Method for manufacturing a micro-nanometric hierarchical structure and micro-nanometric hierarchical structure obtained by such a method

Abstract

Method for manufacturing a micro-nanometric hierarchical structure and micro-nanometric hierarchical structure obtained by such a method The present description relates to a manufacturing method comprising the exposure of a layer of a photosensitive resin to radiation by an optical lithography system comprising a mask, the mask comprising a matrix of pads opaque to radiation, spaced apart by a pitch, and distributed in at least two regions, each region being defined by an area ratio between the area of ​​the opaque pads of the region and the total area of ​​the region, said area ratios of the two regions being different, the pitch being equal, to within 10%, to the minimum resolution dimension of the Rayleigh criterion, and the development of the layer, from which it results at least in obtaining in the layer two pillars (20A, 20B, 20C) of different heights (HA, HB, HC) at the locations of the images of the two regions and of the protuberances (24A, 24B,24C) of nanometric heights at the top of each pillar at the locations of the plot images. Figure for abstract: Fig. 4,

Description

Title of the invention: Method for manufacturing a micro-nanometric hierarchical structure and micro-nanometric hierarchical structure obtained by such a method Technical field

[0001] The present description generally relates to a method of manufacturing a micro-nanometric hierarchical structure, also called a 2D hierarchical structure, comprising pillars of submicrometric, micrometric, or millimetric dimensions and protrusions of nanometric dimensions at the tops of the pillars. Prior art

[0002] Methods for manufacturing a 2D hierarchical structure generally include separate steps for manufacturing the pillars of submicrometer, micrometer, or millimeter dimensions and for manufacturing the protrusions of nanometer dimensions. An example method includes manufacturing a mold including imprinting the pillars and protrusions, generally in several steps, and a step of nano-imprinting by pressure on a resin layer using the mold or an injection molding step using the mold. Another example method includes successively forming the pillars and protrusions in a layer by successive steps of optical lithography and etching.

[0003] A disadvantage of such methods is that they comprise a large number of steps and can hardly be implemented on an industrial scale. Summary of the invention

[0004] One embodiment overcomes all or part of the drawbacks of known methods for manufacturing a micro-nanometric hierarchical structure.

[0005] One embodiment provides a manufacturing method comprising the following successive steps: - exposure of a layer of a photosensitive resin to electromagnetic radiation by an optical lithography system comprising a mask crossed by the electromagnetic radiation, the mask comprising a matrix of pads opaque to electromagnetic radiation, spaced apart by a pitch, and distributed in at least two regions of the mask, each region being defined by an area ratio between the area of ​​the opaque pads of the region and the total area of ​​the region, said area ratios of the two regions being different, the pitch being equal, to within 10%, to the minimum resolution dimension of the Rayleigh criterion; and - development of the layer, from which it results at least in obtaining in the layer two pillars of different heights at the locations of the images of the two regions and protuberances of nanometric heights at the top of each pillar at the locations of the images of the plots.

[0006] According to one embodiment, the optical lithography system comprises a source of electromagnetic radiation, and the minimum resolution dimension (of the Rayleigh criterion) is given by the following relation:

[0007] [Math.l] P =— 1 min i+(j NAS where X is the wavelength of the electromagnetic radiation, NAs is the image-side numerical aperture of the optical lithography system, and o is the partial coherence factor of the electromagnetic radiation source.

[0008] According to one embodiment, the photosensitive resin is a low contrast photosensitive resin.

[0009] According to one embodiment, the pitch of the pads is constant over the entire mask.

[0010] According to one embodiment, each plot has a section inscribed in a square, the dimensions of the side of the square for the plots of the two regions being different.

[0011] According to one embodiment, the difference in heights of the two pillars is between 1 nm and the thickness of the layer, preferably between 50 nm and 2000 nm.

[0012] According to one embodiment, the height of the protrusions is between 0 nm and 200 nm, preferably between 40 nm and 100 nm.

[0013] According to one embodiment, the height of the protrusions depends on the duration of the layer development step.

[0014] According to one embodiment, the resin layer rests on a substrate, the method further comprising a step of anisotropic etching of the resin layer and the substrate, resulting in the transfer of the shape of the pillars and protuberances into the substrate.

