Large-size ellipsoidal mirror coating method

Abstract

The invention discloses a large-size ellipsoidal mirror coating method, and relates to the technical field of photoetching machine part manufacturing, and the method comprises the steps: designing an aluminum simulation mirror, marking X / Y axes, and pasting silicon wafers at intervals as measurement points; adopting linear magnetron sputtering equipment to sequentially sputter Mo / Si layers under optimized vacuum and argon pressure to form a [Mo / Si] 10 periodic film; a gradient mask plate is additionally arranged on the Y axis, the thickness of the mask plate is in direct proportion to the thickness of the film, segmented variable-speed coating is adopted for the X axis, the speed is in direct proportion to the thickness of the film, and the non-uniformity of the film layer is smaller than or equal to + / -1% through closed-loop correction. Through simulation mirror pre-calibration and dynamic parameter regulation and control, the purpose of accurately controlling the thickness of a film layer at different positions is achieved, the problem of large-size curved surface coating uniformity is solved, and the method is suitable for preparation of extreme ultraviolet lithography optical elements of ellipsoid mirrors with the ellipsoid size being 300 or above.

Description

Technical Field

[0001] This invention relates to the field of lithography machine parts manufacturing technology, and in particular to a coating method for a large-size ellipsoidal mirror. Background Technology

[0002] In the development of nanofabrication technology, photolithography has always been a core driving force, determining the feature size of integrated circuit components. The development of photolithography technology has progressed from equidistant photolithography to miniaturized projection photolithography, and the wavelengths used are gradually becoming shorter. Photolithographic resolution has also become an important indicator affecting the development of photolithography technology. Among them, extreme ultraviolet projection photolithography has received widespread attention due to its high resolution and high production efficiency, and is considered an important milestone in photolithography technology with wavelengths of 7nm or even shorter.

[0003] Many factors influence the commercialization of extreme ultraviolet (EUV) lithography, among which the manufacturing of large-size ellipsoidal mirrors is a crucial link. Large-size EUV ellipsoidal mirrors are one of the core components of EUV lithography machines, directly determining the machine's resolution, efficiency, and reliability, and are a key driver for the semiconductor industry's advancement towards more advanced processes. Breakthroughs in this technology are not only milestones in optical engineering but also strategic high ground in the global chip manufacturing industry's competition.

[0004] The main technical challenge in manufacturing large-size ellipsoidal mirrors lies in the need to prepare different film thicknesses at different locations on the ellipsoid, requiring a high degree of uniformity. Traditional planar coating methods result in thickness differences between the edges and the center of the ellipsoid because the curved surface causes varying distances and angles from different points on the substrate to the target. Summary of the Invention

[0005] The purpose of this invention is to provide a coating method for large-size ellipsoidal mirrors to solve the problems existing in the prior art and ensure the uniformity of the coating thickness of the ellipsoidal mirror.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A coating method for a large-size ellipsoidal mirror includes the following steps:

[0008] S1. Fabricate a simulated mirror and matching fixture of the same size as the ellipsoidal mirror to be coated;

[0009] S2. Perform ultrasonic cleaning on the simulated mirror and fixture;

[0010] S3. Mark the X-axis and Y-axis on the surface of the simulation mirror, and attach silicon wafers at intervals on the axes as measurement points;

[0011] S4. Install the simulation mirror into the linear magnetron sputtering coating equipment and evacuate to a background vacuum level of 2×10⁻⁶. -5 Pa to 3×10 -4 Pa;

[0012] S5. Fill the chamber with argon gas and adjust the pressure to 0.05-0.2 Pa;

[0013] S6. Light up the Mo target with a power of 250W-3000W. After stabilization, control the simulation mirror to pass over the target material at a constant speed along the X-axis to sputter and deposit the Mo layer.

[0014] S7. Light up the Si target with a power of 250-3000W. After stabilization, control the simulation mirror to pass over the target material at a constant speed along the X-axis to sputter and deposit the Si layer.

[0015] S8. Repeat steps S6-S7 nine times to form [Mo / Si]. 10 Periodic membrane;

[0016] S9. Take out the sample for XRR test and obtain the periodic thickness of the film layer at different locations;

[0017] S10. Based on the test results, add masks of different thicknesses at different positions on the Y-axis. The thickness of the mask is proportional to the film thickness of the simulated mirror at a certain position on the Y-axis. Design variable speed coating parameters in the X-axis direction. The speed is proportional to the film thickness of the simulated mirror at a certain position on the X-axis.

