Spherical mirror pattern preparation device and spherical mirror preparation method

Abstract

The invention provides a preparation device of a spherical mirror pattern and a preparation method of a spherical mirror, and belongs to the field of precision machining. The preparation device of the spherical mirror pattern comprises a heating plate; a cavity is defined by the shell and the heating plate, and the shell is provided with a through hole; the accommodating assembly is arranged on the heating plate in the cavity, and the accommodating assembly is suitable for accommodating a photoresist solvent; the container is arranged in the accommodating assembly and is suitable for accommodating a substrate, and a photoresist disc is formed on the substrate; wherein the heating plate is suitable for heating a photoresist solvent, the photoresist solvent is evaporated after being heated to obtain steam, the steam flows out from the through holes, the photoresist flows back in the flowing process of the steam, the photoresist is gradually changed into a fluid state from a solid state after absorbing part of the steam, and in the cavity, the steam flows out from the through holes; the flow field of the steam is formed to enable the photoresist disc to be continuously deformed under the action of surface tension until a spherical mirror pattern with a target curvature radius 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 a device for preparing a spherical mirror pattern and a method for preparing a spherical mirror. Background Art

[0002] In the field of optical element preparation, spherical mirrors, as an important optical element, are widely used in various optical systems. However, many problems still exist in the process of preparing spherical mirrors. Currently, common methods for preparing spherical lenses include electric shock melting, laser ablation, dry etching, etc. These methods have limitations and cannot produce spherical mirrors with arbitrary curvature radii. The curvature radius of the spherical mirrors produced is in the range of micrometers to millimeters (μm~mm). In addition, the usable area of spherical mirrors prepared by these methods is very limited, usually only on the micrometer level. In areas deviating from the center of the circle, the surface shape of the spherical mirror will seriously deviate from the ideal sphere, resulting in a decrease in optical performance. Summary of the Invention

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

[0004] Heating plate;

[0005] The shell and the heating plate form a cavity, and the shell has a through hole;

[0006] A receiving component is arranged on the heating plate in the cavity, and the receiving component is suitable for receiving a photoresist solvent;

[0007] The container is arranged in the containing assembly and is suitable for containing a substrate, on which a photoresist disk is formed. The photoresist disk is a photoresist pattern having a disk shape formed by photoresist.

[0008] Among them, the heating plate is suitable for heating the photoresist solvent. After being heated, the photoresist solvent evaporates to obtain steam, and the steam flows out from the through hole. During the flow of the steam, the photoresist is caused to reflux. After the photoresist absorbs part of the steam, it 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 disc 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 comprises:

[0010] a cover body portion, wherein a through hole is formed on the cover body portion;

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

[0012] The preparation device also includes:

[0013] The guide plate is arranged between the accommodating component and the cover body along the flow direction of the steam, dividing the cavity into a first sub-cavity and a second sub-cavity along the flow direction. The guide plate is suitable for evenly distributing the steam on the surface of the photoresist disc.

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

[0015] The size of the through hole and the heating temperature of the heating plate are configured to make the gas pressure of the vapor on the surface of the photoresist lower than the saturated vapor pressure of 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 the through hole are configured so that the flow field at the position where the photoresist disk is located 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 symmetry axis of the cylindrical structure;

[0018] The spherical mirror image is a plano-concave spherical image or a plano-convex spherical image.

[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 surface of the substrate is transformed into a spherical mirror pattern using the above-mentioned preparation device;

[0021] Baking the spherical mirror pattern to solidify the spherical mirror pattern;

[0022] The substrate with the solidified spherical mirror pattern formed on the surface is subjected to reactive ion dry etching to transfer the spherical mirror pattern to the substrate to obtain a spherical mirror.

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

[0024] The spherical mirror is polished or atomic layer etched to make the spherical mirror have atomic-level surface flatness.

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

[0026] placing a substrate on a hot plate, wherein a photoresist disk is formed on the substrate;

[0027] adding a photoresist solvent to the receiving component;

[0028] The photoresist solvent is heated by a heating plate, and the steam generated by the photoresist solvent is used to make the photoresist reflux. During the reflux process, the photoresist disc 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 into the receiving component, the preparation method further includes:

[0030] The substrate was preheated using a hot plate.

