Method for patterning a mask, method for manufacturing an insert or mold, and optical article having surface microstructures

Abstract

The present disclosure relates to a method for preparing an object having a curved surface to be etched, where the resulting etched surface can be used as a mold for manufacturing an optical article. The method includes irradiating the curved surface of the object through a patterned mask placed above or on the curved surface. The patterned mask comprises a curved surface configured to match the curved surface of the object. The curved surface of the patterned mask comprises at least one micrometer-sized area having a different transmission function than adjacent areas. The curved surface is made of a material that undergoes a local change in chemical resistance to a developer when irradiated as described above. The present disclosure further relates to a method for patterning a mask having a curved surface and an optical article having a curved surface with microstructures uniformly perpendicular to the curved surface.

Description

[Technical Field]

[0001] The present invention relates to the field of ophthalmic optics.

[0002] More particularly, the present invention relates to methods for patterning a mask having a curved surface, methods for preparing an object having a curved surface to be etched, and optical articles having a curved surface. [Background technology]

[0003] Myopia has become a major public health problem worldwide due to its increasing prevalence over the past few decades. In recent years, various options have been evaluated to prevent or slow the progression of myopia in children.

[0004] One of these options is the daily use of corrective spectacle lenses that also slow the progression of myopia due to the presence of a particular arrangement of surface microstructures.

[0005] Stellest™ lenses are an example of polycarbonate single vision lenses with a spherical front surface populated with aspheric lenslets. These lenses can be successfully manufactured by injection molding using a concave nickel-phosphorus plated steel insert with a diamond-turned microstructure.

[0006] However, manufacturing such steel inserts is very costly, and diamond turning can only produce a limited variety of microstructures. There is a need for a method of manufacturing inserts or molds with surface microstructures that is more economically feasible for injection molding or casting.

[0007] Furthermore, to produce minus-finish single vision polycarbonate lenses without defects such as weld lines and central distortion, glass inserts are required for injection molding. This is due to the lower thermal conductivity of glass compared to steel inserts, which slows the cooling of molten polycarbonate. However, it is currently not possible to create precise microstructures on the surface of typical borosilicate glass. What is needed is a manufacturing process that is compatible with insert materials that have similar thermal behavior to borosilicate glass and yet allow for the easy formation of microstructures on their surface.

[0008] The present invention has been made in consideration of the above problems. Summary of the Invention [Means for solving the problem]

[0009] According to a first aspect of the proposed technique, there is provided a method for patterning a mask having a curved surface by creating local variations in optical properties across the curved surface, the method comprising: The method includes irradiating a selected micrometer-sized area of ​​a curved surface; A method is provided in which the curved surface is made of a material that, when illuminated as described above, undergoes a local deformation over the illuminated area, the local deformation being associated with a local variation in optical properties.

[0010] A first aspect of the proposed technique makes it possible to provide curved patterned masks that exhibit local variations in optical properties, for example transmittance.

[0011] Furthermore, because the deformation of the curved surface is localized over a micrometer-sized area, a first aspect of the proposed technique enables the patterned curved mask to significantly diffract visible light, thereby enabling it to be used as a curved grayscale mask for visible light by exploiting the wave interference phenomenon.

[0012] Optionally, illuminating selected micrometer-sized areas of the curved surface includes, for each selected micrometer-sized area, displacing the mask so that the selected micrometer-sized area is at a set XYZ position, and illuminating the set XYZ position.

[0013] This allows for better control of the shape of the illuminated areas, regardless of their position on the curved surface.

[0014] Optionally, the curved surface material is photoresist.

[0015] Photoresist is a light-sensitive material. In the case of positive photoresist, the photosensitive material is degraded by light. In the case of negative photoresist, the photosensitive material is strengthened (polymerized or crosslinked) by light.

[0016] Optionally, the method further comprises: - irradiating selected micrometer-sized areas of the curved surface followed by locally dissolving the material of the curved surface to locally expose the coating, e.g., by applying a developer; Optionally, after locally dissolving the material of the curved surface, etching the exposed coating, for example by reactive ion etching.

[0017] In the case of a positive photoresist, the developer dissolves and removes the areas that have been exposed to light. In the case of a negative photoresist, the developer dissolves and removes only the areas that have not been exposed to light.

[0018] A coating is one or more layers or films that cover a substrate. The coating and the substrate have different optical properties.

[0019] Typically, the coating is opaque while the substrate is transparent. Some areas can then be made transparent by locally removing the coating while leaving other areas opaque. The coating left behind after the dissolved areas of photoresist can be, for example, a layer of chromium or a first layer of chromium oxide over a second layer of chromium in the case of a traditional chrome-on-glass mask. However, various other types of coatings are applicable.

[0020] Rather than forming a mask by irradiating photoresist over a coated substrate, it is also possible to form a mask by irradiating certain types of substrate without photoresist and a coating.

[0021] In this regard, optionally, the material of the curved surface is high energy beam sensitive (HEBS) glass.

[0022] For example, some known HEBS glasses can darken when exposed to high energy beams, such as electron beams or laser beams.

