A method of manufacturing an EUV mask alignment mark

Abstract

The application provides a preparation method of an EUV mask plate alignment mark, and relates to the technical field of semiconductor manufacturing, and comprises the following steps: S1: optimizing groove structure parameters of the EUV mask plate alignment mark by simulation means, determining structure optimization parameters of the EUV mask plate alignment mark groove, and improving the accuracy and repeatability of alignment mark position detection; S2: selecting a diamond needle tip cutter according to the determined structure optimization parameters of the EUV mask plate alignment mark groove; S3: performing alignment mark processing on the EUV mask plate by using the selected diamond needle tip cutter in the step S2 according to the determined structure optimization parameters of the EUV mask plate alignment mark groove. The application adopts a diamond machining method to prepare a mask alignment mark groove, can efficiently obtain an EUV mask alignment mark groove with specific structure, and is used for solving the problems of many processing steps, long process, long time, poor repeatability and the like of the existing EUV mask plate alignment mark processing.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically to a method for preparing alignment marks on an EUV mask. Background Technology

[0002] The advancement of the semiconductor industry has benefited from the development of very large-scale integrated circuits (VLSI). Photolithography is a core technology in chip manufacturing; almost every process in the entire chip manufacturing process relies on photolithography. It is through the continuous development of photolithography technology to reduce the linewidth of semiconductor devices that high integration, high performance, and low power consumption of integrated circuits are achieved. Projection lithography, which uses the principle of optical projection imaging to transfer the pattern of a photomask to the surface of a wafer coated with photoresist, is the most widely used and vital photolithography technology on today's VLSI manufacturing lines.

[0003] According to Rayleigh's law, improving the imaging resolution of a projection lithography system can be achieved by reducing the exposure wavelength, decreasing the process factor, or increasing the numerical aperture of the projection lithography objective. Among these methods, reducing the exposure wavelength is considered the most effective way to improve lithography resolution. EUVL projection lithography, which uses 13.5nm extreme ultraviolet light as its working wavelength, has already achieved mass production at the 5nm technology node and is moving towards the 3nm technology node, becoming the most important lithography technology now and in the future.

[0004] In EUVL projection lithography, the chip pattern is projected onto the wafer surface using a mask, essentially copying the pattern from the mask onto the wafer. Besides the pattern to be copied, the mask also needs to contain markers for accurate pattern positioning. Unlike the transmissive masks used in traditional lithography, EUV lithography uses reflective masks. Figure 1As shown, an EUV mask consists of three parts: a substrate, EUV multilayer films, and an absorption layer. The multilayer films are used to generate the pattern for the non-mask areas, while the absorption layer is used to form the pattern for the mask areas. During the deposition and fabrication of the multilayer films and absorption layers, corresponding defects are generated. Both multilayer film defects and absorption layer defects distort the pattern imaged on the wafer surface, causing discrepancies from the expected pattern and severely affecting the quality of photolithography imaging. Defects in the multilayer films mainly cause imaging aberrations, which are either impossible to eliminate or difficult to repair. Defects in the absorption layer mainly cause changes in light intensity and can be eliminated or repaired. During EUV mask substrate processing, multilayer film deposition, and absorption layer deposition, defects are inevitably introduced; therefore, a completely defect-free mask does not exist. To reduce defects introduced during mask fabrication and achieve good mass production, significant investment is required in all aspects, including substrate materials, polishing, cleaning, processing, and multilayer film deposition. However, even with such efforts, it is still impossible to completely avoid the occurrence of a small number of defects. As an alternative method, compensating for defects in the photomask and thus eliminating their impact can greatly reduce the investment in the photomask manufacturing process and rapidly increase the production of photomasks.

[0005] Compensating for defects first requires accurate identification and location. This process necessitates sophisticated defect detection equipment and alignment marks for precise mask alignment and defect localization. Defect localization accuracy in masks used in next-generation EUVL must be less than 10 nm. Three factors influence the defect localization accuracy of EUV masks: the repeatability of alignment mark position measurements, the mask stage movement accuracy, and the repeatability of defect position measurements. Besides being affected by the performance of the precision defect detection system, the specific structure and parameters of the alignment marks also significantly impact the repeatability of alignment mark position measurements.

[0006] Currently, such as Figure 1 As shown, EUV mask alignment marks typically employ a cross-shaped structure composed of rectangular grooves, fabricated through focused ion beam or electron beam exposure followed by etching. The combination of photolithography and reactive ion beam etching can accurately obtain the desired marking structure; however, this method involves numerous process steps, a lengthy process, and poor process repeatability. Focused ion beam etching can conveniently fabricate the mask marking structure in a single step, but fine-tuning is required to achieve specific marking structures, which is relatively time-consuming.