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

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

[0033] The reflow time is determined according to the diameter of the photoresist disk, the heating temperature of the photoresist solvent when the heating plate is used to heat the photoresist, and the type and curvature radius of the spherical mirror pattern.

[0034] According to an embodiment of the present invention, a photoresist solvent is heated using a heating plate, causing the solvent to evaporate and generate steam. A through hole is provided in a housing to allow the steam to flow out through the through hole. The flow of the steam causes the photoresist to reflux, and during the reflux process, a spherical mirror pattern is formed. This spherical mirror pattern with a target curvature radius is used to prepare a spherical mirror. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

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

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

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

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

[0040] Figure 4B Shown Figure 4A The peak-to-valley values of the plano-concave spherical mirror in the figure;

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

[0042] Description of Reference Numerals

[0043] 1 Preparation device

[0044] 10 shell

[0045] 11 through holes

[0046] 12 cover body

[0047] 13. Main body part

[0048] 131 Part 1

[0049] 132 Part 2

[0050] 20 heating plates

[0051] 30 accommodating components

[0052] 40 bases

[0053] 50 containers

[0054] 60 deflector

[0055] 61 diversion holes

[0056] 70 cavity

[0057] 71 First sub-cavity

[0058] 72 Second sub-cavity

[0059] 80 heating device

[0060] 90 diversion device

[0061] 100 integrated cover set DETAILED DESCRIPTION

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

[0063] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the presence of the 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 three-dimensional diagram of a preparation device provided according to an embodiment of the present invention is shown.

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

[0066] The housing 10 is configured to have a through hole 11 and, together with the heating plate 20, define a cavity 70. A receiving assembly 30 is disposed on the heating plate 20 within the cavity. The receiving assembly 30 is adapted to contain a photoresist solvent. A container 50 is disposed within the receiving assembly 30 and adapted to contain a substrate 40 having a photoresist disk formed thereon. The photoresist disk is a disc-shaped photoresist pattern formed of photoresist.

[0067] The receiving assembly 30 may be, for example, a heating dish. The heating plate 20 is adapted to heat the photoresist solvent, which evaporates to form steam upon heating. The steam flows out of the through-hole 11, causing the photoresist to reflux during the steam flow. The photoresist absorbs some of the steam and gradually changes from a solid state to a fluid state. Within the cavity 70, the steam flow field is formed such that the photoresist disc continuously deforms under the action of surface tension until a spherical mirror pattern is formed. The spherical mirror pattern is a photoresist pattern having a spherical mirror shape.

[0068] According to an embodiment of the present invention, the substrate 40 can be, for example, fused quartz or single crystal silicon. The photoresist solvent is heated by the heating plate 20 so that the photoresist solvent evaporates and generates steam. The steam is allowed to flow out from the through hole 11 by arranging the through hole 11 on the housing 10. The flow of the steam causes the photoresist to reflux, and during the reflux process, a spherical mirror pattern is obtained. The spherical mirror pattern is used to prepare a spherical mirror. The preparation device provided by the embodiment of the present invention prepares a spherical mirror pattern by causing the photoresist to reflux. The surface error of the spherical mirror pattern prepared by this method is small. According to an embodiment of the present invention, before the photoresist solvent is placed in the accommodating component 30, the heating plate 20 is also suitable for preheating the substrate 40. After the photoresist solvent is placed in the accommodating component 30, the heating plate 20 is also suitable for heating the substrate 40 and the photoresist solvent simultaneously.

[0069] According to an embodiment of the present invention, the vapor pressure on the photoresist surface is made less than the saturated vapor pressure on the photoresist surface in order to prevent the vapor on the photoresist surface from liquefying and dissolving the photoresist. Since saturated vapor pressure is temperature-dependent, the saturated vapor pressure on the photoresist surface is related to the temperature of the photoresist surface. The substrate 40 is preheated using the heating plate 20 before the photoresist solvent is placed in the receiving assembly 30 in order to prevent the vapor pressure on the photoresist surface from being less than the saturated vapor pressure on the photoresist surface due to the slow heating of the substrate 40.

