Chromium-based coating for photomask substrate, method for preparing same, photomask, and semiconductor element

Abstract

The invention relates to the technical field of semiconductors, and discloses a chromium coating for a photomask substrate, a preparation method of the chromium coating, a photomask and a semiconductor element, the chromium coating is a pure chromium coating and has a single microstructure or a composite microstructure; wherein the single microstructure comprises any one of an amorphous state, a polycrystalline state and an amorphous-nanocrystalline mixed state; the composite microstructure comprises at least two of an amorphous state, a polycrystalline state and a mixed state; and the mixed state is a transition state microstructure of amorphous polycrystalline transformation. By regulating and controlling the microstructure of the pure chromium target, the chromium coating for the photomask substrate can meet the design target of optical density of unit thickness at the wavelength of 193nm under the condition of ultra-thin thickness, so that the three-dimensional mask effect caused by a thick chromium layer is avoided, and the contradiction of insufficient shading of the thin chromium layer is solved. Meanwhile, the mode based on the pure chromium material assisted by magnetron sputtering current regulation and control does not need a complex reaction gas system, the process window is wide, the reproducibility is good, and the method is suitable for industrial batch production.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a chromium-based coating for a photomask substrate, a method for preparing the same, a photomask, and a semiconductor device. Background Technology

[0002] Photomasks are core components in semiconductor manufacturing and micro-patterning, and their pattern accuracy directly determines the linewidth and production yield of integrated circuits. In the manufacturing process of photomasks, chromium (Cr) coatings have become the preferred material for photomask light-shielding layers due to their excellent light-shielding properties, good etch selectivity, and chemical stability.

[0003] In photolithography, the chromium layer, after precise patterning, is used to control light transmission and is the starting point for the entire pattern replication process. Therefore, the thickness, optical properties, and uniformity of the chromium layer are considered key parameters in mask fabrication. However, the fabrication methods used to improve these parameters in related technologies are industrially complex, necessitating a reliable fabrication method that can effectively simplify the industrial process. Summary of the Invention

[0004] This application aims to at least partially solve one of the technical problems in related technologies. To this end, this application proposes a chromium-based coating for a photomask substrate, a method for preparing the same, a photomask, and a semiconductor device. The main technical solutions adopted in this application include: In a first aspect, embodiments of this application provide a chromium-based coating for a photomask substrate, wherein the chromium-based coating is a pure chromium coating; the pure chromium coating has a single microstructure or a composite microstructure; wherein the single microstructure includes any one of amorphous, polycrystalline and mixed states; the composite microstructure includes at least two of amorphous, polycrystalline and mixed states; the mixed state refers to a mixed phase microstructure of polycrystalline and nanocrystalline.

[0005] Secondly, embodiments of this application provide a method for preparing a chromium-based coating for a photomask substrate. The method includes: providing a photomask substrate and placing the photomask substrate in a vacuum environment; using a DC magnetron sputtering process with a pure chromium target as the source, and controlling the sputtering current to perform deposition treatment on the photomask substrate to form a pure chromium coating; wherein the sputtering current ranges from 50mA to 800mA.

[0006] Optionally, the method further includes: controlling the sputtering current to a single constant value and performing a single deposition process to deposit a pure chromium coating with a single microstructure on a photomask substrate.

[0007] Optionally, the method further includes: controlling the sputtering current to change in stages according to preset timing conditions, and performing at least two staged deposition processes to form a pure chromium coating with a composite microstructure on the photomask substrate along the thickness direction; wherein the sputtering current used in adjacent deposition processes is different.

[0008] Optionally, the DC magnetron sputtering process includes a DC dual-target co-sputtering process; the method further includes: setting a first DC target as a first sputtering current and setting a second DC target as a second sputtering current to form a pure chromium coating with a composite microstructure; wherein the DC dual-target co-sputtering processes of the first DC target and the second DC target are performed simultaneously and have the same deposition time.

[0009] Optionally, the background vacuum degree of the deposition process can be in the range of 3 × 10⁻⁶. -4 Pa to 5×10 -4 Pa; the atmosphere is argon atmosphere; the working pressure ranges from 0.45 Pa to 0.55 Pa; the target-substrate distance of the pure chromium target ranges from 10 cm to 20 cm; the substrate temperature of the photomask substrate ranges from 24 °C to 32 °C.

[0010] Optionally, the photomask substrate is a quartz glass substrate.

[0011] Optionally, the purity of the pure chromium sputtering target is not less than 99.95%; wherein, the purity of the pure chromium sputtering target is higher than 99.99%.

[0012] Thirdly, this application also provides a photomask, including a photomask substrate and a light-shielding layer formed on the photomask substrate, wherein the light-shielding layer is a chromium-based coating as described above.

[0013] Fourthly, this application also provides a semiconductor device, including a substrate and a light-absorbing layer, wherein the light-absorbing layer is a chromium-based coating as described above.

