Spherical mirror pattern preparation device and spherical mirror preparation method

Abstract

This invention provides an apparatus and method for fabricating spherical mirror patterns, belonging to the field of precision machining. The apparatus includes: a heating plate; a housing forming a cavity with the heating plate, the housing having a through hole; a receiving component disposed on the heating plate within the cavity, the receiving component being suitable for containing photoresist solvent; and a container disposed within the receiving component, suitable for containing a substrate on which a photoresist disk is formed. The heating plate is used to heat the photoresist solvent, which evaporates upon heating to produce vapor. The vapor flows out through the through hole, causing the photoresist to flow back during its flow. The photoresist absorbs some of the vapor and gradually changes from a solid state to a fluid state. Within the cavity, the vapor flow field is shaped to cause the photoresist disk to continuously deform under the action of surface tension until a spherical mirror pattern with a target radius of curvature is obtained.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to the field of precision machining, and in particular to an apparatus for preparing spherical mirror patterns and a method for preparing spherical mirrors. Background Technology

[0002] In the field of optical component fabrication, spherical mirrors are an important optical element widely used in various optical systems. However, many problems still exist in the fabrication of spherical mirrors. Currently, common methods for fabricating spherical lenses include electrofusion, laser ablation, and dry etching. These methods have limitations; they cannot fabricate spherical mirrors with arbitrary radii of curvature. The radii of curvature of the fabricated spherical mirrors are in the range of micrometers to millimeters (μm~mm), and the usable area of ​​the spherical mirrors fabricated by these methods is very limited, usually only on the order of micrometers. Furthermore, in regions off-center, the surface shape of the spherical mirror deviates significantly from the ideal sphere, leading to a decrease in optical performance. Summary of the Invention

[0003] In view of this, to solve the above problems, a spherical mirror pattern preparation apparatus and a method for preparing a spherical mirror are proposed. The spherical mirror pattern is used to prepare a spherical mirror. The preparation apparatus includes:

[0004] Heating plate;

[0005] The shell, together with the heating plate, forms a cavity, and the shell has through holes;

[0006] A housing component is disposed on a heating plate inside a cavity; the housing component is suitable for containing photoresist solvent.

[0007] A container, disposed within a housing assembly, is suitable for housing a substrate on which a photoresist disk is formed. The photoresist disk is a photoresist pattern with a disk shape formed from photoresist.

[0008] The heating plate is used to heat the photoresist solvent. After being heated, the photoresist solvent evaporates to produce steam. The steam flows out from the through hole. During the flow of the steam, the photoresist is refluxed. After absorbing some of the steam, the photoresist gradually changes from a solid state to a fluid state. In the cavity, the steam flow field is formed to cause the photoresist disk to continuously deform under the action of surface tension until a spherical mirror pattern is obtained. The spherical mirror pattern is a photoresist pattern with a spherical mirror shape.

[0009] According to an embodiment of the present invention, the housing includes:

[0010] The cover body has a through hole formed thereon;

[0011] The main body is located between the cover and the heating plate, forming a cavity with the cover and the heating plate;

[0012] The preparation apparatus also includes:

[0013] A flow guide plate, positioned between the housing assembly and the cover body along the steam flow direction, divides the cavity into a first sub-cavity and a second sub-cavity along the flow direction. The flow guide plate is suitable for uniformly distributing steam on the surface of the photoresist disk.

[0014] According to an embodiment of the present invention, before the photoresist solvent is placed into the receiving assembly, the heating plate is also adapted to preheat the substrate, and after the photoresist solvent is placed into the receiving assembly, the heating plate is also adapted to simultaneously heat the substrate and the photoresist solvent.

[0015] The size of the through-hole and the heating temperature of the heating plate are configured such that the vapor pressure on the photoresist surface is less than the saturated vapor pressure on the photoresist surface.

[0016] According to an embodiment of the present invention, when the ratio of the area of ​​the photoresist disk to the area of ​​the heating plate is greater than 1:1000, the cavity and through hole are configured such that the flow field at the location of the photoresist disk is symmetrical about the center of the photoresist disk, and the area of ​​the photoresist disk is the cross-sectional area on the horizontal plane of the photoresist disk.

[0017] According to an embodiment of the present invention, the cavity is configured to have a cylindrical structure, the heating plate is the bottom surface of the cylindrical structure, the substrate is located in the receiving assembly, and the center of the photoresist disk, the through hole and the center of the receiving assembly are all located on the axis of symmetry of the cylindrical structure.

[0018] The shape of a spherical mirror is either a plano-concave spherical shape or a plano-convex spherical shape.