[0070] According to an embodiment of the present invention, the size of the through hole 11 also affects the air pressure on the photoresist surface. The larger the through hole 11, the lower the air pressure on the photoresist surface. Conversely, the smaller the through hole 11, the higher the air pressure on the photoresist surface. However, the through hole cannot be infinitely large, and it is necessary to ensure that the steam can cause the photoresist to reflux.

[0071] According to embodiments of the present invention, the ideal state for producing spherical mirror patterns using a photoresist reflow method is that the steam flow field surrounding the photoresist disk is 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 steam flow field surrounding the photoresist disk can be considered uniform, and in this case, no special requirements are placed on the location of the through-holes.

[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 the through hole are configured so that the flow field at the position where the photoresist disk is located 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 flow field of the steam where the photoresist disk is located can no longer be considered uniform. In this case, if you want to obtain a spherical mirror pattern, you need to ensure that the flow field at the photoresist disk location is symmetrical about the center of the photoresist disk. For example, the cavity can be configured to have a cylindrical structure, and the heating plate 20 is the bottom surface of the cylindrical structure. The substrate 40 is positioned in the accommodating assembly, and the center of the photoresist disk, the through hole 11, and the center of the accommodating assembly 30 are all positioned on the symmetry axis of the cylindrical structure. The substrate 40 can for example be placed in the container 50 first, and then the container 50 is placed in the accommodating assembly 30. According to an embodiment of the present invention, the diameter of the bottom surface of the cylindrical structure can for example be 125mm, and the height is 34mm. The through hole 11 is circular, and the diameter of the through hole 11 can for example be 1-5mm.

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

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

[0076] like Figure 2 The preparation device shown may also include a guide plate 60. The guide plate 60 is arranged between the containing assembly 30 and the cover body 12 along the flow direction of the steam, dividing the cavity 70 into a first sub-cavity 71 and a second sub-cavity 72 along the flow direction. The guide plate 60 is suitable for evenly distributing the steam on the surface of the photoresist disc. The guide holes in the central area of the guide plate are circular holes with a diameter of 2 mm and are arranged in a close-packed array. The outer contour diameter of the guide holes is 20 mm. Multiple guide holes can be formed on the guide plate 60. The multiple guide holes can be located in the center of the guide plate 60, and the outer contour surrounded by the multiple guide holes can be, for example, circular.

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

[0078] Figure 3 A three-dimensional diagram 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, multiple (four in this embodiment) preparation devices 1 can be integrated to form a preparation system. In this preparation system, the heating plates 20 of multiple preparation devices 1 are integrated to form the preparation system's heating device 80, and the guide plates 60 of multiple preparation devices 1 are integrated to form the preparation system's guide device 90. The covers 12 of multiple preparation devices 1 are integrated to form an integrated cover assembly 100. By integrating multiple preparation devices 1, this preparation system can produce multiple spherical mirror patterns at once.

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

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

[0082] As a second aspect of the present invention, a method for preparing a spherical mirror is also provided, which 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-mentioned manufacturing apparatus 1.

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

[0085] In operation S3 , the substrate 40 with the solidified spherical mirror pattern on its surface is subjected to reactive ion dry etching to transfer the spherical mirror pattern onto the substrate 40 to obtain a spherical mirror.

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

[0087] According to an embodiment of the present invention, a spherical mirror having a target curvature radius can be obtained by controlling the etching rate (dry etching selectivity) of substrate 40 during reactive ion dry etching. The curvature radius R1 of the spherical mirror, the curvature radius 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 converting the photoresist disk formed on the surface of the substrate 40 into a spherical mirror pattern with a target curvature radius, the above-mentioned preparation method further includes: determining the type and curvature radius of the spherical mirror pattern, and determining the reflow time according to the diameter of the photoresist disk, the heating temperature when the heating plate 20 heats the photoresist solvent, and the type of the spherical mirror pattern and the curvature radius of the spherical mirror pattern.

