Method for enhancing contrast of photoresist pattern

Abstract

The invention provides a method for enhancing the contrast of a photoresist pattern, which can be applied to the technical field of super-resolution lithography or surface plasma lithography, and comprises the following steps: depositing a metal film layer on a substrate; coating photoresist on the metal film layer, and exposing and developing the photoresist to obtain a photoresist pattern exposed out of a metal area; and carrying out local charge focusing on the target region by utilizing a focusing electron beam, so that a contrast difference is formed between the photoresist pattern region and the metal region in the target region, and the target region with enhanced contrast is obtained. According to the method, charges in a target area are gradually accumulated when electron beams are focused by utilizing a charge accumulation effect of interaction of the electron beams and substances, and charges are more easily accumulated in a metal area than a photoresist area, so that the contrast of the metal area and the photoresist area is different under electron microscope observation, and the contrast of a photoresist pattern is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of super-resolution lithography or surface plasma lithography, and in particular to a method for enhancing the contrast of photoresist patterns. Background Art

[0002] With the rapid advancement of science and technology, electronic devices are constantly developing towards smaller size and higher integration. This trend has put forward higher and higher requirements for photolithography technology. As one of the core processes in semiconductor manufacturing, the accuracy and efficiency of photolithography technology directly affect the performance and production cost of electronic devices. Especially for super-resolution lithography or surface plasma lithography technology, due to the thin photoresist layer, the contrast of the photoresist pattern after exposure is low, which is not conducive to the observation of the pattern. Therefore, improving the contrast of the pattern after exposure is not only crucial for clearly and accurately observing the morphology of the exposed pattern, but also the key to optimizing the process and improving product competitiveness.

[0003] At present, the industry has explored a variety of methods to improve graphic contrast. The current methods for improving graphic contrast are as follows:

[0004] (1) Optimize lithography equipment:

[0005] Use off-axis illumination technology to optimize the light source: By adjusting the position of the light source, the light is irradiated onto the mask at a non-vertical angle. This lighting method can effectively reduce the interference and diffraction effects of the light, thereby improving the contrast of the exposure pattern. Off-axis illumination technology requires precise design and adjustment of the light source system of the lithography equipment to ensure the uniformity and stability of the light.

[0006] Other equipment optimization: In addition to off-axis illumination, the pattern contrast can also be improved by optimizing the lens system of the lithography equipment, improving the coherence of the light source, improving the exposure control system, etc. These optimization measures often require high-precision processing and assembly technology, as well as in-depth optical design knowledge.

[0007] (2) Use the optical proximity effect to correct the mask pattern:

[0008] Optical proximity effect: During the photolithography process, due to the diffraction and interference of light, the pattern on the mask will change in shape and size when it is exposed to the photoresist. This change is called the optical proximity effect.

[0009] Graphic correction: In order to offset this effect, the pattern on the mask can be corrected in advance so that it can obtain the desired shape and size after the photolithography process. This correction requires accurate calculation of the impact of the optical proximity effect and adjustment of the pattern design on the mask accordingly.

[0010] (3) Optimize the process flow such as exposure dose and photoresist thickness:

[0011] Exposure dose: Exposure dose refers to the total amount of energy that light irradiates onto the photoresist during the photolithography process. Appropriate exposure dose can ensure that the photoresist is fully exposed to form a clear pattern. Too high or too low exposure dose will lead to a decrease in pattern contrast.

[0012] Photoresist thickness: The thickness of the photoresist is also an important factor affecting the contrast of the pattern. Too thick a photoresist may lead to insufficient exposure, while too thin a photoresist may not form a stable pattern. Therefore, it is necessary to select the appropriate photoresist thickness according to the specific process requirements.

[0013] Other process optimizations: In addition to exposure dose and photoresist thickness, the contrast of graphics can also be improved by optimizing development conditions, adjusting baking temperature and time, etc. These optimization measures require a deep understanding of the chemical and physical properties of photoresists, as well as the kinetics of the photolithography process.

[0014] Although the above methods have achieved remarkable results in improving graphic contrast, they also face some challenges. First, these processes are often complicated and require a high degree of expertise and technical experience. Second, they are time-consuming and may increase production costs and extend production cycles. Finally, the implementation of these methods has high requirements for equipment and technology, and requires a lot of resources and funds.