[0015] According to one embodiment, the top of each pillar has an area greater than 1 pm2.

[0016] An embodiment also provides a structure comprising a photosensitive resin layer comprising at least two pillars of different heights and protrusions of nanometric heights at the top of each pillar. Brief description of the drawings

[0017] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0018] [Fig.l] is a partial and schematic perspective view of an embodiment of a 2D hierarchical structure;

[0019] [Fig.2] is a partial, schematic side view of the 2D hierarchical structure of [Fig.l];

[0020] [Fig. 3] is a partial and schematic sectional view of an embodiment of an optical lithography system;

[0021] [Fig.4] and [Fig.5] are partial and schematic top views of embodiments of the mask used in the optical lithography system of [Fig.3];

[0022] [Fig.6] represents contrast curves of photosensitive resins;

[0023] [Fig.7A], [Fig.7B], and [Fig.7C] are partial and schematic side views of structures obtained at successive stages of an embodiment of a method for manufacturing the 2D hierarchical structure of [Fig.1];

[0024] [Fig.8] is a partial and schematic side view of the structure obtained in a step of another embodiment of a method for manufacturing the 2D hierarchical structure of [Fig.1];

[0025] [Fig.9] is a partial and schematic perspective view of a 2D hierarchical structure, obtained by simulation;

[0026] [Fig. 10] is a curve of the evolution of the profile of the 2D hierarchical structure of [Fig.9] along a measurement line at a first measurement scale;

[0027] [Fig.l 1] is a curve of evolution of the profile of the 2D hierarchical structure of [Fig.9] according to the measurement line at a second measurement scale;

[0028] [Fig. 12] shows the height of pillars fabricated using masks having different opaque dot densities and different opaque dot pitches;

[0029] [Fig.13], [Fig.14], and [Fig.15] are images, obtained by atomic force microscopy, of the upper face of pillars manufactured using masks having opaque pads of different dimensions; and

[0030] [Fig. 16] is a curve showing the evolution of the profile of the pads on the upper face of a pillar of [Fig. 14] along a measurement line. Description of the embodiments

[0031] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0032] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed.

[0033] The transmittance of a layer corresponds to the ratio between the intensity of the radiation leaving the layer and the intensity of the radiation entering the layer, the rays of the incoming radiation being perpendicular to the layer. In the remainder of the description, a layer or film is said to be opaque to radiation when the transmittance of the radiation through the layer or film is less than 10%. In the remainder of the description, a layer or film is said to be transparent to radiation when the transmittance of the radiation through the layer or film is greater than 60%.

[0034] Further, the terms "insulator" and "conductor" are herein considered to mean "electrically insulating" and "electrically conducting," respectively.

[0035] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0036] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0037] [Fig.l] is a partial and schematic perspective view of an embodiment of a 2D hierarchical structure 10 and [Fig.2] is a partial and schematic side view of the 2D hierarchical structure 10 of [Fig.l].

[0038] The 2D hierarchical structure 10 comprises a substrate 12 and a layer 14 covering the substrate 12 and having an upper face 16, on the side opposite the substrate 12, and a lower face 18, on the side of the substrate 12, opposite the upper face 16. According to one embodiment, the lower face 18 is planar.

[0039] The 2D hierarchical structure 10 comprises pillars 20A, 20B, 20C of different heights, the height being measured from the lower face 18. For example, in Figures 1 and 2, the 2D hierarchical structure 10 comprises a pillar 20A of average height HA, a pillar 20B of average height HB, strictly greater than the average height HA, and a pillar 20C of average height HC strictly greater than the height HB. However, it is clear that the 2D hierarchical structure 10 may comprise more than one pillar 20A of average height HA, more than one pillar 20B of average height HB, and / or more than one pillar 20C of average height HC. Furthermore, the 2D hierarchical structure 10 may comprise only pillars of two different heights, or pillars having different heights among more than three different heights.The sides of the pillars 20A, 20B, 20C may be substantially orthogonal to the lower face 18 or more or less inclined relative to a direction perpendicular to the lower face 18.