[0007] Previous studies have shown that optimizing the width, depth, and sidewall tilt angle of the trench can improve the measurement repeatability of the alignment mark position. However, in order to achieve trenches with specific structural parameters, the complexity of photolithography mask combined with reactive ion etching and focused ion beam etching methods will be significantly increased, thereby increasing the cost of the above processing methods.

[0008] To address the aforementioned issues, there is an urgent need to research a new method for preparing EUV mask alignment marks, in order to solve the problems of numerous processing steps, long processes, long processing times, and poor repeatability in existing EUV mask alignment mark preparation methods. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned deficiencies of the prior art by providing a method for preparing EUV mask alignment marks. This method uses diamond machining to prepare grooves for the mask alignment marks, which can efficiently obtain EUV mask alignment mark grooves with specific structures. This solves the problems of numerous processing steps, long processes, long processing times, and poor repeatability in existing EUV mask alignment mark processing.

[0010] The objective of this invention can be achieved through the following technical measures:

[0011] This invention provides a method for preparing alignment marks on an EUV mask, employing diamond nanofabrication technology, and includes the following steps:

[0012] S1: The groove structure parameters of the EUV mask alignment mark are optimized by simulation, and the optimized structural parameters of the EUV mask alignment mark groove are determined to improve the accuracy and repeatability of alignment mark position detection.

[0013] S2: Select the diamond needle tip tool based on the determined structural optimization parameters of the EUV mask alignment mark groove;

[0014] S3: Based on the determined structural optimization parameters of the EUV mask alignment mark groove, use the diamond needle-tip tool selected in step S2 to perform alignment mark processing on the EUV mask white plate.

[0015] Furthermore, the structural parameters of the EUV mask alignment mark groove include the lateral width, depth, and edge sidewall shape.

[0016] Further, step S1 specifically includes:

[0017] Using optical imaging simulation software based on electromagnetic field numerical calculation module, the dark field imaging characteristics of different groove width, depth and sidewall shape parameter combinations are simulated. The imaging system parameters used are determined by the optical imaging parameters of EUV mask whiteboard defect detection system.

[0018] Using the dark-field imaging simulation data of the obtained alignment mark structure, the intensity of the scattered signal at the edge of the alignment mark on the EUV mask white plate and the detection error of the alignment mark position calculated from the imaging spot are comprehensively evaluated to determine the structural optimization parameters of the alignment mark groove to be adopted.

[0019] Furthermore, the diamond tip is a tip machined from a single natural diamond particle, and the tip radius of curvature and the included angle of the top surface of the diamond tip are determined according to the optimized depth parameters of the EUV mask alignment mark groove.

[0020] Furthermore, the diamond tips used for edge processing are also polished to achieve the edge shape structure of the EUV mask alignment mark in a single process.

[0021] Furthermore, the diamond tip used for edge processing is polished using a focused ion beam.

[0022] Furthermore, in step S3, an AFM nanopiezoelectric probe and a high-precision two-dimensional moving precision stage are integrated into a nanofabrication system to prepare alignment marks on the EUV mask white plate by scanning.

[0023] Further, step S3 specifically includes:

[0024] S31: Set the scanning range of AFM to 0, so that the AFM tip is close to the surface of the EUV mask white plate. Set the load of the diamond tip according to the required groove depth. Control the piezoelectric ceramic to keep the bending deformation of the AFM cantilever in a constant state, thereby ensuring that the tip load is constant. The depth of the microgroove is controlled by controlling the tip load.

[0025] S32: The controller controls the two-dimensional precision moving stage to move in the x and y directions through the D / A module, that is, the movement of the diamond needle tip in the marking direction and the feed direction, so as to realize the relative movement between the workpiece and the needle tip and complete the marking process of aligning the marking groove.

[0026] S33: Replace with a diamond tip for edge machining to complete the edge structure machining of the alignment mark.

[0027] Furthermore, in step S32, the scribing path of the diamond tip is along the cantilever direction of the AFM, and the feed direction is perpendicular to the micro-cantilever direction.

[0028] During the machining process, the two-dimensional moving precision stage moves along the AFM cantilever towards the cantilever fulcrum, and the moving distance is equal to the length of the alignment mark. After the marking is completed, the needle tip is lifted, and the two-dimensional moving precision stage is returned to the starting point. The two-dimensional precision platform is then moved perpendicular to the AFM cantilever, and the moving distance is the feed amount. The above process is repeated until the cumulative width of the groove reaches the set value.