[0015] Therefore, exploring simpler, more efficient and lower-cost methods to improve graphic contrast will be an important direction. Summary of the invention

[0016] 1. Technical issues to be resolved

[0017] For solving at least one of the above-mentioned technical problems existing in the prior art, embodiments of the present invention provide a method for enhancing the contrast of photoresist patterns. Under electron microscope observation, when focused electron beam is focused on a specific area, based on the charge accumulation effect of focused electron beam and material interaction, the charge amount in this area can be accumulated gradually. Because there are differences in the response of photoresist and metal film layer to the focused electron beam, the metal area is easier to accumulate charge because of its good electrical conductivity, and by contrast, the photoresist area is then relatively difficult for accumulating charge. The difference of this charge accumulation makes the metal area and the photoresist area present obvious contrast contrast under electron microscope observation, thereby enhancing the contrast of the photoresist patterns.

[0018] (II) Technical solution

[0019] In view of the above technical problems, an embodiment of the present invention provides a method for enhancing the contrast of a photoresist pattern.

[0020] According to a first aspect of the present invention, a method for enhancing the contrast of a photoresist pattern is provided, comprising: S1, depositing a metal film layer on a substrate; S2, coating a photoresist on the metal film layer, exposing and developing the photoresist, and obtaining a photoresist pattern exposing a metal area; S3, using a focused electron beam to perform local charge focusing on a target area, the target area comprising at least a portion of a photoresist pattern area and at least a portion of a metal area, so that a contrast difference is formed between the photoresist pattern area and the metal area in the target area, and a contrast-enhanced target area is obtained.

[0021] In some exemplary embodiments, using a focused electron beam to perform local charge focusing on a target area in step S3 includes: placing the sample obtained in step S2 on a sample stage of a scanning electron microscope, and adjusting the position of the sample so that the target area in the sample is within the observation range; setting working parameters of the scanning electron microscope, the working parameters including an acceleration voltage; starting the scanning electron microscope, and aligning the focused electron beam with the target area for local charge focusing, so that charge accumulation occurs in a metal area in the target area, thereby obtaining a contrast-enhanced target area.

[0022] In some exemplary embodiments, the method of depositing the metal film layer on the substrate in step S1 includes physical sputtering, chemical vapor deposition, ion plating, electroplating and chemical plating.

[0023] In some exemplary embodiments, the method of coating the photoresist on the metal film layer in step S2 includes a spin coating method, and coating the photoresist on the metal film layer in step S2 includes: fixing the substrate containing the metal film layer on a rotating tray of a spin coater; using a pipette or a dropper to drop the photoresist on the center of the metal film layer; starting the spin coater to spread the photoresist on the metal film layer and to throw excess photoresist out of the edge of the metal film layer to obtain a uniform photoresist film layer.

[0024] In some exemplary embodiments, the method of exposing the photoresist in step S2 includes super-resolution lithography or surface plasma lithography.

[0025] In some exemplary embodiments, the acceleration voltage in step S2 ranges from 2 kV to 10 kV.

[0026] In some exemplary embodiments, the time for local charge focusing in step S3 is 1 min-5 min.

[0027] In some exemplary embodiments, the thickness of the metal film layer in step S1 is 35 nm-50 nm.

[0028] In some exemplary embodiments, the thickness of the photoresist in step S2 is 18 nm-25 nm.

[0029] In some exemplary embodiments, the material of the metal film layer in step S1 includes one of aluminum, chromium, silver, tantalum and indium.

[0030] (III) Beneficial effects

[0031] It can be seen from the above technical solutions that a method for enhancing the contrast of a photoresist pattern provided by an embodiment of the present invention has at least the following beneficial effects:

[0032] (1) Significantly enhanced contrast: The present invention can significantly enhance the contrast of the exposed photoresist pattern with a metal enhancement layer by focusing the electron beam and the charge accumulation effect, so that both micron-scale and nanometer-scale patterns can be observed and evaluated more clearly.

[0033] (2) Simple and easy operation: Compared with the complicated procedures and high technical requirements in the prior art, the present invention can achieve contrast enhancement by simply performing electron bombardment and focusing operations on the graphic area under an electron microscope.