[0019] As a second aspect of the present invention, a method for preparing a spherical mirror is also provided, comprising:

[0020] The photoresist disk formed on the substrate surface is transformed into a spherical mirror pattern using the above-described fabrication apparatus;

[0021] The spherical mirror pattern is baked to solidify it.

[0022] A spherical mirror is obtained by reactive ion dry etching on a substrate with a solidified spherical mirror pattern on its surface.

[0023] According to an embodiment of the present invention, the above preparation method further includes:

[0024] The spherical mirror is polished or atomically etched to give it atomic-level surface flatness.

[0025] According to an embodiment of the present invention, transforming a photoresist disk formed on a substrate surface into a spherical mirror pattern includes:

[0026] The substrate is placed on a heating plate, on which a photoresist disk is formed;

[0027] Add photoresist solvent to the housing component;

[0028] The photoresist solvent is heated by a heating plate, and the vapor generated by the photoresist solvent causes the photoresist to reflow. During the reflow process, the photoresist disk is continuously deformed under the action of surface tension until a spherical mirror pattern is obtained.

[0029] According to an embodiment of the present invention, before adding the photoresist solvent to the containing component, the above preparation method further includes:

[0030] The substrate is preheated using a heating plate.

[0031] According to an embodiment of the present invention, the fabrication method further includes, before transforming the photoresist disk coated on the substrate surface into a spherical mirror pattern with a target radius of curvature:

[0032] Determine the type and radius of curvature of the spherical mirror pattern;

[0033] The reflow time is determined based on the diameter of the photoresist disk, the heating temperature of the photoresist solvent when the heating plate heats it, and the type and radius of curvature of the spherical mirror pattern.

[0034] According to an embodiment of the present invention, a heating plate is used to heat the photoresist solvent, causing the photoresist solvent to evaporate and generate steam. A through-hole is provided on the housing to allow the steam to flow out. The flow of steam causes the photoresist to reflow, and during this reflow process, a spherical mirror pattern is obtained. This spherical mirror pattern with a target radius of curvature is used to fabricate a spherical mirror. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0036] Figure 1 A perspective view of the preparation apparatus provided according to an embodiment of the present invention is shown;

[0037] Figure 2 A side view of the preparation apparatus provided according to an embodiment of the present invention is shown;

[0038] Figure 3 A perspective view of a preparation system integrating multiple preparation devices provided according to an embodiment of the present invention is shown;

[0039] Figure 4A The radius of curvature of a plano-concave spherical mirror prepared according to an embodiment of the present invention is shown;

[0040] Figure 4B Shown Figure 4A The peak and valley values ​​of the surface shape of the plano-concave spherical mirror;

[0041] Figure 4C Shown Figure 4A The surface roughness of the plano-concave spherical mirror.

[0042] Description of Reference Numerals

[0043] 1. Preparation apparatus

[0044] 10 housing

[0045] 11 through holes

[0046] 12. Cover body

[0047] 13. Main body part

[0048] 131 Part 1

[0049] Part 2 of 132

[0050] 20 heating plates

[0051] 30-unit housing

[0052] 40 base

[0053] 50 containers

[0054] 60 deflector

[0055] 61 guide holes

[0056] 70 cavity

[0057] 71 First Sub-cavity

[0058] 72 Second Sub-cavity

[0059] 80 heating device

[0060] 90 flow guiding device

[0061] 100 integrated cover assembly Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, this invention can be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention thorough and complete, and to fully convey the scope of the invention to those skilled in the art. In the accompanying drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0063] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0064] Figure 1 A perspective view of a preparation apparatus provided according to an embodiment of the present invention is shown.

[0065] like Figure 1 As shown, the preparation apparatus 1 includes: a housing 10, a heating plate 20, a receiving component 30, and a container 50.

[0066] The housing 10 is configured to have a through hole 11 and to form a cavity 70 with the heating plate 20. A receiving assembly 30 is disposed on the heating plate 20 within the cavity, and the receiving assembly 30 is adapted to contain photoresist solvent. A container 50 is disposed within the receiving assembly 30 and is adapted to contain a substrate 40 on which a photoresist disk is formed. The photoresist disk is a photoresist pattern with a disk shape formed from photoresist.