[0023] Optionally, irradiating selected micrometer-sized areas of the curved surface includes irradiating a first selected micrometer-sized area with a first exposure dose and irradiating a second selected micrometer-sized area with a second exposure dose different from the first exposure dose.

[0024] Because the transparency of some known HEBS glasses is a function of exposure dose, irradiating different micrometer-sized areas with different exposure doses allows for precise control of the transmittance of the curved mask across its curved surface with micrometer-order resolution, thereby providing a curved grayscale photomask.

[0025] According to a second aspect of the proposed technique, there is provided a method of preparing an object having a curved surface to be etched, the resulting etched surface being usable as a mould for producing an optical article, the method comprising: The method includes illuminating the curved surface through a patterned mask positioned above or on the curved surface; the patterned mask having a curved surface configured to match the curved surface of the object; the curved surface of the patterned mask comprises at least one micrometer-sized area having a transmission function different from that of an adjacent area; A method is provided in which the curved surface is made of a material that, when irradiated as described above, undergoes a localized change in chemical resistance to a developer.

[0026] Due to its properties, the material forming the curved surface of the object is photoresist, and the object is a laminate including at least two layers: photoresist and substrate. The substrate can be made of any material that can be physically and / or chemically etched. This includes dielectric materials (e.g., SiO2, Si3N4), silicon-based materials (e.g., Si, a-Si, Poly-Si), III-V materials (e.g., GaAs, InP, GaN), and metals (e.g., Al, Cr, Ti). The substrate can be selected for its thermal conductivity, which is preferably within two orders of magnitude of the intended material of the optical lens that will be etched and molded to the curved surface of the object.

[0027] The curved surface of the patterned mask may comprise a plurality of micrometer-sized areas, each with a different transmission function than the corresponding adjacent area. A possible way to obtain such a patterned mask is by patterning a curved mask according to the first aspect of the proposed technique.

[0028] A second aspect of the proposed technique allows for the generation of diverse microstructures on the curved surface of an object, which can then be used as an insert or mold for injection molding or casting, respectively, optical lenses with surface microstructures.

[0029] Thanks to the mask having a curved surface that matches the curved surface of the object, the resulting insert or mold further makes it possible to obtain a weld-line-free finished single-vision polycarbonate lens with a surface microstructure that is geometrically uniform and structurally perpendicular to the curved surface. The resulting insert or mold can further be used as a master to create a microstructured stamp for imprinting.

[0030] Optionally, the patterned mask is a binary mask, for example a chrome-on-glass binary mask.

[0031] Here, a binary mask is understood in the literal sense as a mask having, for example, at least one opaque micrometer-sized area adjacent to a transparent area or at least one transparent micrometer-sized area adjacent to an opaque area.

[0032] The patterned mask may also be an alternating phase-shift mask or an attenuated phase-shift mask, both of which possible implementations are similar to a binary mask.

[0033] Because the area under consideration is micrometer-sized, and because in typical lithography systems the light source illuminating the mask typically emits ultraviolet light with wavelengths of 248 nm and 193 nm, the binary mask is functionally a grayscale mask due to diffraction in the area under consideration.

[0034] Optionally, the curved surface of the binary mask comprises a plurality of micrometer-sized areas having a different transmission function than adjacent areas, said micrometer-sized areas being arranged according to a pattern comprising first regions having a first density of micrometer-sized areas and second regions having a second density of said micrometer-sized areas different from the first density of said micrometer-sized areas.

[0035] Optionally, the patterned mask is a grayscale mask, for example a grayscale high energy beam sensitive glass mask.

[0036] This means that the curved surface of the patterned mask is not simply opaque over some areas and transparent in others, but has transmittance values ​​that vary continuously or in a gradient between one or more intermediate levels between a minimum value corresponding to the most opaque areas and a maximum value corresponding to the most transparent areas.

[0037] Optionally, the curved surface of the greyscale mask comprises a first region having a first transmittance and a second region having a second transmittance different from the first transmittance.

[0038] Optionally, illuminating the curved surface of the object through a patterned mask comprises: illuminating a first area of ​​the curved surface of the object through a first area of ​​the curved surface of a patterned mask such that the first area of ​​the curved surface of the object receives a first exposure dose; and irradiating a second area of ​​the curved surface of the object through a second area of ​​the curved surface of the patterned mask such that the second area of ​​the curved surface of the object receives a second exposure dose that is different from the first exposure dose.

[0039] In one example, one of the first exposure dose and the second exposure dose is different from zero and the other is equal to zero, so that the curved surface of the object may have microstructures only on areas irradiated through a single region of the pattern in the first region and the second region.

[0040] According to a third aspect of the proposed technique, there is provided an optical article having a curved surface with microstructures, the article comprising: An optical article is provided in which the microstructures are uniformly perpendicular to the curved surface.

[0041] Optionally, the optical article is for use in slowing the progression of myopia.

[0042] When surface microstructures are specified as part of the optical design of an optical article, their specified orientation is typically perpendicular to the surface on which the microstructures are formed. For various purposes, among them optical quality, it is desirable that the microstructures actually formed on the surface of the optical article be as close as possible to their specified orientation.