[0034] (3) Strong controllability: By adjusting the size and time of applied voltage, the degree of enhancement of graphic contrast can be precisely controlled to meet the needs of different application scenarios.

[0035] (4) Wide applicability: The present invention is applicable to metal film layers of different materials and thicknesses and different types of photoresists, and has wide applicability and universality.

[0036] (5) Non-destructive processing: By operating within a suitable voltage and time range, the present invention will not cause damage to the photoresist pattern, thus ensuring the smooth progress of subsequent process flows. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above contents and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0038] Figure 1 A schematic diagram of a process of enhancing the contrast of a photoresist pattern according to an embodiment of the present invention is shown;

[0039] Figure 2 A schematic diagram showing the structure corresponding to each step of obtaining a contrast-enhanced photoresist pattern according to an embodiment of the present invention;

[0040] Figure 3 A schematic diagram showing the change of the contrast of a 128 nm period pattern with the local charge focusing time under the same accelerating voltage according to an embodiment of the present invention is shown;

[0041] Figure 4A schematic diagram showing the change of micrometer scale pattern contrast with local charge focusing time under the same acceleration voltage according to an embodiment of the present invention;

[0042] Figure 5 A schematic diagram showing the change of the contrast of the target area under different electron microscopes according to an embodiment of the present invention with the acceleration voltage and the local charge focusing time; and

[0043] Figure 6 The schematic diagram schematically shows the change of contrast of the target area with the acceleration voltage at the same local charge focusing time of the enhanced image according to an embodiment of the present invention.

[0044] Reference numerals:

[0045] 1-substrate; 2-metal film layer; 3-photoresist film layer; 21-metal area; 31-photoresist pattern area. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] The present invention relates to a method for enhancing the contrast of photoresist patterns, which can significantly enhance the contrast by simply operating the pattern area under an electron microscope through focused electron beam bombardment and local charge focusing technology. The present invention has the advantages of high efficiency, accuracy and controllability, and is suitable for micrometer-scale and nanometer-scale pattern observation and evaluation.

[0048] Figure 1 The flowchart of a method for enhancing the contrast of a photoresist pattern according to an embodiment of the present invention is schematically shown.

[0049] like Figure 1 As shown, a method for enhancing the contrast of a photoresist pattern according to an embodiment of the present invention includes steps S1 to S3.

[0050] In step S1, a metal film layer 2 is deposited on a substrate 1. The cross-sectional view of the obtained structure is shown in FIG. Figure 2 (a) in the figure.

[0051] In the embodiment of the present invention, the substrate 1 includes but is not limited to a silicon wafer substrate, a silicon dioxide substrate, a glass substrate, and a sapphire substrate.

[0052] In the embodiment of the present invention, the method of depositing the metal film layer 2 includes but is not limited to thermal evaporation, physical sputtering, chemical vapor deposition, ion plating, electroplating and chemical plating. The specific method is selected according to factors such as process requirements, material properties and cost considerations.

[0053] For example, thermal evaporation mainly uses high temperature to heat the metal sample to the evaporation temperature, so that its atoms or molecules change from solid to gas (evaporation), and then in a vacuum environment, these gaseous metal atoms or molecules will diffuse and deposit on the surface of the substrate 1 with a lower temperature to form a metal film. The process of depositing the metal film layer 2 by thermal evaporation usually includes the following steps:

[0054] (1) Substrate preparation: Clean the surface of substrate 1 to remove oil, dust and impurities, and ensure that the surface of substrate 1 is clean and flat.

[0055] (2) Chamber preparation: Place substrate 1 into the vacuum chamber, close the chamber and evacuate to the required vacuum level.

[0056] (3) Heating the metal sample: Start the evaporation source and heat the metal sample to the evaporation temperature, so that it evaporates and forms metal vapor.

[0057] (4) Vapor diffusion and deposition: Metal vapor diffuses to the surface of substrate 1 in a vacuum environment and is deposited on the surface of substrate 1 to form a metal film.

[0058] (5) Post-deposition treatment: If necessary, the deposited metal film is annealed to improve its performance.