[0067] The housing component 30 can be, for example, a heating dish. The heating plate 20 is suitable for heating the photoresist solvent. After being heated, the photoresist solvent evaporates to produce vapor, which flows out from the through hole 11. During the flow of the vapor, the photoresist is refluxed. After absorbing some of the vapor, the photoresist gradually changes from a solid state to a fluid state. In the cavity 70, the flow field of the vapor is formed to cause the photoresist disk to continuously deform under the action of surface tension until a spherical mirror pattern is obtained. The spherical mirror pattern is a photoresist pattern with a spherical mirror shape.

[0068] According to an embodiment of the present invention, the substrate 40 may be, for example, fused silica or single-crystal silicon. The photoresist solvent is heated using the heating plate 20, causing it to evaporate and generate vapor. A through-hole 11 is provided on the housing 10, allowing the vapor to flow out. The flow of vapor causes the photoresist to reflow, resulting in a spherical mirror pattern. This spherical mirror pattern is used to fabricate a spherical mirror. The fabrication apparatus provided in this embodiment of the present invention fabricates a spherical mirror pattern by causing the photoresist to reflow, resulting in a spherical mirror pattern with small surface shape errors. According to an embodiment of the present invention, the heating plate 20 is also suitable for preheating the substrate 40 before the photoresist solvent is placed into the receiving assembly 30. After the photoresist solvent is placed into the receiving assembly 30, the heating plate 20 is also suitable for simultaneously heating the substrate 40 and the photoresist solvent.

[0069] According to an embodiment of the present invention, the vapor pressure on the photoresist surface is made lower than the saturated vapor pressure of the photoresist surface to prevent the photoresist from dissolving after vapor liquefaction. Since saturated vapor pressure is temperature-dependent, the saturated vapor pressure on the photoresist surface is related to the temperature of the photoresist surface. Before placing the photoresist solvent into the receiving assembly 30, the substrate 40 is preheated using the heating plate 20 to prevent the substrate 40 from heating up too slowly, causing the vapor pressure on the photoresist surface to remain consistently lower than the saturated vapor pressure of the photoresist surface.

[0070] According to an embodiment of the present invention, the size of the via 11 also affects the gas pressure on the photoresist surface. The larger the via 11, the lower the gas pressure on the photoresist surface, and vice versa. However, the via cannot be infinitely large, and it is necessary to ensure that the steam can cause the photoresist to flow back.

[0071] According to an embodiment of the present invention, the ideal state for fabricating spherical mirror patterns using the photoresist reflow method is that the vapor flow field around the photoresist disk can be considered uniform. When the area of ​​the photoresist disk is sufficiently small (the ratio of the area of ​​the photoresist disk to the area of ​​the heating plate is less than 1:1000), the vapor flow field around the photoresist disk can be considered uniform, and in this case, there are no special requirements for the position of the vias.

[0072] According to an embodiment of the present invention, when the ratio of the area of ​​the photoresist disk to the area of ​​the heating plate 20 is greater than 1:1000, the cavity and through hole are configured such that the flow field at the location of the photoresist disk is symmetrical about the center of the photoresist disk, and the area of ​​the photoresist disk is the cross-sectional area on the horizontal plane of the photoresist disk.

[0073] According to an embodiment of the present invention, when the ratio of the area of ​​the photoresist disk to the area of ​​the heating plate is greater than 1:1000, the vapor flow field at the location of the photoresist disk can no longer be considered uniform. In this case, to obtain a spherical mirror pattern, it is necessary to ensure that the flow field at the location of the photoresist disk is symmetrical about the center of the photoresist disk. For example, the cavity can be configured to have a cylindrical structure, with the heating plate 20 as the bottom surface of the cylindrical structure, the substrate 40 located in the receiving assembly, and the center of the photoresist disk, the through hole 11, and the center of the receiving assembly 30 all located on the axis of symmetry of the cylindrical structure. For example, the substrate 40 can be placed in the container 50 first, and then the container 50 can be placed in the receiving assembly 30. According to an embodiment of the present invention, the diameter of the bottom surface of the cylindrical structure can be, for example, 125 mm, the height can be 34 mm, the through hole 11 is circular, and the diameter of the through hole 11 can be, for example, 1~5 mm.

[0074] According to an embodiment of the present invention, the housing 10 may include, for example, a cover portion 12 and a body portion 13, wherein the cover portion 12 is located above the heating plate 20 and a through hole 11 is formed on the cover portion. The body portion 13 is installed between the cover portion 12 and the heating plate 20 to form a cavity with the heating plate 20 and the cover portion 12.

[0075] Figure 2 A side view of a preparation apparatus provided according to an embodiment of the present invention is shown.