[0043] In particular, it is known that some arrangements of microstructures on the surface of an optical article essentially contribute to slowing the progression of myopia when the optical article is worn, due to the intentional formation of a partially blurred image on the wearer's retina. It is of utmost importance that the orientation of the microstructures be precisely controlled so that the optical article forms a desired partially blurred image on the wearer's retina when worn.

[0044] Optionally, the optical article is weld line free and / or free of other types of defects, such as center distortion defects, both of which are known and well described in the art.

[0045] Weld lines are defects that occur when molding optical articles when the material of the optical article has a thermal conductivity that is significantly different from that of the mold. Generally, weld lines can form during injection when an advancing polymer melt front meets another melt front, which can result from filling the mold cavity from multiple gates. This can then lead to head-on collision of separate polymer melt flow fronts, or splitting and converging of the flow fronts due to the presence of an obstruction or excessive transverse thickness variation.

[0046] Optionally, the optical article can be an organic glass, such as polycarbonate, isosorbide polycarbonate, polymethyl methacrylate, polyamide, copolyester, thermoplastic polyurethane, polysulfone, polyphenylsulfone, or cyclic olefin copolymer. Polycarbonate has a light transmittance of 0.2 W m -1 ·K -1 Polymethyl methacrylate has a thermal conductivity of 0.18 W m -1 ·K -1 Polyamide has a thermal conductivity of 0.2 W m -1 ·K -1 Polyphenylsulfone has a thermal conductivity of 0.35 W m -1 ·K -1 Cyclic olefin copolymer has a thermal conductivity of 0.16 W m -1 ·K -1 It has a thermal conductivity of

[0047] Furthermore, considering the underlying causes of weld lines as described above, the method according to the second aspect has a resultant etched surface with a thermal conductivity of 0.02 W m -1 ·K -1 Greater than 0.1 W m -1 ·K -1 Larger than 50W·m -1 ·K -1 Smaller, preferably 25 W m -1 ·K -1 It may be a material with a lower thermal conductivity.

[0048] For a more detailed understanding of the description provided herein and its advantages, reference is now made to the following brief description, which should be read in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. [Brief explanation of the drawings]

[0049] [Figure 1] 1(a)-1(f) show a schematic diagram of a photolithography process for producing rectangular microstructures on a substrate. [Figure 2]2(a)-2(d) show a schematic representation of a grayscale lithography process for producing gradient microstructures on a substrate. [Figure 3] A schematic representation of a chrome-on-glass mask patterned with opaque pixels. [Figure 4] 1 shows a schematic representation of the intensity profile of a pattern obtained by single-slit diffraction. [Figure 5] 5(a)-5(c) show schematic diagrams of the intensity profiles of patterns obtained by diffraction from various possible patterned masks. [Figure 6] 1 shows a schematic representation of the result of a photolithography process. [Figure 7] 1 shows an exemplary result of a photolithography process. [Figure 8] 1 shows an exemplary result of a photolithography process. [Figure 9] Figure 9(a)-(d) show a schematic diagram of the chrome-on-glass photomask fabrication process. [Figure 10] 1 illustrates a schematic representation of an electron beam lithography system. [Figure 11] Shown is a surface containing 2 μm concentric lines obtained by electron beam lithography. [Figure 12] 12(a)-12(d) show schematic diagrams of glass prism arrays obtained by a grayscale lithography process using a high-energy beam sensitive glass mask. [Figure 13] 13(a) and 13(b) show a schematic representation of a 600 nm Fresnel lens obtained by a grayscale lithography process. [Figure 14] 1 illustrates a schematic diagram of a method for manufacturing an insert according to an embodiment of the present invention. [Figure 15] 1 shows a schematic representation of a microlens array on a polycarbonate lens and a corresponding microlens array on an insert made of fused silica bonded to stainless steel, the insert being used to obtain the polycarbonate lens by injection molding. DETAILED DESCRIPTION OF THE INVENTION

[0050] The proposed technique aims to produce inserts for thermoplastic injection molding of lenses with surface microstructures or molds for thermosetting casting. More precisely, the proposed technique aims to produce inserts or molds from silicon wafers or photosensitive or photostructure glass (PSG) using well-established wafer-based semiconductor manufacturing techniques. A further advantage of such inserts is that, thanks to the low thermal conductivity of the insert material, single-vision polycarbonate lenses with surface microstructures can be produced with a weld-line-free finish.

[0051] The proposed technique allows for the creation of surface microstructures that extend precisely over specific micrometer-sized areas of the curved surface of an insert or mold. As will be detailed, this relies on the use of a curved mask to precisely irradiate micrometer-sized areas, allowing for the creation of surface microstructures by etching.

[0052] Patterning a curved mask is a challenge in itself, and patterning techniques are proposed.

[0053] We now propose definitions for various terms and expressions used herein.

[0054] A curved surface of a mask, object, or optical article is the opposite of a flat surface. A curved surface can be spherical, aspherical, or cylindrical. The curved surface of a mold or insert has the same shape and size as the curved front or back surface of an ophthalmic optical lens produced by molding with such an insert.