[0059] Thermal evaporation can produce high-quality nanomaterials and thin films by precisely controlling parameters such as evaporation temperature, evaporation rate, inert gas pressure, substrate temperature, and source-to-substrate distance. Compared with other methods for depositing metal films, thermal evaporation has the advantages of simple equipment, high film purity, fast deposition rate, and strong repeatability.

[0060] In step S2, a photoresist is coated on the metal film layer 2, and the photoresist is exposed and developed to obtain a photoresist pattern exposing the metal region 21. The cross-sectional view after coating the photoresist is shown in FIG. Figure 2 (b) in the figure; and the cross-sectional view after obtaining the photoresist pattern is shown in Figure 2 (c) in.

[0061] In some exemplary embodiments, the method of coating the photoresist on the metal film layer 2 in step S2 comprises a spin coating method, and the method of coating the photoresist on the metal film layer 2 in step S2 comprises the following steps:

[0062] (1) The substrate 1 including the metal film layer 2 is fixed on the rotating plate of the spin coater.

[0063] Before installation, the metal film layer 2 needs to be cleaned and pretreated, wherein cleaning includes using an appropriate solvent (such as acetone, isopropyl alcohol, etc.) to clean the metal film layer 2 to remove oil, dust and impurities on the surface. After cleaning, blow dry with nitrogen or use an oven to ensure that the surface of the metal film layer 2 is clean and dry. Pretreatment includes pretreatment that may be required according to the properties of the photoresist and the characteristics of the metal film layer 2, such as coating an adhesion promoter (such as HMDS) to improve the adhesion between the photoresist and the metal film layer 2.

[0064] (2) Use a pipette or dropper to drop photoresist onto the center of the metal film layer 2, wherein the amount of dropper is determined based on the size of the metal film layer 2, the viscosity of the photoresist, and the required film thickness.

[0065] (3) Start the spin coater, so that the photoresist is spread on the metal film layer 2 and the excess photoresist is thrown out of the edge of the metal film layer 2, thereby obtaining a uniform photoresist film layer 3. The process may specifically include: starting the spin coater, setting a low rotation speed and rotation time, wherein the low-speed rotation helps the photoresist to be evenly spread on the metal film layer 2; after the photoresist is evenly spread on the metal film layer 2, the rotation speed is increased to the set value, and during the high-speed rotation, the photoresist is rapidly diffused into a uniform film under the action of centrifugal force, and the excess photoresist is thrown out of the edge of the metal film layer 2. The rotation speed and rotation time are key factors affecting the thickness and uniformity of the photoresist film layer 3. The faster the rotation speed, the thinner the film; the longer the rotation time, the more uniform the film. The specific rotation parameters should be determined according to the properties of the photoresist, the characteristics of the metal film layer 2, and the required thickness of the photoresist film layer 3.

[0066] The spin coating method has the following advantages: (1) The photoresist can be evenly distributed on the surface of the silicon wafer or other substrate, avoiding the situation where the traditional coating method may cause thick or thin areas in some areas; (2) The ability to quickly coat can significantly reduce the production cycle, improve overall production efficiency, and meet the needs of large-scale production; (3) By adjusting the spin coating speed and time, the thickness of the photoresist film layer can be accurately controlled. The speed and film thickness are inversely proportional, that is, the higher the speed, the thinner the film thickness; the lower the speed, the thicker the film thickness. This precise control is crucial to ensuring the accuracy and consistency of the photolithography pattern. (4) Spin coating is suitable for different types of photoresists and substrate sizes, can meet different process requirements, and has a wide range of applications. Whether it is laboratory research or industrial production, spin coating is a reliable photoresist coating method; (5) The film obtained by spin coating is very smooth and has few surface defects, which is beneficial to improving the resolution and yield of the photolithography pattern, and the obtained film is of high quality; (6) Since spin coating can accurately control the film thickness, it avoids the waste of photoresist and saves a lot of materials. Compared with traditional coating methods, spin coating can significantly reduce the use of photoresist, thereby reducing production costs.

[0067] The method for exposing the photoresist in step S2 includes super-resolution lithography or surface plasma lithography. Among them, super-resolution lithography or surface plasma (SP) lithography uses a negative refractive super lens to achieve nano-level lithography resolution, which can achieve a lithography resolution far less than half the wavelength at a long wavelength, breaking the bottleneck of the diffraction limit of traditional resolution, and can greatly extend the resolution improvement space under a long wavelength light source. The present invention does not limit the specific exposure process, and only needs to meet the exposure requirements and obtain the exposure pattern.