[0076] like Figure 2 The fabrication apparatus shown may further include a flow guide plate 60. The flow guide plate 60 is disposed between the receiving assembly 30 and the cover portion 12 along the steam flow direction, dividing the cavity 70 into a first sub-cavity 71 and a second sub-cavity 72 along the flow direction. The flow guide plate 60 is suitable for uniformly distributing steam on the surface of the photoresist disk. The flow guide holes in the central region of the flow guide plate are 2mm diameter circular holes arranged in a close array, with an outer contour diameter of 20mm. Multiple flow guide holes can be formed on the flow guide plate 60. The multiple flow guide holes can be located at the center of the flow guide plate 60, and the outer contour formed by the multiple flow guide holes can be, for example, circular.

[0077] Continue to refer to Figure 2 The main body 13 includes a first part 131 and a second part 132. The first part 131 is disposed between the guide plate 60 and the heating plate 20, and the first part 131, the heating plate 20 and the guide plate 60 form a first sub-cavity 71. The second part 132, the guide plate 60 and the cover part 12 form a second sub-cavity 72. The second part 132 and the cover part 12 can be integrally disposed or separately disposed, for example, they can be connected by any connection method such as welding, screwing, riveting.

[0078] Figure 3 A perspective view of a preparation system integrating multiple preparation devices provided according to an embodiment of the present invention is shown.

[0079] like Figure 3 As shown, integrating multiple (four in this embodiment) preparation devices 1 can form a preparation system. In this preparation system, the heating plates 20 of the multiple preparation devices 1 are integrated to form a heating device 80, and the guide plates 60 of the multiple preparation devices 1 are integrated to form a guide device 90. The cover portions 12 of the multiple preparation devices 1 are integrated to form an integrated cover assembly 100. This preparation system, by integrating multiple preparation devices 1, can prepare multiple spherical mirror patterns simultaneously.

[0080] According to an embodiment of the present invention, a plurality of flow guide holes 61 are formed on the flow guide plate 60 of each preparation device in the preparation system. The plurality of flow guide holes 61 are located at the center of the flow guide plate 60, and the outer contour formed by the plurality of flow guide holes 61 is circular. On the first side of the flow guide plate 60 facing the heating plate 20, a first groove is formed by inward indentation, and a first part 131 is fitted into the first groove to close the first sub-cavity 71. Correspondingly, on the second side of the flow guide plate facing the cover part 12, a second groove is formed by inward indentation, and a second part 132 is fitted into the second groove to close the second sub-cavity 72. It can be understood that the first side may also extend in the direction opposite to the steam flow direction to form a first protrusion, which is fitted into the first part 131, and the second side may also extend in the direction in the same direction as the flow direction to form a second protrusion, which is fitted into the second part 132.

[0081] According to an embodiment of the present invention, the receiving component 30, the container 50, and the through hole 11 are arranged coaxially.

[0082] As a second aspect of the present invention, a method for manufacturing a spherical mirror is also provided. This method includes operations S1 to S3.

[0083] In operation S1, the photoresist disk formed on the surface of the substrate 40 is transformed into a spherical mirror pattern using the above-described fabrication apparatus 1.

[0084] In operation S2, the substrate of the spherical mirror pattern is baked to solidify the spherical mirror pattern.

[0085] In operation S3, reactive ion dry etching is performed on the substrate 40 with the cured spherical mirror pattern on its surface to transfer the spherical mirror pattern onto the substrate 40, thereby obtaining a spherical mirror.

[0086] According to an embodiment of the present invention, the preparation method provided by the embodiment of the present invention combines a solvent reflux process and a reactive ion dry etching process to realize the preparation of a spherical mirror with an arbitrary target radius of curvature.

[0087] According to an embodiment of the present invention, during reactive ion dry etching, a spherical mirror with a target radius of curvature can be obtained by controlling the etching rate (dry etching selectivity) of the substrate 40. The radius of curvature R1 of the spherical mirror, the radius of curvature R2 of the spherical mirror pattern, and the dry etching selectivity S satisfy equation (1).

[0088] (1).

[0089] According to an embodiment of the present invention, before transforming the photoresist disk formed on the surface of the substrate 40 into a spherical mirror pattern with a target radius of curvature, the above-described preparation method further includes: determining the type and radius of curvature of the spherical mirror pattern, and determining the reflow time based on the diameter of the photoresist disk, the heating temperature when the heating plate 20 heats the photoresist solvent, and the type and radius of curvature of the spherical mirror pattern.