[0040] Generally, the average height of two pillars is not identical to within a nanometer. According to one embodiment, the difference in heights HA, HB, HC between two pillars 20A, 20B, 20C is between 1 nm and the thickness of the layer 14, preferably between 50 nm and 2000 nm. According to one embodiment, the average height HA is between 50 nm and 500 nm. According to one embodiment, the average height HB is between 550 nm and 1000 nm. According to one embodiment, the average height HC is between 1050 nm and 1500 nm.

[0041] Each pillar 20A, 20B, 20C comprises an upper face 22A, 22B, 22C on the side opposite the substrate 12. According to one embodiment, the upper face 22A, 22B, 22C of each pillar 20A, 20B, 20C, seen in a direction orthogonal to the lower face 18, has an area greater than 1 pm2.

[0042] The upper face 22A, 22B, 22C of each pillar 20A, 20B, 20C comprises a matrix of protrusions 24A, 24B, 24C. According to one embodiment, the height of each protrusion 24A, 24B, 24C is between 0 and 200 nm, preferably between 40 nm and 100 nm, a protrusion height 24A, 24B, 24C equal to 0 corresponding to a substantially planar upper face 22A, 22B, 22C. The protrusions 24A, 24B, 24C are arranged in rows and columns. The pitch PA, PB, PC of the matrix of protrusions 24A, 24B, 24C is the distance between the axis of a protrusion 24A, 24B, 24C and the axis of the protrusion 24A, 24B, 24C closest to the same line or an adjacent line.According to one embodiment, the pitch PA is substantially the same for all the protrusions 24A resting on each pillar 20A, the pitch PB is substantially the same for all the protrusions 24B resting on each pillar 20B, and the pitch PC is substantially the same for all the protrusions 24C resting on each pillar 20C. According to one embodiment, each pitch PA, PB, PC is between 330 nm and 410 nm. According to one embodiment, the pitches PA, PB, and PC are substantially identical.

[0043] RA, RB, RC is the radius of the circle in which the section of the protuberance 24A, 24B, 24C at mid-height of the protuberance 24A, 24B, 24C is inscribed. According to one embodiment, the radius RA, RB, RC is between 100 nm and the corresponding pitch PA, PB, PC reduced by 40 nm. According to one embodiment, the radii RA, RB and RC of the protuberances 24A, 24B, 24C are identical. According to one embodiment, the radius RA of the protuberances 24A is strictly less than the radius RB of the protuberances 24B and the radius RC of the protuberances 24C is strictly less than the radius RC of the protuberances 24C.

[0044] The protrusions 24A, 24B, 24C may be arranged in a square mesh, as shown in [Fig.l]. In this arrangement, a protrusion 24A, 24B, 24C is located at each intersection of a row and a column, the rows being perpendicular to the columns. Alternatively, the protrusions 24A, 24B, 24C may be arranged in a hexagonal mesh. In this arrangement, the protrusions 24A, 24B, 24C on a row are offset by half the pitch PA, PB, PC relative to the protrusions on the preceding row and on the following row.

[0045] According to one embodiment, the layer 14 is made of a photosensitive resin. The photosensitive resin is a resin suitable for implementing a grayscale optical lithography process, called grayscale photosensitive resin. According to one embodiment, the layer 14 is made of hydrogen silsesquioxane, or poly(silsesquioxane).

[0046] According to one embodiment, the layer 14 is made of a material other than a photosensitive resin, for example a semiconductor material, for example silicon, or an insulating material, for example silicon oxide, or silicon nitride. In this case, as described in more detail below, the formation of the 2D hierarchical structure 10 is obtained by a pattern transfer method.

[0047] An example of application of the 2D hierarchical structure 10 is the obtaining of a surface having variable and controlled wettability.

[0048] Methods for forming reliefs in a photosensitive resin layer include optical lithography methods which include an exposure step in which the resin layer is exposed to electromagnetic radiation through a mask followed by a development step in which the resin layer is immersed in a development solution, the exposed portions of the resin layer in the case of a positive photosensitive resin, or the unexposed portions of the resin layer in the case of a negative photosensitive resin, being dissolved in the development solution.

[0049] [Fig. 3] represents, in a partial and schematic manner, an embodiment of an optical lithography system 30.