[0068] The embodiment of the present invention is applicable to metal film layers 2 of different materials and thicknesses and different types of photoresists, and has wide applicability and universality. Optionally, the materials in the metal film layer 2 region include but are not limited to aluminum, chromium, silver, tantalum and indium. Optionally, the thickness of the metal film layer 2 region is 35nm-50nm, and this thickness range can not only ensure the good conductivity and mechanical strength of the metal film layer 2, but also avoid the adverse effects of the excessively thick metal film layer 2 on subsequent processes. Optionally, the thickness of the photoresist film layer 3 is 18nm-25nm, and this thickness range can not only ensure the clarity and accuracy of the photoresist pattern, but also ensure the stability of the photoresist during exposure and development.

[0069] In step S3, a focused electron beam is used to perform local charge focusing on a target area, wherein the target area includes at least a portion of the photoresist pattern area 31 and at least a portion of the metal area 21, so that the photoresist pattern area 31 and the metal area 21 in the target area form a contrast difference, thereby obtaining a contrast-enhanced photoresist pattern. The cross-sectional view of the obtained contrast-enhanced photoresist pattern is shown in FIG. Figure 2 (d) in.

[0070] In some exemplary embodiments, step S3 specifically includes step S31 to step S34.

[0071] In step S31, the sample obtained in step S2 is placed on the sample stage of the scanning electron microscope, and the position of the sample is adjusted so that the target area in the sample is within the observation range.

[0072] The sample stage of the SEM is a component that carries the sample and adjusts its position. The purpose of adjusting the sample position is to ensure that the target area can be clearly presented in the field of view of the SEM for subsequent local charge focusing and observation. By accurately adjusting the sample position, it can be ensured that the target area is accurately aligned and observed, providing a good foundation for subsequent steps.

[0073] In step S32, the operating parameters of the scanning electron microscope are set, and the operating parameters include the acceleration voltage.

[0074] Step S32 specifically includes: starting the scanning electron microscope and preheating to a stable state; setting a suitable acceleration voltage according to the material and thickness of the sample, the acceleration voltage determines the energy of the focused electron beam and affects the interaction depth and effect; adjusting other parameters: adjusting other parameters such as scanning speed, beam current, working distance, etc. to ensure image quality. The acceleration voltage is one of the important working parameters of the scanning electron microscope. It determines the speed of the focused electron beam after it is ejected from the electron gun, and then affects the mode and depth of interaction between the focused electron beam and the sample. Different samples require different acceleration voltages to obtain the best observation effect. By reasonably setting the working parameters of the scanning electron microscope, it can be ensured that the focused electron beam interacts fully with the sample, thereby obtaining high-quality image information. In step S33, the scanning electron microscope is started, and the focused electron beam is aimed at the target area for local charge focusing, so that the metal area 21 in the target area accumulates charge and obtains a contrast-enhanced target area.

[0075] Step S33 specifically includes: after ensuring that all settings are completed, starting the scanning system of the scanning electron microscope; accurately aligning the focused electron beam to the target area through the control system of the scanning electron microscope; turning on the local charge focusing function to focus and scan the focused electron beam in the target area, resulting in charge accumulation in the metal area 21. When the focused electron beam bombards the sample surface, it interacts with the atoms in the sample, resulting in charge accumulation. This charge accumulation effect will produce a difference between the metal area 21 and the photoresist pattern area 31, thereby forming a contrast difference, thereby enhancing the contrast of the target area.

[0076] In the embodiment of the present invention, the contrast enhancement effect of the target area is related to the acceleration voltage and the time of local charge focusing. By adjusting the magnitude of the acceleration voltage and the time of local charge focusing, the contrast enhancement degree of the target area can be accurately controlled.