[0014] In the above embodiments, by controlling the microstructure of the pure chromium target, the chromium-based coating used as a photomask substrate can meet the design target of optical density per unit thickness at a wavelength of 193nm with an ultrathin thickness of ≤80nm. This avoids the three-dimensional masking effect caused by thick chromium layers and solves the contradiction of insufficient light shielding by thin chromium layers. At the same time, this method based on pure chromium material and magnetron sputtering current control does not require a complex reactive gas system, has a wide process window and good reproducibility, and is suitable for industrial mass production. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a flowchart of a method for preparing a chromium-based coating for a photomask substrate according to an embodiment of this application; Figure 2a This is a surface morphology diagram of a chromium-based coating provided according to an embodiment of this application; Figure 2b This is a cross-sectional topography of a chromium-based coating provided according to an embodiment of this application; Figure 2c The X-ray diffraction pattern of the chromium-based coating provided according to the embodiments of this application is shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0019] Photomasks are core components in semiconductor manufacturing and micro-patterning, and their pattern accuracy directly determines the linewidth and production yield of integrated circuits. In photomask manufacturing, chromium (Cr) coatings are the preferred material for the mask's light-shielding layer due to their excellent light-shielding performance, good etch selectivity, and chemical stability. In photolithography, the precisely patterned chromium layer is used to control light transmission, serving as the starting point for the entire pattern replication process. Therefore, the thickness, optical properties, and uniformity of the chromium layer are considered key parameters in mask fabrication. Traditional methods in related technologies improve light-shielding performance by increasing the chromium layer thickness, but this can trigger a three-dimensional masking effect, where edge diffraction and phase shift cause the optimal focal plane to drift with changes in pattern size, resulting in deterioration of the uniformity of critical dimensions at the wafer end. While thinning the chromium layer can mitigate the three-dimensional effect, it presents a contradiction between insufficient thickness and decreased light-shielding performance. Therefore, the industry urgently needs to increase the optical density per unit thickness at 193nm wavelength without increasing the physical thickness to meet the dual requirements of ultra-thinness and efficient light-shielding.

[0020] Currently, the mainstream technologies for preparing chromium coatings include evaporation deposition, electroplating, and magnetron sputtering. Evaporation deposition suffers from weak film-substrate adhesion and a tendency to peel; electroplating processes result in significant pollution, poor density, and difficulty in ensuring nanoscale thickness uniformity, and defects such as micropores, pinholes, and cracks reduce light-shielding reliability. In contrast, magnetron sputtering technology offers advantages such as high deposition rate, high purity, high density, and strong adhesion, and is widely used in the industry.

[0021] In terms of material microstructure, amorphous thin films exhibit long-range disorder and short-range order, high atomic packing density, and no grain boundary scattering, but contain numerous defects. They can provide high extinction coefficients within extremely thin thicknesses. Crystalline thin films, on the other hand, possess a long-range ordered structure, and their grain size, orientation, and defect density can be precisely controlled by parameters such as sputtering power, gas pressure, and bias voltage. Furthermore, mixed-phase structures of crystalline and amorphous materials contain numerous grain boundaries and defect-rich regions, which can significantly enhance the scattering and absorption probability of ultraviolet photons.

[0022] The main method used in related technologies to improve the optical density per unit thickness of chromium coatings is to introduce light elements such as nitrogen, oxygen, and carbon into pure chromium, sputtering to form chromium compounds such as CrN, CrC, or CrON. For example, CN105425535A uses DC reactive sputtering technology to deposit a CrN monolayer by controlling the Ar:N2 flow ratio within the range of 1:1 to 1:1.5, which can increase the optical density per unit thickness to ≥0.050 nm. -1 CN113488378A, on the other hand, obtains Cr-C compounds through carbon doping, maintaining optical density while reducing film thickness. However, these schemes all employ a "reactive sputtering" technique, relying on the continuous introduction of reactive gases to achieve compositional control, which has the following inherent drawbacks: (1) The process window is narrow, and the target surface is prone to "poisoning" phenomenon; (2) Closed-loop control of the reaction gas flow rate with ppm-level precision is required, resulting in high equipment modification costs; (3) The cleanliness of the cavity is required to be extremely high. If not careful, defects such as pinholes will be generated in the membrane layer. (4) The complexity of the process increases significantly, the reproducibility is poor, and it is not conducive to industrial production.

[0023] To address the aforementioned shortcomings, there is an urgent need for a more reliable and economical chromium coating preparation scheme that can solve problems such as target poisoning, pinhole defects, and poor process stability in reactive sputtering processes.

[0024] Based on this, embodiments of this application provide a chromium-based coating for a photomask substrate, wherein the chromium-based coating is a pure chromium coating; the pure chromium coating has a single microstructure or a composite microstructure; wherein, the single microstructure includes any one of amorphous, polycrystalline and mixed states; the composite microstructure includes at least two of amorphous, polycrystalline and mixed states; the mixed state refers to the transitional microstructure from amorphous to polycrystalline.