[0029] The method for preparing EUV mask alignment marks of the present invention uses diamond machining to prepare the grooves of the mask alignment marks. This method has simple equipment requirements, fewer steps, shorter processing time, and good repeatability, and can efficiently obtain EUV mask alignment mark grooves with specific structures. By customizing the specific shape of the diamond tip (tool) and controlling the tip load, it is easy to obtain alignment mark groove sidewalls with specific edge shapes, significantly improving the efficiency and repeatability of alignment mark processing. This results in strong detection signals and high imaging contrast in the alignment mark edge region, thereby improving the detection accuracy and repeatability of the alignment mark position, and further improving the positioning accuracy of defects. This is beneficial for subsequent compensation and processing of EUV mask defects. Compared with alignment mark structures prepared by existing methods, the EUV mask alignment marks prepared using the method of the present invention show significantly improved centroid detection accuracy at the imaging spot position of the alignment mark edge. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a front view and a cross-sectional view of the alignment mark on the cross-shaped EUV mask;

[0032] Figure 2(a) shows the edge of the linear beveled mark on the sidewall of the EUV mask alignment mark;

[0033] Figure 2(b) shows the EUV mask alignment with the V-shaped mark edge on the sidewall of the mark;

[0034] Figure 2(c) shows the edge of the curved sidewall marking of the EUV mask alignment mark;

[0035] Figure 3(a) Simulation results of dark-field imaging spot cross-section of EUV mask alignment mark with different edge structures;

[0036] Figure 3(b) Simulation results of energy concentration of EUV mask alignment mark dark field imaging spot with different edge structures;

[0037] Figure 4 A schematic diagram of the machining depth model for diamond needle tips;

[0038] Figure 5 Schematic diagram of a diamond needle tip nanofabrication device;

[0039] Figure 6 This is a schematic diagram of the preparation of EUV mask alignment marks based on diamond tip nanofabrication technology. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.

[0041] To make the description of this disclosure more detailed and complete, illustrative descriptions of embodiments and specific examples of the present invention are provided below; however, these are not the only forms of implementing or utilizing the specific examples of the present invention. The embodiments cover features of multiple specific examples and methods and steps for constructing and operating these specific examples, and their order. However, other specific examples may also be used to achieve the same or equivalent functions and order of steps.

[0042] This invention provides a method for preparing alignment marks on an EUV mask, employing diamond nanofabrication technology, and includes the following steps:

[0043] S1: The groove structure parameters of the EUV mask alignment mark are optimized by simulation, and the optimized structural parameters of the EUV mask alignment mark groove are determined to improve the accuracy and repeatability of alignment mark position detection.

[0044] S2: Select the diamond needle tip tool based on the determined structural optimization parameters of the EUV mask alignment mark groove;

[0045] S3: Based on the determined structural optimization parameters of the EUV mask alignment mark groove, use the diamond needle-tip tool selected in step S2 to perform alignment mark processing on the EUV mask white plate.

[0046] The structural parameters of the alignment mark groove on the EUV mask include its lateral width, depth, and edge sidewall shape. Step S1 specifically involves:

[0047] Using optical imaging simulation software based on electromagnetic field numerical calculation module, the dark field imaging characteristics of different groove width, depth and sidewall shape parameter combinations are simulated. The imaging system parameters used are determined by the optical imaging parameters of EUV mask whiteboard defect detection system.

[0048] Using the dark-field imaging simulation data of the obtained alignment mark structure, the intensity of the scattered signal at the edge of the alignment mark on the EUV mask white plate and the detection error of the alignment mark position calculated from the imaging spot are comprehensively evaluated to determine the structural optimization parameters of the alignment mark groove to be adopted.

[0049] Thus, the optimized groove structure shown by the alignment mark on the linear inclined surface, as shown in Figure 2(a), has the following structural parameters: a width of approximately 5 μm, a depth of approximately 210 nm, and an inclination angle of 70 degrees for the edge of the groove inclined surface.

[0050] Based on the numerical aperture parameters of the dark-field imaging optical system, a V-shaped edge structure alignment mark groove, as shown in Figure 2(b), was further proposed. Using the width, depth, and sidewall tilt angle of the rectangular groove, and setting the depth of the V-shaped groove to be the same as the groove depth, dark-field imaging characteristics were simulated for different combinations of V-shaped groove width and height, optimizing the lateral width at the opening on the upper surface of the V-shaped groove. The 1D dark-field imaging simulation results of the alignment mark show that after adopting the V-shaped structure at the groove edge, the imaging signal intensity at the edge is slightly reduced, but the peak half-width at half-maximum (FWHM) of the signal intensity is smaller, and the signal energy is more concentrated, resulting in higher positioning accuracy of the alignment mark center position.