[0090] According to an embodiment of the present invention, before operation S1 of the above-described preparation method, it is first necessary to determine whether the spherical mirror to be prepared is a plano-concave spherical mirror or a plano-convex spherical mirror, that is, to determine the type of spherical mirror pattern. As can be seen from the preceding analysis, the appearance of plano-concave and plano-convex spherical mirror patterns differs during the reflow of the photoresist disk. According to the principle of preparing spherical mirror patterns according to the embodiment of the present invention, when preparing spherical mirror patterns using the reflow of the photoresist disk, the plano-concave spherical mirror is formed first, followed by the plano-convex spherical mirror. Therefore, it is necessary to first determine the type of spherical mirror pattern. After determining the type of spherical mirror, it is also necessary to determine the radius of curvature. Once the type of spherical mirror and the radius of curvature are determined, the spherical mirror to be prepared is determined.

[0091] According to an embodiment of the present invention, the principle of obtaining a spherical mirror pattern with a target radius of curvature using a photoresist solvent reflow method is as follows: During the reflow process, the photoresist absorbs vapor and gradually becomes fluid. Simultaneously, surface tension begins to take effect, attempting to minimize the surface area of ​​the photoresist pattern. Firstly, in the initial stage of reflow, protrusions form from the periphery of the photoresist disk, and a concave region forms inside the protrusions, with the interior of the concave region being a planar area. As reflow progresses, the peripheral protrusions gradually move towards the center of the photoresist disk, and the areas of the concave and planar regions gradually decrease. At time t1, the planar region disappears, the concave regions merge, and a smooth parabolic surface begins to form in the central part of the photoresist disk. This is due to the continuous absorption of solvent vapor and the flow of the photoresist, causing the photoresist to accumulate in the central region, forming a centrally concave parabolic shape (the central part of the parabolic surface is a flat-concave spherical shape). Subsequently, the surrounding protrusions continue to move closer to the center, the radius of curvature of the central plano-concave spherical surface gradually decreases, and the height of the central concave portion continuously increases until the protrusions merge, forming a plano-convex spherical shape. This plano-convex spherical shape reaches a steady state at time t3. Since the photoresist pattern is constantly changing dynamically, the fabrication method of this embodiment can obtain plano-concave spherical patterns and plano-convex spherical patterns with different radii of curvature. The speed of the above process is affected by the heating temperature of the heating plate, the thickness of the photoresist disk, the size and distribution of the through-holes in the guide plate, and the size and distribution of the through-holes in the cover portion.

[0092] According to the principle of preparing spherical mirror patterns according to embodiments of the present invention, the radius of curvature of the spherical mirror pattern is related not only to the reflow time, but also to the diameter of the photoresist disk, the heating temperature of the heating plate when heating the photoresist solvent, and the type of spherical mirror pattern. Once the diameter of the photoresist disk and the heating temperature of the heating plate when heating the photoresist solvent are determined, the radius of curvature and reflow time of different types of spherical mirror patterns satisfy different relationships, which will be described separately below.

[0093] For a plano-concave spherical mirror pattern, the relationship between its radius of curvature ROC1 and the reflow time is shown in equation (2).

[0094] (2).

[0095] In formula (2), ROC1 is the radius of curvature of the plano-concave spherical mirror pattern, t is the reflow time, t1 < t < t2, where t1 is the moment when the central part of the photoresist disk begins to form a smooth parabola, t2 is the moment when the peripheral protrusions overlap during the reflow process, and a1, b1, and c1 are all parameters. These three parameters can be obtained by fitting experimental data.

[0096] For a plano-convex spherical mirror pattern, the relationship between its radius of curvature ROC2 and the reflow time is shown in equation (3).

[0097] (3).

[0098] In formula (3), ROC2 is the radius of curvature of the plano-convex spherical mirror pattern, t is the reflow time, and a2, b2, and c2 are all parameters. These three parameters can be obtained by fitting experimental data. t2 < t < t3, where t3 is the moment when the central part of the photoresist disk begins to form a smooth parabola, t2 is the moment when the peripheral protrusions overlap during the reflow process, and t3 is the moment when the photoresist pattern reaches a steady state.

[0099] According to an embodiment of the present invention, after the spherical mirror pattern is prepared, an error characterization is required using a white light interferometer. When the error is not satisfied with the first preset condition (for example, the peak-to-valley value of the surface shape is greater than 0.1λ@520 nm, where λ is the measurement wavelength of the white light interferometer, typically 520 nm), the reflow time needs to be finely adjusted according to the error value to ensure that a spherical mirror pattern meeting the conditions is obtained.