[0018] S11. Repeat steps S4-S8 and repeat the coating process with the adjusted parameters;

[0019] S12. Repeat steps S9-S11 until the film uniformity is adjusted to the desired level.

[0020] In an exemplary embodiment, the ultrasonic cleaning frequency in step S2 is 20-200 kHz.

[0021] In an exemplary embodiment, the optimal background vacuum level in step S4 is 9 × 10⁻⁶. -5 Pa.

[0022] In an exemplary embodiment, the optimal cavity pressure in step S5 is 0.1 Pa.

[0023] In an exemplary embodiment, in step S5, the Mo layer thickness is 2.8 nm; in step S6, the Si layer thickness is 4.2 nm.

[0024] In an exemplary embodiment, the optimal Mo target power in step S5 is 1000W.

[0025] In an exemplary embodiment, the Si target power in step S6 is optimally 1500W.

[0026] In an exemplary embodiment, the Y-axis mask is made of aluminum or stainless steel and has a thickness of 0.3-2 mm.

[0027] In an exemplary embodiment, the film non-uniformity is calculated using the formula (maximum thickness - minimum thickness) / (maximum thickness + minimum thickness) × 100%.

[0028] In one exemplary embodiment, the method further includes using a chromium layer as a base layer with a thickness of 10-20 nm before coating.

[0029] The present invention achieves the following technical effects compared to the prior art:

[0030] This invention achieves precise control of the film thickness of a large-size ellipsoidal mirror through simulated mirror pre-calibration and dynamic parameter adjustment. Specifically, it includes:

[0031] 1. Surface adaptability: By establishing a surface coordinate mapping between the simulated mirror markings and the silicon wafer measurement points, the problem that traditional planar coating technology cannot adapt to the geometric distortion of ellipsoidal mirrors is solved;

[0032] 2. Closed-loop optimization: Based on XRR test data, dynamically adjust the Y-axis mask thickness (proportional to film thickness) and X-axis segmented speed change parameters (proportional to film thickness) to control the film non-uniformity within ±1%.

[0033] 3. Process stability: Optimized vacuum (2×10) -5 ~3×10 -4 The combination of parameters (Pa) and sputtering power (250-3000W) ensures [Mo / Si] 10 High reflectivity of periodic films in the 11-14nm wavelength range.

[0034] This method significantly improves the performance reliability of large-size curved optical components in extreme ultraviolet lithography. Attached Figure Description

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A schematic diagram of the simulated mirror and the XYAB axes marked thereon, as disclosed in a specific embodiment of the present invention;

[0037] Figure 2 This is a distribution map of the periodic thickness at different positions on the X-axis measured in step S8;

[0038] Figure 3 This is a distribution map of the periodic thickness at different positions along the Y-axis measured in step S8;

[0039] Figure 4 The thickness of the mask plate at different positions along the Y-axis in step S9;

[0040] Figure 5 This is a distribution diagram of the final film uniformity results along the X-axis;

[0041] Figure 6 This is a distribution diagram of the final film uniformity results along the Y-axis. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings of this specification are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of the invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed in this invention. In the description of this invention, it should be understood that the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are merely for the convenience of describing the invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of those features. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0044] It should also be noted that in the embodiments of this application, the same reference numerals are used to denote the same component or the same part.

[0045] The purpose of this invention is to provide a coating method for large-size ellipsoidal mirrors to solve the problems existing in the prior art and ensure the uniformity of the coating thickness of the ellipsoidal mirror.

[0046] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] This embodiment provides a coating method for a large-size ellipsoidal mirror, including the following steps:

[0048] S1. Fabricate a simulation mirror and matching fixture of the same size as the ellipsoidal mirror to be coated. The material is aluminum, which has a low coefficient of thermal expansion, avoiding errors introduced by temperature deformation, and is easy to manufacture, reducing testing costs.

[0049] S2. Perform ultrasonic cleaning on the simulation mirror and fixture at a frequency of 20-200kHz, preferably 40kHz.