[0090] According to embodiments of the invention, before the operation S1 of above-mentioned preparation method, at first need to determine whether the spherical mirror that needs to be prepared is a plano-concave spherical mirror or a plano-convex spherical mirror, promptly determine the type of spherical mirror figure.As can be known from the above analysis, when the photoresist disk was reflowed, the time that the plano-concave spherical mirror figure and the plano-convex spherical mirror figure occurred were different. According to the principle of preparing the spherical mirror figure of the embodiment of the invention, when utilizing the reflow of the photoresist disk to prepare the spherical mirror figure, what formed first was a plano-concave spherical mirror and what formed afterwards was a plano-convex spherical mirror. Therefore, at first need to determine the type of spherical mirror figure.After having determined the type of spherical mirror, also need to determine the radius of curvature. After having determined the type of spherical mirror and the radius of curvature, promptly determined the spherical mirror of required preparation.

[0091] According to an embodiment of the invention, the principle of the spherical mirror pattern that utilizes the method for photoresist solvent reflux to obtain target radius of curvature is: in the process of reflux, after photoresist absorbs steam, gradually becomes fluid state, and simultaneously, surface tension begins to work, attempts to minimize the surface area of photoresist pattern.At first, in the initial stage of reflux, from the periphery of photoresist disk, form protrusion, can form a circle of depressed area inside the convexity around, depressed area inside is plane area.Along with the carrying out of reflux, the convex portion of periphery approaches the center of photoresist disk gradually, and the area of depressed area and plane area dwindles gradually, at t1 moment, plane area disappears, depressed area merges, begins to form a smooth parabola in the center part of photoresist disk, this is because the continuous absorption of solvent vapor and the flow of photoresist make photoresist pile up in central area, form the parabola shape (parabola center small part area is the shape of plane concave spherical surface) with central depression. Subsequently, the protrusions on all sides continue to approach the center, the radius of curvature of the central plano-concave spherical surface gradually decreases, and the height of the central concave portion continues to increase until the protrusions merge to form a plano-convex spherical shape, which reaches a steady state at time t3. Since the photoresist pattern is always in a dynamic change, the preparation method of the embodiment of the present invention can obtain plano-concave spherical patterns with different curvature radii and plano-convex spherical patterns with different curvature radii. The speed at which the above process is carried out is affected by the heating temperature of the heating plate, the thickness of the photoresist disk, the size and distribution of the guide plate through holes, and the size and distribution of the cover body through holes.

[0092] According to the principles 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 temperature at which the heating plate heats the photoresist solvent, and the type of spherical mirror pattern. Once the diameter of the photoresist disk and the temperature at which the heating plate heats the photoresist solvent are determined, different types of spherical mirror patterns exhibit different relationships between the radius of curvature and the reflow time, as described below.

[0093] For a plano-concave spherical mirror, the relationship between its radius of curvature ROC1 and the reflow time is shown in formula (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 center of the photoresist disk begins to form a smooth paraboloid, and t2 is the moment when the peripheral convex parts overlap during the reflow process. a1, b1, and c1 are all parameters. These three parameters can be obtained by fitting experimental data.

[0096] For a plano-convex spherical mirror, the relationship between its radius of curvature ROC2 and the reflow time is as shown in formula (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 parameters. These three parameters can be fitted using experimental data. t2 < t < t3, where t3 is the moment when the center of the photoresist disk begins to form a smooth parabola, t2 is the moment when the peripheral convex portions 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, it is necessary to perform error characterization using a white-light interferometer. If the error does not meet a first preset condition (for example, the peak-to-valley value of the surface shape is greater than 0.1λ@520nm, where λ is the measurement wavelength of the white-light interferometer, typically 520nm), the reflow time is fine-tuned based on the error value to ensure that the spherical mirror pattern meets the requirements.

[0100] According to an embodiment of the present invention, trifluoromethane is used as a passivation gas during the reactive ion dry etching process in operation S3. The function of the passivation gas is to protect the non-etched areas and prevent them from being accidentally etched. Trifluoromethane is selected as the passivation gas because it can effectively reduce the formation of oxide pseudo-masks on the surface of the substrate material, so that the spherical mirror obtained after etching has a smaller roughness. The formation of oxide pseudo-masks is a common problem in the etching process, which can lead to uneven etching or reduced precision. The use of trifluoromethane helps to reduce the formation of oxide pseudo-masks, thereby improving the etching quality.

[0101] According to an embodiment of the present invention, the above-mentioned preparation method further includes operation S4, namely, polishing or atomic layer etching the spherical mirror to ensure that the spherical mirror has atomic-level surface flatness. During the polishing or atomic layer etching of the spherical mirror, it is also necessary to use an atomic force microscope to characterize the roughness error until the error value meets the second preset condition (for example, the surface roughness is less than or equal to 0.15 nm), thereby ensuring that the spherical mirror with atomic-level surface flatness meets the requirements.

