged defects, and the functional oxide film has an intact overall structure without cracks, holes, or other morphological damage. Such a film with precise patterning and high structural integrity can be directly used for subsequent electrode preparation and device assembly, laying a key morphological and structural foundation for its application in pressure-sensitive devices, gas sensors, and other fields.

[0052] In summary, the present application provides a novel thin film patterning technology, which ingeniously solves the problem of incompatibility between high-temperature thin film growth and traditional photolithography process by introducing a high-temperature-resistant double-layer hard mask and a two-time peeling process. This method is simple, cost-effective, and versatile, providing an effective technical approach for preparing high-performance oxide film devices and has high industrial application value.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0054] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for high-temperature patterning fabrication of functional oxide thin films based on hard mask lift-off technology, characterized in that, Includes the following steps: 1) Forming a patterned photoresist layer on a rigid substrate; 2) Deposit a hard mask layer on the patterned photoresist layer and the exposed substrate surface; 3) Remove the photoresist layer and then peel off the hard mask layer covering it, thereby forming a patterned hard mask on the substrate; 4) High-temperature deposition of functional oxide thin films on the substrate and patterned hard mask surface; 5) Remove the patterned hard mask and then peel off the functional oxide film on top of it to obtain a patterned functional oxide film on the substrate.

2. The method according to claim 1, characterized in that, The hard mask layer is a two-layer composite structure, including... A sacrificial layer is disposed at the bottom, and a high-temperature resistant metal layer is placed over the sacrificial layer.

3. The method according to claim 2, characterized in that, The sacrificial layer is an aluminum layer with a thickness of 50-200 nm, and the high-temperature resistant metal layer is a nickel layer with a thickness of 20-50 nm.

4. The method according to claim 1, characterized in that, The high temperature mentioned in step 4) is 300℃-1000℃.

5. The method according to claim 1, characterized in that, Before step 1), the process includes adding acetone and alcohol to the substrate, cleaning it with an ultrasonic machine, and then subjecting the surface to oxygen plasma treatment.

6. The method according to claim 1, characterized in that, Step 4) involves the high-temperature deposition of functional oxide films, which includes: firstly, depositing a thin seed layer with a thickness of 1-5 nm at a low temperature of room temperature to 300°C, and then continuing to grow the functional oxide film at a high temperature, with the final total thickness of the film being 5-100 nm.

7. The method according to claim 1, characterized in that, The step of removing the patterned hard mask in step 5) includes selectively etching the sacrificial layer at room temperature to 60°C using an etching solution with a concentration of 0.1-2 mol / L, thereby stripping away the high-temperature resistant metal layer and functional oxide film thereon.

8. The method according to claim 7, characterized in that, Before etching the sacrificial layer, a step of spin-coating a protective layer onto the surface of the functional oxide film is also included.

9. The method according to claim 1, characterized in that, The rigid substrate is a substrate that can withstand high-temperature deposition processes and is not corroded by strong alkaline etching solutions, including oxide substrates and silicon substrates. The oxide substrate includes ternary perovskite ABO3 material, alumina, silicon oxide and sapphire substrate.

10. A functional oxide thin film based on hard mask lift-off technology, characterized in that, The functional oxide film is prepared by any one of claims 1 to 9, and has a thickness of 1 to 100 nm and a planar size of 1 to 1000 µm.

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