[0077] Specifically, the acceleration voltage is a key factor in driving the focused electron beam to move in the photoresist and triggering the necessary chemical reactions. Optionally, the range of the acceleration voltage is set to 2kV to 10kV. When the applied voltage is lower than the lower limit of this range, it is impossible to provide enough energy to drive the movement of the focused electron beam or trigger a chemical reaction, resulting in insufficient charge accumulation, which in turn affects the accuracy and resolution of the photoresist pattern in the target area. On the contrary, if the voltage is too high and exceeds the upper limit of this range, too much energy may be generated, resulting in damage to the photoresist, which may manifest as burning, deformation or changes in the chemical properties of the photoresist, thereby destroying the integrity of the photolithographic pattern.

[0078] The time of local charge focusing is also an important factor affecting the contrast enhancement degree of the target area. Optionally, the time range for applying the preset voltage is set to 1 minute to 5 minutes. This time range is determined based on the characteristics of the photoresist and the requirements of the photolithography process. If the voltage is applied for too long, beyond this range, the photoresist pattern will be damaged due to long-term exposure to the high-voltage focused electron beam, including over-reaction of the photoresist, structural changes or performance degradation, resulting in reduced quality of the photolithography pattern. If the application time is too short, a good charge focusing effect cannot be achieved.

[0079] Compared with the complicated procedures and high technical requirements in the prior art, the present invention only needs to perform simple electron bombardment and focusing operations on the graphic area under an electron microscope to achieve contrast enhancement. The present invention does not damage the photoresist pattern by operating within a suitable voltage and time range, thereby ensuring the smooth progress of the subsequent process flow. By regulating the size and time of the applied voltage, the degree of enhancement of the contrast between the photoresist graphic area 31 and the metal area 21 in the target area can be accurately controlled to meet the needs of different application scenarios.

[0080] The embodiment of the present invention is based on the charge accumulation effect when the focused electron beam interacts with the material. Under electron microscope observation, when the focused electron beam is focused on the target area, the charge amount of the target area will gradually accumulate. Since the photoresist pattern area 31 and the metal area 21 have different responses to the focused electron beam, the metal area 21 is more likely to accumulate charge due to its good conductivity, while the photoresist pattern area 31 is relatively difficult to accumulate charge. This difference in charge accumulation causes the metal area 21 and the photoresist pattern area 31 to present different contrasts under electron microscope observation, thereby enhancing the contrast of the target area. Specifically, the present invention uses an electron microscope to bombard the area on the substrate 1 where the photoresist pattern is generated after exposure. By controlling the size and time of the applied voltage, the local focusing degree of the focused electron beam on the target area can be regulated, thereby controlling the area and degree of charge accumulation. The metal area 21 in the charge accumulation area will turn white and brighten, thereby achieving the effect of enhancing the contrast of the pattern.

[0081] The present invention is further described in detail below in conjunction with the accompanying drawings. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

[0082] Embodiment 1:

[0083] In this embodiment, step S11, a metal film layer is deposited on a substrate, wherein the substrate is a glass substrate; the material of the metal film layer is aluminum, and the thickness of the obtained metal film layer is 40nm. In this embodiment, the deposition process of the metal aluminum film layer is simple, and the generated aluminum oxide has extremely strong stability.

[0084] Step S12, coating a photoresist on the metal film layer, performing super-resolution exposure and development on the photoresist to obtain a photoresist pattern, wherein the photoresist pattern exposes the metal area; the method of coating the photoresist is spin coating; the material of the photoresist is polymethyl methacrylate (PMMA); the thickness of the photoresist is 20 nm; the photoresist pattern is a pattern with a period of 128 nm (nanoscale grating pattern).

[0085] Step S13, using a focused electron beam to perform local charge focusing on a target area, the target area includes at least a portion of a photoresist pattern area and at least a portion of a metal area, so that the photoresist pattern area and the metal area in the target area form a contrast difference, thereby obtaining a contrast-enhanced target area.

[0086] In step S13, in order to analyze the effect of the local charge focusing time on the contrast of the target area, the acceleration voltage of the local charge focusing is set to 2 kV. While keeping the acceleration voltage unchanged, the local charge focusing time is changed to obtain the electron microscope images of the target area under different local charge focusing times, see Figure 3 ,in Figure 3 a) The time of local charge focusing is 0 (original image without contrast enhancement); Figure 3 b) The local charge focusing time is 1 min; Figure 3 c) The time of local charge focusing is 3 min.