[0050] In the embodiment illustrated in Figures 1 and 2, each pillar 20A, 20B, 20C is shown joined, that is to say in contact with at least one other pillar. According to another embodiment, at least one of the pillars 20A, 20B, 20C can be separated from another pillar by a groove, extending in the layer 14 over part or all of the height of the layer 14.

[0051] According to one embodiment, the optical lithography system 30 comprises four distinct elements: an illumination system 40, a mask 50, an optical projection system 60 and a resin layer 70 deposited on a substrate 72. The illumination system 40 emits monochromatic exposure radiation R of wavelength X which is diffracted upon passing through the mask 50. The optical projection system 60 makes it possible to collect the diffracted radiation to reconstitute the image of the mask 50 on the resin layer 70.

[0052] According to one embodiment, the illumination system 40 comprises a monochromatic source 42 of the radiation R of wavelength / . and a condenser 44. The source 42 comprises for example an excimer laser based on an argon-fluorine mixture (ArF). The condenser 44 comprises a set of lenses, mirrors, and other optical elements whose role is to collect and filter the radiation R coming from the source 42. For example, the source 42 is arranged at the object focal plane of the condenser 44. Thus, each source point produces a plane wave on the mask 50. This configuration makes it possible to obtain uniform illumination over the entire mask 50.

[0053] The optical projection system 60 comprises several lenses (two lenses 62, 64 being shown as an example in [Fig. 3]) operating in transmission and comprises an entrance pupil 66 and an exit pupil 68. The optical projection system 60 makes it possible to collect the radiation diffracted by the mask 50 and to project it onto the resin layer 70, possibly with a reduction factor M for example equal to 4 or 5. The advantage of having a reduction factor M greater than 1 is that it is no longer necessary to have the patterns of the mask 50 of the same size as the patterns to be printed. This relaxes constraints on the manufacture of the mask 50.

[0054] The numerical aperture NAS of the projection optical system 60 corresponds to the image-side numerical aperture of the projection optical system 60 and describes the capacity of the system to collect the diffracted radiation coming from the mask 50 and which participates in the formation of the image at the level of the resin layer 70. The numerical aperture NAS is defined by the following equation Math 2:

[0055] [Math.2] NAs=n-sin(amax) where n is the index of the medium between the output of the projection optical system 60 and the resin layer 70, generally air, and amax is the maximum half-angle of the cone of the incident radiation on the resin layer 70.

[0056] The lenses 62, 64 of the projection optical system 60 are arranged so that the image of the source 42 through the optical elements of the illumination system 40 is in the entrance pupil 66 of the projection optical system 60. However, the size dl of the source 42 obtained in the plane of the entrance pupil 66 is different from the initial size dO of the source 42. The ratio between the size of the image of the source 42 obtained at the entrance pupil 66 and the numerical aperture NAe of the entrance pupil is called the partial coherence factor o of the source 42 and is given by the following equation Math 3:

[0057] [Math.3] G~ NAe where [3max is the maximum half-angle of the cone of the incident radiation on the condenser 44 and NAe is the object-side numerical aperture of the projection optical system 60.