[0100] According to an embodiment of the present invention, trifluoromethane is used as a passivating gas during the reactive ion dry etching process in operation S3. The role of the passivating gas is to protect the non-etched areas and prevent them from being accidentally etched. Trifluoromethane is chosen as the passivating gas because it can effectively reduce the formation of oxide pseudomasks on the substrate material surface, resulting in a spherical mirror with lower roughness after etching. The formation of oxide pseudomasks is a common problem during etching, which can lead to uneven etching or decreased precision. The use of trifluoromethane helps to reduce the formation of oxide pseudomasks, thereby improving the etching quality.

[0101] According to an embodiment of the present invention, the above-described preparation method further includes operation S4, namely, polishing or atomically etching the spherical mirror to give the spherical mirror atomic-level surface flatness. During polishing or atomically etching of the spherical mirror, it is also necessary to characterize the roughness error using an atomic force microscope until the error value meets a second preset condition (e.g., surface roughness less than or equal to 0.15 nm) to ensure that a spherical mirror with atomic-level surface flatness that meets the conditions is obtained.

[0102] According to embodiments of the present invention, spherical mirrors with atomic-level surface flatness can be used in ultrastable laser reference cavities, which are important components of optical atomic clocks. Due to the Dick Effect of ultrastable lasers, the frequency instability of optical atomic clocks is mainly determined by the frequency instability of the ultrastable laser reference cavity, which is ultimately limited by the thermal noise of the ultrastable laser reference cavity. To approach the thermal noise limit, it is necessary to overcome the white noise introduced by the optical power meter. This requires the precision of the ultrastable laser reference cavity to reach 200,000 or higher, meaning that the cavity mirrors of the ultrastable laser reference cavity must have ultra-high reflectivity, i.e., the surface roughness of the cavity mirrors must be at the atomic level to suppress optical scattering loss. After approaching the thermal noise limit, increasing the spot size of the ultra-stable laser in the cavity mirror can significantly reduce its thermal noise-limited frequency instability. This means that it is necessary to fabricate plano-concave spherical mirrors with ultra-large curvature radii to reduce their frequency instability limit. The spherical mirrors prepared by the method of this invention not only have atomic-level surface flatness, but can also be prepared into spherical mirrors with arbitrary curvature radii, that is, it can realize the fabrication of plano-concave spherical mirrors with ultra-large curvature radii.

[0103] According to an embodiment of the present invention, semiconductor fabrication technology and optomechanical processing technology are combined to achieve the fabrication of spherical mirrors with atomic-level surface flatness and small surface shape error.

[0104] According to an embodiment of the present invention, the photoresist disk formed on the surface of the substrate 40 is transformed into a spherical mirror pattern with a target radius of curvature, including operations S11 to S13.

[0105] In operation S11, the substrate 40 is placed on the heating plate 20, wherein a photoresist disk is formed on the substrate 40.

[0106] In operation S12, photoresist solvent is added to the housing component 30;

[0107] In operation S13, the photoresist solvent is heated by the heating plate 20, and the vapor generated by the photoresist solvent causes the photoresist to reflow. During the reflow process, the photoresist disk is continuously deformed under the action of surface tension until a spherical mirror pattern with the target shape is obtained.

[0108] According to an embodiment of the present invention, before adding photoresist solvent to the containing component, the above preparation method further includes: preheating the substrate 40 using a heating plate 20 to prevent the vapor pressure on the photoresist surface from being lower than the saturated vapor pressure on the photoresist surface.

[0109] Figure 4A The radius of curvature of a plano-concave spherical mirror prepared according to an embodiment of the present invention is shown.

[0110] like Figure 4A As shown, the radius of curvature (ROC) of the plano-concave spherical mirror prepared in this embodiment of the invention is 10m.

[0111] Figure 4B Shown Figure 4A The peak and valley values ​​of the surface shape of the plano-concave spherical mirror.

[0112] like Figure 4B As shown, the plano-concave spherical mirror prepared in this embodiment of the invention has a surface shape accuracy (peak-valley value, PV value) of 0.03λ within a 2mm×2mm scanning range (λ is the detection laser wavelength, which is 570nm in this embodiment of the invention).

[0113] Figure 4C Shown Figure 4A The surface roughness of the plano-concave spherical mirror.

[0114] like Figure 4C As shown, the surface roughness of the plano-concave spherical mirror prepared in this embodiment of the invention can be represented by RMS, and the surface roughness is 0.141 nm within a 5μm×5μm scanning range.

[0115] like Figures 4A-4C As shown, the preparation method of this invention achieves the preparation of plano-concave spherical mirrors with atomic-level surface flatness and small surface shape error.