[0087] Depend on Figure 3 It can be seen that as the local charge focusing time increases, the lines in the target area (in the dotted box) become significantly brighter relative to the color of the overall image. At the same time, according to the processing results of the grayscale image, the peak appears on the left line in the target area, further indicating that the left line in the target area is the brightest or highest contrast part of the image.

[0088] Specifically, Figure 3 b) relative to Figure 3 a) The contrast of the target area is improved by 12.8%; Figure 3 c) relative to Figure 3 In a), the contrast of the target area is improved by 27.6%.

[0089] Furthermore, by comparing Figure 3 a) Figure 3 b) and Figure 3 As shown in c), at the same voltage, the difference in local charge focusing time will lead to a significant improvement in the contrast of the target area relative to other areas. Therefore, at the same voltage, the local charge focusing time can be adjusted as needed to obtain grating patterns with different degrees of contrast improvement in the target area.

[0090] Embodiment 2:

[0091] Step S21, depositing a metal film layer on a substrate, wherein the substrate is a glass substrate; the material of the metal film layer is aluminum, and the thickness of the obtained metal film layer is 40nm. In this embodiment, the deposition process of the metal aluminum film layer is simple, and the generated aluminum oxide has extremely strong stability.

[0092] Step S22, coating photoresist on the metal film layer, performing super-resolution exposure and development on the photoresist to obtain a photoresist pattern, wherein the photoresist pattern exposes the metal area; the method of coating the photoresist is spin coating; the material of the photoresist is polymethyl methacrylate (PMMA); the thickness of the photoresist is 20nm; the photoresist pattern is a micrometer-scale geometric pattern.

[0093] Step S23, using a focused electron beam to perform local charge focusing on a target area, the target area includes at least a portion of a photoresist pattern area and at least a portion of a metal area, so that the photoresist pattern area and the metal area in the target area form a contrast difference, thereby obtaining a contrast-enhanced target area.

[0094] In step S23, in order to analyze the effect of the local charge focusing time on the contrast of the target area, the acceleration voltage of the local charge focusing is set to 2 kV. While keeping the acceleration voltage unchanged, the local charge focusing time is changed to obtain the electron microscope images of the target area under different local charge focusing times, see Figure 4 ,in Figure 4 a) The time of local charge focusing is 0 (original image without contrast enhancement); Figure 4 b) The local charge focusing time is 3 min; Figure 4 c) The local charge focusing time is 5 minutes. Figure 4 It can be seen that as the local charge focusing time increases from 0 min to 5 min, the graphic area of ​​the target area (within the dotted box) gradually changes from being almost indistinguishable to having a clear overall outline, further confirming that the method of the embodiment of the present invention can improve the contrast of the photoresist pattern in the target area, and within a certain local charge focusing time range, as the local charge focusing time increases, the brightness of the metal area in the target area increases, thereby improving the contrast of the target area.

[0095] In addition to the parameters of local charge focusing being set according to the experimental purpose, the main difference between Example 2 and Example 1 lies in the different photoresist patterns, wherein the photoresist pattern in Example 1 is a pattern with a period of 128 nm (nanoscale grating pattern); the photoresist pattern in Example 2 is a micrometer-scale geometric pattern.

[0096] Comprehensive analysis of Example 1 and Example 2 shows that the method for enhancing the contrast of photoresist patterns according to the embodiment of the present invention has good effects on both Example 1 and Example 2, indicating that the method according to the embodiment of the present invention has good effects on both micron- and nanometer-scale patterns.

[0097] In Example 2, in order to further verify that the method for enhancing the contrast of photoresist patterns of the present invention is universal to different electron microscopes, another electron microscope with the same structure as the electron microscope is selected in step S3. Figure 4 The electron microscope in the experiment was used to test different electron microscopes to obtain electron microscope images of the target area under different parameters. Figure 5 .

[0098] in, Figure 5 In a), the accelerating voltage is 1.5 kV and the local charge focusing time is 1 min; Figure 5 In b), the accelerating voltage is 3 kV and the local charge focusing time is 1 min; Figure 5 In (c), the accelerating voltage is 3 kV and the local charge focusing time is 5 min.

[0099] contrast Figure 5 a) and Figure 5 As shown in b), when the local charge focusing time is 1 min, the acceleration voltage increases from 1.5 kV to 3 kV, and the image of the target area (within the dotted box) changes from slightly blurry to clearly visible. This proves that the method of the embodiment of the present invention can improve the image contrast by adjusting the acceleration voltage.