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068] The image-side numerical aperture NAS and the object-side numerical aperture NAe are linked together by the reduction factor M. Thus, the partial coherence o of the source can also be expressed as a function of the image-side numerical aperture NAS according to the following Math 4 relationship: [Math.4] 0-M- NAs In general, the partial coherence o is between 0 and 1. The optical lithography system 30 is characterized by its limiting resolution. This corresponds to the smallest pattern pitch of the mask 50 that can be resolved in the resin layer 70. It is known to use the Rayleigh criterion which links the minimum pitch Pmin of the mask 50 that can be resolved by the optical lithography system 30 according to the following Math 5 relation: [Math.5] p _ 1 3 Dnin- 1+ff NAS According to one embodiment, the ratio l / (l+o) is greater than 0.25. There are different types of optical lithography processes, including binary optical lithography processes and grayscale optical lithography processes. In binary optical lithography processes, the resin layer 70 is exposed over its entire thickness so that, after the development step, there remain resin pillars having the initial thickness of the resin layer separated by spaces where the resin layer has been removed over its entire thickness. The mask 50 used for implementing the binary optical lithography process is generally a mask called a binary mask comprising a support 52 transparent to radiation and pads 54 opaque to radiation. In grayscale optical lithography processes, the resist layer 70 may be exposed over only a portion of its thickness, so that, after the development step, resist pillars of varying thicknesses can be obtained. The grayscale optical lithography process can use a mask 50 more or less transparent to radiation to locally vary the exposure dose received by the resin layer 70. The mask 50 used for implementing the grayscale optical lithography process can also be a binary mask. [Fig.4] and [Fig.5] are partial and schematic top views of embodiments of the binary mask 50. The mask 50 comprises the support 52 transparent to radiation on which rest pads 54 opaque to radiation. As a alternatively, the opaque pads 54 are embedded in the transparent support 52. The ratio FF of a region of the mask 50, in the view of [Fig.4] or 5, is called the ratio between the area occupied by the opaque pads 54 and the total area of ​​the region. The higher the ratio FF, the more a part of the region considered is opaque to the radiation used in the exposure step. The pitch P of the opaque pads 54 corresponds to the distance between a center of an opaque pad 54 and the center of an immediately adjacent opaque pad. In the view of Figures 4 and 5, each opaque pad 54 corresponds to a square, and the measurement of the side of the square is called CD. Generally, the opaque pads 54 may have a shape other than a square, for example the shape of a pentagon, for example a rectangle, a circle, or an ellipse. We then call CD the measurement of the side of the square in which the opaque plot 54 is inscribed.

[0069] In a binary optical lithography method, the pitch P between the opaque pads 54 is significantly greater than the minimum pitch Pmin, indicated by the relation Math 5, which can be resolved by the optical lithography system 30, so that the image of each opaque pad 54 is reproduced in the resin layer 70, and the resin layer 70 is exposed to radiation only between the image of each opaque pad 54 of the mask 50.

[0070] In a grayscale optical lithography process, the pitch between the opaque pads 54 is significantly less than the minimum pitch Pmin that can be resolved by the optical lithography system 30. The opaque pads 54 are not resolved on the resin layer 70. The mask 50 then behaves as having a local transmittance to the radiation which depends on the local FF ratio. The opaque pads 54 are then arranged so as to vary the FF ratio on the mask 50 so that the dose of the radiation reaching the resin layer 70 varies locally.

[0071] According to one embodiment, a method for manufacturing a 2D hierarchical structure comprises the use of a photosensitive resin suitable for implementing a grayscale optical lithography method, the use of a binary mask, and the implementation of a step of exposing the photosensitive resin under conditions different from a grayscale optical lithography method and binary optical lithography.

[0072] Indeed, the pitch P of the opaque pads 54 is chosen to be equal, to within 10%, to the minimum pitch Pmin indicated by the relation Math 5. The inventors have demonstrated that under these conditions, effects specific to both binary optical lithography processes and grayscale optical lithography processes are obtained.

[0073] According to an embodiment illustrated in [Fig.4] and in [Fig.5], the mask 50 comprises regions 56A, 56B, 56C in which the FF ratios are different. As an example, a single region 56A, a single region 56B and a single region 56C are shown as an example in FIGS. 4 and 5. The FF ratio of the region 56A, called the low FF ratio thereafter, is strictly lower than the FF ratio of region 56B, called the intermediate FF ratio thereafter, and the FF ratio of region 56B is strictly lower than the FFC ratio of region 56C, called the high FF ratio thereafter.

[0074] The inventors have demonstrated that, when the pitch P of the opaque pads 54 is equal, to within 10%, to the minimum pitch Pmin indicated by the relation Math 5, after the development step, the resin layer 70 has the structure of the layer 14 of the 2D hierarchical structure 10 of [Fig.l]. More precisely, the inventors have demonstrated that the following are obtained in the resin layer 70 after the development step: - a pillar 20A for each region 56A whose dimensions correspond to the image of the corresponding region 56A, a pillar 20B for each region 56B whose dimensions correspond to the image of the corresponding region 56B, and a pillar 20C for each region 56C whose dimensions correspond to the image of the corresponding region 56C; and - protrusions 24A, 24B, 24C at the top of each pillar 20A, 20B, 20C, the position of the protrusions 24A, 24B, 24C corresponding to the images of the opaque pads 54 of the mask 50.