[0055] The surface microstructures are microlenses or microlenslets or any other type of structure or element with a physical Z-variation / height or depth between 0.1 μm and 50 μm and a width / length between 0.5 μm and 1.5 mm. The Z-variation / height indicates the local deviation of the curved surface from its original spherical, aspherical, or cylindrical surface. These structures preferably have a periodic or quasi-periodic layout, but may also have randomized positions. Preferred layouts of the microstructures are a grid with regular grid steps, a honeycomb layout, multiple concentric rings, or continuous (e.g., no spaces between the microstructures). These structures can modify the optical wavefront in intensity, curvature, or light deviation, where the wavefront intensity is configured such that the structures can absorb and locally absorb the wavefront intensity in the range of 0% to 100%, the curvature is configured such that the structures can locally modify the wavefront curvature in the range of + / - 20 diopters, and the light deviation is configured such that the structures can locally scatter the light at angles in the range of + / - 1° to + / - 30°. The distance between structures can range from 0 (adjacent) to 3 times the "X" and / or "Y" size structures (distinct microstructures).

[0056] Furthermore, the microstructures forming the microstructured major surface of the ophthalmic lens substrate may include lenslets. The lenslets may form bumps and / or cavities (i.e., raised or recessed lenslet structures) on the major surface on which they are disposed. The lenslets may have a round or polygonal, e.g., hexagonal, contour. Specifically, the lenslets may be microlenses. The microlenses may be spherical, toric, cylindrical, prismatic, aspherical, or any combination creating a multi-element shape. The microlenses may have a single vision, a cylindrical power, a multifocal power, or a non-focus. The microlenses can be used to prevent the progression of myopia or hyperopia. In this case, the base lens substrate includes a base lens that provides a refractive power to correct myopia or hyperopia, and the microlenses may provide a refractive power greater than that of the base lens if the wearer has myopia, or a refractive power less than that of the base lens if the wearer has hyperopia, respectively. Lenslets may also be Fresnel structures, diffractive structures such as microlenses each defining a Fresnel structure, permanent technological bumps (raised structures), or phase-shifting elements. Lenslets may also be refractive optical elements such as microprisms, light-dispersive optical elements such as small protrusions or cavities, or any type of element that creates irregularities on a substrate. Lenslets may also be π-Fresnel lenslets, as described in U.S. Patent Application Publication No. 2021109379, i.e., Fresnel lenslets whose phase function has a π phase jump at the nominal wavelength, as opposed to single-focus Fresnel lenses whose phase jump is a multiple of 2π. Such lenslets include structures with discontinuous shapes. In other words, the shape of such structures can be described by an elevation function in terms of distance from the base level of the major surface of the optical lens to which the lenslet belongs, where the function exhibits a discontinuity, or where its derivative exhibits a discontinuity. In a useful range, microstructures may be brand marks, holographic marks, metasurfaces, and the like.

[0057] The lenslets may have a contour shape that can be inscribed in a circle having a diameter of 0.5 micrometers (μm) or more and 1.5 millimeters (mm) or less. The lenslets may have a height of 0.1 μm or more and 50 μm or less. The height is measured in a direction perpendicular to the major surface on which the lenslets are disposed. The lenslets may have a periodic or quasi-periodic layout, but may also have random positions. One layout of the lenslets is a grid with regular grid steps, a honeycomb layout, multiple concentric rings, or continuous (e.g., no spaces between microstructures). These structures can modify the optical wavefront in intensity, curvature, or light deviation, where the wavefront intensity is configured such that the structures can absorb and locally absorb the wavefront intensity in the range of 0% to 100%, the curvature is configured such that the structures can locally modify the wavefront curvature in the range of + / - 20, 500, or 1000 diopters, and the light deviation is configured such that the structures can locally scatter the light at angles in the range of + / - 1° to + / - 30°. The distance between the structures can range from 0 (adjacent) to 3 times the distance of the structures (separate microstructures).

[0058] The microstructures on the mold or insert can be used to mold, for example, refractive microstructures and / or diffractive micro / nanostructures. The microstructures on the mold or insert can be the inverse of the desired final pattern to be formed on the resulting lens after molding.

[0059] A micrometer-sized area of ​​a curved surface is an area having a contour shape that can be inscribed in a circle having a diameter of 0.5 micrometers (μm) or more and 2.0 millimeters (mm) or less.

[0060] 1(a) through 1(f), which are simplified illustrations of a photolithography process for producing rectangular microstructures on a substrate. Wafer-based semiconductor fabrication techniques such as photolithography, resist processing, and reactive ion etching have been shown to enable highly accurate shaping and precise positioning of surface profiles.

[0061] The laminate comprises essentially three layers: a substrate (10), such as a fused silica substrate, a coating (12), such as a chrome plated layer, overlying the substrate, and a photoresist (14) overlying the coating.

[0062] As shown in Figure 1(a), a binary photomask (16) is placed over or on top of the photoresist, and then areas of the photoresist are exposed to UV light through the photomask, as shown in Figure 1(b). A developer is then applied to the photoresist, resulting in the areas exposed to the UV light being dissolved, revealing the underlying coating, as shown in Figure 1(c).