[0051] Based on the aforementioned V-shaped edge alignment mark groove structure, the linear inclined edge shape of the V-shaped edge structure is transformed into a curved edge shape as shown in Figure 2(c). Dark-field imaging characteristics are then simulated to optimize the structure of the curved edge shape. The 1D dark-field imaging simulation results of the alignment mark show that the edge structure has a very direct impact on the dark-field scattering imaging signal.

[0052] As shown in Figure 3(a), compared with the dark field scattering imaging signal peak of the linear inclined plane edge, the dark field scattering imaging signal intensity of the curved surface remains basically unchanged, but the scattered spot is further centered, while the new scattering peak appearing on the right has a negligible impact on the edge position determination. Further quantitative comparison of the energy concentration of the imaging spot was performed, and the results are shown in Figure 3(b). It can be seen that the dark field imaging spot obtained using the curved edge structure, compared with the dark field imaging spot obtained using the conventional 70-degree inclined plane edge structure, has a spot radius corresponding to 80% energy concentration that is reduced by about 20%, indicating a further improvement in imaging quality, which helps to improve the accuracy and stability of marker position detection.

[0053] The diamond tip is a needle tip machined from a single natural diamond particle. The tip curvature radius and top surface angle of the diamond tip are determined based on the optimized depth parameters of the EUV mask alignment mark groove. For example... Figure 4As shown in the left figure, when the machining depth h is greater than the critical depth h1, the diamond tip can be equivalent to a probe model of a hemispherical and conical structure. At this time, the projection S of the contact surface of the tip in the horizontal direction is as follows: Figure 4 The semicircular portion shown in the diagram on the right can be represented by the following formulas (1) and (2):

[0054]

[0055] h1=R0(1-sinα) (2)

[0056] In this case, the width b of the nanogroove obtained by the inscription can be calculated by the following formula (3).

[0057] b=(h-R0(1-sinα))·tanα+R0cosα (3)

[0058] Where α is the included angle of the needle tip, and R0 is the radius of the needle tip.

[0059] Equation (3) shows that the width of the nanogroove is related to the shape of the diamond tip and the depth of the marking. The width of the nanogroove can be controlled by changing the marking depth, which is determined by the properties of the substrate material, the tip structure parameters, and the applied tip load. For example, if a tip radius of 200 nm, a tip half-angle of 100 degrees, and a processing depth of 200 nm are used (this depth exceeds the critical depth, and the intended processing depth of the marking is consistent), the groove width obtained in a single processing step is about 300 nm. Therefore, if a single tip processing method is used, 20 serial processing steps are required to obtain a marking groove with a width of 5 μm and a depth of about 210 nm. Therefore, a tip with a tip radius of about 200 nm and a tip half-angle of about 100 degrees can meet the processing requirements.

[0060] In addition, in order to meet the needs of processing specific structures at the edges of the grooves, the shape of the needle tip used for edge processing needs to be specially treated. The edges of the needle tip are polished using a focused ion beam, so that the required structure at the edge can be processed in one go.

[0061] To meet the processing requirements of alignment mark length dimensions (e.g., 500 micrometers), a nanofabrication system integrating an AFM nanopiezoelectric probe and a high-precision two-dimensional moving precision stage is preferred, such as... Figure 5 As shown, alignment marks are prepared using a scanning method. Step S3 specifically involves:

[0062] S31: Set the scanning range of AFM to 0, bring the AFM tip close to the surface of the EUV mask white plate, set the load of the diamond tip according to the required groove depth, control the piezoelectric ceramic (PZT) to keep the bending deformation of the AFM cantilever in a constant state, thereby ensuring the tip load is constant, and control the micro-groove depth by controlling the tip load.

[0063] S32: The controller, via a D / A module, controls the movement of a two-dimensional precision moving stage in the x and y directions, i.e., the movement of the diamond needle tip in the marking and feed directions, to achieve relative movement between the workpiece and the needle tip, completing the marking process for aligning the marking grooves; such as Figure 6 As shown, the diamond needle tip's marking path is along the cantilever direction of the AFM, and the feed direction is perpendicular to the micro-cantilever direction. During the machining process, the two-dimensional moving precision stage moves along the AFM cantilever towards the cantilever fulcrum (X direction), and the moving distance is equal to the length of the alignment mark (500 micrometers). After marking is completed, the needle tip is lifted, and the two-dimensional moving precision stage is returned to the starting point, so that the two-dimensional precision platform moves perpendicular to the AFM cantilever direction (Y direction), and the moving distance is the feed amount. The above process is repeated until the cumulative width of the groove reaches the set value.