[0075] According to one embodiment, the height of the protrusions 24A, 24B, 24C depends on the duration of the development step.

[0076] In the embodiment illustrated in [Fig.4], the pitch P between the opaque pads 54 is identical for the regions 56A, 56B, 56C and the dimensions CD of the opaque pads 54 are different between the regions 56A, 56B, 56C. The dimension CD for the region 56C is strictly greater than the dimension CD for the region 56B and the dimension CD for the region 56B is strictly greater than the dimension CD for the region 56A.

[0077] According to one embodiment, the wavelength X of the exposure radiation R is equal to approximately 365 nm. According to one embodiment, the image-side numerical aperture NAs is between 0.4 and 1.0. According to one embodiment, the pitch P of the opaque pads 54 is between 300 nm and 420 nm for an exposure wavelength X equal to approximately 365 nm.

[0078] Photosensitive resins suitable for a binary optical lithography process are called high-contrast photosensitive resins or binary photosensitive resins. Photosensitive resins suitable for a binary optical lithography process are called low-contrast photosensitive resins or grayscale photosensitive resins.

[0079] [Fig.6] represents curves of evolution of the normalized remaining thickness TH of a positive photosensitive resin layer as a function of the dose D of the exposure radiation received by the photosensitive resin layer for an ideal binary photosensitive resin (curve C0), an ideal gray level photosensitive resin (curve Cl), a real binary photoresist (curve C2), and a real grayscale photoresist (curve C3). Such curves are also called contrast curves. The normalized remaining thickness TH is equal to the ratio of the thickness of the photoresist layer after the exposure and development steps to the initial thickness of the photoresist layer.

[0080] An ideal binary photosensitive resin (curve CO) exhibits inhibition at low doses, i.e. the solubility of the resin in the developing solution is zero when the dose is below a dose threshold Dmin and increases only when the dose is above the dose threshold Dmin. This means that the remaining thickness of the exposed resin layer is equal to the initial thickness when the dose is below the dose threshold Dmin. Beyond the dose threshold Dmin, all of the ideal binary photosensitive resin is dissolved in the developing solution, which corresponds to the remaining thickness Th being substantially equal to zero after the development step. For a real binary photosensitive resin (curve C2), beyond the dose threshold, a very abrupt but not quasi-infinite decrease in the remaining thickness is observed, the remaining thickness TH however depending on the exposure dose according to a non-linear relationship.

[0081] For an ideal grayscale photoresist (curve C1), the relationship between the remaining thickness TH and the exposure dose D is substantially linear, with a moderate slope. Furthermore, there is substantially no inhibition at low doses, i.e., the remaining thickness TH of the photoresist layer decreases as soon as the dose D is greater than zero. For an ideal grayscale photoresist (curve C3), the relationship between the remaining thickness TH and the exposure dose D is not perfectly linear, but the inhibition at low doses remains very low, and is preferably zero.

[0082] According to one embodiment, the inhibition at low doses of the photosensitive resin is less than 5 mJ / cm2. According to one embodiment, the photosensitive resin does not dissolve completely in the developing solution when the dose is less than 120 mJ / cm2 and the photosensitive resin dissolves completely in the developing solution when the dose is greater than 300 mJ / cm2.

[0083] [Fig.7A], [Fig.7B], and [Fig.7C] are partial and schematic side views of structures obtained at successive stages of an embodiment of a method for manufacturing the 2D hierarchical structure 10 of [Fig.1] in the case where the layer 14 is made of photosensitive resin.

[0084] [Fig.7A] illustrates the structure obtained after the formation of the layer 70 on the substrate 72. According to one embodiment, the initial thickness of the resin layer 70 is between 500 nm and 2000 nm. According to one embodiment, the layer of Resin 70 is deposited by a spin coating process. Layer 70 is made of a low-contrast photosensitive resin suitable for implementing a grayscale optical lithography process.