[0063] Once the pattern on the photomask has been successfully transferred to the laminate by exposing the corresponding areas of the coating, known chemical and / or mechanical etching techniques, such as reactive ion etching, can be applied to further transfer the pattern to the substrate. For example, the exposed areas of the coating can be first etched to expose the underlying substrate, as shown in Figure 1(d), then the exposed areas of the substrate can be etched to form the desired rectangular microstructures in the substrate, as shown in Figure 1(e), and finally any remaining coating material can be removed to retain only the substrate with the transferred surface microstructures, as shown in Figure 1(f).

[0064] For more complex microstructures such as microlenses, prisms, Fresnel lenses, etc., it is necessary to form the gradient structure in the photoresist and then transfer this gradient structure to the substrate by etching, for example, by reactive ion etching. This can be achieved by using multiple binary masks, i.e., by successively providing different binary masks and repeating the operations shown in Figures 1(a) and 1(b), but this approach is time-consuming. In practice, grayscale lithography (GSL) is preferred because it allows a one-step lithography process for forming the gradient structure in the photoresist.

[0065] Reference is now made to Figures 2(a) to 2(d), which are simplified diagrams of a grayscale lithography process for producing gradient microstructures on a substrate, redrawn based on Non-Patent Document 1.

[0066] As shown in FIG. 2(a), a photoresist layer (24) covering a substrate (20) is exposed to UV light through an optically gradient grayscale mask (26) associated with the desired gradient microstructure. After exposure and development, as shown in FIG. 2(b), portions of the photoresist layer are dissolved, and the surface of the photoresist layer has a 3D profile corresponding to the desired gradient microstructure. The desired gradient microstructure can then be transferred to the substrate by, for example, reactive ion etching using one or more etchants (28), as shown in FIG. 2(c). After etching the substrate and removing all remaining photoresist, the desired gradient microstructure is obtained on the surface of the substrate, as shown in FIG. 2(d).

[0067] One of the primary techniques for producing grayscale optical masks is to fabricate a conventional chrome-on-glass (COG) binary mask (30) containing diffraction-inducing sub-resolution opaque pixels (32), as shown in Figure 3. Diffraction occurs in projection lithography using COG masks patterned with opaque pixels when both the pixel size (34) and pitch (36) are close to or less than the resolution of the projection lithography system.

[0068] In a typical projection lithography system used today in the semiconductor industry, light is projected through a patterned mask. With the pattern encoded in the light, a reduction lens system reduces and focuses the pattern onto the photosensitive surface of a wafer. After the pattern is printed, the system shifts the wafer slightly to make more copies of the blueprint.

[0069] By using a binary mask with sub-resolution opaque pixels, the superposition of the wavefronts of light scattered by the sub-resolution opaque pixels allows different target areas on the photosurface to be illuminated with different non-zero target exposure doses. Figure 4 shows a single-slit diffraction pattern (40) along with the corresponding intensity diagram (42). As shown in Figure 4, the light diffracted by the sub-resolution pixels separates into spatial diffraction orders (0, +1, -1, +2, -2, +3, -3, etc.) to form the diffraction pattern. The resolution of a lithography system is limited by the wavelength of light used and the ability of the reduction lens system to capture enough diffraction orders from the illuminated mask.

[0070] The reduction lens system (54) collects one or more of the spatial diffraction orders in the diffraction pattern (52) according to its numerical aperture, making it possible to reconstruct the pixels of the binary mask (50) in the aerial image (56) projected onto the photosensitive surface if at least the 0th and 1st (+1 or −1) diffraction orders are collected, as shown in Figure 5(a). However, if the pixel size and pitch are sufficiently small, only the 0th order is collected by the reduction lens system and focused onto the photosensitive surface, as shown in Figure 5(b).

[0071] The intensity passing through the mask depends on the fill area of ​​each pitch. For example, as shown in FIG. 6, if a mask 60 is designed with square pixels 62 and a set pitch 66 between the pixels, the intensity of light passing through the objective lens and projected onto the photosensitive surface 68 depends on the percentage of opaque area for each pitch. If the pitch is selected to be less than the resolution of the projection system, the distance between each pixel remains less than the resolution. A simple way to adjust the intensity of light passing through the objective lens is to keep the pitch constant and adjust the pixel size. Other applicable methods include keeping the pixel size constant and adjusting only the pitch, or adjusting both the size and pitch. The number of gray levels, along with the minimum pixel size and the increment between subsequent pixel sizes, depends on the resolution and magnification of the projection lithography system. The number of gray levels determines the roughness or precise definition of the profile in the photoresist.

[0072] There is a resolution limit on the minimum pixel size for a given projection lithography system, which sets an upper limit on the area and spacing on the mask. An approximation of the minimum pixel size due to the maximum diagonal spacing between two pixels can be given by:

[0073]

number

[0074] For example, if the resolution of the lithography system is 3.5 μm and the pitch is set to 3.5 μm, the minimum pixel width is about 1 μm.

[0075] If the size of a pixel is below the minimum pixel width defined above, the light diffracted by this pixel will have maximum intensity. The maximum pixel size is up to the pitch size. It is possible to pattern the mask by adjusting the pixel size between these minimum and maximum values.