[0050] S3. Mark the X-axis and Y-axis on the surface of the simulation mirror, and attach a silicon wafer at regular intervals on the axis as a measurement point. The flatness of the silicon wafer can ensure the accuracy of the subsequent XRR test. The interval distance is selected according to the sample and needs, and the range is generally 15-50mm. The silicon wafer size is ≤10×10×1mm, and the optimal size is 10×10×0.5mm.

[0051] S4. Install the simulation mirror into the linear magnetron sputtering coating equipment, and evacuate the background vacuum of the sputtering chamber to 2×10⁻⁶. -5 Pa-3×10 -4 Pa, the optimal value is 9 × 10 -5 Pa;

[0052] S5. Fill with Ar and vacuum the cavity to 0.05-0.2 Pa, with 0.1 Pa being optimal;

[0053] S6. Light up the Mo target with a power of 250W-3000W. The Mo target purity is 99.99%, and the optimal power is 1000W. After stabilizing for 5 minutes, control the simulation mirror to pass over the target material at a uniform speed along the X-axis to sputter and deposit the Mo layer. The specific speed does not need to be limited. The purpose is to control the film thickness, which is about 2.8nm. After the deposition is completed, turn off the Mo target.

[0054] S7. Light up the Si target with a power of 250W-3000W. The purity of the Si target is 99.99%. The optimal power is 1500W. After stabilizing for 5 minutes, control the simulation mirror to pass over the target material at a constant speed along the X-axis to sputter and deposit a Si layer with a thickness of about 4.2nm. After the deposition is completed, turn off the Si target.

[0055] S8. Repeat steps S6-S7 nine times to form [Mo / Si]. 10 Periodic membrane;

[0056] S9. Take out the sample for XRR (X-ray reflectance test) to obtain the periodic thickness of the film at different locations with an accuracy of up to 0.02 nm;

[0057] S10. Based on the test results, add mask plates of different thicknesses at different positions on the Y-axis. The thickness of the mask plate is proportional to the film thickness of the simulated mirror at a certain position on the Y-axis. The material of the mask plate can be Al, stainless steel, etc. with a thickness of 0.3-2mm, with stainless steel being the best. Design variable speed coating parameters in the X-axis direction. The speed is proportional to the film thickness of the simulated mirror at a certain position on the X-axis.

[0058] S11. Repeat steps S4-S8 and repeat the coating process with the adjusted parameters;

[0059] S12. Repeat steps S9-S11 until the film uniformity is adjusted to the desired level.

[0060] The uniformity of the film layer is calculated using the formula (maximum thickness - minimum thickness) / (maximum thickness + minimum thickness) × 100%.

[0061] It also includes using a chromium layer as a base layer before coating, with a thickness of 10-20nm, to fill micro-defects in the substrate, enhance film adhesion (interface energy matching), and prevent peeling.

[0062] In addition to depositing a film of the same thickness on a large-size ellipsoidal mirror, the method of this embodiment can also make the film thickness vary in a gradient. It is only necessary to adjust the thickness of the Y-axis mask and the target-grabbing speed parameters of the X-axis in step S10 as needed.

[0063] Please refer to Figures 1 to 5 The following is a detailed explanation using the uniform film deposition of an ellipsoidal mirror with a diameter of 520mm as an example:

[0064] 1. Design, fabricate, and clean the matching simulation mirrors and fixtures;

[0065] 2. Mark the XY axis and AB axis (45° diagonal axes) on the mirror surface and complete the placement of the silicon wafer, such as... Figure 1 As shown, the silicon wafers used are 10*10*0.75mm ultra-smooth silicon wafers, with one wafer every 25mm along the Y-axis and another every 50mm along the rest.

[0066] 3. Load the coating into a linear magnetron sputtering coating machine and evacuate the base vacuum to 9×10⁻⁶. -5 Pa;

[0067] 4. Switch the coating machine to coating mode, fill it with 50 sccm of argon gas, and observe that the vacuum gauge reading is 0.09 Pa;

[0068] 5. Light up the Mo target with a power of 1000W, stabilize it for 5 minutes, then deposit a layer of Mo at a rate of 80mm / s, and then turn off the Mo target.

[0069] 6. Light up the Si target with a power of 1500W, stabilize it for 5 minutes, then deposit a layer of Si at a rate of 32mm / s, and then turn off the Si target.