[0116] The following are specific embodiments, and in conjunction with Figure 1A detailed description is provided of the fabrication method for a plano-concave spherical mirror with atomic-level surface flatness and an ultra-large radius of curvature. In this embodiment, the fabricated plano-concave spherical mirror has a radius of curvature of 10 m, and the fabrication method includes the following steps:

[0117] Step A: Preparation and preheating of the photoresist disk on the substrate 40 surface.

[0118] In this step, substrate 40 is selected using ultra-fine polishing. <111> A photoresist disk with a diameter of 8 mm was fabricated on the substrate surface using ultraviolet exposure. The photoresist used to fabricate the disk was model S1818. The substrate with the photoresist disk was mounted onto a receiving assembly 30, and the receiving assembly 30 was placed on a heating plate 20. The temperature of the heating plate 20 was set to 53°C to preheat the substrate and prevent vapor generated in subsequent processes from condensing on the surface of the photoresist disk.

[0119] Step B: Reflow the photoresist.

[0120] After preheating the substrate, the temperature of the heating plate is maintained at 53°C, and photoresist solvent, namely PGMEA solvent, is added to the housing component 30. The photoresist solvent generates vapor under the heating of the heating plate 20. The vapor evaporates to the vicinity of the photoresist disk, which absorbs the vapor and, after 240 minutes, its central region flows back under the action of surface tension, forming a plano-concave spherical mirror pattern with a central depression.

[0121] Step C: Bake the substrate with the plano-concave spherical mirror pattern.

[0122] The substrate with the plano-concave spherical mirror pattern was baked in an atmospheric environment at 115 °C for 5 min to evaporate excess photoresist solvent and solidify the plano-concave spherical mirror pattern, which facilitates the subsequent reactive ion dry etching process.

[0123] Step D: Pattern transfer is achieved using reactive ion dry etching.

[0124] After baking and cooling, pump oil is applied to the back of the substrate to enhance thermal conductivity and prevent photoresist degradation during subsequent reactive ion dry etching. The substrate with the cured plano-concave spherical mirror pattern is placed in the main chamber of the reactive ion dry etching process, and etching gases are set and introduced. The types and flow rates of the etching gases are: sulfur hexafluoride 5 sccm, trifluoromethane 10 sccm, and oxygen 25 sccm. During the etching process, a 5-second plasma ignition step is performed first, with the gas pressure set to 20 mTorr and the RF loading power set to 200 W. After ignition, the gas pressure is adjusted to 10 mTorr and the RF loading power is adjusted to 100 W, followed by a 45-minute main etching step to fabricate a plano-concave spherical mirror with a radius of curvature of 10 m within a 2 mm diameter area of ​​the substrate.

[0125] Step E: The surface shape error of the prepared plano-concave spherical mirror is characterized using a white light interferometer.

[0126] The plano-concave spherical mirror prepared in step D is characterized for surface shape error using a white light interferometer. If the peak-to-valley value (PV value) of the obtained surface shape is less than or equal to 0.1λ@520 nm, the preparation is successful. If the surface shape PV value is greater than 0.1λ@520 nm, the parameters of the preparation process are fine-tuned according to the surface shape error.

[0127] Step F: Ultra-precision polishing.

[0128] Using a 15 mm small grinding head polishing pad damping cloth with alkaline silica polishing slurry, the plano-concave spherical mirror successfully prepared in step E is uniformly polished to effectively optimize the surface roughness of the plano-concave spherical mirror at medium and high frequencies, without damaging the surface shape of the plano-concave spherical mirror.

[0129] Step G: Characterize the surface roughness using atomic force microscopy.

[0130] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely 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 within the protection scope of the present invention.

Claims

1. An apparatus for preparing a spherical mirror pattern, wherein the spherical mirror pattern is used to prepare a spherical mirror, characterized in that, The preparation apparatus includes: Heating plate; The housing, together with the heating plate, forms a cavity; the housing includes a cover portion, on which a through hole is formed; A housing assembly is disposed on a heating plate within the cavity, the housing assembly being adapted to contain photoresist solvent; A container, disposed within a housing assembly, is suitable for housing a substrate on which a photoresist disk is formed, the photoresist disk being a photoresist pattern with a disk shape formed from photoresist. The photoresist disk has a diameter of 8 mm, the spherical mirror has a radius of curvature of 10 m, and the heating plate is used to heat the photoresist solvent. After being heated, the photoresist solvent evaporates to produce steam, which flows out from the through hole. During the flow of the steam, the photoresist is refluxed. After absorbing some of the steam, the photoresist gradually changes from a solid state to a fluid state. In the cavity, the flow field of the steam is formed to cause the photoresist disk to continuously deform under the action of surface tension until a spherical mirror pattern is obtained. The spherical mirror pattern is a photoresist pattern with a spherical mirror shape. The preparation apparatus further includes a guide plate, which is disposed between the receiving component and the cover portion along the flow direction of the steam. The guide plate is suitable for uniformly distributing the steam on the surface of the photoresist disk. The size of the through hole and the heating temperature of the heating plate are configured such that the vapor pressure on the photoresist surface is less than the saturated vapor pressure on the photoresist surface. The cavity is configured to have a cylindrical structure, the heating plate is the bottom surface of the cylindrical structure, the substrate is located in the receiving assembly, and the center of the photoresist disk, the through hole and the center of the receiving assembly are all located on the axis of symmetry of the cylindrical structure.