[0076] The maximum pixel size is related to the maximum intensity of the diffracted light. This maximum intensity will, for example, cause complete degradation of the positive photoresist placed behind the mask, while any intermediate pixel size can be selected to be related to an intermediate intensity, or "gray level," of the diffracted light that will only cause partial degradation of the positive photoresist. As a result, after development, a grayscale microstructure corresponding to the mask pattern is formed on the positive photoresist. The same principle can be applied to negative photoresist, which is fully or partially strengthened depending on the intensity of the diffracted light-irradiated areas of the negative photoresist.

[0077] The height of the gray levels depends on many factors, primarily the initial photoresist thickness, the aerial image intensity of each gray level, the absorption coefficient which gives the concentration of both the remaining photoactive compound and the exposure product produced, the development time, and the photoresist contrast. Therefore, multiple grayscale patterns with different pitches and a calibration mask using all available pixels can be used to find both the design limits and thicknesses.

[0078] The pixel pitch can also be adjusted to control the size of the pattern encoded in the light transmitted by the mask when placed in a projection lithography system. However, if the pitch is slightly above the resolution of the projection lithography system, oscillations in the aerial image intensity can occur, as shown in Figure 5(c).

[0079] FIG. 7 shows an example of AZ® P4620 photoresist (70), initially 5 μm thick and 25 μm long, that has been first illuminated by light diffracted by the pixels of the mask and then developed.

[0080] The pixel arrangement on this mask is as follows: the pitch is uniformly equal to 3.5 μm. The pixels are arranged in 30 rows, one row per pixel size. The minimum pixel size is 0.4 μm, with successive increments of 0.1 μm between pixels in successive rows up to a maximum of 3.3 μm. As can be seen from the drawing, below the pixel width threshold, which is approximately 1 μm, the photoresist is fully developed.

[0081] Figure 8 shows another example of AZ® P4620 photoresist (80) that has been first illuminated by light diffracted by pixels of another mask, and then developed. The pixel layout on this other mask is a uniform 3.5 μm pitch, 220 rows of pixels, and 10 rows / pixel size.

[0082] Photomasks can be fabricated using processes similar to the photolithography process for creating microstructures on a substrate already described in Figures 1(a) through 1(f). The main difference is the exposure of the photoresist, which is typically done with an electron beam when fabricating a photomask and with a light beam in the case of the photolithography process. Figures 9(a) through 9(d) are diagrams of the chrome-on-glass photomask fabrication process.

[0083] A photomask blank is provided, comprising a transparent substrate (90) with a chrome opaque coating (92) and a resist (94). As shown in Figure 9(a), an electron beam or laser beam irradiates specific areas of the resist to form a pattern. As shown in Figure 9(b), the resist is developed to expose specific areas of the chrome coating. As shown in Figure 9(c), the exposed areas are etched, and then the remaining photoresist is removed, as shown in Figure 9(d). The end result is a chrome-on-glass photomask, in which the chrome coating forms opaque pixels on the otherwise transparent surface of the substrate.

[0084] The key to COG binary mask-based grayscale photolithography is to encode a specific 3D profile into a dot density pattern, which can be done with the assistance of computer software. The pattern is then written into photoresist with an electron beam or laser beam to form a COG photomask using the process described above.

[0085] Figure 10 shows a schematic of an electron beam lithography system that can be used to pattern commonly used flat COGs. A photoresist coated COG piece (106) is first mounted on an XY motorized linear stage. In operation, the system: - positioning the beam at the location of the first desired exposed pixel (108) of a shape; - using a beam blanker (102) to "unblank" the beam emitted by the electron source (100), i.e. start bombarding the photoresist with electrons; - Pause or dwell for a defined period of time to fully expose the resist at that pixel location; - using the beam deflector (104) to reposition the beam and / or using the motor of the motorized stage to reposition the photoresist coated COG piece, stepping to the next pixel in the feature and pausing to expose that pixel; - Repeat the previous two steps for all exposed pixels in the shape, A beam blanker is used to "blank" the beam, i.e., stop exposing the sample, so that the beam can then be repositioned to the starting pixel of the next shape to be exposed.

[0086] The beam blanker may be controlled by signals output by, for example, an electron beam pattern generator using a dot density pattern provided, for example, in the form of a CAD pattern file. Further, the beam deflector may be controlled by a scan amplifier receiving an analog signal obtained by converting the digital signal output by the electron beam pattern generator.

[0087] Curved COGs can be easily fabricated using typical glass shaping and chrome coating processes. However, generating specific patterns on a curved COG surface is much more difficult than patterning a flat surface. A similar electron beam lithography system with an XY stage (or XYZ stage) with Z-height movement coupled with precise surface mapping is required. The operating principle is similar to 3D printing. As shown in Figure 11, redrawn from Non-Patent Document 2, researchers at Pennsylvania State University (PSU) used a Raith EBPG5200 electron beam lithography system to generate 2 μm-wide concentric lines (112) on a curved surface (110).

[0088] While fabricating conventional chrome-on-glass (COG) binary masks with sub-resolution pixels is a possible technique for producing optical masks suitable for transferring grayscale patterns onto a photoresist surface, an alternative technique is to fabricate "true" grayscale masks, i.e., masks that can be divided into regions where adjacent regions have different absorbance values.