[0025] The photomask substrate can serve as a support substrate. For example, it can be made of quartz glass or other transparent insulating materials suitable for photomasks, and its surface needs to be cleaned to ensure coating quality.

[0026] Chromium-based coatings refer to coatings with chromium (Cr) as the main element and functional component. Specifically, chromium-based coatings can be pure chromium coatings, prepared using a high-purity chromium target with a purity of not less than 99.95% (3N5) ​​as the source material, and formed as the core functional layer through a DC magnetron sputtering process. It is important to note that during DC magnetron sputtering deposition, no metal elements or reactive gases other than chromium are actively introduced to form compounds. Instead, the amorphous and crystalline structure and proportions of the chromium film are actively and precisely controlled by adjusting the sputtering current. This avoids interfacial bonding problems caused by heterogeneous components, improving the adhesion stability between the coating and the substrate. Furthermore, it simplifies the preparation process, eliminating the need for complex gas ratio control and reducing the risk of pinholes and defects.

[0027] Understandably, in order to achieve its design goals for light-shielding performance, the chromium-based coating has a single or composite microstructure.

[0028] Among them, a single microstructure can refer to the fact that the atomic arrangement of a pure chromium coating is consistent in a statistical sense, and it only exhibits one of the amorphous, polycrystalline and mixed states. In other words, a single microstructure means that the coating as a whole is in the same structural state.

[0029] A composite microstructure can refer to a pure chromium coating containing at least two single states. This can mean that the pure chromium coating sequentially deposits at least two of the following states along its thickness direction: amorphous, polycrystalline, and mixed states, thus forming a sublayer with a structural gradient. Alternatively, it can mean that the pure chromium coating deposits at least two of the following states along its planar distribution, thus forming a sublayer with a composite structural distribution.

[0030] Among them, the mixed state can refer to the microstructure of a mixed phase of polycrystalline and nanocrystalline, with partially ordered atomic arrangement, no complete crystal structure but showing a tendency to crystallize, and possessing both the compactness of the amorphous state and the stability of the polycrystalline state.

[0031] In the above embodiments, by controlling the microstructure of the pure chromium target, the chromium-based coating used as a photomask substrate can meet the design target of optical density per unit thickness at a wavelength of 193nm with an ultrathin thickness of ≤80nm. This avoids the three-dimensional masking effect caused by thick chromium layers and solves the contradiction of insufficient light shielding by thin chromium layers. At the same time, this method based on pure chromium material and magnetron sputtering current control does not require a complex reactive gas system, has a wide process window and good reproducibility, and is suitable for industrial mass production.

[0032] This embodiment also provides a method for preparing a chromium-based coating for a photomask substrate, such as... Figure 1 As shown, the method includes the following steps: S110. Provide a photomask substrate and place the photomask substrate in a vacuum environment.

[0033] The photomask substrate, which serves as a support substrate, needs to possess excellent flatness, optical transparency, and chemical stability. Optionally, the photomask substrate can be a quartz glass substrate, thereby providing a stable adhesion carrier for the coating structure without affecting the transmission and precision control of light during the photolithography process.

[0034] Specifically, in the substrate preparation, a quartz glass substrate is first provided, and then ultrasonically cleaned for 30 minutes each with acetone, ethanol and deionized water in sequence to remove surface contaminants. Finally, it is dried with high-purity nitrogen gas for later use as a photomask substrate.

[0035] Furthermore, the sputtering source for preparing chromium-based coatings can be a high-purity pure chromium target. Optionally, the purity of this pure chromium target is not less than 99.95% (3N5). For better coating quality and performance stability, a purity higher than 99.99% is also preferable. Compared to related technologies using Cr / CrO... xFurthermore, a scheme for preparing coatings using multi-component materials such as CrN was proposed. This method, employing high-purity chromium targets, avoids the need to introduce heterogeneous elements like oxygen and nitrogen to alter the coating's chemical composition and adjust performance. Instead, performance optimization is achieved through microstructural control. This effectively avoids the problems caused by heterogeneous interfaces, resulting in chromium-based coatings with superior interfacial adhesion and etching uniformity.

[0036] S220 employs a DC magnetron sputtering process, using a pure chromium target as the source, and deposits a pure chromium coating on a photomask substrate by controlling the sputtering current.