[0085] [Fig.7B] illustrates the structure obtained during the exposure of the layer 70 to the exposure radiation R through the binary mask 50. The opaque pads 54 of the mask 50 are arranged so that the pitch P between the opaque pads is equal, to within 10%, to the minimum pitch Pmin indicated by the relation Math 5. According to one embodiment, the mask 50 has the structure shown in [Fig.4] or 5. According to one embodiment, the pitch P of the opaque pads 54 is between 300 nm and 420 nm for a wavelength X substantially equal to 365 nm. According to one embodiment, the wavelength of the exposure radiation R is between 365 nm and 420 nm. In [Fig.7B], the regions 56A, 56B, and 56C of the mask 50 are schematically represented, and it is illustrated by arrows FA, FB, and FC of different sizes that the dose of the exposure radiation R passing through the region 56A is greater than the dose of the exposure radiation R passing through the region 56B and that the dose of the exposure radiation R passing through the region 56B is greater than the dose of the exposure radiation R passing through the region 56C.

[0086] [Fig.7C] illustrates the structure obtained after a development step of the layer 70, in which the portions of the layer 70 which have been exposed to the exposure radiation through the mask 50 are removed by immersing the layer 70 in a development solution. The 2D hierarchical structure 10 of [Fig.l] is then obtained, the photosensitive resin layer 70 in [Fig.7C] after development corresponding to the layer 14 in [Fig.l] and the substrate 72 corresponds to the substrate 12 in [Fig.l]. According to one embodiment, the development step comprises contacting the photosensitive resin layer 70 in a solution, for example a tetramethylammonium hydroxide (TMAH) solution or a sodium hydroxide solution.

[0087] An advantage of the embodiment of the manufacturing method described above is that the pillars 20A, 20B and 20C and the pads 24A, 24B, 24C are formed simultaneously. Furthermore, the dimensions of the pillars 20A, 20B and 20C and the pads 24A, 24B, 24C can be obtained in an accurate and reproducible manner by controlling the exposure conditions. The method can easily be implemented on an industrial scale.

[0088] [Fig.8] is a partial and schematic side view of the structure obtained at a step of another embodiment of a method for manufacturing the 2D hierarchical structure 10 of [Fig.1] in the case where the layer 14 is not made of photosensitive resin.

[0089] According to this embodiment, the method comprises the steps described previously in relation to steps 7A to 7C and further comprises a step of transferring into the substrate 72 the patterns formed in the resin layer 70 by an anisotropic etching step. The substrate 72 obtained after the etching step corresponds to the layer 14 in [Fig.l].

[0090] [Fig.9] is a partial and schematic perspective view of a 2D hierarchical structure obtained by simulation comprising a single pillar 20A.

[0091] [Fig. 10] is a curve showing the evolution of the height H of the 2D hierarchical structure along a measurement line x at a first measurement scale. The profile of [Fig. 10] includes a plateau P20A, which highlights the formation of the pillar 20A.

[0092] [Fig. 11] is a curve of the evolution of the H profile of the 2D hierarchical structure of [Fig.9] along the measurement line x at a second measurement scale. The profile of [Fig.1 1] includes P24A peaks, which highlights the formation of the 24A protuberances.

[0093] Three tests were carried out using masks 50 each having a constant pitch P over the entire mask 50. For these tests, the minimum pitch Pmin of the mask 50 that can be resolved by the optical lithography system 30 according to the relation Math 5 is equal to 376 nm. The first test is carried out using a mask 50 with a pitch P equal to 200 nm. The second test is carried out using a mask 50 with a pitch P equal to 300 nm. The third test is carried out using a mask 50 with a pitch P equal to 400 nm. For each test, the mask 50 comprises a region 56A with the low FF ratio, a region 56B with the intermediate FF ratio, and a 56C with the high FF ratio. Pillars 20A, 20B, and 20C of different heights were obtained.