[0102] According to embodiments of the present invention, spherical mirrors with atomic-level surface flatness can be used in an ultrastable laser reference cavity, a key component of an optical atomic clock. Due to the Dick Effect of the ultrastable laser, the frequency instability of the optical atomic clock is primarily determined by the frequency instability of the ultrastable laser reference cavity, which is ultimately limited by the thermal noise of the cavity. To approach the thermal noise limit, it is necessary to overcome the white noise introduced by the optical power meter. This requires the finesse of the ultrastable laser reference cavity to exceed 200,000. This means that the cavity mirrors of the ultrastable laser reference cavity must have ultra-high reflectivity, meaning that the surface roughness of the cavity mirrors must be atomic-level to suppress optical scattering losses. After approaching the thermal noise limit, the frequency instability limited by thermal noise can be significantly reduced by increasing the spot size of the ultra-stable laser in the cavity mirror, which means that a plano-concave spherical mirror with an ultra-large curvature radius needs to be produced to reduce its frequency instability limit. The spherical mirror prepared by the preparation method of the embodiment of the present invention not only has atomic-level surface flatness, but also can prepare spherical mirrors with arbitrary curvature radius, that is, it can realize the production of plano-concave spherical mirrors with ultra-large curvature radius.

[0103] According to an embodiment of the present invention, a semiconductor manufacturing process and an optical mechanical processing process are combined to achieve the preparation of a spherical mirror with atomic-level surface flatness and small surface shape error.

[0104] According to an embodiment of the present invention, the process of transforming a photoresist disk formed on the surface of the substrate 40 into a spherical mirror pattern having a target curvature radius includes operations S11 to S13.

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

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

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

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

[0109] Figure 4A The curvature radius of the 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 the embodiment of the present invention is 10m.

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

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

[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 the embodiment of the present invention can be expressed by RMS, and the surface roughness is 0.141 nm within a scanning range of 5 μm×5 μm.

[0115] like Figure 4A to Figure 4C As shown, the preparation method of the embodiment of the present invention realizes the preparation of a plano-concave spherical mirror with atomic-level surface flatness and small surface shape error.

[0116] The following are specific examples, and combined with Figure 1A method for preparing a plano-concave spherical mirror with atomic-level surface flatness and a large curvature radius is described in detail. In this embodiment, the curvature radius of the prepared plano-concave spherical mirror is 10 μm. The preparation method includes the following steps:

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

[0118] In this step, the substrate 40 is ultra-polished. <111> A photoresist disk with a diameter of 8 mm was formed on the surface of a substrate using UV exposure. The photoresist used was S1818. The substrate with the photoresist disk was mounted in a receiving assembly 30, which was then placed on a heating plate 20. The temperature of the heating plate 20 was set to 53°C to preheat the substrate and prevent condensation of steam generated during subsequent processing on the surface of the photoresist disk.

[0119] Step B: reflowing the photoresist.

[0120] After preheating the substrate, the heating plate temperature was maintained at 53°C, and a photoresist solvent, namely PGMEA solvent, was added to the receiving assembly 30. The photoresist solvent, heated by the heating plate 20, generated vapor. The vapor evaporated near the photoresist disc, which absorbed the vapor. After 240 minutes, the disc's center reflowed due to surface tension, forming a centrally depressed plano-concave spherical mirror pattern.

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

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

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

[0124] After baking and cooling, the backside of the substrate was coated with pump oil to enhance thermal conductivity and prevent photoresist denaturation during the subsequent reactive ion dry etching process. The substrate bearing the cured plano-concave spherical mirror pattern was placed in the main reactive ion dry etching chamber, and the etching gas was set and introduced. The etching gas types and flow rates were: 5 sccm sulfur hexafluoride, 10 sccm trifluoromethane, and 25 sccm oxygen. The etching process began with a 5-second plasma ignition step, at which the gas pressure was set to 20 mTorr and the RF loading power was set to 200 W. After ignition, the gas pressure was adjusted to 10 mTorr and the RF loading power was adjusted to 100 W. A 45-minute main etching step was then performed, resulting in the fabrication of a plano-concave spherical mirror with a curvature radius of 10 μm within a 2 mm diameter region of the substrate.