[0037] Understandably, vacuum system preparation is necessary before sputtering to provide a suitable sputtering environment. Specifically, first, the circulating water cooling system and main power supply are turned on, and the mechanical pump and bypass evacuation system are started to evacuate the chamber. When the vacuum level is below 30 Pa, the bypass evacuation valve is closed, and the fore-stage valve is opened. After 10-20 seconds, the molecular pump can be started. When the molecular pump frequency rises to above 90, the gate valve is opened until the chamber vacuum level reaches ≤6.6 × 10⁻⁶ Pa. -4 Pa. Then, 20-30 SCCM of high-purity argon gas is introduced to maintain an argon atmosphere. The vacuum level is then adjusted to the set value using the MKS pressure control system. Specifically, the deposition working gas pressure ranges from 0.45 Pa to 0.55 Pa; for example, it can be 0.46 Pa, 0.49 Pa, 0.52 Pa, or any range thereof. The background vacuum level for the deposition process ranges from 3 × 10⁻⁶ Pa. -4 Pa to 5×10 -4 Pa. The substrate temperature of the photomask substrate during deposition ranges from 24℃ to 32℃. The deposition time is preferably from 100 seconds to 3600 seconds. The target-substrate distance of the pure chromium target ranges from 10cm to 20cm, and the stage rotation speed is controlled at 5-15 r / min to complete the sputtering environment setup. Based on the above sputtering process parameters, impurities are eliminated through a high background vacuum environment and high-purity argon gas, avoiding heterogeneous defects in the coating and improving the bonding stability with the substrate. Furthermore, by fixing the target-substrate distance, stage rotation speed, and controlling the gas pressure / temperature / gas flow rate, uniform coating deposition is ensured, achieving an ultrathin thickness of ≤80nm to reduce the three-dimensional mask effect. In addition, a stable environment is provided for subsequent sputtering current control of the pure chromium coating. While achieving the preparation target, the preparation process does not require complex gas mixing, making it simple and easy to industrialize.

[0038] After the environment is set up, the DC magnetron sputtering power supply can be turned on. Using a pure chromium target as the source, the sputtering current output by the equipment is adjusted so that chromium atoms on the surface of the chromium target are sputtered and detached from the target to form a chromium particle stream, which is then directionally deposited on the surface of the photomask substrate to finally form a pure chromium coating.

[0039] Since sputtering current directly affects the density and energy of deposited particles, thereby changing the deposition rate and microstructure of the coating (e.g., different particle energies lead to differences in atomic arrangement), the current needs to be precisely controlled to ensure that the coating structure and performance meet the standards.

[0040] The sputtering current ranges from 50 mA to 800 mA. Specifically, it can be selected from the ranges of 80 mA to 120 mA, 230 mA to 270 mA, and 330 mA to 370 mA. Different sputtering currents can be used to prepare different microstructures. For example, 80 mA can prepare amorphous coatings, 230 mA can prepare mixed-state coatings, and 330 mA can prepare polycrystalline coatings, providing a process basis for subsequent control of coating structure.

[0041] The final pure chromium coating is formed solely using a high-purity chromium target via DC magnetron sputtering. Based on the sputtering current application strategy, its microstructure can be categorized into two types: "single" and "composite." Single microstructures are formed in a single deposition under constant DC, exhibiting a uniform structural state along the thickness direction, and can display amorphous (long-range disorder), amorphous-nanocrystalline coexistence, or polycrystalline phases. Composite microstructures are obtained through temporal or spatial modulation of the current. For example, by depositing segments with different sputtering current values ​​sequentially from bottom to top along the substrate direction, a continuous monolayer is formed, potentially creating a gradient of nanoscale amorphous → amorphous-nanocrystalline → polycrystalline phases, thus constituting a gradient composite microstructure. If dual-target co-sputtering is used, i.e., applying different sputtering currents simultaneously, particles can be instantaneously mixed on the substrate surface, forming an in-plane composite microstructure. This film exhibits uniform lateral composition, a single crystalline phase, and no macroscopic interfaces. Regardless of the microstructure of the chromium coating, its thickness is no more than 80 nm, and its optical density per unit thickness at a wavelength of 193 nm can meet the design target.

[0042] In the above embodiments, since the preparation process does not actively introduce metal elements other than chromium or reactive gases, interface bonding problems caused by heterogeneous components can be avoided, improving adhesion stability with the substrate, while simplifying the process and reducing the risk of defects such as pinholes. Furthermore, the prepared product meets the light-shielding requirements of light density per unit thickness at a wavelength of 193nm, adapting to the high light-shielding requirements of advanced photolithography processes for thin layers. In addition, this method does not require a complex reactive gas mixing system, resulting in low equipment investment and operating costs. It also offers a wide process window, making it suitable for industrial production.

[0043] In some implementations, the method further includes: By controlling the sputtering current to a single constant value and performing a single deposition process, a pure chromium coating with a single microstructure is deposited on a photomask substrate.

[0044] Specifically, during the sputtering process, a constant sputtering current is maintained throughout the entire process without adjustment of the current magnitude, resulting in a single continuous deposition process. This ultimately forms a pure chromium coating on the photomask substrate with a single microstructure containing only one of the following: amorphous, amorphous-nanocrystalline mixed, or polycrystalline states. Optionally, the sputtering current can be any value selected from the ranges of 80mA to 120mA, 230mA to 270mA, and 330mA to 370mA.