[0094] [Fig. 13], [Fig. 14], and [Fig. 15] are images, obtained by atomic force microscopy, of the upper face respectively of a pillar 20C, a pillar 20B, and a pillar 20A obtained with a mask 50 having a constant pitch P over the entire mask 50 equal to 400 nm, respectively. [Fig. 13] is an image of the upper face of the pillar 20C, the distance CD of the opaque pads 54 of the corresponding region 56C of the mask 50 being equal to 360 nm. [Fig. 14] is an image of the upper face of the pillar 20B, the distance CD of the opaque pads 54 of the corresponding region 56B of the mask 50 being equal to 280 nm. [Fig. 15] is an image of the upper face of the pillar 20A, the distance CD of the opaque pads 54 of the corresponding region 56A of the mask 50 being equal to 222 nm.

[0095] [Fig. 16] is a curve of the H profile of the upper face of the pillar 20B of [Fig. 14] along a measurement line x. The profile of [Fig. 16] includes P24B peaks, which highlights the formation of the protuberances 24B. The protuberances 24B have a maximum height of the order of 25 nm to 30 nm.

[0096] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0097] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. A method of manufacturing a micronanometric hierarchical structure comprising the following successive steps: - exposing a layer (70) of a photosensitive resin to electromagnetic radiation (R) by an optical lithography system (30) comprising a mask (50) crossed by the electromagnetic radiation (R), the mask (50) comprising a matrix of pads (54) opaque to the electromagnetic radiation (R), spaced apart by a pitch (P), and distributed in at least two regions (56A, 56B, 56C) of the mask (50), each region (56A, 56B, 56C) being defined by an area ratio between the area of ​​the opaque pads (54) of the region and the total area of ​​the region, said area ratios of the two regions (56A, 56B, 56C) being different, the pitch (P) being equal, to within 10%, to the minimum resolution dimension (Pmin) of the Rayleigh criterion;and - development of the layer (70), which results in at least obtaining in the layer two pillars (20A, 20B, 20C) of different heights (HA, HB, HC) at the locations of the images of the two regions (56A, 56B, 56C) and protuberances (24A, 24B, 24C) of nanometric heights at the top of each pillar (20A, 20B, 20C) at the locations of the images of the pads (54).;

2. The method of claim 1, wherein the optical lithography system (30) comprises a source (42) of the electromagnetic radiation (R), and wherein the minimum resolution dimension (Pmin) of the Rayleigh criterion is given by the following relationship: [Math.6] P —— 1 min i+o NAS where X is the wavelength of the electromagnetic radiation (R), NAs is the image-side numerical aperture of the optical lithography system (30), and o is the partial coherence factor of the source (42) of the electromagnetic radiation (R).

3. The method of claim 1 or 2, wherein the photosensitive resin is a low contrast photosensitive resin.

4. Method according to any one of claims 1 to 3, in which the pitch (P) of the pads (54) is constant over the entire mask (50).

5. A method according to any one of claims 1 to 4, wherein each pad (54) has a section inscribed in a square, the dimensions (CD) of the side of the square for the pads (54) of the two regions (56A, 56B) being different.

6. Method according to any one of claims 1 to 5, wherein the difference in heights (HA, HB, HC) of the two pillars (20A, 20B, 20C) is between 1 nm and the thickness of the layer (70), preferably between 50 nm and 2000 nm.

7. Method according to any one of claims 1 to 6, wherein the height of the protrusions (24A, 24B, 24C) is between 0 nm and 200 nm, preferably between 40 nm and 100 nm.

8. The method of claim 7, wherein the height of the protrusions (24A, 24B, 24C) depends on the duration of the step of developing the layer (70).

9. A method according to any one of claims 1 to 8, wherein the resin layer (70) rests on a substrate (72), the method further comprising a step of anisotropically etching the resin layer (70) and the substrate (72), resulting in the transfer of the shape of the pillars (20A, 20B, 20C) and the protrusions (24A, 24B, 4C) into the substrate (72).

10. A method according to any one of claims 1 to 9, wherein the top of each pillar (20A, 20B, 20C) has an area greater than 1 pm2.

11. Micro-nanometric hierarchical structure comprising a layer (70) of photosensitive resin comprising at least two pillars (20A, 20B, 20C) of different heights (HA, HB, HC) and protrusions (24A, 24B, 24C) of nanometric heights at the top of each pillar (20A, 20B, 20C).

12. The structure of claim 11, wherein the top of each pillar (20A, 20B, 20C) has an area greater than 1 pm2.

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