[0125] Step E: Use a white light interferometer to characterize the surface error of the prepared plano-concave spherical mirror.

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

[0127] Step F: Ultra-precision polishing.

[0128] Use a 15 mm small grinding head polishing pad damping cloth with alkaline silica polishing liquid to evenly grind and polish the plano-concave spherical mirror successfully prepared in step E to effectively optimize the medium and high frequency surface roughness of the plano-concave spherical mirror without destroying 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 objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for preparing a spherical mirror pattern, wherein the spherical mirror pattern is used to prepare a spherical mirror, characterized in that: The preparation device comprises: Heating plate; A shell, which forms a cavity with the heating plate, and the shell has a through hole; A containing component is disposed on the heating plate in the cavity, and the containing component is suitable for containing a photoresist solvent; A container is provided in the containing assembly and is suitable for containing a substrate, on which a photoresist disk is formed. The photoresist disk is a photoresist pattern having a disk shape formed by photoresist; In which, the heating plate is suitable for heating the photoresist solvent, and the photoresist solvent evaporates to obtain steam after being heated. The steam flows out from the through hole, and the photoresist is caused to reflux during the flow of the steam. After the photoresist absorbs part of the steam, it 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 disc 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.

2. The preparation device according to claim 1, characterized in that The housing comprises: a cover portion, wherein the through hole is formed on the cover portion; a main body portion, disposed between the cover portion and the heating plate, and enclosing the cavity with the cover portion and the heating plate; The preparation device also includes: A guide plate is arranged between the accommodating assembly and the cover body along the flow direction of the steam, dividing the cavity into a first sub-cavity and a second sub-cavity along the flow direction. The guide plate is suitable for evenly distributing the steam on the surface of the photoresist disc.

3. The preparation device according to claim 1, characterized in that Before the photoresist solvent is placed in the receiving assembly, the heating plate is further adapted to preheat the substrate, and after the photoresist solvent is placed in the receiving assembly, the heating plate is further adapted to heat the substrate and the photoresist solvent simultaneously; The size of the through hole and the heating temperature of the heating plate are configured to make the vapor pressure on the surface of the photoresist lower than the saturated vapor pressure of the surface of the photoresist.

4. The preparation device 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 so that the flow field at the position 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 of the photoresist disk on the horizontal plane.

5. The preparation device according to claim 4, characterized in that 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 symmetry axis of the cylindrical structure; The spherical mirror figure is a plano-concave spherical figure or a plano-convex spherical figure.

6. A method for preparing a spherical mirror, characterized in that: include: Converting a photoresist disk formed on a substrate surface into a spherical mirror pattern using a preparation apparatus as claimed in any one of claims 1 to 5; Baking the spherical mirror pattern to solidify the spherical mirror pattern; The substrate with the solidified spherical mirror pattern formed on the surface is subjected to reactive ion dry etching to transfer the spherical mirror pattern to the substrate to obtain a spherical mirror.

7. The preparation method according to claim 6, characterized in that The preparation method further comprises: The spherical mirror is polished or atomic layer etched to ensure that the spherical mirror has atomic-level surface flatness.

8. The preparation method according to claim 6, characterized in that The photoresist disk formed on the substrate surface is transformed into a spherical mirror pattern, comprising: placing the substrate on a heating plate, wherein a photoresist disk is formed on the substrate; adding a photoresist solvent to the receiving component; The photoresist solvent is heated by a heating plate, and the photoresist is caused to reflux by using the steam generated by the photoresist solvent. During the reflux 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 receiving component, the preparation method further comprises: The substrate is preheated using a heating plate.

10. The preparation method according to claim 6, characterized in that Before converting the photoresist disk coated on the substrate surface into a spherical mirror pattern with a target curvature radius, the preparation method further includes: Determining the type and curvature radius of the spherical mirror figure; The reflow time is determined according to the diameter of the photoresist disk, the heating temperature of the photoresist solvent when the heating plate is used to heat the photoresist, and the type and curvature radius of the spherical mirror pattern.

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