[0045] The following description uses different embodiments. It should be noted that the following examples are for illustrative purposes only and are not intended to limit this application.

[0046] Example 1: Preparation of an amorphous chromium-based coating, obtained by the following steps: First, take a quartz glass substrate and ultrasonically clean it in acetone, ethanol, and deionized water for 30 minutes each, then dry it with nitrogen gas for later use.

[0047] Next, the cleaned quartz substrate was placed on the sample tray inside the magnetron sputtering chamber, and a 4N chromium target was installed in the magnetron sputtering instrument. The chamber was then evacuated to a background vacuum level of 4 × 10⁻⁶. -4 After Pa, adjust the target-substrate distance to 15cm, adjust the rotation speed to 5r / min, introduce 30SCCM of argon gas, set the working pressure to 0.52Pa, the substrate temperature to 28℃, and the chromium target sputtering current to any value from 80mA to 120mA.

[0048] First, pre-sputter for 5 minutes, then perform formal deposition for 18-60 minutes, and finally obtain a pure chromium coating with a thickness of 60-80 nm.

[0049] Furthermore, the crystallization characteristics of the prepared thin film can be analyzed using X-ray diffraction (XRD), the surface and cross-sectional morphology can be analyzed using scanning electron microscopy (SEM), and the transmittance at a wavelength of 193 nm can be analyzed using ultraviolet-visible-near-infrared spectrophotometer to determine the optical density per unit thickness.

[0050] Please refer to Figure 2a and Figure 2b It can be seen that there are no defects such as pinholes on the surface of the film, and the thickness distribution is uniform. Figure 2c The curve A in the middle corresponds to its XRD pattern. As can be seen from the figure, there are no obvious diffraction peaks, indicating that the pure chromium coating sample is an amorphous structure.

[0051] Example 2: Preparation of an amorphous-nanocrystalline mixed-phase chromium coating. In Example 2, the preparation process is the same as in Example 1, except that the sputtering current in the parameters of Example 1 is changed to any value between 230mA and 270mA, and the deposition time is changed to 8min. Finally, a pure chromium coating with a thickness of 60nm to 70nm can be obtained.

[0052] Similarly, the crystallinity characteristics of the thin film prepared in Example 2 can be analyzed. Please refer to the XRD pattern for further details. Figure 2c The spectrum corresponding to curve B in the figure shows a small hill-like peak around 44°, indicating the transition region from amorphous to polycrystalline state, i.e., a mixed state of amorphous and nanocrystalline.

[0053] Example 3: Preparation of a polycrystalline chromium-based coating. In Example 3, the preparation process is the same as in Example 1, except that the sputtering current in the parameters of Example 1 is changed to any value between 330mA and 370mA, and the deposition time is changed to 8min. Finally, a pure chromium coating with a thickness of 70nm to 80nm can be obtained.

[0054] Similarly, the crystallinity characteristics of the thin film prepared in Example 3 can be analyzed. Please refer to the XRD pattern for details. Figure 2c The spectrum corresponding to curve C in the figure. It can be seen from the figure that it presents a sharp diffraction peak near 44°, corresponding to the (110) peak, indicating that the pure chromium coating prepared at this time has a polycrystalline structure.

[0055] As demonstrated by the above embodiments, at lower currents, amorphous pure chromium coatings can be fabricated, which is beneficial for enhancing the absorption of 193nm photons through defect scattering. At higher currents, polycrystalline pure chromium coatings can be fabricated, which can effectively improve the photon scattering and absorption path through grain boundary scattering. At medium currents, conditions fall between the two, forming a hybrid transitional structure where amorphous and crystalline phases coexist. This structure simultaneously contains disordered regions of the amorphous phase and microcrystalline regions, possessing the dual advantages of high defect density in the amorphous phase and grain boundary scattering in the crystalline phase, often synergistically optimizing optical density performance.

[0056] In the above embodiments, a pure chromium coating with a uniform and defined microstructure can be stably prepared by setting only a constant parameter (sputtering current) without complex timing programming or multi-target switching. This not only significantly reduces process complexity and operational difficulty, avoiding potential problems caused by multi-layer interfaces, but also greatly improves the reproducibility of the production process and the consistency of the product due to the fixed process parameters, providing a solid foundation for large-scale industrial production.

[0057] In some implementations, the method further includes: By controlling the sputtering current to vary in stages according to preset timing conditions, at least two staged deposition processes are performed to form a pure chromium coating with a composite microstructure on the photomask substrate along the thickness direction.

[0058] The sputtering currents used in adjacent deposition stages are different.

[0059] Preset timing conditions refer to a pre-defined combination of parameters used to control the sputtering current to change in stages according to a specific sequence and duration. It is important to emphasize that this does not mean interrupting the deposition process or preparing multiple independent coatings, but rather dynamically adjusting the magnitude of the sputtering current at different time points during a continuous deposition process through program control.