[0089] To that end, a possibility is to fabricate an all-glass photomask from a piece of high-energy beam sensitive (HEBS) glass whose transmittance is locally modified using an electron beam pattern generator or a laser beam pattern generator. The mask pattern can be written into the surface glass layer of the all-glass photomask.

[0090] HEBS glass is a photosensitive glass made from a base glass, for example, a low-expansion zinc-borosilicate glass also known as white crown glass. The base glass can be made from a glass melt, just like conventional white crown optical glasses. After the glass is melted, drawn, crushed, and polished, the base glass sheet is ion-exchanged in an acidic aqueous solution containing silver in a soluble ionic state. The ion-exchange process involves diffusing silver ions into the glass sheet at temperatures above 320°C to form silver-alkali-halide (AgX) crystals approximately 3 μm wide. m (MX) n This is done for a time sufficient to form a layer containing the complex crystals. HEBS glass can darken upon exposure to high-energy particles, either electrons or ions, due to chemical reduction of the silver ions in the silver-alkali-halide complex crystals, which produces colored specks of silver atoms. The transparency of the photosensitive glass is a function of the exposure dose. The higher the exposure dose, the darker the photosensitive glass. Thus, for example, continuous variations in exposure dose result in continuous variations in the optical intensity of the mask.

[0091] Similarly, HEBS glass can be formed into a variety of curves using typical glass forming and shaping processes. Curved grayscale photomasks can be produced from using curved HEBS glass with the Raith EBPG5200 electron beam lithography system described above.

[0092] Figures 12(a)-12(d) show a prism array (126) produced by a grayscale lithography process using a substrate (120) covered with a photoresist layer (122) illuminated through a flat HEBS glass mask (124), redrawn from Non-Patent Document 3. Prisms with a base area of ​​100 μm x 100 μm were fabricated, with sag ranging from 6 μm to 20 μm.

[0093] Figures 13(a) and 13(b) show a 600 nm Fresnel lens (130) and the corresponding height profile (132) redrawn based on [4], where the Fresnel lens is fabricated by a grayscale lithography process.

[0094] Of course, there are many types of microstructures that can be produced by photolithography beyond the examples above. Using such proven techniques, inserts and molds with complex surface microstructures can be precisely manufactured. However, one particular challenge exists in using photolithography to produce microstructures on curved insert or mold surfaces: ensuring that all resulting microstructures are uniformly perpendicular to the surface. This challenge can be addressed by using a photomask with a shape that closely matches the target surface.

[0095] FIG. 14 shows a process for making an insert or mold having a curved surface with surface microstructures.

[0096] First, a wafer (140) having a curved surface is provided. The wafer can be an all-glass wafer made from photosensitive glass, or can include any transparent substrate and one or more layers including photoresist (142) on the curved surface. The photoresist can be deposited on the curved surface by spin coating or any other suitable known process.

[0097] Microstructures are then formed on the surface of the curved wafer by photolithography using a curved mask (144) followed by etching. More precisely, if the wafer contains photoresist, a developer is applied to the photoresist, and etching, such as reactive ion etching, allows the pattern to be transferred onto the substrate. Conversely, if the wafer is made of photosensitive glass, the exposed, colored areas can also be etched away by known etching techniques.

[0098] The key to forming the desired microstructures on the substrate perpendicular to the curved surface of the wafer is the use of a curved mask having a shape that matches the curved surface of the wafer.

[0099] When the term "matched" is used, it means that the mask and the curved surfaces of the wafer can be abutted against each other at all points with a spacing between them below a predetermined threshold, for example below 0.1 mm.

[0100] The photomask may be a hard glass mask as described above, having a surface profile that matches the target surface. The photomask may also be a mask made of a soft material, such as a polymeric material such as PDMS, and may also have the same shape as the curved surface of the wafer surface originally, or may be a mask adapted to match the surface upon contact.

[0101] The photomask must be in close proximity (eg, <0.1 mm) or in direct contact with the curved surface of the wafer to ensure that the resulting microstructures are perpendicular to the target surface.

[0102] The curved wafer can then be bonded to a base (146), such as a stainless steel base, to form a composite insert (148) having microstructures on its surface using a process similar to that of typical glass-bonded inserts used in injection molding of finished single vision polycarbonate lenses. Alternatively, the curved wafer with surface microstructures can be used directly as a mold for casting a thermoset lens.

[0103] One additional advantage of using fused silica or photosensitive glass inserts for injection molding is that the low thermal conductivity of such inserts, which is very close to that of borosilicate crown glass, allows for the production of single vision polycarbonate lenses that have a fine structure and are finished without weld lines and central distortion defects.

[0104] In addition to creating inserts for injection molding or using it as a mold for casting, the microstructured wafer can be used as a master to fabricate stamps using soft polymer materials such as PDMS. The stamps, which are typically much cheaper than photomasks, can then be used to fabricate additional microstructured silicon wafers by imprinting lithography.