[0070] 7. Repeat steps 5-6 9 times;

[0071] 8. Break the vacuum, take samples, and perform XRR testing to obtain the periodic thickness at different locations, as shown below. Figure 2 , 3 As shown;

[0072] 9. According to Figure 2 Based on the data, design a mask along the Y-axis, and add mask plates of different thicknesses at different positions along the Y-axis, with the thickness distribution as shown in the figure. Figure 4 As shown;

[0073] according to Figure 3 Based on the results, a speed variation was designed in the X-axis direction, specifically using 32.38 mm / s for the first 1 / 3 of the journey, 32 mm / s for the middle 1 / 3, and 32.48 mm / s for the last 1 / 3.

[0074] 10. Repeat steps 2-8 with the new parameters to obtain the following result. Figure 5 The results show that the non-uniformity ((maximum value - minimum value) / (maximum value + minimum value)) is less than 1%, which meets the requirements.

[0075] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0076] If this invention discloses or relates to components or structural parts that are fixedly connected to each other, then, unless otherwise stated, a fixed connection can be understood as: a fixed connection that can be detached (e.g., using bolts or screws), or a fixed connection that cannot be detached (e.g., riveting, welding). Of course, a fixed connection can also be replaced by an integral structure (e.g., manufactured in one piece using a casting process) (except where it is obviously impossible to use an integral molding process).

[0077] In addition, unless otherwise stated, the terms used in any of the technical solutions disclosed in this invention to indicate positional relationships or shapes include states or shapes that are similar to, close to, or approximate with those states or shapes.

[0078] Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured by a one-piece molding process.

[0079] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0080] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0081] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A coating method for a large-size ellipsoidal mirror, characterized in that, Includes the following steps: S1. Fabricate a simulated mirror and matching fixture of the same size as the ellipsoidal mirror to be coated; S2. Perform ultrasonic cleaning on the simulated mirror and fixture; S3. Mark the X-axis and Y-axis on the surface of the simulation mirror, and attach silicon wafers at intervals on the axes as measurement points; S4. Install the simulation mirror into the linear magnetron sputtering coating equipment and evacuate to a background vacuum level of 2×10⁻⁶. -5 Pa to 3×10 -4 Pa; S5. Fill the chamber with argon gas and adjust the pressure to 0.05-0.2 Pa; S6. Light up the Mo target with a power of 250W-3000W. After stabilization, control the simulation mirror to pass over the target material at a constant speed along the X-axis to sputter and deposit the Mo layer. S7. Light up the Si target with a power of 250-3000W. After stabilization, control the simulation mirror to pass over the target material at a constant speed along the X-axis to sputter and deposit the Si layer. S8. Repeat steps S6-S7 nine times to form [Mo / Si]. 10 Periodic membrane; S9. Take out the sample for XRR test and obtain the periodic thickness of the film layer at different locations; S10. Based on the test results, add masks of different thicknesses at different positions on the Y-axis. The thickness of the mask is proportional to the film thickness of the simulated mirror at a certain position on the Y-axis. Design variable speed coating parameters in the X-axis direction. The speed is proportional to the film thickness of the simulated mirror at a certain position on the X-axis. S11. Repeat steps S4-S8 and repeat the coating process with the adjusted parameters; S12. Repeat steps S9-S11 until the film uniformity is adjusted to the desired level.

2. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: In step S2, the ultrasonic cleaning frequency is 20-200kHz.

3. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: The optimal background vacuum level in step S4 is 9 × 10⁻⁶. -5 Pa.

4. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: The optimal cavity pressure in step S5 is 0.1 Pa.

5. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: In step S5, the Mo layer thickness is 2.8 nm; in step S6, the Si layer thickness is 4.2 nm.

6. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: In step S5, the optimal Mo target power is 1000W.

7. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: In step S6, the optimal Si target power is 1500W.

8. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: The Y-axis mask is made of aluminum or stainless steel and has a thickness of 0.3-2mm.

9. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: The film non-uniformity is calculated using the formula (maximum thickness - minimum thickness) / (maximum thickness + minimum thickness) × 100%.

10. The coating method for a large-size ellipsoidal mirror according to claim 1, characterized in that: It also includes using a chromium layer as a base layer before coating, with a thickness of 10-20nm.

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