[0060] Specifically, at least two different sputtering current values ​​can be determined based on the requirements of the target composite microstructure, and the deposition duration and sequence corresponding to each current value can be set. During the deposition process, the sputtering current is adjusted sequentially according to the preset sequence and duration, and at least two staged depositions are performed on the photomask substrate, with each stage continuously connected without interruption. Since different currents can produce different microstructures, after the staged current changes, a pure chromium coating with a composite microstructure containing at least two of the following states—amorphous, polycrystalline, and amorphous-nanocrystalline mixed states—can be formed on the photomask substrate along the thickness direction.

[0061] It should be noted that the entire deposition process described above is a single, complete deposition, and the structural composite is achieved only through staged adjustment of the current, rather than multiple depositions to prepare multiple coatings and then combining them.

[0062] Optionally, the sputtering current can be selected from at least two values ​​in the ranges of 80mA to 120mA, 230mA to 270mA, and 330mA to 370mA.

[0063] The following description uses different embodiments. It should be noted that the following examples are for illustrative purposes only and are not intended to limit this application.

[0064] Example 4: Preparation of a coating with a composite microstructure, obtained by the following steps: Take a quartz glass substrate and ultrasonically clean it in acetone, ethanol and deionized water for 30 minutes each, then dry it with nitrogen gas for later use.

[0065] The cleaned quartz substrate was then placed on the sample tray inside the magnetron sputtering chamber, and a 4N chromium target was installed in the magnetron sputtering instrument. The chamber was then evacuated until the background vacuum reached 4 × 10⁻⁶. -4After Pa, adjust the target-substrate distance to 15cm, adjust the rotation speed to 5r / min, introduce 30SCCM of argon gas, set the substrate temperature to 28℃, set the working pressure to 0.52Pa, and after 5min of pre-sputtering, begin formal deposition.

[0066] For example, the preset timing conditions can be a sequence of low current, medium current, and high current. Specifically, after pre-sputtering for 2 minutes with a sputtering current of any value between 80mA and 120mA, the main deposition takes 5 minutes. Then, after pre-sputtering for 2 minutes with a sputtering current of any value between 230mA and 270mA, the deposition takes 3.5 minutes. Finally, after pre-sputtering for 2 minutes with a sputtering current of any value between 330mA and 370mA, the deposition takes 2.5 minutes. This yields a pure chromium coating with a gradient composite microstructure, exhibiting a continuous monolayer from bottom to top along the substrate direction. Its thickness can be 65nm to 75nm.

[0067] Example 5 describes the preparation of a coating with a composite microstructure. Compared to Example 4, only the preset timing conditions of the sputtering current are changed. Specifically, the preset timing conditions can be a sequence of low current, high current, and medium current. For example, by setting the timing, the coating can be pre-sputtered for 2 minutes using a sputtering current of any value between 80mA and 120mA, followed by formal deposition for 5 minutes. Then, pre-sputtering for 2 minutes using a sputtering current of any value between 330mA and 370mA, followed by deposition for 2.5 minutes. Finally, pre-sputtering for 2 minutes using a sputtering current of any value between 230mA and 270mA, followed by deposition for 3.5 minutes, yields a pure chromium coating with a gradient composite microstructure, and its thickness can be between 45nm and 60nm.

[0068] Example 6 describes the preparation of a coating with a composite microstructure. Compared to Example 4, only the preset timing conditions of the sputtering current are changed. Specifically, the preset timing conditions can be a sequence of medium current, low current, and high current. For example, by setting the timing, the coating can be pre-sputtered for 2 minutes using a sputtering current of any value between 230mA and 270mA, followed by formal deposition for 3.5 minutes. Then, pre-sputtering for 2 minutes using a sputtering current of any value between 80mA and 120mA, followed by deposition for 5 minutes. Finally, pre-sputtering for 2 minutes using a sputtering current of any value between 330mA and 370mA, followed by deposition for 2.5 minutes, yields a pure chromium coating with a gradient composite microstructure and a thickness of 75nm to 80nm.

[0069] Example 7 describes the preparation of a coating with a composite microstructure. Compared to Example 4, only the preset timing conditions of the sputtering current are changed. Specifically, the preset timing conditions can be a sequence of medium current, high current, and low current. For example, by setting the timing, the coating can be pre-sputtered for 2 minutes using a sputtering current of any value between 230mA and 270mA, followed by formal deposition for 3.5 minutes. Then, pre-sputtering for 2 minutes using a sputtering current of any value between 330mA and 370mA, followed by deposition for 2.5 minutes. Finally, pre-sputtering for 2 minutes using a sputtering current of any value between 80mA and 120mA, followed by deposition for 5 minutes, yields a pure chromium coating with a gradient composite microstructure and a thickness of 60nm to 75nm.