[0105] A PC lens was injection molded using an insert with a microlens array on a fused silica substrate bonded to a stainless steel base. In this example, each microlens is a hemisphere with a diameter of approximately 100 μm. The pitch between adjacent microlenses is also uniform, approximately 110 μm. As shown in Figure 15, the microlens array was successfully transferred from the insert (152) to the molded polycarbonate lens surface (150).

[0106] The following non-patent literature is cited:

[0107] Non-patent document 1: Scrymgeour, David, Kemme, Shanalyn A., Boye, Robert R., Ellis, A. Robert, Carter, Tony Ray, Samora, Sally, and Hunker, Jeffrey D. 2013. “Micro-optical grayscale excitation lenses for atom and ion trapping.” United States. https: / / www.osti.gov / servlets / purl / 1297085.

[0108] Non-patent document 2: https: / / www.mri.psu.edu / nanofabrication-lab / capabilities / lithography / electron-beam-lithography-0.

[0109] Non-patent document 3: Christiane Gimkiewicz, Detlev Hagedorn, Juergen Jahns, Ernst-Bernhard Kley, and Frank Thoma, “Fabrication of microprisms for planar optical interconnections by use of analog gray-scale lithography with high-energy-beam-sensitive glass,”Appl.Opt.38,2986-2990(1999)https: / / opg.optica.org / ao / abstract.cfm?URI=ao-38-14-2986.

[0110] Non-patent document 4: Nachmias, Tali & Ohayon, Avi & Meltzer, Shefer & Kabla, Meni & Louzon, Elie & Levy, Uriel. (2009). Shallow Fresnel lens fabrication using grayscale lithography made by high energy beam sensitive mask(HEBS)technology and reactive ion etching. Proceedings of SPIE-The International Society for Optical Engineering.7205.10.1117 / 12.809376. [Explanation of symbols]

[0111] 140 wafers 142 Photoresist 144 Mask 146 base 148 Composite Insert

Claims

1. 1. A method of patterning a mask having a curved surface by creating local variations in optical properties across the curved surface, comprising: The method includes irradiating a selected micrometer-sized area of ​​the curved surface; A method wherein the curved surface is made of a material that, when illuminated as described above, undergoes a local deformation across the illuminated area, the local deformation being related to the local variation in the optical property.

2. 2. The method of claim 1, wherein illuminating the selected micrometer-sized areas of the curved surface comprises: for each selected micrometer-sized area, displacing the mask so that the selected micrometer-sized area is at a set X-Y-Z position; and illuminating the set X-Y-Z position.

3. The method of claim 1 or 2, wherein the material of the curved surface is a photoresist.

4. The method comprises: after irradiating the selected micrometer-sized area of ​​the curved surface, locally dissolving the material of the curved surface to locally expose a coating, for example by applying a developer; Optionally, after locally dissolving the material of the curved surface, etching the exposed coating, for example by reactive ion etching; The method of claim 3 further comprising:

5. 3. The method of claim 1, wherein the material of the curved surface is a high-energy beam sensitive glass.

6. 6. The method of claim 5, wherein irradiating the selected micrometer-sized areas of the curved surface comprises irradiating a first selected micrometer-sized area with a first exposure dose and irradiating a second selected micrometer-sized area with a second exposure dose different from the first exposure dose.

7. A method of preparing an object having a curved surface to be etched, wherein the resulting etched surface can be used as a mold for producing an optical article; the method includes illuminating the curved surface of the object through a patterned mask positioned above or on the curved surface; the patterned mask comprises a curved surface configured to match the curved surface of the object; the curved surface of the patterned mask comprises at least one micrometer-sized area having a different transmission function than adjacent areas; A method wherein said curved surface is made of a material that, when irradiated as described above, undergoes a local change in chemical resistance to a developer.

8. 8. The method of claim 7, wherein the patterned mask is a binary mask, such as a chrome-on-glass binary mask.

9. 9. The method of claim 8, wherein the curved surface of the binary mask includes a plurality of micrometer-sized areas having a different transmission function than adjacent areas, the micrometer-sized areas being arranged according to a pattern including first regions having a first density of the micrometer-sized areas and second regions having a second density of the micrometer-sized areas different from the first density of the micrometer-sized areas.

10. 8. The method of claim 7, wherein the patterned mask is a grayscale mask, for example a grayscale high-energy beam sensitive glass mask.

11. 11. The method of claim 10, wherein the curved surface of the grayscale mask comprises a first region having a first transmittance and a second region having a second transmittance different from the first transmittance.

12. illuminating the curved surface of the object through the patterned mask; illuminating a first area of ​​the curved surface of the object through the first area of ​​the curved surface of the patterned mask such that the first area of ​​the curved surface of the object receives a first exposure dose; illuminating a second area of ​​the curved surface of the object through the second area of ​​the curved surface of the patterned mask such that the second area of ​​the curved surface of the object receives a second exposure dose different from the first exposure dose; 12. The method of claim 9 or 11, comprising:

13. An optical article having a curved surface with a microstructure, The optical article, wherein the microstructures are uniformly perpendicular to the curved surface.

14. 14. The optical article of claim 13 for use in slowing the progression of myopia.

15. 15. The optical article according to claim 13 or 14, wherein the optical article is weld line free.

Images