[0064] S33: Replace with a diamond tip for edge machining to complete the edge structure machining of the alignment mark.

[0065] The method for preparing EUV mask alignment marks of the present invention uses diamond machining to prepare the grooves of the mask alignment marks. This method has simple equipment requirements, fewer steps, shorter processing time, and good repeatability, and can efficiently obtain EUV mask alignment mark grooves with specific structures. By customizing the specific shape of the diamond tip (tool) and controlling the tip load, it is easy to obtain alignment mark groove sidewalls with specific edge shapes, significantly improving the efficiency and repeatability of alignment mark processing. This results in strong detection signals and high imaging contrast in the alignment mark edge region, thereby improving the detection accuracy and repeatability of the alignment mark position, and further improving the positioning accuracy of defects. This is beneficial for subsequent compensation and processing of EUV mask defects. Compared with alignment mark structures prepared by existing methods, the EUV mask alignment marks prepared using the method of the present invention show significantly improved centroid detection accuracy at the imaging spot position of the alignment mark edge.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing alignment marks on an EUV mask, characterized in that, The diamond nanoprocessing technology includes the following steps: S1: The groove structure parameters of the EUV mask alignment mark are optimized by simulation, and the optimized structural parameters of the EUV mask alignment mark groove are determined to improve the accuracy and repeatability of alignment mark position detection. S2: Select the diamond needle tip tool based on the determined structural optimization parameters of the EUV mask alignment mark groove; S3: Based on the determined structural optimization parameters of the EUV mask alignment mark groove, use the diamond needle-tip tool selected in step S2 to perform alignment mark processing on the EUV mask white plate. In step S3, an integrated nanofabrication system combining an AFM nanopiezoelectric probe and a high-precision two-dimensional moving precision stage is used to prepare alignment marks on the EUV mask white plate by scanning. Step S3 specifically involves: S31: Set the scanning range of AFM to 0, so that the AFM tip is close to the surface of the EUV mask white plate. Set the load of the diamond tip according to the required groove depth. Control the piezoelectric ceramic to keep the bending deformation of the AFM cantilever in a constant state, thereby ensuring that the tip load is constant. The depth of the microgroove is controlled by controlling the tip load. S32: The controller controls the two-dimensional moving precision worktable to move in the x and y directions through the D / A module, that is, the movement of the diamond needle tip in the marking direction and the feed direction, so as to realize the relative movement between the workpiece and the needle tip and complete the marking process of aligning the marking groove. S33: Replace with a diamond tip for edge machining to complete the edge structure machining of the alignment mark.

2. The method for preparing EUV mask alignment marks according to claim 1, characterized in that, The structural parameters of the alignment mark groove of the EUV mask include the lateral width, depth, and edge sidewall shape.

3. The method for preparing EUV mask alignment marks according to claim 2, characterized in that, Step S1 specifically involves: Using optical imaging simulation software based on electromagnetic field numerical calculation module, the dark field imaging characteristics of different groove width, depth and sidewall shape parameter combinations are simulated. The imaging system parameters used are determined by the optical imaging parameters of EUV mask whiteboard defect detection system. Using the dark-field imaging simulation data of the obtained alignment mark structure, the intensity of the scattered signal at the edge of the alignment mark on the EUV mask white plate and the detection error of the alignment mark position calculated from the imaging spot are comprehensively evaluated to determine the structural optimization parameters of the alignment mark groove to be adopted.

4. The method for preparing EUV mask alignment marks according to claim 1, characterized in that, The diamond tip is a needle tip machined from a single natural diamond. The tip radius of curvature and the included angle of the top surface of the diamond tip are determined according to the optimized depth parameters of the EUV mask alignment mark groove.

5. The method for preparing EUV mask alignment marks according to claim 4, characterized in that, The diamond tips used for edge processing are also polished to enable the edge shape structure of EUV mask alignment marks to be processed in one step.

6. The method for preparing EUV mask alignment marks according to claim 5, characterized in that, Diamond tips used for edge processing are polished using a focused ion beam.

7. The method for preparing EUV mask alignment marks according to claim 1, characterized in that, In step S32, the scribing path of the diamond tip is along the cantilever direction of the AFM, and the feed direction is perpendicular to the micro-cantilever direction. During the machining process, the two-dimensional moving precision stage moves along the AFM cantilever towards the cantilever fulcrum, and the moving distance is equal to the length of the alignment mark. After the marking is completed, the needle tip is lifted to return the two-dimensional moving precision stage to the starting point. The two-dimensional moving precision stage is then moved perpendicular to the AFM cantilever, and the moving distance is the feed amount. The above process is repeated until the cumulative width of the groove reaches the set value.

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