[0070] Example 8 describes the preparation of a coating with a composite microstructure. Compared to Example 4, only the preset timing conditions of the sputtering current are changed. Specifically, the preset timing conditions can be a sequence of higher current, lower current, and medium current. For example, by setting the timing, the coating can be pre-sputtered for 2 minutes using a sputtering current of any value between 330mA and 370mA, followed by formal deposition for 2.5 minutes. Then, pre-sputtering for 2 minutes using a sputtering current of any value between 80mA and 120mA, followed by deposition for 5 minutes. Finally, pre-sputtering for 2 minutes using a sputtering current of any value between 230mA and 270mA, followed by deposition for 3.5 minutes, yielding a pure chromium coating with a gradient composite microstructure and a thickness of 70nm to 80nm.

[0071] Example 9 describes the preparation of a coating with a composite microstructure. Compared to Example 4, only the preset timing conditions of the sputtering current are changed. Specifically, the preset timing conditions can be a sequence of higher current, medium current, and lower current. For example, by setting the timing, the coating can be pre-sputtered for 2 minutes using a sputtering current of any value between 330mA and 370mA, followed by formal deposition for 2.5 minutes. Then, pre-sputtering for 2 minutes using a sputtering current of any value between 230mA and 270mA, followed by deposition for 3.5 minutes. Finally, pre-sputtering for 2 minutes using a sputtering current of any value between 80mA and 120mA, followed by deposition for 5 minutes, yields a pure chromium coating with a gradient composite microstructure and a thickness of 65nm to 75nm.

[0072] As can be seen from the above embodiments, the core technical effect of using at least two values ​​of higher current, medium current and lower current for coating is that it can synergistically integrate the advantages of various microstructures such as amorphous state, amorphous-nanocrystalline mixed state and polycrystalline state, and is expected to achieve high optical density, low stress and good etchability at the same time.

[0073] In the above embodiments, this time-based current regulation enables the in-situ formation of composite stacks or gradient transition structures with multiple microstructures within the same growing pure chromium coating. By precisely adjusting the key parameter of sputtering current in the time dimension, the active design and spatial arrangement of the microstructures within the pure chromium coating are achieved, thereby integrating the performance advantages of each individual structure and potentially obtaining superior overall optical density performance and interface characteristics.

[0074] In some embodiments, the DC magnetron sputtering process includes a DC dual-target co-sputtering process; the method further includes: setting a first DC target as a first sputtering current and setting a second DC target as a second sputtering current to form a pure chromium coating with a composite microstructure.

[0075] The first DC target can refer to the first high-purity chromium target installed in the magnetron sputtering instrument, and the second DC target can refer to the second high-purity chromium target installed in the magnetron sputtering instrument. The sputtering current of both DC targets can be between 50mA and 800mA, and the settings of the two sputtering currents can be different.

[0076] It should be noted that the DC dual-target co-sputtering process of the first DC target and the second DC target is carried out simultaneously, and the deposition time is the same.

[0077] Specifically, in the DC dual-target co-sputtering process, two high-purity chromium targets are started synchronously, sputtered with the first sputtering current and the second sputtering current respectively, and the same deposition time is maintained. Since the chromium atoms sputtered by the two targets can be instantaneously mixed on the substrate surface when they are deposited together, an in-plane composite microstructure can be formed.

[0078] In the above embodiments, the method of using DC dual-target co-sputtering for deposition, controlling the sputtering current of different DC targets to form a pure chromium coating with a composite microstructure, achieves structural composite without staged operations, and can improve deposition efficiency while ensuring synergistic optimization of coating performance. Furthermore, the formed pure chromium coating achieves an optical density per unit thickness at a wavelength of 193 nm that meets the design objectives. Exemplary examples are described below through different embodiments. It should be noted that the following examples are for illustrative purposes only and are not intended to limit this application.

[0079] Example 10: Preparation of a coating with a composite microstructure, obtained by the following steps: Take a quartz glass substrate and ultrasonically clean it in acetone, ethanol and deionized water for 30 minutes each, then dry it with nitrogen gas for later use.

[0080] The cleaned quartz substrate was then placed on the sample tray inside the magnetron sputtering chamber, and a 4N chromium target was installed in the magnetron sputtering instrument. The chamber was then evacuated until the background vacuum reached 4 × 10⁻⁶. -4 After Pa, adjust the target-substrate distance to 15cm, adjust the rotation speed to 5r / min, introduce 30SCCM of argon gas, set the substrate temperature to 28℃, and set the working pressure to 0.52Pa. After pre-sputtering for 5min, start DC dual-target co-sputtering for formal coating.

[0081] Specifically, the sputtering current of the first DC target can be set to any value between 80mA and 120mA, and the sputtering current of the second DC target can be set to any value between 230mA and 270mA. The deposition time of both the first DC target and the second DC target can be set to 5 minutes to obtain a pure chromium coating with an in-plane composite microstructure and a thickness of 50nm to 60nm.