[0100] By comparison Figure 5 From b) and c) in Figure 1, it can be found that when the acceleration voltage is kept at 3 kV, the local charge focusing time increases from 3 min to 5 min, and the outline of the graph becomes more obvious. However, it should be noted that Figure 5 There is some damage to the pattern of the target area in the lower area of ​​c), which further confirms that the method of the embodiment of the present invention can improve the pattern contrast by adjusting the local charge focusing time, but too long focusing time may cause damage to the pattern.

[0101] Combination Figure 4 and Figure 5 It can be seen that the method of the embodiment of the present invention can achieve the effect of improving contrast by adjusting the magnitude of the acceleration voltage and the time of local charge focusing under different electron microscopes. Therefore, the method has universal applicability.

[0102] In Example 2, in order to analyze the effect of the acceleration voltage on the contrast of the target area, the local charge focusing time was set to 2 minutes. While keeping the local charge focusing time unchanged, the acceleration voltage was changed to obtain electron microscope images of the target area under different acceleration voltages, see Figure 6 .

[0103] in, Figure 6 a) The accelerating voltage is 1.5 kV; Figure 6 b) The accelerating voltage is 3 kV; Figure 6 c) The accelerating voltage is 5 kV. Figure 6 It can be seen that when the time of local charge focusing remains unchanged, as the acceleration voltage increases, the contrast between the photoresist pattern area and the metal area in the target area (within the dotted box) continues to increase, further indicating that by adjusting the acceleration voltage, patterns with different contrasts in the target area can be obtained, thereby improving the contrast of the photoresist pattern.

[0104] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for enhancing the contrast of a photoresist pattern, characterized in that: include: S1, depositing a metal film layer on a substrate; S2, coating a photoresist on the metal film layer, exposing and developing the photoresist to obtain a photoresist pattern exposing a metal area; S3, using a focused electron beam to perform local charge focusing on a target area, wherein the target area includes at least a portion of a photoresist pattern area and at least a portion of a metal area, so that a contrast difference is formed between the photoresist pattern area and the metal area in the target area, thereby obtaining a contrast-enhanced target area.

2. The method according to claim 1, characterized in that: In step S3, locally focusing the charge on the target area by using the focused electron beam includes: Placing the sample obtained in step S2 on a sample stage of a scanning electron microscope, and adjusting the position of the sample so that the target area in the sample is within the observation range; Setting the working parameters of the scanning electron microscope, wherein the working parameters include an accelerating voltage; The scanning electron microscope is started, and a focused electron beam is directed to the target area for local charge focusing, so that charge accumulation occurs in the metal area in the target area, thereby obtaining a target area with enhanced contrast.

3. The method according to claim 1, characterized in that Methods for depositing the metal film layer on the substrate in step S1 include thermal evaporation, physical sputtering, ion plating, chemical vapor deposition, electroplating and chemical plating.

4. The method according to claim 1, characterized in that The method of coating the photoresist on the metal film layer in step S2 comprises a spin coating method, and the method of coating the photoresist on the metal film layer in step S2 comprises: Fixing the substrate including the metal film layer on a rotating tray of a spin coater; Use a pipette or dropper to drop the photoresist on the center of the metal film layer; The spin coater is started to spread the photoresist on the metal film layer and the excess photoresist is thrown out of the edge of the metal film layer to obtain a uniform photoresist film layer.

5. The method according to claim 1, characterized in that The method for exposing the photoresist in step S2 includes super-resolution lithography or surface plasma lithography.

6. The method according to claim 2, characterized in that The acceleration voltage in step S2 ranges from 2 kV to 10 kV.

7. The method according to claim 2, characterized in that: The time for local charge focusing in step S3 is 1 min-5 min.

8. The method according to claim 1, characterized in that: The thickness of the metal film layer in step S1 is 35nm-50nm.

9. The method according to claim 1, characterized in that: The thickness of the photoresist in step S2 is 18nm-25nm.

10. The method according to claim 1, characterized in that The material of the metal film layer in step S1 includes one of aluminum, chromium, silver, tantalum and indium.

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