2. The preparation apparatus according to claim 1, characterized in that, The housing also includes: The main body is disposed between the cover and the heating plate, and together with the cover and the heating plate, forms the cavity; The guide plate divides the cavity into a first sub-cavity and a second sub-cavity along the flow direction.

3. The preparation apparatus according to claim 1, characterized in that, Before the photoresist solvent is placed into the receiving assembly, the heating plate is also adapted to preheat the substrate. After the photoresist solvent is placed into the receiving assembly, the heating plate is also adapted to simultaneously heat the substrate and the photoresist solvent.

4. The preparation apparatus according to claim 1 or 3, characterized in that, When the ratio of the area of ​​the photoresist disk to the area of ​​the heating plate is greater than 1:1000, the cavity and the through hole are configured such that the flow field at the location of the photoresist disk is symmetrical about the center of the photoresist disk, and the area of ​​the photoresist disk is the cross-sectional area on the horizontal plane of the photoresist disk.

5. The preparation apparatus according to claim 4, characterized in that, The spherical mirror pattern is either a plano-concave spherical pattern or a plano-convex spherical pattern.

6. A method for preparing a spherical mirror, characterized in that, include: The photoresist disk formed on the substrate surface is transformed into a spherical mirror pattern using the fabrication apparatus as described in any one of claims 1 to 5; The spherical mirror pattern is baked to solidify it. A spherical mirror is obtained by performing reactive ion dry etching on a substrate with a solidified spherical mirror pattern on its surface.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes: The spherical mirror is polished or atomically etched to give it atomic-level surface flatness.

8. The preparation method according to claim 6, characterized in that Transforming a photoresist disk formed on a substrate surface into a spherical mirror pattern includes: The substrate is placed on a heating plate, wherein a photoresist disk is formed on the substrate; Add photoresist solvent to the housing component; The photoresist solvent is heated using a heating plate, and the vapor generated by the photoresist solvent causes the photoresist to reflow. During the reflow process, the photoresist disk is continuously deformed under the action of surface tension until the spherical mirror pattern is obtained.

9. The preparation method according to claim 6, characterized in that, Before adding the photoresist solvent into the containment component, the preparation method further includes: The substrate is preheated using a heating plate.

10. The preparation method according to claim 6, characterized in that, The fabrication method further includes, prior to transforming the photoresist disk coated on the substrate surface into a spherical mirror pattern with a target radius of curvature: Determine the type and radius of curvature of the spherical mirror pattern; The reflow time is determined based on the diameter of the photoresist disk, the heating temperature of the photoresist solvent when the heating plate heats it, and the type and radius of curvature of the spherical mirror pattern.

11. The preparation method according to claim 6, characterized in that, Trifluoromethane is used as a passivation gas during reactive ion dry etching.

12. The preparation method according to claim 6, characterized in that, For a plano-concave spherical mirror pattern, the relationship between its radius of curvature ROC1 and the reflow time is expressed as follows: ； Where ROC1 is the radius of curvature of the plano-concave spherical mirror pattern, t is the reflow time, t1 < t < t2, where t1 is the moment when the central part of the photoresist disk begins to form a smooth parabola, t2 is the moment when the peripheral protrusions overlap during the reflow process, and a1, b1 and c1 are all parameters. For a plano-convex spherical mirror pattern, the relationship between its radius of curvature ROC2 and reflow time is expressed as follows: ； Where ROC2 is the radius of curvature of the plano-convex spherical mirror pattern, t is the reflow time, and a2, b2, and c2 are all parameters; t2 < t < t3, where t2 is the moment when the peripheral protrusions overlap during the reflow process, and t3 is the moment when the photoresist pattern reaches a steady state.

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