[0082] Example 11 describes the preparation of a coating with a composite microstructure, following the same process as in Example 10. However, when using DC dual-target co-sputtering for formal coating, Example 11 sets the sputtering current of the first DC target to any value between 80mA and 120mA, and the sputtering current of the second DC target to any value between 330mA and 370mA. The deposition time for the first and second DC targets is set to 4 minutes to obtain a pure chromium coating with an in-plane composite microstructure, and its thickness can be 50nm to 60nm.

[0083] Example 12 describes the preparation of a coating with a composite microstructure, following the same process as in Example 10. However, when using DC dual-target co-sputtering for formal coating, Example 12 sets the sputtering current of the first DC target to any value between 230mA and 270mA, and the sputtering current of the second DC target to any value between 330mA and 370mA. The deposition time for both the first and second DC targets is set to 3 minutes to obtain a pure chromium coating with an in-plane composite microstructure, and its thickness can also be 50nm to 60nm.

[0084] In the above embodiments, pure chromium material is used throughout the process, thus avoiding heterogeneous defects and ensuring stable process parameters and good coating repeatability. Furthermore, by simultaneously applying different sputtering currents to dual targets, a composite microstructure pure chromium coating can be directly formed in a single deposition process, eliminating the need for staged current adjustments and resulting in higher deposition efficiency. Moreover, the prepared coating is thin, allowing for the synergistic utilization of the light absorption advantages of different microstructures at ultra-thin dimensions.

[0085] This specification also provides a photomask, including a photomask substrate and a light-shielding layer formed on the photomask substrate, the light-shielding layer being a chromium-based coating as described above.

[0086] For specific limitations regarding a photomask, please refer to the limitations regarding a chromium-based coating mentioned above, which will not be repeated here.

[0087] This specification also provides a semiconductor device, including a substrate and a light-absorbing layer, wherein the light-absorbing layer is a chromium-based coating as described above.

[0088] Specifically, the chromium-based coating can be used as a light absorption layer in semiconductor components such as flat panel displays, spatial light modulators, and tunable filters to adapt to the absorption and modulation requirements of different optical signals.

[0089] For specific limitations regarding a semiconductor element, please refer to the limitations regarding a chromium-based coating mentioned above, which will not be repeated here.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0091] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0092] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0093] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. Since they are fundamentally similar to the method embodiments, the descriptions are relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0094] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

[0095] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A chromium-based coating for a photomask substrate, characterized in that, The chromium-based coating is a pure chromium coating; the pure chromium coating has a single microstructure or a composite microstructure; wherein, the single microstructure includes any one of amorphous, polycrystalline and mixed states; the composite microstructure includes at least two of amorphous, polycrystalline and mixed states; the mixed state refers to a mixed phase microstructure of polycrystalline and nanocrystalline.

2. A method for preparing a chromium-based coating for a photomask substrate, characterized in that, The method for preparing the chromium-based coating of claim 1 comprises: A photomask substrate is provided, and the photomask substrate is placed in a vacuum environment; The pure chromium coating is formed by depositing a pure chromium target on the photomask substrate using a DC magnetron sputtering process and controlling the sputtering current. The sputtering current ranges from 50mA to 800mA.

3. The method according to claim 2, characterized in that, The method further includes: The sputtering current is controlled to a single constant value, and a single deposition process is performed to deposit the pure chromium coating with a single microstructure on the photomask substrate.

4. The method according to claim 2, characterized in that, The method further includes: The sputtering current is controlled to change in stages according to preset timing conditions, and at least two staged deposition processes are performed to form a pure chromium coating with a composite microstructure on the photomask substrate along the thickness direction; wherein the sputtering current used in adjacent deposition processes is different.

5. The method according to claim 2, characterized in that, The DC magnetron sputtering process includes a DC dual-target co-sputtering process; the method further includes: The first DC target is set as the first sputtering current, and the second DC target is set as the second sputtering current to form the pure chromium coating with a composite microstructure; wherein the DC dual-target co-sputtering process of the first DC target and the second DC target is performed synchronously and the deposition time is the same.

6. The method according to claim 2, characterized in that, The background vacuum level of the deposition process is in the range of 3 × 10⁻⁶. -4 Pa to 5×10 -4 Pa; The atmosphere is argon; the working pressure ranges from 0.45 Pa to 0.55 Pa; the target-substrate distance of the pure chromium target ranges from 10 cm to 20 cm; and the substrate temperature of the photomask substrate ranges from 24 °C to 32 °C.

7. The method according to claim 2, characterized in that, The photomask substrate is a quartz glass substrate.

8. The method according to claim 2, characterized in that, The purity of the pure chromium target is not less than 99.95%; wherein, the purity of the pure chromium target is higher than 99.99%.

9. A photomask, characterized in that, It includes a photomask substrate and a light-shielding layer formed on the photomask substrate, wherein the light-shielding layer is a chromium-based coating as described in claim 1.

10. A semiconductor element, characterized in that, It includes a substrate and a light-absorbing layer, wherein the light-absorbing layer is a chromium-based coating as described in claim 1.

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